Big, maybe dangerous motors made by confused newbie

[ryaer]

Hey, this is my first post, (please keep that in mind, I have no idea what I'm doing regarding forums) and I have just recently started building my own motors. I've been interested in rocketry my whole life (All 16 years of it) and have decided to get away from the kit rockets and premade motors into homebuilt rockets with homebuilt motors. I've cast and made two motors ( 1" bore, 7" fuel grain, 1:4 typical nozzle with convergent at 40 degrees and divergent at 12 degrees, and the typical sodium nitrate and sucrose 65/35 mix) and built my own ignitors. However, I've had no luck in getting any motor to start, despite my numerous attempts at trying. Am I doing something wrong? Is it the sodium nitrate? Should I use dextrose? Thanks, as I would rather not blow myself up.

[lloyd]

You lack a suitable 'igniter'. A simple fuse or e-match may not be enough for some compositions. Try 'doping' the end of the grain with a bit of Black Powder prime. It may be all you need to get ignition. If not, try a "perchorate BP" (similar composition, but with potassium perchlorate instead of the nitrate).

 

Lloyd

[Mumbles]

I don't know that I'd call a 65/35 mix of sodium nitrate and sucrose typical, as it's not very common at all. The sodium nitrate may be at fault. It can be quite hygroscopic. If the motors are not properly stored, it can absorb enough water to drastically alter the burn characteristics and render itself much more difficult to ignite.

 

This is part of the reason why it's much more common to use potassium nitrate and sucrose. This on its own has hygroscopic issues. It's fairly common to try to burn a small amount of your fuel in the open. This should give you some idea if it's a fuel issue or an igniter issue.

 

You also don't mention how you preparing the fuel. Melt cast? Ground and pressed? R-candy? Also are you using any core, or is this an end burner?

[NeighborJ]

I agree with Lloyd assuming the fuel is completely dry. I'm curious what you used for the nozzle material?

If water putty was used it can still give off a lot of moisture even after it sets. Sodium nitrate loves to soak up this moisture much more than KNO3. I always pre made a bunch of nozzles about a month before I fastened them to the motor in order to ensure they were as dry as possible,likewise the endplugs were also pre-formed early.

Ahh, mumbles beat me too it.

Edited May 29, 2017 by NeighborJ

[Mumbles]

At least there's no such thing as too much good advice.

[lloyd]

Ah! Mumbles! Now... if only we could get folks to listen to that advice!

 

But then, every one of us need to "learn on our own", no-matter the risk! <don't say YOU didn't, because I did! grin>

 

Lloyd

[ryaer]

Oh lord, thank you for all the replies! Firstly, an update, I cast the nozzle out of water putty yesterday, and casting the grain today ( I did the boil then press method regarding the mixture) I then poured a header for the motor from the same water putty, let dry, and ignited. For ignition, I used a bit of gunpowder mixed with powdered sugar to inhibit it, and a homemade e match (NC lacquer and 40 gauge NiCrome with 18 volts behind it) I ignited the motor, and the grain "burned". The freshly cast grain took 85 seconds to burn 123 grams (Convenient right?) of fuel. This is the first ignition i've had, but it was the worst burn time by far. I think i left a lot of water in the mix when I cast, it was a bit lighter than what I usually go with. When the motor fired, It suppertered, exactly what you would see if the throat was too small. And on terms of hygroscopic, It was freshly cast, and I sealed the ends right after casting. Again, thank you for all the advice, I have little idea what i'm doing.

Oh, and on terms of grain, It's a single core grain (One hole up the middle to about 3/4 till then end of the grain)

[ryaer]

And could any of you give me the theoretical "optimum" for NaNo3 and sucrose? I've just brought some Kno3 online, in addition with magnesium, dextrose, and aluminum for other experiments/fun activities. ( I am aware of the dangers of magnesium, I'll wear a welding mask when burning it )

[AzoMittle]

If the motors are not properly stored, it can absorb enough water to drastically alter the burn characteristics and render itself much more difficult to ignite.

 

 

I've been wondering about this myself. How do you recommend storing them? Storing bp motors?

 

@OP I'm on mobile, I'll get you more info when i get home. A welding mask is not adequate protection though and be careful with hand pressing or casting metal fueled rockets.

[NeighborJ]

The exact value needed for any sugar based rocket fuel changes from brand to brand and sometimes batch to batch. The best method to find the optimum oxidizer fuel ratio is to do burn tests on every batch.

 

When it has too much oxidizer it will leave white clumps of dross and if it is too fuel rich it will leave chunks of carbon behind. It will take a bit of experimenting.

 

The sound you heard at ignition is referred to as chuffing. It can be caused by and imbalanced fuel ratio and/or moisture in the fuel. I assume this is a endburner but on coreburners the chuffing can also be attributed to incomplete core ignition.

[ryaer]

The exact value needed for any sugar based rocket fuel changes from brand to brand and sometimes batch to batch. The best method to find the optimum oxidizer fuel ratio is to do burn tests on every batch.

 

When it has too much oxidizer it will leave white clumps of dross and if it is too fuel rich it will leave chunks of carbon behind. It will take a bit of experimenting.

 

The sound you heard at ignition is referred to as chuffing. It can be caused by and imbalanced fuel ratio and/or moisture in the fuel. I assume this is a endburner but on coreburners the chuffing can also be attributed to incomplete core ignition.

Thanks man, there was a tonne of white clumps. And as to chuffing, I think I'm thinking of liquid fueled rockets..... I'll experiment with Kno3 when I get it. I'll also drop the amount of Nano3 and see if that does anything.

 

 

@OP I'm on mobile, I'll get you more info when i get home. A welding mask is not adequate protection though and be careful with hand pressing or casting metal fueled rockets.

In what way? I'm a noob and want to keep my fingers attached for as long as possible.

[AzoMittle]

http://www.skylighter.com/fireworks/How-to-make-sky-rockets/black-powder-rockets.asp

[Mumbles]

The best insurance to make sure you keep all appendages is to read up on the subject and immerse yourself in all the available resources. There's a lot of worthwhile information out there which will only help you in your endeavors. Doing something right sometimes takes patience though. I found at least one reference to NaNO3 sugar rockets. Hate to say it, but it sounds like they leave something to be desired on their own and are less straight forward.

 

http://jamesyawn.net/nano3/1-19-04c/index.html

 

As far as storage AzoMittle, a desert would be my first choice if you could even cook all the water out of them in the first place.

[Nessalco]

I think I'm thinking of liquid fueled rockets....

Don't.

 

I flew high power hobby rockets that were solid fuel and a liquid oxidizer. To say that they are complex and quirky is putting it mildly. On one occasion I was ground testing a K class motor, and the oxidizer exploded. Peeled an aluminum case, tested to 4000psi, like a banana.

 

An all-liquid motor is far more complex, and far more dangerous.

 

KO

[ryaer]

Don't.

 

I flew high power hobby rockets that were solid fuel and a liquid oxidizer. To say that they are complex and quirky is putting it mildly. On one occasion I was ground testing a K class motor, and the oxidizer exploded. Peeled an aluminum case, tested to 4000psi, like a banana.

 

An all-liquid motor is far more complex, and far more dangerous.

 

KO

I don't plan on it. Hybrid rockets are as far as I'll go presuming rcandy rockets ever get off the ground, pardon the confusion.

 

And on terms of figuring thrust of motors, what sort of kit do you guys use to measure thrust? I've tried calculating it, and had mixed results. And what's calculated on paper may not be what actually happens in reality.

 

And thank you Mumbles for the link, I guess my ratios were way off.

Edited May 30, 2017 by ryaer

[Nessalco]

I use ProPep and BurnSim to model motors with new configurations or fuels. ProPep is open source and available from various sites and with various data files, while BurnSim is proprietary and costs a few bucks.

 

KO

[AzoMittle]

I'll second burnsim, great piece of software. Best advice I can give is to focus on BP rockets, if you haven't yet I would get a professionally made rocket tooling, we have some great vendors here on the forum. Other than that keep browsing through the rocket subforum on here, chances are that other people have had the same or similar questions before.

 

As far as storage goes, ya a desert, other than that the best I've found is ziploc baggies with silica desiccant by the handful. I got something similar to this: https://www.amazon.com/Premium-Desiccant-Indicating-Industry-Standard/dp/B01I5Y2DG6/ref=sr_1_17?ie=UTF8&qid=1496209338&sr=8-17-spons&keywords=silica+desiccant&psc=1 It can be dried out in the oven on the lowest setting.

[ryaer]

Why black powder motors? Are they just easier to make than R-candy? And I have some tooling I built, namely a 1" bore rammer, and a corresponding size and assortment of equipment to cast my nozzles.

[stix]

Why black powder motors? Are they just easier to make than R-candy? And I have some tooling I built, namely a 1" bore rammer, and a corresponding size and assortment of equipment to cast my nozzles.

 

My view is that making bp is more dangerous for the novice than making r-candy. I'm sure I'll have disagreement but the reality is, in my experience, it's far easier to ignite bp than any standard KNSU mix.

 

ryaer, I'd forget about Sodium Nitrate for the reasons that others have already posted. When you get your KNO3, then start over again and ask questions on this forum.

 

Cheers.

[ryaer]

Will do, I'll stick with KNSU or KNDX for the time being, I'm just waiting for my Kno3 to arrive.