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  #11  
Old 02-24-2011, 05:12 AM
kevinj's Avatar
kevinj kevinj is offline
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I'm not following the control linkage setup.

When you say pull-pull I'm thinking of servos and control surfaces linked by two cables that pull the surface both ways.

Is that what you are doing? Around bends?

kj
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  #12  
Old 02-24-2011, 05:38 PM
FlyBack FlyBack is offline
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Default Fuselage Corner Pieces

Kevin,

The pull wires run inside tubing. The bends have a .125in radius. After a great deal of trial and error, I have finally found the combination of materials that make this possible. The wire is 7 strand stainless steel fishing leader line. The tube is made out of PEEK plastic; much harder than teflon, it can be heat formed without collapsing. Photos below show the tool used to bend the tubes (four of them). Getting the geometry right is another story. Careful attention to bend radius and Ackerman are required. More on this in comming posts.

The fuselage corner pieces, after preforming, are shown below. This step makes assembly much easier and eliminates any residual stresses in the glue joints. I also think the compound curves not only look better, but are stronger and use less material.

Regards,

DJ
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Last edited by FlyBack : 02-25-2011 at 09:58 PM. Reason: more verbage and ackerman link
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  #13  
Old 02-25-2011, 07:36 PM
FlyBack FlyBack is offline
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Default Fuselage Shaping

Progress report... and Quiz:

Preformed corner pieces are on and roughly shaped. Inside and outside photos below. Also included, a photo of an Estes StratoBlaster/Centurian fuselage pod next to my Zuni-RBG pod for comparison purposes.

The quiz: Find the rocket in photo #4
Regards,

FlyBack
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Last edited by FlyBack : 04-10-2011 at 09:57 PM.
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  #14  
Old 02-25-2011, 10:29 PM
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jharding58 jharding58 is offline
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What rocket? And yes, those curves do look better.
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  #15  
Old 02-25-2011, 10:38 PM
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jharding58 jharding58 is offline
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Quote:
Originally Posted by kevinj
I'm not following the control linkage setup.

When you say pull-pull I'm thinking of servos and control surfaces linked by two cables that pull the surface both ways.

Is that what you are doing? Around bends?

kj

There are a good few vintage aircrfaft which used cables around corners - even without the benefit of pulleys. The Bowden cable system that used a flexible cable within a semi-rigid tube has been around in R/C aircraft for donkeys. Although initially used for pull applications; bicycle brakes and clutch springs, with a sufficeintly light retrun pressure they could be used to push also.

In this application it is a braided line that can pull-pull around corners without any real binding. For example Berkley Spiderwire is a braided Micro Dyneema line with Teflon impregnated into the braid. You really have to cinch a knot to have it stay simply because the line wants to slip past itself.
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  #16  
Old 02-26-2011, 01:51 AM
FlyBack FlyBack is offline
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Default Waiting for glue to dry

Quote:
Originally Posted by jharding58
with a sufficeintly light retrun pressure they could be used to push also.

This is exactly why I settled on the braided stainless wire. I needed something that was stiff enough in compression to thread back through the tubing after it was bent.
Quote:
Originally Posted by jharding58
For example Berkley Spiderwire is a braided Micro Dyneema line with Teflon impregnated into the braid.

... and it has a really low melting temperature. Not good if exposed to rocket exhaust.

It's counter intuitive, but Spiderwire inside thin wall Teflon tube just doesn't work in this application. Braided stainless wire inside PEEK tubing pulled through tight bends actually has a coefficient of friction very close to Spiderwire in Teflon. Even so, just to be safe, I am using servos that put out 22oz/in and have a very high starting torque. I also need the 9gm servos to balance the model.

Regards,

FlyBack

Last edited by FlyBack : 02-26-2011 at 02:09 AM. Reason: clarification
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  #17  
Old 02-26-2011, 07:06 AM
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kevinj kevinj is offline
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Quote:
Originally Posted by FlyBack
The pull wires run inside tubing. The bends have a .125in radius. After a great deal of trial and error, I have finally found the combination of materials that make this possible. The wire is 7 strand stainless steel fishing leader line. The tube is made out of PEEK plastic; much harder than teflon, it can be heat formed without collapsing. Photos below show the tool used to bend the tubes (four of them). Getting the geometry right is another story. Careful attention to bend radius and Ackerman are required. More on this in comming posts.


Interesting. Not exactly how I'd approach it, but then I've never been a fan of pull-pull.
kj
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  #18  
Old 02-28-2011, 05:06 AM
FlyBack FlyBack is offline
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Default Weight Control

Progress report:

The only sure way to control weight growth I know of is to take regular measurements and compare them with target weights. I will continue to post weights, at regular intervals as the prototype is assembled.

The control system and fiberglass reinforcements have yet to be added. (Not to mention that a really heavy finish and paint job can add as much as full 2oz.)

Finished target weight: 12oz. Wishful thinking target weight: 10oz.

Regards,

DJ
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  #19  
Old 03-07-2011, 11:12 AM
FlyBack FlyBack is offline
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Default A-tail alignment

Progress Update:

Fuselage pod corners have been rounded off. A little more filling and sanding and the upper portion will be ready for glassing.

The A-tail fillet is in. This part also functions as a visual aid to alignment when gluing it on to the graphite booms. Most of it will be removed. The apex joint will be reinforced with carbon tow fiber then glassed.

Cumming up... installing the servos and running the control wires.

Regards,

FlyBack
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  #20  
Old 03-11-2011, 04:53 PM
FlyBack FlyBack is offline
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Default A-tail reinforcement

Quick update:

More work on the V-tail. Photos show the top side of the V before and during glassing.

Regards,

FlyBack
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