Pitot/static leak issues when using a "squat switch"

Everything I've flown with a squat switch (props, turboprops, jets) has
had shock struts.Â* Does the '20 have one of those?

Come to think of it, we use "landing gear down and locked" as a position
for a micro switch in our gear warning systems.Â* It shouldn't be at all
difficult to use a micro switch in the "landing gear up and locked"
position as your "in flight" sensor.Â* But when you lower the gear,
you'll be reporting "on ground".Â* You could also use a toggle switch,
just don't forget to flip it.Â* Or you could simply switch your
transponder from ON to ALT before takeoff and after landing.

On 11/28/2019 4:30 PM, Charles Longley wrote:
I am thinking about a better mousetrap. Probably can’t do a squat switch on the gear because of the configuration on the ASW20. But I’ll think it over.

--
Dan, 5J

Yeah I am familiar with how a squat switch works. There’s no suspension in an ASW-20 except the tire so no place to put the squat switch. I’ll take a look at it when I do the Condition Inspection. Maybe something will come to me.

On Friday, November 29, 2019 at 5:58:13 PM UTC-8, Charles Longley wrote:
Yeah I am familiar with how a squat switch works. There’s no suspension in an ASW-20 except the tire so no place to put the squat switch. I’ll take a look at it when I do the Condition Inspection. Maybe something will come to me.

Can anyone show me the FAA regulation that requires a squat switch in a glider?

There’s no requirement. The issue is if you get down to a low ground speed in flight the transponder might go into the ground mode. I think it’s getting a little overblown on RAS. Trig recommends a squat switch to compensate for it. Some of the other transponder manufactures can compensate for it by programming. I haven’t put a squat switch in any of the power airplanes I’ve installed ADS-B transponders in.

On Friday, November 29, 2019 at 9:25:29 PM UTC-8, Charles Longley wrote:
There’s no requirement.

No requirement for a squat switch explicitly, but there is a (not very clear) requirement for some form of automatic air/ground switching for 2020 compliance and you should want to use something that uh actually works reliably. See my tenth post in this thread.

The issue is if you get down to a low ground speed in flight the transponder might go into the ground mode. I think it’s getting a little overblown on RAS. Trig recommends a squat switch to compensate for it. Some of the other transponder manufactures can compensate for it by programming. I haven’t put a squat switch in any of the power airplanes I’ve installed ADS-B transponders in.

Oh Jesus, yes but none of the aircraft you have installed ADS-B out in are gliders that fly in mountain wave. Nothing of what you have done in those power aircraft installs is relevant here.

The other transponder manufactures do not just "compensate for this by programming". I've got a pretty good understanding of GPS technology and I have no clue how this would be possible. You have no way of knowing that Garmin or other systems that use GPS detected ground speed to switch from air/ground will work in scenarios where those aircraft have near zero groundspeed without problems. A GPS in a glider or any other aircraft hovering in strong enough wave with a near zero ground speed just can't work out if it is on the ground or not. That you don't read about this in Garmin or other install documentation is likely only because those aircraft don't fly in strong enough wave/headwinds to have this problem.

Again we known for several years now this is a problem for gliders in mountain wave. Especially if your glider is going to fly in wave or strong headwinds please pay attention and get this right with a pneumatic pitot switch. Personally I'd install it that way in every glider, because you just don't know where it will end up flying.

Again if you are installing TABS just set the transponder squat switch to "None" and use manual ON/ALT switching on the transponder.

The very worse thing you can do in a glider that has any chance of being in mountain wave or a strong headwind is select GPS based air/ground switching.

If 91.227 did not imply automatic switching was required you would be better off choosing none and just relying on the ON/ALT switch on the transponder.

Darryl Ramm wrote on 11/29/2019 10:36 PM:
Again if you are installing TABS just set the transponder squat switch to "None" and use manual ON/ALT switching on the transponder.

I might forget to switch it correctly. Would using the "gear is down" switch to
change between ground/airborne be a sensible choice? The pattern (and the first
500'-1000' after the takeoff) would be flown showing the glider was on the ground,
of course, but that might be better than having the whole flight showing as on the
ground.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

https://www.amazon.com/United-Pacifi...xpY2s9dHJ1ZQ==

On Saturday, November 30, 2019 at 8:26:42 AM UTC-6, Eric Greenwell wrote:
Darryl Ramm wrote on 11/29/2019 10:36 PM:
Again if you are installing TABS just set the transponder squat switch to "None" and use manual ON/ALT switching on the transponder.

I might forget to switch it correctly. Would using the "gear is down" switch to
change between ground/airborne be a sensible choice? The pattern (and the first
500'-1000' after the takeoff) would be flown showing the glider was on the ground,
of course, but that might be better than having the whole flight showing as on the
ground.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

If you use a squat switch with a Trig transponder, I believe that also puts the Transponder into GRND mode, so it wouldn't be responding to interrogations. The one place you do want ADS-B OUT and your transponder operating is in the pattern. That's where half of the midairs occur. Turning off ADS-S B OUT or your transponder as soon as you lower the gear is a really bad idea.

Actually out of curiosity I looked at the pin out diagram for a Garmin transponder. There’s no pin out for a squat switch. Guess they do air-ground logic through programming as quoted by AOPA. Too bad they don’t make a smaller transponder.

I'm pretty sure the Trig transponder allows the GND/ALT determination to
be made without use of a squat switch.

On 11/30/2019 1:21 PM, Charles Longley wrote:
Actually out of curiosity I looked at the pin out diagram for a Garmin transponder. There’s no pin out for a squat switch. Guess they do air-ground logic through programming as quoted by AOPA. Too bad they don’t make a smaller transponder.

--
Dan, 5J