Saturday, September 29, 2012

Ski Jump.

This is coolbert:

Here with a Q & A with an acknowledged aviation expert. The ski-jump take-off portion of the flight deck as found on the Chinese newest warship Liaoning a positive feature as NOT found on American aircraft carriers.

Q: "That new Chinese aircraft carrier is the Russian Varyag originally and has that ski jump take off front end. And as an aviation expert what is the advantage to such an arrangement?" That Su-33 is the Russian carrier aircraft but does not have the Harrier jet type VTOL or STOL capability? VTOL = vertical take off and landing. STOL = short take off and landing.

"vertical takeoff planes use a lot of fuel to go straight up; the combat load is dramatically reduced. Level take-offs save lots of fuel, but require mile long runways--or steam catapults on carriers. You will see that when launching from land, 'jump jets' rarely do anything other than a full runway takeoff, not using the vertical components of its capabilities at all, or using a minor downward direction during takeoff."

"However, being a 'jump jet' means one doesn't have to build as large a carrier to accommodate the steam catapults, nor the long rear decks needed for landing a heavy plane straight-on for cable/tailhook landings. The thrust of the engines can be partially directed downward for adding engine-created lift, while still providing forward direction to create lift from the wings. Win-win, as some people would say. Moving partially forward while the deck 'assists' the plane in starting upwards (instead of using all that energy from the engines to do the same) helps a lot. Doesn't work so well with engines facing horizontally/level, as is found on most jet planes. However, there is some advantage to downward-directed engines even for non-jump jets. I recall that the F4's engines had a slight downward direction in the design when attached inside the plane--12 degrees from level seems to be what I recall, though it could be less. Without that downward push, the F4 would need a longer runway or more power to develop enough lift to take off."

Even the Harrier type "jump jet" rarely ever used the VTOL capability? Too much fuel consumption. A slight but very helpful advantage gained from the ski-slope take-off with engines the thrust of which is downward directed, even if only to some extent!! Makes sense.


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