Build Thread - MoonShot III Heavy

[jqavins]

Very true. Annealed copper is almost like metal taffy. Never pulled silver or gold. No, I am not Sam the Snowman

Oh, it's more complicated than that. Taffy-like is a property called "malleable" which is rather well correlated to ductility, but not the same. And the safety code probably should refer to malleability.

 

[PayLoad]

PayLoad - do you have a wag on the apogee this beast is going to hit? And am I reading that thrust curve graph right - over 7 seconds of burn? I’d say this rocket is going to put on quite a show!

Trying desperately to manually get the motor thrust curve as an option in Open Rocket so I can sim. Help appreciated.

 

[neil_w]

Trying desperately to manually get the motor thrust curve as an option in Open Rocket so I can sim. Help appreciated.

If you have a motor file in .eng or .rse format, then the rest is easy.

Got to Preferences. Under the General tab, there's a field to enter a directory for custom motor files:

Set it according to your preference, dump your motor file(s) in there, and then restart OR.

 

[PayLoad]

 

[3stoogesrocketry]

It looks like the delays of the boosters knock the cones off and that is what separates the boosters ?

 

[PayLoad]

It looks like the delays of the boosters knock the cones off and that is what separates the boosters ?

Correct, at the 7 second delay point

 

[PayLoad]

I'm familiar with those Apogee strap-on booster hooks and while they are great, I have to question whether they will hold up in a high-power flight... Especially when the boosters are going to be hauling the whole rocket into the air without the central motor helping. I could be wrong but it's something you might want to consider/test.

Definitely make sure though that you inspect the hooks and check the fit of your boosters before every flight. The hooks warp very easily. I've already had to take a lighter to mine to soften them and form them back into shape after a booster got stuck on a bent hook.

I appreciate the heads up in all respects.

The booster thrust point (which takes 100% of the thrust) will be glued & screwed to the body

 

[3stoogesrocketry]

Correct, at the 7 second delay point

Was this picked by design ? To me it seems like if you trimmed the delays down to about 3 or 4 seconds after burn out , you could eject the pods and airstart your main motor , unless you will be burning all 4 at once

 

[PayLoad]

Was this picked by design ? To me it seems like if you trimmed the delays down to about 3 or 4 seconds after burn out , you could eject the pods and airstart your main motor , unless you will be burning all 4 at once

This is my one nod to aesthetics - I don't like the perceived look of the boosters releasing right off the launch rod, and wanted them to come off further into the flight

 

[PayLoad]

FAIL - The plastic booster hooks will not hold the stress of a G. It snaps the plastic "tong" off immediately (I also broke one during assembly)

Anyone willing to build this part out of aluminum for a fee?

 

[PayLoad]

Glued & screwed upper mounts to body tube.

 

[Antares JS]

Did you find some way to strengthen the hooks?

Edit: Also, have you simmed this flight? A seven second delay with a heavy, unburnt motor on board seems like a long time.

 

[PayLoad]

I re-created all the plastic/wood parts of the booster mount in aluminum, then used epoxy & screws.

I have not simmed because I don't have a file for the main motor, which is a 7 second burn.

Also, anyone ever forget to mount the shock cord in a scratch built? I'm, uh, asking for a friend........... (I'm actually going to use eyebolt in threaded top closure of motor)

 

[jqavins]

Yup. Airframe came in ballistic and the nose cone drifted off under the parachute. I got the nose cone back (it was a really low altitude flight) but the body tube was smashed.

 

[Antares JS]

I re-created all the plastic/wood parts of the booster mount in aluminum, then used epoxy & screws.

I have not simmed because I don't have a file for the main motor, which is a 7 second burn.

Also, anyone ever forget to mount the shock cord in a scratch built? I'm, uh, asking for a friend........... (I'm actually going to use eyebolt in threaded top closure of motor)

I would suggest simming with a motor of similar weight to your central motor to see how your boosters perform. I'm concerned that no thrust for 7 seconds with a heavy, unburnt motor on board will lead to a dangerous situation.

I know it's also possible to add custom motors to a sim, but someone else will have to tell you how to do it.

 

[3stoogesrocketry]

I would suggest simming with a motor of similar weight to your central motor to see how your boosters perform. I'm concerned that no thrust for 7 seconds with a heavy, unburnt motor on board will lead to a dangerous situation.

I know it's also possible to add custom motors to a sim, but someone else will have to tell you how to do it.

Ok so what I've gathered is , he is using 3 G motors off the Pad . Then at 2.5 seconds , his central boom stick will light. Around 7 seconds after lift off , his side pods will ( hopefully ) deploy and the pods will fall off . Then at Apogee he just wants a single deployment. Alot of variables , and risks , but a cool project.

 

[PayLoad]

Exactly - I want the boosters hanging on late for aesthetics - not seeming to fall off a quarter second after launch

 

[jqavins]

When you put it that way, seven seconds seems like a long time. Will the booster separation be clearly seen from the ground? Why not three or four seconds?

 

[Antares JS]

Ok so what I've gathered is , he is using 3 G motors off the Pad . Then at 2.5 seconds , his central boom stick will light. Around 7 seconds after lift off , his side pods will ( hopefully ) deploy and the pods will fall off . Then at Apogee he just wants a single deployment. Alot of variables , and risks , but a cool project.

I must have misunderstood... I thought the central motor was starting seven seconds in.

 

[PayLoad]

Launching MoonShot Heavy (simple) model this weekend - testing simply the flight characteristics & stability. Videos Forthcoming



This one will launch on 4 simul-lit G80s

 

[Antares JS]

Good luck to you, sir.

 

[PayLoad]

Good luck to you, sir.

That is appreciated. Any guess as to what will go wrong? Non-simul-ignite my biggest concern, stability & nose-weight second concern. Launched in fields of Kansas, worst case scenario is I lose it - after viewing that it flies well

 

[mbeels]

Yeah, good luck, I hope to see some video!

 

[Antares JS]

That is appreciated. Any guess as to what will go wrong? Non-simul-ignite my biggest concern, stability & nose-weight second concern. Launched in fields of Kansas, worst case scenario is I lose it - after viewing that it flies well

Non-simultaneous ignition is a concern, but the Blue Thunder propellant in G80's lights easier than some other propellants, so I think it's less of one. It might be a good idea to test some spare igniters on whatever equipment will be providing power to them and make sure it will start four igniters simultaneously.

When I look at this rocket, my biggest concern is with it shredding. It's kind of like four minimum diameter rockets stuck together with four punchy (high-thrust-fast-burn) motors. I would worry about the joints between your main and outboard tubes. That said, I see what looks like a pretty thick fillet between the tubes, so perhaps you had the same thought. As far as stability goes, my rough mindsim says long and skinny makes it okay, but my more cautious side worries about those three noses on your outboards. They look like the solid urethane noses from PML and if they are, it might be a large amount of weight to have that far back, but I could be wrong. Have you tried building this in OpenRocket/Rocksim?

 

[PayLoad]

Non-simultaneous ignition is a concern, but the Blue Thunder propellant in G80's lights easier than some other propellants, so I think it's less of one. It might be a good idea to test some spare igniters on whatever equipment will be providing power to them and make sure it will start four igniters simultaneously.

When I look at this rocket, my biggest concern is with it shredding. It's kind of like four minimum diameter rockets stuck together with four punchy (high-thrust-fast-burn) motors. I would worry about the joints between your main and outboard tubes. That said, I see what looks like a pretty thick fillet between the tubes, so perhaps you had the same thought. As far as stability goes, my rough mindsim says long and skinny makes it okay, but my more cautious side worries about those three noses on your outboards. They look like the solid urethane noses from PML and if they are, it might be a large amount of weight to have that far back, but I could be wrong. Have you tried building this in OpenRocket/Rocksim?

First, thank you for your input - it is sincerely appreciated.
I have built in OpenRocket, with strong suggestions for added nose weight, which I have addressed.

My launch controller is a remote 12v 800amp battery with capacitors. It lights up absolutely everything, even when it is not supposed to light up. Touching the contacts when live is an experience.

 

[Antares JS]

First, thank you for your input - it is sincerely appreciated.
I have built in OpenRocket, with strong suggestions for added nose weight, which I have addressed.

My launch controller is a remote 12v 800amp battery with capacitors. It lights up absolutely everything, even when it is not supposed to light up. Touching the contacts when live is an experience.

I think we can feel good about stability and simultaneous ignition then. Just make sure your igniters are fully seated after you have put them all into place - be sure that installing one didn't jostle another. Here's hoping you don't shred. Again, good luck.

 

[jqavins]

Launching MoonShot Heavy (simple) model this weekend - testing simply the flight characteristics & stability.

Good luck indeed. Does RS show a safe rod exit speed if you use only one G80? Or, do you have access to another single motor that will give sufficient speed? If so, that would reduce the likelihood of loss or damage if things (such as the rocket) go sideways. After all, what you've got there is the equivalent of an I320, so maybe you could dial that back.

OTOH, if you do dial it back, fly dummy loads in the pods to simulate the eventual launch mass, CG, and moments of inertia.

 

[PayLoad]

Couple things - Made the trip to CO to launch, dummy loaded for correct mass, prepped rocket completely, stopped by Apogee & drooled for a while..

Then the temp hit -8F. I love rocketry, but not sure of the effect of extreme cold on the motors - Should I be concerned?

 

[PayLoad]

All Dressed up & Nowhere to go - CO & KS Launch scrubbed due to snow & -8F Weather. Seriously considering driving down Rte 78, finding a big farm & knocking on some doors.

 

[DrewW]

Very much looking forward to seeing the videos of this!