REFLECTOR: The Saga of the Gear Circuit

[Ronnie Brown]

But Al, not withstanding scraped bellies and broken prop blades, it sure looks SLEEK and SEXY without all those wheels and gear legs hanging down!!!

(By the way, did we ever figure out what happened to Terry Davies XL-5 in Savannah?)

Cheers
Ronnie  
  ----- Original Message ----- 
  From: Al Gietzen 
  To: reflector 
  Sent: Wednesday, September 15, 2004 11:35 AM
  Subject: REFLECTOR: The Saga of the Gear Circuit


  When the Swings designed the retract system for the Velocity, they put in the hydraulic pump, some pressure limit switches, and a couple of relays.  The gear went up and the gear went down.



  Recognizing the importance of knowing the gear was down for landing, they decided it would be good to have some indicator lights that would confirm the down and locked position.  Everything was fine.



  Then somebody said, "Well, suppose that the pilot doesn't do the landing check list, and doesn't notice that the plane isn't slowing down very well, and then forgets the "GUMPS" check on downwind that we are all taught when flying complex airplanes, and, besides that; doesn't confirm that there are two greens on final."  That would be pretty bad piloting, but they decided to add a warning horn.  That took a couple more switches, and quite a bit more wiring.



  Then somebody said, "Gee, I can't always hear when the gear pump is running, so how can I tell if the gear is actually going up or going down after I flip the switch?"  So some more wires and another indicator light were added.



  Then somebody said, "You know, sometimes, under certain conditions, when you switch to 'gear down', nothing happens."  We all learn that this can happen if the pressure is high on both sides of the hydraulic system, and can be easily remedied by a quick pull on the gear dump valve, which is already within handy reach.  But someone decided we should add some more wires and a 'Gear reset' button to, I guess, make it easier.



  Then someone said, "Sometimes the gear warning horn that was added to save us from bad piloting goes off when I don't want it to.  How can I shut that thing up?" So then some more wires, another switch, and another relay were added for a "horn reset" circuit.



  Then someone said, "What if we accidentally have the 'Master Switch' on, and then accidentally switch the gear switch to 'gear-up' when we are on the ground?  That would be a serious problem."  So then some more wires and an 'airspeed' switch were added so the gear switch (which can't just be bumped but has to be switched deliberately) can't make the gear go up unless the plane is flying.



  Oh, yeah; and while you're at it, if you don't want the Hobbs meter to run until you are actually flying, we can wire that into the gear indicator circuit so it doesn't turn on until the gear is up.



  And then I thought of using the airspeed switch in place of the 'low throttle' switch for the gear warning horn circuit, which can add a another DPDT relay and a bit more wire.



  I think you get my drift. It may be amusing, or it may make one consider the meaning of 'reliability'. For those still building and haven't yet installed all this circuitry, you might want to consider it a bit, or at least install all the gear wiring early in the process; maybe before you put the top on the fuselage.  I installed the basic operating circuit years ago, but didn't start installing all the ancillary circuitry until a few days ago when lots of other wires and things were in the way, and didn't consider the complexity until I had most of it done yesterday.



  I now have a better understanding of why some folks choose fixed gear; and the meaning of P.V.O.T.  It almost sounds like a design done by the government (well, I suppose by any bureaucracy).



  Al





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