This is a reverse on the classic question about a plane taking off on a treadmill. I think it’s been pretty much universally concluded that the only effect will be that the plane’s wheels will spin faster but the plane will still take off and require the same distance to do so.
What happens if you land a plane on a treadmill going in the opposite direction of the plane. Will it reduce the required runway length? Will it make any difference at all? What about the case where a jet is using reverse thrusters?
But for a little friction, I doubt that it would make much of a difference initially. But towards the end of a landing, the plane applies brakes. I imagine that the treadmill would stop the plane even faster.
It won’t help. All that would do would be to stop the plane via friction. It’d be like coasting to a stop in your car. Same force. Obviously brakes are better than just the friction of rubber on pavement; that’s why you shouldn’t lock your wheels when braking hard. The best way to stop the plane is to push against the air either by using antithrusters and spoilers in a jet or using the elevator like I mentioned with my Cessna.
Hmm, I wasn’t even thinking about the brakes. Unless the treadmill was changing speed to match the speed of the plane (and eventually stopping) I guess you could end up going backwards if the wheels were totally locked.
Yes you would, but it probably wouldn’t matter much. It’s rare that I’ve been on a flight where the pilot came to a compled halt on the TARMAC. Usually they keep enough thrust going to get back to the terminal. (Which I’m assuming is not on a treadmill.)
Well yeah, but it’d be negligible. Consider how fast your car comes to a stop from 60 mph (or even 160 in big jets). Not that fast, right? That’s how effective pavement is at stopping rolling wheels. And seeing as how I can stop a plane in a few seconds with those other tools, it’s not all that relevant.
Remember that for a plane, the thrust is provided by the engine(s) pushing against the air. The wheels spin merely as a reaction to the motion caused by the engines - there is no power to the wheels. So whether landing on a fixed runway, a treadmill, or an aircraft carrier doing 30 knots, the plane will perform exactly the same. Well, unless it’s a L1011 trying to set down on a carrier - that wouldn’t work too well…
Yes, but there are wheel brakes so this is a little different than the taking off scenario. If the wheel brakes are applied then the wheels won’t spin or at least will have more resistance to spin (although Chessic Sense and tdn are both pilots and say that the effect of this would be negligible).
I’m having difficulty with this. Aerodynamic braking is quite ineffective particularly at low speeds when the drag is low, even reverse thrust is poor at low speeds. If you want to stop an aeroplane quickly you use heavy braking. I don’t know what’s going on with your Cessna, but you’ve either never really used the brakes properly or they don’t work properly.
No idea. It will depend on the type of work it does. A long haul aircraft will do a lot of hours and not many landings while a short haul aircraft will do much more landings. My impression from the work the engineers do on our aircraft that the pads and discs last a long time.
True, but I wouldn’t call 60 kts “slow”. That’s a lot of wind to push against to brake. Besides, the elevator is huge compared to the disc brakes. So while it’s not very effective per square inch, it totals up to a lot of braking.
I’d call 60 knots slow but it depends on the aeroplane I guess. Whatever you do with your elevator you will slow down a lot quicker if you apply hard braking as well.
Not quite. The exhaust gasses (for a jet) or the propwash (for propeller-driven planes) is forcibly pushed to the rear of the aircraft by the engine(s), which are connected to the airframe. The equal-and-opposite force is applied to the engine itself, and, by extension, the airframe. “[P]ushing against the air” is not how thrust moves an aircraft.
To the OP, stopping a plane on a treadmill is similar in principle to the thread about taking off on a treadmill—it is all about airspeed. The wheels exist solely as a means of keeping the airframe off the ground. Rolling resistance is minimized as much as possible, and is, in practice, negligible and may be considered frictionless. This changes when the brakes are applied, since creating friction is their entire function. The point of “landing” a plane is to slow down its speed with respect to the ambient airflow so that there is insufficient “lift” for the plane to leave the ground. This happens completely irrespective of the plane’s groundspeed, with or without a treadmill.
When I was taking flying lessons, my instructor, an old (72 yo) barnstormer, used 1940’s vintage restored Piper J3 “Cubs” to train his students. We also had Cessna 150s, and, for aerobatic training, Stearman biplanes. Once, he was up with a student when a Florida afternoon thunderstorm came up quickly (as they are wont to do.) He had to get down in a hurry, but the downdraft from the leading edge of the storm was nearly perpendicular to the grass-strip runway, and the storm was approaching too fast for them to travel to another airfield in rural central Florida. He had to attempt a cross-wind landing. The “stall speed” of a J3 Cub is about 40 MPH, which was approximately the gusting of the approaching storm. He made a nearly perfect landing across the width of the grass strip (about 100 ft), landing almost vertically like the Harriers in True Lies.
Once on the ground, applying the brakes to keep the aircraft from rolling backwards was important, and the other people present helped bring the plane to the tie-downs before the storm hit, so all was well.
