Jon S Berndt wrote > On Wed, 7 Jul 2004 22:50:40 +0100 > "Vivian Meazza" <[EMAIL PROTECTED]> wrote: > > >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. > > I thought initially that a spring was not the way to go, but I think > you are picturing a spring that (figuratively) goes from the bow of > the ship to the nose gear, no? This sounds plausible, but it depends > on how the catapult works. Does it maintain pressure along the entire > throw length of the catapult? In this case, a spring is wrong.
The force applied by a steam cat is more or less constant over the cat stroke. Put simply steam pressure is applied to the back of the cat shuttle from steam reservoirs. This initial pressure is resisted by a 'holdback' attached to the back of the aircraft. When there is sufficient pressure a component in the holdback breaks, and the shuttle (and the aircraft) accelerate down the track. Near the end of the cat stroke, ports in the cat cylinder are uncovered, releasing the steam pressure. A probe on the front of the shuttle engages in a water brake and is rapidly decelerated to a stop. The aircraft overtakes the shuttle, and the cat strop falls away or the nose wheel towing arm disengages. Nothing can go wrong ... The volume of the steam reservoirs are large in comparison with the volume of the cat cylinder, so there is only a slight drop in steam pressure over the stroke. As far as simulation is concerned, the cat force could be considered to remain constant over the whole of the stroke. > >> 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. > > Yep. > Yep, we do need to model that, or yep, we just apply a suitable decelerating force at the hook attachment point if the hook engages a wire? So for the cat we apply a suitable force at the cat attachment point, and for the arrester wires at the hook attachment point, remembering that there are vertical as well as horizontal components. Is that enough detail for some initial design? I can dig around in my memory some more, or do some more research if you need it. Regards, Vivian _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
