Rudder Trim

[Bryan Cotton]

You can't take a skin from (say a 1965 built) 150 and fit it to another. If nothing else - none of the rivet holes will REMOTELY line up. And the skins will often not fit for curvature. Hence when repairing - you have to start with a new skin and make it fit. Or have a whole component assembly from the junk yard with a chance the attachment points will line up.

I rebuilt a 1946 Cessna C140 and was amazed at how well parts from one would fit another. I think they had good tooling.

My hand-built (from CNC laser cut parts) Waiex ended up pretty straight and true.

Igor Sikorsky said "If you build an airplane straight, it will fly straight. If you build it crooked, it will fly crooked."

[GraemeSmith]

I rebuilt a 1946 Cessna C140 and was amazed at how well parts from one would fit another. I think they had good tooling.

Course you did! :-) And I'm not being fresh. I suspect the immediate post war planes were much better built. Not that the period in the '60's were not well built - but they were cranking them out. I can't tell you the number of those where stuff just doesn't fit well between planes.

Igor Sikorsky said "If you build an airplane straight, it will fly straight. If you build it crooked, it will fly crooked."

THAT THERE is a good summary of what I've been droning on about!! :-)

[Bryan Cotton]

Graeme, I believe you that the C150/2 series is not the same as the C140. As I said I was really surprised how well parts fit. I did remake a lot of parts from scratch Sometimes that is just a lot easier and ends up better in the end.

[GraemeSmith]

I photographed this today.

Legacy Sonex
200lb pilot left seat
20lb tools etc right side.

So about a 180lb moment in the center of the left seat.

My "aileron trim bungee" pulls the stick this amount to the right.

Which applies this amount of aileron in straight and level flight at 95KIAS

Sorry - didn't get out while in flight with the protractor to measure the angle. Left the parachute in the car today.......

[Skippydiesel]

Latest -

Reduced my rudder trim to 100 x 30mm and lowered my left flap 1/2 turn. Good result! aircraft now straight & level in cruise flight. May attempt to minimise size of rudder trim tab or just leave as is.

Next big push(after test flight schedule completed) is to come up with a better radiator/oil cooler locations, which will mean a change in cowling shape.

[Onex107]

Latest -

Reduced my rudder trim to 100 x 30mm and lowered my left flap 1/2 turn. Good result! aircraft now straight & level in cruise flight. May attempt to minimise size of rudder trim tab or just leave as is.

Next big push(after test flight schedule completed) is to come up with a better radiator/oil cooler locations, which will mean a change in cowling shape.

I found that by adding gap seals to the rudder and elevator it straightened my Onex out without trim tabs.
Onex107

[pfhoeycfi]

Over the years and a bunch of aircraft I have used a simple method to determine the size of trim tabs. A length of a common soda straw is taped to the trailing edge of the surface on the side you want to deflect. Make an educated guess as to the length,(say 8 to 6") and test fly. trim the length to adjust. Once you've got it right, then make an aluminum tab to match.

I tried that this morning and it worked well. I will make a small tab based on the straw dimensions.

[Skippydiesel]

Latest -

Reduced my rudder trim to 100 x 30mm and lowered my left flap 1/2 turn. Good result! aircraft now straight & level in cruise flight. May attempt to minimise size of rudder trim tab or just leave as is.

Next big push(after test flight schedule completed) is to come up with a better radiator/oil cooler locations, which will mean a change in cowling shape.

I found that by adding gap seals to the rudder and elevator it straightened my Onex out without trim tabs.
Onex107