Guess what's on Mythbusters?

[zmiller4]

Mods, sorry to keep th thread going, but...

yes. in fact, its exactly the same.

there will be some MINIMAL rolling/fluid friction from the "conveyor" or river.... but it will be easily overcome by the prop.

END OF STORY.

You're correct that in any river you'd actually take off in, the added drag from the current will not prevent a floatplane from taking off.

However, this is a theoretical discussion, right? You do realize that there is a current speed at which the airplane isn' going to be able to get up to speed, right? (I'm not sure you could get a strong enough current for that in real life, although I'd bet that trying to take off a 150 upstream and downwnd in a strong tidal bore would be pretty interesting).

Just wanted to make sure you knew how different the drag is on a floatplane from anything with wheels, but I'm sure your hundreds of hours of seaplane time and "Cornell of the Skies" education taught you that.

 

[TXaviator]

Mods, sorry to keep th thread going, but...



You're correct that in any river you'd actually take off in, the added drag from the current will not prevent a floatplane from taking off.

However, this is a theoretical discussion, right? You do realize that there is a current speed at which the airplane isn' going to be able to get up to speed, right? (I'm not sure you could get a strong enough current for that in real life, although I'd bet that trying to take off a 150 upstream and downwnd in a strong tidal bore would be pretty interesting).

Just wanted to make sure you knew how different the drag is on a floatplane from anything with wheels, but I'm sure your hundreds of hours of seaplane time and "Cornell of the Skies" education taught you that.

HA nice stab but im never one to go touting my time served at UND....(actually to the contrary, if you duck your head in the UND forum:laff: )

anyhow, yes i realize at some point the floatplane would not take off. i also realize that there is significantly more friction from water than there is rolling friction on a hard surface. i said "yes its the same", because obviously some other people here have a hard time with the first concept, let alone confusing them by adding water! :cwm27:

 

[drew09]

so even if the conveyor belt is going at 60 kts and the plane takes off at 60 kts, its just the wheels that are spinning twice as fast, but the plane will still take off at its normal takeoff speed..

jesus christ..:banghead:

 

[Fly_Unity]

say your in a float plane and the river is flowing at 60 knots and your take off is 60kts will the plane take off going up river?

You know that is a very good argument that the plane will take off

I will add that to my repertoire when I do my debating, haha and if that dont convince anyone I dont know what will

 

[Clocks]

so even if the conveyor belt is going at 60 kts and the plane takes off at 60 kts, its just the wheels that are spinning twice as fast, but the plane will still take off at its normal takeoff speed..

jesus christ..:banghead:

Yes. If you were standing off to the side you wouldn't be able to tell the airplane was even on a conveyor belt as it moved forward and took off like normal, no matter which direction the treadmill was moving and regardless of it's speed.

 

[Number1atNumber2]

Make the bad man stop! :insane:

 

[Clocks]

Make the bad man stop! :insane:

If the bad man is on a treadmill going the opposite.....

 

[Inthedraft]

Sorry for being a newbie who is continuing to beat this dead horse, but I figured I'd throw in my 2 cents. What is it that makes an aircraft fly? It is the lift generated by the air moving over the wing. To successfully fly you need to get the air to move at a certain speed to get the proper amount of lift (I know this is a very basic review, but stay with me for a few minutes). So, the question is, can an airplane on a large treadmill fly? I say yes and no. It all depends on the engines.

Let's put aside other issues such as tire integrity for this scenario. We basically have 4 possible situations that may be created by your engines. For the purpose of this discussion let's say that you have an aircraft that needs to have a forward speed of 100 knots to successfully take off. Let's say that your airplane has engines that will only produce enough power to move the aircraft at a forward speed of 10 knots. Now, put that airplane on the treadmill which we will say moves at 50 knots in the opposite direction and open up the throttles. Your airplane will be moving forward at 10 knots but it will be pushed back by the treadmill moving at 50 knots, meaning that you will be going backwards at 40 knots. You will not produce the lift needed to get off the ground.

Unhappy with the performance of your engines you upgrade and get ones that will cause the airplane to move at 50 knots. You get back on the treadmill and fire up the engines again. You are now moving forward at 50 knots but are also moving backwards at 50 knots. You are standing still. There is no air going over the wing and hence, no lift.

You upgrade again to engines that can move the aircraft along at 100 knots. Back on the treadmill, you go full power again. You are now able to move forward at 100 knots, but the treadmill is moving backwards at 50 knots so your effective forward velocity is 50 knots. You now have wind moving over the wing, but it is not enough to produce enough lift so you are unable to leave the ground.

Frustrated, you head back to the engine shop and the owner promises you that this new set will do the trick. They are able to move the plane forward at a speed of 200 knots. Disgruntled, you get back on the treadmill and start the process over. This time you have a forward velocity of 200 knots but are going in reverse at 50 knots. This gives you an effective forward velocity of 150 knots. You now have enough lift to get you off the ground and away from the dreaded treadmill.

So, to make a long story short (too late) the answer is yes and no. It all depends on how much lift you need and if you are able to produce that lift by overcoming the resistance of the treadmill. Clear as mud?

 

[SlumTodd_Millionaire]

:banghead::banghead::banghead::banghead::banghead::banghead::banghead:

 

[derg]

I know.

But what if the aircraft was full of helium balloons? Prove it would decrease your takeoff distance.. Prove it!

(Heavy amounts of )

 

[SteveC]

Sorry for being a newbie who is continuing to beat this dead horse, but I figured I'd throw in my 2 cents. What is it that makes an aircraft fly? It is the lift generated by the air moving over the wing. To successfully fly you need to get the air to move at a certain speed to get the proper amount of lift (I know this is a very basic review, but stay with me for a few minutes). So, the question is, can an airplane on a large treadmill fly? I say yes and no. It all depends on the engines.

Let's put aside other issues such as tire integrity for this scenario...

Sorry, but you are missing two important facts. The first is that an airplane's wheels spin freely, and the second is that an airplane drives itself forward by pushing against the air around it, not by pushing against the ground underneath it like a car or a person running.

To illustrate the difference, let's use a person who is wearing a set of roller blades as an example. If this person stands on a very large treadmill and tries to skate forward while the treadmill starts to run in the opposite direction, it is obvious that he will have a very difficult time making any forward progress, yes? This is the same as a person running on a treadmill, or a car driving on a very large treadmill - they have to push against the ground to make themselves move forward, but the ground is moving away at the same speed.

The scenario with an airplane is different because it doesn't need to push against the ground. Go back to our roller blader, but now find a tree out in front of the treadmill on solid ground, tie a rope to that tree, and run it all the way back to the roller blader. Now the person can simply pull himself forward by standing still (no leg movement), but pulling on the rope. He will be able to pull himself forward very easily no matter whether or not the treadmill is running underneath him, because the wheels of his roller blades spin freely. The wheels can be spinning at 100 miles an hour backward, yet he can easily move himself forward by pulling on the rope. The only thing that the treadmill affects is that it adds a veeeeeeery small amount of drag caused by friction in the wheel bearings - negligible.

Airplane does the same thing, only it pulls on the air around it, not a rope tied to a tree. The wheels just spin freely underneath it, and it doesn't matter if the ground underneath moves forward or backward or stays still.

In your example the description you give is spot on for any type of vehicle that propels itself by pushing against the ground beneath it, such as a car or truck. When we switch it to an airplane the story changes. The first plane you describe will be moving forward at something like 9 knots, not moving backward at 40. The second plane will probably move backward, but at a very slow pace. The third plane will be moving forward at a speed just barely shy of taking off, and the fourth will fly easily because it can go almost twice as fast as needed to take off.

Two facts:
Airplanes push against the air.
Wheels spin freely.

 

[Matt13C]

Let's put aside other issues such as tire integrity for this scenario. We basically have 4 possible situations that may be created by your engines. For the purpose of this discussion let's say that you have an aircraft that needs to have a forward speed of 100 knots to successfully take off. Let's say that your airplane has engines that will only produce enough power to move the aircraft at a forward speed of 10 knots. Now, put that airplane on the treadmill which we will say moves at 50 knots in the opposite direction and open up the throttles. Your airplane will be moving forward at 10 knots but it will be pushed back by the treadmill moving at 50 knots, meaning that you will be going backwards at 40 knots. You will not produce the lift needed to get off the ground.

Edit:SteveC beat me to it. His is a great way to explain it.

Planes develop thrust from the engines, not the wheels.
Turn your engines on, power them up to taxi power. Turn the treadmill on the opposite direction. The plane will continue to taxi forward at a constant speed relative to an outside observer. the planes wheels will be spinning at a speed of taxi speed + conveyer speed.

Power the engines up to acheive the aircrafts maximum 50kts. Now the wheels are turning at 100kts (50 kts from the treadmill and 50kts from the airplanes forward motion), to an observer standing on the side the plane is moving forward at 50kts.

If you put on more powerful engines capable of 100kts, the plane would become airborne. The plane would be moving forward at 100kts, the wheels would be spinning at 150kts.

Thread over.

 

[Brian Z]

Die please dieanic: Please for the sake of all of our sanity if you cannot visualize that it will fly, just accept that the darn thing will fly because it will.

 

[Thunder-Robo]

Sorry for being a newbie who is continuing to beat this dead horse, but I figured I'd throw in my 2 cents. What is it that makes an aircraft fly? It is the lift generated by the air moving over the wing. To successfully fly you need to get the air to move at a certain speed to get the proper amount of lift (I know this is a very basic review, but stay with me for a few minutes). So, the question is, can an airplane on a large treadmill fly? I say yes and no. It all depends on the engines.

Let's put aside other issues such as tire integrity for this scenario. We basically have 4 possible situations that may be created by your engines. For the purpose of this discussion let's say that you have an aircraft that needs to have a forward speed of 100 knots to successfully take off. Let's say that your airplane has engines that will only produce enough power to move the aircraft at a forward speed of 10 knots. Now, put that airplane on the treadmill which we will say moves at 50 knots in the opposite direction and open up the throttles. Your airplane will be moving forward at 10 knots but it will be pushed back by the treadmill moving at 50 knots, meaning that you will be going backwards at 40 knots. You will not produce the lift needed to get off the ground.

Unhappy with the performance of your engines you upgrade and get ones that will cause the airplane to move at 50 knots. You get back on the treadmill and fire up the engines again. You are now moving forward at 50 knots but are also moving backwards at 50 knots. You are standing still. There is no air going over the wing and hence, no lift.

You upgrade again to engines that can move the aircraft along at 100 knots. Back on the treadmill, you go full power again. You are now able to move forward at 100 knots, but the treadmill is moving backwards at 50 knots so your effective forward velocity is 50 knots. You now have wind moving over the wing, but it is not enough to produce enough lift so you are unable to leave the ground.

Frustrated, you head back to the engine shop and the owner promises you that this new set will do the trick. They are able to move the plane forward at a speed of 200 knots. Disgruntled, you get back on the treadmill and start the process over. This time you have a forward velocity of 200 knots but are going in reverse at 50 knots. This gives you an effective forward velocity of 150 knots. You now have enough lift to get you off the ground and away from the dreaded treadmill.

So, to make a long story short (too late) the answer is yes and no. It all depends on how much lift you need and if you are able to produce that lift by overcoming the resistance of the treadmill. Clear as mud?

epic fail.:nana2:

 

[MQAAord]

Okay, has this been covered enough?

I know I'm the Queen Bee of locking threads, so before slamming the door on yet another plane-on-a-treadmill thread, I'll ask y'all first......

Lock thread yet? Yes or no........ (Serious question actually, I don't want to be accused of squashing discussion, but I gotta say that I really think this has been beaten enough already......)

 

[Berkut]

Yes.

 

[SlumTodd_Millionaire]

I despise thread locking with every fiber of my being, but please, put this one out of its misery. And may God have mercy on Tony's soul for starting it up this time!

 

[MQAAord]

Okay, total votes so far is 3 in favor of closing, 1 in favor of remaining open. I'm in the AIM chat now if anyone wants to give their opinion!

 

[SteveC]

It's a harmless enough thread IMO. I think it's interesting to see how different people think this topic through and explain their viewpoint. Kind of a human study course in interwebnetology. Interestingly, I still haven't quite figured out why people get so exasperated with this topic.

It would make it lots easier around here if we put a moratorium on repeat topics though.

 

[SlumTodd_Millionaire]

Damn you, Steve! The one time I'm actually supporting moderation, and you won't help a brother out? This thread must die!