An interesting illustration of the power of the internet - there is no way I would have thought to examine the actual function of the Gilbert engine. Thank you.

That said, your comments prompted me to study three-port design. I believe, though I am ready to be set straight, there may not be as much blow-back of the fuel/air charge as you suggest. I have no data to back this up, other than the successful running of the engine and the notion that the inertia of the incoming charge itself may go some way towards resisting blow-back before the downward-traveling piston closes off that port. At any rate, it would appear this type of engine produces what power it has at lower RPMs than a reed or rotary valve engine of similar displacement. At some point the moving piston and the inertia of the air itself will achieve equilibrium.

Yes, the Gilbert .11 probably has only the power of a reed-valve .049 Cox, one of the ordinary Baby Bee versions instead of the hot-rod types. I am unsure as to why Gilbert settled for such a design when engine technology in the early 1960s was already well beyond the performance of the three-port design. The planes powered by these engines were fairly narrow chord, built for looks rather than performance, and heavy in their own right. I have had little trouble starting mine in the correct direction; though there have been a few reverse starts, stopping the engine dead is a simple matter of covering the intake vent with a finger.

The engine mount holes require drilling out, as the screw size a stock engine permits is inadequate for quick, safe mounting without liberal use of washers to spread out the load on the mounts. Also, some loctite seems to be in order for the exhaust stacks, whose single attachment screw seems to want to walk itself out during a run. I discovered this during the test phase - perhaps propeller balancing is in order to reduce the vibration? And someone, somewhere, suggested a bit of steel wool stuffed gently into the exhaust stacks might dampen the noise a bit, but I hesitate to mess with them - backpressure can only reduce the output of this engine, to my mind.

I am betting that a 36 inch wingspan combined with a seven inch chord should provide the lift to counter the weight of the engine, tank and fuel. The result will not be fast, but it will perform aerobatics and represent for a generation of flyers who are passing away with every day.

Thoughts?

Steve