"X-Caliber" - A Scratch Build

[BABAR]

On the good side, builders know that the calculated stability from Open Rocket presumes a CG based on the input components, and that once built the actual CG may vary a bit. Thus the true CG, and therefore the actual degree of calculated stability, is unknown. Therefore I suggest the following “handle” for the rocket, which can be changed once it is built.

X-caliber

 

[jqavins]

I’m a complete ignoramus with OpenRocket, but my mind-sim simulates the forward 3/5 of the rocket as a single fin, all of which is forward of the CG. From an aerodynamic standpoint, I would expect a bad positive feedback loop in yaw axis.

Since OR gives the minimum static margin from all around the axis, and the minimum is 2.39/7.86%, it's in the stable region. (As I stated above, if it were me I'd be designing for at least 10%, or 3.04 calibers (what the heck, 3) but it's not me, and I'm not really worried about this unless launch day is really windy.

The standard solution of more nose weight will be a challenge, as there is no forward compartment to place any metal mass, and @lakeroadster is admirably committed to follow the low power safety code and not use metal as part of the nose itself...

Well, if the builder wants to, this would help move the CG forward some:

But oak plywood is pricey, and the joint might be iffy as the sword comes down point first, even under a parachute. But on the other hand, with it coming down point first, oak up there would have its advantages, wouldn't it? I'm overthinking this.

 

[NTP2]

Well, if the builder wants to, this would help move the CG forward some:
View attachment 637364
But oak plywood is pricey, and the joint might be iffy as the sword comes down point first, even under a parachute. But on the other hand, with it coming down point first, oak up there would have its advantages, wouldn't it? I'm overthinking this.

I actually had a nose made from a piece of oak and it really helped with the CG.

 

[BABAR]

Since OR gives the minimum static margin from all around the axis, and the minimum is 2.39/7.86%, it's in the stable region. (As I stated above, if it were me I'd be designing for at least 10%, or 3.04 calibers (what the heck, 3) but it's not me, and I'm not really worried about this unless launch day is really windy.
View attachment 637363


Well, if the builder wants to, this would help move the CG forward some:
View attachment 637364
But oak plywood is pricey, and the joint might be iffy as the sword comes down point first, even under a parachute. But on the other hand, with it coming down point first, oak up there would have its advantages, wouldn't it? I'm overthinking this.

Black Ironwood is pricy, but at least seems available online. 50-100% denser than oak.

This does bring up the “chasing your tail” issue with adding nose weight. The heavier the rocket (no matter where you put the mass), the more “ooomph” you need to get it off the rod or rail. This can force you to need a bigger motor, which adds more mass to tail (and itself adds to net rocket mass), so you add more nose weight…..

I think this explains @Daddyisabar affinity for tractor motors, which are win-win when it comes to stability.

Turning the tables on this design, putting tractors in the hilt and flying it Pommel first


Attribution https://swordis.com/wp-content/uploads/2022/07/longsword_anatomy.jpg

Would likely work, although you might need a long rod or rail.

 

[lakeroadster]

Black Ironwood is pricy, but at least seems available online. 50-100% denser than oak.

This does bring up the “chasing your tail” issue with adding nose weight. The heavier the rocket (no matter where you put the mass), the more “ooomph” you need to get it off the rod or rail. This can force you to need a bigger motor, which adds more mass to tail (and itself adds to net rocket mass), so you add more nose weight…..

I think this explains @Daddyisabar affinity for tractor motors, which are win-win when it comes to stability.

Turning the tables on this design, putting tractors in the hilt and flying it Pommel first

View attachment 637365
Attribution https://swordis.com/wp-content/uploads/2022/07/longsword_anatomy.jpg

Would likely work, although you might need a long rod or rail.

Backwards?​

You're suggesting I design the sword to fly backwards?​

Note to self: Don't take @BABAR to a sword fight. ​

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Since OR gives the minimum static margin from all around the axis, and the minimum is 2.39/7.86%, it's in the stable region. (As I stated above, if it were me I'd be designing for at least 10%, or 3.04 calibers (what the heck, 3) but it's not me, and I'm not really worried about this unless launch day is really windy.

Actual stability, per OR exported flight simulation in Excel, for the E20-4, is 5.26 calibers max, 4.96 calibers min. (see below).​

I'm not sure where the 2.39 calibers is from? Maybe @neil_w has some insight into this?​

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[BABAR]

Along the lines of “if you ain’t cheatin’ you ain’t tryin’”, and also acknowledging your tweaks on Gas stabilized rockets with spin fins.

Apogee sells a rocket called the Slo Mo. looks pretty cool, although I haven’t seen any build threads or other comments (yes I did a search on the forum, maybe I missed it.)

https://www.apogeerockets.com/Rocke...del-Rocket-Kits/Slo-Mo/Review?reviews_id=4792

It uses fins which are canted both to induce rotation as well as fins that canted outward to increase drag (which I theeeeeenk also favorably effects CP), plus punches holes in fins to add drag.

These might be effective tweaks to counter that flat all-to-fin-like blade of a nose cone. Plus who doesn’t like a slow lift off?

 

[Antares JS]

Backwards?​

You're suggesting I design the sword to fly backwards?​

Note to self: Don't take @BABAR to a sword fight. ​

Don't knock it until you've tried it. The butt end of a sword makes a great bludgeon.

https://en.wikipedia.org/wiki/Mordhau_(weaponry)

 

[neil_w]

Actual stability, per OR exported flight simulation in Excel, for the E20-4, is 5.26 calibers max, 4.96 calibers min. (see below).​

I'm not sure where the 2.39 calibers is from? Maybe @neil_w has some insight into this?​

No insight, although it has me curious.

While I don't think there's any need to go to the crazy lengths of the Apogee Slow-Mo, I do think that just a bit of fin cant to induce some rotation would be beneficial here. It would nullify any asymmetrical effects of the blade.

The current design is very pretty BTW.

 

[jqavins]

When I moved for a job, and was living alone in a hotel for a few weeks before the family caught up, I ordered a Slo-Mo and build it with just a little sand paper, wood glue, and my pocket knife. It's (was) a crowd pleaser. It needed many repairs, but bounced back to fly beautifully every time - except once. R.I.P. Slo-Mo.

 

[NTP2]

Note to self: Don't take @BABAR to a sword fight. ​

It’s a technique, a hilt to the head can really do a number on someone…

Ps @Antares JS already said that oops.

 

[BABAR]

Backwards?​

You're suggesting I design the sword to fly backwards?​

Note to self: Don't take @BABAR to a sword fight. ​

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[lakeroadster]

In The Face! In-The-Face​

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[BABAR]

Don't knock it until you've tried it. The butt end of a sword makes a great bludgeon.

https://en.wikipedia.org/wiki/Mordhau_(weaponry)

View attachment 637374

I’ll take your word for it.

 

[lakeroadster]

X-Caliber CAD Drawings

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[terryg]

You could always fly it backwards and have the blast shield be a slotted rock!

 

[Rondaview]

You know what would be a cool 2.0 of this concept? A light saber with a 3D printed semi-transparent blade and an LED light source in the hilt that turns on with liftoff. That would make a pretty cool night flight .