Posts by user "CliveL" [Posts: 162 Total up-votes: 0 Page: 8 of 9]¶

Thanks dazdaz; that's the shot I was trying to post.

@ Volume


Sorry for slight delay; I hadn't a clue and had to ask an old friend who was directly involved in Flight Test. This is his verbatim reply:


I think that is about as much as one could hope for after all this time

I suppose there might have been a combination of system failures that would have caused it to deploy, but AFAIK it never did, so there was nothing to write up.

At low altitude think 455 ktCAS.
Tmo was a long exposure structural limit
Mmo was an intake limit
Vmo was a structural (flutter) limit

Sorry, you will have to excuse my confusing statement as I am writing from. hospital bed and not at my sharpest!

To be clear, the original question related to maximum speed which I took to be Vd - 455 kts from about FL 60 up to about FL 360
This was the flutter clearance and was usually acheived in a dive. Vmo was thenwhat you got by backing off to give the statutory margins. Not strictly a flutter limit though limited by flutter! Vmo of course could be flown dry

Thank you everyone - much appreciated

Bit of a hypothetical question requiring a judgemental response!
My short answer would be not much more than the certified limits - at least not without significant modifications.
FL680 was achieved at the end of a zoom climb, so the Mach No was a lot less than 2.0
M2.23 was in a shallow dive. The object was to demonstrate sufficient margin to avoid surge following the worst temperature transient specified in the TSS regulations. To that end both the intake laws and engine operating lines were tweaked as functions of Mach No to minimise intake flow distortions and maximise surge margin. The result was a long way from the performance optimum one would need for steady cruise.
The power plant was being pushed to its limits at this Mach No.
(As an aside, the subsonic rules make no mention of temperature transients as a cause of Mach exceedences. Some recent incidents suggest this could usefully be reviewed)
The altitude limit could perhaps be more readily expamded. The aircraft normally flew a cruise climb bcause at Concorde cruising altitudes there was no ATC conflict. The altitude was very sensitive to ambient temperature and aircraft weight. FL600 would be associated with end of cruise on a coolish day.
To usefully increase cruise altitude would require more engine thrust, but this could only be obtained by increasing engine TET which would screw the engine fatigue life.
Increasing Mmo from 2.04 would need an increase in Tmo (400 deg K) at any temperature above (from memory) ISA. This in turn would affect the airframe fatigue life unless the structural material were changed. Even then, there were a lot of nonmetallic bits (seals etc) that would also have needed replacement.
Sorry if this is a gloomy assessment, but that is the way I see it!

There was a lot of work devoted to minimising drag of surface discontinuities etc, but almost nothing on skin surface changes. I'm not sure we understood enough about supersonic skin friction with kinetic heating added to really be qualified to speculate on the effects of varying the surface.
The most troublesome parasitic drag items were leakage losses, especially from the powerplant

@tomahawk, pattern is full

You really need an input from a BA pilot, but my memory is that the approach to LHR was up the Bristol Channel not the English Channel.
Original decel point was moved back about 100 n.ml to avoid secondary boom effects over West Couhtry. This put it somewhere south of the southern tip of Ireland

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.

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

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?

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?

@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?

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.

Casper

You might find it useful to read the BEA accident report (in English) f-sc000725a which has all the information you are looking for

@Lancman

Not so on several counts

1. The phenomenon of structural damage arising from internal pressure waves in fuel tanks was unknown when Concorde was designed. Consequently the design made no specific provision for it.
2. 17% ullage is ludicrous on an aircraft for which fuel capacity is of vital importance. The correct value for tank 5 on Concorde is 6%.
3. Tank 5 was filled to 94% capacity at start of roll which would have been normal for any long distance flight. No more fuel was added to it; on the contrary, a very little might have been pumped into tank 1. The fuel transferred forward from tank 11 was put into the engine feeder tanks 1 to 4. This of course was not enough to compensate for the demands of OL593s operating at TOP with afterburner, so these tanks were running down and would have been topped up (tanks 1 & 2) from tank 5 at some point.
5. What actually happened was that the take off acceleration threw the fuel to the back of the tank so that the free surface volume was confined to a small zone in the upper forward region of the tank. When the rubber struck the rear part of the tank undersurface the fuel above it was constrained by a solid wall, which was enough to generate the reflected shock waves.

@Lancman

There a a lot of misinformation sculling around on this.
The final report states that the overfill was 300 litres (237kg) put into the engine feeder tanks 1 to 4. These tanks are grouped to have approximately equal moment about the CG so if it was, as seems likely, 75 kg in each there would have been negligible effect on the CG.

There was no overfill into tank 5.

It is all a long time ago, but as SSDriver says the overfill capability was probably there to cater for extended taxi or waiting time operations.

In this particular case the dispatcher ordered 2000kg rather than the standard AF allowance of 1000 kg to be loaded for taxiing presumably because he/she believed a more distant runway would be used because of maintenance work, but in the event the pilot asked for and was given the usual runway which meant that the aircraft was overweight for take off because only 1000 kg of taxi fuel was used. [Plus of course the additional baggage]

If the intent was to get the CG forward, what would be the point in transferring fuel to anything other than the forward trim tank? In particular why to the engine feed tanks which are arranged to be CG neutral?

However, the BEA report says:
I can't make that compatible with tank 5 being continually topped up no matter how I try

@SSDriver

You are quite right; I should have checked that
A simple check of BEA's figures shows that they were assuming transfer into the feeder tanks.
Their sums say one needs to transfer about 700kg to make a CG shift from 54.2% to 54% (starting with a ZFCG of 52.4%). However, the engineer's panel after the crash showed that he had dialled in the loadsheet ZFCG at 52.3% so the fuel system would have transferred only 350 kg.
I can't see anything to suggest otherwise than that fuel transfer was stopped when TO began and that tank 5 remained at 94% total capacity throughout

We crossed in post, but where did you get the information that transfer was continued through take off? I didn't find anything in the official report