Posts about: "Afterburner/Re-heat" [Posts: 110 Pages: 6]

Well, the 2707 project never advanced to the point where such practicalities were considered - but it's certainly the case that part of the Concorde "B" spec was intended to do away with reheat (afterburner) entirely, and be much more fuel-efficient as a result.

Not necessarily - supersonic travel as a "premium" product was always intended to co-exist with subsonic offerings, much as it ended up doing. There's a revisionist narrative that has the USA betting on mass transit with the 747 versus Europe betting on supersonic transit with Concorde - but all the contemporary material I've read indicates no such thing. Even setting aside the protests within the US against the Concorde, the simple fact is that SST was never going to be a viable domestic solution, so that limited the market for the 2707. Whereas a transatlantic SST was very much a viable proposition due to the transoceanic nature of the journey. It could be argued that even with the oil crisis and the subsequent drop in orders, the UK and French governments gave up on the Concorde project too soon.

If that were genuinely the case, then there would have been no Airbus project or consortium. As Clive correctly points out, the A300 project started taking shape while Concorde was undergoing her proving flights. While there's no doubt that the Concorde project was completed for political reasons most of all, the idea that she was a forlorn hope before she went into service is grossly unfair.

Yet, as alluded to before, the R&D gains and technological knowledge coming from the project helped to lay the foundations of a pan-European aircraft maker which would eventually go toe-to-toe with the best the USA had to offer. The sidestick technology which led to an unprecedented level of commonality between short-haul and long-haul types was first tested on a Concorde airframe (Google "concorde minimanche"). Added to which is the fact that in Concorde, for all the project's problems, an airliner was produced which - on a technological level at least - left every competitor in the world in the dust. That is something that can never be taken away.

No, IIRC the "slaming" was needed to ensure the correct activation of the T/O specific mode, or something like that. Perhaps something to do with the reheat, too.

Thanks for this wonderful thread. Apologies from a non-aviator, but was reheat used in the event of a go around? Did its use depend on conditions, or was it a straightforward yes/no answer?

'Dry' thrust was used for a go-around, except in the case of wind shear when 'contingency' was used. (A bit more than full thrust and reheat).

This post mentions that on three engines, dropping to subsonic, Concorde would lose 30 - 35% range. Much more of a reduction than subsonic planes, but still enough to get to a safe airfield.

On two engines it'll still fly, although with a further reduction in range and possible loss of some hydraulic systems (depends which engines failed).

If I remember correctly, there was some mention of a possible single-engine (plus reheat) go-around, which suggests that at landing weight it might have been able to maintain flight on only one engine.

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?...

• 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.

After about a week of 3-hour nights (not much on the telly) I have finally got to the end of this thread. Let me echo others in praising the patience and technical openness of the main engineering contributors, along with the excellent recollections of the pilots, cabin staff and many others.

I am afraid I have only been on Concorde around a dozen times, and as I live a few miles from Duxford, you'll probably guess that's 101 now in Hangar 1. Standing in the cabin I can only imagine the experience of actually flying in her, but you guys have certainly bought her back to life in my mind at least.

While reading the thread I came up with many questions (around ten or so) and these have been answered in later exchanges on the thread, however I do have a few left over:

1. The speed freak in me always wants to know "how fast"? Notwithstanding the principles outlined on p.55 by CliveL and M2Dude, if the intake system were somehow made "more leaky" and reheat were applied, in theory at least, how much more thrust could the 4 engines produce, in "ideal" conditions (I saw somewhere that -80C had been encountered)? If you then extrapolate the drag, what sort of peak Mach number might be attainable in short bursts (ignoring for now the detrimental effect on the airframe?)

2. There was a discussion or two of the (highly theoretical, expensive and unlikely) prospect of restoring one of the airframes back to flight around p22. However I don't think I saw 101 or 102 mentioned in any of these discussions, are these even further 'gone' (101 having sat outside for 20 years)? On the other hand, would the lack of sponge-like insulation mean less corrosion might have set in?

3. Again on p.55 there is mention of (naff) paint schemes and their bad effect on skin temperature. Was the paint on Concorde specifically chosen to radiate infrared (for example) to help cooling? The SR-71 (which I also visit at Duxford regularly - how lucky am I!) of course is matt black, which presumably radiates even better? When the airframe attained thermal equilibrium at the top of the cruise, what were the relative contributions to cooling of: radiation, cold uncompressed air passing over parts of the skin, the internal aircon (cooling from the inside), etc?

4. M2Dude referred a couple of times to robbing spares from other airframes. Spares that may have been 5-8 years old? What sort of testing regime must these spare parts go through to ensure they are still fit for flight? Is it labour-intensive?


If I can opine (at the risk of having M2Dude chastise me if he still reads this - as I am not staff) the computer he mentioned on page 37 sounds to me very much like a "bit slice" computer. These were typically constructed from discrete logic and quite often had very long words - 64 or 128 bits. I only ever saw one of these in my 30-year career in computing, a rare beast indeed. And yes I remember that Mil Spec TTL - back in the day I used to pop the lid off the ceramic packages and you can look at the gates, and even watch the silicon glow if you apply a bit too much Vcc! But I digress.

Thanks again for a fascinating thread.

@EXWOK


There was a certification requirement for descent time from FL600 down to FL100 if I recall correctly. Can't remember the value though. In flight reverse was developed to trim some fraction of a minute off the time to get inside the requirement


@ a_q

Not sure what you mean by a "leaky" intake. At about 2.2M the first shock would hit the intake lower lip and from that point on the total intake mass flow was frozen. Increased engine mass flow could only be obtained by reducing bleed flow and that gave higher engine face flow distortions driving the engine towards surge and lower intake recovery. So engine mass flow was effectively fixed also.
Then the amount of "dry" fuel which could be added was limited because the higher Mach number increased the engine entry temperature but the maximum turbine entry temperature was fixed.
You could add thrust by using reheat, but you would not get as much as you would like because the final nozzle, being designed for 2.0M would be too small for optimum efficiency at higher Mach numbers.
Overall, IIRC we got to 2.23M in flight test. If you pushed me I would say it might be possible with reheat etc to get to 2.25 or 2.26M, but it would be a blind guess!

@ BN2A

I'm sure the real experts will "adjust" my understanding - but I believe Concorde, loaded for the transatlantic "Sierra" routes, could hit about 5000 fpm peak VS when climbing at 400 KIAS between ~10,000 and ~28,000 feet (wherever 400 KIAS = M 0.99). Leaving a coastal airport (New York, Barbados, Dakar), she would quickly be clear of land and could more or less transition directly through Mach 1 as soon as she reached 28-30,000 feet.

Those 4 Olympus engines could maintain Mach 2 with no afterburner at 50,000+ feet, so they had tons of excess power down low. Again my understanding is that they stayed at 100% dry thrust from brake release until TOD (except for subsonic cruise segments), with the AB added for takeoff, and when accelerating from Mach 0.96 through Mach 1.7.

Mach 2.00 was reached in about 30 minutes @ ~51,300 feet, depending on atmospherics - a relatively long slow slog compared to the initial climb and acceleration.

From inland airports such PDG or Heathrow, there was a "pause" for level subsonic cruise (M 0.94-0.96) in the high 20s until clear of the coastline by 20 miles (over La Manche or the mouth of the Bristol Channel.)

@ leb001 - greenhouse visor, BA livery, and short tail - probably G-AXDN (aircraft 101). Although I'll defer to the experts, as always.

Good day,

Just found this pic on the www and I think the reheat looks a bit ragged compared to the Reheated Engines I have worked on - RR Spey & RB199.

Is this a representative sort of view or a false picture and the real thing is much neater with Mach Diamonds and the like???






regards
Howie