Hey y'all, for whatever reason can't find this easily in my notes; a reminder or a source would be nice.
Consider for the sake of discussion a turbocharged piston engine producing 160 hp flat-rated to 10k ft. (These numbers might seem familiar to at least one of our members.) At a BSFC of 0.4, this should require about 176 SCFM of air.
Consider this engine installed in an aircraft with a stall speed around 50 kts, that may be taking off from airports all the way up to that 10k flat rating. At that altitude, 176 SCFM should correspond to 238 (actual) CFM needed for intake.
Since takeoff operations are being performed at this density altitude (and, of course, power setting), is it appropriate to size the induction intake for the stall condition? This would imply a 6.77 in^2 intake; and that passes the sniff test since it's just a bit bigger than the exhaust tip diameter of ~5 in^2, and the exhaust will have a higher velocity.
I could imagine oversizing the intake to provide full performance earlier in the roll, or just to reduce intake velocity; I could also imagine undersizing it so that it's less massively oversized during climb and cruise conditions. Also, I assume that past the intake the setup here is to expand smoothly into an airbox, to convert dynamic pressure to static when there's excess dynamic pressure (every case beyond the critical one).
Anything else to consider here? What's standard practice?
Consider for the sake of discussion a turbocharged piston engine producing 160 hp flat-rated to 10k ft. (These numbers might seem familiar to at least one of our members.) At a BSFC of 0.4, this should require about 176 SCFM of air.
Consider this engine installed in an aircraft with a stall speed around 50 kts, that may be taking off from airports all the way up to that 10k flat rating. At that altitude, 176 SCFM should correspond to 238 (actual) CFM needed for intake.
Since takeoff operations are being performed at this density altitude (and, of course, power setting), is it appropriate to size the induction intake for the stall condition? This would imply a 6.77 in^2 intake; and that passes the sniff test since it's just a bit bigger than the exhaust tip diameter of ~5 in^2, and the exhaust will have a higher velocity.
I could imagine oversizing the intake to provide full performance earlier in the roll, or just to reduce intake velocity; I could also imagine undersizing it so that it's less massively oversized during climb and cruise conditions. Also, I assume that past the intake the setup here is to expand smoothly into an airbox, to convert dynamic pressure to static when there's excess dynamic pressure (every case beyond the critical one).
Anything else to consider here? What's standard practice?
