Hi Bill,
Just curious how the Eather Undercambered prop worked out for you? did it displayed too much load for the .40VF?
Pretty much all the early experiments in the UC props in this country were done with 46Vfs, not because they didn't work with 40's. but because that's what Ted and David were running at the time. This was around 92-94. I can recall calling Brian about getting some props* after one of our flying sessions - and waking him up since it was about 4 in the morning in Aus. We had them shipped straight the the Executive Inn in Vincennes for the 93 NATs.
The problem I and most of us flying the 40VF at the time was that with our setups, the tendency was to explode in the corners like you lit a JATO bottle. The first-gen 40VF systems, while to the uninitiated, were referred to as "constant speed" systems (because they didn't break from 4 to 2), were not that way at all, they actually had a fair bit of boost. We had no idea why at the time, but the UC props tended to greatly enhance that to the point it was *way* too much of an effect. Now, I think I understand why - a combination of the effective pitch distribution being heavily weighted to more pitch at the tips, and the effect Igor notes above (and first found about 10 years ago) where the drag goes down when the AoA increases. In fact, the way we attempted to mitigate it a the time was to depitch the tips, which sort of worked but wasn't at good as the Bolly. Later, with the PA40, it was even worse with the standard setups because the PA wanted to 4-2 and had much stronger boost and brake to begin with.
David came close to figuring it out on the PA40, by using a non-standard system, but Ted was probably responsible for the majority of the work using the 46VF. He got it running softly enough to take full advantage of the UC prop. When the PA61 came along David figured out how to get it to run kind of like a big 46VF, mostly by keeping it from breaking at all, and just running it in a 4 all the time. It's not like you need a lot of "boost" in the corners running a piped 61 in an old ST46 airplane. The key was unloading the engine enough to make it stay far from the breakpoint, then pumping up the compression, (spigot) venturi, and nitro to get the performance back (since you no longer had to consider what it does to the break). And you didn't have to screw up the performance with lots of diameter. For example, I came in tied for 3rd at the 2000 NATs with a teeny little 11.5-3.6 3-blade that was David's old break-in prop, and that worked just dandy on a 46VF. It turned out to work pretty well with flat-back props, too.
Then the RO-Jett 61BSE (144 deg "Brett Version") came along, with timing (accidentally) just like the 46VF, and, gee, works just like a gigantic 46VF, no muss, not picky about running pretty softly like a VF, but with 33% more displacement. That works with either prop with no real adjustments, once you get the pitch on the UC prop low enough to get the right RPM.
Brett
* we called from a "restaurant" in Napa called "Harry O'Shortals", now quite deservedly closed. I am not sure why, but several good reasons occur to me:
Fell into river when undercut by yearly flooding in Napa River
closed by the County of Napa health department. One time, for reasons that escape me, David, Bill, Kathy, the kids, and I went to Harry O'Shortal's for dinner. Several mice ran along the window sill right next to the table while we were there - yes, the *indoor* side of the window.
proprietors died from either ptomaine poisoning, or embarrassment
Topic: Undercamber props (Read 5178 times)