Sterling P-51 D Strange Trimming problem

[Phil Spillman]

We finally got a nice day without hurricane winds with some sunshine today and my wife agreed to go along flying with me! We do this as a safety precaution as well as a joint venture! My very old but flyable for fun P-51 has been with me since 1992 and generally flies well especially with the FP .20 swinging a 9 X 4 APC prop and running on muffler pressure. The odd thing about this model is that it chops around on inside maneuvers but not on outside maneuvers! The line length is approx 56" .015 cables. It will perform the entire PA pattern but with the choppiness  on the insides! Haven't twisted the flaps in either direction a yet but will pending any input received here! Please give me some of your thoughts on this matter!

Phil Spillman

[Mike Haverly]

If the up line is in the back then it could very well be a flexing push rod.

[Mike Haverly]

I just realized that where the up line is has nothing to do with it.  It is elevator horn location.  If it is on the bottom (normal) the pushrod can flex if it is flimsy and unsupported.

[Phil Spillman]

Thanks Mike, The pushrod is carbon fiber and rigid. The bell crank is of standard configuration ie the "up" line is in the rear!

I think that the flaps need tweked and I am going to try that! If that doesn't work I'll add a trim tab.

Phil Spillman   

[Dave_Trible]

We finally got a nice day without hurricane winds with some sunshine today and my wife agreed to go along flying with me! We do this as a safety precaution as well as a joint venture! My very old but flyable for fun P-51 has been with me since 1992 and generally flies well especially with the FP .20 swinging a 9 X 4 APC prop and running on muffler pressure. The odd thing about this model is that it chops around on inside maneuvers but not on outside maneuvers! The line length is approx 56" .015 cables. It will perform the entire PA pattern but with the choppiness  on the insides! Haven't twisted the flaps in either direction a yet but will pending any input received here! Please give me some of your thoughts on this matter!

Phil Spillman

Well I’m not sure what you mean about ‘chopping around’ but I’m betting the airplane is stalling on the insides.  I’ve seen a number of these fly over the years and built one myself many years ago and sold it after just a few test flights. As far as a stunter goes it has one fatal flaw- the wing is mounted way to far off the thrust line- very low and has very little extra lift/area.  I’m not even sure the kit was done accurately enough to get the wing centerline parallel with the thrust line.  The result is an airplane the turns easily inside (in this case too easily) and a struggle to turn outside.  I think it may be tail heavy and/or has a great amount of control travel that is allowing a little better outside but then stalling inside.  High speed stalls seem like riding a bucking horse when going around in the loop.  The nose rises and drops each time the wing goes to stall.  You may tamp the issue down some by moving your handle top line down reducing the throw in this direction.  This is what we refer to as ‘bias’ adjustment.  See if that helps.

Dave

[Phil Spillman]

Many Thanks Dave! I looked at the linkage this afternoon and you're quite right there is more than enough input at the control horn for the elevators! I'll take a little out to slow it down some as see what that does. It surely isn't a cmpetitive design but definitely is a nostalgic item for me! I never expected it to fly nearly as well as it does until I tried the FP .25's and .20's on it and its Ringmaster companion! These engines develop so much more power than the era specific engines of their day its unbelievable! They really make the wing work much better.

Phil Spillman