why are my rocket motors not providing any thrust?

[Legolessed]

i built some rocket motors using pvc for the casing, clay for the two ends, and pottasium nitrate and sugar as the fuel. Im using a 60/40 ratio of pottasium to sugar. im getting a really nice burn but no thrust, the burn is lasting like 5 or so seconds on them and im getting the thrust directed downward as it should be but again no thrust. what am i doing wrong?

[Guest]

Nozzle?

[Legolessed]

3 minutes ago, Dutch-stoner said:

Nozzle?

ya i have a clay plug that i drilled into, one thing do i need to drill all the way through the rocket propellent? i lit the rocket from the bottom, do i need to use like a string or something to lite it all at the same time?

[Guest]

Might not be a good nozzle. Doubt if I can say this here, but I would suggest making it into a bomb as a test. If it can explode instantly, the burn rate of your fuel is good. If it will just fizzle, you know you screwed up.

 

Also, you might want to look up some mythbusters vids. They made some rocket stuff too, but if I remember correctly, they used candle wax.

[Legolessed]

Just now, Dutch-stoner said:

Might not be a good nozzle. Doubt if I can say this here, but I would suggest making it into a bomb as a test. If it can explode instantly, the burn rate of your fuel is good. If it will just fizzle, you know you screwed up.

 

Also, you might want to look up some mythbusters vids. They made some rocket stuff too, but if I remember correctly, they used candle wax.

ive been looking stuff up and grant thompson or the king of random used some really crappy kitty litter that was basically clay and it worked great. I know its resiliant enough because the fuel chamber was fine after the rocket failed to get off the ground. Is there anything i can add to my ocket fuel to increase its burn rate? and should i put a string in the motor so that the entire rocket ignites at once or no?

[Legolessed]

2 hours ago, Dutch-stoner said:

Might not be a good nozzle. Doubt if I can say this here, but I would suggest making it into a bomb as a test. If it can explode instantly, the burn rate of your fuel is good. If it will just fizzle, you know you screwed up.

 

Also, you might want to look up some mythbusters vids. They made some rocket stuff too, but if I remember correctly, they used candle wax.

@Hackentosher

can i use 5 minute epoxy to glue on a nozzle or is it not heat resistant? also does adding corn syrup to my fuel mix help?

[Hackentosher]

10 hours ago, Legolessed said:

@Hackentosher

can i use 5 minute epoxy to glue on a nozzle or is it not heat resistant? also does adding corn syrup to my fuel mix help?

rocketry is not my area of expertise. If you want to know the properties of some schmoo, google it.

[Legolessed]

1 hour ago, Hackentosher said:

rocketry is not my area of expertise. If you want to know the properties of some schmoo, google it.

ok standard 5 minute epoxy is fine up to about 177 degrees 7 and im using it away from the nozzle and on a mini rocket thats only a couple inches tall. should be good.

[bob345]

21 hours ago, Legolessed said:

ya i have a clay plug that i drilled into, one thing do i need to drill all the way through the rocket propellent? i lit the rocket from the bottom, do i need to use like a string or something to lite it all at the same time?

If there is no hole down the center of the propellant, you are losing nearly all of your potential thrust. When it comes to burning solid fuel quickly, surface area is absolutely key. with a hole or slot down the center, you are able to burn a much larger surface. As the fuel burns, the surface area increases creating an exponential increase in the rate at which the fuel burns. Just burning a solid chunk of fuel from bottom to top, you are just burning a small amount and the surface area never changes as it burns.

 Its why you see shapes like this being used in high power solid fuel rockets

[Legolessed]

1 hour ago, bob345 said:

If there is no hole down the center of the propellant, you are losing nearly all of your potential thrust. When it comes to burning solid fuel quickly, surface area is absolutely key. with a hole or slot down the center, you are able to burn a much larger surface. As the fuel burns, the surface area increases creating an exponential increase in the rate at which the fuel burns. Just burning a solid chunk of fuel from bottom to top, you are just burning a small amount and the surface area never changes as it burns.

 Its why you see shapes like this being used in high power solid fuel rockets

i got a very succesful burn by doing that. thank you so much!

[straight_stewie]

How much fuel is there? A 5 second burn is a LOOOOONG burn for a beginners hobby motor, it may be burning slightly too slowly to provide decent thrust. 

For R-Candy (which is what you are making), you want a solid 1cm roll to burn at a rate of roughly 1 - 1.5 mm a second. You should do this test for every batch.