Posts about: "Landing Gear" [Posts: 67 Page: 1 of 4]¶

I would say not: there wouldn't have been any space in the wheel well.
The gears retracted inwards, and when up, the bogies were right next to each other on each side of the keel. As a matter of fact, the main gear legs had to be "shortened" while they retracted, otherwise they wouldn't even have fitted...
No, because the inside trim wall panels were relatively short (say about 10 ft, don't remember exactly) and each moved with their bit of fuselage (think roof tiles). Same applied to the floor panels, which also were in fairly short sections. The movement was of course hidden by the carpets.
Yes indeed. Flexible sections all over the place.

Hi Nick, thanks again for your comments. As far as not being a commercial success, for the airline this side of the Channel it was a HUGE commercial success (but of course I accept that in manufacturing terms this was far from the case. The project suffered from very poor financial control). Concorde was the first commercial FBW aircraft as you rightly surmised.
A huge amount of Airbus work was 'burried' in the Concorde project; at Filton a large amount of Airbus components came through that were almost identical to those on Concorde. (witness the STRIKING similarity between the A300 main gear and that of Concorde). Apologies if this post is a little tardy, it's done from my IPhone).

Biggles78,

Re your questions about the CofG, this diagram should help you to visualise the CofG "corridor".



It's the one for G-AXDN (01) but the production one is closely similar.

To make some more sense of this.... all those percentages quoted are in terms of the "wing root reference chord".
Mentally cut the wing off the fuselage and measure the length of the cut (including the elevons)..
That's the "root reference chord", and it's 27,76 m.
To give you another reference point: the main gear attachment point is located at 57% ""root reference chord".
So any CofG beyond 57% on the ground, and you have yourself a tailsitter (it's happened)..

Biggles78
This is the minimum Mach number that can be flown with the existing CG. (which would be around 59%). Just as the CG indicator (not shown in this photo) gave minimum and maximum CG for a given Mach number, the Machmeter gave a reciprical indication also). You can also see that as the aircraft is not flying at Vmo any more, being at Mach 2 cruise, that the VSI pointer is now away from the orange and black Vmo bug. At our 'not so coffin corner', now that the aircraft is at maximun alllowable altitude, Vmo would naturaly coincide with Mmo; the orange and black Mmo bug being shown at Mach 2.04. This really superb photo taken by Bellerophon gives a graphic illustration of what the panels looked like at Mach 2. Note that the with the TCAS VSI Concorde retained it's original linear VSI also. (Miust have beeen the only aircraft flying with FOUR VSIs. (The originals had to be retained due to the fact that the autopilot Vert' Speed Mode error was derived from the indicator itself. As far as TCAS goes, R/As werer inhibited above FL300 (on acceleration this would coincide with the aircraft becoming supersonic, and the mfrs would not countenance the aircraft doing extreme manoeuvrs as a result of TCAS RAs at supersonic speeds).
The tail wheel was lowered for all 'normal' gear cycles (not stby lowering of free-fall). It was designed to protect the bottom the nacelles in the case of over-rotation, but in practical terms the thing was a waste of space (and weight) and a simple tail skid (used on the prototypes) would have sufficed. Any time that the tail wheel contacted the ground, it would ALWAYS collapse, damage the tailcone structure and in fact aforded no protection whatsoever. Fortunately these events were EXTREMELY few and far between. The biggest problem with the tail wheel was a major design flaw: On gear retraction the assembly would retract in sequence with the nose and main gear, and as it entered the opening in the tailcone, it would release over-centre locks that were holding the spring-loaded doors open. The doors would then firmly spring shut behind the gear assembly and finish the job. UNFORTUNATELY this was a very poor design; if for any reason one of the two doors had not gone over-centre on the previous gear lowering, it would be struck by the retracting tail wheel gear and cause structural damage to the local skin area, that would have to have a repair done. Unfortunately these events were not quite so rare, and several measures were tried to reduce the chance of this happening. Although not a safety issue, it was an issue that was a total pain. (As a matter of interest, G-BOAC had this happen on one of it's first test flights out of Fairford in 1975).
Nick Thomas
As ChristiaanJ said, the last two BA aircraft WERE lighter than the others, and would be preferred aircraft for certain charters. But that is not to say that any aircraft could not happily do ANY sector. We fortunately had no distorted airframes in the British fleet, so this was never an issue. There was very little spread, regarding fuel consumption between different engines; one of the best parts about the Olympus 593 was that it hade very little performance deterioration with time, it was an amazing piece of kit.
Time on wing for the engines was a real variable. Each engine was built up of modules, each one of these had a seperate life. In the early days of operation, time on wing was quite poor, and MANY engines would be removed on an attrition basis. One of the early failure problem was the fuel vapourisers inside the combustion chamber were failing, taking bits of turbine with it!! A Rolls Royce modification that completely changed the design of the vapouriser not only solved the problem completely, but also increased the performance of the engine. As the engine matured in service time on wing greatly improved, and in service failures became a thing of the past. A 'trend analysis' was done after each protracted supersonic flight, where engine parameters were input into a propiatry RR computer program, that was able to detect step changes in the figures, and if this were the case, more boroscope inspections were carried out. The OLY time on wing was nothing compared to the big fan engines, but the conditions that it operated under bore no comparison. Not really sure about absolute figures on this one Nick, I'll ask one of my Rolls Royce friends and see if I can find a figure.

Biggles78
The tailwheel design really was the one exception in poor design terms, but I'm sure that if the aircraft was doing what she should be doing right now, (you know routinely flying across the Atlantic and beyond, instead of languishing in museums), modifications would have finally put this particular malady to bed). In design terms, the rest of the aircraft was nothing short of a flying work of art, a masterpiece. Having said that though, personally I would rather that four rather than three hydraulic systems had been used. Originally there were four systems in the design, but the RED system was deleted, as it was felt to be superfluous. My own view is that this particular decision was total poppycock. Oh, and Green, Blue and Yellow hydraulic systems was something else that Airbus copied from Concorde.... although we ourselves pinched that idea off of the Comet ).
As far as the hydraulic expansion joints go, I will scour around and see if I can find a diagram for you. Try and picture two titanium (or stainless) tubes, on inside the other, with a sealed chamber being formed at the join. Inside this chamber were multiple lands fitted with special viton GLT seals. They did work incredibly well, although occasionally one of the seals gave out, and things got wet, VERY WET.
As far as the 4000 PSI hydraulic system, as EXWOK quite rightly pointed out, the loading on the flying control surfaces were immense throughout the whole flight envelope. (Picture alone just the T/O from JFK RWY 31L, where the aircraft is tightly turning and the gear retracting, all at the same time). As well as the flying controls and landing gear, you also had the droop nose to consider, four variable engine intakes as well as a couple of hydraulically operated fuel pumps. Oh, and in emergencies, a hydraulically driven 40 KVA generator too. The reason that 4000 PSI was chosen was that if a large amount of hydraulic 'work' was to be done, the only way to keep the size of jacks and actuators to a reasonable size/weight was to increase the system pressure by 25% from the normal 3000 PSI. (On the A380 they've gone a step further and gone for 5000 PSI, saving them over a tonne on the weight of the aircraft).
Concorde used a special hydraulic fluid, Chevron M2V. This is a mineral based fluid, as opposed to the ester based Skydrol, used by the subsonics. The reason that we went for a different fluid was a simple one; Skydrol is rubbish at the high temperatures that Concorde operated at, no good at all in fact, so we needed something better and in M2V we found the PERFECT fluid. As an aside, unlike Skydrol, that attacks paintwork, certain rubber seals, skin, EYES etc., M2V is completely harmless, wash your hair in it. (I did, several times when we had leaks. Thinking about it, maybe THAT is why my hair is such a diminished asset

EXWOK
It's so great having another of my pilot friends diving in to this post, welcome welcome
I remember the Mech' Signalling part of the air tests, my lunch has just finished coming back up thank you. (for interest chaps and chapesses, with mechanical signalling, using just the conventional control runs under the floor, there was no auto-stabilisation).

The artificialfeel system worked incredibly well I thought, I always found it curious that the peak load law in the computer was at the transonic rather that the supersonic speed range. It was explained to me long ago that this was because the controls really are at their most sensitive here, but at high Mach numbers are partially 'stalled out', due to shockwave movements along the surfaces, and were therefore less effective. (For this reason I was told, the inner elevons were so critical for supersonic control, being the most effective of all elevons at high speed).

To all , I forgot to mention in my previous post regarding the engine failure in G-BOAF in 1980; I remember an FAA surveyor, who was taking a look at the carnage within the engine bay, saying that in his opinion, no other aircraft in the world could have survived the intensity of the titanium fire that ensued. Analysis showed that the fire was successfully extinguished, possibly at the first shot of the fire bottle. This was a testament to the way that the Concorde engine bay could be completely 'locked down' when the fire handle was pulled, as well as to the way that the whole engine installation was technically encased in armour plate. To put all this in context, acording to Rolls Royce a titanium fire, once it takes hold, can destroy the compressor of a jet engine in four seconds.


Dude

ChristiaanJ

The way I remember it was

"3-2-1 now" was to ensure that all 3 crew members started their stop watch at the same time i e on the call of NOW as that was the point the throttles were moved rapidy to the forward stops. In fact the noise abatement timing assumed the engines were allowed to accelerate at their own rate, rather than at a rate controlled by the crew

"Green lights" served two purposes
1] To allow the pilots to have a quick reference as to the state of the engines during the Take off

2] Prior to the nose gear mod ona rough runway [when it could be difficult to red the engine instruements] it did give the F/E an indication that the engines had reached the basic power required

3/4 tab. as different T/Os required diferent minimum reheats either 3 or 4
The small 3/4 tab was there just to visually remind crew as a back up to the briefing whether they were on a 3 or 4 reheat day

I have not I believe been on an aircraft where you run up to full power before releasing the brakes, but there again the memory could be fading, and I am sure the sudden release of brakes at full power would not do them any
good

Mind you I could be wrong

DozyWannabe
Good point I suppose, but you could say that the six Concorde prototypes, Pre-Production and Production Series Test aircraft were also development aircraft, and yet more or less worked just as it said on the tin', where the TU144, in spite of all the facilities of Andrei Tupolev's design bureaux, not to mention more or less unlimited Soviet state funds produced a machine that in my opinion really BELONGED in a tin can. (I know this is all off topic, honest guys, I won't mention this stuff again ).
In reality the Soviets really lacked both propulsion technology as well as the systems expertise required to build an aircraft with even a remote hope of Mach 2 cruise, let alone safe and comfortable enough for fare paying passengers. The original aircraft had all for engines in one giant nacelle, and the landing gear retracted into the engine inlet duct itself, great for an undistorted flow path to the engines . The variable inlets were manually operated by the flight engineer as well, no automatics here. In the mid 1970's the Russians even approached PLESSEY to build a digital engine control unit for the TU144. A similar PLESSEY unit had been VERY successfully flight trialled on production series aircraft 202 (G-BBDG) and only lack of funds prevented it being used on the production aircraft. As this unit could obviously be used for Soviet military applications, there was objection from the UK government, and more than just a little trans-Atlantic pressure applied, and so this venture never happened.
Until the advent of the Mig-29 and Sukhoi SU-27 this really was not the case. I'm afraid I'm with galaxy flyer on this; If you look at the air war over Vietnam, when an F4 met a MIG 19 or MIG 21 in an even air-to-air combat, the MIG was going down. (OK this could be partially down to superior US pilot traing etc, but if you look at the handful of skirmishes where the 1960's/1970's Soviet aircraft were engaged in Combat against US or French built fighters, the MIGs never really did very well at all). However, the aircraft that the Russians have been producing from the Mig 29 onwards seem to be in a completely different class now; hope they really are the good guys now.
ANYWAY, back on topic
Lurking SLF
No problem at all Darragh, please keep visiting us and post here also anytime.
Nick Thomas
I'm not sure that I can describe the DEBOW process remotely as eloquently as my friend Bellerophon did, I particularly loved the 'out of balance tumble-drier' bit, but starting a hot or even warm engine, even at DEBOW, you could certainly 'feel' the noise on the flight deck, until the shaft distortions evened out.
Now for the PFM bit, equally eloquently alluded to by Bellerophon:
DEBOW itself was maintained by a special sub-idle datum in the electronic Engine Control Unit, and once the engine was accelerated towards normal idle (61-65% N2, depending on the temperature of the day) even if the switch described by Bellerophon was accidently re-selected, an electronic inhibit gate in the ECU prevented this sub-idle datum from being used again that engine cycle.
You're welcome Nick, actually the roll and yaw trims operated in a similar manner to the pitch, although of course these was applied by a manual trim wheel only. (No French bike bell either ). Rotation of either wheel (more a giant knob actually) merely shifted the neutral datum of the relevant artificial feel unit, which in turn shifted the rudder pedals or control yoke; the resolvers for the FBW system would in consequence demand this 'trimmed' control surface movement.

Dude

My question concerns the Concorde nose gear. It rotates forward for stowage thus against the airflow and perhaps requiring more hyd power than a rear retract mechanism. What were the factors in this design decision - particularly considering that this beautiful machine seemed long enough to accommodate rear retraction?

Thanks

Cron.

I can only echo ChristiaanJ, we all are quite humbled to be able to share our experiences with you guys. Please keep on posting everybody. (There's no such thing as a stupid question here, but as to some of my answers..... ).
And Stlton.. our thanks all go out to YOU, for starting this thread in the first place.
TURIN
Glad to hear that you enjoyed your 'Rocket' time in TBB. As far as plugging the leaks, well things did improve quite a bit. but a fully laden aircraft could sometimes still be a little 'wet' on the ramp.
CRON
The nose leg had to retract forward, purely because the fuselage section of fuel tank 9 was immediately behind. (The nose wheel also had a single steel disk brake, based on an automotive design. (I'm 90% sure it was a Ford Cortina)

Dude

I cannot think of a civil airliner where the nose gear retracts backwards - they all retract forwards. Except the Trident fleets where the NLG was offset from the centre line of the fuselage and retracted sideways. I remember my Avionic colleagues teling me that this was designed specifically because the Cat3b autoland was so accurate they didn't want the pax to have an uncomfortable ride as the nose wheels rolled over the runway lights on landing

No me neither. It helps when gravity extension is required too as the airflow pushes the leg back to the locked down position.

M2Dude thanks, a lot of memories returning with this thread.

Tupolev 114?

Yep I would be curious to know this too... from our FCTM for the B744, landing geometry on a 3˚ glideslope for a flap 30 landing at REF +5 and a 50' glideslope antenna TCH (Threshold Crossing Height): the pilot's eye should be at 66' with the main gear at 31'. Considering that during the flare the attitude will increase by 2˚-3˚ this distance can only increase, so I would hazard that a B744 pilot's eyes are in excess of 35' (10 metres) above the runway at touchdown (I wouldn't know, I usually shut my eyes at the 30' RA call-out, pull back a little and hope for the best ).

Any idea what it is on that splendid machine that is Concorde? (I refuse to speak of it in the past tense)

MD

I'll leave most of the answers to the pilots on this forum, but I can answer two small details.

During 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.

CJ

Nick Thomas

... I think am right to assume there were no spoilers...

Correct.

...so on landing did the act of bring the nose down spoil the lift...

Yes, as with most conventional aircraft, reducing the aircraft pitch attitude (once the main wheels were on the runway) would reduce the angle-of-attack and therefore reduce the amount of lift being generated by the wing. Modern aircraft wings are very efficient and will still be generating a considerable amount of lift during the landing roll, even as the aircraft slows down.

Put simply, spoilers and/or lift dump systems are required to destroy this lift, in order to get as much of the aircraft weight as possible on the main landing gear, which, in turn, allows greater pressure to be applied to the wheel brakes before the wheels start to lock-up and the anti-skid units activate to release the applied brake pressure.

Concorde\x92s wing however developed very little lift at zero pitch attitude, so, once you had landed the nose wheel, there was no need for spoilers.


...is that the reason why the non flying pilot pushed the yolk forward once she was down?...

No.

The reason was that using reverse thrust on the ground on Concorde caused a nose-up pitch tendency, strong enough to lift the nose. The procedure was the handling pilot would call Stick Forward as soon as she had landed the nose wheel and the NHP would apply forward pressure on the control column to make sure the nose didn\x92t rise.

If the handling pilot applied reverse thrust before the nose wheel was on the ground, things could get very awkward very quickly.

Firstly, the nose would probably rise, quite possibly beyond the power of the control column to lower it. Secondly, the wing would still be generating (some) lift and so only reduced wheel braking would be available before the anti-skids kicked in, and the amount of runway left would be diminishing faster than normal.

The solution was to reduce to Reverse Idle power until the nose wheel was back on the runway, however, in the heat of the moment it was very easy to go through Reverse Idle and on into Forward Idle. Not only would this again hinder the deceleration of the aircraft, but it would also run the risk of scraping the reverser buckets on the runway (as the buckets moved from the reverse thrust position to the forward thrust position) so tight were the clearances between the buckets and the runway on landing.


Best Regards

Bellerophon

This thread deserves an award...

I'm not a professional pilot, just a humble owner of a PPL with a very strong interest in aviation and a long time reader here (esp. in the Tech Log board). I've never posted here, because I prefer to read and learn from those who know it better, but this thread has finally managed to lure me out of lurking mode
Like in this video?
YouTube - Concorde late 32 landing at Leeds/Bradford Airport

There is a strange high pitch sound that kicks in for about a second in the same moment the nose wheel makes contact with the ground and before the actual reverse thrust sound can be heard.

Thanks to all for sharing all this information about one of the most fascinating machines ever created by human mankind.

I believe that the main landing gear was shortened to fit into the wheel wells during the retraction sequence.
As I see it, as the gear started to retract, the oleo`s were compressed to something like when the weight was on the wheels. Then a latch would have been applied before the gear reached the full up position to hold the gear strut compressed.
I would like to find out more how this was accomplished.

Runaround Valve
This was quite a neat system, as the gear was retracted, a SHORTENING LOCK valve was signalled, allowing a relatively tiny jack to pull the entire shock absorber body into the body of the oleo progressively as the gear retracted. So the shock absorber itself never compressed on retraction, more like the whole shooting match was pulled inside the body of the oleo. On the ground the shortening lock was disabled, and also isolated by a geometric lock, the weight of the aircraft on the leg holding the shortening mechanism over centre.centre. Hope this helps.

Dude

Makes me wonder... In the event of a complete loss of thrust at Mach 2 (say fuel contamination) would the deceleration be significant ? If so I guess the fuel redistribution / pumping to maintain acceptable CG would become interesting...

Concorde did actually have a four engine failure drill, which covered it's complete speed rsnge including Mach 2.0. There was one assumption made in this drill and that the engines would continue to windmill which would allow them to give you full hydraulic pressure

As you could imagine, If all 4 engines cut at Mach 2.0 the F/E would be quite busy and so the the non flying pilot would use his fuel transfer switch to start the fuel moving forward. This was a pretty basic selection where fuel would be pumped out of Tank 11 using all 4 pumps [2 electrical and 2 hydraulic driven] and into the very forward tank which was no 9.

As a rule of thumb transferring 1000kgs from tank 11 to tank 9 moved the Cof G forward by 1%. Now with all 4 pumps in tank 11 running the tansfer forward was so quick that the pilot had to keep switching the transfer off and then on to stop the Cof G moving forward too quickly. It was usually to everybody's relief when the F/E could find the time to take over the fuel transfer as he had the selections to allow him to be more selective as to where the fuel went and so slow the rate down
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This was quite a neat system, as the gear was retracted, a SHORTENING LOCK valve was signalled, allowing a relatively tiny jack to pull the entire shock absorber body into the body of the oleo progressively as the gear retracted. So the shock

Forther to M2dude's explanation Concorde's main landing gear consisted of 3 seperate metal castings . there was the normal two for the oleo and these two were fitted inside the outer casting, which was the one you could see.
As the gear retracted a mechanical linkage , which was driven by the gear's retraction movement, would lift the oleo assembly up into the outer casing, so shortening the length of the leg . If I remember the shortening jack was just to assist in breking the geometric lock of the linkage
------------------------------------------

The other difference between AF and BA aircraft was the DC electrical system

AF had Nickel cadmium batteries with an automatic charging system

BA had the good old lead acid battery sysytem, well except for AG where the DC system was one of the systems they never changed when AG was incorporated into the BA fleet

Brit312
Right on the button as usual Brit312, the shortening jack DID just assit breaking of the geometric lock, it was the process of retraction alone that did the actual shortening. Humble aplologies to all for this age induced goof.
And as both yourself and EXWOK pointed out, Air France had a ni-cad based DC power system, the same as G-BOAG.

Dude