Originally Posted by
john_tullamarine
No! The nose-wheel steering is likely disconnected at this point (don't know how it works on the 747)
Now, that's something I haven't come across before. While the FT folk might do their tests with NWS physically disconnected to tick the certification box, the idea of such happening out there on the line is a new one. Are you able to add some commentary as to any Types which might do such things, etc ?
it's definitely not designed to have the lever moment generated by the elevator at high speeds loaded onto it.
Likewise, might you be able to provide some evidence to support this contention ?
on the the 744 you would see that you do get better center-line tracking at Vmcg
That probably will be the case for the great majority of aircraft - anything which gives you some cornering forces is going to help. However, it is pertinent to keep very much in mind that the aircraft is going to diverge, regardless. Considering those test chart results I have seen, this applies even at high speed as there is always going to be bit of a delay before the pilot gets the rudder in and the aircraft responds. Generally, you are going to see a small deviation which starts to increase as you get back closer to Vmcg and then things really ramp up and get hairy in the last few knots.
It is that gray area where X-Wind comes in
I'd be a little more concerned than you, I suspect.
First, if there is much crosswind, all certification bets are off. Keep in mind that things like Vmcg are just lines in the sand for other certification activities. The pilot might not need to have a detailed certification knowledge but it sure helps to have an idea of which bits, and where, can bite you ... and badly.
The usual test requirement is nil wind. The old BCARs used 7 kt but we can discard that as being in the dinosaur realm. Consider that your four-motored beast might see something in the order of a, perhaps, 20-30 kt increase in the real world Vmcg with a stiff crosswind. That is to say, even allowing for the other conservatisms, you might find yourself considerably BELOW the real world on the day Vmcg but perfectly legal with your min speed schedule takeoff. The only problem is that, should a critical failure occur on the wrong side of the house, and you elect to continue, you ARE out of control and you WILL go for some tip-toeing through the tulips. In such a situation, V1 becomes irrelevant and the only option is a (slightly) above V1 reject.
Better, if you have the option, just to avoid the potential problem altogether. For example, the situation could well arise for an empty positioning flight from a long runway. If your laptop or RTOW book uses min speeds, then you would have the option to presume a higher weight and take advantage of the relevant higher weight speed schedule. We are just trying to get a suitable buffer to take us out of the nasty region.
Going back many years, I did a training contract on the 732. The operator had a routine positioning flight where this was absolutely relevant (and, often, windy). Once it became apparent that the folk had not thought much about this concern, some directed training quickly and clearly highlighted the problem and a suitable solution. Some of the wide eyed exercises were a delight to behold.
Although certification is pretty good and looks after us pretty well, that only applies most of time. Sometimes we need to read between the lines a tad.
I don't remember anything about nosewheel steering becoming disconnected from rudder pedal input on the 747. That was on the Airbus if I remember correctly......at least the narrowbodies.
Even if the nosewheel does become disconnected on an aircraft type, it doesn't mean that more downward pressure on the nose won't help for directional stability(just like aft elevator helps for directional stability in the 3 point attitude on taildraggers). And, as I have discussed with John before(under a different handle of JammedStab), there is no consideration for crosswind in VMCG calculations, meaning actual VMCG can be much greater or much less than what would be published. It is one of those dirty little secrets that almost training organization/manual/etc never talks about. Then you get a surprise one off accident like the American Airlines A300 in NYC(where we discovered that Va is different than what many people thought it was) and word gets out.