Critical Understanding #9 -Percent of Power and fuel flow.

Builders:

Three things come from article #9 in this series:

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You know  what 100% power is and the fuel burn at that setting

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You know what conditions produce 75% power, and the fuel burn at that setting.

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You know when the engine is at “Substantially reduced power” and understand that Carb heat is required for operation at these settings. (This will be covered in detail in part #10 )

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Piston engines inhale air and fuel, and burn it to make power. If you know the displacement of the motor, the RPM it is running at, and the density of air it is inhaling, you can make a pretty accurate calculation on which setting will produce a given power output and commiserate fuel flow. If you cross reference this with several very accurate dynamometer runs, your calculations will be within a few percentage points of your flight experience.

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Mass Flow:

The number you need to know is How many pounds of air are inhaled by the engine in an hour? Let’s look at an example from a 3,000 cc Corvair:

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3,000cc = 183 cubic inches = .106 cubic feet.

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3,200 RPM is 1600 inhalations on a 4 stroke motor, 1600 x .106 = 170 cubic feet of air per minute.

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170 cubic Ft./Min.= 10,200 Cubic feet per hour.

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At seal level on a standard day, air weighs .08 pounds per cubic foot.  10,200 x .08 = 816 pounds of air per hour.

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Engines without turbos or superchargers don’t inhale with perfect efficiency, the Volumetric Efficiency or VE of a Corvair head is .95 so… 816 pounds x VE of .95 = 775 pounds of air per hour going through the motor at wide open throttle and full RPM on a standard day.

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Engines make their best power at 12 to 1, air to fuel ratio by weight so …

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2,775 cc Corvair – 716 pounds of air per hour + 60 pounds of Gasoline = 100% power

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3,000 cc Corvair – 775 pounds of air per hour + 65 pounds of Gasoline = 100% power

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3,300 cc Corvair – 848 pounds of air per hour +  71 pounds of Gasoline = 100% power

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What is 75% Power?

It is any condition that results in the engine burning 3/4 of weight of air and fuel as the 100% power rating above.

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2,775 cc Corvair – 537 pounds of air per hour + 45 pounds of Gasoline = 75% power

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3,000 cc Corvair – 581 pounds of air per hour + 48 pounds of Gasoline = 75% power

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3,300 cc Corvair – 636 pounds of air per hour +  53 pounds of Gasoline = 75% power

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Any combination of throttle opening and rpm that results in the engine inhaling the 75% weight of air and fuel per hour will yield 75% of the rated power.

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Sea level standard pressure is 29.92″ of mercury.  3/4 of this pressure is 22.5″ If you had an Manifold air pressure gauge ( MAP ) in your plane and took off at SL on a standard day, it would read damn near 29.92″. If you left the throttle wide open and climbed to 8,000 ft. it would then read 22.5″ MAP, and if you leaned the mixture so the fuel flow dropped by 25% to match the reduction in the weight of air, you would now be at 75% power.

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If you were in Denver on an 85 degree day, with a bit of humidity in the air, you are now at 8,000′ Density Altitude (DA) and guess what? you now have a motor that only makes 75% of its rated power. In cruse flight, the plane will not loose 25% of its speed because it is flying through thinner air, but it will have reduced take off  and climb performance, but the people who build airports know this and tend to build longer runways in high places. Denver’s Runway 16R/34L is 16,000′ long, the longest commercial runway in North America.

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You can get a calculator and use the values in the first part of this article, along with an on line  DA calculator, (http://wahiduddin.net/calc/calc_da.htm) and work a great number of examples about your size engine at airports and climate conditions you may flight plan for. Note that your engine will likely not turn 3,200 RPM static, so realize that planes with fixed pitch props don’t start their take off roll at 100% power.

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Rich mixture for wide open throttle, leaned for cruise, a fuel flow variable.

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Aircraft carbs are designed to automatically run rich at wide open throttle. Please read this story to learn :Air / Fuel ratios on Corvair carbs.. They can go as far as a 10.5 to 1 air fuel ratio by weight. That mean our 3,000 cc Corvair  example above could go from 65 pounds of fuel per hour to 74 pounds per hour at a wide open seal level take off on a cool day and hitting 3200 rpm.

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Aircraft carbs are designed to be leaned at cruse if desired. The Corvair at low power settings can be leaned to 14 to 1 air / fuel ratio by weight. On the chart above, a 3,000 cc Corvair cruising at 75% power can possibly be leaned from 48 pounds of fuel per hour to 42.

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How much gas is that?

If you don’t know that gasoline weighs six pounds per gallon right off the top of your head, call up your flight instructor and tell him you want your money back, and he needs to mail his CFI ticket back to Oklahoma City. Seriously, if your instructor didn’t drill that into you, how do you know how much weight you are adding to the plane at the gas pump?  How does one do a weight and balance? These are the kind of skills that have been allowed to degrade in the modern era of  the “CFI Lite”  The man who taught me how to fly got his CFI in the USAF in 1952, when the standard response to a student asking “Is this going to be on the test?” was punching the student in the mouth. ( Sensitive CFI’s with progressive attitudes just slapped people.) Be your own hard core, old school CFI, and that way you will never look stupid around planes.

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If you don’t know this stuff, it’s ok, you are on team Corvair, and I am going to make it my business that you have a fresh chance to really learn it, because I want every moron in experimental aviation to know that Corvair builders know their shit. Being a dopey moron about aircraft operations is why they make Rotax engines and Bing carbs. Set your goal in aviation that just in case Chuck Yeager shows up at your airport on his 100th birthday and says to you “Hey, somebody want to take me flying for an hour?”  and he points at a in a PA-18 super cub on the ramp, you won’t have to be like all the pilots trained on Rotax’s who will have to say “Sorry, I can’t. I don’t know how a mixture control works.”  Besides, Yeager is old school, and he is going to punch those people in the mouth. -ww.

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Note Book Section:

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Make line 9.1 in your Hand book a hand written entry, stating what displacement your Corvair Engine is in both CC’s and Cubic inches.

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Make line 9.2 in your Hand book a calculation for your engine showing the fuel flow in Gallons per hour for your engine, at full rated power,  both at 12 to 1   air fuel ratio and at the auto rich setting of 10.5 to 1. Make a note in CAPITAL letters stating the maximum fuel flow the engine is capable of, and right under that figure out how many gallons it would take for your plane to climb to 5,000′ with a 600′ per minute rate of climb, to learn just how much fuel your plane could potentially use.

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Make line 9.3 in your Hand book a calculations of the DA of your home airport on a standard day, a 25F day, a 75F day and a 100F day. 

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Make line 9.4 in your Hand Book a notation of the fuel flow in Gallons per hour for your engine at a 75% power setting both at sea level and at 5,000′ These will be numbers you use frequently to flight plan.

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Make line 9.5 in your Hand Book a notation for the actual mass flow rate through your engine at it’s static rpm. Express this as a percentage of the mass flow rate of your engine at its rated RPM. This number will be your percent of rated HP available on take off.

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Food for thought on Fuels

Builders,

Below are four observations on fuels, a subject that rarely sees opinions based on numbers and reason. The topic of fuels draws out emotional responses ranging from compulsive cheapness to conspiracy theories, neither of which serve the serious builder. Feel free to use the comments section, keeping in mind I reserve the right to delete any comment which doesn’t have a human name attached to it.

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(1) Yes, high octane unleaded fuel exists. Above is a can of 110 Octane unleaded fuel in my hangar. We use it for dyno tests and other research. The detonation resistance of this fuel meets or exceeds 100LL.  I buy it in our little town, off the shelf, it is about $8 a gallon, a price which includes a healthy profit and the container. It is sold at a little golf cart repair shop near our town’s drag strip. If ordered in a 55 gallon drum, it is substantially less than $5/gallon. Every year I hear “Experts” at Oshkosh talk about how having unleaded fuel with an octane higher than 94 would require a scientific breakthrough.  Reality: it already exists, no one need ask for a federal grant to re-invent it. I strongly suspect that if it were manufactured in the volume of 100LL, it might even be cheaper. Even if it wasn’t, aircraft engines would live a lot longer without lead in them. Extending the life of a motor 20% would offset a substantial price differential. Think it over.

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(2) Fuel cost is a much smaller cost of aircraft ownership than people think. When the price of fuel goes up by a dollar, several people in every EAA chapter will pontificate that “flying just became unaffordable.” Try this at your next meeting: Poll ten people who have a hangar at the airport on how much their hangar rent was last month, and then ask them how many dollars they spent on fuel the same month. 9 of 10 will have bought less fuel than rent, yet they don’t complain with the same venom. Picture this: A lower cost homebuilt which took $25,000 to build, not to mention years of labor, which costs $1,000 a year to insure and $250 a month to store. The builder has an AARP card and may have only 10 or 15 good flying seasons left. If he flies 100 hours a year at 5 gallons an hour, he will spend $1,500 on $3/gallon fuel or $2,000 on $4/gallon fuel.  Only a fool would choose to fly a lot less because his annual operating cost went from $5,500 to $6,000/year. Reality says the sand is running out of the hour glass and you built the plane to fly it, not to protest the price of hydrocarbons.

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(3) Aviation Gasoline is not expensive and apparently here to stay.  Above Is a photo I took at the Palatka Florida airport the day Paul Salters Panther flew. Notice the $3.29 100LL price. This isn’t accurate today, as the price has come down 9 cents in the last 2 weeks. I have worked in aviation basically every day since 1989. In that time I have heard several dozen experts and magazine editors citing “new laws” , “Federal standards”, “lead being outlawed” all predict that 100LL would disappear in 1990. 1992. 1996, 2001, 2002, 2008, 2012, and 2016. Lord knows, there will be people saying it is being outlawed in 2017, and people will believe them, in spite of the fact they have never been right. On the price of 100LL, people like to quote the price at the signature FBO at Miami International Airport, because it justifies their statement “I would fly all the time, but no one can afford to anymore.”  The actual local price of 100LL is a small fraction of this distorted number..

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(4) There is a very ‘popular’ internet forward that states “Gas was $1.89 the day President Obama took office, and it is a record high today at $3.69” People like this, it gets passed around in aviation circles all the time, it just doesn’t happen to be true. The record peak gas price in the US was August 2008, when  George Bush was president, and it was $4.11/gallon. The change to $1.89 in 5 months reflects the economic collapse in the fall, and it says nothing about either president.  The $3.69 was July 2014, the actual national average today is $2.13 a gallon. essentially unchanged in eight years. There are a lot of people who think the price of gas is set in the oval office, and there are even more who decide if they can enjoy their life based solely on which party is occupying the public housing at 1600 Pennsylvania avenue. My personal love of airplanes goes so far back in my life, it certainly predates my awareness of politics. Given an chance to go flying or argue partisan debates with misleading data, I confess to being in the minority, the people who would rather build and fly.

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Dated Sources of Information: Example – Fiberglass fuel tanks

Builders:

I am now about to demonstrate my commitment to the risk management of today’s homebuilders, by “Touching the Third Rail” of homebuilding, I am going to say something that strongly disagrees with a man who since his passing has been elevated to infallible sainthood in homebuilding,  Tony Bingelis. This will certainly generate hate mail, but that’s OK it just keeps the Christmas card list short.

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Before people get up in arms, let me make several statements: Tony Bingelis was a real homebuilder, He made about 10 planes, he wrote a lot of useful articles, particularly in the era when many homebuilts were plans built, and the plans lacked a lot of finishing details. Critically, while his writing didn’t include phrases like “I might be wrong about this” no where did he claim to be infallible. That aspect of his legend came later, not from people who appreciated his books (like me) but from people who wanted to have an infallible saint to follow, who’s comments were often vague enough to seem to support their particular personal myth they wanted to believe.

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Want an example? In his book on power plants, Bingelis’s advice on prop length is  “Keep your prop as long as possible, as long as possible” Sounds like a witty clever idea, but doesn’t constitute any learning, testing or experience. It is just a catch phrase that countless people have used as ‘evidence’  that their belief that props turning over 2200 rpm are inefficient, and any prop smaller than 72″ makes no thrust. Let’s compare an actual data point, from a contemporary of Bingelis: Steve Wittman. get a look at this story: From The Past: With Steve Wittman 20 years ago today. I went flying with him, his prop was a Cessna 150 prop cut down to 62″, and when we were doing 195mph, it was turning 3,600 rpm. Anyone who understands anything about the life’s work of Wittman knows that if the plane would have been 1 mph faster with a 63″ prop, it would have had one. My point is that Bingelis published a lot of great detail design stuff, but when he didn’t have first hand experience, he resorted to vague hangar mythology statements like his one on props, that later generations would treat as some kind of religious body of wisdom, which is a bad concept, in a field where we are supposed to Learn Build and fly.

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One of the first things people are going to say is that Bingelis’s book has a disclaimer in the introduction. It does, stating that none of the information is guaranteed to work. Actually this is one of the things I dislike about his writing. Go back and read it with a fresh set of eyes. Nearly every chapter has a subtitle disclaimer in it saying ‘this may not work for you, you should ask around. Read his comments on tank sealers: he will not come out and say “Don’t use it” he kind of says it but has a CYA, statement about how you should “ask around for yourself. ” If that was how one was to get information, why was the book written?

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What is wrong with a Fiberglass tank in the fuselage? First , It is the least crash worthy of any tank material. Second, they put stuff in fuel today that was not even dreamed of when Bingelis’s book was written in 1986.  The stuff can even be regional, and it might be in the tank of fuel you get on a cross country, after years without issue. Third, fuel tank sealers that worked great 15 years ago, don’t reliably work against the ethanol content in fuel today. Fourth, I have done a lot of high end composite work, and most home made fuel tanks including the one pictures are brittle pieces of crap, because the guy who laid them up had no training, and put about twice as much resin in the weave as desirable.

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So what is the real lesson here? I had a guy tell me that he is building a Pietenpol, and his Piet buddies, told him that Bingelis’s books are “timeless” and that he didn’t need anything other than the plans. I pointed out to him that I own an original set of 1930’s flying and glider manuals, I love them, they worth more than $1,500, but I am not going to build a Pietenpol tank out of soldered tern plate, just because that is what is shown in the plans, and 1930 or 1986, it doesn’t matter, dated information is dated information. Books on aerodynamics structures and physics of flight don’t change, however, books on materials and process do, and only a foolish person would restrict himself to information 30 years old.

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Today, there are lots of sources for proven information. There are modern day Steve Wittmans, and you should follow them, because their suggestions are based not on quaint sayings, but on tests you can study and understand.

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Above, a fiberglass 12 gallon aux tank that flew for several years in the passenger compartment of my friends Caviler, a wooden low wing plane with a 60mph landing speed. The book is one of Bingelis’s three, immensely popular books. In this one, it details all the attributes of making this kind of tank, even on planes where the tank is in the fuselage, with narry a word about the kind of risk this is. The book was published 30 years ago and Bingels has been dead for 15 years. Perhaps if he was alive he might revise his recommendations in light of modern opinions about such tanks.

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If you or your buddy have such a tank in your plane, I am not suggesting that it is “Un-airworthy” , but I am asking you as an intelligent human being to do some research and consider things. If your buddy says, “It’s been in there for years, I have seen plenty of them. besides, it is in Tony Bingelis’s book”  Then he is just the kind of mythology spreader I am speaking of, and it is a waste of time to try to get him to think, he just wants an infallible source to cite as validation for him being too cheap or lazy to change it. Please read carefully: If you have seen my story:Steel tube fuselages, “Safe” planes and 250mph accidents, and you decide that you still are ok with this kind of tank, because you have given it open minded thought, I am ok with that, that is actual thinking, not validation.

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Above, dull hatchet, half hearted swipe, and it is right through. Aluminum would do much better, and I doubt any human could put a dull axe through a rotationally molded plastic tank. There are countless plastic tanks, look at SummitRacing.com and search “Fuel Cell” Yes, they are cheaper than the materials in a fiberglass tank.

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I have been an aircraft mechanic for 25 years. If I was doing an inspection on a 70 year old plane, but only used the AD’s written up to 1986, under the justification that it was a “classic” plane and the information about it couldn’t have gotten any better since 1986, the FAA would take away my License, period. If some one was hurt in the plane because it was not compliant with a post 1986 AD, then I would be looking at a complementary vacation at a federal gated community. Experimental aircraft don’t have AD’s but the logic of using up to date information is exactly the same.

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Why this stuff matters to me: I have been burned over 40% of my body. I have written very plainly about the experience, and written articles like this: Pietenpol Fuel lines and Cabanes but quite frankly, I think most people don’t really care. Improving the fuel lines in a Pietenpol could be done for about $100 and four hours work, yet, years later, 75% of the planes still have hard fuel lines on them. Some people don’t care, others don’t like me personally and will not improve their plane, just because the suggestion came from me. I write this knowing that the great majority of people will not take the information seriously. I am OK with that, I don’t base my happiness on the actions of others.

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To read about the contributions of Tony Bingelis to Homebuilding follow this EAA link:

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http://www.eaa.org/en/eaa/aviation-communities-and-interests/homebuilt-aircraft-and-homebuilt-aircraft-kits/eaa-homebuilt-airplane-programs-and-resources/eaa-tony-bingelis-award/learn-more-about-tony-bingelis

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Air / Fuel ratios on Corvair carbs.

Builders,

Here are some short notes on the topic of carbs.  It is my hope that builders will read and think about them, consider the logic before jumping up to debate. The Comments are based on 25 years as a working aircraft mechanic and working with Corvairs since 1989. These comments are not based on a single planes experience, but take into account all types of testing, education, and practical experience.

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How Rich is right?  Recently, a builder has told people that correctly running aircraft carbs on Corvairs need to have black sooty tail pipes.  I can flatly state that this is way too rich, and there are a number of very good reasons why you should not fly a carb running that rich.

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As a logical base line for what exhausts should look like, perhaps we can all agree that an Exhaust of Certified plane, running 100LL fuel, with a correctly running engine, with by the book performance, a Certified aircraft carb running without adjustment for more than 20 years. is a standard we should use. This engine has never fouled a plug in 17 years, has never harmed the engine in any way. Notice that the inside of the exhaust pipe has a dusty light gray color, and that new paper towel was vigorously wiped on the inside of the pipe, and only produced that light stain between my thumb and the exhaust pipe. This is the correct color and soot content for any Corvair running an aircraft carb.  I know this from working with countless flying Corvair powered planes over the years.

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Why not black and sooty? A correctly running aircraft carb on an air cooled engine will have an air/fuel ratio of about 12:1 in normal cruise. This will automatically go richer, to some thing like 10.5:1 at wide open throttle, and in low power cruise at altitude, it can be leaned to 14:1 for maximum efficiency.  Any engine that is making black soot in the exhaust and can be seen to visibly smoke at 1,000 rpm is running an air/fuel ratio of 9:1 or so. I know this not just from books, and working on certified planes, but from directly reading a laboratory grade A/F meter while running an EFI Corvair on my dyno in 2007:

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Above, An exhaust evaluation as part of an Electronic Fuel injection test on a 2,700cc Corvair in 2007. It is shown running at power on my dyno. With this arrangement, a simple twist of a knob on the computer produced any A/F ratio you wanted to test. This is how I can say what A/F ratio produces visible smoke on a Corvair, and it is part of how I can speak about it’s relationship with power output.

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At any airport with a density altitude less than 3,000 feet, your Corvair should run perfectly smoothly and make good power with the mixture set full rich, just like any Cessna 150 with the same carb will do.  One of the reasons why I use MA3-SPA carbs is so they have the exact same ‘normal’ operation as any certified plane I have flown, and if the carb doesn’t work like it does on a Cessna or a piper, don’t fly it, period.

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A builder with an MA3-SPA carb reciently said his engine only ran correctly with the mixture pulled half way out. He was considering actually doing his first flight in that condition. His home airport elevation is only 516 feet. If I went to his airport, and got in a Cessna 150 and it took pulling the mixture out half way to run correctly, You could only make me fly that plane with a gun to my head. Something is wrong with it, and sane people do not fly planes with things wrong with them. It doesn’t suddenly become “O.K.” because the carb is now on an experimental. Wrong is wrong, time to correct the issue, not to find some condition where it kind of works for the first flight.

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Any guy who would consider flying a plane in that condition, has missed the point of this story: Risk Management, Judgement Error, money in the wrong place. Where Ken Lien was killed on the very first flight of his plane because he didn’t bother to correctly assemble the mixture control on his plane and it moved to idle cut off on its own. If you are in a plane, getting ready for the first flight, and the mixture has to be pulled half way out to run, please explain to me how you know that this isn’t the first sign that the mixture is assembled incorrectly.  You wouldn’t, and there is a significant chance the engine will quit.  People who want to die should step in front of busses, not fly planes that are not set correctly, as using a plane and poor judgment to end ones life only unfairly punishes those of us who practice intelligent flying.

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If the mixture was half way out on the first flight, and the new pilot had to do a go around on the first approach, most pilots would instinctively push the throttle, carb heat and mixture to the firewall.  This works, and it is the correct procedure. However if the pilot is tolerating a plane that must have the mixture half way out, when he does this, the engine will quit, he will overshoot the runway, and smash up the plane on the over run. All the local experts will then say “The Corvair quit, I told him not to use a car engine, he should have used an O-200” Neatly ignoring the fact that it is the same carb as the O-200, and it would have done the exact same thing.  If instead, the same pilot stepped in front of a bus, preferably while holding the hand of the ‘Expert’ who tells everyone not to use car engines, aviation would benefit, and the rest of us would come out ahead. Cold, but you know it is true.

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Engines running black soot are wasting fuel, prone to fowling plugs, can damage the cylinder walls, and will have excessive carbon build up. On the other hand……..wait, there is no upside.

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Anyone who says that an MA3-SPA needs to be jetted differently for different displacement Corvair engines is wrong. Think of how many different engines have run on my test stand, all with the same, untouched in 15 years, MA3-SPA. Note that I have the mixture set full rich on the stand, and it runs cleanly on all engines. And yes, my stand has both EGT and O2 sensors. Beyond this, Dan Weseman and I recently took his 3,000 cc and 3,300 cc Corvairs to one of Florida’s most respected dyno shops and ran them both is a day long session.  What carb did we use? Why the same one off my run stand. It ran perfectly on both motors and the shops very elaborate instrumentation showed that the air/fuel ratio stayed correct through out the power range on both engines, without any kind of adjustment. Aircraft carbs work like that.

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Would you like to know how aircraft carbs are supposed to be operated? Read this story: Cylinder Head Temperature measurement and learn what a Lycoming Operations Manual is.  Down load it, print it, read it and know it. This is what successful people will do.

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Conversely, You could get advice from a guy who is neither an pilot nor an A&P, who has never owned nor flown a plane with a mixture control, teamed up with a guy who has never seen a Corvair turn a prop in person, and another guy who damaged his engine by using a carb no one ever head of so he could save some bucks. Take your pick, but if someone doesn’t like the concept of listening to the professionals and people with experience, again, I am going to suggest that bus thing again, I know it sounds mean spirited, but people willfully doing dumb things shouldn’t even be called ‘accidents’ because they are not really. an accident is someone trying to do the right thing. Willfully choosing not to do the right thing is not an accident.

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This ends the technical part of this story.  No valid technical information follows.

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I am not listening to William Wynne because:

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One: He sounds arrogant, and although I have never met him, and he wrote stories about people he loved: Risk Management reference page in hopes that others could avoid being hurt, I still say he is a jerk because I found two sentences in the 855 stories that are on this site that offended me, and I refuse to learn anything from him since.

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Two: I own a Prius, and he is always mocking people who own Priuses, and I can tell he isn’t kidding, and he feels superior about this, which is stupid because as a Prius owner I alone have a right to feel superior to all other car owners because I know the best way to protest the use of fossil fuels is to buy a car that you can feel superior about.

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Three: When I was in his tent at Oshkosh pontificating about how America has been ruined because no one follows the Ten Commandments anymore, he asked me to name them, and I couldn’t. The year before I said the problem with America was no one followed the Constitution, and he asked me how many articles it had and I said 10, and he said “guess again, you are off by three” , and I guessed 13.  I don’t get the connection that I should read more before being sure I am right.  I never listen to people with long hair, even though William has essentially the haircut as Jesus and everyone at the Constitutional Convention of 1787.

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Four: I don’t listen to people who sell things, because they are trying to make money off me. I only listen to people on the net who’s opinion about how to do things can’t get them a job doing it, nor is it apparently worth money to anyone. Those are the people I trust.  Yes, I know that I should trust William because he has a vested interest in my success even if he actually likes me or not, But I would rather trust people I have never met, who write in nicer tones, who I have a simplistic childish belief are motivated to tell me the truth, unstained by their limited experience, personal bias, and ego.

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If anyone read the above for points and didn’t find them funny, you probably have good taste, and I remind you I am a mechanic, not a comedian. I have a small but consistent group of people, most who have never met me, who remain quite sure that I have a “Condescending tone” and a “Giant ego”.  Before anyone is temped to say those things, I ask that they read the two paragraphs below, which appear both on my website and in every manual we print, and please share with me how this isn’t adequately honest and frank:

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“If you have never met me, but read this and think that I am charmed with myself, you got it all wrong. I know countless humans who are better people than I. They are kinder, smarter, and harder working. I can’t sing nor dance, I learn slowly, and I can’t stand to hear my recorded voice nor see my image on film. If I was once handsome, all trace of it is gone along with my uncorrected eyesight. I can be a conversational bore, and I deeply wish I had given my parents more moments to be proud of me. At 50 I look back on my life with a very critical eye and stand on the far side of a very wide gulf from the heroes of my youth. Even our dog, impeccably honest and loyal as canines are, Loves Grace and only tolerates me.

Honest evaluation leads to harsh thoughts like this. I spend a lot of time alone and have long bouts of insomnia, which can lead to thinking about things excessively. But the secret I would like to share with anyone who at times feels the same way, is that I have a sanctuary where I am insulated from much of my self-criticism, and a have a front, where at 50, I am much better on than I thought possible in my youth. When I am building things with my hands in my shop, I rarely feel poor. Although I now need glasses to do any close work, and my hands have lost a lot of dexterity, I am a far better craftsman than I ever was in my youth. I am not a great craftsman, but over a very long time I have worked to develop these elements in my life, and I compete with no one except who I was last year. While all else fades, these things flourish. It is a gift I am most thankful for.”

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Compression Ratios, Fuels and Power Output

Builders:

Here are three topics that are related. Although the conversion manual covers this in some detail, I will put a short summary here.

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We have 3 popular displacement s for Corvairs 2700, 2850 and 3000 cc (read more: Sources: Choosing a displacement.)  The latter two are made with a very special dish in the piston to lower the static compression, but keep the ‘quench area tight. On any of these displacements you can either put lower compression 95 hp heads, or you can put higher compression 110 hp heads. Right there you have six combinations with different compression ratios, but it is also possible to build engine with high or lower compression, but those six are the popular ones, and having the option allows Corvairs to suit different builders purposes.

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The two basic rules are: The higher the compression, the more power the engine will make….and There is a limit to how much compression you can use with car gas. The commentary here is general, but it comes running engines on our own planes from 7.7:1 compression (1998 2700 engine in our Pietenpol) to 11:1 compression (2005 3100 engine in our 601XL) I write this as a guideline, if you have a specific application, feel free to ask in the comments section.

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Basically any of the three displacements with 95 hp heads will have compression ratios from 8:1 to 8.5:1. Engines built with 110 hp heads will have ratios from 9.0:1 to 9.5:1. The variation is mostly in the machining done to the head gasket area, and the actual gasket thickness.

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The First question is what is the lowest Octane fuel you will ever use in your plane? In the answer is “I will never put anything but 100LL avgas in my plane” then you can use any compression ratio you like up to 11:1. Your engine will make about 5% more power for each whole point you raise the compression. But….you can never, not once, ever, run the engine on car gas, even 93 octane car gas if the compression is much over 9.5:1. 100LL is great fuel. yes engine can be detonated on it, but this is done by leaning the motor out far too much or not having the timing set correctly. Our 11:1 compression engine flew more than 600 hours on two different airframes The first 200hr was 11:1, we dropped it slightly to 10.5:1 for the rest of its time) It never detonated at all, and it never saw a drop of car gas either. 100LL when running slightly rich has a comparative octane of nearly 120.  Keep in mind that many people swear they will use nothing else, but later after the 40 hrs. are flown off, some people start getting cheap, and the are tempted to run car gas in a 9.5:1. They might get away with it under some conditions, but sooner or later, they will pay.

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Let’s say you are going to run ethanol free 93, or some mixture of this and 100LL, how high is smart to go? You could run up to 9.3:1 and get away with it, as long as you don’t excessively lean it. But what is the benefit of running on the ragged edge? If your engine is built with a ratio of 9.0:1, there will be hardly any measurable performance difference, but it will have a large increase in resistance to detonation.

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What about running 91 or 92 Octane car gas? Then it seems prudent to shoot for the lower range offered by using 95 hp heads. I have never been interested in speculation on what “should work”, I am much more interested in builders developing enough judgment to understand they are far better off with set ups that have a greater margin of safety than a slight performance edge.

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Examples:

Woody Harris , who’s plane is pictured below, started flying with a 9:5 to 1 compression 2700. (Flat top pistons and 110 hp heads). Because he was planning on switching to a Turbocharged installation, he went to an 8.25:1 2,850. (dished pistons and 95 heads). Woody had enough fun flying around, that he didn’t get to turbocharging. Woody has long reported that the power output between the high compression 2700 was about the same as the low compression 2850. This isn’t a surprise. Woody mostly flies on 100LL, but if he or anyone else was planning on running 91-92 octane fuel, they would be vastly better off with the lower compression 2850.

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My own 3,000 cc engine: Is set up at 8.3:1 compression (dished pistons and 95 heads) Although it might make 6 to 8 more hp if the compression was raised to 9.5:1, I don’t care because I am not running 100LL, my choice is to run ethanol free boat gas, which here in Florida is 90 octane and sells for about 10 cents a gallon more than 93 with ethanol. This week that is $2.80 a gallon. This is a very clean burning fuel and  it stores for a long time. On a cross country the engine will not care if it drinks some 100LL, again the compression ratio is determined by the lowest octane you will use, not the highest.  A few more hp isn’t going to make the Wagabond into a speed demon, I am after absolute long term reliability and being able to run any fuel available.

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Ron Lendon’s 2,850: Ron built a clone of Woody’s 2,850 engine with dished pistons and 95 hp heads. Recently he changed to flat top pistons and 110hp heads. This changed his compression ratio from 8:1 to 9.5:1. Yes, this will make more power, and it is OK because Ron says that he only runs 100LL . In short, he didn’t start with the highest performance option for the fuel is was going to use. Ron has worked for GM in their enginnering department for decades, so perhaps like most people who saw fuel prices in 2009, he might have been thinking about auto fuel then. But it pays to plan around the fuel you will eventually use. To keep things in perspective, I am sure that a 601 with a low compression engine and wheel pants met a 601 with high compression and no pants, the one with wheel pants might be faster.

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In the above photo, Woody Harris’ 2,850cc Zenith 601B sits at the end of the ramp in North Carolina at First Flight Airport with the Wright Brothers Monument in the background. Woody’s home airport is in California. He has nearly 500 hours on the plane without issues. read more:Woody’s 2,850cc Corvair/601XL hits 400 hours.

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Woody in the Grand Teton National Park WY

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Lest anyone think that low compression engines don’t make good power, above, Woody flying over Grand Teton. He often flies around the Sierras, and has flown to the highest and lowest airport in California in the same day.

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Above, a drop forged, made in the USA piston for the Corvair. The  displacement of this piston is 2,850 cc. read more: Turbocharging Corvair Flight engines Pt. #2

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2005 photo of our 601XL in front of our Edgewater hangar. The engine is a 3100 cc with 140 hp heads, oversized exhaust and 11:1 compression. Because it was a tail wheel and low drag it was fast. With wheel pants and the right prop turning 3,500 rpm, this plane could exceed 145 mph at sea level. People asked about weight, but at the 601’s low wing loading, it is slightly faster when loaded. They are good planes, but other than demonstration purposes, anyone really concerned about getting the last mph out of a 601 probably picked the wrong plane. It beauty is in utility, not speed. Note the size of the inlets: Here we have the most powerful Corvair engine that builders have heard of, yet it cooled itself just fine in hot Florida with 4.75″ inlets and a front alternator. It is a myth that this installation needs giant inlets to cool itself.

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Same plane, at sun n fun 2006. Sensenich prop was faster, but didn’t climb as well. I could have built the same engine for the plane we have today, but instead I chose something on the other end of the compression scale because I don’t wish to be tied to 100LL forever. Take your pick, what ever makes sense to you.

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Above, Dr. Andy Elliott, of Mesa AZ with the same engine on his 601XL. The photo was taken at Oshkosh, so it is safe to say the plane flew without issue. Andy flew the engine another 400 hours. His state has the highest summer temps of anywhere in the US, and yet the high performance engine cooled through the same size inlets. Andy’s plane could do nearly 140 mph. The power was a factor, but aerodynamics matter more and are cheaper. Before selling the engine to Andy, I reduced the compression slightly, but he still knew to always run 100LL.

-ww.

#3410-Nason switch-(For planes with electric fuel pumps)

Builders,

Here is a look at a simple, but important part of the Corvair installations which require electric fuel pumps. Please note: While this part looks identical to the switch we used from 2003-2005, it has a critically different pressure rating, and no Corvair powered plane with electric fuel pumps should be flying with the earlier number. Nason’s part number for the correct unit is SM-2C-5F. I mention this because just this year I found an aircraft in the Corvair fleet still flying the wrong part number.

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The purpose of the switch is simple: If the plane has an accident, and the engine stops but the primary fuel pump is left on, The switch will detect the oil pressure dropping, and automatically cut the primary electric fuel pump off, without the pilot having to act. Note that the system is not used on the back up electric fuel pump, for reasons of having the simplest back up possible.  Our 601XL, N-1777W, may not have been the first experimental aircraft to use such a system, but we were the first people to widely popularize the need for it in all planes with primary electric pumps. It was nominated for an EAA award for safety design of the year, but nothing came of this and the idea was not published beyond our personal efforts.

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There are alternatives to this derived from a Bosch system extracted from German cars which cut off the pump if it detects the coil is no longer firing, but no one should ever connect any device to the Corvairs’s ignition system that it does not need. Here is an example of that mistake: MGL vs Corvair ignition issue. No one should connect a tach, sensor or any other device to the ignition system, it is a failure point. I have been writing that for 20 years, but people still do it, and it has caused issues, but thankfully no one has been seriously hurt…yet. Don’t be the first.

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Above is a 2008 picture from our website, with 13 Nason switches, part No. SM-2C-5F. We were reminding builders then to switch to use. This switch automatically cuts off the fuel pump when the oil pressure drops below 5 psi. The original switch was the same function, but the switched closed at 20 psi.

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We started with the 20 psi switch because we originally used the Corvair’s mechanical fuel pump (We stopped this in 2004 when we conclusively demonstrated that all modern replacement Corvair mechanical pumps were prone to leaking), as the primary. The electric back up fuel pump was automatically activated when the mechanical dropped below 4 psi fuel pressure, and was automatically stopped when the oil pressure was below 20 psi. This prototype mechanical/electric system was replaced by modern system we have today in the summer of 2004. We originaly kept the 20 psi switch.

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However, with many builders retrofitting 5th bearings, some engines would have a hot idling oil pressure below 20 psi, and this could potentially lead to a builder gliding in on final with a hot engine and the low oil pressure cutting off the primary fuel pump. Switching to a 5 psi Nason prevents this from potentially happening, We have promoted this almost 9 years, but some builders with 5th bearings missed this important change.

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We now have a large number of  SM-2C-5F’s in stock and will be glad to supply them at $43 including S&H in the U.S. It is part number #3410 at this link: http://www.flycorvair.com/products.html

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Above is the ignition wiring diagram for a a Corvair system. The Nason switch is on the upper left. Note that it is only wired into the primary fuel pump, not the back up .-ww.

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Fuel lines and Cabanes, part 2

Builders,

Here is part two of the Pietenpol Fuel line – Cabane story. The pictures and text below are taken directly from our 2010 Brodhead/Oshkosh story on Flycorvair.com. I mention this to show that there is a wealth of information there, and that my comments on these Pietenpol components are not new positions.

I recognize that some people have difficulty finding everything on the old site and on this one, even with the built in search capability. To fix this we have the reference pages, both here and right on the front page of Flycorvair.com. This story will be first published as news on Flycorvair.net, but it is also now immediately cataloged with part #1 on the Pietenpol reference page on Flycorvair.com: Corvair – Pietenpol Reference page

 I am putting a lot of effort into making the information more accessible to builders working on specific airframes. The other half of the equation that builders can really help with is sharing the specific links to our stories on discussion groups they work with.  For example, there are several Pietenpol discussion groups, and these two stories really apply to any Pietenpol builder, not just people working with Corvairs. Builders can help by mentioning this stuff and pointing out that it is all organized at the link above.

Below, I put the original 2010 text in blue. Newer, additional comments are in black.

Although this photo is taken from a flying plane, this is not the best way for the front cabane strut to be done on a Pietenpol. The Piet is a very strong aircraft  with a very strong wing. It would be very difficult to break a well made one in flight. This said, in an off airport landing or accident, the weak link in the airplane  is the connection between the wing and the fuselage. In a sudden stop, the forward diagonal cabanes get a massive compression load, and if they’re set up like this, they  will bend like cooked spaghetti, allowing the wing to parallelogram forward, potentially trapping the passenger. The primary reason why people make the cabanes this way  is that they believe the old wives’ tale that the wing of the Piet can be moved forward and aft to resolve any CG issue.

Get a look at two things above: This type of tubing end is what I refer to as “1960s swing set technology.” You can do better than this. Also look at the hard line with the metal clamp fixing it to the rear cabane. This is exactly what I was speaking of in part #1. Don’t think I am picking on a particular builder, I don’t even know who’s plane this is, and about 75% of flying Piets have this kind of issue. It costs very little to correct.

Here is the much preferred methodology of cabane attachment on Pietenpols. While it won’t make the plane as crashworthy as a Grumman AG-Cat or AD-1 Skyraider, it will vastly  improve the strength of the wing/fuselage connection in a survivable accident. This means that the wing could very likely stay in place in a small event. Keeping the  center section in the correct location is also an important factor in not rupturing the fuel lines from the wing tank. The primary reason why people do not make  their cabane struts this way is that they lack the weight and balance data to be sure of the wing’s location before the plane is finished. Now that we have the data,  making a cabane attachment like this can be done with confidence in the final wing location.

Above, Note that this plane has very good cabane arrangement, but it has a rigid metal line. I pointed this out to the builder who corrected this. A small number of well known Piet pilots have made upgrades to their planes on these two issues. Kevin Purtee changed his fuel line before is accident in 2012 and later told me that he thought it was one of the factors that prevented a post crash fire. Think that over, and decide if it is worth a few hours and $80 to change. -ww.

Pietenpol Fuel lines and Cabanes

Builders;

I am up visiting Mom and Dad here in NJ, and I stumbled over this photo from 2000 at Brodhead. It is the perfect one for me to share an important safety lesson for all Pietenpol builders. I have pointed this out many times in the last 10 years, but very few people have paid much attention. It is important, and I write this hoping to get a few more people to reconsider these points.

MWF

Above, I buckle in my seven year old nephew in the front seat of my Pietenpol for his first light aircraft flight. This is Brodhead 2000, a long time ago. (Matthew is 6’4″ and a senior at Duke today.) The guy in the cockpit is Arnold Holmes,  Long time friend and local host of Corvair Colleges #17, 25 and 29. This aircraft, N-1777w, was destroyed in a crash in July 2001.  This photo clearly shows two details that no Pietenpol builder should have in his aircraft.

Looking at the photo today, I cringe at the very idea I put a child in this seat, that as an experienced builder I didn’t see what could happen with this arrangement. While I am not happy that a friend stalled/spun the plane, I am morally thankful that I, and not one of 100 passengers the plane flew, that ended up covered in burns and grafts.  I have made 3 serious mistakes in my life that I live with, but do not forgive myself for. I understand this kind of weight. Speaking just for myself, I could not carry the burden of  someone’s kid or wife being harmed by a part on my plane I was too lazy or cheap to make better.

The two issues here are the fuel lines and the diagonal cabane struts. The design’s four vertical cabanes made shifting the wing forward and aft to fine tune the CG possible. But, in a crash, this works against you, and the inertia of the wing assembly and the fuel in the tank provide tremendous force to displace the wing forward. The only serious thing resisting this are the diagonal front cabanes. If they are built to a size like 1/2″ x .035″ tubing, they will work great in flight, but fold like cooked spaghetti even in a small accident. When this happens, if you have the wrong fuel line or clamping on it, the person in the front seat can get covered in gasoline, just as they are trapped by the collapsing cabanes. I know this from personal experience, and I have since studied other Piet accidents, and this is a common thread on aircraft with light diagonal cabanes.

I have had people with flying planes and small diagonals say to my face “It will be alright.”  Weigh that against my 5 years at Embry-Riddle studying aircraft structures and accident investigation and my 3 square feet of skin grafts and decide who you are going to listen to on this. If you are new to homebuilding, let me point out that people who utter the phrase “It will be alright” don’t actually believe this 100%, they know what they are doing is foolish, but they say the phrase aloud like a mantra they are hoping to indoctrinate themselves with. Listen for it, you can hear it at any airport on any Saturday in any state. If you follow anything that person later says, who are just listening to a lullaby and going to sleep while you are on watch. Roman legionaries who fell asleep on watch were put to death.  In the last 2,000 years the world has become more forgiving of laziness obstructing vigilance, but flight is a throw back, with more in common with the days of Julius Cesar. Deciding that you are just not going to care about these details on your own plane is the eqilivent to letting out a real big yawn when you are on guard duty.

In the photo, you can see the diagonal cabanes on my plane were 5/8″ diameter, with small adjustable ends. This is bad. The minimum size I would use is 7/8″ x .058″, and these need to be welded to the front verticals, not bolted, and really not bolted in with flattened ends like a 1960s swing set. Welding will preclude making later CG adjustments, but I have already taken away this excuse by doing the weight and balance on electronic scales on 30 flying Pietenpols  and publishing this in a 5 part series in the Brodhead Pietenpol newsletter. The data was for everyone, not just Corvair builders. If you would like an example of welded cabanes, search our site for pictures of Dave Minsink’s Piet. Upgrading like this will not make you immortal, but it will be a huge increase in safety in a survivable accident.

Second, the fuel lines: My plane did not have a fuel tank in the center section; instead it what is called a ‘wet wing’, where the center section was the fuel tank. The structure was wood and fiberglass, and it held almost 18 gallons within the standard airfoil shape. To get it to completely drain and be 100% useable with the Piet’s under cambered airfoil, I made the 1.5″ x  2″ x  24″ sump seen on the bottom of the wing.  This was made from 8 layers of vacuum bagged glass. I know what I am doing around composite materials, and this did not rupture nor leak when the plane hit the ground. We are not speaking of a light hit either, the impact drove the left front gear leg through the floor and came up so far it sliced the underside of my chin. The wing parallelogramed the vertical cabanes until the gap I slithered out of was about 10″ high. It took me about 1 minute to get out. What covered me in gas was the two 3/8″ aluminum hard lines being stretched and broken just below the blue AN fittings. The displaced vertical cabanes and having the hard lines tapped to them was the cause. In the photo there were just a few passes of tape on them, but on the accident day I had them taped for about 12″. It looked neat and clean, but it was a bad idea, just like when people use steel or aluminum clamps.  The diagonal cabanes needed to be bigger, the fuel line need to be a real braided steel AN flex line (not a rubber hose) and it needed to be secured with light, weak, plastic zip ties and have some slack in the system.

 I got out of the wreckage by a very small margin. If the gap was 1″ narrower, or I was 10 pounds heavier or wearing a bulky jacket, I would have been trapped. Sliding out, the two open lines poured a steady stream of 100LL on me.  The pilot was knocked out cold for a minute, and was uselessly groggy for several minutes. Although there were people standing there, no one approached the plane, and I dug Jim out by myself. I wasn’t really cognizant of being soaked in gas, but I do remember being very cold from it evaporating. I got Jim out of plane and 100 feet away before the plane ignited, but I had left a vapor trail in the grass that led right to me. It took only 40-60 seconds to do the damage. Rolling on the ground does not put out fuel soaked clothes. Giving in to panic, I was getting up to run, but was fortunately caught by Jim who tackled me smothered the flames.  This is an accident that no one need to repeat.

What do I hope to accomplish by sharing this story a week before Christmas? I was just thinking that there may be 3 or 4 guys who read it who live in cold places and have hangared for the winter decide that this is the winter that they switch to stouter cabanes, or make a better fuel line arrangement. Maybe a few guys building will review the CG articles, calculate their own fixed CG from the examples, and them build welded cabanes.

Will many people switch over to something better? Experience says that most people will just look at their small diagonals and hose clamps on old non-ethanol rubber fuel line and say “It will be alright.”  I will attend Brodhead and hear people talking with great vigor over crap that doesn’t matter like Latex paint vs Stitts, (they both work) How much better a plane 50 pounds lighter glides (all planes have the same glide ratio at gross as they do lightly loaded) and how much better Riblett airfoils are (they are about the same). All the while I will see people with planes flying 2″ out the aft CG limit, with tiny cabanes, welds that look like painted over old chewing gum. I have no explanation for why people want to debate things that don’t matter, while ignoring things that do. If you can figure it out, you are a better man than me.

I just try to say focused on things that I can control, like my own work and what I choose to fly in. I turn 51 next week, and I figure I have 24 flying seasons left, give or take. I have many things still to build and many places to fly and friends to see. There are worthy of real effort and thought, and spend very little time worrying about why most people don’t care enough. -ww.

Fuel Injection – Corvair flight engines reference page

Builders:

Here is one spot where we have collected a number of different stories on Fuel injection for Corvair aircraft onto a single reference page. Like the other reference pages, it is a central starting point on the topic, and easy to keep updated or make additions to. If you are interested in learning more about this topic, read on, there is a significant amount of information here.

If I were to pick a single topic that new builders are interested in, but know little about the applications of, It would be Fuel Injection. This is a topic dominated by misconceptions and myths. Here is a quick check: Do you think that a port fuel injection engine or one with a carb on a long intake manifold makes more power? Would you be surprised to learn that the evaporative cooling effect of the carbs fuel delivery can give it a significant advantage? It does, and to learn this and many other points on reliability, read on. Unlike much of the info on the net from armchair experts, the information below is straight from experience and testing…in aviation settings, not in cars.

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The information below is in the following order:

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1) Links to stories I have written on FlyCorvair,net

2) A full print of my Group numbering system #3700 EFI notes.

3) A reality check story from 2008 on EFI failures

4) Notes on Internet ‘experts’ you should beware of

5) A 385 mph EFI plane and some final thoughts.

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Above, a rear view of the Panther engine. Mounted on the intake is a Precision Mechanical fuel injection system. Initially, these was the planned fuel system for the Panther, but after careful evaluation, Dan Weseman opted to go with a very simple MA3-SPA carb. All of the aerobatic flights on video on the Panther site are done with a one barrel aircraft carb, not injection.

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1) Links to stories I have written on FlyCorvair.net:

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Click on the titles in color to read the full stories:

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Mechanical Fuel Injection Testing

Compares Precision and Airflow performance instalations

Fuel Injected Corvairs

stories on 3 running EFI engines

Group Sources for the new numbering system.

Covers that EFI is Group  #3700 and Mechanical injection is Group #3800.

Panther Prototype Engine 3,000 cc/120 hp to OSH

Another look at the Precision system

Corvair Powered Davis DA-2, w/EFI

The only successful flying EFI Corvair powered plane. A hard won achievement.

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2) A full print of my Group numbering system #3700 EFI notes:

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3700- EFI (Electronic Fuel Injection)

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Many people just arriving in aviation are interested in electronic fuel injection.  Some homebuilders are impressed with its performance in cars or have read about one of the handful of experimental aircraft flying with fuel injection. After listening closely to builders, I discerned their interest originated from five reasons: 1) They thought it would make the engine more powerful; 2) They thought it would reduce fuel consumption; 3) They felt that it would eliminate the possibility of carb ice and eliminate the need for carb heat; 4) They thought it would be more reliable than a carb, or; 5) They just wanted to try it. Experience has shown me that the first four are not true to any meaningful degree, and that #5 is the only reason that makes sense. If you are pursuing EFI for reasons #1-4, you are going to be disappointed, but if #5 is your motivation, then the project may be a success to you.

Let me first say that I am not against EFI, but I think that builders should know the facts before they pursue it. My background on EFI installations in planes is better than most. A guy who works on them all the time in cars, but doesn’t put them in planes, has a long way to go before he learns what he needs to know to be reliably and safely flying. I did a lot of work on Jim Rahm’s 427 cid V-8 Lancair IVP. It had the best EFI system in the air. We had the best people working on it, a nearly unlimited budget and experience that no homebuilder in his garage could match. It took a lot of very hard work to make it the reliable system. Just because Jim’s motor made 600 HP and you only want 120 HP doesn’t mean that solving the installation issues will only cost you 1/5 the time and money. And even if it did, we would still be speaking of time by the calendar years and money by the cubic foot. When I read discussions on the Net about EFI on experimental aircraft, I can quickly tell who has never assembled and flown a system.  95% of the advice on the Net is offered by people without flight experience. Out of the 30,000 experimental aircraft in the U.S., I am fairly sure that less than 300 of them have EFI. I cannot think of a single significant aviation record below 500 HP that is held by an EFI engine. There have been many clever people who put a lot of effort into EFI on planes, with little result. No matter what caliber of auto mechanic you are, experience says that you will find exceeding the performance of carbs or mechanical injectors very difficult, and EFI may never have the reliability record of the simple 1 barrel carb.

Out of the roughly 300 experimentals flying with EFI, the vast majority of them are using 1990s auto engines with EFI from the factory. In this case, the factory engineers did most of the work. If you think about it, there are very few motors like O-200s, VWs and Corvairs flying on EFI. And the ones flying can’t boast the flight record of carbureted engines. I have seen a number of these planes flying with 35psi fuel pumps inside the cockpit with barbed hose connections and hose clamps. No one should dream of flying things like this. Let’s examine the points one by one objectively to learn about the issues and make an informed decision.

1) I have seen claims that EFI makes the same engine 30% more powerful. Nothing of the sort is true.  Engines make power because they burn a mass of air mixed with the right amount of fuel. There is no way that an engine is going to inhale significantly more air because it doesn’t have a venturi carb. This advantage is slight, and would be well below 5% on an engine like a Corvair. To see any more difference than this, the cylinder heads and intake tract would need to be designed for it right from the start, by very smart people with a lot of sophisticated equipment (of the caliber found in Detroit factories). Slapping an EFI system on the Corvair will not have the same effect. Fuel injected motors are said to make slightly more power because the fuel is better atomized. But carbs, even simple ones, are surprisingly good at this. The amount of records still held in racing by carbs should tell anyone that the EFI power advantage is minimal. Carbs have a very serious advantage of vaporizing the fuel well upstream, and having the air/fuel mixture cooled and its density increased. In almost every case, this offsets any gain in power from atomized fuel. When running at power, Corvair intake manifolds are cold to the touch from vaporizing fuel. EFI does not have this effect.

2) EFI will not significantly reduce fuel burn in a Corvair engine. For best economy, engines need to run a lean mixture. EFI has the theoretical ability to atomize fuel slightly better allowing it to run slightly leaner mixtures than a carb could without detonating. In actual use, it is foolish to run an engine this close to detonation. Modern auto engines can do this because they have computer-controlled ignition tied to a knock sensor and the fuel injection. Without these devices, any significant fuel burn advantage is lost. Many of the well known auto power proponents, even those who work with computer controlled EFI engines, clearly state that EFI doesn’t significantly reduce fuel burn for a given HP in aircraft engines. The efficiency advantage in cars is gained by running in “closed loop” with air/fuel ratios near 14:1. Under this operation, the injectors are fine tuned by reading the O2 sensors many times a second. The reality that few new builders understand is that any engine running at 75% or more power has to be running an air fuel ratio of 12:1. At this setting, O2 sensors don’t reliably work, and the system will operate in open loop, forfeiting any efficiency gains while retaining all the complexity and vulnerability. I have never seen any EFI flight engine that will fly at cruise power in closed loop mode. They are all just operating off a set of pre-programmed values based on RPM and MAP. These can be very crude, as some aftermarket EFI systems have RPM increments as rough as 250 RPM. In cars this would be masked by the O2 sensor moderating the injectors, but it can’t when it is in open loop. It is technical reasons like this that allow carbs to often demonstrate smoother operation than EFI in experimental aircraft.

3) EFI is less prone to carb ice, but is not immune to this trouble. There are still conditions that can cause this trouble. Almost all injected engines have an alternate air source. Homebuilt aircraft in Canada are required to have heated alternate air no matter what the fuel system is, and there is good logic to this. For a more complete discussion of this, see the article on carb ice at the end of the Manual.

4) Many people feel that EFI will free them from things like carb ice, reducing their level of risk in flight. While the risk of carb ice would be reduced for a pilot too careless to use carb heat, many new risks are introduced. EFI requires high pressure pumps, regulators and lines; it can be stopped by a piece of trash in the fuel that a carb would easily pass; its numerous electrical connections are prone to failure by corrosion or poor crimping; and the whole thing is so electrically dependant that most people fly with two batteries. Contrast this with a gravity feed fuel system in a plane with distributor ignition which will run for hours on a small battery with no input from an alternator. You cannot focus on the one possible advantage of a system without considering all the downsides that come with it. Automotive EFI installations are reliable today because auto makers spent literally billions to make them so. Brilliant people in Detroit who are specialists in dozens of details of the installations and privy to incredibly accurate statistical data on failures allow them a great corporate body of experience to tap into with every installation. It is my feeling that anyone looking into EFI who states that it is more reliable is making an argument for the car, not what an individual homebuilder can do in a plane, where a single detail of installation may compromise the system.

My observations on reliability are simple: Any system that uses lower pressure fuel is less likely to leak. Gravity is better than 5 PSI, and 5 PSI is better than 40 ; any system that uses no electricity is better than one that uses  a little, and one that uses a little is better than one that uses a  lot, especially if the one that uses a lot needs it to be a  certain voltage; any system that has less parts and connections is less likely to  fail,; digital electronic connections, working a low voltages, are very sensitive  to corrosion, temperature, and vibration, things planes produce more than newer  cars.

5) Being an experimenter at heart and wanting to address the challenges of an EFI installation is a valid reason for trying it. You know a good, reliable and airworthy system is quite a challenge because you don’t see them often. Anyone who achieved this could be justifiably proud of his creation and would learn a lot along the way. A person who is motivated by this will be satisfied when it works, whereas people motivated by #1 – #4 are bound to be disappointed when EFI cannot live up to the overblown claims many armchair/Internet experts make for it. The only good reason to work on an EFI Corvair is because you want a challenge, and this is more important than finishing your plane soon, or operating at a lower risk level. This is a valid position, and I support anyone who knowingly makes it.

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3) A reality check story from 2008 on EFI failures:

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” A Christmas story”

 At 8 a.m. on December 24th 2008, I was driving my 175,000 mile EFI S-10 up I-95 at 75mph. I had promised my parents that I would make it to their house for Christmas Eve dinner. I had never had a bit of trouble with this EFI engine. Near Richmond, Va., it quickly died out, and I was only able to coax it into a truck stop at 10% power. A morning of diagnosis showed that the pressure regulator had died. It was not in an easy place to get to, no one had a replacement and the truck was worth maybe $500 before it was broken. I gave the truck to a 20-year-old tow truck driver wearing a Chevy hat and a Jack Daniels sweatshirt, as a trade for a ride to a car rental place. We got there 10 minutes before they closed. The driver asked me several times if I was really giving him the truck and if I really was from New Jersey. The experience was counter to many things he had been told about people from N.J.  After some reservation, he took the gift of a truck from a Yankee on the eve of the birth of Jesus to have special significance.

 Such a warning less failure in a plane might prove to be lethal. Note that aircraft carbs almost always run even when they are having an issue.  A good look inside Pat Panzera’s Contact! magazine issue #96 shows a destroyed homebuilt aircraft, product of a sudden EFI failure. Here is a story of a guy who may have felt that carbs and engines without O2 sensors were stone age. Maybe, but stone age tools are noted for reliability. I am glad the builder was not more seriously hurt. Over the years, a number of people have written to explain that they are going to engineer their own EFI systems, or use something called “shareware” to program one (the blind leading the blind on the Net). Out of perhaps 50 people who have written this, not a single one of them went on to produce a running EFI engine. Experience tells me that people who arrive with a big flourish and little consideration for what has been accomplished have a very low chance of flying anything.

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4) Notes on Internet ‘experts’ you should beware of:

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A modest search on the internet will reveal many people speaking about EFI for Corvair powered planes. Armed with the information I have printed above, you can debunk most of the claims people make. Still, there are people who present a case to new builders as if they are some type of experienced expert to be followed.

The internet is an odd storage device. I holds more old trash better than any landfill on earth, and it keeps it fresh, even long after the project was abandoned. Let me share by example: Don’t waste the time to look it up, but there is a long detailed website run by “Haynes Engineering.” Sounds official, but it was just one guy in a barn who had never built a flying plane before, offering a long how to session on putting EFI on a Corvair in a Zenith 601. I never met the guy, but I did email him several times, and he spent a long time on Mark Langford’s discussion list, where he had many fans who eagerly awaited Mr Haynes demonstrating all the things he promised from is Harley Davidson salvaged system. Although I offered to publicly test run his engine at a college, Mr. Haynes soon despised me, probably for not recognizing his brilliance. His website is all about putting a Corvair on a 601, but makes no mention of Our success with doing this, or my work at all.

If you have built planes, it was easy to see that Haynes didn’t know much about planes, but had the kind of ego that didn’t like admitting that. He was a foolish cheap skate, ‘rebuilding’ his engine with a used cam and worn gear, and using angle iron to build a motor mount. His EFI system had hard aluminum lines where it needed flex ones, and he spent a lot of time trying to use a little outboard starter. In the end, after getting many green guys excited, he couldn’t make the engine run, and instead started it for 5 seconds on starter fluid, and then wrote a post to the internet silmaltainiously declaring victory and quitting airplane building altogether. Does this sound like a stable person who you can learn from? Is it the kind of information that you want to bet your life on? This was years ago, yet I saw the website just last week, with no mention of the system never working or the whole aircraft project being abandoned.

If you are new to home building, the quicker you learn never to be distracted for real progress by day dreamers and fools without experience, is the quicker that you will learn what really works, and how to incorporate these skills into your own experience and your own plane. The internet will provide an endless stream of people like that. 80% of the people who start a homebuilt do not finish. Be determined to be in the 20%. One of the things that the 20%ers all have in common is not getting sidetracked by fools.

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5) A 385 mph EFI plane and some final thoughts:

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I’m known for advocating simplicity in aircraft engines. This recommendation comes  from my experience on the opposite end of aircraft powerplants. Above,  Arnold Holmes (host of CC#17,#25, #29) and I stand behind the engine installation on a V-8 powered Lancair IV-P.  This is an EngineAir package that I helped develop from 1993 to ’98. It’s 450hp, geared,  injected, intercooled and turboed, and features air conditioning. Get a good look at the size of the 5-blade MT propeller.

  Eventually, about a dozen of these took to the air. They were stunning performers. I flew  from Oshkosh to Daytona Beach in three hours and five minutes in our first airplane, N420HP. This aircraft is on the cover of Sport Aviation in July ’97. If someone suggests I don’t understand EFI, ask them if they have flown in a 385 mph EFI plane they helped develop and build.

 The development of this engine took the work of many clever, dedicated people, and one  guy with cubic yards of money, Jim Rahm. It worked, but taught me that homebuilders at all levels  tremendously underestimate the effects of complication, primarily its delays and expenses.  Whenever I read discussions about electronic injection or computer controlled engines, I  can tell in an instant who has no practical experience with attempting to prepare these  systems for flight.

Evaluate your interest in fuel injection carefully. for most builders, it is a distraction, for some it will become a stumbling block, for a tiny number of people it may become a dangerously complex part of their plane, a part they thought would be the most reliable, but turned out to be the part they trust the least. This is pretty far from the goals that most people have when the first think about putting EFI in their plane.-ww

Mechanical Fuel Injection Testing

Friends,

One of the things that we have been testing lately is a mechanical fuel injection system from Precision, makers of certified aircraft fuel systems.

Precision has developed a single point fuel injection system that is entirely mechanical for engines in the Corvair’s power category. We have had one of these for several months and conducted a number of tests. Below is a quick outline of some of the data we’re collecting.

Above on the left is the Precision fuel injector, on the right for size comparison is an MA3-SPA Marvel Schebler carburetor, the most popular Corvair carburetor. The Precision injector is designed to fit in exactly the same space with the same bolt pattern as an MA3.

Just for starters, let me say that many people do not understand the function of mechanical fuel injectors on aircraft. The above unit is closely related to the operation of an RSA fuel injection system, the gold standard of mechanical fuel injectors. Part of what confuses experimental aircraft builders is the fact that there are a number of carburetors that include in their name the misnomer “throttle body injector” or “Aero injector.” Both the Ellison and the Aerocarb are useful carburetors but in no way shape or form are they fuel injectors. They are simply flat slide carburetors that do not have float bowls.

The defining characteristic differentiating a mechanical fuel injection system and any other type of carburetor is simply that the mechanical fuel injector meters off density, not off volume. Anything that meters fuel off the volume of air flow that comes through the throttle is a carburetor. Such systems will always change their air/fuel ratio as the density of air changes. Conversely, mechanical fuel injectors, such as the Precision unit, meter off density. When they are set to a specific air fuel ratio they hold it, no matter what altitude you climb to, nor how the conditions change. If you look closely, there are four chambers on the diaphragm of the Precision unit. These four chambers allow this to function as a very precise pressure regulator and metering device based on the mass flow of the air passing through the assembly.

To give you some idea of the quality of this unit, and its adaptability to different airframes, the directions actually spell out that it can be run on any fuel pressure unregulated between 20 and 80 PSI, and it will handle momentary over pressures to 180 PSI without damage. Because of the diaphragm assembly, the pressure can actually fluctuate between any of these pressures and it will not change the air/fuel ratio.

The primary difference between the Precision system, and typical certified aircraft systems, is that this is a single point injector that does not have injector nozzles in the intake ports. It has one nozzle that is in the body of the unit after the throttle plate. This unit is immune to carburetor icing. Yet in operation the fact that the fuel is vaporizing 18 inches upstream of the intake ports allows a very significant evaporative cooling effect. Unique to this unit is the fact that it is equipped with a very potent accelerator pump that gives it instantaneous throttle response that one associates with port fuel injection.

Above, the Precision injector mounted on a 3,000 cc Corvair on our engine test stand. Bolting on the injector in the place of our typical MA3 only took 30 minutes. Even the throttle arms are in the same location. As far as I know, this is the first mechanical fuel injection system that has ever been used on a Corvair engine turning a propeller.

The system is not cheap. Its suggested retail price is more than $2500. If you are building a Pietenpol and were planning on using a Stromberg, you’re probably not going to change plans and pick up one of these injectors. However let’s look at this from a different perspective. People who are spending $18,000-$20,000 to buy a Rotax 912 or a Jabaru 3300 will find that their engines are equipped with one or two Bing motorcycle carburetors. Although these carburetors are allegedly altitude compensating, in practice they are far from it. You can ask any operator of a Jabiru engine and they will tell you that at high power settings and high altitudes, their engines are very thirsty, and they have no way to compensate for this.  These expensive buy-it-a-box engines come with Bing carburetors because they are cheap. 

Now let’s look at the 3 L Corvair engine with the injector above. It is the most expensive Corvair powerplant I have built in the past couple of years; the price of the engine complete without the fuel injection on it is $11,500.  At $14,000, it is $4000-$6000 less expensive than imported engines fed by motorcycle carburetors. Combine this with the Corvair’s made in America pedigree, and its reputation as tough as nails, and many people find that it’s a choice they’re interested in. Corvairs are not for everybody. Most people don’t actually care where their products are made, or if they will be serviceable in five years. It’s a free world and those people can find engines that suit their needs. For people with different value systems, I am glad to conduct R&D to find out what is a real value in high-end engines.

Above, the engine runs on the stand in front of our hangar. The fuel line leads down to a rack of instrumentation, a high-pressure pump, and an external pressure regulator used for testing purposes. The engine ran very smoothly, and passed our early tests. I will have the unit on display and more information in our NO34 booth outside Building C at Sun N Fun all week.