01 Aug 2012

Droning About Drones: Flying Wings and Gyroscopes

Lockheed is apparently working on a next-generation carrier based unmanned fighter aircraft, the “Sea Ghost.” At least, they are “working” on it in the sense that they paid some graphic designer to make some CGI glamour shots of something that might be a UAV, sitting on the deck of what is presumably an aircraft carrier. As press releases go it’s a little underwhelming, but whatever.

From the rendering, it appears that the Sea Ghost is a flying wing design, which is interesting for a number of reasons. Flying wings are almost as old as aviation in general, but have proved – with a few notable exceptions – to be largely impractical, despite having some nice advantages on paper over the traditional fuselage-plus-wings monoplane design. It’s one of those ideas that’s just so good that, despite a sobering list of failures, it just won’t die.

One of the big problems with flying wings is yaw control. Since they lack a tail and traditional rudder, getting the aircraft to rotate on the horizontal plane is difficult. Typically – in the case of the B2, anyway – this is accomplished by careful manipulation of the ailerons to create drag on one wing, while simultaneously compensating on the other side in order to control roll. This is, to put it mildly, a neat trick, and it’s probably the only reason why the B2 exists as a production aircraft (albeit a really expensive one).

I suspect that the Sea Ghost is built the same way, if only because it’s been proven to work and the Lockheed rendering doesn’t show any other vertical stabilizer surfaces that would do the job.

But a thought occured to me: if you can make a drone small and light enough (actually, a small enough moment of inertia), you don’t need to do the B2 aileron trick at all. You could maneuver it like a satellite. That is, by using a gyroscope not simply to sense the aircraft’s change in attitude, but actually to make it move about the gyroscope. Simply: you spin up the gyro, and then use servos to tilt the gimbal that the gyro sits in. The result is a force on the airframe opposite the direction in which the gyro’s axis is moved. With multiple gyros, you could potentially have roll, pitch, and yaw control.

This isn’t practical for most aircraft – aside from helicopters which do it naturally to a degree – because they have too much inertia, and the external forces acting against them are too large; the gyroscope you’d need to provide any sort of useful maneuvering ability would either make the plane too heavy to fly, or take up space needed for other things (e.g. bombs, in the case of most flying wing aircraft). And that might still be the case with the Sea Ghost, but it’s not necessarily the case with all drones.

The smaller, and more importantly lighter, the aircraft the easier it would be to maneuver with a gyroscope rather than external aerodynamic control surfaces. Once you remove the requirement to carry a person, aircraft can be quite small.

It wouldn’t surprise me if you could maneuver a small hobbyist aircraft with a surplus artificial horizon gyro. To my knowledge, nobody has done this yet, but it seems like a pretty straightforward merger of existing technology. You’d need a bunch of additional MEMS gyros, which are lightweight, to sense the change in attitude and stop and start the manuevering gyro’s movement, but there’s nothing that seems like an obvious deal-breaker.

The advantage of such a system would be that there’s no change to the outside skin of the aircraft in order to make it maneuver (within the limits of the force provided by the gyro). That would mean a lower radar cross section, and potentially less complexity and weight due to fewer moving parts in the wings.

Just one of the many intriguing possibilities you come up with, when you take 80 kilos of human meat out of the list of requirements.

Almost enough to get me back into model airplanes again.

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