Thrust testing 85 and 100 hp engines


Here is another set of testing from the days at our Edgewater hangar.  Thrust testing is a very common number to quote, but it is also the most commonly faked or deceptive piece of data people quote.  It is very easy to set a ground adjustable prop so low on pitch that it produces fantastically high thrust numbers, but the plane would be required to have a 40mph cruise speed to use them. (airboats operate in this range)

For data to be useful for more than inpressive sounding number in a brochure or website, it must have two elements. First, the prop pitch must be realistic to the type of flying you will be doing. Second, you have to use the same equipment on the same day to test known engine prop combinations like the O-200 C-150 for comparison.

All of this can take time and be a real bother comparied to just making up a number that sounds good.  After years of this type of testing, a am going to guess that 75% of the numbers people quote on this topic are simply made up. Just stop and think about how many times the numbers you have seen came without any kind of photo of the test being conducted. I have found that people wo like to talk about planes they will build one day most often cite numbers known to be fake. On the other hand, buiolders who are working on the plane they will finish and fly  follow data like this story.


Thrust Testing;

Zenair 601, Cessna 120, Cessna 150, Hudson Corvair, Shop Corvair, Corvair Turbo


Over the years we’ve done a lot of thrust testing in order to compare the output of engines, the thrust of different propellers, and the effects of systems installations. The method used to measure thrust is a hydraulic cylinder attached to a remote gauge. It is easy to calibrate because you can hang a known weight from it. In our case, the thrust is 1.54 x the number shown on the gauge. This is because the piston in the hydraulic cylinder has more than 1 square inch of area.

A few days ago, we tested a lot of different combinations at the hangar for comparative purposes. All tests that we’ve done recently are conducted on 100ll fuel. All of the Corvairs were tested with 32 degrees total ignition advance. The only exception to the ignition was the turbo engine, which was set at 22 degrees total. A $300 digital, optical tachometer was used to measure rpm. Weather conditions are measured on the spot with digital instruments. Here you’ll see tests of certified engine and propeller combinations also. Over the years I’ve been working with alternative engines, I’ve noted that many people who are fans of alternative engines know very little about certified engines. Being an A&P mechanic, I have the greatest respect for certified powerplants. I like everything about them except for the expense of obtaining and operating them. All my work with the Corvair motor is patterned after the success of certified engines. I use their performance as a baseline, and their level of reliability as a goal. Anyone who tells you that alternative engines have superior reliability, or fantastically better performance than certified powerplants is either not telling the truth or has no practical experience with them. In our case, we own, maintain and fly certified powerplants in addition to our work with Corvairs. This gives me a greater range of experience and a more balanced view of the capabilities of alternative powerplants, specifically the Corvair. The next time you hear somebody comparing alternative to certified powerplants, either pro or con, ask them if they’ve owned and operated both and you’ll find that very, very few people have personal experience in both fields.

The Zenvair 601

Above is our 601’s engine measured as installed in the aircraft. The only thing different about this engine is that it has roller rockers and our modified cylinder head intake pipes. I doubt either one of these mods would have a substantial effect on the output of the engine. The prop pitch setting of 11.5 degrees at the tips would be an appropriate setting for a direct drive Corvair motor to move the 601 at 140-150mph. If the prop was set flatter for a slower speed airplane, or used a slightly larger diameter prop, the thrust numbers would be even higher.

Engine: Corvair

Displacement: 164cid, .060 over

Carburetion: MA3-SPA

Exhaust: Collected, open

Cowling: WW 601 Corvair Cowling, 13″ spinner

Propeller: Warp Drive 2-blade HP hub and blades, stock tips, 66″ diameter, 11.5 degrees pitch measured at tips

Temperature: 85F

Humidity: 35%

Pressure: 30.11

Density Altitude: -174

Wind: 4-9mph headwind


Thrust: 347 pounds static

RPM: 2550

MAP: 29″

1946 Cessna 120

In the photo above is Gus Warren’s 120 that he rebuilt from a basket case to 1998 Oshkosh Champion. It lives in our hangar. The engine has about 100 hours on a first class overhaul. It has flow matched Superior cylinders.

Engine: C-85-12 Continental (85hp, redline 2575rpm)

Displacement: 188cid

Carburetion: Stromberg NAS-3, 1 3/8″ Venturi

Exhaust: Stock 120

Cowling: Stock 120

Propeller: McCauley 71×46 Met-L, aluminum (This is a climb prop for a 120)

Temperature: 85F

Humidity: 35%

Pressure: 30.11

Density Altitude: -174

Wind: 4-9mph headwind


Thrust: 340 pounds

RPM: 2350

MAP: 29″

Larry and Cody Hudson’s Corvair Engine

This father/son team from Indiana built their own engine, in the photo above, from our Conversion Manual and components last year. They dropped it off at our shop before Sun ‘N Fun for a break in on our test stand. The prop installed is appropriate for a 180mph airframe. This is why it has low static thrust numbers. It is good for comparative purposes, and is the same prop used on some of the 2002 tests. This engine is not fully broken in, as it has less than two hours of test stand time on it.

Engine: Corvair

Displacement: 164cid, .030 over

Carburetion: MA3-SPA

Exhaust: Cast iron manifolds, automotive muffler

Cowling: None, cooling baffle only

Propeller: Sterba 62×58

Temperature: 82F

Humidity: 51%

Pressure: 30.05

Density Altitude: -122

Wind: 5-7mph headwind


Thrust: 225 pounds

RPM: 2445

MAP: 29″

Cessna 150

Pictured above is our neighbor Arnold’s 1959 Cessna 150. The engine in this aircraft is one that is the subject of the AD that requires the timing to be reduced to 24 degrees. The engine is a mid-time engine that just came out of a 100-hour inspection. It can be considered to be in good working order. Contrary to what most people think, O-200s in 150s are only certified to use propellers up to 69″ diameter. No 150 left the factory with a propeller diameter of 72″.

Engine: Continental O-200, 100hp, 2750rpm redline

Displacement: 200cid

Carburetion: MA3-SPA

Exhaust: Stock 150

Cowling: Stock 150

Propeller: McCauley Clip Tip 68″ diameter, aluminum, standard pitch

Temperature: 82F

Humidity: 51%

Pressure: 30.05

Density Altitude: -122

Wind: 5-7mph headwind


Thrust: 335 pounds

RPM: 2332

MAP: 29″

Shop Test Engine

We built up a test engine, below, from parts in our shop. We built it up to use in potentially destructive ground testing. Since it’s made of used parts, it is not only dirty, but also fully broken in and has very low internal drag. I believe this is why it will turn slightly higher numbers than the Hudson engine. We utilized the same distributor, intake, carb and exhaust on this engine and the Hudson engine. The only difference would be the status of the internal assemblies.

Engine: Corvair

Displacement: 164cid, standard bore

Carburetion: MA3-SPA

Exhaust: Cast iron manifolds, automotive muffler

Cowling: None, cooling baffle only

Propeller: Sterba 62×58

Temperature: 75F

Humidity: 71%

Pressure: 30.06

Density Altitude: -133

Wind: 2-3mph headwind


Thrust: 231

RPM: 2520

MAP: 29″

Turbo Test Engine

The engine above is the same as the test engine, with the addition of a new Garrett turbocharger, which we had specifically sized and set up for a drawthrough condition. I wanted to test this on a junk motor with a mild steel exhaust to evaluate the sizing of the turbo, and to ensure that it produced boost in the rpm range we wanted. Turns out that the sizing and the trim of the turbo are nearly dead on. We’re going to run a lot more ground tests, and then develop our flight installation package. Based on early tests, we should have absolutely no problem getting 100hp at 10,000 feet on a 164cid engine. While the installation looks very Mad Max, it gave us the data we needed. Keep in mind that everything on this installation was less than optimal, and it has already met my expectations. Despite being told by armchair experts of the antiquated nature of drawthrough installations, and the requirement for an intercooler, this simple installation of a modern, efficient turbocharger worked exceptionally well. At full output, you could reach up and put your hand on the steel intake manifold, and it was not too hot to touch. While it would be hotter at altitude, I think the installation’s off to a great running start. A little practical testing has once again shown that you can learn a lot more by testing rather than talking.

Engine: Corvair

Displacement: 164cid, standard bore

Carburetion: MA3-SPA

Exhaust: Cast iron manifolds to Garrett T04B turbo, 2.5″ outlet pipe 18″ long

Cowling: None, cooling baffle only

Propeller: Sterba 62×58

Temperature: 74F

Humidity: 62%

Pressure: 29.92

Density Altitude: -1

Wind: 3-4mph tailwind


Thrust: 331 pounds

RPM: 2950 (there was more power available, but I did not want to boost the motor past 45″ without working EGT in place)

MAP: 45″


We have more testing lined up on the turbo engine, and we’re going to maintain a separate Turbo Testing Page on for it. We have a 72″ Warp Drive propeller we’ll be installing for a maximum thrust test, which will give fans of 80-120mph aircraft a better idea of the potential of the powerplant in their speed range. Please keep in mind when you read these statistics and look at the pictures that all the data is factual. I frequently read stories where people claim to have VWs which produce 500 pounds of thrust and Subarus which produce even more. We professionals in experimental aviation get a good chuckle out of inflated numbers from advertising brochures and press releases. But, people new to sport aviation should know that you can come down to my hangar any time and I’ll gladly duplicate these tests.

Thank you.

William Wynne

Torque, HP and Thrust tests


Here is a look at a classic testing story from our days at the Edgewater Florida hangar . The years we spent there (2004-2008), maked the sucessful completion of many planes and hosting a number of outstanding colleges. The pace of testing was going into high gear then. The story notes that we had previously run 50 engines on the run stand before it was converted to a dyno. In the years that followed, we ran more than 100 engines on the dyno, most of the in public or at college where we invited people to study the system and verify the conclusions.

Today, the run stand we use at the college is made from many of the same parts we used on the dyno. It has been simplified to allow much faster engine changes required to run many engines at a college. If you look at the engines in all the tests, you can see that they are all 2700s that pre-date any of our Gold system components. (Gold oil systems eleminate the need to verify the stock oil bypass as shown in the story) The engines we build today, the 2,850s and 3,000cc power plants, are even more powerful than the engines in the tests, with no sacrifice in reliability. As we have extracted more power, we have done it largely by increasing the displacement of the engine, so the power output per cubic inch has stayed about the same, keeping the stress on the engine to very conservative levels.

Torque, Horsepower and Thrust Testing

September 21, 2004


Here’s the second engine being run on our dynamometer. We ran this a few hours ago. In the photo above, Gus is checking the timing with a light. We spent some time this week upgrading the dynamometer in its details. Visible is its new paint job, but it got a lot of detail work to facilitate rapid engine changes, and multiple tests. I contacted Darryl at Warp Drive Propellers today, and he’s sending us down a matched set of smaller diameter blades which will allow us to graph the horsepower at high rpm settings. These blades will become part of the permanent setup. The engine shown here in the test is a virtual clone of our 601 engine. The only significant difference is that this engine has GM steel rockers, while our 601 engine has roller rockers. I built this engine to represent our standard engine configuration, and use it as a test engine for the dynamometer. It’s fully airworthy and has many nice details like ARP close tolerance through case studs. After the break in and dyno runs, this engine will be for sale.

Here’s a side view of the same engine running, above. This engine has the inward leaning, welded on aluminum intake tubes that fit in our 601 Nosebowl. The intake manifold has four rubber slip joints in it that allow it to mate to many different intake pipe configurations. In photos below, you’ll see the PC Cruiser engine, which has a different intake pipe configuration. The adjustable intake manifold for the dynamometer quickly mated to both motors with a minimum of fuss. These types of details will allow many engines to be evaluated on the dyno. There are 5/8″ and 3/8″ tubes welded into the left valve cover. These mate up to the readily available and highly effective air/oil separator sold by Wick’s and Spruce. The gauge measures mechanical oil pressure. Temperature and rpm are measured remotely. We’ve painted the heavy duty baffle box green. The exhaust system is currently stock iron manifolds with 1 1/2″ down tubes. Shortly, we’ll have mufflers in place.

Above is the front and right side of the engine. The right valve cover has the oil filler neck welded in at the back. The starter motor is the Ultra Low Profile configuration, which fits inside the 601 Nosebowl. The alternator is not yet mounted, but the corner of the front alternator bracket is visible at the edge of the Ring Gear. The Pulley to drive the front alternator is just ahead of the Ring Gear. Pushrod tubes on all of our production engines have always been painted white. While many people believe that oil returning to the crankcase through the pushrod tubes is cooled by airflow through the motor, our testing has shown that just the reverse is true; the pushrod tubes run significantly hotter than the oil in the sump. We paint the tubes white to help them reflect heat.

The photo above shows a very important piece of test equipment that we use on all the motors we build. We use this to evaluate the condition of the oil cooler bypass in the engine. The cooler bypass performs a crucial function in the Corvair. It has a tradition of trouble free operation, even in engines 30 years old. The Corvair’s oil system has a very good track record, and the design of the cooler bypass contributes to this. However, in the interest of truly knowing its condition, we built this tool. The bypass is a pressure sensitive check valve set to relieve at 7 to 8 psi differential. When operating correctly, it allows the motor to warm up the oil quickly. But if it leaks or has a weak spring, the engine will have hot oil temperatures no matter how big a cooler you put on it. This tool, made from a modified oil cooler mount, bolts on to the stock cooler mount and allows me to measure the exact pressure at which the bypass relieves. This is done when the oil pump is being primed with a drill motor, long before the engine is ever run.

Above is the cooler bypass tool in action. Although the photo is a bit blurry, you can see an 8psi differential on the two gauges. The engine is sitting on the dyno being dressed out. What’s driving the oil pressure is a half inch electric drill using a dummy distributor housing and distributor shaft without a drive gear on it. You’ll see this priming tool in many photos. It’s painted orange like many of our shop tools. I primed this motor for 20 minutes with the drill turning the pump at a speed that would be comparable to a high idle on the engine. During this time, I turned the propeller over slowly by hand a bunch of times, allowing the oil to flow through all the passages in the engine. This technique is very effective. This motor has Sealed Power hydraulic lifters, and these, combined with priming, did not let out a single tick when we started the engine an hour later. These hydraulic lifters will maintain their adjustment for the life of the motor. It’s attention to detail like this that pays rewards no matter what type of engine you’re building.

Stay tuned for the test data and horsepower calculations. We’re going to run this motor for a few more hours before we give it full power runs on the dyno.

Thank you.

William Wynne

September 9, 2004


Here is the first run on our newly built engine dynamometer. There are many types of engine dynamometers. One of the most simple and easily made measures the engine’s torque reaction. Our own stand has a motor mount which is free to pivot along the crankshaft axis. This is restrained from rotating by a hydraulic cylinder. It is a simple calculation verified by a simple test, and you can ascertain the amount of torque the engine is producing at any given instant by reading the hydraulic pressure. It is accurate, and if you have the capability of measuring the rpm of the engine very accurately at the same moment, a simple calculation will give you the exact horsepower that the engine is producing. Shown above is the very first run we did on the dynamometer. Its details are still being finished, but it works very well.

Above is the view of the dynamometer with the engine removed. Its operation is very simple. Everything seen in blue rotates on the crankshaft’s axis. If you look closely, you can see that the bearing is the front spindle, hub and wheel removed from a late model Corvair. The bed type mount is slung low so that the crankshaft centerline lines up exactly with the spindle. The reinforcements below the engine contact a bearing at the bottom of the stand for additional support. This is a Corvair blower bearing rolling sideways on a steel plate. It effectively has no drag. Below the spindle is the mounting point for the hydraulic cylinder. The green oxygen bottle has been converted to a gravity feed fuel tank on the test stand. It hold 2.5 gallons of fuel, and has a very accurate sight gauge on it which allows precision measurement of fuel burn.

Another view of the first run is above. Just ahead and above the battery is the hydraulic cylinder. A stainless braided line running out of the picture goes to the remote gauge. Our rpm measurement is by digital optical tachometer. This is one of the few types of tachs accurate enough to give good test information. Many people will recognize the chassis of the dynamometer as our previous engine run stand. The old stand served us well, and broke in many famous Corvair engines, such as Mark Langford’s 3100. Although we never kept count, I’m pretty sure 50+ engines were run on it. The new dynamometer is capable of everything that the old run stand could do, plus its obvious new function of measuring horsepower. In the coming year, we’d like to run as many engines as possible and anyone converting a Corvair for flight reading this is certainly welcome to bring their engine for a run. We took the time to manufacture a very special intake manifold for the dynamometer which is compatible with any style of cylinder head used in Corvair flight motors. Details like this will make installing and running engines a quick and simple process.

Gus monitors the engine run, above. Note the newly constructed heavy duty baffle box to provide cooling air to test engines. I’ve said it many times, but it’s worth repeating that you should not run your motor even briefly without a cooling system in place. The carburetor in this run is an MA3-SPA from an O-200. This will be the dedicated carburetor on the dynamometer, although we will be able to evaluate others. The propeller is a 72″ 2-blade Warp Drive. In the background in this photo is the Corvair Trimotor fuselage.

Above is another view of the running engine. The baffle box is made of 50/1000″ aluminum, although 25/1000″ would be plenty for a box you’re only going to run for a few hours. We plan on getting a lot of work out of this, so we built it heavy duty. You’ll notice that the 12-plate oil cooler is outside the baffle box. Engines run on the test stand traditionally have very cool oil temperatures. I kept the cooler outside the baffle to give the oil a chance to warm up. When set up for flight inside a cowl, the engine will have normal oil temperature and it will be appropriate to have full air flow over the cooler.

Here is the same engine pictured running on this page. We built this engine specifically for the Corvair Personal Cruiser, a single seat aircraft designed for Corvair power. This engine will be installed on the prototype, now under construction. In the photo above, the engine is sitting on the mount for the Cruiser. Shown in silver is the intake manifold for the aircraft. We built this from mild steel tubing. The horizontal inlet is built specifically to mate with an Ellison EFS-3A. Also of interest, note the layout of the sparkplug wires. When oriented like this, the cap can be removed for inspection without removing the wires. Additionally, the distributor can be rotated to set the timing without the wires becoming slack or taut. Doing dozens of engine installations over the years has allowed me to perfect small details that allow the operation and maintenance on the motor to be done far more easily.

Very shortly, we’ll provide the next batch of photos sharing the test data and the calculations. Additionally, we’ll show you the calibration procedure, which allows everyone to understand how accurate this simple machine can be.

Thank you.

William Wynne

Dynamometer testing the Corvair and O-200


Here is an older story of testing from 2004.  It is a good example of how our testing has been an integral part of the work we have done. Although the machinery is simple, the comparitive testing is sound and the meathod is valid. The information gathered in these tests has served builders for a nearly a decade. In the story I mention that the three of us totaled 55 years of work as A&P’s. Today that number is now 84 years of working experience.

O-200 Torque and Horsepower Testing

October 2004


Here’s the O-200 on our dynamomemter, and your test crew from left to right, above: Gus Warren, Detroit Institute of Aeronautics, A&P 1990; Steve Upson, Northrop University, A&P 1976; yours truly, William Wynne, Embry-Riddle Aeronautical University, A&P 1991. While the way we dress may be slow to catch on in high fashion circles, we certainly know our stuff about all types of aircraft powerplants. This is 55 years of A&P experience working on engines in the field nearly every day. This experience, along with a good technical background, puts us in a good position to do real world testing.

On the left above is the Continental O-200 as removed from a 1959 Cessna 150. This engine is considered the standard against which all other 100hp class engines are measured. It is a direct drive 4-stroke, 4-cylinder engine of 200cid. It carries a horsepower rating of 100 at 2,750rpm. I have read that Continental produced about 50,000 O-200s. On the right is a 170cid Corvair engine. For size comparison, the O-200 is 32″ wide without the baffling. The Corvair is 28″ wide.

To adapt the O-200 to our dynamometer required making a new mount. Everything seen in gray, above, is part of that mount. The red cap at the center is a dust cap covering the bearing on which the mount pivots. This red cap is in exact alignment with the O-200’s crankshaft. This way, the rotation against the torque is in line with the crankshaft. The mount was made from a Corvair wheel, a pirated VariEze motor mount, some spare tubing, and a Corvair blower bearing. This bearing is at the bottom, and rides on a steel U channel. This provides additional support to the mount, and restrains it from turning full circle. The vertical element is a 1.5″ diameter steel tube. There is a pin on the back of this tube that engages the hydraulic cylinder. By comparing this mount to the blue Corvair bed mount seen in previous dyno tests, It is apparent how we can change the configuration in a few minutes. This is the charm of using the 5×4.75 bolt pattern wheel as the basic element.

The first photo on this page shows the engine with its stock McCauley prop. Above we see the engine fitted with our primary test prop, a 2-blade 60″ Warp Drive. Since we normally use this prop on Corvairs, the blades here are turned around to work as standard rotation pusher blades. This will effectively load the engine for torque testing. The prop is ground adjustable, so we can fully load the engine at any rpm we desire. The carburetor is an overhauled MA3-SPA. The engine has new Slick mags. It is less than 500 SMOH. We first tested the timing at 24 degrees as per the AD, and then tested it at the pre-AD setting of 28. Differential compression showed all over 70. The engine turned its full rated static rpm with the certified McCauley prop, indicating it was a very healthy engine.

Above is an overview of the test rig. We used two different methods to measure the torque output. First, we used a hydraulic cylinder. This cylinder is located just above and in front of the battery. Second, we measured it with a digital scale. The scale is located just out of view, but it is driven by the 8-foot metal beam clamped onto the mount. We had 4 feet of it extending on each side, so that its weight would not affect the scale reading.

Above is a closeup of the hydraulic cylinder. The braided line runs to a remote gauge. You’ll notice it’s on the opposite side of the stand now. The O-200 has a different rotation than the Corvair, requiring the hydraulic unit to be moved to the other side of the stand. The gauge reading was calibrated by hanging weights on a 4-foot lever arm in 5 pound increments. The needle valve on the output of the cylinder is required because pulses on the line when cranking the starter motor are so fierce, they will damage the gauge. This is true with both the Corvair and the O-200.

In the photo above, you can see the electronic scale sitting off to the side. Pressure is put on the scale by the vertical stick clamped to the steel arm. We’re going to refine this and make it a lot cleaner looking shortly, but for these tests, it worked flawlessly and provided repeatable accuracy. If you’re wondering how all this stayed together in the prop blast, you’re forgetting that the prop is functioning as a pusher. I was only concerned that some of the equipment would be inhaled. Although we got both methods of torque reading to agree, I feel in the future we’ll probably use the electronic scale more often because it’s subject to fewer variables. The dynamometer is also rigged for simultaneous thrust measurement, so we’re going to put the hydraulic unit to that function for simultaneous readings.


After a full day of testing, which included several dozen test runs, we came up with some surprising data. The engine performed substantially below its 100hp rating. I initially suspected that the engine was not performing at peak power, or that the test equipment was flawed. During the testing, we conducted all of the standard mechanics’ tests to evaluate the condition of an engine, including differential compression, timing, and fuel flow. All of these showed the engine to be in good condition. The most telling test was that the engine turned its full static rpm with the certified propeller. It would not do this if it were down on power. Keep in mind that we use a digital optical tach to ensure that there is no error in rpm measurement.

We retested and calibrated the hydraulic cylinder system. It showed itself to be accurate. To doublecheck it, we came up with the digital scale system to corroborate the data. They both told the same story. As an A&P mechanic and a big fan of certified engines, I was very reluctant to conclude that the O-200’s 100hp rating is probably a “gross” rating, as opposed to a “net” rating. If you’re a fan of car engines, you probably know that in the 1960s, many car engines had gross hp ratings. These optimistic numbers had things like the fricitional drag of the engine and the accessories factored out. In the 1970s, net hp ratings became more popular. This is the power output you’d actually see at the prop flange. All of the numbers that we test are net. This is the only type of external measurement we can do. It is also the real world power output of the engine that you are going to use to go flying.

The torque peak of the O-200 occured at 2450rpm. The engine produced 160 foot pounds of torque. If you use the formula Torque x RPM / 5252 = HP, you’ll see the engine was producing 74.6hp. We established the torque peak by running the prop at many different pitch settings until we homed in on the peak of 160.

The hp peak of the engine was very close to its rated peak of 2750rpm. We tested numbers slightly higher than this. However, I was reluctant to run the motor in the 3000s because it’s above the engine’s redline, it’s a borrowed engine, and it’s a certified piece of equipment which will very likely go back into another certified plane. So it behooves us to operate it accordingly. At this rpm, we measured the torque at 144 foot pounds. Using the formula, you’ll see that the engine produced 75.9hp. Again, these are net horsepower numbers.

The temperature outside was 85F, and the RH was 60%. The pressure was almost standard, and we’re only a few feet above sea level. A rudimentary calculation to account for the temperature difference above a standard 59F shows that the corrected hp output of the engine is in the neighborhood of 80-81hp. Again, keep in mind we worked all day in an attempt to raise this output. If you’re reading this and thinking there’s something we’ve missed, I can understand that. It’s difficult to convey the work of three mechanics over a 12-hour period in a few paragraphs and photos, but I can assure you we left no stone unturned in our search. At the end of the day, I largely came to the conclusion that the 100 horsepower rating was a gross rating.

Keep in mind that I’ve been doing installations on planes for 10 years. In this time, we had numerous comparative studies which showed that the Corvair was a very powerful engine, and in many circumstances, could easily match the O-200. One which stands out in my mind was the break-in run of Mark Langford’s Corvair engine at Corvair College #3. He had a pusher prop from an O-200 mounted on his Corvair. The manufacturer of the prop told him on the phone that the Corvair could never turn up the prop to any substantial rpm. When it did, the propmaker was something between impressed and stunned. Even though Mark’s engine is a 3100, it was exceeding what the O-200 could do by a good margin. Over the years, a lot of circumstantial data like this makes more sense in light of finding that an O-200 has a far lower net output than previously suspected.

Does this mean that an O-200 is a bad engine? Does this mean that the VSI in every Cessna 150 isn’t telling the truth? Of course not. The engine is and remains the standard measuring stick of 100hp engines. They have worked for nearly half a century, and will continue to do so. This said, I can assure you from our dynamometer testing that standard displacement Corvair engines will exceed the O-200’s power output handily. This being true takes nothing away from the O-200’s status. It just puts numbers on the success we’ve seen with the Corvair motor over the years.

As a coincidence, a few days after the testing we had a visit from Al Jonic. I worked with Al on the installation of the V-8 in Jim Rahm’s Lancair IVP. Al won the EAA’s highest honor for engineering, the August Raspet Award, for this work. He’s a veteran of thousands of dynamometer runs. Although he’s used much more sophisticated equipment, he was duly impressed with our setup and approach. He offered to send us sophisticated programs to use to correct the conditions for standard day performance. He also offered 40 years of insight on the value of dynamometer runs, correction factors, and gross vs. net ratings.

This dynamometer testing is an ongoing business. I didn’t build it to run it a few times, and prove a few points. I regard it much more as an everyday tool. It takes all the talk out of engine building, and replaces it with hard testing. It is the perfect complement to our ability to rapidly flight test any modification. We’re currently running an entire series of Corvair engine tests. Most of these will be done by Corvair College #8. The Corvair is already exceeding the power output of the O-200. We’re just working to define by how much. When we have this data complete, we’ll put it all on the Web page here.

Thank you.

William Wynne

Who is William Wynne?

Above, A photo taken at Sun n Fun 2006. My wife Grace Ellen and myself, in front of the first Corvair powered Zenith, our own N-1777W. The plane was the first XL model with conventional gear.  Grace is a skilled pilot in her own right. She has been a pilot longer than I have, holds more advanced ratings and owns two aircraft. As a point of ethics, we do not promote, advocate nor sell things we have not personally flown behind.


Who is William Wynne?

Modern consumer sales logic dictates that that business should ‘de-personalize’ themselves so consumers find nothing objectionable about the provider while they are spending money.  That model may work elsewhere, and even have advocates experimental aviation, but I don’t buy it.  I contend that Aviation is a different arena, and who you are dealing with, and their ethics, experience and perspective matters.

Building a plane or an engine is a marriage of sorts between the builder and his airframe or engine company. I believe that it is best if everyone goes into it well informed with their eyes wide open. I am always surprised how few people even Google the name of a person they are thinking of working with. You don’t need to see eye to eye with them on every point nor even love them, but the relationship must absolutely have trust and respect operating in both directions. In 25 years I have seen many builders try to justify buying a product from a provider they didn’t really trust. It never works out. It doesn’t matter how good it looks, what it costs or how great it is supposed to work, if it is from a bad guy, it isn’t worth buying.

I could write a quick paragraph about how I am a pilot, a 22 year A&P mechanic, and that I hold both an AS degree in Maintenance and a BS in Professional Aeronautics (accident investigation) From the worlds #1 aeronautical university, Embry-Riddle , but I don’t think that any of that explains my commitment to builders nearly as well as the flying planes of our builders and things we have accomplished. Henry Ford said “A man can not base his reputation on what he says he will do; only what he has done.”

I am plain spoken. to understand why, read the ‘Effective Risk Management’ story below. I have many friends who are experienced aviators who value plain talk. This type of speech also tends to offend people who dabble in aviation and would rather read polite things that align with their pet opinions. I am in aviation to share experience builders need to know, not say things people want to hear. Below are a selection of stories, some humorous, but all with a point, that give people a better understanding of who I am. From there you can decide if you choose to work with me as your engine mentor.

a) Fixing America is going to cost each of us $1.69

b) Greatest Book on Flying Ever Written, (Is your life worth $16?)

c) In defense of plain speaking……

d) Turtles and Cell Phones, 6/24/13.

e) A thought on Easter….

f) Happy Father’s Day William E. Wynne Sr.

g) Effective Risk Management – 2,903 words


Fuel lines and Cabanes, part 2


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 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 This story will be first published as news on, but it is also now immediately cataloged with part #1 on the Pietenpol reference page on 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


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.


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.

William E. Wynne Sr. turns 88 today.


My Father, the ‘real William Wynne,’ turns 88 today. Here are a few shots from the family album to celebrate the life of my hero:

img005Above, My Father as a 17 year old enlisted man in WWII. He stands between his beloved pony Bob, his constant companion since he was a little boy, and his own father. My grandfather served in every station on the Passaic NJ police department from patrolman, Chief of Detectives to assistant Chief. Passaic was a very large tough working city with a significant organized crime problem.  Recognized as incorruptible, he was targeted by the mob, but would not be intimidated.  The only years he took off from law enforcement in his adult life were 1917-1919 when he was a Sargent in the 78th division in France where he saw savage combat in the trenches. His only real wish in life was that his own son would not have the same experience. It didn’t come true, as my father went to both Korea and Vietnam.

img018 Above, the love of my father’s life, my mother at age 17 also.  Mother lived in Irvington NJ, about 20 miles away. They met at the NJ shore in the summer of 1946, and have been married since 1950.img008 Above, my mother at age 26, standing in front of their 1950 Buick super eight Convertible. Mom had just had my older brother 6 weeks before. My father was being shelled in Korea at the moment of his son’s birth. You can read the story of my brother’s arrival at this link:

MCW is 60 today.

img003Above, Dad as the base XO at Davisville RI in the 1960s, shooting a Garand. He is wearing a shooting jacket, but the uniform and the shoes suggest he came straight from the office. He held Expert ratings with both rifle and pistol. Dad has always been good at anything that required hand eye coordination.


 Above, Father at the table (holding the papers) Military Assistance Command, Vietnam (MAC-V) in Saigon, 1966. Almost all of his work in South East Asia 1966-74 was working on infrastructure.  You can read about some of it at this link:

Happy Father’s Day William E. Wynne Sr.


Above is Father’s 1966 office door sign from Saigon. OICC stands for “Officer in Charge of Construction”. The construction budget for The Republic of Vietnam in 1966 was one billion dollars, the largest construction project in the world to that point. My father was one of many Americans who felt that the South Vietnamese deserved to live the same life that South Koreans had gained 12 years before. To understand my fathers perspective, read this link:

William Edward Wynne Sr. – Father’s Day Notes


Above, Father in Cambodia, playing the role of civilian for a day in a country that only was ‘neutral’ in title only. The photo was from the early 1970’s when we lived in Thailand. With dad is the US ambassador. The Cambodian communist genocide that killed millions of people following the US withdraw was documented in the film “The Killing Fields” To many people, it was a horrific story about people in a far off land they had only a passing interest in. To my father there were real human beings, people with families that he knew and fought beside. America has many fine points, but we have a terribly short national attention span that has cost others dearly.

img009    Above, Our Family in 1974, when we lived in Thailand. Alison, Michael, Melissa, Mother me and Dad.  In the background is the actual bridge on the river Kawai.  The train ride from Bangkok was many hours. All along the tracks were cemeteries for the 350 POW’s that died per mile, tortured by the Japanese army to build the rail line from Bangkok to Rangoon, later called “the death railway.” We had many happy times growing up, but my father made sure that we fully understood how lucky we were to have been born in a free country.  Many Americans of my generation and younger who were blindly raised in suburbia, have the twisted view that America’s beacon to the world is one of capitalism and material wealth.  My father raised us to know that our home was the beacon of the world for human rights, the value of individuals, and freedom.

When I was little, we went to the Jefferson Memorial and read the words inscribed on the inside of the dome:

“I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man.”

This is what my father taught us was at the very core of being an American. He has lived all his adult life by this code, as his father lived before him. It is his lasting gift to us his children, just as it was bequeathed by his own father. It remains, a gift I am most thankful for.  – WewJr.

December Schedule


We will be out of the hangar and visiting family from December 14th until after Christmas. Today, the 13th is my last day in the workshop. At 3 pm I am getting in the truck to drive to New Jersey for my Fathers 88th birthday on the 16th. He is getting older, but in good spirits, my brother and his sons are taking dad to the Army-Navy game in Philly tomorrow. Father graduated from the Naval Academy 64 years ago, and the game organizers graciously found indoor seating for him. My father does not expect, nor even like, anything that hints at special treatment. Although he travels in a wheelchair, he doesn’t like using handicapped parking spaces, insisting they be left for “people who need them.”  If you are traveling by air soon and want something to feel good about this country, I will attest that the TSA personnel find my father and mother waiting in line at airports, dad with his ball cap that says either ‘CVN-65’ or ‘WWII-Korea-Vietnam’ on the back, and ask him if he wouldn’t mind bypassing the line that day.  They have been courteous and kind to my parents without exception.

I will be using some of the next two weeks to catch up on Email and phone calls. There are also a hand full of stories I want to share, notably one on the life of Gary Collins, by the end of the year. Grace has a very large batch of orders going out today, and we have been working very hard to clear off as many orders as possible. New work is traditionally very slow through winter, affording us the time to build complete engines before the season starts. In previous years we have started this work after the first, but this year I am going to hit it earlier, as we are only about 75 days away from Corvair College #28 in Texas.

If you have a chance, take a minute to look at our main page, Grace updated it by installing the ‘reference pages’ as updated links on it. I have about a half dozen more to organize by the end of the year before the update is complete. This is the first major update to the original site since we launched this one 24 months ago. We are working to have the information presentation as accessible as possible for 2014, so the focus can solely be on building and flying.

If you have a question you would like covered in the next two weeks, please email it to me, I will make the time to cover it. Both Grace and I hope each of you spend time with Family and friends and take a few hours to reflect on and consider things we can be thankful for. -ww.

Flying 2,850cc Cleanex, Clarence Dunkerley


The following note came in from Florida builder Clarence Dunkerly about the first flight of his Corvair powered Sonex airframe:




Today, about 11:00 am, a smoothly running Corvair aircraft engine strongly pulled the Cleanex and this old man skyward on its first flight from the Pompano Beach Airpark. What a thrill to pilot an aircraft and engine that Don and I built. Thanks for the Corvair colleges, Conversion Manual and support from others to make this a dream come true.

Clarence Dunkerley
Plans built Sonex 1306″


Clarence has been to a number of events over the years, but getting his engine running at CC#21 sticks out as particular memory. Clarence and his brother came to the College in Barnwell SC and put in the work to get their 2,850 running. Below are some photos of the day.


Clarence Dunkerley came from Florida to the College with his brother Don, who also assisted in building his engine. They had a very good time, especially when the engine fired up and ran great

Above, Clarence Dunkerley beside his 2850 cc Corvair. His engine features all of our Gold components, our 2,850 piston/rod/cylinder kit and a Weseman 5th bearing.  Photo taken at Corvair College#21.


Hats off to Clarence Dunkerley, the newest member of the ranks of Corvair pilots, builders who made both their airframes and their engines.

Carburetor Reference page


This page is a collection of notes on the broad variety of Carbs that have flown on the Corvair, and some thought on why I choose simplicity when it is available, and the development of our intake manifolds.

Above, an overhaulled NAS-3 that went on the Pietenpol of Dave Minsink.




Below is a list of stories have written on Corvair carburetors. You can click on any color title to read the whole story:

Stromberg Carbs

The world’s most prolific light plane carb

MA3-spa carb pictures, Wagabond notes.

The MA3 is the most popular carburetor on Corvairs today

Carb applications, choices people make

A story of why builders professional background tend to choose carbs.

Intakes and Internet myths

Notes on why the intake works so well.

In Search Of … The Economical Carburetor

A story of testing a $160 carburetor.

A question of Carb location…..

A warning about top mount carbs.

Deal of the Day,simple MA3 carb. (Sold at 1 am, 9/1/13)

Good photos of a straight MA3.




Below are the Group numbers of our intakes and the numbers we assigned to the popular Corvair carbs. You can see how this is part of our Group numbering system by studying the complete numbering system on the “Prices” section of our main page,


Intakes and carburetors  group (3600)

3601(S)- Standard Intake manifolds

3602(A)- Marvel MA3-SPA

3602(B)- Stromberg NAS-3

3602(C)- Ellison EFS-3A

3602(D)- Sonex AeroCarb  –  38mm

3602(E)- Zenith 268

3602(F)- Rotec #3

3602(G)- 1 barrel Carter downdraft




Below are to section from my Group numbering notebook. The first is the introduction to the carb section, and the second is an outline on intake manifold options.  Where most companies are just trying to get you to buy something, my goal is to have you learn about, and really understand the machine you are building. The starting point on any subset of knowledge that goes into your plane is understanding the mechanical philosophy behind the choices made by successful builders.




When it comes to carbs, I like Strombergs and MA3s because they have literally millions of hours feeding air and fuel into flight engines. I know them and trust them, and if I had any little issue with one, I have mountain of expertise to draw on, not just other people flying one, but pros at fuel system repair stations. These carbs will always be my first choice to put on a plane because they are aircraft carbs, they are not just playing the role. They are doing the job they were designed to.

My father is a lifelong military engineer who spent a lot of time working in places where the people who don’t like your project are literally going to try to kill you. He upholds that the piece of machinery that has the greatest reliability requirement is the combat firearm. In these tools, reliability is an absolute requirement. All other considerations about them – weight, accuracy, firepower, cost, etc. – all are meaningless if you ever need to use one and squeezing the trigger produces a soft noise rather than a loud one.

Notice that the requirements of aircraft carbs are very much like combat firearms. When you push the throttle in, you really want to hear a loud noise, not a soft one. If your glide path leads to a place 200 feet short of the runway threshold, and pushing the throttle in gives the undesired soft noise, you will not be comforted by thoughts of how cheap, how light, how available, easy to tune or install it was, or any other factor that made it attractive in the hangar. Reliability alone gets you back to the airport.

Consider this: The Stromberg on my wife’s plane was made just about the same time that the Soviet Red Army adopted a device called the AK-47. Sixty plus years later, both of these devices have been used in countless numbers all over the  globe. Both are often criticized as outdated, inefficient, inaccurate and stone age. Notice that their continued use in the face of all criticism is justified by the same three word sentence, “It is reliable.” People who have held either one in their hands, stared at its metal parts and though about how they would need to count on it, will have some appreciation for that three word sentence. If I can teach you only one thing about experimental aircraft, let it be this: There is no characteristic more important than reliability. Anything you could get in trade for reliability isn’t worth it.

A lot of builders question the length of the intake runners on our systems. Contrary to appearance, in operation, the throttle response is nearly instantaneous. Look at any modern car; designers are going to great trouble to make the intake runners much longer, not shorter. They are after more torque in the rpm range that direct drive engines fly at. A long intake tract doesn’t mean less power, and I am not sure where that myth started, but you can take a look at things as diverse as a tunnel ram with dual quads on a V-8 and see that even 7,500 rpm drag cars benefit from longer runners. But you need not be concerned with theory, I have a lot of dyno information that compares a huge variety of induction systems, and I can assure you that a long tract with a single carb pays no penalty while offering many advantages.

 Many people are yet to understand that the reason why you can go out and fly a Cessna 150 and expect it to work is that Cessna made one in 1959, made it work perfectly, and for the next 18 years produced clones of it, and had an army of mechanics making sure the clones stayed clones, and didn’t develop individual personalities. You can make this work for you on your Corvair carb of choice as long as you understand the difference between the terms “Clone” and “Replica.” Listed below are a number of carbs that have proven over time to work on a Corvair. No matter which one you choose, I strongly suggest you make your fuel system a clone of a flight proven aircraft using the same carb you select.

Pick any carb you like, and install and operate it just like a person who is successfully flying the same carb on a Corvair. And then don’t worry about what anyone else is doing. This will work every time. Here is what never works: A guy jumping from idea to idea and getting speculation and commentary to make a choice for him, having it not work because the system he builds is subtly different than others. Maybe he is not good at taking input from others, and when it is all said and done, he publicly pronounces that there is something wrong with each of the carbs, or maybe the Corvair’s intake design, or auto engines in general. Many people are actually prone to taking the second path because they are more comfortable being negative, “proving” that things won’t work, (even though they are flying on other planes), and passing negative judgments on things. It is just how some people are. I try to ignore it because teaching people about aircraft, not correcting social disorders, is the focus of my work.

You don’t need a majority of builders to like the carb you are going to use. Here is what is needed in the carb you choose: To have flown on the same airframe, with the same fuel system (i.e. gravity feed or fuel pumps); it needs to have flown more than a year and 100 hours with someone you can converse with or who shares their notes; and you need to be able to buy the carb, parts and service for it. That’s it. That constitutes a system that can be successfully cloned.

One of my favorite sayings: “Early bird gets the worm, but the second mouse gets the cheese.” If you don’t want to get your head caught in a trap, be the second mouse, build a clone. Right now, in the land of Corvairs, you can clone a system of any of the first four carbs I list.  You are going to have to do some pioneering work on the other installations. Every variable you add as the first mouse has the possibility of putting a big dent on the back of your head. If the imagery isn’t appealing, you can avoid the subject entirely by building a clone.

It is my strongest recommendation not to use any type of motorcycle carb. This includes a Revflow, a Keihin, an S&S, an Altimizer, a Mikuni, a Harley-Zenith, and especially not a Bing. If I were required to list all the ways that a motorcycle or other non-aviation design carb could fail, I would have a long list. For example, the Bing throttle isn’t connected to the cable, and many CV motorcycle carbs have this “feature.” The two biggest failures  that I can name is  throttle systems that are operated by bicycle cables and the fact that most  motorcycle carbs don’t have any way in which you can attach a serious fuel line.  A piece of fish tank tubing and a hose clamp is not serious, and if it works on a Rotax 503 in a cowl-less pusher application, that doesn’t mean it will live in a sealed engine compartment in a traditional aircraft. Throw in that they have no mixture control, and often don’t fit where aircraft carbs do, and you get to a better understanding why there isn’t anyone saying how well the combination worked on the first 100 hours on his Corvair powered plane. My least favorite carb in this genre is the Bing. It has a tendency to lean out on long manifolds, and it will actually shut off if subjected to ram air. In 2012, we had a builder who insisted on using one and did $3,000 in detonation damage to his engine on the first flight. The same plane would have flown perfectly fine on a $500 Stromberg. I am sure the bystanders to this event were far more willing to see the issue as a Corvair problem than to understand that it was caused by a poor German motorcycle carb mis-applied to a proven engine. Carbs salvaged off snowmobiles, outboards, imported cars and lawn equipment are never going to have a good record on planes, and their advocacy is limited to people who wish to impress others with cleverness, but never actually impress people by going flying. Again, I don’t find it my responsibility to define all the ways that will not work for people who don’t wish to go with something proven. I spend my time trying to illustrate positive examples of how to do things that will work economically, but above all else, reliably.

3601- Intake Manifolds

The Intake manifolds that we make for Corvairs evolved slowly over time and testing. Originally we made individual manifolds out of welded sections of mild steel tubing. We tested both 1.375” and 1.5” tubing, both on the ground and in the air. After a lot of evaluation, we went with the larger size from 2001 on.  In 2003, we started having the main tube of the manifolds bent by a CNC tubing bender as a single piece. This eliminated a lot of welded joints and gives the manifolds a much cleaner appearance. We looked at several different materials and selected thin wall 304 series stainless steel tubing. The primary reasons for this choice are that it is essentially immune to stress cracks when TIG welded and purged correctly, it remains clean on the inside and will not rust even if the aircraft sits for a long time in humid weather, and it is as light as an aluminum manifold because the aluminum would have to be made much thicker to have the same strength and crack resistance. After nearly 10 years of continuous production, our manifolds still have a perfect track record.

When first looking at the layout of the manifold, many people think that it will not have sharp throttle response, or the length of the runners will hurt the power output. A builder with a background in motorcycle racing confessed that he first thought of a steamship’s engine telegraph where the bridge swings a big lever on a pedestal that rings a bell in the engine room and makes a hand on a clock face point to the words “Full Ahead.” After he built his Corvair engine, he was surprised to find out that the throttle response on it was just as fast as a typical car. On aircraft, the limiting factor on how fast it can change rpm is the moment of inertia of the propeller assembly. On Corvairs, this is inherently low and the engine accelerates noticeably faster than other aircraft engines, even with a long intake tract.

I have years of dyno testing of every type of intake length and carb configuration that conclusively shows that the length of the intake run has no effect on power output.  For years this was a favorite Internet debate topic among people who had never seen a Corvair turn a prop, but felt certain that the world needed to hear their impression of how it worked in their imagination. A number of these people also advocated putting the carb on top of the engine. I am going to flat out say that I have never found a single good reason to do so, and there are a number of very good safety reasons to have it on the bottom. I have seen people run every carb on top from Bings to Webers, and none of these installations worked nearly as well as even Bernard Pietenpol’s 1960s installations that featured tractor carbs mounted below the engine. I have seen more than one person plan on running an AeroCarb with a fuel pump mounted on top of a Corvair engine. Such a combination is virtually guaranteed to leak fuel onto the engine in operation. If a person is that interested in cremation, they should just find the professional service in the Yellow Pages and skip all the hassle of building a plane. I will not knowingly assist anyone who puts a carb on top of an engine or uses the leak prone stock Corvair mechanical fuel pump, and especially not in combination.

There are always “experts” who claim that individual runners to each intake will make more power, that something is wrong with the offset intake pattern on the Corvairs intake log, or that the log should be removed. These are all myths that I long ago disproved with our dyno on back to back runs. In section 3700 look at the photo of Mark Petniunas’ EFI engine running on my dyno; it has individual runners and made no more power; the offset intake patter appears on many other aircraft engines such as Rangers and Allison 1710cid V-12s (good enough for P-38s P-40s and P-51Bs, probably good enough for homebuilts). The log part of the head is an important part of the mixture distribution, and it is structurally part of the head. If you mill it off you will weaken the head and blow the head gasket because the upper row of head bolts will no longer have a stiffener. Do not listen to anyone who suggests such modifications to the heads.

We make several different manifolds for the Corvair. The most common is the 3601(S) which is the standard manifold for anyone mounting a Stromberg, MA3 or any other float type carb on their engine. This fits all the Zeniths, KRs, Tailwinds, etc. The second design is a 3601(E) which is the same manifold with the carb flange rotated 13 degrees forward. This is specifically made to serve Zenith builders who are putting a flat slide carb like an Ellison, Rotec or an AeroCarb on a tricycle landing geared airframe. The rotated carb flange provides clearance to the nose gear.  The 3601(C) manifold is specifically made to fit a Corvair into a Sonex or Waiex airframe using the Wesesman’s installation components. The fourth manifold is the 3601(P) which is specifically designed to use on single seat aircraft and those with narrow upper motor mount spacing, such as some Pietenpols. If you need further guidance, look at out parts catalog at, give us a call or send a note.