Yaw Stability Augmentation
The BobCat uses a gyro

The design of any airplane, large or small, entails compromises to achieve a variety of desired performance characteristics.
The fact that modern fighters like the F-16 or F-18 can accomplish multi task, air to air and air to ground missions, means that some compromises had to be made.
One of the design goals of the BobCat was to minimize the number of control surfaces that had to be constructed, hinged, rigged and thoughtfully operated.
To eliminate the need for a separate speed brake or flap system, we oriented the landing gear to activate into the relative wind. This allowed a very simple landing gear door system (laser cut panels bolt to the retract unit) to provide enough drag to offset the engine thrust at idle.
Because these doors (air brakes), in the extended position have a moment about the vertical axis of the model, the slightest "upset" can cause some yawing.

Gyros and Jet Models

Adjustable gain piezo electric gyros are one of the benefits of today's technology, so why not use them. Every swept wing jet can experience what is termed Dutch Roll. A gyro on the rudder will totally dampen this effect and make you and your model look great.
The popular flying wing designs also look better when gyro stabilized.
Variable rate (gain control) gyros to compensate for yaw are absolutely a part of the jet modeling experience. Our scale F-4, F-100 and Rafale utilize them. So, it is not a bad thing to introduce a new jet jockey to their use should he get started with a BobCat.

How to set it up

First, we recommend using a top-of-the-line unit like the JR 450. We tried one of the less expensive types but it did not provide sufficient rate change or accuracy.
Next, be sure to read the instructions that accompany the unit and be absolutely positive that the reverse switch is in the correct position. Move the model's nose "left", the rudder should deflect "right".
A "y" harness connecting the gyro to the nose gear steering servo can also reduce your work load on take-off. Our factory BobCats however, do not use this feature, but some more narrow stance models like a Sabre Jet can benefit with this application.
Now, use your "trick transmitter" to slave the gyro gain channel to activate with the gear switch. Adjust the gyro gain (on a BobCat) to about 40% activity for gear up and about 80% for gear down. The servo monitor feature on the JR transmitter is handy to view these settings.
Flight testing will allow you to fine tune these settings, then you can deactivate the gyro gain channel dial and forget about it.
Note that windy days may require more "gain" adjustment to smooth things out.

The Economics

A JR 460T gyro sells for about $160.00. To activate a separate speed brake, a very powerful servo or an air cylinder with a control valve and servo would be required. Pay yourself a few bucks an hour for the extra time to rig it and it is a "wash". A gyro on a jet is a good application of technology.

Bob Violett