Posts about: "Super-cruise" [Posts: 13 Pages: 1]

Approach handling was an interesting exercise - being so far down the back of the drag curve (over 100kts below best L/D) very accurate thrust handling was required.

The autothrottle was always used for approach if servicable, except for a two-engined approach, and was absolutely excellent. There were two, operating in parallel, and if the speed was more than a couple of knots out for more than a few seconds it was unusual. In IAS ACQ mode there was an active input from the INS which tracked grounspeed and so enabled anticipatory throttle movements during wind changes - if an autoland runway was available the preferred method of dealing with an approach likely to experience windshear was to carry out an autoland. (I think I speak for everyone, though, if I express a preference for the just going somewhere else option).

In Supercruise one autothrottle only was rearmed if the associated autopilot was engaged - it wasn't active but was available to cater for sudden drops in temperature which could cause unpleasant sudden high rates of climb if the temp shear was sufficient.

The rest of the flight - basically manual thrust, usually with the throttles fully forward.

Maybe one day we'll start making aeroplanes with such sophisticated systems again...........there's still lots that hasn't been hinted at on this thread

To conclude this slightly o/t story :

The Tu144D was the last production model of the Tu144.
With improved engines and other refinements, it was capable of supercruise (Mach 2 without afterburners). Only five were built, and they came too late ; the aircraft went out of service, and were put into storage.

Tu-144D s/n 77114 was brought out of mothballs (with less than 83 hours "on the clock") for the joint NASA/Russian program in the '90s and modified, with completely new more powerful engines (same as those of the 'Blackjack' Tu-160 bomber) and a fit of sensors and test equipment, to become the Tu-144LL (flying laboratory). A total of 27 flights were made.

The entire "High Speed Civil Transport" study indeed cost over $300M, but the actual work on the Tu-144LL reputedly cost less than $20M, although it's not known exactly what that bill represents.

CJ

Nick Thomas
This of course is one for one of my pilot friends to answer properly again, but as galaxy flyer says, it's an 'eye to wheel' issue here when compared to other aircraft.
galaxy flyer
Again best answered by learned gentlemen such as my friends EXWOK or Bellerophon, but to the best of my feeble knowledge a resounding NO, at least as far as CRUISE flying was concerned. As the majority of the flight was carried out between FL500 and FL600 there was really no weather as such to avoid during supercruise. (As has been previously posted, at Mach 2 you would invariably be above FL500). Only at extremely low latitudes where the tropopause could theoretically extend up to around 70,000' was there ever any chance of seeing any cloud anywhere near your cruise altitudes. The only turbulence as such you would ever encounter was as the result of a temperature shear, but these never felt to be too much in the way of 'bumps' to me. And again, only at very low latitudes did you encounter severe shears anyway; anything encountered on the North Atlantic was generally very mild and civilised.
A CONCORDE PARADOX
The tropopause issue here is an interesting one, in that the coldest stratospheric temperatures we ever encountered were close to the equator, whereas the WARMEST temperatures possible are over the POLES , where the tropopause can be as low as 22,000'. This is just one of the many paradoxes involving Concorde, and the reason why the aircraft would never be routed over the poles, BECAUSE THE DARNED TEMPERATURES ARE TOO HIGH, in terms of the stratosphere. The result here would be that the aircraft is temperature (Tmo) limited all the time to 127 deg's C. (I previously mentioned in another post in this thread that only 5 deg's C above ISA, -51.5 deg's C, would mean Tmo being reached at Mach 2; any warmer and we HAD to slow down) The relatively high polar temperatures mean that we are unable to fly anywhere near Mach 2. Another paradox would then come into play, the slower your cruise speed, the HIGHER your fuel burn. It was originally proposed in the early 1970's that Concorde would fly from London to Tokyo, and the routing for that needed two things: It could not be polar, and possibly just as important , you required a refuel stop. The Soviet Union amazingly proposed granting a supersonic corridor over Siberia, refuelling at the Siberian city of Novosibirsk. This was hardly an ideal routing (definitely far from a great circle) but was arguably one of the very few that was possible at all. This by the way was not some early iteration of glasnost, but the Soviets fully expected that flying thoroughbred, the TU-144 (bad dude ) to be a success, and could compete side by side with Concorde.
ANOTHER CONCORDE PARADOX
If anyone wonders why when you flew faster you burned less fuel, it was primarily down to drag, actually a thing frighteningly termed as 'pre-entry spill drag'. As most people (???) are aware, the Concorde engine inlet utilised a series of carefully controlled and focused shockwaves to slow the air down entering the engine; in 14 feet of engine intake you lost in the order of 1,000 mph of airspeed! Now most of these different shocks varied with a combination of intake variable surface angle, intake local Mach number and also engine mass flow demand. However the oblique shock coming off the top lip of the intake produced a shock that varied with Mach alone, and would project downwards, just forward of the intake bottom lip. Due to the air downstream of this fairly weak shock still being supersonic, a measured amount of this air spills downwards, away from the intake. If you can possibly picture it, we have this wall of air spilling downwards over the lower lip of all four intakes, the combined effect of this supersonic forespill is a fair amount of drag. The faster we go, the more accute the angle of the shock and therefore the less air is spilled, and in consequence the lower the spill drag. Remembering that cool temperatures could produce a higher Mach number, temperature really could either be our friend or enemy, but cool was COOL
I hope this explanation does not sound like too much gibberish, but it really was a fact that 'More Mach = Less Fuel'. Hope it makes some sense.

Dude

Interesting & nostalgic thread. Nice to see this monumental aviation achievement still generates such passion...

In case it's of interest (and suitable health warning as the memory fades)...

The heat did evaporate water vapour in the airframe - reducing corrosion. I remember when the 5 BA aircraft were returned to service, after the post-accident mods, their weight and balance certificates were prepared and found to be out by (IIRC) more than a tonne. This represented water in the airframe present after a year on the ground, and was gone again after a couple hours of supercruise on return to service. Back to the weighbridge for new W&B Certificates....

Vortex lift caused buffet which felt very similar to a conventional wing's stall/low speed buffet. At landing weights (I hate the trend of using the term "mass": weight is a force, mass is not!) you felt the buffet start as you reduced speed (CAS: Vc) to about 250kts. It was handy as a reminder that you should select visor down / nose to five below 250kts (the recommendation was as you slowed through 270kts, but latterly we were in the habit of holding at 250kts nose/visor up - I think TCAS was quoted as a backup to the more limited visibility in that config). At takeoff weights, the buffet went at more like 270kts accelerating. So I'm pretty sure there was no vortex lift at AoA > 7 degrees (250kts at LW).

Recommended subsonic cruise at MTOW was F260 / M0.95 which was equal to Vmo of 400kts (CAS). It was best cruise because Vc=400kts was also min drag at MTOW. F280 meant a slightly more draggy speed of 384kts, but some preferred it because when cleared to climb & accelerate supersonic (the official expression was "go for it") it gave you a bit of slack against Vmo when eng put the reheats in. But we tended to ignore the overspeed warning anyway: it was supposed to go really really fast...

We never flew with visor down and nose up unless it was bust - that config was only used during pushback (except one captain who always thought it looked better visor up....). Visor down max Vc was 325kts/M0.8 so it would limit subsonic cruise, and besides it made a racket like that.

It was a beaut in x-winds - a total lack of yaw-roll couple meant you just straightened the 'plane up with rudder and carried on into the flare as normal. No roll to counteract, and the sideways "lift" created by the rudder deflection on the fin pretty much equalled the x-wind drift. Nice.

Wind limits were Crosswind 30kts (15kts contaminated or autoland), Headwind for autoland 25kts (or manual "reduced noise" approach: that's a technical way we used to reduce the noise footprint down to 800' by flying at 190kts then reducing to a target speed of Vref+7kts at that point). Tailwind 10kts. All these limits were, of course, subject to "on the day" performance limits calculated at the time. I seem to remember there was an over-arching limit of 6000' on r/w length, subject again to "on the day" performance limits. OK, I cheated on this paragraph and dug out FM Vol 2a.

There were loads of other limitations which were, by and large, more "esoteric" than a conventional airliner and which had to be learned for the conversion course. It really made the head hurt, and would have been impossible without a big loverrly picture of the beast on the wall chucking out yellow smoke and making noise. Even a static picture of her seemed to make noise...

No one who flew it could really believe their luck, but one thing for sure is "they don't build them like that any more"...

Ahhhhhhhhhhhhhh..........

Nick Thomas


... on shorter charter flights was there a mininium ammount of fuel that had to be loaded just to always have enough fuel for CofG movement...

Yes, 35,000 kgs, at take-off, for a short supersonic flight. This would allow sufficient fuel to be transferred rearwards in order to achieve a CG approaching 59%.

If the flight was to remain subsonic, the fuel figure dropped to 25,000 kgs, as the required CG for subsonic cruise was 55% not 59%.

Both these figures were at take-off, so the estimated taxy fuel had to be added to these figures in order to arrive at the minimum fuel figure required to be loaded.


...was it possible to be in a position where trip fuel, fuel to an alternate etc was less than the fuel required for CofG movement after take off?...

No, at least it should not have been!

However, a situation was sometimes reached in flight, generally only towards the end of the planned supercruise portion of a LHR-BGI sector, where, with the aircraft at M2.00 and FL600, it was no longer possible to maintain a CG of 59%, as the "ballast" fuel, which had been transferred aft into tank 11, was now required forward again as "fuel" fuel, to top up other tanks which had reached their minimum permitted levels.

In this case, once the forward transfer of fuel had begun, the CG would also be slowly moving FWD, and one would be compelled to commence the decel and descent earlier than desired, something EXWOK touched on here much earlier in this thread.

Best Regards

Bellerophon

M2Dude wrote:

You'd have to say that designing and building the aeroplane probably isn't the tough issue. I mean you could probably adapt a military design - a Tornado can lift more than six tons of stores can it not? So that's a ton of people, a ton of bling to keep them comfortable and four tons of fuel ...... oh.

The tough thing needed, the really clever thing that Concorde did and no other aeroplane, sorry, only one other aeroplane - our 'honorary Concorde' the SR71 - would be to design the engine /intake /nozzle configuration that would let our 'Tonkorde' supercruise at Mach two, while running on the smell of the stuff.

Roger.

'Dude -

I didn't ever use this mode, and never saw anybody else use it.

Significant turbulence was almost unheard of in supercruise - light to mod was the worst I ever had. Subsonic one would be subject to the same air as the blunties, but in an aircraft which had a high wing loading and good controls. Once you got down into the low-level turbulence on a windy day (say 2000' and below) you were in vortex lift and this seemed even better.

I flew this machine through some vicious conditions and it was - by a country mile - the best aeroplane I've ever flown in bad air, better even than the 747. I could bore you with war stories, but will illustrate the point with the time we asked Tower to advise the aircraft following us that it was pretty wild below 2000', only to hear that everyone else had cleared off owing to the wind conditions.......

The only people that really got a rough ride were the flt crew, who were at the front of a long extension ahead of the really stiff part of the hull, which tended to whip around long before it got bumpy in the cabin.

It wasn't like flying a transport aircraft at all in rough conditions, and this was a real help in keeping a prestige operation in the air when bad wx appeared. (Of course it wouldn't have helped in the present BAA-induced debacle).

Concorde would produce contrails in the same conditions that a conventional aircraft would. I've seen pics of it contrailing in supercruise, and it's a big trail.

Outbound, for reasons of best efficiency, the subsonic cruise would be at FL260 or 280 so contrailing was unlikely, but I would expect the occasional contrail inbound (cruising in low- to mid-30's) so you were unlucky not to see one if you were looking at the right time.

It would have been no more or less visible on primary or secondary radar than other commercial types.

It would be hard to see with the naked eye, unless the sun was reflecting off it.

Now you didn't really mean that pun did you?

My reticence on using composites springs from the fact that, although it is little known, there are doubts about the life of the resins that bind the carbon fibres together when the material is exposed to a combination of high temperature and low atmospheric pressure over a long period. I know the Americans were worried about it for their 'supercruise' fighter designs and were experimenting with various exotic, expensive and obnoxious materials. Since all this was over 20 years ago and they now have their supercruise I expect they have a solution by now, but it is probably secret (I don't know that for sure however, it may well be in the public domain, I just haven't been following it). But even if they have a solution for military aircraft there is a world of difference between something that is OK for military designs with a supersonic 'life' of say 5000 hrs with a safety factor of what? 1.5? and a commercial transport with a life requirement of 50,000 hrs with a factor of 3.

BTW, if you thought the underfloor mixing unit was complex, you should have seen it in the original BAC project that didn't have electric signalling so the mechanical mixing was non-linear to try to account for varying flight condition demands

CL

CliveL
Thank you for your reply, what you describe is absolutely fascinating; It seems that composites may not be the panacea for all aircraft structural problems after all. I confess. I'm afraid that I did intentially use that awful pun (sorry ).
Regarding strucural materials, I remember reading what Ted Talbot wrote in the manuscript for his brilliant work 'Mach 2 and Bit' (not sure if he ever did get it published) when he spoke about the Bristol 188. He said something like 'the never to be repeated experiment of making an aircraft structure out of stainless steel'. One can only imagine the manufaturing problems that Brisol must have had with that one. (I seem to remember that the strucure was welded and not rivetted together ).
Yes the US now has a supercruise aircraft (the F-22 Raptor) but not of course for up to 3 hours of up to 400\xb0K either. (Although a truly superb aircraft nonetheless). And as you say, military structural material airworthiness standards in no way apply to a civil project.
I can only imagine what the original Bristol (for the Type 223?) mixing unit you described must have looked like. The Concorde unit certainly dominated the whole underfloor picture in quite a sizeable area down the back; here's a diagram of the beasty:
For all it's complexity however I can never recollect any problems occuring there.

It looked far more intimidating in the flesh under the floor however.

Best regards
Dude

No thrust vectoring. The secondary nozzles did go to 'divergent' setting from 'convergent' for supercruise, but the thrust was always in the same direction (rearwards).

If the thrust had been angled downwards, it would simply have induced a nose-down pitching moment. Most undesireable!

I have a query about the thrust of Concorde's engines. The quoted static thrust of the Olympus 593 is 32,000lb, but it has been frequently stated that in supercruise, the majority of the thrust was provided by the intakes. That being so, how much thrust was actually produced overall at Mach 2, and how was this measured (if indeed it ever was)?

I suspect that, given the Concorde's rather unusual fuel consumption figures, the most efficient climb profile was also the fastest one, since pretty much anything other than the M2.0 cruise-climb was fairly inefficient. From way back in the thread ( here ) the minimum time to hit M1.0 was about six minutes, and M2.0 came at 9 minutes (although a few posts later someone mentions that these figures may be wrong as the fuel transfer rate wouldn't allow such a fast climb).

Some questions from me, after reading through the thread:

- Someone mentioned that, as a result of Concorde's sustained supercruising across the Atlantic, the twenty-odd Concordes have more supersonic flight hours than all other aircraft combined. Does anyone know what the figures are?

- What was the minimum range for supersonic travel to be worthwhile? Obviously if you were only going a few hundred kilometres it'd make more sense to cruise at 29000ft an M0.95 rather than climbing all the way up to 40000ft+ and M2.0.

- What other aircraft are/were more efficient supersonic than subsonic? The modern supercruising fighter jets (eg. the F-22) are still more efficient at subsonic speeds. The original Tu-144 would certainly have been much more efficient subsonic (since it couldn't supercruise); I'm not sure about the later models. The SR-71 was more efficient at high supersonic speeds than at low supersonic speeds, but I can't find anything about subsonic fuel consumption. And that leaves the XB-70, which is just a big unknown.