Knife edge with GWS P-51

[Peter Khor]

Well if no answer here I might re-post to park flyer forum (seems to be not much traffic here). Other than setting up a pitch/roll coupling mixer to help out with knife edge (haven't really needed it yet), my problem is this - roll left, full right rudder, it will knife edge quite nicely, nose it up about 15 degrees or more - BUT the problem is that only a couple of feet out into knife edge, the plane starts to steadily loose altitude. I'm running an 8 cell pack (2/3 A, so it's a little heavy). I am thinking either:

* AOA of the nose too high,
* prop stalls out
* We need more power, Scotty!

Suggestions? (I've only been able to maintain knife edge for a couple of seconds, not enough time to check out pitch/roll coupling behavior)

[flyfalcons]

Try these three things:
1. move the CG back some.
2. Use a more powerful motor.
3. Add a more powerful rudder servo.

These are the things that I go through when trying to get my bigger planes to knife a little better.

[Peter Khor]

Thanks for the tips, I will try it out this weekend (other than putting in a bigger power plant). The CG's already at recommended and it seems a little tail heavy, but I'll see if I can get away with moving it back futher. As for a more powerfull rudder servo, I don't think I'm having a problem with aerodynamic forces getting in the way.

Then again, maybe more practice ;-)

[Troy]

As Tim Allen always said best,
"MORE POWER!"
If it's just sliding out as you get into knife edge, you've got a power issue. You've got the rudder authority, you're keeping the line, the altitude drops because the plane slows down. P-51's don't do slow knife edges unless they have massive amounts of huevos under the hood. ;)

[alvinm]

what prop and gearing are you using,I have done extensive research(actually blowing money!)on different combos.

[Bill Glover]

The P-51 has little fus. side area ahead of the CG, so would need a lot of power & speed to hold knife-edge ... almost certainly impossible with the stock setup.

One easy thing to try though is a bit LESS rudder. You did ask about AOA, and yes, you can sometimes 'stall' the fus. - significant if you are relying on lift from that as opposed to raw thrust (the upward component of it) to maintain height.

Good luck, but frankly I think you're onto a loser here - sorry!