"cavelamb" wrote in message
m...
Peter Dohm wrote:
"brian whatcott" wrote in message
...
I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately,
you have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the
tail rotor pitch. The device takes over when a rotate ("pirouette')
command stops, and stops the tail dead on that heading - fast, and holds
it against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add
another $40 on it.

Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super
cheap altitude hold/augment?)

Brian W

One of the avionics makers, Bendix IIRC, had a system available about 25
or so years ago that used an air stream across a pair of resistance
elements, or two pairs of resistance elements for a two axis autopilot.
Basically, each pair of elements was an uninsulated resistor on each side
of the airstream for heading hold and top and bottom for pitch hold--not
really the same thing as altitude hold but possibly usefull in smooth VFR
conditions. AFAIK, the system worked because the resistance of each
element (for most materials) tends to increase with rising temperature
and decrease with falling temperature--so that the system can work by
comparing the resistances with little regard for the actual resistance
values. My best recollection is that the device could also maintain a
standard rate turn.

I only vaguely recall that there may have been an article in one of the
homebuilding magazines--possibly in the early 1980s.

Peter




Electro-Fluidic Autopilot.
Sport Aviation -


May '78
Preliminary Report-Development of a Poor Man's VFR Autopilot/Don Hewes

March '79
Update On The Poorman's Autopilot... by Donald E. Hewes

February '80
Autopilot System For Homebuilt Airplanes... by Don Hewes

August '80
Fine Tuning The Electro-Fluidic Autopilot.. . by Doug Garner

April '81
Muscle For Your Homebuilt Autopilot... by Don Hewes

November '81
A Magnetic Heading Reference For The Electro Fluidic Autopilot,Part I
by Doug Garner

December '81
Magnetic Heading Performance For The Electro Fluidic Autopilot
Part 11 . . , by Doug Garner

--

Richard Lamb



Thanks, Richard, I had forgotten where I saw it--and completely forgotten
that there were really a series of articles!

Peter