hiroboz

My cores are cut and I'm ready for sheeting. Before I sheet both sides I want to run 2 spars through the entire length of the one piece 80" wing. This is what I'm thinking I will do:
Sheet the entire wing on one side with balsa,
router 2 channels through the opposite unsheeted side and place hollow aluminium spars in the cut groove. Then complete the sheeting. I will use Monokote over the balsa for my finish.
2ND IDEA
Sheet one side, cut groove to accept 1 wood spar close to TE for hingeing Ailerons. Finish sheeting wing with balsa, fiberglass with cloth & clear polyester resin, sand for 1 year and finish with auto paint.
Am I way out on this one? Will either way work for me?
I will appreciate any and all help
Thanks
It's a 1/4 scale Extra 300, fiberglass fuse. My first completely scratchbuilt plane.

Ollie

What makes you think the wing will not be strong enough without strengthening? If you give the thickness and chord at the root, the density of the balsa you intend to use and the weight of the plane without the wing, I will calculate how many G's the wing can pull without failing. Then you will have a rational way of desiding to reinforce or not.

BTW, using denser balsa sheeting at the thickest part of the wing can double or even tripple the wing's bending strength compared to medium or low density balsa.

scale only 4 me

My Feedback: (158)

I made the mistake of not using a spar in the same size and type of plane a couple years back
the wing folded on the 3rd flight. just out side where I hade glassed the joint
The next time I routered and epoxied in a 1/2 x 1/2 hardwood spar top and bottom about 16" from the tips. then sheeted and Monocoted the wing
This set-up was very strong. if your going to fly the plane hard I suggest you insert a spar!!

A10FLYR

My Feedback: (1)

The A-10 in my avitar has a 115" span, a 20" cord at the root, a root thickness of 3.5" and no spar. The plane weighs 54.5 pounds wet with turbines and has pulled some very high "G"s. In fact, none of my planes with ONE piece foam wings have spars.

More free advice;>)

hiroboz

I feel that I'm treading on ground I might not be able to handle. Wow! looking at your avitar's and listening to the posts I feel as though I should be standing in line to take pictures of your guys' planes. Ollie I'm sure yours is right up there too
I guess we all start somewhere, I'll do my best
My wing, which I designed (drew)in Winfoil is 18.25 inches at the root with a thickness of 2.25 inches. It spans exactly 80.25 inches, with a tip that measures 10 inches x 1 inch thick, it is a double taper. I have not yet purchased the sheeting, I plan on buying 4"x48" 1/16 sheets. Is the balsa labeled for density? The fuse is not yet finished but, as it sits in the picture I am a hair under 6lbs. Idealy I am focusing on ready to fly a maximum weight of 16lbs with a Super Tigre 4500 under the cowl.
The reason I figured I needed spars is for strength and also for attaching my control surfaces. I thought of glueing plugs into the foam and hingeing from them, along with sealed control surfaces but, it just seems that it would not be enough. This project is already two years in the making with a six month break for my Heli. It has been rekindled because of my post about ARF's and kits in the Questions and Answers forum.
Thanks guys I certainly appreciate the help.
Steve

Ollie

Ten pound per cubic foot balsa has a compression strength with the grain of 1700 pounds per square inch. Taking a portion of the wing skin at the thickest part of the wing, 6x1/16 inches in crossection for strength calculation, the skin can take 637.5 pounds of compression load. Estimating the average thickness of the wing over that 6 inches of skin at the center of the wing as 2 inches, the maximum allowable bending moment is 637.5x2=1275 lb-inches. The center of lift of the wing is at about 18 inches out along the span. That will allow each wing half to carry 1275/18=70.8 pounds. The total load carrying ability of the wing will be about 70.8x2= 141.6 pounds. Assuming the weight of the fuselage, tail, engine, fuel, etc. is 14 pounds, then the wing will be capable of about 10 G's. By going to very hard balsa for the sheeting over the thickest part of the wing, the capability can be increased to about 14 or even 16 G's. This calculation is conservative in the sense that the wing skin beyond the thickest part of the airfoil is not assumed to contribute to the wing bending strength.

The above calculation is for the bending strength at the center of the wing. The bending load at half the distance to the tip is less than1/4 the load at the center and goes to zero at the tip. This allows you to taper the hard balsa sheet from 6 inches wide at the root to zero at the tip without risking wing failure during highG maneuvers within the design load.

A piece of balsa 1/16x4x48 inches contains 12 cubic inches of balsa. At 10 pounds (160 ounces) per cubic foot and 1728 cubic inches in a cubic foot, the sheet of balsa will weigh 1.11 ounces. At a 14 pounds per cubic foot the same size sheet will weigh 1.56 ounces and at 16 pounds per cubic foot the sheet will weigh 1.78 ounces. By taking a postal scale to the hobby shop you can select your wood. If you are ordering your wood from a mail order supplier, you can pay a small premium to have them select the density that you want.

hiroboz

Ollie, that's an incrediblely informative reply. You helped me a lot. I have my scale ready for the next time I visit the hobby shop! Thanks for all your effort, not only just for the calculations either, you gave me new confidence in my 1st scratchbuilt project. Thank-you very much. I was really leaning towards the aluminium, your advice and knowledge just saved me a bunch of weight too.
Thanks again
Steve

scale only 4 me

My Feedback: (158)

If you can get that plane all up at 14 lbs. It should fly fantastic
Mine with a Brison 3.2 /smoke/ etc wieghed more like 18lbs wet
I guess it all depends on how violently you fly the plane?

Good luck