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Author Topic: Remote needles  (Read 1283 times)

Offline airbrush

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Remote needles
« on: November 20, 2006, 09:25:28 PM »
 Hey all,
  I have an OS40LA-S cl engine with a remote needle, will this work and give me the 4-2-4 break I want?
Thinking about it, it seems that the rich fuel in the line from the needle forwards would have to be
used up before the lean mix could make it to the venturi, and by then the airplane would be coming
out of the maneuver. Thiis engine is nib. so I haven't tried it out yet, still has the purdy wrappings :)
thanks all,
 airbrush
aka james
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Offline Steve Helmick

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Re: Remote needles
« Reply #1 on: November 20, 2006, 11:02:25 PM »
It'll work, but you won't like it. Slow response to adjustments and painfully long burping around when it's running out of fuel. The OS .40LA has been a wimpy little brother to the .46LA, but there is some information coming available now. This is an engine that runs well on the 10.5 x 4.5 APC. Don McClave's got one working well in his Tucker Special. Just click on the link.  :! Steve
http://flyinglines.org/McClave.LA40.html
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Offline airbrush

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Re: Remote needles
« Reply #2 on: November 21, 2006, 10:44:43 AM »
I'm assuming from the article that the ST venturi/nva was installed and the remote needle setup done away with?
Thank you for the link, it was a very interesting article
air
aka james
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Offline phil c

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Re: Remote needles
« Reply #3 on: November 21, 2006, 11:31:48 AM »
I haven't had much in the way of problems with the OS remote needle valve.  The biggest thing appears to be that the threads are a bit loose and sometimes the O ring doesn't seal too well.  A tiny, two turn spring of 015 music wire that drops into the NV body and pushes the needle out a bit helps a bunch. A heavy coat of waxy, Nev'r Sieze on the threads help keep things stable too, along with a short piece of silicon fuel line over the end of the needle.

The other easy trick, turn the backplate 90 deg. to the right, when viewed from the back.  This puts the needle just outboard of the exhaust stack.  Grind a small relief in the boss on the muffler and the needle valve will fit just fine.  If you can still get the parts, OS sold a metal bracket with a bolt-on version of the needle valve that install with no grinding.  Tower may still have them.  Now the fuel follows the same path it does with a conventional needle valve, down under the engine, which gets rid of all the starting and running problems.  You will have to reverse the fuel spigot in the venturi too.
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phil Cartier

Online Manuel Cortes

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Re: Remote needles
« Reply #4 on: November 21, 2006, 12:01:01 PM »
About that "logical" and very interesting sugestion:

Thinking about it, it seems that the rich fuel in the line from the needle forwards would have to be
used up before the lean mix could make it to the venturi, and by then the airplane would be coming
out of the maneuver

My opinion is that what works really in leaning or richening fuel mixture is the more or less dificult to suck the fuel in the venturi (try to pinch the fuel line near the carburettor or near the tank, the results are identical.
Hope to be helpful.
Regards.
Manuel.
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Alan Hahn

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Re: Remote needles
« Reply #5 on: November 21, 2006, 04:05:17 PM »
When you close the needle, the flow rate adjusts quite rapidly, basically since the fuel tubing is not really that compressible (at these pressures). So you don't have to empty the tubing before the mixture changes. I have used remote needles and the biggest problem is that there are more opportunities for leaks (more fittings). Air leaks are what really cause problems because air is so much less viscous than the fuel.

Fuel mixture in the crankcase (or lack thereof) probably is what causes the major time delay between adjusting the needle and noting a change in rpm.
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Offline phil c

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Re: Remote needles
« Reply #6 on: November 21, 2006, 07:28:46 PM »
There is no "rich" fuel in the line between the needle valve and the venturi with the remote NVA.  The venturi lowers the airpressure at the fuel fitting.  Some of that pressure drop pushes the fuel through the fuel fitting in the needle valve.  The rest of the pressure drop pushes the fuel through the needle valve.  With two restrictions the actual hole size the fuel flows through in the needle valve will have to be a tiny, tiny bit larger than if the NV is in the venturi.

I think most of the run problems come from running the fuel line down, then up to the needle valve, and then back down to the engine.  I believe Al Rabe proved years ago with his Sea Fury tests that putting large vertical loops in the fuel line could cause problems.  The loops would tend to collect air bubbles that could disturb the fuel flow.  On a profile plane it is almost impossible to completely eliminate some offset in the fuel line.  The shortest, most direct route will be the best.  That is where the stock OS remote falls down.
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phil Cartier

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