I hate built-up wings!
 

I've been building a CGB superchipmunk for a few weeks now. Fuse is almost done, tail is done, wing is, well, done. Done in a bad way as far as the wing goes. Landing gear blocks have been beefed up, but I screwed up, and a lot of the glass I put in to re-enforce hasn't fully adheared to the wooden structure. The sheeting is crappy, and the servo mounts are wrong (I glued in the ones for the bellcranks, then switched ideas..

I hate built up wings. A lot of work, but fragile, and if you're not a wood craftsman, but you are a perfectionist, VERY aggrivating.

Here's my question. I'm going to have a set of foam cores cut, and I'm going to vac bag them with glass/epoxy. What, as far as a spar, will I need? Also, any articles on mounting retracts (I'm going retracts now) in the foam wing? I'm concerned with damaging the wing on a landing due to bad retract mounting, and considering I've never installed them before, I'm sure I could use the help.

Thanks!!!

I hate built-up wings!
 

Thanks for the help! your criticism wasn't constructive, therefore a waste of your time and mine.

I've built several foam wings for my gliders over the years, I'm sure I can make one for a power plane that doesn't see near the load that a 130" wing does on a full winch launch.

I hate built-up wings!
 

TheoA, I know eactly what you mean. I flew sailplane when I lived in Socal in the same club (SULA) that many of the F3B champs (Joe Wurts, Daryl Perkins) were in. It was amazing to watch them put the hammer down on the winch and stretch the line by flying side to side at the end of the launch before release to zoom up another 200-300 feet. No glow engine plane would have survived 3 seconds into a launch like that. :)

Anyway, to answer your question, no, spars are not always necessary. I'm sure you'll hear differing opnions on this, but typically, if you use full sheeting or full composite coverage on the wing, you can do without spars, or at most use balsa square stock for spars. If you vac bag, you have to use a solid core with no lightening holes anyways, so that'll be stronger still. If you do use fiber glass though, I would suggest running some widths of carbon tape under the FG on the thickest part of the wing to stiffen up the wing and add strength.

Ultimately, whether you should add wood spar or not really depends on the wing design. Good luck.

I hate built-up wings!
 

I'm with Volfy on this. You shouldn't need spars, but I would use a good wing joiner as you would usually use on a foam wing.

just for good measure
 

I'm going to run uni carbon down both sides on the wing as a "spar", and I'm going to slip some pre-cured stuff in as an I beam spar. I've done this on a Discus launch glider, and it works well. Most of the gliders that I've done have had fully finished LE and TE. The foam cores I bought today do not, so I'll need to shape a wood LE before bagging.

I'm going to try to hinge the ailerons/flaps with a rod and some robart hinges, rod glued to TE of wing, and the aileron LE rounded out. Hinges will go through the rod. Never tried that on a power plane, so if you guys have any more suggestions, please lemme hear them!

I hate built-up wings!
 

Theo:
I use the same setup in a Cap 10. I used a piece of 1/4 in. carbon fibre tube which has a 3/16 hole for the Robart to epoxy into. I also glued balsa blocks into the back of the core where the hinges will go to strengthen it up. I also used 1/64 ply set into the top and bottom T.E. to cover the hinge gap.
Hope this helps.

I hate built-up wings!
 

Sounds like your on the right track. I would set some ply plates into the foam for the gear to mount on though. Maybe 1/4 thick by 1/2 wide and put it under the sheeting. When you glue it in, use epoxy with cotton flox to glue it in instead of micro baloons. Either will work, but flox is way stronger. You can get it at aircraft spruce. In building full scale, I was taught never to use micro balloons in epoxy where you need streangth. It is a good filler. You will probably get lots of different opinions on this, but I figure Burt Rutan knows what he is talking about. Anything you use will be stronger than the foam. Try to make the cuts as clean as you can so you don't have to do a lot of fill when you glue them in. I wouldn't use spars in a foam wing either.


Sounds like you were trying to use glass for streangth on the gear on the build up wing? Just for what it is worth, I streangthen gear in a build up wing with triangle stock. I wouldn't use glass there. I know it can be done, but you can get more surface to glue to with triangle stock and stiffen the ribs with 1/8 inch ply. You won't add a lot of wieght and you will get really good gear. Have a blast.

I hate built-up wings!
 

I definitely understand what you are saying! Unfortunately for me it would be the exact opposite way around as I can build a built up wing with no problems but I sure do wish that I could do the composite wing! Just have not gotten the knack of fiberglass down yet.

I hate built-up wings!
 

Check out;

http://rcgroups.com/links/index.php?...at=237&id=4169

or;

http://www.paonline.com/hayman/video.htm

I hate built-up wings!
 

Say TheoA,

Don't give it up. You're doing yourself discredit. Try again. You succeeded elsewhere. Why should the wing be any different?

Its flight should prove intersting if the wing is a different material

I've never worked foam wings as they don't look strong.

Kraus

I hate built-up wings!
 

You won't notice much diff in the flight charecteristics. The foam wing glassed will be stronger than a build up wing. It won't matter much. I have a Dirty Birdy with a build up wing and one with a foam wing. 6 of one, half a dozen of the other.

Re: just for good measure
 

Theo:
Wrong way round.

Make the groove in the TE of the wing, and the LE of the aileron rounded to fit closely into the wing's TE groove.

Then the pivot point of the hinges should be the center of the part circle shape of the aileron's leading edge.

Bill.