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Concorde question

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Concorde question

Old 20th Dec 2016, 14:29
  #1961 (permalink)  
 
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Reverse Thrust in the air - Limitations
  • Inboard engines (either or both) only
  • Idle power only
  • Between 30,000 ft - 3,000 ft AGL only
  • Subsonic only
  • Max speed 370 kts over most of the allowable range
  • Min speed 250 kts above 15,000 ft
  • Min speed 225 kts below 15,000 ft
  • 4 minutes only
The descent profile was planned without the use of reverse thrust, but it was available, and used, when required.

The principal benefit of reverse thrust in the air, in my view, was the ability to reduce speed quickly in a shallow descent, whilst keeping the aircraft attitude (and so the cabin floor) substantially level. Passengers found this more comfortable than using reverse thrust, at a constant IAS, to achieve a very high rate of descent, with the consequent steep nose down attitude.

If a runaway bar trolley, dragging a stewardess behind it, thumped into the back of the flight deck door, you had probably overdone the nose down attitude!
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Old 21st Dec 2016, 06:02
  #1962 (permalink)  
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I can imagine !


Thanks for that BP, just to clarify you say inboard engines only either or both, so you might use reverse on only one engine ? any assymetric issues with that ?


Also, why the 4 minute restriction ?
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Old 21st Dec 2016, 16:48
  #1963 (permalink)  
 
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4 min limitation, of my memory serves, is because reverse thrust blocks off the cooling air flowing over the engine mounted accessories. The limitation is then to stop them cooking up.

Regarding an earlier question, you really need a flight crew member to answer, but looking at the RHS panel on the Concorde Heritage site it looks to me that the symbol is the landing gear indication - nose, two mains and a tailwheel. Haven't a clue what the other indication might be.
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Old 28th Dec 2016, 18:18
  #1964 (permalink)  
 
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One of my amusing recollections of "The white lady" on 14 th November 1976 Manchester was graced for the first time when G-BOAA was diverted due to fog at Heathrow to Manchester. She arrived in the late evening ( ex Washington I suspect?). She was parked across the end of B pier as we had no tow bar at that time.
One of the local radio stations erroneously reported she would be departing back to London at 1 am. Clearly this was not accurate for two reasons, crew hours and Heathrow's night jet ban.
However at 1am Ringway's switchboard lit up with complaints about the noise. Unperturbed sleeping beauty dozed peacefully on stand 11.
Oddly the next departure was just after 0200 when the Aer Lingus freighter 9213 set forth for Dublin. Ironically operated by an Aer Turas Brittania as the Aer Lingus 737QCs were scattered across Europe in passenger configuration due to weather.
Two of Bristols finest together, one of the quietest and certainly the loudest.
Thank you to all our contributors, finest thread on pprune of the millennium, without a doubt.

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Old 3rd Feb 2017, 11:28
  #1965 (permalink)  
 
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n5296s has posted elsewhere
Apparently landing Concorde in a strong headwind could lead to a very nasty surprise because of the huge relative height difference between the back of the wing and the rest of it. So the trailing edge is much more in ground effect than the rest. As it gets very close to the ground, the headwind reduces due to ground friction. At some point the part of the wing that is doing the most work drops out of - well, not the sky, but where it is.

I don't pretend to follow the detailed math/aerodynamics, but the net effect is a "did we land or were we shot down" landing.
Can someone knowledgeable relate what aerodynamic gremlins were at work?
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Old 3rd Feb 2017, 11:43
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Avgas Dinosaur: Thank you to all our contributors, finest thread on PPRuNe of the millennium, without a doubt.
And soon to celebrate reaching its 100 page. Utterly outstanding!

Rob
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Old 3rd Feb 2017, 13:37
  #1967 (permalink)  
 
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That's because it's better, hard to admit as it is, than an Islander... Or any other heavy jet with lots of glass inside and carbon outside!!!

😉
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Old 3rd Feb 2017, 15:31
  #1968 (permalink)  
 
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Can any of our pilot contributors confirm n5296s's remarks re landing in a strong headwind?
For my part I was never aware of any complaints
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Old 3rd Feb 2017, 15:56
  #1969 (permalink)  
 
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Clive

Must admit I'm surprised as well, I would have thought that trailing edge, so to speak, would have been benefitting from ground effect just before touchdown.
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Old 3rd Feb 2017, 17:35
  #1970 (permalink)  
 
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I didn't find any problems in strong headwinds.

We used to use Vref+10 instead of Vref+7 if it was windy (which made a bigger difference than the numbers may suggest) and, if anything, this made it easier.
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Old 3rd Feb 2017, 19:30
  #1971 (permalink)  
 
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Yes I would have bet that a higher airspeed would be recommended (not even a problem since headwind will reduce GS, and only GS is a problem in a landing).
However I would have added something like up to half the wind

Only 3kt ?? That's a huge surprise
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Old 4th Feb 2017, 00:11
  #1972 (permalink)  
 
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Many thanks for the answers folks. Can't beat getting it from the horses mouth.
We used to use Vref+10 instead of Vref+7 if it was windy (which made a bigger difference than the numbers may suggest) and, if anything, this made it easier
EXWOK, could you expand on the whys and what fores?
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Old 4th Feb 2017, 05:35
  #1973 (permalink)  
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Were both BA and AF involved / lend aircraft to the short lived Braniff Concorde operation flying the aircraft subsonic from Washington Dulles to the Dallas Fort Worth airport ?


I read somewhere that the aircraft owner, whether it was BA or AF always had one of their captains as an observer in one of the cockpit jumpseats on these flights ?


Not sure if that's true but any other insights or information on this unusual arrangement
would be welcome.
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Old 4th Feb 2017, 07:26
  #1974 (permalink)  
 
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This may be overtaken by later postings, but a couple of reasons why n5692s's explanation might not work:-

Most of the lift is generated on the upper surface and is dominated by the vortex lift which is a product of vortex strength and airspeed. The vortex strength depends on the local aoa at the leading edge. As the aircraft enters ground effect the passage of air under the wing is restricted so more has to go over the top and the local LE aoa is increased along with vortex strength. The important bit of the wing for this bit of lift increase is the front half which is in the higher part of the wind profile. But in any case, following our old friend Bernoulli, the upper surface suction will depend on the resultant circumferential velocity as the vortex scrubs its way across the wing upper surface, and I can't see a knot or two of wind making a big difference to the circumferential velocities under those vortices.

The undersurface flow is of course restricted. and the lift is more Newtonian in character. A reduction in local airspeed because of the wind height profile could give a reduction in lift due to ground effect near the TE. However, in the normal course of events this additional lift is accompanied by a nose down pitch which is countered by a steadily increasing back stick movement as the pilor maintains the more or less constant pitch attitude "flare" manoeuvre. This up elevator gives an increasing negative lift to maintain pitch control which, since the effective cop of the elevator lift is at the elevon hinge line means that the net gain in overall lift from this part of the ground effect is quite small. If this undersurface TE lift were to be reduced by the wind gradient the effect would. be that the nose down pitch would be smaller than usual and the pilot would have to apply less back stick, but I doubt he would notice this in a dynamic situation (remembering that strong winds are usually accompanied by turbulence).

So I can't identify any gremlin job specification that might support n5296s's argument.

Kaypam: Remember the Concotrde was certificated to TSS Standards not JAR25. The certificated approach speed is Vref, Vref plus 7 if memory serves, was introduced as an approach noise reduction and became anaccepted norm so Vrefplus 10 should be OK for 20 kt winds?

Last edited by CliveL; 4th Feb 2017 at 08:30.
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Old 4th Feb 2017, 10:47
  #1975 (permalink)  
 
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Stilton:

Braniff that the subsonic Concorde flights, IAD to Texas with British Airways or Air France crews handling the subsequent supersonic overseas flights to Europe and the UK.

I understand the observer positions taken up by British crew was mainly due to insurance concerns. I have no knowledge of the Air France arrangement regarding observers, but hopefully one of our good contributors will clear that one up.
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Old 4th Feb 2017, 19:22
  #1976 (permalink)  
 
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stilton

... so you might use reverse on only one engine? any assymetric issues with that ?...

No issue at all, on the one occasion I can remember that it happened to me.


... why the 4 minute restriction ?...

I believe the correct answer has been given by CliveL, but, when asked during ground school, the BAe instructors’ traditional answer was “Noise Abatement”. (as in a Concorde hitting the ground makes a lot of noise!)


... BA or AF always had one of their captains as an observer in one of the cockpit jumpseats on these flights ?...

Before my time, so I can’t say if BA crew flew on the jump seat, or in what capacity they were acting if they did, but I believe there is at least one contributor to this thread who may yet post an answer.



CliveL

... Can any of our pilot contributors confirm n5296s's remarks re landing in a strong headwind?..

Speaking personally, I never noticed any problem, and as EXWOK has said, I found using VREF +10 made life a lot easier.

However, Mike Riley, a well respected base training instructor on the fleet (and a past British Aerobatics team member) discussed this point in his “The Concorde Stick and Rudder Book”, where he says that there was a greater incidence of hard landings when landing into a strong headwind and goes on to discuss some of the possible reasons why and what to do about it.

His main recommendation was to leave the auto throttle in later than usual, down to 20R instead of 40R, and maintain a constant attitude to touchdown.


... The certificated approach speed is Vref, Vref plus 7 if memory serves, was introduced as an approach noise reduction...

Yes, VREF +7 was used for Reduced Noise Approaches that were flown whenever possible, and which were generally considered easier to land from than VREF approaches.

Last edited by Bellerophon; 6th Feb 2017 at 23:31. Reason: Loss of formatting
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Old 5th Feb 2017, 05:10
  #1977 (permalink)  
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Thanks for that Bphon, yes the noise abatement makes sense now !
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Old 5th Feb 2017, 08:00
  #1978 (permalink)  
 
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Bellerephon:

Interesting!
About eighteen months ago a MD11 piloting friend and I had a close look at that machine to see if we could identify any features that might explain its poor hard landing record. We came up with a tentative explanation that the shortish tail arm combined with high pitch inertia led to a slight, but significant, increase in the delay between elevator application and flight path response (negative elevator lift effect) and that this could make attempts to make flight path corrections from very near the ground hit or miss affairs (no pun intended!). The response was crisper at higher airspeeds and (with admittedly limited experimentation) he concluded that leaving the autothrottle engaged down to a lower height above the runway improved matters. Avoiding late corrections and just taking the medicine could also be a good idea.

One of the boffins at RAE Bedford raised this elevator negative lift effect as a possible Concorde concern about the time of first flight, but experience then and for some time after suggested this was not a big problem.

Now I am wondering whether the sequence :- increased wind/greater turbulence/more chance of needing last minute (second?) corrections/negative elevator lift effect/more hard landings might be a reasonable explanation of the question posed in the OP.

Did Mike Riley offer anything along these lines? or if not what did he come up with?
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Old 8th Feb 2017, 09:25
  #1979 (permalink)  
 
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I'm not sure the 'negative elevator effect' was ever a practical issue in flight (as opposed to on rotation) - the response was entirely normal and I reckon that the increase in lift is near enough instantaneous. Aircraft with tailplanes would have a similar theoretical effect.

I don't recall hard landings being an issue on windy days - quite the opposite.

If there was an influence due to wind I would say it's more likely to be that in the gusts one may be tempted to 'tweak' the attitude: Putting the nose down by half a degree at 50' would have very disappointing consequences....

From memory, we had 4 speeds available:

Vref 'Normal' final approach speed (actually not used that much)
Vref+5 Engine out speed
Vref+7 Noise reducing approach speed (used as often as possible)
Vref+10 If the headwind component was over 25(?)kts

Most were at +7.

Vref was least nice - you had a higher attitude to start with, and needed more flare, which meant tail clearance was tight. It also meant that if you picked up a high RoD at 50' or so, it was VERY difficult to catch. One *could* add a bit of thrust at 30' or not close the throttles at 15', but this was not without drawbacks.

Vref+5 was better - the reason it was used was to give better g/a performance on 3 engines (there are obviously a lot of square laws at play here, because it made a significant difference).

Vref+7 was used off pretty much every ILS approach to a decent length of runway, where we would carry out a noise-reducing approach. This is probably explained elsewhere in the thread. These days it would be called an unstable approach! It gave you more lift margin into the flare and also more room to make pitch inputs (i.e. space for another half- to one- degree of flare).

Vref+10 was for windy days. I liked it! If you arrived at 40' in the right place, you basically just held the attitude and the ground effect did the rest. It did still *feel* like you had flared, as the ground effect would push the nose down and so back stick was still required to hold the attitude.

I hope that has answered CliveL and Megan's questions somewhat?
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Old 8th Feb 2017, 12:56
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@EXWOK

I like your last paragraph - that is exactly the advice we gave Trubbie before first flight!

No problem either with your view that negative lift was never a practical problem, but on paper the time before the cg started to lift was just under 0.5 sec longer than a contemporary tailed aircraft for a step elevator input at approach speeds.
Don't want to sound clever/clever, but the height response at the cockpit would be earlier than the cg movement, which might be why you saw a fairly normal response.
But from Mike Riley's work it sounds as if some pilots had different experience in strong headwinds does it not?
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