By Pass Ratios?
Hi all!
At the moment I'm teaching powerplants to an ATP theory class. I've got a question about By Pass Ratios that I tend to have trouble explaining.
A straight jet will have a 0 BPR as no air bypasses the hot section, that one's simple.
A turbofan engine will have a bypass of anywhere around 2:1 to 5:1 as there is air bypassing the hot section, not taking part in combustion.
When it comes to a Turboprop, I allways claim that they have an even higher bypass ratio. The engine is driving heaps of air that does not take part in combustion. The students normally follow on this line, but it starts getting silly when discussing it with rotary wing pilots claiming that a turboshaft has an extremely high BPR. At this point students start asking difficult questions and I must admit that I'm not quite sure of where to draw the line. The CT7-B gas generator for example uses all air it ingests, and looking it that way, it would seem it does not have a BPR at all.
What's right and wrong in this?
/LnS