Jump to content
Sign in to follow this  
kccustom

Can the plane take off?

Recommended Posts

The question isn't statics and dynamics; but rather fluid mechanics. the airspeed across the wings is what generates lift. The wheels don't have any bearing in the equation; if they did, then a float-plane wouldn't be able to take off against the current of a river.

 

I disagree, the question is very clear. And I believe the response and "conclusion" are incorrect. Because whoever this guy is, he is obviously not an aerospace engineer. There are several factors that determine if a plane can fly.

 

1. Lift

2. Drag

3. Angle of Attack (or the aggression or pitch of the flight surface of the plane)

 

All the engines do is push the plane to its rated "lift off" speed for a given weight. A plane at its dry weight is built to overcome its drag at a predetermined speed. The reason for bigger more powerful engines is to drive the plane to that given speed with a greater than "dry" load, and will be a very marginal factor in the planes lift characteristics. If this were not the case what would you need such a large wingspan? If the engines were responsible for the lift. The engines only account for 5%-10% of the planes overall lift potential. (That is for a C-130 slick anyway)

Share this post


Link to post
Share on other sites
The thrusters propel the aircraft through the air; not down the runway. The wheels merely hold the Fuselage above the surface of the runway; and thus play no role in the question, the wheels would merely have twice the angular velocity as compared to taking off on a regular runway.

 

The thrusters can't push the plane through the air, if the conveyor belt moves in the opposite direction at the same speed. It doesn't matter how hard the engines are working, as long as the conveyor belt can match the forces created by the planes propulsion system, the plane will remain stationary. So since there is is no airflow over the wings, there is no lift. Without lift, the airplane can't take off and fly.

Share this post


Link to post
Share on other sites
I disagree, the question is very clear. And I believe the response and "conclusion" are incorrect. Because whoever this guy is, he is obviously not an aerospace engineer.

 

HAHAHAHAHAHA

 

I'll have you know I have a BS in Mechanical Engineering and a BS in Aerospace Engineering. I've also taken/passes the Fundamentals of Engineering exam and am a certified Engineering Intern (that's why my title here is "Resident EI").

 

Sounds like you're probably a pilot; but you obviously don't understand the aerodynamics of airplanes.

 

There are several factors that determine if a plane can fly.

 

1. Lift

2. Drag

3. Angle of Attack (or the aggression or pitch of the flight surface of the plane)

 

All the engines do is push the plane to its rated "lift off" speed for a given weight. A plane at its dry weight is built to overcome its drag at a predetermined speed. The reason for bigger more powerful engines is to drive the plane to that given speed with a greater than "dry" load, and will be a very marginal factor in the planes lift characteristics. If this were not the case what would you need such a large wingspan? If the engines were responsible for the lift. The engines only account for 5%-10% of the planes overall lift potential. (That is for a C-130 slick anyway)

 

1. Lift is generated by airflow across the wings; the curved profile of the airfoil results in a faster air velocity over the top of the wing (slower below the wing); resulting in a low pressure region above the wing (and high pressure below the wing)

 

2. Drag is caused by the friction of the air moving over the exterior surfaces of the aircraft

 

3. The angle of attack of the airfoil results in more lift for a given airspeed.

 

The thrusters pull the aircraft through the air creating lift (as outlined in 1); if the airspeed is high enough such that the the lift (created by the airspeed) is greater than (or equal to) the weight of the aircraft, then the plane can lift off.

 

During a take-off run the accelerates till it's airspeed is 115% of the stall speed (slowest airspeed at which the plane can maintain level flight); at this speed the aircraft rotates to increase the angle of attack, resulting in significantly higher lift and thus allowing it to quickly gain altitude.

Share this post


Link to post
Share on other sites
HAHAHAHAHAHA

 

I'll have you know I have a BS in Mechanical Engineering and a BS in Aerospace Engineering. I've also taken/passes the Fundamentals of Engineering exam and am a certified Engineering Intern (that's why my title here is "Resident EI").

 

Sounds like you're probably a pilot; but you obviously don't understand the aerodynamics of airplanes.

 

 

 

1. Lift is generated by airflow across the wings; the curved profile of the airfoil results in a faster air velocity over the top of the wing (slower below the wing); resulting in a low pressure region above the wing (and high pressure below the wing)

 

2. Drag is caused by the friction of the air moving over the exterior surfaces of the aircraft

 

3. The angle of attack of the airfoil results in more lift for a given airspeed.

 

The thrusters pull the aircraft through the air creating lift (as outlined in 1); if the airspeed is high enough such that the the lift (created by the airspeed) is greater than (or equal to) the weight of the aircraft, then the plane can lift off.

 

During a take-off run the accelerates till it's airspeed is 115% of the stall speed (slowest airspeed at which the plane can maintain level flight); at this speed the aircraft rotates to increase the angle of attack, resulting in significantly higher lift and thus allowing it to quickly gain altitude.

 

I was referring to this post.

 

http://www.straightdope.com/columns/060203.html

Share this post


Link to post
Share on other sites
The thrusters can't push the plane through the air, if the conveyor belt moves in the opposite direction at the same speed. It doesn't matter how hard the engines are working, as long as the conveyor belt can match the forces created by the planes propulsion system, the plane will remain stationary. So since there is is no airflow over the wings, there is no lift. Without lift, the airplane can't take off and fly.

 

If the discussion were about a car you'd be correct about no absolute velocity; since the car is propelled by the engine turning the wheels.

 

However, in the case of an aircraft, the airspeed is the defining factor (ground speed is irrelevant). The thrusters (be it propeller or jet) push/pull the aircraft through the air; the rotation of the wheels is a result of the plane's movement with respect to the ground. If the airspeed is high enough (even if the ground speed is 0) the plane will still take off.

 

This is the reason why small (private) aircraft are tied down when they're parked on the tarmac; gust winds have been known to pick up small planes.

Share this post


Link to post
Share on other sites
I was referring to this post.

 

http://www.straightdope.com/columns/060203.html

 

If that's the case, then why did you quote my post; as I didn't provide that link.

 

The question isn't statics and dynamics; but rather fluid mechanics. the airspeed across the wings is what generates lift. The wheels don't have any bearing in the equation; if they did, then a float-plane wouldn't be able to take off against the current of a river.

 

IMO the person who wrote the previously linked response provided a dumbed down version that just about everyone should be able to understand.

Share this post


Link to post
Share on other sites

An example of the above post would be watching birds flying into a strong wind. Sometimes you can see them staying aloft like normal but in relation to the ground, they're not moving forward, and sometimes they go backwards.

Share this post


Link to post
Share on other sites
If the discussion were about a car you'd be correct about no absolute velocity; since the car is propelled by the engine turning the wheels.

 

However, in the case of an aircraft, the airspeed is the defining factor (ground speed is irrelevant). The thrusters (be it propeller or jet) push/pull the aircraft through the air; the rotation of the wheels is a result of the plane's movement with respect to the ground. If the airspeed is high enough (even if the ground speed is 0) the plane will still take off.

 

So you are saying that argument states that the airspeed is concurrent with the ground speed? Sorry, but I didn't take that from the initial question. If that were the case then yes the plane would in fact fly, and would be more like a kite than any other object I would imagine.

 

And I am not a pilot, I was a crew chief, and FE in the USAF for a number of years.

 

And actually I have a complete understanding of fluid dynamics. But I'll disregard that as you thought I was referring to you as not knowledgeable in this area. I was in fact referring to the link I have posted previously. :)

Share this post


Link to post
Share on other sites
An example of the above post would be watching birds flying into a strong wind. Sometimes you can see them staying aloft like normal but in relation to the ground, they're not moving forward, and sometimes they go backwards.

 

Or for that matter a person swimming upstream in a river.

Share this post


Link to post
Share on other sites
HAHAHAHAHAHA

 

I'll have you know I have a BS in Mechanical Engineering and a BS in Aerospace Engineering. I've also taken/passes the Fundamentals of Engineering exam and am a certified Engineering Intern (that's why my title here is "Resident EI").

 

Sounds like you're probably a pilot; but you obviously don't understand the aerodynamics of airplanes.

 

 

 

1. Lift is generated by airflow across the wings; the curved profile of the airfoil results in a faster air velocity over the top of the wing (slower below the wing); resulting in a low pressure region above the wing (and high pressure below the wing)

 

2. Drag is caused by the friction of the air moving over the exterior surfaces of the aircraft

 

3. The angle of attack of the airfoil results in more lift for a given airspeed.

 

The thrusters pull the aircraft through the air creating lift (as outlined in 1); if the airspeed is high enough such that the the lift (created by the airspeed) is greater than (or equal to) the weight of the aircraft, then the plane can lift off.

 

During a take-off run the accelerates till it's airspeed is 115% of the stall speed (slowest airspeed at which the plane can maintain level flight); at this speed the aircraft rotates to increase the angle of attack, resulting in significantly higher lift and thus allowing it to quickly gain altitude.

Well, I'll have you know that I am full of "BS" and do agree with your theory!:P

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×