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FT Tiny Trainer glider for high start

Martin82

Junior Member
#1
Hi guys,

so I am building my first FT model ever, and it's a TT. I want it as a 2 channel glider, so I extended the polyhedral wing by 20 cm. I will enlargen the vertical stabilizer and the rudder a bit, to still get good rudder authority.
I also want to highstart it, so I reinforced the main spar with a thin carbon fiber rod.

I got the foam boards from a local architecture supply store ("sandwitchplatte"), since I am located in Austria, central Europe. They are certainly heavier than what you guys are working with, but I believe they will also be more durable.

So far I have semi-completed the wing, but now I have to wait for the colored packing tape to arrive, because I want to tape it before I put the polyhedral into it. For the fuselage and the glider nose I will pretape the board.

I will make my own high start from some 20m bungee and about 70m kite line. I have never done this before, so I will probably fail hilariously. I think I've read up about it enough so I can do it safely though.

IF I get it up in the air in one piece AND high enough I hope it sores well enough to hunt for some thermals, despite the heavy weight foam.

Just wanted to share my project, as I am soooo excited about it! Any tips will be helpful and appreciated!

And wish me luck, I am gonna need it! ;)
 

Craftydan

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#2
I've done an up-start with the tiny trainer -- 10m tubing, 30m cord. effectively it's a low-power, lower altitude version of the high start for training and smaller airframes.

Results were . . . interesting. Key-ring near the end, hooked to a peg in the TT's finger-hole, stretch it back 80m or so and let it go. It's about as much stupid-fun you can have without a propeller ;)

That being said, even the up-start is hard on the TT wing. With just the foam spar expect the wing to fold within a few flights. Replacing it with a carbon spar (arrow shafts work great) will dramatically improve the lifespan, but the polyhedral tips will eventually fold. In either case the airframe will probably come down hard. you'll only be out a sheet of foam (cheap here, but in Austria?) but it will likely end the day for that airframe.
 

Martin82

Junior Member
#3
I am perfectly well aware, that the plane probably won't survive it, but I just HAVE to try it! ;)

I am doing it mainly for the fun, and as a learning experience.

One thing though: You can stretch your 10m tube 80m? My bungee line can only be stretched by 110% roughly, witch makes me think the pulling forces will be WAY bigger. But I did not want to invest in a "real" high start tube.
 

Craftydan

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#4
High start line may be a bit more stretchy than your bungee line. It's generally around 6:1. At that, for an 80m pull with a 30m stringer, I'm only stretching the line 50m, so 5:1.

Energy is energy, but the fact your defelction is so much lower you'll be pulling harder over a shorter time and distance. It's going to be much harder to get a good amount of energy into the airplane without ripping the wings off.

If you're willing to spring for it . . .

http://www.hobbyking.com/hobbyking/store/__10329__HobbyKing_174_8482_6mm_Silicon_Rubber_Bungee_Hi_Start_Cord.html

http://www.hobbyking.com/hobbyking/store/__10609__HobbyKing_174_8mm_Silicon_Rubber_Bungee_Hi_Start_Cord.html

Cheap stretchy tube. Not really a "Real" high-start, but not at high-start prices either. Doesn't beat the "free" which you have now, but it's much better suited to your goals. I've used the blue before, on the TT and other projects, but the red may be better suited for the TT.
 
#6
Haha, This is a funny coincided, I just bought the red high-start from HK and High-started the TT. First attempt.....The wings folded. I did learn some thing though, If you add some polyhedral to dihedral The plane flies much better. On the second wing I added a paint stick inside the wing.

P.S. Don't leave the high-start out in the sun unless necessary, It will fade.
 

Craftydan

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#7
um . . . more than fade, it weakens. UV is no good on these.

I'd avoid yanking on faded or cracked tubing. There's a good chance it'll snap back.
 

Martin82

Junior Member
#8
Thnx for the tipps guys, especially Dan! You are such a helpful man!

I've finished the wing now and taped it too. It seems to be very rigid, thnx to the heavy foam and my carbon spar. I am pretty confident it will not fold, even with my bungee.

It came out to be terribly heavy though: 173g (6,1oz). So now I am more worried about it gliding properly.

Well, I guess we'll just see! ;)

P.S.: Pictures later. I go by the rule "anything is pretty that flies"...
 

Heavy313

Senior Member
#9
My TT with Sportwing, AUP was 383g and glided really nice.. I would think at about half the weight you will have some fun with your bungee!
 
#10
Thnx for the encouragement Heavy313, thats great news!

I promised some pics and here they are. They are made with my mobile phone, so they don't really do the "wrinklyness" of the tape justice. I am still kinda proud, its my first build after all!
 

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#13
I cant tell. maybe. it just looks like the fuselage is slanting down on the top at the tail. I could be wrong tho. weird perspective....I think it will fly fine. i mean, i dont really know what it is but, it might just change the incidence, but I don't know how that affects flight characteristics....
 
#16
Yesterday night I installed the servos, and I need your advice pls:

Somehow my control horns were bending badly. I managed to install some foam pieces and now its much better. Still:

How bad is it, that one servo is humming? It has problems recentering completely, I believe its because there is still some stress to it because of the bending.

I know thats bad, but HOW bad is it? Is it worth cutting up the fuselage trying to fix it? The plane is not going to be a precision machine anyway, and the servos are budget, so i figure I finish it, give it a few gentle tosses to see how it handles and decide then what to do.

Any advice is welcome! Thnx a lot in advance!
 

Craftydan

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#17
How much stress is on the servo? Is it straining to hold position or jittering?

Having the control rod's bend press against the servo a little bit is fine, but the linkage should still move smoothly, and when centered the servo shouldn't be pulling/pushing the rod down the guide -- it should be bending-stress only. Straining can wear the servo out early and becomes a weak link waiting to break -- easier to strip an already straining servo in a crash.

So what's Jitter? Jitter is really the horn vibrating back-and-forth around the commanded angle, never quite getting close enough to be happy and stop. These aren't high-end servos -- jitter is common. Give the radio a click or two of trim on the noisy servo and see if it quiets down. If that's the case, you can readjust the linkage stopper to be trimmed neutral to a quiet position (so long as it's close to center) . . . or put up with the noise.
 
#18
Thnx Dan!

Actually I am not completely sure what it is, but you make me confident not to cut the thing up now. I don't think there is terrible stress on the servo, just a tiny bit. I completed the plane today, and will do some test tosses tomorrow.

Unfortunately it came out terribly heavy (about 400g), since I had to add lots of weight in the nose for balance. If its not gliding well at all I might build the power nose, and forget about the highstart thing, since there is no point if its not a glider.
Or I might still do it for the fun and start building a storch... ;)

But maybe it is not so bad, I keep you guys updated once I tested it. Anyhow, here it is:
 

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Craftydan

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#19
Martin,

If you're up for a little easy tweeking, build a second longer nose -- you can take the plans and stretch it just before the curved pieces. Don't forget to add the extra length to the inner spacers and to the center strip at the hatch. Add another 50-75mm and rebalance with the ballast as FAR forward as you can. You could also strip the paper off the tail-boom and re-tape to lower your tail weight.

I think in either case you'll be surprised how much less ballast you'll need.
 
#20
A longer nose is a great alternative to the power nose! Especially since I don't have a place near, where I can fly a powered model. Well, I can, but its not allowed.

So I will try that if the test tomorrow happens to be unsuccessful, as you seem to be expecting.

Getting rid of the paper is something I will probably not do. I'd rather rebuild the fuselage and tail completely, since that gives me the opportunity to solve that servo problem also.

Thnx again for helping out!
Cheers!