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For sure I agree, testing cooling factors on aircraft is one of the most
difficult things I've encountered. Keep in mind testing is what I did all
of my career. 8 years at one company where basically every test involved
heat transfer. It's really tough to change multiple parameters with our
aircraft. Just as you describe. Also difficult to measure how much affect
the change had. I agree on those points.
A few years ago, the "too many variables" argument would have been true.
Not any more. Things changed in the last few years. With fractional
factorial testing it's unreal what you can accomplish. One of the
benefits of computers. Zeitlin uses this method too. You can ask him
about Taguchi testing. Since using Taguchi method, I've never encountered
anything too complex. They may be out there, but I've measured a number
of things that the experts said could not be done. The cool thing, you
get done with your experiment, and you know just how much effect "noise"
has. I've done experiments with lot's of noise (uncontrollable
variables), yet still found significant factors. I had Taguchi test all set up for my Cozy. But one of the factors yielded
cooling way beyond my expectations (turbulators ahead of NACA). So I
abandoned test. I'll have to do the test now with new engine, as I'll be
running at much higher hp.
-al wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
timing. Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
On Sun, 20 May 2007 14:33:33 -0400 John Slade <sladerj@sbcglobal.net>
writes:
>You guys could improve the test. Just throwing out the concept.
I don't doubt your sincerity, Al, and the objective is admirable, but I think it would be VERY hard to achieve any real science comparing different installations, even on the same aircraft type at the same place on the same day. There are just too many variables. Inlet duct size & shape, outlet size, airflow through the cowl, position of the heat exchangers, augmentation system design, overall drag, engine model, accurate measurement of actual results... the list is endless. There would always be enough noise in the data to render it meaningless, especially with plans built airplanes like the Cozy. I believe that the ONLY way for each individual to approach the optimum is first to establish what it is and then for them, then approach it scientifically by changing things one at a time measuring airflow, cooling and drag effects accurately as they go. This will be a very tedious exercise involving lots time consuming redesign and rework, and its what many here have done over the years to get us newbies to the point we're at today. The reality of putting one of these installations together from scratch is an exercise is that you read and learn, look carefully at what other flyers have done, decide what you think is best of all you have seen and learned, then assemble your own approximation of a solution to meet your own particular goals. There's enough information around these days that, with a bit of luck, your first shot will work well enough to fly without overheating. Once you reach this point you can begin the exercise of improving the cooling / cooling drag equation by experiment. The holy grail is getting something that works (ie meets your own design criteria) first time. It's EZ to err to the side of cooling drag and get something that cools but wont go fast. Its a lot harder to hit the target of something that goes fast and still cools enough. Its all about experimentation and compromise, with a little luck thrown in.
John Slade
--
Homepage: http://www.flyrotary.com/
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-al wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
timing. Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
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