I'm having a total blast with my PBF, but something's been bugging me about it. In a vertical hover, it wants to start falling over backwards. If I don't catch it with elevator IMMEDIATELY, nothing I do will save it. Full power and full down elevator have no effect, and it comes straight down. I'm using an OS 25 FX, and have 2" of throw. It balances at 5-3/8" back from the LE.

Is this a common problem, and what can I change to fix it?

Thanks,
John

aerobat66,
it is a common problem...i had to name mine
GEO EXPLORER i dorked it so many times from that attitude. you do have to catch it right now with the elevator to prevent it.you just sort of get use to it after a while and make the correction with out thinking about it. also where is your cg?should be at about 5 3/4 " back from le or even 6".
if your falling over on its back and your more than one or two mistakes high you should be able to fly out inverted with full power.

Exactly what Hacker said. Your CG is too far forward. Even then, they still hover best at a slight angle.

I agree. Your CG should be at 6.0" back to make it hover better. You'll still need to add some down elevator as the PBF gets vertical, but not as much as with your current CG. And even then, a PBF is difficult to maintain a vertical hover.

If you want a more stable plane for true vertical hovering, try a QHOR, or a PQHOR.

I agree; get a Qhor. Ive also heard of guys developing some "un-natural" recovery techniques from flying their PBF's too much. Some of those habits dont all translate over to well for more "conventional" models.

Adam