Lakeroadster's "Claim The Moon" Rocket

the rocketry show
rocket sok
eggtimer rocketry
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
lakeroadster

lakeroadster

When in doubt... build hell-for-stout!
Joined
Mar 3, 2018
Messages
8,703
Reaction score
10,788
Location
Central Colorado
Snowy weather seems to spawn rocket designs... well at least for me it has.

I saw this Mechanix Illustrated, February 1957 or 1961 (there seems to be some confusion as to which year). Seems like a long way to go.. just to plant a flag.

Looks like a neat rocket to clone.

6679488315_940ee4cd40_b.jpg

6" diameter sphere, 29mm power & (4) A10P-0 motors in the pods, just for smoky goodness.

2022-03-06 Open Rocket Simulation 001.jpg 2022-03-06 Open Rocket Simulation.jpg


2022-03-06 Comparison.jpg
 
That's cool.

I don't believe your placement of the base drag hack is correct, though... if it applies (I'm never sure in weird situations like this) then it would go directly behind the front ball, because that is what's generating the base drag. Putting the cone all the way at the back will give you an overly optimistic view.
 
neil_w said:
That's cool.

I don't believe your placement of the base drag hack is correct, though... if it applies (I'm never sure in weird situations like this) then it would go directly behind the front ball, because that is what's generating the base drag. Putting the cone all the way at the back will give you an overly optimistic view.
Click to expand...

Well.. I kind of did put it right behind the sphere... see if you can follow my logic here:
  • The sphere is 6" dia. so the cone length would be 6" x 3.14 = 18.84".
  • I have to put the cone at the far end of the rocket ( can't just put it wherever, right?), so I just truncated the cone length as if the large end of the cone stopped about 19" from the back of the 6" sphere.
  • I felt that perhaps making the cone 6" diameter was overly conservative, so I split the difference between the 6" sphere, and the 3" rear closure... and made the cone 4-1/2" diameter.
:dontknow:
 
lakeroadster said:
Well.. I kind of did put it right behind the sphere... see if you can follow my logic here:
  • The sphere is 6" dia. so the cone length would be 6" x 3.14 = 18.84".
  • I have to put the cone at the far end of the rocket ( can't just put it wherever, right?), so I just truncated the cone length as if the large end of the cone stopped about 19" from the back of the 6" sphere.
  • I felt that perhaps making the cone 6" diameter was overly conservative, so I split the difference between the 6" sphere, and the 3" rear closure... and made the cone 4-1/2" diameter.
:dontknow:
Click to expand...
Assuming you're subsonic, the back part of the sphere works as a tailcone and thus the base drag workaround IMO doesn't apply. As presented I think it will cone like mad.
 
lakeroadster said:
The swing test should help to determine stability.... here's a visual of what I was trying to explain.
Click to expand...
Yup, I get it, you explained it quite well. It's a reasonable attempt, but there is little or no way for us to know how well it represents reality.

Note that the large ring, which is not included in CP calc is in front of CP in your picture there... That's just going to pull it farther forward, and not going to help your cause. Any way to move it back?
 
neil_w said:
Yup, I get it, you explained it quite well. It's a reasonable attempt, but there is little or no way for us to know how well it represents reality.

Note that the large ring, which is not included in CP calc is in front of CP in your picture there... That's just going to pull it farther forward, and not going to help your cause. Any way to move it back?
Click to expand...

Sure, but then it will no longer look like the Mechanix Illustrated sketch.

I'll put this on the build pile, give it a go.. and swing test it. If it's unstable, it'll be barn or garage art.

Ye Ole Oddroc Scum crap shoot.
 
It seems to me like spheres are kind of their own thing...
Fortunately, they're one of the few shapes for which we actually know the exact right answer for where the CP is -- it's at the center of the sphere.

So a reasonable strategy is to set up the sphere, without any other fins and whatnot, add some hack to put the CP in the right place, then add all the other stuff.
Playing with OpenRocket, the answer seems to be a cone the same diameter as the sphere and 1/4 the length:
Screen Shot 2022-03-06 at 1.35.40 PM.png
 
Jeff Lassahn said:
It seems to me like spheres are kind of their own thing...
Fortunately, they're one of the few shapes for which we actually know the exact right answer for where the CP is -- it's at the center of the sphere.

So a reasonable strategy is to set up the sphere, without any other fins and whatnot, add some hack to put the CP in the right place, then add all the other stuff.
Playing with OpenRocket, the answer seems to be a cone the same diameter as the sphere and 1/4 the length:
View attachment 507979
Click to expand...

Hmm? Following your lead... I get this with a massless cone the same diameter as the sphere and 1/4 the length.

Sphere CP.jpg
 
Last edited:
That's quite odd. Why do two different OpenRocket designs which look the same give radically different CPs? Here's my OR file, can you post yours?
 

Attachments

  • sphere_hack.ork
    649 bytes · Views: 6
Jeff Lassahn said:
That's quite odd. Why do two different OpenRocket designs which look the same give radically different CPs? Here's my OR file, can you post yours?
Click to expand...
When I pull up your file, sphere_hack.ork, in Open Rocket Version 15... I get this.

1646606312060.png

What version of Open Rocket are you using? I opened the file with OR-15, OR-19 and OR-22... and got the same result each time?

Here's the file I created..
 

Attachments

  • Sphere CP.ork
    638 bytes · Views: 6
Last edited:
lakeroadster said:
What is "cone like mad"... :dontknow:
Click to expand...
If you have fins sticking into clear air, the rocket will keep pointing the way you want.

If your fins are in the turbulent wake of something "ahead" of them, they have less control.

I think your rocket will shimmy as the rear end bounces off the sides of the cone you're carving in the sky.
 
I've seen a soccer field rocket fly, the old thread is here on the forum. It needed a lot of drag beyond the Soccer ball top and A LOT OF POWER! It was a Youngling basically flying a brick or monolith.

I tried to fly a finless, clustered Easter Egg without streamers or a tail, thread also here on the forum. This lead to my permanent file flight card being labeled in the RSO comment section as "rocket inherently UNSTABLE." A permanent black mark of pushing the envelope too far. The Jedi do not forget.

As the Croc Hunter would say in a heavy Aussie accent: DANGER, DANGER, DANGER! It needs a long tail of some sort out of the way of top end spherical airflow disturbance. At least that is what my initial mindsim output looks like. The sphere and the outboard motors rock! Spontaneous cluster ignition and balanced thurst is a bigger issue. Will need something to lesson any sin. No one expects the Inquisition.
 
lakeroadster said:
Sure, but then it will no longer look like the Mechanix Illustrated sketch.

I'll put this on the build pile, give it a go.. and swing test it. If it's unstable, it'll be barn or garage art.

Ye Ole Oddroc Scum crap shoot.
Click to expand...
Looks are the most important element to the villainous scum. We must be cautious.
 
something that you may or may not have considered: launch lug placement.

with my Tank Killer, the toilet float nose cone would normally have required a considerable lug stand-off. Instead, I routed launch rod with an extra “lug” that ran parallel to the main rocket body THROUGH the cone. You may find this workable with your large ball forward section. It will help if you run a soda straw (or a MicroMaxx size body tube or equivalent) alongside an extension of your body tube INSIDE the ball. I suspect you are planning on the ball splitting in half and holding the chute. If you run a stuffer tube forward, put a plunger or piston in the forward half of the ball for alignment, and use a soda straw parallel to the stuffer tube, it will be easy to thread the rod through the tail and and forward end lugs (and the internal lug causes no DRAG!), and a small hole in the forward half of the ball will need to be lined up at each launch, but shouldn’t be difficult.

in your case, with a short plunger or piston attached to the center of the forward ball half, you can probably go with no wadding or baffle at all. Just make sure you have good motor retention and the piston slides easily. You’ve got the whole world’s (or moon’s) worth of space for shock cord and chute, so packing should be loose AROUND the stuffer tube.

I am no expert in stability, but if you aren’t a purist, running the ring OUTSIDE the outer boosters, moving it back a bit, and making it longer from front to back will help. Also, the tube segment caudal to the rear attachment fins IMO doesn’t add much in the looks department and really hurts you by pushing motor position caudal. Lose that segment and your motor position moves up that many inches, should give you a significant improvement in CG.

another option is adding a SECOND ring around the tail section. It is still in the “shadow” or slipstream of that big ball, but hopefully some of the airflow will flow back medially past the ball and make your rear fins effective. I like rings for many reasons, two of which are
1. They provide a lot of surface area
2. That surface area is displaced outward from the body, so it has even greater effect,


Then again, nobody has ever accused me of being a purist, so the cosmetic effect of the above changes my not be acceptable to you.
 
BABAR said:
something that you may or may not have considered: launch lug placement.

with my Tank Killer, the toilet float nose cone would normally have required a considerable lug stand-off. Instead, I routed launch rod with an extra “lug” that ran parallel to the main rocket body THROUGH the cone. You may find this workable with your large ball forward section. It will help if you run a soda straw (or a MicroMaxx size body tube or equivalent) alongside an extension of your body tube INSIDE the ball. I suspect you are planning on the ball splitting in half and holding the chute. If you run a stuffer tube forward, put a plunger or piston in the forward half of the ball for alignment, and use a soda straw parallel to the stuffer tube, it will be easy to thread the rod through the tail and and forward end lugs (and the internal lug causes no DRAG!), and a small hole in the forward half of the ball will need to be lined up at each launch, but shouldn’t be difficult.

in your case, with a short plunger or piston attached to the center of the forward ball half, you can probably go with no wadding or baffle at all. Just make sure you have good motor retention and the piston slides easily. You’ve got the whole world’s (or moon’s) worth of space for shock cord and chute, so packing should be loose AROUND the stuffer tube.

I am no expert in stability, but if you aren’t a purist, running the ring OUTSIDE the outer boosters, moving it back a bit, and making it longer from front to back will help. Also, the tube segment caudal to the rear attachment fins IMO doesn’t add much in the looks department and really hurts you by pushing motor position caudal. Lose that segment and your motor position moves up that many inches, should give you a significant improvement in CG.

another option is adding a SECOND ring around the tail section. It is still in the “shadow” or slipstream of that big ball, but hopefully some of the airflow will flow back medially past the ball and make your rear fins effective. I like rings for many reasons, two of which are
1. They provide a lot of surface area
2. That surface area is displaced outward from the body, so it has even greater effect,

Then again, nobody has ever accused me of being a purist, so the cosmetic effect of the above changes my not be acceptable to you.
Click to expand...

Chock-Full-O-Ideas. Thanks @BABAR

The plan is to make the rocket a rear eject (similar to my red columbine rocket), the launch lug runs right through the sphere, along side the T-300 recovery bay.

2022-03-14 Open Rocket Simulation.jpg

__________________________________________________________________________________
Rear deploy Red Columbine
008.JPG
 
teepot said:
There are 12" foam balls available. There is also foam primer. The primer needs to be put on real thick. There are also 12" and larger plastic Christmas ornaments that are clear plastic and hollow. I've used both. I have used many foam balls on builds. I used 2 16" plastic bowls to make a round rocket. I have used foam rings to make a ring fin rocket. Anything odd and I have tried it. Some of my early attempts my not be flight worthy though. I didn't know then what I do now.
Click to expand...
 
Jeff Lassahn said:
Craft stores sell foam spheres for flower arrangements and such. The surface is rough and squishy, you'd need to coat it with something.
Also worth checking out toy stores and the internet for plastic balls intended for games.
Or I suppose you could do like the grade school kids do and make it from paper mache using an actual soccer ball as the form.
Click to expand...
 

Latest posts

Back
Top