Major Pain

Hey Guys, have a problem with my Dual Ace that maybe someone can help with. Plane is twin Thunder Tiger 46 engines. When I put together the plane, since it is a ARF I did't check all incidence and since then I have paid for it. Have read entire DA thread and I seem to be only one having problems. Blanced on 95mm as per most others have balanced there or more rearward. First flight plane left ground in very steep climb, reduced power and down trim and plane still required almost half down stick to fly level. After very harrowing landing, took back to shop to recheck everything. Since horizonital stab is epoxyed in I leveled the stab and fuse with Robart Incidence Meter to 0 degrees. I then set wing to 0 degrees (wing leading edge was about 3 degrees down). Back to field for second flight. Little better but still extreme climb under full power. Another scary landing. Back to shop. Check engine thrust, both had about 4 or 5 degrees of down thrust. Don't know how that happeded since engine compartments both fit very well. Would that much be designed into plane? Insturctions do not give any incidence or thrust directions. Set engines to 0 degrees thrust. Everything is set as close to 0 degrees as I can get it. Back to field. Third flight was better, could trim level at half throttle, but still climbing at full throttle. I have flaparons on the ailerons set to a dial on my radio. They are set with wing as close as I can tell.(by sight). Do you think moving dial up or down while flying would help solve problem? All my flying buddies think that may be the problem but I'm almost out of nerve trying to fly this THING. Im out of options and thinking of selling it, but everyone local is afraid of it because they have seen it try to fly. It is a very good looking plane and I want to get it right. I have had 2 other twins in the past with no problems, but I did build them. Hope I posted this in right forum, if not feel free to move. Thanks for any help.--------Revver Bro#164

BMatthews

This is a very normal reaction to a model that is trimmed for a regular amount of pitch stability. The "fix" is to make it less stable by moving the CG back a little and then trim the elevators for level flight at around the 2/3 power range. Work the CG back and keep trimming in down trim until the model shows an amount of throttle induced climb that you can live with as you go from idle to full throttle.

Major Pain

Thanks BMatthews for advise except I'm a little leary of making the plane more unstable by moving CG back because it is almost unflyable as it is. Could you explain a little more? All in Twin Forum on RCU agree manual is wrong on balance point of 85mm from leading edge and most are flying anywhere from 95mm to 110mm back and having good results. Mine is on 95mm and should be in ballpark. Thanks for your help--------Revver Bro#164

jlsmith54

My Feedback: (6)

I have some information that might be helpful to anyone that flies a Dual Ace. My CG on the DA is 105 mm. The plane handles great at 105 mm. I have magnum 46 on mine. I had to add nose wt. at that setting. She flies beautiful.

Major Pain

Thanks jl, I guess I'm gonna give that a try I've run out of ideas, and that does sound like a good idea.-----------Revver Bro#164

Major Pain

Hey guys, its just that I'm concerned about flying a plane with the CG moved further back when it already flys like it is very tail heavy.---------Revver Bro#164

da Rock

Hey Major,
Do me a favor. Get a yardstick and measure your airplane for me.

half span of the wing and of the stab/elevator
root chord and tip chord of the wing and of the stab/elevator
sweep (if any) of the wing and stab
distance from LE of wing at root to stab at root.

Accurate to a quarter inch is good enough.

Major Pain

Here it is Rock: Each wing half is 31 3/4", total wingspan is 70". Wing root cord is 15", wing tip cord is 10 1/2", wing has no sweep in leading edge. Stab/elevator span is 26". Stab/elevator root cord is 7", stab/elevator tip cord is 5". Stab/elevator is swept back about 1", best I can measure. Distance from leading edge of wing to leading edge of stab/elevator is 31 3/4". Since information manual has no information does anyone know what incidence should be on this plane? Set wing,stab and motors to 0 degrees, I would think it would at least fly decent there. Thanks for any help. -----------Revver Bro#164

da Rock

OK, Major,
I just now spotted your 6:01pm post. I plugged the numbers into the geistware CG application. It uses the formulas that've been tried and true for years. Saves us the effort to do the math.

It shows the model should be safely stable with a CG from 3" to 4.37". That would be with a static margin of 20% to a static margin of 10%. I usually set a CG at a 15% static margin for my model's maiden flights and they all have flown great. I almost always wind up moving the CG back a bit but haven't ever wanted it farther back than the 10% static margin location.

The 15% that geistware computes would be a CG that's 3.75" back from the LE of the wing at the root.

Typing this has taken longer than it did to plug your numbers into the geistware app.

That app is at http://www.geistware.com/rcmodeling/cg_super_calc.htm

Major Pain

Thanks da Rock: Mine is set on 95mm or 3.75", so its not the balance thats causing the problem. I have flaprons set on my Futaba 8U on a dial on transmitter that can be turned down for flaprons or up for spoilerons, I will double check to see if dial might have got turned off center. Thanks----------------Revver Bro#164