From Frustration to Flight: A Renewed Avionics Upgrade Journey for my 252

[201Steve]

42 minutes ago, tony said:

On 8/8/2024 at 11:13 PM, PT20J said:

Skip,  just be careful making an investment in those switches.  Remember an AC is not regulatory, it’s just guidance.  If you go further down

I always like to ask in these moments of regulatory caution: When a user is acting in good faith, with reasonably sourced material, with some reasonable citation, has the FAA ever gone out of their way to show up to someone’s house with a pocket knife? Or, are we just obsessed with mechanics and operators trying to be armchair lawyers? This is far from installing switches from Autozone and calling it good. Over and over and over, someone always wants to cite a different version of a reg that posits a situation MIGHT be questionable. I think part of the regulatory strangle on 50 year old personal aircraft is partially a self imposed myth that almost never gets enforced on unless you’re just taking egregious liberties eg autozone. 
 

it’s an aircraft switch. It’s installed with logical aircraft theory and hardware. Let’s stop furthering our self imposed restrictions with the arm chair rhetoric. 
 

* not a personal prosecution of the individual commenter. 

[PT20J]

4 hours ago, tony said:

Skip,  just be careful making an investment in those switches.  Remember an AC is not regulatory, its just guidance.  If you go further down into the Advisory circular it defines what a standard part is.

Standard Part. Is a part manufactured in complete compliance with an established U.S. Government or industry-accepted specification, which includes design, manufacturing, and uniform identification requirements. The specification must include all information necessary to produce and conform to the part. The specification must be published so that any party may manufacture the part. Examples include, but are not limited to, National Aerospace Standard (NAS), Air Force/Navy (AN) Aeronautical Standard, Society of Automotive Engineers (SAE), Aerospace Standard (AS), Military Standard (MS), etc.

Just be sure that these switches  can meet that guidance.

The AC is nonregulatory, but most A&P/IAs have interpreted the Discrete Electrical and Electronic Component Parts section to include components such as switches as standard parts. Standard parts are not defined in the FARs other the phrase in 21.303(b)(4)  ‘‘Standard parts (such as bolts and nuts) conforming to established industry or U.S. specifications.’’ 

To clarify, the FAA issued a legal interpretation back in 1997 that relaxes and broadens the requirements for industry standards and specifically broadens the definition of electrical component standard parts. It also clarifies that installation of standard parts is regulated by Part 43. 

97-5437.pdf

[shawnd]

Time for an update. The aircraft has been at the shop for about 2 weeks and there has been quite a bit of progress both on and off the aircraft. It took a bit to untangle the mess left behind by the previous shop but that's now finally done. GMU-44 has been installed and grounds pulled in (previously there were several by the wing tip). They are going through the stock harness now to see what's needed and what's not. In parallel, we have been working on panel iterations, and of course, scope creek on avionics  @donkaye I talked to the shop and managed to get a good deal on a 750Xi so the the nav/comm stack will be completely Xi series GTNs paired with the G500TXi and the GI-275s.

Did have one question for folks that did a full panel transformation. Did you end up retaining the RF filter in the circuit breaker panel? Or replace with something new? Or just get rid of it?

Picture time...

This is what the panel looked like when I flew it in on ferry permit:

 

The rat's nest (harness built by previous shop that was just $..T) and it's undo-ing:

 

Panel area now:

[PT20J]

I believe the filter you are talking about is for the alternator output. On my M20J there is a pi filter (series inductor with a smaller capacitor to ground on either side of the inductor) which Mooney buys from a supplier and a large electrolytic capacitor to ground. I replaced my capacitor because it was easy to do, the capacitor was cheap and it was nearly 30 years old and aluminum electrolytic capacitors don't last forever, but I saw no reason to mess with the filter.

[shawnd]

Yep, asked Matt to replace the blue capacitor for the same reasons you have.  He was curious about retaining the RF filter (gray box) where the alternator output connects to (far right) in the picture. Tempted to replace that too while we are in here. 

 

[EricJ]

9 minutes ago, shawnd said:

Yep, asked Matt to replace the blue capacitor for the same reasons you have.  He was curious about retaining the RF filter (gray box) where the alternator output connects to (far right) in the picture. Tempted to replace that too while we are in here. 

 

There's no reason not to replace the capacitor.    The filter can be tested pretty easily in an electronics lab, if that's useful. 

 

[MikeOH]

2 hours ago, EricJ said:

There's no reason not to replace the capacitor.    The filter can be tested pretty easily in an electronics lab, if that's useful. 

 

Any idea what the 3dB point is?

[EricJ]

1 hour ago, MikeOH said:

Any idea what the 3dB point is?

No, but if it's broken it probably won't have one. 
 

[shawnd]

2 hours ago, MikeOH said:

Any idea what the 3dB point is?

Learned something new today! 

The "3 dB point," also known as the "half-power point" or "cutoff frequency," is a term used in electronics and signal processing to describe a frequency at which the power of a signal has dropped to half its maximum value. This corresponds to a -3 decibel (dB) reduction in power, which is why it's called the 3 dB point.

https://en.wikipedia.org/wiki/Cutoff_frequency

[Max Clark]

On 8/8/2024 at 9:22 AM, Pinecone said:

I agree that you should move to a 750Xi.  You no longer have to leave a card in, and the start up time is significantly shorter.

Ask the shop how much the difference would be.  They may be willing to take the 750 in trade for the Xi.  That is basically what the other shops are doing.

When I did my panel, I switch to all toggle switches.  No more rockers.

 

Toggles vs Rockers pros/cons???

[Pinecone]

Just now, Max Clark said:

Toggles vs Rockers pros/cons???

The caps don't break.   And they look cooler.

I don't see any cons to toggles.

You can also color code them with caps.

[shawnd]

7 minutes ago, Max Clark said:

Toggles vs Rockers pros/cons???

Really boils down to looks and personal preferences. Mooney went Carling Contura V switches for the newer models and this is what the Maxwells recommend as well. You can get them straight from Mooney or through Carling distributors. I prefer their looks and you can get custom actuators (switch covers) and design them to your heart's content. They are cheap to replace and you can stock up if you are worried.

[Marc_B]

33 minutes ago, Max Clark said:

Toggles vs Rockers pros/cons???

Do they make toggles with integrated circuit breakers?  I have several rocker switches that are breaker switches.  Might be a con for that application if so.

Depending on your panel labeling, the wording on a wide switch may be easier to see.  Black wording on a white switch is pretty easy to read.  Also since the wording is on the switch rather than necessarily the panel, you can change/delete/add/move switches more easily in the future if needed without having to use sticker labels. 

[shawnd]

With a new panel, after you remove the 3 engine gauges in the CB panel there’s enough room to accommodate CBs for the switches. It also allows you to move the headphone/mic jacks into the panel vs having them on a separate metal piece below the panel.

[Fly Boomer]

4 hours ago, Marc_B said:

Do they make toggles with integrated circuit breakers?

This popped up in 2 seconds.

https://skygeek.com/potter-brumfield-w31-x2m1g-1-amp-circuit-breaker.html?utm_source=googlebase&utm_medium=shoppingengine&utm_content=potter-brumfield-w31-x2m1g-1-amp-circuit-breaker&utm_campaign=froogle&msclkid=978e18afcbcd132a3c087e631336b0b0

[MikeOH]

Save a few bucks by ordering from Mouser:

 

[shawnd]

Not sure yet who can test the RF filter but part of the investigation led me to a FAA/PMA source for noise filters:

https://lonestaraviation.com/product-category/filters/?v=47e5dceea252

Turns out they also sell on Aircraft Spruce and the 100 amp one is now FAA/PMA certified.

Any leads on who can test the existing one will be appreciated. 

 

 

[Aerodon]

I have two spare RF filters like the ones shown above on the RHS, from 1996, not 1986 if you want to get newer....

I'm not tempted to replace mine.

Don

[shawnd]

Thanks Don, appreciate it. But its cheap enough (compared to everything else), where might just get a new one if the need arises. Really want to figure out a way to test it..

[Pinecone]

On 8/26/2024 at 11:04 AM, Marc_B said:

Do they make toggles with integrated circuit breakers?  I have several rocker switches that are breaker switches.  Might be a con for that application if so.

Depending on your panel labeling, the wording on a wide switch may be easier to see.  Black wording on a white switch is pretty easy to read.  Also since the wording is on the switch rather than necessarily the panel, you can change/delete/add/move switches more easily in the future if needed without having to use sticker labels. 

Yes they do.  A number of mine are.  If you look very closely at the pictures, the normal ones the end of the toggle is rounded.  The break ones are flat with a number for the CB rating.

I grouped my switches so you don't have to really look too closely

[PT20J]

18 hours ago, shawnd said:

Really want to figure out a way to test it..

Hard to test unless you know the specs. It’s a pi low pass filter which is third order so it should roll off at 18 dB/octave but you’d have to guess the cutoff frequency unless you can get a spec sheet. I guess you could put a signal generator on the input and an oscilloscope on the output and plot the frequency response to see if it looks reasonable. Crown probably has the test equipment from when Larry was there and did bench repairs.

Its purpose is to filter out rectified DC noise from the alternator. The best test is whether you heard alternator whine in your radios before the upgrade. If not, it’s working. 

[shawnd]

Yeah I figured it works given there have been no issues with headphones prior to things getting torn apart. But the geek inside me wants to get data to re-assure myself 

I will ask Matt about the test equipment, he might be interested in it as well. 

[EricJ]

16 hours ago, PT20J said:

Hard to test unless you know the specs. It’s a pi low pass filter which is third order so it should roll off at 18 dB/octave but you’d have to guess the cutoff frequency unless you can get a spec sheet. I guess you could put a signal generator on the input and an oscilloscope on the output and plot the frequency response to see if it looks reasonable. Crown probably has the test equipment from when Larry was there and did bench repairs.

Its purpose is to filter out rectified DC noise from the alternator. The best test is whether you heard alternator whine in your radios before the upgrade. If not, it’s working. 

Yes, it could be swept with a Network Analyzer or use a signal generator and a Spectrum Analyzer, or even just a signal generator and an oscilloscope, or a few other ways as well.   If it has a reasonably low pass function with good attenuation above some reasonably low frequency, enough to cut off alternator whine, I'd call it good.    If any of the components are failing, it'll be obvious in one way or other depending on what failed, but it won't look right.   I don't think specs are required to tell if it is working or not, and there was probably enough slop in the components that they're not precision devices, anyway.   Its job is fairly simple.

[PT20J]

I don't know who made the one that Mooney used, but Lone Star Aviation makes one and the website has a Bode plot https://lonestaraviation.com/wp-content/uploads/2017/09/70-Amp_freq_graph.pdf?v=47e5dceea252

Looks like the cutoff frequency (-3 dB) is about 13kHz and maximum attenuation is about 70 dB at 220 kHz. The load resistance for the test is unclear -- probably 50 ohms to match the signal generator impedance.

[EricJ]

3 hours ago, PT20J said:

I don't know who made the one that Mooney used, but Lone Star Aviation makes one and the website has a Bode plot https://lonestaraviation.com/wp-content/uploads/2017/09/70-Amp_freq_graph.pdf?v=47e5dceea252

Looks like the cutoff frequency (-3 dB) is about 13kHz and maximum attenuation is about 70 dB at 220 kHz. The load resistance for the test is unclear -- probably 50 ohms to match the signal generator impedance.

Yeah, it's not a very sophisiticated filter.   Most test equipment that goes into RF frequencies doesn't go low enough to test the audio frequency response, which is partly what you care about with these, but if it generally has a LPF shape with reasonable attenuation, that's what it's supposed to do.   That's pretty easy to test in many labs.    If it's not doing that, then it's broken.