Sig Super Chipmunk

I am getting ready to build the Sig Super Chipmunk. It will be my very first full fuselage build. Is there anything i need to change or need to get before building this plane? Or is there any advice or anything i need to know before building?

I would strongly suggest that you not use any of the plastic componets, they are quite heavey.

Walter

This is a nice kit but wheel pants and cowl are heavy. They come out nose heavy. I would make tank removeable and use a good uniflow tank. Brodak or RSM. The original kit did not use plastic cowl.
Dan

A flying buddy built one box stock from the SIG kit last year. He's a very good builder who knows how to build light, but it still came out heavy -- primarily due to the dense kit wood, in his opinion. Given this, it flies well with an LA 46 for power. Only way I'm aware of to get this plane light is to basically to not use the kit wood -- but then what's the point of buying the kit? Just make sure you don't skimp on power.

Andrew,

I might have a little experience with this kit.

1. move the gear blocks from mid rib so it sits back up against the wing spar. Much sronger this way. Also use 1/16" ply doublers on the front half where the gear is mounted, the kit has balsa doublers.
2. don't mold the top of the fusalage as the kit does it, very hard to do. If you are capable, I'd make a foam mold and mold the top piece separately from the fusalage, and in one piece, easier and maybe a bit lighter. Mold it in one continous peace, meaning don't cut out a space for the cockpit, leave the wood there or you will develop stress cracks around the canopy by the wing trailing edge.
3. if you use the plastic cowl, which works fine, make sure you cut out the very front holes for engine cooling.
4. and yes, make the tank removable, good advice.
5. add a box for ajustable tip weight
6. add ajustable leadouts.
7. use a larger belcrank and flap horns if you can get them. Don't eliminate the balances on the elevator. this helps reduce control loads.

It is a good flying plane. The kit wood tends to be heavy, if you have a good source for wood, might want to replace any heavy stuff. Any of the modern 40's or 46's should be lots of power, even a smaller 35 if you keep it light. Have fun.

Adding to David and Dan's comments, wood has been mentioned, but check each piece for weight. SIG does not hand select wood for their kits. They just pull randomly from the pile and it varies greatly in density. I once bought three SIG Mustang kits, romoved the wood from each kit, weiged each piece and reassembled the kits into lightest, medium, and heaviest wood. The kit with the heaviest wood weighed over a pound heavier than the kit with the lightest wood. And this was just from a random draw of three kits.

So weigh out your wood and you shouldn't have to replace everything, but if some piece is over heavy, do replace it (unless it is in the tail section in which case it may help with the balance.

One other thing that hasn't been mentioned is the gear. This is made with simple 90 degree bends, but the final bend that goes upright through the gear block in the wing is not long engough for an extension. It is going to begin to wobble on you if built as-is. I would remake the gear legs with a longer upright that goes through the block and then add a small block of maple motor mount stock above the gear block for this to fit through as well. That will lock the gear solidly in place so you have no problems.

I have built two of these--one light, one heavy. They are good flyers if kept reasonably light. (The light one used all stock wood. I was lucky. The heavy one--should have weighed the pieces and replaced a few).

As an aside, I just weighed three Twister kits. Now you have to remember, there is extra wood in here that is not used in the build and we are also weighing the packaging. One kit weighs 40.5 ounces, one weighs 41.5 ounces and the third weighs 42 ounces. They are pretty consistent, but there still is an ounce and a half difference between the three. If we were to separate the parts from each kit into light, medium, and heavy, there would be a considerably greater difference, I am sure. So you may have some wood that could, and maybe should be replaced. Just check things before you assemble. Weight the ribs and put the heavier ribs on the outside. Same with sheeting. You can save a little weight (less tip weight needed) that way.

Have fun.

>1. move the gear blocks from mid rib so it sits back up
>against the wing spar. Much sronger this way. Also use
>1/16" ply doublers on the front half where the gear is
>mounted, the kit has balsa doublers.

The stock design is to mount the gear blocks floating in the rib, and you glue it to balsa? Wow. I am surprised that doesn't break in the way the field.

Brett

Dave had a lot of good suggestions, and I'll add one very important hint, based on experience that I had from my SIG Chipmunk.

I built from the kit parts, which included control horns that had nylon horns molded around the steel wire joiners. At the Nats in 2003, when it got windy, the nylon horns flexed to the point that flap and elevators were not getting the movement needed to pull even the loops. Result: pancaked into the L-pad tarmac. No more Chipmunk. So I caution the use of these items. Go to the steel horns for assurance of a quality control linkage system.

Don

Gentlemen,

The SIG Chipmunk design has a 1.5 inch wing offset.

Do you recommend going with the plans or should the inboard offset be reduced.

T Michael Jennings
Knoxville, TN

I don't remember it being that much, it could be that I didn't build mine with that much.

I wouldn't go any more than about 1" asymetry. If I remember, on the plans, they just included an extra rib bay on the inboard side, way too much.

Dave,

Thanks for the info.

T Michael Jennings
Knoxville, TN

>I am getting ready to build the Sig Super Chipmunk. It will
>be my very first full fuselage build. Is there anything i need
>to change or need to get before building this plane? Or is
>there any advice or anything i need to know before building?

Print out everything that David Fitz posted and put it above your building board. I can only add a couple of things. The Chipmunk wing is a very good wing that is easy to build straight and strong. It can carry extra weight very well. Lighten up the ribs if you need to, and try to make the leading edge as round as you can, avoid a sharp leading edge. Use the best controls that you can. If your kit has the SIG control horns with the nylon arms, change them out. Tom Morris controls would be worth the investment, and maybe at least make the elevator horn adjustable.. Add some ply gussets to the engine mounts, or carry the top sheeting all the way to the front with an extra former. You could also shorten the nose an inch at that time, just make sure you can still install at least a 5 or 6 ounce tank if you need it. A shorter nose will help with any nose heavy tendencies. You could also make the tail moment ans inch longer if you wanted to. Plastic cowl will do fine, just work slowly and carefully with it. Wheel pants should be made removable. They can be sanded thinner to make them lighter if you want, just be able to remove them if you need to to help balance and vertical CG. Don't go over board on the finish. That's where a lot of weight builds up fast. I don't think anyone ever built a 20 point airplane on their first full fuse model. Just keep it simple and pleasing to your eye. MonoKote wings and tail surfaces with painted fuse is fairly easy and light. As for power, lots of guys used the venerable ST.46 on them back in the day, and today's LA.46 would be a good substitute. If you want to follow the current trend of over powering a model, the current ST.51 would be a good choice also. The Chip is a fairly large model for a .40 size airplane, and like I said before will carry a bit of extra weight well. If it finishes up at 45 ounces, great! If it finishes up at 50 t0 55 ounces, that won't be the end of the world either. The absolute main thing is to built this or any model as straight and true as you can. An efficient airframe is the first step in overcoming any other short coming that you may build into it. Like David said, It's a good flying model, and I would like to build me another one someday.
Good luck and have fun,
Dan McEntee

Thanks Guys. I really apreciate all of the advice. I know more will come in. Now let me ask you this. What is the best and lightest weight glue to use when building this kit?

>Thanks Guys. I really apreciate all of the advice. I know
>more will come in. Now let me ask you this. What is the best
>and lightest weight glue to use when building this kit?
>
Glue, to me , should be considered a tool. There is a right one for almost every job, some can be used for several different purposes but work best of one or two. One thing to keep in mind is that glue usually will need to be sanded at some point during the construction. Instant glues are great, but tend to not sand very easily. They can also buld up weight because they do not gas off or have any water or solvents that disapate as they dry. They let you work quickly, but have several trade offs like fumes that can be irritating to some peoples lungs and eyes. Solvent based glues tend to smell and that bothers some people also. Water base glues like Elmers and TiteBond are quite popular, inexpensive and easy to find. And they sand fairly easy when you need them to. Epoxies are used for high stress joints and laminating doublers and such. There are fast and slow varieties of epoxies also. I have lots of tools in my tool box to do lots of different types of work, I have several different types of glue on my work bench and use them where I think they work best. For general constuction, I use instant glue where I know I might not have to do much sanding (both thin and thick), Ambroid and Elmers wood glue where I know I will have to do a lot of sanding, and 30 minute epoxy for anything that needs epoxy like motor mounts, bell crank mounts, landing gear blocks, ply doublers snd such. And one thing that I have learned over the years, is that if you have glue oozing out of a joint, you have used too much glue. Excess glue is no substitute for a bad glue joint and any glue is only as good as the fit up of the parts being glued. Hope this helps. The rest you'll learn from experience.
Good luck and have fun,
Dan McEntee

THANK YOU!!!! I have three types of glue. I will look at them and decide what will be best.

Is there a profile version of the Super Chipmunk?

>Is there a profile version of the Super Chipmunk?

http://stunthanger.com/smf/index.php?topic=23163.0

Don't forget to get that leading edge as blant as possible

I think you mean, Blunt.

Yes, do not make it sharp, take a long sanding block and make sure it has been sanded well. the long block is important because you want the radius as uniform as possible along the entire length, as well as inboard/outboard.

If not, you will end up with different airfoils along the wing or inboard/outboard and different lift along the wing, making flat corners very difficult.

THANK YOU EVERYONE!! I am just about to complete the fuselage Jig. Cant wait to dig into it. Any more info or help and advice is greatly appreciated.