Speedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0 Posted (6 years 10 months 1 week 2 days 11 hours ago) and read 12393 times:
After reading a different thread, I was reminded that I still don't know the what accounts for the difference between flight and ground idle; hopefully, I have the terminology correct. I have a few questions:
Assuming flight Idle is generally higher than ground idle, what causes the difference? Is it part of FADEC software?
In non FADEC engines, is it still some kind of automatic mechanical thing?
Is it simply the result of aerodynamic forces on the engine in flight that makes the difference (windmilling, of some sort)?
is there a detent on the throttle quadrant for it?
Are quicker spool-up times from flight-idle to maximum power a primary reason for the difference, or as before, is it just a natural/practical consequence of high airspeed?
Thanks for any replies,
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
Tristarsteve From Sweden, joined Nov 2005, 3713 posts, RR: 34 Reply 2, posted (6 years 10 months 1 week 2 days 8 hours ago) and read 12342 times:
Flight idle is always higher than ground idle.
Nowadays it is controlled by the FADEC, but on the RB211 there was a FI/GI solenoid connected to the FFR. Ground Idle is set as the slowest practical speed the engine will operate with bleeds on.
Flight idle is set top acheive the idle to take off acceleration speed required by regulations. FAR is 5 secs, and CAA used to be 6 secs. If the engine will not accelerate from ground idle in this time, then in flight the min speed is set to acheive this. It is very necessary in large fan aircraft where flight idle can be much higher than ground idle, but in small fans it is not always necessary. I await MEL to say something, but I can't remember it on the JT8D-15, or the Spey.
HAWK21M From India, joined Jan 2001, 31228 posts, RR: 58 Reply 3, posted (6 years 10 months 1 week 2 days 7 hours ago) and read 12316 times:
From What I recollect offhand.On the RB211-535E4.
The Idle Reset Solenoid on the FFG sets High or Low Idle.
High idle is only used during Landings and when Engine Cowl A/I is on in Flt.High Idle is used for Descent in Icing conditions to prevent possible Engine problems and is used during Landings to reduce time for the Engine to spool up to Maximim rpm if needed in case of G/A.
When the Idle Reset Solenoid is De-Energized Idle speed increases.At sea level the Acceleration time decreases by approx 2 secs.[regular 5-6 secs].
In Flt with Flaps up & Gear retracted.Low Idle is used.When Flaps lowered to Landing position & Engine A/I selected or NLG lowered,Idle Reset solenoid is DeEnergised & speed Increases.
On Touchdown The Solenoid Energizes after a Time Delay of 5 seconds.
113312 From United States of America, joined Apr 2005, 538 posts, RR: 1 Reply 7, posted (6 years 10 months 1 week 1 day 21 hours ago) and read 12132 times:
Of course, you're only discussing Flight or Ground Idle for tubofan engines. They really shouldn't be called "Flight" or "Ground" at all but rather High and Low.
Many of the high bypass engines in use basically have a closed "throttle" speed of "Ground Idle" (low) on the ground and in the air. They only switch over to "Flight Idle" (high) in the air with a landing configuration such as gear and flaps extended. The reason for this is to facilitate rapid engine response for go around (aborted landing) and reverse thrust after touchdown.
No. Ground Idle is exactly what is sounds like - idle thrust for on the ground. It is the same detent at Flight Idle, but also requires the Weight on Wheels switch to show that it is on the ground. Tripping the WOW switch will tell the FADEC to spool the engines down to Ground Idle.
Troubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5 Reply 9, posted (6 years 9 months 4 weeks 1 day 21 hours ago) and read 11841 times:
Quoting Chksix (Reply 1): I'm interested to know the limits for the 737NG. I know ground idle is at 20% but can't find info on Flight Idle.
Note that IDLE is always based on N2 speed.
For the CFM56-7 there are three IDLE modes: GROUND IDLE
above 58%. Idle speed will increase with increase of OAT, generator load and bleed demand FLIGHT IDLE
during flight the FADEC maintains a N2 speed of 72% APPROACH IDLE
the FADEC goes into this mode (72-79% N2) if following conditions occour:
- either cowl anti-ice is swiched on
- either main landing gear down and locked below 15.000 ft
- TE flaps are equal or more than "15" below 15.000 ft