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Old May 31, 2011, 09:21 AM
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Jwm
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Oh you will also notice the addition of winglets, and a vertical stab on both. With my original glider it did not show any signs of any yaw instability in flight, however if anything hit the wingtip it would go into a solid flatspin in which im not sure you could get it out of if it was RC. therefore i added a vertical stab as well as winglets. On the Larger version i incorporated a vertical stab in the construction of the fuselage. Winglets i can add later if further assistance is needed, however i don't believe there will be. In all the test throws it is extremely stable.
Do you have a favorite to build? The flat spin is a winner with me. Why not add a large rudder in case you want to try it?

Charles
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Old Jun 01, 2011, 02:12 PM
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Originally Posted by canard addict View Post
Jwm

Do you have a favorite to build? The flat spin is a winner with me. Why not add a large rudder in case you want to try it?

Charles

Even with a large rudder it wouldn't be enough to invoke a cost spin. It is going to be a pushprop, therefore there is no prop wash over the rudder. Plus it has no "tail" so the rudder has very little leverage
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Old Jun 02, 2011, 05:54 AM
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That's a pretty-looking tandem design. I hope to see you evolve the model into using real wing sections instead of the Kline ....thing. If you are seeing 40:1 glide ratio though, that's downright astounding.

Cheers,

Carl
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Old Jun 02, 2011, 03:23 PM
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D
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Originally Posted by Haole View Post
That's a pretty-looking tandem design. I hope to see you evolve the model into using real wing sections instead of the Kline ....thing. If you are seeing 40:1 glide ratio though, that's downright astounding.

Cheers,

Carl
well currently i am sharing a 15x15 dorm room, as USAF doesn't necessarily consider prociding shop space.... but with my 2d mock up it had an amazing glide in the hall way. That's the only testing j have been able to do, I am not expecting the same with the real kodel as it will be much heavier in comparison. Also I decided on the K-foil as i dont have much room or time for a full detailed build while im here. Maybe in the future if this proves to work as good as it seems i will further develope it! thanks!
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Old Jun 02, 2011, 04:14 PM
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Let me state my serious doubts regarding the 40:1 glide ratio.

Expect 8:1 rather, in lucky cases 15:1.

In that small room, you can get any result from 1:1 to 1:-1 if you like.

That being said, your tandem wing glider looks very nice and in your situation I'd not hesitate to build an 60' RC slope glider just for the looks of it.

Sorry for the scepticism, though.
I don't want to spoil it all, just throw some real world experience towards it.

biber
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Old Jun 02, 2011, 05:20 PM
What could possibly go wrong?
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Carl
Quote:
I hope to see you evolve the model into using real wing sections instead of the Kline
I too am a big fan of "proper" balsa airfoils, built up with ribs and spars.

But if you go to this Polaris thread you'll find an awful lot of people who have had a great deal of fun with flat panel depron, reinforced with cf strips. I have built a Polaris kind of a plane using the wing from Charles' Delta Duck, which is a classic ribs and and spars build. It looks good and it's satisfying to see it flying but I can't say honestly that it flies any better than the flat panel wing on the Polaris I built from the kit. I wish I could.

Have a look at some of their flying videos.

Cheers

Nick
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Old Jun 02, 2011, 08:36 PM
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Twin Duck Canard Wing

Here are pictures of the canard wing so far. I am happy with accuracy. I believe that the trick lies in cutting all ribs from one piece of card stock so that the straight line bottom rear of the ribs is common. The ball point ink lines are cut completely away as each rib is cut from sheeting. This gives a very accurate up angle as each rib is glued in.

Charles
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Old Jun 03, 2011, 03:02 AM
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Originally Posted by biber View Post
Let me state my serious doubts regarding the 40:1 glide ratio.

Expect 8:1 rather, in lucky cases 15:1.

In that small room, you can get any result from 1:1 to 1:-1 if you like.

That being said, your tandem wing glider looks very nice and in your situation I'd not hesitate to build an 60' RC slope glider just for the looks of it.

Sorry for the scepticism, though.
I don't want to spoil it all, just throw some real world experience towards it.

biber
No problem, but ypu did read wrong. The test flights are done in a 200ft straight hallway and I am working on permission to try it in our C130 hangar.... my results are in the HALLWAY. The 15x15 dorm is talking about working space and not having the tools nor space available to build a large true aircraft with a proper air foil. Again those results were a simple 2d glider. As stated previously i am not expecting anywhere near the same results for the full size consisting of electronics fuselage, etc. I do believe i had previously stated all this and in no way was trying to mis lead anyone. I was simply stating that if the mock up design flew that well, then I can expect a fairly decent flying scaled up version.

PS. on an unrelated side note, I also came up with a very good single sheet paper airplane that was a great walk along glider! Standing on the horiz stab of the C130 the little glider (when dropped) flew right out the hangar doors! =]
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Old Jun 03, 2011, 09:21 AM
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Jwm, Learning how to deal with the force of gravity is a fascinating challenge. Building with light weight materials and using two wings still has me hooked. It reminds me of the man powered machine that was developed
some years ago. Please continue with your thoughts and share with us.

Charles
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Old Jun 04, 2011, 12:40 PM
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Human Powered Flight

http://www.purpleopurple.com/inventi...-aircraft.html
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Old Jun 04, 2011, 04:30 PM
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I started making what I called "bedroom gliders" (because I flew them in my bedroom) back around 1967-1968. They can be an extremely useful tool for exploring new concepts. The operating Reynolds numbers of some of them were in some cases less than 20. (no, not twenty thousand, just 20.0, the result of less than 1/16" chord at less than 0.5 mph flying speed)

However, you are typically working with much lower Reynolds numbers than the design that they are simulating, so you must take that into account, both in the design and construction of the model (such as using thinner airfoils in the smaller model), and in the interpretation of the results. The smaller models tend to be good at comparing one concept to another, but getting true, valid, QUANTITATIVE measurements of things like L/D is very difficult.

In particular, the possibility of an L/D even remotely close to 40:1 is simply impossible for model that size. In general, due to Reynolds number ("Re") effects, the performance of a smaller model will be substantially less than for it's larger counterpart, especially with regard to L/D. OTOH, getting accurate measurements of L/D can be extremely difficult, with large effects from air currents in the flying area, and in particular the effects of your launching technique. Any excess speed in your initial throw shows up as additional distance, making the L/D look substantially better than it really is.

Also, the K-F airfoil made a big stir when first announced many years ago, but has since been essentially discredited.

Simple profile models from things like sheet foam are also useful, but need to consider some additional factors. In particular, the effects on yaw stability and damping from the profile fuselage tend to be significantly stronger, both pro and con, than for a non-profile fuselage. You need to consider both the portions ahead of the C/G as well as those behind it as addiitional fin area.

Also, unless you have ballasted the extremities, your inertia about the yaw axis in particular tends to be much lower than scale, which makes the model appear to have better yaw damping than scale.

As I said, a useful tool, but make sure you are aware of and adequately consider the things about your little model that are not the same as the bigger one it's supposed to represent.
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Old Jun 04, 2011, 11:25 PM
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Originally Posted by Don Stackhouse View Post
I started making what I called "bedroom gliders" (because I flew them in my bedroom) back around 1967-1968. They can be an extremely useful tool for exploring new concepts. The operating Reynolds numbers of some of them were in some cases less than 20. (no, not twenty thousand, just 20.0, the result of less than 1/16" chord at less than 0.5 mph flying speed)

However, you are typically working with much lower Reynolds numbers than the design that they are simulating, so you must take that into account, both in the design and construction of the model (such as using thinner airfoils in the smaller model), and in the interpretation of the results. The smaller models tend to be good at comparing one concept to another, but getting true, valid, QUANTITATIVE measurements of things like L/D is very difficult.

In particular, the possibility of an L/D even remotely close to 40:1 is simply impossible for model that size. In general, due to Reynolds number ("Re") effects, the performance of a smaller model will be substantially less than for it's larger counterpart, especially with regard to L/D. OTOH, getting accurate measurements of L/D can be extremely difficult, with large effects from air currents in the flying area, and in particular the effects of your launching technique. Any excess speed in your initial throw shows up as additional distance, making the L/D look substantially better than it really is.

Also, the K-F airfoil made a big stir when first announced many years ago, but has since been essentially discredited.

Simple profile models from things like sheet foam are also useful, but need to consider some additional factors. In particular, the effects on yaw stability and damping from the profile fuselage tend to be significantly stronger, both pro and con, than for a non-profile fuselage. You need to consider both the portions ahead of the C/G as well as those behind it as addiitional fin area.

Also, unless you have ballasted the extremities, your inertia about the yaw axis in particular tends to be much lower than scale, which makes the model appear to have better yaw damping than scale.

As I said, a useful tool, but make sure you are aware of and adequately consider the things about your little model that are not the same as the bigger one it's supposed to represent.

well, as stated previously, I in no way shape or form expect the same results out of the larger model. I also stated that from a normal "paper airplane" type throw. You are taking it as if I ACTUALLY did an analysis in a control, which is only possible in a wind tunnel. I simply did a "toss test" and got extremely pleasing results. As far as the K-foil, it may or may not drastically improve anything, however causing some sort of lower pressure zone over the top of the wing could be better than none. I DO believe results are not ACCURATE as I have yet to get permission to do a "drop" test in our C130hangar, which would be the only area available to me to ACTUALLY test glide ratio.

Again nothing was Accurate, however a 20ft glide to 6 inches of drop in a straight hallway is not bad in my experience, and that is ALL I was saying.

Before ripping someone apart please read exactly what they posted....
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Old Jun 05, 2011, 12:00 AM
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No ripping intended, just a reality check. Just passing on a few things I've learned, often the hard way.

If you've done your test right, the performance of your larger model (due to Re effects) should be significantly better than the small one.

And, it is very possible to study all sorts of issues with these small models, without having to resort to a wind tunnel, as long as you understand what is really going on. Don't sell them short, just make sure you understand what you are seeing. Small models can be used very effectively for things like verfying C/G calculations, studying tradeoffs between fin area and moment vs. wing dihedral, new control concepts, etc..

They can also give valid comparative performance measurements of different concepts that are both modeled and tested at the same size. The actual performance will not translate reliably to that of the larger model, but the relative performance of the two concepts compared to each other in most cases will.

Yes, 20 feet using 6 inches of altitude is indeed 40:1, but I guarantee that about 2/3 to 3/4 of that distance came from either air currents in the hallway, or (more likely) excess energy in the throw. However, practicing your launch technique so the model leaves your hand in a steady-state condition at its natural airspeed and glide angle will improve your results. Start with too little airspeed so that the model drops initially after leaving your hand, then gradually increase the launch speed until it maintains a constant glide angle for the entire flight path. With really good launch technique, you CAN get accurate L/D measurements in a small area, but it takes a lot of practice.

Flying in a much larger area such as your C130 hangar should give you much better results, since the "experimental error" introduced by things like launch will be far less significant.

Go for it!
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Old Jun 05, 2011, 12:19 AM
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the profile mock up model was just to test idea. because of the full fuse i added the vertical stab. If it needs more, i will do winglets on the main wing. the profile glider was mainly to tell how it would fly, and where CG would be. I am not expecting any of the same flying characteristics with the RC, scaled up version due to the many changes taking place. Such as, the addition of a motor, full fuse, and weight of the reciever, bettery, and servos. This additional weight will also cut down on glide rate.
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Old Jun 05, 2011, 12:28 AM
who has rabbit ears down
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This is a great topic! kinda like when i handlaunched the hopeful;" Sarah" to find it's true nature as 'contraption' !
Johnny
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