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Author Topic: Air Force Could Pursue Stealthy Aerial-Refueling Tanker  (Read 26321 times)

Offline marauder2048

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #30 on: September 23, 2016, 01:08:58 pm »
I think most of the blended wing body proposals (that the AF has funded at least) have had notional tanker variants.

Offline sferrin

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #31 on: September 23, 2016, 03:48:48 pm »
The obvious solution is right here.  Tanker, transport, and cruise missile carrier, all in one.  And cheaper than a "stealth" tanker. 
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Offline NeilChapman

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #32 on: September 23, 2016, 05:56:57 pm »
The obvious solution is right here.  Tanker, transport, and cruise missile carrier, all in one.  And cheaper than a "stealth" tanker.

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.

Ran some numbers and a C-17 would be >~US$300Million including EMD costs in 2016 dollars.  Can't expect the LM design to be any less expensive in acquisition. Sounds like operational costs would be dramatically reduced though.

Don't see it going into a high contested area to bring back a receiver though.  Still see a need for a stealthy tanker (with a boom) in the 2025-2035 - if - the A2/AD projections are correct.


Offline bobbymike

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #33 on: September 23, 2016, 11:07:55 pm »
The obvious solution is right here.  Tanker, transport, and cruise missile carrier, all in one.  And cheaper than a "stealth" tanker.
And a couple hundred AMRAAMs or longer range next generation AAM cause you have lots of space now.
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Offline kaiserd

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #34 on: September 24, 2016, 12:30:03 am »
Realistically if we are talking about really survivable tanker assets to refuel in high-level contested airspace there will be the need for a multiple platform approach, while being realistic about what can be achieved.

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). Not a perfect solution but part of a workable affordable solution.

A B-21 capable of refuelling a B-21 could also refuel smaller fighters but apart from relatively one-off specific missions not sure of the wider role/ utility as a more general tanker (B-21 not that big an aircraft, considerably smaller than a B-2 and with much smaller fuel load than an actual tanker aircraft - not much fuel to give away). Hence only likely to be a small niche player as a tanker.

As the range and capability of air defences improve there is an argument for making a whole range of aircraft filling a range of roles (transport, tanker, AWACS, CnC, ASW etc) more survivable so can enter future less-contested airspace. However the cost and technical challenges behind really pushing for high levels of survivability makes this a laudable but probably unrealisable goal - no one (not even China or the US) likely to prioritise this aspect, will just be another factor deterring peer powers from actually going to war with each other.
« Last Edit: September 24, 2016, 12:44:59 am by kaiserd »

Offline TomS

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #35 on: September 24, 2016, 03:37:10 am »
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.

Offline kaiserd

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #36 on: September 24, 2016, 04:30:28 am »
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.

All reasonable points.
As stated above I appreciate it wouldn't be a perfect solution but considering the very low likelihood of any significant numbers of stealthy survivable tankers (with flying booms) ever being fielded then equipping at least part of your future deep strike force with both types of refuelling probes (and be able take fuel from Navy tankers too) has the advantages of at least being technically achievable and affordable.
And the buddy tanker would be more survivable than any likely new boom-equipped stealthy tanker/transporter.
All in all a solution scaled to the need (capability needed to help deter a major peer war but recognising the low likelihood it will be needed and if it is it won't be for long,  given likely nuclear escalation if not ended rapidly).

Offline r3mu511

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #37 on: September 24, 2016, 06:27:53 am »
- 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...

Offline AeroFranz

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #38 on: September 24, 2016, 07:53:08 am »
I appreciate the effort to put numbers to this - by the way, i had yet to see expressions like the ones you used in the discussion of RCS, this is very useful! The example doesn't make it sound too bad...
But just wondering if this (of necessity) simplification takes into account radar bouncing off one of the vehicles onto the second one. After all the majority of the signature reduction measures aim first and foremost at redirecting energy somewhere other than at the emitter. It seems like with multiple objects in close proximity you're going to have a hard time controlling unintended spikes. Granted, two bounces are going to decrease the amount of energy re-emitted, but I wonder if you don't unintentionally end up with an air vehicle formation which forms a corner reflector.
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Offline sferrin

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #39 on: September 24, 2016, 08:48:18 am »
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. 
« Last Edit: September 24, 2016, 08:51:33 am by sferrin »
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Offline sferrin

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #40 on: September 24, 2016, 08:53:12 am »
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.)
"DARPA Hard"  It ain't what it use to be.

Offline r3mu511

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #41 on: September 24, 2016, 09:21:54 am »
@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...

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #42 on: September 24, 2016, 12:33:07 pm »
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.

Offline Mat Parry

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #43 on: September 24, 2016, 02:35:58 pm »
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!


Offline NeilChapman

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Re: Air Force Could Pursue Stealthy Aerial-Refueling Tanker
« Reply #44 on: September 24, 2016, 02:56:18 pm »
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.