Obscure Harrier variant: MiniCAS for USMC

stever_sl

stever_sl

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Back in the late 1980s or early 1990s (my hard drive failed a couple of months ago and I haven't been able to reconstruct all of my records) I was working in the general area of AV-8B, and specifically its vulnerability to combat damage. The USMC came to us and asked what would be the smallest, hardest (in a vulnerability sense) AV-8B variant that was technically feasible by the year 2000. The word "smallest" became very important, as it turned out, because in order to make the Harrier any less vulnerable we knew that we'd have to add a significant amount of weight, which wouldn't be possible with the current Pegasus engine, and we couldn't use a new engine because that would add billions of development dollars that the Marines simply didn't have, so if any way could be found to reduce the size of the aircraft, we might find some offsetting weight savings.

We had just finished doing the AV-8B vulnerability analyses by hand, which involved looking at a lot of drawings of the AV-8B and its subsystems, and it occurred to me that the only major thing in the entire aft fuselage was some sort of electrical panel (relays maybe? it was a long time ago) and it (they?) could easily be relocated, leaving an empty space whose only purpose was to provide structural support for the tail surfaces. Cut all of that away, fair off the back end, move the horizontal tails in front of the wings to become canards, borrow new vertical tails from F/A-18s, and an interesting-looking canard-delta(ish) configuration emerged. We knew we could get more engine thrust if we had longer inlet ducts, so those got pushed forward which gave us the space we needed to mount the canards. At the time, the Marines were pretty vocal about not liking the AV-8B's 25mm gun, so that got tossed and replaced with the 4-barrel version of the A-10's 30mm gun. There wasn't room for it internally so it went under the belly, but that got in the way of the nose landing gear, and the additional loss of the location for the main landing gear led to a beefing up of the wing structure so that the outriggers became essentially main landing gear housings. I built a model to show the concept, our manager took it on the road, it generated enough interest to do more work on the configuration, but ultimately it didn't go forward. I still have the model on my shelf, and the company took this one photo to document the idea. Just thought any Harrier variant geeks might get a kick out of it.

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The rear fuselage was never the ideal place for avionics though, the thermo-acoustic fatigue from the rear nozzles was always a problem to some extent.
This concept looks pretty ungainly but there was some merit to the idea I think, certainly with refinement it might have worked. Wind tunnel tests might have revealed a few snags I dare say.
 
lastdingo said:
By the look of it I say hot air ingestion killed it.

Besides, the AV-8 tail was far from empty. Many small things incl. black boxes and antennas were in there.
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Moving the inlets forward would have helped the hot air ingestion, actually, from what I can recall. And the only things in the back end apart from those panels were some small ECM bits, the pitch/yaw RCS and its piping, the control linkages for the rudder and stabilators, and the chaff/flare dispensers. All of that would have been relocated forward with no problem, we really did know what we were getting into and had expert designers and systems integrators on board with MiniCAS. One of the most fun projects I ever worked on, and most unusual.
 
Hood said:
The rear fuselage was never the ideal place for avionics though, the thermo-acoustic fatigue from the rear nozzles was always a problem to some extent.
This concept looks pretty ungainly but there was some merit to the idea I think, certainly with refinement it might have worked. Wind tunnel tests might have revealed a few snags I dare say.
Click to expand...
You're so right about avionics but they had to go somewhere. There was literally no room for them further forward, and further back they would have caused c.g. problems. Like all aircraft, AV-8B was the embodiment of compromises, and MiniCAS would have had to face the same sort of decision-making process. With the advantage of hindsight, some of the things that we later looked at for Harrier III might have worked very well on MiniCAS, such as the dorsal "bump" idea that we borrowed from A-4M as a place to move the avionics to while keeping them close to the center of the aircraft. But we never got that far along before everything was shut down.
 
I don't really understand how it balances in the hover with engine right at the back. Isn't the CG further forward than the front nozzles?
 
lastdingo said:
By the look of it I say hot air ingestion killed it.

Besides, the AV-8 tail was far from empty. Many small things incl. black boxes and antennas were in there.
Click to expand...
This begs the obvious question. Are you saying that all of the above can only be housed in the original single vertical? I think not.
 
stever_sl said:
With the advantage of hindsight, some of the things that we later looked at for Harrier III might have worked very well on MiniCAS, such as the dorsal "bump" idea that we borrowed from A-4M as a place to move the avionics to while keeping them close to the center of the aircraft. But we never got that far along before everything was shut down.
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Sounds like the Harrier III had more sensible way to change the engine other than taking the wing off!
 
red admiral said:
I don't really understand how it balances in the hover with engine right at the back. Isn't the CG further forward than the front nozzles?
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All I can tell you is that our analyses showed that it would work. It's been too long ago for me to remember details, and since it never progressed beyond concept feasibility work, in the pre-digital age, everything would have been on paper and nothing would likely have been saved.

It's just sheer luck that the model itself still exists. I built it, McDonnell Douglas made the base for it and a lovely little fitted box to put it in for taking around and showing to people. When it was decided to drop it, the deputy program manager wanted to keep the model for his office but agreed that it was my property, so he offered me the cost of the 2 kits that I bashed to create it - about $10 if memory serves! He said that was all I'd spent on it myself, so it was a fair offer in his opinion. Mind you, this guy drove a classic old Rolls Royce to work, but he wouldn't budge on the price, so I took the model back. He wouldn't, however, let me have the box that was specially fitted for carrying it, because the Company had paid for that! It's kind of a miracle that he didn't think of applying that same logic to the stand. :)
 
Hood said:
Sounds like the Harrier III had more sensible way to change the engine other than taking the wing off!
Click to expand...
Harrier 21 certainly did, because it had a completely different core packaging design. The other 2 levels of Harrier III - I just can't remember. I think they were still "wing off" but I know that other options were explored, just not by the part of the group that I was in. The problem is that the engine is so big that there's no way to jack the aircraft itself high enough to drop it out the bottom, and the fuselage tapers enough in the midbody area to make it impossible to slide out the back even if you arranged a fuselage break back there somewhere, not to mention that big aft fuel tank and the saddle tanks to the sides. A whole new fuselage would probably have to be designed and our tiny little Advanced AV-8 group didn't really have the resources to do that - or the charter to create basically an all-new aircraft, as the ASTOVL group eventually reminded us.
 

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