Sugar Rocket Motor Mods

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wjwj
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Joined: Sat Mar 12, 2016 6:15 pm

Sugar Rocket Motor Mods

Postby wjwj » Sat Mar 12, 2016 6:17 pm

Hi,

A question for any of you rocketry/chemistry experts out there. I am a radio-control enthusiast who has recently been experimenting with rocket motors. What I am trying to do is create a "rocket plane", but unlike typical rocket planes, I am putting much time and care into making a craft that is both light and aerodynamic to achieve high flights.

Here is my question: I want to use sugar motors (KNO3 and sucrose) to power this thing. I have made a few already, but the problem is that they burn way too fast with too much thrust. What I want to do is modify the motor to slow the burn. Here is my idea:

Add baking soda to the KNO3/sucrose mixture since baking soda is non-flammable. I know this is done to create a delay charge, but I don't want it to burn that slow. Also, I would probably decrease the nozzle diameter to accommodate the pressure decrease.

What are your thoughts on this? Does it seem doable? Are there any formulas/methods for determining how much baking soda to add? If I could extend the burn from ~2s to ~10s then I would be happy.

Thanks for your help!

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tfish
Posts: 17
Joined: Thu Feb 04, 2016 11:54 am

Re: Sugar Rocket Motor Mods

Postby tfish » Sat Mar 12, 2016 7:35 pm

I've never played with Sugar..only AP. I really doubt your get a 10 second burn. I'd be surprised is you could get 4 seconds. There are a few things to keep in mind. As you add in this dry powder in what ever %..let's say 4% just to have a number. That 4% is a very fine and dry material. It's going to make the rest of the propellant even more dry and brittle then it already is.
I "tried" something similar with 3% dry chem powder in a AP mix.
https://www.youtube.com/watch?v=sfZ2zSZO19k see 3:50 into video..

Tony

wjwj
Posts: 3
Joined: Sat Mar 12, 2016 6:15 pm

Re: Sugar Rocket Motor Mods

Postby wjwj » Sat Mar 12, 2016 8:30 pm

Thanks for the thoughts - and nice vid!

Perhaps you could explain what you mean when you say "dry" and "brittle"? (forgive me as I am new to this.)

There must be some way to do this. The reason I say that is because there are such "long burn" motors sold online. Take the Aerotech F10 for example. It has 7.8sec of burn with decent power. If I could basically mimic that motor, but in a slightly larger size (looking for a G-ish motor), then I would be set.

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tfish
Posts: 17
Joined: Thu Feb 04, 2016 11:54 am

Re: Sugar Rocket Motor Mods

Postby tfish » Sat Mar 12, 2016 9:50 pm

The propellants physical properties must be up to the task of not cracking and holding together during the burn. A quick google search of brittle sugar motors will show some issue with some sugar formulas and being brittle. I believe this is why they use various sugars to avoid being brittle. I did say I've never done sugar motors right?
Even AP formulas must maintain certain physical properties to work properly. The "fast burning" motor in the video I linked, had propellant that was to dry in that it did not have enough liquids (think of liquids as glue) to hold everything together during the burn..cracking chunks breaking off etc = way to much surface area and the motor lets go.
There are ways to make AP motors and maybe even sugar motors (I'm guessing) burn longer. For AP if you reduce the solids loading (solids = all the things that give the propellant it's umph (technical term)). You wants to fly a road flare that can't even lift itself? There is a chemical called Oxamide that can reduce the burn time by 20% (?) when used @ about 6%. Oxamide is about $30 a pound.
The other way is by grain geometry. Moon burners, c-slot or D grains http://www.aerorocket.com/AeroIsp/AeroIsp.html. The longest burning motors are end burners. The problem with long burning motors is protecting the motor case during the burn. Our normal Phenolic paper liners are good for abut 4 seconds with some mild propellants. You're talking 10 seconds burn times.
One thing I learned a few years ago was, no matter what I think I'm not the first guy to try "blah blah blah" in regards to rocket motors. Somebody else has tried it maybe it's on line some place https://www.google.com/search?q=long+bu ... A&dpr=0.85

Tony "the first guy to fly a rocket using a Billiards Ball for a nozzle!"

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wjwj
Posts: 3
Joined: Sat Mar 12, 2016 6:15 pm

Re: Sugar Rocket Motor Mods

Postby wjwj » Sat Mar 12, 2016 11:39 pm

Here's a page that seems to be explaining exactly what I am looking for. What are your thoughts on this?

It appears that the burn time can be extended significantly by simply using and end-burner motor.

http://www.jamesyawn.net/endburner/

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tfish
Posts: 17
Joined: Thu Feb 04, 2016 11:54 am

Re: Sugar Rocket Motor Mods

Postby tfish » Sun Mar 13, 2016 7:34 pm

See...somebody already has been playing around with long burn sugar motors. That looks totally doable as a DIY home project. Keep us posted on how it goes!

Tony


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