Airplane and Belt Conveyor

[jcthorne]

There is no lift, no air going over the wing the plane is stationary relative to the earth. If the wing tips are wider that the belt you would see no positional difference relative to the ground. Engine speed has nothing to do with it. It is like a car being Dyno tuned. Is it moving?

Lets back up. Do you agree that the engines provide thrust which is a large force pushing forward on the aircraft? If so, what force do you believe is counter acting that to keep the plane at rest?

A car on a dyno will move ALOT if its not strapped down while applying the large force to the rollers. The plane is not strapped down but neither is it applying force to the belt (rollers on a dyno) as the wheels are not driven. But this has nothing to do with the aircraft scenario, the wheels to conveyor belt interface is not applying any meaningful force to the plane or the belt. Also the speed and direction of the conveyor has no bearing on the ambient air, for this example its assumed stationary, ie no wind.

The engines push the plane forward with sufficient force to bring it up to speed. The speed (relative to the earth, not the belt) is the same as the air speed over the wing, that creates the lift. The width of the belt and thus relative position of the wing tips have no bearing on this. The plane moves through the stationary air.

I am really trying here and not doing a very good job explaining it. If I come off sounding condescending, it absolutely is not my intent, just friendly conversation on a technical subject.

 

[jcthorne]

That will only work on a forward prop plane pushing wind over the wings. Not a jet. It sure seemed to me it was moving faster than the belt was pulled. Look at the pylons move as the belt is pulled:dontknow:

The lift works the same way no matter if the prop is up front, to the rear or a jet engine. The engine provides thrust, not air over the wings. Look at the size and position of the prop relative to the wing span. If what you say is true, a wingspan not much wider than the prop would lift the plane just as easily. Simply not true. The video shows exactly what happens.


It also does not matter that the conveyor is not exactly the same speed. If it had the effect many hear think it does, if it were even a significant portion of the same speed it would keep the plane from take off. In the video it was obviously a significant percentage of the plane speed and did not reduce lift at all. The plane took off at its normal lift off speed. The pilot even says this and he did not expect it to take off at all.

If all this discussion and a very well done video of the subject cannot convince you, then it seams you will never quite grasp the laws of physics. Stick with what you are good at and I will go back to managing my heard of cats....errr engineers.

 

[jcthorne]

This ought to answer the question!

Thanks for finding that and posting it. Explained it perfectly. Folks that still do not believe or understand likely think the Apollo lunar landings were a hollywood production too.

 

[ahh-cool]

I have to put in my .02.
If you don't have airflow surrounding the wings you cannot get lift.

Here is my 4 questions that need to be answered.
1) The airflow over the wing is low pressure. Does it pull the wing up?
2) The airflow under the wing is high pressure. Does it push the wing up?
We know jet engines suck and blow.
3) Low pressure in front of the engine. Is the airplane moving into a vacuum?
4) High pressure behind the engine. Is it pushing it forward?

 

[bruiser]

The high pressure air above the wing exerts a downward force while the low pressure air below the wing exerts lift. That's the simplest way to explain it.

Jet engines-I worked on them for twenty years. The basic engine consists of a compressor, hot section and turbine. The compressor pulls air in and compresses it to create high pressure air at the back of the compressor. That air moves in to the combustion, or hot section, and is heated. This heated air drives the turbine. All this together creates thrust, which in turn pushes the aircraft forward. The front of the engine does create a vacuum but this has no effect on the movement of the aircraft.

 

[Magdave]

JC I have been flying planes for years and know very well the principals of lift. You said your self there must be forward velocity of the wing surface to create lift or a force that causes air to pass over the wing in sufficient volume to create it. When this thread started I never though about a front prop air plane or even a dual wing conventional engine but a jet with either wing or tail engines. That scenario would prevent lift because there would be no airflow over the wings to create the Bernoulli effect. Even though the MB video shows it taking off if the belt were moving at the same speed that equaled the thrust of the engine the best that would happen would be for the plane to rise relatively straight up and begin moving forward. Obviously that video does not show that, in fact it shows the plane moving down the belt as the belt was moving slower than the thrust of the plane. If the belt was at the same speed as the thrust of the plane the cones would be stationary. Obviously they were not.:thumbup:

 

[Magdave]

The high pressure air above the wing exerts a downward force while the low pressure air below the wing exerts lift. That's the simplest way to explain it.

Jet engines-I worked on them for twenty years. The basic engine consists of a compressor, hot section and turbine. The compressor pulls air in and compresses it to create high pressure air at the back of the compressor. That air moves in to the combustion, or hot section, and is heated. This heated air drives the turbine. All this together creates thrust, which in turn pushes the aircraft forward. The front of the engine does create a vacuum but this has no effect on the movement of the aircraft.

 

[bruiser]

Simply put.

 

[Yazz]

Think Myth Busters is busted.

The ultralight was moving faster than the conveyer belt, it went past the cones. Which meant it was going faster than the conveyer belt and there was wind flowing over the wings. Also, most ultralights are Short Take Off and Landing, STOL.

Would like them to try that with a heavier aircraft like a twin engine plane. Doesn't matter if it's a prop or turbine engine, just something heavier than FAA regulations for an ultralight.

Sorry, but flying an aircraft is all about airspeed. Blow on that piece of paper one more time. You can talk about how much grunt you have under the hood, but that doesn't cut it in aviation. Not going to bore anybody with the physics.

Have flown backwards via ground speed, and had the stick pointed down for landing and gained altitude. Both were weird, but they happened because of the wind currents around the plane.

If you haven't flown an aircraft, you don't know...

 

[ARCTIC]

It is absolutely MIND BLOWING that someone could actually think that the conveyor could actually prevent a takeoff.

 

[Bob Denman]

:shocked: I can't wait for my riding season to start...

 

[bruiser]

Throw aviation physics out the window

https://youtu.be/g8f3Jto_fjU

 

[Magdave]

It is absolutely MIND BLOWING that someone could actually think that the conveyor could actually prevent a takeoff.

Actually the prop on that plane probably could not generate enough prop wash to generate lift over those wings without forward movement. The air flow would be close to and around the body not the entire wing. Not enough lift generated over the entire wing and the section close to the body is only partially able to provide lift. The section attached to the body itself will not generate any. See above video. Only 1 side of the wing will get any airflow. It takes 2. To me it is mind blowing that anyone thinks the engine provides enough air flow to provide lift. All it does is provide thrust for the ENTIRE fuselage so it moves forward and creates air flow over the wing surfaces. If it provided enough air flow over the wings by it self you would see all the little planes hop like bunnies around the airport. :roflblack:

 

[ursamajor35126]

It is absolutely MIND BLOWING that someone could actually think that the conveyor could actually prevent a takeoff.

:agree:.... the ONLY thing the conveyor does is change the rotational velocity of the wheels. Which has NO relationship to the air speed and therefore the lift. It MAY increase drag slightly because of the increased friction but that is all. What is amazing to me is that even the pilot in the Mythbuster test thought the plane would not fly.... was HE ever surprised!:yikes:

 

[Magdave]

:agree:.... the ONLY thing the conveyor does is change the rotational velocity of the wheels. Which has NO relationship to the air speed and therefore the lift. It MAY increase drag slightly because of the increased friction but that is all. What is amazing to me is that even the pilot in the Mythbuster test thought the plane would not fly.... was HE ever surprised!:yikes:

Your MB post was so bogus. It is obvious the plane was moving forward look at the cones. the belt was not moving at the same speed as the thrust. Once moving forward the engine thrust and forward movement ( causing air flow on the wings) provided lift on the wings. I have seen those UL planes take off in under 100 yrds at our airport just like it does in the video.hyea:

 

[aeroshots]

https://youtu.be/g8f3Jto_fjU

Awesome no doubt. Here is one that actually impresses me more. Does this change any minds or adjust anyone's thinking relative to prop effect or other factors?

edit -- I just think it is a cool airplane and video. I should know better than to stoke the heat. Good, in a way, to see the passion in this thread.

 

[ursamajor35126]

:shocked::shocked::banghead::banghead: SMDH!

 

[Magdave]

Didn't say it wasn't possible with a short forward movement once again a STOL plane. Why doesn't this one magically lift off the ground when the engines are full out. Answer no forward motion to provide airflow over the wings. And for the last time the MB plane WAS moving forward not stationary on the belt.

 

[jcthorne]

JC I have been flying planes for years and know very well the principals of lift. You said your self there must be forward velocity of the wing surface to create lift or a force that causes air to pass over the wing in sufficient volume to create it. When this thread started I never though about a front prop air plane or even a dual wing conventional engine but a jet with either wing or tail engines. That scenario would prevent lift because there would be no airflow over the wings to create the Bernoulli effect. Even though the MB video shows it taking off if the belt were moving at the same speed that equaled the thrust of the engine the best that would happen would be for the plane to rise relatively straight up and begin moving forward. Obviously that video does not show that, in fact it shows the plane moving down the belt as the belt was moving slower than the thrust of the plane. If the belt was at the same speed as the thrust of the plane the cones would be stationary. Obviously they were not.:thumbup:

We are going to have to agree to disagree.

The thrust has no speed, its a force. the belt cannot move slower or faster than thrust, only slower or faster than the plane, which you already stated was not moving.....

The net force on the object causes the mass to accelerate. If the thrust alone is not causing an acceleration of the plane, there must be some other force acting on the plane equal and opposite to the thrust. You have yet to tell me where you think that force is coming from. Hint, its not the wheels. And that is the whole point. The conveyor cannot exert a force on the plane opposite of the thrust applied by whatever type of engine is on the plane. The conveyor also cannot effect the air flow over the wings of the moving plane. Prop or jet makes no difference here.

 

[jcthorne]

Think Myth Busters is busted.



If you haven't flown an aircraft, you don't know...

No MB was correct and one does not need to fly a plane to understand perfectly well how basic physics works. The vast majority of aeronautical engineers are not pilots.

It is scary to me that there are so many pilots that have no basic understanding of the physics that keep them in the air and how to interact with it. Perhaps pilot education needs to be updated.