F-35B safer and looks more stable in terms of VTOL capability.
What is the basic difference between Harrier II and F-35B's VTOL technology?
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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 covers closed. Roll control at low speed comes from bleed air from the front fan in the engine.
The Harrier uses a much larger version of a bleed system from a single engine to provide both forward located vertical lift/thrust and a similar total diversion system for rearward lift/thrust through four rotating nozzles. All nozzles are working all the time and rotated to a lift/thrust position. A separate bleed system provides roll and pitch control at low speed.
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 high and low pressure turbines mounted on two concentric, counter-rotating shafts. This minimises gyroscopic coupling effects and makes it possible to control the Harrier in hovering flight manually, without the aid of an automatic stabilisation system. All four nozzles can be rotated through 98.5 degrees allowing for vertical takeoff and landing. Thrust vectoring can also be used in combat to enhance manoeuverability, a technique pioneered by the USMC. The F35B uses a separate engine driven fan in the forward fuselage in addition to thrust vectoring to provide vertical lift. The Harrier system is much less complex mechanically and avoids the need for the lift fan which is only used for take off and landing and is dead weight the rest of the time, and which also takes up a lot of space in the F35B's forward fuselage.
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 bells and whistles of a modern fighter.