More KC-46A woes....

[brakedwell]

Frankentanker uses bits from several different airframes?
767-200ER fuselage
767-300F cargo door, floor and landing gear
767-300F wing
767-400ER flaps
767-400ER engines
787 cockpit

Should make a nice airplane.

[tdracer]

BEagle, that's not quite correct:

767-400ER engines
787 cockpit

The KC-46 uses the PW4000/94" engine - which was never on the 767-400ER. The engine itself is identical to the one flying around today on hundreds of 767s and 747-400s, some of the engine buildup has changed for tanker specific reasons.
The ONLY part of the 787 cockpit that is being used is the displays - structurally the cockpit is the same as 767-400ER, some of the avionics have been upgraded but are still based on the 767-400ER.


Don't believe everything you read

[brakedwell]

Some people believe what they want to believe

The B767 was the most reliable aircraft I ever flew.

[BEagle]

OK, so 767-300F engines with modified ancillaries and a cockpit which is a 767-400ER / 787 hybrid.......

No risks there then.....

[TBM-Legend]

No more risk than the C-130J over the C-130H or the UH-60M over the L etc...

At least it is basically production and known stuff. The E-7 for example has a modified CFM56 to meet the electrical loads etc. Seems to work real fine...

[BEagle]

No more risk than the C-130J over the C-130H...

Well, that programme didn't go particularly smoothly, did it?

An ex-RAF air-wheel, employed by Lockheed, decided that he'd rather resign than peddle any more lies for them....

[vascodegama]

Stilton

Does that include other people's apostrophe abuse?

[KenV]

This is gibberish of the finest water on so many levels I won't even start. Maybe someone else will point out why the Kestrel/Harrier was developed; why the Hornet was never an option for the RAF (though I did control a couple of trials with F15 and E3A in 1975) and why they RN thus conceived the SHAR in the "through deck cruiser" era.

OK, so some don't like the Hornet/Harrier comparison (even though both are made by the same company.) If such a comparison is offensive, how about the French Rafale M, or the Russian SU-33? The point is, the RAF is forced to operate STOVL aircraft and prevented from operating CATOBAR aircraft and even STOBAR aircraft from RN carriers because of the "facility" the aircraft must operate from. STOVL aircraft are the quintessential example of a weapon system specifically designed to solve a facility constraint.

BTW, the USMC has a similar facilities constrained problem. Evne though the USMC owns and operates Hornets and Intruders, they also own and operate STOVL aircraft like the Harrier and the F-35B because their forward "facilities" cannot handle Hornets and Intruders. This is yet another weapon procurement decision based on "facility constraints".

Indeed, CATOBAR aircraft are specifically designed (some woud say compromised) by the constraints imposed by the facility they operate from. All the USN would have to do is scale up their aircraft carriers and they could operate conventional fighters from their carriers and thus not have to fly around with thousands of pounds of extra weight in their aicraft to handle catapult launches and arrested landings, not to mention folding wings. The H-60 series of helicopters have that unique "lizard" look because they were required to fit inside a C-141 without major disassembly. The Gripen (and most modern Swedish fighters) are designed to be able to operate from Swedish highways. The US Army's "Stryker" vehicle design is constrained by the C-130's loading envelope and payload limitations. Indeed C-130 compatibility is a design constraint of a large majority of US Army vehicles. C-17 compatibility is a design constraint of virtually EVERY US Army ground vehicle and many USAF/USN/US Army helicopters. These are but a few of the numerous weapon systems designed around a "facility" constraint. So, yes, I continue to challenge the notion that weapons systems are never designed or constrained by the facilities they must operate from.

And separately, does anyone know how it is that a Roman military design constrained the design of the Space Shuttle?

[KenV]

Frankentanker uses bits from several different airframes?

I don't understand this whole "Frankentanker" fetish.

If the mission calls for a short fuselage, then yes, you start with a -200. MRTT does the same thing. But if the mission also calls for higher gross weights than a -200, then obviously you use the sronger landing gear and wings of the higher gross weight -300 version. And if the mission calls to operate into and out of shorter fields at higher weights, you use the high lift system from the -400 version. And if the mission calls for a cargo door and floor, you use the cargo door and floor from the freighter version. What is Frankensteinish about that? It's just plain good engineering to use an existing design that is proven and works rather than start over with something new. It's the same reason the KC-46 uses a modified KC-10 refueling boom. It also uses existing off-the-shelf wing aerial refueling pods and cockpit displays. They're proven and they work. Nothing Frankensteinish about that.

The various iterations of the 737 BBJ do exactly the same thing, mixing and matching fuselage length and heavy or light weight landing gear and wings to fit the customer's needs. That's also what was done to create the Wedgetail and the Poseidon, both based on the 737 airframe. It's good business and engineering practice, not freakish.

Earlier in this thread it was noted that the MRTT can be equipped with the freighter's cargo door. Is that Frankensteinish? An argument can be made that it might be because an A330 with the freighter's cargo door but not the freighter's cargo floor nor the freighter's nose gear is kind of a freak. What's the point? And is flying around in a two engine airplane with a wing designed and built for four engines freakish? I don't think so, but apparently there are those who would say so. And is having a large airframe tanker with no boom to refuel UARSI equipped aircraft freakish? I don't think so, but it might be penny wise and pound foolish operationally. Even ancient KC-135s can go "both ways".

[KenV]

If Airbus/Boeing took the longgggview they'd be working on an A380/B777 tanker for 2030......................

One A380 would be able to refuel every aircraft that the RAF will have by then in one go

May I point out that it's smaller size was a big reason why the KC-10 was chosen over the KC-747 back in the day. The amount of fuel available for offload is very often less important than the number of available offload points (tanker orbits). The bigger the tanker, the fewer tankers will be bought and so the fewer tanker orbits will be available. And if the tankers are forward deployed, as they often are by USAF, those tankers need to share precious ramp space with fighters, bombers, transports, and other tankers. USAF calls that MOG (maximum on ground). MOG is often a serious constraint in a forward theater. Because of their size, A380s are significantly constrained in the number of airfields they can operate in and out of even in airline operations, which would almost certainly make them a poor choice for a tanker, as would a 747-8.

The A350, 787, or maybe 777X would almost certainly make a better choice to replace KC-10s in the future. Although the 777X would likely be outsized for the job.

If "bigger" were indeed "better", then the MRTT would be based on the A330-300 rather than the -200 and there never would have been an A310 MRTT.

[dagenham]

Oh oh oh me sir..... Roman war chariot dictated width of British road, which dictated the width of railways..... Railways dictated width of tunnel..... Which was between Morton thiokol plant and the Kennedy space centre so boosters had to be made to the width of a Roman war chariot..


Do I get a budgie badge?

[LowObservable]

KenV - You are stretching the facilities argument a bit.

Correct, lots of things are designed within the limits of C-130s and aircraft carriers. But those in turn are designed within limits: You can easily make a bigger transport but it will cost more (A400M). Carriers are pushing all sorts of ship-size limits. The bigger carrier and transport will also cost more to operate, where a bigger ramp only costs more when you have to shovel the snow off it. Concrete is far, far cheaper than anything that moves.

As for STOVL: a full-time operational STOVL base costs the same as a CTOL base. The Marines did not want cheaper facilities; they wanted to be free of facilities altogether.

Tanker orbits do count. But in the case of the KC-X competition both sides were required to produce the same numbers.

And BTW, the Roman connection to the SRB diameter is mostly hoggus washus. http://www.snopes.com/history/american/gauge.asp

[KenV]

As for STOVL: a full-time operational STOVL base costs the same as a CTOL base. The Marines did not want cheaper facilities; they wanted to be free of facilities altogether.

Which was pretty much my point from the beginning. Navy aircraft spend about half their time ashore where they don't need launch bars, arresting hooks, folding wings, etc etc. A US Navy master jet base costs about as much as a USAF jet base. That was NOT my point. My point was that facilities constraints often drive weapons system design and also weapon system procurement decisions. The buyer often CANNOT alter his facilities constraints, whether it is due to cost or to physics or to politics or to something else. CATOBAR aircraft are designed and built differently than CTOL aircraft due to differing facilities constraints. STOVL aircraft are designed and built differently because they have still more different facilities constraints. The notion that weapon system designers and weapon system buyers can always build or alter facilities to cater to the weapon system is simply false. More often it is the other way around. Engineers routinely design weapon systems to fit facilities constraints and buyers routinely make purchase decisions based on facilities constraints.

And all this relates directly to the USAF tanker competition which took into account much, MUCH more than simply how much fuel can be offloaded at X range.
KC-46 has essentially equal fuel offload capability.
KC-46 has essentially equal boom performance (after an expensive redesign.)
KC-46 has a significant disadvantage in passenger carrying ability
KC-46 has a significant advantage in home basing costs.
KC-46 has a significant advantage in MOG when deployed.
KC-46 has a significant advantage in ferry range
KC-46 has a much more flexible mission suite (which includes its cargo door, cargo floor, and level loading attitude on the ground) which gives it a significant advantage in cargo carrying and medevac ability and lessens A330's passenger carrying advantage.)

When ALL the factors that the user (USAF) listed and prioritized are considered, KC-46 won. Of course it helped that the factors listed and prioritized favored the KC-46. And yes, some of that was due to politics. And my employer, Northrop Grumman, read USAF's list and priorities (not to mention the political winds) and came to the conclusion that they could not win with an A330 based offer. So they pulled out. And Airbus chose to go it alone, despite the very slim likelihood of a win. Perhaps Airbus's strategy was NOT to win, but to hold Being's feet to the fire and force them to make expensive changes to their offer AND to low-ball their bid and make Boeing's win a Pyrrhic victory. Which makes strategic business sense since Airbus and Boeing compete directly.

[D-IFF_ident]

Has an official and comprehensive explanation as to why the KC-46A was chosen instead of the KC-45, in the third KC-X bidding process, ever been published?

[vascodegama]

Ken

I am not convinced by the argument of the superior ferry range although both ac have the option of receiving fuel to increase their range. I would agree that the AAR equipment fit of the 767 is better ie all 3 hoses and a boom but at the end of the day I guess the USAF would just like a new ac soon. This replacement ac was supposed to have been in service a long time ago.

[D-IFF_ident]

The KC-45 had all 3 hoses and the boom too.

[vascodegama]

Pity we didn't go for that option!

[BEagle]

If one excludes the ability to receive fuel in flight, then comparison of ferry range obviously depends upon the maximum fuel load of each aircraft and their fuel burn rates.

Some years ago I was involved in a multinational AAR study. One topic to be covered was practical maximum fuel loads for future tankers. But rather than believe manufacturers' glossy brochure boasts, I set the following conditions for the departure and arrival aerodromes: Sea Level, ISA, still air, 10000 ft runway. Hardly very demanding and reasonably typical of most large European aerodromes.

The US representatives immediately asked for 12000 ft - which we refused on the grounds that neither Heathrow nor Frankfurt were typical tanker bases.

After each group had crunched the numbers, the answer was that both the A310MRTT and A330MRTT could operate with max fuel under those conditions. The 73.5T ex-ba B767-200ER proposed by TTSC for the FSTA contract was also just able do so.

But it all went rather quiet when the US team revealed their calculated figures for the KC-46 (or whatever it was called then). Because, despite uprated engines and brakes, it could only operate with around (IIRC) 84% of its max fuel even under such benign conditions.

I gather that the expensively-extended Pratica di Mare is already proving a challenge for the smaller-capacity KC-767I (which doesn't have the uprated systems of the KC-46A), so (as confirmed to me many years ago by a Boeing FSTA bidder), it is highly likely that the ability of the KC-46A to operate at MTOW will be somewhat limited in practice. Some idiot USAF fighter general once spouted runway performance figures for the KC-46A, but it was clear that he'd never heard of scheduled performance or balanced field requirements....

So I doubt very much that the KC-46A will prove in practice to have a better unrefuelled ferry range than the A330MRTT.

We also looked at a standard 4 hr time on task AAR mission scenario on an AARA situated about 60 min from the take-off and landing aerodromes, using the same 10000 ft aerodrome conditions, in order to obtain a figure for the maximum available offload assuming that the tanker would land with 1 hr to tanks dry. The result was that the A310 could offload about 53% of the A330's figure - and the KC-767 about 59%....

[LowObservable]

"Aerodrome". Such a reminder of the French lead in aviation in 1910-14.

The idiot fighter general must have been an F-16 guy, where the response to an engine failure beyond the early stages of takeoff is WHOA BETTY! tug BANG and does UTC make ties?

[KenV]

Ken, I am not convinced by the argument of the superior ferry range although both ac have the option of receiving fuel to increase their range. I would agree that the AAR equipment fit of the 767 is better ie all 3 hoses and a boom but at the end of the day I guess the USAF would just like a new ac soon. This replacement ac was supposed to have been in service a long time ago.

Keep in mind that ferry range is range with max fuel and zero payload, with no inflight refueling. All airplanes (generally) are designed to carry a payload, they can never reach max takeoff weight with just fuel. At max fuel they always have some take off gross weight margin which is used for carrying a payload. The inverse is (generally) also true. When loaded with their maximum payload, they cannot carry a full fuel load.

This results in two "knees" in the payload/range curve of (virtually) every aircraft.
The first knee occurs when the aircraft has at maximum payload and is then filled with fuel to its max takeoff weight. The curve slopes down to the right, with each pound of payload taken off compensated by a pound of fuel added. The second knee occurs when the aircraft reaches it's fuel volume limit. At that point removing a pound of payload cannot be compensated by a pound of additional fuel. The curve slopes down much more steeply, with the range increase resulting only from the lower gross weight of the aircraft.


The 767 and A330 are designed this way. Both carry fuel only in their wings. When they reach their fuel volume limit, they still have significant gross takeoff weight margin to carry passengers and cargo.

The MRTT, like the A330, carries all its fuel in its wings. It cannot trade payload for additional fuel.

The KC-46 has belly tanks. It can trade payload for additional fuel in those belly tanks. Basically, the belly tanks move the second knee in the payload/range curve to the right.

The result is that the KC-46 has a ferry range advantage over the MRTT. This also means that MRTT has a payload advantage over the KC-46 when each are loaded with max fuel. But USAF did not prioritize cargo capacity when these tankers are full of fuel for a tanker mission. Why? Basically because USAF uses the KC-135s and KC-46s as EITHER a tanker, OR a transport, not both simultaneously. USAF uses their larger KC-10s as BOTH a transport and a tanker on the same mission. For example, when deploying a fighter squadron the KC-10 carries support equipment for the fighters at their deployment base, as well as providing fuel to the fighters enroute to their deployment base. Once forward deployed, the smaller KC-135s and KC-46s provide tanking services in the theater. USAF has the luxury of a mixed fleet of tankers which are optimized for different employment scenarios. Which also makes USAF's procurement decisions different than other nations' procurement decisions.

BTW, returning to the subject of size. Boeing could have offered a KC-46 with the -200 fuselage and the wings and landing gear of the -400ER, instead of the -300ER, making up much of the A330's advantages. Why didn't they? Because then their offer would have lost its advantage in MOG and MILCON.

And oh yes. USAF has announced where the first KC-46 squadrons will be based and where the KC-46 "school house" will be based. McConnell and Altus were chosen because these bases required the least MILCON to accomodate the new aircraft.

And finally, the AAR equipment of the KC-45 and KC-46 were essentially the same, with 3 drogues and 1 boom. And after an expensive redesign of the boom by Boeing, the two booms had essentially the same performance.