HMS Illustrious (Now incl photographs)

[DBTW]

How much kinetic energy does an aircraft gain by using a "ski jump"?

After the throttle slam the aircraft picks up speed very quickly. NB: you get an acceleration from the engine, I suppose about 80ish knots, and then whatever the wind speed is on top of that. The aeroplane becomes airborne on a mix of upward trajectory from the ski jump, jet borne thrust from the nozzle deflection (which you input just as your bumline leaves the ship) and wing lift. The amount of nozzle deflection is usually around 35-40 degrees from fully aft. As the aeroplane accelerates, you smoothly move the nozzles aft and this increases the acceleration. During this period you are transitioning between depending on the the jet borne thrust component for a portion of your lift to total wing borne flight. Due to the ski jump, the transition occurs while the aerplane is "falling with style" (Thanks Buzz Lightyear) in an upwards trajectory off the front of the ship. Using the same technique off a flat deck means you settle much more off the front, and that in itself means you can carry less relative to the ski jumping aircraft or you may fall in the oggen.

...increases ability to handle ship pitch motion and reduces pilot handling workload.

The aeroplane leaves the ski jump having been specifically placed in a climbing attitude by the ski jump angle. All the pilot has to do is hold that attitude (normally about 12 degrees nose up). IE you don't have a pitch up which is normally associated with a catapult and you don't have a massive sink, normally associated with a flat deck.

Similarly, the pilot controls when to slam so he cannot be launched into a sea wall (as can occassionally happen with catapult launches) unless he does it himself, and thus he has more control over when the aeroplane leaves the deck. Normally, the pilot slams the throttle as the deck commences its bow down motion from its highest pitch. Simply by watching the motion during the start up you get an excellent feel for the cycle of the pitching motion. In the time it takes the engine to spool, the brakes to skid, the aeroplane to accelerate and approach the ski jump edge, the ship will have pitched through the trough and be passing the deck level attitude on its way up when the aeroplane becomes space borne. (stuff ups can be spectacular!)

However to use a ski jump you do need the aircraft to be fitted with an attitude control system that is effective at speeds below normal wing stall speeds.

The aeroplane must be able to be controlled at speeds below flying speed. In Harriers this is done using reaction controls. At MAUW, you can be leaving the ski jump at speeds well below wing borne speeds. As stated above, and much more succinctly by John Farley on several occassions, the aeroplane enters "flight" with a mix of ski jump induced upward trajectory, jet borne thrust supplanting components wing borne lift, and the other components of wing borne lift provided by the accelerating airspeed.

Because the thrust level from a Harrier engine is so high (relatively), the aircraft quickly accelerates to flying speed and transitions away from the jet borne requirement. I understand the F35B will also have a form of reaction controls and some fairly clever electronic control inputs.

Hope this help?

Ski jump launch advantages apply to all aircraft to some extent. Even a conventional fighter can gain an advantage during take off with ski jump assistance, as can be witnessed when, with all the adrenalin pulsing through his/her veins, a newbie Harrier jock forgets to take the nozzles at the deck edge. In that instance, the aircraft nose will pitch up as the aeroplane flies away at high AOA. IE the aircraft will need to rotate to a nose attitude to gain the same effective lift as the jet borne component provided had the nozzles been in! Even though there is no reaction control available with the nozzles aft, the aeroplane will still be going up throughout the ski jump trajectory. It's just that the pilot will have startled themselves with the nose pitch.

All in all, ski jump launches are really easy. To my knowledge, no-one has dropped in the ocean due to bad ski jump technique. It is quite a forgivable way to go because you are physically forced upwards to begin with.

Coupled with vertical landings, aeroplanes become a lot less dependent on external machinery to stay operational.

[Flying Lawyer]

Aur
Sorry, I missed your question.
I didn't get any pics with Lossiemouth in the background.

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Alongside in Oslo, 28 June 09







Entering the shipping lane from Oslo Harbour - passing the old Dyna Fyr lighthouse

(Some distortion - pic taken through a window)


Engine Control Room


Starboard Engines


Marine version of Olympus engines (as used in Concorde)



Harrier beyond forward lift






Admiral's Dining Room




FL

[Double Zero]

I knew a Flight Test engineer, who when joining Dunsfold was asked to describe the effect of the ski - ramp; after a few mumblings, he said " well the thing goes ballistic, doesn't it ! ".

He was then accepted, that was the word they wanted to hear, and he proved a fine Flight Test engineer...