Tri-Pacer Trim and engine thrust line angle question

[Subsonic]

I'm lucky to have hangar neighbors with another Tri-Pacer like mine. Mine is stock 1956 PA-22 150, and their partner owned TP is a '60 PA-22 160. Nice guys. I've been up with one of them twice now in their plane and noticed our trim handle "neutral points" are much different. Mine is pretty far forward in the slot, maybe 3/4" back from the front, while their neutral point is more than half-way back in the slot, maybe 2" further back than mine. I also noticed their oil cooler sits higher in the opening window under the prop than mine. Upon comment, one of them said the conical rubber mounts at the crankcase can become elongated vertically with wear, and the engine will sag downward over time, lowering the oil cooler in the opening, like mine. If my thrust line is now vectored with the spinner a bit down from the design standard as new, the relationship of that thrust line to wing chord will be upset and may explain why my neutral trim handle point is further forward...That was supposed to be a question. Thanks for your consideration and comments on this topic.

[Gilbert Pierce]

You may be right and on the other hand the relationship between the actual trim and the indicator is some arbitrary.
The trim indicator is connected to the stabilizer by a thin piano wire that passes thru a hole in the indicator and is twisted to secure it.
Set both stabilizers at their mid points with a digital level or machinist protractor and then compare the location of the indicator.

You will probably find the difference is as you suggested; engine thrust line.
Using the digital level you could compare their wing to engine angle compared to yours. Use the bottom of the butt rib and the crankcase split line for the comparison angle measurements.

[rocket]

Hmmm, interesting.
I Find that optamum takeoff and landing trim to be the same and my walk around note that the LE point of the elevator is down about 2 inches. I havnt looked at the trim indacator in years and I count turns keeping my head outside the plane. It's so automatic that the number of turns escapes me until I'm in the plane and I trim for pitch. Again by feel: pitch for airspeed, power for rate of decent.
In another life I designed, built, and flew 1/2A free flight. Doesnt take much to rekit one. Good way to learn why piper angled the planes the way they did. Mess with any of that majik and you can run out of trim fast.

ive added shims between the lower aft rubber and mount flange to get the nose back up accordingly. They must be making the mounts out of the wrong rubber compound: too soft to begin with then brittle too soon...

[Subsonic]

Thanks Gilbert and Rocket. So, If I want to go ahead and just change the rubber mounts, what name brand, or who might you recommended as selling the best ones made? Then again, if it's Chinese rubber, I know from restoring old motorcycles with Chinese repop rubber that it's mostly crap. Original English or Spanish rubber (seals, fork wipers, boots and stuff) from the '60's and early 70's is still good if kept out of harsh sunlight. If not, try to find original good ones because the C-knockoff stuff lasts about 2 years...Rocket, how thick were your shims?

[Dennis Savarese]

I'm wondering if it is possible for Lycoming, Lord or another company to obtain a PMA or STC for engine mount rubbers which are manufactured in China? Anyone know?

[Steve Pierce]

You can measure the angle of the engine by putting the level across the rocker covers. Measure the angles of the stabilizer vs the bottom of the wing for comparrison. Bottom line is they all fly a little different and it is hard to put your finger on it.

[rocket]

Sub,
i miss-remembered this (I sound like a back peddling politition)
we instaled four spacers .100" I'm thinking. We were battling a muffler too close to the firewall if I recall correctly.
Monger bolts also

rocket

[Driskells]

I recently removed the prop off a 1955 PA22-135 Tripacer and found that the gear starter ring was sitting low in the front engine cowling around the 5 o'clock position. And in fact the oil cooler is starting to rub the against the front cowling. The engine bushing were replaced about 6 months ago and set to 1.84". From what I have read on this site and others is that it engine should be 4 degrees down and 2 degrees to the right. I have looked over the engine mount assembly for bends and other defects but, did not find any.
So my first question is what are the best practices to measure these angles and from where? Which Piper drawings should I refer to as a guide? Could the front cowling be used as a rough estimate to get to those angles? And once I have those angles what are the best ways to correct. And if shims / spacers are used what are the max allowed to correct the angles?
IMG_8109.jpg
Thanks
Stephen

[Steve Pierce]

Yes the engine is 4 degrees down and 2 degrees right. This is in the engine mount drawing. Firewall should be 90 degrees to centerline of aircraft. Lay a level across the rocker covers to check engine angle. Can you loosen cowling screw and adjust the angle of cowling? Where did you get the engine mount bushings and who was the manufacturer. Had issues with non-Lycoming bushings years ago and have used factory Lycoming ever since with no issues.

[Driskells]

So firewall is 90 degrees vertical and horizontal to aircraft center line. Then using level to check the vertical 4 degrees down and some type of right angle protractor to check the horizontal 2 degrees right. Yes, I have tried to adjust the cowling and each time the top cowl will not line properly with lower cowling when I do. The bushings are Lycoming part #71032 purchased from Aircraft Specialties Services. Where is the best place to get the engine mount drawing Univar, SWPC or other source? So I assume if found out of tolerance and no damage or out of adjustment is found what are some ways to correct this issue?
Thank for the reply.