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HelicopterGasser Model RC HelicoptersOther › Bending tubes and Tank Construction
11-28-2005 04:05 PM  12 years agoPost 1
AceBird

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Utica, NY USA

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I have been asked to elaborate on bending brass tubing for fuel tanks so here is my long and drawn out lecture.

*There are plenty of photos in my Gallery under the heading of “tank construction” that may help you visualize this procedure.

Typically the brass tubes come in about a 3 inch length but you can usually buy a 12 inch length from you local hobby supply if you ruin the ones that come with your tank on your first try.

The tubes measure .125 +-.002 OD. So get a small piece of aircraft ply that is 1/8 inch thick. Wood is better to use than metal or plastic because you can crush its thickness so the brass tubing will be slightly gripped by the vice while the plywood anvil is greatly gripped by the vice. Of course this requires the wood to be thicker than the brass tube. If it is not just add layers of tape so it is. If you are head strong about using a plastic or metal anvil then is must be .002-.003 thicker than the OD of the tube.

1. First sand, grind, file, what ever, the radius you want the bend to be on one corner of the plywood anvil. The corner radius should be larger than the tube diameter. Maybe you want to try 3/16 for the first time. The bigger the radius the easier it is to bend and the less likely it is to kink (you knew that already).
2. Measure where you want the bend to be and put a mark on the plywood.
3. Tape the tube to the edge of the plywood at the mark. I used colored masking tape to make it show up better in the pictures. Any tape will work if it is not slippery to the point that it allows the plywood to move in the vice.
4. Another piece of 1/8 plywood is “V” grooved about 1 inch wide to use as a blocking tool that actually makes the bend. It is best if the “V” groove is put in the edge of the plywood that has the most end grain plies. Here you could use plastic or metal but it must be slightly thinner then the clamped distance of the vice.
5. Clamp the taped tubing and plywood into the vice jaws crushing the wood until the outside edges of the brass tube are gripped. There should be enough space in the top of the jaws for the tube to fit into when it gets bent. It will be easier to bend the tube in two steps. For example, 45 degrees at a time for a 90 degree bend.
6. By hand push the side of tube as shown in the photo, starting at the cornered radius and follow the tube as it bends right into the space between the vice jaws.
7. Remove the tube from the vice and the tape from the tube and immediately start grinning with pride on how nice you bent the tube.

Make sure you spit on the tubes (lubrication) before inserting them into the stopper. If the tubing has been cut be sure that the ends do not have sharp edges especially on the fuel pick up line. The clunk should be ¼ inch away form the end of the tank when it is hung straight down. Many people make this too close which can prevent it from swinging freely in the tank. They don’t realize that when you tighten up the bung it tends to move inward toward the opposite side of the tank. BTW I use thin walled Neoprene tubing between the brass tube and the clunk. It is very flexible but will not collapse or kink during use. I do not use any type of wire tie or clamps on the inside of the tank.

The vent tube has to be gently bent by hand after the stopper nut and screw are assembled. Some tanks have a vent bubble for the end of this tube to enter while others have no provisions. You do not want the tube rubbing on the inside surface of the tank. Gassers run for a long time. It isn’t worth wearing a hole in the tank just so you can get 3 more cc of fuel in it.

I hope this is a help to anyone having trouble bending brass tubing and avoided using the stopper access to the tank as a result of the difficulties bending the tubes.


Ace

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11-29-2005 01:24 AM  12 years agoPost 2
GREYEAGLE

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Flat Land's

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I purchased a $3 dollar Du Bro bender & my self and about four others use the heck out of it. Prior to that I used to slip a piece of sullivain 504
cable or throttle cable down it / make the bend / then pull it out - never had one collaspe. To cut the tubing I just roll it under my knife, if you want it necked down a bit so it doest chaff the fuel tubing use a 1/8" Ridged tubing cutter. Always debur the inside and always wire wrap unless you like to ponder over fuel problems and do a tank arckology dig at the field and tear down. The trick is to stretch the tubing around the radius with out collasping it.

greyeagle

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11-29-2005 04:53 AM  12 years agoPost 3
ShempHoward

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San Francisco, Ca - too many beggars + bad drivers

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What Planet are you guys on??? Haven't you ever heard of annealed brass fuel tubing??? You can easily bend any shape you want with your hands unlike the stiff non-annealed brass fuel tubing you guys are speaking of. No jigs or tools needed to bend it other than a way to make clean burr free end cuts.
You can also anneal your own stiff brass fuel tubing by heating it with a butane/propane torch but this process takes some skill to acquire. Have your LHS order annealed brass fuel tubing. K+S makes it.

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11-29-2005 02:44 PM  12 years agoPost 4
AceBird

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Utica, NY USA

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QUOTE>

What Planet are you guys on??? Haven't you ever heard of annealed brass fuel tubing??? You can easily bend any shape you want with your hands unlike the stiff non-annealed brass fuel tubing you guys are speaking of. No jigs or tools needed to bend it other than a way to make clean burr free end cuts.
You can also anneal your own stiff brass fuel tubing by heating it with a butane/propane torch but this process takes some skill to acquire. Have your LHS order annealed brass fuel tubing. K+S makes it.

END QUOTE>


Last I looked out the window it was still earth.

I was PM’d a while back on how I would bend the brass tubes for use in a typical fuel tank. The above post is my answer. It took awhile to get the photos made and uploaded to my gallery that should help clarify any confusion in my discussion.
ShepHoward are you the guy that complains of fuel leaks around the tubes in the bung because you use dead soft tubing that collapses over time? Or are your tubes used for other applications and you don’t run them through the bung anyway?? You can anneal the tube at the bend but not where it goes through the bung … that gets hairy. The annealing process would be difficult to do accurately enough with a flame.

GreyEagle, I was unaware that you could buy a tubing bender for 3 bucks. However, some people enjoy making their own tools. I would be one. Once you know what is required to make a successful bend you can modify your tool to make more complicated bends. Some tubing benders will not allow you to make two bends very close to each other.
Now you mentioned throttle cable as a mandrel for bending. I can’t picture making a 3/16 diameter, 90 degree bend with throttle cable (or anything else) and still be able to get it out of the tube. Also, the cable you speak of is 1/16 which would allow the tube to collapse considerably and reduce flow. Do you have a picture of such a bend? It has been my experience that you do not need to wire tie the neoprene hose in the tank. I would suggest not wire tying the tubing because it might be cut by the wire. The G-forces that a fuel tank sees in an airplane can be ten times that of a helicopter. I have yet to see a tube come off inside one of my tanks even in a full bore crash which is the maximum G-force the tank will see.
I use a ¼ inch drill by hand to deburr the inside of a cut tube but it is the outside edge that is most important to deburr because that is what will cut the tube as it flexes.

Now here we have completely opposing viewpoints. That is not uncommon in this hobby is it? We should not look at these as arguments that turn into insults. Let the reader decide for themselves what makes sense to them. If they choose a path and it doesn’t work out for them they will change and never go back.

Ace

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11-29-2005 08:41 PM  12 years agoPost 5
ShempHoward

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San Francisco, Ca - too many beggars + bad drivers

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Ace - My apologies if I offended you but it struck me as very odd that you did not mention the ease of use of a quality brand of annealed brass fuel tubing when assembling your tanks. I have been using it for many years now in both planes (mostly) and helis and I cannot understand why anyone would opt for the non-annealed version. No problems with inserting the tubes in the stoppers and/or end caps and no leaking problems either using this type of tubing.

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11-30-2005 02:08 AM  12 years agoPost 6
FCM

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Surrey, England

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This may help:

To anneal brass tubing, first rub some normal everyday soap onto the tube, then hold over your flame until the soap turns black, then quench, preferably in a sulphuric acid bath but if the missus won't let you have one of these in her kitchen (strangely enough mine won't), then use water. The black soap residue is easily cleaned off before you start your bending.

Also works for aluminium and copper. Does NOT work for aluminium alloy.

Paul.

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11-30-2005 02:52 AM  12 years agoPost 7
GREYEAGLE

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Flat Land's

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Maybe it's a sullivain 503, All I know I carry a bodacious inventory and all sizes are always slidding off the pegs and the cat runs off with em. Far as wire tie I do it. If it can be safed, or prevented, eliminate risk. I have one bird I can wrench so hard I fling the clunk to the front / clunk stays on. If you really want to practice try aluminum and wind a smoke coil to fit inside your muffler, or copper to make a cooling coil for liquids. For those of you needing tie material find some one who works with underground utilities and ask for a piece of drop trunk line that still has the paper wrap on the 200 individial 30 guage solid strands. 3 'chunk will last along time although I'm on my fourth. Take a 3" piece, pull the paper off, fold it back, twirl it tight with hemostat's, STOP before you pinch cut it, fold it back, cut it off with your toe nail clippers.

I dont' fix other's fuel tanks at the field, I came to fly. You want to learn how to dry out a fuel soaked bird ?

greyeagle

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11-30-2005 02:08 PM  12 years agoPost 8
AceBird

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Utica, NY USA

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QUOTE>

Ace - My apologies if I offended you but it struck me as very odd that you did not mention the ease of use of a quality brand of annealed brass fuel tubing when assembling your tanks. I have been using it for many years now in both planes (mostly) and helis and I cannot understand why anyone would opt for the non-annealed version. No problems with inserting the tubes in the stoppers and/or end caps and no leaking problems either using this type of tubing.

END QUOTE>


It has come apparent to me that the way I communicate is not the message that I intend to give. It seems that when I contradict someone’s viewpoint I do it is such a way that it gets received as condescending, belligerent, or demeaning. I am truly sorry that I come across this way. I wish I had more skills in communication to match the technical skills that I have acquired.

To answer your post:
You haven’t offended me. I see every opposing viewpoint as a challenge of ideas, nothing more. I guess where I go wrong is where I use sarcasm with the intent that it will make you think as opposed to getting you angry.

The trouble with the word “annealed” is it doesn’t say much. All drawn tubing and wire (same process) has to be annealed several times in order to make it. The question is how many dies has it gone through after the last annealing process. This will determine its temper. If the tube that you claim is annealed were dead soft you could collapse it with your fingers. If it were fully hard it would snap like macaroni. Obviously these tubes are somewhere in between. You will never get temper specification out of hobby suppliers. It is a marketing game selling mostly perceived notions.

I did mention buying raw stock tubing (12in length) from a hobby shop.

I am a little perplexed at FCM’s post on his annealing process. The minute you quench a metal it will get harder. Annealing requires heating the metal to a point (different for every metal) and then bringing the temperature down slowly. Usually it can be just cooled in air, but some metals require a very controlled cooling process. Air harden tool steel would be one of them.

My word of caution for annealing is the oxidation that will occur on the inside of the tube. This will flake off and clog filters, or the carburetor jets. FCM’s acid bath will clean the tube of this oxidation. So maybe he has seen an annealing process somewhere and assumed that the acid bath was for quenching when actually it is for cleaning.

The advantage of not messing with the tubes that are supplied with the tank is that after they are bent they will stay because the tube is now harder then is was at the bend. I would have to say that the tubes that come with the tanks are of the right temper for their intended use. The bending process that I have previously outlined can be done by anyone with time and patience. Or you can buy a tubing bender. Some of them work well and some don’t.

Ace

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11-30-2005 07:27 PM  12 years agoPost 9
avator

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New Jersey

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The G-forces that a fuel tank sees in an airplane can be ten times that of a helicopter.
Since when???

Apparently, you've never seen anyone perform the wall with a heli. G- forces come from a change in direction, such as, pulling out of a dive. I haven't seen any plank that can change direction faster than a heli. Airplanes pulling ten times the amount of G's as a helicopter....absurd.

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12-01-2005 06:52 AM  12 years agoPost 10
FCM

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Surrey, England

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Yes, acid is best but even if you use this, there is still a risk that deposits formed by the heating will cause FOD. On occasions when I have done this, I try and ensure the tubing is thoroughly cleaned afterwards, both inside and out, before I work the tubing into shape.

The trouble is, there is no real easy way to anneal brass tubing without oxidation deposits occuring.

Paul.

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12-01-2005 10:58 AM  12 years agoPost 11
gyan

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Surrey, BC Canada or Blaine Wa.

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ACE I know copper is annealed by quenching in water, but I don't know about brass.

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12-02-2005 05:51 AM  12 years agoPost 12
wedge

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Victoria BC, Canada

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Here is the way I bend tubing, I ve done it with alum, and brass, I just find a piece of electrical wire that fits good inside the tubing, bend it with a tube bender, I ve used a automotive bender, this gives bigger radius, or anything round you can use, after the bend is made pull the wire out, you get a perfect bend with no kinking. It really does work, great give it a try.

Victoria BC, Canada, Century Swift,Trex SA 450, Hummingbird V3.

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12-02-2005 02:19 PM  12 years agoPost 13
AceBird

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Utica, NY USA

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QUOTE>

I haven't seen any plank that can change direction faster than a heli.

END QUOTE>>>

Really? I thought you had a lot of experience?

OK, I admit, ten times may be an exaggeration but two or three wouldn’t. Without getting into computations, a jet pilot has a device that squeezes his legs and thighs to try and keep the blood in his brain so he doesn’t black out during maneuvers. I have never heard of such a thing for a helicopter pilot.

>>>>>>>>>>>>>>>

QUOTE>

ACE I know copper is annealed by quenching in water, but I don't know about brass.

END QUOTE>>>

Reference:
http://www.key-to-metals.com/Article25.htm

The above link will explain Annealing and tempering. Brass has copper in it.

There is no way the average hobbyist will have the controls necessary to get accurate tempering. Hobby supply shops do not have access to the exact composition of the tubes they sell. So with out that information heat treatment is futile. The curse about annealing a brass tube is the oxidation that will occur inside the tube that you better clean out before you use it for fuel.

Tube Bending:

There are two methods of bending tubing. One is to use a mandrel … put something inside the tube before bending and remove it afterwards. This method is not appropriate for 90 degree sharp bends because you cannot extract the mandrel. A version of mandrel bending is to pack a tube full of sand, or powdery substance and seal the ends of the tube then bend it. Then unseal the ends of the tube and remove the media. This doesn’t always work that well. The second method is the die method. A die contains the outside shape of the tube so it can’t go egg shape while bending. It also dictates the radius of the bend. The die must fit closely to the outside diameter of the tube to prevent collapsing. The drawback is a different die is required for every size tube and for every size radius of bend. My method is a version of the die method where you sand the wooden anvil to the radius you want and contain the outside diameter of the tube with the jaws of the vice. You will be hard pressed to beat the quality of the bends for sharp radii if you use this method.

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12-03-2005 02:56 AM  12 years agoPost 14
wedge

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Victoria BC, Canada

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You are talking about realworld planes and heli's, and that would be a G-suit you are refering to, well, sorry we are talking about model heli's and model planes. There is no way in the world a real heli can fly like a model heli, and even if it could there is no way a pilot could stand such a style of flying as 3D in a real heli. I would say G-forces in a model heli are far more then a model plane.

Victoria BC, Canada, Century Swift,Trex SA 450, Hummingbird V3.

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12-03-2005 05:11 AM  12 years agoPost 15
3dwanabe

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Huntersville, NC

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Fixed wing models can produce much greater G-loads than helicopters. They can achieve higher terminal velocity before pulling out of a dive. State of the art DS sailplanes can easily fly over 200MPH!

Roy

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12-03-2005 05:57 AM  12 years agoPost 16
wedge

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Victoria BC, Canada

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I still dont think fixed wing can change direction as fast as a heli, which will produce allot of gforce, we can sit here and type back and fourth all day and it will do no good. If anybody has an acellerometer that can put on an heli and a plane, then get real world numbers, but I dought thats going to happen.

Victoria BC, Canada, Century Swift,Trex SA 450, Hummingbird V3.

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12-03-2005 08:22 PM  12 years agoPost 17
AceBird

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Utica, NY USA

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You don't need an accelerometer. Just time any loop or roll. It is that simple.

Ace

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12-03-2005 11:42 PM  12 years agoPost 18
TheRickster

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Beaumont Texas

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Never thought much "Rocket Science" involved in Tank plumbing.. Usually bend the lines by hand between forefinger and thumb. If it tries to kink a bit I squeeze it with pliers to open it back up. If it is too stiff to bend smoothly I heat it till it turns a purplish tint then quench it in water, anneals it for me.. I usually cut a "Donut" of the fuel tubing being used and put a collar around the fuel line where it pushes up on the brass tubing or the clunk itsself as a "procured tensioning device"I hope that is a technical enough term warrant my post being left in the thread)..

I never looked at plumbing a fuel tank as being a real technical achievement, I quit my job at NASA.... IF the clunk follows the fuel and the vent vents and the tank does not leak>>>>SUCCESS IN MY BOOK

It has worked for me anyways for many years....

Rick

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12-05-2005 04:47 PM  12 years agoPost 19
avator

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New Jersey

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Once again ace, your attack is based in ignorance and arrogance.

QUOTE>

I haven't seen any plank that can change direction faster than a heli.

END QUOTE>>>

Really? I thought you had a lot of experience?

I certainly have much more than you. Athough, no one here has as much experience running their mouth as you do.

Your arrogance won't let you admit to yourself that someone can be more knowledgable in a subject than you. Most people on this forum are more experienced and knowledgable regarding rc helicopters than you, yet you still insist on telling everyone they are wrong.

A full scale F-16 can pull maybe 9 or 10 G's, a model can pull 40. And while a loop can pull a relatively high number of sustained g's; a model heli can pull a hugh amount of g forces instantaneously.

You said:
The G-forces that a fuel tank sees in an airplane can be ten times that of a helicopter.
That is your qoute and what started this exchange.

You also said that you use sarcasm to provoke thought
All you do is insult people and make them angry and then you don't understand why they retaliate against you.

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