Attached is the schematic of my circuit and a photo of the pump with the new relays, as well as a photo of the squat switch I use.

I use a squat switch to prevent accidental gear retraction on the ground, but this switch is not rated for inductive loads.  The coils of the original lancair-supplied electro-mechanical pump relays are inductive so, to protect the squat switch, I now use solid state relays to turn on the pump. These new relays energize with an input current around 10 ma, and the input circuit is non-inductive. This should keep the squat switch from deteriorating.

The squat switch should really be called an airspeed switch: it is triggered by Pitot/Static pressure difference.  The switch is adjustable, and I adjusted it to allow retraction at Indicated Air Speed above 85 knots. For a Legacy or a IV I would probably set this a bit higher. MPL used to stand for Micro Pneumatic Logic, but a google search for that company does not find it.  I got the switch from http://www.mic-tec.com/ . Perhaps they bought the MPL line.  There seem to be many sources for this switch. Someone is still making it, but it seems the company name has changed.

The relays I chose are Crydom type D06D100, which cost $125 each at digikey. 

The relays are quite tough, but they need protection from the inductive spike that can happen when the the relay cuts off the current to the motor.  For that I use an SPR300A diode connected across each pump motor connection.    

Here is my understanding of how these protection diodes work. We know the motor draws less than 50 A when it is running. When the relay opens it breaks the current to the motor. The motor has substantial inductance, so it begins to develop a negative voltage, because the derivative of current is negative (recall: V= L dI/dt). This negative spike causes arcing across conventional relay contacts. When using a solid state relay it can damage the MOSFET in the relay. This is where the protection diode does it's thing.  The diode clamps the negative spike, limiting it to about 1 volt.  The negative voltage from the motor winding turns on the diode, with the same current flowing in the diode that, moments before, was flowing in the relay.

At this point the diode is forward biased, about 50 amps flowing, at -1 volt. This negative voltage ramps the current gently down to zero. The diodes I am using have a surge current limit at 140 A, so they can readily handle the spike.  For extra protection there is actually another diode inside the relay.

Since I deleted the original mechanical relays I no longer have the extra contacts that up-to-now turned on the "transit" light.  I decided to install two LEDs to distinguish transit UP from transit DOWN.  At first I hooked these indicators directly to the UP and DN motor wires.  However, I found that both lights came on when the pump moved in either direction.  So, I moved the indicators to the input side of the relays as shown in the schematic.  

I have done about five cycles of retraction/extension on the ground and so far all is well.  

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Jeff Peterson
L-360, 20 hours