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Old Sep 13, 2010, 02:23 PM
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GPW, I personally would follow Burt Rutan's methods rather than the Myth Busters. At least if I wanted any usable data I would. Burt built a fixture that he bolted on the front of a car (in the free stream air), because he had no wind tunnel available. He rigged the fixture with a means of changing AoA, and a couple scales so he could measure lift and drag. He used this contraption to get the data for his first aircraft designs. Recently he had to evaluate a number of options to fix a problem with the control surfaces of Spaceship One. He had no time to get a wind tunnel, so back to a fixture bolted to a vehicle. It worked out just fine.

Viking, sorry for the temporary loss of the plane, but glad you got it back. I'm always jealous when I look at your videos. All that room with little or nothing to hit. All that fantastic scenery too.

Fred, you don't have to be NASA to make/use a wind tunnel. The Wright Brothers built one to test wing and propeller designs. My Alma Matter had two low speed wind tunnels and one supersonic tunnel that we undergrads could use. The big low speed tunnel had a 6 foot by 6 foot test section. The most unusual thing I ever saw tested was a full sized traffic signal suspended from cables. How I wish I could have a few days with one of those wind tunnels now.

Roger
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Old Sep 13, 2010, 03:55 PM
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OK, glad to hear others have issues with ailerons on KFm3 wings, and I am not alone. Saw KFm2 doesn't exhibit this same trait as posted ny Cybernaought. But then, the SE5 showing the same thing?

Well I was going to go ahead and do an undercamber wing for my night flyer Blue Baby, but have instead started a KFm2 wing, with ailerons, and lights. Lot of work because of the lights included, but necesary. Hope that this won't be aggervating in another exercise to not acheive my mission, which is a faily easy plane to fly in the dark.

Anyway, all good for contributing to the 'test data base.

My main worry, I still want 2 degrees of dihedral for some self righting capability, since the demands in total darkness are something I have experiance with. Any opinions on that dihedral contributing to aileron issues? Guess a true test between both wings would be to keep the dihedral, or I couldn't fairly say it was all related to KFm3 if that was changed too.

Fred
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Old Sep 13, 2010, 04:03 PM
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I did a 60" KFM3 wing for a RET Blue Baby AP1. Later I added ailerons. The wing had the standard (4 degrees I think) dihedral. It worked amazingly well considering the dihedral that had to be overcome. It needed a lot of rudder. Not because of adverse yaw, but because of dihedral. Your 2 degrees should be no problem.

Roger
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Old Sep 13, 2010, 06:22 PM
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Bohol Philippines
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Quote:
Originally Posted by Freddie B View Post
... I still want 2 degrees of dihedral for some self righting capability ....
I remember reading in RCM, I think it was back in the '80s, that a cabin job like the BB has the equivalent of a couple of degrees of dihedral by being a high wing configuration. I think it may be quite stable with a flat wing.

Steve.

(Mostly Lurking!)
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Old Sep 13, 2010, 07:15 PM
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Quote:
Originally Posted by Cybernaught View Post
I remember reading in RCM, I think it was back in the '80s, that a cabin job kike the BB has the equivalent of a couple of degrees of dihedral by being a high wing configuration. I think it may be quite stable with a flat wing.

Steve.

(Mostly Lurking!)
My old school data, when building RC (back from the old free flight days), top wing cabin model 0-3 degrees dihedral tames the beast. Mid-wing models 3-5 degrees, and low wing 5-7 degrees.

I'll state again I have made many airplanes with no dihedral. Flat plate foamies are classic. Our moderen RC gear can compensate greatly for this, where a full scale plane might not! In designing lot's of planes, there are those times I just think it makes the most sense. But who knows, not I because I'm 'new' to KFm.

So I could go with a flat wing, but 2 things now pull me to keeping the dihedral.

1. Night flying, in a street setting in front of my house, lots of stationary objects to manuever around, drop in steep and pull out to land in minimal space, the dihedral takes some work load off. I know there will be times that you need to 'panic' or land in trees, slice throug light poles, or disapear over roof tops! Daytime, I'm all for it, but this is my preferance for my night flyer.

2. How could I really judge the differance in KFm3 (failure), to KFm2 comparison, unless most things remain fairly equal.

Someone may want to shake their head now, because I will put different wing tips on the KFm2 wing!

Fred
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Old Sep 14, 2010, 12:58 AM
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Back in the air with different wing tips

Friends,

The 'grounding' was only temporary; by late today, my test aircraft was back in service. I decided to add on some new more extensive elliptically up-swept wing tip panels in the process; the photos below show the results.

The outer / upper edges of these up-swept wing tips extend 3-1/4" above the main wing's lower surface- quite possibly more than is needed, but a good test of the affect. The idea was to see just how much 'virtual polyhedral' affect these extended wing tips would have on the wing.... (you never really know until you build it & fly it, after all...)

While the previous wing tips with their much lower profile left a wing that was 'busy' to fly, this wing does handle more as if there was a fair amount of dihedral built into the wing structure... yet the center 48" of this 58" wing is built totally flat with a simple one piece tubular CF spar. The result is a very stable wing that is far less 'busy' to fly in variable & turbulent air. At the same time, it still rolls well and handles inverted flight and outside loops easily.

It was late when I finally had a chance to get out with some light cool winds keeping thermals from forming, so I'll do more test flying of this wing setup before I try to describe more of how it's handling. I'll be back to optimizing the wing / aircraft setup for best glide efficiency.

The last photo below is a view in one direction across my landing area; the sky in all other directions is about equally wide-open and unobstructed. It really is a blessing to have this kind of flying site this close to our home!

VIKING
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Old Sep 14, 2010, 01:46 AM
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Fred,
Your old school data pretty much reflects what I remember reading too.

Bruce,
Earlier I think you mentioned the Philips entry and I believe you said it really helped to reduce drag and gave better glide over a leading edge that's just rounded. Is that right?

Steve.
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Old Sep 14, 2010, 12:21 PM
just Some Useless Geek
Chicagoland
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Bruce, are you saying that the upswept wingtips alone accounted for the vast improvement in stability you experienced on your latest wing test?

By the way, along with all the other flyboys on this board, let me just say that you suck for having such a perfect place to fly. Die! Die! Die! As long as I get your flying space, of course. Is that a public area? Or do I have to marry your widow to have access to it?
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Old Sep 14, 2010, 12:35 PM
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Fairplay, South Park, CO
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Quote:
Originally Posted by Cybernaught View Post
Fred,
Your old school data pretty much reflects what I remember reading too.

Bruce,
Earlier I think you mentioned the Philips entry and I believe you said it really helped to reduce drag and gave better glide over a leading edge that's just rounded. Is that right?

Steve.
Steve,

Quick summary: if the entry point of a more or less flat bottomed wing is very low, the wing will be more prone to getting bounced around in winds and air variations; it will also have a fairly dramatic difference in trim from an ideal low throttle elevator trim, to the wide open throttle elevator trim. And the more 'blunt' the leading edge is, the less wind penetration capability it will have in power-off gliding mode.

So shaping the leading edge's top surface down beyond being merely 'nicely rounded' can produce a wing which allows the air to separate and flow more smoothly over the front section of the wing (=less drag, more potential lift) on a KFm2 as a 'virtual camber line' is created in the airfoil shaping process. And by rounding up the lower surface somewhat at the leading edge, you can end up with a wing which flies better in winds and which goes from low throttle to full throttle with minimal trim change needed.

Below is the rough diagram of the KFm3 modifications to the MH32 airfoil; this is how I built the Komet's wing at the center. I used the secondary step / filler panel only in a modest area, behind the primary step in the inboard ~40% of the wing. My primary step is run from 50% of chord at the center, to 40% of chord at the wing tips, and the thickness and step height taper down to a lower profile towards the wing tips as the tapering chord narrows.

Note that the maximum thickness on this wing is ideally at 30.9% of chord, and the thickness then decreases as you go back to the primary step back at 50% of chord at the center section of the wing. Also note the 'Phillips Entry' shaping of the underside of the leading edge. All of these contour details work together to result in one of the very best wind-penetrating KFm wings which I've built to date. All of the attention to shaping really can pay off... but it does take some extra time & attention to the details.

Hope this info & the diagram & photo help!

VIKING
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Old Sep 14, 2010, 04:06 PM
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Quote:
Originally Posted by A Useless Geek View Post
Bruce, are you saying that the upswept wingtips alone accounted for the vast improvement in stability you experienced on your latest wing test?
Yes, that's exactly what I was trying to get across. This otherwise flat-built aileron wing with the up-swept wing tips coming up to 3-1/4" from the lower wing surface may be rather similar, stability-wise, to a dihedral wing where each wing tip has roughly the same amount of total rise at it's wing tips.

The advantages are that the wing is easy to build flat, and it responds very well to aileron control, and can roll fairly axially. I fly both rudder and ailerons when I'm hunting / chasing thermals, and I often use cross-control input, where the rudder produces yaw in one direction while opposite aileron is used to keep the sailplane in only a very shallow bank while coming around in a circle. This helps hold altitude in light lift.

Quote:
Originally Posted by A Useless Geek View Post
By the way, along with all the other flyboys on this board, let me just say that you suck for having such a perfect place to fly. Die! Die! Die! As long as I get your flying space, of course. Is that a public area? Or do I have to marry your widow to have access to it?
Luckily, no one needs to expire prematurely over this... this particular site happens to be on a section of state land. A rancher has a lease to allow a few head of cattle grazing somewhere out there, which wander over a large area. I've flown there occasionally for the last ~20 years. there's definitely room for more of us out there, and no one minding this use!

VIKING
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Old Sep 14, 2010, 05:07 PM
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Bohol Philippines
Joined Aug 2008
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Bruce,

I hear what you say. Please have a look at the picture below.

To keep it simple...
Generally speaking, if I reshape to where the red lines are I should see some improvement in speed, penetration and glide. Is that correct based on ;your experience? Or would you keep the entry point a bit higher?

Thanks in advance for the input.

Steve.
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Old Sep 14, 2010, 09:50 PM
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Fairplay, South Park, CO
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Steve,

you have the idea- your red lines look like a good place to start. Go for it!

Idea: if your foam is firm enough to forego a lot of the 'beauty work', you can consider doing that initial shaping, test fly it, and then see if further sanding / shaping might improve it's handling a bit more.

VIKING
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Old Sep 14, 2010, 11:32 PM
just Some Useless Geek
Chicagoland
Joined Oct 2008
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Bruce, I'm not sure that Steve can get that fine a granularity in the foam he's using. I kinda like your heat shaping technique with the covering iron, but that really takes a deft hand and quite some bit of experience to get right, doesn't it?

[NOTE: let's not let this get too far off into build-land, else we need to take it to the other thread. Heh. I'm one of the worst offenders, of course.]
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Old Sep 14, 2010, 11:36 PM
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Bohol Philippines
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Quote:
Originally Posted by viking60 View Post
Steve,

you have the idea- your red lines look like a good place to start. Go for it!

Idea: if your foam is firm enough to forego a lot of the 'beauty work', you can consider doing that initial shaping, test fly it, and then see if further sanding / shaping might improve it's handling a bit more.

VIKING
Gotcha! tnx...

Good point Marty, let's put things where they go.

Steve.
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Old Sep 15, 2010, 09:19 AM
gpw
“There’s no place like Foam”
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Get out the hot wire !!!
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