Go Back  PPRuNe Forums > Aircrew Forums > Military Aviation
Reload this Page >

More KC-46A woes....

Military Aviation A forum for the professionals who fly military hardware. Also for the backroom boys and girls who support the flying and maintain the equipment, and without whom nothing would ever leave the ground. All armies, navies and air forces of the world equally welcome here.

More KC-46A woes....

Old 10th Nov 2014, 07:54
  #121 (permalink)  
 
Join Date: Jul 2006
Location: by the Great Salt Lake, USA
Posts: 1,540
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).


Last edited by GreenKnight121; 10th Nov 2014 at 08:09.
GreenKnight121 is offline  
Old 10th Nov 2014, 08:06
  #122 (permalink)  
 
Join Date: Feb 2002
Location: NSW
Posts: 212
The KC-46 will work out just fine. The KC-135 series certainly have...
TBM-Legend is offline  
Old 10th Nov 2014, 08:41
  #123 (permalink)  
 
Join Date: Apr 2004
Location: Planet Earth
Posts: 1,815
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.
stilton is offline  
Old 10th Nov 2014, 10:00
  #124 (permalink)  
 
Join Date: Feb 2002
Location: NSW
Posts: 212
The DC-10 is a short coupled aircraft vs. MD-11 therefore smaller surfaces needed..
TBM-Legend is offline  
Old 10th Nov 2014, 13:10
  #125 (permalink)  
 
Join Date: Aug 2014
Location: New Braunfels, TX
Age: 65
Posts: 1,954
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.

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.
Really? That's an intersting assertion. Pray tell, why is there a cargo door and floor on a KC-135? And a KC-10?

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....
Interesting that you brought that up. And BTW, you're dead WRONG. It was NOT "insignificant" in the Scooter. USAF used JP-4, US Navy used JP-5. These fuels not only have different mass densities, but also different energy densities. I had to recompute CG, range, my fuel ladder, weapons load, and other factors during mission planning depending on whether my Scooter was loaded with JP-4 or JP-5. So yes, I'm very familiar with the concept of fuel density and its affect on aircraft performance and limitations.

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.
KenV is offline  
Old 10th Nov 2014, 13:17
  #126 (permalink)  
 
Join Date: May 2011
Location: London
Posts: 295
Really? That's an interesting assertion. Pray tell, why is there a cargo door and floor on a KC-135? And a KC-10?
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.

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.
Mil-26Man is offline  
Old 10th Nov 2014, 13:25
  #127 (permalink)  
 
Join Date: Aug 2014
Location: New Braunfels, TX
Age: 65
Posts: 1,954
then why not buy more freighters? tha damn thing is supposed to be a TANKER, not a glorified DC-8F
Really? On what is this assertion based? Look at the USAF designations. They are KC-45 and KC-46. The C stands for cargo. Yup, these are multi-mission aircaft which include not only tanker and freight missions, but also passenger and medevac missions, along with a few more.

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.
KenV is offline  
Old 10th Nov 2014, 13:33
  #128 (permalink)  
 
Join Date: Aug 2014
Location: New Braunfels, TX
Age: 65
Posts: 1,954
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
That depends on the nature of the contract. The tanker contract is firm-fixed price. 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.
KenV is offline  
Old 10th Nov 2014, 13:36
  #129 (permalink)  
 
Join Date: May 2011
Location: London
Posts: 295
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.
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.
Mil-26Man is offline  
Old 10th Nov 2014, 13:41
  #130 (permalink)  
 
Join Date: Aug 2014
Location: New Braunfels, TX
Age: 65
Posts: 1,954
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.
KenV is offline  
Old 10th Nov 2014, 13:44
  #131 (permalink)  
 
Join Date: Dec 2000
Location: UK
Posts: 375
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.
vascodegama is offline  
Old 10th Nov 2014, 13:51
  #132 (permalink)  
 
Join Date: Aug 2014
Location: New Braunfels, TX
Age: 65
Posts: 1,954
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.
That's a bold assertion, and one that does not comport with reality.
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?
KenV is offline  
Old 10th Nov 2014, 14:02
  #133 (permalink)  
 
Join Date: Aug 2014
Location: New Braunfels, TX
Age: 65
Posts: 1,954
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.
Boeing may or may not make money later on. It depends on the contract. KC-46 is a high stakes gamble. Northrop Gumman pulled out early rather than accept the risk. Airbus accepted a lesser risk by bidding a higher price.

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.
KenV is offline  
Old 10th Nov 2014, 14:03
  #134 (permalink)  
 
Join Date: May 2011
Location: London
Posts: 295
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?
Mil-26Man is offline  
Old 10th Nov 2014, 14:36
  #135 (permalink)  
Thread Starter
 
Join Date: May 1999
Location: Quite near 'An aerodrome somewhere in England'
Posts: 25,432
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
  • 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.
BEagle is offline  
Old 10th Nov 2014, 14:45
  #136 (permalink)  
 
Join Date: Aug 2014
Location: New Braunfels, TX
Age: 65
Posts: 1,954
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 used A330-200 data publicly available from Jane's.
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.
KenV is offline  
Old 10th Nov 2014, 16:17
  #137 (permalink)  
 
Join Date: Aug 2014
Location: New Braunfels, TX
Age: 65
Posts: 1,954
All of which kind of leaves me scratching my head then, wondering why the USAF actually chose the KC-45.
Technically, they chose KC-30, which was the Northrop Grumman designation for their A330-based tanker offer. The very first round in 2006 (which included a 777 based offer from Boeing) was structured very differently than the 2007 competion. Northrop Grumman/EADS threatened to pull out in 2006, so the competition was rejiggered to enable the A330 to compete.

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.
KenV is offline  
Old 10th Nov 2014, 16:48
  #138 (permalink)  
 
Join Date: Aug 2014
Location: New Braunfels, TX
Age: 65
Posts: 1,954
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
Really? That would be a pretty good trick. A LOADED 463L pallet can be over 7 ft tall and can weigh up to 10,000 lbs. The USAF requirement was for a LOADED 463L pallet compatible with C-17 and C-130 for transhipment. Restacking the pallet in the theater for transhipment was not allowed. The A330's lower hold dimensions are not even compatible with a CH-46 configured 463L pallet.

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.
Its not the stretchers that need to be compatible. A small helicopter can carry stretcher patients. The aircraft needs to be compatible with USAF's existing stretcher stanchions that stack stetcher patients 3 high. With the overhead luggage bins in the aircraft and no freighter floor, that is impossible.

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.
Once again, without a cargo floor to go with the cargo door, the pallet weight is severely restricted. And without a revised nose gear to go with a cargo door and cargo floor, pallet loadability is highly restricted.

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.
KenV is offline  
Old 10th Nov 2014, 17:12
  #139 (permalink)  
 
Join Date: May 2011
Location: London
Posts: 295
Why did Airbus not offer a cargo door in the USAF competition?
They did.

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.
Mil-26Man is offline  
Old 10th Nov 2014, 18:58
  #140 (permalink)  
Thread Starter
 
Join Date: May 1999
Location: Quite near 'An aerodrome somewhere in England'
Posts: 25,432
Mil-26Man, you'll only confuse him if you supply factual information.....
BEagle is offline  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.