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Very Hot Topic (More than 25 Replies) Pratt & Whitney "Wasp" R-1340 (Read 3694 times)
Craig 3
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Re: Pratt & Whitney "Wasp" R-1340
Reply #11 - Apr 9th, 2018 at 5:03pm
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Okay, that didnít take long. In a spirit of levity, I actually cut new inner discs out of the bottom of the box a Guillows 402 Mustang kit came in. They were easy to keep round, the hole left by the Olfa cutter didnít hog out like it did in the balsa, and consequently they lined up nicely on my high-tech jig. As a bonus, the fin count came up perfect. Looks like Iím making eight more...
« Last Edit: Apr 9th, 2018 at 7:10pm by Craig 3 »  

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Re: Pratt & Whitney "Wasp" R-1340
Reply #10 - Apr 9th, 2018 at 5:02pm
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I save my cereal boxes for the cardboard.  It's probably thinner than a Guillows kit box.  But I use them to make flexible straight edges.  I can use a Sharpie ultra thin point marker to mark panel line breaks etc which makes putting panel lines on a model much easier.  A bit of masking tape to hold in place and I get a nice sharp line. Using the masking tape for the stopping point gives a nice clean stop without running past a line also.
Tom
  

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Craig 3
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Re: Pratt & Whitney "Wasp" R-1340
Reply #9 - Apr 9th, 2018 at 4:02pm
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But, speaking od cardboard, before I jump into prototyping a cylinder head, I'm going to try something and see if I can turn out a lower cylinder I like better than these. I cut a surfeit of manila discs, so it should be a quick job. I'm shooting for 11 fins in a 5/16" stack. Changing the cylinders out at this point would be easy.
  
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Craig 3
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Re: Pratt & Whitney "Wasp" R-1340
Reply #8 - Apr 9th, 2018 at 3:58pm
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Tom, you're right- I should have been more specific and said "Guillows box thickness," We all know the cardboard in a Guillows box is heavier than the equivalent cardboard in say, a Diels box Smiley Smiley Smiley
  
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Re: Pratt & Whitney "Wasp" R-1340
Reply #7 - Apr 9th, 2018 at 11:49am
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I know it's bad to assume anything, but I'm assuming the "Guillows box" reference is for the cardboard material of the "Guillows box" rather than a special Guillow's tool!† †Grin Wink

I know some have used Brass tubes of the proper internal diameter to use as a punch by sharpening the opening with a round jewelers file to get a very sharp edge.  I've done this often for various lightening tools for wing ribs etc.  I cut several with the tube before using a dowel to punch out the discs from the tube.  resharpen as needed and punch more.  The brass works well.

I've noticed that some of the fellows on HPA are starting to use a craft cutter machine to cut out those discs and wing ribs, as well as various fuselage formers.† Click Here
  

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Craig 3
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Re: Pratt & Whitney "Wasp" R-1340
Reply #6 - Apr 9th, 2018 at 8:56am
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Mike, I got pretty good at cutting circles out of the manila and ovals out if the balsa with the circle cutter- that tool takes some finesse, for sure, but my experience with punches and dies was similar to yours. On the next one, Iíll use something like a Guillows box for the inner discs- my calculations say I should have eleven fins at this height and I have only eight, but I still think itíll look better than spiral-wound thread. Live and learn! Oh, and perfection is the mortal enemy of ďgood enoughĒ
  
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Re: Pratt & Whitney "Wasp" R-1340
Reply #5 - Apr 9th, 2018 at 6:49am
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Thank you for paving the way here and a great job on your creation. I started on the same road as you for the engine for my Marcoux Bromberg (and a couple of other race planes with P&W engines) and tried the manila folder (and bond paper) cylinder method but could not keep them flat and my experience with the circle cutter was rather a mess. I did however paint the manila pieces with thin white glue and clamped between two boards and waxed paper and that worked pretty well, it even thinned them down a bit. Bought a Harbor Freight punch and die set to make the fins but the fit between the punch and die was so bad the tool is now a door stop on a windy day. I'll be following right behind you soon.
Mike
« Last Edit: Apr 9th, 2018 at 8:20am by New Builder »  

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Craig 3
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Re: Pratt & Whitney "Wasp" R-1340
Reply #4 - Apr 9th, 2018 at 6:38am
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Some progress- but I imagine I'll be lucky to crank out one upper cylinder a day.
  

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Craig 3
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Re: Pratt & Whitney "Wasp" R-1340
Reply #3 - Apr 8th, 2018 at 9:22pm
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Figured I'd split the cylinders into upper & lower sections to see how this idea would work- since the lower section has a straight profile and the upper section gets complicated rather quickly. Alternating discs of 1/32" balsa and manila folder, over a base made of a1/32" flange and a 1/16" disc before the fins start. Not perfect, but I think it will work OK.
  

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Craig 3
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Re: Pratt & Whitney "Wasp" R-1340
Reply #2 - Apr 8th, 2018 at 6:48pm
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Thanks, Tom- I'll probably fake the fasteners with whatever I can whip up- it's almost a 4 hour round trip to the "Local" hobby shop Smiley

Got a bit more done- meaning the pushrod tube bosses, made of 3/16" brass tubing to accept 1/16" aluminum pushrod tubes. From the period photos I can find of this ac, the front crankcase was probably painted gray, with the remainder of the crankcase bare aluminum (like the illustrated engine). Also, it looks like the ignition harness was in the back, again like this one.

Now for the fun part- trying to make cylinders with fins that look like fins instead of thread trying in vain to simulate fins. I can see a lot of time with the Olfa cutter and some card stock in my future...
  

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Re: Pratt & Whitney "Wasp" R-1340
Reply #1 - Apr 8th, 2018 at 5:40pm
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Very nice Craig.... thanks for sharing this build with us.  If you have a Model Rail Road shop in your area I'd recommend a visit.  They usually have all kinds of miniature fittings and bolt and screw heads that might fit your needs.  Sometimes a strategically sanded (hex or octagonal sides) balsa dowel rounded from 1/16" sq or small strips might work for you.  Check our JohnO's tutorials for some ideas.
Tom
  

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Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Craig 3
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Pratt & Whitney "Wasp" R-1340
Apr 8th, 2018 at 11:27am
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In the queue, there are two aircraft which seem, because of the complexity & scale accuracy of the plans, are destined to be static builds. One is the Cleveland plan for "Mr Mulligan," the Howard DGA-6 of racing fame, and one is the Megow's plan for the Stinson Reliant SR7-A, another really complex build. Both ar in 3/4" (1/16) scale.

While the Howard was powered by a P&W Wasp of 850 horsepower, with the Stinson being propelled by a Lycoming† R-680-4 of 225 hp, they were both 9-cylinder radials and quite similar, save for size, in construction and appearance.

I'm going to start cutting balsa for one of them pretty soon. Well, I flipped a coin and technically I guess I have. I like starting with the engine anyway.

While the Wasp I did for the F4B was ok for for a "flier," it was at best stand-off scale, and fortunately for me had a shroud over the crankcase. Not so on the Howard- so I'm going to have to step it up. I got this much done in the wee hours, and a couple hours this morning. I gotta go find some teeny bolts now.
  

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