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

Converting to a D has NOTHING to do with the firewall!! It’s the skin that covers the cowl tank. It must be stainless. It also has nothing to do with the gas tank. You must:

Put a stainless steel skin over the gas tank

Make sure the orifices in the MLG are correct

Limit elevator up trsvel to 9 degrees

Have the ¾” trim tab

I believe these are required for the 1320 STC with the possible exception of the stainless steel skin.

Surely somebody must remember what to do. As far as I know an approved 337 is all it takes. Many C models were converted to D models to get that extra 140 pounds! A lot of people bought Ercoupes that were registered as 415C models and later got the FAA CD and were shocked to find the 337 that converted it to a 415D! At the time that meant a sport pilot couldn’t fly it (no longer the case).

I'm half way through the 1400 pound increase. I have the 337 approved but so far i can't figure out how to change the designation with faa. I contacted a dar that I've used previously and he said he needed to research it. If you know how that step is completed, I would live to know

As I understand it, There is a certification requirement that the firewall not be aluminum. During certification, there were numerous modifications, one being the larger cowling that extended over the gas tank with only an aluminum sheet separating the passenger compartment from the engine. Nobody thought about how that compromised the "firewall" separation. The inclusion of the steel sheet in the STC is to correct that oversight.

i am curious to understand how changing the stainnless steel cowl cover affect the capacity of the ercoup to carry more weight

Sorry I'm so late responding! Why buy the 1320 STC when you can just upgrade your coupe to a D model and have a gross weight of 1400? MOSAIC lets you fly it! You get 80 more pounds and the only difference in requirements between the STC and the D model conversion is the stainless steel cowl cover!

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!"