Is there a way to sim a rocket with spherical fins?

[terryg]

 

[neil_w]

You could create the model with pods. However, it won't be stable: the spherical fins won't contribute to CP.


ORK attached below.

 

[Daddyisabar]

Gotta have some balls to push the button on that oddroc abomination!

 

[Daddyisabar]

Ping pong balls on model rockets ROCK!

 

[Daddyisabar]

Yes Mr. RSO. Base drag is my friend!

Do the gaps give a good place to put the launch rod?

All those balls remind me of an SNL skit with ole shoot-em's Baldwin.

 

[Daddyisabar]

You could create the model with pods. However, it won't be stable: the spherical fins won't contribute to CP.
View attachment 625891

ORK attached below.

Time for no good, stinking mindsim!

 

[Daddyisabar]

Yes Mr. RSO. I'm just an oddroc base drag hack! Had to input a big one to maker her stable! Out to the Far Far Away pad again. Fire support team ready!

 

[terryg]

Yes Mr. RSO. Base drag is my friend!

Do the gaps give a good place to put the launch rod?

All those balls remind me of an SNL skit with ole shoot-em's Baldwin.

There is space for a 3/16" rod to go through. I have a brass tube as a guide above the balls. Will post a final picture after it is painted. Will spin test it then also.

 

[kjhambrick]

I think I have rocket envy

 

[terryg]

Champion Sports 1 Star Table Tennis Ball Pack - Solid Multicolor Ping Pong Balls, Set of 6, with 40mm Seamless Design - Recreation Table Tennis Equipment, Accessories​

https://a.co/d/88m9rnR

Bt 60 coupler tube I had lying around.
Super glue to attach the balls.

 

[Daddyisabar]

There is space for a 3/16" rod to go through. I have a brass tube as a guide above the balls. Will post a final picture after it is painted. Will spin test it then also.

Swings tests rock! Cardboard cut outs roll! So many tools to quell the fear.

 

[lakeroadster]

Yep, I'd perform a swing test. Eazy Peazy Lemon Squeezy.

 

[terryg]

I have no doubts it will be stable. I am just wanting to get altitude estimates and the delay times needed.

 

[Daddyisabar]

Depending on how the balls are attached just go with the old, high drag oddroc rules. Lots of thrust, short delay, no wind, big field.

 

[terryg]

I also have an insane idea for a High Power Night Launch rocket.

https://blinkee.com/product/mood-sphere-centerpiece-3-inch/

 

[neil_w]

I have no doubts it will be stable.

Why?

I am just wanting to get altitude estimates and the delay times needed.

The file I posted should be reasonably accurate as far as drag is concerned (I think?)

 

[terryg]

Mainly because it has a fairly heavy nose cone and is quite long. I am new to using open rocket (a long time rocksim user). Will look at the drag calculations on the file you posted.
Thank you for doing that, it is much nicer than the one I created!

 

[Buckeye]

CFD

 

[dhbarr]

Nice smokey motor?

 

[DigBaddy]

Hopefully the shock cord doesn't get behind those balls and castrate it when the chute opens.

Won't steer very well after that.



I'll see myself out....

 

[neil_w]

Now that is an image I did not need.

 

[terryg]

Painted! Masking off ping pong balls is a pain in the a$$.

 

[neil_w]

Mainly because it has a fairly heavy nose cone and is quite long. I am new to using open rocket (a long time rocksim user). Will look at the drag calculations on the file you posted.
Thank you for doing that, it is much nicer than the one I created!

Keep in mind: spheres provide no lift and no base drag. That is why they don’t contribute to CP at all. This is essentially a rocket with no fins.

Now, if the balls provide some restoring force due to otherwise unaccounted-for phenomena, I’ll be interested to learn more. But I’m not optimistic for it. Be cautious with this one.

 

[DigBaddy]

So if the spheres show some divine unaccounted for lift and base drag, then they're Holy Balls?

 

[dhbarr]

They provide quite a lot of skin and interference drag, though.

 

[neil_w]

They provide quite a lot of skin and interference drag, though.

Neither of which factors into stability. Net effect of the balls on CP is zero.


And no base drag to help out either.


I think it's conceivable that the balls are small enough that they will actually generate some base drag when the rocket gets moving fast enough, but I couldn't predict how much that'll help. Would be interesting to see a CFD analysis here.

Now I'll wait and see how this works out.

 

[terryg]

Interesting! Sounds like a swing test will be critcal and I will do one after the paint cures.

 

[NTP2]

I’m with @neil_w on this… anyone up for betting?

 

[Buckeye]

Keep in mind: spheres provide no lift and no base drag. That is why they don’t contribute to CP at all.

Plenty of base drag and lift as air flows over the curved surfaces.

According to the man himself, Barrowman says base drag does not contribute to CP since it is an axial force, not a normal force.



The balls may be a little small to provide enough planform area, but I wouldn't call it "finless." I think it will fly.

 

[techrat]

In my head, I see that the ping pong balls would HAVE to provide some drag when the rocket is moving. Air flows over them, they stick out from the rocket body and therefore, they act as minimal fins, but the problem might be that your balls are too small. Of course, if you launch it, you get bigger balls. ;-)