Day: January 28, 2017

Builders,
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Pictured below are two carbon fiber, ground adjustable prop blades from two known and respected US manufacturers, who have been on business 30 years (L), and 80 years (R) respectively. Let me share with you what you can tell by eyeball about the performance of each of these different blades.

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Above, A Warp Drive blade with nickel leading edges on the left. There are more than 150 of these flying on Corvair powered planes. I have been a WD dealer for more than 20 years, and you can look at pictures of my Pietenpol from that far back and see a 66″ two blade on it. The prop on the right is a Sensenich Saber blade, in the correct airfoil and pitch distribution to be a fair comparison to the WD prop. It has not flown on a Corvair, it was directly provided by the factory as a test article, the blades still have the node marks from their in house vibration survey. I have been a Sensenich dealer for almost 15 years.

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Here is what you can tell about their performance comparison by Eyeball : Nothing. The only valid commentary that will come, will be from impartial testing, period. Plenty of people will offer some comment on nearly any prop, but will they buy you a new one if it doesn’t work? I haven’t seen that yet. Ask any group of people at an airport or an EAA meeting about a kind of prop, and wait for the first guy to answer, then ask the four questions his expert opinion neglected to include: Have you ever flown that type of prop on the engine I asked about ?  Are you a dealer for that brand so you would have full access to their support staff? Have you ever had any formal training on propulsion, A&P work or worked in a prop repair station? Has anyone ever paid you a dime for you opinions on props, or is your advice worth exactly what you charge for it, nothing?

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Without even asking, you can pretty much guess the answer to the questions.  On the other hand, even though I had Dr. Ernest Jones as a mentor in propulsion at ERAU, am a 25 year A&P, have been a prop dealer for decades, Have worked in a certified prop repair station, and was paid about $80K a year by a global prop manufacturer, my experience tells me that you can’t tell anything valid by eyeball, only real testing counts. Show the picture above to the guy at your EAA meeting who dispenses advice on every subject that comes up, and ask him which blade will perform better. Regard it as a study of aberrant humans, not valid performance advice.

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-ww.

Builders,

In the previous story, The small world of Experimental Aviation , I mentioned how much N-1777W changed over the years. He is a look at some of it:

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This is the plane at Oshkosh 1970. The picture made it to the back cover of Sport Aviation in January 1971. Notice it once had 140HP heads, and other well meaning, but weak ideas. If you have the Tony Bingelis book “Firewall Forward” the Pietenpol/Corvair pictures in it are all of this plane, in this era. Bingelis didn’t like auto engines, and his writing spread a lot of old wives tales. He was a good guy and a highly influential writer, but he held opinions that testing by his contemporaries like Wittman and Monnett showed to be wrong.

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Fast forward to 1995. Want to know how I became the expert on Pietenpol weight and balance? Want to know why I think it is annoying when people who can’t do a simple calculation, or have never weighed a plane on electronic scales question my work on Piet W&B?  Start with this photo: The reason why the cowl has a 6″ wide expansion in it is simple. After getting the plane, I found out the weight and balance, done on bathroom scales was dangerously wrong. I carefully measured, and in a single day, made a mount 6″ longer and plugged the cowl for test flying. In the picture is Gus Warren who did a lot of the work with me and covered much of the flying. It was an instant improvement in safe flying behavior. I have written extensively about this testing and work, you can find the links here: Corvair – Pietenpol Reference page, but today, the majority of Pietenpol builders willfully ignore the information. Much of this is driven by people in the Pietenpol community who personally dislike me for my tone or experience.

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Above, same plane 1999. This is an entirely different motor mount, the first high thrust line (#4201-C Pietenpol Motor mounts, now on the shelf, ready for shipping.)  and a completely different set of gear legs.(New die spring landing gear on a Pietenpol, 10 a.m.-4 p.m.)  Bring up the topic of axle location, gear leg length, CG changes or thrust lines, and people will tell you they think it makes no difference. Of course their opinion is not based on any testing, just a guess, something they heard from a guy. When I speak of these things on a Pietenpol, it was because for a number of years, ready to cut up a good flying plane, or a mount that I had made a month before, in search of something better. Some opinions are made of guesses, mine are made of testing.

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If you look in the upper corner of the picture, there is a blond girl sitting in the grass. She was getting away from her job as a newspaper editor. She liked planes a lot, and had a very pleasant way about her. Her name turned out to be Grace.

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Above, side view of the same plane, taken just before Corvair College #1. Notice how much longer the gear is than when the fuselage was orange. Also note where the axle is located. In the last few years, we have had two Corvair powered Pietenpols heavily damaged by being put on their back, even though I warned people to move the axle forward if using brakes. It is frustrating to not be able to motivate people to correct things like this before an accident. When you see what I was willing to rework on my own aircraft to make it better, it is obvious that I don’t operate things in a condition that simple work and modest money will fix. If you are too tired to improve things, pick a different hobby, this one has potentially harsh penalties for the lazy.

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-ww.

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