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Old Sep 14, 2014, 04:03 PM
Hurts so good!
Joined May 2008
249 Posts
Build Log
Doubler II SIG kit from the 1970's. Vintage quarter midget racer!

I've never posted a build log before but have always wanted to :-) I do enjoy reading other members contributions though. After recently posting a discussion thread inquiring about .15 size engines for the Sig DOUBLER II I am preparing to build, a fellow member responded suggesting I do a build thread for this old kit since he has the same unbuilt kit. I thought to myself 'why not?'

I'm not sure the difference(s) between the Doubler 2 vs. the original Doubler in which Austin Leftwich modified for pylon racing and subsequently became the 1/4 midget racing champion in 1969, 1970 and 1973. I can only hope it is for the better. This kit is dated 1977. #RC-40

I've never been a big fan of SIG kits. I built only one, the Astro Log err Hog. I think SIG kits have too much carving and whittling involved for my taste. After reviewing the contents of this NIB kit I purchased here from a fellow member, it is very similar. There are chunks of wood which will no doubt need to be carved and sanded to become useful parts on this airframe. There are a few sheets of 'print wood' which will need to be cut out. I will be purchasing a scroll saw in the next few days for completing this task.

For a power plant I will use an NOS OS .15 CV-A engine I have in the closet. Unsure as to electronics yet but I suspect they will be smaller, lighter and vastly improved over what was offered in the late 70's

I believe I will try and reproduce the color scheme of the white/black livery of the bird on the box cover.

I'm a slow builder as I still have a career. With that said, I love to build and do not an on dragging this build out for a year. Mainly because I have more kits to build LOL. This kit definitely does not qualify itself as a difficult build, thus should lend itself well to my first build log. All of the pictures will be taken with my phone as it is the only digicam I own

Follow along if you are so inclined, and don't be shy about sharing your thoughts and suggestions!!

Regards KoP
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Old Sep 14, 2014, 04:06 PM
Hurts so good!
Joined May 2008
249 Posts
Step one for me was to iron the huge folded plan sheet in order for it to be flat enough to build upon. This must be before plans were rolled vs. folded
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Old Sep 14, 2014, 04:09 PM
Team Fearless
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United States, MD, Piney Point
Joined Mar 2005
1,714 Posts
Neat plane! Subscribed.
I'll be watching.

Shawn
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Old Sep 14, 2014, 05:12 PM
Hurts so good!
Joined May 2008
249 Posts
Next up I am joining 18" pieces of 1/16" thick balsa sheet to form 36" lengths. This sheeting will be used for the upper and lower leading and trailing edges. I contemplated just going to the LHS and purchasing some 36" lengths of 1/16" sheet for this step. I decided not to at this point as this wood is pretty darn nice and the added expense seems unnecessary.
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Old Sep 14, 2014, 05:26 PM
Registered User
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Joined Dec 2007
1,366 Posts
With that engine this plane should bolt along with ease could go past 100mph.

APC Pylon prop 6.5x6.5 cut to 5.8 x 6.5 if at 20k rpm 123.1mph.
6 pitch at 19k rpm= 108mph / 5P 90 mph / 4p 72mph

CV-A:
RPM range: 2,500 - 19,000
BHP: .50

CV-X
RPM range: 3,000 - 30,000
BHP: .68
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Old Sep 14, 2014, 05:44 PM
Hurts so good!
Joined May 2008
249 Posts
Thank you for the info AA
If one had the CV-x would one just remove the buggy heat sink head and replace with the aero head?
I suppose the tuned pipe is needed to get the 30k rpm. Then there is the slide carb / linkage to adapt to airplane use?
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Old Sep 14, 2014, 07:26 PM
Hurts so good!
Joined May 2008
249 Posts
Sanded the (now) four pieces of wing sheeting surfaces. Long edges are now straight and true.
Next I will remove the (nicely) die cut wing ribs from the two supplied sheets. Only 12 ribs make up this 36" wing.
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Old Sep 14, 2014, 08:00 PM
Hurts so good!
Joined May 2008
249 Posts
Wing ribs stacked and pinned as per instructions. I lightly sanded the stack to even them up. Not perfect but I didn't want to get too aggressive as I did t want to alter the airfoil and I believe further sanding would have diminishing returns.

The tabs at the trailing edge are supports that will be cut off after the wing is lifted from the plans.
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Old Sep 14, 2014, 08:21 PM
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Joined Dec 2007
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Yea was just fyi so everyone following along knows the A design has a X version. I would imagine your engine design is structurally sound enough to bust 20k depending how you prop it.
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Old Sep 14, 2014, 09:00 PM
Luis Claudio - Rio - Brazil
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Brasil, RJ, Rio de Janeiro
Joined Apr 2005
2,429 Posts
IŽll be watching also!
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Old Sep 14, 2014, 09:03 PM
Registered User
United States, WA, Mt Vernon
Joined Jun 2014
176 Posts
Look forward to the build!
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Old Sep 15, 2014, 06:23 AM
Registered User
Australia, ACT, Canberra
Joined Dec 2011
335 Posts
Hello, I'm the guy you mentioned in your first post so I best be tagging along for a look see
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Old Sep 15, 2014, 07:00 AM
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Sweden
Joined Jan 2008
970 Posts
Great to see the older ones get build too. I prefer the die cut stuff over the burnt laser cut jigsaw puzzle that we get nowadays...
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Old Sep 15, 2014, 07:04 AM
Hurts so good!
Joined May 2008
249 Posts
Hello All :-)
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Old Sep 15, 2014, 10:22 PM
Hurts so good!
Joined May 2008
249 Posts
This evening I was able to build some until the sun started setting and my lighting went bad.
I was able to purchase 3/16"x3/8" x36" spars today at the LHS. I wanted to buy one piece leading and trailing edges too but they're an odd dimension. LE = 5/16" square and TE = 1/8"x5/32".
I joined the LE and TE pieces in the kit with a bit of epoxy early in the day. Sanded the joint smooth after work and then started constructing the wing.

Although the spars are one piece, I still added the two spar splices in the center wing bay.

Lastly I used wood glue on the plywood wing holdown plate at the leading edge.
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