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-   -   [Spaceships] Black powder Rockets? (http://forums.sjgames.com/showthread.php?t=156986)

Marasmusine 04-16-2018 04:11 AM

[Spaceships] Black powder Rockets?
 
Lag‚ri Hasan «elebi was said to have made a manned ascent in a gunpowder rocket WP

Assuming this legend was true, what would be the statistics for a Spaceships black powder rocket? I can find information on the specific impulse of small modern rockets (about 80s), but I'm not sure about what this would be with 17th-century materials, and I've no idea what the thrust-to-weight ratio is. I'm imagining it would be quite low, sub 1G.

Any ideas? Thanks.

Agemegos 04-16-2018 04:35 AM

Re: [Spaceships] Black powder Rockets?
 
Quote:

Originally Posted by Marasmusine (Post 2171442)
Lag‚ri Hasan «elebi was said to have made a manned ascent in a gunpowder rocket WP

Assuming this legend was true, what would be the statistics for a Spaceships black powder rocket? I can find information on the specific impulse of small modern rockets (about 80s), but I'm not sure about what this would be with 17th-century materials, and I've no idea what the thrust-to-weight ratio is. I'm imagining it would be quite low, sub 1G.

Any ideas? Thanks.

If it were below 1 gee it wouldn't take off.

Lots of chemical rockets have pretty good thrust-to-mass ratios, and I think that solid-fuel and hybrid rockets' mechanical simplicity means really low weight-to-thrust.

Marasmusine 04-16-2018 04:41 AM

Re: [Spaceships] Black powder Rockets?
 
Quote:

Originally Posted by Agemegos (Post 2171443)
If it were below 1 gee it wouldn't take off.

Are you familiar with GURPS Spaceships?

Marasmusine 04-16-2018 06:04 AM

Re: [Spaceships] Black powder Rockets?
 
By that, I mean, in GURPS Spaceships each rocket component gives some amount of acceleration. If a rocket gave 0.5 G, and the spaceship had three rockets, the spaceship would have 1.5 G acceleration.

When scouring for information, I've seen thrust-to-weight ratios of 3:1, 4:1 or 5:1 when discussing the minimum thrust for competitions of model rockets (the fuel for which I'm guessing is close-ish to black powder)

According to the GURPS Spaceships designer's notes, 5:1 would give 0.25 G (so you'd need 5 rocket components to achieve lift off).

I don't know if I'm interpreting this right, or if the figures scale up to a manned rocket.

Agemegos 04-16-2018 06:14 AM

Re: [Spaceships] Black powder Rockets?
 
Quote:

Originally Posted by Marasmusine (Post 2171444)
Are you familiar with GURPS Spaceships?

A little. 10

Agemegos 04-16-2018 06:18 AM

Re: [Spaceships] Black powder Rockets?
 
Quote:

Originally Posted by Marasmusine (Post 2171453)
When scouring for information, I've seen thrust-to-weight ratios of 3:1, 4:1 or 5:1 when discussing the minimum thrust for competitions of model rockets

Bear in mind that in GURPS Spaceships' terms the model rocket motors you buy consist of a engine and some fuel tanks, not just an engine. Listed thrust-to-weight ratios in the spec will be for the fully-fuelled motor at ignition, not for the almost-empty motor at flameout.

Anaraxes 04-16-2018 06:22 AM

Re: [Spaceships] Black powder Rockets?
 
Quote:

Originally Posted by Marasmusine (Post 2171453)
model rockets (the fuel for which I'm guessing is close-ish to black powder)

The commercial Estes model rocket engines are basically black powder. A modern formulation, of course.

Model/amateur rocketeers use all sorts of propellants, though, including liquid fuels. So just be sure your sources are specific.

Humabout 04-16-2018 06:36 AM

Re: [Spaceships] Black powder Rockets?
 
My understanding of black powder motors is that they are prone to cracking. That probably causes issues when you try to make something the size of an SRB. On top of that, aluminum perchlorate is far easier to cast and has a higher energy density than powder.

Fred Brackin 04-16-2018 08:26 AM

Re: [Spaceships] Black powder Rockets?
 
Quote:

Originally Posted by Marasmusine (Post 2171442)
I can find information on the specific impulse of small modern rockets (about 80s), but I'm not sure about what this would be with 17th-century materials,

Black Powder of that generation is usually assumed to be 60% to 80% as effective as later BP.

When the Mythbusters tried this in a segment called "Chinese Astronaut" or something like that their main result was scorch marks on Buster.

Nevertheless, the thing you seek could be built in Ve2. When I look there I see that TL3-4 solid fuel rockets are given a performance roughly 1/5th of that assigned to TL7 types. The only way to compensate for this would be to shorten the burn time. 6 to 12 seconds instead of 30 to 60 seconds.

Moving on to Spaceships I believe you would lower the Delta-V per tank by a similar percentage.

Marasmusine 04-16-2018 09:02 AM

Re: [Spaceships] Black powder Rockets?
 
Quote:

Originally Posted by Humabout (Post 2171458)
My understanding of black powder motors is that they are prone to cracking. That probably causes issues when you try to make something the size of an SRB. On top of that, aluminum perchlorate is far easier to cast and has a higher energy density than powder.

Yes I intend to give the rocket a good chance of catastrophic failure!


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