More KC-46A woes....
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I would rather that the USAF had bought 100 KC-10Bs (my personal designation for Mil-Spec tanker/cargo versions of the MD-11, fitted out as per the KC-10 but updated [the 60 KC-10As were built in the mid-1980s]).
These would be ordered in ~1995, and would be based on the MD-11F freighter, which was the last version in production (last deliveries 2001). They would, in addition to the under-tail hose/drogue unit, have hose pods under the outer wings.
Comparison of MD-11F and DC-10-30F - to the right DC-10-30F, to the left MD-11F (note the cargo door under the "AR" in the airline name).
These would be ordered in ~1995, and would be based on the MD-11F freighter, which was the last version in production (last deliveries 2001). They would, in addition to the under-tail hose/drogue unit, have hose pods under the outer wings.
Comparison of MD-11F and DC-10-30F - to the right DC-10-30F, to the left MD-11F (note the cargo door under the "AR" in the airline name).
Last edited by GreenKnight121; 10th Nov 2014 at 08:09.
Agree, looks like a great aircraft.
The photo of the DC10 next to the MD11 illustrates very well the main reason for the latter's stability issues over the years, look at how much smaller the horizontal stabilizer is on the MD11 compared to the older DC10.
Most of the accidents with the MD11, and there have been plenty were with aircraft operated by cargo carriers operating routinely at higher weights, just like a tanker would be doing very commonly.
In other words using the MD11 as a tanker is not a good idea and fortunately wasn't tried.
The photo of the DC10 next to the MD11 illustrates very well the main reason for the latter's stability issues over the years, look at how much smaller the horizontal stabilizer is on the MD11 compared to the older DC10.
Most of the accidents with the MD11, and there have been plenty were with aircraft operated by cargo carriers operating routinely at higher weights, just like a tanker would be doing very commonly.
In other words using the MD11 as a tanker is not a good idea and fortunately wasn't tried.
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Do you actually understand the concepts of specific gravity and the effect of temperature on SG? Such factors may be insignificant in some little mini-jet such as an A-4, but they are highly significant in large aircraft such as the A330.
Total tank volume in the A330-MRTT is 139000 litre. Assuming you can do sums, you might like to calculate the total mass at different specific gravity values, then adjust that for temperature deviation.
Total tank volume in the A330-MRTT is 139000 litre. Assuming you can do sums, you might like to calculate the total mass at different specific gravity values, then adjust that for temperature deviation.
Oh my goodness. Those undies really are in a wad now.
All figures that follow are for A330-200 and taken from Jane's (which coincidentally are the same as wiki's)
Here's the density of the most widely used commercial and military jet fuels:
Jet A: 6.7 lb/gal
Jet B: 6.8 lb/gal
JP-4/F-40: 6.7 lb/gal
JP-5/F-44: 6.8 lb/gal
JP-8/F-34: 6.8 lb/gal
OEW= 263,700 lb
MTOGW = 534,000 lb
Volumetric fuel capacity = 36,740 gal (US)
Let's do some math:
36,740 x 6.7 = 246,158 lb = max fuel capacity
36,740 x 6.8 = 249,832 lb = max fuel capacity
534,000 - 263,700 = 270,300 lb = total fuel plus cargo capacity
No matter which fuel one loads into an A330, the airplane will volume out before it masses out.
For the airplane to mass out with just fuel the fuel density would have to be:
270,300lb / 36,740gal = 7.36 lb/gal. Even if the above fuels were cooled to just above their freezing points, they would not approach a density of 7.36 lb/gal. So given these facts, please name the fuel (and/or temperature of fuel) the RAF loads aboard their Voyagers that has a density of 7.36 lb/gal.
Yeah, I thought so.
Again, the USAF needed cargo floor and door in the Frankentanker because the B767's normal, somewhat limited underfloor cargo space is further compromised by the center tank plugs needed to meet the AAR requirements of the KC-X competition.
But rather than muddy the water with other aircraft, let's look at just THREE of the hundreds of requirements of the recent USAF tanker RFP.
Load a full military 463L pallet.
Load a standard medevac litter stanchion.
Mission reconfigure time under 1 hr.
MRTT could accomplish NONE of the above.
KC-46 could accomplish ALL of the above.
Perhaps you're saying those three requirements were not really "needed" and were just USAF goldplating to ensure the KC-46 won. You're welcome to believe that, even if that belief does not quite comport with reality.
Edit:
Such factors may be insignificant in some little mini-jet such as an A-4....
One more BTW. I also operated the P-3C for several years. When I was on a 12 hour or longer mission over blue water and was loitering one or more engines during the mission and operating at both high and very low altitudes and operating at max range cruise AND max undurance cruise during different parts of the same mission, and expending stores during the mission, I made damned sure I was certain about my fuel computations. So your assumption about my awareness of fuel density on aircraft performance is a fail.
Last edited by KenV; 10th Nov 2014 at 14:25.
Really? That's an interesting assertion. Pray tell, why is there a cargo door and floor on a KC-135? And a KC-10?
A main floor cargo deck and door aren't desirable features in themselves, it's just that the other platforms you name require them due to a lack of available cargo space elsewhere.
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then why not buy more freighters? tha damn thing is supposed to be a TANKER, not a glorified DC-8F
And about that airbus MRTT designation? The MR stands for Multi-Role and the TT stands for Tanker Transport. Once again, a multi-mission aircraft.
Given the missions USAF wants to execute with their aircraft, the KC-46 met those mission needs better.
Given the missions RAF wants to execute with thier aircraft, the A330 met those mission needs better.
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The US will discover, as the British have, that once you have a single supplier then your negotiating position is zero - you HAVE to buy from them
And so you finish up with even bigger cost overruns and kit that just doesn't work
And so you finish up with even bigger cost overruns and kit that just doesn't work
Any cost over runs are borne by the manufacturer, NOT the government. Any equipment that does not meet spec must be redesigned/modified to meet spec at the cost of the manufacturer, not the government. Boeing is going to lose a LOT of money on this contract.
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The MD-11 being stretched relative to the DC-10, it not only had a longer moment arm for the horizontal stabilizer, the MD-11 had a fuel tank in the horizontal stabilizer which the DC-10 did not have. The tail tank enabled fine tuning the CG inflight. This had two effects: it enabled reducing trim drag caused by the tail to increase range. It also meant there was a narrower CG range to deal with, so the stabilizer could be made smaller.
Last edited by KenV; 10th Nov 2014 at 14:30.
Ken
I have said it before but for clarity your max wt and empty weights don't tie up. The resultant max fuel using the figures I gave earlier means a max fuel of 239k =109 t.
I have said it before but for clarity your max wt and empty weights don't tie up. The resultant max fuel using the figures I gave earlier means a max fuel of 239k =109 t.
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For the same reason that the KC-46A needs them and the MRTT doesn't, no? All of the former are unable to fully utilise their underfloor cargo spaces because of the need to fit auxiliary fuel tanks. Without the need for auxiliary tanks, the MRTT is able to utilise all of its underfloor cargo space, and so doesn't need a main deck cargo floor or cargo door.
Can the MRTT carry full 463L military pallets in either the belly or main deck? Nope.
Can the MRTT carry medevac litter stanchions in either the belly or the main deck? Nope.
Can the MRTT be reconfigured from the tanker mission, to the cargo mission, to the passenger mission, to the medevac mission in under one hour? Nope.
Can the MRTT use USAF's existing roll-on/roll-off mission kits? Nope.
The answer is "Yes" for all the above for the KC-46.
If the abilities above are important to the customer, and one aicraft can do them and the other cannot, which should the customer choose?
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Boeing may lose money on the $4 billion EMD contract (the only contract so far awarded), but it will make this back in spades on the full-rate production contract. If it were any other way, they would simply pull out.
The A380 was a very high stakes gamble for Airbus. They may or may not make money on that gamble.
The 747-8 was a high stakes gamble for Boeing. They may or may not make money on that gamble.
The airplane business is not for the feint of heart. The vast majority of airplane companies no longer even exist.
All of which kind of leaves me scratching my head then, wondering why the USAF actually chose the KC-45.
You said yourself, politics had a big part to play in them opting to go with the KC-46A at the second (or third) time of asking, so you have to ask yourself how many of those capabilities you list are actually required by the USAF, as opposed to being drawn into the requirements in order to get the 'correct' outcome when the competition was rerun?
You said yourself, politics had a big part to play in them opting to go with the KC-46A at the second (or third) time of asking, so you have to ask yourself how many of those capabilities you list are actually required by the USAF, as opposed to being drawn into the requirements in order to get the 'correct' outcome when the competition was rerun?
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The A330MRTT can carry:
None of which requires any loss of AAR capability.
On the subject of cargo containers, the A330MRTT can carry a total of 27 x LD3 universal cargo containers in the lower holds. Whereas the KC-46A is compromised by ol' Bubba's initial failure to ensure that LD3s could be carried in pairs in the 767 - its fuselage is too narrow. Unlike the A310 or A330, which both have the same 222" fuselage cross-section and are able to carry LD3s in pairs.
- 4 x 463-L military pallets in the forward lower cargo hold, plus another 4 x 463-L pallets in the aft lower cargo hold
- 28 NATO stretchers, 6 x critical care modules, 20 medical staff seats and 100 passengers on the main fuselage deck.
- If customers find that they want more upper deck cargo space, an option is to have a cargo door and a potential 26 x 463-L pallets on the optional upper deck.
None of which requires any loss of AAR capability.
On the subject of cargo containers, the A330MRTT can carry a total of 27 x LD3 universal cargo containers in the lower holds. Whereas the KC-46A is compromised by ol' Bubba's initial failure to ensure that LD3s could be carried in pairs in the 767 - its fuselage is too narrow. Unlike the A310 or A330, which both have the same 222" fuselage cross-section and are able to carry LD3s in pairs.
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Ken, I have said it before but for clarity your max wt and empty weights don't tie up. The resultant max fuel using the figures I gave earlier means a max fuel of 239k =109 t
If the Voyager's weight data is different, you're welcome to provide the Voyager's OEW, and MTOGW data. As I said previously, OEW makes a big difference. But if OEW is the only difference, Voyager's OEW would have to be over 20klb higher than A330-200 OEW. Which is certainly possible, but seems unlikely.
Last edited by KenV; 10th Nov 2014 at 16:19.
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All of which kind of leaves me scratching my head then, wondering why the USAF actually chose the KC-45.
The politics were complicated. The 2007 competition was driven by USAF's tanker boys which were hold overs from the old Strategic Air Command (SAC). Previously, ALL tankers belonged to SAC. When SAC ceased to exist, some tankers went to Air Combat Command (ACC) and some to Air Mobility Command (AMC). The former SAC guys, now ACC bomber guys, strongly favored a DC-10 sized aircraft, and Northrup Grumman/EADS won that competition for 800 aircraft (800!!) with the KC-30, which was based on the A330-200.
But Boeing formally protested and the Government Accountability Office (an independent arbiter not affiliated with USAF) threw out that competition after USAF admitted to several flaws in their bidding process. An "expedited recompetition" was convened by DoD rather than USAF. This second competition was for a more "realistic" 400 (400!) aircraft with more detailed performance requirements and mission criteria. But this competition collapsed early and did not get out of the starting gate. That was in 2008.
In 2009 USAF started over. The do-over was for a "possible" 179 aircraft. The process stretched into 2010. By now the old SAC guys were gone. ACC's tankers only supported their bombers, so they had a rather narrow vision of the tanker mission. But by this time the tankers were taken from ACC and all of them belonged to Air Mobility Command (AMC). AMC had a completely different vision for their tanker than ACC because AMC was responsible for deploying and supporting the Army, deploying and supporting USAF fighter and bomber units, and for supporting USN and USMC. And by "support" that means both operational support (in-theater air tanking) AND logistics support (providing "bombs, bullets, and butter" for in-theater units). AMC also had the medevac mission. So the AMC guys included a plethora of additional missions not included by the former SAC guys now ACC bomber guys during the first competition. And besides the requirements being very different, this new RFP was for a Firm Fixed Price rather than a cost-plus with incentive fees.
The A330 could still meet the additional requirements, but ONLY if Airbus offered an A330-200F based MRTT. Airbus simply refused. We (NG) never could figure out why, because unlike the first competition, Airbus now had a fully developed freighter version of the A330 and did not need to develop it for the tanker competition. So this is yet another factor in the "politics". Why did Airbus refuse to offer a freighter based MRTT? I don't know. But without a freighter based tanker to offer NG pulled out, and Airbus decided to go it alone with the passenger based version. And predictably, Airbus lost.
I hope this clarified.
Last edited by KenV; 10th Nov 2014 at 20:00.
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The A330MRTT can carry:
4 x 463-L military pallets in the forward lower cargo hold, plus another 4 x 463-L pallets in the aft lower cargo hold
4 x 463-L military pallets in the forward lower cargo hold, plus another 4 x 463-L pallets in the aft lower cargo hold
And it's one thing to load a light (or empty) 463L pallet into the lower cargo hold of an A330 with a passenger nose gear. I's quite another to load a loaded pallet with that passenger nose gear. The freighter version of the A330 has a revised nose gear which gives the aircraft a level attitude on the ground. Not offering that nose gear for MRTT severely restricted pallet loadability.
28 NATO stretchers, 6 x critical care modules, 20 medical staff seats and 100 passengers on the main fuselage deck.
BTW, have you ever tried to get a stretcher patient up the airstairs of an airliner and then make a 90 degree turn inside the airplane to move aft? It's pretty close to impossible. It's one thing to advertise the ability to carry 28 stretchers. Its entirely another thing to be able to actually load 28 stretchers with patients on them.
If customers find that they want more upper deck cargo space, an option is to have a cargo door and a potential 26 x 463-L pallets on the optional upper deck.
But here's the real rub: Why did Airbus not offer a cargo door in the USAF competition? And still does not offer a cargo floor or a revised nose gear on the MRTT? I don't know. Do you? And can you see how not offering those features on the MRTT could hamper an Airbus offer relative to a Boeing offer? Especially if the purchaser "NEEDS" those features?
Last edited by KenV; 10th Nov 2014 at 20:07.
Why did Airbus not offer a cargo door in the USAF competition?
KC-45 Aerial Refuelling Tanker Aircraft - Airforce Technology
Cargo
The main deck can carry 280 passengers or 26 463l pallets. Loading and unloading is through a 141in x 100in cargo door. The lower deck can carry an additional six pallets. The KC-45 cargo loading system is supplied by AAR Cargo Systems which is based in Livonia, Michigan.
