At 11/11/02, Jon Berndt wrote:
> At 11/10/02, Jon Berndt wrote: > >Michael: > > > >What are your design references for the two WWI aircraft? > > > Do you mean how did I get the aero data? > > Regards, > MichaelYes, and any other information used to model them. Jon
Your word "design" threw me. I don't do any design when it comes to building a model; I do a lot of analysis and some estimation. The result is an engineering model, not a tuned model, albeit I might have to settle for some "placeholders" pending more "discovery".
The first step is to gather all relevant data that I can find, e.g. 3-views, controls surface throws, mass data on a component-by-component basis, performance and handling data, etc. After doing this, things will be missing. But it's like a puzzle w/ parts missing and you start putting things together. It's hard at first, then things start falling in place. As for missing data, in the end (if I pick the right kind of airplane for which there is a lot of data) I can make some reasonable estimates and do sanity checks. Ultimately, things come into focus. It helps being a pilot and an aerospace engineer/prof. When it's all done, you could call it reverse engineering.
That's the answer in broad stroke.
Details are taking all the mass data, and coming up w/ the moments of inertia. In the process I can find the c.g. and compare that w/ what it should be (or what I think it should be). I might have to move some parts around to get it all to work out, but to my surprise I am usually within 1-3 inches of the proper c.g. on the first pass. I keep track of all this in a spreadsheet.
Then I start working out the aero data using many sources: background knowledge, NACA/NASA reports and others, books (e.g. Roskam's and specialized books on particular aircraft), and then several analysis codes (e.g. Cmarc/Pmarc, XFOIL and things I have written). One area of focus for me is the nonlinear aero data so that things like stall, hammer heads, tail slides, etc are mostly right (especially so w/ the ASW-20). Since I've been doing aero work (largely design related: aircraft, wind turbines, motorsports, yachts, etc), I have a good handle on getting things close and/or close enough. In this step I am mostly using linux (Fortran, Matlab, and specialized codes).
Some important effects that I include: [1] model data over a wide range, e.g. +-90 or 180 deg and [2] apparent mass effects (important for low wing-loading aircraft).
I have David Megginson to thank for the uiuc gear modeling code. In FGFS, I put gear and other contact points where they're supposed to be w/ reasonable spring constant and damping data, and it works! The ground-reaction behavior of the ASW 20 is amazing to me.
I am weak on the engine data, focusing more on aero. Lately the engine is tuned so that I at least get the max rate of climb and max speed right. I have a model thrust curve that I tweak to nail down these points and others if I can get them. It's a "90%" estimate for now, and admittedly it is one area where I do tune things. For the ASW 20, my estimate of zero thrust is 100% right!
I am weakest on the 3D external visual model. In this area, thanks to open source projects like this, amazing things happen!
I've been picking aircraft carefully and strategically.
* The Airwave-like hang glider was picked because I wanted to try and model the flare on landing. This really soft flare is a consequence of apparent mass effects, which I included. Also, I've always wanted to fly a hang glider, but those are dangerous as my dad explained back in the 1970s. He was an actuary and knew the poor statistics.
* I picked the Wright Flyer because there is some wind tunnel data as a starting point, and of course the centennial is nearly upon us. After I started working on the Flyer, I became aware that MSFS will be coming out w/ a special shrink-wrapped special edition Wright Flyer model.
* The WWI aircraft are interesting because of the biplane and triplane wings as well as the gyroscopic forces from the engine. Apart from that, they're simple, not very sophisticated fighting machines relative to a F15. It helped to have some motivation from the Discovery Channel.
* The ASW 20 was picked because I am a sailplane pilot, and the engine was out of the picture so doing the aero right would pay more dividends (no engine effects to "mess things up").
* My next aircraft is the Extra 300s aerobatic airplane. I like watching all the weird things aircraft can do in flight. This one will be a challenge!
* There's also icing. Flying in icing conditions is simply not safe. One can envision ways of giving the pilot more information in the cockpit to make it safer. That's what we're doing in a nutshell.
There's been no premeditated strategy to pick MSFS aircraft --- Sopwith Camel, Extra 300s, Wright Flyer. But it does provide an interesting basis for comparison.
Regards,
Michael
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Prof. Michael S. Selig
Dept. of Aero/Astro Engineering
University of Illinois at Urbana-Champaign
306 Talbot Laboratory
104 South Wright Street
Urbana, IL 61801-2935
(217) 244-5757 (o), (509) 691-1373 (fax)
mailto:m-selig@;uiuc.edu
http://www.uiuc.edu/ph/www/m-selig
http://www.uiuc.edu/ph/www/m-selig/faq.html (FAQ)
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