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Tube vs. fin stabilized

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powderburner

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No wonder mine wouldn't stay still when I cut the last one!








(has this taken a big left turn into "sick" or what?)
 

MarkII

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You can also just use a "mitre box" and a razor saw to cut the tube off... I've done it both ways...

(a mitre box is a three-sided (two sides and a bottom) box with slots cut in it, usually at 45 degrees, into which you place the object you want to cut (the tube) and put your saw blade into the groove made by the slots to hold your saw blade at the prescribed angle as you saw through the material... they sell them at Hobby Lobby sized for the X-acto razor saws (which they sell as well) but you can make your own with any angle you want from lumber or use a regular carpenter's miter box from the lumberyard if your saw will fit it.

Good luck! OL JR :)
But my method is neater. :neener:

Plus with a template, I can make the bevel any angle I want. With a miter box, I am limited to using the angles of the slots in it. And just try to cut a compound miter with a razor saw and a miter box.

It took me longer to type out the description in the post than it does to actually carry it out.

MarkII
 
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MarkII

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You have to sedate them first or the screaming gets very distracting.
:rolleyes:
Be careful, though - PETPPB might be reading this.

Ping-pong ball vivisection - who knew? :shock:

MarkII
 

MarkII

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Just make it quick so that the PPB doesn't feel any pain.

MarkII
 

luke strawwalker

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But my method is neater. :neener:

Plus with a template, I can make the bevel any angle I want. With a miter box, I am limited to using the angles of the slots in it. And just try to cut a compound miter with a razor saw and a miter box.

It took me longer to type out the description in the post than it does to actually carry it out.

MarkII
Well, yeah, but I'm just pointing out alternatives... Like Commander Decker said, "that's the job of a first officer-- to point out alternatives."

I personally do it the way you do-- use a template to establish the oval pattern around the tube and cut it freehand... works for me...

I've even cut some shaped sorta like F-14 Tomcat intakes-- starting 90 degrees to the tube and then curving into a bevel cut of about 45 degrees...

ONLY way to do those is freehand... :) OL JR :)
 

MarkII

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Well, yeah, but I'm just pointing out alternatives... Like Commander Decker said, "that's the job of a first officer-- to point out alternatives."
I can understand that. Been there.

I personally do it the way you do-- use a template to establish the oval pattern around the tube and cut it freehand... works for me...

I've even cut some shaped sorta like F-14 Tomcat intakes-- starting 90 degrees to the tube and then curving into a bevel cut of about 45 degrees...

ONLY way to do those is freehand... :) OL JR :)
You could probably do it with multiple templates. Use one to outline the angle at one part of the intake, overlay another template to outline the different angle at another point in the intake, and so on until you have outlined the entire compound curve of the bevel. What Jim said is true; when you "unwrap" a hollow cylinder that has an angled face at one end, the shape has a wave-like form. This caught me by surprise when I printed out a bevel template for the first time. Since the template shape was continuously curving, I didn't see how it could produce a beveled edge that was even and flat across the plane. But that's exactly what it does, as I found out when I cut the tube.

MarkII
 

troj

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Now tell him how to cut ping pong balls...
Ping pong balls are easy.... Stand the tube on the ball, trace around it. Use a knife to cut just a little inside the line, then sand to a nice fit. Slip ball over tube, use a bright enough line that the tube is visible on the back side of the ball. Draw line, cut inside, sand to a nice fit.

Voila. 'tis quick and easy.

Now, if I could just remember whose fault it is I needed to master that skill... :cool:

-Kevin
 

accooper

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One nice thing about tube fins is that you can make them fron scraps that you though you would never use.

I have built about five tube fin rockets, I guess every time I get enough scraps I build one.

But I have never seen plans for a two stage tube finned rocket.

Hmmmm....

John are you thinking what I'm thinkin'?

Andrew From Texas
 

jflis

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Ping pong balls are easy.... Stand the tube on the ball, trace around it. Use a knife to cut just a little inside the line, then sand to a nice fit. Slip ball over tube, use a bright enough line that the tube is visible on the back side of the ball. Draw line, cut inside, sand to a nice fit.

Voila. 'tis quick and easy.

Now, if I could just remember whose fault it is I needed to master that skill... :cool:

-Kevin
Guilty as charged! :D
 

accooper

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You are one sick individual. That's why I like you! Your as sick as I am! :)

Andrew
 

MarkII

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One nice thing about tube fins is that you can make them fron scraps that you though you would never use.

I have built about five tube fin rockets, I guess every time I get enough scraps I build one.

But I have never seen plans for a two stage tube finned rocket.

Hmmmm....

John are you thinking what I'm thinkin'?

Andrew From Texas
That's an interesting idea. Two-stagers have a tendency to weathercock during the booster phase because of all the fin area that is on board. With toobers being resistant to weathercocking, it might be worth exploring.

But in the meantime, have you seen this sweet-looking model?



MarkII
 

JAL3

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One nice thing about tube fins is that you can make them fron scraps that you though you would never use.

I have built about five tube fin rockets, I guess every time I get enough scraps I build one.

But I have never seen plans for a two stage tube finned rocket.

Hmmmm....

John are you thinking what I'm thinkin'?

Andrew From Texas
http://www.rocketryforum.com/showthread.php?t=3466
 

accooper

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That hybrid is not what I mean. I mean where both stages have tube fins

Andrew
 

MarkII

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Understood, and if it interests you, then go for it and then tell us about it. I just wanted to mention the SW Tuber because I think it is a really cool design that includes tube-fin stabilization in one of the stages anyway. I don't know of any zweistufiger design that has tube-fin stabilization in both stages, but that doesn't mean that there aren't any.

MarkII
 

JAL3

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That hybrid is not what I mean. I mean where both stages have tube fins

Andrew
The Tuber is a great performer, great enough to be hard to recover on our field.

If you like the look of it, you might try to copy the sustainer and make a tubed booster. You might also shoot for 18mm if you don't want to cross the barbed wire too often.
 

cjl

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That hybrid is not what I mean. I mean where both stages have tube fins

Andrew
The issue is that if tube fins get too long and narrow, they start to effectively block the airflow, and become vastly less effective. You'd have to use fairly large diameter tube fins. It could definitely be done though.
 

accooper

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Yea, that design is kool lookin'. I will have to see what I can come up with. That kit would be a place to start.

Andrew
 

Wild Doogie

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Three perfect flights and still going strong. If you can see it launch then good luck! It flew true and everyone liked the design...thanks to Layne. Built out of BT5 tubing...planning my L3 7.5" Blue Tube for next year....

Wild Doogie

IMG_0538_t.jpg
 
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