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Old Mar 23, 2015, 06:41 PM
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F-15 Thunderwing Mk. II RC Rocket Glider

This is the F-15 Thunderwing Mk. II radio controlled rocket glider!

Well I'm taking some advice from someone at the rocket club and "winging it", pun intended. It is based on Wernher Von Braun's space plane as it was featured in Disney's 1955 "Man in Space" program.

It has a span of 62 inches and will be launched on a G sized rocket motor to a couple hundred feet and glide back down. It will also sport an 18mm C sized motor that can be triggered in flight to give it a small boost and prolong the flight.

The wings are made of foam-core board and the body is from a damaged Estes Leviathan. It will have a T-tail and fixed landing gear.

Still open to suggestions.
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Old Mar 23, 2015, 08:31 PM
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What motor are you planning, what is your auw and cg shift?
I think based on size the 18mm will be sort of worthless, and just add complexity/weight, but what the heck.

you want to watch the wing stiffness, the span looks pretty long.

the 29mm g25 is good if you can stay around 40 ounces..

heavier you start getting into higher thrust short burn motors that make boost more challenging.
frank
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Old Mar 23, 2015, 09:28 PM
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I'm planning on a G40, I found with the F-13 Thunderwing Mk.I that the lower thrust and longer burn motor would dramaticaly improve performance. The only problem being the low speed off launch.

This aircraft wound up being much larger and heavier than the Mk. I so I am planning to make a better launch easel for it. I discovered with the Mk.I that an angle of 45 degrees or less made it easier to control and allowed it to gain altitude through lift instead of burning up all of the fuel. This also means that the motor is not dead lifting all of the weight vertical so I can go over the limit just a bit. I'm also going to make the new easel with ground steaks and extensions to keep the craft stable longer as it launches. Perhaps some wheels to reduce friction.

There are also 2 carbon wing spars and one wood one so I should be able to pull a loop in this thing without worrying about damage, though I doubt it would be able to perform such a maneuver anyway.
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Old Mar 23, 2015, 09:38 PM
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Ok, you will get a 2 second burn with the g40, well see how it works out for you, looking forward to it.

frank
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Old Mar 23, 2015, 10:41 PM
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Me too, won't be ready for the SOAR launch this weekend though, I want ti get it up to snuff first.

The Mk.I did alright on an E9, (several videos on my youtube) but it always pitched up real bad after coming off of the easel due to the low speed and then rocket upward. Thats why I want a better easel with a much longer track. The power to weight ratio is so good on these motors if I can just give it 2 -3 more feet of easel it should work like a dream. A better easel will also let me get lower angles like 30 degrees, it is rather large after all.
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Old Mar 25, 2015, 10:33 AM
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Quote:
Originally Posted by evildave42 View Post
Me too, won't be ready for the SOAR launch this weekend though, I want ti get it up to snuff first.

The Mk.I did alright on an E9, (several videos on my youtube) but it always pitched up real bad after coming off of the easel due to the low speed and then rocket upward. Thats why I want a better easel with a much longer track. The power to weight ratio is so good on these motors if I can just give it 2 -3 more feet of easel it should work like a dream. A better easel will also let me get lower angles like 30 degrees, it is rather large after all.
The Mk1 looks like an Edmonds canard glider, I forget the name but it used a free floating canard during boost which locked at a appropriate angle for the glide at burnout. If the Mk1 didn't do that it would explain the pitch up.

Very interested in how this works out and how the folded depron wing stands up to a G-40.


Richard
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Old Mar 25, 2015, 11:14 AM
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No the Mk1 was very simple, just some elevons. In hind-sight even some regular elevators on the canards would have made it easier to control.

It's shape was actually inspired by Wernher Von Braun's very first version of the space plane from the late 40's.

The folded depron wing was suggested by a guy at my local RC club who does a lot of scratch builds. It is actually foam-core board (that foam that has the paper laminated to both sides) it should be plenty strong enough. I was a bit worried about how well the wing-spars were mounted though so I pored some of that expanding foam into a few sections on top of them.
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Old Mar 26, 2015, 10:16 AM
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I did not realize the paper was still on as I've always removed it. With the foam inside, it should be strong!

I know the space plane you refer to and had at one time planned to make a Bonstel [sp] variation. Got the wing done anyway. Now that you've got me thinking about it I'll have to go and dig it out.


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Old Mar 26, 2015, 01:59 PM
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Yeah, the paper makes it real strong, hence why I'm concentrating on the wing spars. In the future I think I'll stick with wood ones for this as they tend to glue better.

Making the wings is actually kind of interesting. I followd instructions from a friend at the RC club, each side is only one piece. A "V" grove is scored where the leading edge should be, then the paper on the INSIDE of the top part is removed. You curl it a bit by rolling it over something, add a foam spar (not load bearing) inside that goes out to the tip and supports the highest part of the wing and glue it all together. Makes for a surprisingly strong wing for a medium or large aircraft. I wouldn't recommend this technique for anything very small tho, too heavy.
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Old Mar 26, 2015, 03:52 PM
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You want to avoid full span elevons and watch flutter especially on the higher thrust motors, I know from experience.

Frank
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Old Mar 26, 2015, 04:17 PM
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Originally Posted by burkefj View Post
You want to avoid full span elevons and watch flutter especially on the higher thrust motors, I know from experience.

Frank
"full span elevons"? so you think I should just put them at the tips? I was planning to go full span like the 50's design. Incidentally not having them full span would make it easier to fit on the launch easel without damaging them. Also I'm not planning for elevons as it will have a T-tail, so classic ailerons and elevators, probably a rudder too.

Also, after a few successful flights I'm thinking about testing a gyro with presets for accent stability assist and glide-slope, the idea being that a future Mk.III could use a very powerful motor to take it up higher than normally possible without losing control by misjudgement when it is too high to see clearly. Or (more likely) test to stabilize a future Mk.III for launch from an RC mother-ship (a la X-15).

BTW, for anyone out there with experience with T-tails, should I have it at the same angel of attack as the main wing when mounting or tilted at all? I've seen some models were they were not exactly parallel.
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Old Mar 26, 2015, 04:31 PM
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Yes, I was thinking outboard ailerons, not necessarily to the wing tip. Full span controls can make flutter more likely. If I was doing a T tail I would not have any angle offset compared to the wing till I had flown it to understand any pitch/trim needed.

Here's a good video showing what can happen with some wing flex(not span flex but twisting), full span elevons. and high speed. Interestingly on a G-40 as well, auw for this model was around 45 ounces.
In this model the T tail was fixed and I just used elevons.

Wing flutter failure (0 min 42 sec)
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Old Mar 26, 2015, 05:48 PM
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Yeah, I meant outboard as well.

I see what you mean by flutter, was that unlaminated depron? I think these wings will be much more stiff, still it would make for a bad maiden flight. I'll have to see how much it weighs when complete to see if I can get away with an F for the maiden flight. Though the design philosophy I'm using is make a strong RC plane first that just happens to be powered by a rocket instead.

The biggest differences I have encountered so far is the G-force on launch. Can't use a normal firewall and have to make the fuse strong enough to keep the wings and everything else in place for that short acceleration and survive a few seconds at potentially very high speed. The Mk. I did this poorly but was saved by the underpowered motor, this one might not have that issue. Though I will probably be pushing close to 16 ounces when loaded, hard to tell at this point.

I see from your Youtube you have RC experience too, and that you launch most of your gliders vertical. The easel launch was suggested at the SOAR club for my Mk.I, it was so under powered that it made a big difference. I've been balancing mine like an airplane (not the best for a rocket tho) is that how you do yours?

Since starting all of this I've been thinking that maybe I should go a different route for the Mk.III and make a much smaller and lighter one for vertical launch on a dual cluster of C's (I have the parts laying around).

PS: love your X-15
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Old Mar 26, 2015, 06:02 PM
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The wing was double ply laminated 6mm depron with a 1/4" spar, but the span was long and the TE surfaces were balsa with a 1/16" laminate, so they had mass and the wing was able to twist.

I like to launch vertically with neutral surfaces, the advantage of no airfoil to cause pitch moments on boost, just makes things easy.

I launch mine slightly tail heavy and then trim glide for nose heavy. My cg shift in a 40" model is about 1 to 1.25", I start about 1/4" behind the nominal flight CG, and wind up about 1" nose heavy or so. With the profiles the cg range is pretty broad and I can get away with it. Wings can be a bit pitch sensitive on boost when you are tail heavy, then run out of pitch when nose heavy, ala a ME-163 komet.

Problem with clusters are they are heavy, you have two motors with cardboard casings, as opposed to a single D, if you can keep to around 9 ounces or so, the quest D-5 might be the ticket...4 second burn, reasonable price...

The large X-15 really boosts hands off on the G-40's and G-25's it's a very nice flying model.


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Yeah, I meant outboard as well.

I see what you mean by flutter, was that unlaminated depron? I think these wings will be much more stiff, still it would make for a bad maiden flight. I'll have to see how much it weighs when complete to see if I can get away with an F for the maiden flight. Though the design philosophy I'm using is make a strong RC plane first that just happens to be powered by a rocket instead.

The biggest differences I have encountered so far is the G-force on launch. Can't use a normal firewall and have to make the fuse strong enough to keep the wings and everything else in place for that short acceleration and survive a few seconds at potentially very high speed. The Mk. I did this poorly but was saved by the underpowered motor, this one might not have that issue. Though I will probably be pushing close to 16 ounces when loaded, hard to tell at this point.

I see from your Youtube you have RC experience too, and that you launch most of your gliders vertical. The easel launch was suggested at the SOAR club for my Mk.I, it was so under powered that it made a big difference. I've been balancing mine like an airplane (not the best for a rocket tho) is that how you do yours?

Since starting all of this I've been thinking that maybe I should go a different route for the Mk.III and make a much smaller and lighter one for vertical launch on a dual cluster of C's (I have the parts laying around).

PS: love your X-15
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Old Mar 26, 2015, 06:23 PM
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I see, my Mk.I has the wings in back close to the motor so the CG shift from an E9 wasn't even noticeable, this Mk.II may be different but then again it is still a large plane on a comparatively small motor. If I do go small on the Mk.III I think it will be a much bigger issue. My original Mk.I design had an electable nose weight so it would be balanced as a rocket until the parachute would normally come out. You think it might be worthwhile to revive the idea for a smaller glider?

I'll have to build it for higher speeds, maybe something long with a delta like a space shuttle or an X-15-3 or maybe just wing it.
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