Flight idle?
 

Hey there,

I was just doing some research into stall speeds and found out that the stall speed is calculated with the engine (on a prop) at flight idle.

Can someone please explain to me what is meant by flight idle (on a prop)?

I apologise if this is a really dumb question ;)

Minimum power. High power from a prop increases airflow over the wing and delays wing stall to a lower speed over a lot of the wing, so the stalling speed decreases significantly. So if you specify a stalling speed for a prop driven plane, you should really specify at what weight and power on/off.

I'm only a glider guider but..

I suspect the minimium recommended flight idle rpm is higher than the minimium recommended ground idle rpm.

Flight idle is the prop pitch that the prop is limited to in flight. Ground idle is a finer pitch (resulting in more drag, thus unsuitable for use in flight), usually available only after weight on wheels and time delay on landing (the extra drag reduces landing roll).

In jets, the flight Idle is the minumum thrust so can select in flight to ensure no flame out of the engine. Ground Idle is always smaller. I guess a turboprop will work the same.

Thanks for that, I was getting abit confused as I was thinking they calculate the stall speed with the aircraft at constant height and normal cruise attitude but of course they can't because then it wouldn't stall would it :rolleyes:

Thanks again.

Ground idle (for turbines) is usually set to meet a very low thrust level for taxi, but it generally takes a long time to spool up.

Flight Idle is set to meet a spoolup time requirement (xx seconds from flight idle to TOGA); ergo F.I. is a higher rpm that G.I.

Recip engines generally don't have thus issue and so "one size fits all". :}