Brett, some pipe questions

Do you know the exaust tining of the .25 VF?

I read at the Pampa site a text by Randy, and he mentions two aproaches.

1)The long pipe leans setting, that he recomends for a low drag light loaded model, which is the kind of ship I intend to use (a chizler)

2) the "KING KONG" (!) setup, short pike, big venturi,rich mixture more shims. that would deleer lots of torque, and an incease under load.

the second aproach seems more apealing to me,sinde I like running on a wet 2 cycle.

Would you be so kind to through some lite in this subject?

You'll find Randy's comments at

http://www.clstunt.com/htdocs/dcforum/DCForumID1/8467.html

Thank you ain advance!

Ion,

No fair posting same basic question twice.

When it comes to answering any sort of question involving engine runs, mufflers and pipes, Mr. Buck seems to have left the building.

Drive on up for the 2004 NW Regionals, we'll help you out then and there.

Dan,it'a looong drive!!

The pipe notes are not from Randy, just the chart is. I put those notes together a few years ago from posts from the 2 C/L forums. I then posted it on the SSW Forum for comments.

If you did those notes, I'll be asking you the questions.

All the questions above, plus;

Is that KING KONG setup running in a 2 or a 4 cycle?

God bless you!

In Christ,

>Do you know the exaust tining of the .25 VF?
>
>I read at the Pampa site a text by Randy, and he mentions
>two aproaches.
>
>1)The long pipe leans setting, that he recomends for a low
>drag light loaded model, which is the kind of ship I intend
>to use (a chizler)
>
>2) the "KING KONG" (!) setup, short pike, big venturi,rich
>mixture more shims. that would deleer lots of torque, and
>an incease under load.
>
>the second aproach seems more apealing to me,sinde I like
>running on a wet 2 cycle.
>
>Would you be so kind to through some lite in this subject?

Sorry - I have been off the forum for a while, and also doing 16 hour days, so I haven't seen this before now.

The chart looks like the one supplied with Randy's engines, and it's pretty definitive. Note that this measurement can be to the first baffle, the second baffle, or the tail cone - but stick with the first baffle unless you really know what you are doing, and are able to really debug the system.

I don't know the exhaust duration of the 25VF. I would be willing to bet its somewhere between 140 and 145 (like the 40 - and by the way, my best 40 is 143 degrees). But measure it with a degree wheel.

As I mentioned to you a couple of years ago, I don't know any really well-proven setup for this engine. Several have been run locally with some success but it really never got developed fully. So what follows is an educated guess, and where I would start -

Prop - something like a 10 to 10.5-3.5 to 3.75 2-blade, or maybe a narrow-blade 11
RPM - 11,500-12,000 to start.

You need to play the revs off against the pitch to find a sweet spot, then tweak with minor pipe adjustments. My guess is that you will need some revs to max out the engine. When in doubt, run the pipe shorter rather than longer, particularly when you start out. The 40 was notorious for cutting off on hard inside corners when new if the pipe is too long.

Pipe length - 16.5"
Uniflow tank, no pressure to start with
Venturi - maybe .250-.255 with ST needle.
Fuel - 10% 50/50 with 222% total oil.
Glow Plug - Thunderbolt R/C, Thunderbolt 4-Cycle, or Glo-Devil #300, but I would be surprised if it's too picky. The only one I know not to use is a Rossi of any variety.

An easy way to tell if the pipe is too long for the setup, if it's too slow and you are continuously trying to lean it out to speed it up, but it's very unresponsive to the needle. That's an effect of the pipe preventing it from going any faster no matter how lean you get it. If it's significantly too short, it will be very touchy on the needle. Sometimes, if the pipe is just a teeny bit too long, it will slow down as the flight progresses. If it's a tiny bit too short, it will sometimes speed up as the flight goes along. This IS NOT a reliable indicator of "rightness" the overall pipe length, as it only happens occassionally, no matter where the pipe is.

If the airplane "charges" in corners, lengthen the pipe by 1/8" at a time until it stops. If it sags or seems "flat" in the corners, shorten the pipe until it stops. I would start with the 3.5-3.75" pitch until proven that it's no good. this sill cut down on the number of variables, and I'm pretty sure the engine will run in the RPM range required. If you have to go over 12000, then I would consider adding pitch 1/4" at a time until the ground launch revs are between 11,500 and 12,000.

Don't go crazy with pipe adjustments. Just because you CAN adjust it doesn't mean you need to, or that whatever problem you have is a pipe length issue. The pipe lenght is likely to be the least likely source of problems. Unless you are getting consistent performance, fiddling the pipe will just distract you from all the other things that are more likely to be wrong with it.

Also, very, very important - face off the mating surface on the exhaust flange and the header with 240 grit wet/dry sandpaper on a piece of thick glass (shove a piece of paper towel in the exhaust to prevent crud going into the engine). Then clean it off with lacquer thinner and don't touch it with you fingers afterwards. Then put a very thin but complete layer of silicone bathtub caulk on the header side, and bolt the header on. Let sit overnight if possible. This is VERY important because ANY leak at all, even a tiny one, near the front end of the pipe, will cause all sorts of bad things to happen and you will NEVER get it to work. Also rough up the back end of the header with medium sandpaper to give the rubber coupler something to "bite" and clean all the oil off of that before assembly, too.

You are definitely out on a limb with this system. I'm not tryingn to discourage you, but you must understand that you really need a certain pretty high skill level and a pretty high analysis capability to be able to tell when it's right, a little off, or a lot off. This is beyond what most people do - you are doing development, not getting a proven system that might need slight tweaks but is more-or-less figured out.

Forget the King Kong/Lean run setup thing- truth be told, these are just minor tweaks to a turn-key system. The fact that some of us want to argue about .008 worth of head gaskets, 5% vs. 15% nitro, and .010 of venturi size like these were opposing religious camps is about as silly as it sounds. We are all running the PAs very close to each other, and the difference in the way I run mine vs. say, Curt Contrata, is very, very minor in the big scheme of things.

Just try to get a decent level slight speed with a medium 2-stroke, and just enough boost in the maneuvers, and above all, repeatability.

Sorry - I have been off the forum for a while, and also
>doing 16 hour days, so I haven't seen this before now.

Brett, you don't have to be sorry, as far as I know i ain't payin' you (yet) a salary to be my advisor, so I'm the one that gota sorry for - like we say in Brazil - renting you...

> The chart looks like the one supplied with Randy's
>engines, and it's pretty definitive. Note that this
>measurement can be to the first baffle, the second baffle,
>or the tail cone - but stick with the first baffle unless
>you really know what you are doing, and are able to really
>debug the system.

My pipe has only one baffle, i think. It's a Nering Carbonmaster. But I did't understand this business of measuring to nothing else that the first baffle.

> I don't know the exhaust duration of the 25VF. I would
>be willing to bet its somewhere between 140 and 145 (like
>the 40 - and by the way, my best 40 is 143 degrees). But
>measure it with a degree wheel.

I did some measuring, and it appears to be 145º.
I'm using a .256 venturi with a PA spraybar, that I filed in order to gain some venturi area.
OS remote NVA to keep my digits *stock*, and 10% nitro ,22%total oil (just some 3% castor.
The APC has been used by Mike and by Billy, lauching at 12 and 10 G respectively.

To have the kind of ship (low drag, light) I'm going to power it with in a decent lap time I'll have to use the APC 10 X 3 launching at some 11.500 /12,000 rpm, like you said.

> As I mentioned to you a couple of years ago, I don't
>know any really well-proven setup for this engine. Several
>have been run locally with some success but it really never
>got developed fully. So what follows is an educated guess,
>and where I would start -
>
>Prop - something like a 10 to 10.5-3.5 to 3.75 2-blade, or
>maybe a narrow-blade 11
>RPM - 11,500-12,000 to start.
>
>You need to play the revs off against the pitch to find a
>sweet spot, then tweak with minor pipe adjustments. My guess
>is that you will need some revs to max out the engine. When
>in doubt, run the pipe shorter rather than longer,
>particularly when you start out. The 40 was notorious for
>cutting off on hard inside corners when new if the pipe is
>too long.

That's a good piece of advice!

>Pipe length - 16.5"

16.5"is exactly the length I setteled for, afer two days of fidlin' around.

>Uniflow tank, no pressure to start with

I'm using a DuBro 4oz w/clunk modified for uniflow.Do folks put pressure nipples on carbon pipes?

.
>Fuel - 10% 50/50 with 222% total oil.

I have to disagree with you, IMHO 222% total oil is too greasy for my taste...

>Glow Plug - Thunderbolt R/C, Thunderbolt 4-Cycle, or
>Glo-Devil #300, but I would be surprised if it's too picky.
>The only one I know not to use is a Rossi of any variety.

It seems to be happy with an OS nº 8, I'll use it until I can gt my hand on some thunderbolts, or maybe a CB Nº 2, it's a helluva plug and it's made in São Paulo, Brazil.

>An easy way to tell if the pipe is too long for the setup,
>if it's too slow and you are continuously trying to lean it
>out to speed it up, but it's very unresponsive to the
>needle. That's an effect of the pipe preventing it from
>going any faster no matter how lean you get it. If it's
>significantly too short, it will be very touchy on the
>needle. Sometimes, if the pipe is just a teeny bit too long,
>it will slow down as the flight progresses. If it's a tiny
>bit too short, it will sometimes speed up as the flight goes
>along. This IS NOT a reliable indicator of "rightness" the
>overall pipe length, as it only happens occassionally, no
>matter where the pipe is.

Good to hear that, it hapened to me. with 17.25" i leaned the daylights out of it gut it wouldn't go beyond 11G.

> If the airplane "charges" in corners, lengthen the pipe
>by 1/8" at a time until it stops. If it sags or seems "flat"
>in the corners, shorten the pipe until it stops. I would
>start with the 3.5-3.75" pitch until proven that it's no
>good. this sill cut down on the number of variables, and I'm
>pretty sure the engine will run in the RPM range required.
>If you have to go over 12000, then I would consider adding
>pitch 1/4" at a time until the ground launch revs are
>between 11,500 and 12,000.
>
> Don't go crazy with pipe adjustments. Just because you
>CAN adjust it doesn't mean you need to, or that whatever
>problem you have is a pipe length issue. The pipe lenght is
>likely to be the least likely source of problems. Unless you
>are getting consistent performance, fiddling the pipe will
>just distract you from all the other things that are more
>likely to be wrong with it.
>
>Also, very, very important - face off the mating surface on
>the exhaust flange and the header with 240 grit wet/dry
>sandpaper on a piece of thick glass (shove a piece of paper
>towel in the exhaust to prevent crud going into the engine).
>Then clean it off with lacquer thinner and don't touch it
>with you fingers afterwards. Then put a very thin but
>complete layer of silicone bathtub caulk on the header side,
>and bolt the header on. Let sit overnight if possible. This
>is VERY important because ANY leak at all, even a tiny one,
>near the front end of the pipe, will cause all sorts of bad
>things to happen and you will NEVER get it to work. Also
>rough up the back end of the header with medium sandpaper to
>give the rubber coupler something to "bite" and clean all
>the oil off of that before assembly, too.
>
> You are definitely out on a limb with this system. I'm
>not tryingn to discourage you, but you must understand that
>you really need a certain pretty high skill level and a
>pretty high analysis capability to be able to tell when it's
>right, a little off, or a lot off. This is beyond what most
>people do - you are doing development, not getting a proven
>system that might need slight tweaks but is more-or-less
>figured out.
>
> Forget the King Kong/Lean run setup thing- truth be told,
>these are just minor tweaks to a turn-key system. The fact
>that some of us want to argue about .008 worth of head
>gaskets, 5% vs. 15% nitro, and .010 of venturi size like
>these were opposing religious camps is about as silly as it
>sounds. We are all running the PAs very close to each other,
>and the difference in the way I run mine vs. say, Curt
>Contrata, is very, very minor in the big scheme of things.
>
> Just try to get a decent level slight speed with a
>medium 2-stroke, and just enough boost in the maneuvers, and
>above all, repeatability.
>
> Brett

Thanks a lot ,Brett, I hae been doing exactly as you wrote, but ya know, I wanted to make sure I wasn't doin' anything stupid...

I feel more confident now.

God bless ya!