12th Sep 2010, 12:05
permalink Post: 329
Hi Steve, good question. You could not prime Alt ACQ directly from MAX CLIMB/MAX CRUISE, but I'm sure the guys would confirm that FL600 was nonetheless set in the AFCS altitude window. If you did come close to FL600, then you would get an altitude alert audio and visual warning anyway, but the crew would obviously know anyway. The guys will have to confirm this but I think that ALT HOLD would be selected at this point, and the autopilot would now constrain the altitude by varying pitch attitude. You would normally be flying in nice cold conditions for this to occur, hardly ever on the North Atlantic, but on the LHR-BGI sector it would occur as often as not. (As usual, apologies to my all flying pals if I'm talking rubbish again
).
Dude
).
Dude
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:
|
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.
|
Dude
3rd Dec 2010, 13:37
permalink Post: 829
M2Dude
There was an unconfirmed report - so no doubt completely baseless - that ...er...another operator... noticed a rather unusual but highly favourable wind component on a JFK...er...Easterly... crossing, as they passed through FL520 or so, giving them a magnificent groundspeed.
Deciding that they would like to maintain this groundspeed, they went ALT HOLD and MACH HOLD at around FL530. They maintained their groundspeed, so the story goes, but the autothrottle then progressively reduced the N1, as the aircraft weight reduced, over the next couple of hours, into the prohibited range!
Did you ever hear of any such event?
Best Regards
Bellerophon
Quote:
| the dodgy sustained N1 band for the Olympus 593, this was 88-91% N1. This figure was never an issue in service as at cruise...the N1 was always run at the flat rate limit of 101.5%. Below ISA -7 the intake system would progressively reduce N1...falling to 97.4% at ISA -24 |
Deciding that they would like to maintain this groundspeed, they went ALT HOLD and MACH HOLD at around FL530. They maintained their groundspeed, so the story goes, but the autothrottle then progressively reduced the N1, as the aircraft weight reduced, over the next couple of hours, into the prohibited range!
Did you ever hear of any such event?
Best Regards
Bellerophon
4th Dec 2010, 09:17
permalink Post: 832
Bellerophon
Ahhh this 'other operator' (I'd quite forgotten our code for *** ******). And as for this obviously baseless story
.... er yes it did happen. I should really have qualified my post and said 'The controlled N1
as long as the aeroplane was operated
CORRECTLY
was always at least in the upper 90's, well away from our blade resonance area'. I don't quite recall after the engines were removed post-flight (At Rolls-Royce's insistance) whether the entire LP compressor sections or just the first few stages had to be replaced at the engine overhaul base. In either case it was a rather expensive piece of experimentation.
ChristiaanJ
Certainly my friend (but hey, remember that I'm an old Volts and Amps and Ohms ancient at heart too
).
The lighting of a reheat flame can be achieved in three ways:
1) By using an electric arc ignitor.. the least reliable system, although relatively simple in concept.
2) Catalytic ignition, where the reheat fuel is sprayed over a platinum based catalyst, spontaneously igniting. I recall that although generally reliable, eventually the catalyst compound erodes away and you are left with no ignition source.
3) Hot streak injection (or ignition). I this case a sizable jet of fuel is injected through a single injector placed the the combustion chamber of the engine, a powerful streak of flame then 'shoots out' of the turbine, and ignites the reheat fuel. Generally reliable as long as the injector itself does not carbon up (as our new friend Howiehowie93 pointed out). What amazed me with this system when we were looking at it for Concorde, was that the Olympus 593 designer I spoke to at Rolls-Royce told me that it has a negligible effect on turbine blade life, as the hottest part of the flame does not hit the blades themselves, and also of course it is a very short duration burn anyway (1 - 2 seconds).
And Christian my friend, you should indeed 'rabbit on' here about some of your observations regarding Concorde electronics technology, you have a unique insight here as (probably) the only Concorde systems designer that regularly visits 'here'. I'm sure I speak for many of us here when I say that your experiences are unique and your contributaions are always illuminating. Come on, let's have some Volts/Amps and Ohms
Best Regards
Dude
Quote:
| Deciding that they would like to maintain this groundspeed, they went ALT HOLD and MACH HOLD at around FL530. They maintained their groundspeed, so the story goes, but the autothrottle then progressively reduced the N1, as the aircraft weight reduced, over the next couple of hours, into the prohibited range!Did you ever hear of any such event? |
.... er yes it did happen. I should really have qualified my post and said 'The controlled N1
as long as the aeroplane was operated
CORRECTLY
was always at least in the upper 90's, well away from our blade resonance area'. I don't quite recall after the engines were removed post-flight (At Rolls-Royce's insistance) whether the entire LP compressor sections or just the first few stages had to be replaced at the engine overhaul base. In either case it was a rather expensive piece of experimentation.
ChristiaanJ
Quote:
| Can somebody explain to a "Volts and Amps and Ohms ancient" what "hotstreak injection" is/was (without getting scabrous)? |
).
The lighting of a reheat flame can be achieved in three ways:
1) By using an electric arc ignitor.. the least reliable system, although relatively simple in concept.
2) Catalytic ignition, where the reheat fuel is sprayed over a platinum based catalyst, spontaneously igniting. I recall that although generally reliable, eventually the catalyst compound erodes away and you are left with no ignition source.
3) Hot streak injection (or ignition). I this case a sizable jet of fuel is injected through a single injector placed the the combustion chamber of the engine, a powerful streak of flame then 'shoots out' of the turbine, and ignites the reheat fuel. Generally reliable as long as the injector itself does not carbon up (as our new friend Howiehowie93 pointed out). What amazed me with this system when we were looking at it for Concorde, was that the Olympus 593 designer I spoke to at Rolls-Royce told me that it has a negligible effect on turbine blade life, as the hottest part of the flame does not hit the blades themselves, and also of course it is a very short duration burn anyway (1 - 2 seconds).
And Christian my friend, you should indeed 'rabbit on' here about some of your observations regarding Concorde electronics technology, you have a unique insight here as (probably) the only Concorde systems designer that regularly visits 'here'. I'm sure I speak for many of us here when I say that your experiences are unique and your contributaions are always illuminating. Come on, let's have some Volts/Amps and Ohms
Best Regards
Dude
22nd Feb 2014, 03:16
permalink Post: 1789
ruddman
...Being that the Concorde looks like a slippery sob, how were the descents planned?...
The distance required to decel/descend from M2.0 in cruise/climb down to 3,000 at 250 kts was obtained from a checklist chart. Entering with the (expected) FL at Top of Descent and then correcting for the average wind component expected in the descent and also for the temperature deviation from ISA gave the required track miles. It wasn\x92t used a lot, because generally the more critical descent requirement was to decelerate so as to be (just) below M1.0 at a specified point on the arrival route, for noise reasons, to avoid booming land.
There was a second chart, utilised in the same way as the first, which provided this information. Sometimes this distance might need to be increased a little, as, if a subsonic cruise was expected before continuing the approach, the engines were \x93warmed\x94 up at M0.97 and after passing FL410, by the application of power, for one minute, by the Flight Engineer.
...Did you just pull the throttles back to flight idle?...
Only if you were willing to run the risk four pop surges from the engines and the near certainty of a clip round the ear from your Flight Engineer.
Usually the pilots handled the throttles from \x93Power Up to Gear Up\x94 and from \x93Gear Down to Shut Down\x94. The Flight Engineer generally did all the rest, which, thankfully, left all the tricky drills and procedures as his responsibility.
...Or was there a little more engine management and more gradual handling of the engines and descent?...
On a normal decel/descent, the handling pilot would select ALT HOLD and then ask the Flight Engineer to reduce power to 18\xba TLA (Throttle Lever Angle). The speed would decay to 350 kts IAS (Indicated Air Speed) IAS HOLD was engaged and the descent flown at 350 kts IAS. The next power reduction (32\xba TLA) came when, still flying at 350 kts IAS, the Mach number reduced through M1.50.
...And I'm guessing the approach speeds were fairly high so hitting the touchdown zone was pretty important?...
In terms of not running off the end of the runway, touching down in the correct spot was as important on Concorde as on other aircraft types.
However, due to the geometry of Concorde on landing, the tail, engine pods and reverser buckets were already fairly close to the runway. Add in a \x93firm\x94 touchdown, or if the wings are not completely level, and ground clearance becomes marginal, so a prolonged flare and floated landing, with an increasing aircraft attitude, was not acceptable. The risk of a pod, tail or a reverser bucket scrape on Concorde was greater than on most conventional jet aircraft.
... So if things got out of shape a little, and a G/A was required, how do you handle what looks like 4 rockets on the wings and applying the right amount of power?...
...Being that the Concorde looks like a slippery sob, how were the descents planned?...
The distance required to decel/descend from M2.0 in cruise/climb down to 3,000 at 250 kts was obtained from a checklist chart. Entering with the (expected) FL at Top of Descent and then correcting for the average wind component expected in the descent and also for the temperature deviation from ISA gave the required track miles. It wasn\x92t used a lot, because generally the more critical descent requirement was to decelerate so as to be (just) below M1.0 at a specified point on the arrival route, for noise reasons, to avoid booming land.
There was a second chart, utilised in the same way as the first, which provided this information. Sometimes this distance might need to be increased a little, as, if a subsonic cruise was expected before continuing the approach, the engines were \x93warmed\x94 up at M0.97 and after passing FL410, by the application of power, for one minute, by the Flight Engineer.
...Did you just pull the throttles back to flight idle?...
Only if you were willing to run the risk four pop surges from the engines and the near certainty of a clip round the ear from your Flight Engineer.
Usually the pilots handled the throttles from \x93Power Up to Gear Up\x94 and from \x93Gear Down to Shut Down\x94. The Flight Engineer generally did all the rest, which, thankfully, left all the tricky drills and procedures as his responsibility.
...Or was there a little more engine management and more gradual handling of the engines and descent?...
On a normal decel/descent, the handling pilot would select ALT HOLD and then ask the Flight Engineer to reduce power to 18\xba TLA (Throttle Lever Angle). The speed would decay to 350 kts IAS (Indicated Air Speed) IAS HOLD was engaged and the descent flown at 350 kts IAS. The next power reduction (32\xba TLA) came when, still flying at 350 kts IAS, the Mach number reduced through M1.50.
...And I'm guessing the approach speeds were fairly high so hitting the touchdown zone was pretty important?...
In terms of not running off the end of the runway, touching down in the correct spot was as important on Concorde as on other aircraft types.
However, due to the geometry of Concorde on landing, the tail, engine pods and reverser buckets were already fairly close to the runway. Add in a \x93firm\x94 touchdown, or if the wings are not completely level, and ground clearance becomes marginal, so a prolonged flare and floated landing, with an increasing aircraft attitude, was not acceptable. The risk of a pod, tail or a reverser bucket scrape on Concorde was greater than on most conventional jet aircraft.
... So if things got out of shape a little, and a G/A was required, how do you handle what looks like 4 rockets on the wings and applying the right amount of power?...
- Disconnect the autothrottles.
- Apply FULL power without reheat.
- Rotate to 15\xba and level the wings.
- Check for Positive Climb then call for the Gear Up.
- Maintain 15\xba and accelerate (you will accelerate!)
- Passing around 210 kts, reduce power to 95% N2.
- Approaching 250 kts, engage Autothrottles for 250 kts
- Reduce Pitch Attitude, aiming to achieve 2,000 fpm RoC.
- Do not miss the level off altitude for the GA profile.