Weight difference between r-candy and pressed BP

[yoyo]

Hello,

 

How much would a 3-lb BP rocket that's 10 inches long weigh? I'm making r-candy rockets and was wondering if it is necessary to make them also 10 inches long (7/8" ID) to approximate the equivalent BP rocket (and weight)?

 

Also, would adding small gas vent holes half-way up the rocket tube help flame burning by drawing in more oxygen, or would the difference be negligible?

 

Thanks.

[MrB]

The rocket fuel already has all the oxygen it needs to burn (Or rather, should have)

Adding a hole on the side will just cause it to create thrust perpendicular to the hole, and since it weakens the tube, might make it cato. I wouldn't do it.

B!

[ddewees]

Three pound motors usually weigh around 300 grams or slightly more.

[stix]

Hello,

 

How much would a 3-lb BP rocket that's 10 inches long weigh? I'm making r-candy rockets and was wondering if it is necessary to make them also 10 inches long (7/8" ID) to approximate the equivalent BP rocket (and weight)?

 

Also, would adding small gas vent holes half-way up the rocket tube help flame burning by drawing in more oxygen, or would the difference be negligible?

 

Thanks.

 

My average r-randy density is around 1.75 grams per cubic centimeter - slightly more than BP which is around 1.7 (I believe). Therefore you would be looking at very similar packing volumes.

 

As mentioned, probably not a good idea to have 'vent holes' as it would weaken the structure. Anyway, why would you think you need to "help the flame burning"???... If you've made good r-candy it should burn extremely well unassisted.

 

Cheers.

[Col]

Hello,

 

How much would a 3-lb BP rocket that's 10 inches long weigh? I'm making r-candy rockets and was wondering if it is necessary to make them also 10 inches long (7/8" ID) to approximate the equivalent BP rocket (and weight)?

 

3lb rockets are 1" id, 7/8" is a 2lb

[stix]

... if it is necessary to make them also 10 inches long ...

 

I'm assuming that you are making 'end burning' rockets? (not core/bates grains).

 

If so, the length of the fuel will determine the burn time only - therefore the answer is no, you don't need to make it 10 inches long.

 

Best to start shorter to see what sort of thrust you are getting before wasting too much fuel.

 

Cheers.

Edited November 16, 2014 by stix

[schroedinger]

I would wonder if a r-candy rocket of that size would even be able to carry the stick if it is a end burner.

 

Also don't forget about the difference in isp.

[stix]

I would wonder if a r-candy rocket of that size would even be able to carry the stick if it is a end burner.

 

Also don't forget about the difference in isp.

 

I agree. Even with the addition of red iron oxide, it doesn't burn as quick as good BP. You would have to have a much smaller nozzle diameter which I don't like the idea of.

 

The specific impulse of BP is around 80 secs, whereas r-candy can yield around 130. I have managed to achieve 100 with a bates grain configuration.

 

This 'H' class motor delivered an isp of 96, burned for approx. 3 seconds with a max. thrust of 15 kilos.

2 bates grains totaling 14.5cms in length, 220 grams of fuel, 3.5cms OD, 1cm core.

 

Suited to model rocketry, not pyrotechnics.

 

I can't see being able to get this sort of result with an end burner and it likely wouldn't even leave the launch pad.

Edited November 16, 2014 by stix

[yoyo]

My process is not perfect, so I still see a lot of variation in thrust. I was able to get a max thrust of about 3 kilos once (~2 second burn time) on a 4.5" long rocket. The following was 6.5" long.

 

https://www.youtube.com/watch?v=KMRXEBHODuM

 

All of my rockets are end-burners, as I don't know how to have a bentonite cap and also a nozzle simultaneously. When they don't explode (reuse of old tubes or fuel is too powerful) they have no problems getting up.

[stix]

I checked out the vid - not bad, and it did take off.

 

I'm assuming that this was a nozzleless motor?

 

When making nozzles, are you pressing bentonite then drilling out?

[yoyo]

Yes to both questions (actually I hammer the bentonite). I've thought of rockite but haven't gotten around to it yet.

[stix]

No probs. I actually liked the way it took off - mine take off too quick which means you have to stand way back to appreciate it.

[yoyo]

That will be the last to use a 60/40 mix. I've had rockets using the same mix, without iron oxide, that are about 4" long take off much faster, but this is still too slow. Everything after will use a 65/35 mix with 2% iron oxide and 5% titanium.

 

I actually made one rocket that also included 5% aluminum flitters, but that was a mistake, as it proved impossible to incorporate into the mix and wound up getting stuffed into the tube. The result was 2 minutes of sparks and smoke that didn't get off the ground.