12th Sep 2010, 15:39
permalink Post: 330
Hi Dude,
Thanks for the reply, I never knew you couldn't prime ALT ACQ from MAX CLIMB / MAX CRUISE.
I was thinking though that if you had ALT HOLD selected then the autopilot wouldn't be able to vary the pitch attitude and it would hold at the ALT HOLD level. Once there it wouldn't be able to use pitch to increase or decrease speed if necessary. I can see how the autothrottles could hold the speed back but if it were to get warmer then even at full power it may not be able to maintain speed at a fixed altitude.
I'm sure there is a simple answer which will leave us saying "oh yeah, how obvious, didn't think of that"
Just strange it doesn't seem to be written anywhere.
Thanks,
Steve.
Thanks for the reply, I never knew you couldn't prime ALT ACQ from MAX CLIMB / MAX CRUISE.
I was thinking though that if you had ALT HOLD selected then the autopilot wouldn't be able to vary the pitch attitude and it would hold at the ALT HOLD level. Once there it wouldn't be able to use pitch to increase or decrease speed if necessary. I can see how the autothrottles could hold the speed back but if it were to get warmer then even at full power it may not be able to maintain speed at a fixed altitude.
I'm sure there is a simple answer which will leave us saying "oh yeah, how obvious, didn't think of that"
Just strange it doesn't seem to be written anywhere.
Thanks,
Steve.
13th Sep 2010, 01:18
permalink Post: 336
spfoster
Hi again Steve. At FL600 your aircraft is going to be relatively light, and your autopilot is set to ALT HOLD mode. As the aircraft continues to burn fuel it will 'try' and climb, but the ALT HOLD mode will of course slightly reduce pitch attitude to keep prevent the aircraft from climbing. The autothrottle in MACH HOLD mode can keep us from straying from Mach 2, large positive temperature shears were to my knowledge almost unheard of, and so any speed reduction was exceedingly unlikely. We really need a pilot's input here to further clarify the realities of LHR-BGI supersonic cruise; that's the way the AFCS was designed to do things however.
Dude
Quote:
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I never knew you couldn't prime ALT ACQ from MAX CLIMB / MAX CRUISE. I was thinking though that if you had ALT HOLD selected then the autopilot wouldn't be able to vary the pitch attitude and it would hold at the ALT HOLD level. Once there it wouldn't be able to use pitch to increase or decrease speed if necessary. I can see how the autothrottles could hold the speed back but if it were to get warmer then even at full power it may not be able to maintain speed at a fixed altitude.
I'm sure there is a simple answer which will leave us saying "oh yeah, how obvious, didn't think of that" 
Just strange it doesn't seem to be written anywhere.
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Dude
6th Jan 2011, 21:06
permalink Post: 1077
CliveL
, You wrote:
"We (BAC) were going to do the AICU development so it made sense for 101 to get the early hybrid units. [If you were cynical you might equally say that there was no way we were going to let AS have them first!]."
Is that a typo and did you mean "it made sense for 102 to get the early hybrid units."?
I think M2dude had more fun with the air intakes at the time than I had with the AFCS, although getting MAX CLIMB and MAX CRUISE to work was, to say the least, "interesting".
Christian
"We (BAC) were going to do the AICU development so it made sense for 101 to get the early hybrid units. [If you were cynical you might equally say that there was no way we were going to let AS have them first!]."
Is that a typo and did you mean "it made sense for 102 to get the early hybrid units."?
I think M2dude had more fun with the air intakes at the time than I had with the AFCS, although getting MAX CLIMB and MAX CRUISE to work was, to say the least, "interesting".
Christian