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Subsonic Flights - Is 55% CG always the rule?


Ray Proudfoot

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Ray Proudfoot

On subsonic legs of a supersonic flight fuel was transferred rearwards until 55% CG was reached. Once able to go supersonic the rearward transfer of fuel would continue to reach the optimum 59% CG.

But on purely subsonic flights what was the ideal CG? I'm finding it extremely difficult to maintain 55% for the duration of the flight until ToD. Once a CG of 55% has been achieved with a rearward transfer there is still fuel remaining in tank 9 but transferring it rearwards immediately results in the CG exceeding the 55% target.

The only way I've found of keeping it within 0.3% of 55% is to transfer fuel from 2 to 1 and 3 to 4 until 9 is empty.

Is this how it was done in actual flights or is the 55% CG rule flexible given the bugs easily allows 55-57?

I should add that the cruise level was 280 and my test flight is EGLL-EIDW.

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Fabrice Estienne

Hi Ray

We assume the GW of the baby was about 145 t because you decided to fly her at Mach 0.95 and FL280, optimal level in still air.

The trim transfer is normally automatically sequenced and controlled from he flight engineer's panel (forward and reward).

For the occasion when the tank 11 is empty the flight engineer shall augment the trim transfer in the forward trim condition by a reduced level operation in collector tanks 2 and 3 by means of transfer into collector tanks 1 and 4 as these last are located well forward.

This operation is necessary because the flight manual enforces the crew to fly scrupulously with the optimal CG (screen shots in french)

CG 57% may trigger the first level CG warning, an awkward position.

I thing myself that the automatic flight engineer should provide this process.

Cheers

Fabrice Estienne

 

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Ray Proudfoot

Hi Fabrice,

Thank you for your help. A few facts for my test flight from Heathrow - Dublin...

GW was 116.1T with 91 pax. FL260 and 395kts for cruise. Tank 11 was empty when fuel was loaded. 1354Kg was transferred from 9 to 11 for a 52.5% CG take-off.

If I understand you correctly the aft transfer switch was left in the forward position and fuel pumped from 9 to tanks 1 and 4 as they were the forward-most tanks. Is it possible to transfer fuel that way in Concorde-X? I know there is a Virtual Flight Engineer but some of us have that switched off so we can handle fuel transfers ourselves.

If we set tank 11 to a very low value and start the aft transfer fuel should go straight to 5 and 7 and from there to 1 and 4. Or can we pump it direct from 9 to 1 and 4?

It does make more sense to transfer from 9 to 1 and 4 as the CG would not change significantly. Can you describe how to pump from 9 directly to 1 and 4 please assuming I have understood you correctly?

Also, at what stage in the flight does the transfer start from tanks 5a and 7a? I'm starting the transfer soon after take-off especially on these shorter flights.

Is it allowed to have a CG up to 56%? That is still within the two bug limits?

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Fraser Gale

Ray,

the perspective tended to be that the CG should be kept as close to the centre of the two bugs as possible apart from on takeoff (where three standard options were used due to flap effect considerations) and at 59% where the bugs "tightened up" due to reducing margins. This was because the optimum is considered to be in the middle. The subsonic position was a standard 55% because it gave good margins for varying airspeed/Mach and for handling considerations. The bugs should still be quite far apart at this speed but 55% is the optimum.

The 0.3 margin was probably more to the calculated possible errors in the CG computer, where you transferred the correct fuel to all the right places but the computer gave a slight difference. Ideally, it would always be exact. 

Whilst it would be perfectly safe to not fly at 55% it might effect fuel burn due to trim considerations and therefore is not ideal. 

Everything on Concorde was exact which is why the crews enjoyed flying her - you had to know your stuff and it took practice to get it right!

Frazz

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Ray Proudfoot

Thanks Frazz. Being so rigid at 55% CG for subsonic is a little surprising because the forward limit bug is at 54.5% or thereabouts. Very little to play with.

However, you've given me the answer. 55% CG had to be adhered to.

Care to comment on Fabrice's post about how the fuel was moved around? Can it go directly from 9 to 1 and 4 or does it have to go via 5 and 7?

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Fraser Gale

It would depend on how short your flight is as to the procedure. If aircraft weight is less than 140T you would transfer the fuel from 5A & 7A when 55% CG is obtained. You would maintain 55% by adjusting the trim tank contents (9, 10, 11) so there is no mention of transferring to or from the collector tanks. Aft trim switch wouldn't be used with this low a fuel quantity as you have to switch back to normal when you have the equivalent of the refill level left in the main transfer tanks to fill 1 and 4 to normal levels. 

Basically you use fuel in tanks 9 and 11 to change the CG so you would transfer aft from 9 after takeoff to 11 and shuttle fuel back and forwards to maintain 55%. If you don't have enough fuel you could take some from 5 and 7 or 6 and 8 via the trim gallery but I don't see why you would be in a position to have it going from 9 to 1 and 4 according to the BA manual. 

It also states that it can take 25 mins to empty tanks 5A and 7A so you should do that transfer at least 25 mins before landing. Normally this should be started when weight is not less than 140T. I haven't flown light for a while but I will try to soon, I will also keep looking in the manuals to see if there is more info somewhere. 

Frazz

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Fabrice Estienne

Hi Ray,

According the specs when the Trim Transfer auto master selector is FORWARD the system switches ON the Tank 11 pumps and open the inlet valve of tank 9. When tank 9 reaches the preset load limit or high level, the tank 9 inlet valves are closed and, in turn, the tank 5&7 inlet valves are open if necessary. Fuel is not directly moved into tanks 1&4.

9 to 1+4 or 11 to 1+4, I guess if you open the standby inlet valves of the collectors tanks 1 & 4. Nevertheless I did not try out this experiment on Concorde-X.

I will try to sum up the trim transfer augmentation according the specs of the real aircraft:

1) Afterward condition:

By positioning the tank 1&4 switch of AFT / TRIM which selects a reduced fuel level operation (40% of the normal operation) in tanks 1&4 and inhibit the under full warning.

2) Forward condition:

- No dedicated switch, hence no affect on the monitoring pump rate which feed the collector tanks 2&3.

- Switching off these pump is to be avoided.

- The safe solution on myself is to opening the collector tanks 2&3 jettison valves and the standby inlet valves of the collectors tanks 1&4. This allows fuel to flow to the forward collector tanks 1&4 through the trim transfer pipes.

I will try to take the time to reproduce your flight and I will come back over this discerning matter.

Cheers

Fabrice

 

 

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Ray Proudfoot

Thanks Fabrice. Your suggestion to move fuel from tanks 2 and 3 into 1 and 4 is one I tried on an earlier flight. But the reason for moving so much fuel forwards was because I had perhaps moved too much from 9 to 11 in the first place.

I tried Frazz's suggestion of moving fuel from 9 to 11 on taxi to get the correct CG for take-off (52.5%CG). After that and once airborne I moved fuel from 5a and 7a into 5 and 7. I also moved what fuel remained in 9 into 5 and 7 rather than pumping it all the way into 11.

This way the CG of 55% was much easier to maintain. I look forward to hearing how you got on. :)

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Fraser Gale

As a rule of thumb, use the tanks in the fuselage (9 - 11) for CG movement, wing tanks for occasional lateral trim (never really needed on Concorde X) and feeding engines. 

Aft trim switch should only be used on supersonic flights to cancel the "A" tanks transfer - it should always be selected back to normal when the sum of tanks 6 + 8 equals the amount required to refill tanks 1 and 4 to normal levels. Otherwise you can get into problems with lower levels in 1 and 4 on landing. 

I can only assume the method that Fabrice is using is an Air France way of doing - there were many subtle (and some not so subtle!) differences between the BA and AF procedures. I stick with BA because that's the documentation I have.

Frazz

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Fraser Gale

Further to my last post, I should mention that the less the standby inlet valves are used the better, as they cancel the high level protection system that leaves an air gap at the top of the tanks.  Automatic protection is important due to the workload of the crew especially on short sectors. 

From what I have read and heard, AF used the standby inlet valves to bypass the high level protection on several occasions, including one that I'm too sad about to mention. 

Frazz

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Ray Proudfoot
1 hour ago, Fraser Gale said:

As a rule of thumb, use the tanks in the fuselage (9 - 11) for CG movement, wing tanks for occasional lateral trim (never really needed on Concorde X) and feeding engines. 

Aft trim switch should only be used on supersonic flights to cancel the "A" tanks transfer - it should always be selected back to normal when the sum of tanks 6 + 8 equals the amount required to refill tanks 1 and 4 to normal levels. Otherwise you can get into problems with lower levels in 1 and 4 on landing. 

I can only assume the method that Fabrice is using is an Air France way of doing - there were many subtle (and some not so subtle!) differences between the BA and AF procedures. I stick with BA because that's the documentation I have.

Frazz

On this very short flight - around 250nm, with 25.5T loaded - there is no fuel in tanks 6 and 8. Neither is there anything in 5 and 7! :D We have fuel in 1-4, 5a and 7a and 9. This limits my options quite a bit.

What I did on my last flight is pump 9 to 11 during taxi to get take-off CG of 52.5%. Once airborne and around 10,000ft I switch on 5a and 7a to feed 5 and 7. The 5 and 7 fuel pumps are still off at this point.

I dial a Tank 11 limit of my current fuel in 11 and turn on the Tank 1/4 aft switch. This moves fuel from 9 into 5 and 7. Once I have more than 200Kg in those I turn on the fuel pumps to feed 1-4 monitoring CG as I do this.

By the time I get to ToD 9 is empty, 11 has the load limiter set to zero and I dial in to 9 the landing amount required (758Kg). During descent I turn on tank 11 fuel pumps and after 9 has its 758Kg the remaining fuel goes into 5 and 7.

By the time I land CG is forward of 53% and 11 is empty. That sounds pretty close to how you describe the procedure and different to Fabrice's procedure. But then I am flying BA so maybe that's what I should be doing.

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Fraser Gale

Out of curiosity, what was your landing weight and fuel on arrival?

There were times when doing short sectors that the fuel flight plan was constructed based on landing weight in order to carry more fuel for ballast. I personally would just take more fuel! Although company policy was minimum fuel due to burn, for a short flight I would aim to arrive at just under maximum landing weight, at which you would still have quite a bit of fuel left but it makes balancing easier. 

There were times when Concorde did charters for experience flights that they would arrive at the TMA still over landing weight so would do a little sight seeing for the passengers, to burn off fuel.

Frazz

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Ray Proudfoot

The CPS-X landing report states 14.0T of fuel at destination and a landing weight of 105T. I remember having 12.5T when parked so I guess that makes my landing weight around 104T.

I don't know whether you have CPS-X yet but if you do and want to try this yourself here is the plan:-

CPT UL9 KENET UN14 OKTAD DCT MEDOG UL18 LANON DCT ABLIN

I appreciate it's not your typical flight but Concorde did do lots of short hops like EGLL-EGCC so this CG scenario would have been used.

Because I carried 100 pax on this flight I didn't need any extra fuel. With fewer pax on earlier flights I did need to load extra fuel to get to minimum safe T/O weight.

 

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Fraser Gale

I don't have CPS, no. I would definitely be using a fuel plan based on landing weight as would have been used on shorter flights. With such a short stage length the extra fuel used to carry the extra fuel (if that makes sense) would be minimal. 

When I get time I will work a plan out but in the meantime, try the same flight but load an extra 5 tonnes which will still make you under max landing weight on arrival but will give you some more ballast. 

Am I correct in thinking you are loading flight plan fuel, i.e. the amount required to do the flight plus normal reserves or are you taking more already? 

The other thing I was thinking was that if you get to the point you can't move the fuel to keep 55%, slow down to move the fwd bug up. Try M0.93 which is an authorised cruise speed anyway - in fact it is the maximum authorised speed when hand flying a subsonic cruise, people often don't realise that if you were to cruise at M0.95 the AFCS had to be used because the shockwaves had already began to start bouncing around on the fuselage. It was permitted to hand fly if continuing to accelerate though, and I'm sure this rule was probably ignored on more than one occasion!

Frazz

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Ray Proudfoot

Hi Frazz,

CPS-X works out the fuel based on the normal requirements for 45mins holding plus enough for a divert to EGOV. I haven't added any 'extra' fuel but will try adding 5T as you suggest.

Actually, maintaining CG at 55% was okay with my last flight after I stopped moving fuel to 11 after take-off. It goes into 5 and 7 instead and CG remains at 55 pretty much without any intervention by me.

I'll change the cruise speed to M0.93 - normally I just dial up 395kts and at FL280 that equates to M0.97. More later...

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Ray Proudfoot

Just completed EGLL-EIDW with an extra 5T as suggested. This did not go well. I couldn't get CG beyond 54.6%. :( The problem was there was near full capacity in tanks 2 and 3 so trying to move fuel from 1 and 4 into those didn't work. I didn't pump any extra fuel into 11 after take-off. Perhaps I should have. But I didn't do that on my previous flight when I was 5T lighter.

I'm not sure what's best really. Adding the extra 5T so some of it can be moved back to 11 for a 55% CG or load less and not need to pump into 11 once airborne.

I landed with around 17.4T of fuel remaining.

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Fraser Gale

I still don't understand why you would be moving fuel between the collector tanks (1-4) because they are purely for engine feed, the only time they are used for trim is during A tank transfer but even then only when there is still a significant level of fuel left. On a short sector like you are doing you should not need to use these tanks for trim. I'm starting to suspect the simulation but until I have time to fly it myself I can't help. 

Remember that you can allow the collector tanks to run down to 1000kg before you are at risk of fuel pumping issues and this would often be done. Try not transferring into 1-4 until moving the CG forward via T5 & 7 and see if you have more luck. I'll try to fly this weekend if I have time. 

Incidentally, you should not be cruising above M0.95 unless you are at M2.00 because the transonic drag and shockwaves cause significant efficiency penalties. The rule is: hand flying M0.93, using autopilot system M0.95

Frazz

 

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Fraser Gale

By the way, in normal circumstances the 3 hour routes would never have had 45mins holding fuel so I hope this option is adjustable in CPS?

The most holding fuel I've seen on a plan was 13 minutes.

Frazz

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Ray Proudfoot
1 hour ago, Fraser Gale said:

I still don't understand why you would be moving fuel between the collector tanks (1-4) because they are purely for engine feed, the only time they are used for trim is during A tank transfer but even then only when there is still a significant level of fuel left. On a short sector like you are doing you should not need to use these tanks for trim. I'm starting to suspect the simulation but until I have time to fly it myself I can't help. 

Remember that you can allow the collector tanks to run down to 1000kg before you are at risk of fuel pumping issues and this would often be done. Try not transferring into 1-4 until moving the CG forward via T5 & 7 and see if you have more luck. I'll try to fly this weekend if I have time. 

Incidentally, you should not be cruising above M0.95 unless you are at M2.00 because the transonic drag and shockwaves cause significant efficiency penalties. The rule is: hand flying M0.93, using autopilot system M0.95

Frazz

 

Yes, my mistake in my attempt to get the CG further rearward. What I should have done with that extra 5T was move it back to 11 instead. Or as much as was needed to get CG to 55%. But I don't think I need that extra 5T. CPS-X is pretty good at working out fuel so unless there are exceptional circumstances I'll stick with what it comes up with.

Yes, aware that I can run 1-4 down to 1000Kg. That is often the case on supersonic flights.

To answer your second post yes, the holding time is adjustable. It just defaults at 45m. I'm not sure 13m is permitted but I'll try it. And I'll also stick to M0.93 for my next test. :)

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Fabrice Estienne

As regards the holding (Final Reserve)  AIR OPS say :

Final reserve fuel, which should be:
(i) for aeroplanes with reciprocating engines, fuel to fly for 45 minutes; or
(ii) for aeroplanes with turbine engines, fuel to fly for 30 minutes at holding speed at
1 500 ft (450 m) above aerodrome elevation in standard conditions, calculated with
the estimated mass on arrival at the destination alternate aerodrome or the
destination aerodrome, when no destination alternate aerodrome is required.

Fabrice

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Ray Proudfoot

Thanks for that Fabrice. CPS-X insists on a minimum of 6500Kg of holding fuel which equates to around 32-35 minutes. If you set a lower holding time the holding fuel is automatically increased to 6500Kg.

My last flight went a lot better. No 5T extra. Just the fuel CPS-X calculated - 24467Kg. I pumped fuel to 11 until take-off CG of 52.5% was achieved.

Once airborne and passed FL100 I turned on 5a and 7a pumps and also started to pump fuel from 9 to 11 until 55% was achieved. There was around 1000Kg remaining in 9 by the time that was achieved. The remainder went into 5 and 7.

Once 5 and 7 tanks were empty CG stabilised at 54.9%. Not a problem I assume. I had no fuel to pump rearward into 11 except that in 1 and 4. I decided it wasn't needed.

Descent was standard and CG on landing was 52.8% which was inside the recommended 53%. I cruised at M0.93 and ignored the moaning from my rich passengers who wanted M0.95. I just gave them some extra champagne. :D

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Fraser Gale
7 hours ago, Fabrice Estienne said:

As regards the holding (Final Reserve)  AIR OPS say :

Final reserve fuel, which should be:
(i) for aeroplanes with reciprocating engines, fuel to fly for 45 minutes; or
(ii) for aeroplanes with turbine engines, fuel to fly for 30 minutes at holding speed at
1 500 ft (450 m) above aerodrome elevation in standard conditions, calculated with
the estimated mass on arrival at the destination alternate aerodrome or the
destination aerodrome, when no destination alternate aerodrome is required.

Fabrice

Regardless of what AIR OPS says (I'd be curious to know where you got this information from though?) this did not happen on Concorde and you can ask any BA crew member who will tell you that to arrive with the legal minimum of 6500kg at destination or alternate you did not have room for 45mins of holding fuel. There was a way to plan for diversion from FL100 in the descent which allowed more margin but generally speaking unless the captain added more fuel because he had room to and he suspected delay on arrival the most room for manouver would be around 30 mins. A captain once told me you could really only do once round a hold before diverting to your nearest alternate and on once occasion when a Concorde arrived at that alternate and couldn't get in because of weather, it arrived at a third destination with so little fuel that even though the weather was well below visual limits the could go nowhere else. When the first officer asked what decision altitude would be used the captain replied "when it goes bump!"

Remember that to carry an extra tonne of fuel on Concorde you burned an extra tonne, you couldn't afford to carry any more than you had to,

Frazz

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Fraser Gale

Further to my last post, I have looked out a couple of authentic Concorde flight plans. One for the BA189 London to Washington flight gives a diversion time of 9 mins (2750 kg) and an additional of 9 mins (2000kg). The legal reserve is stated as 6500kg estimated at 30 mins but this should not be used, you had to land with this in the tanks or else the Feds came after you!

Frazz

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Ray Proudfoot

Frazz,

Having read your reply what would you say should be the minimum time in CPS-X for holding? Pierre has always made 15-45 available but if you choose less than 34 minutes the holding fuel is increased to 6500Kg which really makes 34 mins the minimum.

Maybe you could post your comment in the CPS topic as well as here if you feel it needs attention.

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Fabrice Estienne

Hi  Frazz and Ray,

The Transport Coefficient as regards Holding fuel and the destination alternate fuel is included into the trip fuel computation since one considers the landing weight at the destination airport.

Landing Weight = ZFW + Holding Fuel (Final reserve) + Destination Alternate Fuel + Extra Fuel at the discretion of the commander.

As regards Concorde the transport coefficient is stated at 1.7 for Atlantic legs.

The Transport Coefficient for the trip from London to Dublin may be sensibly assumed at 1.2

For the record, the ICAO annex 6 and their enforcement into AIR OPS (EASA or FAR-FAA) are mandatory in the ATPL syllabus. Hence, "fuel to fly for 30 minutes at holding speed at 1 500 ft (450 m) above aerodrome elevation in standard conditions" shall be obeyed.

Regards

Fabrice Estienne

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Ray Proudfoot

Thanks Fabrice. This is above my head I'm afraid. I'm going to have to defer to those with greater knowledge like Frazz and hopefully Pierre if he would like to join this discussion.

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Fraser Gale
1 hour ago, Fabrice Estienne said:

Hi  Frazz and Ray,

The Transport Coefficient as regards Holding fuel and the destination alternate fuel is included into the trip fuel computation since one considers the landing weight at the destination airport.

Landing Weight = ZFW + Holding Fuel (Final reserve) + Destination Alternate Fuel + Extra Fuel at the discretion of the commander.

As regards Concorde the transport coefficient is stated at 1.7 for Atlantic legs.

The Transport Coefficient for the trip from London to Dublin may be sensibly assumed at 1.2

For the record, the ICAO annex 6 and their enforcement into AIR OPS (EASA or FAR-FAA) are mandatory in the ATPL syllabus. Hence, "fuel to fly for 30 minutes at holding speed at 1 500 ft (450 m) above aerodrome elevation in standard conditions" shall be obeyed.

Regards

Fabrice Estienne

I'm sure what you quote is quite correct for modern times and aircraft but in practice when flying Concorde, not very possible when flying at 250kts in a holding pattern. Also remember that it is generally agreed that Concorde would have been stopped by now even if she had continued beyond 2003, mainly because of the changes in rules and regulations that are now vastly different from 1976 when she started. 

In the Concorde flight planning computer (the real one, not CPS) trip fuel was the amount required from start of takeoff to arrival overhead destination. It did not include any extras. On to this would be added the legally unusable reserve of 6500kg, which you call holding fuel but if you used it to hold it can't be final reserve, a variable additional of 2000kg for the departures and arrivals routes and a variable diversion figure. The captain could then add more (if there was room) if he considered it prudent to do so. The extra fuel and diversion fuel would be used for holding so if you got into the hold and were not sure how long the delay was going to be you would have to divert once the diversion fuel plus the 6500kg were the only fuel remaining.

In the winter months when strong westerly winds were common at higher altitudes, it could be that the trip fuel plus the reserve, additional and diversion gave you more that full tanks, dependant on traffic load etc. If this happened, there was an option to plan the diversion from 10,000ft which required less fuel because you could fly direct to it at higher airspeed, although the crew had to make the decision before this point requiring accurate weather information. If this didn't reduce the fuel required below full tanks, you had to offload bags or passengers or both! 

Sometimes we have to remember that Concorde is not an aircraft, she is a Concorde!

Frazz

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Pierre Chassang

I agree with Frazz when he says:

Quote

Sometimes we have to remember that Concorde is not an aircraft, she is a Concorde!

AF and BA procedures got some differences.

The AF holding paterns was:

Quote

1) FL <= 140, IAS 250 kt, 1 m leg, 30° bank.
2) FL >= 150, IAS 280 kt, 1 m 1/2 leg, 30° bank.

The minimum holding reserve was 6400 kg / 30 min FL60. (CPS-X assumes minimum 6500 kg / 34 min but depending the instantaneous aircraft weight and up to 45min.)

Concerning the subsonic cruise CG of 55%, is depending of initial CG and instantaneous aircraft weight at cruise level.
CPS-X being a planner it can't predict these parameters.

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Ray Proudfoot

A longer test flight today. EGLL-LSZH. This time I balanced the CG by moving fuel purely between 9 and 11 and vice versa to maintain 55%.

Only at one point where CG was 54.9% did I have a small problem because there was nothing forward to pump rearwards except tanks 1 & 4 and Frazz has already advised against that.

Landed with CG of 52.8% which is fine. So CPS-X calculations are very good. Only area of concern is CPS-X calculated 15.1T remaining on landing but I had 13.2T but this can be tweaked by changes to the aircraft files. I'll await others guidance on that.

 

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Ray Proudfoot
3 hours ago, Pierre Chassang said:

It may be interesting to using tool for recording aircraft data during flight in the goal to analysis.
Here are some tools which can help to do that:

Herve Sors Utilities.

Pierre,

I have the log produced by Electronic Flight Bag if that's any help. It show the fuel remaining at each waypoint of a flight plan.

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Fabrice Estienne

Frazz,

Holding regulations are quite antique.

ICAO stated them in the fifties are they were enforced from the outset to Concorde. Then they became European JAR and then EASA.

Now 6500 kg increase the landing weight and therefore the computation of the trip fuel.

The crew if necessary has at one's disposal the 6500 kg for holding. This is the rule.

Into the regulations the fuel for holding is termed as Final Reserve.

The Transport Coefficient K is defined as change of TOW / change of LW.

Change TOW = Change Tripe Fuel (as regards Holding, Alternate + Extra) + Change LW.

The integrated cruise tables (base on the Bréguet Formula) gives the air distance from the change of the GW.

All FCOM of certified transport aircraft supply these tables and Concorde makes no exception.

Hope Pierre has taken into consideration this matter into his tool.

Cheers,

Fabrice Estienne

 

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Fraser Gale

Fabrice, 

regardless of ICAO or JAR regulations I use the Concorde Flying Manuals, Performance Manual, Cruise Control Manual, Load and  Balance Manual, Navigation Manual, Barbados Planning Notes and Flight Planning Computer Notes and the reserves used on a day to day basis by BA are as I have previously stated. 

If ever the fuel levels did get down to the final reserve you had balance issues to the point you may have had to move PAX around to achieve a landing CG and use the cross feed valves to ensure fuel to engine delivery. There was an incident in the early 1980s with a Concorde returning from the USA where they had used more fuel than expected due to hydraulics problems (I think) and the flight engineer recommended landing at Shannon for a fuel stop. The first officer agreed but they were overruled by the Flight Manager Technical who was captain on this occasion (this was pre CRM!) and they had to declare a fuel emergency on approach to Heathrow and after landing couldn't allow passengers off until fuel was loaded to secure the balance of the aircraft.

Frazz

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Ray Proudfoot

Fabrice,

Only Pierre can answer your question. I wonder if he has different code in CPS-X for AF and BA to comply with their rules? That might be difficult.

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Pierre Chassang

CPS-X only use real AF flight manuals, abacus, tables and data.
I add that I'm working for 3 years (1969-1972) at Aerospatiale on Concorde, and I well known André Trurcat, and still have contact with a real Concorde pilot who helped me when I was ConcordeX beta tester and during the CPS development.

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Fraser Gale

I don't think the differences in terminology and procedures are important enough to be debated anyway. 

BA had to develop some creative planning in order to run the Barbados route which needed all the fuel and had very limited alternate options. You simply did not have enough fuel to hold on arrival and still land with the final reserve. 

It seems the terminology is the biggest difference here, where final reserve is called holding fuel by some of us but to me you have to land with it still in the tanks and therefore can't use it for holding at all. As I say, just different ways of looking at it and unimportant for simulation purposes.

Incidentally, I too am in contact with former crew members (BA) and they are always extremely helpful.

Frazz

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Ray Proudfoot
2 hours ago, Pierre Chassang said:

CPS-X only use real AF flight manuals, abacus, tables and data.
I add that I'm working for 3 years (1969-1972) at Aerospatiale on Concorde, and I well known André Trurcat, and still have contact with a real Concorde pilot who helped me when I was ConcordeX beta tester and during the CPS development.

With credentials like that CPS-X is in good hands.

Going back to my original question I think it has been answered. 55% CG for all subsonic flights.

But I would like to know the optimum altitude for those flights. Given Concorde could remain subsonic up to FL310 and perhaps beyond what is the optimum FL for flights <1000nm? FL260/280 does seem quite low and on my flight from Heathrow to Zurich yesterday there was a lot of turbulence. That wouldn't have made for a very pleasant flight for my passengers.

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Fraser Gale
1 hour ago, Ray Proudfoot said:

With credentials like that CPS-X is in good hands.

Going back to my original question I think it has been answered. 55% CG for all subsonic flights.

But I would like to know the optimum altitude for those flights. Given Concorde could remain subsonic up to FL310 and perhaps beyond what is the optimum FL for flights <1000nm? FL260/280 does seem quite low and on my flight from Heathrow to Zurich yesterday there was a lot of turbulence. That wouldn't have made for a very pleasant flight for my passengers.

I will have a look at my cruise control manual and get back to you.

Frazz

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Ray Proudfoot
46 minutes ago, Fraser Gale said:

I will have a look at my cruise control manual and get back to you.

Frazz

Cheers Frazz. :)

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Pierre Chassang

The optimal FL in subsonique flight is mainly depending of the aircraft weight.
At VMO/M0.95:

180t = FL258 VMO
170t = FL260 M0.95
160t = FL270
150t = FL281
140t = FL295
130t = FL310
120t = FL325
110t = FL341
100t = FL365

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Ray Proudfoot

Thanks Pierre. My latest test flight of EGLL-LSZH at FL280 resulted in a greater fuel burn than that calculated by CPS-X.

I shall fly it again probably tomorrow at FL320 / M0.95 and report back both here and in the CPS forum.

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Fabrice Estienne

Ray + Frazz

Affirm, CG 55% for subsonic.

Pierre has the right data.

Ray, I guess you will be cleared for FL310 after initial climb and for a final cruise at FL340 (M.95 AP+AT).

GW 116.1T (with 91 pax), it would seem to me a little light in fuel to fly from London to Dublin. What's up the obtained ZFW ?

The trip fuel is roughly 8 t which includes the flight from brakes release to an ILS procedure + speed 250 kt forced under FL100 (I do not use CPS, only the AF FCOM).

The Holding 6400 kg + alternate to Shannon  6000 kg are added.

Hence 20 400 kg is the minimum in my opinion.

For the record the minimum fuel policy for Concorde (AF) is collector tanks 1-4 full + 5950 kg in tank 9 for CG balance = 23.8 t (with density 0.79)

In the end there's been lot of discussion about the rule of CG 55%.

I was pleased to be able to share our respective opinions on this discerning matter.

Cheers

Fabrice

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