Would this be stable?

I noticed this fanciful design in dixontj93060's avatar:



I am thinking of modeling it in SolidWorks so I can come up with an OpenRocket design. So far it looks like a nose cone and a transition for the boat tail, with no tube.

I'm a complete n00b to rocket design. Does this look unstable right out of the box?

Looks good to me. You can make just about anything stable. Rocket stability is not about looks. It is all about pure science.

Daddyisabar said:

.....It is all about pure science.

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which translates roughly into, "just keeping adding nose weight until it flies straight".

s6

simonov said:

I noticed this fanciful design in dixontj93060's avatar:

I am thinking of modeling it in SolidWorks so I can come up with an OpenRocket design. So far it looks like a nose cone and a transition for the boat tail, with no tube.

I'm a complete n00b to rocket design. Does this look unstable right out of the box?

Click to expand...

Well, it's very similar to the PemTech 3FNC so I'm sure it could be made stable (with large enough fins and enough nose weight.)

stealth6 said:

which translates roughly into, "just keeping adding nose weight until it flies straight".

s6

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And the necessary thrust to lift it nice and quick! It might want to wobble a bit but that is OK as long as it keeps going up.

Okay, so I have modeled in in SolidWorks:



I'll work out the scale so I can figure out how to model it with OpenRocket. The main fuselage is two nose cones butted together, as I suspected. So are the fin nacelles. The engine nozzle wold be a custom piece. Not sure whether I even want that. Maybe the motor should stick out the bottom instead.

It needs a little martian and anthropomorphized bunny.

Salvage-1 said:

It needs a little martian and anthropomorphized bunny.

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You beat me to it!!

Make it look like a cluster ala "Hareway to the Stars"? Have a center MMT cor the actual motor and surround it with dummy tubes. I can find some pics later to illustrate the idea.

You could go card stock like this one - https://pembertontechnologies.com/wp-content/uploads/2013/09/TRFLogoRocket051813.pdf

rbelknap said:

Well, it's very similar to the PemTech 3FNC so I'm sure it could be made stable (with large enough fins and enough nose weight.)

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And PML's "Little Lunar Express":
https://publicmissiles.com/secure/images/lillunamark&robsmall.jpg

And the Fat Cat K-1:
https://www.rocketreviews.com/fat-cat-rockets---k-1.html

It can easily be made flight stable.

See also:
https://www.rocketryforum.com/showthread.php?111826-Martian-Maggot

Here is a link to the toon. It may give you some ideas.
[video=youtube;srgWnW81bCQ]https://www.youtube.com/watch?v=srgWnW81bCQ[/video]
It's not exactly as I remember it but it's close.

I am thinking a 24mm mount with 6 or 13mm dummy tubes around it would give it a retro cartoon look that would fit well with the rest of the rocket.

simonov said:

Maybe the motor should stick out the bottom instead.

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In most cases the loaded motor weight is one of the heaviest components of the whole rocket. Moving it aft (to "hang" out the back end) will have the effect of making your rocket less stable, or to say the same thing another way, moving the motor aft will require more nose ballast which in turn will reduce the flight performance.

If you can stand the appearance, I recommend keeping the motor as far forward as you can without recessing it inside the body---you don't want to scorch the insides of the rocket. And if you set the nozzle too far inside it will also start to kill the motor thrust (this is called the Krushnic effect).

powderburner said:

If you can stand the appearance, I recommend keeping the motor as far forward as you can without recessing it inside the body---you don't want to scorch the insides of the rocket. And if you set the nozzle too far inside it will also start to kill the motor thrust (this is called the Krushnic effect).

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Here's a link to the latest Peak of Flight newsletter from Apogee. This could be a way to help improve the stability of the rocket. Since I know no more about this than what its in the article, I would suggest this as a means to improve the stability margin if you are just barely at an acceptable margin. Maybe someone can weigh in and offer more insight on this.

Thanks guys. Sounds like it's doable, but more research is needed.

I created a model of the rocket using off the shelf (OTS) components, though plenty of lath work will be required. On the left is my original model and on the right is the version built up from OTS stuff:





The rocket is 20 inches high and 2.64 inches (fuselage) and 12 inches (overall including fins) in diameter .

Bill of materials:

6 x Quest PNC25 plastic nose cones (fin nacelles)
1 x SEMROC BZ-1625P nose cone (nozzle)
2 x SEMROC BNC-80HAO nose cones (fuselage)
1 x BT-65 coupler tube (3.75 inches)
1 x 19mm motor mount tube (2.76 inches long in this model; can be longer of course)
4 x centering rings for nozzle and motor mount tube
Plus some fin stock

The nozzle needs a lot of work:



The fuselage is two of the SEMROC BNC-80HAO nose cones with their shoulders cut off and butted end to end. A BT-65 coupler is used to hold them together. I don't know if there is enough room in there for the recovery system:



There's enough lathe work that I wonder whether it might be just as easy to make the conical pieces from scratch on a lathe and not bother with the OTS stuff. Especially as SEMROC is no more.

I'm going to have to CE this idea away! That's going to be a sharp looking bird!

What are the consequences of building it with a plastic for at least the lower half? I realize that there are several areas of construction that it will affect, but it does provide for a bigger laundry room.

Of course it's gonna fly my friend, mine is a great (fat) flyer too )))))



[video=youtube_share;_4Av5B1qtPk]https://youtu.be/_4Av5B1qtPk[/video]

That was a very interesting article.

Screaminhelo said:

Here's a link to the latest Peak of Flight newsletter from Apogee. This could be a way to help improve the stability of the rocket. Since I know no more about this than what its in the article, I would suggest this as a means to improve the stability margin if you are just barely at an acceptable margin. Maybe someone can weigh in and offer more insight on this.

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