inhibitor recommendations for sugar endburner

[nils]

What inhibitor materials do you recommend for 50mm diameter sugar endburner?

I would like to make inhibitor tubes first and then cast the fuel iside.

[dagabu]

I like virgin kraft paper myself since it is very strong for it's thickness. I am rolling inhibitors that are 0.75" OD (19mm) and 18mm ID so they will fit inside a standard 0.75" tube. I am playing with drop-in grains with clay nozzled tubes and epoxied in bulkheads for sustainer motors.

 

Good luck!

[nils]

What glue do you use? How many layers? And do cover the paper fully with glue or only partially?

[stix]

My "Alpha" motor is a similar size to what Dags posted. 3/4" (19mm) OD.

 

I use Manilla Card wrapped around (approx. 2 layers) on a 17mm mandrel.

 

I use slightly watered down PVA. The finished product allows me to cast the fuel into the inhibitor sleeve, then insert it into the main motor casing.

 

There is a bit of slack. To ensure there is no burn through or propagation of the flame up the sides, I coat the final grain with high heat resistant RTV silicone. This also helps to insert/slip the grain into the casing. It's a "snug" fit.

 

A 50mm OD Sugar Rocket END BURNER???... You must have some amazing fuel comp. Do tell.

 

[EDIT]

I would be starting with smaller motors (19mm). Sometimes people think that just ramming powdered or melted KNSU into a cylinder, then chucking a nozzle into the end of it is easy. Yeah, sure it may work. Perhaps KNSU doesn't have the volatility of BP, but never under-estimate it's power or potential for an accident.

 

Be careful, be safe.

Edited January 23, 2019 by stix

[uncrichie]

Some High Power Rocket guys use Rosin paper from Home depot or Lowes. It is used Under hardwood floors between the sub floor and the hardwood. It is Pink in color and comes in long rolls.

 

They use regular wood glue thinned with water to what ever consistency works. Its used for propellant casting tubes but not for the liner tube.

 

There is a whole section devoted to it in the Restricted Research area on "The Rocketry Forum", unfortunately you need to have a Level 2 Certification from NAR or Tripoli to gain access. Your mileage may vary, good luck.

[nils]

My smaller 32mm sugar endburners are stable and work very well without inhibitor too. But my 50mm, motors are not jet stable without inhibitor when I want to reduce nozzle diameter to get bigger pressure=faster burning=more thrust.

Here is my current under construction test motor(s).

http://kodu.ut.ee/~nils/source/sugar_rocketry/50_mm_motor_with_recovery/50_mm_v2.jpg

[stix]

... "The Rocketry Forum", unfortunately you need to have a Level 2 Certification from NAR or Tripoli to gain access...

 

Yep, it's a shame to lock out people who just to like to experiment, but rules are rules I guess.

 

@Nils, when you say "My smaller 32mm sugar endburners are stable and work very well without inhibitor too" what does work very well mean? Does it take off with reasonable force? I say this because it's not that simple to "scale up" a proven motor especially with KNSU end burners.

 

If you can get a 50mm diameter sugar rocket END BURNER to take off (successfully), that is to say, with stability and plenty of thrust, then I'll go Gay. (I guess we will have agree on the criterea). If it was that easy, then I spose we could all fly to the moon atop a huge endburner sugar rocket. Inhe?

 

You may want to look at internal burners, which are much more efficient and powerful at bigger grain diameters.

 

[EDIT] A nice diagram does not translate into a nice working model. Good job though.

Edited January 24, 2019 by stix

[nils]

Today I made firs test with inhibitor. Inhibitor was 3-layers of construction cardboard and water based 2-component lacquer as a glue.

No delay charge, no ejection charge. Just inhibitor and nozzle test.

Here is the video:

Here is the data:

http://kodu.ut.ee/~nils/source/sugar_rocketry/50_mm_motor_with_recovery/50mm_inhibitor_test.jpg

Edited January 27, 2019 by nils

[stix]

Nice test Nils.

 

Now, lets make some basic evaluations,

 

Looking at the graph. I reckon at best about 25 Newtons average thrust. Convert that to kilos/grams = 2.55 kilos of thrust over maybe 5.5 seconds??. Respectable indeed.

 

How much would you say the motor weighed. Also, what was the weight of the fuel (approximately)?.

 

Knowing these two things will enable you to make an evaluation of how the motor+stick (or body) will take off. The fuel weight will tell us the Specific Impulse (efficiency) of the fuel. My gut feeling is that the motor+stick for a basic launch would not have enough thrust to make a successful launch.

 

By successful, I mean go up and keep going up out of harms way. Otherwise, it goes up and immediately arcs over. Potentially dangerous.

 

I'll give an example:

 

I'll gesstimate that the total rocket motor (fuel+casing) weighs around 500+ grams? Therefore we can divide the average thrust: 2550/500 = 5.1.

 

The 5.1 means G's. Then we minus off 1g to account for the motor to alleviate it's own weight. We end up with 4.1g's.

 

A general basic rule that believe in, is that you would like to have at least 5g's at launch. I don't think we have that.

 

What is required, is to know the context. I mean, it's all well and good to show the measured thrust in a graph, but without knowing the weight of the fuel and casing, then it's just a guess and the results are pretty much meaningless. You have to back the results up. It has to be qualified, shown, displayed in some detail.

 

There are REAL limitations to consider.

 

What you do have is good methods, and measuring equipment, and obviously a desire to achieve what you want. That's three key ingredients that makes a good researcher.

 

Cheers.

Edited January 28, 2019 by stix

[Arthur]

Nomex paper is used in the winding of some transformers -see whether it's available from Mouser or DigiKey.

[nils]

Some more specs about this particular test:

Fuel grain: 42mm diameter, 80mm lenght. 3 layers cardboard inhibitor
65 parts KNO3, 35 parts suckrose, 1 part red iron oxide. Cooked by completely
dissolving ingredients and then boiling the water out.
Burn rate was about 14mm/seconds. Pure fuel grain weight 200 grams.
Fuel temperature was room temperature, out of warm car.

Bodytube, endcap, nozzle, inhibitor, reinforcement combined was around 100 grams.
Polypropylene bodytube, cardboard and fibreglass tape reinforcement, plywood endcap and nozzle.

Total weight of the motor 300 grams.
Nozzle diameter 9mm.


I have 2 identical motors waiting. Next test will show if NC lacquer is enough to protect from moisture.

I created a custom motor with my graph in OpenRocket. Then inserted all other stuff like nozecone, bodytube, fins and payload(200 grams smartphone). Simulation showed that it will fly much higher than my goal is. Goal is 150 meters that is local limit by law for unmanned flights 30 kilometers away from airports. Thats without permission.