It is no secret that most legal ultralight gyros don't fly very well, especially with heavier pilots. In contrast, the Gyrobee is a very solid performer. Much of this can be attributed to the fact that the Gyrobee is a very light gyro flying on a 25 foot rotor disc - significantly larger than the 22-23 foot rotor systems on most smaller single-place ships. The result is a very light disc loading, between 0.9 and 1.0 pounds/square foot (psf) compared to the 1.2-1.4 psf of other ultralights and Experimental single-seaters. This may not seem like a big difference, until you realize that a 20% lighter disk loading (0.2 psf) is equivalent do dropping 20% of the gross weight of the aircraft - 100 pounds! This is one of the major factors that permits the Gyrobee to perform well on only 40 horsepower!

The light disc loading has other consequences that are not so obvious, one of these being a low rotational speed for the rotor system. A gyro rotor doesn't do any more work than necessary to generate the lift needed to keep the craft in the air. Because of its light disc loading, the Gyrobee's rotor turns at only 305 rpm in flight, compared to 400 rpm or more for the typical single-seat machine. This has two positive effects. The first is low parasitic drag. Parasitic drag increase with the square of rotor speed, so much less of the power of the engine is needed to overcome parasitic blade drag in the Gyrobee and that's more of the available power to fly the aircraft. The second effect of the low rotational speed of the rotor system is that the Gyrobee is quite insensitive to the blades you use. For example, riveted blades (like the Brocks) are often notably less efficient on most gyros compared with laminar flow designs. Since the blades are rotating more slowly on the Gyrobee, these differences are much less pronounced.

The engine, reduction drive, and prop are well-matched, yielding very close to an optimum static thrust coefficient. What that means is that a 40 hp engine provides plenty of power for the aircraft. The Gyrobee cruises at 50 mph at only 5000 rpm (about 30 hp), which is excellent for any gyro, let alone an ultralight. Because the engine size is modest and cruise rpm is low, the Gyrobee is a very quiet gyro - also very unusual. I am often asked about the use of larger engines. While the Gyrobee would accommodate a 503 or larger engine if you used light blades, the power is not needed and can only get you in trouble!

The Gyrobee features a tall mast, which puts the mass of the rotor system a greater distance above the engine thrust-line. This has a tendency to raise the vertical center-of-gravity. In addition, the engine is mounter upright, further raising the vertical center of gravity. As a result, the engine thrust-line is very close to (about 1-inch above) the vertical center-of-gravity. This, along with the use of an effective horizontal stabilizer, results in outstanding pitch stability.

The tail boom is quite long, which makes the rudder very effective at any airpseed, but not over-sensitive as is often the case in a close-coupled design. While the horizontal stab is small, it is very effective because of the longer tail boom. I am often asked about replacing the present tail with a tall tail configuration. This would complicate airframe design and the result in terms of improved handling would be marginal. Because of the long tail boom, very little rudder deflection is required to counter the already modest P-factor with the 40 hp engine. The result is a very minor drag penalty.

The Gyrobee landing gear is optimized for operation from grass strips, including bungee-loaded struts to absorb stresses and strains that would otherwise be transferred to the rotor control system and blades. The very wide main gear track is a pain when it comes to trailering the machine but results in extremely solid ground handling. One of the biggest problems with most gyros is that they can turn-over relatively easily when landed off-field in anything other than a perfect touch-down attitude. These turn-overs are the single biggest factor in damage and/or injury in the case of off-field landings. In contrast, the Gyrobee, with its wide gear stance, sits down solidly with no tendency to tip, even with the high mast.

The Gyrobee sits quite flat, which means that it does not rotate back significantly when the nose wheel lifts. You will read that the gyro needs to rock back at least 10 degrees to get a short take-off run. This is not the case with the Gyrobee. What is critical is the angle of the rotor disk and the Gyrobee's rotor comes back just as far when it "rocks" back as any other machine. What you don't have to do with the Gyrobee is any fancy balancing on the main gear as you do your take-off run. You just "drive" it down the runway until the rotor and airpseed are high enough to fly and then it does! Any gyro take-off is much more complicated than a fixed-wing, but the Gyrobee is closer to what you would expect in a fixed- wing than any other gyro.

I am often asked about the possible pilot weight range with this aircraft. Note that performance has been specified on the basis of a 215 pound pilot weight, not the mythical 170 pound wimp favored by the FAA. We flew the aircraft over a wide range of disc loading values early in development and, based on those tests, pilots up to 250 pounds should be quite happy with the performance of the aircraft, even in hot weather.

There is nothing magic about what it took to get the Gyrobee to perform the way it does. Basically it was a matter of treating it as an ultralight design problem, rather than reverse-engineering an existing Experimental model. There are two factors which would serve to reinforce how positively we feel about how the Gyrobee worked out. First, neither Don or I are the least bit tempted to build an Experimental gyro. Second, if we were to build another, we would essentially clone the prototype!

I hope this serves to satisfy some of the curiosity that has been expressed about the aircraft. I would be happy to answer questions, within reason, and can be reached at the e-mail address below.