Jump to content

Sign in to follow this  
kerosene31

Something to think about

Recommended Posts

Guest enave

>(can not be bothered to read the whole post, will take a>week)Well then I can't be bothered to tell you why you're wrong.

Share this post


Link to post

This reminds me of an incident many many years ago. I was going to work and I was passing KTOA (Zamperini) on an extremely windy day. I noticed this Cessna 150 (with full flaps, don't know why) trying to land. It was inching its way down ever so slowly....almost at a standstill. For all I know he is still hanging in the air (LOL).Abe

Share this post


Link to post
Guest Adverse Yawn

Arrggghhhhhhh!!

Share this post


Link to post
Guest jboweruk

Because of the way a treadmill works, the plane would still pick up speed, eventually it would gain enough forward momentum to takeoff, however by then the tires might have blown, somebody would have to tell the treadmill how fast to go anyway because a plane's wheels have nothing to do with it's speed, it comes from thrust generated by the engines. So ultimately the treadmill would not work thus allowing full normal takeoff.

Share this post


Link to post
Guest contaegious

Maybe we should suggest askin Discoery Channel Mythbusters....

Share this post


Link to post

Yes, the airplane could take off. The physics are easy when the airplane is a Harrier.Geez, and to think that nobody has thought to mention the effects resulting from the boundary layer interactions between the air mass and the moving runway surface...A huge pile of implied conditions and effects here.If you're asking will a non-VTOL airplane take off while remaining at a fixed point over the surface of the earth in a calm air mass...nope. But the original post did not ask if the aircraft would takeoff while remaining in a fixed position. It asked if it would take off. And it said nothing about a still air mass, either.If you're asking will the airplane be constrained from accelerating forward in space by the moving runway...again no, in the conditions stated in the original situation (the runway moving at the same speed but opposite direction to the aircraft). The airplane will accelerate forward in space...but the wheel speed will be 2x the actual forward speed of the acft relative to the earth's surface.Could a theoretical moving runway (treadmill) keep a plane from accelerating forward...maybe, for example if the runway moved so fast that wheel bearing friction were to become a factor (tires, wheels, and bearings would all be long gone by then). But the original question stated the runway would move at the same speed as the acft. But of course, if the treadmill surface speeds were that high, the aforementioned boundary layer interactions might generate a significant enough airflow to generate lift and an artificial ground effect, taking weight off the wheels and reducing the coeffecient of friction, preventing deceleration...aaaaaaaaaaarrrrrrrrgh!!Or, alternatively, if you're in Kansas, the plane would take off due to the intelligent design of a higher being. (I think his name was Orville Wright)CheersBob ScottATP IMEL Gulfstream II-III-IV-V L-300Santiago de Chile


Bob Scott | AVSIM Forums Administrator | AVSIM Board of Directors

ATP Gulfstream II-III-IV-V

System: i9-10900K @ 5.2GHz on custom water loop, ASUS Maximus XII Hero, 32GB GSkill 3600MHz CAS15, eVGA 2080Ti XC Ultra, Samsung 55" JS8500 4K TV@30Hz, 5xSamsung SSD, eVGA 1KW PSU

SB XFi Titanium, optical link to Yamaha RX-V467, Polk/Klipsch 6" bookshelf spkrs, Polk 12" subwoofer, 12.9" iPad Pro, PFC yoke/throttle quad/pedals with custom Hall sensors, Coolermaster HAF932 case, Stream Deck XL button box

Share this post


Link to post
Guest Iceman07

OK, I've read the first few responses, and the last few, so forgive me if someone has pointed this out already:If you are arguing thatt he airplane will not take off, becuase for some reason the wheels are part of the whole momentum thing, I ask you this:How does an airplane that is on skis take off from a icy runway? For all intents and purposes, there is no friction between the skis and the ice, escpecially once the wings start to gain lift. Are you going to argue that somehow the propellor transfers momentum through the skis?Man, that's gonna come as a big surprise to all the guys flying down in Antarctica (not to mention Canada and the upper Mid West)

Share this post


Link to post

couldnt this be solved by buying a the largest treadmill out there and getting a small radio controlled airplane and just see what would happen, i fly rc all i need is someone to give me a treadmillciao!Brian S


Ciao!

 

 

Share this post


Link to post
Guest Iceman07

Actually, it already has been solved. There is a well-known airshow act that has been performed for years and years: Put a small platform on the top of a car, put a light plane on the platform, have the car drive down the runway at takeoff speed, and the airplane will still take off and land. And guess what? The wheels are not turning. What a surprise!Also, in southern Californis, out in the desert, pilots used to fly C-150s and C-172s along a freeway, and then do "touch and go's" on the top of semi truck trailers. This used to be very common until a few years ago, when a guy hit a electrical wire.Oh, and guess what? The wheels aren't turning then, eithier.

Share this post


Link to post
Guest drewhosick

I do have something to add...If you take the wheels out, just leave the plane on it's belly somehow(let's pretend the prop isn't touching the ground and has clearance with the plane on it's belly. You accelerate, what happens? The plane doesn't move right? The thrust doesn't overcome the friction on the ground(unless you have a #### of an engine)... put that plane on a treadmill, it's gonna stay still(if the treadmill was a normal one with usual speed the plane would move backwards but because it matches the speed of the wheel or belly in this case it would just sit still...And if the plane had a big enough engine to move the plane forward on its belly it would still stand still on the treadmill because the treadmill would turn at the right speed for it to stand still(the friction will keep it from moving forward... as soon as the plane tried to move forward, the treadmill would counteract... Friction keeps it from moving)Now put it on the wheels... There little friction but it's there... as minute as it may be, it's there... And no matter how much thrust you get from the prop, the little amount of friction in the wheels will counteract it... Maybe very little friction compared to the whole belly but it's still there. The prop just can't counteract the friction when the belly is on the ground and theoretically those wheels will turn as fast as they have too to match the thrust on the prop but if the belt is turning in the opposite direction at the speed of the wheels, it doesn't matter... that little amount of friction just grows exponentially as the wheels turn superfast...By the way, for the person that mentioned the skis... No they don't turn like wheels, but the engine counteracts the friction caused between the two(and there is some) and overpowers that force... Put those skis on a plane on a treadmill that will move back at the same speed the plane tries to move forward and it won't go anywhere cause it had even more friction then the wheels.

Share this post


Link to post
Guest wyoming

What makes an A/C take-off is the speed of the air flow over and under the wing. Not the speed in relation to the ground. The 2 are related in real life but not in your example, since by hypothesis, you stay at the same spatial coordinates and the air-mass stays put as well. If your treadmill runs at several hundred miles/hour, you could possibly generate enough "wind" to take off.Conversely, you can take off without ground speed and enough air-speed (which is why A/C are tethered in windy conditions).(answer to the OP w/o reading the posts).

Share this post


Link to post
Guest PARADISE

Airplanes fly, and ONLY fly because of the speed of the air over the wings(airspeed). It has nothing to do with the speed of the wheels (groundspeed).Some have also suggested in the past that an airplanes wheels should turn at a rate to match the landing speed of the aircraft so as to save on tire wear. Simple physics tells us that if you did this and the airplane landed at 100 mph it would accelerate to 200 mph as soon as you touched down.Along the same lines.... couldn't we build a spinning device ( arm attached to an nuclear engine, for example ) in space that could accelerate it's tips to ( and beyond ) the speed of light? Kind of like a huge propeller in space. Instruments at the tips could tell us what and/or where they go.John M

Share this post


Link to post

Somehow I missed this aging thread. Fun was had here!For all the folks that don't understand the difference between the system interfaces....let me try (ps...the plane does take off!)Of course this has been said many times and refuted each time by folks that insist on relying on their intuition...thinking about folks walking on a treadmill.....Go to the gym, have a friend help...stand on either side of a treadmill. Hold the ends of a bar with a wheel resting on the treadmill. Now together, walk the barbell forward....did you and your friend move with respect to the air? Did the treadmill move backward (as if by magic) stopping you and your friend from moving forward? you and your friend are analagous to the engine/propellor. you and your friend are creating an action/reaction off a reference different from the treadmill just as in the airplane case.Since the propellor is pulling on the air (which is isolated from the treadmill runway)it pulls the wheels along the runway, as opposed to a car or a person really walking on the treadmill in which the forces are opposite. Just as you and your friend "pulled" the wheel along the treadmill, causing the wheel to rotate, the treadmill to most likly have no reaction, or if anything a slight forward rather than backward movement depending on the friction in the wheel assembly.Imagine for a minute that the airplanes emergency brakes are on, but the propellor is strong enough to move the airplane anyway. "feel" the directionality of the forces now applied to the treadmill...they're in the opposite direction from what you are seeing in your minds eye as you imagine the system. The wheel would try to move the treadmill in the same direction as the airplane is moving, not the opposite direction. Now, lets imagine that we've released the brake, the treadmill stops moving in the same direction as the airplane becuase now the reaction to the force imposed on the treadmill by the bottom of the tire is reacted by dynamic motion of the wheel, but there are no forces in the rearward direction applied to the treadmill...CheersB

Share this post


Link to post
Guest
This topic is now closed to further replies.
Sign in to follow this  
  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
  • Donation Goals

    AVSIM's 2020 Fundraising Goal

    Donate to our annual general fundraising goal. This donation keeps our doors open and providing you service 24 x 7 x 365. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. We reset this goal every new year for the following year's goal.


    22%
    $5,550.00 of $25,000.00 Donate Now
×
×
  • Create New...