Lets spare a moment to those pilots who lost their SU-31 due to inflightbreakups.........

I have bought a SU-31 and want to make it a bit stronger.
Seems like the wing is a weak part of the plane and has a tendency to break.

Where does it break?
Does any one know a good way to strengthen the wing without cutting open too much of it.


Many thanks

Ground sucks!!!

I believe the wing failure was overhyped on this forum as the actual failures could be counted on your fingers only, and that is out of kit runs exceeding 500 each.

Prior to assembling all my ARF's, I visually inspect each component thoroughly then go through a twist, tug and bend physical. If any part seems substandard, it goes back for replacement. Modifications come next but only if I am going to power it outside of the manufacturers recommended engine range.

My Sig Sukhoi was powered with a BME 44. No mods were made, all pieces passed my personal criteria so it was assembled. The wing could be used as a surfboard in it's stock condition! The plane flew great and survived all manuevers, good and bad, I put it through. It's second owner is still doing the same during it's second year of use.

It's only mishap occured while carrying it into the house, I tripped and fell on it, smashing the aft fuse flat between the cockpit and tail feathers. A new fuse had it in the air again in several weeks.

Check out the parts, assemble it and go fly. It is a fine model and plenty strong. Sig will handle any parts you are wary of. Use your modeling judgement and proceed.

The wing to saddle fit must be a good fit to start with, if the wing is mounted to where you have to really tighten the heck on the hold down bolts just to get the gap to close up then a great deal of stress is where the wing meets the saddle . This can really stress the wing in that area...it seems to me that most of the failure happen just out past where the wing meets the saddle. So if you bolt the wing on and see the fuse/monokote starting to start to wrinkle as the bolts are being tightened the some work needs to be done to make a better fit.
The reason I say this is because I saw first hand a GP Giles 202 ARF wing break just about .5in. past where the wing meets the saddle. The owner had to really tighten the heck on the bolts just to close up th gap anf the fuse was buckling bad in that area.
Just wanted to mention this as a heads up and not accusing anyone of anything.

I have one with a BME 50cc engine. The plane wieghs 16.0 lbs complete. Use good servos and hardware. Make sure the ailerons and elevator fit well with no gaps before you epoxy them in place. I found much of the assembly time for me was getting all the hinges to fit well.

I heard many second hand horror stories about the wing but it seams very strong to me. There are only a few first hand reports of wing failures.

It does take 2-2.5 dgrees of right thrust and its not built in and it takes 20 degrees of up elevator mixed in to get a good knife edge.

But it does real well in the pattern work and looks real nice.

I get lots of compliments about it out at the field.

Joe Brannon

I guess I'll reply the opposite as the previous posts. I bought an earlier kit and had it together ready to fly. Then they sent out new horizontal fin and elevators because they forgot to put hard points in the elevators. I tore out the old and put in the new and removed that plastic fairing that fits around the vertical fin and replaced it with wood and ultracote. I also used 3/4 cloth on the horizontal fin from center to about 4 inches out because when I was removing the old one, with very little pressure the fin snapped in two pieces. There were no spars in the horizontal fin. Only ribs, leading and trailing edge and bad sheeting.
Then I had it ready to fly again until I read about some wings failing where the inside aileron meets the rear of the wing. When I shook my wing it rattled with loose balsa(before it was ever flown) so I removed the lower covering and was amazed at how many ribs were broken and cracked and the lack of sheeting between ribs and the poor job of glueing that had been done. I fixed or removed the bad areas and glued in new sheeting and epoxied the trailing edge to new spars. I also took the time to mount the aileron servos flat and secure unlike the sig design which is on their side and on that bendable plywood that is supplied.
Mine flies great with an mvvs 2.1. Unlimited and floats in for landings. I also feel secure knowing that I took the time to look beneath the covering to see what was really there. I don't think my wing would have held up to very many snap rolls if I hadn't of fixed it. Jim

Dick T.
Is that your picture that is on this forum where you broke your fuselage in half? That was funny. Thanks for the humor.

I can assure you that there were more than a few wing failures of the SU31. So much so that Sig is out of wing assemblies, and has been for some time. I have been in virtual constant contact with Mike Lee of Sig about a replacement wing for my SU31. That happened three almost four months ago, still no wing. Just last week he pulled two ARF SU31's from distributors in order to send me a replacement wing. Both wings on these two were also bad. I can show you the emails if you wish. It is a crap shoot whether or not you get a decent wing. You may think you have a good wing, but you cannot be sure until you actually remove the covering. Then you will see what some of us already know. Broken ribs, split ribs, spliced sheeting, cap strips cut too short, sheeting too soft....and on and on.

The SU31 was made by a firm that Sig used only for this ARF. Quality control was almost non existent. Sig's regular manufacturer is now producing the new SU31, due to be out soon. I expect the quality will be much improved.

I am flying my SU31, after repairing the wing, but currently not to it's capabilities.

I must give credit to Mike Lee and Sig. He has been up front with me through this whole ordeal. Not once did he question me about something I may have done to cause the wing to fail. Mike has made a generous offer to me as a form of settlement for the problems I have had with the SU31, and I have accepted it. However I still want a replacement wing for my SU31 when they become available.

Vince

Yes, that was my Sukhoi broken over the couch arm, I still chuckle when I recall that day.

I won't deny there have been some failures of this ARF but many were probably builder induced. That topic has been pounded already so i won't go there. The important thing is that Sig has stood behind all but a few complaints concerning their ARF's, even replacing some that were poorly assembled or grossly overpowered (based on first hand observation).

One only needs to read the posts here on RCU about ARF's to ascertain some folks will never be satisfied with any one of them. At this point, most ARF's are an exceptional value for the cost but the bashers, whiners and know it all's are slowly driving the prices up.

I have had a few ARF's that were marginal in quality but for the price, and as a long time modeler, I just fix it and go fly. They are still a good deal.

I, unfortuately have to fly ARF's because of an allergy to most new glues we now use. What is fortunate, are the advances in quality that most importers are putting into the products they sell. That being said, I still have learned to take the time to inspect and fix anything that looks suspect. If it needs beefing, I beef; tri-stocking, I tri-stock. I don't buy anything that is first on the market without reading what others experience. After reading the posts on the Sig Sukhoi, I did strip the covering off of the underside of the wing for inspection. I made some mods to my satisfaction, and the wing is very strong. This whole proceedure took about 1 1/2 hrs. I also added tri-stock to the stab section, and parts of the interior fuse that looked weak. I ahve a G-45 on mine, and it flies great........

Rather than take a chance on Sig's questionable quality I just choose to avoid them and purchase planes from Yellow Aircraft or other manufacturers that don't have those kind of problems. I one of the many that had a flutter problem with the Sig Cap - they never responded to my letter so I never purchased another Sig product. I have built quite a few ARFs and none needed the covering cut to check the wings. I never had a flutter or structural problem with any other ARF.

Just my experience - take it for what it's worth!

After reading your posts I decided to cut open that wing to see for my self.

I would not be confortable flying around not knowing if that wing was going to quit on me.

Now Im happy I did. The spars had many cracks ond even some pieces missing.

I also put some heavyduty aileron horns on.

The fuse has also had a makeover.
Hope I have not made it too heavy for the 3W, 35cc eng.


Ground Sucks.