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Not looking to start a pi$$ing match here, but if the A400 costs nearly as much as a C-17, what is the advantage of the A400 to justify the multi-billion Euro development costs (rather than just buying more C-17s)? Or was it mainly nationalism/NIH/politics?
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Width
Ken, I hope I can give the authoritive answer: In 1995 when it was a paper airplane the proposed width was 6" narrower. The driver was two landrovers side by side. I was at JATE at the time. A new version of the landrover had been introduced which carried the spare wheel on the side not the bonnet as was traditional. The manuals we were working to required access down each side. You know it was a long time ago and I cant recall if the side seats had to be down for carrying troops as well as carrying the vehicles.
I really am pleased it finished up as wide as it did as there is adequate space to walk down each side outboard of the 108" rails.
I really am pleased it finished up as wide as it did as there is adequate space to walk down each side outboard of the 108" rails.
Cargo bay dimensions
I should remember the story without notes but it is a long time since I talked about this part of the aircraft in that kind of detail but....
The dimensions of the cargo bay were driven by the loads the Nations wanted to carry. Each provided its longest, widest, tallest and heaviest.
The payload of 32 tonnes was driven by the Warrior recovery vehicle then at 31.5 tonnes. Then an extra 5 tonnes was allowed for additional military gizmos: defensive aids and other extras.
Height was driven by the Patriot missile system.
Width was driven by2 Landrovers side by side plus passengers in the sidewall seats and other items.
Length was driven by ??? (Can't remember)
You have to remember that increasing the cross-section, especially, of the cargo bay increases weight and drag leading to a need for more power and more fuel which in turn means more weight. The net result is increased cost in both production and operating.
The dimensions of the cargo bay were driven by the loads the Nations wanted to carry. Each provided its longest, widest, tallest and heaviest.
The payload of 32 tonnes was driven by the Warrior recovery vehicle then at 31.5 tonnes. Then an extra 5 tonnes was allowed for additional military gizmos: defensive aids and other extras.
Height was driven by the Patriot missile system.
Width was driven by2 Landrovers side by side plus passengers in the sidewall seats and other items.
Length was driven by ??? (Can't remember)
You have to remember that increasing the cross-section, especially, of the cargo bay increases weight and drag leading to a need for more power and more fuel which in turn means more weight. The net result is increased cost in both production and operating.
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Range I believe is pretty poor up close at max ZFW.... am I correct that east coast at max ZFW is pretty much the limit?
these (FRES SV) fit well when MZFW is considered, think range is pretty poor though...
these (FRES SV) fit well when MZFW is considered, think range is pretty poor though...
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The position of the horizontal stabiliser (HS)(or tail plane) is relatively easily explained. As it is an all flying tail plane ( as with most modern aircraft) it needs a motor to drive it. This motor is normally at the base of the fin but, because of the opening back end, the door goes into the space at the tail of the aircraft and there is insufficient structure to house the motor. It is, therefore necessary to move the HS up the fin. Once you have moved it up there are then aerodynamic reasons to go all the way just as in the C17.
Putting the horizontal stabilizer on the fuselage was not feasible on the C-17 because there was no place to put the carry-thru structure. The C-17 (like the A400 and C-130) has a large upward opening door aft of the downward opening ramp. On the C-17 the area above the door is presssurized, is accessible in flight, and is used to store mission equipment (ramp toes, center line troop seats, roller conveyors, etc, etc.) So there's no place to put carry thru structure in the rear of the fuselage. I'm assuming that the Atlas uses that space the same way. The An-124 (like the C-5 and C-141) has petal doors aft of the ramp and this area is unpressurized and inaccessible in flight, so it's possible to put the horizontal stabilizer on the fuselage. And the Russians/Ukranians did.
The C-17 and A400 both have swept/raked vertical fins, so the horizontal stabilizer moves aft as it moves up, providing greater moment arm and therefore greater pitch control authority. Note that the A400's stabilizer is highly swept aft. It does not fly at jet speeds so that is not necessary aerodynically as it is on the C-17. But sweeping the stalizers aft further moves their center of pressure aft, which further increases control authority.) That is very important because both aircraft are designed for heavy cargo airdrops where there is a HUGE shift in CG and hence necessitates a very powerful stabilizer and elevator. The C-5 and C-141 also had T-tails for that reason, even though they had the available fuselage volume for a fuselage mounted stabilizer. To the best of my knowledge, the An-124 was not designed for airdrop operations and so did not have to deal with a big CG shift while in flight.
The C-130 does not have a swept/raked vertical fin, so moving the stabilizer up had no advantage. In addition, on the C-130 the entire empennage is attached to the unpressurized "beaver tail" structure aft of the cargo door. I don't know if it could properly be called part of the fuselage.
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Not looking to start a pi$$ing match here, but if the A400 costs nearly as much as a C-17, what is the advantage of the A400 to justify the multi-billion Euro development costs (rather than just buying more C-17s)? Or was it mainly nationalism/NIH/politics?
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Length
length probably driven by a number of 463L Pallets including one (or was it two) on the ramp.
or two 24 ft Type V airdrop platforms at 16 tonnes each with parachutes for split sticks between them. Did not leave much room.
or two 24 ft Type V airdrop platforms at 16 tonnes each with parachutes for split sticks between them. Did not leave much room.
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Aaah, thanks,
On the C-17 the floor width was driven by three factors:
1. Ability to carry two rows of 463L pallets (in the 88 inch wide direction.) but that was possible with less than 16 feet of width.
2. Ability to carry two rows of 463 pallets or two rows of HMMWVs and carry drivers/troops on the sidewall seats.
3. Ability to carry two rows of 8x8 and 10x10 HEMMTs with room only for the drivers on the sidewall seats.
That drove the C-17's width to 16 ft.
C-17 cargo floor length was driven by 14 463L pallets on the main floor plus 4 more on the ramp.
A400's 13 ft seemed odd to me because 13 ft does not enable two rows of 463L pallets, which seemed pretty important to me, and does not allow two rows of HMMWVs, never mind room for drivers and troops. But Landrovers are not nearly as wide as HMMWVs, so now I understand the 13 ft width. Do France and Germany also operate narrower vehicles like the Landrover?
On the C-17 the floor width was driven by three factors:
1. Ability to carry two rows of 463L pallets (in the 88 inch wide direction.) but that was possible with less than 16 feet of width.
2. Ability to carry two rows of 463 pallets or two rows of HMMWVs and carry drivers/troops on the sidewall seats.
3. Ability to carry two rows of 8x8 and 10x10 HEMMTs with room only for the drivers on the sidewall seats.
That drove the C-17's width to 16 ft.
C-17 cargo floor length was driven by 14 463L pallets on the main floor plus 4 more on the ramp.
A400's 13 ft seemed odd to me because 13 ft does not enable two rows of 463L pallets, which seemed pretty important to me, and does not allow two rows of HMMWVs, never mind room for drivers and troops. But Landrovers are not nearly as wide as HMMWVs, so now I understand the 13 ft width. Do France and Germany also operate narrower vehicles like the Landrover?
Before I attended the FLA (as it was then) meetings to decide the specification I'd had the task to assess the C-17 cargo hold in co-operation with a Loadie from JATE. Together we described the C-17 cargo floor as 'Bombproof', as it was obvious that the C-17 had been designed around the cargo hold out and the only weight saving had been the removal of the gold plate. We 'suggested' a similar concept for the FLA; flip over roller, built-in side guidance, power operated locks, underfloor built in winch etc but as the A400M design progressed it was depressing to watch a pennypinching PT and a clueless Airbus strip capability from the cargo hold. Airbus further delayed the project by removing engineers from the project to work on the A380 freighter, whatever happened to that project? And the first cargofloor delivered from the American sub contractor was described by one German engineer as being "built by an apprentice on his first day at work".
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Only an electrical engineer so forgive me...
Probably a really silly question for those in the know...but how do you get the inboard and outboard engines to rotate props in different directions ie. one clockwise, one anti-clockwise? Is it simply a gearing issue?
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New RAF Transport
Folks, I think all of you who have come up with the technical explanations regarding the tail assembly are overthinking it.
They just went to the boneyard and removed as many C141 tails as was required in order to save money. ;-)
They just went to the boneyard and removed as many C141 tails as was required in order to save money. ;-)
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prop rotation
Here is my first post, so go easy on me! I am an aerodynamicist not aircrew by trade, so maybe I will be banned, but on the other hand you may occasionally find it mildly entertaining to read my ramblings.
Prop rotation partly covered by xherc previously, but could add the following:
The choice of prop rotation direction was a long and involved story with advantages and disadvantages for each possibility. The only decision made early on I believe, was NOT to have all the props rotating in the same direction. This is, I believe, the case for the Herc and it does have some advantages including only a single prop and gearbox type which must be cheaper, less spares etc, however the downside aerodynamically is enormous. You basically have an asymmetric wing loading due to the influence of the prop wash on one wing being mostly upwash while on the other being mostly downwash. This must be a nightmare for low speed stall characteristics as well as poor for high speed drag and I imagine it gave Lockheed a massive headache to get the C130J to an acceptable low speed performance when they stuck those bigger engines on it......would be interesting to hear any views on this angle from any C130J crew.
The next decision for A400M was prop rotation direction. If you get your paper and pencil out and to some front-view sketches, you will realise there are lots of options. For high speed cruise, the lowest drag config was likely to be inboard-up rotation on all props. This is because the wing in general then experiences the most upwash. This reduces vortex drag significantly. I would guess it is one reason why the Osprey props also rotate inboard-up...or maybe just a happy co-incidence. Same reason birds fly in a V formation...to catch that free upwash.
Noise is lower if props on same wing do not cross each other.....you can probably imagine the shearing going on if they do, so lower noise if 'up between engines' or 'down between engines'.
Best for low speed was something else again.
Final config was the best compromise.
The Filton boys certainly put alot of effort into the wing design and did a thorough job. Hope it all comes good for the end user.
Prop rotation partly covered by xherc previously, but could add the following:
The choice of prop rotation direction was a long and involved story with advantages and disadvantages for each possibility. The only decision made early on I believe, was NOT to have all the props rotating in the same direction. This is, I believe, the case for the Herc and it does have some advantages including only a single prop and gearbox type which must be cheaper, less spares etc, however the downside aerodynamically is enormous. You basically have an asymmetric wing loading due to the influence of the prop wash on one wing being mostly upwash while on the other being mostly downwash. This must be a nightmare for low speed stall characteristics as well as poor for high speed drag and I imagine it gave Lockheed a massive headache to get the C130J to an acceptable low speed performance when they stuck those bigger engines on it......would be interesting to hear any views on this angle from any C130J crew.
The next decision for A400M was prop rotation direction. If you get your paper and pencil out and to some front-view sketches, you will realise there are lots of options. For high speed cruise, the lowest drag config was likely to be inboard-up rotation on all props. This is because the wing in general then experiences the most upwash. This reduces vortex drag significantly. I would guess it is one reason why the Osprey props also rotate inboard-up...or maybe just a happy co-incidence. Same reason birds fly in a V formation...to catch that free upwash.
Noise is lower if props on same wing do not cross each other.....you can probably imagine the shearing going on if they do, so lower noise if 'up between engines' or 'down between engines'.
Best for low speed was something else again.
Final config was the best compromise.
The Filton boys certainly put alot of effort into the wing design and did a thorough job. Hope it all comes good for the end user.
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Originally Posted by NWSRG
Probably a really silly question for those in the know...but how do you get the inboard and outboard engines to rotate props in different directions ie. one clockwise, one anti-clockwise? Is it simply a gearing issue?
ALL turboprop/turboshaft engines have a gearbox between the engine and the propeller/rotor, which reduces the RPM of the engine to the proper speed for the prop/rotor.
Has the cost changed? Back in the 90s when the J was first announced, I seem to remember the cost ratio was 3 FLAs to 1 C17? I guess the C17 is also cheaper now as they do the end of line special editions!
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and does not allow two rows of HMMWVs, never mind room for drivers and troops. But Landrovers are not nearly as wide as HMMWVs, so now I understand the 13 ft width. Do France and Germany also operate narrower vehicles like the Landrover?
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Has the cost changed? Back in the 90s when the J was first announced, I seem to remember the cost ratio was 3 FLAs to 1 C17? I guess the C17 is also cheaper now as they do the end of line special editions!
But keep in mind that the A400 is a different airplane with different capabilities. It could be that A400's capabilities are worth the cost. It's biggest advantage relative to the C-17 is its soft field capability. I've seen figures as low as CBR 6 for the A400, which seems unlikely. To put this in perspective, a twin-engine C-27J (one fourth the size of an A400) has a CBR of 6 and the venerable Herc (half the size of the A400) has a CBR of 8/9.
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Before I attended the FLA (as it was then) meetings to decide the specification I'd had the task to assess the C-17 cargo hold in co-operation with a Loadie from JATE. Together we described the C-17 cargo floor as 'Bombproof', as it was obvious that the C-17 had been designed around the cargo hold out and the only weight saving had been the removal of the gold plate.
Cargo floor and ramp width and length were determined by the width and length of two rows of 463L pallets, HMMWVs, or HEMTTs.
Cargo hold "shoulder" was determined by width and height of US Army Expansible Van.
Height under wing was determined by AH-64 Apache rotor head height (no Longbow radar)
Height aft of wing was determined by CH-53 height with rotor removed.
Strength of floor and ramp was determined by weight of M1A1 Abrams tank.
The cargo floor also had integrally designed into it:
-flip up bi and omni directional rollers
-flip up logistics rails w/powered locks compatible with 463L pallet system
-hinge up airdrop rails w/powered and digitally adjustable variable restraint locks (VRL) compatible with standard airdrop platforms
-integral load equalization system to equalize pallet loads on VRL system
-CDS rails/locks compatible with standard CDS bundles/pallets
-25,000 lb capacity omni-directional tie down eyes on a 20 inch grid
-powered winch with power to pull a disabled Abrams tank up the ramp
-lights in cargo floor "curb" to facilite chaining down vehicles
-individual fold down troop seats above the floor curb.
-provisions for attaching centerline seats and stretcher stanchions
Only until all of the above (and more) was designed into the floor was the fuselage designed around that floor with a wing of sufficient span attached to provide the specified range with the specified engines. The original span could not meet the on-ground requirements of fitting three C-17s into a defined small austere field (relates to MOG). The original solution was to add folding wing tips, but that was simplified to having "permanent" folded wingtips in the form of large blended winglets.
We 'suggested' a similar concept for the FLA; flip over roller, built-in side guidance, power operated locks, underfloor built in winch etc but as the A400M design progressed it was depressing to watch a pennypinching PT and a clueless Airbus strip capability from the cargo hold.
And the first cargofloor delivered from the American sub contractor was described by one German engineer as being "built by an apprentice on his first day at work".
And incidentally, the C-17 is built the same way it was designed: from the floor up. The floor is literally built first, then the fuselage is built around the floor, and then the wing is aligned to the floor and attached to fuselage fittings.