The Physics of Vertical Takeoff

No, this isn’t trick photography. This is a very good pilot at this year’s Farnborough Air Show, performing a vertical takeoff in Boeing’s new Dreamliner — roughly 225,000 kg taking off like a rocket.

But — isn’t it common knowledge that

vertical flight = stalls = crash?

Remember Colgan Air 3407?

So — what’s going on here?

What you’re seeing is a vertical flight path. Flying horizontally first, the airplane pitches up until the nose is pointing straight into the sky.

Rocket

You don’t need thrust for this. Even gliders can do it. What you’re seeing is  kinetic energy (speed of the plane on the runway)  converted to potential energy —  and accelerating 250 tons to nearly 200 miles per hour builds tremendous kinetic energy! With so much potential energy, vertical flight can be maintained for several seconds, until the aircraft runs out of speed and stops in midair.

In the video, I count about 6 seconds of vertical flight before the pilot drops the nose. 

In aerobatics, this maneuver is called a stall turn or a hammerhead stall.

hammerhead

Numbers: 

For a craft weighing x kg you need g*x Newtons of thrust, minimum, for sustained vertical flight. For each metric ton of weight you need around 9.81 kN of thrust. The Dreamliner has a operational empty weight of 225 tons, so it would need 2453 kN of thrust to sustain a vertical climb. Its 2 GEnx engines, each producing 330 kN, don’t provide nearly enough power. This is why it is necessary to pitch up to vertical while shedding speed — making this awe-inspiring manouever  possible without thrust.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s