any 18 mm motors larger than D

[MarkII]

I am not sure how much more punch would be possible in the small 18mm case. Warp 9 might give more impulse, but without reliable ejection delays it would have limited use (dual deploy in an 18mm rocket any one?).

I'm sure it can be done. I have heard reports of people working on DD in MicroMaxx rockets!

 

[Initiator001]

I am not sure how much more punch would be possible in the small 18mm case. Warp 9 might give more impulse, but without reliable ejection delays it would have limited use (dual deploy in an 18mm rocket any one?).

Twenty years ago, Scott Pearce at AeroTech made some single-use D80 motors in the 18mm x 70mm case using the same propellant found in the G300 motor.

Biggest problem was getting the delay material to ignite and stay burning.

Cool motor. It sure made a classic Estes Bandit kit 'teleport' off the planet.

 

[edwinshap1]

I am not sure how much more punch would be possible in the small 18mm case. Warp 9 might give more impulse, but without reliable ejection delays it would have limited use (dual deploy in an 18mm rocket any one?).

well u gotta remember, burn rate isn't the same is ISP. ISP would actually be the best in a mojave green propellant

 

[bobkrech]

I'm sure it can be done. I have heard reports of people working on DD in MicroMaxx rockets!

Micro-max Barbie? You must have been smoking some good stuff!!!

Using a thin-walled steel motor casing and the best experimental solid military propellant possible, you would be hard pressed to get a 10% B in a micro-max form factor casing, and that's without a delay or ejection charge. That's with twice the micromax-II 0.5 g propellant weight resulting in a 1 impulse class jump and 6.4 times the Isp with the best propellant resulting in an additional 2.8 impulse class jump!

Bob

 

[bobkrech]

Twenty years ago, Scott Pearce at AeroTech made some single-use D80 motors in the 18mm x 70mm case using the same propellant found in the G300 motor.

Biggest problem was getting the delay material to ignite and stay burning.

Cool motor. It sure made a classic Estes Bandit kit 'teleport' off the planet.

You appear to be confused by total impulse and average thrust.

The chart I posted yesterday lists the letter type impulse class designations. All rocket motors with a total impulse between 10 Ns to 20 Ns are classified as a D-motor.

The average thrust of a motor is the total impulse divided by the burn time. A D80 has an average thrust of 80 N and will have a miniumum burn time of 10/80 = 0.125 seconds and a maximum burn time of 20/80 = 0.25 seconds depending on it's total impulse.

Total impulse in a motor casing is limited by the volume of the casing and the specific impulse of the propellant. The SRB shuttle propellant, which is better than any hobby rocket propellant, has an Isp of 242 seconds at sea level or 2.38 Ns/gram, and with a density of 1.89 g/cc, 4.5 Ns/cc. An 18 mm x 70 mm propellant grain has a volume of 17.8 cc and could contain 80 ns however that won't fit inside an 18 mm x 70 mm motor casing. The propellent volume in an AT 18 mm casing tube is 5.25 cc not accounting for a c-slot or bore, and if filled with Shuttle propellant would generate not more than 23.6 Ns or 18% E. The old SU 10%E25 was a good attempt to pack the maximum total impulse into a SU 18x70 casing with a delay grain and ejection charge.

Even if you used the insulating liner as the casting tube and increased the propellant volume to 8.5 cc eliminating the spacer and delay grain, you only get 38 Ns at 100% density with shuttle propellant, but you would get less because you need either a c-slot or bates grain cnetral bore.

No matter what you use for propellant in an 18 x 70 casing, it will never be more than an E casing because you can't physically fit any more propellant into it.

Bob

 

[MarkII]

Micro-max Barbie? You must have been smoking some good stuff!!!

Using a thin-walled steel motor casing and the best experimental solid military propellant possible, you would be hard pressed to get a 10% B in a micro-max form factor casing, and that's without a delay or ejection charge. That's with twice the micromax-II 0.5 g propellant weight resulting in a 1 impulse class jump and 6.4 times the Isp with the best propellant resulting in an additional 2.8 impulse class jump!

Bob

What? I was talking about dual deployment in micro rockets, flown on standard, certified MicroMaxx motors. terryg said:

... (dual deploy in an 18mm rocket any one?).

And I said:

I'm sure it can be done. I have heard reports of people working on DD in MicroMaxx rockets!

Not that it would ever be necessary, of course. It's an interesting technical challenge, though. It would be something to do just to say you did it. I don't know anyone who is attempting this, but I have heard vague rumors of some efforts toward it.

Two-step (or two-stage) deployment of the recovery system at such a scale might or might not involve black powder ejection charges or even electronics. I'm thinking standard motor ejection charge at apogee, and subsequent deployment of the main recovery device via a tiny clockworks-type mechanism and a spring. But this is just speculation. More exotic things have been done in miniature by hobbyists, though, so I don't think it's out of the realm of possibility. It would all likely happen very fast, but even if the timing between the two events was only a second or so, one could legitimately claim to have pulled off a dual deployment with MicroMaxx rockets.

What were you talking about?

 

[Initiator001]

You appear to be confused by total impulse and average thrust.

The chart I posted yesterday lists the letter type impulse class designations. All rocket motors with a total impulse between 10 Ns to 20 Ns are classified as a D-motor.

The average thrust of a motor is the total impulse divided by the burn time. A D80 has an average thrust of 80 N and will have a miniumum burn time of 10/80 = 0.125 seconds and a maximum burn time of 20/80 = 0.25 seconds depending on it's total impulse.

Total impulse in a motor casing is limited by the volume of the casing and the specific impulse of the propellant. The SRB shuttle propellant, which is better than any hobby rocket propellant, has an Isp of 242 seconds at sea level or 2.38 Ns/gram, and with a density of 1.89 g/cc, 4.5 Ns/cc. An 18 mm x 70 mm propellant grain has a volume of 17.8 cc and could contain 80 ns however that won't fit inside an 18 mm x 70 mm motor casing. The propellent volume in an AT 18 mm casing tube is 5.25 cc not accounting for a c-slot or bore, and if filled with Shuttle propellant would generate not more than 23.6 Ns or 18% E. The old SU 10%E25 was a good attempt to pack the maximum total impulse into a SU 18x70 casing with a delay grain and ejection charge.

Even if you used the insulating liner as the casting tube and increased the propellant volume to 8.5 cc eliminating the spacer and delay grain, you only get 38 Ns at 100% density with shuttle propellant, but you would get less because you need either a c-slot or bates grain cnetral bore.

No matter what you use for propellant in an 18 x 70 casing, it will never be more than an E casing because you can't physically fit any more propellant into it.

Bob

I think you have mis-understood my post.

Back when I was working at AeroTech, we were often coming up with crazy ideas for rocket motors.

Scott Pearce was working on ways to get the highest average thrust D motor in a 18mm x 70mm casing.

He made some D40 motors which worked very well. Scott then tried to make a motor in the same size case that used some 'special' propellant that was originally used in the AeroTech G300 motor.

Scott managed to cast the propellant into tubing that would fit in the 18mm phenolic case material.

We test fired one on the stand and it came out as a D80 with a little less than 20N-sec total impulse.

It was a neat motor. Too bad we could never get the delay column to reliably ignite.

I have another Scott Pearce special motor in my collection. It is a 24mm x 70mm E110-7.

 

[bobkrech]

I think you have mis-understood my post.

Back when I was working at AeroTech, we were often coming up with crazy ideas for rocket motors.

Scott Pearce was working on ways to get the highest average thrust D motor in a 18mm x 70mm casing.

He made some D40 motors which worked very well. Scott then tried to make a motor in the same size case that used some 'special' propellant that was originally used in the AeroTech G300 motor.

Scott managed to cast the propellant into tubing that would fit in the 18mm phenolic case material.

We test fired one on the stand and it came out as a D80 with a little less than 20N-sec total impulse.

It was a neat motor. Too bad we could never get the delay column to reliably ignite.

I have another Scott Pearce special motor in my collection. It is a 24mm x 70mm E110-7.

Seem like I did. In reading this complete thread, I perceived some confusion between case size, total impulse and thrust, so I attempted to address this. I didn't realize you worked for AT in a former life, but as someone who worked for a motor manufacturer, you know the difference.

AT, Kosdon. and CTI (and others) have all worked with fast burning propellants and developed and/or marketed very high thrust G and lower impulse motors. They sure are fun to launch, and watch the reactions of folks who have not seen them before.

Bob

 

[cwbullet]

I love the 24 mm CTI reloads. I think they sell well for some groups. I love to see a minimum diameter go up on one - espcially the vmax.

 

[RoyAtl]

Twenty years ago, Scott Pearce at AeroTech made some single-use D80 motors in the 18mm x 70mm case using the same propellant found in the G300 motor.

One of my favorite flights EVER was at the first high power launch I ever attended back in 1989. Someone (maybe Rocketjunkie?) flew a LOC Minnie Magg with a G300.

 

[cwbullet]

G 300? I love the H400. I build a Santa rocket that I mistakenly put a H400 in, wow the grey hair flew. Imagine an H600 which would be on scale with a G300. It would have flown apart.

That kind of motor takes special talent to build a rocket around. That sure sounds like rocketjunkie.

 

[luke strawwalker]

However there are real limitations on what you can do with an 18 mm casing.

The bore of a propellant grain is a duct that conducts hot gas to the nozzle throat. As the length to bore diameter get larger, the higher thegas velocoty gets over the last propellant grain. At some point, the velocity gets high enough to initiate eerosive burning which can cause a multitude of problems such as over pressurization and liner spitting. Both phenomenon can cause a cato, or at minimum, very strange and unpredictable thrust curves. To avoid this, the bore ID much be increase if the propellant is lengthened. When this point is reached, the thrust increased due the increased burning area, but the total impulse flattens or decreases as the total mass of propellant either remains constant or actually decreases as the bore get larger. Since is costs money to process a propellant grain, excessively long motors of small diameters cost significantly more than shorter but fatter motors which perform better, and thus there is no commercial market for really long skinny motors.

See the referenced thread for details. https://www.rocketryforum.com/showthread.php?t=22616

Bob

Sounds like some of the diminishing returns problems they were having with the longer SRB's proposed for Constellation's Ares I and V rocket boosters... even going from the four segment SRB to the five segment for Ares I posed more problems than they originally figured, which upped the costs, and when Ares V started needing 5.5 segment or even 6 segment boosters they quickly hit a wall of diminishing returns-- the booster really needs a diameter increase, but then you have to have all new casings and they are no longer rail transportable, which means you have no way to transport them from Utah to the Cape and have to build a whole new factory somewhere so you can transport them by water (too heavy and cumbersome to transport by air or highway).

Physical laws can be a real b!tch sometimes... LOL

Later! OL JR

 

[Rocketjunkie]

One of my favorite flights EVER was at the first high power launch I ever attended back in 1989. Someone (maybe Rocketjunkie?) flew a LOC Minnie Magg with a G300.

I confess...

 

[bobkrech]

I love the 24 mm CTI reloads. I think they sell well for some groups. I love to see a minimum diameter go up on one - espcially the vmax.

Quick Calculations for a 6 oz. minimum diameter rocket on a Pro24 68F240.

180 G max, 0-1100 mph in 0.29 seconds @ 300', 4000' apogee in 12 seconds.

Not too shabby.

Bob

 

[Rocketjunkie]

Quick Calculations for a 6 oz. minimum diameter rocket on a Pro24 68F240.

180 G max, 0-1100 mph in 0.29 seconds @ 300', 4000' apogee in 12 seconds.

Not too shabby.

Bob

I put one in my balsa and cardstock saucer and it went LOTS :y: higher than I thought it would but it did survive :eyepop: It only weighs 2 oz without motor.