Retro Design

[jqavins]

Here's the inspiration for something I might design, and then might build, and then might have an opportunity to fly.

It's something I thought of long ago, one fin swept back and one swept forward (and two tube fins). Then I thought that making them swoopy fins would look cool. Now I'm thinking that this might be a good starting point to make an old, pulp sci-fi design, though what I've got here is FAR from ready. Never mind the tube fins; I'd make it with two or three swept back and one forward. While I like the two flat fins and two tubes concept, it doesn't have the pulp vibe we're looking for here.


I might steel this from @boatgeek for a cluster (but not the fins).

 

[boatgeek]

Here's the inspiration for something I might design, and then might build, and then might have an opportunity to fly.

It's something I thought of long ago, one fin swept back and one swept forward (and two tube fins). Then I thought that making them swoopy fins would look cool. Now I'm thinking that this might be a good starting point to make an old, pulp sci-fi design, though what I've got here is FAR from ready. Never mind the tube fins; I'd make it with two or three swept back and one forward. While I like the two flat fins and two tubes concept, it doesn't have the pulp vibe we're looking for here.
View attachment 674313

I might steel this from @boatgeek for a cluster (but not the fins).
View attachment 674311

Looks like I need to kick-start that design again so that I beat you to it!

 

[bad_idea]

I might steel this from @boatgeek for a cluster (but not the fins).
View attachment 674311

@boatgeek , that's a lovely transition. Cool fins too. I missed this project, could you link it?

 

[boatgeek]

@boatgeek , that's a lovely transition. Cool fins too. I missed this project, could you link it?

This (and down to the bottom of the page) is as far as it has gone so far.

https://www.rocketryforum.com/threads/more-half-baked-designs-thread.155195/page-18#post-2599967

 

[SolarYellow]

I might steel this from @boatgeek for a cluster (but not the fins).
View attachment 674311

I like it. If I do it, I'll just rip off the Starfighter's fin and stabilizer. Already building a Short Star, might as well build a Twin Star and launch on a coupler G80s

 

[jqavins]

OK, (if I continue) I'll go simpler than boatgeek's beautiful twin engine boat tail. I'll go with a cluster of 8 13 mm tubes around a central 24 mm tube all inside a BT-70. It should look like cigarettes and a central cigar sticking out the back.

Get or make a BT-70 to 3 inch boat tail, 3 inch tube, nose cone with a cockpit, silver (OK, aluminum) leaf finish plus decals and maybe greebles. I'd make the tail section able to vent ejection gas from 13 mm motors, and also make the rocket flyable with the 24 mm motor alone.

 

[lakeroadster]

Here's the inspiration for something I might design, and then might build, and then might have an opportunity to fly.

That's a bunch of "might" there Joe. ​

 

[lakeroadster]

OK, (if I continue) I'll go simpler than boatgeek's beautiful twin engine boat tail. I'll go with a cluster of 8 13 mm tubes around a central 24 mm tube all inside a BT-70. It should look like cigarettes and a central cigar sticking out the back.
View attachment 674687
Get or make a BT-70 to 3 inch boat tail, 3 inch tube, nose cone with a cockpit, silver (OK, aluminum) leaf finish plus decals and maybe greebles. I'd make the tail section able to vent ejection gas from 13 mm motors, and also make the rocket flyable with the 24 mm motor alone.

Max Lift Off Weight of a 24mm BP motor doesn't leave much room for rocket weight (tubes, fins, etc) with all those 13mm motor weights adding up.​

 

[jqavins]

That's a bunch of "might" there Joe. ​

Yes, indeed. I have this in mind, and maybe I'll get it built and flown in time, but no one should be holding their breath.

Max Lift Off Weight of a 24mm BP motor doesn't leave much room for rocket weight (tubes, fins, etc) with all those 13mm motor weights adding up.​

Max liftoff weight for the 24 mm motor is important only if the 13 mm motors are absent. The 13 mm motors add lift capacity along with weight. I'll calculate a bunch of combinations* then pick a target dry weight. Later, I'm supposed to be working now.

Remember, when secure, build light for sure.

* C11, D12, and E12 each alone; each of those along with 2×, 4× or 8× ¼A3, ½A3, A3, and A10. Compute the weight and max liftoff weight for each configuration, and the resulting allowed dry weight for all 12 configurations. Try to keep the dry weight down to the lowest of those, or at least decide which ones can't be achieved making those configurations disallowed.

 

[jqavins]

Correction: it's 39 configurations. And the answer is:

• If I can keep the dry weight under 75 grams (not likely, I think) then it can go on any configuration.
• If I can keep it down to 275 grams, it can go on any configuration with a D12 central.
  • This will be my target, so the flight for the contest (if I ever get that far) can go on a D12 only. KISS.
• If I can get it down a little, to 250 grams, it can even go with a C11 if there are at least 4× A10, A3, or ½A3, or 8× ¼A3.

Here are the complete results. Sorry it has to be a picture, but there is not enough ability to format tables in the editor here. The Excel spreadsheet is attached.

EDIT: Also, I guess it might need a changeable nose weight system to cover the full gamut, but I won't know about that until (if) I get a plausible design into RS.

 

[neil_w]

What are your assumptions about how many motors light?

 

[NTP2]

this is looking like one of my favs for this contest.

 

[jqavins]

What are your assumptions about how many motors light?

All of them, which is not realistic. And is also why the plan for a demonstration flight is to use only one. For more, I'd make a spider.

I just realized that I never described the motor mounting adequately. The boat tail would be hollow, with a CR for only the 24 mm motor tube as a front bulkhead, and CRs for all the motor tubes, one as the aft bulkhead and one an inch or inch and a half forward. The space between the middle and forward CRs would be vented to space. So ejection charges from any 13 mm motors are vented, and the ejection charge from the 24 mm engine gets into the body tube cavity to push out the parachute. Unused 13 mm tubes can be left empty, no plugs needed.

 

[boatgeek]

All of them, which is not realistic. And is also why the plan for a demonstration flight is to use only one. For more, I'd make a spider.

I just realized that I never described the motor mounting adequately. The boat tail would be hollow, with a CR for only the 24 mm motor tube as a front bulkhead, and CRs for all the motor tubes, one as the aft bulkhead and one an inch or inch and a half forward. The space between the middle and forward CRs would be vented to space. So ejection charges from any 13 mm motors are vented, and the ejection charge from the 24 mm engine gets into the body tube cavity to push out the parachute. Unused 13 mm tubes can be left empty, no plugs needed.

MGJ ematches in parallel work pretty nicely for cluster BP ignition, no spider needed. I often add a touch of BP in the nozzle to make absolutely sure.

That said, I haven't tried it up to this many motors. I don't see why it wouldn't work though.

 

[lakeroadster]

MGJ ematches in parallel work pretty nicely for cluster BP ignition, no spider needed. I often add a touch of BP in the nozzle to make absolutely sure.

That said, I haven't tried it up to this many motors. I don't see why it wouldn't work though.

Will the MGJ ematches fit into a 13mm motor orifice?​

 

[bad_idea]

Will the MGJ ematches fit into a 13mm motor orifice?​

The MJG BP starters will. Probably not the full-sized ematches.

 

[boatgeek]

Will the MGJ ematches fit into a 13mm motor orifice?​

Caveat: I don't fly 13mm motors very often, and I don't have any of the small MGJ ematches.

I have lit a 13mm motor with the flash off of one of the bigger ones (~1/8" across the flat). If I was clustering, I would probably add a little BP to the throat for insurance.

 

[neil_w]

Caveat: I don't fly 13mm motors very often, and I don't have any of the small MGJ ematches.

I have lit a 13mm motor with the flash off of one of the bigger ones (~1/8" across the flat). If I was clustering, I would probably add a little BP to the throat for insurance.

Can't hurt, but I've read around here that the MJG BP starters are very effective for clustering, not sure if the extra BP is really needed.

 

[boatgeek]

Can't hurt, but I've read around here that the MJG BP starters are very effective for clustering, not sure if the extra BP is really needed.

It probably isn't, but I also bought a pound of BP some time back, and it's kind of nice to amortize that a bit. At the rate I'm consuming it, I'll run out in about 2097.

When I've used the MGJ ematches on their own, I like to stand the motor up on the head like it does fit in even if it doesn't. That seems to work well.

 

[jqavins]

More and more I don't see myself getting this done in time for a contest entry. (OK, I can try to finish a design and enter that, but I'm not likely to get points for completing a build or flying, which will make my entry non competitive.)

If I do continue, and if I take @NTP2 up on your offer of some 3D printing, I'll try to come up with something along the lined of what I talked about over here in @frogglicker's thread.

 

[NTP2]

you can withdraw if you need, not saying you should but I don't want to pressure you.

Ps BTW I can help with the CAD models if you tell me what you need.

 

[jqavins]

you can withdraw if you need, not saying you should but I don't want to pressure you.

Ps BTW I can help with the CAD models if you tell me what you need.

Thanks, I figured you would, but didn't want to assume. I'm also more and more thinking that I want to build this anyway, over the winter, so we'll talk later about what I want and what you're willing to do for me.

Thanks.

 

[Azamiryou]

More and more I don't see myself getting this done in time for a contest entry. (OK, I can try to finish a design and enter that, but I'm not likely to get points for completing a build or flying, which will make my entry non competitive.)

Competitiveness comschmeditivenwss, the more the merrier. Keeping the design in the contest helps the contest whether or not there's an actual build and flight.

 

[frogglicker]

Thanks, I figured you would, but didn't want to assume. I'm also more and more thinking that I want to build this anyway, over the winter, so we'll talk later about what I want and what you're willing to do for me.

Thanks.

When you start your thread, if you need assistance, just send up a flare. You will probably get more help than you expected. Winning isn't derived from the most points (well, kinda) but jumping in and showing a different perspective is a great way to learn and share at the same time. Your help for my design has been huge and I appreciate everything you and the others have contributed.

::sing-song voice:: We have cookies...

 

[pugachu]

::sing-song voice:: We have cookies...

Wait... the winner gets cookies? I thought it was just 'bradding rights'... this just got real...

 

[jqavins]

When you start your thread...

This is my thread, as far as I do or don't get with the project.

 

[frogglicker]

This is my thread, as far as I do or don't get with the project.

I got lost. So many threads... ma'bad

 

[NTP2]

I got lost. So many threads... ma'bad

 

[jqavins]

I've done a starting design in RockSim. I have the back end, a nominee for the nose cone, and a plane 4" tube in between. The fins are temporary stand-ins for the swoopy ones that inspired the project. Generating those will be a PITA, so I sized some plane trapezoidal fins and will duplicate their total area in the swoopies. I also don't have a color scheme or decals. Well, that's only partly true; I have the decal theme, but haven't generated a file that I can use in RS. My work computer has the software that I'm familiar with and feel comfortable using, but at home I don't have it. So I'll have to do it on the work computer then email it to myself.

The decals will be a mix of two geometric designs. They both use the same swoopy pieces as the fins. The first resembles some sort of throwing weapon, and is a symbol of warrior might:


The second is a symbol of peace and harmony:


The rocket is now called "Peace Through Strength".

I'm also contemplating a small change to the fin shape:

or


That would make the decal symbols

or


I like the circular eye for the peace symbol. The symbols with the shorter fin root look better, but that would make the fin span really large to get the area I need.

So, I guess you could say I have concepts of a plan.