Posted for "terrence o'neill" <troneill@charter.net>:

Marv,
Thanks (on behalf of all) for a nice explanation of how stall speed varies
greatly with load and with Gs, whereas the AOA does not. But an auto-gear
activation is fixed at an airspeed.
The effect of flap deflection can been seen in Abbott & Doenhoff's Theory
of Wing Sections, Fig. 100. The lift peak for a similar (to L235-320)airfoil
moves about 2 to 3 degrees, for a flap range of 5-up to 50-down. Not much, so
AOA is a fixed and reliable indicator of how close the pilot is pulling his
wing up toward it's stall AOA, regardless of weight or Gs. I used to have a
web site when I sold my AOA vanes, that had a similar explanation. The Navy
had the same problem in the 1950s when it transitioned to jets which landed at
130 instead of 90, and had great weight (and stall airspeed) fuel variance)
making it tough for the jocks to avoid hitting the 'spud locker'. So they
bought the British meatball Fresnel lens to control the glideslope, and put
AOAs in all carrier aircraft to reduce the sweat and pucker-factor for the
pilots and the LSOs who had too little time to send corrections to the zippy
planes ... cutting landing accidents 50% the first year. But I don't believe
the Navy connected a landing gear warning system to the AOA back then, leaving
that to the LSOs Two different problems.

I am trying to figure how to put a simple automatic landing gear system in
our L235/320, something like in the Piper PA-28R. Just indicated airspeed
input to activate the gear ... to go up, if the wheels are down already, and
down, if they're already up. I'd like to see a schematic of how Robert's
landing gear system works.
I was thinking of a three-position indented switch, auto in the middle,
and up or down as an override, to the hydraulic pump. As one who is
electronically challenged, I wonder where I could find an
air-pressure-sensitive switch that would respond to increasing pitot pressure
to signal retracting the wheels; an, above that pressure from higher airspeed
the switch would stay closed until the pitot pressure reduced, to ...
automatically switch the pump circuit to extend the gear. Maybe a kind of
like a temporary normally-in-extend gear position, an extend-retract toggle
switch, which pitot pressure would move to "Fly" and held there until pitot
pressure reduced (at the selected airspeed) and switch the circuit back to
"Land" (on) the gear.
The saying is that one kind of pilot is one who has not landed wheels up
--- yet. Even Poberezny did it. Haven't made that mistake yet, and with an
auto-gear, at least I'd have some machinery to blame it on.
Any suggestions or comments would be appreciated.
Terrence
L235/320

[You're welcome, Terrence... I worked all the airshows with Jim Frantz for a number of years selling his AOA devices so 1) I'm a firm believer in AOA for its fidelity at lower airspeeds, 2) its precision, 3) its ability to provide stall warning independent of airspeed and/or wing loading, and 4) its being able to provide other flight critical data, like proper approach and L/D max AOAs as well.  Folks flying AOA on the approach typically find they are able to land shorter and more precisely hit their "spot", which equals better control and reductions in both tire and brake wear.  Flying the pattern when you're low and slow are the most dangerous periods in any flight, both during takeoff and landing, and having AOA information available can really save the day when it's time to tighten that base-to-final turn or during the period of rotation from ground roll to Vy during takeoff.  When the AOA yells "angle, angle, push!" at you you quickly realize that you need to get the nose down or you're going to stall.

As for the landing gear device... the washing machine pressure switches can probably do both of those jobs for you depending on their electrical characteristics.  While they typical actuate the switch at some preset pressure while the pressure is rising, the switch can either make or break a contact (SPDT) or pair of contacts (DPDT) and allow you to do different things with the changes in the electrical signals that are available.  Deciding how to wire it all up turns into a simple exercize in logic, and you can get very sophisticated if you use the pressure switch signals to drive various relays which can also have multiple poles and multiple contact combinations.  Once you identify exactly what you want to do and the criteria that have to be met to make the decisions, coming up with the circuitry is actually pretty easy.  Back in the days before solid state devices became so all pervasive and everything started going digital, when you wanted automation you relied on ladder diagrams to define the schematics of operation of all the switches and relays that controlled everything in your process.  This application is a piece of cake.

   <Marv>    ]