Critical Understanding #2, Absolute Minimum Static RPM.

Builders:

Full static RPM is the actual rpm the engine turns when the plane is held still by the brakes.  The minimum static rpm is important  to having the engine make proper power on take off, but it is critical to preventing the engine from detonating on take off and climb.

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On a Corvair flight engine, the absolute minimum static rpm is 2,700. If the engine is built and running correctly, the sole factor determining the static rpm is the propeller selection and setting. If the number is lower than this, the engine will not make expected power on take off and climb. This will extend the take off roll and reduce the rate of climb, but the really critical issue is the same as other direct drive aircraft motors: A moderate but significant reduction in the static rpm at full load leaves the engine vulnerable to detonating under a full load.

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Many people ask “How much difference can 100 rpm make?” In reality, it will make a lot. An engine being held back to 2,550 rpm and run on 93 octane fuel with the timing at 30 degrees has almost no margin against detonation on a 90F day. The exact same engine with a lower pitch prop with the static rpm at 2,700 will have vastly increased margin of safety. I have said this many times, but still builders persist in believing the myth that lower rpm is somehow ‘easier’ on the engine, when just the reverse is true.

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To demonstrate that this doesn’t just apply to Corvairs, below is an excerpt from the FAA Type Certificate Data Sheet for a Piper PA-22 “Tri-pacer.” Notice the phrase “Not under“, this is the manufacturer specifying an Absolute Minimum Static RPM for a combination of engine and prop on their plane. The number is different, but the concept is identical. On a certified plane this is the law, in the case of Corvairs,  I can’t force anyone to use my number, I can only point out that an engine failure on take off is the eventual result of too low a static rpm.

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“2. Propeller (with Lycoming O-290D or O-290-D2 engine) – fixed pitch metal    (a)  Sensenich M76AM-2  or +25 lb. (-50)  (b)  Sensenich M74DM +30 lb. (-50)  Airplane Flight Manual shall be revised to reflect the subject propeller and limits. Landplane:    Static r.p.m.:  Not over 2450, not under 2150    Diameter:  Not over 74 inches, not under 72.5 inches Seaplane:    Static r.p.m.:  Not over 2450, not under 2350    Diameter:  Not over 74 inches, not under 72.5 inches”

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The primary group violating this Critical Understanding of Corvairs are builders who have made their own props and builders using a ground adjustable props with too much pitch in the setting. There will be pushback on my number on discussion groups, where people will say “So and So has done flown with a static rpm of 2,450 for years” Great, that is a testimony to the toughness of the Corvair, but his engine is likely protected by a retarded timing setting or a very rich carb setting. Notice how people repeating a BS endorsement of low rpm don’t even understand that the ignition timing, the A/F ratio and even the camshaft profile and timing marks play critical roles in the minimum acceptable static rpm. Consider that Grace flew B. H. Pietenpols’s personal Aircamper, and it’s static rpm was near 2,800; consider that no person on earth has spent more time running Corvair flight engines on dynos and developing their engine installations than myself, and Ernest Jones was my mentor in aircraft propulsion at Embry Riddle. Yet some people think that having a “a big, good looking” wood prop on their plane or taking the advice of a local ‘expert’ outweighs my recommendation.

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 It is a free world, they can make that choice, but when their engine breaks, I have a right to expect them to ‘own it’ and tell everyone that they chose not to listen to my experience. Ironically a lot of these people develop amnesia after an engine failure or a crash, and they have absolutely no recollection they ever failed to follow any recommendation of mine, or at least that’s what they tell the people in their EAA chapter, the internet, the FAA and their lawyer.

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(Make Vx line 2.1 in your Hand book)

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(Make Vy line 2.2 in your Hand book)

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-ww.

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Critical Understanding #1, Take off distance.

Builders,

Walk up to a pilot who just flew a plane, and ask them a simple question: “What is the pilots operating handbook (POH) take off distance for your plane?”  and 75% of them will not be able to answer you with a real number. Yet this is a critical fact for the Pilot in Command (PIC) to know.

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Would you like to read a story about a guy killing himself and his wife by ignoring the published take off distance for his plane? I wrote one several years ago about a 2007 accident, you can read it here: Couldn’t have happened to a nicer guy…… Notice that the PIC rolled 2,500′ into a 10 mph before his plane lifted off, that is five or eight times as long as it should have taken to get airborne. He had 60 seconds to pull the throttle back and roll to a halt, but didn’t. Even at the 2,500′ mark he could have aborted, and easily stopped on the remaining 1,500′ of runway, but he didn’t. Instead he chose to die and kill his wife also.

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Current Zenith Aircraft literature clearly states a 650 with a 110 hp engine at gross weight has a take off roll of just 500′ There are published numbers for every model of their planes, but 600′ is representative of most of the 600 series Zeniths with 100 hp. As an additional free resource to our builders, I operate our private Zenith/Corvair Database and discussion group, where more than 100 builders can directly share this information. Read: “Zen-vair” and “Piet-vair” Discussion Groups, your resource. Thus any builder has acess to know just how long it should take his plane to get off the ground before he ever flies it.

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Since I published the crash story years ago, We have had the discussion groups for years, and Zenith has always had performance numbers available, the easy conclusion is that no one should have been hurt in an accident like the one detailed above, right? Guess again: In the last 3 years, we have had four other pilots destroy their planes in nearly identical accidents just like the one above.  These accidents were directly the pilot in Command’s fault, period. If a plane is supposed to take off in 600′ and the pilot is still holding the throttle in when the plane passes the 1,000′ mark on the runway, than every single thing that happens after that, injuries and damage, is absolutely and solely his fault, no matter what he and his attorneys want to claim. In the case of the 2007 accident, the only redeeming thing Ray Blondin did was make sure there were two less scum lawyers in the world, and I gladly praise him for it.

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Since 2009, we have had a “Flight Operations Manual”, that includes a proven format for running a Zenith specific flight test program, and a number of articles specifically about flight test protocols. Half the articles in the Manual were written by Zenith pilots. I wrote a list of ten things never to do on a first flight, and one of the pilots who ignored standard take off distance and destroyed his plane less than 60 seconds into his first flight, broke four of the rules, and he brought a passenger, fueled his plane with gas 9 points below the required octane, and wait for it: Ignored an email from me the day before the flight telling him his plane was not airworthy. If you think I am kidding about this, just read this: Understanding Flying Corvairs Pt. #6, 98% DNA not enough.

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 If that story isn’t bad enough, I have another where a Zenith pilot with his prop pitch set wrong turned his engine 3,800 rpm Static. He did his first flight from a pave 5,000′ runway, and later said that his plane took 4,000′ to break ground, and had less than 50′ altitude at the end of the runway. This was his first flight, he flew “cross country” that way for a few minutes until he hit a small tree. Because God has a sense of humor I am yet to understand, he lived.

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Here is the bottom line rule: No matter what kind of plane it is, no rational PIC sitting in the cockpit about to take off, pushes the throttle forward without knowing the exact distance it will take to get his plane airborne, and all rational pilots decide before they start moving, they will abort the take off the second the plane goes past the take off point and is still on the ground. There are no exceptions here, there is no excuse for rolling down the runway and hoping the plane gets off the ground.

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Before getting in the plane, the pilot must know:

The POH take off roll for his plane on a standard day.

(Make this line 1.1 in your Hand book)

The adjustment made to this number for his available HP output.

(Make this line 1.2 in your Hand book)

The adjustments made for the atmospheric  conditions that differ from standard

(Make this line 1.3 in your Hand book)

And he must have a physical distance marker (like counting the number of runway lights that make up the distance, at our airport they are 200′ apart, and if a Zenith isn’t airborne by the third, the take off would be aborted.)

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If your own personal POH for your plane doesn’t have the first three written down in it before the first flight, your not just taking a stupid chance without a plan, your plane is not airworthy in my book, period.

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If that sounds like too much to for a guy to know, he is with the majority of pilots flying, who just guess at these things, but if you want to know what you are doing around planes, you will be able to answer anyone who asks these questions. The alternative is just being part of the herd that just pushes the throttle forward and hopes things turn out for the best. Take your pick.

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-ww.

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Critical Understanding Reference Page

Builders,

I am writing this as an index page for a number of articles to follow. As I write them, their titles will appear here in addition to being the lead story on my website.

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I cover a lot of topics on the website, but a review of working with builders this year has focused my attention on a simple fact: We have too many builders operating planes taking enormous unnecessary risks, often without really thinking about it. These builders are a product of two factors that didn’t affect previous generations of pilots: Today we have badly eroded standards of instruction in light aviation, and second, we are in an era that invests more interest in avionics and paint jobs than fundamentals of intelligent decision making.

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While I can make the case that Corvair builders are far better than average, I don’t teach with the goal of merely beating a sadly lowered bar. My goal is the traditional aviation standard, mastery. Any builder who is willing to read and consider with an open mind can greatly reduce his risk and that of his passengers, for whom he is solely responsible for. That will not fix people who don’t care, but it will teach you to recognize such people and give them a wide berth.

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If that sounds harsh, consider how serious the subject is, and tell me who would be served my me sugar coating it?  We have had a number of aircraft destroyed and some people killed, by pilots who doing indefensibly stupid things. Notice, I didn’t say they were stupid people, just that they were doing stupid things in an environment with serious penalties for bad logic, impatience, and lack of understanding.

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My #1 goal for this year is to have a very high percentage of builders read, understand, and utilize the information in  these articles. I want to encourage builders to develop their own POH for their plane and print and keep these notes as a manual. To develop their basic hand book I will write questions in this color and font: (Make your own hand book) at the end of each article for builders to answer and form the basis of their handbooks.

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  Other companies might be happy just selling parts, but I have always been motivated to share what I have learned. How important is this? I spend a large part of my working year on educational tasks like writing and Colleges, neither of which generates a dime.  Preventable accidents ruin the reputation of Corvairs, make insurance more costly, lower sales that cover the costs of Colleges, wreck planes, injure people , occasionally kill  builders, and worst, they have hurt and killed passengers. If anyone objects to how plainly I am going to speak in these articles, please direct them back to this paragraph and point out to them when I said it polite enough for Girl Scouts, many people thought listening was optional.

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 With the goal of minimizing this in 2017 and beyond, We have this index page and the articles that will be linked here. -ww.

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Read: Thought for the Day: Mastery or?

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Critical Understanding #1, Take off distance.

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Critical Understanding #2, Absolute Minimum Static RPM.

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Critical Understanding #3, Rate of Climb, the critical prop evaluation.

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Critical Understanding #4, ANY loss of RPM is Detonation.

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Critical Understanding #5, Knowing “+ROC/5” Rate of Climb on Five cylinders

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Critical Understanding #6, The “Two Minute Test”

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Critical Understanding #7, The Most Qualified Pilot, ALONE.

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