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Static/Pitot/AOA Line mounting

grayforge

grayforge

Well Known Member
Hi folks,

I've seen the Vans' method of mounting the various plastic air lines in our planes. Seems a bit more work than necessary...

I spent a bit of time experimenting with different types of air line mounting methods.

I used 3 different types of blind rivets to rivet 1/4" nylon loop clamps to a scrap piece of aluminum. These clamps have a temperature range of -40? to +185? F, sourced from McMaster Carr. I also installed a nutplate and attached a clamp via a #8 screw. These all seemed to work well, though the AD-41-ABS blind rivet was a bit short. I also looked at Adel clamps.

DSC00088.JPG


DSC00093.JPG


I weighed the options. My scale is pretty sensitive, measuring to .005 lbs. or about .08 oz. I weighed batches of 10 connection types for more accuracy. Here are the results. This is the weight for a single mounting assembly (divided the weight of 10 of them by 10).

Blind Rivet + Plastic Clamp: 0.03oz
#8 Screw + Platenut + AN1097 rivets + Plastic Clamp: 0.12oz
#8 Screw + Platenut + AN1097 rivets + Metal & Rubber Clamp: 0.21oz

Quite a difference in weights, though the weight in total isn't that much. However, I'm anal and want to do everything within reason to keep my plane light. Plus, the lightest weight option is the easiest.

So what do people think about using these 1/4" plastic clamps for air lines? Maybe the Vans method is good for mounting them to longerons while blind riveted plastic loop clamps would work well for clamping to bulkheads and ribs?
 
Your nylon loops are a good idea. Fastening these loops with rivets is a quick and easy method.
If you need to remove or just move these, you can just drill them out.

Now you just have to work out the tube routing.:D
 
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What I do is use cable ties and mount them using a pop rivet and a small washer. Cheap and easy. I took a couple of photos for you, but I see that I am not authorized to post attachments.
 
OK, so I see you have to link pictures from other sites. Here's a photo of how I use the mounting ties. Nothing special, but it is cheap, easy and fast.
d91059f2.jpg
 
Very nice Mark. Where are those zip ties from? Doesn't look like a standard zip tie.

Thanks,
Russ
 
I drilled #30 holes in the longeron and zip-tied the tubing to the longeron. This is lighter than all three of your methods.


In the second picture, the zip-tie pads holding the wires in place are glued down with Goop Automotive Trim Adhesive. Do not rely on the adhesive pads, they will fall off in the summer.

Regarding using a pull rivet vs. a plate nut, always go in favor of ease of maintenance. Later on, you may not have access to the rivet with a drill. Also, I used cap screws in most places rather than Phillips head screws because they are easier to remove when you are working upside down and backwards. I also used cap screws on my fuel tank covers because there is virtually no way I could remove those pro-sealed screws with a stubby screwdriver.

PS. See www.mcmaster.com for 8-32 cap screws (and a lot of other cool stuff).
 
Static loop

One final thought
Make sure when your lines come down to the static ports there is no sag in the line. This can result in water laying in the tubing and causing you major headaches if flying in the winter Or if you have parked your aircraft in a rainstorm.
On our jets we use static plugs but I never see any RV owners using them. I will.

Smilin Jack
 
N941WR said:
I drilled #30 holes in the longeron and zip-tied the tubing to the longeron.
Click to expand...

I always cringe when I see un-filled holes in primary structure (this includes any non-structural fastener like pop rivets or screws) unless the structure was designed with those holes.

If you don't have approval from engineering, I would refrain from randomly drilling holes in primary structure (which the longerons definately are) :eek:

Perhaps I missed where Van's has approved this on the prints somewhere or said it's ok?
 
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Walt said:
I always cringe when I see un-filled holes in primary structure (this includes any non-structural fastener like pop rivets or screws) unless the structure was designed with those holes.

If you don't have approval from engineering, I would refrain from randomly drilling holes in primary structure (which the longerons definately are) :eek:

Perhaps I missed where Van's has approved this on the prints somewhere or said it's ok?
Click to expand...

Walt, would bulkheads be considered primary structure? If you aren't supposed to drill holes in any primary structure (assuming bulkheads are indeed primary structure), how exactly do you route wiring from the back of the plane to the front of the plane? Vans sells conduit for this purpose, yet to use it, I think you have to drill holes.
 
Mark Dickens said:
Walt, would bulkheads be considered primary structure? If you aren't supposed to drill holes in any primary structure (assuming bulkheads are indeed primary structure), how exactly do you route wiring from the back of the plane to the front of the plane? Vans sells conduit for this purpose, yet to use it, I think you have to drill holes.
Click to expand...

I understand your rational, however, just because Van's sells conduit and you need to run some wires doesn't necessarily mean they are automatically giving you approval to drill holes for the conduit anywhere you feel like. I believe in the past I have seen approval for holes in bulkheads and ribs for just this purpose.

I may just send Van's an email and ask for some guidance on this to pass on to the group. I know in the world I grew up in, drilling holes in primary structure without some type of approval would get you in lots of hot water.

There are also levels of primary structure, some are more critical than others. The primary fore/aft longeron is likely a more critical part than a bulkhead or rib in this case. Would you drill a hole in your spar or motor mount because it was convenient to do so?

Edit: I just reviewed the RV7 drawing for attaching clips to the longeron for the static lines, Van's specifies using aluminum brackets attached with AD3 rivets. If they thought it was ok to just drill holes in the flange and use pop rivets or wire tyes they likely would have specified it that way.
 
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I'm no A&P/IA, etc., but I'd be surprised if Van's felt that there was any significant structural difference between using a pop rivet (as I do) and a solid rivet to hold some wires. I agree, you don't go willy-nilly drilling holes here and there, but it would have been nice if Vans had given any guidance at all on this in the plans. That the RV-7 plans have this guidance is surprising to me since there's very little of it in the -8 plans. Let us know if you talk to Vans, I'd be interested in hearing what they say.
 
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