Wondering if anyone has any good pictures and can explain the system to me. As I've been working on my Bearhawk horizontal stab mounts I've been thinking a PA-20 trim system might not be too difficult to install. There looks to be some cables and springs and I can't figure out what they are for; I'd like to get a good understanding of the jack screw and how it mounts before I make a final decision.

These are horrible pictures and may totally be of no use to you, but I'm sitting here and have the pictures so here you go.

This is of the Clipper (PA-16), so not the Pacer but with some similarities:




Love your build thread by the way.

CW

Get in touch with m. moyle. He's rebuilding a pacer from the tubes up.

From a friend who has built several Pipers: If you use this type of trim system use the "double row pulley" setup.

My understanding is this double pulley system makes two wraps of the cable on each end which minimizes the slippage of the cable.

http://javroninc.com/index.cfm/pageid/46

Thanks for the pics CW, they do help. I thought about getting a hold of Mark M but I'm not to the point I could ask any specific questions. I'll try to find some time tomorrow to pull up some pics of the things I can't figure out and ask some questions.

Av8r3400's suggestion was a good one. The jack moves the entire horizontal stabilizer to change its angle of incidence. I have flow many Pipers with trim cables that slipped. It was not a big issue with me, as I stayed low. I just ground adjusted the jack until I got it right for cruise and used hand pressure on the stick for the short time of climb and descent.

I just had a conversation with Bob about fitting a trimmable H-stab on the Bearhawk and I don't think I'm going to do it. He did fly the prototype with no front strut on the H-stab for ~10hrs but feels I'd need to increase the size of the leading edge tub if I wanted to run without the strut permanently. Just too many changes and where I already have a built H-stab I don't want to cut into it.

Sorry I wasted ya'lls time.

The jack screw trim system is pretty nice. Is it a ton of work to cut and grind the old tube off and replace it with a stiffer tube rather than to fab, hinge, cover, and rig a tab? Used rigs on eBay are less than a couple hundred end to end, and new ones are about 450 for the entire assembly (double sheaves).

Very cool project...making me rethink what I want as a project. A fellow about 2 hours from here has a BH project going too.

I ordered my empannage from Avipro so they are done; painted, ready to have the trim parts installed and covered. I can't cut apart something I paid for. If there was a significant benefit it would be worth the weeks of rework and design but I don't think the added value is there. There might a a couple MPH to gain and some stability with an aft CG if a jack screw trim was used but I plan to run big tires so the speed won't be there and we can increase the stability with the standard trim system by reducing the servo action of the trim tabs.

If Bob had told me I could run without the front H-stab strut I'd probly install a jack strut trim. I think it would only improve an already great aircraft but from where I'm at it is just too much of a step back in the progression of my project.

Bob flew his Bearhawk prototype without the front horizontal stabilizer struts. Charlie Center of crosswind STOL has a modification that adds the stabilizer struts to the jack screw set up on pipers. You'll need a continuous cable if you choose to go with a jack screw set up. http://javronaviation.com manufactures jack screw assemblies and that continuous cable...should be able to make one to your specifications. You'll also need different ends...ones that swivel on the tail wires. If you need pics of the trim cable system...let me know...I switched to the double groove sheave system...the single groove slipped or became non-op when below freezing. Don't think the jack screw modification would be difficult...the time consuming part...is adding the pulleys for the continuos cable and the single strand trim indicator wire/cable.
Mark