Andy Ross wrote
 
> David Megginson wrote:
> > Once we support ground reactions with a moving surface 
> (like the deck 
> > of a ship), why not just model the catapult as a faster moving 
> > surface?
> 
> Because the gear don't simply rest on the catapult to be 
> pulled along via friction, they're actually bolted to it 
> during the launch.  

Hmm, bolted? Don't forget that the cat force is adjusted for the aircraft
type and launch weight.

It would have to be modelled as a spring 
> force acting on the nose gear to be correct.  Even that's not 
> quite good enough, since on real cat shots the gear is 
> artificially compressed to keep the nose from tipping 
> backwards during the shot. 

Not exactly, and not in all cases. The F4K had an extending front leg which
raised the nose into a take-off angle. When the cat was tensioned for a
Buccaneer the nose wheel came off the deck, and a retractable tail bumper
came into play. With a nose wheel tow, when the cat is tensioned a downward
force is applied to the nose, since the attachment point is above the oleo.
When the cat is fired more downward force is applied, as well as forward. 

> All of this would have to be 
> modelled; none of it shares any meaningful behaviour with 
> ground friction.

 Quite, but I believe that this should all be reasonably straightforward to
simulate.

> And arrestor wires have their own complexities.  They need to 
> be "tuned" to the landing aircraft weight to produce the 
> right amount of deceleration.  This is a manual process on a 
> real carrier, but we'd have to fake it somehow.
> 

Do we need to model that? We know the mass of the aircraft, just apply a
suitable decelerating force at the hook attachment point if the hook engages
a wire.

Regards

Vivian 




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