ORIGINAL: 757jonp
I've been flying an old Goldberg Obsession 120 weighing near 14 lbs powered by a DLE 20 and controlled by a 9Cap for about a year now. Overall I've been very impressed with the performance of this engine. Other than not having unlimited vertical or the ability to hover at will
Put that DLE20 on an AW PROX260 "Freestyle" and at 7 lbs you can hover easily & pull-outs are like a missile.
Hovering is all about the thrust to weight ratio......but you knew that.
I've tried tuning it out, played with the geometry of the linkage, applied expo, modified the throttle curve, etc, etc to no avail, the RPM surge, followed by a slow return to idle is still there.
ahicks gave a very good overview of what's happening.
A little more about my previously mentioned 2-stage idle off a tx switch;
The pro fliers we see at events like Joe Nall, Tuscon Areobatic Shootout, FG Huckfest's, and other events, often fly such extreme maneuvers that they found sometimes the engine could die, or nearly so. Since the normal eng idle was too low & really meaningless while in flight, they came up with a 2-stage idle off a tx switch.
When taxing around, during takeoff, and on final ready to land, a lower idle setting is preferred. On these DLE20's I set mine at around abouts 1700-1800 rpm for that portion. For in flight/flying I set mine slightly above around abouts 2000-2200 rpm. Some adjusting to suit YOUR preferences may be needed. But the end result is the lower switch/idle setting forces the throttle to come down below the odd #4 ign curve issue, and the 2-stage idle off a tx switches just plain eliminates the odd ign curve issue. It still exists, but is no longer any concern.