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Author Topic: OS 10FP Venturi Bore  (Read 1276 times)

Offline Tim Wescott

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OS 10FP Venturi Bore
« on: June 24, 2023, 06:34:24 PM »
I have an OS 10FP that I bought from a guy who bought it from a guy -- so all history on the thing is lost.

It runs about 12500 RPM on a 8x4 prop cut down to 7x4.  Even accounting for the prop blades being a bit wide that seems slow -- especially because it's really quiet -- it sounds like you'd expect an engine to sound running at half throttle.

It features someone's hand-machined venturi, with an oddball profile (the snout is necked down, then it opens up where the spraybar passes through).  I'd like to try just making my own, machined to the original OS standard size.

Anyone know what that is?  The spray bar appears to be the original size.
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Offline GERALD WIMMER

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Re: OS 10FP Venturi Bore
« Reply #1 on: June 25, 2023, 05:17:04 AM »
Hello Peter Chinns Model Airplane New test of 1977 report of the similar OS10FSR had the C/L venturi at 6mm and the spray bar as 3.4mm with an effective choke area of 9 square mm

Regards Gerald
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Offline kenneth cook

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Re: OS 10FP Venturi Bore
« Reply #2 on: June 25, 2023, 05:23:07 AM »
              I have two FP .10's. Both are control line versions from OS. What I will say is that the original OS FP .10 spraybar and needle is specific to this engine. It's also quite rare and unobtainable. The finish of those needle were black oxide. I don't know how to post pictures on here as I find it extremely confusing.  I can offer you the venturi size, I just have to get the engine out. I also feel your trying to offer the .10 far too much prop with the 8".Even though the prop is cut down to 7", the blade area of a 8 compared to a 7 is quite substantial. A thinner Master Airscrew 7x4 should turn up pretty good. I'm thinking you should be in the high 17K range. I used the APC 6.3x4 quite a bit with this engine with good results.
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Offline katana

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Re: OS 10FP Venturi Bore
« Reply #3 on: June 25, 2023, 05:56:44 AM »
Quote from: Tim Wescott on June 24, 2023, 06:34:24 PM
It features someone's hand-machined venturi, with an oddball profile (the snout is necked down, then it opens up where the spraybar passes through).  I'd like to try just making my own, machined to the original OS standard size.

I wonder what the 'machinists' thought processes were to come up with that solution? The basic physics of a venturi requires a higher gas speed that gives a lower pressure at the restriction just to induce fuel flow - the above venturi is completely backwards thinking - strange!  n1
« Last Edit: June 26, 2023, 03:35:37 AM by katana »
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Offline Tim Wescott

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Re: OS 10FP Venturi Bore
« Reply #4 on: June 25, 2023, 09:17:40 AM »
Quote from: GERALD WIMMER on June 25, 2023, 05:17:04 AM
Hello Peter Chinns Model Airplane New test of 1977 report of the similar OS10FSR had the C/L venturi at 6mm and the spray bar as 3.4mm with an effective choke area of 9 square mm

Regards Gerald

Thanks.  That's perfect.  I know what I need to know.

Quote from: katana on June 25, 2023, 05:56:44 AM
I wonder what the 'machinists' thought processes were to come up with that solution? The basic physics of a venturi requires a higher gas speed that gives a lower pressure at the just to induce fuel flow - the above venturi is completely backwards thinking - strange!  n1

It's very pretty -- doesn't that justify all?

This came from a batch of airplanes that a friend of mine bought; there were other planes with similar venturi design, that benefited greatly by having normal venturi's bunged in there.

We're pretty sure that the original builder never actually flew the planes.

Quote from: kenneth cook on June 25, 2023, 05:23:07 AM
I also feel your trying to offer the .10 far too much prop with the 8".Even though the prop is cut down to 7", the blade area of a 8 compared to a 7 is quite substantial. A thinner Master Airscrew 7x4 should turn up pretty good. I'm thinking you should be in the high 17K range. I used the APC 6.3x4 quite a bit with this engine with good results.

I was going with what I have on hand.  The only from-the-factory 7" prop I have is an old white nylon one -- I'm not going to run that.  I need to order some props for it -- if the LHS has any nitro props they aren't going to be that small.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Motorman

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Re: OS 10FP Venturi Bore
« Reply #5 on: June 25, 2023, 02:29:30 PM »
APC 7-3 sport prop would be good for that one.
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Offline Tim Wescott

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Re: OS 10FP Venturi Bore
« Reply #6 on: June 25, 2023, 03:02:31 PM »
Quote from: Motorman on June 25, 2023, 02:29:30 PM
APC 7-3 sport prop would be good for that one.

I just bought six different sizes of prop from APC -- including that one -- to play with.
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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

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Re: OS 10FP Venturi Bore
« Reply #7 on: June 25, 2023, 04:43:23 PM »
Quote from: katana on June 25, 2023, 05:56:44 AM
I wonder what the 'machinists' thought processes were to come up with that solution? The basic physics of a venturi requires a higher gas speed that gives a lower pressure at the just to induce fuel flow - the above venturi is completely backwards thinking - strange!  n1

   That is pretty typical of C/L racing engines in events that are venturi-diameter-limited. The idea is to put the spraybar in a larger-diameter section of the venturi so the choke area is not affected by the spraybar.   It works because the Bernoulli effect is not the primary way you get fuel suction, you have pressure loss across any obstruction upstream, so it will suck fuel just fine that way.

  Why you need this arrangement on a 10FP, I can't see, or what advantage it would provide.

    Brett
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Offline Tim Wescott

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Re: OS 10FP Venturi Bore
« Reply #8 on: June 25, 2023, 08:51:32 PM »
More normal-looking venturi installed.  Whoever did it changed to a 4mm spraybar and opened up the choke to compensate -- my math says it's 10 square mm.

Waiting on those little props to see if one of 'em makes it go faster.
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AMA 64232

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

Offline Steve Helmick

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Re: OS 10FP Venturi Bore
« Reply #9 on: June 27, 2023, 11:19:51 AM »
Quote from: Brett Buck on June 25, 2023, 04:43:23 PM
   That is pretty typical of C/L racing engines in events that are venturi-diameter-limited. The idea is to put the spraybar in a larger-diameter section of the venturi so the choke area is not affected by the spraybar.   It works because the Bernoulli effect is not the primary way you get fuel suction, you have pressure loss across any obstruction upstream, so it will suck fuel just fine that way.

  Why you need this arrangement on a 10FP, I can't see, or what advantage it would provide.

    Brett

Interesting explaination, thank you. I would bet that some R/C groups flew .10FP pylon and had some sort of venturi size rule. I'd speculate that .10FP's would be easier to deal with, being more tolerant of electric fingers than smaller engines.  H^^ Steve
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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.

Online Dave Hull

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Re: OS 10FP Venturi Bore
« Reply #10 on: June 27, 2023, 08:21:41 PM »
Which is why the rules may specify the venturi geometry beyond just a minimum bore size:

4.7.1 "The venturi shall have an inside circular bore of not more than .292". The venturi will maintain this diameter for at least 0.155" at the throat of the venturi where the spraybar will be located at the midpoint of the area."

This is one of the rule subsections for Quicky Rat. Full rules available at: http://nclra.org/Rules/TQR.php

Dave
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Online Brett Buck

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Re: OS 10FP Venturi Bore
« Reply #11 on: June 27, 2023, 11:09:11 PM »
Quote from: Dave Hull on June 27, 2023, 08:21:41 PM
Which is why the rules may specify the venturi geometry beyond just a minimum bore size:

4.7.1 "The venturi shall have an inside circular bore of not more than .292". The venturi will maintain this diameter for at least 0.155" at the throat of the venturi where the spraybar will be located at the midpoint of the area."

This is one of the rule subsections for Quicky Rat. Full rules available at: http://nclra.org/Rules/TQR.php

Dave

  WAM Sport Race must have missed that meeting!

    Brett
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Offline spare_parts

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Re: OS 10FP Venturi Bore
« Reply #12 on: June 28, 2023, 12:07:21 PM »
I think it's F2D where only orifice size is spec'd. Some older engines have very tall venturi. Current crop isn't much shorter.
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Online Brett Buck

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Re: OS 10FP Venturi Bore
« Reply #13 on: June 28, 2023, 05:45:18 PM »
Quote from: spare_parts on June 28, 2023, 12:07:21 PM
I think it's F2D where only orifice size is spec'd. Some older engines have very tall venturi. Current crop isn't much shorter.

   Various regional racing series (AKA WAM Sport Race, which is where I first saw it), too. Looked much like your picture.

    Brett
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Offline Tim Wescott

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Re: OS 10FP Venturi Bore
« Reply #14 on: June 29, 2023, 01:40:55 PM »
To the folks who suggested truly smaller props: thank you.  It turns up to 18000 RPM on an APC 7x3 -- I'll be starting with that for test flying, then see what I like best.
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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

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Re: OS 10FP Venturi Bore
« Reply #15 on: June 29, 2023, 06:34:54 PM »
Quote from: Steve Helmick on June 27, 2023, 11:19:51 AM
Interesting explaination, thank you. I would bet that some R/C groups flew .10FP pylon and had some sort of venturi size rule. I'd speculate that .10FP's would be easier to deal with, being more tolerant of electric fingers than smaller engines.  H^^ Steve

   You would think, if they were very sharp, they would know to restrict the choke area as described above, not the diameter.

      Brett
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Offline Steve Helmick

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Re: OS 10FP Venturi Bore
« Reply #16 on: June 29, 2023, 11:39:47 PM »
Quote from: Brett Buck on June 29, 2023, 06:34:54 PM
   You would think, if they were very sharp, they would know to restrict the choke area as described above, not the diameter.

      Brett

Sure, IF they were very sharp. It's also possible that they'd wait and see what sort of work-arounds guys would come up with, just for a giggle as they DQ'd them under the sportmanship rule. Cheap trophies aren't cheap, ya know. VD~ Steve
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"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 Lauri Malila

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Re: OS 10FP Venturi Bore
« Reply #17 on: June 30, 2023, 01:13:41 AM »
.
« Last Edit: June 30, 2023, 02:44:00 PM by Lauri Malila »
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