Planes can take off from a runway (concrete, asphalt, grass, or dirt), ice, or water. But they are supported by that surface.
Mythbusters vs. The Moon
- Thread starter Trekker4747
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Planes can take off from a runway (concrete, asphalt, grass, or dirt), ice, or water. But they are supported by that surface.
I enjoyed the shark week episode, as stupid as it may have been in spots.
I thought the robo-shark was pretty cool. It didn't really prove anything, since people actually have fended off shark attacks by poking the eyes (and they even mention it in the episode), but as builds go I thought it was one of their better ones.
Robo-dog though was pretty lame. Not very convincing. Even if the sharks had went for it, all it would have proven was that sharks will attack robots. Which may have been a better myth actually. Robot Vs. Shark.
Robopup was pretty damn cool! But I don't think his "dog paddle" was violent enough. Look at when the real dog dog-paddled and how violent it looked in splashing the water compared to what Robopup was doing.
Seemed like they tested the "commotion/action in the water attracts sharks" myth several different ways in this episode. Splashing dog, frantic swimmer, injured fish, etc. But otherwise it was a cool episode and the filming/underwater moon lights on the shipwreck was really damn cool. Wish I had watched this in HD.
And, as always, Kari was lovely.
Planes need a support surface to rest on until they get into the air. They also need that surface to move along until they reach takeoff speed.
Sure, and the purpose of that surface is to exert an upwards force on the plane to keep it from tumbling down to the Earth's core. That's pretty much all.
There is no drive train attached to the wheels. They have nothing to do with accelerating the plane forwards, and probably exert less backwards force than simple wind resistance does.
A plane uses the same engine to propel itself whether it's in the air or on the ground. The *only* difference, physically, between those situations is whether the upwards force on the plane is due to lift or normal force.
A plane can sit on its belly and be pulled by its engines without a wheel. It wouldn't be good for the plane or its paintjob but it can do it.
The only reason why they have wheels is so they can move easily along the ground. But it doesn't NEED the wheels to work.
Look, I agree with you. But lets say you're taking off from a wet grass runway. If the wheels sink into the mud you're not going anywhere. The plane needs a firm surface to roll out on. Fabric lying on asphalt is not that firm surface. The asphalt is.
A Cessna lying on its belly will not get airborne.
That's true, but irrelevant to the case of a moving treadmill. Friction is obviously important, which is exactly why planes have wheels, but rolling friction is such a minimal component of the hindrance to lift-off. Although rolling friction may increase as wheel rotation speed increases, it will still be a very minimal backward force compared to things like wind resistance.
If you have a treadmill (or don't mind looking a little foolish at your local health club) you can test this. Get a Hot Wheels car, attach a string to it, and see if you can pull it along a moving treadmill. No matter how fast you set the treadmill you will easily be able to pull the car forward and with a negligible change in the force applied.
In that analogy, you pulling on the string is the same as the planes engines providing thrust. Both are independent of the wheels. The toy car's wheels will spin crazy fast but there simply isn't enough rolling friction in the wheels to prevent forward movement.
-MEC
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Doesn't that support my thought that the fabric being dragged along the asphalt would have no impact on whether the plane can take off or not?
That analogy was what was able to finally convince some fairly intelligent people.
I said if i pull that string an inch, do you agree the car will be 1 inch closer to me, no matter how fast or slow the treadmill is moving?, no pretend the hot wheel is a plane and the string is its propeller. There was a little silence on the other end of the phone and then an acceptance.
Why wouldn't a Cessna lying on the ground not get airborne? Other than the fact that the propellor likely wouldn't have the clearance it needed.
Ever seen a sea-plane?
I could be wrong, but water isn't all that "firm"
The only thing that might stop a plane stuck in the mud is maybe the mud's forces against the plane is greater than the force the plane can exert.
Yes, it would. The fabric is shown wrinkling because of the rough nature of asphalt. The point: additional friction is flawing the results.
The concept is still the same argument from day 1. Everyone else is just splitting hairs.
Yes - the treadmill will have no effect. But I thought you were arguing that an actual treadmill would be able to prevent takeoff. I apologize for that.
-MEC
Pretty much.
If we want to split hairs, I'll say they used an Ultralight and not a jet.
I loved the argument that some used on their message board that their graphic for the myth showed a plane standing still on a treadmill and taking off "in place." Saying the myth they tested in practicality wasn't the same as their graphic -designed to "explain the myth."
I guess the people playing that card forgot about all of the times graphics were used/showed things way out of the context of what they're (trying) to do. The graphic is just an entertainment bumper to the segment and most likely done by the production end of things and not the MBs themselves.
A sea plane first gets up on the step before it can take off. It has to hydroplane on the surface of the water first. Until it gets up out of the water it can't take off.
A Cessna lying on the ground might wiggle around some but it won't move forward fast enough (because of friction, drag, whatever you want to call it) to reach takeoff speed.
Now that's just splitting hairs.
Fine. In a perfect world. With a plane with a powerful engine, and in a "guide system" to keep it from wiggling, washing, and squirming will move forward and take off sitting on the ground. Wheels or no.
The very first airplane didn't even have wheels.
If you can solve the structural problems that comes with attaching a pair of CFM56s to a Cessena then you betcha your ass it'll take off with or without landing gears with those two babies at full throttle.
If you can solve the structural problems that comes with attaching a pair of CFM56s to a Cessena then you betcha your ass it'll take off with or without landing gears with those two babies at full throttle.
The Wright Brothers plane took off from rails. It wasn't lying on the ground. A Cessna lying on the ground will develop too much drag.
1. There is no such thing as ground drag. Drag is a technical term which refers to only fluid resistance.
2. Wright Brothers didn't have engines available to them that can produce 100,000 pounds of thrust.
Come on! Not drag in an aerodynamic sense, drag as in too much resistance to forward motion. And what does 10,000 pound thrust engines have to do with anything? The Wright Brothers didn't take off from the ground. The plane moved along rails to expedite achieving takeoff speed.
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