I am building a Sig kadet Sr. The standard build calls for the use of rubber bands to hold the (78") wing on. I'd like to convert it to a bolt down wing setup. As a new builder, my primary concern is doing this in a way that is safe and sound structurally. After some searching I've seen this mod done to this plane a couple of different ways.

First I've seen dowels added that protrude forward out of the Leading Edge of the wing that are inserted into holes in some new structure added to the fuselage right in front of the leading edge of the wing. As you insert the dowels into the holes in the fuselage you lower the wing onto the fuselage and secure it with two bolts/screws above the trailing edge. I suspect this a pretty common approach. I have attached some pics below of a Kadet Sr. that was modified in this way.

The other approach I've seen used two ply pieces shaped almost like hooks. These hooks were integrated into the wing structure. They hung down under the wing and projected forward under the Leading Edge. A dowel was run across the inside of the cabin area of the fuse (just below the leading edge of the wing). The idea was to hook these wing hooks underneath the dowel as you laid the wing down onto the fuselage and then secure the wing with 2 bolts/screws at the trailing edge. The benefit to this approach was not having to add the additional structure to the fuselage that sticks up in front of the leading edge of the wing which can be difficult to make look aesthetically pleasing.

So the main area of question is what kind of structure you might recommend I add to properly integrate either the dowels or the plywood hooks into the wing structure? And also whether you believe other modifications are called for in order to better strenthen the center section of the wing given this new design?

The current wing halves I've built (according to the plans) really don't have much for inner structure in the center where they meet. You just epoxy the inner most balsa ribs together after inserting a thin ply spar doubler that is inserted 1/2 into one wing half and 1/2 into the other. Lastly balsa sheeting is added over the first couple of bays on each side and then a strip of fiberglass cloth is epoxied around the very center. Simple wing structure. Just font and rear spar and 3/32 ribs. Thats it. Photo below of one of the wing halves that I've build.

I've learned a lot during this build but do still struggle on how to properly introduce strength and structure when making modifications. Thanks in advance for any thoughts, guidance or insights you might share.

-Matt

I would use the dowel method. In the wing photo I see a fairly large gap at W1 and W2 behind the main spar. Is this where the plywood brace goes? Either way, you need a piece of plywood behind the main spar, just like the sheer web in front of the main spar. I add another piece of plywood halfway between the sheer web and the back of the leading edge. This gives you 2 plywood hard points to glue the dowel to. The 2 plywood pieces get glued to the top and bottom center section sheeting and glassed over.

Scott

Scott,

Thanks very much for the reply and advice. I decided a picture of these ply braces would be better. I inserted them into one wing half and took the pictures below. They are 1/8" ply and are 1/2" by 12" where 6" is inserted into each wing half. That is really all there is for reinforcement as mentioned. Except for balsa sheeting over the first couple of bays and the wrap with fiberglass cloth around very center.

I think I understand what you are recommending. So 2 pieces of plywood to hold the dowels - one piece behind the front/main wing spar - I'll call this the front dowel support. And one piece about midway between the front and rear wing spars - I'll call this the rear dowel support. I get it.

So this brings up another question (sorry!). Since the inner-most ribs on the wing halves are literally right against each other in the center (and epoxied to each other) it seems like I either need to make each of these dowel supports in 2 pieces (one on either side of the centermost ribs) or I make each out of a single piece of ply and cut a slot in the centermost ribs so the support runs right through them?

Last question, what kind of additional structure/support, if any, might you use around the rear plywood dowel support since it won't have the luxury of adhering to the spar like the front support will? Or would you just simply adhere it to the ribs (it either passes through) and/or on either side of it?

Again thanks for all the help!

p.s. That looks like an early 70's Camaro in your avatar. With a blower no less. Do you ever drag race it?

-Matt

Matt, those braces are what I expected. The rear most plywood piece will glue to the rear of the 2 braces after the wing halves are joined. Kind of another plywood sheer web behind the front spar (This is the main spar). The other plywood piece goes halfway between the main spar and the square leading edge. This piece can only be glued to the wing ribs initially, but is glued to the top and bottom sheeting. You will end up with 4 pieces, 2 on each side.

The car in my avatar is indeed a 70. It is a street car, but has turned high 7 second quarters through the mufflers. I don't own it, I am just an engine builder. It has a 434 inch blown alky small block in it. Here are couple pics of the engine and me tuning it for an evening of "Performance Comparisons".....

Scott

OK, thanks Scott. I understand the recommendation. Appreciate the help. I understand the recommended direction. I think I'll build it on paper a bit and see if I can drop the dowels down low so they protrude forward from under the wing rather than directly through the wing leading edge as in the photo I had posted above. That way I could avoid building up a "large" structure right in front of the wing to catch the dowels. That structure is not normally there. Maybe have some ply fastened to the inside of the cabin's front bulkhead. Thanks again.

For the most part, people have absolutely no idea how fast a 7 second quarter is. That kind of capability in a street car is really almost unheard of. Must have some serious HP! Best I ever ran was high 10s on street night in an AC Cobra replica I built. And I thought that was fast.

Matt, you could easily extend the plywood down below the bottom of the wing and sheet around it. This would put the dowels below the wing, or you could split the difference and set them at the lower spar and bring them out just below the leading edge. Draw it out in profile and it will tell you where they need to be.

The car does have some serious HP. Between 1400 and 1800, depending on the tune up I have in it. On alky, so we need to have a truck follow us around with fuel jugs. A drum a night is about average. The problem is traction, with 10.5" slicks it doesn't hook up very well, so we usually end up killing a set of slicks every night as well.

Scott

Here is one way to do a Telemaster wing.

http://www.balsaworkbench.com/?page_id=145

Originally Posted by JimboPilotFL

Here is one way to do a Telemaster wing.

http://www.balsaworkbench.com/?page_id=145

I followed this method on my RCM basic trainer and it works great.

Originally Posted by JimboPilotFL

Here is one way to do a Telemaster wing.

http://www.balsaworkbench.com/?page_id=145

Yup, that is the idea. The difference between my post #6 and this is that I would use 2 dowels. I have great respect for Balsaworkbench, his workmanship and kits are top notch for sure. I still would use 2 dowels. Personal preference, as obviously 1 will work.

Scott

There are lots of ways that work. And I think we each end up with our favorite ways.

Mine is that since I already have a spar which is a strong hard point I prefer to use one or two screws located at the spar. This takes the main loads with very little extra structure. So it promises to be somewhat lighter overall. Mind you it depends on the fuselage structure and where the best place is to harden the fuselage for the tie down points to take the screws.

In your case with the rather open cabin structure you really need to study the situation and figure out what the best way is to harden either the leading and trailing edge areas for dowel and/or screws and which way will provide that strength in the easiest and lightest manner.

Bruce,

Would you mind sharing a bit more about how you use screws instead of dowels? Wasn't able to understand how you are using the screws located at the main spar? I had planned to use 2 nylon screws at the rear of the wing that would be screwed into hardwood blocks in the fuselage that were drilled and tapped. Do you somehow use screws to tie down the front of the wing as well? I've attached a photo of the fuselage plan that shows the wing cross-section sitting on top. And also a picture of the current fuselage "cabin" area where the wing sits.

Matt,
Using 4 screws on wings is fairly common. All of the race planes use this method. Looking at the fuselage structure I think front dowels will be easier. A vertical blade of plywood at the front of the cabin framing, and a couple hardwood blocks at the rear where the triangle shaped braces are. This would have the dowels below the wing.

Scott

Follow-up question, what do you typically use for the hardwood blocks that you drill and tap for the nylon screws? What dimensions typically?

Just wanted to add...I have 1/4" aircraft ply already. (I actually have 1/16, 1/8, 5/32 and 1/4 aircraft ply). Laminate to make thicker? Don't laugh but I also have some leftover 3/4" oak flooring that I could slice up into just about any size?

Don't hesitate to recommend the "right" size & right type of wood. Just always trying to use something I have vs. trying to order RC lumber with the minimum order size and all.

Thanks,
Matt

Matt, if you have true aircraft plywood I would glue a piece of 1/8" to the front for the dowels to go through. I would cut small circles of 1/8" ply, probably 3/4" in diameter or so to place at the dowels, so they go through the full 1/4". For the wing bolts, glue in 1/4" plywood. Drill and tap it for 1/4 - 20 nylon wing bolts. Wick thin CA into the threads and allow to dry overnight. Run the tap back through the holes and repeat one more time. This will harden the threads and the wood around them.

Scott

hello, I have built my bolt down wings several ways, The easiest I think is with round dowels as stated previously, But I have also done several as pictured here on larger wings, guess its just your preference