Originally Posted by
Lifer
What did you do that improved it so much?
Reducing weight by 10% was an improvement, but not quite as much as I would have thought. However, where I really went WRONG was my initial prop choice... a Mejzlik 29x10S. This prop was wonderful when the DA120 was on the nose of a slow, draggy, LONG, 146" span Hempel Decathlon, but a disaster on a fast, short-coupled, tiny tail-feathered Gee Bee. The gyroscopic precession effects of that huge prop were creating havoc with directional stability as the reaction to pitch and yaw corrections were directionally 90 degrees ahead of the directional change. In flight, the airplane felt UNTRIMMABLE - and it WAS
Switching to a Mejzlik 26x14TH reduced the GP affects by a factor of 10. Combined with some throttle / rudder and aileron / rudder mixing, the airplane is MUCH-improved.
Although it should not be necessary to mix rudder with aileron, I am convinced that engine dome right thrust is excessive for a DA120 and so the airplane is fighting another dynamic that can be compensated for with rudder, but only corrected by reducing engine right thrust. I CAN do this, but then of course my prop shaft no longer perfectly aligns with the front of the dummy radial... .and WHAT is more important? A good LOOKING Gee Bee or a good FLYING Gee Bee?
Of course, the BEST thing to do - to get both - is simply replace the DA120 with an Evo 7 (like Hannes) and completely re-re-re-do ALL my internal modifications for the resultant CG shift... then I can have looks, sound, AND performance!
I suppose, however, to truly LOVE this plane, one must have a personality similar to Delmar's.... like Delmar, "I get bored EASILY and have to get in and MIX IT UP!" Which is why I have flown this plane with: DA100, DA120, DA150 and 3W157CS; CGs from 66mm to 80mm from the leading edge; Props of every size; two elevator servos, one elevator servo, with and w/o a gryo; long gear, short gear; 31 pounds up to 36 pounds; ... and I cannot say with certainly that I have in fact arrived at PERFECTION... perhaps that's a good thing, as perfection can be BORING
