Sugar Rocket Issues

[Redrocketman]

Yes I have to agree. Ive made 300 - 400mm nozzless motors that were just darn crazy. ( just fixed to a balance stick though - a long time ago ) Im obviously limited by the thrust ring. 8" length max including deployment charge. I was trying to make a nozzle less motor to save all the effort of having to fabricate the proper delay grain bulkhead required with a full nozzle motor ( case pressure is too much for shortcuts when motor is nozzled ). NO such luck.

 

In relation to ' screaming off the pad ' I fit a pressurisation burst plugs to my pvc motors allowing them to build full case pressure instantly upon ignition, so I find that they have way more initial thrust than nozzle less designs and also have a very neutral and fast burn.(approx 1.5 - 1.8sec ) Thats something I have worked on for a while now and have it down pat. Its kind of like turning a light switch on and off quickly.

 

Thanks heaps for the info on density, Ill be making some more grains today, so ill take all that into account. Just need my new ball mill so get here as Im just out of BP for chute charges. (You think AU $240 inc shipping is fair for a double jar mill?? Skylighter copy )

 

I want to start making small pressed BP motors for Estes rockets but thats another kettle of fish all together

[stix]

Someone can correct me if I'm wrong, but I believe the average density of a kettle of fish is around 0.9 grams /cubic cm.

 

That's why I prefer the re-crystalised pan fried method where most of the water is driven off and a thin crust remains - yielding a higher density of around 1.3. I've also found the addition of RIO certainly makes it burn quicker but can leave a nasty taste. It doesn't plate up very well either.

 

As NJ said, weighing then calculating the volume of a cylinder will help you work out the density of your fuel. There's probably an excel worksheet out there (or here) that would make it easier. I know there's one for fish, but it all depends on how heavy the kettle is.

 

[dagabu]

There is much controversy!

 

http://cdn2.btrstatic.com/pics/showpics/large/527993_KRLdBhcG.jpg

[kramrocket]

Stix, sorry to sound dumb, but how do u determine fuel density? I've still got sooooo much to learn....

The density (Specific Gravity or 'SG' ) of a solid or a liquid, is a number using pure water as a baseline.

 

1 gram of water = 1 cubic cm = so an SG of 1.

 

To know your SG would require you to work out the volume in cubic cm and weigh it in grams. So if you have 220 grams of fuel and its volume is 130 cubic cm, the SG (density) is 1.69.

 

So density is 'weight divided by the volume' expressed by saying the 'SG' or 'density' of the fuel.

 

Most pressed or melted BP or KNSU fuels have an SG of somewhere between 1.2 and 1.8.

.

[stix]

So back on track regarding fuel density:

 

Here's a worked example using the simple volume calculator found here:
https://www.google.com.au/#q=calculate+volume+of+a+cylinder

The specs and calculations are for grains where the core extends all the way through the fuel. Also in this instance the grain has been cast into an inhibitor sleeve and therefore the weight of the sleeve has to be taken into account when weighing.

Specs for SKINT 20 Motor (using s_BETA_36.7 design) units are in grams & centimetres.

Grain Length: 14.5
Grain Outer Radius: 1.75

Core Length: 14.5
Core Radius: 0.5

Inhibitor Sleeve: 0.675 grams per centimetre.

Now it's just a matter of calculating the actual fuel volume using the calculator. The actual fuel volume is worked out by subtracting the core volume from the total grain volume so you'll need to work out both.

eg.

Fuel Volume = Grain Volume (139.51) minus Core Volume (11.39) = 128.12 cubic centimetres.

The total measured weight of the cast grain was 230.19 grams, so then we subtract the weight of the inhibitor sleeve, which I already have worked out as 0.675 grams per centimetre. 0.675 x 14.5 length = 9.78 grams. We then subtract that from the measured grain weight and end up with 220.41 grams for the actual fuel weight.

Density = weight/volume. 220.41/128.12 = 1.72 grams per cubic centimetre.

Why bother working out the density? If we follow the same method of making and casting the fuel, then a lower measured density can alert you that there may be voids in the fuel leading to CATO. Not the case with powder pressed but inconsistent density would change the burn rate and possible cato as well.

 

[EDIT] I almost forgot, one reason for wanting to attain a higher fuel density is that you can pack more into your motor. This means less overall weight for the casing and therefore more g-force and higher altitudes???

Hope the above calculations make sense - I couldn't really think of an easier way to explain it.

-

I got sick of working it out myself all the time so I created a solution in FileMaker. (images attached). The software allows for up to 6 grains, true bates or inhibited 1 or both ends. It works out the density and possible more importantly also the Kn ratios. The software is a database and therefore can keep records of various tested or proposed motor designs.

The software does not require excel and is able to run as a 'stand-alone' application. It works on WinXp and Win7, not sure about 8 or 10 but should work in compatibility mode.

 

If enough people are interested I'll make a few modifications and upload the software.

Edited September 3, 2016 by stix

[kramrocket]

 

So back on track regarding fuel density:

 

Here's a worked example using the simple volume calculator found here:

https://www.google.com.au/#q=calculate+volume+of+a+cylinder

 

The specs and calculations are for grains where the core extends all the way through the fuel. Also in this instance the grain has been cast into an inhibitor sleeve and therefore the weight of the sleeve has to be taken into account when weighing.

 

Specs for SKINT 20 Motor (using s_BETA_36.7 design) units are in grams & centimetres.

 

Grain Length: 14.5

Grain Outer Radius: 1.75

 

Core Length: 14.5

Core Radius: 0.5

 

Inhibitor Sleeve: 0.675 grams per centimetre.

 

Now it's just a matter of calculating the actual fuel volume using the calculator. The actual fuel volume is worked out by subtracting the core volume from the total grain volume so you'll need to work out both.

 

eg.

 

Fuel Volume = Grain Volume (139.51) minus Core Volume (11.39) = 128.12 cubic centimetres.

 

The total measured weight of the cast grain was 230.19 grams, so then we subtract the weight of the inhibitor sleeve, which I already have worked out as 0.675 grams per centimetre. 0.675 x 14.5 length = 9.78 grams. We then subtract that from the measured grain weight and end up with 220.41 grams for the actual fuel weight.

 

Density = weight/volume. 220.41/128.12 = 1.72 grams per cubic centimetre.

 

Why bother working out the density? If we follow the same method of making and casting the fuel, then a lower measured density can alert you that there may be voids in the fuel leading to CATO. Not the case with powder pressed but inconsistent density would change the burn rate and possible cato as well.

 

[EDIT] I almost forgot, one reason for wanting to attain a higher fuel density is that you can pack more into your motor. This means less overall weight for the casing and therefore more g-force and higher altitudes???

 

Hope the above calculations make sense - I couldn't really think of an easier way to explain it.

 

-

 

I got sick of working it out myself all the time so I created a solution in FileMaker. (images attached). The software allows for up to 6 grains, true bates or inhibited 1 or both ends. It works out the density and possible more importantly also the Kn ratios. The software is a database and therefore can keep records of various tested or proposed motor designs.

 

The software does not require excel and is able to run as a 'stand-alone' application. It works on WinXp and Win7, not sure about 8 or 10 but should work in compatibility mode.

 

 

If enough people are interested I'll make a few modifications and upload the software.

 

Or use simple maths and a 4 dollar calculator from Woolworths ....

[stix]

Or use simple maths and a 4 dollar calculator from Woolworths ....

 

That's true Kram, but you forgot about the piece of paper, pen and also the trusty Abacus.

 

It's quicker to get results without doing long tedious calculations by simply using the online volume calculator - why re-invent the wheel?.

 

I was doing too many many calculations the hard way - which are very boring, so I developed my own simple software solution. The great thing is that with my software, it's very easy to come up with "what if" scenarios. This especially relates to Kn ratios. I can, in a matter of seconds, "know" what the Kn ratios will be for a given geometry.

 

It's the only way to fly.

[kramrocket]

 

That's true Kram, but you forgot about the piece of paper, pen and also the trusty Abacus.

 

It's quicker to get results without doing long tedious calculations by simply using the online volume calculator - why re-invent the wheel?.

 

I was doing too many many calculations the hard way - which are very boring, so I developed my own simple software solution. The great thing is that with my software, it's very easy to come up with "what if" scenarios. This especially relates to Kn ratios. I can, in a matter of seconds, "know" what the Kn ratios will be for a given geometry.

 

It's the only way to fly.

Yes but to get an SG value will require accurate measurements of volume and weight of the sample... no software or online calculator can do that.

[stix]

Yes but to get an SG value will require accurate measurements of volume and weight of the sample... no software or online calculator can do that.

 

Perhaps it's "unobtainium". Of course the simple basic measurements using a decent ruler (or vernier calipers etc.) and a set of accurate scales are a prerequisite.The math has already been worked out for us over many years. Call it "wheel math" .

 

Accurate measurements become easier with the tools we have and Software takes the drudgery out of it. How you interpret the data you have is something to be considered. Software enables you to look at an "overall view". bla bla bla...

 

If we/they are that brilliant in measurements and data analysis, then the spaceX- rocket wouldn't have exploded on the launch pad!!. I actually liked the fact that it fucked up - and the other one that exploded not long after take-off. Fortunately no persons were killed.

 

That tells you something. It's very difficult to scale up and make big rockets. The "Big Boys" have got it wrong on this occassion. So, in some peverse way in my mind I think that it's open for all contenders... te heeeeee.... .

 

Taking short cuts is a big no no. NASA did the big things, and hopefully will always be at the forefront. I'll never trust an organisation that is motivated by money. NASA was motivated by a driven force and the words of JFK, to beat the Soviets into space. The "Space Race". If it wasn't for that, who knows... But since then the world has gone backwards.

[kramrocket]

From what I can gather, the Falcon 9 blew up due to human blunder, not miss-calculations in its design by the tech heads, shame though...

 

WASHINGTON — The explosion Sept. 1 that destroyed a SpaceX Falcon 9 rocket and its satellite payload took place not during a launch attempt but instead in a pre-launch test that is all but unique to SpaceX.

The explosion at Space Launch Complex 40 at Cape Canaveral Air Force Station occurred while the Falcon 9 was being filled with liquid oxygen and kerosene in preparation for a static-fire test, where the rocket’s nine first stage engines are briefly ignited on the pad a few days before the scheduled launch.

The static-fire tests have been a standard part of pre-launch preparations for Falcon 9 launches throughout the vehicle’s history. They are intended to serve as full dress rehearsals for launches and also verify the performance of the first stage engine.

- See more at: http://spacenews.com/falcon-9-pad-explosion-highlights-unique-aspect-of-spacex-launch-campaigns/#sthash.1su7pxjW.dpuf

[Mumbles]

All the more reason to use software instead of relying on the error of humans and their fat fingers with their 4 dollar Woolworth's calculator then.

[stix]

From what I can gather, the Falcon 9 blew up due to human blunder, not miss-calculations in its design by the tech heads, shame though...

 

The reported reason does point to human blunder - which in my view is worse than a mathematical mis-calculation.

 

Perhaps they took a few too many shortcuts - which is what you do if money is the motivation. I feel it everyday with the degradation of basic services and the rise in the cost of living.

[kramrocket]

All the more reason to use software instead of relying on the error of humans and their fat fingers with their 4 dollar Woolworth's calculator then.

 

Certainly true in many cases, but this was about simple density calculations I thought... so for that task, the ability of taking accurate measurements in volume and weight are most important I believe.

Since I do have fat fingers, I use an $8 calculator with large keys from Officeworks !!!

[kramrocket]

 

The reported reason does point to human blunder - which in my view is worse than a mathematical mis-calculation.

 

Perhaps they took a few too many shortcuts - which is what you do if money is the motivation. I feel it everyday with the degradation of basic services and the rise in the cost of living.

 

Yes, one of many costly human blunders... Challenger SRB 'O'rings and Hubble telescope mirror to name a couple ...

[kramrocket]

 

Well, your density is better than any melted version I've ever made. My average is around 1.72. So that's good for your "powder pressed" method. It would be good if you knew exactly what pressure you are using. Time to implement a pressure gauge Kram?

 

I'd also be very interested to know what density others get with their sugar fuel (melted or dry). Perhaps a bit too technical for some? Not that hard to work out though.

 

Crazy hard to determine the actual pressure that was applied to get the SG of 1.81.

 

A gauge would not be helpful with my method especially when scaling up a good working fuel.

 

The method I use for maximum density is...

 

Load the tube with a powder height of about four times the diameter of tube and slowly press until it feels firm while accurately monitoring any changes in tube diameter.

If I notice any increase in tube diameter it means I was way too aggressive with the applied pressure over time, this rarely happens now that I have mastered the technique.

 

So I load the tube with another portion of powder and so on...

 

The result is high density and consistent burn rate results !!!

[stix]

Well, well, well... something I've just realised is that the average density I've been getting was based on melted KNDX (my known working fuel). ie. the fuel being dextrose/glucose powder. @ SG ave. 1.72

 

Until know I've never bothered to check the differences. Looking at previous results using KNSU I got at average of 1.77 and at best 1.82 - not bad.

 

I also checked out Richard Nakka's resources http://www.nakka-rocketry.net/succhem.html and on the second table down the page you'll see "Density, as cast: 1.8"

 

So what that says to me is that DX is less dense. As I've pointed out before, there is a trade-off with castability.

 

At the moment my favoured fuel (due to castability) is KNSB, SB being Sorbitol. I haven't made an actual motor but I have cast grains, so I should get off my arse and check the density.

[stix]

As a side issue but complimentary to this discussion, I decided to do some simple calculations to determine what significance fuel density makes to the geometry of the fuel as in grain length, and therefore the casing length.

 

Grain density 1.7

Grain diameter 18.2mm

Grain length 70.0mm

Core diameter 5.3mm (through length)

 

Changing the density to 1.8:

 

Grain density 1.8

Grain diameter 18.2mm

Grain length 66.5mm

Core diameter 5.3mm

 

That means due to a higher density, a reduction of 3.5mm over the length of a small grain. Smaller motors like this one - perhaps no big deal, but the larger you go then the fuel density becomes a larger factor in performance due to extra weight, which ultimately affects final altitude.

 

Anyway, It wasn't too hard to work out this "what if" scenario using my wonderful software.

Edited September 11, 2016 by stix

[jbeuckm]

Sorry about the hijack - I don't have perms to start a new thread yet.

 

I am working from the Nakka KNO3-sucrose PVC dimensions but having some problems with making good propellant. I have built a few motors but with issues. Two lit (with difficulty) but burned inconsistently, "coughing" and puffing along. One I was unable to light with several igniters. I cut it open and found the fuel to be rubbery and doughy and easy to deform or smoosh out of the casing. It was solid and dry when I loaded it.

 

 

The problem might be the way I was building the plugs. I would cut a circle of card stock to keep the water putty from touching the fuel or running down the core. But I didn't seal the joint before pouring the concrete plug. Is it possible that enough moisture was sucked out of the concrete into the propellant to make it rubbery wet?

[NeighborJ]

Yeah I think the construction teqnique is the issue. The water putty in the end cap and the nozzle are generally dried completely before gluing them to the casing. This prevents the moisture from absorbing into the fuel, as you have already discovered. I also wait a few weeks before assembly to give the putty plenty of time to cure and dry then I coat the exposed putty with pvc glue while gluing to seal it. I then wait at least 24hrs before launch so the glue is cured.

 

 

Oh by the way welcome to the forum. j

Edited January 29, 2017 by NeighborJ

[stix]

Yeah, I think it's pretty much as you suspect and what NJ has pointed out that the fuel is absorbing moisture from the uncured water putty.

 

Not sure if you already do, but It's a good idea to roll a couple of test strands. That way you can easily test the batch of fuel - even before casting. Then at least you'll know that the fuel burns well. It should burn smoothly and leave little residue.

 

Welcome to the forum.

[jbeuckm]

I cooked some more and my test strand would not maintain a burn. I tried before and after curing to brittle hardness. It's peanut butter color. I have been using generic powdered sugar but I'm worried about the corn starch content and I'm going to try some with granulated table sugar. My KNO3 is Haifa mini prills 13-0-46. I'm dissolving the KNO3 in hot water in a griddle and then stirring in the sugar and barely boiling until paste and snap test.

[jbeuckm]

It was the powdered sugar. "Market Pantry" brand powdered sugar from Target is useless for rocket motors. With Market Pantry granulated sugar, the fuel cooked up ivory colored and burns cleanly. Thanks for reading and responding.

[NeighborJ]

Different sugar brands have verried fuel values but they all are close enough to at least burn steady. The oxidizer ratio can be adjusted for all types by observing the dross and carbon byproducts. What mix are you using and are you certain all the water is cooked out?

[lloyd]

Neighbor... "brands", or "types"? Table sugar (Sucrose) is sucrose, once the water's been driven-off.

 

There's certainly a difference between sucrose and dextrose or lactose...

 

Lloyd

[OldMarine]

Lloyd, NJ may be referring to powdered sugars. Those have differing amounts of an anti-cake additive. I'd use King Arthur because it has no additives (and I have it in my larder) so wouldn't have the effect the above poster had. Though I've never built a sugar rocket I have iced many cakes and cookies and I can tell you for certain that the sugar makes a difference. I'd prefer the pure sugar with a trigger sifter for my baking needs and think they'd be best for rocketry as well!

Cuisine heureux!