Previous in Forum: The Onion - Spirit rover beginning to hate Mars Next in Forum: Transit of Mercury
 Page 2 of 2: « First < Prev 1 2 Last »
Anonymous Poster

11/01/2006 1:29 PM

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction) instantly.

Will the plane be able to take off?

I think no, because if the treadmill accelerates to compensate for the thurst generated by the engines, airspeed will be 0 while ground speed will be whatever speed the treadmill is.

Interested in this topic? By joining CR4 you can "subscribe" to

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Active Contributor

Join Date: Dec 2006
Posts: 18
#85
Find in discussion

### Re: Airplane on a Treadmill?

12/12/2006 4:03 AM

The more I think about it, the proof goes back to the distance traveled by each wheel rotation. Your 767 traveling at 120 mph on the treadmill is covering 176' per second or 12 wheel rotations per second with a wheel whose circumference is 14.67'.

So your wheel cannot be moving at 240 mph unless your wheels are moving at 24 rotations per second. If they are, then the treadmill is moving at 120 mph backwards while the plane is moving 240 mph forward, for a combined forward ground speed of 120 mph....which is contrary to the original premise of the treadmill matching the plane's speed on the ground.

Also think of the wheel rotation when the plane lands. The wheel has zero rotation until it hits the ground, when it suddenly must accelerate to 12 wheel rotations per second at 120 mph. The wheel cannot be moving faster than the speed of the plane on the ground.

Active Contributor

Join Date: Dec 2006
Posts: 18
#86

### Re: Airplane on a Treadmill?

12/12/2006 4:31 AM

Instead of a treadmill, think of a super aircraft carrier that can slowly accelerate to 120 mph. You can put a plane on the deck and apply sufficient thrust to match a 120 mph airspeed and hold the wheel brakes on. As the carrier reached a speed of 120 mph the plane could rotate and be airborne directly over the same spot on the deck, almost like a Harrier only already at 120 mph matching the carrier's speed. If you were sailing into a strong 60 knot headwind, the plane would take off when the carrier reached 60 knots....and the plane would still appear stationary over the same spot on the carrier with 120 knots airspeed but only 60 knots ground speed.

Now imagine an aircraft carrier that is several miles long. It is sailing in a direction opposite of the plane's takeoff direction. The carrier slowly accelerates to 120 mph on a heading of 90 degrees while the plane slowly matches that acceleration to 120 mph on an opposite heading of 270 degrees. What is the plane's ground speed during this entire process? Zero. What is the plane's airspeed. Zero. It effectively has a 120 knot tailwind due to the carriers reverse speed that counters the forward 120 knot speed of the plane. Thus the plane would need to accelerate on the long carrier to 240 knots before it had sufficient forward 120 knot airspeed to lift off.

Active Contributor

Join Date: Dec 2006
Posts: 18
#89

### Re: Airplane on a Treadmill?

12/12/2006 11:47 PM

One final point and then I will hang it up.

Picture this 10 mile long aircraft carrier standing still with the front of it under the Golden Gate Bridge and a jet facing the opposite direction directly under the bridge. The carrier starts to move forward out of the bay just as a jet on the end starts to move in the opposite direction. The jet accelerates at the same rate as the carrier in the opposite direction. The pilot notes that the bridge is still directly above him even though he knows he is moving on the carrier deck and the carrier is moving out of the bay at a high rate of speed. What happens when the jet reaches the end of the 10 mile long carrier and it is still directly under the bridge?

It drops into the water under the bridge because the jet had no air moving over its wings so therefore no lift. It was moving fast over the deck of the carrier, but not at all versus the true ground and its corresponding air.

Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#92

### Re: Airplane on a Treadmill?

12/13/2006 7:40 AM

I'm going to try to change the subject ..You have a UFO accelerating straight up with 2 treadmills on either side of it going down. There are wheels on either side of the ufo touching the treadmill. Are the Martians green or red? Ha. Nothing to do with Masu who has changed from red to blue. (Probably from threads like this which have turned into a lengthy docudrama.) Congrats on Guru status Masu. I'm outta here.

Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#93

### Re: Airplane on a Treadmill?

12/13/2006 8:57 AM

Thank you for the salutation. There are three currently three theories about the change in colour

1/. After procrastinating for so long on threads like this one I feel like I have been talking till I am blue in the face to people that aren't or don't want to listen.

2/. The continual burning of fossil fuels and rising levels of atmospheric CO2 have caused hypoxia and CO2 toxicity.

3./ The red face is a red shift from running at near light speed from infuriating threads like this and the blue face is a blue shift as I search for less exasperating discussions.

Any theorizing as to the cause of my change from black to read and now blue is welcome so please feel free to post your hypothesis.

__________________
An elephant is a mouse built to government specifications.
Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#94

### Re: Airplane on a Treadmill?

12/13/2006 9:14 AM

Could it be like a mood ring? (remember those from the '60s) When you're exasperated the face is red and when you're happy it's blue? Maybe some visine would be good for the eyes;)

Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#106

### Re: Airplane on a Treadmill?

09/23/2008 5:30 AM

I'm almost frightened to bring this up after the frustration of previous posts but nonetheless cop this ally you doubting Thomas types.

I just saw a Mythbusters episode that dealt with exactly this idiotic idea that an aeroplane on a treadmill wouldn't take off but remain in position or takeoff without moving.

Ok so what happened?

Well exactly what several gurus and myself had predicted, the aeroplane moved with respect to the stationary surrounds and air and took off.

The only thing that happened was that the takeoff run with respect to the stationary surrounds was slightly longer due to the increase in wheel friction but it took off and the treadmill could not arrest the forward motion of the plane through the air.

So, now I get to say:

__________________
An elephant is a mouse built to government specifications.
Power-User

Join Date: Sep 2006
Posts: 451
#107

### Re: Airplane on a Treadmill?

09/23/2008 5:42 PM

There is nothing like a few good facts to ruin an argument. It will do it every time.

BAB

__________________
Make it so.
Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#108

### Re: Airplane on a Treadmill?

09/23/2008 10:36 PM

Good Grief! This ole thread resurrected? Where's the wind and air-mass under (and over) the wings? (at speed) -From a stand-still?? I guess if if rocket engines were employed... ehh...

Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#109

### Re: Airplane on a Treadmill?

09/24/2008 1:18 AM

G'day steve-o,

• I guess if if rocket engines were employed... ehh...

Of course you do realize that technically speaking rocket engines are a form of jet engine as they both employ a JET of gas to propel the vehicle they are attached to.

Regardless of everything else the simple explanation is that everything to do with the way an aircraft performs is governed by the way it interacts with the air that it flies through. Since the treadmill has little to no effect on the air it also has little to no effect on the way the aircraft handles or performs.

It all comes down to Newtons Laws of motion,

• First Law: It is possible to select a set of reference frames, called inertial reference frames, observed from which a particle moves without any change in velocity if no net force acts on it. In other words things don't start or stop moving in regard to a given frame of reference unless acted upon by a force that is relevant to that frame of reference.
• Second Law: Observed from an inertial reference frame, the net force on a particle is proportional to the time rate of change of its linear momentum: Momentum mv is the product of mass and velocity. Force and momentum are vector quantities and the resultant force is found from all the forces present by vector addition. This is the Newton speak for F=ma.
• Third Law: Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line. This is usually quoted as the for every action there is an equal but opposite reaction law.

In the case of our aircraft on the treadmill the relevant frame of reference is the air and not the treadmill. Since the treadmill has little to no effect on the air there is little to no effect on the performance of the aircraft.

Next we get to the third law. Regardless of the type of engine all aircraft produce thrust or a jet of air or gas that is propelled in the opposite direction that they are travelling. The equal and opposite reactive force is then the force that drives the aircraft forward and since this has nothing what so ever to do with the treadmill it doesn't change the way the aircraft accelerates through the stationary air until it ultimately reaches a speed through that stationary air that is sufficient to lift the aircraft off the ground.

__________________
An elephant is a mouse built to government specifications.
Anonymous Poster
#110

### Re: Airplane on a Treadmill?

09/24/2008 8:33 AM

That's a lot of fancy talk.

However, it is clear that the wheels of the plane must first move before the plane can takeoff. We can see that just by observing a takeoff. So, if the conveyor keeps the plane's wheels from moving (as the question clearly states), then the plane cannot take off.

It's just like a car with the brakes on. You can't move.

Therefore, the plane will not fly because the conveyor keeps its wheels from moving. If the wheels are not moving, then there is no inertia, so the first law does not apply to this situation.

If the question was about just an ordinary plane taking off from an ordinary runway, then what you say would be true. But in this case the runway is going backwards, and the plane is going backward with it. All the plane's thrust cannot make the plane move forward, because as soon as it does, the runway speeds up and drags the plane back.

Look at the Mythbusters video. They had to HOLD the model plane to keep it from going off the conveyor belt BACKWARDS! Last I checked, planes only fly when going forward.

Regardless of everything else the simple explanation is that everything to do with the way an aircraft performs is governed by the way it interacts with the air that it flies through.

I think this is where you got confused. You can't assume the plane is flying. That's like assuming that 2+2 = 8 and starting your proof with the assumption that 8 is equal to 2+2.

Since the treadmill has little to no effect on the air it also has little to no effect on the way the aircraft handles or performs.

Park the airplane sideways on the treadmill, and see if it has little to no effect.

Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#113

### Re: Airplane on a Treadmill?

09/24/2008 12:09 PM

G'day guest whoever you are,

• However, it is clear that the wheels of the plane must first move before the plane can takeoff. We can see that just by observing a takeoff. So, if the conveyor keeps the plane's wheels from moving (as the question clearly states), then the plane cannot take off.

What you are trying to say is that the rotation of the wheels is retarding the forward motion of the aircraft through the air.

The mistake you are making is to draw a parallel with a car on a treadmill.

The car and aeroplane use completely different methods of producing and measuring forward motion. Lets look at both in some more detail:

1. The Car on a Treadmill: The car produces and measures its motion with respect to the road surface. The accelerating force comes from the torque that is applied to the wheels and ultimately interacts with the road surface to produce the forward motion. So, if we had a vehicle moving at 10ms-1 in one direction and the road surface moving at 10ms-1 in the opposite direction then the net would be a stationary vehicle.
2. The Aeroplane on a Treadmill: Aircraft produce and measure their motion with respect to the air not the surface of the runway. The reactive force produced by the thrust of the engines acts directly on the airframe of the aircraft and no power of force is transferred to the wheels. The wheels and undercarriage are just there to support the aircraft until the wings can produce enough lift for the aircraft to fly. In this case if we have an aircraft moving at 10 ms-1 in one direction and the runway moving in the opposite at 10ms-1 the aircraft still moves with respect to the air and stationary ground and the wheels end up rotating at 20 ms-1.

Moving on now we get to the following:

• Therefore, the plane will not fly because the conveyor keeps its wheels from moving. If the wheels are not moving, then there is no inertia, so the first law does not apply to this situation.

This is not the case because the convey doesn't keep the wheels from moving as they can't transfer any horizontal force due to their ability to rotate. As a result they can't retard the forward motion and the only difference is a doubling of the rotation speed.

• I think this is where you got confused. You can't assume the plane is flying.

Nobody is assuming that at the beginning but ultimately the aircraft will end up becoming airborne as was shown in both the model and light aircraft experiments.

Lets look at an example second by second with an aircraft that has the following specifications:

Mass: 1,000 kg

Take Off Speed: 50 ms-1

Engine Thrust: 10 kN

Engine Lag: 1 second

1. 000 sec: The aircraft and treadmill are both stationary, the engines are at idle and producing no thrust, there is no motion of either the aircraft or treadmill and there is no wind.
2. 001 sec: The throttles on the aircraft are pushed forward, the engines produce thrust and the engines start to spool up and begin to produce thrust but at this stage everything is still stationary.
3. 002 sec: The engines are now 10 kN of thrust which is interacting with the 1,000 kg mass of the aircraft to produce an acceleration of 10 ms-2 but as yet nothing has moved as the thrust has only just commenced.
4. 003 sec: The aircraft has now been accelerating at 10 ms-2 for 1 second and now has a speed of 10 ms-1. As a result the treadmill is now being driven in the opposite direction at 10 ms-1. However since the thrust of the engines is acting directly on the aircraft the aircraft is moving through the air at 10 ms-1 and as the treadmill is going in the opposite direction the wheels are rotating at 20 ms‑1. Against the stationary point the aircraft has now moved 5 m forward while with respect to the surface of the treadmill the aircraft has moved 10 m.
5. 004 sec: The engines have now been producing 10 kN for 2 seconds and the airspeed is now 20 ms-1 while the treadmill is going in the opposite direction at 20 ms-1 and the wheels are turning at 40 ms-1. The aircraft has now moved 15 m with respect to the stationary starting point and 30 m with regard to the starting point on the treadmill.
6. 005 sec: The same as at + 003 except the airspeed is now 30 ms-1 the treadmill speed is 30 ms-1 wheel speed 60 ms-1 and has moved 45 m from the stationary start and 90 m from the start on the treadmill.
7. 006 sec: The same again except the airspeed is no 40 ms-1 the treadmill speed is 40 ms-1 wheel speed is 80 ms-1 and has moved 80 m from the stationary start and 160 m from the treadmill start.
8. 007 sec: The aircraft has now accelerated to an airspeed of 50 ms-1 while the treadmill is moving at 50 ms-1. However, the aircraft has now reached its take off speed of 50 ms-1 so is now airborne. The distance from the stationary starting point is 125 m while to the start on the treadmill it has moved 250 m.

The mistake people are making is to not use the correct frames of reference. With a car the force, speed and distance are measured with relation to the treadmill and as a result the negative speed of the treadmill counters the speed of the car. With the aircraft the force, speed and distance are measured with respect to the stationary air and while the net result is a doubling of the speed the wheels are rotating the airspeed through the stationary remains the same and the aircraft moves with respect to the stationary air and ground till it reaches flying speed and becomes airborne.

• Park the airplane sideways on the treadmill, and see if it has little to no effect.

We are talking about trying to retard the forward motion of the aircraft so I can't see why having it sideways would be in any way relevant to the problem. Yes the aircraft would move with the conveyor and soon get pushed off the side by the thrust but that's not what we are discussing here.

Regardless of everything everybody has posted, when the Mythbusters tried to retard the forward motion of an aircraft by moving the surface of the runway (ok it was a tarpaulin but it is a valid analogue) in the opposite direction the aircraft still moved forward, achieved flying speed and became airborne.

PS: I knew it was probably a bad idea to dig this up again. This has gone on for so long now that I could just about write a book on the subject.

__________________
An elephant is a mouse built to government specifications.
Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#114

### Re: Airplane on a Treadmill?

09/24/2008 1:55 PM

Yeah it is a useless thread. I thought it was gone, but like a bad penny...

- OK, if it was a Harrier jet it could take-off using downward and forward thrust Same thing with a helicopter..

Anonymous Poster
#115

### Re: Airplane on a Treadmill?

09/24/2008 8:58 PM

I think you may be confused about flight. In an earlier post, you said that the thrust was directed backwards. It is really directed forwards, as shown here. If thrust were directed backwards, then it would be adding to drag.

Also you are correct that airspeed is required to make a plane fly, but in this puzzle we cannot have any airspeed, because as soon as we get any, the plane gets pulled backwards by the conveyor, because of the tire flat spots, bearing friction, etc. Then the conveyor stops (matching the zero airspeed) but the plane continues backwards for a second. This generates a reverse airspeed, which causes the conveyor to run forward. Seems like the plane would go back and forth, but not take off.

Wouldn't the plane fall off the front or back of the conveyor?

With the aircraft the force, speed and distance are measured with respect to the stationary air and while the net result is a doubling of the speed the wheels are rotating the airspeed through the stationary remains the same and the aircraft moves with respect to the stationary air and ground till it reaches flying speed and becomes airborne.

With aircraft, it seems like the force should be measured with respect to the aircraft mass, not the air. The idea is, I think, that the force of the engine accelerates the plane, rather than moving all the air backwards around the plane. If it moves the air, then there would have to be a ring of air around the earth the the plane flies through.

I wasn't sure what you meant by "rotating the airspeed through the stationary remains". I think you are saying that the wheels are rotating the airspeed, but I think the engines do that (but if there are two, the rotation cancels).

You have probably seen a plane take off. They start off really slow. The Mythbusters experiment was like yanking a tablecloth out from under the plane. A real conveyor would move just as slowly as the plane, and slowly pull it back with respect to the air. Mythbusters is just a tv show, and they could have rigged things.

In a wind tunnel, the air moves, but the plane stays still. If you are thinking along those lines, then you'd need a lot of really big fans, instead of a conveyor. Seems like you'd need something to keep the plane from getting blown back. The engines couldn't have enough force to counteract all that air rushing past. Maybe you've seen an airport after a tornado.

I think you can see now why the plane would not take off if it can't move through the air.

Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#116

### Re: Airplane on a Treadmill?

09/25/2008 5:17 AM

G'day folks,

• I think you may be confused about flight. In an earlier post, you said that the thrust was directed backwards. It is really directed forwards

Thrust is actually a pair of forces as per Newton's third law which when translated from Newton speak states:

For every action there is and equal but opposite reaction.

In this case the pair of forces involved are the force acting on the air which is accelerated by the aircraft backwards and the resultant reaction to that which propels the aircraft forward. The forward force is then countered by the drag which is a function of the air speed so the aircraft will accelerate until the drag increases to the point that it counters the forward acting force the engines are producing.

It depends on how you look at it and technically you are correct in that the thrust is a forward acting force but it is also common and I suppose technically incorrect to refer to the rearward moving air that the propellers or jet exhaust produce as the engine's thrust.

• You have probably seen a plane take off. They start off really slow. The Mythbusters experiment was like yanking a tablecloth out from under the plane. A real conveyor would move just as slowly as the plane, and slowly pull it back with respect to the air. Mythbusters is just a tv show, and they could have rigged things.

A lot more than that, I have had a pilots licence for over 30 years and although not current have experience in single engine powered aircraft as well as high performance 15 m, sports and open class gliders.

First off lets look at the difference in the way cars and aircraft measure their speed.

A car uses a mechanical connection to the wheels that are driving the vehicle forward and as a result are a measure of the speed they are moving across the road surface.

Aircraft don't measure their speed this way but rather a system as shown in the image on the right.

Basically you have two ports a static port which measures the static air pressure and a Pitot head which measures the dynamic air pressure due to the aircraft's forward motion. The two pressures are then fed into what is basically a barometer which then subtracts the static air pressure from the dynamic air pressure. The result is a measure of the aircraft's effective speed through the air.

So, if you have the conveyor moving backwards at the same speed as the aircraft is moving through the air it will not arrest the forward motion of the aircraft, just double the speed at which the wheels are turning. As a result the aircraft will continue to move forward and will ultimately become airborne when the air speed is great enough to develop sufficient lift to raise the aircraft off the ground.

What you are intimating is that rather than having the treadmill moving at the same speed the aircraft is moving forward is to have it moving fast enough so the friction in the wheel opposes the forward motion of the aircraft. Unfortunately this is just never going to happen as was shown by the Mythbusters episode.

With the full scale experiment they did not start moving the tarpaulin until the pilot started to open the throttle and no matter how hard of fast they had the tarpaulin going in the opposite direction they could not retard the forward motion of the aircraft. Jamie actually stated that no matter what he did he couldn't stop the aeroplane and at one time he had the tarpaulin going considerably faster than the aircrafts take off speed.

The end result was the aircraft becoming airborne in what was almost exactly the same distance as it would have if there were no tarpaulin (read analogue for treadmill).

Even if you had the wheel brakes on I doubt whether you would be able to overcome the forward motion of the aircraft as in most aircraft the engines can overwhelm the brakes and move the aircraft forward. Back when I was doing my flight training my instructor got me to hit the engine volume control while standing on the toe brakes. We only did it for a few seconds as it can damage the brakes but regardless of how much I applied the brakes I could not arrest the aircrafts forward acceleration and motion.

G'day steve-o,

• It's been a while.

I've been a little swamped lately. My better half and I moved from Adelaide to Sydney and the space available for my workshop has dropped by about 80%. Nonetheless, I have come up with a workable design for a workshop and have been spending most of my time getting it completed and operational. It's taken a lot longer than I anticipated but I should be completed before the end of the year at which time I will be resurrecting the deHavilland DH98 Mosquito 1:8 scale flying replica blog. If enough people are interested and I have the time I will post a thread on the CR4 Workbench Creations blog about the workshop and how I went about fitting a double garage sized workshop into a room 2.5 by 1.4 m room.

• I dont know why I posted that, I suppose that I was playing the devil's advocate after a few glasses on wine last night. You're right, the plane will take-off. The engines apply pressure to the surrounding air mass moving the aircraft forward, and the wheels are just along for the ride .

You're pretty close to being spot on whit the exception of that bit about apply pressure to the surrounding air mass moving the aircraft forward. It's actually the Newton's third law of equal but opposite reaction to the acceleration of the gasses in the engine or produce by the propeller rather than pushing or pulling on the surrounding air.

I know it's being pedantic but if it was the exhaust of the engines or propeller pushing against the surrounding air then we would never be able to travel through space where there's a vacuum. The same argument was used for years to say why we could never travel through space but in reality it is the reactive force to the exhaust of the engines that causes the movement hence the ability for rockets to accelerate and travel through space.

Then again, if you listen to the conspiracy cranks the world is flat and the moon missions were all staged so you can't believe in anything including this thread.

__________________
An elephant is a mouse built to government specifications.
Guru

Join Date: Aug 2006
Location: Santiago Chile.
Posts: 845
#118

### Re: Airplane on a Treadmill?

09/25/2008 10:10 AM

Hello Masu...

Because of this post and your long and detailed replies I have made a startling discovery!!!, and am going to present it to the navy.

Why for god sakes use this very complex, expensive overkill catapult system to shoot an airplane of the deck of an aircraft carrier, when you can simply use a little conveyor belt?

All rights reservedÂ© for you and me. Whatever they pay (and I am sure they will) will split 50/50. Is this a deal?

Wangito.

__________________
Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#112

### Re: Airplane on a Treadmill?

09/24/2008 10:20 AM

Hi Masu!

It's been a while. I dont know why I posted that, I suppose that I was playing the devil's advocate after a few glasses on wine last night. You're right, the plane will take-off. The engines apply pressure to the surrounding air mass moving the aircraft forward, and the wheels are just along for the ride.

Guru

Join Date: Aug 2006
Location: Santiago Chile.
Posts: 845
#117

### Re: Airplane on a Treadmill?

09/25/2008 9:40 AM

Meaning a glider will not?...

Wangito.

__________________
Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#119

### Re: Airplane on a Treadmill?

09/25/2008 12:43 PM

?? A glider has no engine. It cannot take off under its own power..

_________________________________________________

Anyhow, this may have been posted already, but here it is again:

Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#120

### Re: Airplane on a Treadmill?

09/26/2008 3:35 AM

Exactly, no matter how hard you try and how fast the tarpaulin (read treadmill) goes in the opposite direction you just can't stop the plane from moving forward and taking off.

• A glider has no engine.

Not necessarily, there are gliders that have small engines that they use to become airborne then fold up inside the fuselage like the one below.

This sort of glider has been becoming steadily more popular as it doesn't need the infrastructure standard gliders need to get airborne. They are also becoming more and more cost effective as the cost of operating tugs has been rising far faster than the average inflation rates for nearly 20 years now.

The added mass of the engine is not as much of a handicap as one might expect. With gliders it's common to carry water ballast in tanks in the wings to improve its performance. It's sort of analogous to a rock and screwed up piece of paper that both have the same coefficient of drag. If you throw both of them at the same speed the rock will go a hell of a lot further because the ratio of kinetic energy loss due to drag is much less for the rock than the paper.

In gliders the added kinetic energy means they loose less height per distance flow when gliding between thermals which is offset by a reduced rate of climb when thermalling. By adjusting your speed (slow when in the thermals and bat out of hell between thermals) by adding extra mass you can end up with an overall performance improvement.

By the way, yes the winglets or upturned wing tips do give you a measurable improvement in performance. It's not uncommon for older gliders, like the 30 year old Hornet VH-GEY in the images below showing it before and after, to have winglets added in order to enhance their performance.

No, it's not me flying but it is a friend of mine and I have flown this aeroplane fairly extensively. Even though it's 30 years old it's still a nice aircraft to fly and has a carbon fibre reinforced wing spar, glass reinforced epoxy foam filled structure and Kevlar reinforced cockpit and canopy hoop to protect the pilot in the event of an accident. The Hornet is a bit of a handful when taking off and landing but with a bit of practice you can soon develop techniques to overcome it's tendency to drop a wing on take off or balloon during the flare and hold off.

__________________
An elephant is a mouse built to government specifications.
Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#122

### Re: Airplane on a Treadmill?

09/26/2008 1:04 PM

Interesting. I didn't know of powered gliders. I thought he was talking about conventional non-engine gliders that require a tow-plane.

____________________________________________________

Anyway, this thought occurs to me.. Say you have a large industrial fan (electric motor, long extension cord) that is powerful enough that when placed on the 'high' setting will actually tilt itself over. (I know that they don't build them that way but...theoretically, if..) placed on the treadmill pointing towards the rear of the treadmill. Turn the treadmill on, turn the fan on; the fan, I believe, will still tilt itself over. Now install wheels on the fan, the fan should propel forward regardless of the backward motion of the treadmill. Now install wings on the fan for lift.. etc..

Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#123

### Re: Airplane on a Treadmill?

09/27/2008 12:58 PM

G'day steve-o

• Anyway, this thought occurs to me.. Say you have a large industrial fan (electric motor, long extension cord) that is powerful enough that when placed on the 'high' setting will actually tilt itself over. (I know that they don't build them that way but...theoretically, if..) placed on the treadmill pointing towards the rear of the treadmill. Turn the treadmill on, turn the fan on; the fan, I believe, will still tilt itself over. Now install wheels on the fan, the fan should propel forward regardless of the backward motion of the treadmill. Now install wings on the fan for lift.. etc..

You've got to be more careful about what you suggest, you never know who is reading what you write on CR4. Have a butchers at the Antares 20E paying particular attention to the sections on Propulsion and Technical Data.

Does anything sound sort of familiar to you?

__________________
An elephant is a mouse built to government specifications.
Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#124

### Re: Airplane on a Treadmill?

09/27/2008 2:54 PM

Nice Plane, what does that have to do with being careful about posting my 'fan on a treadmill'?

Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#125

### Re: Airplane on a Treadmill?

09/28/2008 3:32 AM

Considering it uses a prop that's pretty much like one of those bloody great industrial sized fans you were talking about, driven by a brushless DC motor, has wings etcetera the only thing we need to add is the treadmill and we've got you design ready to try.

I must admit the thought of an electrically powered self launching glider sounds extremely good to me. Batteries and electronics are a so much easier to maintain than all those moving parts in an engine and you don't have to worry about the heat from the exhaust damaging the airframe. It also reduced the fire risk in the event of things going wrong.

Most people don't realize it but in an aircraft accident is usually not the crash that kills people it's the fire that starts shortly after that gets everybody. Unless you do something like fly the aeroplane into a cumulo-granitus (pilot speak for cloud with a mountain inside it) at full speed there's a very good chance that nearly everybody on board will be alive when the wreckage comes to rest. This is born out by the autopsies of aircraft accident victims which nearly always show the effects of smoke inhalation and burning to the airways and lungs so they must have still been breathing when the fire started.

__________________
An elephant is a mouse built to government specifications.
Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#126

### Re: Airplane on a Treadmill?

09/28/2008 9:05 PM

Sounds logical to me.

Now all we need is a light-weight battery

Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#128

### Re: Airplane on a Treadmill?

09/29/2008 2:03 AM

The battery pack in the Antares 20E utilizes a bank of 24 LiIon SAFT VL41M cells each individually monitored and controlled that give you a total gain in height of around 10,000 feet. Normally a glider is towed to about 2,000 feet above the ground so you should get about 4 to 5 launches out of a single charge.

That all adds up to about 12 minutes at full power which should be well and truly enough for the treadmill experiment. Now all we need is a 300 m (1,000 feet) long treadmill and we can do a full scale true to the initial post experiment that once and for all proves that the aeroplane can take off.

Then again, judging by some of the responses to the two documented real world experiments so far posted in this thread some people wouldn't believe it if they were in the bloody thing when it took off. I wonder if there is any connection to the perpetual motion energy from nothing mob that steadfastly refuse to accept the laws of physics and insist that we engineers and scientists don't know what we are talking about.

__________________
An elephant is a mouse built to government specifications.
Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#129

### Re: Airplane on a Treadmill?

09/29/2008 3:24 AM

As a post script to my last post.

If there are any super wealthy bloggers out there that are willing to fork out for the Antares 20E and a +300 m long conveyor belt I would be glad to donate my time to setting it up the experiment and flying the glider. I would also be pleased to remove and dispose of all the equipment after the experiment.

Well, you've got to ask. You never know who's reading this rubish and the Antares 20E would be guaranteed of a good home not to mention looking really good in the hangar I would build for it.

__________________
An elephant is a mouse built to government specifications.
Power-User

Join Date: Sep 2006
Posts: 451
#130

### Re: Airplane on a Treadmill?

09/29/2008 5:38 PM

Hi Masu

The Antares 20E web site didn't mention the price tag for the wing thing.

Any idea what they are worth or what they cost?

I suspect it would make one light headed and would certainly lighten the wallet thus reducing the weight load.

BAB

__________________
Make it so.
Power-User

Join Date: Jun 2006
Location: Southwest Virginia, United States
Posts: 366
#131

### Re: Airplane on a Treadmill?

09/29/2008 6:50 PM

Hehe-- I'd say so.

Seeing that pic again, looks like the wingspan of that thing is 100 ft

Power-User

Join Date: Sep 2006
Posts: 451
#132

### Re: Airplane on a Treadmill?

09/29/2008 7:02 PM

The 20 indicates 20 metres, therefore 65 feet near enough of whiz-bang composites for the ancient imperialist.

BAB

__________________
Make it so.
Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#133

### Re: Airplane on a Treadmill?

09/30/2008 5:10 AM

The only price I have been able to find is €153,000.00 which comes in at AU\$273,000.00 or US\$220,000.00.

Which sounds about right to me. The last glider I had any thing to do with the purchase of was a Grob G-103 Twin II which was about AU60,000.00 but that was for a second hand glider and about 12 years ago. At the time I think the Discus which is a single seat 15 m glider with carbon fibre main spar was about AU\$100,000.00 new so if you add inflation and the cost of the batteries, electronics, motor, prop and additional 5 metres of wing €153,000.00 would be a realistic price.

__________________
An elephant is a mouse built to government specifications.
Power-User

Join Date: Sep 2006
Posts: 451
#127

### Re: Airplane on a Treadmill?

09/28/2008 9:08 PM

Hi Masu,

Nice link, thank you very much.

BAB

__________________
Make it so.
Guru

Join Date: Jun 2006
Location: Port Noarlunga, South Australia, AUSTRALIA (South of Adelaide)
Posts: 3051
#121

### Re: Airplane on a Treadmill?

09/26/2008 4:07 AM

So far the best copy of the Mythbusters segment that I have found it this YouTube version.

__________________
An elephant is a mouse built to government specifications.
Anonymous Poster
#134

### Re: Airplane on a Treadmill?

01/28/2009 2:41 PM

The answer is YES and it has been proved.

Anonymous Poster
#135

### Re: Airplane on a Treadmill?

01/27/2010 3:03 PM

Of course the plane will take off its generating thrust and pushing the plane not driving the wheels which are what will be touching the ground, ground speed means nothing in this experiment. the wheels will simply turn faster as the plane pushes forward now had the plane been driven at the wheels then it would be a different story. they would have to overcome the ground speed. at least this is what i think

 Reply to Forum Thread Page 2 of 2: « First < Prev 1 2 Last »
Interested in this topic? By joining CR4 you can "subscribe" to