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Falco

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I see where some put the igniter just inside the nozzle and some stuff it all the way up the grain. Just so I'm straight on this, what would be the difference between the two on performance? (or anything else for that matter) Also, wouldn't stuffing it up to the end change the delay charge timing? Being a newby at this rocketry thing I wasn't sure if this was the right place to post this. On another note, this is the most fun I've had in quite awhile building and flying these without getting arrested!


Thanks
Falco
 
APCP motors are generally inserted all the way to the top of the motor, endburners and Black Powder (Estes and older Quest black powder) are inserted just inside the nozzle.
 
rharshberger said:
APCP motors are generally inserted all the way to the top of the motor, endburners and Black Powder (Estes and older Quest black powder) are inserted just inside the nozzle.
Click to expand...
There are a very small number of APCP motors in Aerotech's line that are not inserted all the way to the top. All in the 24mm/29mm hobbyline sizes.
 
heada said:
There are a very small number of APCP motors in Aerotech's line that are not inserted all the way to the top. All in the 24mm/29mm hobbyline sizes.
Click to expand...

That is only the case when the propellant itself doesn't go all the way to the top of the motor case, like the 29/40-120 E and F reloads that have an internal spacer.
 
with Estes BP motors, the ignitor is inserted as far as it will go (all the way forward), with the AT 24mm and 29mm motors the ignitors are inserted to the top of the propellant( which, if you followed the instructions and put tape on the forward end of the propellant stack is as far as it will go(see the theme here)).
Rex
 
Falco said:
) Also, wouldn't stuffing it up to the end change the delay charge timing? Thanks
Falco
Click to expand...
Composite motors with core...
Delay begins burn when motor lights, and continues after burn. example: [7 sec delay] motor has 2 second burn, delay has 9 so actual 7 occurs AFTER motor burn out.
This is how most [99%] of high power motors function.
When using Estes or many blackpowder motors they do not have a core [like high power] to insert the igniter to top, so it remains just inside nozzle.
Burning from nozzle to forward end [end burner] in this case the delay only burns AFTER motor fuel is done.

Please continue having fun!!!;)
 
Last edited:
Falco said:
I see where some put the igniter just inside the nozzle and some stuff it all the way up the grain. Just so I'm straight on this, what would be the difference between the two on performance? (or anything else for that matter) Also, wouldn't stuffing it up to the end change the delay charge timing? Being a newby at this rocketry thing I wasn't sure if this was the right place to post this. On another note, this is the most fun I've had in quite awhile building and flying these without getting arrested!


Thanks
Falco
Click to expand...

Thanks for the replies, things are starting to make sense now. I've had 4 launches now with mixed results. The first went up about 50ft, did a 90 degree turn, and exited stage right for about 300 yrds across the Snake river and landed about 10 ft from shore. Second started an end for end right after launch. Third blew the top plug out. And the forth just sat on the launch pad and burned all the fuel. (too big of a hole in the nozzle) Just about done with the fifth. I'll keep ya posted. o_O

Thanks again!
 
Falco said:
Thanks for the replies, things are starting to make sense now. I've had 4 launches now with mixed results. The first went up about 50ft, did a 90 degree turn, and exited stage right for about 300 yrds across the Snake river and landed about 10 ft from shore. Second started an end for end right after launch. Third blew the top plug out. And the forth just sat on the launch pad and burned all the fuel. (too big of a hole in the nozzle) Just about done with the fifth. I'll keep ya posted. o_O

Thanks again!
Click to expand...


What motors you using?
Sounds/looks like your making your own !!
 
Yes I am making my own. I don't know what size they would be called but they're made of the schedule 40 pvc in 1", 1 1/2", and 2" and potassium nitrate and sugar. (haven't blown anything up or caught myself on fire yet so I must be doing something right) Another thing I'm wondering about is the balance. I've flown just about everything there is when it comes to radio control (although, the heli's seemed to want to attack me just after lift off) so I know how important it is getting the balance correct. I've watched the guy on youtube swing the rocket around for balance but I'm pretty sure they do it another way for the larger rockets that weigh 50 lbs or more. Any info on this would be great!

Falco
 
Please contact your local Tripoli Rocketry prefecture (aka club) and see if they can set you up with a mentor. I see a couple of things that you are doing that aren't very good ideas. I don't do much with sugar motors, so there are probably more. You definitely want to re-think PVC pipe. If you get your nozzle too small, it will turn into shrapnel that can't be seen on X-rays. 2" motors are also getting pretty big, into the area where the FAA probably would take an interest in what you're doing, and not in a good way.

Sounds like you have some stability issues. Normally, you want the center of pressure (aka center of drag) to be at least one body tube diameter (aka one caliber) towards the nose from the center of gravity. You'll need a little more if you go above Mach. OpenRocket is a free download and it can help you out here.

The first flight may have taken the turn because you didn't have enough thrust so it wasn't going fast enough once it left the launch rail/rod. That's another thing that OpenRocket can help you with, though you will need to have a good sense of what kind of thrust your motor is putting out.
 
From the NAR webpage on high power rocketry:

A rocket exceeds the definition of a model rocket under NFPA 1122 and becomes a High Power rocket under NFPA 1127 if it:

Uses a motor with more than 160 Newton-seconds of total impulse (an “H” motor or larger) or multiple motors that all together exceed 320 Newton-seconds;
  • Uses a motor with more than 80 Newtons average thrust (see rocket motor coding);
  • Exceeds 125 grams of propellant;
  • Uses a hybrid motor or a motor designed to emit sparks;
  • Weighs more than 1,500 grams including motor(s); or
  • Includes any airframe parts of ductile metal.
If a rocket you are launching meets ANY of these criteria then you MUST have FAA clearance to launch your rocket. Based on what information you have provided so far I am willing to bet that your rockets are high power based on at least two of these categories.
 
@boatgeek er your definition of the desired cg/cp relationship it should be the otherway around with the cp aft of the cg, else the rocket will skywrite.
Rex
 
boatgeek said:
Please contact your local Tripoli Rocketry prefecture (aka club) and see if they can set you up with a mentor. I see a couple of things that you are doing that aren't very good ideas. I don't do much with sugar motors, so there are probably more. You definitely want to re-think PVC pipe. If you get your nozzle too small, it will turn into shrapnel that can't be seen on X-rays. 2" motors are also getting pretty big, into the area where the FAA probably would take an interest in what you're doing, and not in a good way.

Sounds like I need to downsize to keep the FAA off me. I've given some thought about whether or not I've built a pipe bomb or a rocket. So far we've been ducking behind whoever showed up with the oldest car with plywood covering the area under the car. (safety first) I know, sounds kinda hillbilly-ish but I don't want anyone to get hurt on my account.

Sounds like you have some stability issues. Normally, you want the center of pressure (aka center of drag) to be at least one body tube diameter (aka one caliber) towards the nose from the center of gravity. You'll need a little more if you go above Mach. OpenRocket is a free download and it can help you out here.

I've got it but haven't really played with it much. I will now.

The first flight may have taken the turn because you didn't have enough thrust so it wasn't going fast enough once it left the launch rail/rod. That's another thing that OpenRocket can help you with, though you will need to have a good sense of what kind of thrust your motor is putting out.
Click to expand...

I was putting the fuze just inside the nozzle and not all the way up like I've been told from an earlier post. It was a slow launch as you suggested.

Thanks for the info! I'm learning all kinds of new s...tuff from this forum! Thanks again.
 
heada said:
There are a very small number of APCP motors in Aerotech's line that are not inserted all the way to the top. All in the 24mm/29mm hobbyline sizes.
Click to expand...

Don't forget the AT 38mm I49 and I59N both end burning Warp9 propellants. They have a tiny depression in the aft grain that the "Starter" (ignitor) sits in.
 
Rex R said:
@boatgeek er your definition of the desired cg/cp relationship it should be the otherway around with the cp aft of the cg, else the rocket will skywrite.
Rex
Click to expand...

Derp. You are absolutely right. I re-read the rest of what I said and I think it's OK.

Also, OP, if you are using a true fuse (light the end and stand back), you shouldn't be. Use a real igniter like a FirstFire or many others. That lets you call off the launch up to the moment of pushing the button launching. The slow liftoff may well have been because of poor ignition from only lighting the bottom of the fuel.
 

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