Patuxent River Ski Jump Video (No F-35Bs on it)

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Unread post17 Oct 2019, 17:44

Another nice ski jump explanation from 'ENGINES' at pprune. Always good to be reminded that some know their stuff.
17 Oct 2019 'ENGINES'

“...A conventional fixed wing aircraft can launch from a ski jump, but only at weights well below normal land based MTOWs. That's because the design basis for most ski jumps (to date) is that the STOVL aircraft they support can use their vectored lift systems to generate an optimal flight profile after ramp exit. They leave the ramp at BELOW flying speed, but at a high positive rate of climb generated by the ramp profile. After ramp exit rate of climb starts to fall, but is still positive. Because they're STOVL aircraft, they set their thrust vector independently of angle of attack to optimise acceleration while ensuring a positive (albeit falling) minimising rate of climb. As speed builds up, wing lift increases, and thrust is vectored further aft. At a known distance out from the ramp, the rate of climb stops falling and starts to increase again. This is known as the 'inflection point', and for a Sea Harrier it was about a kilometre out. Effectively, the ski jump has generated a 'runway in the sky'. This delivers a very significant increase in launch weight. The same happens with the F-35B.

Conventional aircraft can't do this. Their thrust vector is fixed relative to the aircraft axis and when they leave the ramp they have no option but to adopt a high angle of attack to generate as much wing lift as they can, and also get some lift from their (fixed) thrust system. However, that generates very high drag, so more thrust is needed to accelerate the aircraft. The result is a significant reduction in available takeoff weight. I know that some launches from the Chinese and Russian carriers involved the aircraft climbing then descending back towards the sea as they built up airspeed, before climbing away. Pilots tell me that's not an optimal situation. (I'm paraphrasing to remove the more agricultural language most of them used). The Chinese are working on catapult carriers for a reason. It's all about the physics....”

Source: ... st10596629
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