How fast would a plane have to fly TANGENT to Earth to escape into space?

Even if the wings and engines of an aircraft could propel it out of orbit (which it can't), I agree with lanab...about 25,000 mph. You are correct that the speed (and hence power required) would diminish the higher in altitude the plane was before beginning its acceleration burn, because the radius of the aircraft/spacecraft from the center of the Earth comes into play. You will see why this is by reading this article:

https://en.wikipedia.org/wiki/Escape_velocity

The theoretical number is approximately 25,000 mph, but it is irrelevant because no ordinary airplane, "say a Boeing", can fly fast enough, with a sufficient climb rate and angle to achieve escape velocity, nor can one sustain engine power at very high altitudes due to lack of oxygen for combustion. In addition, at extreme altitudes the air is so thin there would also be no aerodynamic control, and furthermore the airframe could not withstand the stresses and temperatures generated by the speed required to escape the atmosphere. .

Hi.

I answered a question about friction for a car moving in a circle:

https://uk.answers.yahoo.com/question/index?qid=20...

In a comment to my answer, you wrote:

"You could have added that the friction and centripetal force cancel out, since they act in opposite direction; "

That is wrong. You have misunderstood what centripetal force is. If you look at the above link, I have added an explanation of why this is so at the beginning of my answer.

Sorry to be a pain, but I'm a (retired) physics teacher and I like to dispel misunderstandings! The belief that centripetal force is some sort of 'new' force that comes into existence when an object moves in a circle is a very common misconception amongst physics students.

Sorry to use the current question, but there is no other way I know to message you.

Steve

Escape velocity. About 25,000 mph.

Assuming it had a rocket engine that would continue to work as it cleared the atmosphere.

17,000 mph you can achieve a stable low earth orbit, but to break free of earth completely you need to reach escape velocity.

Engines would need to be rocket engines (something with an oxygen source) because, as the air thins, a jet turbine would lose power and die for lack of oxygen to burn the fuel. The speed would need to be about 40,270 km/h (25,020 mph): https://en.wikipedia.org/wiki/Escape_velocity

won't do anything, once the air gets too thin the plane will lose lift, stalling. Look at the U2 spy plane, notice how thin but huge the wings are on that plane for flying in the super thin air.

escape velocity is a scalar. the direction is irrelevant as long as you're pointed at the sky.

oh, and you want to be doing slightly more than 11 km/sec.

The escape velocity from planet Earth is 11.2 km/second or 40,300 kph -

https://en.wikipedia.org/wiki/Escape_velocity