Jump to content

Is 59.3 the ideal CG before descent?


Ray Proudfoot

Recommended Posts

Ray Proudfoot

Flying the route now. I loaded an extra 3T. CPS-X decided to load fuel into 6 and 8 and left 5 and 7 empty. I've treated 6 and 8 as though they are 5 and 7 but it has resulted in CG going aft to 59.3 early so I had to use your procedure to move it forward to 59.0.

Also, if 5 and 7 are using fuel faster than 5a and 7a can deliver is it acceptable to turn off the pumps on 5 and 7 allowing 5a and 7a to catch up?

1090nm to go.

Link to post
  • Replies 150
  • Created
  • Last Reply

Top Posters In This Topic

  • Fraser Gale

    68

  • Ray Proudfoot

    61

  • AdrianSmith

    6

  • Andrew Marshall

    6

Top Posters In This Topic

Popular Posts

Oh, and somebody not to far away also made a Concorde profile for PFPX that was reasonably accurate.... so even if CPS does become unusable at some point, we will survive!

I would hope the virtual pilots would already be well aware of the systems that were and still are ahead of their time. Anyway, short of reopening the Airman's Training Centre at BAC Filton, I th

Just as a small addenda to this discussion, I have finally found the "old" instructions regarding fuel management dated 1988 which are basically the way that I normally use: - trim transfer in no

Posted Images

Ray Proudfoot

Landed with 15T remaining which seems fine. Couple of images showing state of fuel when 6 and 8 levels matched difference between 1/4 and 2/3 and another at Decel point.

CG was not as far forward as I would have liked for landing (>53) so that needs looking at. 700Kg in 9/10 for landing but there's something amiss.

Conc_6&8FuelSwitch.png

DecelFuel.png

Link to post
Fraser Gale

Why are you concerned about your landing CG? The normal range is 52.5% to 53.5% for stability reasons. The absolute forward limit is 52% but I've never landed at that.  The more forward the CG the more up elevon is required on approach.

I don't think you followed the procedure exactly as I typed it because you still have 2&3 near full with 1&4 quite low which tells me you didn't turn off the pumps to 2&3 as stated.  It is ok to do this as long as you switch off the aft trim when you still have enough in 6&8 to refill 1&4, returning them to equal levels. 

No need to turn of pumps in 5&7 when transferring from the A tanks as far as I know, it is purely for transfer so as long as there is at least 100kgs in the tanks when you first start the pumps there shouldn't be an issue. 

Good reserves on landing, if my sums are correct you must have taken 58T and I recommended 60T for a 16T landing.  Thus would match because carry a tonne to burn a tonne means if you had taken 60 you would have landed with 16!

Link to post
Ray Proudfoot

I was concerned because it's always been around 53% or just forward of it for landing. Maybe the way the fuel was distributed it made the difference. CPS-X does load fuel in such a way that landing CG should be 53% or just forward of it. No big deal.

I did follow your procedure. I printed it out and followed to the letter as much as I was able given I had to feed fuel into 1-4 from 6 and 8 rather 5 and 7. Maybe that makes a difference.

I don't like leaving pumps on when the tank is struggling to deliver fuel. The collector tanks were taking it faster than 5a and 7a could deliver. Remember 5 and 7 didn't have much fuel in them - just the remainder of 9 and 10 plus 5a and 7a.

I loaded 55.2T that included 3T extra. 1-4 never dropped below 1T although 1 and 4 did get close.

I'll try something a bit different tomorrow. Maybe Hawaii to LAX.

Link to post
Fraser Gale

If I get time later today I'll fly this route and see how it goes.  The fuel distribution for landing depends on ZFCG which is affected by everything other than the fuel.  A chart is used to determine ballast fuel (if any) to put in tank 9 or tank 11 but often the engineer would just manually pump fuel into tank 9 until the CG was at or forward of 53.5% because by that time in the flight they would know that the CG computers were giving accurate data.  I wouldn't want it forward of 53 though, as the autostab would be constantly working the trim to keep the nose up once speed is reduced to Vref+7 or just Vref. 

Surely if you switched off the pumps in tanks 6 and 8 that feed tanks 2 and 3 when there was still around 2200kgs the level of 2/3 should be lower as they weren't getting fuel? This is the reason for this bit of the procedure, so that the collector tanks return to more equal levels. 

Link to post
Ray Proudfoot

Frazz,

I can only say I followed your instructions regarding fuel pump switches for 6 and 8. Maybe if you load my fuel for your flight you can better see how it looks. Here's how CPS-X decided on fuel load.

FuelEGLLGCTS.png

Link to post
Ray Proudfoot

Frazz,

After switching off the pumps in 6 and 8 that feed 2 and 3 the CG is slowly moving forward. Now at 58.4 with 200Kg left in 6 and 8. I presume that's expected.

Link to post
Fraser Gale

According to your screenshot you were planning takeoff with a 53% CG, but that was only used with takeoff weight less than 140T and yours was calculated at 144T. Fuel loading roughly matches my charts here. I can't check tank 9 landing contents without knowing your ZFCG and landing fuel weight. 

CG will move forward when tank 2/3 contents reduce as they are aft of the Centre of pressure.  Maybe you need to make sure you only pump into 1/4 when moving fuel forward and when returning aft CG switch to normal. 

I have to say though, that because this was a light weight flight you would have to use the procedures for a flight at light weight which is why this may not have worked for you.

Link to post
Ray Proudfoot

Just completed PHNL-KSFO. I'm attaching the CPS-X doc for EGLL-GCTS so you have all info.

This is state of fuel at Decel point for today's hop. Looks pretty good. I landed with 12.1T, CPS-X calculated 11.9T which is pretty damn good.

Regarding the light take-off I have to trust what CPS-X does. Only the 1 and 4 fuel switches were on when moving fuel from 6 and 8. AS per your instructions. Anyway, on the latest flight everything went according to plan and 1 and 2 were never close to the 1T limit. It felt the best fuel management flight I've done. Good teacher! :D

 

PHNLKSFO_Decel.png

EGLL-GCTS.pdf

Link to post
AdrianSmith
On 9/27/2018 at 10:08 AM, Fraser Gale said:

- when CG reaches 57.5% set T11 pumps to auto and close the inlets to T5/7

CofG alarm comes on at anything below 58% so how can that be correct?

I have to admit that I "invented" some of my fuel management procedures, particularly for Barbados, like opening all four cross feed valves if any collector tank gets even close to 1000 Kgs just in case of cavitation the others will keep it going.

One flight when I was trying to balance 6 and 8 laterally I got distracted and didn't open all the cross feeds before I switched off the feed pumps for 3 and 4. Ever had a double engine flame out at Mach 2? grabs your attention. I managed to get them restarted.

  • Haha 1
Link to post
Ray Proudfoot

Hi Adrian,

I'm guessing 57.5% would be during the descent. It stayed within the limits during the cruise/climb but CG did move forward with the switches in those positions.

Currently flying OMDB-FIMP (3000nm) to further test these new procedures. That's Dubai - Mauritius for those that don't venture away from the North Atlantic runs. ;)

Link to post
Ray Proudfoot

OMDB-FIMP. 2997nm, 86 pax, 80.6T fuel loaded. ZFW 88477. Departed OMDB 07:30 UT Mon 1 Oct.

Bit of a tight one for fuel. Didn't load any extra as I wanted to gauge CPS-X fuel calculations. I was a couple of Ts below the calculated but still with 9T remaining.

This is the fuel status at the Decel point.

 

OMDB-FIMP_Decel.png

Link to post
Fraser Gale
7 hours ago, AdrianSmith said:

CofG alarm comes on at anything below 58% so how can that be correct?

I have to admit that I "invented" some of my fuel management procedures, particularly for Barbados, like opening all four cross feed valves if any collector tank gets even close to 1000 Kgs just in case of cavitation the others will keep it going.

One flight when I was trying to balance 6 and 8 laterally I got distracted and didn't open all the cross feeds before I switched off the feed pumps for 3 and 4. Ever had a double engine flame out at Mach 2? grabs your attention. I managed to get them restarted.

I agree Adrian but that's what the real manual says....! I actually wonder if it is a miss print and should be 58.5 to be correct. 

Link to post
Fraser Gale

Ray, that looks spot on.  The last time I did BGI to LHR it looked like that at decel. 

According to the manual the procedure allows you to keep the CG aft for as long as possible, but I'm not totally convinced because it moves forward as 2/3 empty anyway...

I'll go and do some more reading!

Link to post
Ray Proudfoot

Thanks Frazz. I’ve noticed that when we switch off the two pumps on 6/8 that feed 1/4 the CG moves forward very slowly. That is by design of course because we are filling 1/4 and not 2/3. Maybe your checking will find a refinement to keep that CG aft longer.

By the time 6/8 are empty there should - I assume - be equal amounts in 1-4. As fuel continues to be used I’m also guessing that 1-4 will be very close to 1T at the decel point. Preferably 1.2T as it takes some time for the aircraft to slow down and go down. Maybe I should load that extra tonne of fuel! :D

I do have a lot more confidence in my ability to handle fuel now and for the first time since I switched the VFE off really feel I’m managing fuel as it was done by the crew. Just a few extra instructions from you have made all the difference.

The acid test is EGLL-TBPB which is another 40 mins of flying and another 15T of fuel. But first I want to try a flight around 3500nm as a final test before the Barbados hop.

Link to post
Ray Proudfoot

EIDW-TBPG looks to be ideal for my next test flight. Bit shorter than from Heathrow which might be the difference between making it a legal flight and not! :D

EIDWTBPB99.pln

Link to post
Fraser Gale

Having checked the last edition of the flying manual, there is the "conditional" procedure as I explained above for moving fuel forward if CG goes aft of 59% or the elevons go further than 1 degree down (which is actually what a really switched on engineer will be watching, not the CG computer), but the only conditional procedure for moving fuel aft is for "elevons not between 0 or 1 degree down".  This purely states to switch the aft trim switch to aft, which is already part of our working, so we are doing it correctly.

If you do your sums properly and time the switching off of the pumps in 6/8 then yes, all collector tanks should have an equal quantity when 6/8 are empty.  I landed with 11200kgs at Heathrow from Barbados without delays which was quite good going, and I managed to do a maximum performance departure which saves quite a bit of fuel.

Link to post
Ray Proudfoot

I can’t ever recall seeing the elevons out of alignment. How far does the fuel need to be unbalanced before it shows?

I was a little late switching the pumps to 2/3 off. Perhaps 200Kg too late, not massive but on today’s flight I shall make sure I nail it.

The return to Heathrow should be easier shouldn’t it with the prevailing westerlies once you’re in more northerly latitudes?

Link to post
Ray Proudfoot

I abandoned EIDW-TBPB. 28 is just not long enough. Instead I'm continuing my Indian Ocean adventure with FIMP-YPPH. 3182nm, 87.9T, 95 pax. Great tail winds helping keep pax numbers high.

Link to post
Ray Proudfoot

The FIMP-YPPH flight went great. This time I paid great attention to tanks 6 and 8 levels and when 2.7T difference between 2/1 and 3/4 I changed the switches. This was the result when 6/8 were empty. Looks like those instructions should be included in the tutorial Frazz.

 

FIMP-YPPH_6&8Empty.png

Link to post
AdrianSmith

On your previous photo Ray, OMDB-FIMP, I would have had the cross feeds open just as a bit of insurance :) but other than that it is pretty much what mine looks like at ToD for Barbados.

Fill to 100% fuel capacity (95680Kg) and try 9 crew 60 passengers. Heathrow is long enough at max weight (just).

I find CofG is a bit too far aft at the holding point, so I override the auto stops on 9&10, then when they wont fill any further pump from 11 to 5&7 until you get 54% (maybe 54.1) then let her go. Nerves of steel required as the end of the runway is coming at you at 190 knots or so! (try at least ten knots headwind on the runway for first go).

Link to post
Ray Proudfoot

Adrian, I’ve never used the cross feeds. Under what circumstances would they be used? Given none of 1-4 had much above 1T would it have helped?

The Barbados run is certainly the ultimate challenge but after my successes this week I feel ready for it. Might have to choose a past date depending on the wind element at altitude. Thanks for the tips on getting CG to the right value. I have noticed the nose comes up quite quickly when CG is 54. Just need a little less back pressure on the yoke.

Link to post
Fraser Gale
9 hours ago, Ray Proudfoot said:

I can’t ever recall seeing the elevons out of alignment. How far does the fuel need to be unbalanced before it shows?

I was a little late switching the pumps to 2/3 off. Perhaps 200Kg too late, not massive but on today’s flight I shall make sure I nail it.

The return to Heathrow should be easier shouldn’t it with the prevailing westerlies once you’re in more northerly latitudes?

I think you misunderstood my post - the elevons alignment would be used to check for lateral balance and fuel moved across the ship to even things out, but collective elevon position (all up or all down) would be used to check logitudinal balance - higher than 0 degrees and the fuel needs to move back, lower than 1 degree and it needs to go forward.  This was used in the case of CG computer failure also. 

I never worry about fuel on a Barbados flight as long as I plan it properly and keep checking it, but I am always slightly nervous for about 10 minutes right in the middle of the route where a double engine failure (just as likely as a single one on Concorde) would mean you couldn't reach dry land! Even a hydraulic issue that causes you to go subsonic could make it rather tricky!

Link to post
Fraser Gale
2 hours ago, AdrianSmith said:

On your previous photo Ray, OMDB-FIMP, I would have had the cross feeds open just as a bit of insurance :) but other than that it is pretty much what mine looks like at ToD for Barbados.

Fill to 100% fuel capacity (95680Kg) and try 9 crew 60 passengers. Heathrow is long enough at max weight (just).

I find CofG is a bit too far aft at the holding point, so I override the auto stops on 9&10, then when they wont fill any further pump from 11 to 5&7 until you get 54% (maybe 54.1) then let her go. Nerves of steel required as the end of the runway is coming at you at 190 knots or so! (try at least ten knots headwind on the runway for first go).

Pre takeoff burn off is done by selecting the inlet valves to tanks 5/7/9/10 to closed, selecting the standby inlet valves to 1/2/3/4 open, selecting the final tank 11 fuel in its load limit controller and setting the transfer auto master to forward. This meant the correct amount was removed from tank 11 under auto control but directly to the collector tanks.

I think I'm correct in saying that this was a change to procedure within BA after the Paris accident to prevent the over filling of tanks 5/7 which is where the fuel would normally have gone.  It is true that a "switched on" engineer in the old days would use the override switches to pump the required fuel into 5/7 especially at London where the taxi was short, without I may add any risk at all because the amount of fuel put in there still didn't completely fill the tanks and it was being sent to the collectors to be burnt anyway.  Unfortunately it was this that compounded issues in Paris because the engineer left these open and the T11 pumps on so that the CG would move forward during takeoff (or because he forgot to put them off) which meant that tank 5 was continually being "topped up" with fuel from 11. When the bit of tyre hit the wing it did so with such force it caused a hydraulic magnification effect in the fuel which had nowhere to go because there was no air space, forcing a patch of the tank skin outwards, causing the huge leak etc....so sad but I shall keep my opinions to myself. What I have stated here is from credible sources. 

 

Link to post
Fraser Gale
2 hours ago, Ray Proudfoot said:

Adrian, I’ve never used the cross feeds. Under what circumstances would they be used? Given none of 1-4 had much above 1T would it have helped?

The Barbados run is certainly the ultimate challenge but after my successes this week I feel ready for it. Might have to choose a past date depending on the wind element at altitude. Thanks for the tips on getting CG to the right value. I have noticed the nose comes up quite quickly when CG is 54. Just need a little less back pressure on the yoke.

Cross feeds were only used for abnormal drills like feed pump failures, engine failures etc.

  • Like 1
Link to post
Ray Proudfoot
54 minutes ago, Fraser Gale said:

I think you misunderstood my post - the elevons alignment would be used to check for lateral balance and fuel moved across the ship to even things out, but collective elevon position (all up or all down) would be used to check logitudinal balance - higher than 0 degrees and the fuel needs to move back, lower than 1 degree and it needs to go forward.  This was used in the case of CG computer failure also. 

I never worry about fuel on a Barbados flight as long as I plan it properly and keep checking it, but I am always slightly nervous for about 10 minutes right in the middle of the route where a double engine failure (just as likely as a single one on Concorde) would mean you couldn't reach dry land! Even a hydraulic issue that causes you to go subsonic could make it rather tricky!

I don't think I do Frazz. If fuel isn't laterally balanced then won't that will be reflected in the elevons showing one side down compared to the other? I've never seen that in P3D despite one side having hundreds of Kg more than the other.

CPS-X never seems to want to completely fill her up even for the Barbados run. I assume this is for good reason as you allude to in your other post. Some air should be left in tanks even on the longest hops.

Link to post
Fraser Gale

Yes, but I wasn't talking about lateral balance in the procedures I mentioned above, I was talking about using the elevons as a very accurate (more than the computers) of CG position.

The full tanks figures take into account the air space so the charted values should always be achievable. 

Link to post
Ray Proudfoot

But my question was about lateral fuel imbalance and how that would be shown by the elevons. I never ever see them in anything other than a straight line when airborne.

If one wing had 2T more than the other would that be reflected in the elevons?

I’m not sure even on a 32” FullHD display it is clear enough to see their precise position. And if you hover the mouse over them there’s no pop up showing the actual value assuming there is one.

Link to post
Fraser Gale
52 minutes ago, Ray Proudfoot said:

But my question was about lateral fuel imbalance and how that would be shown by the elevons. I never ever see them in anything other than a straight line when airborne.

If one wing had 2T more than the other would that be reflected in the elevons?

I’m not sure even on a 32” FullHD display it is clear enough to see their precise position. And if you hover the mouse over them there’s no pop up showing the actual value assuming there is one.

But my post was about procedures for logitudinal balance which came from your original question, nothing to do with lateral balance as we've discussed all that before, including it being difficult but not impossible to see in the sim. And yes, 2T will make a difference enough to cost the company extra money in fuel bills and thank goodness there isn't a hover pop-up, how unrealistic! 

I fly 2D panel on a full HD TV with a second HD TV above and forward with the virtual cockpit view for a realistic "out of the window" feel with nose and visor active.  Perhaps it is easier to see on the 2D panel or maybe I just imagine it is happening from time to time - never go on fuel levels in tanks for this. 

Interestingly a highly switched on flight engineer once said that the Olympus engines burnt fuel very evenly and that the tank layout worked so well that he often didn't need lateral trim. 

Link to post
Fraser Gale

Scrub what I said about the pre takeoff burn off procedure being changed after the accident - I checked a 1996 edition of the manuals and the procedure was always to transfer directly into the collectors under auto control.  This would be the reason that a short taxi sometimes led to the SEO using the override switches to also pump some fuel into 5/7, because until the burn off was complete there wouldn't be fuel being pumped from 5/7 into the collectors. 

Makes the events in Paris even more mind boggling.

Link to post
Fraser Gale

Also just had a thought regarding CPS not giving you full tanks - have you reduced your ZFW and made sure you have a forward ZFCG? Barbados was weight limited for range to allow for full tanks and I think passenger loads were restricted to 85, maybe less on warm days. This is why there were often two Concorde's sent out to BGI on the same day if bookings were up.

Link to post
Ray Proudfoot

I've read your earlier post about elevon position being used to check fuel was balanced properly. But wouldn't the amounts in the various tanks be confirmation of that? And as it was the FE's job how could he see elevon position from his seat?

The 2D panel is certainly clearer and sharper than the Virtual Cockpit which is the mode I use. But with ChasePlane I have various preset views that include a close-up of the engine section but even then seeing any lateral disparity is difficult.

Regarding reducing ZFW I don't touch that directly. I mostly select a random number of pax and apart from the longest routes that's fine. When Max Take-off weight is exceeded I reduce pax numbers. There is a ZFCG indicator that moves according to pax loads and where they sit. All very clever. You should try it.

I did wonder how they guaranteed pax a seat if conditions were unfavourable. Maybe the second Concorde only had a few pax. That would have been expensive for BA.

Link to post
Fraser Gale
7 hours ago, Ray Proudfoot said:

I've read your earlier post about elevon position being used to check fuel was balanced properly. But wouldn't the amounts in the various tanks be confirmation of that? And as it was the FE's job how could he see elevon position from his seat?

The 2D panel is certainly clearer and sharper than the Virtual Cockpit which is the mode I use. But with ChasePlane I have various preset views that include a close-up of the engine section but even then seeing any lateral disparity is difficult.

Regarding reducing ZFW I don't touch that directly. I mostly select a random number of pax and apart from the longest routes that's fine. When Max Take-off weight is exceeded I reduce pax numbers. There is a ZFCG indicator that moves according to pax loads and where they sit. All very clever. You should try it.

I did wonder how they guaranteed pax a seat if conditions were unfavourable. Maybe the second Concorde only had a few pax. That would have been expensive for BA.

Imagine you have a complete CG computation failure, all three computers go down.  Would you know what the CG is just by looking at the gauges? Especially once it starts moving around? There is a chart in the abnormal and emergency checklists to help and in later years a small computer program in the HP200LX pocket computer that crew members carried (I have one and have written the programs from scratch to replicate it) to calculate the CG from fuel quantities. However, continued cruise without CG indication was done by trimming to elevon angle as previously discussed.  If you have ever sat in the flight deck of Concorde you should know that everything was so close together that it was easy to see nearly everything from wherever you were, after all the SEO called the height on landing from the radio altimeters on the front panel! 

There you go trying to get me using CPS again Ray! The fact is I don't need it.

I just wondered if you might have reached a fuel limit because of having a high ZFW. I think they would have only put on the second Concorde if they had at least half an aircraft of passengers.  Back in the early 90's break-even load factor was around 40%

Link to post
AdrianSmith

Fraser, out of interest how do you balance 6 & 8 in cruise, 8 always has more than 6. I used to use the "valve (5-8)" switch but it didn't always work as expected and also required me to do some maths to calculate (5+6) to equal what was left in 8 and I didn't always get it right.

Now once 5 and 7 are empty (and of course 5A/7A emptied) I select cross feeds all open, switch the engine feed pumps for 1 & 2 off then let 8 get to within 100 Kgs of 6, open all engine feed pumps again then cross feeds off.

Link to post
Ray Proudfoot

Frazz,

In that situation then no, I wouldn't. But how many times did that happen on the Concorde fleet in 27 years? Was it just a backup procedure that was never used in anger?

I appreciate it's a small flight deck. I've sat in AC at Manchester and the one at Brooklands. The FE can also see the timer to advise when reheats need cancelling.

I only suggested you try CPS-X so you could observe its behaviour. I'm not a salesman as it's not for sale. ;)

Link to post
Fraser Gale
54 minutes ago, AdrianSmith said:

Fraser, out of interest how do you balance 6 & 8 in cruise, 8 always has more than 6. I used to use the "valve (5-8)" switch but it didn't always work as expected and also required me to do some maths to calculate (5+6) to equal what was left in 8 and I didn't always get it right.

Now once 5 and 7 are empty (and of course 5A/7A emptied) I select cross feeds all open, switch the engine feed pumps for 1 & 2 off then let 8 get to within 100 Kgs of 6, open all engine feed pumps again then cross feeds off.

If the elevons are in alignment i.e. not lateral displacement then you wouldn't do anything.  If you want to even up the levels then the only real way of doing is as for lateral trim: for example move from right wing to left - use the jettison valves in one of the right hand collector tanks (usually 3 because 4 will be down at 2000kg for aft trim) to pump into 11 via right hand valve then pump from left hand pump into tank 5 and leave it there until needed. 

The recomended method is to note down the current T11 contents before moving anything so that you return it to the same level.  For what you are asking I would decide on the difference in fuel from left to right, because assuming T5 is empty that is the amount you want to pump over (while returning 11 to noted level).  If you already have fuel in 5 for trim purposes just add the required amount to it. 

It would be considered bad practice to use the cross feeds in the way you describe because as I said to Ray they tended to only be used for abnormal situations like multiple feed pump failures, extremely low fuel level, engine failures etc. It is also difficult to keep track of exactly how much fuel is where. 

The transfer valves that you mention I must confess I never use because they work purely on gravity, attitude and sloshing! They could be used if pump failures meant you needed to get to the fuel but as you say they can be unpredictable.  I once had a problem a few years ago when for some reason the fuel panel loaded with one of these valves open instead of shut and I (terribly) didn't notice (because I never use them I didn't expect them to be open...bad airmanship!) and part way in the climb I had fuel in places I didn't expect but it took me half of the cruise to sort it out because to move the fuel you needed space in certain tanks...

Link to post
Fraser Gale
7 minutes ago, Ray Proudfoot said:

Frazz,

In that situation then no, I wouldn't. But how many times did that happen on the Concorde fleet in 27 years? Was it just a backup procedure that was never used in anger?

I appreciate it's a small flight deck. I've sat in AC at Manchester and the one at Brooklands. The FE can also see the timer to advise when reheats need cancelling.

I only suggested you try CPS-X so you could observe its behaviour. I'm not a salesman as it's not for sale. ;)

I don't know how often it happened but there were often gauging pack errors/failures indicated by the little yellow lights above the CG computer readout (return flight on the ITVV program the A tank ones are on...) and remember that the computers are only required to be accurate to within 0.3% either side of the needed CG, so there is still quite a margin there. Failure of one CG computer gauging channel meant that the CG could become unreliable because the two channels took fuel quantity from different wings/sides of the aircraft, the two sides being summed, averaged and failure monitored by the main channel. Engineers were taught to trim to elevon angle because the target was half a degree down which gave the least drag. 

The engineers could see the timers but the first officers called "three two one noise" in case the engineer was reading his paper! 

  • Haha 1
Link to post
AdrianSmith
13 hours ago, Fraser Gale said:

If the elevons are in alignment i.e. not lateral displacement then you wouldn't do anything.

As Ray said, it is quite difficult to see small differences in elevon positions.

If there is little or no difference in elevons, but a significant difference between 6 & 8 (frequently in the order of two tonnes) then surely when 6 empties 1 & 2 will no longer be topped up and will drop well below 3 & 4, which if you are in AFT TRIM mode means 1 will get well too low by the time you reach ToD.

Without balancing the contents laterally I would never get to the same situation as Ray's last photo where 1,2,3,4 are almost identical

Link to post
Ray Proudfoot

Adrian,

Check the contents of 5,6,7 and 8 before your next flight. I'll do the same after using CPS-X to load the fuel. Logically 5 and 6 should match 7 and 8 otherwise there's an imbalance before we start.

Frazz doesn't use CPS-X so I wonder how he loads fuel. Manually through the FSL interface I imagine. But how does he know how much to put in each tank to ensure equal loads? His BA charts perhaps.

By switching off the feeds from 6 and 8 to 2 and 3 at the relevant time it ensures all four collector tanks have equal amounts when 6/8 are empty. Have you tried that procedure yet?

Link to post
Ray Proudfoot

I'm going to fly EGLL-TBPB this morning using wx from 1/10 as there's a average tail wind of 6kts, not headwind of 13kts using today's wx.

CPS-X has calculated 95.7T. So every tank looks to be full.

Link to post
Ray Proudfoot

This is the fuel load for EGLL-TBPB. There is an imbalance of 1470Kg in the loads of 5/6 compared to 7/8. All other tanks are either equal or centrally located. Any suggestions why?

TBPB_Fuel.png

Link to post
  • Ray Proudfoot changed the title to Is 59.3 the ideal CG before descent?

×
×
  • Create New...