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Re: Repairs

Posted: April 16th, 2010, 5:44 am
by Amatuer
I don't know if this quite belongs here, but I didn't really know where else to put it. Our plane weighs roughly 8-9 grams and I wanted to lighten the weight a little bit. Do you guys know anywhere that would be safe to sand and not endanger the plane breaking? I didn't want to shave off the motor stick too much, but it is slightly front heavy at the moment. Any ideas?

Re: Repairs

Posted: April 16th, 2010, 11:45 am
by blue cobra
It seems it has been kicked to the second page, which is likely why you didn't see it, but there is a thread for exactly that. It can be found here.

However there isn't much in that thread, but you should read what is there. More details about your plane are needed. If you used wood far too large or far too dense (most likely large; I can build to <7g without measuring density, although you should) it will be very difficult. One thing you may be able to do is taper or shorten your tail boom- but you don't want it too short. That may not be enough though. Again, more details are required.

Re: Repairs

Posted: April 16th, 2010, 12:10 pm
by leetx
It's not easy to remove weight. For me, I would do some sanding of the motor stick. But only if you can do so without increasing motor stick twist nor bow at launch. Otherwise, you will have to spend more time dealing with changes in flight behavior. That said, the way that motorstick is typically trimmed is that the thickest and tallest point is in the middle of the motor stick, and the shorter, thinner at the ends of the motorstick. So basically, a taper in both width and height, from the middle to the ends.

With the tailboom, you can taper from the start of the boom to the end of the boom, in both width and height. Again, you must take care to not cause excessive flex. HOWEVER, do not shorten the tailboom to save weight. Shortening the tailboom has two very negative effects -- first, it reduces the distances between the two lift surfaces, which is not good aerodynamically. Second, shortening the tailboom shortens the distance between the stab and the CG and reduces stability margin. The only reason I would shorten a tailboom is to stiffen it -- never to save weight.

On one of our freedom flight planes I shortened the tailboom by 1-2 inches. It flies faster and sinks faster than our other freedom flight planes. It is also harder to trim. And it flies significantly shorter duration than our other planes. I didn't know all this when I shortened it, and I won't do it again!!

Re: Repairs

Posted: April 19th, 2010, 8:34 pm
by jgan96
Anybody have ideas for a emergency repair kit? So far, we have:
*Mylar
*Mylar cutter and glue (jander14indoor)
*Wood
*Knife
*Hobby Glue (Ambroid)
*CA [and accelerator (jander14indoor )]
*Acetone
*Scissors
*Tape
*Ruler (jander14indoor)
*More?


Also, we have just managed to build a plane in 2 weeks :D. However, during our test flights and building, we will have trouble with the fragile, thin stab ribs getting hit and smashing. How do we fix this (on the go) and preserve their bend?

Re: Repairs

Posted: April 20th, 2010, 3:39 am
by jander14indoor
Hm, never needed Acetone myself for emergency repairs, not saying it can't happen, but haven't needed it.
I don't use tape for repairs, some do. Too heavy.
Need an appropriate glue for the mylar patch, thinned spray glue in a bottle works. A small brush to apply. In a pinch saliva works, brush is still handy.
Insta-set is real handy to set the CA NOW during a contest. Speeds the repair.
Micro-precision superglue applicator so you can use SMALL amounts of CA for the repair. Two reasons, keep the weight down (ALWAYS important) and keep the mess down. A full drop of CA can run everywhere gluing the plane to everything, including you.
Ruler to check measurements.

Jeff Anderson
Livonia MI

Re: Repairs

Posted: April 20th, 2010, 4:53 am
by jgan96
jander14indoor wrote:Hm, never needed Acetone myself for emergency repairs, not saying it can't happen, but haven't needed it.
I don't use tape for repairs, some do. Too heavy.
Need an appropriate glue for the mylar patch, thinned spray glue in a bottle works. A small brush to apply. In a pinch saliva works, brush is still handy.
Insta-set is real handy to set the CA NOW during a contest. Speeds the repair.
Micro-precision superglue applicator so you can use SMALL amounts of CA for the repair. Two reasons, keep the weight down (ALWAYS important) and keep the mess down. A full drop of CA can run everywhere gluing the plane to everything, including you.
Ruler to check measurements.

Jeff Anderson
Livonia MI
Yes, I forgot a ruler!

I find acetone necessary because I have experienced problems with CA where it won't glue. Apparently, CA won't glue on top of other hardened CA, but if you remove/weaken it with acetone, it will work almost instantly.

Thanks,
Jason

Re: Repairs

Posted: April 20th, 2010, 10:48 am
by beaker
I find that you dont actually have to repair minor repairs in the mylar. Sometimes in trying to repair the plane you make it worse. We flew a plane with a broken wing and still had +1min flight.Also if the Ca is not drying they sell an accelerant that instantly cures it on contact, but use very very liitle and DO NOT get it on the mylar.

Re: Repairs

Posted: April 26th, 2010, 5:57 pm
by blue cobra
I just measured my wing, and it looks like it might be, like, half a millimeter out of specs (these things are so hard to measure). But I'm really positive I built to specs- building is certainly my strong point. But regardless now I'm out, this is my only plane, and States is this Saturday. What can I do?

Re: Repairs

Posted: April 26th, 2010, 6:27 pm
by andrewwski
That's tough. You certainly have enough time to modify/rebuild a wing, but doing sufficient testing might be difficult.

You could also try carefully sanding, but that might increase the chances of breaking your spars. Would also affect your flight but probably somewhat moderately depending on the mass lost.

Either way, better to get into tier 1.

Re: Repairs

Posted: April 26th, 2010, 6:48 pm
by jcollier
blue cobra wrote:I just measured my wing, and it looks like it might be, like, half a millimeter out of specs (these things are so hard to measure). But I'm really positive I built to specs- building is certainly my strong point. But regardless now I'm out, this is my only plane, and States is this Saturday. What can I do?
So, your wing is too wide, huh? This was discussed before on one of the topics, not sure it was repairs. My son had the same problem, just a hair too wide. If you have an extra rib, you can glue it inside the end rib, preferably on the right side of the wing. Also you'd want to put a little glue stick on the top of the rib to get the mylar to stick to it. Carefully cut the original rib off once the new one sets up fully. If you have end plates, you will have to cut the original outside rib off the end plate, then glue the end plate to the new end rib. It seems to fly as well or better than ever. Maybe just circles a bit tighter, but not much. A little more involved than sanding, but less risky. Good luck