Harrier and Sea Harrier

[Thorvic]

Your probably better looking at modernising the P1216 with newer composites, engine, avionics and software as the design process basically addressed the issue and limitations of the Harrier design.

To be honest in hindsight they would have been wiser to look at revemping the P1216 using systems and software common with the JSF for the USMC/UK and let the USAF/USN develop a common stealth Strike fighter without the design restrictions of making it STOVL.

[Weaver]

Your probably better looking at modernising the P1216 with newer composites, engine, avionics and software as the design process basically addressed the issue and limitations of the Harrier design.

The revised shapes that lead to the P.1216 configuration were driven by the desire to make it a supersonic fighter, which meant that the high-energy exhaust gas had to be separated from the fuselage to avoid trashing the latter with acoustic damage. What I'm considereing is something different: a pure, subsonic attack/close support aircraft with no attempt at supersonics or any air-to-air capability beyond self-defence. Essentially, the same operational requirement as the Harrier, but issued in the 21st century.

To be honest in hindsight they would have been wiser to look at revemping the P1216 using systems and software common with the JSF for the USMC/UK and let the USAF/USN develop a common stealth Strike fighter without the design restrictions of making it STOVL.

Given the P.1216 timeframe, they could have given it common avionics with the Eurofighter and had it in service at about the same time or sooner. Hell, getting it in service with Blue Vixen in 1990s would have been possible with a serious effort...

[kitnut617]

A comment on the thread about the new Aussie LHA got me wondering: what would happen if you kept the Harrier's concept and layout (proven to work) but re-designed it from scratch using the latest materials and systems?

Thoughts? Ideas?

I had exactly the same thoughts some time ago Harold only mine would be supersonic, it's taken a back seat again but here's the build so far:

http://www.whatifmodelers.com/index.php/topic,33379.0.html

[Hobbes]

The latest Pegasus produces up to 23,800 lbf (106 kN). The engines designed for the JSF show what can be done with a modern engine:
F-35B:

The STOVL variant, F135-PW-600, delivers the same 43,000 lbf (191 kN) of wet thrust as the other types in its conventional configuration. In STOVL configuration, the engine produces 18,000 lbf (80.1 kN) of lift thrust. Combined with thrust from the LiftFan (20,000 lbf or 89.0 kN) and two roll posts (1,950 lbf or 8.67 kN each), the Rolls-Royce LiftSystem produces a total of 41,900 lbf (186 kN)

The Boeing X-32 had an engine with a simpler configuration: two front nozzles and a swiveling rear nozzle, similar to the Pegasus.
This produced much less power (when comparing dry thrust), but at a lower weight: Boeing estimated the VTOL components added 700 lb/300 kg, while the F-35 LiftSystem adds 4000 lb/1800 kg.

F-119 Dry thrust: 28,000 lbf (125 kN)
    Thrust with afterburner: 43,000 lbf[11] (191 kN)

The biggest limitations of the Harrier were lack of thrust, aerodynamics unconducive to supersonic flight (mainly due to the massive intakes) and heat/vibration issues in the rear fuselage due to the exhaust from the hot nozzles. The P.1216 layout was one way to fix the heat/vibration issues, but the JSF has shown that a less extreme solution with the main exhaust at the aft end of the fuselage also works.

If you were to install the F-35 liftfan horizontally ahead of the main engine, with swiveling nozzles, you'd get an installation similar to the Pegasus with 42 klb/186 kN of dry thrust.

[PR19_Kit]

The F-135 is considerably larger than a Pegasus and with the lift fan mounted with its axis common to the main engine it's be a larger, fatter engine too, the fan is HUGE! Mounted like that flying supersonic would probably be out of the question which could add weight to the original thread idea.

[sandiego89]

I like weavers idea, and have also thought about it myself- strictly sub-sonic with a big, high-bypass modern tubofan. Two or maybe four large side swiveling nozzels for the cold exflux, and perhaps a single hot nozzle, like the yak-141 layout. Yes it would be a plumbing nightmare and be very thick in the middle. The latest 737/320 engines produce about 27,000 lbs and have a 61 inch fan diameter, with the next gerneration looking at 69 inch or 78 inch fans from CFM with up to 28,000 to 32,000 lbs of thrust and more. Others from GE and Pratt and Whitney. This compares to the latest pegasus engines with 23,800 lbs and a 48 inch diameter.

A really fat harrier, yes it would be a very compromised design, but i like it. 

[rickshaw]

A comment on the thread about the new Aussie LHA got me wondering: what would happen if you kept the Harrier's concept and layout (proven to work) but re-designed it from scratch using the latest materials and systems?

The first thing I'd do is make it bigger. The size of the Harrier was governed by the size of the engine, which was in turn governed by the fact that it was derived from pre-existing components: an Orpheus gas generator and an Olympus fan. The available thrust limited useful payload to the point where early prototypes could only just take off carrying nothing, and payload/range has always been the type's weakest feature. High-bypass turbofan technology has moved on in leaps and bounds since then, so basing an all-new Harrier around a completely new, modern and bigger engine, together with a lightweight all-composite structure should give a much larger disposable load, which could be used for fuel or weapons. It wouldn't be any faster because the net exhaust gas velocity would still be low due to half of it being bypass air, but we've long got past the early-'60s idea that attack aircraft have to be supersonic.

Thoughts? Ideas?

Could work.  However, building a Harrier with a bigger turbofan would inevitably lead to a bigger aircraft and that would bring associated drag problems.  If you design it purely to be sub-sonic, as effectively a bomb truck, it could work.  It would mean sacrificing supersonic performance but I wonder how often Harriers have ever really been able to fly faster than Mach 1 except in a steep dive when carrying a full load?  One of the big commercial turbofans would work, I believe.  If you mixed some of the cold fan air with the hot core air, you'd be able to keep it's temperature lower and hence eliminate one of the problems all the attempts to put a more powerful engine in a four poster design like the Harrier encountered (P.1154, etc.).

Modelling this would be difficult though.  Does anybody know of a say a 1/60 scale Harrier kit?  Otherwise you'd need to go from scratch.  If you're doing it from scratch, then you may as well go for a P.1214-15-16 design, which had superior performance anyway.

[Weaver]

There seems to be an idea here that the Harrier's lack of supersonic performance is down to "drag" from it's massive intakes. This is wrong, or rather it's describing the symptom, not the cause. The problem is not caused by the size of the intakes per se, it's caused by what happens to the air after it goes into them. Half of that air ONLY goes through the fan, not the core of the engine, so it only gets a modest "push" and this is the real problem: the net exhaust velocity of the whole aircraft is too low. It doesn't matter how many cubic meters of air per second you flow through the engine, it still won't fly forwards faster than the exhaust is coming out backwards. Put it another way: if an aircraft had the same size intakes as the Harrier, but with something like an SR-71's J58 behind them, it'd be plenty fast....

[Weaver]

Here's a thought, based on things that Kit and sandiego89 have posted:

An excessively wide fan would indeed be a problem, not becase of intake drag (see last post), but because it would force the fuselage in front of it and behind it to be excessively large. So, what about two fans, side-by-side? You use something like the F-135, but instead of the clutch, you have it permanently driving two horizontally-mounted fan in front of it. Some of the fan air is ducted into the engine, and the rest goes into vectoring front nozzles. It still has the "flat fall" failure case advantage of a single engine, but it has a packaging form factor more like a twin.  

[rickshaw]

I assume these lift fans would be in tandem, rather than side-by-side?   Would still make for some interesting plumbing.  Also the use of two gear boxes to drive them would increase likelihood of a failure.  However, it has potential.  I'd still prefer one, large fan.  It would require a broad flat fuselage but that could lead to advantages in the form of either internal weapons bays (for stealth) or forward lift, from a suitably shaped fuselage, thereby reducing the wing area and therefore drag.

I've been looking at commercial turbofan sizes and the IAE V2500 is clearly the winner here, with up to 35k lbs thrust in it's most powerful version, with a 1.6m fan diameter, which is larger than the 1.2 of Pegasus but not exorbitantly so.

[PR19_Kit]

I've been looking at commercial turbofan sizes and the IAE V2500 is clearly the winner here, with up to 35k lbs thrust in it's most powerful version, with a 1.6m fan diameter, which is larger than the 1.2 of Pegasus but not exorbitantly so.

The larger CFM56s come very close to those figures, the -5C4 version used for the A340 in particular.

[Weaver]

I assume these lift fans would be in tandem, rather than side-by-side?   Would still make for some interesting plumbing.  Also the use of two gear boxes to drive them would increase likelihood of a failure.  However, it has potential.  I'd still prefer one, large fan.  It would require a broad flat fuselage but that could lead to advantages in the form of either internal weapons bays (for stealth) or forward lift, from a suitably shaped fuselage, thereby reducing the wing area and therefore drag.

I've been looking at commercial turbofan sizes and the IAE V2500 is clearly the winner here, with up to 35k lbs thrust in it's most powerful version, with a 1.6m fan diameter, which is larger than the 1.2 of Pegasus but not exorbitantly so.

Nope, you've misunderstood me: they're not "lift fans", they're turbofan fans with vectoring nozzles behind them. Put it this way: what you'd really like is an oval fan, thats wider than it is high, but that's technically impossible, so the next best thing is a pair of smaller circular fans side-by-side.

[sandiego89]

I assume these lift fans would be in tandem, rather than side-by-side?   Would still make for some interesting plumbing.  Also the use of two gear boxes to drive them would increase likelihood of a failure.  However, it has potential.  I'd still prefer one, large fan.  It would require a broad flat fuselage but that could lead to advantages in the form of either internal weapons bays (for stealth) or forward lift, from a suitably shaped fuselage, thereby reducing the wing area and therefore drag.

I've been looking at commercial turbofan sizes and the IAE V2500 is clearly the winner here, with up to 35k lbs thrust in it's most powerful version, with a 1.6m fan diameter, which is larger than the 1.2 of Pegasus but not exorbitantly so.

Nope, you've misunderstood me: they're not "lift fans", they're turbofan fans with vectoring nozzles behind them. Put it this way: what you'd really like is an oval fan, thats wider than it is high, but that's technically impossible, so the next best thing is a pair of smaller circular fans side-by-side.

I get it Weaver and like the idea, and have thought about that also- what Weaver is proposing is the first stage compressor- the fan you see looking at the front of a jet engine, actually being two first stage compressors coming off a singe engine core.  So two smaller first stage compressors, merging into a single core.  The majority of the cold bypass air would then go to both sides of the core where it could be thrust vectored, with some air from each compressor going to the common core- feeding the hot section with air.  Compressor aft of the hot section drives a shaft that goes back forward to spin the compressor(s). Would need a differential coming of the shaft to split the power to the two compressors. 

Hot section could also be diverted- and have an afterburner/reheat for convetional mode.  
This allows for a smaller front section, and a layout compatiable with an intake on each side of the fuselage (Yak-141 style)

A very crude keyboard mockup, when viewed from above.  The double row XX represents a port and starboard first stage compressors.  

                 _________________________________
                         XX     [                                         [    ]
 Right intake       XX     [  downward                        [  second nozzle for
                         XX     [  nozzle/flap                       [  top half of cold air
                       <XX>   [                                        [    ]
                         XX     [                                         [   ]
 ______             XX---------------------------------------------------------
            \___      XX            X    X                                                X     Hot nozzle/
 Cockpit        \ -------------- X –-X--common shaft-- Hot section     X     Afterburner>>>>    tail
              ___/    XX            X    X                                                X
 ______/            XX---------------------------------------------------------
                         XX     [                                         [    ]
 Left t intake    <XX>   [  downward                        [  second nozzle for
                         XX     [  nozzle/flap                       [  top half of cold air
                         XX     [                                        [    ]
                         XX     [                                         [   ]
             ___________________________________  

[Weaver]

That's pretty much right, except I only see one cold nozzle behind each fan. The ratio of fan:core is still the same as a Pegasus (50/50) it's just that the fan is split into two.

You're absolutely right that arranging the drive to the twin fans is an issue. Doing it some way is definately possible. Doing it without too many heavy, power-sapping shafts, gearboxes and joints is the tricky bit.....

[kitnut617]

In the real world, RR had a design for an upgraded Pegasus, only it had a bigger fan front (3" bigger IIRC).  But the engine wouldn't fit inside the Harrier air frame so a new fuselage would have had to be designed and built.  In my 'Alternative Harrier Replacement' build I went with just that, a new fuselage but I went with a fan front which worked out to be 6" bigger than the Pegasus'.

This is basically the difference between the two