# Using gyroscopes to turn airplanes

Could multiple gyroscopes be used to change direction in a flying vehicle? Im a physics noob and don't really know what else to add...

If having one gyroscope allows you to change your direction in 90° by adding an outside force to the gyro, would it not be possible to change into any direction by altering the orientation of multiple gyroscopes?

I see many benefits of using gyroscopes to change direction vs our traditional methods which is either adding drag to one side of the vehicle or adding thrust to the other side of the vehicle. Additionally it could add stability to the plane and remove complex mechanisms found outside the fuselage. Maybe even remove the gyroscopic prop effect?

P.S. I have tried to research my question but the results are either too complex to follow or a simple introduction to gyros.

Edit: I don't have enough karma to upvote these great answers. Thank you for taking time out of your Saturday to explain to me like I'm a 5th grader, it has been very informative!!

• Yes. but no. They are too weak, by a huge margin. Jul 17, 2021 at 17:28
• This should be in Engineering SE, I believe. Jul 17, 2021 at 17:35
• @PcMan Actually they are not too weak. When a plane takes off, the pilot has to counteract the gyroscopic effect of the axis of rotation of the engines changing, otherwise the plane will veer to one side as the nose lifts off the ground. If you are flying an unfamiliar aircraft, it is essential to be sure which way the engine(s) rotate as part of the pre-flight preparation, because not all engines turn the same way! Jul 17, 2021 at 18:02
• @alephzero there's a HUGE difference between needing to fight the gyroscopic effect, and using it to purposely steer an airplane. Your analogy is like saying that the rubber on a car's tires cause it to accelerate. It does, but it really, really does not. Jul 17, 2021 at 18:05
• Do you understand how airplanes work? Mainly they turn by banking (with the ailerons), which turns part of the lift vector sideways, just like a bicycle. What the rudder does is produce some side-force by putting the aircraft side-on to the wind, but this is insignificant compared to bank. All this stuff about gyroscopic effect is malarkey, unless you're flying a Sopwith Camel. Jul 17, 2021 at 23:23

What you are referring to are not called gyroscopes (which usually refer to sensors in this context), but reaction wheels or momentum wheels (not the same device). Reaction wheels spin the craft in the opposite direction that the wheel is spinning, while momentum wheels are a spinning wheel where the axis of rotation is mounted on a gimbal and when the gimbal changes the axis of rotation of the wheel relative to the craft, the craft turns in the opposite direction (think trying to hold a big spinning wheel in your hands horizontally and then moving it so it is vertical. It exerts a force to resist you which means that you actually push off the wheel to turn yourself if your feet weren't on the ground). Both are used in satellites.

The problem with both devices on something like an airplane is that they need momentum comparable to the airplane allow the airplane to maneuver with sufficient speed. That means they need to be heavy or to spin very fast. Heavy is bad for an airplane and spinning fast is dangerous.

Control surfaces, on the other hand, do not suffer from either of these issues and also contain less moving parts and consume less power (I believe).

If you look at WW2 warbirds with enormous propellers on the front acting as a gyroscope, or the very few airplanes with rotary engines where the entire engine acts as a gyroscope, these airplanes roll in one direction faster than the other. And yet, the control surfaces still are powerful enough to overcome this and allow the airplane to roll in the other direction. And keep in mind that in the case of the rotary engine, you have the a significant mass of the engine spinning and yet it is still too weak to dominate over the control surfaces.

• I think that in the case of multi-engine aircrafts engines often a counterrotating configuration was used, in order to cancel out a sizable portion of the angular momentum. As to the case of a single rotary engine aircraft. My understanding is that the pilot had to work with the gyroscopic effects rather than try to overpower them. In order to turn: initiate the corresponding pitching, and then the gyroscopic effect from the rotary engine converts that to yawing motion (with the pilot using the ailerons to match the rate of turn). Jul 17, 2021 at 17:51
• @Cleonis contra-rotating twin engines are a pain in the ****, because you need access to twice as many "left and right handed" parts for repairs and maintenance. And if one engine fails, the contra-rotation is no longer useful in any case. Jul 17, 2021 at 18:09
• @Cleonis In a dogfight, sure, you work with the roll. But my point was that the airplane isn't incapable of turning in the other direction just because the propeller is there. If you're just cruising and you want to turn right, you're probably not going to do a left-handed loop. You're just going to turn right. Jul 17, 2021 at 18:48

No, what you describe is not a possibility.

To explain why let me make a comparison with the technology of using gyro stabilization in luxury yachts.

The gyrostabilizer is oriented with respect to the hull in such a way that it is set up to suppress rolling.

In order to suppress rolling the gyrostablizer needs leverage. A boat, being elongated, has strong opposition to pitching motion.

The typical use case is when the yacht on its way to some destination, and it so happens that the sea swell is parallel to the hull, causing the ship to roll from side to side. The gyrostabilizer system can then suppress that roll.

The roll suppression is an active system. Strong actuators change the orientation of the spin axis, in counter motion to the tendency to roll.

This active shift of the orientation of the gyro wheel spin axis uses a torque in one direction to exert another torque in a direction at 90 degrees to it.

The ability to suppress roll comes from exerting force in a direction that tends to make the ship pitch (up/down, as the gyrostablizer opposes roll to the left/right). But that pitching torque is no problem because the ship has just from the way the buoyancy works strong opposition to any pitching.

In an aircraft you don't have any of that leverage.

A gyro unit with enough angular momentum to give a useful rate of yaw will pitch the aircraft. So that only makes flying the aircraft more complicated.

Incidentally, there was a period where small high performance aircrafts had a single rotary engine. With a rotary engine the crankshaft is stationary, the engine is rotating, and the propellor is bolted onto that rotating engine. The air frame would be as light as possible.

I remember reading an interview with a pilot who had flown a rotary engine aircraft. In order to turn left or right you had to initiate that turn by starting the corresponding pitching motion, and vice versa. Very, very tricky to fly.

• Could the second momentum wheel be the "water" in this scenario to prevent the craft from pitching? Of course this question ignores all the other downsides you mentioned in your answer. Jul 17, 2021 at 19:01
• in your yacht roll suppression example the wheel is trying to counteract a huge force "water" while in the air or space the wheel will be counteracting several weak forces (gravity, air) therefore I don't think your example works. Furthermore, a rotary engine does not properly utilize the formula for angular momentum which shows that the radius of the wheel is more important than the weight of the wheel. Jul 18, 2021 at 17:03

Thank you to the responses which pointed me to the correct scientific terms so that I could further my research. Upon initial reading the responses felt correct, but I had a nagging feeling that the examples presented did not correlate to the question.

I have done more research and I'd like to direct everyone to this video by Tom Stanton. https://youtu.be/4kfBEaTncjI

Please also see this patent which I believe outlines my hyopthesis https://patents.google.com/patent/WO2006004581A2/en

Here you can clearly see that small reaction wheels can indeed control a flying vehicle and not only are minimal wheel sizes needed, but the spin required is easily achieved by a small electric motor. Angular momentum seems to be counter intuitive upon first glance and I think that is why the answers fail to properly discount my hypothesis.

So to my point on airplane efficiency. If instead of using drag or thrust to direct a vehicle (both of which require more fuel on board) the plane could instead use electrical power to spin a wheel to achieve a proper heading. The wheels mass has less importance than the radius (this is why the bike wheel is used for the classroom example to show angular momentum fighting gravity, and not a steel disc)

So I'm going to have to say, yes, my hypothesis is correct. Two or three reaction wheels can control the direction of any vehicle and can be done with today's technology.

• There are two directions to consider, direction of pointing and direction of travel. Reaction wheels affect the direction of pointing, not travel. To affect the direction of travel, there needs to be an overall lateral force from outside. Airplanes do that by tilting the lift vector so that it has a horizontal component. Jul 19, 2021 at 12:09
• @MikeDunlavey at no point am i claiming a reaction/momentum wheel can change location of an object. BUT that being said, what is a tire on a motorcycle if not a reaction/momentum wheel + friction. AKA: Rotation + Friction = location Ex: drop two identical golf balls, but give one of the balls a spin before dropping it. Now watch as the two balls end in different locations because of their rotation. Jul 19, 2021 at 23:20
• You stated your question very clearly: "Could multiple gyroscopes be used to change direction in a flying vehicle?" The answer is no! Reaction wheels or gyros could be used to turn an airplane along the pitch, roll, or yaw axis, but that does not make it travel in a different direction. It only does that when aerodynamic forces (i.e. relative wind) push it in the different direction. Jul 20, 2021 at 1:24