Phrak said:
I only noticed that after watching several YouTube clips. The poor landings usually involved the pilot rotating the nose inline with the runway before touchdown, and a (yaw induced?) roll and overcorrection, recorrection, and so on.
I forgot to add, of course, using aileron to hold the wings level throughout, which becomes especially important with some of the lower-slung engines. There's always landing with crossed controls, but it's not well advised... (or thought of).
Didn't think about that, and it could be somewhat of a problem, but again, it only takes about half a second, at most, for the tires to come up to speed. By that time we're still in a crab, but will begin correcting momentarily.
And again, I forgot to add that the slots and flaps are only partly for lowering stall speed. One of their major functions is to create drag, which, after pulling the throttles to idle, results in a fairly rapid deceleration of the aircraft. So after the second bounce, er, "when the mains are firmly on the runway," we're usually well below stall speed and will remain there throughout.
The other function is that to maintain required velocity, we have to keep the engines spooled up considerably higher than we would if we were using less flaps. This may seem counterintuitive, as some would say, "yes, but doesn't this reduce your available power?" The answer is "yes, but we have power to spare. Of more importance is how long it takes that power to spool up to useable levels." By keeping the engines spooled up, useable power is about half as many seconds away as it would be if we were near flight idle throughout our descent.
If you could judge the skid time by the time the tires smoke on the runway, then a half second or even less seems right. But it seems the back wheels would carry the plan to the upwind side of the runway in the remaining second or two before the front wheel touches down. Or do you exepct some amount of sideways motion during touchdown?
While landing in a crab to counter right to left crosswind, and we maintain centerline until touchdown, by the time the mains are spun up, we're slightly left of centerline. The aicraft rapidly begins correcting to the right, but we're correcting with rudder, so it works out fairly even by the time the nosewheel touches down.
In theory...
DaveC426913 said:
I had envisioned it as part of the rim, thus not needing repalcement with every tire.
But of course! Nice catch. I'd always envisioned them being molded into the tire. A simple vane kit attached to the wheel would indeed be much lighter.
Ooh. I hadn't thought of that. Both loss-in-speed and gyroscopic effects would be something you'd very much like to avoid the moment before touchdown.
Well, the velocity loss due to wheel spinup occurs at touchdown, but as I mentioned, it's not much, only a couple of knots at the most. And the landing gear are probably about the strongest item on the aircraft given their weight, simply because we only use them for taxi and take-off, and haul 'em around as luggage the rest of the way!
So both effort and expense are put into making them as light as possible while retaining high enough strength to literally skid sideways without failing, to take the entire weight of the aircraft, fully loaded, in a hard landing without breaking, and to full stop in a fully loaded (MGTOW) aircraft after reaching V1.
In a Boeing 777, that's 288 tons at 180 kts, max braking, with brakes at min allowable thickness!
http://www.youtube.com/watch?v=f4LFErD-yls"for the actual test. And then, after stopping, the plane has to be able to taxi, and then either taxi or stand still for five minutes while the brakes are at approximately 3,000 deg C (5,432 deg F). That's for the estimated maximum of five minutes it could take the fire engines to reach the airplane. But the 777 is a newer design, and the plug blows, relieving the pressure. On earlier aircraft you'll see warnings involving staying well clear of the axels, as the whees tended to blow themselves apart parallel to the axels, hence the requirement to "gather off the nose" or "gather off the tail."
Still, even in much older aircraft (fifty years) the landing gear is a lot stronger than most people would imagine. You'll usually bend the airframe in some way before you break the landing gear. Now this applies to airliners, as a measure of passenger safety. I wouldn't try pranging the gear in a SEL, prop Cessna, Piper, or Beechcraft, as you may very well break the gear. Then again, they usually touch down around 50 kts, not 120!
