Piper down thrustline

[49clipper]

Anyone know why Piper put a negative 2 degree thrustline in the j3, SC, lines? I found about why they put a -4 degree incidence in the tail of the Vag, but why the engine.
Vag 4699H

[Pacerfgoe]

My guess is stability designed in for the masses.....with varied piloting abilities

[Pacer 24C]

Anyone know why Piper put a negative 2 degree thrustline in the j3, SC, lines? I found about why they put a -4 degree incidence in the tail of the Vag, but why the engine.
Vag 4699H

The Pacer / Tripacer is unique in a way- I checked my incidences trimmed for normal cruise and found "0" between the wing and stab - how does it keep the nose up? Down trustline - the crankshaft to wing relationship establishes the incidence for stability not the tail load as is conventional

[49clipper]

Pacer and Tripacer are different in that the stab is adjustable in flight. I understand why Howard Piper did the stab like they did. It was because the CAA made them build in some trim authority for a power off glide. It had none prior, althought they said it flew fine and passed the rest of the flight test regime. But the engine makes me wonder. My new motor mount has no side thrust build in either. I am adjusting that now. I see no measurements from the drawings on that. I know Steve had mentioned 2 degrees, but I cannot find that anywhere in the plans.
These old pipers, everyone I have measured is different in many ways.

[andya]

Anyone know why Piper put a negative 2 degree thrustline in the j3, SC, lines? I found about why they put a -4 degree incidence in the tail of the Vag, but why the engine.
Vag 4699H

would like to hear about the Vag tail wiht -4 deg incidence, if you could. I presume neg incidence would effectively provide more nose up moment

[49clipper]

would like to hear about the Vag tail wiht -4 deg incidence, if you could. I presume neg incidence would effectively provide more nose up moment

I got that -4 degrees from the plans, also from a letter I have from Howard Piper discussing why. The CAA back then would not sign off on the Vags test flight envelope due to it not having enough trim authority in a power off glide. So, they moved the stab down, increased the size of the trim tab, and added the spring on the up elevator. Fixed the problem, but most likely slowed the aircraft down about 5-10 mph. I would like to hear from others who have also measured their Vag. Mine has a - incidence on the wing root when the plumb bob is over the centerpunch in the crosstube. Piper says it should be 0 degrees incidence on the wing. thats why I say, they are all different.

[deandayton]

FWIW I was taught that many light planes have a negative thrust line so that the addition of power will help in stall recovery (or at least not negatively impact stall recovery).

[49clipper]

I think you may be right. They did try to build them as safe as possible for the average pilot.

Pacer24. That could be ture also. Anyway, I have mine set now, so on to the next hurdle.

Thanks for the replies.
Jim

[Steve Pierce]

Clopper, Pacer, Tripacer and 150 hp Pawnee have r degrees down and 2 degrees right built into the engine mount.