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Engine offset

Flaugherpa12

Registered User
I recently noticed on a PA 22/20 that the engine was offsite approximately 2 inches to the right when measuring from the leading edge of the wing to the centerline of the prop in the horizontal position.
My question is what is that same offsite for a PA12 with an 0320?
Is the prop in perpendicular to leading edge of the wing and normal to the center line of the fuselage?
Or does this offsite change/increase when you increase horsepower due to P factor?


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Zero. It’s perpendicular to the wing. If you a using the PA-22 Crossover exhaust called out in the Kennmore 150 Stc, it will need to be modified on one side so it doesn’t contact the mount. That’s not in the instructions.
 
Thanks KJC,
That is what I was hoping, as my 12 measures very close to that.
Kind Regards
Jeff


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KJC,
I have a follow up question, You mentioned perpendicular to the wing, I’ve got that,

With the airplane level, I’ve got the plum bob leveled to the punch mark just inside the door, if I put a digital level on the prop flange vertical centerline, should it also be perpendicular to the thrust line. Mine is measuring about 5 degrees nose down.
Should it be 90 degrees to the thrust line? I’m afraid mine might be bent?


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Lol, it's not bent. That's normal on 12/18's.
But if you want to look into the benefits of a zero thrust mount, it has been discussed on here up down and sideways, mostly on 18's. The knowledge base on 12's with zero thrust, is alot less available.
The original Cubs did have zero thrust mounts. Till the PA11, and if you look closely; there are more than a few 11's, that are real performer's are running a J3 mount.
Good Luck
E

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Thanks E,
That’s good to hear!
Thanks for sharing
I’ve been reading some of the threads on zero thrust mounts you mentioned, but didn’t know the PA12 had the engine tilted down. Someone mentioned it was done to see over the nose better.
It’s great to have a group like this to learn from.
Appreciate you

Jeff


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E,
I had a PA11 for 10 years with a O235-L2C 118hp that was an amazing performer..
Not sure if the Dynafocal engine mount designed was at zero thrust line in both directions.



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TurboBeaver is correct, it should be down a few degrees. I’d forget about the plum bob method and use the firewall. A perpendicular firewall also makes it level. When doing this, you may want to check the engine mount bushings, especially the bottom inners and top outers. The compress over time and cause the engine to sag. The oil cooler then begins to rub on the cowling. There is a proper compression distance on those bushings as well. I can’t remember the number........? Maybe someone here knows. 1.87” maybe....?
 
.........but didn’t know the PA12 had the engine tilted down. Someone mentioned it was done to see over the nose better.
This is just uneducated BS. Many airplanes have down thrust or offset to the side thrust built it on purpose by the original manufacturer. There are many reasons for which a book could be written.
 
Thanks E,
That’s good to hear!
Thanks for sharing
I’ve been reading some of the threads on zero thrust mounts you mentioned, but didn’t know the PA12 had the engine tilted down. Someone mentioned it was done to see over the nose better.
It’s great to have a group like this to learn from.
Appreciate you

Jeff


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Jeff, Ya have got some good responses that gives the reasons for the offsets. We as one of the (Ol Cratchty Farts tag line here sez) are all ignorant to things we don’t know about.
If ya stay around long enough you’ll hear a heaping helping of ‘uneducated BS’ from folk here who are trying their very best to help ya as they uneducatedly slap you around while doing it!
 
Thanks E,
That’s good to hear!
Thanks for sharing
I’ve been reading some of the threads on zero thrust mounts you mentioned, but didn’t know the PA12 had the engine tilted down. Someone mentioned it was done to see over the nose better.
It’s great to have a group like this to learn from.
Appreciate you

Jeff


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I THINK the 12, 11 and 18 have the 4deg. downthrust angle to counteract pitching up with power application. Better visibility is a happy by-product, but have my doubts as to that being the driving force behind the engineering. Or I could be completely full of it. Be quiet Gordon...
 
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PA16, 20, 22 and 25-150 have 2 degree to the right and 4 degrees down angle on the engine mount. PA12 and PA18 are 4 degrees down and no left or right.
 
Ok guys after triple checking all aspects of rigging, and making adjustments accordingly, I flew Piper this morning, PA-12 and she flew great, except for I have to hold a touch of right rudder to center the ball. With that rudder input she flys perfectly straight at cruise.
Note, I had bent the leading top edge of the vertical stabilizer to the left as suggested and it helped the ball being center by half of what it was, but I still need to go a bit more. (160hp)

My first attempt of bending the stabilizer was by hand and I’m just starting to get/see wrinkles in the fabric.

Does anyone have pictures or a detailed description of the best technique for bending it over more.
Thanks in advance for the support!

Jeff
PS. I took a video with the drone this morning and will try to post that for reference.



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..Note, I had bent the leading top edge of the vertical stabilizer to the left as suggested and it helped the ball being center by half of what it was, but I still need to go a bit more. (160hp)
Jeff
Bear in mind that the more power you are pulling, the more right rudder is required. If you were to cruise at a higher power setting the ball should move to the right.
 
Last edited:
Bear in mind that the more power you are pulling, the more right rudder is required. If you were to cruise at a lower power setting the ball should move to the right.
You sure about that last part? Maybe I'm mis-reading, but all else equal I think reducing cruise power would reduce right rudder requirement and shift the ball left.
 
Ok guys after triple checking all aspects of rigging, and making adjustments accordingly, I flew Piper this morning, PA-12 and she flew great, except for I have to hold a touch of right rudder to center the ball. With that rudder input she flys perfectly straight at cruise.
Note, I had bent the leading top edge of the vertical stabilizer to the left as suggested and it helped the ball being center by half of what it was, but I still need to go a bit more. (160hp)

My first attempt of bending the stabilizer was by hand and I’m just starting to get/see wrinkles in the fabric.

Does anyone have pictures or a detailed description of the best technique for bending it over more.
Thanks in advance for the support!

Jeff
PS. I took a video with the drone this morning and will try to post that for reference.



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I take the palm of my hand on the leading edge of the fin and my other palm on the rudder post and push. There is spring back so you have to go a little past. It doesn't usually take much. This is why I offset the fin prior to cover.
 
I take the palm of my hand on the leading edge of the fin and my other palm on the rudder post and push. There is spring back so you have to go a little past. It doesn't usually take much. This is why I offset the fin prior to cover.

Thanks for the feedback Steve,
I really appreciate the support you guys!!!
I’m headed up to the hanger this morning to give it a go.
Will keep you all posted.

Jeff



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One mechanic that adjusted mine took two boards and clamped them front and back with c-clamps over the fin's top. He may have removed the rudder before that but don't recall. There was a gentle twist until the fabric just slightly loosened then he relaxed. I flew at normal cruise to test and was satisfied. On floats at a slower cruise speed it took water rudder offset to correct. It was a great PA-18A but had some bumps along the way.

Gary
 
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