Some odd ideas...

[Brainlord Mesomorph]

In the concept stage of my next sci fi oddrock.
And I wondered if anyone had any experience with some strange ideas I've had:

1. Hollow point nosecone?
I'd like the front of it to look like a cannon. I was thinking of 3d printing a shape almost exactly like a hollow point bullet. I could also try a 13mm tube, a 19mm tube a couple centering rings and hiding a 13mm nosecone inside it.

Once it flight wouldn't that pocket just fill with air, and then the other air would just flow around it? How much drag are we talking about? (if that won't work I guess a lens shape would do)

2. Redirecting an ejection charge?
If ejection baffles work, I should be able to send an EC around a couple of corners, right?

The idea is rear ejection without blowing out the engine mount. Imagine three tubes. A center tube and two smaller side tubes, glued along their length, but also connected at the top. I'm not sure if there is a cross-tube between them or some 3d printed or balsa construction, but they are interconnected and sealed for pressure at the top.

Now you put two small parachutes and tailcones on the side tubes. When the EC goes off (it splits in half and goes around two corners?) and blows out both chutes out the back like twin drogues. Hmm? Workable?

Or you could do it the other way, put two engines in the side tubes, and one bug chute and tailcone in the middle.

Anyone do (or try) anything like this?

 

[kuririn]

In the concept stage of my next sci fi oddrock.
And I wondered if anyone had any experience with some strange ideas I've had:

1. Hollow point nosecone?
I'd like the front of it to look like a cannon. I was thinking of 3d printing a shape almost exactly like a hollow point bullet. I could also try a 13mm tube, a 19mm tube a couple centering rings and hiding a 13mm nosecone inside it.

Once it flight wouldn't that pocket just fill with air, and then the other air would just flow around it? How much drag are we talking about? (if that won't work I guess a lens shape would do)

2. Redirecting an ejection charge?
If ejection baffles work, I should be able to send an EC around a couple of corners, right?

The idea is rear ejection without blowing out the engine mount. Imagine three tubes. A center tube and two smaller side tubes, glued along their length, but also connected at the top. I'm not sure if there is a cross-tube between them or some 3d printed or balsa construction, but they are interconnected and sealed for pressure at the top.

Now you put two small parachutes and tailcones on the side tubes. When the EC goes off (it splits in half and goes around two corners?) and blows out both chutes out the back like twin drogues. Hmm? Workable?

Or you could do it the other way, put two engines in the side tubes, and one bug chute and tailcone in the middle.

Anyone do (or try) anything like this?

1. Hollow point nosecone: See the thread here:

https://www.rocketryforum.com/threads/seeking-centuri-bulldog-plans.145254/

And plans for the Ramjet here:

https://www.spacemodeling.org/jimz/est1994.htm

2. Redirected ejection charge:
There are actually a couple of kits that do this. The Gemini DC was an old Estes kit that had dual chutes coming out of the rear of two side pods. The ejection charge came through slots in the body tube and pods. Simultaneous deployment of the chutes, however, was iffy. Usually only one deployed, when the ejection charge popped one side open the pressure was released and the other side's chute would remain in the tube.
The US Rockets "Dual 18mm Rear Eject" rocket (yes, that was it's name) had just the reverse: a two engine cluster in side pods blowing out a chute in the main tube rearwards. Same slotted ejection ducting. The recovery compartment on this kit was very small, and the chute had to be tightly packed to fit. This did not help in deployment.

 

[Brainlord Mesomorph]

There are actually a couple of kits that do this. The Gemini DC was an old Estes kit that had dual chutes coming out of the rear of two side pods. The ejection charge came through slots in the body tube and pods. Simultaneous deployment of the chutes, however, was iffy. Usually only one deployed, when the ejection charge popped one side open the pressure was released and the other side's chute would remain in the tube.
The US Rockets "Dual 18mm Rear Eject" rocket (yes, that was it's name) had just the reverse: a two engine cluster in side pods blowing out a chute in the main tube rearwards. Same slotted ejection ducting. The recovery compartment on this kit was very small, and the chute had to be tightly packed to fit. This did not help in deployment.

Thank you!

I thought about slots, given the minimal contact area between two cylinders. I wondered if it was enough.

Given this static test of an EC I did last week:

I was thinking more along the lines of foil-lined 13mm duct work.

 

[jadebox]

The Dual 18mm Rear Eject kit is still in production.

The concave nosecone idea may work okay. As long as the rocket flies straight, the hole in the cone should have little effect. My concern would be with what happens if the rocket's angle of attack changes due to passing through a change in wind speed or direction. The cavity could catch the air and help to destabilize the rocket. Larger fins, however, could counteract this, though.

 

[jqavins]

Anyone do (or try) anything like this?

I haven't, but that's never stopped me before from shooting ideas around.

For the nose cone, 3D printing, while a cool and useful technique for many things rocket related and otherwise, is not the way I'd got with this one. I'd use a solid balsa nose cone and a drill press.

1. Clamp a piece of scrap lumber to the drill press table, and make a hole to accept the nose cone's shoulder. This will let you position the nose cone just so under the drill.
2. Drill out a cavity, 13 mm if you plan to take the next step.
3. (Optional) Cut the shoulder off of a hollow 13 mm nose cone and glue it into the cavity point down.

To make sure the drill doesn't tear up the balsa, just be sure to use a really sharp one and go slow.

As to the drag, I suspect you'r right about the cavity holding static pressure so more air goes around it. That will be little if any worse than a solid flat front, but that's still not negligible. Another option, which may or may not be better and would certainly look no less cool, is to add side ports that let air pass through. That would be more drill press work, but not quite as easy. I'd think up some sort of jig because everything I try to do without one comes out like crap, but you may be better at this sort of thing.

For the ejection, another way would be to make a 3-into-1 manifold (now there's a job for a 3D printer) to let the EC gas into the main tube. Place a baffle (for the one engine design, or two baffles for the cluster design) in between the motor mount(s) and the manifold to protect the latter from burning particles.

 

[GlenP]

https://www.rocketryforum.com/threads/centuri-bulldog-clone.18473/

Centuri Bulldog uses a centering ring and transition at the tip of a nose cone to simulate an optical sensor window, not sure if that would work for the cannon look you are going for. You could add a short length of body tube to the tip also.

https://www.primeportal.net/hangar/bill_spidle2/agm-83_bulldog/

 

[jqavins]

Perhaps I misunderstood what you want here. My suggested drill and build would give the look of a cannon muzzle. If you want more like the exhaust end of an aerospike pointing forward then use step 3 above but with the inner cone point up.

 

[lakeroadster]

In the concept stage of my next sci fi oddrock.
And I wondered if anyone had any experience with some strange ideas I've had:

1. Hollow point nosecone?

2. Redirecting an ejection charge?

1. Make an insert to place into the cavity during flight... remove it for static display.

2. Use tubing elbow(s) glued into the body tube to direct the ejection blast so it is has more of a smooth laminar flow.

The old "Form Follows Function" rule.

 

[les]

And while it does impact performance, you don't need a pointy nosecone....