longdan

Hi all
I'm designing my own ugly stick-type plane. This is going to be a thrash around plane that I will fly like it belonged to someone else. I have a supertigre .45 that I plan to mount in it. The spars in the wing will be 48" long.

Which would be better - 1/4" hardwood wing spars or 3/8" balsa? I know that many will say that if you can fit 3/8" balsa, why not go with 3/8" hardwood? But in the interests of efficient design and weight saving, I have (for now) limited myself to 3/8" balsa or 1/4" hardwood.

The wing will be a symetrical foil with a top and bottom main spar with 1/16" shear webbing on both sides of the spar for the full length of the wing.
Any opinions?

Dr1Driver

I'd use 1/4" bass spars. Bass gives some flex (needed) but is much stronger than balsa. It's much easier to work with than spruce, which I DO NOT recommend. That plane won't need 3/8" hardwood spars, it's just a weight penalty.

I have a self-designed 48" sport plane that does 3 rolls per second, snaps too fast to follow and cuts its own tail off in an outside loop - all on 1/4" bass spars.

Dr.1

Edwin

My Feedback: (2)

Just as another observation. The last scratch I did was a modified bandito grande 82" ws with a ryobi 31cc gas engine. Pretty lively flying. I used 1/4"x1/2" hard balsa spars with 1/8" shear webing out to the tips. Held up fine with for a couple of years, until I flew it through some power lines. Could of swore I was on this side of them. Anyway, bass wood would do fine if you really want to.
Edwin

Mike Connor

My Feedback: (5)

I suspect our models often reach or exceed 10 G's. Your spars seem too light to me unless you build in extra strength with wing sheeting. I use CF tubes for light weight and high strength.

FlyerInOKC

My Feedback: (6)

Just an f.Y.I the SIG LT-40 Trainer has 3/8" Spruce for the main spars (I beam design) with shears 2/3 of the way out The rear spar is 1/4" balsa and the over all wingspan is 71 inches. It has no problem flying with a .40 engine.

Dr1Driver

Just an f.Y.I the SIG LT-40 Trainer has 3/8" Spruce for the main spars

All overkill! You'd be surprized how much wood you DON'T have to put into a properly-designed plane for it to be strong.

Dr.1

Edwin

My Feedback: (2)

My current project is a balsa usa 1/4 scale cub, actually 2. The wing spars are 3/8"x1/4" balsa set verticle on the forward and 1/4" square balsa on the rear one built "C" channel style with 1/16" shear webs. The wing span is 108". Then again, its not designed to be flown like a speedster. I have a super sportster 60 with 1/4" square bass wood spars and glassed center section. I can do a full throttle dive straight down and pull up hard without snapping the wing, a true beater plane. Its all in the purpose. You CAN build incredibly light for just lolly gagging around. Just my opinion, for your thrasher stick I would use the 1/4" square bass wood and build it "D" channel (ie:1/16" shears webs on both sides of spar) to about 2/3 the wing. A single shear web the rest of the way. Then use a 1/4" ply spar joiner in the center section for about 2 ribs, and glass with about 4oz fiberglass about 3" or 4" wide. Overkill for sure, but it would definately be a thrash around plane. Like DR1 says, if you build for a specific use, you'd be surprised how much wood you dont need.
Edwin