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More KC-46A woes....

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More KC-46A woes....

Old 4th Feb 2019, 15:08
  #861 (permalink)  
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Apart from the few USAF tankers fitted with wing pods, all the other options you describe facilitate on single receiver AAR. Refuelling a 4-ship with such a limited system, particular the nightmarish BDA, takes way too long - blindingly obvious to me. Ever tried prodding the BDA? I did so once using a Q-fit (8 missiles and 3 tanks) F-4 against a KC-135 without the benefit of any previous dual training and it was very difficult - as the Italian Air Force Tornado force discovered on Night One of GW1. During which the USN far preferred prodding against the VC-10K with multiple hoses than queuing up behind a USAF tanker - no doubt the letters of thanks are still with the squadron.

Much easier to let fuel flown downhill in an anhedral wing than it would be to pump it up the pronounced dihedral of an A340, given the pressure drop at such a distance from the centre tank - which would probably dictate a need for larger pumps and wider-bore pipes that are required for the A330MRTT . Following the demise of the Valiant, the multi-hose Victor had quite a long gestation period before it was a total a success - and that was with the urgent service need plus the design work of a major aerospace manufacturer rather than some independent contractor touting for profit

The TriStar pod programme foundered on cost and complexity- and in the end was deemed unnecessary due to the preference for modification of the VC10 C Mk 1. Because 'hoses in the sky' are perceived to be of greater importance than the total fuel volume available.

Have you actually studied the wing planform of an A340-233/300 outboard of the outer engines? Quite a narrow chord and winglet, with little structure available upon which to hang a pod pylon between the slats and ailerons or to provide sufficient pod clearance from the slats and ailerons.
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Old 4th Feb 2019, 15:14
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Originally Posted by weemonkey View Post
Bollox, he has history. xxx.
Indeed. Who was the first to point out on the F-35 mega thread that the F-35 was not designed as an air superiority fighter, but as a tactical bomber with fighter-like agility? And got creamed by dozens of folks for saying so. Is there anyone today who doubts that the primary mission of the F-35 is tactical bombing? And who was it who dared contradict Beagle who claimed that with full fuel, the A330MRTT can carry no cargo? I got creamed by the armchair pundits for that one also. But Just this Once recently posted "source data" supporting my position. So yes, I have "history" of going against the flow in a cause celebre where a bunch of armchair pundits are on a roll, like the F-35 and the KC-46. And that just cannot stand. Hence the very personal attacks. For which, despite your best efforts to justify, there is no justification. And that best effort? Weak. Downright feeble. "I have a history." I'm just a "floor sweeper" and not an engineer. Really? That's even weaker than the feeble attempts made on this forum to discredit my service as a USN pilot. Which were proven utterly false.

Originally Posted by LowObservable View Post
Indeed he has, Including such things as a long thread derailment concerning the F-35's helmet-mounted display, and how come he knew that a far superior Block 4 (or whatever) was right around the corner.
Oh please. That helmet mounted display subthread/derailment was going strong before I even waded into the fray and it died not long after I entered it because the whole helmet mounted display rubbish was just that. Rubbish and a total distraction. And BTW, if you'd read what I actually wrote you'd know how I knew about the F-35's helmet mounted display system. So you wouldn't have to ask now "how come I knew..."

Let's face it guys, your problem is not with the substance. You're problem is with who is delivering it. And that's just pathetic.


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Old 4th Feb 2019, 15:53
  #863 (permalink)  
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Returning to the scheduled broadcast, the cost of fitting booms, operator stations and remote vision systems to airline-type aircraft (except for those which already have a modification available, such as the A330 and KC-767 / KC-46) is very considerable. People have occasionally asked Omega whether they looked at it, but the €millions needed was the reason why not! Had they deemed the cost/benefit positive, they would probably have invested. But they're run by a very shrewd CEO and he would have needed to see a very sound business plan before doing so.

KenV, I can't recall what you flew in the USN - or when? But if it meant you did some KC-135 BDA jousting, I'm sure you'll know what a PITA that was. As I mentioned earlier, the Italian Tornado force launched 8 jets on Night One; one turned back quite early as it had a problem, of the remaining 7 only 1 was able to prod the KC-135 in the dark turbulent conditions. That brave crew pressed on as a single ship, but were subsequently shot down and taken captive.

On the topic of MRTTs, if a true multi-role tanker still has an availability to carry any cargo with full tanks, the obvious question would be why didn't the designer fit bigger tanks? So that with normal crewing and no cargo, the ZFW would be such that full tanks would take it to MTOW. The trade-off between cargo mass offered and fuel required for the AAR mission has always been an interesting exercise, particularly on trails when the AT planners and AAR planners might not always have seen eye-to-eye...
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Old 4th Feb 2019, 16:21
  #864 (permalink)  
 
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Originally Posted by BEagle View Post
Apart from the few USAF tankers fitted with wing pods, all the other options you describe facilitate on single receiver AAR. Refuelling a 4-ship with such a limited system, particular the nightmarish BDA, takes way too long - blindingly obvious to me. Ever tried prodding the BDA? I did so once using a Q-fit (8 missiles and 3 tanks) F-4 against a KC-135 without the benefit of any previous dual training and it was very difficult - as the Italian Air Force Tornado force discovered on Night One of GW1. During which the USN far preferred prodding against the VC-10K with multiple hoses than queuing up behind a USAF tanker - no doubt the letters of thanks are still with the squadron..
One more time, this is a commercial fee for services contract. Those commercial service providers are not going to be operating in a war zone. That's where the KC-46 will operate.

Much easier to let fuel flown downhill in an anhedral wing than it would be to pump it up the pronounced dihedral of an A340, given the pressure drop at such a distance from the centre tank - which would probably dictate a need for larger pumps and wider-bore pipes that are required for the A330MRTT . Following the demise of the Valiant, the multi-hose Victor had quite a long gestation period before it was a total a success - and that was with the urgent service need plus the design work of a major aerospace manufacturer rather than some independent contractor touting for profit.
Much easier? Perhaps. But probably not. A330 and A340 have the same wing with the same static dihedral. But the A330 has significantly greater inflight dihedral than A340. Those outboard engines on A340 provide lots of wing bending moment relief. KC-10 has a significant dihedral. Lotsa "uphill" flow there. And besides, the plumbing and pumping is sized to provide good flow even when the tanker is flying in a bank where the "uphill" may be much more pronounced than the "uphill" provided by dihedral. Further, the plumbing is already designed and sized to provide high flow to facilitate fuel dumping. That high flow can be accomplished with a very simple jet pump with quite low head and output pressure. The pod then only has to bump up the pressure sufficient for what the hose system needs.

The TriStar pod programme foundered on cost and complexity- and in the end was deemed unnecessary due to the preference for modification of the VC10 C Mk 1. Because 'hoses in the sky' are perceived to be of greater importance than the total fuel volume available.
Once again, this is a commercial fee for services contract. Thus far those services have not emphasized the number of "hoses in the sky." And there is zero indication that a future commercial services contract will emphasize "hoses in the sky."

Have you actually studied the wing planform of an A340-233/300 outboard of the outer engines? Quite a narrow chord and winglet, with little structure available upon which to hang a pod pylon between the slats and ailerons or to provide sufficient pod clearance from the slats and ailerons.
No, I have not "studied" the A340 wing planform. As far as the amount of room that is available for a WARP, Victor's wingtip area was quite small and WARP was mounted on a pylon that placed the pod well below the wing and below the aileron. Same thing with the WARP on KC-135. There's not much structure nor much room and lots of "uphill" toward the tip of a KC-135 wing, but the Boeing folks managed it, as seen in the photo below. I'm confident the Airbus/BAE folks are no less competent than the Boeing folk. Apparently you disagree.

And besides, the point is moot. There's nothing in the fee for services contract that requires WARP in the first place.

http://s0.geograph.org.uk/geophotos/...3_992013ad.jpg
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Old 4th Feb 2019, 16:41
  #865 (permalink)  
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Nice photo! But I was thinking more about a generic aircraft design than the specific requirements of the services contract. Whoever bids for the contract will presumably have future options in mind?

Pressure drop and the need for higher volumetric flow rates to provide the required pod pressure for the TriStar pod programme led to the need for larger pipe bores than initially specified - getting the fuel all that way to the pod pylon wasn't very easy. Whereas the A330MRTT has the huge benefit of taking advantage of the redundant outboard engine locations of the A340 and the existing fuel feed pipework.

The Victor K2 pods were low to the ground and the wing area where they were located was fairly generous - they weren't mounted at the wing tips either. So low were they that a plan to base the Victor at Scampton was ruled out due to the undulating nature of Scampton's taxiways and the need for much more cleared space adjacent to the taxiways than was required by the Vulcan.
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Old 4th Feb 2019, 16:46
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Originally Posted by BEagle View Post
KenV, I can't recall what you flew in the USN - or when? But if it meant you did some KC-135 BDA jousting, I'm sure you'll know what a PITA that was.
Oh yeah! We called it the "Iron Maiden" for a reason: she was deadly! All the other baskets are some kind of fabric, while the 135's BDA basket is metal!! If you hit that basket just a tiny bit off center, instead of guiding the probe in, it would instead pop out and slap the aircraft. And even if you got the probe in just right, the hose did not reel in/retract but instead would form a curve. Curve too much and it'll form a loop that can wrap around the probe, around the aircraft nose, smack the canopy, or a number of other very bad things. Pulling out was also problematic, with the basket often pranging the probe. But that was on aircraft where the probe was fixed stuck out ahead of the fuselage. On aircraft with retractable probes where it sticks out of the side of the fuselage, it can prang the fuselage. Not a good day. I'm told the BDA on the French KC-135s is the same as the USAF ones, but my personal experience says otherwise. They seemed more forgiving.

I'm guessing that perhaps the Italian Tornado pilots you mentioned having all that trouble tanking from a BDA equipped KC-135, this was their first experience with the Iron Maiden? That has to be a heart stopper doing that the first time on an actual combat mission with live ordnance.

And about the airplane I flew? You mockingly called it a "mini-jet" or some such. A-4 Skyhawk and finally F/A-18.

On the topic of MRTTs, if a true multi-role tanker still has an availability to carry any cargo with full tanks, the obvious question would be why didn't the designer fit bigger tanks?
You and a few other folks have already answered that one. Because it "does not need" it. It has "plenty of fuel off load" without belly tanks. Just as it has "plenty of cargo capacity" with just a belly cargo hold.
Beyond that, you'll have to ask Airbus and the operators of the A330MRTT. Or maybe ask Just This Once. He claims to have "source data" for A330MRTT and might have some "source data" that addresses the reasoning behind this design.

Last edited by KenV; 4th Feb 2019 at 17:42.
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Old 4th Feb 2019, 16:57
  #867 (permalink)  
 
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Originally Posted by BEagle View Post
Nice photo! But I was thinking more about a generic aircraft design than the specific requirements of the services contract. Whoever bids for the contract will presumably have future options in mind?
I was specifically addressing the fee for services contract that Lockheed and Airbus are teaming to provide. My point being that Lockheed/Airbus would have a heck of a time competing on price against today's commercial fee for services operators who all operate used aircraft converted into tankers. Not to mention the various folks who will potentially bid using Ukranian airframes already built as tankers from the factory.

Further, the KC-707 Omega uses has a centerline (i.e. internally fuselage mounted) hose and drogue system. That is a rather unique development not used by any military aircraft I'm aware of. They managed to afford that just fine. How difficult/expensive would it be to adapt that system to the A340? Or for that matter to adapt the existing centerline hose and drogue system on the A330 to the A340? The aft fuselage structure of the A330 and A340 are very similar, if not essentially identical. Depending on the nature of the services to be provided, an A340-500 (the one with the higher TOGW and the higher fuel capacity.) with a boom and centerline hose and drogue system and no WARP would be easy and cheap to develop and provide some eye-watering fuel offload numbers.

Last edited by KenV; 4th Feb 2019 at 17:31.
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Old 4th Feb 2019, 17:13
  #868 (permalink)  
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Well, the A310MRTT could have had 5 x ACT, but when the numbers were crunched it was realised that an increase in allowable MTOW would have been needed if max fuel was carried - and the Net Flight Path limits at the tanker's MOB were significant even though the RW length was not. So 4 x ACT was the final choice. In the case of the A330 though, it already had a 111 tonne max fuel capability, so it was retained for the MRTT, although with the added structural mass it is rare that 111 tonne can actually be carried, I gather it's normally around 109.

KC-46 needed some centre tank extensions over the base -200ER, but the number crunchers came up with a compromise which met the spec. and still allowed some cargo capacity with full tanks - as was the case with the VC10C1K. Fair enough, but it could have carried more fuel had that been necessary.

With you on the Iron Maiden! Wretchedly horrible device - and if you missed the boomer would then move the thing, losing you the previous visual reference. After my first couple of jousts, I had to ask the young lady driving the boom to keep the darned thing still. Fortunately when in contact the onload rate was vastly superior to that from a Victor. Having completed my Teach Yourself BDA Prodding lesson, the Russians we were after decided to turn for home before we got much further North.
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Old 4th Feb 2019, 17:54
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Originally Posted by BEagle View Post
With you on the Iron Maiden! Wretchedly horrible device - and if you missed the boomer would then move the thing, losing you the previous visual reference. After my first couple of jousts, I had to ask the young lady driving the boom to keep the darned thing still. Fortunately when in contact the onload rate was vastly superior to that from a Victor. Having completed my Teach Yourself BDA Prodding lesson, the Russians we were after decided to turn for home before we got much further North.
Ooooh yeah, the boom operator moving the boom and totally fouling up your approach! I was fortunate in that it only happened a few times, but what a mind bender that was for me. All of a sudden my visual cues changed in mid approach. The addition of WARP on KC-135 has got to be huge for USN and other probe equipped aircraft refueling from the KC-135. But like KC-10 not all were so equipped which is more the pity. But at least the KC-10 has a decent centerline basket.

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Old 4th Feb 2019, 18:24
  #870 (permalink)  
 
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Originally Posted by BEagle View Post
Well, the A310MRTT could have had 5 x ACT, but when the numbers were crunched it was realised that an increase in allowable MTOW would have been needed if max fuel was carried - and the Net Flight Path limits at the tanker's MOB were significant even though the RW length was not. So 4 x ACT was the final choice. In the case of the A330 though, it already had a 111 tonne max fuel capability, so it was retained for the MRTT, although with the added structural mass it is rare that 111 tonne can actually be carried, I gather it's normally around 109.
According to wiki, OEW of A330-200 is 265,900lb. 256,900 + 244,200 (111 tonne) = 501,100lb. MTOGW is listed as 533,519. That leaves 12,419 lb for payload/cargo with fuel fuel. OK, the A330MRTT OEW is higher because besides the full passenger suite, it's carrying the tanker stuff. But nearly 6 tons for the tanker stuff? And Voyager doesn't have a boom and boom camera system. So what got added to Voyager to bring its OEW up nearly 6 tonnes, or got changed that brought its MTOGW down nearly 6 tonnes? Or is this a runway limitation? Is the runway so short that it needs to be below MTOGW to meet critical field length requirements?
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Old 4th Feb 2019, 19:52
  #871 (permalink)  
 
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Beags

I take it you were comparing the BDA on load with the Victor wing pod. If memory serves, by choice we used to refuel Phantoms on the HDU with a rate of 4500 lbs a min
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Old 4th Feb 2019, 22:13
  #872 (permalink)  
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KenV , the 'wiki' figure you quote for Maximum Take-Off Weight does not agree with the Airbus brochure figure for the A330MRTT, which is 233T (514 000 lb).

The same figure is quoted by Wikipedia, which further states that the OEW is 125T. Thus 125+111 exceeds MTOW by 3T, so my estimate of a day-to-day maximum fuel figure of 109T was fairly close, assuming rounding errors. Which means that with max fuel it cannot carry any cargo.

I have no idea why the 'normal' 242T MTOW for an A330-200 wasn't used for the MRTT.

Yes, vascodegama the comparison I was making between the KC-135 BDA and the Victor was indeed with the Mk20 wing pods. By choice I would prefer to prod the centreline, but we usually worked in pairs so were stuck with the pods.
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Old 5th Feb 2019, 06:14
  #873 (permalink)  
 
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The preference was to refuel one at a time on the HUD even allowing for swap over it was far quicker since the HDU had an off load rate 4 times that of the pod. The only time I remember using pods was on a trail when the AARC had planned for that option.
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Old 5th Feb 2019, 09:13
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The problems at Scampton were not caused by the wing mounted AAR pods but by the ground clearance below the Underwing Fuel Tanks on the K2. The pods were head high, whereas the clearance below the tanks was only about 18 inches. So low that they were likely to hit any snow depth warning indicators next to taxiways. At Paine Field (Washinton State,USA) my Nav Rad and Crew Chief had to navigate us about 2 miles, on foot, over these as we taxied in to the parking area for an airshow. One other snag at Scampton was the "lumpy" nature of the runway construction which would have had severe consequences for the Victor fatigue life. This together with the need to remove concrete kerbs and refuelling pipes at all the dispersals was too expensive to rectify for the, then, proposed life of the Victor K2.

The choice of using the wing pods or centre line HDU was also a function of the flow rate of the various receiver types. The Mk 20 pod on the Victor, which had an integral 1000lbs fuel tank, had a flow rate of 1500lbs/min whereas the HDU was 4000lbs /min. With aircraft such as the Lightning and Jaguar, which took fuel at 1100 lbs/min, it was quicker to refuel a pair on the pods rather than sequentially on the HDU. The F4 took fuel at 4000lbs/min, so would empty the pod fuel tank fairly quickly, which would not pass any more fuel until it had filled to half fuel again. Hence it was quicker to refuel a pair of F4s one at a time, with continuous fuel flow, on the HDU.

The VC10 had the Mk 32 pod, which did not have an internal tank, and gave a fuel flow of 2800lbs/min, however the VC10 fuel system only allowed 2200lbs/min if both pods were in use together. The HDU was the same on both types. So, again it could be quicker to use the HDU for a pair of F4s than to use the wing pods.

All of the above figures are from memory of 30+ years ago, so anybody with the reference books can challenge me without me getting upset or descending to personal abuse.
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Old 5th Feb 2019, 10:19
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Originally Posted by BEagle View Post
I have no idea why the 'normal' 242T MTOW for an A330-200 wasn't used for the MRTT.
Depends on MRTT version (ARBS).
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Old 5th Feb 2019, 11:54
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Originally Posted by BEagle View Post
KenV , the 'wiki' figure you quote for Maximum Take-Off Weight does not agree with the Airbus brochure figure for the A330MRTT, which is 233T (514 000 lb).

The same figure is quoted by Wikipedia, which further states that the OEW is 125T. Thus 125+111 exceeds MTOW by 3T, so my estimate of a day-to-day maximum fuel figure of 109T was fairly close, assuming rounding errors. Which means that with max fuel it cannot carry any cargo.

I have no idea why the 'normal' 242T MTOW for an A330-200 wasn't used for the MRTT.
Now its starting to make sense. Yet not. It makes sense that with a reduced MTOGW the MRTT can reach MTOGW with just a full load of fuel. It makes no sense at all that Airbus reduced the MTOGW of the basic airframe by 9 tonnes to produce the MRTT. In effect, every MRTT has a max weight restriction relative to the baseline -200? How does that make sense? Because fuel is a dense payload, tankers are usually based on the highest gross weight version of an airframe. But for the MRTT Airbus went the other way and reduced the MTOGW? But OK. I concede the point. Which raises the following question for Just This Once: why does your "source data" not agree? You know, the "source data" used to justify grievous personal attacks.

FWIW, I was hesitant to use the Airbus MRTT brochure because it seems to be a marketing tool, not a technical document. For example, this leading phrase in Airbus' brochure states: "The A330 MRTT can carry up to 111 tonnes of fuel; this is the highest capacity of all tanker aircraft, even those which have additional fuel tanks in the cargo deck." This is total nonsense. Both the KC-10 and KC-747 (granted only two of the latter were built) carry much more fuel (161 / 165 tonnes respectively). Dutch Air Force and Commercial KDC-10 also carry more fuel (159 tonnes). And depending on the source, Il-78 also carries more fuel (138 tonnes).

Last edited by KenV; 5th Feb 2019 at 13:16. Reason: Added IL-78 fuel capacity
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Old 5th Feb 2019, 12:12
  #877 (permalink)  
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Just this Once... , how does increased OEW with the ARBS make any difference to MTOW? Surely it will simply reduce max fuel weight?

233T MTOW is straight out of 'Global Enabler', the glossy brochure handed out to attendees of the 2013 AMUG in Getafe - a critical audience if ever there was one.

For many years, Airbus used a figure of 0.78 for the fuel SG in its brochures. My suspicion was that this meant that sales brochures could state higher ZFW with max fuel, promising higher payloads. Whereas most military operators assume an SG of 0.80.

The A330MRTT has a max fuel capacity of 139000 litre, so the civil brochure probably stated that max fuel is 139x.78=108.4T, whereas the MRTT brochure uses 139x.8=111.2T. Then it was discovered that with typical ZFW, with 111.2T the aircraft would exceed 233T MTOW - but this doesn't appear to have given the operators any problems.

I found similar issues with early quotes for the A310MRTT where 0.78 had been used and queried why, since 0.80 is the normally accepted value. Trying to turn volumetric figures into typical weight values proved quite a problem...unless accurate SG was taken into account!

Last edited by BEagle; 5th Feb 2019 at 12:29.
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Old 5th Feb 2019, 13:05
  #878 (permalink)  
 
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ARBS reduces the maximum pitch angle available.
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Old 5th Feb 2019, 13:09
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I'm still waiting for Ken to explain why the required fuel pressure for a mid-span fuel hose increases when an aeroplane banks.

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Old 5th Feb 2019, 13:11
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Beagle is correct SG is important - a change 0 0.05 in the SG figure makes a difference of 0.05 of a tonne
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