0
$\begingroup$

In a promotional video for the Paris 2015 airshow, this video was released promoting the new Boeing 787's near vertical takeoff capability. Whilst highly impressive, I was wondering if there is any practical benefit or advantage of such an aircraft being able to perform this manouevre?

If there is no benefit of being able to climb at this angle of attack, then why was this aircraft designed with such a capability. But if the 787 wasn't designed to intentionally perform this, then does this mean other Boeing aircraft can do this? And if other aircraft can do this, then why hasn't this manouevre been marketed in such a way before?

In other words, why even bother to design an aircraft capable of this, if it serves no real benefit? And why market the aircraft as being able to do so in the first place?

$\endgroup$
1
5
$\begingroup$

The 787 was not designed to perform such a maneuver. Any jet airliner could do this.

What you need for such a steep climb is a good thrust to weight ratio (or enough excess speed to bleed off during the maneuver). A passenger twin-jet is designed such that it can still climb with at least 2.4% climb gradient after a single engine failure during a takeoff at the maximum takeoff weight (see e.g. this answer). When the aircraft carries no passengers and only enough fuel for a short demonstration flight, it is much lighter than that (source):

Aircraft Operating Empty Weight Maximum Takeoff Weight
Boeing 787-9 284,000 lb / 128,850 kg 560,000 lb / 254,011 kg

As you can see, the empty weight of a 787-9 is only about half its maximum takeoff weight. And if both engines are operating, that gives you a lot of excess performance for such a maneuver. At normal weights, the 787 could not perform such a steep climb and there is also no "practical benefit" in doing so since clearing terrain must still be possible after an engine failure, which results in much less climb performance.

Also note that the aircraft was not flying at a high angle of attack. It was flying at high pitch (although not nearly vertical). The angle of attack is the angle between the average chord line of the wings and the relative airflow. When climbing steeply, the angle of attack is therefore not necessarily high.

$\endgroup$
4
$\begingroup$

The 787 (and other commercial aircraft) are built to carry large loads, whether lots of cargo, or lots of passengers and bags.

So, when empty, their performance is much better. If it can do a normal takeoff when full, then it can do a rocket-like takeoff when empty.

The near vertical takeoff is, indirectly, a demonstration of how much power it has when empty, and therefore, how much weight it can hold. The maneuver itself is not useful.

However, its mostly just a visual spectacle. Any commercial jet can do visually stunning moves when not weighted down. But it sure looks cool in front of an audience.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.