Re: Pulling a Stop to Runway Overruns
I knew someone would say that ....
The problem is that the case where the nosewheel is most heavily loaded by the braking forces is the case where the brakes are ALREADY WORKING WELL!
For the case where you are most at risk of an overrun - poor braking action - the nosewheel reaction due to braking is small.
Consider the fulcrums and levers everyone here is so keen on. The cg might be, say 5ft above the mains (for a smallish jet). The nosewheel may be 25ft ahead of the mains 9and perhaps more, depending how 'stretched' it is.
Let's assume decent braking action, equivalemnt to 0.25'g' decel. That means that, taking moments about the mains, there's an inertia force of 0.25*aircraft mass acting 5ft above the mains. If that is ALL 'thrown forward' onto the nosegear, the reaction there will be 0.25 * aircraft mass * 5ft / 25ft = 0.05 * aircraft mass.
In other words, even with pretty reasonable braking effectiveness, theres only another 5% mass onto the nose. If braking is poor - say 0.10'g' decel - the effective reaction increase at the nose is only about 2% of aircraft weight. Not enough to overcome full back stick; not even close for some types.