|Quoting Pilotpip (Reply 3):|
The amount of time from idle to full power is dictated by regulation (don't recall what time that is)
|Quoting Vikkyvik (Reply 4):|
Far as I remember, isn't it about 6 or 7 seconds?
|Quoting Vikkyvik (Reply 4):|
I also seem to remember reading that on some airplanes, when powering up for takeoff, the pilots first advance the levers to some low N1 setting above idle, and let the engines stabilize there before setting full takeoff thrust? Or was that on pre-FADEC aircraft?
|Quoting PhilSquares (Reply 7):|
What this ensures is the engines spool up at a fairly uniform rate. Thus, you are minimizing any directional control problems that could occur if you went right from idle to the calculated takeoff thrust setting.
|Quoting Fr8Mech (Reply 6):|
The short answer is air management. Controlling the air through the engine via VSV/VBV/bleed valve manipulation is
|Quoting Speedracer1407 (Reply 12):|
In my experience as a passenger, FADEC equipped engines can spool from idle or a low "stabilizing" setting to takeoff power almost instantly; probably little more than a second or so.
As a passenger, I've experienced a quick spool-up at least once on every modern plane equipped with FADEC I've flown on in recent years (A320, 738, EMB170, ERJ145), and each time was memorable because of the sudden whack of thrust,
|Quoting Max Q (Reply 16):|
The JT8D'S on the MD80 series are purely hydromechanical in their fuel control, they also have the slowest spool time of any jet engine I have flown.
|Quoting Max Q (Reply 18):|
You also mention your timed tests are done from approach idle, there is a big difference in acceleration time from approach idle or ground idle.
Spool up from ground idle took a loong time.
|Quoting SpeedBirdA380 (Reply 14):|
As this topic is about engine spool ups someone once told me Rolls Royce engines spool up faster than other engines because of their three spool stage design compared to two spool stage engines.
Is this true?
|Quoting VC-10 (Reply 21):|
The throttles also had to be slammed forward to ensure the throttle master switches were operated. If the throttles were moved in a less forceful manner,the relevant systems may not respond in the expected manner.
|Quoting CanadianNorth (Reply 23):|
As a related topic, I was wondering the other day are there any large turbofans (or pure jets too) that make use of bleed ports such as those found on helicopter engines (T-53, Allison 250, etc)? The purpose of them is basically to unload the compressor for faster acceleration which is often needed in a helicopter, but I've never heard of such an installation on a fixed wing. Anyone heard of one?
|Quoting Jetlagged (Reply 24):|
Older JT9Ds had a number of such valves which opened under certain conditions, such as starting, at low rpm and in reverse thrust. They opened during starting to offload the HP compressor and make it spool up quicker. The bleeds opened in reverse thrust to improve stability and prevent surge. Later JT9Ds (-7Q onwards) had variable bleed valves rather than a number of fixed ports.
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