# How can an aircraft hover almost vertically?

(Source: https://fat.gfycat.com/)

The aircraft in this GIF (although being an RC plane) seems to be flying vertically, just meters above the ground. How is this possible? How is it possible to control it in this scenario? Would this be possible with a real aircraft?

• I'd bet my house that that isn't a real aircraft – Ben Nov 6 '15 at 8:13
• It's radio controlled, the RC on the video kinda gives it away – GdD Nov 6 '15 at 8:50
• I did some editing magic, maybe this will salvage the question to be on topic, even though it's an RC plane, the question whether this is possible for real aircraft is valid. – SentryRaven Nov 6 '15 at 9:44
• @SentryRaven: That seems to be a problem to be solved by Mr Musk. – mins Nov 6 '15 at 9:55
• I'm surprised that this turbojet/ducted fan aircraft can do that... I've seen propeller-driven aircraft able to do this, and the control was provided by the airstream flowing over the aircraft control surfaces due to the propeller wash. I wonder if this model has some sort of thrust vectoring going on. – Steve Nov 6 '15 at 17:50

The aircraft in the video is a remote-controlled (rc) airplane. Why it can "hover" is simply:

The thrust generated by a big fan / rc-jet-engine is much higher than the weight of the plane. If the force generated by the turbine is the same than the downward-force of weight of the airplane, it hovers. By very carefully adjusting the thrust and placing the aircraft in this "nose-up" position, a skilled rc-pilot can hover the plane until the battery runs out or fuel gets low.

As example: An aircraft that weights 10,000 kg's produces a downforce:

$$F=m\cdot g=10,000 \cdot 9.81 = 98,100N$$

To make this aircraft hover, you have to create a upward force of min. $98,100 N$. If you manage to do that and you can align the generated thrust / downforce perfectly on the Y-Axis the aircraft will hover:

$F_{down} - F_{up} = 0N$, the two forces will cancel each other out and you don't have any movement in the Y-Axis.

However, if you have engines that create more thrust than the downforce, the following will happen:

$F_{down} - F_{up} \geq 0N$, that means the aircraft will climb vertically (On the Y-Axis).

The same principle applies to other "real" aircraft, like the Sea-Harrier:

It uses the engine to create a force facing upwards. Because the force is greater than the downward-force created by the aircrafts weight, the Harrier can land / takeoff vertically.

The hovering airctaft is controlled by a trust-vectoring fan / turbine. Controlling the plane with the "normal" surfaces is not possible, because the airflow over the controll-surfaces on the wing is to slow. Therefore, only planes with trust-vectoring capabilities COULD hover like the rc-plane in your question.

• So this maneuvre is impossible with a real jet? – bos Nov 6 '15 at 8:17
• @bos In theorie. As long as the upward-force is greater or the same as the downward-force, you can hoover any object. Keep in mind that a pilot, to make it in a real jet happen, has to keep the balance perfectly. – jklingler Nov 6 '15 at 8:36
• You have about 3 zeroes too many in the example. – Jan Hudec Nov 6 '15 at 9:07
• @JanHudec Thank you, eddited that. – jklingler Nov 6 '15 at 9:11
• @bos "If you impart a sufficient thrust vector, even a pig can achieve orbit." – voretaq7 Nov 6 '15 at 17:24

Hovering is far easier and more common is propellor driven RC planes than jets. Very few RC jets have thrust vectoring, and even fewer have hovering capabilities.

Propellor driven aerobatic RC planes are able to hover, also due to a thrust to weight ratio > 1, however, they are controlled by the normal control surfaces rather than thrust vectoring nozzles. Hovering is only possible in models that have large control surfaces and large propellor diameters. The large surfaces are needed to attain the necessary control, and large propellor pushes more air over those control surfaces, making them more effective.

When hovering, the elevator and rudder are used to keep the nose pointing straight up, and the ailerons are used to prevent rolling due to engine torque.

The video below shows several examples of hovering, as well as other slow speed aerobatic maneuvers.

• This is true for rc-aircraft with a propellor, but an rc-jet, like the one in the question, or an rc-plane that has the propellor on the tail, can't maneuver with the controll-surfaces. – jklingler Nov 9 '15 at 12:25
• These days, thrust vectoring is not that uncommon in RC "jets" or more specifically in RC planes with electric ducted fan motors, especially in scale models of military jets that have thrust vectoring. – quiet flyer May 25 at 8:40

Its an rc basically you have more power more thrust and the airplane body is light as paper so u can hover with thrust and control with normal control surfaces.

In real aircraft its hard.

• Control is via paddles in the exhaust flow since flow over the control surfaces is of very low speed, but otherwise I agree. With aircraft like the X-31 it is even possible in real aircraft. – Peter Kämpf Nov 6 '15 at 8:46
• @PeterKämpf: For RC turbines control is typically via thrust vectoring -- moving the nozzle itself – slebetman Oct 11 '16 at 4:32