Posts by user "CliveL" [Posts: 162 Total up-votes: 0 Page: 1 of 9]ΒΆ

CliveL
December 19, 2010, 17:12:00 GMT
permalink
Post: 6131740
Gentlemen,

I am new to this thread, and indeed to Pprune. PBL pointed me at this fascinating Concorde thread and I think I may be able to throw in a few points from the point of view of one of the original design team.

It may take a while because there are so many interesting aspects, so I propose to start with early postings and work through. My apologies if this results in some duplication!

I suspect I may have worked with some of the major contributors.

Subjects: None

CliveL
December 19, 2010, 17:24:00 GMT
permalink
Post: 6131750
Autotrim

It wasn't quite as simple as that. The fuel transfer system really fixed long term problems like getting the elevator trim broadly at optimum throughout (and really at optimum in cruise of course). The Mach trim/autotrim really worked on a shorter timescale to maintain stability at constant CG.

Sure the autopilot made it superfluous to some extent, but to certificate the aircraft it had to be conventionally stable when flow manually, and applying a nose down command to get a speed increase is a basic airworthiness requirement for all aircraft.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Auto-pilot  C of G

CliveL
December 19, 2010, 17:35:00 GMT
permalink
Post: 6131769
Sure, Concorde was the first aircraft to fly with FBW flight controls, but electric signalling on a major aircraft system was introduced on the Proteus engines that powered the Bristol Britannia. These were of course built by the same company, Bristol Aero Engines, that built the Olympus.

There are some (I am not among them) who would say that the Concorde project was a good way to learn how NOT to run a major international collaboration

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FBW (Fly By Wire)

CliveL
December 19, 2010, 17:48:00 GMT
permalink
Post: 6131785
Concorde was unique in having take off performance scheduled for a 'point'CG. Before that all aircraft had FM performance based on the most adverse CG in the certificated range - normally the forward limit. I well remember lying on the grass on the airfield at Madrid waiting for Concorde to get back from a 'hot and low performance' test flight and chatting to the CAA surveyor responsible for that aspect of the certification and speculating on whether we could cash in on the ability to control the CG accurately.

After about half an hour we came to the conclusion that provided we put certain checks in place, and still retaining the 'classic' performance in the Flight Manual, we could insert a special TO technique using a single point CG which would give, from memory, about 1.5 tonnes more TO weight - something not to be sneezed at when your payload fraction is as low as Concorde. Needless to say this 'special' soon became the norm. I doubt if we could get agreement on such a topic in that timescale today!

I noted in another post that memory was blurring after seven years from active flying. I am writing about events thirty or even forty years ago, but I still have my notes.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): C of G

CliveL
December 19, 2010, 18:01:00 GMT
permalink
Post: 6131812
I haven't worked out how to reply to postings and quote the relevant remarks yet - cut and paste doesn't seem to work, sorry.

Anyway, after that 1980 engine fire incident we did find a couple of small holes in the centrewall and as a result we fitted some ceramic coated steel plates in the vulnerable areas.

But as stated, the fire precautions built in did a good job. In this connection though it is worth saying that the cooling air passing over the engine comes from the ramp bleed in the intake and that it is controlled by 'secondary air doors' in the corners left between the circular engine and the square nacelle. These are there to stop air flowing back from the engine bay into the intake during takeoff and are opened once the pressure diferential between intake and engine bay is favourable. Part of the fire drill was to close these doors so the engine fire was deprived of oxygen, which helps a lot

CliveL

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Bleed Air

CliveL
December 19, 2010, 18:13:00 GMT
permalink
Post: 6131827
Way back in August Tim 00 was asking about preset limits on the fuel transfer system.

One of the major challenges was to match the fuel transfer rate and initiation point to the aircraft performance. Once started the fuel pumps change the rate of CG shift in a more or less constant manner, but the aircraft acceleration through the transonic range is very dependent on weight and OAT, so the actual CG at any one mach number will vary from flight to flight. But it must be possible to make an emergency deceleration form any point in the acceleration backdown to subsonic conditions where the aerodynamic centre will be further forward and hence there is a risk that the aircraft might get into unstable conditions.

A lot of work went into this problem and the allowable CG boundaries reflect thsi to some extent.

CliveL

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): C of G  Fuel Pumps

CliveL
December 21, 2010, 10:19:00 GMT
permalink
Post: 6135263
quote:Re the autotrim, tell us some more?unquote

It is a little complicated, but let me go back half a step.
Concorde was not certificated to FARs or BCAR (the French code was essentially a straight translation of FAR) but to completely new set of requirements known as TSS (Transport Supersonique Standards). The old UK ARB had initiated discussions about these even before cooperation negotiations had started. The result was that young, junior engineers got to debate the basics of airworthiness rules with older, experienced airworthiness specialists. In hindsight it was wonderful training!

But to get to the point, it was this thinking that allowed us to ignore some of the older rules which, although great for the aircraft flying at the time they were written, had little or no relevance to SSTs. We could interpret that as trying to find out what the pilots really wanted the aircraft to do and then to try and provide it.

In the particular case of trim/speed stability it was quite clear that what they wanted was an aircraft that could be flown with minimal trim changes and which once trimmed would not go wandering off all over the place. We also knew that in some cases the 'elevator angle per 'g' ' could get as low as one degree/g in some cases and that the pilot could not tell exactly where his hands were positioned to that precision, although he would always know if he was pushing or pulling. So we could abandon the old rules for stick movement and instead supply classic stick force stability for deviations from the trimmed state.

All this had to be matched to the varying aerodynamics through the transonic region (where everything varies rapidly) and the fuel transfer system characteristics. The resulting Mach trim laws were quite complex and were not, in fact just Mach Number sensitive. We also had two airspeed (Vcas) terms, one of which had a variable gain which was itself Mach dependent and kicked in above Vmo = 5kts and the other was a straight nose up elevator command as a function of Vcas. The Mach trim itself was highly nonlinear. The best way to illustrate this is probably a diagram but now I've run into another gap in my knowledge of this thread - how do I do that?
Anyway, the result was that the fuel transfer held the trim setting variation down to between 2 deg down to 1.5 deg up through the acceleration from 0.95M up to 0.5 deg down at Mach 2.0. Without fuel transfer the trim at Mach 2 would have been closer to 10 deg. The trim between say 0.95 and 1.2 varies in a nonlinear fashion and the Mach trim law shows roughly similar variations.

But the best measure of our success is the comments we are getting here from the guys who actually had to fly it.

Clive


[IMG]file:///C:/Users/Clive/AppData/Local/Temp/moz-screenshot.png[/IMG][IMG]file:///C:/Users/Clive/AppData/Local/Temp/moz-screenshot-1.png[/IMG]

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Auto-trim  Mach Trim  Vmo

CliveL
December 21, 2010, 10:31:00 GMT
permalink
Post: 6135279
quote:The only real area of concern was the crown area (the roof ). There was a design flaw here in that the structure had not been designed fail-safe (allegedly by designed a Korean designer at A\xe9rospatiale who, it was said, went a bit loopy) unquote

I think he was Vietnamese actually, cerainly there was a guy of that nationality working in the Sud Aviation Stress Office, but he wasn't loopy - just cussed!

Clive

Subjects: None

CliveL
December 21, 2010, 10:34:00 GMT
permalink
Post: 6135285
quote:You then needed the zero fuel weight (ZFW) and zero fuel CG (ZFCG);unquote

So you need to know where the payload is going to be. Sud did flirt wit a 'bumsonseatometer' but eventually settled for allocated seating and simple preflight calculations (by the dispatcher I think, but ex-pilots would be able to help out on that)

Clive

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): C of G

CliveL
December 21, 2010, 10:54:00 GMT
permalink
Post: 6135331
quote:I don't know why this popped into my head but what was her glide ratio if all the engines stopped? Maybe because I remember from my early training being told the a B707 had a better glide ratio than the PA28-140 I was learning in. Now that was an eye opener at the time.unquote

A lot depends on how fast you were flying. You can get pretty good values of Lift/Drag ratio (that defines the potential glide slope with all engines operating, if that is not a contradiction in terms) from the Concorde B pages of the Concorde SST site. The actual glide slope with engines out would have been a lot worse than those numbers because of windmilling and (supersonically) intake spillage drag.

Nowhere near any subsonic values!

Clive

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Glide

CliveL
December 21, 2010, 11:09:00 GMT
permalink
Post: 6135352
quote: One has to remember that the aircraft is effectively statically unstable in pitch at approach speeds, so a pilot up-elevator input would soon be followed by a countering autostab elevon-down to contain the tendency to keep pitching up, and vice-versa.unquote

Sorry EXWOK, but I just don't agree that the aircraft was statically unstable in pitch at approach. When I think of the hours we put in trying to straighten that damned pitch curve!

It WAS designed to operate with low CG margins on approach, and that meant that the elevator (elevon) deflection needed to trim any desired incremental 'g' was quite small. On the other hand the pitch inertia was high and the elevon moment arm low, so if you just applied the elevon needed for the final state the pitch response would have been pathetic. This meant that the elevon needed to be 'overdriven' to get the aircraft moving and then backed off to hold it to the desired final state. Maybe the apparent reversals you are seeing in the video come from this source.

CliveL

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Auto-stabilisation  C of G  Elevons

CliveL
December 21, 2010, 11:21:00 GMT
permalink
Post: 6135362
quote:Also, regarding the 4000psi pressure adopted - the control surfaces most definitely did need powerful actuators; as you now know they were very active, especially on approach and transonic, and as well as IASs of up to 530kts you have all the lever arm changes brought by shifting centres of pressure over the surfaces caused by shockwave movements.unquote

Yup, I agree with that. I did the original control hinge moment calculations before we joined up with Sud, and the static hinge moments generated are quite impressive!

In fact the most critical zone is the transonic region and some (most) of the CG boundaries in the 'transonic corridor' are defined by hinge moment capability to provide the necessary manoeuvre 'g', especially with one system inoperative. The control rates aren't all that demanding, but the static hinge moment definitely was critical, and as you say, frontal area is everything and the jacks lie outside the wing section profile.

CliveL

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): C of G  Shockwave

CliveL
December 21, 2010, 11:26:00 GMT
permalink
Post: 6135372
quote:I remember at Fairford in mid 1974, a CAA test pilot (I honestly forget the gentleman's name) was taking the British pre-production A/C 101 (G-AXDN) for a special test flight.unquote

It was almost certainly Gordon Corps, possibly the finest 'engineering' test pilot I have ever worked with. After Concorde certification Gordon went to work at Toulouse wher he did most of the development flying that led to the A320 FBW system. BZ was the public 'face' of the design, but knowing the two men I have a very shrewd idea as to who did the original thinking! Perhaps Andy could confirm?

Tragically Gordon died young whilst trekking to an A300 crash site somewhere in the Himalayas

ClivL





Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Air France 4590  FBW (Fly By Wire)  Fairford  G-AXDN  Toulouse

CliveL
December 21, 2010, 12:04:00 GMT
permalink
Post: 6135427
quote:Rolls Royce did some analysis on the flight, and were amazed at how well the propulsion systems coped with some of the temperature sheers that we encountered, sometimes 4 to 5 deg's/second. They said that the prototype AFCS had been defeated by rises of only 0.25 deg's/second ).unquote

Just for the record, the intake control system was designed to cope with a temperature shear of 21 deg C in one mile (about 3 seconds)

quote:Not meaning to go off onto a (yet another) tangent; Negative temperature shears, very common at lower lattidudes, always plagued the development aircraft; you would suddenly accelerate, and in the case of a severe shear, would accelerate and accelerate!! (Your Mach number, quite naturaly, suddenly increased with the falling temperature of course, but because of the powerplant suddenly hitting an area of hyper-efficiencey, the A/C would physically accelerate rapidly, way beyond Mmo). Many modifications were tried to mitigate the effects of severe shears, in the end a clever change to the intake control unit software fixed it. (Thanks to this change the production series A/C would not be capable of level flight Mach numbers of any more than Mach 2.13, remembering that Mmo was set at 2.04).unquote

Not temperature shears, and not AICU modifications (which I see has been discussed in a later posting). But back to the 'shears':

Most of Concorde's flight testing was, naturally, done out of Toulouse and Fairford, i.e. into moderate latitude atmospheres where the tropopause is normally around 36,000 ft so that the supersonic flight testing was done in atmosphers where the temperature doesn't vary with altitude. The autopilot working in Mach hold would see an increase in Mach and apply up elevator to reduce IAS and recover the macg setting. But at the lower latitudes around the equator the atmosphere is different in its large scale characteristics. In particular the tropopause is much, much higher and can get as high as 55,000 ft. Nobody had been up there to see what it was like! Now when the A/P applied up elevator to reduce IAS it went into a region of colder air. But the speed of sound is proportional to air temperature, so as the aircraft ascended the IAS dropped alright but since the ballistic (true) velocity of the aircraft takes a while to change and since the speed of sound had dropped the Mach number was increased, so the A/P seeing this applied more up elevator and the aircraft went up and the speed of sound dropped and ........

Like solving crossword clues, the answer is obvious once you have spent some time finding it!

This phenomenon rather than temperature shears (encountered mainly over the tops of Cb clouds) was the reason for the autopilot modifications which included that clever use of autothrottle (I can use that adjective since it was my French colleagues that devised it)

And before anyone asks; yes, the same problem would relate to subsonic aircraft operating in Mach hold driven by the elevators and flying below the tropopause, but:
a) Subsonic aircraft are old ladies by comparison with Concorde in that they fly at only half the speed. At Concorde velocities even modest changes in pitch attitude can generate some pretty impressive rates of climb or dive!
b) Subsonic aircraft are normally constrained by ATC to fly at fixed flight levels - the use of elevator to control Mach number is not really an option - you have to use an autothrottle.

There was that other problem, also described in later postings, where the aircraft regularly 'rang the bell' when passing through the Vmo/Mmo corner in the lower latitudes, but this was simply due to the additional performance one got in these ISA minus conditions in comparison to the temperatures encountered around the same corner in higher temperatures.

Anyway, the flight test campaign got me my first sight of sunrise over the Arabian desert and my first trip to Asia, so it goes into my Concorde memory bank.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AFCS (Automtic Flight Control System)  AICU (Air Intake Control Computer)  Auto-pilot  Auto-throttle  Fairford  IAS (Indicated Air Speed)  Mmo  Temperature Shear  Toulouse

CliveL
December 21, 2010, 15:22:00 GMT
permalink
Post: 6135732
OK Christiaan willdo

CliveL

Subjects: None

CliveL
December 21, 2010, 15:53:00 GMT
permalink
Post: 6135786
quote: d putting further Concorde's achievements in terms of stability; the world's only previous large delta winged Mach 2 aircraft, the B58 Hustler, had the slightly awkward feature in the case of an outer engine failure at Mach 2, in that the yaw forces were sufficient to tear the fin off. This happened on more than one occasion during service life of the Hustler, but engine failure (or far more likely a deliberate precautionary shut-down) although hardly a non-event in the case of Concorde, it was routinely dealt with without drama or danger.unquote

To rub it in, a typical double engine surge - they were nearly always double surges as the first surge expelled the ramp shock waves and turned the flow into a pitot with a large standing shock ahead of the intake that screwed up the flow into its neighbour - would produce about 1 degree sideslip and 2 deg bank. There would be a +/- 0.2g variation in normal acceleration and that was it! Through Christiaan's kind offices I am posting the records of such an event.

Hustler pilots eat your heart out!

CliveL

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Engine Failure  Engine Shutdown  Engine surge  Sideslip

CliveL
December 21, 2010, 16:13:00 GMT
permalink
Post: 6135841
Grrr

quote n boarding Concorde, I gave my business card to the purser, asking that she pass it forward. A few minutes later as the door was closing she came back to pass along an invitation from the skipper to join them in the cockpit.

For the balance of the climb I plied the guys with questions and received courteous and detailed answers to every one, I stayed through the supersonic acceleration until I thought I'd worn out my welcome at cruise climb, returning to my seat in the mid cabin area for lunch. They invited me back for the descent and approach, which was very well appreciated.unquote

When I retired I flew to Wsahington and back with BA and when the crew found I was on board I also got invited to view TO and approach from the jump seat. The main difference was that it was me that was plied with questions

My main memory is that it is one thing to argue with the airworthiness authorities about 'pilot delay times' when calculating balanced field lengths, but when you are sitting at the sharp end and getting towards V1 the end of the runway is approaching at a helluva lick which puts a degree of realsim into one's thoughts!

The other memory is the sheer beauty of London when approached sitting in the front of a Concorde on a clear winter's evening when the lights are on.

CliveL

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): British Airways  V1

CliveL
December 21, 2010, 16:38:00 GMT
permalink
Post: 6135881
quote:Interestingly, all the supersonic transport designs of the era (Concorde,Tu-144, B2707, L2000) can trace their ancestry back to NASA (NACA?) public-domain studies of the late fifties, that demonstrated the advantages of a slender delta for a supersonic transport aircraft.unquote

You guys are making me look out all the books/reports on Concorde that I had filed long ago!

I think there are a lot of guys who used to work at Farnborough that wouldn't agree with you here Christian. UK work on the possibility of designing a supersonic transport kicked off in November 1956 and that certainly included studies involving slender delta wings based on work that had already been started by the RAE at Farnborough. I was reading a lot of NACA material at that time and I don't remember anything demonstrating the advantages of a slender delta for supersonic transports. Do you have any references?

CliveL

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RAE Farnborough

CliveL
December 21, 2010, 17:09:00 GMT
permalink
Post: 6135936
quote uring landing, Concorde isn't flared at all, it is flown onto the ground at a constant pitch attitude.
What does happen is that the ground effect over the last 50 ft or so of height considerably flattens the trajectory, so you do not touch down with the same vertical speed as during the final approach !
What also happens is that the ground effect produces a pitch-up moment, so the pilot has to push forward on the stick to maintain the same pitch attitude.

Putting the nosewheel down after touchdown is enough to completely \x93ruin\x94 the lift, so that there is no need for \x93lift-dumpers\x94 or spoilers.unquote

Sorry Christan, but I did the original pre first flight work on this one, so I know you are mistaken here. You are abolutely correct in saying that the ground effect cushions the aircraft beautifully so that all the pilot needs to do is to hold constant attitude, but the ground effect also produces a nose DOWN moment, so the pilot must exert a steadily increasing pull on the stick to maintain the correct attitude.

So far as lift on the ground is concerned, the aircraft attitude (and therefore the AoA) is substantially zero. without any flaps then the lift is also zero so, as you say, leif dumpers would be useless. They could of course act as airbrakes but you wouldn't add their weight and complexity just for that.

I see I have covered about 10 pages out of the 45 or so, but I don't want to hog this thread so I had better shut up for a while

CliveL

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AoA  Landing Gear

CliveL
December 22, 2010, 07:29:00 GMT
permalink
Post: 6136929
Originally Posted by Mr Vortex
I'm wondering that does the auto-stab function in yaw axis does apply some
rudder when pilot fly the aircraft by his hand to prevent the sideslip or
dutchroll or not?

Also, does the auto stab does "modify" some pilot input to minimize the effect
of the turbulence all the time when airplane encounter the turbulence or only
when the AP are in the "TURB" mode? Does it help to reduce the stress on the
aircraft like the "load alleviation" on the moder aircraft like A380?

And final the final question, how the camber help to reduce the shifting
position of the center of pressure on the Concorde and if possible where is it
on the wing?
Firstly; Thanks AZR!

Then, yes the autostabiliser does provide yaw damping to control the Dutch roll, but there was also (from memory) some roll damping.

No, there is no load alleviation function. Concorde had a very low aspect ratio wing which gives in turn a very low lift curve slope, so the loads coming from hitting gusts are quite modest and load alleviation was not needed. The autostabiliser was working all the time, not just when A/P was engaged. Since the span was also low the manoeuvre bending moment was also small so again load alleviation was not required. BTW, I believe that the A380 load alleviation is just this manoeuvre case not gust loads. The A320 had gust load alleviation on early models, but it proved to be a pain in the neck and was gratefully dropped when the MTOW went up and made manoeuvre loads the critical design case.

Finally, the camber is spread all over the wing. In cross section it looks like a banana with the bent bit like a shallow 'U' and the leading edge drooped downwards, so the whole thing lookss like a distorted 'S'

CliveL

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Auto-stabilisation  Rudder  Sideslip  Vortex