insulation under avionics access panels

[Vance Harral]

Airplane is a 1976 M20F with no windshield mods.  It has the original avionics access panels just forward of the windshield.  It came from the previous owner with "blankets" of fiberglass insulation laid over the avionics, underneath the panels.  For over a decade, we've dutifully removed and reinstalled these every time the avionics bay is accessed.

At our recent annual, we discovered a rodent had taken up residence in the airplane.  Fortunately no serious damage found, but it did chew up one of the insulation blankets.  Aircraft Spruce sells material that appears to be very similar (http://www.aircraftspruce.com/catalog/cspages/fiberglassinstall.php).  But before simply replacing with the same stuff, it occurs to me to ask just exactly what this stuff is supposed to do.  I can find no reference to it in my parts manual, and I'm not sure if it was original equipment or something added by an avionics shop at some time in the past.

In theory I suppose this stuff provides insulation against noise and outside temperatures.  One of the partners has also speculated that it provides some further protection against rain if the rubber seals aren't perfectly efficient.  But I'm not convinced.  Wondering if it might be best to simply leave it out.  Alternatively, wondering if it makes sense to replace it with the same closed-cell, sticky-back stuff specified in SB208B rather than fiberglass.  Would appreciate comments/tips from anyone with similar experience.

[carusoam]

Thoughts...

1) 65C had no insulation there.

2) Can't imagine fiberglass improving a water seal. It is more likely to get in the way of the water seal.

Just a PP, not a mechanic.

Best regards,

-a-

[mike20papa]

I thought Mooney long ago decided fiberglass batt insulation was bad because it held moisture.  I think there was even a AD or SB to remove it all out of the cockpit as it was causing corrosion of the steel tube cage.  At any rate, you probably are correct in assuming it was used in hopes of diverting water from entering any radios.  There are some great sealing tapes you can use on those outer access panels.   Closed cell, adhesive one side, compresses to approx. .03"  and found in the aviation parts department at Lowes!  Stuff that wasn't around when your F model was built. 

My windshield and glass in my A model was all originally set with old painter's putty, that linseed oil & titanium oxide "Stuff".  I didn't use that material when I replaced all of my glass, and I didn't think the FAA will now throw a fit - but who knows.

 

[rbridges]

25 minutes ago, mike20papa said:

I thought Mooney long ago decided fiberglass batt insulation was bad because it held moisture.  I think there was even a AD or SB to remove it all out of the cockpit as it was causing corrosion of the steel tube cage.  At any rate, you probably are correct in assuming it was used in hopes of diverting water from entering any radios.  There are some great sealing tapes you can use on those outer access panels.   Closed cell, adhesive one side, compresses to approx. .03"  and found in the aviation parts department at Lowes!  Stuff that wasn't around when your F model was built. 

My windshield and glass in my A model was all originally set with old painter's putty, that linseed oil & titanium oxide "Stuff".  I didn't use that material when I replaced all of my glass, and I didn't think the FAA will now throw a fit - but who knows.

 

Moisture was the first thing that came to my mind, also.

[Vance Harral]

Thank for the replies so far, keep 'em coming.

To be clear, the insulation blankets sit entirely inside the avionics compartment.  They are not "pinched" into the seal where the panels screw into the fuselage, and would not interfere with that seal.  But the rubber in that seal is pretty old, and I'm not sure how tight it is.  We rarely fly actual IMC, have never flown in hard rain, and I've never hit the panels with a high pressure water stream to see how good the seal is.

To the extent the "protect from water" theory is true, the whole argument is the fiberglass would absorb any water that dribbled through the seals, and it could be easily removed to dry out later.  Unlike insulation behind the interior panels, these avionics "blankets" are easy to get to, and don't rest up against any of the steel tubing that makes up the structure of the fuselage.  Between that and the fact the airplane is hangared in a dry climate, I'm not particularly concerned about them being a source of airframe corrosion.  Still, not sure it's worth the trouble and expense of replacing the damaged one if it's not serving any real purpose.

[Yetti]

I would think:

Don't really want fiberglass parts being blown around the radios and cabin.   There is positive ventilation provided up there from the starboard side intake vent and clear line.

Don't want water logged stuff on top of electronics

Don't want insulation blocking the airflow to the radios and such.

 

As far as sealing the access panels.    Pulled the gunky foam out of the channels.   stainless wire brushed the glue out.  Used two part contact cement below to put in I believe 1/2" round caulk backer (Ace Hardware - maybe says for driveways).   Plane has not been in the rain to see if it works, but by my shade tree gineering I can't see why not.

 

[N601RX]

I believe when I 1st got my 67F it still had the original cover panels.  The inside of them was covered with something that resembled heavy tar paper. The 3 piece access panels were in pretty bad shape and I replaced them with a single piece of aluminum. I later added the 201 window. 

The stick on insulation and soundproofing from spruce would probably work well.

[Guest]

You can replace the insulation which the mice like or get one of these:

[bonal]

There is no material under the access panel in our 64

[Vance Harral]

2 hours ago, M20Doc said:

You can replace the insulation which the mice like or get one of these:

Yes, keeping the mice out is a separate problem from the insulation and I like your thinking.

[rbridges]

13 hours ago, M20Doc said:

You can replace the insulation which the mice like or get one of these:

how does a cat seal up the panel?  just shove it in there real hard?

 

 

 

 

j/k  we have 2 cats

[Marauder]

You can replace the insulation which the mice like or get one of these:

Purrrfect! One of the avionics shops I used had one. I now know it was because they were soooo sloooow doing work that they needed one!

Sent from my iPad using Tapatalk

[Andy95W]

2 hours ago, rbridges said:

how does a cat seal up the panel?  just shove it in there real hard?

I understand cats really like it when you do that...

[rbridges]

Just now, N1395W said:

I understand cats really like it when you do that...

.  gross.

[Guest]

12 hours ago, rbridges said:

how does a cat seal up the panel?  just shove it in there real hard?

 

 

 

 

j/k  we have 2 cats

This cat is one of three retired cats at home, there's another working one at the shop. He prefers Comanches but will work on Mooney's if needed.

Clarence

[rbridges]

18 minutes ago, M20Doc said:

This cat is one of three retired cats at home, there's another working one at the shop. He prefers Comanches but will work on Mooney's if needed.

Clarence

Does he have his A&P or does he have someone sign off his work?

[Guest]

3 minutes ago, rbridges said:

Does he have his A&P or does he have someone sign off his work?

He's still working on his licence.  I told him that he has to help put the interior in CGHIJ after he does a Cat scan on the tubes.  Here is his reaction:

Edited February 5, 2016 by M20Doc

[C-GHIJ]

I'll take all the help I can get !!!!!  

[takair]

My 64E has the same aluminum tape backed foam that is in the nose wheel well.  It is yellow in color (the foam).   It has adhesive and is mounted to the panels.  I replaced them a few years ago, you can get the same material from Spruce.  I had assumed they were OEM and I also assumed they were for, both, noise and to prevent condensation.  They do nothing to keep water out.  That is worth a whole other thread.  As far as noise reduction, perhaps a bat can tell.  Condensation?  Who knows....never in there when it might happen.