Posts about: "Thrust Reversers" [Posts: 27 Pages: 2]

First of all a hearty 'Happy New Year' to all our readers. As I've been 'away' for a week or so, I hope you will all indulge me as I answer a few posted points. (I totally agree with what Bellerophon said about restricting our posts to the 'techy' and nostalgic stuff, so will not respond to anything else here) .

CliveL
I accept and understand of course Clive that this was a difficult issue to predict with any certainty, it was just a shame that's all, that the Type 28 never fully lived up to its promise and potential. However, the one aspect of the SNECMA design that was very poor indeed was Secondary Nozzle system integrity. Throughout the operational life of Concorde, there were almost more operational disruptions due to short-fallings here (bucket runaways) than any other issue. It was only near the very end of Concorde's operational life that modifications were finally forthcoming from SNECMA to address this.

Poornamechoice
I am so sorry to dispel this particularly charming story, but there were absolutely no keys as such for Concorde, Sorry (But I am so glad that you are enjoying this wonderful thread).

ChristiaanJ
Oooooh speaking for myself (and I suspect a whole lot more of the BA Concorde familly) there is a void alright. Having lived with the 'lady' day in, day out for almost 30 years (up to November 2003) there was an absolutely yawning chasm left for me personally. (The world of the blunties is just not the same.. just a whole lot slower ).
What is gratifying though, is the enormous amount of interest that there still is for Concorde; both in this thread and in the world at large. I guess she lives on after all.

These pictures of 101 etc are absolutely marvellous; I really like the 'sexy' wing shape photo's. One little unique point about 102; she flew with a different intake control system to any other Concorde, being an 'improved' Ultra Electronics analog system. (Although the intake itself was aerodynamically the same as the later aircraft). Never really understood why our French friends chose this particular path with this aircraft. (Perhaps CliveL can shed some light on this??).
Very best regards to all.

Dude

As usual Dude you beat me to it! I really must give up having another life

As Dude says, the 'cruise' condition was set by the aircraft specification for transatlantic range on an 85% (ISA +5) day and the chosen mach Number was 2.0 (of which more anon). This gives a Total Temperature of 400.1 deg K. [Dude, I know your pipe-smoking thermodynamicist and he was having you on - he is quite capable of memorising the square/square root of 407.6 or whatever!]
To give margins for sudden changes in ambient temperature (we had to cater for a 21 deg change in one mile) the Mmo was set at 2.04 which matches 400 degK at ISA +1. In theory then we could have flown faster than our chose Mmo at anything colder than this, but there are two limits:

1) The object is not to fly as fast as you can but to fly with minimum miles/gallon. If you have a nice cold day and enough thrust to go either faster or higher which do you choose? For best specific range you go higher every time.
2) The thing that everyone forgets is that civil aircraft have to have margins around their authorised envelope. In Concorde's case these were set principally by the intake limits and engine surge.

Dude also says quite correctly that 101 flew to 2.23M but the production aircraft was limited to 2.13M. Now you may not believe this, but 101 could fly faster than the production aircraft because she (101) leaked like a sieve!.

I doubt I will get away with that without some explanation

Once you get past a certain Mach Number the airflow into the intake is fixed. The performance (intake pressure recovery and engine face flow distortion) then depends on how this air is shared between the engine and the throat 'bleed'. This bleed was ducted over the engine as cooling air and then exhausted (in principle) throught the annulus formed between the expanding primary jet and the fixed walls of the con-di nozzle. But if you took, or tried to take, more bleed air the intake pressure recovery went up and the primary jet pipe pressure went up with it. This meant that the primary jet expanded more and squeezed the available annulus area which restricted the amount of bleed air one could take.

Obviously if there are alternative exit paths between intake and final nozzle then you can take more bleed air off and the engine face flow distortions will benefit along with the surge margin. 101 was fairly 'leaky' in this respect, particularly around the thrust reverser buckets on the original nozzle design. This meant that 101's intake distortions were lower than the production aircraft so she could fly faster without surge - at least with the first attempt at intake control 'laws'. We managed to tweak most of the margin back eventually. Engine bay leaks were good for surge margin but VERY bad news for m.p.g.!

Here are a couple of diagrams to show what I mean. the first shows the surge lines for the various aircraft variants and also the N1 limiter Dude was talking about. NB: the X-axis is LOCAL Mach Number not freestream. The difference comes from the compression of the underwing flow by the bit of the wing ahead of the intake. Mmo + 0.2 is shown

">The next shows the surge free boundaries in sideslip and normal acceleration. You can see the zero 'g' capability Dude was enthusing over. ">

As for 'high speed stall', I don't think we ever contemplated trying it! Our requirements in 'g' capability were defined and that was it. Besides, the aircraft would fly like the proverbial stone-built outbuilding at those sorts of conditions so I don't think one would have been able to get anywhere near a stall in the conventional sense. Stall as commonly defined for subsonics (deterrent buffet) might have been another matter, but I don't remember anything.

Cheers

I so remember the BAe AST images from the 1980s, I always thought what a potentially nice looking aeroplane she was. I guess that vastly improving the L/D & T/W ratios could go quite a long way to improving the operating economics, but the noise issue was always going to be the crippler. (I know that they were looking at a 'leaky' version of the OLY593, ie. a very low bypass ratio, but this of course would still not really cut the mustard as far as noise goes). I guess there are no current takers then
Clive, you really surprise me when you say you don't think that composites would be used from a future SST, is there a material reason for this? (I'm curious because being of a simple avionic brain, I always assumed composites would be used. But if anyone knows this stuff, you certainly would Clive ).
To answer Mike-Bracknell's original query, as far as avionics goes we can really go to town. For her age Concorde had some truly amazing aircraft systems, for instance the flying controls. To enable mechanical control (both FBW channels failed) there was a highly complex and heavy mixing unit under the rear floor. (To mix pitch and roll pilot mechanical demands into differential elevon demand inputs). This of couse would have to be done away with, as well as the relay jacks and replaced with a pair of side-sticks. (See posts on previous page). A 2 crew operation would obviously be the way to go, but neither desirable or possible in my view when Concorde was designed. A triplex or quadruplex flying control system (possibly even integrating autoflight) would replace the Concorde collection of several analog boxes with a very small handful of lightweight digital units.. The powerplant control will have major weight savings, just take a look at this lot. 8 Engine Control Units, 4 Bucket Control Units, 2 Nozzle Angle Scheduling Units, 4 Reheat Amplifiers, 8 AICUs, 4 Air Intake Sensor Units and a single Air Intake Test Unit could potentially be replaced by just 4 multi-channel EEC type units. (On subsonic aircraft the EECs are mounted on the engine itself, not sure if that's a good idea for an SST, given the operating environment. Air Data and Navigation systems take a major simplification and weight saving, the 3 INUs and 2 ADCs (All of them straight from the 'rent a hernia' store as far as weight goes), could be replaced by a single ADIRU and a SAARU. The fuel indication/management side of things (2 FQI packs, 2 level switching packs and 3 CG computers) would probably be replaced by a single Fuel Processing unit. Ahhhh perchance to dream

Best regards
Dude

Hi,

I've been following this thread with great interest. I hope some of you silver haired Captains (yes, with a capital C) can answer a question that has been bugging my mind for the last few days.

After watching the ITVV Concorde video it is apparant that you check the Reversers and air shut off valve. How do you do this test and what are you looking for?
I've been trying to get it to work in the FLS ConcordeX , but so far without luck. The buckets move accordingly in the air and when selecting reverse. And they say it's simulated as well.

Thanks,

Martin

I was recently able - for the first time in about twenty-five years - to visit the London Science Museum. Not only which, I was able to spend the whole day, on my own , with no children dragging me along. As always, the Aviation Gallery occupied a lot of my time there, but I was quite surprised that there is very little about 'our lady', when I should have thought she was sufficiently 'white heat of the technological revolution' to qualify for a whole display to herself?

Going on from remarks about tracing the number of 593s still around, there is one there. Right at the back corner of the Aviation Gallery, on a yellow trolley and next to an RB211. Very little explanation to it and none whatsoever of the astonishing intake/engine/thrust bucket combination.

The only other Concorde exhibit, that I could find, was a beautiful 'cut away' model, standing on a mirror. The model was so detailed and interesting, I took a photograph of it, as I did of the 593, but I find my "PPRuNe Posting Rule" do not allow me to post attachments.

Is it not slightly surprising that there is not more about Concorde there? After all, I was able to revisit an 'old friend' of mine - the original EMIScanner MkI CT scanner from Atkinson Morley's Hospital - that I used to look after back in the day.

Roger.

As others have done before, I'd like to add my thanks to the many contributors who continue to make this such an engrossing thread

As I look to my left, on the wall is a framed, fading, roughly A2 photo of three of these fabulous aircraft, outside the hanger at Filton in the mid-seventies - presented to my grandfather, who worked there on Concorde production. When I was about ten years old, I was lucky enough to be taken by him on a tour of the works, and can remember being allowed to have a good look around the inside of the aeroplane.

The photo that hangs next to it was taken a few years ago by my bestest flying buddy, Alex, as we thermalled out together over the Brecon Beacons, sitting in bucket seats, suspended, by looms of kevlar, from large, sailcloth kites...

Not too difficult to see where my own inspiration for flying came from

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.