engine response time vs vapp
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engine response time vs vapp
Good morning everybody
I have been recently told by a flight instructor that the normal engine response time from idle to go around thrust which is normally 6-8 sec increases when the aircraft is at or below vapp to approx. 14 sec.
any inputs, thoughts, references on the subject?
Thanks a lot
I have been recently told by a flight instructor that the normal engine response time from idle to go around thrust which is normally 6-8 sec increases when the aircraft is at or below vapp to approx. 14 sec.
any inputs, thoughts, references on the subject?
Thanks a lot
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depends on the engine.
the magic on the jt8d series was 42percent N1. above it, quick response, below it, slow response. has to do with a certain valve!
when you get to jets, ask the real instructor about that particular jet.
if you are at vapp (vref plus additives)and you are at idle, bad
if you are at vapp and steady above min spool, good!
the magic on the jt8d series was 42percent N1. above it, quick response, below it, slow response. has to do with a certain valve!
when you get to jets, ask the real instructor about that particular jet.
if you are at vapp (vref plus additives)and you are at idle, bad
if you are at vapp and steady above min spool, good!
I have been recently told by a flight instructor that the normal engine response time from idle to go around thrust which is normally 6-8 sec increases when the aircraft is at or below vapp to approx. 14 sec.
BS
. The FAR requirement is 8 seconds - doesn't mention airspeed. Most modern aircraft (and anything currently produced by Boeing) has an "approach idle" setting that is automatically selected when landing flaps are selected (basically anything over flaps 20 for Boeing). Approach idle to go-around thrust will take less than 8 seconds regardless of airspeed (I've tested it on various Boeing aircraft sitting static on the ground - it usually takes about 6 seconds).
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For the GE CF6, 40% N1 is a good number to remember as a minimum for "spooled up" or "approach thrust". Approach idle is around 27-31%, depending on temperature and altitude. It takes a good portion of those 8 seconds to go from idle to 40%...
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Idle?
In a good stable approach the thrust levers should never be pull pack to the stops until the flare. If one need to have them back at the stops, I would suggest a missed approach is in order prior to the pulling the damn things back! I'm speaking of narrow to wide body jet aircraft. In my Cub, it is great fun, but the response is also rather quick.
Just my two cents...
Just my two cents...
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If you at/near approach idle thrust, arent you supposed to spool up at the MA location?
This timeframe in the discussion, if ref engine spoolup alone, is a bit troublesome from a procedure design perspective.
The momentary descent (50 feet) was based on a 7 second reaction time.
The reaction time included pilot decision making to GA of 2 seconds, 3 seconds for the action to place the ac in GA mode, and 2 seconds for the aircraft to react...
This discussion seems to say that it takes 6-8 seconds for the engine to go from approach idle to GA thrust.
That means 11 to 13 seconds for the ac to react...that is a hell of a lot more than 50' of momentary descent.
This timeframe in the discussion, if ref engine spoolup alone, is a bit troublesome from a procedure design perspective.
The momentary descent (50 feet) was based on a 7 second reaction time.
The reaction time included pilot decision making to GA of 2 seconds, 3 seconds for the action to place the ac in GA mode, and 2 seconds for the aircraft to react...
This discussion seems to say that it takes 6-8 seconds for the engine to go from approach idle to GA thrust.
That means 11 to 13 seconds for the ac to react...that is a hell of a lot more than 50' of momentary descent.
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Not sure of the FAR wording but this is what EASA say:
CS 25.119 Landing climb: all-enginesoperating
In the landing configuration, the steady gradient of
climb may not be less than 3·2%, with the engines at
the power or thrust that is available 8 seconds after
initiation of movement of the power or thrust
controls from the minimum flight idle to the goaround
power or thrust setting (see AMC 25.119);
and
(a) In non-icing conditions, with a climb
speed of VREF determined in accordance with CS
25.125(b)(2)(i); and
(b) In icing conditions with the “Landing Ice”
accretion defined in Appendix C, and with a climb
speed of VREF determined in accordance with CS
25.125(b)(2)(ii).
In the landing configuration, the steady gradient of
climb may not be less than 3·2%, with the engines at
the power or thrust that is available 8 seconds after
initiation of movement of the power or thrust
controls from the minimum flight idle to the goaround
power or thrust setting (see AMC 25.119);
and
(a) In non-icing conditions, with a climb
speed of VREF determined in accordance with CS
25.125(b)(2)(i); and
(b) In icing conditions with the “Landing Ice”
accretion defined in Appendix C, and with a climb
speed of VREF determined in accordance with CS
25.125(b)(2)(ii).
have been recently told by a flight instructor that the normal engine response time from idle to go around thrust which is normally 6-8 sec increases when the aircraft is at or below vapp to approx. 14 sec.
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I've seen between 12 and 20 seconds when carrying out slam accelerations. According to the clever blokes with spanners it can be caused by putting a new MEC on an old donk.
Don't ask me why though.
Ah yes LSM, the MEC (Main Engine Control) - the carburetor of jet engines. Along with their Pratt counterpart, the JFC (Jet Fuel Control)(MEC is/was a GE/CFM term).
Just like the carb on a high performance car, the MEC/JFC required periodic adjustment (aka "trim") to work properly.
With a hydromechanical control, as an engine deteriorated, it would accel slower (all else being equal). And the normal wear on a hydro tended to make it shift 'lean', which also slowed the accel. Just like the carb on a Jaguar, a simple turn on a few adjustment screws could fix the problem. The requirement has always been 8 seconds - if it didn't/couldn't meet that, maintenance was needed. I recall a 767 operator telling me they "trimmed" the JFC on their JT9Ds once a month
.
FADEC has pretty much eliminated that as an issue. FADECs control use "N2 dot" (rate of change of N2) as the control parameter during an accel, and will simply add fuel (subject to other limits) to obtain the necessary N2 dot. Only a severely deteriorated FADEC engine (as in no EGT margin) will fail to meet the 8 second go-around accel requirements.
Not sure about the 'other guys', but Boeing hasn't delivered a non-FADEC commercial jetliner in over 10 years.
Just like the carb on a high performance car, the MEC/JFC required periodic adjustment (aka "trim") to work properly.
With a hydromechanical control, as an engine deteriorated, it would accel slower (all else being equal). And the normal wear on a hydro tended to make it shift 'lean', which also slowed the accel. Just like the carb on a Jaguar, a simple turn on a few adjustment screws could fix the problem. The requirement has always been 8 seconds - if it didn't/couldn't meet that, maintenance was needed. I recall a 767 operator telling me they "trimmed" the JFC on their JT9Ds once a month
. FADEC has pretty much eliminated that as an issue. FADECs control use "N2 dot" (rate of change of N2) as the control parameter during an accel, and will simply add fuel (subject to other limits) to obtain the necessary N2 dot. Only a severely deteriorated FADEC engine (as in no EGT margin) will fail to meet the 8 second go-around accel requirements.
Not sure about the 'other guys', but Boeing hasn't delivered a non-FADEC commercial jetliner in over 10 years.
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Not sure about the 'other guys', but Boeing hasn't delivered a non-FADEC commercial jetliner in over 10 years.
I believe the last non-FADEC 747s were the two VC-25's for the SAM fleet. The rationale was to ensure the donks were unaffected by EMP (electromagnetic pulse) from a nuke.
