Janekom

Janekom

Well Known Member
Patron
Just wondering about the use of a solid copper wire (edited - should read tubing/pipe - sorry) from the engine to the firewall.
Recently we have seen an RV7A here in South Africa ( imported used ) had a catastrophic engine failure with a con rod through the crankcase! The reason - there was a solid cooper pipe (1/8" I think ) between the engine and the firewall from where it was connected to the oil pressure gauge.

Yesterday I have helped someone on a used RV6A ( also imported ) and this baby had the same copper wire for the oil pressure as well as the fuel pressure.

I really thought this is not a good idea and these should be done with a braided SS flexible hose.

What does the experienced guys say about this?
 
Last edited:
There is considerable movement of the engine on start and shutdown. Also, there is always vibration. The solid copper tubing will fatigue and fail. It work hardens very easily. SS braided hose is the way to go.
 
Last edited:
No way....

...should copper tubing be used on either the oil pressure or fuel sender lines!

Pardon the pun but this is playing with fire!

Best,
 
Speaking of this: I used the 1/8" copper tube for the primer lines (per van's suggestion and some certified planes). Should I periodically take it off and anneal it?
 
This is common

kevinh said:
Speaking of this: I used the 1/8" copper tube for the primer lines (per van's suggestion and some certified planes). Should I periodically take it off and anneal it?
Click to expand...

As long as it is installed correctly with a few "loops" in the line between the engine and the firewall, normal inspection for cracks should be all you need.
 
Perhaps...

kevinh said:
Speaking of this: I used the 1/8" copper tube for the primer lines (per van's suggestion and some certified planes). Should I periodically take it off and anneal it?
Click to expand...

...the original poster mistook a 1/8 copper pressure line (instruments or primer) that is 1/8 tubing for a solid copper connection?
 
The 1/8" copper tubing isn't just Van's method, this is the standard engine installation method. When I installed mine, I put in 2 sets of two loops, at right angles to each other. Probably overkill but I wanted plenty of tubing to allow for vibration. The difference between the primer and oil pressure in the application of the copper tubing is that the primer is pressurized with fuel only when you are actually priming the engine, which you wouldn't be doing in flight, whereas the oil pressure would always be pressurized when the engine is running. While a failure would not be a good thing, you can see the difference.
 
Solid copper lines are appropriate for plumbing a toilet, not an airplane.

But having said that, my 44 yr old Cherokee has solid copper lines for the oil pressure and fuel pressure guages... from the factory. But there is a section of flex hose in each one that connects to fittings on the engine to handle vibration.

PS: No jokes about a Cherokee being a flying toilet, please. :D
 
Last edited:
Why would you build an RV-7A like that? Plans specifically call out for a flex hose for oil pressure (and fuel pressure too).

Had the pre-buy been done on this airplane?
 
I do not like the copper.

The solid copper tubing will fatigue and fail.
My experience with the primer system on my Citabria is that the copper tubing has failed twice with the fatigue loops and all. You will not find any copper on my 7A. I am not so sure about the aluminum loop connection on the brakes either, although I built them that way at the time. That is on my list of things to replace when I take it down for inspection next time. You can review those discussions here and I reccomend that new builders do so.

I believe that some of the issue is that aerobatics that seems to stress the copper more than streight and level flight :rolleyes:
 
Janekom said:
Just wondering about the use of a solid copper wire from the engine to the firewall.
Recently we have seen an RV7A here in South Africa ( imported used ) had a catastrophic engine failure with a con rod through the crankcase! The reason - there was a solid cooper pipe (1/8" I think ) between the engine and the firewall from where it was connected to the oil pressure gauge.

Yesterday I have helped someone on a used RV6A ( also imported ) and this baby had the same copper wire for the oil pressure as well as the fuel pressure.

I really thought this is not a good idea and these should be done with a braided SS flexible hose.

What does the experienced guys say about this?
Click to expand...

As has been posted, solid copper is used on lots of aircraft - factory built, military, and experimental. It's not a problem if installed properly.

Copper does work harden over time, but an easy way to fix this is to anneal the tube every once in a while (like at annual inspection). If the tube is otherwise undamaged, annealing makes it good as new.

More disturbing about the above post is the fact that a break in the copper line apparently caused oil starvation and engine failure. This is why you must use a restrictor fitting at the engine. If the line breaks, you will get zero oil pressure indication immediately, but at least the restrictor should buy you plenty of time to land before all the oil goes overboard.
 
...the original poster mistook a 1/8 copper pressure line (instruments or primer) that is 1/8 tubing for a solid copper connection?
Click to expand...

Sorry guys - I have meant tube or pipe and NOT wire :mad:
I have edited my post.

Radomir asked about a pre buy - it was done on the second one where I found two of these pipes. Not sure about the first one.

I fully agree with Toolbuilder - there must be restrictors as well.
 
Primer valve on engine?

I'm about to plumb the primer circuit on my O-320, and it occurred to me that I could avoid running copper line from the firewall to the engine by simply mounting the little Parker primer valve on the engine. Has anyone ever tried this?

I envision mounting the primer valve in a convenient location on the accessory case near the engine-mounted mechanical pump, and plumbing a copper line from the inlet of the pump to the inlet of the primer valve. This arrangement would preserve the flow schematic while eliminating the infamous firewall-to-engine copper line.

I know it's bad practice to mount pressure sensors to the engine, but I've used little solenoid valves like the ubiquitous Parker primer valve in industrial applications, and they're pretty durable buggers. Given the billet stainless construction of the valve body, i can't imagine a catastrophic failure mode that engine vibration could induce.

Thoughts?
 
foka4 said:
I envision mounting the primer valve in a convenient location on the accessory case near the engine-mounted mechanical pump, and plumbing a copper line from the inlet of the pump to the inlet of the primer valve.

i can't imagine a catastrophic failure mode that engine vibration could induce.

Thoughts?
Click to expand...

Do NOT install a copper line from the fuel pump inlet to the primer valve, when the copper line breaks (and it will) you'll be leaking fuel (especially when you turn on the aux pump) and the engine will quit at the same time :eek:

Sounds "catastophic" to me.

Copper lines are only acceptable on the outlet of the primer valve that way if one of those break it will only leak fuel during priming, the rest of the time it'll suck air which other than a lean cyl is not going to kill you.
 
I fabed a primer system with 1/8 inch copper tubing... Fed with large loops from the electric primer valve that was mounted on the firewall.. After fixing breaks 2 or 3 times, I just removed the complete system... I prime pumping the throttle couple times while cranking to start... Primer system, not needed (in my case)..
 
Sheldon said:
I just removed the complete system... I prime pumping the throttle couple times while cranking to start... Primer system, not needed (in my case)..
Click to expand...

This is exactly what I recommend to people that ask. Unless you are in really cold climates a primer is not really needed. Just pump the throttle a few times while cranking and it will do the same thing.
 
Walt said:
This is exactly what I recommend to people that ask. Unless you are in really cold climates a primer is not really needed. Just pump the throttle a few times while cranking and it will do the same thing.
Click to expand...

I don't know what you consider cold, but I'll still take the priming system for for winter starts, as well as summer (first start of the day)...........over the cranking method. I like the way my engine easily starts, without pumping fuel up through the carb.

I have the Van's setup, with 1/8" lines from the primer solenoid, to three ports. Plenty of loops in the copper before they get there. And... being in the air conditioning business for many years, and dealing with copper tubing, I'll notice any fatique problems. So far, there are none.

L.Adamson --- RV6A
 
RV fire (from my previous post)

Yesterday was sobering experience for me!

I got a call from a local A&P/AI who needed advice about an RV-6 that he had been asked to rebuild. I went over to have a look at the RV-6 and was shocked by what I saw, which I share for your safety.

This older RV had just had an IO-360 and blended prop installed professionally at another airport. The owner had flown to our airport (KFFC) and was about to depart for his homedrome. He was in the runup area beside an avionics shop. While performing his runup, his RV engine area burst into flames. Several mechanics rushed out with extinguishers, put the fire out, and got the pilot out with some burns on his legs.

When I looked at the RV yesterday, the tip up canopy, cowl, seats, and all instruments and radios had been removed.

Another mechanic and I surmised that a small 1/8" copper tube from the rear-mounted mechanical fuel pump to a fuel pressure sending unit broke during the runup, allowing fuel from the 1/8" copper line to spray out above the exhaust. This fire only lasted a few minutes due to the quick response by the mechanics. In that short time, every wire and hose firewall forward was either melted or damaged. The entire panel wiring was a melted mess. The interior floorboard 1" black insulation was mostly melted.

Apparently, the fire was like a blow-torch as the windblast from the runup caused the lower firewall and lower cowl exit area to direct the fire down and underneath the RV.

Incredibly, the canopy and cowling are useable. The cowl will need some repairs, but it did not burn thru.

Even though the paint under the airplane did not burn off, and no rivets 'popped' I am concerned that the thick bottom skin in front of the wing spar may need replacing due to tempering from the heat. Certainly the mags, fuel pump, and prop gov need overhauling due to possible heat damage. The firewall seems OK.

My points: if this plane had taken off, the heat from the fire would have really burned the pilot, possibly incapacitating him quickly. His instruments and accessories would have failed shortly. An aluminum airbox would have soon allowed flames inside the cockpit. All this from the fuel spray from a 1/8" line! What would the main fuel line do? (I know-I've witnessed that also)

So, next time your cowl is off, take a critical look at your systems. Everything firesleeved? Have you got any stiff copper lines? Do lines have service loops/slack in them? Any 'stiff' lines used to join the shaking engine and the fixed firewall? All B-nuts tight? All openings in the firewall sealed? Any hidden chafing ready to wear through?

Another area we RV'ers might look at is at our brake lines and fittings which is another potential fire source for our RV design. What about leaking fuel tanks allowing fuel to seep in under our seats and ignite due to electrical devices under the floor boards?

In my AF days I survived a number of inflight fires and explosions. It's no fun when the smoke is so thick and pungent you can't see the fire handles glowing bright red!

We have a fun hobby and we all want to fly safe. Join me in taking another look at your RV to keep it that way!

Yesterday was sobering experience for me!
 
You must log in or register to reply here.