Someone build this for (any reason other than) the summer contest

[modeltrains]

Just to add to the challenge, does anybody else see that this is pretty much a ringfin kitbash on a Saturn V??

Now that I'm reading through all 3 pages of the thread, Yes.

 

[BABAR]

I shall offer a quick digression on the ring-equivalent sim method I am using.

1. calculate the circumference of the ring
2. create a fin set with the following characteristics:
   1. rectangular shape
   2. root edge same as ring width
   3. position same as ring
   4. Total area of fin set equal to area of ring

Originally, this was done while also making the height of the fins equal to the distance from the inner BT to the ring, so that it looks the same in side view. In this case, for the front ring, that would have required more than 8 fins in the set (disallowed by OR) so I made the fins taller and used... I think 7 of them, or thereabouts. A 3" ring generates quite a bit of "fin area" when wrapped around a BT60.

If anyone wants to weigh in on whether this has any likely connection to reality, I'm all ears. To me it passes the basic sanity test because the fin set is roughly equivalent to chopping up the ring into small pieces and attaching them to the body. In cases where the diameter of the ring is closer to the diameter of the inner BT (how close exactly? dunno), and the airflow might not be as free, this whole thing almost certainly doesn't work. Given how short the rings are, and the substantial distance between them and the inner BT, I thought it would work in this case.

Actually that makes a lot of sense. With seven attachment fins and your conversion of the ring fins to standard fins my spider sense has calmed and the robot voice ceased.

Thanks

 

[neil_w]

Actually that makes a lot of sense. With seven attachment fins and your conversion of the ring fins to standard fins my spider sense has calmed and the robot voice ceased.

The fact that it makes sense doesn't make it correct. But in this case I hope it is.

As long as this build would indeed keep the CG fairly far foward, there should be enough stability provided by the rings to make the whole things fly.

I'm still waiting for someone to volunteer to build it, or else I'm gonna get stuck with it.

 

[BABAR]

Call it the USS Vaxinator!

 

[neil_w]

Call it the USS Vaxinator!

That's not bad.

After modeltrains' recent post I was thinking "Chronic Illness". Also "Fuel Injector" also popped into my head recently.

 

[jqavins]

Orbit Injection. (After K'Tesh's inadvertent(?) suggestion.)

RocSim does ring fins. My computer is packed up and on a moving truck or I'd sim this, but surely there's someone reading who can do it.

Also, if the bottom of the plunger - where the thumb pushes on a real syringe - is a solid plate rather than a ring then you benefit from base drag. There was an article in Peak of Flight years ago about simulating that effect by adding a cone that sticks out the back. Make it a conical transition with no shoulders; 1 mg mass, because RocSim doesn't allow zero; 10 µm forward diameter, because RocSim doesn't allow zero; aft diameter equal to the base diameter; and length, if I remember right, equal to the base circumference, i.e. π times the diameter. Search the archive topic index for "short fat" and you should find it.

 

[neil_w]

I think this was addressed previously. Putting a plate at the back would add base drag stability, but I don't think it's necessary for this design, and it would kill performance. On the other hand it would look more "realistic". I've experimented with the base drag correction cone in the past; seems to work OK but I get nervous that the results end up being overly optimistic. But that's just my brainsim getting in the way of (alleged) reality.

Of course anyone who builds this (still no takers?) could do it however they like, but if it ends up being me then it'll be a ring until proven impractical. Although I'm not one to generally shoot for max altitude, and this rocket will never be a competition flyer, I've also found that rockets that are *too* draggy and basically don't go anywhere aren't much fun to fly. So I try not to go too crazy with the excess drag.