Appendix 2 - Firewall Forward

Motor Mount

The motor mount determines the location of the eingine and its distance from the firewall. since the Super2 was designed for a range of engines and engine weights, the motor mounts need to vary to account for the different required distances fromthe firewall. the Corvair is at the lighter end of the engine spectrum and the Lycomming O-320 is at the other. Since the Corvair is one of the lighter engines, it will need to be spaced further from the firewall to maintail the correct C.G.

The method I have used to determine the correct motor mount configurations is to fabricate a motor mount from mild steel (cheap and easy to work with) as a prototype. Once the aircraft is built and an accurate weight and balance spread sheet can be generated, the engine placement may be adjusted accordingly. It is my hope that several motor mount designs will ultimately be presented here reflecting the experience of builders.

I am going to model and do all of the firewall forward work on an engine stand so I can get everything worked out so I do not have to worry about messing up my real firewall till I confirm everything fits.  I have cut a mock firewall from ½” plywood and will fabricate a motor mount from mild steel, a non flight worthy prototype and mount them on an engine stand.

CAUTION:  The dimensions I have currently posted on this page are preliminary and have not been confirmed as of this writing.  I will remove this notice once all the dimensions are worked out.

I built my Corvair engine mount per the Flycorvair conversion manual using the recommended tube sizes and thicknesses.  There are only a few dimensions that define a custom motor mount that are required beyond the information contained there manual.  These include the firewall motor mount hole locations (located on the firewall drawing), the engine offset (0 degrees up, 0 degrees to the side), the distance of the top of the tray from the lower firewall motor mount hole center line, and the distance from the rear engine mount bolt centers to the firewall.

I used stainless steel washers as I was unable to locate unplated steel washers locally ( will sell them to you) as I did not want to use zinc plated washers.   Welding a zinc plated washer commonly found at the corner hardware store release toxic fumes—bad news.

There is a steel structure behind the firewall that transfers the engine load to the stand, you can not rely on the plywood to do it.

Tubing and washers required for Engine Tray



Stainless Washer and mild steel tube for engine mount


Welded Engine Tray

Motor mount on engine stand ready for the Corvair