SV-GPS-2020 mounting under the cowling?

swatson999

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What kind of test?

BTW, a very similar discussion with very similar points on each side is occurring in Van's aircraft with about an equal chance of resolution to the satisfaction of all concerned.
I'd say performance tests (normal cruise attitudes, typical maneuvers), RF compat tests (gotta do those regardless of where you put the antenna), validations (fly several types of approaches...this is not *verification*, but validation), for starters.

You have to do these anyway...it doesn't depend on antenna installation. Garmin has a post-installation checklist that is a pretty good start. Dynon should do something similar.

Yeah, this comes up about once a year on VAF. This time it includes discussions of paint. It never ends.

There are so many variables out there (under cowl or not? paint or not? glareshield or not? temp limits, sky visibility requirements, etc.)...*I'M* satisfied with mine, so about all I can do is tell people what has worked for 8+ years for me and let them satisfy themselves with whatever installation they want. No skin off my nose however they choose to do it, is it? :)
 
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RV8JD

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My RV-8 has the SV-GPS-2020 mounted under the cowl (non-metallic paint) on a shelf attached to the firewall:



And this is the Satellite reception I consistently see:

 
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GalinHdz

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IMHO, do things the way the manufacturer confirms it is correct and you greatly reduce the possibility of failure. Now if you want to experiment and are willing to take the risk, then do whatever you want. Personally I fly with my family in actual IMC conditions and am not willing to take the risk so my GPS pucks are installed according to Mfg specs.

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DBRV10

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RV8JD

That may work fine, not as per the manual though. Match it with another GPS alongside, and you may suffer sub-optimal performance.

Just because that works does not make it "best practise"
 

airguy

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RV8JD

That may work fine, not as per the manual though. Match it with another GPS alongside, and you may suffer sub-optimal performance.

Just because that works does not make it "best practise"

Your point about "best practice" is true and accurate - but that does not mean that it's the only way. Other things may work other than those proscribed by the good and holy "installation manual" - but they bear testing to confirm. My airplane has had this arrangement for 5 years and almost 800 hours without issue, looking up through the cowling and non-metallic pigment paint.

Yes, I was outside the bible according to the manufacturer, and knew I might have to change it. I tested it, it works, has never given me trouble and I'll keep flying it. "The Way" is not the only way.

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RV8JD

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RV8JD

That may work fine, not as per the manual though. Match it with another GPS alongside, and you may suffer sub-optimal performance.

Just because that works does not make it "best practise"
I never said it was 'best practice', nor did I recommend it. I just showed my installation along with Satellite reception data/results, which no one else has bothered to do. (To quote DanH on VAF, "In God we trust, all others bring data!" ;)) That's all I did. YMMV!

BTW, If I'm not mistaken, in previous thread posts you said that your installation doesn't show any Green Satellite reception, only Yellow at best. Here it is:

 
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swatson999

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I note that nowhere in the GNS430W installation manual, for the antenna, does it say the installer *must* do anything. Every single criteria listed uses the words "should", "should not", or "avoid", but none of them are "must" or "must not".

If you're going to appeal to authority, make sure the authority is actually saying what you believe they are saying.
 

RV8JD

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Some 'data' from the SkyView Installation Guide on acceptable Sat reception performance, i.e., the proof is in the pudding, so to speak.
Also, note the very last paragraph.

 
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WorkingWarbirds

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Another factor many may not be considering is that signal will be worse the farther north you go. What works 'fine' in Texas may not work at all in Alaska. The installations instructions are there for a reason. Someone else will own the airplane after you.
 

kellym

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I don't think it "needs" a full 360 degree view to perform sufficiently well. Yes, the solution uncertainty decreases with a wider-spaced geometry of satellites, but beyond a certain point, when you've got 10 or more satellites in view all over the sky, adding one or two more isn't going to change the dilution of precision by very much. You only need 4 to get at least *some* solution, and I've never seen less than 8 or 9.

In addition, if you are careful and mount it high enough, just underneath the cowling, and on a shelf so it's a fair distance forward of the firewall, the mask will be very small, perhaps 5 degrees or so. You can easily see if/how many satellites are masked by looking at the GPS status page. On mine, I only every see 1, maybe 2, at a very low elevation that are masked and not being received (and one of two things will happen...they'll come into view and get locked in, or drop below the horizon and it won't matter anymore).

I've never had any problems with GPS signals or solutions in this location, on either box (SV or 430W) because of insufficient satellites.
You may not "think" what something needs. For IFR flight your equipment needs to meet the requirements of the TSO approval, which includes the installation instructions for antenna placement. You may "think" you are okay for penetrating clouds with an install that doesn't meet the TSO requirements, and you may get away with it for a long time. Do you really want to bet your life and your passengers life on that? The requirements are there for a reason. If your 430 antenna is not located in a position approved in its installation manual, it technically isn't legal for IFR flight. Likewise with the GPS2020...Dynon demonstrated it met the requirements of the ADS-B regulations when installed according to the instructions. Given that both other aircraft and you are depending on the position being correct, which you can't know if you don't have full integrity verification of the satelites, these are not things to experiment with. It is one thing when you experiment with items on your aircraft that are unlikely to affect anyone else. It is another to experiment with navigation equipment that you clearly don't have a full understanding of the pitfalls, that affects everyone in the airspace near you. If you put the 430 antenna where it belongs, and use the 430 as the position source for your ADS-B out, you only need one antenna outside the aircraft skin.
 

swatson999

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You may not "think" what something needs. For IFR flight your equipment needs to meet the requirements of the TSO approval, which includes the installation instructions for antenna placement. You may "think" you are okay for penetrating clouds with an install that doesn't meet the TSO requirements, and you may get away with it for a long time. Do you really want to bet your life and your passengers life on that? The requirements are there for a reason. If your 430 antenna is not located in a position approved in its installation manual, it technically isn't legal for IFR flight. Likewise with the GPS2020...Dynon demonstrated it met the requirements of the ADS-B regulations when installed according to the instructions. Given that both other aircraft and you are depending on the position being correct, which you can't know if you don't have full integrity verification of the satelites, these are not things to experiment with. It is one thing when you experiment with items on your aircraft that are unlikely to affect anyone else. It is another to experiment with navigation equipment that you clearly don't have a full understanding of the pitfalls, that affects everyone in the airspace near you. If you put the 430 antenna where it belongs, and use the 430 as the position source for your ADS-B out, you only need one antenna outside the aircraft skin.

OK, I'll play this game. Here are the 430W installation instructions, straight from the Garmin document:

1. Mount the antenna as close to level as possible with respect to the normal cruise flight attitude of the aircraft. If the normal flight attitude is not known, substitute the waterline, which is typically referenced as level while performing a weight and balance check.
2. The GPS antenna should be mounted in a location to minimize the effects of airframe shadowing during typical maneuvers. Typically mounting farther away from the tail section reduces signal blockage seen by the GPS antenna.
3a. The GPS antenna should be mounted no closer than two feet from any VHF COM antenna or any other antenna which may emit harmonic interference at the L1 frequency of 1575.42 MHz. An aircraft EMC check (reference VHF COM interference check in Post Installation Checkout procedures) can verify the degradation of GPS in the presence of interference signals. If an EMC check reveals unacceptable interference, insert a GPS notch filter in line with the offending VHF COM or the (re-radiating) ELT transmitter.
Note: When mounting a combination antenna (ex. GPS and COM, GPS and XM), the recommended distance of two feet or more is not applicable to the distance between the antenna elements provided the combination antenna is TSO authorized and has been tested to meet Garmin’s minimum performance standards.
3b. The GPS antenna should be mounted no closer than two feet from any antennas emitting more than 25 watts of power. An aircraft EMC check can verify the degradation of GPS in the presence of interference signals.
3c. To minimize the effects of shadowing at 5° elevation angles, the GPS antenna should be mounted no closer than 6 inches (edge to edge) from other antennas, including passive antennas such as another GPS antenna or XM antenna.
4. To maintain a constant gain pattern and limit degradation by the windscreen, avoid mounting the antenna closer than 3 inches from the windscreen.
5. For multiple GPS installations, the antennas should not be mounted in a straight line from the front to the rear of the fuselage. Also varying the mounting location will help minimize any aircraft shading by the wings or tail section (in a particular azimuth, when one antenna is blocked the other antenna may have a clear view).

An under-cowling installation can meet all of these requirements. (And I'll admit that I violate the one that says it *should* be mounted 6"edge-to-edge from other GPS antennas).

I've been flying with the Dynon for ADS-B Out for several years now, and have never had a failed report or a notice of problems from the FAA (which they send you when your system fails to meet the requirements during a flight).

WRT this: "you can't know if you don't have full integrity verification of the satelites"...I don't NEED to know this. The system itself is doing that analysis continuously, and alerts the pilot if integrity is lost (the 430W will do this when the aircraft goes inverted). We don't have to compute RAIM before a flight anymore, and FDE in the GPS receiver does all the "integrity checking" it needs to do to assure a valid solution.

But thanks for the lecture. That's sure to sway opinions.
 
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swatson999

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Oh, and for good measure, here's Dynon's *Guidelines* (not requirements):

Like all GPS devices, for most reliable performance, the SV-GPS-250/SV-GPS-2020 require a clear, unobstructed “view” of the sky. The SV-GPS-250/SV-GPS-2020 are designed to be mounted on the upper fuselage of the aircraft for an unobstructed (360° view) of the sky during maneuvers. If the SV-GPS-250/SV-GPS-2020 is mounted inside the fuselage (for example, on the top of the panel or underneath a cowling), the SV-GPS-250/2020’s view of the sky is partially or fully obstructed and GPS performance may be marginal in situations such as insufficient number of satellites “in view”.
Observe the following guidelines when choosing a location for an SV-GPS-250/2020:
• The optimal location for the SV-GPS-250/2020 is a rigid surface on the upper fuselage of the aircraft.
• Mounting location should be relatively level (the base of the SV-GPS-250/2020 is flat).
• Do not locate the receiver within 3 feet of transmitting antennas.
• Avoid antenna shadows (i.e., obstructions that block the antenna’s view of the sky).
• All four of the SV-GPS-250/2020’s wires should all be connected to each SkyView system display for redundancy.

Yes, there's a caution in there about putting it on top of the panel or underneath the cowling, but again, there's no REQUIREMENT not to do so.

Again...this is EXPERIMENTAL aviation, and part of an experiment is to verify that whatever you're doing works. As noted many times, plenty of us have done that, via flight test, RF compat tests, looking at the visible sats and status page to ensure minimal masking, and so forth.

No location on an aircraft with the possible exception of the top of the VS is going to have a complete, unmasked, complete hemispherical FOV from horizon to zenith in all 360 degrees. Put it on the aft fuselage? Most of them slope backwards in normal flight, masking low-altitude satellites in the forward direction.

So I stand by my statement...full hemispherical view is NOT required. Unless someone can show me the documentation that requires it, I maintain that it's, well, not required.
 
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kellym

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Oh, and for good measure, here's Dynon's *Guidelines* (not requirements):



Yes, there's a caution in there about putting it on top of the panel or underneath the cowling, but again, there's no REQUIREMENT not to do so.

Again...this is EXPERIMENTAL aviation, and part of an experiment is to verify that whatever you're doing works. As noted many times, plenty of us have done that, via flight test, RF compat tests, looking at the visible sats and status page to ensure minimal masking, and so forth.

No location on an aircraft with the possible exception of the top of the VS is going to have a complete, unmasked, complete hemispherical FOV from horizon to zenith in all 360 degrees. Put it on the aft fuselage? Most of them slope backwards in normal flight, masking low-altitude satellites in the forward direction.

So I stand by my statement...full hemispherical view is NOT required. Unless someone can show me the documentation that requires it, I maintain that it's, well, not required.
B.S. Many aircraft, including many Vans aircraft cruise in a nose low attitude so the rear fuselage is very close to level. Ditto most Cessnas, Cirruses, etc. If you look far enough in the documentation, most certified GPS do need as close as possible to full view of the sky.
My GPS250 will find plenty of satellites sitting inside my hangar with the door open. The certified Garmin antenna won't see any because it has higher integrity requirements and needs clear view of the sky.
uAvionics has found adequate coverage mounting in the wing or tail nav light position, because it gets very close to full view of the sky. You could mount your antenna in a fiberglass wingtip, it would be level and very good view of sky with none of the heat of the engine compartment.
In many Vans aircraft with canopies there are mounting options inside the canopy that meet the suggestions.
When installing TSO'd equipment, "should" generally means "shall" unless other is approved by manufacturer and/or FAA. Doesn't matter if it is in experimental or certified airframe. I suppose you are going to "experiment" with an old Hartzell compact hub prop that has had an AD for cracks for the last 10 years or so, or a Lycoming oil pump that doesn't comply with the AD on it (compliance deadline was July 31, 2001).
Yeah, I know, you think experimentals are "exempt" from AD's.
You totally miss the point that there are appropriate things to experiment with and totally inappropriate things. Navigation equipment that provides separation from other aircraft and or terrain is one of the latter, because it affects people that didn't agree to be part of your "experiment". Building one airplane does not necessarily make you an "expert" on regs or equipment.
KellyM
A&P/IA
EAA Tech counselor
 
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