"HellFire" Baby J, J1600 build

The Rocketry Forum

Help Support The Rocketry Forum:

timbucktoo

Well-Known Member
Staff member
TRF Supporter
Global Mod
Joined
Jun 13, 2014
Messages
8,249
Reaction score
1,345
Location
Cocoa Beach
Anything left of the grains? Or can you show us a grain (close up) of what you’re about to burn?
 

PayLoad

I don't do spirals
TRF Supporter
Joined
Aug 21, 2020
Messages
555
Reaction score
648
Location
Orefield, PA
Grains 1 & 2 burned, grains #3 & #4 were ejected un-lit. With regards to what I am trying with this one, I call it the inverted nipple cut / modified end burn
 

PayLoad

I don't do spirals
TRF Supporter
Joined
Aug 21, 2020
Messages
555
Reaction score
648
Location
Orefield, PA
28 inch core. 5/8 to 3/8 to 1/4, staggered depths to a total of 12 inches. Inverted (stretched) nipple
 

PayLoad

I don't do spirals
TRF Supporter
Joined
Aug 21, 2020
Messages
555
Reaction score
648
Location
Orefield, PA
12 and 16, yes. We learn by the wisdom of others. When that is not available, you experiment.
 

3stoogesrocketry

Well-Known Member
Joined
Feb 26, 2012
Messages
1,472
Reaction score
272
Get me into the [Restricted]Research part of the forum and I'll share.
Why ? You buy your grains from RCS . All needed info is on the RCS page about fuel specifics . It is not research to share what your grain fuel choice is , core size , KN , or expected performance. You only need to be in the research area to discuss compositions.
 

CalebJ

Well-Known Member
TRF Supporter
Joined
Jan 20, 2020
Messages
695
Reaction score
474
Why do you think it's 'going pear shaped' when people are asking you basic questions?
 

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
6,137
Reaction score
400
Location
Central Illinois
12 and 16, yes. We learn by the wisdom of others. When that is not available, you experiment.
That might burn pretty hot and destroy the case with a 12 inch long end burn grain. I'd bury it in the ground to be honest with you. Case could melt. If nozzle fails with the end grain still burning like a flare, the heat soak (if it doesn't melt the case in two) will probably severely compromise the strength of the case.

Kurt
 

3stoogesrocketry

Well-Known Member
Joined
Feb 26, 2012
Messages
1,472
Reaction score
272
Don't be upset , you've mastered tracking smoke lol . In all seriousness , you took on one heck of a challenge , and I am sure have learned a lot. Don't give up , just start smaller . Learn to master a 18 inch motor first.
 

neil_w

Good at some things
TRF Supporter
Joined
Jul 14, 2015
Messages
11,639
Reaction score
4,439
Location
Northern NJ
[dumb joke is dumb, deleted]
 
Last edited:

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
6,137
Reaction score
400
Location
Central Illinois
Well ****.... Now I am done.

For cripes sake man. Chalk it up as a learning experience as long-necked motors are a REALLY big challenge to get right in any diameter even with a cool burning mixture. Hang in there!

Try some shorter motors and work your way up. If anyone around there in your area is known to be a mixer, go to them or their club.
I learned a lot of stuff in a TRA club (now defunct because the prefect died) that did a lot of communal mixing. Bring your "stuff" casting tubes, chems and such and have at it. We'd figure out what recipe to use and did the "ball and pack" routine as there were plenty of members who'd show up to help out even if they weren't able to bring chems to the mixes. Suffice it to say the prefect made sure anyone who helped out, got some grains in what size the participant would like whether the person brought "stuff" or not. Those were heady days for me. We guys had a lot of fun too.

I saw others misfortunes and learned from them too. Burnsim is a tool that is not absolutely perfect. Good but not perfect. The posted "numbers" A and N one has to trust whomever ran them on whatever equipment they used if using a borrowed mix formula. Use them as a starting point. The longer one uses it (Burnsim) and compares it to their test burns, the better they will become at testing motors and determining motor length and how to "step" grain cores. (To a degree mind you because if one steps over the line of too high an L/D ratio there may be nothing that can help them if they go too far.)

I think I might have had the prediction right in #46 above.

"That might burn pretty hot and destroy the case with a 12 inch long end burn grain. I'd bury it in the ground to be honest with you. Case could melt. If nozzle fails with the end grain still burning like a flare, the heat soak (if it doesn't melt the case in two) will probably severely compromise the strength of the case."

The longer one does this, the better they will get at making predictions and it makes it that much more fun!

Soooooooooo, have at it and keep going.

Kurt Savegnago
 

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
6,137
Reaction score
400
Location
Central Illinois
Ooops,

I might be wrong. Thought nozzle blew. If that didn't happen, might be the throat was too large. But then getting it right with that long of motor would be a challenge. The igniter cap looks like it flew up and I thought that was the nozzle. Me bad. Hope OP posts some more details.

Kurt
 

PayLoad

I don't do spirals
TRF Supporter
Joined
Aug 21, 2020
Messages
555
Reaction score
648
Location
Orefield, PA
OK, so, nozzle DID stay in, my assumption is the nozzle throat was too large and core not deep enough. It was an "almost". Melted case by the end.

Trying to look at the bright side - at least this one did not out & out explode like the last 2.

I have to take a break making these for a while, as my wife is giving me "the look" when discussing purchasing more parts, all of the old ones now in my garbage can.
 
Top