I said in my last post “
A fully enclosed installation such as the SE5a isn’t the place to bed-in a new engine “. Of course it isn’t ideal for any air-cooled engine new or old so extra care has to be taken to prevent over heating; the full sized was water-cooled. To explain how I hope I’ve overcome the problem I’ve used some old photos as well as a couple of new ones.
The SE5a has some positive points; there is a hole directly in front of the cylinder head for cooling air to enter.
And there is a large opening in the fuselage behind the engine for heated air to escape.
However, things are not as straightforward as they seem; hot air wants to rise but the exit hole is in the bottom of the fuselage. Once the model is moving forwards the air flowing over the hole should produce a venturi effect and suck the hot air out, but this is where the SE5a designers throw another spanner in the works!
Below the engine shaft there is an even bigger air entry hole, air entering here will not help with the cooling but will have the effect of “pressurising” the bottom half of the engine compartment and restricting the outflow of hot air.
The easiest solution would be to mount the engine inverted but because of the position of the engine shaft this would mean either a much larger model or the cylinder head sticking out the bottom of the fuselage, so this is a non-starter.
The engine plate has a hole corresponding to the one in the fuselage, so the hot air can transfer to the bottom half of the engine compartment.
A template, this is where you’re glad you paid attention in all those geometry lessons, is drawn and stuck to litho plate.
When cut out and bent up it produces an air scoop that forces air entering below the engine shaft upwards into the top half of the engine compartment where it can help to cool the engine.
Also with little or no pressurising of the bottom half of the engine compartment the venturi effect can work and suck out the hot air; a win / win situation!
Linear Mode
