Hatz Biplane Association

Several months ago I contacted Jeff at Makelan regarding the engine mount shown in the CB-1 plans sheet. He stated they had used that plan to fabricate engine mounts without incident. Which is good news. I too fabricated the same engine mount being exceptionally careful regarding how the joints align and fit. After completing the mount I began to wonder if it was going to be strong enough based on what I've seen on certificated aircraft.

Watching a Lycoming or Continental start up and or shut down with the cowling off I can see there is quite a bit of vibration. G-loads imposed during flight added to my concern regarding strength. I've looked at a lot of certified engine mounts and see most if not all have reinforcements welded into the tubing structure. Sometimes it is at the tubing cluster where the mount bolts to the airframe, sometimes where tubes intersect a doubler is welded over the junction. As of now, my engine mount is exactly to plan and does not have any welded in reinforcements. Should there be reinforcements and if so, where and what thickness of metal. I want it strong but don't want to add unnecessary weight.

Attached is a photo of my engine mount (Lycoming O-320-E2D) and locations that may need reinforcement.

I don't know what reinforcement by the fuselage attach you're referring to. I have seen flat strapping attached between the tubes at that point but that's for conical type mounts (non-dynofocal) to keep engine mount alinement. I have seen cracking on the lower cluster where the four tubes intersect, most common on early Lycoming powered Cessna 172's, finger strapping the cluster took care of the problem.

Several months ago I cut a piece of .040" 4130 plate to make a reinforcement at the four tube intersection. Never got around to welding it on. With your observations, Al, I'll make a point to follow through. Thank for the reply.