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GlassfibreMan

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I picked up a couple of bottle rockets at a knock down price. When I went onto Richard Nakka's site and tried the simulation utility there I realised that water power had potential as a first stage booster.

Because I am always 'pushing the boundaries of 'low power' BP, i.e. building bigger rockets than I should, I can get slow realistic takeoffs but not much height because most of the energy of a couple of D's is used up in the first 25'

A 2 litre Coca Cola with 1ltr water pressurised to 150 lbs p.s.i produces a total impulse of 33 N-Sec and a specific impulse of 44 N-Sec/Kg, Could someone tell me what that is equivalent to in normal motors?

I wouldn't utilise that much pressure unless the bottle is encased as in my pic on next posting but the bottles are apparently tested to 200lbs p.s.i.

The pic on this posting is of the original bottle rocket as it came (holds 500ml, total) with the launcher.

There are more details on my site:Rays Rocketry
 

GlassfibreMan

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Here's a pic of my all glassfibre 4" bottle rocket with pyro device for parachute recovery. It hasn't flown yet but it will do so in a couple of days when I get my new 'chute' from edwardw. The next stage is to fit some boosters that will be airstarted and after that a transition in place of the nose cone to take a BP powered second stage.
 

Karl

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Originally posted by GlassfibreMan
A 2 litre Coca Cola with 1ltr water pressurised to 150 lbs p.s.i produces a total impulse of 33 N-Sec and a specific impulse of 44 N-Sec/Kg, Could someone tell me what that is equivalent to in normal motors?
y
It is equivalent to a Aerotech E7 but is only 3N-Sec's away from a Aerotech E12.


Karl
 

hokkyokusei

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Originally posted by Karl
It is equivalent to a Aerotech E7 but is only 3N-Sec's away from a Aerotech E12.
How did you work that out Karl?
 

edwardw

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That is a nice looking water rocket there! What style is your launcher? I know when I flew water rockets mine were not near as cool looking. I made a fincan out of another bottle and put small foamy fins on. I added another cut bottle for a nose cone and found a golf ball was the correct weight to make it stable and go the furthest! I then found 2 stagers, but those are a lot more complex. I haven't had near the success.

Edward
 

Karl

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Originally posted by hokkyokusei
How did you work that out Karl?

I used the 'Big List' feature on Thrust Curve.

Karl
 

GlassfibreMan

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Hi Edward

I'll be flying when I get the 'chute you posted. That's if it will fly. I have looked up a load of sites on water rockets and it seems that no one has combined them with conventional pyro motors. It makes sense to me to use it as a launch booster.

Even if it only lifts to 50' if the motors are airstarted it should add quite a lot to the eventual height.

The launcher uses hozelok fittings - the garden hose type things. They screw into the bottle (replacing the cap) and lock into the launch base. They are released when the handle is closed like a bicycle brake lever. A bowden cable pulls down on the hozelok and releases the beastie.
 

Daedalus

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OK - so you have been to Maplin's rocketry department - I saw them and thought they were pretty smart. I may have to go back and see if they have them on sale still.

Interesting mod to it - hope it flys well. Photoas and report back please:D
 

hokkyokusei

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Originally posted by Karl
I used the 'Big List' feature on Thrust Curve.

Just by matching the total impulse?

If that's the case then it's probably not a very good match. I would expect a water rocket to have a much higher and shorter thrust than the motors you suggest are "equivalent".
 

GlassfibreMan

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Here's another one I made earlier, shown on the attachment below. It's based on the original bottle rocket with a transition bonded to the top of it. The transition houses a perfecflite timer and docking section for the BP powered upper stage. After say 1 second of acceleration the 'G' switch on the lower stage timer will ignite the BP motor on the upper stage.

The upper stage is made from BT70 body tube and one of my own frp nosecones. It contains an altimeter and a beeper location device plus parachute. It will fly on D's or E's. I'm waiting for a SWARM club meeting to test fly this one.
 

r1dermon

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why not launch it on a spring or something...build a tower and use a car spring...lol. that puppy will get some height. it seems to me that bottles wont have that much impulse.
 

OARJeepr

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have you ever tried to compress an auto coil spring? It's a major pain without a decent shop spring compressor. When replacing springs on my jeep i just let the axle sag until I could pull the springs off. Not the safest idea either. Those springs have a lot of energy when you do get them compressed.
 

r1dermon

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ever tried a comealong? i know how much energy is in a spring...i've had one catapult right by me and hit my wall over 40ft away in my garage...that was when i was doing a shock tower job in my lumina...old school. i had rot coming through the shock tower so it wasnt like i had any other options, i had to get a compressor, but when the prong slipped off the top it catapulted forever...i'll never use one of those types of compressors again...i guess they have these belt ones that you wrap the middle of the spring with and then tighten...i'll have to check it out next time im doing coil overs.

how about some type of elastic launcher? make the tower and then tie a couple elastics to each side and under the rocket, then pull it down with some type of wince....let er go and KAPOW, that rocket is airborne.
 

GlassfibreMan

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I like the idea of the 'bungee' elastics. problem is making the launch setup. I'll see if the water rockets work first though.
 

r1dermon

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im seriously interested in how much thrust a 2 liter bottle can actually produce.
 

hokkyokusei

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Originally posted by r1dermon
im seriously interested in how much thrust a 2 liter bottle can actually produce.
From the first post:


A 2 litre Coca Cola with 1ltr water pressurised to 150 lbs p.s.i produces a total impulse of 33 N-Sec and a specific impulse of 44 N-Sec/Kg, Could someone tell me what that is equivalent to in normal motors?


Which is an E of some description.

OK, so I downloaded and ran the "whoosh" program for a 90mm diameter, 2 litre bottle, with a 22mm throught, filled with 1 litre of water and pressurised to 150psi, and here is the output:
[pre]
TIME AIR VOL dV/dt JET VEL. PRESS. THRUST
sec litre l/sec m/s psi N
.000 1.00000 17.31388 45.57 150.0 788.99
.005 1.08387 16.26913 42.82 132.4 696.65
.010 1.16298 15.39737 40.53 118.6 623.99
.015 1.23806 14.65412 38.57 107.4 565.20
.020 1.30968 14.00957 36.87 98.2 516.58
.025 1.37829 13.44286 35.38 90.4 475.63
.030 1.44422 12.93886 34.06 83.7 440.63
.035 1.50776 12.48633 32.86 78.0 410.35
.040 1.56915 12.07667 31.79 73.0 383.87
.045 1.62859 11.70319 30.80 68.5 360.49
.050 1.68623 11.36061 29.90 64.6 339.69
.055 1.74224 11.04466 29.07 61.0 321.06
.060 1.79672 10.75187 28.30 57.8 304.27
.065 1.84979 10.47939 27.58 54.9 289.04
.070 1.90154 10.22483 26.91 52.3 275.17
.075 1.95206 9.98619 26.28 49.9 262.47
.080 2.00143 9.76177 25.69 47.6 250.81
Total impulse = 34.55 N-sec.
Specific impulse = 34.55 N-sec/kg.
[/pre]
I think this is saying that 34.55 N-sec is produced in 0.08 seconds, making it equivalent to an E432? (34.55/0.08) Is that right?
 

Daedalus

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Originally posted by hokkyokusei

OK, so I downloaded and ran the "whoosh" program for a 90mm diameter, 2 litre bottle, with a 22mm throught, filled with 1 litre of water and pressurised to 150psi

<snip>

I think this is saying that 34.55 N-sec is produced in 0.08 seconds, making it equivalent to an E432? (34.55/0.08) Is that right?
A 22mm through sounds much too big for a Hozelock fitting - I would have guessed more like 8mm. Without the benefit of Whoosh ratio the areas 8^2 / 22^2 gives 0.132 so E432 becomes E57 and a run time of 0.6 seconds. Does that sound reasonable? Still much more pokey than an E7!!!
 

edwardw

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When I did single stage water rockets I could get a 2L bottle with about 1.25 liters water pressurized at 100 psi to travel nearly 200 yards. If I went straight up I got about 600 feet altitude. They definitely fly off the launcher, especially if you are using a piston type one.


Edward
 

hokkyokusei

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Originally posted by Daedalus
A 22mm through sounds much too big for a Hozelock fitting - I would have guessed more like 8mm. Without the benefit of Whoosh ratio the areas 8^2 / 22^2 gives 0.132 so E432 becomes E57 and a run time of 0.6 seconds. Does that sound reasonable? Still much more pokey than an E7!!!

Ah, that's what I was missing. The program asks you to describe the bottle, which I did, but as you say the nozzle is smaller than that! Rerunning whoosh gives:


TIME AIR VOL dV/dt JET VEL. PRESS. THRUST
sec litre l/sec m/s psi N
.000 1.00000 2.28542 45.49 150.0 103.96
.020 1.04493 2.20930 43.97 140.2 97.15
.040 1.08842 2.14053 42.61 131.6 91.20
.060 1.13060 2.07797 41.36 124.0 85.95
.080 1.17157 2.02070 40.22 117.3 81.27
.100 1.21145 1.96798 39.17 111.2 77.09
.120 1.25032 1.91922 38.20 105.8 73.32
.140 1.28825 1.87392 37.30 100.8 69.90
.160 1.32530 1.83169 36.46 96.3 66.78
.180 1.36153 1.79216 35.67 92.2 63.93
.200 1.39700 1.75506 34.93 88.4 61.31
.220 1.43175 1.72013 34.24 85.0 58.89
.240 1.46582 1.68716 33.58 81.7 56.66
.260 1.49925 1.65596 32.96 78.7 54.58
.280 1.53207 1.62637 32.37 75.9 52.65
.300 1.56431 1.59825 31.81 73.3 50.84
.320 1.59601 1.57148 31.28 70.9 49.16
.340 1.62718 1.54595 30.77 68.6 47.57
.360 1.65785 1.52155 30.29 66.5 46.08
.380 1.68805 1.49821 29.82 64.4 44.68
.400 1.71779 1.47584 29.38 62.5 43.35
.420 1.74709 1.45437 28.95 60.7 42.10
.440 1.77597 1.43375 28.54 59.0 40.92
.460 1.80444 1.41391 28.14 57.4 39.79
.480 1.83253 1.39480 27.76 55.8 38.72
.500 1.86024 1.37637 27.40 54.4 37.71
.520 1.88759 1.35859 27.04 53.0 36.74
.540 1.91459 1.34142 26.70 51.6 35.82
.560 1.94125 1.32481 26.37 50.4 34.93
.580 1.96758 1.30874 26.05 49.2 34.09
.600 1.99360 1.29317 25.74 48.0 33.29
.620 2.01931 1.27808 25.44 46.9 32.51
Total impulse = 34.62 N-sec.
Specific impulse = 34.62 N-sec/kg.

Or an E56, which agrees nicely with your calculation. Thank you.
As you say, pretty pokey ;)
 

OARJeepr

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Well yeah I could compress a spring if I needed to. It's just a lot safer to unbolt the axle and let it droop. The biggest problem I can see with a spring would be an accurate and reliable release mechanism. The bungee idea seems much more workable.

Wow, E57, just water and plastic....amazing.
 

hokkyokusei

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Originally posted by OARJeepr

Wow, E57, just water and plastic....amazing.
Yeah, but it's a very heavy motor for what it is.

Just for kicks, here's an ENG file ;)


;Water rocket made from 2 litre Virgin Cola bottle
;using 1 litre of water presuurised to 150psi
;Curve generated using whoosh
;DJL 20041216
E56 90.0 340.00 0 1.00000 1.05000 VirginCola
0.00 103.96
0.06 86.12
0.12 73.13
0.28 52.49
0.44 41.53
0.62 31.85
0.62 0.00
;


Made it in RockSim's EngEdit. Haven't tried "flying" it yet.
To use this just cut and paste the from first ';' to last ';' (inclusive) and save in a file ending in .eng
 

Const Star

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ok i may sound like a dumbass here, but if ur using water pressure for thrust, how exactly do u stage it? i mean am i missing something, cause i just dont see how anything could trigger another blast.
 

GlassfibreMan

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Const Star said:

if ur using water pressure for thrust, how exactly do u stage it?
If you mean how do you stage a pyro motor then as I said in an earlier posting a timer that detects takeoff (perfectflite mini timer with 'G' switch) under water power can be set to ignite a BP motor after say 1 second. The rocket I built to do that is pictured below.

If you want to stage bottle rockets, that can be done too. There's loads of sites on water rockets. Here's one that describes staging:

http://www.geocities.com/wrgarage/
 

r1dermon

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there's a timer out there thats designed for this. it detects the G forces of liftoff, and then it detects the forces of decelleration. these can be timed from the time of decelleration (burnout) of the booster stage, then they will fire the top (sustainer) motor which will be the second stage. the sustainer stage is fully prepped and ready to go when its loaded onboard, with an igniter inserted and hooked up to the timer, which fires a jolt of electricity when it gets the desired time. and thats how high power staging works. its a lot different than CHAD staging, which is how estes motors commonly stage, they ignite each other in succession by shooting flame up the next motors nozzle. the reason that wont work with composite motors is because they are core burners, and have to be lit from the top or else they'll CATO. so an igniter is a must.
 

rstaff3

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The timer GlassfibreMan describes detects launch using a G switch, counts one second, and fires an ematch. There are numerous products that do this. You can find the Perfectflite web sign and maybe this will describe the product better.

There are also products that detect the decelleration, such as the G-Whiz altimeter. This can detect launch, motor burn-out, apogee, and then a set altitude (400 or 800 feet) on the descent. Some fancier altimeters, such as the ARTS add more features, such as having a timer on each of these events.

Here http://www.info-central.org/index.cgi?electronics is some more info if you are interested.

Some clarification on terminology. Black powder motors (Estes and others) are direct staged by using a staging motor (ie D12-0) that has no delay or ejection charge and, as described, the flame from the staging motor lights the upper motor. This is typically done in a 2-stage (or 3-stage etc) rocket, in which the booster motor is mounted in a part of the rocket. In CHAD staging, there is not bottom part of the rocket, and the booster motor is merely taped to the bottom of the 'upper stage'. Hence CHeap And Dirty staging. If you want to do this, ensure that the rocket will be stable! Many won't be with the extra weight of the booster motor.

Didn't mean to write a book on the latter...not enough coffee....yet....
 

Daedalus

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Originally posted by hokkyokusei
Or an E56, which agrees nicely with your calculation. Thank you.
As you say, pretty pokey ;)
I would like to see E56 and E432's available as nice light weight BP or composite motors. They could be great fun - especially the E432 explode-a-matic. How many G would an Estes Alpha pull on that? I bet you could use a 6" launch rod and find the speed of balsa before it left the rod. Very sick:kill:
 

andysrockets

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Originally posted by GlassfibreMan
A 2 litre Coca Cola with 1ltr water pressurised to 150 lbs p.s.i produces a total impulse of 33 N-Sec and a specific impulse of 44 N-Sec/Kg, Could someone tell me what that is equivalent to in normal motors?
150 PSI is stretching it with a 2litre PET bottle. We used to lob at 120-150 regularly when I was at uni, and i'll tell you now, that the bottle will be warping at those pressures. If not immediately, then certainly after a few flights. Anything over 130PSI, and the bottle will come back a slightly different shape each time.

We did manage to hit about 170PSI once, but then our valve arrangement let go, and despite repairs, we could never get much past 120 PSI after that.

Larger PET bottles tend to be thinner and warp more. 1.5 Litre are probably best. 2 litre are almost as good. 3 litre you'll see visible stretching of the bottle on the pad by 120-130PSI.

100PSI will be a realistic pressure, and from memory and our 'guestimated sims' from 10 years ago, that will give you about 70% of the thrust of 150PSI.
 

GlassfibreMan

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andysrockets wrote:

150 PSI is stretching it with a 2litre PET bottle. We used to lob at 120-150 regularly when I was at uni, and i'll tell you now, that the bottle will be warping at those pressures. If not immediately, then certainly after a few flights. Anything over 130PSI, and the bottle will come back a slightly different shape each time.
Yes, but don't forget the 2 litre bottle is a snug fit in a fibreglass bodytube. From the websites I have visited it would seem that those into water rockets are reinforcing the bottle with various materials just so they can go for more pressure, even more than 150 p.s.i.
 
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