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! ;)

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 ?

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.

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.

n5296s has posted elsewhereCan someone knowledgeable relate what aerodynamic gremlins were at work?

And soon to celebrate reaching its 100 page. Utterly outstanding! :ok:

Rob

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!!!

😉

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

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.

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.

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 :p

Only 3kt ?? That's a huge surprise

Many thanks for the answers folks. Can't beat getting it from the horses mouth.EXWOK, could you expand on the whys and what fores?

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.

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?

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.

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.

Thanks for that Bphon, yes the noise abatement makes sense now !

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?

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?

@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?

It would appear so....but I wonder if Vref+10 came about as a result of earlier experience and that was the source of the story?

I get what you mean about the height response at the cockpit vs flightpath response....but given that we're talking about landing, then it's the height of the undercarriage that matters.

FWIW, like all long-bodied aircraft, a last-minute pull has the capacity to drive the u/c into the ground harder because the pitch change happens before the flightpath change. That could well be exaggerated by 'negative elevator' effect.

A video of a landing could be quite telling if you could see the elevons - there's a very marked and increasing 'up' input to counter the pitch down from ground effect. I suspect that, in ground effect, this negative elevator effect would be swamped by all the other things that are happening.

I think we are pretty much on the same page.
Since the cg is generally close to the landing gear longitudinally, to all intents and purposes the height changes are the same on most aircraft. Pitch change before flight path change is an essential part of the negative lift effect.
But I agree, there is so much happening that it is difficult to separate out individual effects.

No, you've just raised more EWOK. :p Why would the +7 approach be deemed "unstable" today. Actually, thank you to all the contributors, fascinating stuff.

A slightly tongue-in-cheek comment, Megan.

The BA Ops Manual requires an approach to be fully stable at 1000'R. It used to be slightly more relaxed, but even then a 'reduced noise' approach was an exception to the policy.

Basically we flew at a higher speed (190kts) until 800', then reduced speed to achieve final approach speed at 300'.

This had two benefits - thrust required at 190kts was a lot less than 160kts so flew a quieter and less-thirsty approach, and the portion between 800' and 300' was quieter still.

Vref+7 gave better control and performance margins at the end of this manoeuvre - I'll try to find a reference as to why +7 came about (I recall there was a specific reason for that number, but not the detail).

looking at the Concorde instrument panel lately brings up a couple more questions:

Why is the radar altimeter positioned where the altimeter is normally placed ?
Did the designers decide it was more important for the radalt to have a more
prominent position in the pilots scan for a particular reason ?

While on the subject of radar altimeters Concorde has a fairly unique VSI, at least
for civil aircraft, it's vertical strip presentation is a clever way of saving space in
a compact, crowded panel.

But in the era that Concorde was designed a popular option on other jet transports was a vertical strip radar altimeter.

The radalt, after all is an instrument that is only used very briefly at the final stages of the approach and landing and is
situated accordingly, easily seen but not part of the classic 'T' airspeed, attitude, altimeter, HSI, of primary instrumentation

But in Concorde it literally has the most 'prime location'

For some reason I wasn't consulted on cockpit design despite going to school
with John Cochrane's son but surely a more conventional design would have had:

Altimeter, top right , VSI bottom right in their usual place and a vertical strip radalt
taking the place of the vertical strip VSI.

Curious as to the design choices, anyone with further insight ?

I'll always bow out to the pros did the actual design and flying - but this book quote may be one insight.

The Concorde, Christopher Orlebar, 2017, p. 55

From the point of view of the most critical phase of human piloting, the radio altimeter was far more important in the scan than the baro altimeter. Baro altitude was generally a problem for the automated part of the envelope, or the FE, while the guys up front needed only spare it a glance (most of the time) only twice a minute or so (or less often?)

Thanks for that, useful information.


Another question, there is what appears to be a fixed red line marked on the airspeed indicator opposite or pointing to around 190Kias.


Anyone know what this was for ?

It's actually a window, with a red warning annunciator/flag behind it, that flags a problem with the functioning of the Vmo needle (yellow and black "speed-limit" barber pole.)

See section 4 on this web page: Heritage Concorde

On the extreme right - microscopic explanatory type (sorry!)

Since one of its triggering events is a loss of electrical power, the red flag will be showing unless the aircraft electrical system is powered up (my guess). So it shows red in most cockpit photos.

stilton

...there is what appears to be a fixed red line marked on the airspeed indicator opposite or pointing to around 190Kias...

Could you please show us which picture you are looking at, as there was no such red line on the ASI on BA aircraft and I can't think what purpose such a line might serve?

The only thing I can think of is that there was a VMO Failure Flag window, cut into the face of the ASI dial, adjacent to 190kts.

When the flag was displayed, this indicated a failure of the VMO pointer, something that was very important on Concorde.

This flag had an all red background and bore the letters VMO on it in black.

I just wonder if perhaps what you are looking at might be the edge of the VMO Pointer Failure Flag which has not fully retracted into its window, leaving just its lower red edge displayed, which could look like a red line.

That's certainly possible, I was looking at the picture of the Captains instrument panel taken in level cruise at FL600.


It appears as a thin red line on the face of the instrument itself opposite 190 knots
approximately.


The picture i'm referring to is on page 4 of this thread reply #66 posted by yourself !
And on further examination I think I can see what you're saying, it does look like
the lower red edge of the warning flag just visible in that window.


Thanks again BP and for the person that did the very useful indexing which made finding that picture a breeze.

stilton

I'd forgotten I'd posted that photo, but now that I've looked at it again, it is indeed the bottom (red) edge of the VMO failure flag that you saw.

A thread you started nearly 7 years ago has now reached 100 pages, generated nearly 2,000 replies and been read roughly 900,000 times. :D

Who knew a question about an APU would start all that!

Kudos

Thanks for the clarification BP and for your many informative and fascinating
replies enlightening all of us on this incredible and unique aircraft.


I didn't think a simple question about an APU would take off into a
delightfully detailed account of Concorde's technical achievements and even
better, personal accounts of operating her 'on the line'


Thank you, I feel fortunate that I asked !


Best wishes

Departure & Arrival
 

Couldn't get this to post as an embedded video. May have been posted before and may even feature a PPruner or three. Beautiful...

https://youtu.be/1bjzoh3iQJc

Only slightly envious of doing circuits in Concorde!! :*

https://youtu.be/ZqCO1qBUY88

Or this little jolly.... :{

https://youtu.be/fB-smagT0O4

Now if there was only a method of downloading the whole thread as a pdf my life would be fulfilled! :D

It's not exactly elegant, but if you have Firefox you can select 'reader view' on the right hand side of the url box. This will basically give you a printable version of just text. You could then print and scan.

It's not ideal, but may be of help.

PPruNe has an archive where more posts are displayed per page.
So below you can get the whole thread in just 8 pages.

Concorde question [Archive] - PPRuNe Forums

Why do you want a pdf, for your ebook reader? Guess it doesn't work with just saved html.

In Google Chrome you can save pages as PDF via the printing dialog.
Font is a bit small though.

There are also some webservices that can convert a web page to pdf. Have never used them though.

I'm on a mac so I can print pdf directly from the print dialogue box. Brilliant suggestion from both you and standbykid.

Thank you! :ok:

(Well, N5296s, but that was close). I don't often look at this forum, so only just saw this.

I read this in The Concord Stick and Rudder Book, though my summary of the explanation may not do the author justice.

Good Evening Stilton, M-2 Dude and others.
I am having a nostalgia evening as 20 years ago today I had a flight in G-BOAC from CYYZ to “no-where”.
Actually, it was down to New York out over the ocean for around 30 minutes at FL 550 and Mach 2. For one in the “industry” it was a real treat to be able to have a flight in such an iconic aircraft.
Things I will always remember going out of “reheat” (a more elegant description then afterburner) after noise abatement from being pushed back into one’s seat to being momentarily weightless, the brilliance of the sky at FL 550, the cabin windows being hot at Mach 2 and seeing the gap between the flight engineers panel and the bulk head at Mach 2 due to the aircraft heating. I could go on about the engineering, observing the crew coordination from the cockpit visit (sadly pre-9/11) and there is a certain story about how our group sweet talked our way into the first-class lounge in YYZ and drained all the bubbly British Airways had in the fridge that day but…….
Reading the thread on this aircraft has been fascinating and thank you to all that has contributed to this wonderful story a sincere thank you.