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Is it possible to convert a McDonnell Douglas/BAE Systems AV-8B Harrier II Plus into an effective and usable supersonic aircraft, perhaps by changing the engine or applying some modifications on the airframe?

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    $\begingroup$ The harrier would benefit far more from having extra fuel than it would from being capable of supersonic flight (presumably at the expense of using more fuel that it already doesn't have). $\endgroup$ Sep 22 '15 at 16:42
  • $\begingroup$ @RhinoDriver, then why is F-35 there? $\endgroup$
    – user8792
    Sep 22 '15 at 20:43
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    $\begingroup$ What does the F35 have to do with the AV-8B, they are two separate aircraft? Also, due to the added weight of the extra fan, the Marine variant of the F35 has its own set of unique problems. $\endgroup$ Sep 23 '15 at 3:18
  • $\begingroup$ Yes you could make it supersonic if you added another engine to it. Or you could change the engine, but you would have to change the design of the plane. Its really too much money to do that though. $\endgroup$
    – Ethan
    Sep 23 '15 at 9:07
  • $\begingroup$ The answer is yes. Just like you could also take a supersonic fighter like the FA-18 and by "changing the engines and making some modifications to the airframe" you could make it capable of vertical takeoff and landing. Almost anything is possible with enough engineering time and money, but sometimes it is better to start with a clean sheet of paper... $\endgroup$ Jul 25 at 17:39
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There was actually a plan to convert the Harrier into a supersonic aircraft.

The original plan that lead to the development of the Harrier actually had a supersonic variant, the Hawker Siddeley P.1154. The P.1154 was supposed to be a supersonic aircraft using the Bristol Siddeley BS100 engine, which used Plenum Chamber Burning(PCB).

In the BS100 engine, cold bypass and hot core turbine airflows are split between two sets of nozzles, front and rear, like the Rolls Royce Pegasus engine which powered the Harrier. The PCB called for additional fuel and afterburning applied to the front cold air nozzles only, increasing thrust. The PCB increased the thrust from 116 kN to 160 kN.

Plenum Chamber Burning

Source: aeromodelbasic.blogspot.com

However, the P.1154 never saw the light of the day due to various reasons and the subsonic Hawker P.1127 was developed into the AV-8 Harrier.

Later, Hawker and McDonnel Douglas joined to develop the AV-16 concept, basically a plan to double the range and payload of the Harrier. One version of the AV-16 called for supersonic flight too.

Some modifications that were considered in the study for supersonic aircraft were,

  • A more powerful engine (called Pegasus 15) which used PCB
  • A bigger fuselage for the bigger engine
  • A larger 'supercritical' wing
  • A lengthier, more slender fuselage

This version was called HS.1185, as shown below.

AV 16

Source: harrier.org.uk

However, in March 1975, Hawker pulled out due to budget cuts and other reasons.

Later, Rolls Royce (ground) tested Plenum Chamber Burning in the Pegasus engine and made some progress in the 1980s. This was supposed to be used in yet another (supersonic) variant of Harrier. One of the versions was the HS. 1205, which had redsigned F-16 type inlets.

HS 1025

Source: harrier.org.uk

However, this also came to nothing and the project was shelved. For a full list, see Harrier site

To answer your question, it would be possible to make the Harrier go supersonic using more powerful engines and modifications to airframe (listed above).

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  • $\begingroup$ Then why was F-35 and the related budget-draining? $\endgroup$
    – user8792
    Sep 22 '15 at 20:39
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    $\begingroup$ @anonymous F-35 is a completely different aircraft, in a different era, for a different purpose- replace a number of aircraft in USAF, USN and USMC. That it had VTOL is because USMC insisted on it. I doubt if USAF and USN would've ever accepted a subsonic frontline combat aircraft. $\endgroup$
    – aeroalias
    Sep 23 '15 at 2:09
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    $\begingroup$ Not to mention the F-35 is stealthy, the Harrier is decidedly not. $\endgroup$
    – MD88Fan
    Jul 25 at 14:31
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To add to what has been said. Rolls-Royce abandoned plenum chamber burning (PCB) in the end, because they could not get it to work. There were also unresolved intake design issues over hot gas reingestion, and over the conflicting design demands, especially intake size, for VTOL vs. supersonic flight. The supersonic Harrier was basically abandoned because it's a lot harder to do than it looks.

But the project had continued to evolve. What was by now B.Ae Kingston turned to a split-tail design concept, which became the Mach 1.5-ish capable P.1216 with F-16 style intake, and a new Rolls-Royce engine in the "tripod" format with single rear nozzle, in the manner of the later F-35 (but without the forward lift fan). By the late 1980s the Ministry were forced to choose between the P.1216 and the already-flying and significantly faster B.Ae EAP (Experimental Aircraft Programme), as they could not afford to buy both. They chose the EAP, which was effectively adopted as the prototype for the Eurofighter Typhoon.

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