I'm working on my Hunter build, and have a question regarding fully enclosed engine installations and jet pipes.

The kit comes with a simple single walled jet pipe, and I'm thinking of replacing it with a dual walled pipe, primarily to help keep the rear fuselage cool. The engine is fully enclosed within a sealed bypass, and I can't see how a dual walled pipe would work in this case. There is no airflow path to get bypass air into the rear fuselage for the ejector part of the dual wall pipe to extract. I'm assuming that the front face of the pipe fits inside the end of the bypass ducting to make a continuous flow path from the intake to the rear of the plane. Does both the inner and outer bypass path of the pipe fit inside the engine bypass?

The kit was also supplied with a spun aluminum bell-mouth, which I assume fits inside the rear of the bypass to protect the glass bypass from the heat.[]

I have seen a picture where some holes were cut into the contraction portion of the bypass, to spill some air into the rear fuselage. Is this standard?

Any advice on installing dual walled pipes on a bypass, including pictures would be appreciated.

Thanks

Paul