Trent's RV14 Build: Smoke System: Plumbing and Testing

Now i've established where the smoke tank will be located, i was able to plan out where the connections for the electrics / smoke hose could potentially be located in the baggage floor, and therefore where the pump and control box could be located on the tank.

Before the pump can be mounted, i needed to do some testing on the best way to plumb the system. In principle, the plumbing is fairly simple. The pump sucks the smoke oil out of the tank, and runs via a hose to the injectors in the exhaust. A needle valve restrictor to control the flow to the injectors in the engine needs to be installed in the supply hose - but is this better to go before or after the pump?

Smoke Pump Testing

To work this out, I run a number of tests on the bench. The pump was setup to pump some water out of a bucket and i used a multi-meter inline with the pump control box supply wire to measure the current draw of the system. I used some air hose fittings on the end of the pump outlet hose as a facsimile for the restriction caused by the smoke injectors in the exhaust. For each test i closed the needle valve to get 1 litre every 30 secs (2 lt/min) flow out of the system - as it is recommended to use 1/2 a USG a minute flow as a starting point. Obviously i was pumping water, so this will not be the final setting of the needle valve, but it gave me a good test point.

Needle valve on the outlet side of the pump. The measuring jug is used to calibrate the needle valve position.

Needle valve on the inlet side of the pump

A frankenstein of air hose connectors represents the exhaust injectors.

The first test was with the needle valve on the outlet side of the pump. This showed good flow out of the hose, however, when the needle valve was closed to the desired flow, the amps rose very significantly. This was due to the pump being 'bogged down' somewhat. I didn't think this was a good scenario.

So the next task was to redo the test with the needle valve on the inlet side of the pump. I found that this had lower amps, but the flow was not great. The output was not consistent and was 'splurting'.

After much testing i realised that the test rig was sucking air into the pump inlet where the needle valve was connected. I had just used some dodgy cable ties to make this connection. So I used the opportunity to make a safety wire hose clamp tool! This sealed up the connection, and i was then seeing much lower amp draw and pretty consistent flow.

A home made safety wire hose clamp tool!

This stopped the pump sucking air through these connections.

The pump i am using has an internal pressure switch. So if the pressure builds up too high (105 psi), then the pump will electrically shut off. I am planning the system to support the use of a smoke solenoid in the supply line - if this were to suddenly halt the flow to the injectors (used when doing skytyping etc), then the pump just shuts off and is ready to run again in an instant when the valve opens up again.

In the end i decided to mount the pump on the forward side of the tank, and have the needle valve on the inlet side of the pump.

Whenever i do anything remotely electrical, there is always crap everywhere!!

Mounting the Pump and Control Box to the tank

To mount the pump on the forward side of the tank I used some 'c' channel from the local Big Box Hardware Aviation Department (aka Bunnings Aerospace). This was drilled for the pump attach bolts and my initial plan was to use use some JB Weld to attach the brackets. However, once i had the pump in hand i decided it was actually heavier than i thought - combined with some G force, i didn't trust the epoxy by itself. So i match drilled the brackets through the tank and used both JB Weld and some LP4-3 pull rivets. I covered the heads of the rivets on the inside of the tank with JB Weld.

I planned out the location that the pump needed to be to make the pluming connections work.

I was able to reach in through the tank filler opening to complete these rivets.

Each bracket was glued and pull riveted to the tank

The rivet heads were on the insides of the tank

A small bit of left over fuel tube flare was used to seal the heads of the rivets in the tank.

The pump mounted to the tank.

Next up i completed all the plumbing connections, using safety wire hose clamps. The threaded NPT fittings were sealed with Loctite thread sealer.

Finally, the control box was mounted to the side of the tank using JB Weld only. I drilled holes through the plastic case and countersunk them on the inside. To provide some 'mechanical' holding power for the control box. All the electronics are mounted to the lid of the box - so can be easily removed. Once dry, i made the electrical connections to the pump using a basic molex from the local electronics shop.

The countersinks will hopefully provide some 'mechanical' bonding to the tank side.

Molex really are a PIA - but i couldn't justify the cost of a DTM in this case.

The completed tank.

Drilling the baggage floor!

Now the pump was completed, i was able to plan out where the 9/16" hole would go for the AN-6 bulkhead connector, as well as the 14 pin CPC connector - both which will be mounted in the baggage floor behind the right hand seat.

The wooden block represents the height of the bulkhead fitting, and the ruler represents where the seat backs will be located.

I made up a template for drilling the female CPC - this is the type which has a mounting flange and 4 x 4-40 threaded inserts, so i can push the connector up through the hole in the completed floor skin, then attach it with screws and lock washers.

Drilling the large (28mm) hole for the CPC was pretty stressful!!

This is how the connectors will look once finished - ready to accept the smoke tank.

This is the underside of the baggage floor skin - the wiring will be pinned into the CPC connector, and the smoke supply hose will connect to the flare fitting - both are installed from below and held by fasteners on the upper side.

I used some left over 'safe-t-tie' which is used to 'lock wire' hard to access bolts at work to hold dust caps for the smoke oil hose fittings. The CPC has an integrated dust cap held on a chain and one of the attach screws.

Adding Connectors to the tank and final test fit:

Once the location of the connectors in the floor was known, i was then able to complete the pinout of the electrical connector and cut the hose to length and add the connector. I was then able to do a final test fit into the airframe.

All cut to the same length

The nice thing about the Series 1 CPC connectors is you can have power (18 AWG) pins as well as signal pins in the same connector. This is one of the 18 AWG power pins (purple stripe).