SIG 40 wing
 

I have a SIG-40 kadet that has a straight wing. Having to recover the wing and was wondering if it is possible to make dihedral in the wing. Would have to split it then put a stiffener with dihedral and epoxy back. I was want to do away with the straight wing. Thanks. gphil

Yes, it can be done, but as you seem to realize it will require a good amount of work. I recently had to rebuild a broken cub ARF wing which included replacing the broken center dihedral brace. It was a lot of work to cut out the old dihedral brace without destroying the pocket by the spar that housed it. It took a combination of drilling out as much as possible without weakening the upper and lower spar wood, then with an assortment of wood chisels, files, hobby knife blades, sanding sticks, and sharpened screwdrivers to restore the pocket area so a new plywood brace could be installed. I was not changing the dihedral angle and both root ribs were in tact so I had less to do than you will. You will have to change the root rib angles by either replacing them at the new angle or fabricate a new center rib that is wedge shaped to mate the existing root ribs at the new angle. You might consider just creating a new dihedral brace pocket area just aft of the current one, just make it strong and of course directly attached to the backside of the spar.

Yes, it can be done, but as you seem to realize it will require a good amount of work. I recently had to rebuild a broken cub ARF wing which included replacing the broken center dihedral brace. It was a lot of work to cut out the old dihedral brace without destroying the pocket by the spar that housed it. It took a combination of drilling out as much as possible without weakening the upper and lower spar wood, then with an assortment of wood chisels, files, hobby knife blades, sanding sticks, and sharpened screwdrivers I restored the pocket area so a new plywood brace could be installed. I was not changing the dihedral angle and both root ribs were in tact so I had less to do than you will. You will have to change the root rib angles by either replacing them at the new angle or fabricate a new center rib that is wedge shaped to mate the existing root ribs at the new angle. You might consider just creating a new dihedral brace pocket area just aft of the current one, just make it strong and of course directly attached to the backside of the spar.

Don't know how I did a double post !!!:p

That is ok, I did a double take......lol No the plane never had dihedral but from what you wrote, won't have either .... I knew it would be work but had rather just purchase another wing. . . Thanks for the reply. . . gphil

Any particular reason you want to put dihedral into the LT40 wing? Just curious. The LT40's a great plane, super fun to fly, and with a straight wing it should be even more capable/responsive than it already is with dihedral. Again, just curious.

Yes of course it possible and since you are recovering its not that big a deal, a small amount of dihedral will indeed make the airplane fly better

I have hacksawed quite a few genairic forty trainer wings in two with the intent of changing to anhedral. flat to dihedral is a piece of cake. The alternative method I am going to suggest is far easier and just sligjhtly heavier. I have also used this same method on my four engine Senior Cadets (extended wing) and also on my Catalina Cadet a cross country airplane that has a senior wing extended 16 inchs.

The idea is to literally use a hack saw and cut the wing in two down the center of the root rib Does not have to super accurate. Completely ignore the main spar pockets and we are not going to try to clean that out, just forget it for now. Next you cut a pair of new root ribs and remove the old ones, with the wing on the table prop it up to the dihedral you want and hand cut/fit the main spars to a simple butt joint and do the same for the rear spars. then fit the leading and trailing edged to that simple butt joint and epoxy the thing together.

Now it is quite well but stable so carefully cut the rib nose sections ahead of the main spar out to how long you want the brace. to allow for a doubeler plate forward of the main spar. Its a little tedious but not that big a deal The doubler plated is cut from birch ply and epoxied to the main spars. 1/8 inch is plenty for your forty sized airplane The next step it to cut in whatever patchs you needs to resecure the forward rib nose sections to the new forward doubler.

Next is to do the same behinds the main spar perhaps agine 1/8inch. After the same procedure is used behind the spar and you fill in the ribs the sheeting is restored in the normal manner. This works and works very well.

John


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Correct it does fly well, but at my stage I need a little more stability. I got the plane for a song and it is just a little ahead of my learning curve. I am a senior and need all the help I can muster lol. I can fly it ok but sometimes get into that low wing situation and don't pull hard enough and get confused and turn into the bank. You have surly been there in early days, I think I am better than really am.... So yes the plane flies great but is old has been a yard dart quite often and was thinking that is once more in I.R.A.N. that I would do that. Thanks for the response. gphil

Thanks for the pics. I was thinking of somewhere along 3 degrees maybe.....I built a 60 size Stick and had the option of straight of dihedral and I elected the flat wing. It flies great for a more advanced pilot, which I am not. . . Maybe 12 hrs of total time now. Point the thing and it goes there. I just like stable flying craft. Thanks once more. gphil

Absolutely GP using a little dihedral will indeed make your airplane fly more comfortably and do not be embarrassed about doing it. Actually the typical trainer that has been converted to a totally flat wing makes for a rather poor flying airplane. Aerobatically speaking going beyond flat and using anhedral of about the same amount as it formerly used dihedral. But that is not what I am recommending in your case, yes a milld degree of dihedral would be most beneficial.

I am getting up there too (70) its amazing how we must constantly keep changing our techniques and equipment to remain a viable and competent pilot.

As far as hack sawing a wing in two, you will never do it and the wing will just mold in the shop. But if you take just five minutes to hack the wing in two then the rest of the mod will go faster than you think.

John:cool:

Confusion in a low wing situation is quite normal when learning to fly but there are two techniques to counter this confusion. 1) with the airplane coming at you, you counter the low wing by moving the right stick towards the low wing. or, 2) You simply point the transmitter antenna in the direction the airplane is traveling (not AT the airplane). Either method works. Some folks do better with #1 than #2 and vice-versa. Eventually, you will simply react as required to the low wing situation without even thinking about the technique.

Thanks John... I am a 20 year old locked in a 74 year old body. How is that song,,,,,,,,"I am as good once as I once was, but not as good as I always was." lol Going to crack the wing. Thanks..gphil

Loopdeeloop, yup but I still have the tendency to stare like a deer in the headlights. It will come. Going to keep at it as long as it takes. Could get expensive .....gphil

gphil,
The LT410 is a good plane. Not trying to be a smarty pants but what it sounds like is you need stick time. Maybe try throddeling back some
and slow the plane down. Don't know if you are a thumb flyer or not, but if you learn now with your fingertips you will find things a lot smoother.
Jusy my opinion but I don't think dehideral is gonna make that much difference.

No never think ill of any advice I can get. Strange you should bring up the thumbs.... Went on a trip and buddy and I went to another fellas field to do a little air splitting etc. He insisted , being new, me , that I start using my thumbs. I had been flying for some time with the fingers and I had one hell of a time trying just to hit the field seem hard. . . I am assuming that flying with the fingers for a while, trying to switch to the thumbs at that point was not a good thing. Too many habits had been pounded into my head at that point, Sort of set me back. I just do not get flying as much as I should. Going back to my own ingrained ways. No you are not a smarty pants , just another view to me and thanks. . . .gphil

John and I both gave you similar advise with two differences.........he suggested a new dihedral brace to be placed both in front of and aft of the spar. Two braces, good idea, it will surely be strong enough. The other difference is what I described as "a good amount of work", John described it as " its not that big a deal" ! :) I'll let you be the judge of that after you have completed the mod. As to your sometimes indecision on what to do when you have a wing drop low, here is what a friend taught me when I was just learning and it helped me....... With the plane coming at you (this is when it's not automatic to correct), you tell yourself you want to "prop up the low wing" and you do that by putting the stick under it, meaning move the aileron stick toward (under) the low wing. Maybe this thought in your head will help you always do the correct movement with the aileron stick. It worked for me, and I have used this explanation when teaching others.

Its not really clear exactly which Cadet you have GP. There was never a Cadet known as a Forty Cadet. Yes LT40 is the modern variation but it also could be much older Cadet Mk1 or !!'s. It would be helpful is we zero in on what you have.

Anyway assuming that is a shorter wing variant (less than the 78 or 80 inch wings. To answer your question as to how much dihedral to add if you decide to do that and the airplane has ailerons. What I believe will make your airplane a far better flyer is to add two inchs under the wing tips. Now if this airplane has no ailerons then four inchs under the wingtips minimum

Yes the simple learning metaphor Larry describes is exactly what I do with every student and it works. Propping a low wing up when its coming at you with the aileron stick works well and requires no serious thinking.

Just as a last thought about dihedral, especially since you describe some orientation problems. Many seldom think of this but it really is a vital factor. Airplane configuration plays a vital roll in the ability to maintain orientation. The very easiest to maintain orientation is the hi wing cabin trainer with dihedral If the dihedral is gone then that moves this airplane much further down the list. I am not gonna list each configuration as most have there own ideas cas to where each would fit in but will say that at the bottom of the list is many flying wings. I have flown a wide variety of aircraft configurations and you would be surprised at how important aircraft configuration is to the ability to maintain orientation.


So GP just think of this additional ease of orientation simply by adding dihedral as an added perk I'll bet you never thought about.



John:cool:

Is this airplane green gray and white? If so it was never built with dihedral. Cutting the wing in two would be a pain. Dihedral isn't going to help that much. But if you must I think you'd be better off building a new wing

I din't know if your LT-40 is an ARF or a kit built version. I just checked on the Sig site and a replacement wing for a LT-40 ARF will run you $80.00 plus a $20. shipping surcharge (what ever that is). So it's $100 ! A replacement wing kit for a kit built LT-40 is priced at $49.99. Let your wallet be your guide !