Ercoupe 415-C 9CF Baggage Compartement STC and 1320lb Gross Weight STC

That's pretty much how mine was before the larger tab. "Cruise" (nose down) trim in the 'coupe is basically "no trim" since the highest the tab goes is level with the elevator. But "take off/landing" (nose up) setting will be where you really notice it, because when the larger trim tab deflects downward its a LOT more effective.

At 105-110 mph cruise, I have the trim lever somewhat forward of center, and for 75 mph in the pattern it's slightly after of center.

But that's not a good way to compare planes because there's quite a bit of play in the trim wire and sheath, and your trim wire ends won't be set the same as mine.

When I replicate my trim lever settings on the ground, in cruise trim my tab is deflected down very slightly... perhaps 1-2 degrees, In landing trim its deflected down maybe 5-8 degrees. There's plenty more nose-up trim that I'm not using... And that wasn't true before the longer tab. 

Seriously, go for the new tab.  It's inexpensive, non-invasive, and I can specifically remember my first flight with it thinking "oh nice it actually worked!"

 

Thanks Brooks for that clarification. As it stands now my trim tab needs to be pretty far nose up to work, its really only that last inch of swing aft where the trim is usable, any further forward then its too much nose down trim. I wonder if this new trim tab install would make that better or worse.

The trim tab upgrade is a piece of cake.

The existing trim tab (really just a long piece of piano hinge) stays right where it is, you don't even need to disconnect the cable.

The new trim tab is just a long aluminum strip that gets riveted to the existing tab to extend it. You just need a drill and a rivet squeezer. I got a used one from Vernon, clamped it to the existing tab (which becomes the hinge), match drilled the existing holes, and riveted it on.

The new trim tab is so much more effective that I now only use about one inch of "throw" in the center of the trim control. I feel better about having a lot more excess trim authority - it would be much more feasible now to land the plane if I somehow lost an elevator cable.

I can get you some photos of the new tab if you would like them. If you end up buying the Univair version, I'm not sure it's pre drilled but again, no biggie. The instructions are probably (but don't take this as gospel) something like "drill a rivet hole every 1.5 inches" because it really is a simple upgrade. 

The below is from the Ercoupe Tech Note that covers elevator trim tabs. I can only find in it that if you have a C85 then you go to the 1 3/8" trim tab. Else if you have the C75 it is the 3/4" trim tab. Mine sticks out a little bit from the elevator trailing edge so I'll have to measure mine. I'll defer to Ronald or Brooks.

Elevator Tech Note:
dyzz9obi78pm5.cloudfront.net/app/image/i...rcoupe-tech-note.pdf

Thank you guys for the feedback and suggestions, It looks like a good way forward it to see if Vernon has a pre-made cargo compartment i can install to save some time.
To answer your question Ronald, converting to a 415-D seemed like more work than it was worth. 
Allong with the weight increase stc and baggage compartment, I am also installing a earth-X battery so by the end of these upgrades my useful load should be around 450lbs. 
I didnt see any specific requirments to limit the elevator travel for the 1320# stc either and I am feeling like I am missing something 

Brooks, thank you for the detailed post! This is great and really makes this project feel more doable. I hope that people in the future with similar questions see your post. 

Additional question, is there a general guide on replacing the narrow trim tab with the 1 3/8" tab?  
 

After reading the description of required modifications for the 1320 STC (Alpha Aviation), I don't see any requirement to adjust the elevator travel. It appears you keep the 13 degree up limit of the 415C. This STC only existed because of the Light Sport eligibility weight limit of 1320#. Due to recent changes, that limit is now much higher. Have you considered just converting to a 415D and getting the 1400# limit? (that does require a 9 degree up elevator limit).