STA or AD on removal of sound dempering material on 67Bs

[AP AVM]

Was there a STD for the removal of all sound dempering material/charcoal gray pads from the internal structure of the fuselage of 67 337Bs and O-2A/B by FAA due to corrosion build up between the pads and aluminum skins or panels.

I have been asked by a 337 specialist to remove these from the side walls, top and from the floor of my AVM. This stuff has been glued pretty good for last 49 years and is giving hard time to come off by using lacquer thinner.....

[Skymaster337B]

I thought those pads were more than sound dampening, but also for harmonics control. But I'd be curious of any documentation to remove them.

[skymstr02]

After you removed the items, how did you account for them on your weight and balance? The total weight would not have been negligible.

[LostKiwi]

From the maintenance manual...

3-43. SOUNDPROOFING.
3-44. DESCRIPTION. 337-Series aircraft are insulated with spun glass, mat-type insulation. Two types of vibration dampening materials are used.
A brush-on type compound on the inner surfaces of the baggage and cabin area and a sheet type that is held in place with an epoxy adhesive.


Ipso facto... be very very careful in just yarding it out and then going flying. You're essentially making your aircraft unairworthy.

I've seen people talk about how its in there as a vibration thing, now we have a manual reference that confirms it.

As an A&P / IA would I recommend taking it all out to check the structure for corrosion? absolutely! Its held on with glue! Thats a recipe to trap water and set up a corrosion cell. By all means, take it out - BUT you need to fit new stuff (or a modern equivalent).



DrDave, I tip my hat to you sir. That is not a small job.
Have photos of the finished product?




Leighton.

[DrDave]

I've heard that some people have removed the little gray patches that are glued on. I've also heard that the best way is with a heated pressure washer. Here's the old sideways picture thing. I have limited abilities at posting pictures I rarely try.

Dave

[kilr4d]

Check out Herb's refurbishment thread:

http://www.337skymaster.com/messages...ead.php?t=2309

Read the whole thing, but he starts discussing those stick on dampeners in post #21.

[LostKiwi]

Looks like you're doing a real nice job, Dave.

Nothing more demoralizing that cleaning 40 year old goop from inaccessible areas, but the end result looks great.


Leighton.

[DrDave]

Leighton:

When you get down into the inside of the belly with a pressure washer you can uncover years of grunge that has been coated in hydraulic fluid. You can make the inside look brand new. You will also find enough loose nuts, screws, clamps, etc. to start a small hardware store. There are a number of unpleasant smells lingering in the belly of the plane. All of those will be washed away.

It is so much nicer to work on a plane that is clean and goop free. When I figure out how to post a picture that is not turned 90 degrees I'll send more.

Dave

[JAG]

Hi Dave,
When I click on the thumbnail, it opens up correctly (O2 bottles on the top) on my computer! Keep the photos coming.
JAG

[DrDave]

I wonder why it's off 90 degrees in the thumbnail

Dave

[AP AVM]

I don't have a facility to power diesel wash the inside of the fuselage at my airport to remove them. I'll use heat gun to warm up the glue and try to scrape them off with plastic spreaders.

After reading through all the comments, I think it's wiser to remove most if not all.

[DrDave]

That sounds like a long messy day. Once you get the interior stripped out you will likely want to scrub the belly out as well. You may be surprised at how yucky the belly is.

Dave

[DrDave]

After you clean everything it's a good idea to carefully rinse the areas where you've cleaned. You want to be as gentle as you can. Here's how I did it.

Dave

https://youtu.be/kbOyOf4A8EM

This is exactly how interior of my C337B is currently, it's all gutted and I even took more out of it to it's bare bones. There are no instruments or radios , yokes in the cockpit, just wires, cables, couple old heat ducting hoses, mechanisms for yokes and trimming dials. All my floor panels will be replaced as they all are corroded but it looks as inside the belly is still pretty good yet full of dirt n grime from sitting out in elements for last 12-15 years..


AP-AVM

[DrDave]

If you are gutted down to the bare bones I would really make an effort to get in there with the corrosion treatment and a hot water pressure washer in the whole thing. It will pay dividends for years to come. I'm sure you can rent the things too.

Dave

[Skymaster337B]

I like the way a good pressure washing looks, but I don't remember anything during my formal A&P training about pressure washing. I never read anything in the maintenance manual or the old AC 65-15 about pressure washing. I'm not judging, but I'm curious about tech data for cumulative fatigue on aluminum during a pressure wash....I'm sure it's dependent upon pressure, metal thickness, area, etc. Not to mention, that not all Skymasters are equal...pre 1973 used thinner aluminum. Looking for a discussion, not a shooting match.