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Old Mar 09, 2002, 11:14 PM
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Gyro for Gliders

I'd like to try a gyro on the elevator of a glider for pitch-locking, or at least pitch-stabilization, for use during those times when the plane is hard to see, e.g. way up in a thermal above me.

Anyone know of any brands particularly suited for this?

Thanks all
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Old Mar 09, 2002, 11:55 PM
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I'm using a really nice gyro in my Hornet micro-heli. It's a GWS PG-03 Piezo gyro. It weights in at a couple of grams. Something close to 5 grams, I believe. Works really well for stabilization.
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Old Mar 10, 2002, 12:04 AM
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Re: Gyro for Gliders

It won't work. A pitch rate gyro will only affect pitch damping, and virtually all gliders already have plenty of pitch damping.

What you actually want is a way to more solidly control glide airspeed (or equivalently, glide CL). The simplest way to do this is to move the CG forward, and then add up-elevator trim or increase decalage to restore trim. The glider's pitch attitude will now be less sensitive to the precise elevator stick position.

Somewhat OT:
There are only two practical applications for a rate gyro on an RC glider:

1) Yaw gyro driving the rudder. This improves yaw damping, and slightly increases spiral stability.

2) Yaw gyro driving the ailerons. This can greatly increase spiral stability. See
http://members.cox.net/evdesign/page...lity_gyro.html

- Mark
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Old Mar 10, 2002, 12:44 AM
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Just going by its namesake, does a pitch rate gyro sense angular rate about the pitch axis? I thought I read, somewhere, reports of people using pitch gyros on sailplanes with some success; dreaming?

As another approach, is anything available (commercially) where an absolute pitch orientation could be established as a setpoint, where elevator corrections are issued when the model strays from a desired pitch angle? The only thing I've seen in this regard is a horizon sensor based on the difference in IR sensed by two photosensors.

Seems like something along that line, e.g. leveling bubble as an absolute reference, could be used, plus gain adjustable to the pitch response of the particular plane.
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Old Mar 10, 2002, 12:49 AM
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"What you actually want is a way to more solidly control glide airspeed (or equivalently, glide CL). The simplest way to do this is to move the CG forward, and then add up-elevator trim or increase decalage to restore trim. The glider's pitch attitude will now be less sensitive to the precise elevator stick position."

This will enhance pitch stability, but at some L/D expense, no?
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Old Mar 10, 2002, 07:25 AM
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Quote:
Seems like something along that line, e.g. leveling bubble as an absolute reference, could be used, plus gain adjustable to the pitch response of the particular plane.
I want to say the "PAL", Pilot Assist Link available at Tower is such a system. Check it out. I may be wrong, but I have thought of using it for the same purpose (thermal flying).

Here's some info:
http://www.futaba-rc.com/radioaccys/futm0999.html
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Old Mar 10, 2002, 08:27 AM
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Which kind and setup for discus launching

I guess thats yaw damping
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Old Mar 10, 2002, 12:33 PM
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Wy not use a system that controlls the elevator by mesuring airspeed?

It could be done. Just get yourselfe on of those digital airspeed gadgets and couple it to your elevator servo.

If someone would make this kind of thing, soaring chapionship pilots should be knocking down the door.
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Old Mar 10, 2002, 12:45 PM
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Quote:
Originally posted by green66
Just going by its namesake, does a pitch rate gyro sense angular rate about the pitch axis? I thought I read, somewhere, reports of people using pitch gyros on sailplanes with some success; dreaming?

As another approach, is anything available (commercially) where an absolute pitch orientation could be established as a setpoint, where elevator corrections are issued when the model strays from a desired pitch angle? The only thing I've seen in this regard is a horizon sensor based on the difference in IR sensed by two photosensors.

Seems like something along that line, e.g. leveling bubble as an absolute reference, could be used, plus gain adjustable to the pitch response of the particular plane.
There are two types of gyros:

1) A "rate gyro" senses rotation rate. The common RC gyros are of this type. Any rate gyro can be used as a roll, pitch, or yaw gyro (or some combination thereof) depending on the orientation the gyro when it's bolted to the airframe.

2) A "position gyro" senses orientation angle relative to some preset reference angle. These are sometimes used in RC helicopters, and are called "heading hold gyros" or some such name.


In principle a position gyro which senses the glider's pitch orientation could be used to maintain airspeed, but in practice it wouldn't work. Just one degree of error or drift will have a drastic effect on the glider speed, especially on a clean glider. The only reliable way to do it is to sense airspeed.

- Mark
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Old Mar 10, 2002, 12:58 PM
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Quote:
Originally posted by Kimble_Schmitz
Wy not use a system that controlls the elevator by mesuring airspeed?

It could be done. Just get yourselfe on of those digital airspeed gadgets and couple it to your elevator servo.

If someone would make this kind of thing, soaring chapionship pilots should be knocking down the door.
Yes, it could be done, but it's not as simple as you describe. At first glance one might try adding up-elevator if going too fast, and down-elevator if going too slow. Unfortunately this will probably produce a phugoid instability. The glider will perform a roller-coaster flight path with ever-increasing vertical excursions.

In practice it is necessary to measure both airspeed and pitch rate, and combine the two signals appropriately into the elevator. The relative mixing will likely have to depend on the current airpseed for the system to behave properly. This is a standard pitch-autopilot design problem.

On a glider it would be necessary to turn off such an autopilot at times, such as when turning tightly in a thermal. The banked glider then has a strong nose-up pitch rate which is normal. However the airspeed-hold autopilot will think the glider is entering a half-loop and try to apply down-elevator to "compensate". This is very definitely not what you want.

- Mark
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Old Mar 10, 2002, 02:13 PM
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Quote:
necessary to measure both airspeed and pitch rate
A dual-feedback control system, e.g. airspeed on outer loop, tempered by pitch rate on inner?

Quote:
The glider will perform a roller-coaster flight path with ever-increasing vertical excursions
Seems that, with proper gain and damping, the oscillatory tendency could be compensated, no? Does being at model scale tend to make response hyper-sensitive to corrective inputs, or create a set of control parameters stable only in a narrow range?
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Old Mar 13, 2002, 09:02 PM
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Magnetic Field Sensor

A guy named Maynard Hill flew a model airplane to about 30,000 ft. (see http://www.flightlines.com/aircrafts/worldrecords.htm). I believe he used a magnetic field sensing device of his own design to keep his plane level. Do a little searching on the web and you should be able to find a construction article on the device. I've seen one in action on a glider. It was unbelievable. The guy had a zero dihedral aileron wing on a small glider. He flipped a switch on his transmitter and the plane flew hands off in windy turbulent conditions. The wings stayed absolutely level. I think the model plane that flew across the Atlantic also used this deice. I was tempted to try and build one but I figured it would make flying too easy and too boring (i.e., no crashes). Sorta like model sail boats. They never crash so you never have an excuse with your better half to buy a new one.

Good luck.
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Old Feb 08, 2008, 10:56 PM
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Electric field, actually. You should see what one of these things does when there's a thunderstorm not far away. Or on a day when the field gradient is not quite right.

You probably saw Helmut Lelke with his two meter. He could fly pretty well with it turned off, too. He could win contests at a 15 oz wing loading, too. Once saw him climb out from about 20 feet or so with this thing. It was like watching control line speed with no one in the middle.
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Old Feb 09, 2008, 06:10 AM
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Quote:
Originally Posted by markdrela
Yes, it could be done, but it's not as simple as you describe...
Has been done by Kurt Schreckling over 10 years ago for F5B. Used only during lap flying. Used a small electric motor with cardboard prop as speed sensor, coupled to elevator servo and set to 100kph. During lap flying he just pushed the stick controlling elevator all the way forward. Worked well in the straights, but the turns were awkward...
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