# Could flywheel type gyros stablize a plane?

An aircraft carrier has massive spinning gyros to keep the ship upright against waves. Do planes of any type have gyros like those used in satellites? Not instrument gyros. In the picture below spinning this one when suddenly stopped could move the plane in flight significantly allowing it to correct from a flat spin? It would spin in the event of a flat spin and stop suddenly to correct it, but it would not spin in normal flight. Or it can be used to shoot backwards momentarily. Can they be used this way for more control of the plane with the fins?

• @mins yes not the same as the one found in the instruments, much bigger and I have not found anything so far.
– user20435
Commented Jan 30, 2017 at 2:47
• They had this a century ago. They were actually bolted to a big fan in the front, so the pilot could stay cool. Google for "rotary engine" if you need more information. Commented Jan 30, 2017 at 8:29
• Flying wings don't exhibit flat spins. Commented Jan 16, 2018 at 23:57
• Flying....WHAT? Commented Jan 18, 2018 at 5:32

I actually have a lot of experience in the shipboard systems that you are talking about.

First, the gyro's do not keep the boat upright, they counter the rolling effect of waves but they cannot completely remove them. Gyro's of all designs work on the principle of conservation of angular momentum. That means that a spinning object will tend to impart a force 90° opposite of the force applied to it to conserve angular momentum.

In order for this to have a tangible effect on something of significant mass, the gyro itself (more specifically, the flywheel) must also have a significant mass. In shipboard systems this means that they usually use many (for an aircraft carrier, I would assume dozens even) of these devices that spin a flywheel weighing in the magnitude of tons. That is a lot of mass to be moving around!

So the first issue you have is to get the mass spinning fast enough to have an effect. Getting something that large spinning takes significant amounts of energy and time. Getting something that large to stop spinning can be equally problematic. Yes, you could use brakes (and many do), but you need to dissipate a lot of energy (heat).

So, taking into account that these gyros don't change speed very fast, and that they very heavily counter forces, you have a number of problems off the bat:

• You have to carry a LOT of extra weight.
• You need to have a lot of extra fuel/motors/generators to get the mass spinning.
• Once spinning, the mass will counter changes in momentum, this will make the aircraft difficult, if not impossible, to bank (aka: turn).

So could they be used to correct a flat spin? Not really. In order to counter the flat spin you'd have to have a gyro mounted 90° to the angle of the spin, and then change the momentum of the gyro to counter the spin. Flat spins are not (apart from what Top Gun may have you believe) impossible to recover from given altitude and control authority. This happens in the world of aerobatics quite frequently (and on purpose).

Can they be used to control the plane? Again probably not. You are talking about changing the angular momentum of a huge mass very quickly. This would work for the braking side, but not the speed-up side. That means you'd have an aircraft that can perform a maneuver once in one direction, then have to fly off while the aircraft builds up gyro's again.

By the way, spacecraft use control moment gyros that work by using gimbals to rotate a gyroscopic flywheel to impart a rotational force on the spacecraft. These work because of a reduced gravity/drag in the operational environment of the spacecraft itself. The masses don't have to be as big as they would on earth.

• Interesting answer. Regarding the last paragraph about CMGs, does gravity (weight) really affect their efficiency. Isn't that all about mass: Both for the amount of torque produced and the amount of spacecraft torque to counter (if the CMG is at the center of mass)?
– mins
Commented Jan 30, 2017 at 8:27
• One thing to note with CMGs (and their less elegant cousins the reaction wheels), is that there is a limit to how much angular momentum change they can impart to something on their own. In spacecraft this is fixed by reversing the action of the wheels while correcting the rotation of the ship another way, e.g. thruster. I don't know how these issuse would complicate terrestrial use. Commented Jan 30, 2017 at 8:29
• @mins Huh. I'll have to read about cmgs more. I'd actually thought they were the same thing as RWs untill going through that article. (I mainly know about saturation from discussions about the magical nature of KSP and SpaceEngineers's RW/gyro objects…K Commented Jan 30, 2017 at 8:38
• @muze , only once though, you still need a lot of mass and to get it spinning again. You are adding a lot of weight for a relatively small gain. Adding control surfaces would be much more effective. Commented Jan 30, 2017 at 13:28
• @mins Yes and no. In an aircraft (on which I'm answering) there are additional external forces applied to keep the aircraft heading straight (ie: rudder). That means that a CMG-like device would need to counter both the mass of the aircraft, and the external forces imparted on it, so not so much gravity I guess, but other forces. Commented Jan 30, 2017 at 14:59

Big rotating masses were once fitted to light aircraft, but for propulsion, not for control. Those were called rotary engines, and they made the aircraft rather harder to control. Every commanded pitch motion would be accompanied by an uncommanded yawing motion and vice versa.

This answer discusses the effects of spinning masses in detail.