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More KC-46A woes....

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More KC-46A woes....

Old 24th Jan 2019, 15:36
  #761 (permalink)  
 
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Originally Posted by esscee View Post
Maybe NG and Airbus "took a view" that it was not going to be viable and "let" good ole Boeing to suffer all the grief and hassle that has proven to be the case. As for using very very old engines, makes me wonder if GE decided that they did not wish to support their old design CF6 for many more years to come which left only PW.
Seems highly unlikely. Providing support is a very lucrative part of any engine sale. Indeed, supporting the engine generates much more revenue than selling the engine. Further GE is already committed to providing long term USAF support for CF6s which are on the VC-25, E-4B, KC-10, and C-5M fleets.

Let's face it, they would have only chosen an American built engine after all the PR "moaning" etc that went on when Boeing did not win in the earlier "contests".
Sorry, but this is false. The RR engine in this thrust range is not a bad engine, but it is a poor match for the airframe. That's why the RR powered KC-767I performed so poorly and why out of 1240 767 ordered, only 40 had RR engines. Almost all of those 767 sales were not USAF sales, so no pressure to "buy American."
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Old 24th Jan 2019, 16:13
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Originally Posted by Just This Once... View Post
The fuselage is so large that the main cargo door can swallow a heck of lot as standard - the MRTT modifications do not change the basic freight capacity of the aircraft (which is rather capacious to say the least). The only in-service pain with no large upper door fitted is for aeromed.


A330 Cargo Deck
That's not a really complete picture. Yes, the belly of a A330MRTT is large, But so is the belly of a KC-10 and it has a cargo door and floor. What USAF wants and needs (among other things) is the capability to haul "outsize cargo." That's cargo too tall to fit in the belly cargo hold of any airliner. Further they want the capability to routinely do aeromedical evac. That can't be done without a cargo door. Although a cargo floor is not required, the floor does require special fittings. The next time you fly in an airliner, imagine taking a non ambulatory patient on a stretcher with an IV in their arm thru the passenger door and then making a 90 degree turn to get the patient and stretcher down the aisle into the aircraft. Now stack the stretchers two or three high and add overhead fixtures for IV bottles and the like with the overhead bins in place. Consider that USAF's dedicated aeromedical evac aircraft (C-9 Nightingale, based on DC-9) had a main deck cargo door. USAF's fleet of Nightingales has been retired and the KC-46 had to have its capabilities. That includes besides the cargo door and provisions for stretcher stanchions in the floor and IV bottles in the overhead, the addition of over a dozen 115V, 60Hz, single phase electrical outlets to power standard medical equipment, special ventilation equipment for patients needing isolation or other special care, a separate station in the cargo hold to control the temperature and ventilation systems, several therapeutic oxygen outlets, on board refrigeration for storing whole blood and medications, and more. So the oft repeated mantra that a main deck cargo door "is not needed" is utter folly when you consider USAF's needs and how they operate/employ their tankers.

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Old 24th Jan 2019, 17:42
  #763 (permalink)  
 
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ou look at a KC-135 the entire lower fuselage is full of aircraft systems and fuel tanks and, with the exception of the boom op area, the lower fuselage is outside of the pressure hull.
Are you sure about that-?? The ' upper floor' stresses would be significant whereas in a tube, hoop stresses are much easier to handle and uniform ...
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Old 24th Jan 2019, 19:09
  #764 (permalink)  
 
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Originally Posted by KenV View Post
That's not a really complete picture. Yes, the belly of a A330MRTT is large...So the oft repeated mantra that a main deck cargo door "is not needed" is utter folly when you consider USAF's needs and how they operate/employ their tankers.
Who said USAF needs, other than you? For the USAF program the A330 was offered with an upper cargo deck.




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Old 24th Jan 2019, 19:41
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Originally Posted by CONSO View Post
Are you sure about that-?? The ' upper floor' stresses would be significant whereas in a tube, hoop stresses are much easier to handle and uniform ...
Yes!

I could add that the KC-135 also has a fuel tank in the upper fuselage too, mounted aft below the fin leading edge.

Worth noting that around the same time the UK had a go at fitting nice square windows for jet passengers.

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Old 24th Jan 2019, 20:00
  #766 (permalink)  
 
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Originally Posted by Just This Once... View Post
Yes!

I could add that the KC-135 also has a fuel tank in the upper fuselage too, mounted aft below the fin leading edge.

Worth noting that around the same time the UK had a go at fitting nice square windows for jet passengers.
I was referring to the the comment re lower lobe being outside the pressurized upper deck .

While that was true re the B-29's, re fore and aft pressure sections- I'm not aware that the 707 and KC 135 pressure hulls were that different being built on the same tooling ..



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Old 25th Jan 2019, 00:17
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Originally Posted by KenV View Post
Really? Lockheed is investing billions now so it can maybe earn a big profit beginning in 2039 or 2049? Really?


From whom?
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Old 25th Jan 2019, 01:13
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Originally Posted by weemonkey View Post
From whom?
relax -kenv likes to pettifog various issues like this

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Old 25th Jan 2019, 02:33
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Originally Posted by esscee View Post
As for using very very old engines, makes me wonder if GE decided that they did not wish to support their old design CF6 for many more years to come which left only PW. Let's face it, they would have only chosen an American built engine after all the PR "moaning" etc that went on when Boeing did not win in the earlier "contests".
Boeing is still producing new CF6-80C2 powered 767 freighters for FedEx and others - with a planned lifetime of 40 years. As Ken noted, the CF6-80C2 engine is also used on other USAF applications such as the C-5M. GE has committed to supporting the CF6-80C2 for many more decades. We actually took a quick look doing a re-engine for the KC-46 using the GEnx-2B (from the 747-8), but it didn't pencil out well. The GEnx is far heavier than the PW4000 or CF6-80C2 (close to two tons/engine!), it's over a foot larger in diameter (hence ground clearance/landing gear concerns), and costs about twice as much. Further, while it had much better fuel burn, due to it's much higher weight contribution to the aircraft empty weight, at the same MTOW it's fuel offload wasn't any better for the spec refueling missions than the PW4000 or CF6.

As for a Rolls engined KC-46, the RB211-524G/H that goes on the 767 has been out-of-production for over 15 years - Rolls was never even a possibility. Back when Boeing launched the 747-8, they offered real good pricing on the last 747-400s to fill out the line before switching to the 747-8 production. Cathay came in and ordered six 747-400F, and being a long time Rolls operator wanted RB211-524 engines to be common with their other 747s. That's 24 engines, plus spares - something in excess of $150 million order. Rolls flat said no - they were not interested in building any more RB211 engines. So Cathay got PW4000s on their new 747 Freighters...
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Old 25th Jan 2019, 07:14
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Originally Posted by CONSO View Post
I was referring to the the comment re lower lobe being outside the pressurized upper deck .

While that was true re the B-29's, re fore and aft pressure sections- I'm not aware that the 707 and KC 135 pressure hulls were that different being built on the same tooling ..
The 707 and KC-135 are different aircraft designs that happen to share the same family tree. The 707 and the military derivatives such as the E-3 have a lower lobe that is inside the pressure hull.

The apparent similarities between the 707 and KC-135 do cause confusion (see the RJ thread for example). You could say they were almost identical apart from the nose, forward fuselage, fuselage barrel, wings, primary structure, fin, rudder system, tail, overall dimensions et al.
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Old 25th Jan 2019, 07:58
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Old 26th Jan 2019, 01:31
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Cool

Originally Posted by Just This Once... View Post


The 707 and KC-135 are different aircraft designs that happen to share the same family tree. The 707 and the military derivatives such as the E-3 have a lower lobe that is inside the pressure hull.

The apparent similarities between the 707 and KC-135 do cause confusion (see the RJ thread for example). You could say they were almost identical apart from the nose, forward fuselage, fuselage barrel, wings, primary structure, fin, rudder system, tail, overall dimensions et al.
Errrr ------ https://www.globalsecurity.org/milit...craft/b707.htm

The Dash 80 outgrowth was privately financed by Boeing with a view toward commercial passenger use and military tanker use, both of which were achieved. The 132 inches (3,350 mm) fuselage of the Dash 80 was only wide enough to fit 2+2 seating (in the manner of the Stratocruiser). Boeing soon realized that this would not provide a sufficient payload, so the fuselage was widened to 144 in (3,660 mm), the same as the KC-135 Stratotanker, which would allow six-abreast seating and the shared use of the KC-135's tooling. But Douglas launched the DC-8, with a fuselage width of 147 in (3,730 mm). The airlines [and passengers] liked the extra space, and Boeing was obliged to increase the 707's cabin width again, to 148 in (3,760 mm). This meant that little of the tooling for the Dash 80 was usable for the 707.
Now about claimed differences 707-kc135 ... Boeing leased some parts of 707 tooling FROM the airforce.for several years
And the early models of KC used water injection for takeoff especially from the relatively short renton airfield... about 5000 feet useable and they were loud loud loud !!
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Old 26th Jan 2019, 04:26
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Boeing soon realized that this would not provide a sufficient payload, so the fuselage was widened to 144 in (3,660 mm), the same as the KC-135 Stratotanker, which would allow six-abreast seating and the shared use of the KC-135's tooling
Shared tooling was to have been the case if the 707 & 135 shared the same fuselage diameter, but they didn't, so difficult to see how they shared tooling. Boeing themselves say,
The Dash 80 prototype led to the commercial 707 and the military KC-135 tanker. Both planes shared the basic design of the Dash 80 but were very different airplanes, neither one being a derivative of the other.
The only similarity between the -80, 707, 135, is the looks.
Are you sure about that-?? The ' upper floor' stresses would be significant whereas in a tube, hoop stresses are much easier to handle and uniform ...
CONSO, The below floor area of the 135 is unpressurised, except for the area immediately below the cockpit, and of course the boom operators compartment at the rear.
the early models of KC used water injection for takeoff
As did the early 707 and 747.



Last edited by megan; 26th Jan 2019 at 04:38.
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Old 26th Jan 2019, 05:44
  #774 (permalink)  
 
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Shared tooling was to have been the case if the 707 & 135 shared the same fuselage diameter, but they didn't, so difficult to see how they shared tooling. Boeing themselves say,
depends on what version of boeing documents/newsletters/ wiki/ etc you read- compared to friends of mine who worked tooling issues in renton.

https://en.wikipedia.org/wiki/Boeing_707
The 132 in (3,352.80 mm) wide fuselage of the Dash 80 was large enough for four-abreast (two-plus-two) seating like the Stratocruiser. Answering customers' demands and under Douglas competition, Boeing soon realized this would not provide a viable payload, so it widened the fuselage to 144 in (3,660 mm) to allow five-abreast seating and use of the KC-135's tooling.[11] Douglas Aircraft had launched its DC-8 with a fuselage width of 147 in (3,730 mm). The airlines liked the extra space and six-abreast seating, so Boeing increased the 707's width again to compete, this time to 148 in (3,760 mm).[12]

...
this only part of story . . .

Traces of the 707 are still found in the 737, which uses a modified version of the 707's fuselage, as well as the same external nose and cockpit configurations as those of the 707. These were also used on the previous 727, while the 757 also used the 707 fuselage cross-section.
.... The 707-120 was the first production 707 variant, with a longer, wider fuselage, and greater wingspan than the Dash 80. The cabin had a full set of rectangular windows and could seat up to 189 passengers.[32] It was designed for transcontinental routes, and often required a refueling stop when flying across the North Atlantic. It had four Pratt & Whitney JT3C-6 turbojets, civilian versions of the military J57, initially producing 13,000 lbf (57.8 kN) with water injection. Maximum takeoff weight was ..

https://faculty.haas.berkeley.edu/leonard/Active%20Papers/What%20Killed%20Douglas%20Aircraft.pdf

....
Subsequently, the development of the military KC-135 tanker and the civilian 707 diverged. First, the Air
Force demanded that the prototype’s 132” diameter be expanded by 12” for the KC-135. Then Juan
Trippe of Pan Am, wielding the threat of Douglas’ planned wider fuselage DC-8, pressured Boeing to
widen the 707’s diameter. Boeing’s decision to bring the 707’s diameter up to 148” was accelerated by
United Airline’s defection to the DC-8’s six-across seating. With the plan for a common fuselage
scrapped, but still with largely common wings, the 707 and the KC135 would share at least 20% of their
parts and tooling (Lawrence). The two were also produced in the same government plant. Boeing could
also benefit from R&D spillovers....

Last edited by CONSO; 26th Jan 2019 at 05:55. Reason: update a few links
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Old 26th Jan 2019, 13:42
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On NG's decision to stay out: I would speculate that it was not all a matter of perceived difficulty or risk. Once the initial win had been overturned, it was established that there was no extra credit to be had for the fact that the A330 was a larger airplane with more lift capability. This made the final tanker contest LPTA (lowest price, technically acceptable) and Boeing had (a) more money than NG and (b) a strategic interest in fending off an Airbus manufacturing bridgehead in the US. And by the time the second contest started, NG had, 'ow you say, d'autres chats fouetter.

Conversely, Airbus had an interest in staying in, if only to force Boeing into (a) losing a little blood on the deal and (b) making a highly US-optimized tanker that might not be as appealing for export. Mission accomplished.

Oh, and can we all quit with the "I could tell you but then I'd have to use a worn-out cliche from a mediocre movie with dubious shirtless volleyball" stuff about sekret wiring and cloaking devices? I would be astonished if the KC-46 was to be equipped with/for anything other than the standard DIRCM, ROBE has been unclassified since its inception in 2003 and various special configs are all over the Intertubez.
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Old 27th Jan 2019, 00:24
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Now about claimed differences 707-kc135 ... Boeing leased some parts of 707 tooling FROM the airforce.for several years
Because the USAF operates the 707 under a few guises, C-137, E-3, E-8
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Old 28th Jan 2019, 12:54
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Originally Posted by Just This Once... View Post
Who said USAF needs, other than you? For the USAF program the A330 was offered with an upper cargo deck.


Who said USAF needs a main deck cargo door and floor? USAF said this. And so did you with your reply. A number of folks here claimed USAF did not need a main deck cargo door and floor. That's bollocks

And for the record, the photo you posted was for an A330-200F. Airbus did not propose an A330MRTT based on the A330-200F freighter airframe. They proposed an A330MRTT based on the A330-200 airliner airframe, just like every other MRTT. Yes, a freighter door and floor could be added, but as an option. It was not a basic feature of their proposed tanker. Further, the airliner airframe does not have the lowered nose gear and nose blister to house it that the freighter airframe has. And why didn't Airbus propose a freighter based tanker? Perhaps it was because the A330MRTT was already certified as a tanker and that cert was based on the airliner airframe, not the freighter airframe. Proposing a tanker based on the freighter airframe would require an entirely new flight test and certification campaign, further adding to the cost, but more importantly, further adding to the development time. USAF's RFP had a very aggressive schedule. The conjecture is that proposing a freighter based tanker would have meant not being able to meet USAF's schedule. You'll have to ask Airbus to confirm that.

By comparison, Boeing proposed a tanker based on the 767-200LRF (Long Range Freighter) airframe. The freighter configuration was the baseline of their proposal, not an option.

In short, anyone who buys an A330MRTT is buying an airliner based tanker. Anyone who buys a KC-46 is buying a freighter based tanker. The customer has to decide which better fits their needs. You and I are in agreement that the USAF customer wants and needs a freighter based tanker.

Last edited by KenV; 28th Jan 2019 at 13:13.
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Old 28th Jan 2019, 13:50
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...the USAF customer wants and needs a freighter based tanker.
So they opted against basing a freighter of an airliner, and instead went with a freighter that is based on an airliner. Glad we cleared that up.

Last edited by Mil-26Man; 28th Jan 2019 at 14:09.
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Old 28th Jan 2019, 14:04
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Originally Posted by CONSO View Post
Are you sure about that-?? The ' upper floor' stresses would be significant whereas in a tube, hoop stresses are much easier to handle and uniform ...
Consider that every pressurized low wing aircraft has a big section of fuselage that is not hoop loaded, specifically the area of the center wing tank. The tank structure takes those non hoop pressurization loads. The KC-135 lower lobe has integral fuselage tanks that extend well ahead and well behind the center wing tank. Those tanks take those loads as they are primary structures and not bladder/secondary structures installed in a pressurized section of the lower lobe. In contrast the KC-46's belly tanks are secondary structures, similar to the aux tanks in the bellies of some 737, but of course larger.

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Old 28th Jan 2019, 15:47
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In short, anyone who buys an A330MRTT is buying an airliner based tanker. Anyone who buys a KC-46 is buying a freighter based tanker. The customer has to decide which better fits their needs.
Travel in the A330MRTT (or even the A310MRTT) in transport role and you travel in normal wide-body airline comfort - the Voyager has a seat pitch extended to cope with troops in bulky clothing in particular.

Travel in the KC-46 in its transport role and it's the same windowless, palletised seating rendition-class comfort as the KC-135...
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