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Old Apr 13, 2009, 11:56 AM
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F-9 Panther scratch build from SketchUp **Successful Flight**

A while back I was looking for plans for a F-9 Panther parkjet and found only a couple of builds and not many plans. So I figured I could make this my first scratch build project. Since then Hobby Lobby started selling a F-9. RC Lander came out with a great version and Beanie started a build. Well Ö.. better late than never.

Iíll get started.
Ported 3 views into SketchUp and built a model from that.
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Old Apr 13, 2009, 12:32 PM
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Making plans from the model

The concept is to build an airplane with 2 inch thick insulation foam. A SketchUp model can be sliced up into even increments to create cross section templates. These can then be used to hotwire cut the foam sections. Sections can be glued together to then create an airplane.

Background:
SketchUp is a free 3D modeling software you can get from Google.
http://sketchup.google.com/
There is a 3D warehouse that you can down load models from if you donít want to build your own. There are plenty of airplanes modeled but I could not find an F-9 and thus created my own.
There are a couple of threads here in RC Groups that can give you more information about how to use SketchUp to model airplanes
http://www.rcgroups.com/forums/showt...826409&page=10
http://www.rcgroups.com/forums/showthread.php?t=920416
And there is SketchUp for Dummies with tutorials on the basics
http://www.aidanchopra.com/
Here are some specific to building airplanes
http://www.youtube.com/profile?user=...ht&view=videos

http://www.phlatforum.com/viewforum.php?f=52
View the videos by Crash, kram242 and AnyAirRc of them using SketchUp
to create 3D models of aircraft, then unfolding the model to have flat
parts to print as patterns to cut out the actually flying RC model
airplane.

Ruby scripts are available to automate some tasks. There is a slice plugin that I used to slice my model in even 2 inch increments then lay them flat so plans can be printed.

http://www.phlatforum.com/viewtopic.php?f=11&t=95
Must have Sketchup Scripts/Plugins - these are used in the above
videos.
Examples: jf_unfoldtool.rb, progressbar.rb, weld.rb,
repair_broken_lines.rb, Slicer3.rb

http://www.phlatforum.com/viewtopic.php?f=11&t=98
skin25.zip

http://www.foamcasualty.com/cad.shtml
SketchUp screenshots of F6F Hellcat and FW-190 unfolded, ready to print.
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Old Apr 13, 2009, 12:39 PM
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Slicing the model

After the model was built and scaled, I used a Sketchup plugin that slices it in even increment. The plugin also puts all the cross section slices on the same plane. I then cleaned them up and got them ready to print. BTW, none of this is easy. To get the plugin to work I had to orient the model in the Z axis. Lots of clean up and rearranging before printing. Printing to the right scale is difficult. Instructions are in a post on one of the other threads. I will include it here later on in the build. I will also post the plans once I have a flying model.

Here are some more pictures
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Old Apr 13, 2009, 03:18 PM
My plans are in my blog
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Very nifty. I once seen one of theres in a thread/vid that used a 40 mm EDF, it looked entirely cool. Yours will too I bet.
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Old Apr 15, 2009, 11:18 AM
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Templates cut

Started cutting sections.
Foam must be squared up and marked with a line on 3 sides to ensure proper template alignment.
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Old Apr 15, 2009, 12:27 PM
Mike
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Very interesting. I've seen something like this done for a large scale B17 one time. I will be watching with interest. What kind of foam wire cutter are you using? Is it the standard $20ish one that I've seen at Hobby Stores and JoAnn Fabrics? Seems that would work for 2 inch increments that aren't to large. Just curious.

-mike
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Old Apr 15, 2009, 03:42 PM
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Quote:
Originally Posted by i12flyrc
Very interesting. I've seen something like this done for a large scale B17 one time. I will be watching with interest. What kind of foam wire cutter are you using? Is it the standard $20ish one that I've seen at Hobby Stores and JoAnn Fabrics? Seems that would work for 2 inch increments that aren't to large. Just curious.

-mike
I have 2 home built hot wire cutters. Unfortunately no great pictures at the moment. One is a table made with a scrap piece of laminated shelving and some 1 x 2 lumber. I used a 5/8 threaded rod with 1" washers and nuts. The threaded rod supplies the tension. The wire is steal fishing lead. I don't know what guage. Power supply is a car battery charger.

To cut foam wing cores I made a cutting bow with 1/2 x 1" trim. It is hard to see but one end (left side of picture) is fixed and the other end can rotate to supply tension. Tension is from a rope (see picture).
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Old Apr 16, 2009, 12:03 PM
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SUBSCRIBED!!! Very nice work using SU. I've been trying to talk myself into learning this program and this is very inspiring. The F9 Panther is one of my favorit jets ever since I saw these pics from a Top Gun airshow here in Lake Land FL.

I can't wait for the plans. Best of luck on the build and on the maiden.

Ev
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Old Apr 16, 2009, 01:27 PM
Fly it like U stole it
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Champaign, Il
Joined Mar 2008
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Subscribed!
I just started teaching myself sketch up, Your links are a great help, thanks! I have only modeled a coffee mug so far but I can appreciate the great work you have done.
This is going to be a great thread to learn from, keep the posts a coming

Is this an edf or pusher? And do you have a wingspan?

Matt
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Old Apr 16, 2009, 03:31 PM
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So, to line up the templates you must have foam that is squared off on one end relative to the surface you pin the templates to. I leveled my work bench and let gravity pull the cutting bow straight down. That creates an even squared off cut Ö. Right?? Well it seemed like it worked for a few cuts, then the cuts started getting inconsistent. My guess is that the path of the hot wire is affected by gremlins. My second guess is that the grain of the foam and/or density variation play a part in the path of the wire.

What I do now is clamp the bow to my work bench, hold 2 carpenter squares on either side of the foam and use them to guide the wire and my hand as I pull the foam up. Obviously you need metal squares to guide a hot wire.

Lay a template down and mark a dot on the foam where the template center line is. Use a square to draw a line that connects on 3 sides of the foam. If every thing is square, the line on the bottom should be directly below the line on the top and the templates will line up just right. Itís been working for me.
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Old Apr 16, 2009, 06:54 PM
Fly it like U stole it
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LOL I am glad I am not the only one suffering from the gremlins I ended up doing the same thing with the squares, sure thought gravity would do all the work for me
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Old Apr 16, 2009, 07:55 PM
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osprey- very neat build technique! looks like its gonna be great!
-beanie
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Old Apr 20, 2009, 11:22 AM
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Templates out the wazoo

Lots of work accomplished.
If I use this tecnique again in the future for an EDF version, I will work the ducting into the plans such that they can be cut with each section and eliminate the need for separate fabrication. I would guess that you would have to glue sections sequentialy and spackle the seams in the ducts as you go. I'll leave that issue for another day.
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Old Apr 23, 2009, 11:30 AM
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Some more progress.
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Old Apr 23, 2009, 12:29 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
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Hi Osprey Engineer,

Here are a couple of my and MarineA4 builds using this type of construction, I favor EDF and the ducting is cut at the time I cut the section as you have surmised. It works very well but is labor intensive at times with all the cuts.

http://www.rcgroups.com/forums/showthread.php?t=521119

http://www.rcgroups.com/forums/showthread.php?t=700697

http://www.rcgroups.com/forums/showthread.php?t=932642

Cheers,
Eric B.
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