REFLECTOR: Back-up gear switch, Implement at your own risk!

[Scott Derrick]

By "Squat Switch" I assume you mean the pressure switch that is tied 
into the pitot line? There isn't a squat switch in the Velocity as far 
as I know.

I can't say that I like the idea of my gear dropping automatically.  
Never liked the system in the piper..

Having an audible and visual alert that goes off if the gear is up and 
I'm flying less than 85 knots sounds like a good idea, though we do have 
the throttle alert that whines if the throttle is pulled back and the 
gear is up... 

People have been known to ignore those warnings, probably most gear up 
incidents were accomplished with the gear up alert song being played in 
their headsets. 
 
I've always liked the military tower protocol of the "Gear Check" on final.

Scott

cgputney at peoplepc.com wrote:

> Back-up gear switch
>
> Most of you that fly RG aircraft know the old axiom "there are those 
> who have and those who will, land with the gear up" Not wanting to 
> join that group during some distraction, I have emulated the original 
> Piper system on my Velocity. Simulated flights on the ground show that 
> it works. Flight tests to follow.
>
> The implementation is quite simple:
>
> 1) Remove original squat switch.
>
> 2) Replace it with an adjustable differential pressure switch (Dwyer 
> 1910-5, 1.4-5.5 W.C. $35, one pound, for example. See their web site.)
>
> 3) Attach squat switch wires to "common" and "normally open" terminals 
> to retain the original squat switch function. Be sure original wire 
> from gear toggle switch "up" terminal goes to "common" on the 
> differential pressure switch.
>
> 4) Add wire from gear toggle switch "down" terminal to "normally open" 
> terminal on differential pressure switch.
>
> 5) Plumb pitot pressure tube (formerly going to squat switch) to high 
> pressure fitting on differential pressure switch and add a static 
> pressure tube going to low pressure fitting.
>
> 6) I calibrated the trip airspeed by disconnecting the line going to 
> the pitot tube and extending it with 5 feet of poly tubing. Originally 
> I used a bucket of water (3.16 in.=80mph) but found success by 
> watching the airspeed indicator and pressurizing carefully by mouth. 
> First I adjusted the trip point to approximately 85 mph, with 
> electrical power off, using a continuity checker across the switch. 
> Full ground tests followed with AC up on wing and nose jacks.
>
> Results to date:
>
> 1)With gear switch down and AS< 85mph, gear is down.
>
> 2) With gear switch up and AS< 85mph, gear is down.(squat switch function)
>
> 3) With gear switch down and AS >85mph, gear is down.
>
> 4) With gear switch up and AS < 85mph, gear is down (new back-up function)
>
> 5) With gear switch up and AS > 85mph, gear is up
>
> These switches have a "dead band" wherein trip points with increasing 
> AS may be 85mph, but decreasing AS trip points may be 6 mph lower.
>
> Mount the switch vertically with elastomeric isolators to minimize 
> effects of turbulence.
>
> As you can see, the gear switch can be used as before because this 
> system is transparent.
>
> Conversely, leaving the gear switch up results in an automatic mode!
>
> Manipulating the circuit breaker near the gear switch allows one to 
> control when the gear comes down.
>
> Implement at your own risk. Piper apparently had problems, both 
> technically and with liability. One Piper pilot sued because he failed 
> to reach an intended airport when his engine failed, due to gear down 
> drag.
>
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