Pietenpol Weight and Balance project

Builders,

Besides covering the world of Corvairs, I have done a number of additional projects in Experimental Aviation. One of the most important of these other projects was the Pietenpol Weight and Balance project, 2010 -2012. We did this project to serve all builders of this design, not just the builders using a Corvair. The work was covered in a series of five articles in the Pietenpol newsletter. There is information at the bottom of this story on ordering the back issues.

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Above, My Pietenpol at the last hours of Sun n Fun 1996. From L to R, Gus Warren, Steve Upson and a much younger version of me. I have been around Pietenpols my entire 25 years in aviation. Take a moment to look at all the aspects of this on our Pietenpol page at this link:

Corvair – Pietenpol Reference page

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The nature of the issue: People who know the design well, understood that a great number of these planes were being finished and flown near their aft CG limit or behind it. This is a dangerous situation. The problem was driven by a number of factors: people using light engines like A-65’s, pilots who are far past the 170lb FAA example, and the fact many people had no examples to follow, and operated on old wives tails. The Aircamper is extraordinarily sensitive to poor planning because the pilot sits entirely behind the rear spar of the wing, much further aft than a typical tandem cockpit light plane such as a J-3.

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Additionally, many planes were built with their main landing gear too far back. This lead to several airplanes being put on their backs. Combining axle placement from 1930s drawings with modern brakes caused this.

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Although there had not been any fatalities directly attributable to CG and axle placement, there had been significant preventable damage done. I also suspected that the poor utilization of a great number of finished planes was due to the undesirable handling caused by these issues.

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A weight and balance document that Bernard Pietenpol developed in the 1960’s with an example of showing correct axle placement for brakes, an example of W&B that allowed a 290 pound pilot to be in limits, and stating in all capital letters that the CG of his design was 15″ to 20″ and that it was never to be flown aft of this, was available, but largely ignored by builders. Additionally, I weighed “The Last Original, ” Bernard’s personal plane, confirming his design data. I can think of no other design where builders routinely ignored designers CG limits. Our goal was to demonstrate that there is no reason to.

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The project was done with the support of many well known Pietenpol people like Doc and Dee Mosher and Bill Knight. We also had great participation for pilots who allowed us measure their aircraft and weigh them. The project had broad support.  A gentleman who was personal friends with BHP told me that it was the single most constructive project undertaken since Bernard had passed in 1984.

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The data collection: In 2010,2011 and 2012, I brought a set of very accurate electronic scales to Brodhead and weighed more than 30 different Pietenpols with Corvair Ford and Continental  engines. All of the measurements of the aircraft, such as fuselage length, motor mount length, landing gear location and wing to fuselage location were accurately taken. I used the same set of scales every year. A number of the aircraft we weighed had very poor bathroom Scale type W&B reports. Several planes had not been weighed in years, or were purchased second hand and had W&B data that was clearly copied from a different aircraft. About 1/3 of the aircraft had flown to Brodhead at or beyond the designs 20″ aft CG limit. All of these pilots expressed thanks at learning the situation and made plans to correct it.

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The data showed many parts of builders lore to be foolish myths; Both long and short fuselage models were shown to be equally prone to CG issues;  Fuel and passenger weight was shown to have little effect; we proved that building a longer engine mount had very little effect on CG compared to wing placement; Lighter was not better, as the lightest planes as a group had the most aft CG.

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We did additional measurements on planes in 2011 and 2012. I used the same scales in Florida and South Carolina to measure several other planes. The total data set is now 33 aircraft, enough to cover the design thoroughly. For an example of a specific CG change and performance change in a Pietenpol going from a 65Hp engine to a Corvair read: Pietenpol Power: 100 hp Corvair vs 65 hp Lycoming.

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Bob Lester strikes the “Intrepid Aviator” pose with his Pietenpol.  Bob weighs 210 fully dressed up for open cockpit flying. with his Lycoming, his plane was flying near the back of the CG range at 19.1″. With the Corvair we moved it forward to 15.9″ This is a dramatic shift, and it would now take a pilot over 320 pounds to move his CG to the aft limit. This is a much better position to be in.

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The project was started at Brodhead 2010. With the help of the above crew,  we performed a weight and balance on 14 Piets. From left to right above, Ryan Mueller, Jess (whose shirt says “Real men fly  Pietenpols”), Emory Luth and myself.  Gathering the data was a quick process,  taking less than 10 minutes per plane once we had the drill down.

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The calculations and results: Technically every pilot and A&P must know how to do a weight and balance calculation to pass his test. The reality I know is 50% can’t do a weight and Balance calculation to save their lives. On the other hand, I am particularly good at this, especially the complex variable of adjusting the wing fuselage location to correct the issue.

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One of the first things Ryan and I did was develop a complex computer algorithm that we could plug each planes data into and it automatically spit out the maximum pilot weight that the plane could take before it went out the aft limit of the design at 20.” There were several planes we measured that had A-65 Continentals that could only take a pilot of 130-135 pounds before going out the aft limit of the envelope. Several of these were being flown by 180-190 pilots. You can get away with this as long as you have the engine running creating high air flow over the tail, but if the engine quit and the speed decayed, the plane would be very prone to an unrecoverable condition.

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Rational people do not build airplanes to see what they can get away with, they do it to effectively master the skills and utilize the design correctly. Anyone arguing that it is “OK” to build and fly a plane at or beyond the CG limit because he has evidence that it has been gotten away with before isn’t a person who should be taken seriously, and their judgment can rightly be called into question. Using our data, any plane, even one with a light motor can be set up correctly to fly with a pilot of 220 pounds. Planes using a Corvair, Ford or O-200 can be set up to fly 300 pound pilots in CG.  Several of the examples we weighed could have pilots over 305 pounds and still be in CG. There is no reason to build your plane and not have it operate in the designers CG limits.

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Where you can find the full data set. Click on this link:

Pietenpol Weight and Balance article source

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 Most people don’t view it as their task to correct negative or dangerous things others advocate. They value “getting along.”  For a reason explained below, my loyalty lies elsewhere.

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I earned my A&P license from Embry-Riddle in 1991. It was in an era when the department was run by men who were former military, who had come of age in WWII,  Korea, the Cold War and Vietnam. They took aviation very seriously, they all had seen its potential costs. They were tough.  I am biased, but I do think the program was without peer.  At the end of training, a handful of select students, I among them, elected to take a solemn oath in a private ceremony  to swear our unwavering allegiance to aviation safety.

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We did not swear to protect our employers, nor to defend the FAA or their rules, nor did we swear to defend our friends, careers or egos. We didn’t even take an oath to protect pilots. The only people we were taking an oath to protect was unwitting passengers who would fly in planes, people who had supreme trust and the belief that their fellow man, an aviation professional, was trustworthy with their very life.  The critical element of the oath is that we might be the passengers last line of defense, and if it was so, we were to “forsake every other consideration to protect them.”

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To have some understanding of my perspective, spend an evening reading my Risk Management reference page.  If you only have some time, just read this story: Effective Risk Management – 2,903 words ” It include the statement “This was the first time I can clearly say I understood the cost of keeping your mouth shut. This was the first step to me becoming the kind of “Bastard” who publicly points out people doing dangerous things.” At the conclusion of the CG project I wrote the paragraph below when a builder sent me a photo of an 8 year old kid flying in a plane with an aft CG. Few people outside professional circles understood the tone, but I did get one short note from a guy who graduated from Embry-Riddle before I was born, when the school was still in Miami. He knew without asking I had taken the oath as he had, and the tone made perfect sense to him.

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” Many builders over 160 pounds with light engines are actually flying behind the aft CG limit, which is a great idea if you feel you have already accomplished every thing you wanted to do in this life. In my book if, you want to knowingly fly out the aft cg limit of a homebuilt, it’s your choice, I don’t base my happiness on the actions of others. If someone wants to tell other people this is a good thing to do, then they will find me disagreeable. If a guy wants to go a step further and fly passengers who know nothing about CG, like little kids, they will find me to be a vocal opponent of theirs, no matter who they are. When it comes to speaking up for the safety of unwitting passengers, I am not intimidated by any combination of the offending pilots wealth, experience, popularity or physical size far less peer pressure or being thought of as a mean spirited sob.”