BeanerECMO:
You're welcome. Yes, the mechanical linkages can work, but tend to get pretty complicated when you want to do stuff like this. It sounds like you need to have have a "Y" cable on the flap channel with one leg going to the flaps and the other going to an external flaperon/elevon mixer on your ailerons rather than relying on transmitter mixing. For some of this weird mixing the simple transmitter mixing isn't up the the task. That's why I started thinking of using external mixers in conjunction with limited use of the transmitter mixing.
ORIGINAL: wsmalley
The Su is supposedly a fly-by-wire plane, so the question is what effect LE flaps, by themselves, will have. I just had to have them to add to the scale.
By themselves, the LE flaps should help the airplane handle higher angles of attack such as in turns and aerobatics without bleeding off as much energy as the wing without LE flaps. Or, at least that's what they're supposed to do.
I designed and flew an F-106 with fixed LE flaps without any problems. This model was based upon an earlier design called the Apex. That model's designer described in the article his early attempts at a pure delta that did not have the LE flaps. He said that the model lost a lot of momentum through the turns and the LE flaps cured this problem.
As long as the controls are torsionally rigid and don't deflect under air loads, you shouldn't have any problems with them. I seem to remember an article by either BoB Fiorenze or Dennis Crooks that was about adding LE flaps to a large Y/A F-18 twin DF. It was only used in conjunction with the flaps and featured a pin, operated off an air cylinder that went into a pocket built into the LE flap root to 'lock' the LE flap into place for high speed flight (a relative term given the power systems available at the time). Obviously they worked because he wrote and published an article.
But, his were only used at relatively low speeds when the flaps were being deployed and not active all the time. On a model the size of yours, I think one 1/4-scale servo per LE flap should be enough to actuate it, but also not be deflected by airloads. You could always build a Q&D test fixture and run it down the road in your car at 90mph to get an idea of how it would work. I did this to test free-floating foreplanes for jets and it allowed me to test my idea without wasting a lot of time building it into a model only to find out it won't work or that it needs more development in order to work.