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Old Apr 22, 2014, 01:40 PM
Capt. Kelso
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United States, FL, Yulee
Joined Dec 2011
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Scratch built 1/6 PT-19

Have been considering building a kit PT-19 but could not find a kit that I thought would fit my needs. Most that I saw advertised where older and I was concerned about the quality of wood and construction techniques. Sooooooooo, I decided to jump in and scratch build my own 1/6 version.

Why the PT-19? Because it was my first RC plan. A control line Cox PT-19 Trainer.

To get started I obtained a copy of Chuck Hollinger circa 1958 Plans and a set of Jetco PT-19 plans. The wing span is 72" Estimated the amount of balsa needed and placed my order.

The original Hollinger plans have the spars running through the ribs and multi piece wingtip construction. I thought it would be easier and more stable to add spars on top of the ribs (1/4 x 1/2 forward and 1/4 x 1/4 rear) and make a one piece wingtip. Also, I will be adding aileron servo's to the wings.

I had a problem trying to use a drill bit to place holes in the ribs to run the servo wires. Seems every time I tried to drill a hole it tore the wood up! The, I remembered a brass 3/4" pipe coupling I had, sharpened the edge and used a hammer to pop a hole in the rib. Worked out pretty good, 34 ribs later, wing is starting to take shape.

Next step will be to join the wings.
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Old Apr 23, 2014, 05:40 AM
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Moab, Utah, USA
Joined Apr 2003
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Interesting project. Your wing looks great, but where is the aileron?

Larry
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Old Apr 23, 2014, 07:10 AM
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United States, KY, Taylorsville
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Nice!
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Old Apr 23, 2014, 01:06 PM
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Old Apr 23, 2014, 03:20 PM
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United States, CA, San Diego
Joined Apr 2000
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Quote:
Originally Posted by Capt. Kelso View Post

I had a problem trying to use a drill bit to place holes in the ribs to run the servo wires. Seems every time I tried to drill a hole it tore the wood up! The, I remembered a brass 3/4" pipe coupling I had, sharpened the edge and used a hammer to pop a hole in the rib. Worked out pretty good, 34 ribs later, wing is starting to take shape.
Were you trying to use regular drill bits?

They're "okay" to use on hard woods but they really tear up balsa even when pressed between hardwoods. Wood bits or better yet Forstner bits are what should be used but unless you're a prolific kit/scratch builder the cost to have these around may not be cost effective.

I like using your method but find that twisting while pushing helps prevent crushing. However that is hard on your ole fingers unless you also make/or buy a hard wood handle. I also like to use the hard brass tubes K&N sells as they are a thinner wall.

But in the end, whatever works right?

Mike
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Old Apr 25, 2014, 03:30 AM
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United States, VA, Petersburg
Joined Mar 2012
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very nice.
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Old Apr 25, 2014, 06:05 AM
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Traverse City, Michigan
Joined Dec 2005
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Quote:
Originally Posted by CryHavoc View Post

. Wood bits or better yet Forstner bits are what should be used but unless you're a prolific kit/scratch builder the cost to have these around may not be cost effective.



Mike
I use Forstner bits to place holes in my ribs for servo wire tubes. A set of them can be quite expensive, but buying one or two, in the sizes that you need, isn't too bad on cost.
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Old Apr 25, 2014, 07:11 AM
Capt. Kelso
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United States, FL, Yulee
Joined Dec 2011
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Have used my Forstner Rockler Bits but didn't have much success on softer wood. Maybe it was the speed. If a tore a rib up drilling, had to cut a new one. I found it safer to use the coupling.
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Old Apr 25, 2014, 10:30 AM
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United States, PA, Beaver
Joined Sep 2001
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Holes in balsa:
I make up various sizes by using any tubing, or cylindrical thin walled metal I can find (usually make them when I find I size I don't have) and sharpening one end with a conical stone in a Dremel (not sharp per say, just take the square edges off) . Then plug the other end with some hard wood so I can chuck in a drill press. Drill a hole in this plug. Then run the press at a slow speed. Can stack drill a few holes this way. After you drill a few, un-chuck and poke a small wire through the hole in the plug you drilled earlier to remove the balsa plugs.
Sounds harder than it really is. I am still using ones I made YEARS ago. Also you don't need tubing per say. I have a few I made up using cans from old brushed motors. Use a 2-56 or 4-40 bolt as the shaft (passing through where the motor shaft was) to chuck in the drill press.
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Old Apr 25, 2014, 07:47 PM
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I drill small hole then use rat tail file or dowel rod wrapped with sand paper. Makes nice holes that can be angled, say, for CL lead outs.
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Old Apr 25, 2014, 08:46 PM
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United States, VA, Petersburg
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I have had great luck with Forestner bits and if you want a cheap set go to lowes. They sell a porter cable set that is pretty inexpensive. I have been using them with great results.
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Old Apr 27, 2014, 11:07 AM
Capt. Kelso
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United States, FL, Yulee
Joined Dec 2011
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Thanks everyone for the feedback. This is my first scratch build project, so any tips and tricks are welcomed.

The biggest issue I faced joining the wings was trying to determine the correct dihedral. As you can see from the pictures, the angle of the wing gusset on the Hollinger plan is very aggressive. I did find a reference on the Jetco plans that noted 6 degrees was scale. Also did a google search which confirmed 6 degrees was the correct setting.

I cut the front and rear wing gussets from 1/4" ply and set the wings with 30 min epoxy. Once the wings were set, cut out the ailerons, added the aileron servo mounts and installed the landing gear braces.

Lots of sanding and shaping to do, especially the wing tips. I built the leading edges from 3/4"x2" x 36" balsa. Because of the taper this size worked out well. Just cut one piece with the correct taper and got two leading edges.

Not sure yet about starting the fuselage next or the rudder and stabilizer? Haven't resolved all the issues with building the fuselage.

Interesting find on the Jetco plans was a 1958 application for AMA membership. Clip the application and send in your $2.50. In 1958 I was still hoping the Brooklyn Dodgers would come back to NY.
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Old Apr 27, 2014, 02:35 PM
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Traverse City, Michigan
Joined Dec 2005
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Send in the AMA application. maybe they will honor the price.
If you haven't figured out the fuselage construction, you can stall, and build the tail section next.

You have some good builders following your progress. I'm sure that they will help with the fuselage if you need it.

The wing is looking good.
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Old May 02, 2014, 09:51 AM
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Salem, SC
Joined Mar 2003
517 Posts
A GREAT choice of subject!

I lusted over Hollinger's PT-19 ever since the mailman delivered my August 1956 issue of "Air Trails" and I moaned about it periodically. In 2003 I scanned the magazine plan (I see you're building from my scans), but still couldn't find a round tuit. Finally, to shut me up, in 2011 a friend gave me the Jetco kit, left unsold from his Chicago area hobby shop (at $24.95 it was wildly expensive for its day).

That was the needed prod. Like you, I wanted to make changes (one-piece wing, scale dihedral, ailerons with separate servos, etc), so I preserved the kit and based my design on the A.T. article. It was a very rewarding build!

I used an OS FS-48S but spaced the firewall for an FS-70S in case the 48 wasn't enough. The FS-48S with 12x6 prop and 12.5% fuel is plenty for my 6.39 lb model, in fact it's perfect! Majestic! Most flying is at half throttle but at full throttle it climbs rapidly and can pull through a large loop (but prettier loops at 2/3 throttle after a shallow dive). Great fun to sideslip down to a greased landing. Rolls are very slow and sloppy - this definitely is not a 3D plane.

I redesigned the ribs but I kept the tapered captured spars, and they were a pain. I used standard servos for rudder & elevator and HS-81 HobbyKing equivalents for throttle and ailerons. 50mHz Sombra Labs rcvr and 4x2000MAH Eneloop NiMH battery. RST-8 tank. Silver HobbyKing covering with Monocote flat black trim (sure wish HK had flat black). My 3/16" landing gear is adequate but none too stiff for grass fields. Barbie now flies it from rear cockpit, but I still need to add dummy engine exhaust.

Toughest part was wing fillets. I glued 1/32" ply fillet base to saddle, filled in with foam, shaped, and epoxied a couple layers of glass cloth.

Enjoy the build and have great fun flying it!

- Dave Plumpe
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Last edited by DPlumpe; May 02, 2014 at 10:40 AM.
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Old May 04, 2014, 04:49 AM
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Joined Mar 2014
4 Posts
I have a top flite gold edition .60 corsair plan.Is it possible to make it a balsa profile rc plane glow powered (scratchbuild)?
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