Jet Engines

[Black Hole]

Watching Guy Martin last night (he bodged a working jet engine out of a big turbo), I understand the principle of jet engines except for one rather important detail: why doesn't back-pressure from the combustion chamber oppose the incoming airflow?

 

[TimK2015]

Could it be that the path of least resistance is out the back of the engine?

 

[antipodean]

Could it be that the path of least resistance is out the back of the engine?

I think that is why they need an auxillary source of moving air to get the engine rotating and create a draft before adding fuel and ignition source. The air pushing in the front then pushes the combustion products out the back, where the path is easier.

 

[Black Hole]

I guess what you're saying is that so long as the shaft is rotating, there is a multiplication factor between the turbine and the compressor. Seems reasonable, but it's not obvious (at least, not to me!).