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Author: Subject: Making a new serie of rockets
Adar
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[*] posted on 8-7-2006 at 07:12
Making a new serie of rockets


Some friends of mine made a serie of 9 rockets roughly a year ago. I was somewhat involved but lived quite far away so they did most of the work. We managed to get one rocket above 300m but the rockets weren't exactly the most effective since fast drying concrete was a major component...

My goal is to create a new serie with an improved engine compartment (the rest of the rocket doesn't really need much since it's a cardboard tube with a pointy tip and a weight to improve stability). My first engine is being built of a tincan (11cm high, 7cm diameter) with furnace putty on the inside (just 2mm thick) and an exhaust made of just furnace putty (I am using a funnel as the mould and I will then attach the funnel shappety putty onto the tin can and add another layer on it for a total of roughly 5mm). The fuel will be a cylinder of KNO3 and sugar attached to the bottom of the tincan, we used to always add some Iron(III)oxide to the mixture to improve the oxidation. I don't have any at home so that is sadly imposible and I am not sure on how to compensate for that (I am currently planning to make the exhaust opening smaller to increase the pressure). The ignition will be a sparkler (tomtebloss for the Swedes) stuck into the cylinder and have coming out of the exhaust opening.

I especially want advice on two things. At what (weight) ratio should I mix the sugar and the KNO3? and how much do you think I should use?
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DeAdFX
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[*] posted on 8-7-2006 at 07:49


Did you use concrete as a nozzle material? I have had no luck using that stuff as a nozzle at all. The concrete isn't rigid so it flys out of the rocket after the propellant has been ignited. Clay would be a lot more effiecent.
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enhzflep
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[*] posted on 8-7-2006 at 08:07


Firstly, the ratio is 65:35 by weight of Pottasium Nitrate to Sugar.

Next, how heavy do you anticipate the rocket to be?

The ISP of R-Candy (Rocket Candy) is around the 100 seconds mark.

I had a rocket once that was a two-stager, that flew on two estes C6-6 motors. Total Impulse being around 20NS. Weight of the entire rocket now escapes me.

That's around 25gms of fuel @ ISP of around the 80seconds mark.

We successfully made many, many motors using 17.5mm OD aluminium tubing, cut into 70mm lengths. We would ram around 13-14mm of crushed kitty litter mixed with 10% motor oil for the nozzle. The tip here is to create a tight-fitting nipple that has a 3.5mm diam nail protruding from by around (13-14mm+3-4mm) 16-18mm. If you try to ram the nozzle and then drill it out, you will be greeted by failure more often than not.

Anyway, there's so much to this topic. Here's a site that may be of some assistance

--->http://www.jamesyawn.com/syrup/index.html

Oh, and btw - you'll get greater thrust and height if your nozzle is around 14 degrees total included angle, and around 3 times the area at the exit point as at the throat. Too great an angle and the gas can't follow the nozzle - this results in a noisier rocket :) but less thrust.

We only ever used black-powder(commercial, ball milled after purchase)
and dabbled (very carefully) with the use of double-based propellants (AS-30N shot-gun powder)

[EDIT: We made twin-stage 17.5*70mm motor-powered 'ultra-light' rockets that easily passed 400m - I'll find a photo of some of my older creations in a minute then post the attachment]

[EDIT#2: Couldn't find that image. My back room's in a bit of a mess athe moment:o
The packet is from the two-stager I described as having bought. The blocks of wood are used to prevent paper-cased motors from bursting during the ramming phase.
The CD is there for scale.
The two brown-bodied rockets are 100% home made, the silver one was bought in a starter kit for about $75 - and from left to right we have:
A commercial D-sized motor, one of our 26mm monsters, a 17.5mm alloy job, a 17.5mm paper motor, a bent 9mm ID spindle, a usable 9mm ID spindle, the MONSTER 26mm ID spindle, a few ram-rods and finally the 1 1/4 inch bolts used to ram the monsters with :D
Tools - we made with a lathe. But, if you can cut off the shaft of a bolt accurately, you may then drill a hole for the spindle to fit into, in the head of the bolt. You'll get the idea]

[Edited on 8-7-2006 by enhzflep]

[Edited on 8-7-2006 by enhzflep]

Rockets And Tools.jpg - 466kB
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Adar
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[*] posted on 8-7-2006 at 08:36


Quote:
Originally posted by DeAdFX
Did you use concrete as a nozzle material? I have had no luck using that stuff as a nozzle at all. The concrete isn't rigid so it flys out of the rocket after the propellant has been ignited. Clay would be a lot more effiecent.


Yeah fast drying concrete. What you have do is that you make the whole engine compartment of concrete. The problem is that if the muzzle is too small will it blow up. We generally had the problem that the top blew up which caused an overpressure inside the rocket which in turn jettisoned the engine out of the rocket. This one time turned ugly as the engine flew on it's on and made a half circle around us before it stopped. I suggest you put two nails from the "rocket body" into the concrete, they should open up the concrete abit so the engine doesn't fly far on it's own (or it justs rips off some cardboard and doesn't help, we haven't tried it yet).

Raketmotor.JPG - 3kB
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Adar
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[*] posted on 8-7-2006 at 11:56


Quote:
Originally posted by enhzflep
Next, how heavy do you anticipate the rocket to be?

The ISP of R-Candy (Rocket Candy) is around the 100 seconds mark.

I had a rocket once that was a two-stager, that flew on two estes C6-6 motors. Total Impulse being around 20NS. Weight of the entire rocket now escapes me.


The rocket will hopefully by quite abit lighter than 0,5kg. The engine compartment actually weighs less than 100g so the counterweight in the top won't be very heavy either. The main weight will be fuel and the cardboard tube for the body.

Also what does ISP mean? (I assume rocket candy is KNO3 and sugar). I'm not very familiar with english/internet nomenclature. I do okay with the chemistry (I've spent a year at uni with english textbooks) but the physics is quite beyond me (but please keep using the "hard" words, I'll ask about it and learn from it).

Oh yeah two more questions, how do you measure the impulse (are you using some kind of pressure measure and then view it on film frame by frame?) and how much should I preheat the KNO3 (we had quite good protection gear so we just melted the sugar with KNO3 and mixed it in a mortar before putting it in a mold*).

*That's what we did when I was present. They also managed to set the mixture on fire in a guys garage as they used a heating pistol on it while wearing shorts and t-shirt...
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enhzflep
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[*] posted on 8-7-2006 at 19:49


Okay, so your rocket will weigh around 5 Newtons.

ISP is a measure of the amount of thrust that may be provided.

I forget exactly how it is derived, but basically having an ISP of 1 second means that the fuel will provide it's own weight in thrust for 1 second. Similarly, an ISP of 80 seconds means that 100gms (for example) of fuel will provide 100gms of thrust for 80 seconds, or 8kg for 1 second, or 4kg for 2 seconds.

The higher the ISP (specific impulse) of the fuel, the less of it you need to do the same job. Military rockets commonly use fules with an ISP of over 200 seconds or even 300 seconds.

I forget how to apply the calculations to determine the height that will be attained from a certain rocket configuration. You'll be able to look this up. Try a google for Richard Nakka, he's got some pretty good stuff on his site.

Take for example commercial hobby rocket engines. A C class motor has a total impulse of 10NS - the same power that is delivered by 1kg for 1 Second. Since the ISP of blackpowder is around 80seconds, you need around 12-13gms of fuel.

To hover stationary, i.e not go higher and not go lower - you need to provide a thrust that is equal to RocketWeight(in kg) * 9.8. To accelerate at 1G, you need RocketWeight(in kg) * 9.8 * 2. To accelerate at 2G you need RocketWeight(in kg) * 9.8 * 3.

From this you can see that if you make a rocket accelerate at 1 G for 1 second, your rocket will move upwards in 1 seconds the same distance as it would fall due to gravity in the same time, i.e about 5m.

As I mentioned in a previous topic, this is a huge subject though not too hard if you can find somebody better able to describe the principles than I.

Good luck and regards...

[EDIT: don't know how hot to heat the propellant - never tried KNO3 + sugar.
On the subject of measuring ISP - you can use software to calculate a theoretical value, OR you can place a motor upside down on a set of scales and video tape the thrust being supplied. From there you would plot a graph of time vs thrust, calculating the average thrust provided over the time interval concerned. If for example you had a thrust of an average of 1kg for 2 seconds, using 20gms propellant you would have 20NS thrust provided by 0.2N of propellant. This would give you an ISP of 20NS / 0.2N = 100 seconds.]

[Edited on 9-7-2006 by enhzflep]
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Adar
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[*] posted on 9-7-2006 at 07:33


I've just run into my first major setback, the putty I used is too flimsy too hold on it's own. Basicly I need to find a steel funnel or something to provide the muzzle.

Did you use cat litter and motor oil forthat? :o
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YT2095
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[*] posted on 9-7-2006 at 08:20


just a quick Tip for the second poster here, get youself a staple gun, and pop in 4 staples around the base of the tube (90 degrees appart) where you`re going to set your nozzel cement, in effect it`ll act as rebar and stop it blowing out :)

[Edited on 9-7-2006 by YT2095]




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enhzflep
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[*] posted on 9-7-2006 at 18:15


@Adar. Not 100% sure of what you mean. We used a steel tool to hold the nozzle as it was being compacted from powder.

I have attached a small diagram that illustrates the concept.
Note:
1) Images not to scale
2) Hollow ram-rod not shown
3) Solid ram-rod not shown

At full speed, 1 person can make about 10 of these an hour.
Reffer to the image Rockets and Tools in a previous post for
a photo of aforementioned tools.

[Edited on 10-7-2006 by enhzflep]

ConstructionCrossSection.jpg - 23kB
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JohnWW
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[*] posted on 10-7-2006 at 01:59


That "ConstructionCrossSection.jpg" link has been broken. Do you think the CIA could be responsible?
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enhzflep
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[*] posted on 10-7-2006 at 17:18


Don't know to be honest. I've just tried it now and it's fine. Did you try opening in a new tab or new window? If I right-click and hit "Save Link As" the filename I'm prompted with is "viewthread.php".

Surely though, it can't be that much of a 'slow news day' for the cia to be bothering with something so trivial...
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tumadre
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[*] posted on 10-7-2006 at 22:51


don't know if this would be of any help
I would use a piece of tile/ceramic to drill out a nozzel from
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