Original Posted By: rhartwig11(at)juno.com
> not having access to a wind tunnel isn't really a limitation if someone> wants to test the FC-10, since automobile highway speeds are a pretty> good match for Pietenpol airspeeds. If you had the proper test rig, you> could mount an airfoil section in, say, the bed of a pickup truck,> poking up well above the cab to get it into clean air, and collect data> at night on a smooth section of rural highway.I've done the truck-testing bit, a friend and I wanted to know the realforces put onto the servo actuating an R/C Pattern plane's rudder, with andwithout balance tabs (the difference was dramatic). Back in high school, Ialso did some real wind-tunnel testing in a Florida Tech's low-speed tunnel(at the time, it was one of the best in the country) for a science fairproject with variable-camber airfoild (took first place at state, so I guessI wasn't complete clueless back then.) My guess is that the truck methodcould give you some OK data, but if you're serious about getting really gooddata, then you really would need to do a bit more and go for the tunnel. Theproblem is that the fine differences between two airfoils (or to get a goodbaseline on the FC-10) would need to be measured with very smooth, laminarairflow and sensitive instruments, you need to know not only the airspeedbut precise AOA, pressure, and forces acting on teh wing section. Moreimportantly, the conditions need to be identical between the control testwith the old airfoild, and the experimental test with the new one. As wediscovered with the rudder test, you have very strong boundary layer andother effects generated by the vehicle itself that will destroy your abilityto get really good data. In our case, we figured this out and built aboundary layer diverter (similar to that found on the intake of an F-15 orsimilar jet) but we still had some effects of the vehicle. You could put atest section on a long truss way out in front of the truck to get betterresults, but then every bump will be magnified and really screw up the forcebalance or whatever you're using to measure the forces. Plus, turbulencefrom other vehicles, wind, fog, etc. will all affect things too.Here's what I would do (and no, I'm not volunteering as my plate is too fullalready...) I would get in touch with a college with an aeronautical programand a wind tunnel. You want to figure out the typical Reynolds number thatthe Piet flies at (low and high speeds) and then find a tunnel that can dothat. Then try to find a sympathetic prof to work with you and connect youwith a group of students so that they can learn, while generating usefuldata. Dr. Michael Selig has done a lot of work at UIUC (I think) so thatmight be one place to start. I think the guy I was working with went toPurdue. (BTW, for those who don't know, the Reynold's number basically justtakes into account the size of an airfoil, the air density, speed,viscosity, etc. and adjusts it for scale effects, thus allowing you tocompare airfoils of different sizes. With some exceptions and modifications,you will get very close to the same performance as the full-size aircrafthas by adjusting the speed and density of the air passing over a small-scaletest model such that it has the same Reynold's number as the real one doesin flight. That's how they can test planes like the C-5 and 747 in a regulartunnel.) As the test section's chord is a factor in the Reynold's number,and it's impractical to build a test section at too small a scale, you'dneed to figure all this out to get teh right combination to be bothrpactical to build as well as what will suit the tunnel that's available. Idon't think it would be too hard to find someplace that could test a half-or third- scale test section properly.Bear in mind that a wind-tunnel test is typically going to produce 2-D testdata, which is invaluable, but not the whole story. The Piet, like allplanes, has a lot of 3-D effects going on... not only at the wingtips, but alot of interesting stuff may be happening between the wing and fuselage,especially for a plane with a radiator there. There may well be asignificant difference between having a cut-out and a wing flap too. You'lleven get different wing sections where the covering sags between the ribs,which could be significantly better or worse than the section on a rib. Sodon't expect any single test to yield all-encompassing results. But it willallow you to validly compare to other airfoils.If anyone is interested in the full story of the truck testing I took partin, let me know privately and I will send it to you (the list server doesn'tlike ZIP file attachments.) It contains a writeup with our test results anddescription of how we did it, as well as the test data. At highway speeds,several times, the airflow on the standard rudder section was stronger thanI was... I pity those poor little servos trying to move the typical patternplane rudder!Just some thoughts,MikeMike Whaley merlin@ov-10bronco.netWebmaster, OV-10 Bronco Associationhttp://www.ov-10bronco.net/___________________ ... ______Date: Mon, 9 Feb 2004 07:19:11 -0600Subject: Pietenpol-List: Brodhead Pietenpol Fly-In
Pietenpol-List: Brodhead Pietenpol Fly-In
Re: Pietenpol-List: Brodhead Pietenpol Fly-In
Original Posted By: "Fred Weaver"
Subject: Re: Pietenpol-List: Brodhead Pietenpol Fly-InIn a message dated 2/9/04 7:21:00 AM Central Standard Time, rhartwig11(at)juno.com writes:> I would like to see weight and balance done on everyone willing to participate with their plane, like they did in '94. Scales, and a no-wind conditionwould have to be met for that, in other words, in a hanger. The biggest problem is the fuel. The pilot must know the precise fuel onboard, so it can beremoved in the paperwork, then an 'Empty Weight Center of Gravity' can be done. EWCG is the base line where you can figure any configuration of loading the plane. Another thing I would like to ask, is if there are any flyers who would like to participate in an organized formation flight. Long rows of Two by Two,for a couple of low passes, then re-group in the air to some other formation. Toss in a photo plane, and there would be some very unique pictures available. This would all have to be gone over in detail in a Pilot Flight Brief.Only those in the briefing would be allowed to participate in the formation flight.Chuck GantzerNX770CG________________________________________________________________________________
Subject: Re: Pietenpol-List: Brodhead Pietenpol Fly-InIn a message dated 2/9/04 7:21:00 AM Central Standard Time, rhartwig11(at)juno.com writes:> I would like to see weight and balance done on everyone willing to participate with their plane, like they did in '94. Scales, and a no-wind conditionwould have to be met for that, in other words, in a hanger. The biggest problem is the fuel. The pilot must know the precise fuel onboard, so it can beremoved in the paperwork, then an 'Empty Weight Center of Gravity' can be done. EWCG is the base line where you can figure any configuration of loading the plane. Another thing I would like to ask, is if there are any flyers who would like to participate in an organized formation flight. Long rows of Two by Two,for a couple of low passes, then re-group in the air to some other formation. Toss in a photo plane, and there would be some very unique pictures available. This would all have to be gone over in detail in a Pilot Flight Brief.Only those in the briefing would be allowed to participate in the formation flight.Chuck GantzerNX770CG________________________________________________________________________________