I've been thinking about this since the abduction of the British sailors, it would be good to have a stealthy transport, even if it was just a light transport such as the Osprey for covert insertion and extraction. You'd want VTOL capability though, so more powerful lift fans would be needed, but that doesn't seem like such a big problem, compared to making a tilt-rotor stealthy.

I wonder just how stealthy you could make a transport?  If you could,  I'm not convinced the military could afford to build such craft for limited purposes.  Much as I like the idea of the lift-fan as the future successor to the tilt-rotor, I'm just not convinced its worth the money required to make it stealthy. I suspect for the time being, they'll just have to fly low. Some of the pics I've seen of the V-22 show it flying very low in "fixed wing mode".  I suspect this will be their "stealth" capability.  (note: this makes me wonder what the V-22's minimum altitude is for transition from horizontal to vertical?)

Making a transport stealthy shouldn't be that much harder than making a fighter stealthy. The bulk of the body might preclude getting its RCS as low as a fighter but some stealth is always better than none at all. It would probably be more practical to make the aircraft large enough for airborne operations, where stealth might be more advantageous. Still probably not going to happen. But fun to fantasize about.

I agree with the concept of a stealthy STOVL transport.  I too recall reading about the possibility of using an F-35B as the basis for a stealthy transport-although I doubt it is anything more than concept at this point.  In fact, it has a lot of favorable points over the current Osprey.

 

1) Mature technology.  We've been using SVTOL tech for decades, whereas the tilt-rotor technology is relatively new and still has bugs to be worked out.  At best tilt-rotor will be expensive and unreliable until the technology matures.

 

2) More capable-a jet powered transport will be far more capable/survivable than any tilt-rotor.

 

3) Stealth--the aviation technology of the future is stealth.  Tilt-rotor aircraft are not a design suitable for stealthyness (except if they fly low, under the radar, but close to ground fire).  Whereas we already know that stealth and STOVL is compatible with stealth.

 

4) Cost--because the aircraft could be piggy-backed on the JSF program and the technology is more mature, development costs would probably be less, even as the capabilities are better.

 

The main counter-argument to stealthy transports is that transports are not supposed to go in harm's way until the hot-shots have cleared things up, and thus don't need expensive stealth tech.  History has shown that's not true.  Transports go into harm's way all the time.

This idea is insane.  There are actually reasons we don't strap jet engines on assault support aircraft.  Do you think there's really an engineer at Boeing slapping his forehead and saying,"Damn, why didn't I think of that?!?"

 

V/STOL aircraft and rotorcraft/tiltrotors do not manuever in the same manner during a verical landing.  Rotorcraft work via tilting the rotor disk, and in the case of the Osprey, differential pitch.  V/STOL aircraft, like the Harrier, use their normal airplane controls augmented by tip jets.  The difference is like balancing a ball on top of a plate vice a pencil.  Note how controlled a Harrier's descent is vice a helo's.  A Harrier's wind envelope is very restrictive.

 

Vectoring the thrust of a jet is difficult, and results in a huge loss of efficiency--witness the use of a shaft-driven fan as a vertical lift element in the JSF.   Shaft-driven fan to proprotors isn't a big leap.  Within its inherent speed limitations, a turboprop, or variant thereof, is the most efficient way to turn JP5 into energy into airflow.  In addition, ground effect will not help a jet until it is going fast enough for wing-borne lift, whereas it is a huge player in the low-altitude regime where assault supports live. 

 

These concerns are on top of the fact that a jet-driven assault transport would suck vast amounts of fuel and turn LZs into brush fires, not to mention that turbofans are FOD magnets and LZs tend to have more than a little of same.  The Harrier is expeditionary on prepared surface runways only.  For example, when they landed in Kandahar, they shut down on the runway and were towed to the line to avoid FOD.

 

V/STOL is not a mature technology by any means.  Only now is a V/STOL aircraft even coming remotely close to the performance of conventional strike aircraft, and that's by using new innovations to make it happen.

 

 

I don't believe you'd simply strap a couple of F-35B's on the side of a transport hull. The F-35 deflects its tail exhaust down - you'd fry all your troops with the fires it would start.  Instead I'd envision just using the F-35's ducted fan, with at least 4 to 6 of them. Finding the engine to drive them would be interesting. Additionally you'd still have to find forward thrust and probably use clutches on fans etc.  I don't think you'd want to tilt the fans as now you're into the V-22's issues.

 

You're into quite a design. Throw stealth into the mix and you're into a whole lot of money. I'd still like to see at least a non-stealth demonstrator - maybe start out using a CH-47 fuselage.  But then Lockheed has already talked about using the lifting fan for something like this. I however doubt its gotten much farther than talk.

The lift-fan from the F-35B generates something like 20,000lbs of lifting thrust (when some 20,000hp is applied to its clutched drive shaft). An empty CH-47 is something like 24,000lbs empty, with a max load of something like 50,000lbs for a net max cargo and fuel load of about 26,000lbs.  If you could strap 4 of the F-35B's lift-fans on a CH-47 body, and say add only 15,000lbs in additional engine and fan weight, your weight empty weight should be around 40,000lbs, but you might have 80,000 lbs of lift - giving you approximately 40,000 lbs of cargo and fuel capacity.  Thats vs 26,000lbs  for the CH-47. Not too shabby. 

 

Of course you're going to have figure out what turboshaft engines to use. The CH-47 currently uses 4000 shp turboshafts. IIRC, the F-35's lift fans can get something like 25000shp from its engine. You might need every ounce of that extra 14,000 lbs of capacity for fuel.

 

Admittedly its 3rd grade arithmetic and design, but Lockheeds lifting fan is amazing. I believe Lockheed was proposing only two of them (one in each wing) for the light transport they had in mind. 

...than strapping a couble of F-35B style engines on a chopper airframe.  But it isn't rocket science.

 

With enough power a milk truck will fly.

 

The principle is sound.  If you can build a VTOSL fighter, you can build a cargo plane.  The fighter is far more technically complex.  Granted, it won't be as fast or sleek as a fighter, but it will fly.  The same is true for stealth.  It doesn't have to be C-17 sized (as we know from the V-22). 

Fine.  Physically possible perhaps.  A rocket-propelled HMMWV or a nuclear-powered toothbrush are also possible, but impractical and a poor use of resources.

 

Radar is not the primary threat to assault aircraft.  IR MANPADS and small-arms are.  Even accepting the theoretical possibility of a jet-powered assault, you're introducing a level of complexity far beyond even the Osprey to solve a corner case.  If I have a radar threat to contend with, I'm better off saturating the area with electronic attack aircraft and HARMs than spending a gajillion dollars to build a stealth assault aircraft.  I'm just not going to insert a company of Marines deep behind the FEBA alone and unafraid, and the movie-style secret mission inserts of SOF hundreds of miles behind the lines aren't really all that common, either. 

 

In a low-threat environment, the current inventory of special operations aircraft are more than sufficient.  In a high threat environment, I'm not going to put a team 500 miles inside of China or North Korea on a suicide mission.  9/10s of special ops is surveillance and reconaissance, and there are more practical means of doing it in that circumstance.  The secret raids to strap a satchel charge on a headquarters building are a Hollywood invention.

 

Outside the box thinking is great, but a lot of the ideas I see on this site are kind of Walter Mitty-ish, or perhaps While E. Coyote-ish.  ACME products, anyone?

I can accept the argument that transports don't operate in high risk areas (by doctrine) and thus don't need to be high speed or stealthy.  But we aren't just talking about heavy transports here.  Rather than a stealthy, VTOSL C-17, I'm talking about more of a stealthy, jet powered UH-60. 

 

How many US choppers have gone down in Iraq and Afghanistan?  Choppers suffer from a number of fatal flaws:

 

1) They can only operate at low altitude

Most choppers operate at 8500 feet or lower, which is within range of MANPADs.  Moreover, there are environments where this limits what they can do--places like Afghanistan and Colombia where there is a need for choppers because of the poor transportation infrastructure, but the high mountains limit what they can do and where they can go.  For example, choppers have to be specially modified just to operate in Bogota, which is at 8500 feet.  They're at the limit of what they can do.

 

2) They're slow.

This makes them easy targets for even small arms.

 

3) They aren't getting any better.

Today's choppers are tougher than past ones and can carry more weight, but they aren't that much better than they were in Vietnam.  The technology just does have much room for improvement.  Ospreys are a step up, but not a huge improvement.

 

Okay, so let's look at the cost.  An Osprey costs $100 million (or more) each.  That's more than a modern supersonic fighter.  A C-17 costs $180 million.  And a C-130 costs $160 million each in spite of the efficiencies of about the largest production run of any military transport.  Air transports are just plain expensive.

 

So could you produce a tactical stealthy VTOSL transport for $100 million a piece?  Without a doubt.  It's only a matter of making the commitment. 

 

But is it worth doing?

 

Obviously, you don't need if for flying troops long distances to friendly places.  And admittedly the stealth aspect wouldn't be much use in a low-intensity conflict like Afghanistan or Iraq.  But the ability to fly at high altitude (out or range of small arms and MANPADs) at faster speeds and longer distances would be useful.  And the stealth would be useful in a high-end conflicts or for covert operations.

 

Okay, for the sake of argument, let's drop the stealth.  That will make it cheaper.  Do you think it's worth doing then?

 

One would think that the lift-fan cargo craft - would have a lower RCS than the disk of a heli or V-22.  Maybe some additional RCS mitigation could be possible, but in the end the cargo craft is large. However, Lockheeds proposal suggested lift-fans IN the wings. Could this imply some sort of small BWB to accomodate the thickness of the fan?  Given Lockheeds stealth expertiese, they might be thinking stealthy already.

 

Wouldn't it be most useful to reduce the IR signature as IR MANPAD's probably represent the greatest threat to any VTOL?  Helicopters use various techniques for this already as their engines are on the top of the fuselage. The V-22 would seem to have a huge IR sig, pointed right to the ground when in VTOL. On the lift fan, if the fans are close to the body, they might actually help hide the engine IR exhaust signature when viewed from below.