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Test flying, hi-dpeed taxi and "crow" hops?

EAABipe40FF

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I posted this on Chris's AS thread where it's out of place/off topic.


Hi speed taxi tests? (all opinion)

It depends on several factors. My experience dates back to when I got my Pitts S1C 40 years ago. I had no high performance bipe experience having had 200 hours in my C120 and 50 hours in a O1D Bird dog.....

I decided to do a "moderate" speed taxi run not realizing how fast the thing would accelerate and must have gotten almost up to lift off speed when I chopped the throttle and almost lost it. My mentor observed it and when I got back told me to , "NEVER EVER DO THAT! When you push the throttle forward it should only be with the intent to fly". The next time I pushed the throttle forward I did fly but the TO was still an "Experience".

Since then I've decided that high speed taxi of a new homebuilt "may" not be a bad idea? But whether it can be "safely" done depends on a few factors. These include first of all, PILOT ABILITY coupled with CURRENT EXPERIENCE. In the case of my old S1C for instance. After I had 100 hours experience in that airplane I could have easily aborted a take-off at full throttle/lift off speed, exactly the same condition that almost wrecked the airplane on that first trial. Other factors. Coupled with pilot ability is the power to weight ratio of the airplane. Field length is coupled into the power/weight ratio. Even if the pilot is sharp enough, can you easily get up to speed and easily then stop in available runway? Note that a sort of inverse relationship is in play here, A plane with high acceleration can get up to speed quickly and stop in a relatively short space where a lower powered plane might not be able to stop in the same length runway?

Another factor also coupled with pilot ability is turf/grass vs. hard surface. For instance, I might do a high speed run in a high powered airplane on grass knowing that I would be able to control it but would not do it on hard surface because I'm not that sharp. (BTW, that first Pitts experience of mine was on grass and I still almost lost it) OTOH, if I know I'm not that sharp maybe I shouldn't be doing it?

Bottom line. If there is enough runway and the pilot is sharp high speed taxi is relatively safe. I recently decided to do it with my Acroduster 2. I did progressively faster runs to get acquainted so to speak and I believe it was helpful. That said, with only 160 HP things weren't happening that fast and on grass the airplane was easily controllable. If It had a IO540 one would have had to be more careful. One reason I wanted to do it in the AD2 was I had a concern about whether I had enough runway with only 160 HP. I hoped it would get out/off by mid field and the only way to know was to try. In retrospect it was all a non event compared to my first take-off with Bill F. in the S2C. Exactly as Bill said about my first flight(and the high speed runs), "It will be a piece of cake" Again it's pilot ability. That 2 hours in the S2C was a very good idea!

Crow hops. Short flights in ground effect. These can be useful maybe to check rigging and trim at least that seems to be the suggestion. I've seen them done on slower aircraft and even higher performance aircraft given enough runway. That's the key, to have enough runway! It's been my intent a couple times to do crow hops but they didn't work out as by the time the airplane was flying the runway was fast approaching.


BIG caution as already suggested. High speed runs should NEVER be done unless both the pilot and airplane are completely ready to actually fly.

Indeed, I learned this the hard way. Indeed all the cautions about including pilot experience and being ready to fly were driven home to me in one very ill advised hi speed taxi test I once tried. I had purchased a Tailwind project from a guy and when I went to fetch it found he had a PA22-135 project that was (I thought) a real deal. After getting the Tailwind home I fetched(on a trailer) the PA22 and sublet a hangar at IW3. After I got it assembled and running I decided to taxi it around. While I had flown my PA16 and PA20's I had never flown a PA22. After I had "played" with it a couple times I decided to do a crow hop(how hard can it be?) The airplane was NOT ready to fly and didn't have any fairings at all. So I gave it all the O290D2 had and figured it would fly well before half way down the 2000' grass strip. Maybe it might have with wing fairings but it didn't and I continued too far and decided to fly it rather than venture into the corn field. It finally flew but not very well. I managed to get it around and down but I think I have now used up any luck I might have ever had.

So please be careful out there.



Jack
 
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