Zuni RBG build

[FlyBack]

Thought it might be interesting to see what could be done with the wing from an ArtHobby Zuni-V R/c glider.

[FlyBack]

Design Features:

Added about 10 degrees wing sweep on trailing edge to get C.G to work out. Inverted V-tail for exhaust clearance and proverse yaw. Twin booms to allow use of an electric motor with pusher propellor instead of a rocket motor. Pull/pull control wires to the ruddervators. Will use an AeroTech E6-RCT motor.

[FlyBack]

Construction progress so far...

[Ltvscout]

Excellent! This is what we like to see, a nice photo progress report of a project.

[FlyBack]

Thanks Scott... will update as I get further along.

[shockwaveriderz]

flyback, looks great. Can't wait to see more.


terry dean

[FlyBack]

... will update as I get further along.

Finally. Now that construction of my BlackStar (http://forums.rocketshoppe.com/newreply.php?do=newreply&p=69379) model is completed, I have a bare workbench. I've decided to resume work on this design, instead of moving on to Config 2 of the BlackStar (have to finish CAD drawings of Config 1 first).

Latest construction photos attached below. More to come later this week.

Regards,

DJ Miller

[FlyBack]

For the engineers out there:

Here are the preliminary specifications. Latest photos added to post #7 above.

Preliminary Specs:

Wing Root Chord (A): 6.0

Wing Tip Chord (B): 4.375

Wing Sweep Distance (S): 5.375

Wing Half Span (Y): 21.75

Stabiliser Root Chord (AA): 5.5

Stabiliser Tip Chord (BB): 3.625

Stabiliser Sweep Distance (SS): 2.875

Stabiliser Half Span (YY): 6.0

Distance between both LE's (D): 17

Static Margin 12.5 %

Mean Aerodynamic Chord MAC = 5.23

Sweep Distance at MAC (C) = 2.55

From Root Chord to MAC (d) = 10.31

From Wing Root LE to AC = 3.85

From Wing Root LE to NP = 5.63

From Wing Root LE to CG = 4.98

Wing Area = 225.7

Stabiliser Area = 54.8

Wing Aspect Ratio = 8.39

Tail Volume Ratio, Vbar = 0.73


Aircraft Weight (estimated) : 12.7 ounces

Max Lift Coefficient : 1.0

WING LOADING : 7.85 oz/sq.ft

CUBIC LOADING : 6.27 oz/cubic.ft

STALL SPEED : 13.9 mph



FlyBack

[jharding58]

A very nice looking boost glider. You have really got a flair with design. How much will you have to reduce the elevators at the vertex so they do not foul each other on down?

I recall seeing a Zuni with a 24mm mount located just at the dihedral break with a slight tail high configuration to allow the exhaust to clear the V tail. I think the tail was also finished in matte black to further reduce the cleanliness issues.

[FlyBack]

How much will you have to reduce the elevators at the vertex so they do not foul each other on down?


Thanks,

The clearance on the ruddervators is about a 1/2 inch. I used 3/16 inch balsa for the side pieces. They were preformed by first soaking in an amonia/water mix then taping in place. After 24 hrs they take on a permanent set. The corner strips will be done the same way.

Regards,

FlyBack

[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

[FlyBack]

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 (http://www.smallparts.com/dp/B000FMYV9O/ref=sp_dp_g2c_asin) 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 (http://www.qmfc.org/school/ackerman.htm) 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

[FlyBack]

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

[jharding58]

What rocket? And yes, those curves do look better.

[jharding58]

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.

[FlyBack]

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.
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

[kevinj]

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 (http://www.smallparts.com/dp/B000FMYV9O/ref=sp_dp_g2c_asin) 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 (http://www.qmfc.org/school/ackerman.htm) 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

[FlyBack]

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

[FlyBack]

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

[FlyBack]

Quick update:

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

Regards,

FlyBack

[Rocketflyer]

Progress report... and Quiz:



[B]The quiz: Find the rocket in photo #1

Regards,

FlyBack


Still looking (for the rocket). :D

[cas2047]

Still looking (for the rocket). :D

Me too! I saw NO rocket in that picture. :D

[samb]

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 #1

Regards,

FlyBack

I don't know... she looks kinda pissed. Nice build thread though.

[FlyBack]

I don't know... she looks kinda pissed. Nice build thread though.
Thanks! More updates coming soon... I think she looks pissed because there hasn't been a decent replacement for the Estes Centurion in production for years (one that was a decent glider at any rate). I know I am...

Back to building: Glassing technique.

Photos below show the method used to do all of the fiber glass reinforcements on this model. Handling and cutting light weight glass cloth and carbon tow fibers can be difficult. I like easy. So... I use "helper" materials. Not shown is a can of 3M 75 spray adhesive. Used sparingly, it makes handling of the cloth easy (oh... and I mean very sparingly). Peel ply is your friend guys. It makes it possible to get very dry layups without vacuum bagging. It also leaves a surface that requires very little filling or sanding that can be bonded to.

Regards,

FlyBack

[FlyBack]

Progress Update: Rigging the control system

The most difficult part of the build is now behind me. The V-tail is finished and attached to the booms. The fixed portion is covered in Esake Silk. The rudder-vators are covered in Japanese Tissue. Water based polyurethane was use as the binder.

My technique for bending the PEEK tubing has been refined, and the servo tray is ready to install. Bending the control runs (PEEK tubing), without collapsing the wall, had me stumped for a while. I finally found some stainless steel, braided leader wire that was just under the ID of the tubing. Threading that through the tube to be bent, and then heat forming it around my mandrel worked like a charm.

Weights now include hardware for aileron servos. I had hoped to do this with rudder and elevator alone but have decided to go for full control on all three axis.

Latest weigh in:

Airframe - 170.9 grams
Servos - 31.2 grams
Rx - 7.4 grams
Battery - 15.6

Regards

DJ Miller

[FlyBack]

More photos...

Uploaded some photos of the servo tray before it gets installed. It took some time to get the servo height just right to line up with the cable runs... but worth the effort.

Cutting slots in the wing for the tail booms creates an enormous stress concentration. The photos of the wing show the area where I have added a fiberglass reinforcement (shown with and without peel ply). The bottom side will be glassed also.

Latest weigh in results:

Servo Tray 4.0 gm
PEEK tubing 1.5 gm
Glass on wing 15.0 gm

Airframe 191.8 gm

Total 8.3 oz 235.6 gm



Regards,

FlyBack

[FlyBack]

Todays topic: Control horns and negative Ackerman...

Not a lot to say here, most of the really good "Ackerman" links (http://www.qmfc.org/school/ackerman.htm) have already been posted. If I have gotten the angles on the control horns wrong, they will bind. Since they are now installed, I will know as soon as I pull the control wires and start testing (sometime tonight or tomorrow... stay tuned)..

The photo set below shows some of the steps involved in making control horns from scratch. I tend to build right off the drawing board. It saves time. A light coat of white primer on the graphite sheet makes it easy to see pencil markings. Sticky paper templates invariably peel or shift when working on parts this small. Eventually I will go back and do CAD drawings of the finished parts (when I am sure the parts I am drawing actually work).

Safety Warning: Use protective gear when working with carbon fiber. (See attached photo).

Regards,

DJ Miller

[FlyBack]

It works...

On the ground at least. The pull/pull control system is installed and tested. No binding, zero slop. Photos attached:

Regards,

FlyBack

[FlyBack]

More details...

The servo horn screws hold the tension on the wires. Attachment to the control surface horn is a simple overhand knot tied in the wire.

Latest weigh in includes the servos, receiver and battery pack:

Total 241.82 gm (8.53 oz)

Parts remaining: Aileron push rods, Fuselage hatch, hatch mounting points (for nylon screws - four places).


FlyBack

[Rocketflyer]

This is just an amazing build thread and project. Super! :D

[FlyBack]

Rocketflyer

Thanks! After a long lay off I am back in work on this project. Expect regular updates to follow.

Its been a hard year with a job change, relocation to Atlanta, buying a new house and setting up my (new and improved - larger) workshop. Anyway, back to work. I have been messing with this model too long to NOT finish it.

Regards

FlyBack

aka: DJ Miller
(newly of ATLANTA, GA)