OS LA 25 RC to CL conversion

[Steve Dwyer]

This is no doubt a very old question but I'm having difficulty. I have an RC OS LA 25, are parts available to make the conversion to CL?  Aeromanic has an old listing showing Towers part numbers but I don't think Tower carries them any more. I need a back plate, gasket, venturi and needle valve to eliminate the remote. I know Eric Rule has the venture and gaskets, where can I locate the back plate and NVA?

Steve

[James Holford]

This is no doubt a very old question but I'm having difficulty. I have an RC OS LA 25, are parts available to make the conversion to CL?  Aeromanic has an old listing showing Towers part numbers but I don't think Tower carries them any more. I need a back plate, gasket, venturi and needle valve to eliminate the remote. I know Eric Rule has the venture and gaskets, where can I locate the back plate and NVA?

Steve

Jim lee or randy or ebay for nva... backplate... find a junker .25fp n use that plate

Sent from my SAMSUNG-SM-G891A using Tapatalk

[Brett Buck]

This is no doubt a very old question but I'm having difficulty. I have an RC OS LA 25, are parts available to make the conversion to CL?  Aeromanic has an old listing showing Towers part numbers but I don't think Tower carries them any more. I need a back plate, gasket, venturi and needle valve to eliminate the remote. I know Eric Rule has the venture and gaskets, where can I locate the back plate and NVA?

  Why do you want to remove the remote needle? Get the venturi and "nozzle", you are all set. The backplate is fine as it comes.

     Brett

[Randy Cuberly]

Well, the backplate is fine as it comes, however it won't stay fine for very long.  Typically they start to leak after about 50 engine runs especially if the screws are over tightened and can't be successfully sealed after that!

There are some after market ones available just do a search on the forum.

The remote needle set up does work fine but there is a little delay between needle adjustment and engine reaction that can be a bit of a pain!

Randy Cuberly

[Tim Wescott]

I've had two that came to me with the stock backplate, and both have been fine.  My best advice on overtightening is that if you never remove the backplate, you'll never overtighten it.  If you do take it off, "tight enough" is just a hair more than finger tight -- it's easy to overtighten metal backplates of that design, and far easier yet to overtighten the plastic.

As for the "delay" with remote needles -- all of my OS LA engines (and my Tower 40) show a delay between adjusting the needle and the final speed of the engine.  This is a population of engines that's split 50/50 between remote and front needle valve locations.  I think it has everything to do with temperature and nothing to do with the needle arrangement (I cover the vent tube on the tank to lean the engine to peak, then check the RPM after it's settled from that -- I get a much more reliable RPM setting that way).
 
The thing that a remote needle WILL do to you that a normal one won't is that on a profile it's almost inevitable that the siphon action will break at the spraybar, and air will be sucked back to the needle.  So you need to give it a healthy enough prime that it'll get fuel pulled to the spraybar in time to keep working.  This isn't hard, it's just something to be mindful of.

For rather screwy reasons involving doing software testing on a gizmo that Howard Rush uses in his electric, I have a remote needle in my big stunter.  I've had all kinds of other problems with my setup, but not the needle.

[Chad Hill]

Steve, have you tried "The Control Line Store" on e-bay? I just did a cursory check of his OS parts and he has the venturi and a metal back plate (after market maybe). Message him about the other stuff, he has a lot of things not listed online. The guy is 100% trustworthy; I have bought lots of things from him. Chad

www.ebay.com/str/The-control-line-store

[Brett Buck]

I've had two that came to me with the stock backplate, and both have been fine.  My best advice on overtightening is that if you never remove the backplate, you'll never overtighten it.  If you do take it off, "tight enough" is just a hair more than finger tight -- it's easy to overtighten metal backplates of that design, and far easier yet to overtighten the plastic.

As for the "delay" with remote needles -- all of my OS LA engines (and my Tower 40) show a delay between adjusting the needle and the final speed of the engine.  This is a population of engines that's split 50/50 between remote and front needle valve locations.  I think it has everything to do with temperature and nothing to do with the needle arrangement (I cover the vent tube on the tank to lean the engine to peak, then check the RPM after it's settled from that -- I get a much more reliable RPM setting that way).

   The "delay" is about 66 microseconds from the needle position difference - less that 5 degrees of crankshaft rotation at 12,000 rpm. That's getting pretty picky.

      I have maybe 150 flights on the plastic backplate and I haven't noticed any issues, except the one I expected - when the airplane was pancaked into the ground inverted, it broke off. Then again, I haven't taken it apart or tried to improve it, so my results might not be as good as all those engine experts manage.

     Brett

[eric rule]

Everything noted above is correct. If you wish to have an engine with what most of us would refer to as a "normal" set up just order what you need from RSM Distribution.com. We can supply the following items:

C/L Venturi.
ST Needle valve assembly (to replace the remote needle with one that runs through the crankcase at the "normal" venture location)
Gaskets and socket head screws for back plate (this will stop the nylon back plate from leaking)
New socket head bolts for the head.

[Tim Wescott]

   The "delay" is about ...

I failed to point out that the delay I'm referring to is present on all of my engines, regardless of needle style.  I think it's because when you first crank in the needle the engine speeds up a bit, but doesn't warm up -- that's why I use the procedure I mentioned.

I wasn't referring to the speed of sound in methanol-filled silicone fuel line, or whatever it is you're using for your 66ms figure.

[Dan McEntee]

   I have nothing against rear needle valves, just this particular needle valve that OS brought back for the LA series. UIt uses the O-ring to seal it and they are prone to leak air. It was a problem before and is again unless you find the exact right size O-ring. The rear needle valve that was used on the final FP-series engines worked much better, and was based on the needle valve assembly that was on some of their smaller R/C carbs, and can even be used directly mounted to a venturi in the "spigot" mode, The only issue I found with rear needle set ups is that you need to choke the engine more, and tank position is important for a quick shut off when the fuel runs out. I set up several of Sean's models with this when he was younger and still "prop shy." I don't think I ever witnessed any "delay" that has been mentioned. The engine ran the same, except for the conditions I mentioned.
  Type at you later,
   Dan McEntee

[Tim Wescott]

I set up several of Sean's models with this when he was younger and still "prop shy."

The biggest reason I like them is because you can set them up to be out of the way in a crash (I like putting them parallel to, and behind, the cylinder on a profile).  With a typical needle setup on a profile you break the needle valve on every post-hole crash and inverted landing -- with a properly set up remote needle you don't.

It uses the O-ring to seal it and they are prone to leak air.

I think you just helped me fix one of my wife's planes, Dan!

[Dan McEntee]

The biggest reason I like them is because you can set them up to be out of the way in a crash (I like putting them parallel to, and behind, the cylinder on a profile).  With a typical needle setup on a profile you break the needle valve on every post-hole crash and inverted landing -- with a properly set up remote needle you don't.

I think you just helped me fix one of my wife's planes, Dan!

   A quick way to test that is to coat the o-ring with the heaviest grease that you can find and try a flight. If the symptoms go away, you know what to do. It's a common metric o-ring I think, but the clearance isn't tight enough so it can't always seal. You can try several o-rings and see which seats the tightest. Heavy grease works but doesn't last vary long.
   Type  at you later,
   Dan McEntee

[Brett Buck]

I failed to point out that the delay I'm referring to is present on all of my engines, regardless of needle style.  I think it's because when you first crank in the needle the engine speeds up a bit, but doesn't warm up -- that's why I use the procedure I mentioned.

I wasn't referring to the speed of sound in methanol-filled silicone fuel line, or whatever it is you're using for your 66ms figure.

    Right, since it works the same way with either needle position. Its 66 microseconds, not milliseconds.


    Brett

[Tim Wescott]

Read "micro" hear "milli" in my head. What's a factor of 1000 between friends, eh?