Quote:
Originally posted by GrayHam:
Quote:
Originally posted by NY Madman:
[b]
Thrust alone is not enough to achieve viable flight. If it were, aircraft carriers would never need their catapults. Without the additional forward motion provided by the catapults, every plane would crash leaving a carrier, regardless of the amount of thrust it's engines put out.
confused

Aircraft carriers use catapults because their runways are exceedingly short.

You're right; lift is as essential as thrust. Lift is created by thrust:
Thrust forces the aircraft forward, generating airflow over an airfoil. When the flow of air is fast enough, enough lift is generated, and the aircraft lifts off.

The catapult aids the F-18 in generating the airspeed necessary to get enough lift to haul the Plastic Bug into flight.
On an aircraft carrier's short flight deck, there is not enough room for the F-18's engines to generate enough thrust and airspeed over the wings to get the F-18 up on its own. So they use a catapult aid.
Same F-18 taking off from Miromar? No problem. Runways are plenty long.

Thrust from jet turbines is not instantaneous. Like any other object accelerating from a dead stop, it takes some runway to reach speed. The catapult helps shorten the time needed by magnifying the force of thrust that can be generated by the F-18's own engines.[/b]
I realize the fact of the short runways for the catapults, but if engine thrust were as intregal as being argued here, that problem could have been overcome in other ways besides the use of catapults.

As you have mentioned, the forward motion through fluid air... acceleration is also required for the lift needed for viable flight.

In the scenario proposed I doubt the plane could achieve viable flight. In such a situation I believe a conventional jet would crash.

Does anyone have any links to an actual physics web site that ponders this question? Maybe a link to a test where they did this with a plane.. on in ground rollers maybe (like those used to accelerate car wheels... only on a larger scale)?
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