News:


  • March 28, 2024, 12:29:59 PM

Login with username, password and session length

Author Topic: Plastic uniflow clunk tanks  (Read 13663 times)

Offline Bootlegger

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2710
Plastic uniflow clunk tanks
« on: April 23, 2017, 10:31:34 AM »

  Hey Guy's
How about some diagrams of how you plumb the uniflow of your clunk tanks.  Thanks a lot
8th Air Force Veteran
Gil Causey
AMA# 6964

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Plastic uniflow clunk tanks
« Reply #1 on: April 23, 2017, 11:17:53 AM »
From this thread comes the picture below.  I suggest you read the thread, I think it'll answer your basic questions.

If you know how to use the search utility, search on +clunk +uniflow -- there's lots of results.

AMA 64232

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

Offline Akihiro Danjo

  • 23 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 164
Re: Plastic uniflow clunk tanks
« Reply #2 on: April 24, 2017, 12:52:42 AM »
This is my setup for 4oz tank.
Aki
« Last Edit: April 24, 2017, 05:16:30 AM by Akihiro Danjo »

Offline Perry Rose

  • Go vote, it's so easy dead people do it all the time.
  • 2015
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1654
Re: Plastic uniflow clunk tanks
« Reply #3 on: April 24, 2017, 04:52:18 AM »
I agree with Mr. Danjo and Mr Wescott except for the second bend in the uni flow pipe and soldering the pipes together.  One bend towards the tank wall about half way into the tank works and without soldering you can adjust the pipe by turning it up or down. On a clunk tank the clunk can get caught on the uniflow pipe if it's too long.
« Last Edit: April 24, 2017, 10:15:16 AM by Perry Rose »
I may be wrong but I doubt it.
I wouldn't take her to a dog fight even if she had a chance to win.
The worst part of growing old is remembering when you were young.

Offline Peter Grabenstein

  • 2020 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 328
Re: Plastic uniflow clunk tanks
« Reply #4 on: April 24, 2017, 08:43:51 AM »
I build one like this for a CL Buddy many moons ago for his Profile and it works just PERFECT.
Inside the tank, I use thin wall Silicone fueltube (ebay) for max flexibility.
The clunk must be able to touch upper, lower and sidewall for normal and inverted flight.
If not, your clunk is to light or your fueltubes are too thick walled or both.

http://www.tulsacl.com/ClunkTank.html

Our Thanks to Nils Norling


Peter



« Last Edit: April 24, 2017, 11:34:31 AM by Peter Grabenstein »
I hate pessimists, I prefer optimists.
Impossible is done immediately, miracles take longer.
I don't care who your father is ......... as long as I fly here,
Nobody walks, runs, floats or flies across my circle ......... not even to fetch fish, wine or bread.

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Plastic uniflow clunk tanks
« Reply #5 on: April 24, 2017, 10:23:55 AM »
I agree with Mr. Danjo and Mr Wescott except for the second bend in the uni flow pipe and soldering the pipes together.  One bend towards the tank wall about half way into the tank works and without soldering you can adjust the pipe by turning it up or down. On a clunk tank the clunk can get caught on the uniflow pipe if it's too long.

I, on the other hand, do like the idea soldering the tubes together, because my plastic clunk uniflows all seem to want to adjust themselves -- I'd rather have a positive and adjustable system for holding the tank in place, and a tube that doesn't budge with respect to the tank.

You're absolutely right about not bringing the uniflow to the back of the tank -- I make sure that the clunk swings freely without contacting the uniflow: if it doesn't, I fix things.
AMA 64232

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

Offline ray copeland

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 871
Re: Plastic uniflow clunk tanks
« Reply #6 on: April 24, 2017, 07:48:58 PM »
Regarding a 6 oz. plastic uniflow clunk tank, which I need 4.5 or so ounces of fuel on my la46 sized models. I have always thought the reason they tend to lean out beginning around the start of the overheads is the uniflow tube becoming uncovered. Is this correct thinking on my part?
Ray from Greensboro, North Carolina , six laps inverted so far with my hand held vertically!!! (forgot to mention, none level!) AMA# 902150

Offline Randy Cuberly

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3674
Re: Plastic uniflow clunk tanks
« Reply #7 on: April 24, 2017, 08:20:10 PM »
Regarding a 6 oz. plastic uniflow clunk tank, which I need 4.5 or so ounces of fuel on my la46 sized models. I have always thought the reason they tend to lean out beginning around the start of the overheads is the uniflow tube becoming uncovered. Is this correct thinking on my part?

Yes that's highly likely!  The farther forward the uniflo line is in the tank the sooner this will occur!  Some engines are more sensitive to this change than others!

Randy Cuberly
Randy Cuberly
Tucson, AZ

Offline Chuck_Smith

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 685
Re: Plastic uniflow clunk tanks
« Reply #8 on: April 25, 2017, 03:33:51 PM »
Interesting.

I find, and physics backs up the empirical evidence, that a uniflow tank goes rich once the vent is uncovered, since the pressure in the empty part of the tank increases once the vent is open to the ambient pressure.


I think a lot of people mis-understand exactly what happens in a uniflow tank. It automagically adjusts the pressure of the empty part of the tank in order to keep a constant pressure and thus constant suction head at the pickup as the tank empties.

Perhaps the most elegant engineering solution ever put on a model aircraft, originally done on FF.  
AMA 76478

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Plastic uniflow clunk tanks
« Reply #9 on: April 25, 2017, 05:01:37 PM »
Yes that's highly likely!  The farther forward the uniflo line is in the tank the sooner this will occur!  Some engines are more sensitive to this change than others!

Randy Cuberly

Which is why I try to put my uniflow as far back as I can while still having free movement of the clunk.
AMA 64232

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

Offline RknRusty

  • 2019 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2689
    • My Tube channel
Re: Plastic uniflow clunk tanks
« Reply #10 on: April 25, 2017, 06:18:38 PM »
When I first started using clunks, I tried different ways for making uniflow. I gave up on making a uniflow follower tube that moved with the pickup line, as it was always interfering with the movement. I tried making a uni line with a bend that went 3/4 of the way back to the outside corner and could be rotated for adjustments, but never got great inverted runs. I finally just wire-wrapped and soldered the two vent tubes at the very top, touching but chamfered to avoid sucking up to the top wall.
This arrangement gives me steady runs all the way up to one or two laps before shutoff when it leans and speeds up before cutting off clean with no fuel in the tank. Except for inverted, both during laps and at the tops of some maneuvers, the two siamesed vents stay dry the whole time. That consistency may not be true of my 6 inverted laps if there were less than an almost-full tank, but that early in the pattern, it's not an issue.

I'm not at all arguing with anybody because I didn't expect it to work so well, just saying this is how it worked for me with my LA 46 and FP 25, 35 and 40 engines, and it's easy to do. They all ran the same RPM inverted and upright.
Rusty
DON'T PANIC!
Rusty Knowlton
... and never Ever think about how good you are at something...
while you're doing it!

Jackson Flyers Association (a.k.a. The Wildcat Rangers(C/L))- Fort Jackson, SC
Metrolina Control Line Society (MCLS) - Huntersville, NC - The Carolina Gang
Congaree Flyers - Gaston, SC -  http://www.congareeflyer.com
www.coxengineforum.com

Offline ray copeland

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 871
Re: Plastic uniflow clunk tanks
« Reply #11 on: April 25, 2017, 07:17:35 PM »
Rusty K, you just might be on to something! I will give this a try sometime and see how I like the run.
Ray from Greensboro, North Carolina , six laps inverted so far with my hand held vertically!!! (forgot to mention, none level!) AMA# 902150

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Plastic uniflow clunk tanks
« Reply #12 on: April 25, 2017, 07:21:17 PM »
...
I finally just wire-wrapped and soldered the two vent tubes at the very top, touching but chamfered to avoid sucking up to the top wall.
...
This arrangement gives me steady runs all the way up to one or two laps before shutoff when it leans and speeds up before cutting off clean with no fuel in the tank.
...

You're probably using muffler pressure.  That's not a uniflow tank at all, but with the LA engines, a standard-vent tank on muffler pressure can give a very steady run.
AMA 64232

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

Offline RknRusty

  • 2019 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2689
    • My Tube channel
Re: Plastic uniflow clunk tanks
« Reply #13 on: April 25, 2017, 09:25:43 PM »
Tim, yes I am using muffler pressure. I prefer it because at our grass field, especially in the winter, dried grass bits are getting kicked up and we've seen crap traps get clogged with them on open vent uniflow systems. So I tried the closed loop with the muffler line to the tank and the problem was solved. Without a venturi filter, it's not 100% closed, but good enough. Also, it's always windy there and it eliminates the richening while flying into the wind. I've never tried a clunk with an open vent.

Ray, the first clunk I ever used was on the Skyray/fp .35 you gave me as a Beginner. It had a copper tube almost all the way back to the pickup, which I also ran to the muffler. But with new tanks that I assembled, I never could replicate the good run I got from it, so I came up with the solution I showed above.
Rusty
DON'T PANIC!
Rusty Knowlton
... and never Ever think about how good you are at something...
while you're doing it!

Jackson Flyers Association (a.k.a. The Wildcat Rangers(C/L))- Fort Jackson, SC
Metrolina Control Line Society (MCLS) - Huntersville, NC - The Carolina Gang
Congaree Flyers - Gaston, SC -  http://www.congareeflyer.com
www.coxengineforum.com

Online RC Storick

  • Forum owner
  • Administrator
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12393
  • The finish starts with the first piece of wood cut
    • Stunt Hangar
Re: Plastic uniflow clunk tanks
« Reply #14 on: April 26, 2017, 09:45:21 PM »
AMA 12366

Offline RknRusty

  • 2019 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2689
    • My Tube channel
Re: Plastic uniflow clunk tanks
« Reply #15 on: April 26, 2017, 11:11:39 PM »
Maybe I was using the wrong type fuel tube when I was doing that, I never could get it to fall into all the corners with the two tubes connected together.
DON'T PANIC!
Rusty Knowlton
... and never Ever think about how good you are at something...
while you're doing it!

Jackson Flyers Association (a.k.a. The Wildcat Rangers(C/L))- Fort Jackson, SC
Metrolina Control Line Society (MCLS) - Huntersville, NC - The Carolina Gang
Congaree Flyers - Gaston, SC -  http://www.congareeflyer.com
www.coxengineforum.com

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Plastic uniflow clunk tanks
« Reply #16 on: April 27, 2017, 10:07:38 AM »
Maybe I was using the wrong type fuel tube when I was doing that, I never could get it to fall into all the corners with the two tubes connected together.

Part of the uniflow magic is that the vent tube stays in one place.  A uniflow with two flexible tubes is going to behave differently.  I'm not sure differently how, but it'll behave differently.
AMA 64232

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

Offline Allan Perret

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1892
  • Proverbs
Re: Plastic uniflow clunk tanks
« Reply #17 on: April 27, 2017, 12:11:46 PM »
Heres another way to do the feed and uniflow tubes together.  I ground a groove in side of clunk (with edge of thin cutoff wheel on an angle grinder) to make a recess to solder in the brass tube.  I install this assy with brass tube outboard and the hole in side of brass tube is engine feed, and the clunk is the uniflow.  The end of brass tube is crimped and soldered shut.  I am using this in a profile with 6 oz slant oval tank so there really is no vertical movement of assy to speak of.  Getting a cleaner shut off than before with more conventional setup.  There is a shorter time between uniflow and feed becoming uncovered.

Correction, just took closer look at tank and my clunk assy is about 1/4" from rear tank wall and this does allow clunk to move vertically, looks like plus minus 1/2" relative to tank centerline.  And this setup is working good, don't understand why, but it does..
« Last Edit: April 27, 2017, 12:54:07 PM by Allan Perret »
Allan Perret
AMA 302406
Slidell, Louisiana

Offline Avaiojet

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 7468
  • Just here for the fun of it also.
Re: Plastic uniflow clunk tanks
« Reply #18 on: April 27, 2017, 12:27:37 PM »
Heres another way to do the feed and uniflow tubes together.  I ground a groove in side of clunk (with edge of thin cutoff wheel on an angle grinder) to make a recess to solder in the brass tube.  I install this assy with brass tube outboard and the hole in side of brass tube is engine feed, and the clunk is the uniflow.  The end of brass tube is crimped and soldered shut.  I am using this in a profile with 6 oz slant oval tank so there really is no vertical movement of assy to speak of.  Getting a cleaner shut off than before with more conventional setup.  There is a shorter time between uniflow and feed becoming uncovered.

Allen,

Wouldn't it work the same without that side hole and not soldering the tube end shut?

CB
Trump Derangement Syndrome. TDS. 
Avaiojet Derangement Syndrome. ADS.
Amazing how ignorance can get in the way of the learning process.
If you're Trolled, you know you're doing something right.  Alpha Mike Foxtrot. "No one has ever made a difference by being like everyone else."  Marcus Cordeiro, The "Mark of Excellence," you will not be forgotten. "No amount of evidence will ever persuade an idiot."- Mark Twain. I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King.   Proverb 11.9  "With his mouth the Godless destroys his neighbor..."  "Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane." David McCellan, 1980.

Offline Allan Perret

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1892
  • Proverbs
Re: Plastic uniflow clunk tanks
« Reply #19 on: April 27, 2017, 12:29:04 PM »
Part of the uniflow magic is that the vent tube stays in one place.  A uniflow with two flexible tubes is going to behave differently.  I'm not sure differently how, but it'll behave differently.
Yea that's the theory , but I have read where others put the uniflow attached to feed clunk and reported it works great. This in a full fuse using rectangle tank with normal clunk vertical movements.  Planning to validate this myself in next full fuse build, but will be using the Sullivan round and/or cylinder tanks.
Allan Perret
AMA 302406
Slidell, Louisiana

Offline Allan Perret

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1892
  • Proverbs
Re: Plastic uniflow clunk tanks
« Reply #20 on: April 27, 2017, 12:31:04 PM »
Allen,

Wouldn't it work the same without that side hole and not soldering the tube end shut?

CB
No, with engine feed and uniflow that close together the engine would be sucking air bubbles from the uniflow.  You need at least 3/8" separation between them..
Allan Perret
AMA 302406
Slidell, Louisiana

Offline Allan Perret

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1892
  • Proverbs
Re: Plastic uniflow clunk tanks
« Reply #21 on: April 27, 2017, 12:45:52 PM »
Neat tip from John Blanchard.  Solder brass nut to tube for easy adjustments.  This is the 6 oz Slant Oval tank.
Allan Perret
AMA 302406
Slidell, Louisiana

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Plastic uniflow clunk tanks
« Reply #22 on: April 27, 2017, 01:29:46 PM »
Yea that's the theory , but I have read where others put the uniflow attached to feed clunk and reported it works great.

I've seen that and don't disbelieve it.  I'm just not sure it should be called "uniflow" -- although, maybe for lack of a better term that's the one to use.
AMA 64232

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

Offline John Rist

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2944
Re: Plastic uniflow clunk tanks
« Reply #23 on: April 27, 2017, 01:45:14 PM »
Heres another way to do the feed and uniflow tubes together.  I ground a groove in side of clunk (with edge of thin cutoff wheel on an angle grinder) to make a recess to solder in the brass tube.  I install this assy with brass tube outboard and the hole in side of brass tube is engine feed, and the clunk is the uniflow.  The end of brass tube is crimped and soldered shut.  I am using this in a profile with 6 oz slant oval tank so there really is no vertical movement of assy to speak of.  Getting a cleaner shut off than before with more conventional setup.  There is a shorter time between uniflow and feed becoming uncovered.

Correction, just took closer look at tank and my clunk assy is about 1/4" from rear tank wall and this does allow clunk to move vertically, looks like plus minus 1/2" relative to tank centerline.  And this setup is working good, don't understand why, but it does..

It works because it is in the same relative position to mother earth inverted and up right.   I have tried the same setup but used the clunk as the fuel feed.  I think what you have done is a better way to do it.  I am guessing the purists are using rigid tubing.  ala the nut to twist the tube as posted above.   y1
John Rist
AMA 56277

Offline Avaiojet

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 7468
  • Just here for the fun of it also.
Re: Plastic uniflow clunk tanks
« Reply #24 on: April 27, 2017, 02:20:42 PM »
No, with engine feed and uniflow that close together the engine would be sucking air bubbles from the uniflow.  You need at least 3/8" separation between them..

Allen,

OK, I see.

I'll be using the 6 oz. Sullivan round/cylinder tank.

Only difference is my tank will be forward of the engine, or ahead of it. It's a pusher configuration. See how it goes.

CB
Trump Derangement Syndrome. TDS. 
Avaiojet Derangement Syndrome. ADS.
Amazing how ignorance can get in the way of the learning process.
If you're Trolled, you know you're doing something right.  Alpha Mike Foxtrot. "No one has ever made a difference by being like everyone else."  Marcus Cordeiro, The "Mark of Excellence," you will not be forgotten. "No amount of evidence will ever persuade an idiot."- Mark Twain. I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King.   Proverb 11.9  "With his mouth the Godless destroys his neighbor..."  "Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane." David McCellan, 1980.

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Plastic uniflow clunk tanks
« Reply #25 on: April 27, 2017, 02:27:11 PM »
It works because it is in the same relative position to mother earth inverted and up right.   I have tried the same setup but used the clunk as the fuel feed.  I think what you have done is a better way to do it.  I am guessing the purists are using rigid tubing.  ala the nut to twist the tube as posted above.   y1

Oh, that's the reason for the hexagonal thing on the tube -- to make it ambiguous whether you're commenting on the mechanism or the pilot when you say "the nut is twisting the tube"!
AMA 64232

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

Offline Chris Wilson

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1710
Re: Plastic uniflow clunk tanks
« Reply #26 on: April 27, 2017, 04:10:06 PM »
Part of the uniflow magic is that the vent tube stays in one place.  A uniflow with two flexible tubes is going to behave differently.  I'm not sure differently how, but it'll behave differently.

Hi Tim, a fixed uniflow vent is only stationary in regards to the fuel jet in the venturi- it is in effect a tuning device for invert to upright running.

A roaming (two tubes) uniflow vent disregards the fuel jets position and is not tuneable.

The roaming uniflow (attached to the clunk in effect) seems to work better inside a tank that has little hieght and therefore little vent movement to complicate things.
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline Steve Helmick

  • AMA Member and supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 9920
Re: Plastic uniflow clunk tanks
« Reply #27 on: April 27, 2017, 08:45:15 PM »
Why would you want to use a round tank in a CL model? It seems to me that you'd have a tough time getting the tank out and returned to the same clocking, which would mean you'd have to keep messing with the uniflow's internal (infernal?) end. On the other hand, you could just crank the tank (rhyme not intended, but...) to adjust for uniflow height. But how would you make it stay put from flight to flight, or even start>finish during one flight?

FWIW, the scheme RknRusty diagrammed is much the same as a Hayes tank. If you want to use a clunk tank, the Hayes tanks are easily the most leak resistant and easiest to use. Not 100% certain they work the best, but Dirt still liked them the last we heard from him.  ;) 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 Randy Cuberly

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3674
Re: Plastic uniflow clunk tanks
« Reply #28 on: April 28, 2017, 12:21:21 AM »
Interesting.

I find, and physics backs up the empirical evidence, that a uniflow tank goes rich once the vent is uncovered, since the pressure in the empty part of the tank increases once the vent is open to the ambient pressure.


I think a lot of people mis-understand exactly what happens in a uniflow tank. It automagically adjusts the pressure of the empty part of the tank in order to keep a constant pressure and thus constant suction head at the pickup as the tank empties.

Perhaps the most elegant engineering solution ever put on a model aircraft, originally done on FF.  


Of course you're absolutely right Chuck!  I must have been asleep last night when I answered that question.  The engine will go slightly rich when the uniflo line is uncovered with fuel.  The exception of course is if there is a leak in the tank or the tank is actually not plumbed as a uniflo system, which I suspect is the case in Mr Copelands set up!

My apologies for complicating the question.  They tell me I'm a smart guy except when I'm OLD and it's past my bedtime!   LL~ LL~

Randy Cuberly
Randy Cuberly
Tucson, AZ

Offline Allan Perret

  • 2017
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1892
  • Proverbs
Re: Plastic uniflow clunk tanks
« Reply #29 on: April 28, 2017, 08:39:56 AM »
But how would you make it stay put from flight to flight, or even start>finish during one flight?
 Steve
Allan Perret
AMA 302406
Slidell, Louisiana

Offline Avaiojet

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 7468
  • Just here for the fun of it also.
Re: Plastic uniflow clunk tanks
« Reply #30 on: April 28, 2017, 09:12:50 AM »
Allen,

Similar to my application except my tank is sideways and in front.

So I guess it's not similar at all.  n~

Nice engine.  H^^

CB
Trump Derangement Syndrome. TDS. 
Avaiojet Derangement Syndrome. ADS.
Amazing how ignorance can get in the way of the learning process.
If you're Trolled, you know you're doing something right.  Alpha Mike Foxtrot. "No one has ever made a difference by being like everyone else."  Marcus Cordeiro, The "Mark of Excellence," you will not be forgotten. "No amount of evidence will ever persuade an idiot."- Mark Twain. I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King.   Proverb 11.9  "With his mouth the Godless destroys his neighbor..."  "Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane." David McCellan, 1980.

Offline Fredvon4

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2099
  • Central Texas
Re: Plastic uniflow clunk tanks
« Reply #31 on: April 28, 2017, 10:42:20 AM »
I always focus on these threads and think I have a fair understanding of How Uniflo works

But I can say with a lot of certainty trying to make any plastic, under 3 Oz tank, a clunk uniflo is exceptionally frustrating....especially any 2.5 Oz with a slant front opening for a profile

Sure do wish there was a good source for true Hayes 3 Oz to 3.5 Oz  tanks....I have 2 Hayes 4 oz but they are long narrow and not well suited for BBTU on profile at all

My Pseudo BBTU powered RST has a Brodak standard vent 2.5 Oz wedge on muffler and runs very well for my hack sport flying

« Last Edit: April 29, 2017, 07:01:20 AM by Fredvon4 »
"A good scare teaches more than good advice"

Fred von Gortler IV

Offline Akihiro Danjo

  • 23 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 164
Re: Plastic uniflow clunk tanks
« Reply #32 on: April 29, 2017, 11:21:36 AM »
OK Model aka Pilot bland 80cc (3 oz) tank fits and works well on profile models like S-1.
I use the tank for my S-1 and Skyray with FP/LA 20/25.
Aki

Offline Fredvon4

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2099
  • Central Texas
Re: Plastic uniflow clunk tanks
« Reply #33 on: April 29, 2017, 12:05:53 PM »
Akhiro

Doumo arigatou gozaimasu

Thank you very much

I will seek out one or more of that tank to try
"A good scare teaches more than good advice"

Fred von Gortler IV

Offline Ara Dedekian

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 488
  • Ara Dedekian
Re: Plastic uniflow clunk tanks
« Reply #34 on: May 20, 2017, 04:28:04 AM »
This is my setup for 4oz tank.
Aki


          This my set up using Aki's diagram. I left out the overflow and tip the plane on it's nose to fuel throught the vent. The flight I had with this tank was flawless.

          I started flying C/L at about nine or ten years old and am still at it. I'm 74(?) now. This setup gave me the confidence, for the first time, to attemp the last three holdout maneuvers on the pattern; the vertical eights, the hourglass and the cloverleaf. It's great not to worry about the plane and just concentrate on cleaning up the maneuvers.

          The model is an RC swap shop Twister upgraded with taped hinges, proper control throws and a pushrod keeper. My OS FP 40-9/5 prop up front.

          Ara

Offline Richard Imhoff

  • 2019 supporter
  • Trade Count: (0)
  • Lieutenant
  • *
  • Posts: 109
Re: Plastic uniflow clunk tanks
« Reply #35 on: May 20, 2017, 12:06:37 PM »
Here's the setup I have been using a clunk uniflow and an adjustable mount. Just glue the tank to a plywood or aluminum mount with Shoe Goo, this stuff stick anything to anything permanently.

Dick Imhoff  AMA 58502
 
Combat, Racing, Stunt, and big time fun flyer, and Maybe a bit of carrier.

Offline kiwibrit

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 50
Re: Plastic uniflow clunk tanks
« Reply #36 on: January 02, 2019, 02:57:08 PM »
Heres another way to do the feed and uniflow tubes together.  I ground a groove in side of clunk (with edge of thin cutoff wheel on an angle grinder) to make a recess to solder in the brass tube.  I install this assy with brass tube outboard and the hole in side of brass tube is engine feed, and the clunk is the uniflow.  The end of brass tube is crimped and soldered shut.  I am using this in a profile with 6 oz slant oval tank so there really is no vertical movement of assy to speak of.  Getting a cleaner shut off than before with more conventional setup.  There is a shorter time between uniflow and feed becoming uncovered.

Correction, just took closer look at tank and my clunk assy is about 1/4" from rear tank wall and this does allow clunk to move vertically, looks like plus minus 1/2" relative to tank centerline.  And this setup is working good, don't understand why, but it does..

Thank you for your very useful post.  I directly followed your advice on preparing the uniflow pipe and soldering it to the clunk. The output tube was connected to the central tank neck tube facing outboard.  The inflow tube was concocted to the lower neck tube facing inboard.  The tank was located in its usual position on the model (a little above the centre line of my OS FP40 powered profile model).  The result was an excellent even run throughout the flight.  The only minor snag is there is almost no warning of engine cut out.  Not a problem when flying the schedule on a known volume of fuel, but I do keep an eye on the clock when free flying to practise specific manoeuvres.

Offline Paul Smith

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 5793
Re: Plastic uniflow clunk tanks
« Reply #37 on: January 13, 2019, 06:58:14 PM »
You're probably using muffler pressure.  That's not a uniflow tank at all, but with the LA engines, a standard-vent tank on muffler pressure can give a very steady run.

Finally - one other person who understands that a pressure tank is NOT really uniflow, even if the pressure input is submerged.
Paul Smith

Offline kiwibrit

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 50
Re: Plastic uniflow clunk tanks
« Reply #38 on: January 14, 2019, 02:32:27 AM »
As I understand it, a uniflow tank is  a sealed tank with the air vent (uniflow) submerged in the fuel. I can't see that whether or not the vent is pressurised changes that.  In any case, semantics apart, what I am after is a tank that gives an even run throughout the flight - though some warning a lap in advance of the engine cutting is nice. Thus whether or not the tank should be called 'unfilow' if under pressure does not matter.  My own experience is that for most of my engines, a uniflow tank benefits pressurised runs as well as unpressurised runs.  In the case of my tank I referred to above, the vent has muffler pressure.

That said, I know that people have strong opinions about tanks.  Whatever works for you is fine.  But we can sometimes benefit from seeing what works for someone else and trying it. So whether or not my tank is uniflow as I am using it under muffler pressure, I am grateful to Allan Perret because his clunk arrangement has solved a persistent problem I had.

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13716
Re: Plastic uniflow clunk tanks
« Reply #39 on: January 14, 2019, 10:54:50 AM »
Finally - one other person who understands that a pressure tank is NOT really uniflow, even if the pressure input is submerged.

    I am not sure what point you are trying to make, but you are probably wrong. It works the same, all you are doing is changing the pressure reference from atmospheric pressure to muffler pressure. The effect is to raise the feed pressure to the muffler pressure, but otherwise it holds the a setting independent of the fuel depth, and to first approximation, holds the mixture constant.

     It contains (hypothetically) two additional negative feedback loops.

The first is where the mixture is also controlled by the muffler pressure, which is (imagined to) go up with RPM, in which case the mixture is richened, which (presumably) slows the engine, (possibly) lowering the muffler pressure to go back down. This is all presumptive of the fact that that the muffler pressure goes up as the engine leans out/speeds up. That might happen, but at best the effect is weak, and it is not clear to me that this is what would happen in flight, given that the residual combustion pressure on the firing strokes is MUCH higher in the 4 than in the 2 (which is also why you don't get twice as much power when it goes from 4 to 2).

     Ram air into the (open) uniflow vent has the same effect, and is more reliable - and sometimes works too well. Most people prefer to run neutral or slight ram air effects over at least pipe pressure.

The second is where the exhaust heat warms the fuel through the flight, causing the fuel viscosity to go down, slowly making the engine go richer - or suddenly causing it to foam from vibration, which provides positive feedback and an unstable system. When/how this happens seems pretty unpredictable, and only certain cases are reliable in this sense. It also changes radically when your starting fuel temperature not constant - cold days has much more drastic effects, particularly near the end of the tank, when the volume of fuel goes down, it heats up faster, and if it was really cold to start with, you have opened the needle a lot to get the fuel, and now it needs to be closed down again.

  Testing is the only way to tell what is going to happen in any specific case. I would greatly prefer to not use muffler pressure because of the sometimes unpredictable behavior, but when it works it definitely has a beneficial effect, uniflow or suction.

    Brett

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13716
Re: Plastic uniflow clunk tanks
« Reply #40 on: January 14, 2019, 11:08:31 AM »
Thank you for your very useful post.  I directly followed your advice on preparing the uniflow pipe and soldering it to the clunk. The output tube was connected to the central tank neck tube facing outboard.  The inflow tube was concocted to the lower neck tube facing inboard.  The tank was located in its usual position on the model (a little above the centre line of my OS FP40 powered profile model).  The result was an excellent even run throughout the flight.  The only minor snag is there is almost no warning of engine cut out.  Not a problem when flying the schedule on a known volume of fuel, but I do keep an eye on the clock when free flying to practise specific manoeuvres.

   You want the "no warning cutoff", because that way you don't have to suffer with the engine changing in the last few maneuvers, or putting in a lot of extra fuel to avoid it.

    The old problem with attaching the uniflow to the clunk is that it tends to bind up the movement of the clunk. Your fellow countryman Peter "Greasy Pete" Deane showed us a different method, where the end of the uniflow tube was a conventional brass/copper tube, but with a loop of wire where the tube was captured but a slip fit, so the clunk could move freely without the restriction of two silicone tubes, rigidly connected, cause. You can make it work the way you are doing it, but I have always had to intentionally curve some preload into the rubber tube to force the clunk to the outside of the circle.

   An alternative is to use this tubing:

https://www.hobbyzone.com/sullivan/sul211.html?utm_source=Google&utm_campaign=Google+Shopping&msclkid=43fe5e16c582140bc09a022a0a9c0fa9

    which is exactly as advertised, very flexible, almost as flexible as gum rubber tubing, but not prone to self-destructing after a few months.

   For clunk tanks I always ended up with fixed vent tubes, just copper that goes up against the side of the tank, so it was adjustable for height. I am not a big fan of them, but they do seem to have greatly reduced flow restrictions over the usual rigid tanks (something that was discovered in the 4-stroke hype days) for reasons I don't really understand.

     Brett

Offline Dave Hull

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1901
Re: Plastic uniflow clunk tanks
« Reply #41 on: January 14, 2019, 02:43:30 PM »
Regarding the apparent reduction in flow restriction with a plastic tank:

It may be possible that the tank is flexible enough to help compensate for the "square wave draw" coming from the rotary valve. If you imagine an absolutely rigid tank the fuel is going to have to stop and start very rapidly, which will take more energy and impede the average flow. If a flexible tank is soft enough, it may allow the fuel to move with less acceleration/deceleration on its way to the needle. Of course, it is not that simple. If the tank is vented, then the incoming air should provide compensation.

I don't have anything like the necessary instrumentation to directly observe the effect to refine the idea, to disprove it, or to confirm....

I'm imagining a bench setup with an old, thirsty, slow-running cross-flow engine being feed thru a glass tube right before it goes into the needle valve. Next, mix a non-abrasive impurity to use as a "marker" in the fuel. Think about some flecks evenly suspended in the fuel and you get the idea. Then use an extremely high speed camera with a close-up lens to observe the fuel delivery rate thru the glass tube. The sample rate should be >10 times per engine revolution to really confirm what is going on. Run the test for a very rigid tank and then for a flex tank and compare.

Of course, we can keep doing what we always do--fiddle with the tank and the tubing until it works pretty good. Or just start swapping tanks, engines, fuel, filters, etc. until we can live with it--or give the plane away and start another random trial....

I am a little skeptical of the muffler pressure viscosity argument. My reasoning is that there is not going to be a lot of heat involved. By definition, the tank is part of a closed system using pressure, and the most "flow" you should get is exactly one tank volume. So we have the delta T of ambient temp (fuel temp) and say 3 or 4 cubic inches of heated exhaust with some oil contaminants. It would be interesting to do the calculations and see exactly how many degrees temp rise that would have if the heat transfer to the fuel was 100% (it won't be), and if it was fully mixed (probably a pretty good assumption due to the maneuvering.) Then look at the temp-viscosity chart and see how much change to expect. Of course, while the oil chart should be easy to come by, we'd have to create our own fuel viscosity chart.  I've run similar calculations for full scale aircraft bleed air systems and the heat content was not nearly what I assumed (hoped?) it would be.

Dave

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Plastic uniflow clunk tanks
« Reply #42 on: January 14, 2019, 05:11:18 PM »
   You want the "no warning cutoff", ...

If you want a "short warning cutoff" (about 1/3 lap) use a remote needle valve.   >:D
AMA 64232

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

Offline kiwibrit

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 50
Re: Plastic uniflow clunk tanks
« Reply #43 on: January 15, 2019, 12:25:08 PM »
As a related point, if you go to about 2:20 on this video, it is very interesting to see what is happening to the fuel in a clunk tank, once a fair amount of fuel has been used.


Offline GERALD WIMMER

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 622
    • Auckland Free Flight Club
Re: Plastic uniflow clunk tanks
« Reply #44 on: January 17, 2019, 04:29:19 AM »
Hello Thanks Kiwibrit, Shug's video was interesting watching, the fuel was all over the place depending on the attitude the model was in. Looks like the engine must take in some air as it sloshes about, particularly at the end of the run.
Regards Gerald

Online katana

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 161
Re: Plastic uniflow clunk tanks
« Reply #45 on: January 17, 2019, 06:35:16 AM »
Hello Thanks Kiwibrit, Shug's video was interesting watching, the fuel was all over the place depending on the attitude the model was in. Looks like the engine must take in some air as it sloshes about, particularly at the end of the run.

But surely that's the point of having the 'clunk' on the feed line - it goes where the fuel goes. It was interesting that the fuel seemed to vary more top to bottom via G forces but didn't seem to be thrown to back of the tank through forward momentum?

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13716
Re: Plastic uniflow clunk tanks
« Reply #46 on: January 17, 2019, 07:51:55 AM »
But surely that's the point of having the 'clunk' on the feed line - it goes where the fuel goes. It was interesting that the fuel seemed to vary more top to bottom via G forces but didn't seem to be thrown to back of the tank through forward momentum?

   The forces driving it fore/aft are far, far less than the centrifugal force. In level flight there is no tendency at all to go to the back of tank, for instance - no fore/aft acceleration, it's steady level flight. In the maneuvers, the fuel wants to go forward, and to the back slightly when exiting. But that probably never gets as big as 1 G. The centrifugal force just flying level is 2.5Gs and in the round maneuvers it's something like 8 Gs, getting up to around 13-14Gs in the corner.

   Brett

Offline Dave Hull

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1901
Re: Plastic uniflow clunk tanks
« Reply #47 on: March 15, 2019, 02:45:52 PM »
Just ran some initial tests on fuel viscosity. I lack calibrated instrumentation, but the results should be valid for relative comparisons.

Fuel:  5N/18Techniplate/77Methanol

Setup:  Gravity feed from 5 fl. oz. syringe with 2" long medium diameter silicone fuel outlet. This was a convenient substitute for a calibrated viscosity cup, which I do not have. So no direct comparison can be made in actual centistokes

Sample volume:  5 fl. oz.  (When heated, the expansion produced a little more than 1/8 fl. oz. increase, which I kept in the same to retain mass/energy)

Baseline tests all around 60F. Very good repeatability. Timed duration right at 51.4 seconds (3 samples)

Heated samples in the range of 120 and 125F had a duration of approximately 48 seconds. A total of 8 runs so far, between 108F and 130F.

Still getting a significant amount of data scatter on the heated samples, probably because there is a lot more happening, and I only have two hands.

Hope to try some cold samples as well in order to get a curve fit.

I have a few different fuel filters I would like to put into the line and see the impact of that. Including a Sullivan 187 double screen filter. Next, it would be nice to include an OS needle valve assembly set to about 3-1/2 turns as a typical restriction. And see how the duration varies. Of course, it would be interesting to test some 10N/29C/61M fuel and see how it behaves.

No time yet to do the calcs on the heat content of the tank "inerting" with muffler exhaust. Maybe soon.

Divot McSlow


PS--I did not find any chemistry of the viscosity of mixtures--and I probably would have been skeptical anyway--so a test was the only way forward.
« Last Edit: March 15, 2019, 06:18:32 PM by Dave Hull »

Offline Dave Hull

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1901
Re: Plastic uniflow clunk tanks
« Reply #48 on: March 16, 2019, 04:35:46 PM »
Collected a bit more data in between sanding an ever-changing cowling design and cleaning the shop....

Adding a Sullivan filter creates a restriction that increases the gravity drain duration to 62.13 seconds, or by about a third. The comparison measurement was a little off due to iphone stopwatch mishandling. Lost my real watch at the last racing contest...

If you figure that the needle valve needs to be the governing restriction in the fuel line, it can be opened up to compensate for other fuel line restrictions. But when the total losses (lines, bends, fittings, filters, and needle valve) become great enough to reduce flow below the engine needs in the most critical orientation, then its going to burp lean. If the critical condition is longer duration, it won't just be a burp, it will last until the conditions change back to something more favorable. I would think that muffler pressure would have the positive stabilizing effect of increasing the fuel flow as rpm increases since the venturi size is fixed.

Dave

Online Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13716
Re: Plastic uniflow clunk tanks
« Reply #49 on: March 16, 2019, 08:41:32 PM »
If you figure that the needle valve needs to be the governing restriction in the fuel line, it can be opened up to compensate for other fuel line restrictions. But when the total losses (lines, bends, fittings, filters, and needle valve) become great enough to reduce flow below the engine needs in the most critical orientation, then its going to burp lean. If the critical condition is longer duration, it won't just be a burp, it will last until the conditions change back to something more favorable.

   The apparent mechanism is that the fuel flow required to hold the mixture constant isn't remotely steady. The fuel flow is both pulsing in 185 Hz spurts, it also needs to vary as the air flow changes (on a fractions of a second basis). When air flow goes up, the draw goes up, too, but it also tends to go lean because the restrictions don't permit the fuel flow to change as much as necessary. That's why reducing the restrictions tend to reduce or eliminate the momentary (fraction of a second) lean/2-stroke blips and chirps.

   There is*no* issue with the overall average flow, even the smallest passages are OK for the largest stunt engines in a static sense. It's not necessarily good enough in a dynamic sense.

   Again, plenty of people will argue that their engines "never do this" and/or that it's normal or desirable. Even when it is pile-driving them towards the ground.

Quote
I would think that muffler pressure would have the positive stabilizing effect of increasing the fuel flow as rpm increases since the venturi size is fixed.

     The positive feedback for the muffler or pipe pressure is a very slow effect. The fact that the pressure is there constantly might actually make the effect worse, because it reduces the size of the worst restriction of all - the restriction at the needle - because you have to screw the needle in to get the right steady-state mixture.

    Brett


Advertise Here
Tags:
 


Advertise Here