RCU Forums - View Single Post - Has anyone used a gyro on rudder
View Single Post
Old 03-14-2021, 08:17 PM
  #4  
otrcman
 
Join Date: Oct 2004
Location: Arroyo Grande, CA
Posts: 734
Likes: 0
Received 4 Likes on 4 Posts
Default

Originally Posted by valleyk View Post
I have a fokker DR1 that like to ground loop on takeoff. Wonder if a gyro is going to make this plane someday takeoff in a straight line.

Make it take off in a straight line ? Well, a gyro will help some, but the DR1 has a lot of strikes against it for the gyro to be a perfect solution. The most you might hope for is that the gyro will slow the action down enough for you to steer it straight as if it were a nosewheel airplane.

A rate gyro is quick, far quicker than any R/C pilot in detecting the very first inkling of a swerve that builds up into a ground loop. So that's to the good.

But, no matter how quickly the gyro perceives an incipient swerve, it still needs some leverage to keep the airplane straight. Will the DR1 rudder be big enough to provide the necessary leverage ? I don't know. All you can do is try it.

At the very beginning of the takeoff run, your tailskid will help, providing it is steerable with the rudder. Here again, the tailskid needs some leverage. If it's just a metal pad on a hard surface, you can bet it won't be too effective. On grass, it will work better.

Another problem with the tailskid (or a tailwheel, for that matter) is that the skid has no effect at all after the tail comes off the ground. For that reason, it's in your best interest that the tail stay on the ground until the plane has gained enough speed for the rudder to have some effectiveness. The down side to keeping the tail on the ground is that the plane may take off prematurely if you hold up elevator for too long.

If you incorporate a pitch gyro in addition to the yaw gyro, you may find that the tail doesn't pop off the ground as soon as you add throttle. That can be a big help. In an ideal world, the tail should stay on the ground until you have at least 25% or so of takeoff speed.

The other reason for slowing the rate at which the tail raises is called gyroscopic precession. You can look up that term on your computer, but the bottom line is that the spinning propellor will cause the nose to swing left as the tail raises. The faster the prop is spinning, the weight of the prop, and the rate at which the tail raises up, all contribute to the left swerving tendency. As soon as the tail reaches level and stops rising, the precession force also stops. There are still some subtle effects that cause the airplane to swerve, but they're small potatoes compared to precession.

There are many other things that can help to alleviate ground looping, but you asked about the gyro, so that's what I have focused on.

One last thing about gyros: The type you want is properly called a "rate gyro". That means the gyro will react to pitch rate or yaw rate. You don't want a heading hold gyro. Heading hold sounds seductively attractive, but will give you no end of troubles in actual usage. Heading hold gyros work great on helicopters, but not so well on fixed wing airplanes.

Dick

Last edited by otrcman; 03-14-2021 at 08:21 PM. Reason: spelling