Ok, so I am scratch building a gremlin and have glued the wings halves together and it seems that there is a considerable amount of flex in the wing. Now I have made a few mods to try and stiffen it up a bit. For one I have glued 1/8" fiberglass rods down the top and bottom of the wing close to the high parts of the chord. Two, I replaced the 1/8" ply would main spar with a 1/4" piece of lexon plexi glass. The top fiberglass spars are glued to the top of the plexi and the bottom spar runs full lenth of the wing. Now that it is dry if I put one wingtip on the ground and hold the other and try to flex it, I get a considerable bend and it seems to be bending only in the center of the wing where the cut out for the fuse is . It flexes both directions. Now I do not have a standard stock wing to check it with but can anyone tell me if this is common with the stock ones. I have not put the strapping tape on yet but with the fiberglass rods it should be about the same or better. I also do not think the the fiberglass tape will solve the problem if the center of the wing is flexing.

I know that in the air the upward forces on the wing will not be at the wing tips but rather spread along the whole wing, more in the center and tappering out towards the ends so maybe this may not be a problem. I am just conserned about a high G loop or the wings fluttering in a high speed dive. I have not done many foam wings in the past but my wiffle ball bat combat with a 6 foot wing does not seem to have as much flex as this 4 foot wing and it has the same fiberglass spars top and bottom but without the cutout in the middle.

Any suggestions or comments welcome.
Thanks.
John

John,

I typically build my 60-64" combat wings from "blue" foam and also run 1/8" FG spars along the length at the high points glued in with PU glue ( Gorilla ). I have found it is not until you apply the Bi-Di FG tape that they really become stiff. The spars by themselves ads some rigidity, but it is the tape that really binds it all together. I also use 3M Super 77 spray glue to lay down my tape with and set it with a low temp covering iron. The resulting wings have always been extremely strong and rigid. Hope that helps.

BNC

I have sheeted my wings with 3/32 balsa on the bottom and 1/16 balsa on top. I have also used fiber glass cloth on top and bottom. Sheeting makes the best flying gremlin, however its too much work for a gremlin. The Bi-Di tape method is the best. I lost 5 gremlins in mid airs last year. The sheeted one's make the loudest bangs!!

thanks for the replies. I just got some tape tonight, Man that bi di tape is expensive. Does anyone have a good inexpensive source for the stuff. It is too bad that it is not reusable.

Alex has the wide rolls of bi-di for faster covering.

[link]http://www.treneffrc.com/[/link]

I run a couple of full length strips of bi-di then cover the rest of the wing with colored packing tape to hold down the tape cost.

You didn't say what you're going to power this with, so I'm assuming a stock 25 size motor with nothing special for speed.

I think you'll find you get diminishing returns when you try to "beef up" a Gremlin. If your goal is to simply have a nice sport flyer, then by all means go to town and experiment. The gremlin is a great starting place for that.

However, the original design was meant to be a "disposeable" entry level low investiment way to get guys into combat. If built stock, it does that very well and you don't have to worry about it coming apart unless you overpower it.

If you keep adding stuff to fix perceived flaws, you end up with a plane that doesn't turn very well, and if you're into combat against other planes, the name of the game is turning quick and weight is your worst enemy.

My original plan is just for a sports plane (wing). I have a royal .28 BB to put on it. There is nobody in my current club who flys combat now but this plane was going to be a way that I could introduce a few from the club an affordable way to get into combat. I was hoping for something like "what does this guy have, that will not handle well at all, ........rrrrrrrrRRRRRRRRR...... wow, that thing really goes, and look at how smooth it is and how fast it can turn,, How much did you say you had into that again, It only took you 6 hours to build,,,,wow."

Well maybe I am hoping for too much but if it doesn't turn out this way then I want to scale up to a 46 size for a good handling fun to fly plane.

Then you're missing the SPAD combat planes for affordable flying and good flying combat planes. The only thing they lack is third generation durability of the new, modern, top of the line combat ships that really are more surf boards then light flimsy things like the Gremlin. They assemble faster, bounce better and have an overall lower investment cost then the Gremlin.

For under 30 size, build a HOR or Sickle or one of the other Open B designs. I love the Gremlin, but I got tired of watching them disappear in a snow shower.

Clean, I have looked at the spads and was just about to dive into them at one time. I went around town and picked up all the election signs the day after election one year. I never did get one built though. At that time I think they were still a bit heavier than a foam wing could be built. Now with the 2mm stuff, spads can be really light and I may still give them a try, but right now I am sitting on 20 sheets of 2' x 2'x 8' foam in the garage I got for a dollar a sheet and have a foam cutter already made. The templates only take me about 15 minutes to make ( I only make the airfoil template and turn the foam core over to cut the other side), and I am still working on other things besides pvc for the fuse. I am thinking of making the next one on rails like some of the spads and the battle axe.

Well, you could always cut a bunch of floats....

But seeings how you're already invested, might as well make gremys.

Well I flew it today and needed no trim adjustment after takeoff. It weighed in at 3.4 lbs dry. I was flying with a royal 28 engine with can muffler. I used a 9x4 prop because I had one and I thought it may have a little more takeoff power because I was launching it alone. It did quite well although not quite as fast as I was thinking it was going to be. With a 9x6 it will probably really come to life in the air. With the speeds it was traveling today, I don't think I will have to worry about the wing flex I have. I did full outside loops and inside loops at full speed and comming out of a dive and all seemed well.

Now on to the next project since this one flew so well. A slightly upscaled version with my .46 engine.

I fly a Gremlin with a Webra Speed 40 on a tuned pipe. I didn't scale it up at all and it goes great. I did however build it too heavy.
I really like [link=http://www.snhflyingeagles.org/pdf_files/GremlinConstructionPhotos.pdf]these (click here)[/link] alternative construction instructions and on page 7 it shows how to taper the end of the ailerons to avoid high speed flutter with the bigger engine. On mine to further avoid flutter, I also did not taper the aileron towards its trailing edge (used flat balsa sheet), I added many more hinges than stock and I pinned all of the hinges. With these mods, I get no flutter at any speed including wide open straight down. My mistake was to use bidirectional strapping tape over the entire wing. That stuff is heavy. I think if I was to do it again I'd use the standard construction methods (plus the anti-flutter mod's) but maybe just push the glassfiber bandage center out an extra inch or two.

All the best

Barry

Add vertical shear webs between the spars out at the wing tip. 3" long webs of soft 1/8" balsa epoxied and wrapped together with carpet thread or glass cloth will solve your flexing problems. Foam offers very little shear resistance when the wing is loaded.