Thoughts on a cylinder oddroc???

[curtisheisey]

Many years ago at one of our club launches, someone brought a "tube" rocket made out of a single wrap of that thin insulating sheet. From what I recall, it was about 12 in in diameter and 3 feet long. It had something to support a motor mount and a launch rod up the middle. It flew about 20-30 feet up on a "D" impluse motor. I did not take any photos of this.

I am trying it out using a 3d printed motor mount. I envision three of them: two at the bottom to hold the motor tube in place, and one at the top for support.

I tried to model this in OpenRocket, but it could not compute the CP. What is the CP of just a tube?

Has anyone built/launched anything like this?

Thoughts? Design tips?

 

[curtisheisey]

My only thought on the aforementioned rocket, is that it could be unstable. It just happened to fly up on the first 20 feet, but the large drag slowed it to an immediate stop. Putting a larger impluse motor might bring out the unstable nature of this. Or maybe it is just stable?

 

[les]

I believe it will be unstable.
The CP of a tube should be the midpoint of the tube.
The CG will be down below this midpoint with the weight of the motor at the bottom, and no fins to provide a restorative force once it starts tilting...

 

[neil_w]

To get an actual simulation in OR, enter phantom body tube (0 diameter) and add a single tube fin. Body tubes are presumed to be closed on the front (no internal airflow) so you cannot model it with a body tube.

For the flight sim (if you can make it stable) you might be bitten by the tube-fin drag bug (to be fixed next release), but I expect that evaluating stability is all you're after here.

 

[curtisheisey]

The CG will be down below this midpoint with the weight of the motor at the bottom, and no fins to provide a restorative force once it starts tilting...

Yes, I was thinking that ... to add some weight at the top.

 

[Daddyisabar]

The oddroc tube design you love is calling out for dark art forces to fly. Put canted tractor motors on top. A tube worm rocket I once built could pull up a tail, providing parasitic worm flying fun for the whole family.

Motors at the top may seem unnatural, but they sure do provide lots of power while avoiding all that no good, stinking, performance robbing nose weight! The Jedi say to keep the motors an fins at the bottom of the rocket, WHERE THEY SHOULD BE! But you are flying a silly tube oddroc, the dark side is calling.

Put a motor on top in the center with enough bypassing airflow flow to avoid a call from Mr. KRUSHNIC. No fins down low, gas dynamic stabilization, Mindsimming, Oh no! What are they talking about? My pure, unsullied ears! You have entered the Restricted Section in the Hogwarts library. Very naughty! Detention for such impure thoughts. You will poke your eye out flying such abominations. Or worse yet, you might mess up your nose. Forever looking like He Who Must Not Be Named.

Beware. Any derivation from the 3-4FNC standard may lead you down a dark path, forever guiding your destiny.

It looks so funny it must be unstable! Danger! Danger! But actually, it was the most stable rocket at the launch that day. No, no, say it ain't so!

 

[curtisheisey]

I was able to model this in OpenRocket. To open, ones need a recent version, as it has phantom tubes.

This took me through a cascading set of design issues:

1. First discovery is that the CP is 3/4 the way up the cylinder, ahead of the CM.
2. To move the CM forward, requires a large amount of weight on a thin pole sticking out of the top of the rocket. I will wrap in foam for safety.
3. Because the rocket is now heavy, this requires a large thrust (high-E, maybe F impulse)
4. Now the concern is that a thin foam walled cylinder may collapse under the force
5. This would lead to a design with cardboard walls and glassed

It will use tumble recovery.

I'll build this one up, but definitely 1st flight in absence of other people.

 

[BigMacDaddy]

If I was going to try to do this I would push the motor all the way to the front of the foam ring tail, put a small nosecone on it, couple of centering rings -- can make them canted to try to induce spin -- and rely on GDS to help with stability. Maybe make the motor rear eject so the cylinder would glide down...?

 

[David Schwantz]

https://www.rocketryforum.com/threads/how-to-figure-base-drag.156237/#post-1946253

 

[curtisheisey]

BigMacDaddy Ah, that's a great idea ... better than Rube Goldbering the weight​

​

 

[Daddyisabar]

If I was going to try to do this I would push the motor all the way to the front of the foam ring tail, put a small nosecone on it, couple of centering rings -- can make them canted to try to induce spin -- and rely on GDS to help with stability. Maybe make the motor rear eject so the cylinder would glide down...?

View attachment 602816

I feel the dark side of the force surrounding this one. Could it have Sith like telescopic take off and flight qualities?
A pop pod with a tubular glide back is very unnatural, but you must fulfill your destiny and fly the rockets you love.

 

[Daddyisabar]

I was able to model this in OpenRocket. To open, ones need a recent version, as it has phantom tubes.

This took me through a cascading set of design issues:

1. First discovery is that the CP is 3/4 the way up the cylinder, ahead of the CM.
2. To move the CM forward, requires a large amount of weight on a thin pole sticking out of the top of the rocket. I will wrap in foam for safety.
3. Because the rocket is now heavy, this requires a large thrust (high-E, maybe F impulse)
4. Now the concern is that a thin foam walled cylinder may collapse under the force
5. This would lead to a design with cardboard walls and glassed

It will use tumble recovery.

I'll build this one up, but definitely 1st flight in absence of other people.

The fun is to have it fully mindsimed, beautifully finished and getting that first flight pad assignment gleaming with confidence. Yes Mr. RSO, silly oddroc failure is not an option. Think outside the 3-4FNC box!

Thin, light BT 101 is old school, but it can be made super strong with an internal thin CA soak. IT'S SMOKIN'! Cough cough, choke coke, gasp for air! Fully non toxic. Poor Boy Phenolic is also unnatural. Do you really need it?

Shave the weight and grow the thrust! Tractor motors rule! They can open your eyes to a much larger world.

But Master Jedi, as the Tractor motor(s) burn, it, unlike a traditional rocket design, becomes less stable as propellant weight up front decreases. Must we now think and mindsim backwards?

No young Padawan! Keep the motors and fins at the back of the rocket where they should be. No mindsiming and do not be seduced by exotic, finless, tractor motored oddroc abominations!

 

[Daddyisabar]

If I was going to try to do this I would push the motor all the way to the front of the foam ring tail, put a small nosecone on it, couple of centering rings -- can make them canted to try to induce spin -- and rely on GDS to help with stability. Maybe make the motor rear eject so the cylinder would glide down...?

View attachment 602816

Making it spin is just sick! A Bridge too Far! An extreme RSO frightening machine!

 

[Daddyisabar]

The discovery that your CP is 3/4 the way up your rocket should signal that you are firmly in the realm of EXTREMELY POOR ROCKET DESIGN. Walk, no RUN away as fast as you can! You will poke your eye out!

Foam will flex and burn. A foamy horror show, just like the Estes Spaceship One E. I am now frightened beyond rational thought!

 

[Daddyisabar]

To get an actual simulation in OR, enter phantom body tube (0 diameter) and add a single tube fin. Body tubes are presumed to be closed on the front (no internal airflow) so you cannot model it with a body tube.

For the flight sim (if you can make it stable) you might be bitten by the tube-fin drag bug (to be fixed next release), but I expect that evaluating stability is all you're after here.

TRUST THE MACHINES!

 

[curtisheisey]

TRUST THE MACHINES!

No, I don't trust the machines for an unusual geometry such as this. I'm just using its suggestion as a rough 1st cut.

 

[curtisheisey]

Making it spin is just sick! A Bridge too Far! An extreme RSO frightening machine!

I did build the tractor rocket in George Gassaway's thread, and I recently have built a moncopter and bicopter.

 

[Daddyisabar]

I did build the tractor rocket in George Gassaway's thread, and I recently have built a moncopter and bicopter.

Who needs stinking fins when you have a SPINNERELLA! GO TAZ! THE WHITE TORNADO!

 

[Pem Tech]

I feel the dark side of the force surrounding this one. Could it have Sith like telescopic take off and flight qualities?
View attachment 602857A pop pod with a tubular glide back is very unnatural, but you must fulfill your destiny and fly the rockets you love.

Wow...
And I thought I flew weird sh*t...

 

[Daddyisabar]

No, I don't trust the machines for an unusual geometry such as this. I'm just using its suggestion as a rough 1st cut.

Yes, mindsim is the way. Navigate the big tube ships through the dynamic atmosphere! Prepare a report of your results to be distributed within the guild. 0-0-0

 

[Daddyisabar]

Wow...
And I thought I flew weird sh*t...

Tube rockets are soooo cool. Who needs stinking fins and nose cones!

 

[BABAR]

quite do-able.

http://www.spacemodeling.org/jimz/eirp_56.htm

 

[lakeroadster]

I was able to model this in OpenRocket. To open, ones need a recent version, as it has phantom tubes.

This took me through a cascading set of design issues:

1. First discovery is that the CP is 3/4 the way up the cylinder, ahead of the CM.
2. To move the CM forward, requires a large amount of weight on a thin pole sticking out of the top of the rocket. I will wrap in foam for safety.
3. Because the rocket is now heavy, this requires a large thrust (high-E, maybe F impulse)
4. Now the concern is that a thin foam walled cylinder may collapse under the force
5. This would lead to a design with cardboard walls and glassed

It will use tumble recovery.

I'll build this one up, but definitely 1st flight in absence of other people.

You're model has the main tube made from styrene? Change that to styrofoam and the apogee goes up to 354 ft.

And a 1/4" diameter tube... with 21 ounces of ballast... yikes.

 

[boatgeek]

Wow...
And I thought I flew weird sh*t...

Nobody flies weird sh*t like @Daddyisabar...

Which is intended as the highest praise!

 

[curtisheisey]

Here is how it is shaping up. I omitted the forward weight and am going to rely on GDS as BigMacDaddy suggested.

I ended up 3d printing two hub and spokes for the motor mount. Then I 3d printed a launch rail guide for the bottom (which might need to be replaced every flight.

7.5 in diameter, 24 in length, 332g w/out motor. 29-mm motor mount

I don't know whether to call it the "Boston Eye" (aka London Eye) or the "Flying Cylinder".

 

[neil_w]

Rama (lama ding dong)

 

[BigMacDaddy]

Here is how it is shaping up. I omitted the forward weight and am going to rely on GDS as BigMacDaddy suggested.

I ended up 3d printing two hub and spokes for the motor mount. Then I 3d printed a launch rail guide for the bottom (which might need to be replaced every flight.

7.5 in diameter, 24 in length, 332g w/out motor. 29-mm motor mount

I don't know whether to call it the "Boston Eye" (aka London Eye) or the "Flying Cylinder".

All my GDS rockets also have lots of nose weight. Not sure how various factors work together to get them stable and I may be over-conservative in some cases and too optimistic in others.

Anyway, at least a foam rocket is soft and light so you can always experiment with the design.

 

[GlenP]

I wonder if you might get a strong duct flow that creates suction in that tube if it might collapse in on itself without some additional centering rings or structural stringers between the centering rings. How strong is the foam tube if you squeeze it in the middle of the rings? Is it pretty stiff or does it flex at all?

 

[curtisheisey]

I wonder if you might get a strong duct flow that creates suction in that tube if it might collapse in on itself without some additional centering rings or structural stringers between the centering rings. How strong is the foam tube if you squeeze it in the middle of the rings? Is it pretty stiff or does it flex at all?

You are right ... it's not strong at all. I expect, though, that the velocity will be really low. Kinda like the Estes Dude rocket. I could always glass it.

I'm 3d printing a NC so I can experiment with NC, no NC and various NC weights

 

[Daddyisabar]

Tractor motored, tubular, flexible rockets sure soak up that lovely thrust. Give off a nice, quick, serpentine motion as they go up. Someone in the crowd always goes "What the heck was that?" "Was that supposed to do that?" After landing: "Was that a successful fight?"


We strive for really good rocket design that is hallmarked by super strong, stiff and light body tubes. 3-4FNC. On this one I guess I just missed it a bit.

Son, ya shouldda glassed it solid. A terrible waste of lovely rocket thrust. Very sloppy, inefficient and draggy. Trains are not meant to fly vertically under rocket power. Stop listening to Ozzie and that Crazy Train hard rock music. It will rot yer mind.