REFLECTOR:Tube and bucket doesn't work!

[Laurence Coen]

If you stick a tube into a bucket of water 3.16", water will rise inside the 
tube and the resulting pressure will be the difference between the level of 
the water inside the tube and the surface of the water in the bucket. 
Instead, use a clear plastic tube bent into a "U".  One end goes to the 
pitot connection and the other open to the air.  Fill the "U" half way with 
water.  now you can adjust the open end up or down till you have a 
difference of 3.16" between the two legs of the "U" and you're done.  I used 
this method to calibrate my Rocky Mountain air speed indicator and when I 
had it certified it was bang on from 70 to 200 knots.

Larry Coen
N136LC
  ----- Original Message ----- 
  From: cgputney at peoplepc.com
  To: Reflector -
  Sent: Friday, November 04, 2005 10:53 AM
  Subject: REFLECTOR: Back-up gear switch, Implement at your own risk!


  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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