Is there a twist in fuselage?
- Thread starter louie
- Start date
Crash
GONE WEST
Nikiski Alaska
Louie
Louie, where did you hear there is a 17 degree twist built into a PA-18 fuselage? I have not heard this. My new fuselage shows 0 degrees at the front and 0 degrees at the rear. Why would there be twist built into it. Guys twist them when turning around at the end of a strip and dropping the tail wheel in a hole, but that's follwed by a lot of cussing. Crash
Louie, where did you hear there is a 17 degree twist built into a PA-18 fuselage? I have not heard this. My new fuselage shows 0 degrees at the front and 0 degrees at the rear. Why would there be twist built into it. Guys twist them when turning around at the end of a strip and dropping the tail wheel in a hole, but that's follwed by a lot of cussing. Crash
RYAN_WINGS
Registered User
Tucson, AZ
not aware of any twist, but the PA18 does have the top longeron bend down by about 1 and 7/8 of an inch over the last 29 and 7/8 of the top longeron total length.
I believe the original J3 has a straight top longeron.
Is this what you are thinking about?
I believe the original J3 has a straight top longeron.
Is this what you are thinking about?
Longwinglover
Registered User
Charlotte, NC
The original J-3 is the same as the Super Cub airframe. The lower longerons are straight all the way from the gear to the tailpost, the uppers bend down the last few feet.
The verticle fin should be offset (by physically twisting) such that the upper edge of the fin lines up with a string from the top of the tailpost to a point half way from the centerline of the fuselage to the left side of the fuselage along the rear edge of the skylight. If the verticle fin is in line with the fuselage centerline, you will constantly need right rudder in cruise flight to counteract torque.
When rebuilding your Cub remember to temporarily hang the rudder to help you correctly place the verticle fin. Otherwise you may get the fin too high or too low. Then the hinges won't line up!
To twist the verticle fin grasp it firmly at the upper corners and pull (or push) the forward corner in the correct direction. If, when you fly after rebuild, you find that you need more (or less) twist, you can fine tune by the same method.
John
The verticle fin should be offset (by physically twisting) such that the upper edge of the fin lines up with a string from the top of the tailpost to a point half way from the centerline of the fuselage to the left side of the fuselage along the rear edge of the skylight. If the verticle fin is in line with the fuselage centerline, you will constantly need right rudder in cruise flight to counteract torque.
When rebuilding your Cub remember to temporarily hang the rudder to help you correctly place the verticle fin. Otherwise you may get the fin too high or too low. Then the hinges won't line up!
To twist the verticle fin grasp it firmly at the upper corners and pull (or push) the forward corner in the correct direction. If, when you fly after rebuild, you find that you need more (or less) twist, you can fine tune by the same method.
John
