Clark Cable Tie launcher Benchmark and Launch Tube Question

Discussion about Compressors, hose, pipes, fittings, launchers, release mechanisms, and launch tubes.
T86157
Advanced Member
Advanced Member
Posts: 27
Joined: Wed May 02, 2012 11:25 pm

Clark Cable Tie launcher Benchmark and Launch Tube Question

Post by T86157 »

In regards to the infamous Clark Cable Tie launcher, I am lead to believe this is the most reliable and robust method for making a bottle rocket launcher for its price. Has anyone performed a benchmark on this and determined maximum pressures that the cable ties can sustain? How much pressure can the ties hold for each additional tie added onto the pipe?
Do the cable ties lose their elasticity after a while under extreme stresses which requires replacement every so once in a while?

I am currently looking into building a bottle rocket launcher where the launch tube can fit into the majority of the rocket. i.e. a 60 inch FTC rocket will have a 55 inch launch tube inside of it. A question I have is, is PVC that sturdy for that long of a tube for the rocket to launch vertically while still maintaining a very fit hug within the bottle neck? If PVC is sturdy enough for this, then cable ties would then be my first choice of a holding mechanism but still would like to know if the FTC reinforced with fiberglass or carbon fiber would fail before the cable ties would or visa-versa?
User avatar
Nick B
Internet Troll
Posts: 347
Joined: Tue Apr 03, 2012 8:47 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by Nick B »

supposedly.......... over 1000 psi
Nick and Dad B.
KubaLibre
New Member
Posts: 1
Joined: Thu May 03, 2012 5:34 pm

oh its great

Post by KubaLibre »

I think that's right!
waterside
WRA2 Member
WRA2 Member
Posts: 3
Joined: Sun Sep 18, 2011 9:53 am

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by waterside »

Your results will likely depend on your choice of materials and construction technique.

You can get away with almost anything at lower pressures (say, under 100 lbs), but as you ramp up, some of the limiting factors include:

1) the attachment of the cable ties to the launch tube
2) flexing of the cable ties
3) lengthwise stretching of the cable ties
4) flexing/breaking of the bottle flange

In my own experience, 200 pounds has been about the practical limit.

I'd encourage you to do your own experimentation and see for yourself. If you are planning on building a reinforced FTC rocket, you will certainly be doing a lot of it!

Have fun!
User avatar
Nick B
Internet Troll
Posts: 347
Joined: Tue Apr 03, 2012 8:47 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by Nick B »

Nick and Dad B.
User avatar
Nick B
Internet Troll
Posts: 347
Joined: Tue Apr 03, 2012 8:47 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by Nick B »

waterside wrote:Your results will likely depend on your choice of materials and construction technique.

You can get away with almost anything at lower pressures (say, under 100 lbs), but as you ramp up, some of the limiting factors include:

1) the attachment of the cable ties to the launch tube
2) flexing of the cable ties
3) lengthwise stretching of the cable ties
4) flexing/breaking of the bottle flange

In my own experience, 200 pounds has been about the practical limit.

I'd encourage you to do your own experimentation and see for yourself. If you are planning on building a reinforced FTC rocket, you will certainly be doing a lot of it!

Have fun!

AG

I cannot envision the bottle flanges handling much more than 600/800 psi without shearing. nor the ties or tie holder.

I'm looking for the stomp/cannon rocket C02 guy site, to review his process... But cannot find it right now.
Much easier to load up a rocket with 300 psi and cannon it up with 2k psi during launch...... :mrgreen:
Nick and Dad B.
T86157
Advanced Member
Advanced Member
Posts: 27
Joined: Wed May 02, 2012 11:25 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by T86157 »

waterside wrote:Your results will likely depend on your choice of materials and construction technique.

You can get away with almost anything at lower pressures (say, under 100 lbs), but as you ramp up, some of the limiting factors include:

1) the attachment of the cable ties to the launch tube
2) flexing of the cable ties
3) lengthwise stretching of the cable ties
4) flexing/breaking of the bottle flange

In my own experience, 200 pounds has been about the practical limit.

I'd encourage you to do your own experimentation and see for yourself. If you are planning on building a reinforced FTC rocket, you will certainly be doing a lot of it!

Have fun!
Yeah, I would have to normalize the experiment somehow. It is going to be difficult to find cable ties with consistent polymer composition without having to ask for proprietary information from the manufacturing companies. But as far as lengthwise stretching, that is a matter of using a tensile yield strength test. But like Nick B says, the flange may fail before the cable ties do, or even the pvc piping if the launcher is made out of that.

It's amazing where technology is today. There are gas tanks used for pneumatics in Battle Bots that can contain 9000 PSI within a container about the size of a 2 liter bottle. I can't imagine somehow tapping into that and creating a very robust custom water rocket. It would not longer be made of PTE, so then were getting into the fuzzy area where water rockets start crossing over into other dimensions with other hobbies. But-I'm off topic.


Another test I would like to test would be to have a pipe within a pipe where you have the inner diameter of one pipe can fit snuggly the outer diameter of another pipe to reinforce the rigidity and also allow for a higher pressure. The only problem then though is that the FTC would have a larger volume displacement due to a "thicker" tube. Increasing pressure at the cost of volumetric displacement; another benchmark I'll have to perform... unless someone else is more ambitious than me to jump on it.
air.command
Senior Member
Senior Member
Posts: 183
Joined: Wed Jul 09, 2008 5:20 am

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by air.command »

T86157 wrote:The only problem then though is that the FTC would have a larger volume displacement due to a "thicker" tube. Increasing pressure at the cost of volumetric displacement; another benchmark I'll have to perform... unless someone else is more ambitious than me to jump on it.
The volume displaced will be the same regardless of whether the launch tube is solid or hollow. Consider the end condition as the rocket is about to leave the launch tube. If it is solid then you have removed that "cylinder" of volume from the rocket and increased it's volume by that amount and hence reduced the pressure inside the rocket by a proportional amount. If you consider a thin walled hollow tube that is about to leave the rocket, then the air from inside the rocket flows into the launch tube volume that is now outside of the rocket effectively increasing the volume of the system to the volume inside the rocket + volume inside the launch tube. As it turns out the pressure inside the rocket drops by the same amount as with a solid tube. This is also why water rocket simulators don't include launch tube wall thickness as a parameter in their simulations. Now there are a number of other reasons why you may actually want a hollow tube, but not because of the increase in volume. ;)

- George
http://www.AirCommandRockets.com
User avatar
Nick B
Internet Troll
Posts: 347
Joined: Tue Apr 03, 2012 8:47 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by Nick B »

air.command wrote:
T86157 wrote:The only problem then though is that the FTC would have a larger volume displacement due to a "thicker" tube. Increasing pressure at the cost of volumetric displacement; another benchmark I'll have to perform... unless someone else is more ambitious than me to jump on it.
The volume displaced will be the same regardless of whether the launch tube is solid or hollow. Consider the end condition as the rocket is about to leave the launch tube. If it is solid then you have removed that "cylinder" of volume from the rocket and increased it's volume by that amount and hence reduced the pressure inside the rocket by a proportional amount. If you consider a thin walled hollow tube that is about to leave the rocket, then the air from inside the rocket flows into the launch tube volume that is now outside of the rocket effectively increasing the volume of the system to the volume inside the rocket + volume inside the launch tube. As it turns out the pressure inside the rocket drops by the same amount as with a solid tube. This is also why water rocket simulators don't include launch tube wall thickness as a parameter in their simulations. Now there are a number of other reasons why you may actually want a hollow tube, but not because of the increase in volume. ;)

- George

I respectfully disagree to a small extent.

The way I see it, with a hollow launch tube, the volume of the rocket includes the launch tube ID, the launcher plumbing ID, and the total ID cubic sq inch/footage length of any support hose, up until the source of compressor or tank, and or including the tank if the storage psi is the same as the rocket.

So, excluding the tank, if you have two rockets competing, and you have one with 4 feet of 1000 psi supply tube, and the second with 50 feet of supply tube, the one with 50 feet of supply has the greater volume and a decided advantage.

Same goes with launch tube length during launch.






and while i'm at it...


I would like to spend a second here to give thanks to your...... "open source".... rocketry website.
I am humbled by it.

You have given so much to the hobby, that is immeasurable.
Nick and Dad B.
User avatar
Nick B
Internet Troll
Posts: 347
Joined: Tue Apr 03, 2012 8:47 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by Nick B »

T86157 wrote: is PVC that sturdy for that long of a tube for the rocket to launch vertically while still maintaining a very fit hug within the bottle neck?


Well, the PCV is not really under pressure until the rocket begins to travel up the launch tube. It is within the rocket pressure vessel and subject to THAT ambient.
So the launch tube would not really be seeing much pressure until the rocket reached the tip of the tube before it exits the rocket. This is why, for example you see a rebound/snap/whipping action of the tube in launches or in such videos as US rockets launch vids. As you launch, one pressure vessel becomes two, both discharging air pressure.

Granted as the rocket launches and travels along the tube during it's greatest thrust phase, as the total volume pressure drops, the depressurization of the tube is unzipped or travels like a wave thru the launch tube, following the rocket nozzle.
Nick and Dad B.
air.command
Senior Member
Senior Member
Posts: 183
Joined: Wed Jul 09, 2008 5:20 am

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by air.command »

Nick B wrote: I respectfully disagree to a small extent.

The way I see it, with a hollow launch tube, the volume of the rocket includes the launch tube ID, the launcher plumbing ID, and the total ID cubic sq inch/footage length of any support hose, up until the source of compressor or tank, and or including the tank if the storage psi is the same as the rocket.

So, excluding the tank, if you have two rockets competing, and you have one with 4 feet of 1000 psi supply tube, and the second with 50 feet of supply tube, the one with 50 feet of supply has the greater volume and a decided advantage.

Same goes with launch tube length during launch.
I too agree with what you are saying. This was the reason I mentioned the desire to have a hollow launch tube. ARBs (Air Reservoir Boosters) on the launcher have been used for many years. They supply extra air up the launch tube to compensate for the increase in volume inside the rocket. This is why simulators include launcher volume as a parameter. Robert Youens used a 30L ARB on his launcher. http://txsnapper.eezway.org/txsnapper/insaneair.html

There are also other small effects that determine the difference between hollow and solid tubes such as the behaviour of the water inside the rocket during launch.
Nick B wrote:and while i'm at it...

I would like to spend a second here to give thanks to your...... "open source".... rocketry website.
I am humbled by it.

You have given so much to the hobby, that is immeasurable.
Thanks very much for the nice words Nick, though we are only a small part of the whole water rocket community. We too are inspired by many people who share their designs and experiences openly. That is how we learned to build rockets and launchers in the first place.

Cheers

- George
http://www.AirCommandRockets.com
User avatar
U.S. Water Rockets1
WRA2 Member
WRA2 Member
Posts: 1778
Joined: Sat Feb 03, 2007 3:24 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by U.S. Water Rockets1 »

Nick B wrote:supposedly.......... over 1000 psi
It is actually not hard to calculate the force that a cable tie launcher is capable of holding.

If you have a cable tie rated for 100 pounds, and you put 32 of them around your rocket nozzle then you have a system capable of holding 3200 (100 * 32) pounds of force. If you have a nozzle with 1 square inch of opening area then you could hold a rocket pressurized to 3200PSI. Since most rockets use smaller nozzles than this at lower pressures, then you can see that the average rocket will never cause a cable tie launcher to fail.

If you use our o-ring design as we explain in our launcher tutorial http://www.uswaterrockets.com/construct ... torial.htm, then you will have a seal that will allow the rocket to move up and down up to 1/2 of an inch and not lose contact with the o-ring, so the slight stretching of the cable ties will not be a factor.
Team U.S. Water Rockets
Visit USWaterRockets.com
Visit our Blog
Tune in to our YouTube Channel
Visit our Facebook page
Visit our Twitter Page
Opportunity is missed by most people because it is dressed in overalls and looks like work. --Thomas Edison
User avatar
U.S. Water Rockets1
WRA2 Member
WRA2 Member
Posts: 1778
Joined: Sat Feb 03, 2007 3:24 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by U.S. Water Rockets1 »

Nick B wrote: I respectfully disagree to a small extent.

The way I see it, with a hollow launch tube, the volume of the rocket includes the launch tube ID, the launcher plumbing ID, and the total ID cubic sq inch/footage length of any support hose, up until the source of compressor or tank, and or including the tank if the storage psi is the same as the rocket.

So, excluding the tank, if you have two rockets competing, and you have one with 4 feet of 1000 psi supply tube, and the second with 50 feet of supply tube, the one with 50 feet of supply has the greater volume and a decided advantage.

Same goes with launch tube length during launch.
There seems to be a lot of confusion surrounding the use of a launch tube and hose.

Before getting into the theory it should be pointed out that a person using a 4 foot hose to compete for a record would probably not be following the rules which require 50 feet of distance between the rocket and the people. The "buffer" provided by 50 feet of line is probably sufficient enough to make up for any launch tube you could reasonably expect to use on a water rocket.

As for what happens in a launch, it appears that some of the simulators are not accurately modeling the action of a launch tube. Take a rocket using a launch tube with a thick wall and a tiny hole through it. As the rocket moves up the launch tube, the pressure inside the tube is the same as the pressure inside the rocket. The pressure inside both the tube and rocket will decrease in proportion to the volume displaced by the launch tube cylinder MINUS the volume contained inside the hole through the tube.

Imagine if you will, the launch tube is melted down and turned into a liquid and poured into the rocket. A thin wall launch tube will displace a smaller amount of air inside the rocket as compared to a nearly solid launch tube. The simple fact is that as the rocket moves up the launch tube, the pressure will drop in proportion to the space occupied by the launch tube (as if it were melted into liquid). The thick walled launch tube will always cause more of a drop than a thin one.

The next effect to consider is how much volume of air is in the entire launcher and rocket together. You can calculate how much of a buffer that a 50 foot hose provides be computing the volume. We use a 1/4" diameter hose and the volume in the hose is a fraction of the volume of the rocket, so it really doesn't help a huge amount. It helps a small percentage, but it is not like it supercharges the rocket. Since we designed the system to set records, we tried to take advantage of every single place where we could gain even a tiny bit of performance. You can see that we use a thin walled launch tube to try and squeeze as much out of the launch as possible.

It doesn't make any sense that the rocket could be at a lower pressure than the supply, because the rocket and hose and launcher are all connected together as a system and the pressure should be balanced between them all. If there was a difference in pressure in the hose or compressor, then this would be because of some kind of blockage or restriction in the hose preventing the flow and causing the differential. If such a blockage existed, then it would also prevent the air from flowing fast enough into the system to be of any help during the milliseconds the rocket is traveling up the launch tube.

Unfortunately, the thin walled tube tends to randomly flex during launches, and the water column jet can strike the launch tube top and cause it to become bent and needs to be replaced.

You also seem to imply that you believe that once the rocket leaves the launch tube that they become two separate pressure vessels acting together. It seems as if you are suggesting that the air inside the launch tube is going to have a profound effect at lifting the rocket from below. This is possibly true, but it would be the same net effect regardless of the length of the launch tube or if there were no launch tube at all. Consider also that the air is spreading out as it exits, so the jet effect is decreased exponentially over distance from the air source, so the very brief time the rocket is close enough for this to matter the air jet is most likely to be completely deflected by the water exiting the rocket and the rocket is not being contacted at all by the jet. A few microseconds later the rocket is so far away from the jet that it doesn't matter.

Also, if you do use a launch tube, then make sure you take care not to get the water inside when filling because it will be lost from the rocket and will change the amount of reaction mass that is available. It will be as if that water was never inside the rocket because it will remain inside the launch tube until the rocket flies off and then jet ejected by residual pressure in the launcher.

Hopefully, this information will be useful to you in your rockets.
Team U.S. Water Rockets
Visit USWaterRockets.com
Visit our Blog
Tune in to our YouTube Channel
Visit our Facebook page
Visit our Twitter Page
Opportunity is missed by most people because it is dressed in overalls and looks like work. --Thomas Edison
User avatar
Nick B
Internet Troll
Posts: 347
Joined: Tue Apr 03, 2012 8:47 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by Nick B »

U.S. Water Rockets1 wrote:
Nick B wrote:supposedly.......... over 1000 psi
It is actually not hard to calculate the force that a cable tie launcher is capable of holding.

If you have a cable tie rated for 100 pounds, and you put 32 of them around your rocket nozzle then you have a system capable of holding 3200 (100 * 32) pounds of force. If you have a nozzle with 1 square inch of opening area then you could hold a rocket pressurized to 3200PSI. Since most rockets use smaller nozzles than this at lower pressures, then you can see that the average rocket will never cause a cable tie launcher to fail.
I see what you are saying, but how the manufacturer rates the load and tests is at question.

Is it applied with stretching action along the length of the tie, or perpendicular and with shear force, or at one small focal point of a .050 x .250 x .250 area. not to mention what shear force the clamp holding the ties, or the bottle neck flange can handle.

If you have realized these pressures with the ties, then that's really cool, but the assembly as a whole in actual use sounds like the extreme limits for all plastics involved. Armchair conjecture on my behalf, at full speed here. Respectfully. :)
Nick and Dad B.
User avatar
Nick B
Internet Troll
Posts: 347
Joined: Tue Apr 03, 2012 8:47 pm

Re: Clark Cable Tie launcher Benchmark and Launch Tube Quest

Post by Nick B »

U.S. Water Rockets1 wrote:
Nick B wrote: I respectfully disagree to a small extent.

The way I see it, with a hollow launch tube, the volume of the rocket includes the launch tube ID, the launcher plumbing ID, and the total ID cubic sq inch/footage length of any support hose, up until the source of compressor or tank, and or including the tank if the storage psi is the same as the rocket.

So, excluding the tank, if you have two rockets competing, and you have one with 4 feet of 1000 psi supply tube, and the second with 50 feet of supply tube, the one with 50 feet of supply has the greater volume and a decided advantage.

Same goes with launch tube length during launch.
There seems to be a lot of confusion surrounding the use of a launch tube and hose.

Before getting into the theory it should be pointed out that a person using a 4 foot hose to compete for a record would probably not be following the rules which require 50 feet of distance between the rocket and the people. The "buffer" provided by 50 feet of line is probably sufficient enough to make up for any launch tube you could reasonably expect to use on a water rocket.

As for what happens in a launch, it appears that some of the simulators are not accurately modeling the action of a launch tube. Take a rocket using a launch tube with a thick wall and a tiny hole through it. As the rocket moves up the launch tube, the pressure inside the tube is the same as the pressure inside the rocket. The pressure inside both the tube and rocket will decrease in proportion to the volume displaced by the launch tube cylinder MINUS the volume contained inside the hole through the tube.

Imagine if you will, the launch tube is melted down and turned into a liquid and poured into the rocket. A thin wall launch tube will displace a smaller amount of air inside the rocket as compared to a nearly solid launch tube. The simple fact is that as the rocket moves up the launch tube, the pressure will drop in proportion to the space occupied by the launch tube (as if it were melted into liquid). The thick walled launch tube will always cause more of a drop than a thin one.

The next effect to consider is how much volume of air is in the entire launcher and rocket together. You can calculate how much of a buffer that a 50 foot hose provides be computing the volume. We use a 1/4" diameter hose and the volume in the hose is a fraction of the volume of the rocket, so it really doesn't help a huge amount. It helps a small percentage, but it is not like it supercharges the rocket. Since we designed the system to set records, we tried to take advantage of every single place where we could gain even a tiny bit of performance. You can see that we use a thin walled launch tube to try and squeeze as much out of the launch as possible.

It doesn't make any sense that the rocket could be at a lower pressure than the supply, because the rocket and hose and launcher are all connected together as a system and the pressure should be balanced between them all. If there was a difference in pressure in the hose or compressor, then this would be because of some kind of blockage or restriction in the hose preventing the flow and causing the differential. If such a blockage existed, then it would also prevent the air from flowing fast enough into the system to be of any help during the milliseconds the rocket is traveling up the launch tube.

Unfortunately, the thin walled tube tends to randomly flex during launches, and the water column jet can strike the launch tube top and cause it to become bent and needs to be replaced.

You also seem to imply that you believe that once the rocket leaves the launch tube that they become two separate pressure vessels acting together. It seems as if you are suggesting that the air inside the launch tube is going to have a profound effect at lifting the rocket from below. This is possibly true, but it would be the same net effect regardless of the length of the launch tube or if there were no launch tube at all. Consider also that the air is spreading out as it exits, so the jet effect is decreased exponentially over distance from the air source, so the very brief time the rocket is close enough for this to matter the air jet is most likely to be completely deflected by the water exiting the rocket and the rocket is not being contacted at all by the jet. A few microseconds later the rocket is so far away from the jet that it doesn't matter.

Also, if you do use a launch tube, then make sure you take care not to get the water inside when filling because it will be lost from the rocket and will change the amount of reaction mass that is available. It will be as if that water was never inside the rocket because it will remain inside the launch tube until the rocket flies off and then jet ejected by residual pressure in the launcher.

Hopefully, this information will be useful to you in your rockets.

Good stuff here.

Thank you.

As far as I can tell, we are discussing launcher systems outside competition and in general.
Nick and Dad B.