KC-Z / Next-Generation Air Refueling System (NGAS)

[sferrin]

The simplist and most obvious part of the solution would be to make greater use of buddy-refuelling; a F-35 refuelling a F-35, a B-21 refuelling a B-21, etc. This hasn't been part of US airforce culture/ thinking (luxury of large SAC sourced refuelling force) and has obvious limitations (some platforms having limited fuel loads they can give away, limiting the range extension for the receiver, etc). However has the advantage of being relatively cheap, potentialy providing many survivable platforms that are more "disposable" than a few very high cost but with higher refuelling capability platforms. Examples would include naval air arms and the French Mirage IV force (which also used KC-135 support for uncontested airspace refuelling).

Problem being that the USAF boom refuelling system is inherently incompatible with buddy fuelling. You can't just strap a boom onto an aircraft in the same way you can put a hose reel in a pod and hang it from a hard point. Even assuming the simple mechanics could be dealt with via, say, a pallet in the bomb bay, the crew skills are totally different. The boom operator actually flies the boom onto to receiver; it's a highly specialized skill that you can't just make a secondary job for a normal navigator/copilot.

The alternative is to switch to hose and drogue, which means a) refitting the entire Air Force and b) taking much longer to refuel large aircraft. The USAF didn't adopt the boom just to be contrary. It passes gas much faster than the hose and drogue approach. Using a hose and drogue would mean staying connected and detectable for much longer in hostile airspace.

Buddy refueling is a terrible kludge. (See the current USN situation where half their strike force has to be fitted out as tankers.)

 

[r3mu511]

@AeroFranz:

you can see the mathematical treatment for this in section 14.3 written by J. Shaeffer in the book "Radar Cross Section" by E. Knott... the treatment there assumed no mutual interaction between the individual scatterers (ie. no corner reflectors formed between objects, etc)...

---

corner reflection would require surfaces whose normals are perpendicular/orthogonal to each other (for the case of surface specular reflection), or edges whose normals are also perpendicular to one another (for the case of edge diffraction)... so I could imagine a case where if you had two aircraft (A and B ) flying side by side and both had wing leading edges swept back at 45 deg... given an incident wave whose direction of propagation is parallel to the fuselages would result in an edge diffraction off of aircraft A's wing leading edge which would result in a cone of diffraction with a half-angle of 45 deg which would then be incident onto the leading edge of aircraft B's wing, leading to another cone of diffraction also with a half-angle of 45 deg which would thus be in the backscatter direction, effectively giving a corner reflector for edge diffraction effects (the same result can be achieved by side by side aircraft with different leading edge sweepback angles so long as the sum of the two sweepback angles totals 90 deg)...

for the case of refueling where one aircraft is behind and slightly below the other aircraft, I can't really think of a way to form orthogonal surfaces or edges in a way to result in a corner reflector with it's axis of reflection in the forward direction...

 

[Ian33]

When the X47B was doing its aerial refuelling thing, there was talk of a low observable boom for high threat areas.

A faceted job like an RCS test pylon.

 

[Mat Parry]

When the naval demonstrator (X-47B) was doing it's hose & drogue aerial refuelling thing, a low observable boom (faceted or not) would've been virtually useless. What would it be used for?

A stealthy boom mounted on a US navy X-47B's could:
(1) refuel lost US air force aircraft?
(2) refuel other X-47B's (but no other US navy carrier platforms).

If mounted on a non stealthy platform.... oh wait!

 

[NeilChapman]

I like the LM design - C-5 cargo capacity with 1/2 the C-17 fuel consumption. It's a 'technology leap' and the history of technology leaps is long development times, unexpected costs and under performance. Like to see more risk reduction to better ensure the tech maturity is there before a program is begun.

I'd think this design would be less risky, and far more useful, than a full BWB or stealth solution. Also, the only way "technology leaps" are accomplished are by doing them. They don't come for free.

"Like to see more risk reduction to better ensure the tech maturity is there before a program is begun."

Like what? They're already (supposedly) planning on flying a subscale X-plane. Aside from that what else is there to be proven? All the construction methods are already being used. All the required avionics could be based on existing hardware. Aside from the shape, there is no required new "tech" for this design.

Autonomous refueling
Simultaneous multiple boom operations w/large aircraft
Whatever is required to ensure loads and constructed weight of a blended wing this size
Engine tech maturity - 700k lbs w/2 engines ?
STOL performance expectations
What will it's Load Classification Number (LCN) be? # of runways available to it

I'm concerned about a 'kitchen sink' approach that takes forever to accomplish. Would rather see meeting the perceived needs w/multiple aircraft.

There is a need for an aircraft w/a C-5 load & LCN. Don't know if it needs the austere airfield capability as well as a tanker role.

 

[lastdingo]

Commonality between

tanker
ElInt aircraft
AEW&C aircraft
A/G radar aircraft

as was achieved with the C-135 series (Boeing 707) would be very desirable.
Stealth makes sense only for the first two, while the other two are beacons with their huge radar emissions. Those others would rather benefit greatly from a very fast platform that allows to get away from threats or delay the time till supersonic threats have a situation for a promising missile shot at the platform.
Stealth would help them only if they would switch off their radars after missile launch was detected and then run to break contact, trying to avoid that the threat platform can send correct mid course updates. Yet even then the "run" part would greatly benefit of 20-25% more speed.

So if anything I'd say rear aspect LO modifications may make sense (though that's exactly where reducing RCS is the hardest), but in general go for minimum Mach 0.9 capability (with big radar antennas and 80% fuel). Also, towed decoys.

 

[marauder2048]

Engine tech maturity - 700k lbs w/2 engines ?

Where are you getting those thrust requirements? The re-engined C-5s have ~ 200k lbs
or roughly the same output you get from 2 x GE9X which the LM guys modeled (roughly via the Genx)
for the HWB.

 

[marauder2048]

Commonality between

tanker
ElInt aircraft
AEW&C aircraft
A/G radar aircraft

as was achieved with the C-135 series (Boeing 707) would be very desirable.
Stealth makes sense only for the first two, while the other two are beacons with their huge radar emissions.

Assuming the last two aren't receivers in a bistatic configuration.

 

[sferrin]

Autonomous refueling

That's not airframe specific. There's no reason they couldn't build a new tanker without it and implement it at a later date. For that matter, there's no reason they couldn't do that with older tankers.

Simultaneous multiple boom operations w/large aircraft

Given that no existing tanker has multiple booms, how would you test this without building an aircraft with multiple booms? And why would you want or need to?

Whatever is required to ensure loads and constructed weight of a blended wing this size

?????

Engine tech maturity - 700k lbs w/2 engines ?

You mean like the 777-300ER that's been flying for well over a decade?

STOL performance expectations

???

What will it's Load Classification Number (LCN) be? # of runways available to it

Why would it be any different than any other heavy aircraft? The runway doesn't care what's above the wheels. Furthermore, there's nothing that says you have to have a 700,000lb aircraft, or if you do, that it needs to weigh that going into every airfield.

I'm concerned about a 'kitchen sink' approach that takes forever to accomplish. Would rather see meeting the perceived needs w/multiple aircraft.

Don't see how that's the case here at all. Pretty much every tanker in the US (aside from the Super Hornet) is a tanker/cargo aircraft, hence the "KC".

There is a need for an aircraft w/a C-5 load & LCN. Don't know if it needs the austere airfield capability as well as a tanker role.

So build the C-5 replacement as a HWB and make the KC-Z a smaller HWB.

 

[NeilChapman]

- two aircraft flying in formation more than double the individual RCS

theoretically the total rcs from a collection of scatterers is the square of the phasor summation of the square-roots of the rcs of each scatterer...

so for two objects the maximum (ie. coherent sum) of the echo cross section would be (given: a=rcs of 1st object, b=rcs of 2nd object):

(a^1/2 + b^1/2)^2

if both objects had the same rcs value (ie. a=b) then the maximum coherent sum would be 4 times the rcs of the individual object...

if one object had a fractional rcs as compared to the other object's rcs, ie. b=k*a, where 0<k<1, then the coherent maximum would be:

a * (1 + k^1/2)^2

so if for example your "stealth" tanker had an rcs of 1 sqm and your fighter had an rcs of 0.001 sqm, the maximum coherent rcs of the two combined would be: ~1.06 sqm, or just a bit over 6% higher than that of the tanker alone...

if you got your tanker down to an rcs of 0.1 sqm together with the same 0.001 sqm fighter, then the coherent rcs of the two combined would be 0.121 sqm, or around 21% higher than your tanker alone...

one can also add in the rcs of the boom as a 3rd object in the system and work the math to figure out what ratios of rcs for each object in the system would be needed to get an acceptable rcs increase for the combined system over that of the tanker alone...

R3, thank you for running these numbers. Any thoughts to what would happen if you added a third aircraft?

Scenario is a four aircraft strike package converging on a tanker w/two fighters refueling on two booms simultaneously.

 

[NeilChapman]

Engine tech maturity - 700k lbs w/2 engines ?

Where are you getting those thrust requirements? The re-engined C-5s have ~ 200k lbs
or roughly the same output you get from 2 x GE9X which the LM guys modeled (roughly via the Genx)
for the HWB.

Sorry - wasn't clear. I was talking about the max weight of the aircraft.

I presume it starts w/where can these beasts operate. US seems to experience a number of general limitations on moving material in wartime.
eg.
Political limits - Countries refuse access.
Runway strength - LCN
Runway length for landing
Runway length for take off
Ramp area for the qty of aircraft
Some airfields may be unavailable due to working Maximum On the Ground (MOG) or airfield damage
Air mobility enterprise is dependent on commercial partners to meet surge wartime requirements

Austere airfields typically include the following

Runways <4000ft and as narrow as 60 ft
Payloads contained by runway length and weight bearing capacity
Ramp space <100k sq ft w/single narrow taxiway and not turnaround areas at end of runway
Ground support & equipment usually nonexistent

Ideally, new airframe designs will open up more airfields for operational use - not the same or less. C-5 certainly doesn't use austere airfields. My concern is that I wouldn't expect a 700-800k lb aircraft to have a critical field length for takeoff of ~8000ft (NATO spec) with qty 2 75k lb Genx engines. If that's the design, I'd be concerned that weight gain during EMD would put right back where the C-5M is today.

So two concerns w/engine development.
1) If the design is for use on austere airfields and C5 can't do it today then I don't see how 75k lb thrust GEnx accomplishes task.
2) If design is for new C-5, concern is that 'weight gain' during EMD will get us right back to C-5 specs w/5000-6000 ft minimum runways.

 

[r3mu511]

@NeilChapman:

if you work the general equation for the case of 1 tanker and N fighters you get (again this is assuming no mutual interaction between scatterers, so no corner reflectors formed between objects, etc):

given:

a = rcs of tanker
b = rcs of fighter = some fraction of tanker rcs = k*a, where 0<k<1
n = no. of fighters

total echo cross section = a * (1 + n*k^1/2)^2

so for two fighters = a * (1 + 2*k^1/2)^2

using the rcs values in the previous example, "stealth" tanker rcs of 1 sqm, fighter rcs of 0.001 sqm, then total echo area is ~1.13 sqm, around ~13% higher than the tanker alone...

if tanker rcs is smaller at 0.1 sqm, fighter rcs is still 0.001 sqm, then total echo area is 0.144 sqm, 44% higher than the tanker alone...

---

if you explicitly include boom rcs in the system:

c = boom rcs = some fraction of tanker rcs = p*a, where 0<p<1

then the equation for 1 tanker, 2 fighters, with 2 booms would be:

a * (1 + 2*k^1/2 + 2*p^1/2)^2

if you used for example, tanker rcs of 1 sqm, fighter rcs of 0.001 sqm, and boom rcs of 0.002 sqm (boom isn't as "stealthy" as your fighter), then the total echo area would be ~1.33 sqm, 33% higher than the tanker alone...

for a smaller tanker rcs of 0.1 sqm and with the same fighter and boom rcs used previously, total area is now ~0.22 sqm, a full ~2.2x larger than that of the tanker alone...

 

[NeilChapman]

Autonomous refueling

1. That's not airframe specific. There's no reason they couldn't build a new tanker without it and implement it at a later date. For that matter, there's no reason they couldn't do that with older tankers.

Simultaneous multiple boom operations w/large aircraft

2. Given that no existing tanker has multiple booms, how would you test this without building an aircraft with multiple booms? And why would you want or need to?

Whatever is required to ensure loads and constructed weight of a blended wing this size

3. ?????

Engine tech maturity - 700k lbs w/2 engines ?

4. You mean like the 777-300ER that's been flying for well over a decade?

STOL performance expectations

5. ???

What will it's Load Classification Number (LCN) be? # of runways available to it

6. Why would it be any different than any other heavy aircraft? The runway doesn't care what's above the wheels. Furthermore, there's nothing that says you have to have a 700,000lb aircraft, or if you do, that it needs to weigh that going into every airfield.

I'm concerned about a 'kitchen sink' approach that takes forever to accomplish. Would rather see meeting the perceived needs w/multiple aircraft.

7. Don't see how that's the case here at all. Pretty much every tanker in the US (aside from the Super Hornet) is a tanker/cargo aircraft, hence the "KC".

There is a need for an aircraft w/a C-5 load & LCN. Don't know if it needs the austere airfield capability as well as a tanker role.

8. So build the C-5 replacement as a HWB and make the KC-Z a smaller HWB.

1. Wasn't suggesting it's aircraft specific. It's an advantage that reduces complexity/crew in the mission and if you want it it should work prior to having airframes waiting for the tech. Sort of like the AAG problems on the Ford-Class.

2. a. I'm not an AE but I expect it can be modeled then tested. b. Lot's of airspace and ramp space around a tanker. Also reduces wait times for fighters on cap missions or striking time sensitive targets of opportunity. Strike mission of 4 F-35's refueling time cut in half + requires two tankers today increasing airspace and ramp space.

3. Can they build a blended wing this size that meets the load requirements within the weight target or will it end up heavier which cuts into aircraft capability?

4. 777 has a 10k foot takeoff requirement. NATO spec is for 8k foot runways. Austere is 4k ft.

5. LM provided fuel savings and load info. Provide specs comparing it to C-5 or C-17 for other design expectations like runway requirements, single engine takeoff limits at specific temp requirements, fuel load at max load, etc etc.

6. I agree. C-5 was designed to fly into unimproved airfields. AF doesn't use it for that because the MCR has been so crappy, it's not capable of reversing unless it's basically empty and engine blast creates a FOD hazard. If the LM proposal is basically for outsized material only and will fly into basically the same 5 pacific en route airfields and still won't do airdrop missions then set that exception up front.

7. LM proposal looks like a C-5 replacement w/tanker thrown in - hence kitchen sink comment. There are divergent requirements for inter-theater lift vs intra-theater lift vs tanker cargo augmentation. It will be incumbent upon the USAF to set requirements and not change them - and not want a 100% solution.

8. Whatever fits the mission. Just want the technology maturity (for whatever particular purpose) to be there prior to getting started on the new airframe.

 

[NeilChapman]

@NeilChapman:


if tanker rcs is smaller at 0.1 sqm, fighter rcs is still 0.001 sqm, then total echo area is 0.144 sqm, 44% higher than the tanker alone...

---

for a smaller tanker rcs of 0.1 sqm and with the same fighter and boom rcs used previously, total area is now ~0.22 sqm, a full ~2.2x larger than that of the tanker alone...

Thanks for doing that!

Isn't that still pretty low compared to the RCS of a KC-46 which is probably, what, 100?

This rcs would allow the stealth tanker to operate much closer to the battlespace than the KC-46 - no? Perhaps with the advantage that should a threat approach the stealth tanker can button up and disappear - or - use whatever remote weapons systems control the b-21 will have (same as F-35?) to engage the threat.

Well, it's a lot of conjecture. Too many 'ifs'.

 

[CiTrus90]

Just thinking out of the box here: wouldn't creating and deploying a dedicated LaWS interceptor, maybe based on the B-21 platform, and flying close to tankers, solve the issue without the need for building a complex large stealth aircraft for the tanker role?

You'd just have a laser equipped aircraft (stealth in this case) working as a sort of goalie for all kind of threats to the tanker force, which could then fly pretty much in the same way they've usally done.

Moreover, I suppose laser weapons will be operational between early to late 2020's, while developing a large stealth tanker would at least take 15 to 20 years (being overly optimistic...) from now.

And while at it add ECM capabilities to said LaWS interceptor.

 

[AeroFranz]

@ r3mu511: thanks for the reverence and working out the examples

 

[sferrin]

1. Wasn't suggesting it's aircraft specific. It's an advantage that reduces complexity/crew in the mission and if you want it it should work prior to having airframes waiting for the tech. Sort of like the AAG problems on the Ford-Class.

There's no reason to hold up hardware development while waiting on software, when one isn't dependent on the other. A new tanker can function just fine without autonomy, or reduced manning. You're holding up production of the 2017 Corvette while waiting for the perfect sound system to come along. It's not justifiable.

2. a. I'm not an AE but I expect it can be modeled then tested. b. Lot's of airspace and ramp space around a tanker. Also reduces wait times for fighters on cap missions or striking time sensitive targets of opportunity. Strike mission of 4 F-35's refueling time cut in half + requires two tankers today increasing airspace and ramp space.

The point remains: how are you going to test an aircraft with two booms without building an aircraft with two booms? Any aircraft you tried to scab two booms on wouldn't be a BWB and therefore the results would be of limited use.

3. Can they build a blended wing this size that meets the load requirements within the weight target or will it end up heavier which cuts into aircraft capability?

How will you know without doing? How do you know what you propose isn't already being worked?

4. 777 has a 10k foot takeoff requirement. NATO spec is for 8k foot runways. Austere is 4k ft.

And? Your comment was about the viability of a 700k twin. You just tacked on shorter runways after the fact, but that really changes nothing. It's a function of lift, drag, and power, all of which can be dealt with.

5. LM provided fuel savings and load info. Provide specs comparing it to C-5 or C-17 for other design expectations like runway requirements, single engine takeoff limits at specific temp requirements, fuel load at max load, etc etc.

See above.

7.LM proposal looks like a C-5 replacement w/tanker thrown in - hence kitchen sink comment. There are divergent requirements for inter-theater lift vs intra-theater lift vs tanker cargo augmentation. It will be incumbent upon the USAF to set requirements and not change them - and not want a 100% solution.

Are the KC-135, 10, 130, and 46 "kitchen sink replacements"? Why would this be any different?

8. Whatever fits the mission. Just want the technology maturity (for whatever particular purpose) to be there prior to getting started on the new airframe.

Powerpoint only takes you so far. A big part of the problem things are so expensive anymore, and progress is so slow, is because we're terrified of risk and would prefer to endlessly navel-gaze. And no, nobody is proposing we be reckless. (Unless you consider those who produced the Blackbird, F-117, 747, XB-70, KC-135, B-52 etc. etc. etc. "reckless"?) The HWB could easily be done with today's technology. The only thing in question is the shape which is being tested with a demonstrator.

 

[lastdingo]

Isn't that still pretty low compared to the RCS of a KC-46 which is probably, what, 100?

Maybe rather 10 sq m.
http://www.globalsecurity.org/military/world/stealth-aircraft-rcs.htm

 

[NeilChapman]

Isn't that still pretty low compared to the RCS of a KC-46 which is probably, what, 100?

Maybe rather 10 sq m.
http://www.globalsecurity.org/military/world/stealth-aircraft-rcs.htm

Guess I figured KC-46 would be closer to B-52 than B-1. Dimensions are similar and it's a wide-bodied jet whereas the B-1 has that nice narrow frontal aspect.

 

[NeilChapman]

There's no reason to hold up hardware development while waiting on software, when one isn't dependent on the other. A new tanker can function just fine without autonomy, or reduced manning. You're holding up production of the 2017 Corvette while waiting for the perfect sound system to come along. It's not justifiable.

Well - that was the plan for F-35.

I disagree with your premise. But I don't hold it against you.

The point remains: how are you going to test an aircraft with two booms without building an aircraft with two booms? Any aircraft you tried to scab two booms on wouldn't be a BWB and therefore the results would be of limited use.

Don't know. If the requirement is formulated such that dual-boom is only for smaller aircraft then it's moot. USAF dual fuels fighters daily today via drogue. Much less critical to dual fuel aircraft on long inter-theater runs.

How will you know without doing? How do you know what you propose isn't already being worked?

That's my point. I hope it is.

And? Your comment was about the viability of a 700k twin. You just tacked on shorter runways after the fact, but that really changes nothing. It's a function of lift, drag, and power, all of which can be dealt with.

Comment was about viability of C-5 size replacement that is part of the Air Mobility Command.

Yep - Hate to have an airframe that, by design, is close to the margins in its ability to meet the mission requirements prior to EMD. Weight tends to grow when providing engineering solutions to problems encountered during EMD. So this includes the engines planned for the aircraft. Engines seem to take the longest to develop. Perhaps it's a no-brainer to scale up a GEnx to 100k lbs of thrust - don't know. I'm sure you're right that it can be dealt with. Rather it's before there's a plane waiting for the solution.

Are the KC-135, 10, 130, and 46 "kitchen sink replacements"? Why would this be any different?

They are primarily tankers w/a cargo augmentation. The aircraft the size of a C-5 is primarily an outsized cargo aircraft. You just can't fill it with enough pallets to get close to it's load capability so maybe adding a tanker capability makes sense. But it may be that it wouldn't be used enough in that context to make it worth the added costs. It may be that it takes up too much space on the ramp. The question is whether it 'works' as a tanker in the AMC model for moving equipment around the world.

Powerpoint only takes you so far. A big part of the problem things are so expensive anymore, and progress is so slow, is because we're terrified of risk and would prefer to endlessly navel-gaze. And no, nobody is proposing we be reckless. (Unless you consider those who produced the Blackbird, F-117, 747, XB-70, KC-135, B-52 etc. etc. etc. "reckless"?) The HWB could easily be done with today's technology. The only thing in question is the shape which is being tested with a demonstrator.

I'd disagree. There is a reality that B-2, F-22 and F-35 all took an extremely long time to produce. Changing specs and co-development are significant factors. US built US$48Billion worth of MRAPS very quickly. B-21 is hopefully a 10 yrs IOC (still too long). I like what's going on today where US is looking around to see how they can reuse existing solutions to meet new requirements.

Critical point is that there are other ways of doing things. Come up with the business case for what's needed and see if you've got the tech to accomplish it. If not, change the strategy of accomplishing the business case and start a program to buy-down the risk on the preferred solution for future development.

Can't wait to see the demonstrator.

 

[Sundog]

It seems to me that this could be one for NG to have the advantage on, by modifying the B-21 into a tanker. It may not be ideal for the specs, but if they can offer it at substantially lower cost due to using a common airframe, since it will be going into production, it would also lower operational costs. BTW, was it Northrop that demonstrated the unmanned hose and drogue refueling technique?

 

[sferrin]

There's no reason to hold up hardware development while waiting on software, when one isn't dependent on the other. A new tanker can function just fine without autonomy, or reduced manning. You're holding up production of the 2017 Corvette while waiting for the perfect sound system to come along. It's not justifiable.

Well - that was the plan for F-35.

I disagree with your premise. But I don't hold it against you.

Cheap shot. The F-35 REQUIRES its software to perform its mission. The software required to perform autonomous refueling needn't be a requirement out of the box. A KC-Z could be a great success without ever getting software for autonomous refueling at all. In other words, apples and oranges. Also orders of magnitude different in complexity.

And? Your comment was about the viability of a 700k twin. You just tacked on shorter runways after the fact, but that really changes nothing. It's a function of lift, drag, and power, all of which can be dealt with.

Comment was about viability of C-5 size replacement that is part of the Air Mobility Command.

Yep - Hate to have an airframe that, by design, is close to the margins in its ability to meet the mission requirements prior to EMD. Weight tends to grow when providing engineering solutions to problems encountered during EMD. So this includes the engines planned for the aircraft. Engines seem to take the longest to develop. Perhaps it's a no-brainer to scale up a GEnx to 100k lbs of thrust - don't know. I'm sure you're right that it can be dealt with. Rather it's before there's a plane waiting for the solution.

The GE90 has been rated at 115k, and used in service on several models of the 777 as such for over a decade. It actually holds the world's record at 128k. Rather than trying to uprate a GEnx to 100k just use a GE9X, which would already be there, and is being developed for the 777X. Considering the C-5A has been successful for most of its life on a grand total of 164k I'm not seeing what the concern is, particularly since an HWB would have much more lift.

http://www.geaviation.com/newengine/

http://www.geaviation.com/commercial/engines/ge9x/

Are the KC-135, 10, 130, and 46 "kitchen sink replacements"? Why would this be any different?

They are primarily tankers w/a cargo augmentation. The aircraft the size of a C-5 is primarily an outsized cargo aircraft. You just can't fill it with enough pallets to get close to it's load capability so maybe adding a tanker capability makes sense. But it may be that it wouldn't be used enough in that context to make it worth the added costs. It may be that it takes up too much space on the ramp. The question is whether it 'works' as a tanker in the AMC model for moving equipment around the world.

Either it would be or it wouldn't be. The fact of the matter is having tanker and cargo capability in the same airframe is nothing new, certainly nothing to be considered "risky".

 

[Ian33]

It seems to me that this could be one for NG to have the advantage on, by modifying the B-21 into a tanker. It may not be ideal for the specs, but if they can offer it at substantially lower cost due to using a common airframe, since it will be going into production, it would also lower operational costs. BTW, was it Northrop that demonstrated the unmanned hose and drogue refueling technique?

NG also did unmanned boom refuelling demonstration. There were pics online a while back on their site.

 

[Mat Parry]

In the public domain NG did some demonstrations with 2 global hawks using a hose and drogue set up. Albeit a reversed situation where the aircraft being refuelled took position upfront & extended a hose and drogue, the plan was that the buddy tanker would insert it's probe into the drogue and pump the fuel forward /uphill to the receiver. (I never figured out the reasons for this set up). As I recall no fuel was actually exchanged

http://www.nasa.gov/centers/dryden/status_reports/global_hawk_status_10_05_12.html

https://www.flightglobal.com/news/articles/darpa-completes-autonomous-high-altitude-refuelling-377447/

 

[NeilChapman]

In the public domain NG did some demonstrations with 2 global hawks using a hose and drogue set up. Albeit a reversed situation where the aircraft being refuelled took position upfront & extended a hose and drogue, the plan was that the buddy tanker would insert it's probe into the drogue and pump the fuel forward /uphill to the receiver. (I never figured out the reasons for this set up). As I recall no fuel was actually exchanged

http://www.nasa.gov/centers/dryden/status_reports/global_hawk_status_10_05_12.html

https://www.flightglobal.com/news/articles/darpa-completes-autonomous-high-altitude-refuelling-377447/

This is an interesting concept. It's been researched (IIRC) in Europe. The basis of the research was to determine what level of fuel savings one would achieve by launching commercial aircraft 'light' for long trips and refuel in the air en route. This keeps the weight down thus the fuel savings. Expectation was for up to 30% fuel savings.

Concept is for traditional USAF boom method, but in reverse - with the receiver above and in front of the tanker.

The receiver would have a drogue type basket extended from the tail and the boom would intercept from below and behind. Tanker would 'fly' the boom into the drogue. Much simpler and likely much safer and requires much less modification to the commercial fleet.

Pretty cool stuff.

 

[Mat Parry]

This is an interesting concept. It's been researched (IIRC) in Europe. The basis of the research was to determine what level of fuel savings one would achieve by launching commercial aircraft 'light' for long trips and refuel in the air en route. This keeps the weight down thus the fuel savings. Expectation was for up to 30% fuel savings.

Concept is for traditional USAF boom method, but in reverse - with the receiver above and in front of the tanker.

The receiver would have a drogue type basket extended from the tail and the boom would intercept from below and behind. Tanker would 'fly' the boom into the drogue. Much simpler and likely much safer and requires much less modification to the commercial fleet.

The set up is almost identical to any commonly used hose and drogue except that the fuel exchange is reversed. I'm surprised at this as I imagine the hose, drogue and reel would be heavier than the probe (note this is not the same as a boom).

Question, Why would the aircraft being refuelled carry all the heavy kit?

(1) Is it to give the tanker more range?
(2) Is the pumping kit that the tanker carries actually quite heavy? (Might have to be a bit more robust due to pumping uphill?)
(3) Are they going for a more equal weight distribution between tanker and reciever, might be an advantage in a buddy refuelling set up ?(which is what this really is)

 

[Mat Parry]

NG also did unmanned boom refuelling demonstration. There were pics online a while back on their site.

Do you recall which platforms were involved, I have only seen speculation & simulation regarding autonomous boom refuelling

http://foxtrotalpha.jalopnik.com/is-this-proof-that-the-us-air-force-can-aerially-refuel-1702048915

http://news.northropgrumman.com/news/releases/northrop-grumman-u-s-navy-test-autonomous-aerial-refueling-for-unmanned-combat-air-system-demonstration

 

[CiTrus90]

The set up is almost identical to any commonly used hose and drogue except that the fuel exchange is reversed. I'm surprised at this as I imagine the hose, drogue and reel would be heavier than the probe (note this is not the same as a boom).

Question, Why would the aircraft being refuelled carry all the heavy kit?

(1) Is it to give the tanker more range?
(2) Is the pumping kit that the tanker carries actually quite heavy? (Might have to be a bit more robust due to pumping uphill?)
(3) Are they going for a more equal weight distribution between tanker and reciever, might be an advantage in a buddy refuelling set up ?(which is what this really is)

I think the answer is more simple: you don't want to maneuver a commercial liner for aerial refueling due to passengers comfort.

This way, the job would be all up to the tanker aircraft and its crew.

 

[Mat Parry]

I think the answer is more simple: you don't want to maneuver a commercial liner for aerial refueling due to passengers comfort.

This way, the job would be all up to the tanker aircraft and its crew.

Thanks for the answer, but Please note I was only discussing autonomous refuelling of 2 global hawks as per NG demonstrations. I didn't bring the commercial airliner red herring to the table. So I'm afraid your answers don't relate to my question

 

[CiTrus90]

I think the answer is more simple: you don't want to maneuver a commercial liner for aerial refueling due to passengers comfort.

This way, the job would be all up to the tanker aircraft and its crew.

Thanks for the answer, but Please note I was only discussing autonomous refuelling of 2 global hawks as per NG demonstrations. I didn't bring the commercial airliner red herring to the table. So I'm afraid your answers don't relate to my question

Oh, I'm sorry. I thought your question was related specifically to that. My bad.
Maybe, in this case, it was just to demonstrate the proof of concept, though.

 

[NeilChapman]

Cheap shot. The F-35 REQUIRES its software to perform its mission. The software required to perform autonomous refueling needn't be a requirement out of the box. A KC-Z could be a great success without ever getting software for autonomous refueling at all. In other words, apples and oranges. Also orders of magnitude different in complexity.

Didn't mean for it to be a cheap shot. Just pointing out that co-development has had it's drawbacks. DoD seems to have been getting away from this process since F-35 and Ford-class.

The GE90 has been rated at 115k, and used in service on several models of the 777 as such for over a decade. It actually holds the world's record at 128k. Rather than trying to uprate a GEnx to 100k just use a GE9X, which would already be there, and is being developed for the 777X. Considering the C-5A has been successful for most of its life on a grand total of 164k I'm not seeing what the concern is, particularly since an HWB would have much more lift.

http://www.geaviation.com/newengine/

http://www.geaviation.com/commercial/engines/ge9x/

Great news.

Either it would be or it wouldn't be. The fact of the matter is having tanker and cargo capability in the same airframe is nothing new, certainly nothing to be considered "risky".

It's important for the USAF to determine how they want to augment the current capability of the AMC. If they want a replacement for the C-5, great. Build a replacement for the C-5.

For reasons mentioned in prior posts a KC replacement that carries much more fuel than the KC-46 would be helpful as the KC-10's start to age out in 2040. That aircraft doesn't need to be stealthy nor fly into austere airfields. It would be great if it were dual boom for low threat air cap support but it's less necessary for inter-theater flights. If the USAF feels differently then I'd hope they will help us understand that new requirement. They typically do a good job of that in congressional hearings.

I definitely see a potential need for 'more stealthy' intra-theater C-17 sized transport that will fly into non-traditional, makeshift, austere airfields as A2/AD areas are expanded. But I don't see it rising to a critical need. There are lot's of ways to provide C-17's with more protection w/o a new airframe - and - they are generally in pretty good shape today.

But because of the USAF requirement for air supremacy in its battleplans my immediate concern is for a 'very stealthy' tanker in support of its current fleet of fighters and bombers, including B-21 in high threat environments. With B-21 in EMD, it's expected sensor, network, and data fusion capabilities, along with an ability to conduct electronic warfare and surveillance, to me, this is an obvious choice for a tanker variant in the 2025-2030 timeframe.

Just my opinion.

 

[NeilChapman]

I think the answer is more simple: you don't want to maneuver a commercial liner for aerial refueling due to passengers comfort.

This way, the job would be all up to the tanker aircraft and its crew.

Thanks for the answer, but Please note I was only discussing autonomous refuelling of 2 global hawks as per NG demonstrations. I didn't bring the commercial airliner red herring to the table. So I'm afraid your answers don't relate to my question

Sorry Mat et al. - didn't mean for it to be a red herring. When you mentioned the reverse refueling it reminded me of the 'other' reverse refueling research. I mentioned it only as an 'interesting aside'. Probably should have sent that as a message instead of a post.

 

[sferrin]

Didn't mean for it to be a cheap shot. Just pointing out that co-development has had it's drawbacks. DoD seems to have been getting away from this process since F-35 and Ford-class.

Again, apples and oranges. A bit like saying we should have not produced the F-16 until the AIM-120 was ready because "co-development is bad". One has very little to do with the other.

 

[marauder2048]

Didn't mean for it to be a cheap shot. Just pointing out that co-development has had it's drawbacks. DoD seems to have been getting away from this process since F-35 and Ford-class.

Again, apples and oranges. A bit like saying we should have not produced the F-16 until the AIM-120 was ready because "co-development is bad". One has very little to do with the other.

What exactly would need to be co-developed for the HWB? I would think the greatest risk (after control laws) would be
achieving good STOL performance without the C-17's externally blown flap; the LM guys have some ideas from CCW to various forms of TVC.

 

[sferrin]

What exactly would need to be co-developed for the HWB? I would think the greatest risk (after control laws) would be
achieving good STOL performance without the C-17's externally blown flap; the LM guys have some ideas from CCW to various forms of TVC.

Or just a huge lifting surface.

 

[marauder2048]

What exactly would need to be co-developed for the HWB? I would think the greatest risk (after control laws) would be
achieving good STOL performance without the C-17's externally blown flap; the LM guys have some ideas from CCW to various forms of TVC.

Or just a huge lifting surface.

It wasn't clear to me how much lift the forebody generates at high AoA.
It's not inconceivable that conventional high lift devices would enable it to meet the STOL requirements
but the LM paper spends some time on dedicated powered lift systems.

 

[Flyaway]

Not only must it be stealthy but it also has to fire lasers as well.

http://m.aviationweek.com/defense/us-air-force-wants-stealthy-laser-shooting-next-gen-tanker

 

[CiTrus90]

Not only must it be stealthy but it also has to fire lasers as well.

http://m.aviationweek.com/defense/us-air-force-wants-stealthy-laser-shooting-next-gen-tanker

For the life of me I can't understand why that would make sense in their opinion.

As I wrote 2 pages ago, just having dedicated Laser Interceptors flying in protection of the Tankers could solve the issue, with a sort of aerial Aegis system, without the need to make overly complex "stealth-airborne laser-tankers".

Stealth is not magic, you can't just say "we need a stealth tanker, and while at it make it capable of this, this and that".

Tankers, cargos and AWACS, at large, are not survivable assets, and will probably never be. They need to operate in safe areas as long as air superiority and the removal of A2/AD are not established.

If the enemy defenses range increases, the focus should be on changing tactics or adapting technologies in a reasonable way to get around a problem, not on creating a panacea/miracle aircraft to operate as in previous air-campaigns (and for the time being, "waiting" till that happens).

Moreover, there is no way a stealth-tanker could be reasonable from a cost-effective point of view, with 2 of its main capabilities (stealthiness and laser defences) that will be of use only in conflict.

And, once more, if radar developments catch up before a stealth-tanker reaches IOC we're back to square one, with a large aircraft which, at that far point in the future, may even have laser defences on board, but which stealthiness would be pretty much useless (unless, in the meanwhile, that too doesn't make exponential advancements, like being cheaper for example).

The people making the choices should ask themselves: "Is the problem now, in 10 years or in 60 years?".

Throwing ideas around is fine for creating a fertile environment, able to come up with solutions, but certainly not for much else.
"Be open-minded, but not so much so that your brains fall out".

 

[Sentinel36k]

The stealth tanker isn't all that new of an idea, this strike tanker wind tunnel test is from the airforce in 2005.

Sentinel

 

[Mat Parry]

http://m.aviationweek.com/defense/us-air-force-wants-stealthy-laser-shooting-next-gen-tanker

"The KC-Z would likely come online in the 2030-40 time frame"

How does this compare with production schedules for B-21? Gut feeling, this indicates that they aren't considering a B-21 based solution.