Um… are you saying an airplane can’t take off in a tailwind?
ANY tailwind?
Ever?
Perhaps he means that given a strong enough tailwind it won’t take off.
In the aircraft I fly, the wheels would exceed their maximum tire speed with a tail wind of 65 kts.
Just out of curiosity, why can’t you just taxi to the end of the runway and turn around?
Well, only light tail winds. Say under 400 or so mph. 
I was just positing the rolling resistance = thrust for some high value of ground speed. The tail wind would merely cause the ground speed to be even higher with respect to the airspeed.
Señor Death Ray, what sort of airplane to you operate? I’ve been goofing around with finding real world numbers for tire speed limits.
You mean like this?
That’s a nice link, DS. As a designer and some-time engineer (junior class) I always get a kick out of how little extra capacity is incorporated when it’s not really needed.
It seems to me that for the tailwind to duplicate the treadmill matching the aircraft speed (not the wheel speed), the tail wind would need to equal the takeoff speed. This would make the wheel speed twice that of a normal takeoff and should double the takeoff run. The takeoff run for a Cessna Skylane is listed in their data sheet as about 640 ft. On the main runway at Albuquerque airport the main runway is 15000 ft long and that should be adequate for a downwind takeoff with a wheel speed equivalent to the treadmill case even if it is at 4000 ft above sea level.
For a takeoff speed of 60 mph the wheel speed would be 120 mph and many of the tires in the cite in my post above are rated for that.
If you assume a jet takes off in 7500 ft at that altitude at a speed of 160 mph the wheel speed would be 320 mph and I strongly suspect that few tires are rated at that speed. So a jet would most likely blow the tires before it could lift off with a 160 mph tailwind.
Whoa, let’s move those speeds up a little. The takeoff speeds are indicated airspeeds and at 4000 ft altitude would be about 65 and 173 mph true airspeed respectively. the Cessna would still make it but it would be close on the tires and too much for some of them. The jet would be even worse off.
Well, David Simmons has found you a pretty good site by the looks of it.
I fly a Dash 8 turbo-prop, the max tire speed, from the flight manual, is 165 kts. There’d be some fat built into the limitation of course. The take-off speed at max weight is 100 kts.
That take-off speed is for a flap setting of 5°, the speed for flap 15 is about 10 kts slower from memory.
I’m not sure I would count on a safety factory being built into the tire max speed. At least not into the tire makers max speed. According to Goodyear’s site that speed is equivalent to the airplane red line speed. A sample of the tire has been tested to that and although it might not come apart immediately above it there are no guarantees.
Well no, you can’t count on a safety factor.
Hmmmm… so translate that to the conveyor belt problem. Under the most agreed-upon interpretation of the scenario, in fact the plane wouldn’t take off due to tire failure (plane moving forward at 160mph + conveyorbelt moving backward at 160mph = 320mph, resulting in tire failure). Real-world tire ratings are one part of this that we’ve treated very little in the topic.
Once again, this is a hypothetical question. Mechanical tolerances have nothing to do w/ it.
Also, if the plane is going 160mph, relative to the treadmill, and the treadmill is going 160mph in the opposite direction, then the plane is stationary, relative to the ground, and the wheels are turning at a rate equal to 160mph, not 320mph.
No, he was referring to the original “Cecil” interpretation which has the aircraft moving forwards at 160mph relative to the ground, the treadmill moving backwards at 160mph relative to the ground, and the aircraft moving forwards at 320mph relative to the treadmill. This is the interpretation where the aircraft takes off.
When I first saw this, my brain hurt a bit until an image popped into my mind: a hydroplane.
You know? The ones with no wheels, but little pontoons to land on water with. When they take off, the pontoons do absolutely nothing to assist the plane in going forward (much like wheels on a runway)…they just hold the plane up.
On smooth seas, like a smooth runway, takeoff is pretty uneventful. Against a current, however, the little plane would need to overcome the friction of water against it’s pontoons before moving forward.
The basic argument (or “real-world” scenario) is that a conveyor that merely matches forward speed can’t overwhelm the plane with enough friction to hold it back. Even if it can counter forward speed of the plane, the plane isn’t relying on the wheels to go forward but it’s ability to pull at the air (with it’s props, jets, whatever).
Argument #2 (or the “hypothetical”) is that the acceleration of a conveyor can impart backward momentum beyond just friction. But as Cecil pointed out in his followup article (linked somewhere above), generating enough acceleration to match the force of a plane trying to take off is fairly impractical to even think about.
Does this help anyone? JohnnyLA?
InkBlot
Ah, budgies! I posted in the wrong airplane thread.
I didn’t mean to dabble in necromancy, honest!
InkBlot