>> 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
>
> ------------------------------------------------------
> 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.
I like the night landing scenario.
Once I had to land without a landing light. Fortunately the runway was
lighted, but still it was a high pucker factor landing, one that I would
not
like to repeat. After that I started practicing night landings without the
light, which I should have been doing all along. Still, at a strange
airport, the gadget would sure be nice insurance. Never know just how the
landing lights are placed.
Doc Custer
Retired Software Engineer and sometime Audiologist
The width of the runway can throw off your depth perception
both day and night. I have landed a light plane at SFO and Oakland
and at some Mexican airports with real wide airliner runways.
Paul Lamar ...No rotor no motor.
Paul,
You are sure right about the depth perception being thrown off. I'll
never forget my first landing at Castle Field, former B-52 base. The
runway is 11,280' long wihout the runoffs! More important it's 400'WIDE.
That can really throw you off. I flattened my decent at about 10-20
feet above the runway! I didn't flare as I had been warned by my CFI to
be careful. I just pulled power and let it settle, after all I had 2
miles! That damm runway is so big it has it's own weather. That taxi
back seemed to take forever though.
Bill Jepson
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