Wing tube advice
 

I want to convert a 99 inch long wing into a two piece wing but I dont know how. Wing requires 6° dihedral. Plans show 1/4" ply brace.
what diameter tubes?
What length?
How to figure out placement?

Size depends on the type of airplane but 1" to 1.25" should work just fine. I would go somewhere around 18" into each wing panel. Wing tube should go between spars and tied to spars with shear webbing. Dihedral will require some math, the hole for the wing socket in the root rib will be influenced towards the top spar, in the rib at the end of the socket it will be influenced towards the bottom spar. Most important thing when considering dihedral is to make them the same, anything between 4 and 8 degrees will fly the same, just do what looks right.

Conversion for something like this is best done during the initial build. Are you getting ready to build or is it built already? Cutting the built wing apart and adding the joiners is certainly possible but just way different so it would help us to help you to know which situation it is you have here.

Bruce, this is the wing we are helping on the 3/4" balsa spar.

Scott

In that case I would suggest looking at wing tube setups as used on RC gliders. Namely the right way is to house the liner tubes in the middle of the spar between the upper and lower spar caps. The way to do this is to embed a liner tube for the joiner in between the upper and lower spar in a putty made from epoxy and sawdust.

On the topic of the big solid piece of lumber you feel you need for the spar I again suspect that you have misread the plan. I can't find the plan for the big version but I see that THIS SMALLER SIZE ROBIN HOOD uses a more normal top and bottom spar caps which are then joined with pieces of vertical webbing between the ribs. I suspect that this is the true case on your 99 version. And as such encapsulating the liner tube between the upper and lower caps and sealing them in with front and rear webbing caps to keep the epoxy and sawdust "putty" in place until it cures would work just fine.

Check out build of wing for Mister scale Zero...
it has wood wing joiner cut on angle of dihedral that sits in box between spars on bottom of wing.
That's where idea came from.
My plane is big 1 piece wing....not built yet......yes,joined by ply joiner glued in place.
I don't see how to put tube between spars and still have dihedral. ..tube would be short with dihedral .....that's why I'm thinking wood joiner .
wing just not very thick so tube would have to be small outside diameter to extend far enough into wing.
Any thoughts???

You can use a wood joiner but if you do you would want to wrap the box formed by the upper and lower spar caps with kevlar thread to withstand the scissors like shear forces at work. And if you do this I would not want to use plywood since half the layers have the grain running in the wrong directions. Instead you'd want to get some cherry, maple, birch or similar hard wood and make your joiner from that so the grain is all running in the optimum direction. Or laminate up some G10 fiberglass board or similar.

I think you're misunderstanding how the tube with round rod joiner works. Have a look at the sketch below.

The nice thing about this tube and rod arrangement is that the filler putty made from epoxy and sanding dust bonds all the parts well and you absorb the prying scissors like forces through all the epoxy putty and webbing to a far better degree. And a model the size of a RH 99 can easily handle the weight of an 6 or 7 inch piece of 3/8 steel rod and not notice at all.

How much angle you can get with how much tube and rod depends on the airfoil and the spar caps. For a 99" span I'd like to see the spar caps made from spruce or yellow pin or just good tight growth ring white pin that are 3/16 thick by 3/4" wide. That should give you lots of room between the caps for the tube.

This is also an illustration of what we were suggesting in the other thread asking about the large balsa strip wood. What you see here with front and back webbing is how you really should be doing the main spar. As noted 1/16 plywood front and back for the inner 1/4 of the wing each side out from center. Then 1/16 very hard balsa. Find some where you have a hard time making anything more than a shallow mark with a heavy fingernail press. That would be what you use front and back out to the wing tips.

The resulting closed in box will be very strong and stiff.
https://cimg2.ibsrv.net/gimg/www.rcu...8f313a88dc.jpg

So to continue with Bruces' idea, and assuming that the wing calls for the 3/4 x 5/8 balsa spar, that leaves us with probably a 5/8" wing joiner tube. Wrap it in parchment and laminate sleeves using fiberglass cloth and epoxy. The end result should be a tube about the 3/4" width of the spar. I would probably still laminate 2 pieces of 3/8 x 3/4 balsa and cut it down to 5/8" and run some carbon uni top and bottom, but that is just me. Tying the wing tube properly into the spars is extremely important as Bruce pointed out. I have never thought of using resin filler, I always cut shear webs out of very hard 1/4" balsa and fit each one to the gap between the tube and spar, but I always make my wing sleeves out of carbon. The resin filler and fiberglass sleeves are much easier and less costly by about a car payment.

Scott

Good stuff!!!
I took pencil to paper and tried to remember my trigonometry. ..
If I am correct I can go 10.5 inches into wing using 1" o.d.tube, but spares are 3/4 wide..will this mean I must use 3/4 tube?
I have 1.575 between top and bottom spar.
I want 2.5 Deg dihedral each side.
I will redo my calculations for a 3/4 tube to check how long tube must be.
next question....how thick tube wall needs to be?

Found 3/4 aluminum by 24" long set sleeve and tube with .045 wall for 45 dollars???
sound right?

Hold on a minute here.....
If I remember correctly the idea is a 2 piece wing with a tube joiner. In that case ..
Yes, the wing tube is 3/4"
NO, you don't buy a 3/4" tube.

Remember, for this to work you are not dealing with a tube, but 2. One inside the other. To end up with a 3/4" diameter tube to match your spar, you need an outer sleeve that is 3/4" outside diameter, For that to work you will be buying a tube with about an outside diameter of 5/8" or so. You will wrap it in fiberglass and epoxy and make a sleeve that is glued into the wing. I would probably use 3 layers of about 8 ounce fabric. This will give you a sleeve that is a tiny bit shy of the 3/4" mark. This will be fine. If you refer back to Bruces illustration (He is just showing off by posting those drawings by the way) you will notice that if the sleeve is a bit smaller that the width of the spar the gap will be filled with the resin. If the sleeve is even a tiny bit too large, when you glue the 1/16 plywood to the spars it will put enough pressure on the sleeve to flex it making it just about impossible to insert the tube.....

So you need to go looking for a 5/8" ish OD tube. I use either carbon or titanium, so hopefully Bruce of Shawn will chime in with an answer to your question of wall thickness on the tube.

Scott

Web site says matching set....tube and aluminum inside tube....at least that's what I think it was....I will double check..thanks

Web site sells sleeves and tubes as a set...you are correct about the sleeves being bigger than 3/4....
so they have a 5/8 tube with matching sleeve with .720 outside diameter.
Aluminum tube .049 wall thickness
now the question is....will a .625 dia aluminum tube with .049 wall be strong enough???
Don't know where to go to get that information 😞

That sounds kind of light to me. That being said, I don't use aluminum. Shoot off a PM to Shawn (Speedracer) and Bruce and ask them.

Scott

Is the only way to use joiner tube between spars?

No, but it is the only way that works....

Scott

What is this tube set intended to be used for?

Plus you realize that you only need 8 inches or so for the joint, right? The outer tube is also only to act as a slip tube and to give you something to pot into place with the filler goop. It does not need to be structural.

If you're keen on using aluminum tubing you need to be sure that it is proper aircraft alloy with a higher number "T" spec. LIke 6061 T5 or T6 or 7075 T5 or T6. This isn't a place to use basic hardware store extrusions that bend like Play Doh under much of any load.

Will this work? It's a 125% Kadet Senior that I'm scratch building.

Wingspan 98"
Cord 18.75"

The wing is 3 pieces. There is a center section that is 36" wide. Then a 31" tip panel that will attach on each side for the total 98" span.

There will be a massive plywood dihedral brace on the center section. That will set my angle. Each side will have a 3/4" CF tube and sleeve that is 36" long. So 18" into the center section and 18" into the tip panel. Both sides for a total of 6ft of CF tube.

I'm hoping this will work as laid out. I can build my spars with either balsa or spruce. There is a mixture of balsa and plywood ribs. 1/8" width. I plan to cut plywood reinforcing donuts and fit them around each spot where the tube passes through the rib.

https://cimg5.ibsrv.net/gimg/www.rcu...313653640d.jpg
https://cimg4.ibsrv.net/gimg/www.rcu...5bad094397.jpg
https://cimg6.ibsrv.net/gimg/www.rcu...b680b1f427.jpg
https://cimg7.ibsrv.net/gimg/www.rcu...6d4b24822f.jpg

You really need to have your wing tube between the spars with some shear webbing connecting the spars to the tube socket.

Agreed, and this was addressed in posts 16 and 17.

Scott

Spars are 1/2" x 1/4"
Tube is 3/4"

How do I squeeze the 3/4" tube into a 1/2" space?

I've seen wings with tubes behind the spar many times. Not trying to be argumentative... just don't understand how else to do it.

Am I missing something here? The picture you posted is of the wing in question, is it not? It looks to me that there is plenty of room between the spars for the wing tube. Drill another hole in the ribs between the spars for the wing tube. When you assemble the wing, put the outer tube in the ribs and add top and bottom sheer webbing between the center of the spar and the tubing. Alternately, you could use 2 sheer webs in each rib bay by placing one in front and one in back of the spar, glued to the edge of the spar, and each glued to the wing tube. Hope my explanations make sense, it is easier to do than to put into words.

Scott

Scott,
The tube is 3/4" diameter

The spars are only 1/2" wide.

So how do I shear web it with 1/8" sticking out past the spars front and back?

I'm gonna re-drill the hole directly behind the plywood shear webs. So 1/8" behind the spar is gonna be the outside of my 3/4" tube.

The tube will nest/glue directly to the shear webs on the back of the main spar.

First of all, center the holes for the wing tube between the spars. This will leave 1/8" of the wing tube in front and in back of the spars. There are two ways to sheer web from the tube to the spars. The most common is to cut small pieces of sheer web material to fit between the top of the wing tube and the center of the underside of the top spar. Do the same for the bottom . The other method is to cut 2 top and 2 bottom sheer web pieces for each rib bay. For the top 2, the bottom of each piece will be sanded to an angle to match the contact point of the wing tube, and the top portion will be glued to the front and back edges of the wing spar. Either method will work, if you choose to use the 2 web, front and rear method, use thinner / lighter material for the webs as there are two of them.

Scott