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

OK so I fly a glider which has nothing in it except a radio and basic instruments. I have an Oudie to keep me out of trouble. I just bought a FLARM brick with ADS-B in. Which I’ll install this winter. I’ll probably install a Trig Transponder next winter with ADS-B out. I’ve installed several different ADS-B out transponder systems in power airplanes.. I haven’t yet installed a squat switch in any of them. Generally power airplanes are faster than gliders. But there’s obviously Cub types that will fly at glider speeds so why don’t they have squat switches. I am just spit balling here. But it’s a good question.

On Monday, November 25, 2019 at 10:22:16 PM UTC-8, Charles Longley wrote:
OK so I fly a glider which has nothing in it except a radio and basic instruments. I have an Oudie to keep me out of trouble. I just bought a FLARM brick with ADS-B in. Which I’ll install this winter. I’ll probably install a Trig Transponder next winter with ADS-B out. I’ve installed several different ADS-B out transponder systems in power airplanes. I haven’t yet installed a squat switch in any of them. Generally power airplanes are faster than gliders. But there’s obviously Cub types that will fly at glider speeds so why don’t they have squat switches. I am just spit balling here. But it’s a good question.

Why don't you ask the person who did the installation in any "cub types" how they intended it to comply with 14 CFR § 91.227 (d)(1)? And what happens in strong headwinds like those giving near zero groundspeed? Ask them if they plan flying in those conditions.

The simple assumption many power installations will make is to use GPS based air/ground switching... and slow enough GA aircraft will have issues if they get into a strong enough headwind. But they likely do not fly often in those conditions or have never thought about it. We should be thinking about it in gliders as earlier ADS-B Out installations ran into immediate problems in wave.

Heck in strong wave locations towplanes may well run into this issue, so for those operators at places like Minden it might be a good idea in the towplane as well, what the FSDO wants for approval, if anything, if the STC says use GPS determination is up for discussion with them.

I tried to explain what I understand the regulations to say, and point out what folks operating in wave conditions want to avoid (GPS groundspeed switching saying you are on the ground when at altitude in wave). If it was not the apparent need for automatic switching we would likely be better off selecting "none" as a TT22 switch setting and just rely on the pilot switching the transponder manually between ON and ALT.

I am not 100% sure a squat switch is needed in a glider. Here’s a quote from Garmin through an AOPA article-
For aircraft without retractable gear aircraft, Garmin ADS-B equipment analyzes various data available to the system for air/ground determination. This includes groundspeed; vertical rate; airspeed; radar altimeter, if available; a rotorcraft’s collective position, if available; comparison of aircraft altitude to nearby airport elevation, if available; and comparison of groundspeed and/or airspeed to aircraft stall speed, Garmin’s Stone said.

Trig is the preferred transponder for gliders due to size. Does anyone know if a Trig transponder analyzes data like Garmin equipment?

On Wednesday, November 27, 2019 at 10:59:06 PM UTC-8, Charles Longley wrote:
I am not 100% sure a squat switch is needed in a glider. Here’s a quote from Garmin through an AOPA article-
For aircraft without retractable gear aircraft, Garmin ADS-B equipment analyzes various data available to the system for air/ground determination. This includes groundspeed; vertical rate; airspeed; radar altimeter, if available; a rotorcraft’s collective position, if available; comparison of aircraft altitude to nearby airport elevation, if available; and comparison of groundspeed and/or airspeed to aircraft stall speed, Garmin’s Stone said.

Trig is the preferred transponder for gliders due to size. Does anyone know if a Trig transponder analyzes data like Garmin equipment?

Uh yes, that's the "GPS" setting under "Select Squat Switch type".

You keep making statements about stuff or asking questions about about things that is already well settled and has been mentioned here many times.

This is years old information. I identified this GPS groundspeed determination in Trig Transponders as a problem in early glider installs. I let Trig know about that. I've described it all over r.a.s. I mentioned at it at an SSA convention talk. I've worked with every Trig glider dealer in the USA to let them know about it and to get squat pitot switches available. And when Trig updated the GPS algorithm recently I checked with them and they continued to state that this GPS based algorithm was *not* intended for use in glides or other aircraft that could have vey low (or negative) ground speed.. And I posted that on r.a.s. as well.

The very worse thing you can do for a glider that will fly in wave is to use GPS based determination.. It very likely will fail. For 2020 Compliance if 91.227 did not imply that automatic switching was required people would likely be better off with manual switching. For TABS installs just leave it manual. I don't know how many times I have posted this on r.a.s.

Garmin GPS based algorithm will likely fail in similar situations, you can ask Garmin what they are.

So you’re the RAS police Darryl?

On Thursday, November 28, 2019 at 10:42:19 AM UTC-8, Charles Longley wrote:
So you’re the RAS police Darryl?

No, but when people keep posting confused/wrong stuff here, especially where it has the ability to affect safety, I will keep correcting them. Sadly I did not see your update before you posted, or I would not have said anything. Since you are an A&P IA I expect people in this community to believe you will get stuff right. And unfortunately amongst the useful stuff you post there are some posts from you about UAT Out use in towplanes (with no warnings about compatibility issues), this stuff, etc. many of which would be answered or clarified to you if you searched this forum for past threads. Other discussion on the pitot switches were posted in another r.a.s. thread just days, including where I quoted Trig on the updated GPS firmware not being intended for gliders with possible low/negative ground speed.

So if you followed what I said you would see I was asking a question. I am not overly familiar with the Trig product line. But I am liking what I am seeing.

I disagree with your statement about the Garmin products. But it’s a moot point since it’s not an appropriate product for gliders.

What I don’t like is when someone asks a question you loudly proclaim, “We’ve talked about this before!� Well if you want to say anything at all why don’t you calmly point out the pertinent conversation? Our how the original poster asked about pitot/static leaks when you install a squat switch. You could have pointed out that a pitot/static check with a calibrated tester is required when installing it.

Happy Thanksgiving by the way! I am off to stuff my face.

But there’s obviously Cub types that will fly at glider speeds so why don’t they have squat switches.

Trying to apply logic here is risky, but maybe because the STC doesn't ask for it because the airplane is not intended to fly at zero groundspeed and so emitting ground mode while flying would be inadvertent.

If the glider is intended for wave and/or not experimental, then the STC would ask for the switch and zero groundspeed in the air would be expected. So being able to convince an investigator that you did a good faith effort in emitting the right signal "during the appropriate phase of flight" would lead one to the extra switch.