soarrich

My Feedback: (98)

I cut two sets of cores today for a 36" flying wing. The wing is constant chord with a 15* sweep, and uses a Bw050209 airfoil. One of the wings will be Norvel .61 powered the othe will be electric. I plane on putting a fuse under the wing, and fins at the tips. I thought about making one with the wing sweeping forward, but I don't know if I should.

Some pictures of my cutting the wings. I just used some 15# foam I had laying around. I use one templet for the bottom cut, the another templet for the top cut. I cut the bottom first, that way I don't have to figure in the kerf, the to part just falls down onto the bed making in effect a ) thickness cut, the top cut the wire is out side the core so I don't have to worry about the kerf there either. I don't cut with radiant heat, my wire actually touches the foam as I drag it through the foam.

combatpigg

My Feedback: (3)

Nice project Rich. I'm curious about radiant heat cutting......never heard of it.
I found a nice source of solid stainless wire at the tackle shop...it was priced so cheap I didn't want to celebrate right there in front of the store owner or he might charge double next time........

soarrich

My Feedback: (98)

They use it when the wire is CNC driven. I spoke to a guy in PA. that said he spent $1500 on the temperature control of his foam cutter, he guaranteed his wing cores to me within .002". The thing with radian cutting is the wire and foam never touch, the foam melts away before the wire touches it so there is no drag on the wire. I could turn my $35 variac up higher and cut the foam that way, but the core would be junk, you have to have very precise speed control, and if you're cutting tapers you have to figure a larger kerf on the slow end. I get by with my hand held bow by keeping the cores short and I've ruined a lot of foam getting to be good at cutting. You can get away with a lot if you're sheeting the wing with wood. I was at my friends house, he's a famous designer and builder, and I would have thrown away the foam cores he was using for his latest plane, which when he was done was his usual beautiful masterpiece.

I try to make the cores good enough that the could be glassed and bagged without wood, but right now I'm in the mood for working with wood, not a wet sandwich of epoxy, glass, an mylar, it makes great wings, but there's no fun in it for me.

combatpigg

My Feedback: (3)

I see now, thanks for explaining. I'm happy with the low temp method, then.

Is the guy in PA Phil Cartier at The Core House?

soarrich

My Feedback: (98)

No, I forget his name now, he's a old German with a real thick accent. I think he was making cores for sailplanes mainly, I know he said he did cores for Mark Drela's DLG.

Jaspur_x

My Feedback: (1)

ok guys , I have never tried cutting foam wings/cores or any of the like. I`m a really poor model builder , I stick to the simplest methods of building due to this. I`m dis-satisfied with my work after building from a jit for crying out loud.
Here is my question: why can`t you just use the fiberglass resin to coat the wing without the glass? it would still be strong enough until you get to the more extreme maneuvers wouldn`t it if you use a balsa trailing and leading edge?

soarrich

My Feedback: (98)

First:
Epoxy just holds the glass, Kevlar, or carbon, those have the strength.

Yes you can just use the foam on a wing this small, it would be strong enough for most flying. Foam is very strong in compression, but not very strong in tension. You could easily fly this wing through any maneuver if you covered it with packing tape. You don't need balsa anywhere on this wing the foam would be fine. With that said, I'm not building this because I need another plane, I have way too many already, I just like to build, so I'm in no hurry, and I don't care that I can get a comparable ARF for much less than it will cost to build.

Jaspur_x

My Feedback: (1)

I see , I`m trying to understand some of the building concepts that I have never used , this is one of those techniques , like I said , I`m not very skilled at building.
I have been trying to pick up info. anywhere I can. I have been asking some really dumb questions here and there trying to learn the pros and cons of the varried wing designs as well.

"The dumbest question you have ever had is the one you never ask" as pappy used to say.

BMatthews

Guys, if you're interested in trying something new what about newsprint applied with WBPU? I did a couple of .15 CL combat models with it many years ago and they held up great other than to the bellcranking prowess of my opponent.

To get it to have some decent strength it takes about 5 to 6 layers around the motor mount and some long tapered "diamond" shaped spars that you lay on before the last layer that covers the whole wing. Any other stress points, such as the tail boom exit point, also receive multiple layers.

And if you use the funnies and colorful advertising pages you even end up with a topical decoration scheme.... Or you can just be boring and get blank newsprint from an arts and crafts store.

The last one I had that I couldn't use anymore because Mel (CP, yep OUR Mel) moved us over to nostalgia diesel combat and foam was out. I finally get my hot setup going with a construction method that builds uber fast and I get obsoleted by the darn rules. Anyhow I took the last airframe and started hammering the floor with the engine mounts to see just what it would take to get it loose from the foam. I finally had to resort to a full on over head all effort swing to bust it loose. Up to then it was solid as a rock. I was frankly quite amazed. Paper mache is strong stuff when used correctly.

soarrich

My Feedback: (98)

No such thing as a dumb question, only dumb answers.[X(]

soarrich

My Feedback: (98)

I made a nose of an Bobcat with it, I think of it as poor man's fiber-glassing. It was used a lot in the English magazines in the 80's, they where big on tearing brown bags into 2" squares. You want to tear the pieces rather than cutting them to feather the edges.

icerinkdad

Cutting foam wings is really pretty simple and inexpensive if you are hand cutting. Google "foam wing cutting" and take a look at the 8 minute video my son sells on the subject. The toughest part is accurate templates beyond that it is mostly practice.
On covering with paper... I quit using newsprint as it soaks up too much glue. Instead I buy "banner paper" from the office supply store that is about the weight of typing paper and many times stronger along the grain than newsprint. That only takes one layer with a diamond at the center of the wing to absorb the loads at that point. I use white glue thinned with water to the point where it can be brushed on to adhere the paper. This is on Fox 36 powered combat wings used in 75mph combat.
Bob

MJD

My Feedback: (1)

Hi Jaspur - ask away. If someone thinks a lot of typing can be saved by directing you to a handy "how-to" versus a direct answer, that still helps you out anyway.

Resin itself doesn't do much for the structure - it has no structural additives and is somewhat brittle. The resin is designed to bond the glass fibres to the structure and to each other to form a composite matrix. Fibreglass itself is what adds the strength, the resin only has the word "fibreglass" in it because you use it with fibreglass or other reinforcing materials. The best composite structures minimize the resin:fibre ratio, or maximize the amount of glassfibre relative to the resin. A decent layup might be in the ballpark of 50:50 by weight, round number.

"Strong enough" is entirely relative. You can build a glider or gentle power model with unreinforced foam wings , or you can tear a well built glassed foam wing apart in a high-G turn on a different model.

Also, since you are early in the fibreglassing game - don't ever make the mistake of thinking that automotive or marine "fibreglass resin" you find at retail is of any use around foam, or of any use in model airplane building whatsoever with minor exceptions. Those are polyester resin systems, which are full of styrene monomer (versus polystyrene) which is a wonderful solvent for foam. Poof, gone.. nada, zip, where did my foam core go..?

In general there are three common (generally common, not model airplane common) resin systems used:

- polyester [cheap, stinky, brittle, cataliytic cure using MEKP "hardener", poorest mechanical properties of the three]
- vinylester [costlier than polyester, and generally supoerior structurally and in other ways. Catalytic cure, makes excellent structural layups, commonly used on boat hulls if polyester isn't used. Also has excellent chemical resistance and is often the resin of choice for compostite fuel tanks.]
- epoxy [doesn't stink, toughest system of the three, addition reaction cure i.e. part A and part B in a specific ratio, used as structural adhesive as well as a composite resin system]

Polyester or vinyl ester can be used to make decent fuselages and other structural parts, but that is a decision I would suggest making after gaining some experience with the stuff. In the model av world vinylester generally only appears at the mfg level to make such parts. Modellers have easier access to polyester and epoxy which are common at retail level.

MJD

soarrich

My Feedback: (98)

I imbedded a HS-125MG servo in each wing, then sheeted the wings.

Andrew

Rich -

What are you using to stick your sheeting down?

andrew

soarrich

My Feedback: (98)

3M 77 spray contact adhesive. It works well. is fast, and easy to get at HD.

soarrich

My Feedback: (98)

I didn't like the way the leading edges came out so I planed them off and put on 1/4" squares, then sanded them to shape.

I glassed the center with 2 layers of .75oz cut on a 45* bias using Glass and CA, I then used lightweight speckling compound to fair in the edges.

I cut the ailerons out of the wing, tomorrow I'll sheet face of the aileron and the wing cut out with 1/16 sheeting.

soarrich

My Feedback: (98)

I finished the wing. Somehow I got the one servo 1/2" too close to the center[:@] measure twice, cut once. The bottom of the wing is all red. I have more up than down in the elverons, flying wings don't need much down.

I am laying out the fuse now, I decided to go electric, the other set of cores will be a slimer and swept foreward.

icerinkdad

Actually more up than down may be good if I am remembering my introduction to aviation technology class right... something about drag induced turns and using differential movement to make use of it. Try flying that way before making any changes.
Bob

soarrich

My Feedback: (98)

I wanted it that way. I may change the arms on the elverons though, I think they're too short I had to cut the radio's throws down to about 40%, long er arms would help prevent flutter also, the little arms exaggerate any slop.

soarrich

My Feedback: (98)

I've decided to use a Cox .049 Bee for power, it looks like all up weight will be 14oz. The wing is way overbuilt with blue foam and 1/16" sheeting, I positioned everything and it balances so I won't need any lead. The fin sits on a hollow CF .156" tube I had laying around. The tube was glued in with polyurethane after I attached the fin, the other end of the tube will hold the firewall. I will build a light fuse to hold the RX and the battery.

soarrich

My Feedback: (98)

Done!

AUW 13.7oz

Reedy race #1, look out Tar Heels.

soarrich

My Feedback: (98)

I flew it a couple of times the other day. It is semi fast, but that's the motor, very stable, even though it's slightly tail heavy it has great slow speed handling. On hand launching it you have to hold up in it or it dives at the ground, as the speed comes up you take the up out or you wind up in a steep slow speed climb. The tail seems very effective, there's none of that slow yawing that some sweep wing wings have.

I like the handling so much I may use the other set of cores that I cut to make a Navy Cutlass F7U

Andrew

Rich -

Is that a box full of Ambroid in the background of the big pic? If it is, is it new manufacture?

andrew

soarrich

My Feedback: (98)

Yes it's new. Horizon sells it, though they say it's temporarily out of production, I got a case last fall.
http://www.horizonhobby.com/Products...?ProdID=AMB102