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RTV silicone on D-sub

D

Dave J

I'm New Here
Good day all,
I’m finishing up the final stages on a -12iS tailcone kit. On page 11iS/U-10 step 3: Seal all openings on the wire insertion side of the servo’s D-sub using RTV.

Does this mean both d-sub housings or just the ast servo motor side? It’s the bottom half of this connection.

Also, should the silicone be forced into the pin insertion area or just form a blob around the wires to prevent bending the wires at the pin crimp?

Thanks, This site is a tremendous source.
 
Odd. Typical silicone is acidic. Not good near electronics. However there is electronics-safe (non-corrosive) silicone, like Dowsil 737.

Finn
 
FinnFlyer said:
Odd. Typical silicone is acidic. Not good near electronics. However there is electronics-safe (non-corrosive) silicone, like Dowsil 737.

Finn
Click to expand...

I think it is RTV sealants that are usually acidic. Simple silicone sealants are not, and sensor safe RTV as well. In this case though, we haven't found that it matters because the sealant is only being applied to the plastic in the d-sub, and a bit of the insulation on the wires


The intent of the instruction step is to prevent water from getting into the d-sub via the pin sockets which is why it describes it as sealing the pin insertion side of the connector. the primary need is to do the one that is at the top because gravity will make water migrate down into the connector, but there is nothing wrong with doing the one on the bottom as well.
 
This is what can happen if you do not seal this connector

The autopilot in my RV-10 started disconnecting in heavy rain in IMC. I found water intrusion at the roll servo which has the D-sub socket facing up. Thankfully the servo is not damaged.

I was just looking for a way to seal that connection. Glad I found this as I asked Garmin, and they did not have an answer.
 

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bsvantho said:
The autopilot in my RV-10 started disconnecting in heavy rain in IMC. I found water intrusion at the roll servo which has the D-sub socket facing up. Thankfully the servo is not damaged.

I was just looking for a way to seal that connection. Glad I found this as I asked Garmin, and they did not have an answer.
Click to expand...

The process being discussed here is not using RTV on the connect pins between two mating D subs, but the back side where the wires enter the D sub.
For your situation I would use a heavy application of Dow Corning #4 silicone grease before joining the connectors and then wipe away the excess.
Another alternative would be to purchase some of the gel seals that can be used for D subs. They come in different sizes depending on how many pins are in the D sub connector.
 
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bsvantho said:
The autopilot in my RV-10 started disconnecting in heavy rain in IMC. I found water intrusion at the roll servo which has the D-sub socket facing up. Thankfully the servo is not damaged.

I was just looking for a way to seal that connection. Glad I found this as I asked Garmin, and they did not have an answer.
Click to expand...

Interesting. May be a good idea to wrap the whole connector and inch or two of the harness with silcone tape after affixing it to the servo. Easy enough to remove when servicing.
 
rvbuilder2002 said:
The process being discussed here is not using RTV on the connect pins between two mating D subs, but the back side where the wires enter the D sub.
For your situation I would use a heavy application of Dow Corning #4 silicone grease before joining the connectors and then wipe away the excess.
Another alternative would be to purchase some of the gel seals that can be used for D subs. They come in different sizes depending on how many pins are in the D sub connector.
Click to expand...

Yes it is clear that the RTV would be on the back side. I suspected that the vertical wiring might be collecting water and then running down to the pins and then the socket. I will probably RTV behind pins and seal the socket connection per your suggestion.

It appears that the water probably came through the tooling hole in the spar. The tie-down ring hole is just forward of that tooling hole, which I did not have plugged. I have taped over that tooling hole and will find some caps for the tie-down ring hole.
 
Why use a connector at all? How often is the servo removed from the airplane? Even if the servo is replaced, a connector must be installed on the new servo. Why not just permanently splice the 5 sets of wires together? If the servo has to be replaced, just cut the splices and make new ones. That is what I did. I soldered each pair together and covered each splice with heat shrink tube. All of the splices are hidden inside of a cushion clamp which prevents vibration from breaking the joints. An observer will not even know that any splices exist.
 
rvbuilder2002 said:
I think it is RTV sealants that are usually acidic. Simple silicone sealants are not, and sensor safe RTV as well. In this case though, we haven't found that it matters because the sealant is only being applied to the plastic in the d-sub, and a bit of the insulation on the wires


The intent of the instruction step is to prevent water from getting into the d-sub via the pin sockets which is why it describes it as sealing the pin insertion side of the connector. the primary need is to do the one that is at the top because gravity will make water migrate down into the connector, but there is nothing wrong with doing the one on the bottom as well.
Click to expand...

If the need and requirement is for a connector system that keeps liquid moisture out I sure wouldn't be using D-Sub series connectors. This is an area where round MIL (aka Cannon) connectors excel. They have a rubber insert system that makes a good seal around the inserted pin and wire. If you are having to goop up your connector with silicone sealant to try to achieve adequate performance for your application you might should rethink your design approach.
 
bbaggerman said:
If the need and requirement is for a connector system that keeps liquid moisture out I sure wouldn't be using D-Sub series connectors. This is an area where round MIL (aka Cannon) connectors excel. They have a rubber insert system that makes a good seal around the inserted pin and wire. If you are having to goop up your connector with silicone sealant to try to achieve adequate performance for your application you might should rethink your design approach.
Click to expand...

You clearly have a low level of understanding of what the L in LSA stands for and how much effort must constantly be put out to maximize its meaning ;)

Canon plugs are great for military aircraft. LSA, not so much.



For those not aware.... LSA - Light Sport Aircraft
 
I guarantee that weatherproof Deutsch connectors would weight as much or less than D-Subs. Similar to Weatherpack, Deutsch has silicon seals and can even be booted if desired. And hand tools can insert and remove pins.
 
Snowflake said:
Because you can get these apart with a razor blade... They're not soldered together.
Click to expand...

Sounds good on paper but have you ever actually tried doing that in the airplane with a 26ga wire?
(I have tried, not worth the effort, will just cut them off if I run across them and splice or install a connector)
 
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subpar_bucker said:
I acknowledge this isn't according to the plans, but this video from Stein Air shows another elegant way to connect these wires without using a D-sub (and it's probably lighter than a D-sub :)

https://www.youtube.com/watch?v=f8DCvBV2V4M
Click to expand...

Then why in the world spend money on the expensive crimp pins? If you anyway have to get in there with a razor blade you surely can get there with a soldering iron.
Or do what Walt suggests and simply cut through the solder joints with a side cutter. You're going to lose less than 1/4" of the wire lengths.

Finn
 
rvbuilder2002 said:
You clearly have a low level of understanding of what the L in LSA stands for and how much effort must constantly be put out to maximize its meaning ;)

Canon plugs are great for military aircraft. LSA, not so much.
Click to expand...

Clearly low level.

The occasional Canon (or Deutsch, or Souriau) when called for (like in a tail section exposed to the elements) won't break the weight budget. There are some really exceptional light weight automotive connector systems but a lot of times they take some oddball tooling. Canon connectors can use the same Daniels crimping tools used for crimped D-Subs with just a different positioner. Super easy.

For those doing wiring harness work it is worth taking a look at some of the high reliability environmentally sealed round connectors such as the MIL-C-38999 series. One of them might be just the thing for a harsh (i.e. wet or high vibration) connector location.
 
For ALL?

rvbuilder2002 said:
The process being discussed here is not using RTV on the connect pins between two mating D subs, but the back side where the wires enter the D sub.
For your situation I would use a heavy application of Dow Corning #4 silicone grease before joining the connectors and then wipe away the excess.
Another alternative would be to purchase some of the gel seals that can be used for D subs. They come in different sizes depending on how many pins are in the D sub connector.
Click to expand...

Scott, Just curious, would you recommend coating the contact surfaces of all connectors with Dow Corning #4 silicone as an extra preventative measure?
 
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