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21

VTOL aircraft can have more than one engine. It is just that the design process of the Harrier and F-35 led to a situation where only one engine was required. The main challenge in any VTOL aircraft is to have the engine produce thrust in two different phases of flight: during cruise and during takeoff/landing. This basically requires the powerplant on the ...


21

The main load bearing landing gear is in a bicycle setup, with 2 outriggers for stability. This allows the gear to be lighter, stay close to the center and out of the way for the jet blast. The Lockheed U-2 also has its gear in the bicycle configuration and takes off and taxies with detachable "pogo" outriggers for stability.


17

The Harrier is designed around its rather large centerline engine with its 4 non-standard exhaust ports. In order to balance properly, the engine's nozzles have to be in just the right place and we can't have annoyances like landing gear doors opening just before landing and deflecting the thrust stream that is keeping the thing in the air. Fighter jet ...


13

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, ...


9

How does the Harrier avoid engine damage from dirt ingestion during rough-field operations? The short answer is that they don't. They avoid using these FOD-laden strips if possible, but doesn't have any kind of active method for reducing FOD damage from debris ingestion. This is supported by an RFP that NAVAIR put out asking for proposals to reduce FOD for ...


9

Because when selecting aircraft the requirements were for close air-support and to be able to operate from amphibious assault ships like the USS Tarawa and the USS Nassua. These ships have very small decks that aren't geared towards launching larger aircraft like the F-18.


4

This was the lowest mass solution at the time of P1127 development. Remember that weight is at a premium for vertical take off. The first hover tests of the P1127 prototype were only possible with fuel for only 3 minutes in the tanks and 700 lbs of equipment stripped from the airframe. A conventional landing gear would had made hovering impossible in 1960. ...


4

And if the Harrier had been a conventional terrestrial fighter, it probably would have used a ubiquitous tricycle landing gear. The driver for Harrier's unusual landing gear configuration is the requirement to hover via an unconventional single engine vs available fuselage space. This necessitated that the Rolls Royce Pegasus engine to be located directly ...


4

the F35 has a ton of electronics that the Harrier could only dream about, but I will focus on propulsion differences. The biggest is that the F35B uses a separate lift fan in front of the engine, oriented to provide vertical lift that balances the vectored thrust from the rear of the engine. The lift fan is disconnected when flight speed is obtained and ...


3

The big problem faced by VTOL is getting the thrust-to-weight ratio above unity. So anything that reduces thrust or adds weight is bad. The P.1127/Harrier, being the first practicable solution, wwas uncomfortably close to the borderline. Long tailpipes waste energy and reduce thrust, so it had to be short. But a long rear fuselage then gets in the way. De ...


3

Why does Harrier have split hot exhaust nozzles? Because a central tail exhaust is too far from the two front exhausts which are fed by bypass air. The split exhaust makes all ducting mercifully short, so the airframe can be lightweight and compact. Don't forget that pressurized gas cannot be ducted in air conditioning pipes; it needs heavy pressure pipes ...


2

Many VTOL aircraft have two engines: Bell 212, EC135, MH-53. There is even one with three engines, the CH-53E. Yes helicopters are aircraft too. These have all engines drive one propulsion device, and that conveniently means there is no change in the location of the thrust point if an engine fails. As @Ryatt Broach mentions, the V-22 has a complicated ...


2

Don't forget about the V-22. The V-22 has had problems in the military because two engines may cause different amounts of thrust in each engine, So it may cause a problem. For example a sudden loss of thrust on one side due to a mechanical issue, surge, FOD, etc. The attitude may end up in a position that does not favor an ejection.


2

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'...


2

In the Harrier, the bypass air from the large diameter low pressure compressor of the Pegasus engine is ducted through the front pair of nozzles while the remaining gas output from the engine passes through the rear pair. Rolls Royce designed the Pegasus engine with the main rotating components, the low and high pressure compressors and the corresponding ...


1

How about a six-engine supersonic VTOL jet? Second prototype of the VJ 101 in hovering flight (picture source). By using swivelling wingtip-mounted engines, a twin-engine STOVL jet is feasible and it will be much easier to swivel the whole engine, so avoiding the complexity and efficiency losses of sviveling exhausts. The downside is twice the likelihood of ...


1

The F-35B can automatically do a VTOL landing while the Harrier is manual. Also the F-35B has a more powerful engine that has an air opening on the top of the jet to increase air intake for VTOL operations. The performance difference is that the F-35B can go faster than the speed of sound while the Harrier cannot. Not to mention the F-35B has all the ...


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