This is not real automatic landing system so much as
it is an automatic flaring system.
Sharp makes a GP2DO2 solid state distance measuring sensor that can be
interfaced to the PICAXE It measures distances from 4 inches to 32 inches
with high rez. It uses the same principle the British Dam Busters
use in WW II to destroy German dams. It measure the angle the sensor
sees looking at a spot of infra red light reflected off the
runway surface.
You set up a decent rate of a couple hundred feet per minute
and let the auto flare unit take over at 32 inches. You might also
want to monitor the air speed so it does not flare after stall :)
The rest is software.
If you have a PIXAXE auto pilot altitude hold
you already have most of what you need. The idea here is mount
the sensor on the main landing gear axle and measure the distance
100 times a second and control the elevator to flare
the airplane. If anyone is interested in this let me know
and I will upload info from a book I have on interfacing
PICs.
This could be handy for landing sea planes on glassy surfaces
or land planes at night.
Paul Lamar ...No rotor no motor.
32 inches sounds kind of low to flair.
How does this Autoland system deal with cross winds?
Mark W
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Hopefully it will maintain altitude plus or minus 4 inches or so
until the speed slows from 1.2 times stall speed and 3 or 4 feet
per second sink rate to nearer stall speed and .5 feet per second,
or below, sink rate.
Mark S's 60 inch rather than 40 inch range distance sensor will
ease the situation.
For cross winds the pilot will have to forward slip or yaw using
the aileron and/or rudder. Perhaps we need two sensors. One on each
axle and the PIXAXE takes the distance from the lower one.
I would not try the yaw approach on a tail dragger as there is a
de stabilizing moment of up to the weight of the airplane times the
distance the CG is behind the main gear tires upon touch down. This
assumes a 10 degree yaw angle on touch down, or more, with the full
weight of the airplane on the main gear and on pavement. On grass or
dirt the situation is eased as the coef. of friction between tires
and the runway is much less than one. Rubber tires on pavement
develop maximum side force around 10 degree angles and zero
camber angle. (The ME109 and other airplanes with cambered tires
is a whole different story.)
For an example on pavement; if the CG is one foot
behind the CG, the airplane grosses 2000 pounds and the tire yaw angle
is 10 degrees or more there will be a de stabilizing moment about
a vertical axis through the CG of 2000 ft/lbs.
A forward slip, properly done, will reduce the yaw angle of the tire
relative to the pavement to zero but that situation is
too complicated for the simple one axis auto flare system to
handle IMHO. The pilot must forward slip into the wind just enough
so there is no lateral drift. In other words the required roll angle
of the airplane in a forward slip will change with the magnitude and
direction of the cross wind. Hence the required gain of the simple
elevator/height closed loop servo system will need to change with roll
angle. Perhaps a few more sensors and an F16 computer system will
do the trick :)
If it is a nose gear airplane with the CG ahead of the main gear the
same moment becomes a stabilizing moment and the aircraft will tend to
automatically straighten itself out no matter what. This I think the
auto flare system can handle. I have landed my C182 in Baja on a dirt
strip with a 30 kt cross wind. Drunk tail dragger pilots were standing
down near the runway approach end waving me off with beers in hand.
I was congratulated and offered free beer after I landed.
The big problem with this is people might forget how to land
without it working :)
Paul Lamar ...No rotor no motor.
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