Flight Models?

Doing research and looking for information on: 'How the Planes Flew,' in the words of the pilots themselves. Can anyone help out and point me in the right direction. Thx.

"Flying the Old Planes" by Frank Tallman is pretty interesting. I don't recall which ones he covered but I know the Fokker D7 was one.

Speaking as someone who did this for a living for a few years, I can only say that the "words of the pilots" are, unfortunately, not terribly useful. Some will be accurate, some will not be (and wildly so), and there's no way to tell which is which.

I was lucky enought to be working on modeling WWII aircraft, and research at the NASM Archives, the USAF Museum at Wright Patt, and the IWM garnered us reams of actual flight test documentation carried out with rigorous accuracy. This is what we used for our flight models.

Now the interesting thing is after you've seen a series of flight tests which all agree with each other, you can then go back and read what the aces said, and it was very interesting how wrong they were. That's not to say they were in any way untruthful, but they often attributed performance differences to the aircraft, when in actuality (after seeing the real data) what they saw was differences in pilot capabilities. For example, it's very easy to find high-ranking WWI German aces who will insist that their 109's could outturn a Spit. Sorry, no, not if the pilot of the Spit had any clue where the edge of his envelope was.

What's even more frustrating is that right after WWI, the US did quite a bit of serious testing of various WWI types. I found all of the orders and the status reports at the national archives. This was part of the Sarah something or rather collection that was brought to the archives from Wright Patt at some point. The frustrating thing is that every single enclosure (that actual test reports) had been removed. This particular collection goes all the way up to the '50s, and the bottom line is that someone out there has a goldmine in flight test data that they stole before the boxes made it to the archives. The folks at the NASM archives have made a few attempts to find out what happened to the enclosures with no result- it's one of the great mysteries of those seriously involved in aviation research.

Whoops, wandering far afield here. What I meant to say is don't use the words of the pilots. There's a better way. Go to http://www.x-plane.org/ and get yourself a copy of x-plane, which does a pretty phenomenally accurate job of creating accurate flight models based on the real geometry and thrust output that you plug into it. In other words, if you can get the airfoil shapes (and I've seen quite a few that appear to have been accurately measured) and a good three-view (easy enough to get) x-plane should be able to spit out some fairly accurate performance figures. You'll have to make some assumptions for prop efficiency (guess low) and hp output, but I think this is the best you're going to get.

Jay, with regard to prop efficiency, does the model take into account the difference between a big, high-torque prop such as was used with the actual aircraft vs a short-stick hi-rev, low-torque prop that modern aircraft use? I remember reading a comparison of flight characteristic differences by a single pilot who had flown two full-scale reproductions, one with a modern engine and one with an original. The gist was that the difference between the two was quite dramatic, and that reproductions using modern powerplants should not be used to judge the performance of the original aircraft. Theory was that the original big but low-speed prop pushed a lot more air out over the wing surface.

Ed, with respect to X-Plane I'm speaking more from the words of others (that I trust) than myself- I've fiddled around with it a bit, enough to confirm that it's a steal for the money ($40), but no more. As I recall for the prop you input a generalized airfoil shape, diameter, and pitch, and it calculates the efficiency. One friend that's used it said it tended to be optimistic with prop efficiencies, hence my suggestion to guess low, along with the simple fact that WWI props weren't very efficient compared to modern designs.

As for what you said about modern vs. original props, yes, there's a definite difference but not (IMO) in the way you said. The amount of air a prop pushes back is going to define the thrust, whether it's a large diameter or small diameter. The only real differences I could see between a large diameter, slow revolving prop that creates as much thrust as a small diameter, higher-revving prop is going to be the amount of wing surface area with disturbed flow, and the overall "torque" effects. First, because the thing is larger and heavier, there should be a greater torque moment. Second, the larger slipstream (rotating) should also create a greater roll-axis moment as it strikes both the wings and the empennage, and last, I'd think the P-factor would be larger also. And because it's affecting a larger percentage of the wing area, you'd probably see a reduction of lift compared to a smaller diameter prop.

If you meant that modern powerplants with modern props generate alot more thrust than the originals, I'd agree with that.

Take all that with a large grain of salt though, my guesses are based upon experience but these things (especially in WWI types with all sorts of stuff sticking out all over the place) can be really nonlinear.

Yes, my understanding is that the period props pushed the air over a wider (span not chord) wing surface area than modern short-stick ones, leading to differences. And I agree that modern propeller/engine combinations produce more thrust. I guess what I'm saying is that I believe that there are problems in placing a large, heavy prop on engines designed for light, short, higher-revolution props and expecting to duplicate the performance of the original aircraft. And that, conversely, putting the modern combination of short, light, hi-rev prop on an aircraft designed for the other combination also won't give you an accurate measure of performance.

Try this for a start -

http://www.hq.nasa.gov/office/pao/Hi...-468/cover.htm

Navigate through the table of contents.

BoL / Byron