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Old Feb 01, 2013, 07:07 AM
Build straight - Fly twisty
Whiskers's Avatar
Australia, QLD, Little Mountain
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Jack, the reason for building the wing that way was to make it relatively easy to standardize everything about the flight.
I am amazed that the thing flies as it does. It really behaves as if the wing was not asymmetrical. I fully expected much more difference.
And the test was only about difference, especially in regard to stalling.
Perhaps a greater difference would show up if I sanded the Ca to have a better shape and give it a finer TE.
I may do that in the interests of science and the pursuit of enlightenment.
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Old Feb 01, 2013, 08:42 AM
treefinder
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Since it's just a bit of standing, I'd slick up both sides LE's and make them the same to maybe 25% chord, or the peak of the conv. foil. See if that exaggerated the difference
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Old Feb 01, 2013, 08:56 AM
Jack
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Joined May 2008
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Quote:
Originally Posted by Whiskers View Post
Jack, the reason for building the wing that way was to make it relatively easy to standardize everything about the flight.
I am amazed that the thing flies as it does. It really behaves as if the wing was not asymmetrical. I fully expected much more difference.
And the test was only about difference, especially in regard to stalling.
Perhaps a greater difference would show up if I sanded the Ca to have a better shape and give it a finer TE.
I may do that in the interests of science and the pursuit of enlightenment.
I understand that and was not trying to be critical of what you did or ungrateful for your efforts. I just thought may isolating it to one airfoil on each plane might make the difference more apparent.

With separate planes and if it was going to bear out the results of the JetPlaneFlyer tests I would expect the KFm version to fly well, be a little slower across the ground, and to have a flight duration that was about 40% shorter.

Just idle chatter...

Jack
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Old Feb 01, 2013, 10:15 AM
RC beginner
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excellent test whiskers. imo one of the few valid experiments conducted by anyone here. little room for "placebo" effect. different planes cannot be flown in the same way under same conditions so this is very much more controlled. it never occured to me to try with kf but i did vary aspect and loading on one side and found even slight differences caused major spinning and/or roll. so imo your test was very scientific in nature. thanks.
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Old Feb 01, 2013, 10:22 AM
treefinder
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Here's another spin on it (no pun intended, well, maybe not). how about making two gliders as identical as practicable except for the respective airfoils, then launching them at the same time/direction/speed using a bungee launch and watch the results?
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Old Feb 01, 2013, 10:27 AM
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thats pretty much what jack suggested but imo not as good as current method which REALLY nails the variables. (and twice as much work )
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Old Feb 01, 2013, 10:43 AM
KlonWarz
Joined Dec 2012
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Aw heck!
I'm really interested in the results and have far too many projects on the slate...

If someone builds a suitable scale wind tunnel with measuring device I'll contribute my centrifugal fan to science. It's parcel size.

PM for more details and pics if interested.
rc
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Old Feb 01, 2013, 11:06 AM
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Yeah, but with the additonal twist of launching both planes into the same air/wind, etc. parallel not sequential. I agree with all those who contest that it's impossible to have the identical environment in sequential flights. W's test shows differences, but they are confounded at least a bit, so doing both same plane different wing halves and two planes with their own wings could perhaps provide another bit of info. (really, I'm just trying to keep him busy, so he won't feel bad about not getting on with that seaplane!)
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Old Feb 01, 2013, 02:57 PM
Build straight - Fly twisty
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I do not believe that I could build multiple planes that would satisfy me in the *identical* thing.
I'm not that good.
The comparative stalling performance of the 2 sections was so easy and accurate with this method.
The problems involved in accurately assessing this by using separate planes are enough to give me a severe attack of the heebie jeebies.
I'm now thinking of testing a flat plate and KF hybrid.
I bet there will be a difference there, but how those differences manifest themselves could be entertaining.
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Old Feb 01, 2013, 06:16 PM
treefinder
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oh, c'mon, sure you are! but I'll submit to my elders that it probably won't be as easy to detect differences.....
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Old Feb 01, 2013, 07:11 PM
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Just an idea... wouldn't a flying wing make any difference between the sides more evident? I'm thinking that fin on the back must add some stability, but I'm no expert.
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Old Feb 01, 2013, 07:51 PM
Build straight - Fly twisty
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Toll, that could be so but I started building little chuckies when I was a young boy (long long long time ago) and I really know how they can be expected to fly.
With flying wings I'm not so confident. I can see sweep-back introducing a dreaded variable, as could reflex.
The rectangular plan-form I chose to use was in an attempt to minimize side-to-side variables apart from the wing-sections.
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Old Feb 02, 2013, 08:59 AM
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United States, DE, Bear
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I tried to solve the problem by building one fuselage and using multiple wings. That made the wing the only variable. I instrumented the plane, tufted the wing, and had on-board cameras to record the tufts.

I never got past the KFM2 wing, before I crashed the plane. I haven't had the ambition to rebuild. I just found it impossible to maintain an airspeed within 5 mph. At the Reynolds numbers we are using, that difference is important in the data. I think the instrumentation I used (Eagle Tree) may not be sufficiently accurate to my needs. I don't know. I just know that getting usable lift drag data at our scale is incredibly difficult.

The smaller the airplane you use to test with, the more outside influences affect your results. Any twist or warp in your wings will skew your results. Not having a sharp TE on the standard airfoil shape, will bias the results toward the KF airfoil, as will a poorly shaped LE. If you use a foam cutter, you can cut identical cores for the standard and KF airfoils, and then cut the notch to make the KF step. This will give the best results.

Trying to determine stall behavior by throwing a glider is not going to give you any usable data. If you want to do a stall test, take the glider up to altitude (tow or carry it), and then do stalls in still air by radio.

I don't meant to dissuade anyone from testing. I just wanted to share what I've learned over a few years of testing.

Roger
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Old Feb 02, 2013, 10:04 AM
KlonWarz
Joined Dec 2012
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I would agree with you, Roger... far too many variables in a small, flexy model for a precision estimation of quality.

Many moons ago... when Lockheed was in the process of shutting down Kelly Johnson's Skunkworks in Burbank to move operations out of state, they had massive, and continuous salvage operations conducted at their facility. We bought truckloads of stuff from them for pennies on the dollar.
Among the assortment was a solid aluminum model of an aircraft for some sort of testing.

..solid aluminum... are the key words! It was rigid.

Wish I had it today! It was quite nice!!!
We were in the venture for a quick return, so it went to the scrapper as much of the volume that couldn't be used immediately on our own projects...
rc
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Old Feb 02, 2013, 10:22 AM
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Very interesting thread! I haven't read enough and should keep my nose out, but I'll offer an anecdote that might be useful. A long time ago I was involved in a model rocket project with some school kids. We (I?) wanted to establish the drag characteristics of our rocket and hit on the idea of using a car as a cheap wind tunnel on wheels. Basically we had a support structure for the rocket on the passenger side...simple spring scale attached to the rocket for force measurement; cruise down a long straightaway with little or no traffic and build up a collection of data points at different speeds. It worked pretty well. Something like this with the paired wing sections, KF & conventional, on an axle through their center, spring scale restraining rotation and measuring torque and the axle able to be tipped upward to varying AOA...might produce some good data. It's neat to run into KF airfoils again; saw articles about them back in the 60s or 70s and then it all just seemed to disappear.
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