Reingestion!
Hello fellow rotorheads;
I have a question about engine placement on helicopters. Recent studies i have been doing resulted in my finding of the following problem:
At Ng above 85% when hovering IGE with a strong tailwind the exhaust gases deflected to the engine intake may be recycled in the engine resulting in a partial stall of the axial compressor also in a downwind hovering situation there is a tendency for hot exhaust gases to re-circulate into the engine intakes. This has the effect of reducing the mass flow (less dense air) and increase the temperature in the intake which can result into surge. This is commonly known as reingestion.
I have searched if some kind of engine placement (angle, direction etc.) could solve this problem, but i couldnt find any papers or anything at all for that kind of matter. (except for 2 papers written in 1982, which is sold for 30$ each, almost never cited, so i couldnt trust them enough to buy =) )
What are the solutions to this problem? Is there some precautions for pilots when doing HIGE or strong-tailwind situations to overcome the reingestion problem, or is this a complete engineering problem that can be solved with different air intake or compressor designs? Have you ever seen such documents? What is the most effective solution to overcome this, engine placement , inlet/compressor design or rotor design?
I have heard that the engine control system also arranges the engine such that the reingestion problem does not affect the engine very much. Is that true?
Lastly, can i ignore the reingestion effect in small helicopters (which are about 5000kg)?
Thanks for your help