News:


  • March 29, 2024, 12:52:43 AM

Login with username, password and session length

Author Topic: Pros and cons of having a remote nva?  (Read 1146 times)

Offline frank mccune

  • AMA Member
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1621
Pros and cons of having a remote nva?
« on: June 11, 2017, 10:47:27 AM »
     Hi All:

     I am thinking about adding a remote nva to one of my OS .35 powered profile stunt planes and was concerned about what advantage if any. would there be in doing so.

      Perhaps the fact that my fingers will be in a safer position when adjusting the needle valve.  I have an OS .40 with the remote needle valve on profile stunter and I have grown to enjoy the extra distance from the spinning prop for safety reasons.  At the present time, I have an OS.35S with a ST nva which is more or less the standard replacement for these engines.  It works very well but, my fingers are still close to the spinning prop.

     I have the complete remote nva assembly to drop into the .35 to replace the ST nva.  Oh yes, what would be a suitable venturi bore for the remote nva set up if I decided to make the change?

      Any thoughts or comments?

                                                                                                             Tia,

                                                                                                             Frank McCune


Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Pros and cons of having a remote nva?
« Reply #1 on: June 11, 2017, 11:02:32 AM »
     Hi All:

     I am thinking about adding a remote nva to one of my OS .35 powered profile stunt planes and was concerned about what advantage if any. would there be in doing so.

Probably the biggest practical advantage is that you can mount it so that it doesn't stick above the top of the plane, so it won't get damaged in an inverted landing or crash.

      Perhaps the fact that my fingers will be in a safer position when adjusting the needle valve.  I have an OS .40 with the remote needle valve on profile stunter and I have grown to enjoy the extra distance from the spinning prop for safety reasons.  At the present time, I have an OS.35S with a ST nva which is more or less the standard replacement for these engines.  It works very well but, my fingers are still close to the spinning prop.

If that's your concern, then I think it's sufficient.  I'd say that I haven't gotten my fingers in a prop since my 049 days, but just a couple of weeks ago at the regionals I stuck my hand into the back of the prop and earned a tingling blood blister for my pains (my flying partner reports that was mapping out how to get the engine stopped before he barfed if there was blood -- he claims to have trouble around blood, although I haven't seen it.  I need to try him out with some Karo syrup an red dye some time.)

     I have the complete remote nva assembly to drop into the .35 to replace the ST nva.  Oh yes, what would be a suitable venturi bore for the remote nva set up if I decided to make the change?

If the remote spray bar is the same diameter as the ST NVA then just bung it in and go.  If it's smaller, then you need a smaller venturi bore -- you need to match the venturi area.  Also, if it's smaller, it won't fit your crankcase correctly, and bushing it to size will be a bear.  For me, that would be a show-stopper, or a reason to machine my own spray bar.

      Any thoughts or comments?

You forgot to ask about downsides.  Remote NVA assemblies are more prone having the fuel drain back from the spray bar, and when it happens the fuel line takes much longer to fill.  There's also, theoretically, an issue that if you get a bubble in the fuel line it'll cause a bleb of fuel to go into the engine when the bubble hits the needle, and then fuel starvation when the bubble hits the spraybar.  I haven't had problems with this since I learned how to keep bubbles out of my fuel system, though.  Remote NVA assemblies also attract negative attention from folks who just cannot believe that they'll work, and people who have memorized the rule about fuel tank location with respect to the needle get confused (the fuel tank location needs to be correct with respect to the opening in the spraybar).

Overall, if you have or can get or make a spraybar the same diameter as what you have now, I say go for it.  I have, for a couple of strange reasons, a remote NVA in the Atlantis that I inherited from Paul Walker.  So far it's worked great.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13717
Re: Pros and cons of having a remote nva?
« Reply #2 on: June 11, 2017, 01:33:30 PM »
    Hi All:

     I am thinking about adding a remote nva to one of my OS .35 powered profile stunt planes and was concerned about what advantage if any. would there be in doing so.

      Perhaps the fact that my fingers will be in a safer position when adjusting the needle valve.  I have an OS .40 with the remote needle valve on profile stunter and I have grown to enjoy the extra distance from the spinning prop for safety reasons.  At the present time, I have an OS.35S with a ST nva which is more or less the standard replacement for these engines.  It works very well but, my fingers are still close to the spinning prop.

     I have the complete remote nva assembly to drop into the .35 to replace the ST nva.  Oh yes, what would be a suitable venturi bore for the remote nva set up if I decided to make the change?

     I haven't found any significant issue with remote or rear needle systems on several systems. The only problem was figuring out how and where to mount it, in the case of remote needles. Most of the analysis related to "lag" is wrong, the lag simply from having the needle 2" away is well under a millisecond. There may be other effects but I haven't found any consequential performance issues.

    The original OS 35S needle is probably superior to the ST, I sure wouldn't change to the ST for performance reasons alone. People do it all the time and usually it's OK, but you're not gaining anything much and adding the chance of the ST turning into a tuning fork occasionally.

   The choke area should be the same, remote needle or not. Presumably you are using a conventional spraybar with the needle hole blocked for the spraybar, so it should be the same size as it was before.

    Many people, without realizing it, replaced the OS with the ST spraybar and concluded it "needled better" - which in some cases, it does, because the ST spraybar is much bigger around than the current OS needle. On the 20/25FP and 25LA, that has the super-great effect of killing about 1/3 the power, what a great modification, then you can go on the internet and tell that idiot from California that he's a liar (as has happened repeatedly).  On the OS-35s, the original spraybar was also 4mm like the ST, so at least you don't change the choke area, and you can put the original spraybar back in because the case and venturi haven't been damaged, er, "modified for lucky best stunt run".

    BTW, the "core" of the OS RC carburetor can be unscrewed and used as a remote needle/metering block. OS used to sell it for that purpose. So if you have any 80's+ OS RC carbs lying around, you can use that. Just like the front needle assembly, the needle is stiffer and supported much better than the ST, and you have click stops and very fine thread. If you think you need to change it between clicks, you probably have something else wrong.

    Brett
« Last Edit: June 11, 2017, 04:07:11 PM by Brett Buck »

Offline frank mccune

  • AMA Member
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1621
Re: Pros and cons of having a remote nva?
« Reply #3 on: June 11, 2017, 02:08:38 PM »
       Hello:

       
       Thanks for taking the time to answer my question!

                                                                                                        Frank McCune

Online Lauri Malila

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1629
Re: Pros and cons of having a remote nva?
« Reply #4 on: June 12, 2017, 10:01:03 AM »
Hi

I can't comment on needle response vs distance as I allways put my remote valves as close to venturi as possible, typically just an 1/2" of fuel tubing connecting them. I use remote valves only because I like the idea of isolating the valve from engine heat and some vibrations. And of course, it's nice to be able to remove the engine without removing the valve.
When everything is well, the only negative thing I can think of is a slight richening of engine after there is no more fuel in fuel line before the valve.

L

Offline RandySmith

  • Administrator
  • Trade Count: (0)
  • Admiral
  • *****
  • Posts: 13747
  • Welcome to the Stunt Hanger.
    • Aero Products
Re: Pros and cons of having a remote nva?
« Reply #5 on: June 12, 2017, 01:58:09 PM »
I maybe more sensitive  to run than others,  but I mos t  definitely can feel a difference in the  break transition, it is delayed from a bar in the front, plus  it primes easiers/more consistent , and with the  same side  front  NVA ,  it makes  using the front a no brainer for me,  now  if your running a wet 2 stroke, it maybe  no difference

randy


Advertise Here
Tags:
 


Advertise Here