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Author Topic: LA 25 needle valve for combat  (Read 648 times)

Offline J Motta

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LA 25 needle valve for combat
« on: May 13, 2021, 08:06:36 AM »
In converting la25 to combat I was told that the remote needle valve wonít work with a bladder. Is the needle assy I need for a super tiger or a fox? Ordered the fox but itís too big unless Iím supposed to do some drilling.

Offline Dan McEntee

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Re: LA 25 needle valve for combat
« Reply #1 on: May 13, 2021, 10:26:35 AM »
  Maybe the stock needle valve that comes with the engine won't work, but the older rear needle valve that doesn't use an Oring may. It is also the same assembly that was in the older carburetors also and could be purchased separately. It's all metal, and can be attached to a metal bracket that is attached to a convenient lace on the airplane. I'm sure this has been covered before and some one may know what I'm referring to.
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Offline Reptoid

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Re: LA 25 needle valve for combat
« Reply #2 on: May 13, 2021, 12:38:50 PM »
     In converting la25 to combat I was told that the remote needle valve wonít work with a bladder. Is the needle assy I need for a super tiger or a fox? Ordered the fox but itís too big unless Iím supposed to do some drilling.
Depends on what you mean by "won't work". That remote needle will work if the o-ring is good (Doesn't leak) and the needle will close off completely. It won't be ideal because it is rather coarse for high pressure. The needle setting will be a few clicks from full rich to full lean. The old OS needle valve (remote or from RC carb) is better because it has a longer taper on the needle and is widely used for speed limit combat but it's still pretty sensitive until you get used to it. The old OS needle from the OS .10 worked even better but is unobtanium. The smaller the engine, the more sensitive because smaller engines use less fuel.
     Bill Maywald makes a block that uses a Fora 15 needle assembly (the one with a nut) and then you need a bracket to mount it. The Fora needle is designed for F2D so it's very fine taper and threads to suit the 15 running on a bladder. You can contact Bill on Facebook messenger.
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Offline kenneth cook

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Re: LA 25 needle valve for combat
« Reply #3 on: May 13, 2021, 01:36:47 PM »
             I've seen Phil Cartier use the up front .20-.46 OS needle assembly many times on various engines.

Offline Air Ministry .

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Re: LA 25 needle valve for combat
« Reply #4 on: May 13, 2021, 08:03:30 PM »
seen a electric wire connector slid over the fuel tube , with the short ( remote NVA ) spraybar .

wind in the ' cable screws ' to lean . Maybe one of the two ? for ' fine tune ' .  Mounted up forward but where the tubes still flat .

Likely a finer thread'd be a lot better ? .

Online Motorman

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Re: LA 25 needle valve for combat
« Reply #5 on: May 14, 2021, 07:10:03 AM »
You'll have to drill out the hole with #21 drill if you want to use an (original) Supertigre or a PA spraybar. Can't recommend anything Fox.


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Offline kenneth cook

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Re: LA 25 needle valve for combat
« Reply #6 on: May 15, 2021, 05:26:04 AM »
            I also remove the spraybar from a Cox .049.  postage stamp backplate. This would be the version with the brass needle valve and no knob on the end of it which is the 128 threads per inch. You can solder it into a wheel collar. Using a 1/8' wheel collar, remove the set screw, drill out the threads to a 1/8" hole and solder in a small piece of 1/8" tubing a 1/2" long. Remove the plating on on the sides of the wheel collar and solder in the Cox spraybar aligning the spraybar hole with the set screw hole you soldered the tubing into. This needle assembly uses the black plastic friction sleeves which are still available and require changing every now and then. Of course fuel tubing would substitute but this assembly works very well. I fabricate a bracket then to hold the assembly to the engine.

Offline phil c

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Re: LA 25 needle valve for combat
« Reply #7 on: July 17, 2021, 05:36:37 PM »
The LA 25 will work fine if you can get the right needle valve from OS.

Combat requires an extra fine thread NVA.  They made one as a generic venturi mounted stunt needle valve.  The threads are 0.35mm pitch (distance between thread edges)  They make a nearly identical unit for larger engines which uhas 0.45mm. pitch.  It is too coarse to work on a bladder or pacifier, although will likely work just fine on a larger engine.

The other is a carburetor part for 0.10-.25 engines.  OS 1a is the the most common designation.  This has to be mounted in a bracket (I use a heavy duty control horn cut down to fit on the engine.)  Mount the NVA in the base of the control horn.  Drill it so it has to be threaded in.  You may want to add the mounting nut be if the fit is tight it isn't needed.

Mount in on the upper left backplate bolt.  Use a small washer to spread the load.  On most combat motor mounts  that puts the fuel line about 3/8 in. above the mount for fuel line clearance.  Depending on what fuel iine you use you may find you need to solder a fine gauge sole wire wrapped close to the end.  That will keep any correct size fuel line from slipping.

The third alternative is to get a Fora F2D needle valve assembly.  It has a slightly finer thread.  It will require some surgery on the venturi mount because the Fora valve is too short.  The boss on each side of the venturi needs to have the hole enlarged to fit the NVA but don't go too deep!  It can be done by hand with hand drills just twisting them.  The aluminum is pretty soft.  Or, you can get a machinist friend to do it for you for a case of beer, or maybe just a thank you.
phil Cartier

Offline Dan McEntee

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Re: LA 25 needle valve for combat
« Reply #8 on: July 17, 2021, 06:44:27 PM »
The LA 25 will work fine if you can get the right needle valve from OS.

Combat requires an extra fine thread NVA.  They made one as a generic venturi mounted stunt needle valve.  The threads are 0.35mm pitch (distance between thread edges)  They make a nearly identical unit for larger engines which uhas 0.45mm. pitch.  It is too coarse to work on a bladder or pacifier, although will likely work just fine on a larger engine.

The other is a carburetor part for 0.10-.25 engines.  OS 1a is the the most common designation.  This has to be mounted in a bracket (I use a heavy duty control horn cut down to fit on the engine.)  Mount the NVA in the base of the control horn.  Drill it so it has to be threaded in.  You may want to add the mounting nut be if the fit is tight it isn't needed.

Mount in on the upper left backplate bolt.  Use a small washer to spread the load.  On most combat motor mounts  that puts the fuel line about 3/8 in. above the mount for fuel line clearance.  Depending on what fuel iine you use you may find you need to solder a fine gauge sole wire wrapped close to the end.  That will keep any correct size fuel line from slipping.

The third alternative is to get a Fora F2D needle valve assembly.  It has a slightly finer thread.  It will require some surgery on the venturi mount because the Fora valve is too short.  The boss on each side of the venturi needs to have the hole enlarged to fit the NVA but don't go too deep!  It can be done by hand with hand drills just twisting them.  The aluminum is pretty soft.  Or, you can get a machinist friend to do it for you for a case of beer, or maybe just a thank you.

      The last generation of FP engines. ( the ,20, 25. .35 and .40) were all rear needle valve and used this metal NVA that Phil describes. I used these on my son's models when he was still prop shy as a little boy, and they worked well. I did the single wire wrap/solder trick as described to provide a "barb" for the fuel line to stay on. Carefully polish it with some fine sandpaper and you can work the 4mm nut over it still so it can be attached to the bracket. Using Prather fuel line helped a lot. The metal brackets that were used resemble the brackets that they use on the LA series engines but are different and pretty versatile. Keep your eyes peeled into guys junk boxes and barrels and odds and ends at swap meets for them. I don't know if they are still available separately but may be. Next time I need one I'll have to try the heavy duty control horn bracket. For you guys still working on flying inverted and doing outside maneuvers with a profile model, mounting one of these modified NVAs so that it is horizontal and behind the engine keeps it from getting damaged when hitting the ground..
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Offline mike londke

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Re: LA 25 needle valve for combat
« Reply #9 on: July 19, 2021, 10:13:47 AM »
As Phil Mentioned the OS1A works well. It came in 2 versions the 1A#10 and the 1A#15 both are pictured and both are suitable. The new old stock is gone everywhere but they can be easily obtained at RC Swap meets by scouring junk boxes for clapped out FPís and pulling them off the carbs. The other NVA pictured is the Traxxas RC car assy. Although I have not tried one myself many were using them at the Nats with good results. Good luck.
AMA 48913  USPA D-19580  NRA Life Member  MI State Record Holder 50 way Freefall Formation Skydive  "Don't let the planet sneak up on you"

Offline Dan McEntee

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Re: LA 25 needle valve for combat
« Reply #10 on: July 19, 2021, 03:34:07 PM »
As Phil Mentioned the OS1A works well. It came in 2 versions the 1A#10 and the 1A#15 both are pictured and both are suitable. The new old stock is gone everywhere but they can be easily obtained at RC Swap meets by scouring junk boxes for clapped out FPís and pulling them off the carbs. The other NVA pictured is the Traxxas RC car assy. Although I have not tried one myself many were using them at the Nats with good results. Good luck.

   The Traxxas unit looks interesting. Clean and simple. Does it use an O ring to seal it like the newer OS units? I need to stop by the hobby shop and check those out. Lots of other uses besides combat.
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Offline Steve Helmick

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Re: LA 25 needle valve for combat
« Reply #11 on: July 21, 2021, 07:02:22 PM »
Around here, I've often seen OS .10 FP nv assemblies used on Nelson & Fora .36's. They're usually just hanging by the fuel hoses and not mounted. That's for bladder tanks, which I assume our OP will be using.

I tried the stock .25LA rear nv setup on suction (Skyray 35) and didn't like it at all unless starting with an electric finger. For hand starting, the fuel would drain back out of the hose between the needle and the venturi, and the needle response was sluggish. Of course, neither is a problem with a bladder tank.  #^ Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline mike londke

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Re: LA 25 needle valve for combat
« Reply #12 on: July 21, 2021, 08:56:53 PM »
Around here, I've often seen OS .10 FP nv assemblies used on Nelson & Fora .36's. They're usually just hanging by the fuel hoses and not mounted. That's for bladder tanks, which I assume our OP will be using.

I tried the stock .25LA rear nv setup on suction (Skyray 35) and didn't like it at all unless starting with an electric finger. For hand starting, the fuel would drain back out of the hose between the needle and the venturi, and the needle response was sluggish. Of course, neither is a problem with a bladder tank.  #^ Steve
They don't work on a bladder. The needle taper is really "fat" and the threads are too coarse, it's hard to get a good setting on them.....
AMA 48913  USPA D-19580  NRA Life Member  MI State Record Holder 50 way Freefall Formation Skydive  "Don't let the planet sneak up on you"

Offline Steve Helmick

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Re: LA 25 needle valve for combat
« Reply #13 on: July 22, 2021, 06:17:21 PM »
They don't work on a bladder. The needle taper is really "fat" and the threads are too coarse, it's hard to get a good setting on them.....

Which "they" are you referring to?  H^^ Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline mike londke

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Re: LA 25 needle valve for combat
« Reply #14 on: July 22, 2021, 07:25:28 PM »
Which "they" are you referring to?  H^^ Steve
The latest NVA that came on OS engines either as a bolt on remote or that was molded into the backplate. Sorry for the confusion.
AMA 48913  USPA D-19580  NRA Life Member  MI State Record Holder 50 way Freefall Formation Skydive  "Don't let the planet sneak up on you"


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