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Building Tips and technical articles. => 1/2 A building. => Topic started by: Gary Schrader on September 27, 2013, 07:25:52 PM
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Hi all.
Here are some pics of my almost completed 1/2a P-40 semi scale stunter, own design for Cox reed valve .049. Inspired by Aeromodellers "Kittywasp, which I have wanted to build since i was 12 years old. This is larger but has no flaps. Span 30" with approx. 165 sq." area. Airfoil from Pat Johnson P-40 but no leading edge wing taper. Weight is 8.2 oz. with no fuel tank of color as shown. Need some advice from Design Man: Set up advice for this combo using standard early white plastic backplate with wire circlip reed retainer. What cylinder and glowhead (bee or TD)? as i Have all types of cylinders and cox type glo heads available. Will this 3 bladed prop be any good? Fuel tank size? How much nitro and lastly line length recomendation. I am at sea level. Many questions I know......
Thanks in advance.
Cheers Gary
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I hear and respond! Wow, what a nifty plane design and build!
The weight and wing area ratio is excellent! You can go with whatever cylinder you want and adjust line length to suit.
The venturi diameter is the real key to performance v/s fuel draw on the reedies. Put on the hottest cylinder and high compression head (extra gaskets may be needed) and start with the 5x3 "rubber duckie" black Cox prop on 40' Spectra lines (lightest available, round, not flat braid).
Handle line spacing about equal to the bellcrank spacing
15% Nitro should be fine, but at least 50% Castor in the fuel. 15/10/10 is a really good fuel for steady performance and long engine life. The Synthetic will keep the engine free of varnish, too!
You are on your own in tuning the mode for even better performance. If the engine is really solid, try the 3 blade prop. Adjust line lenqth to reach a balance of reliable control vs lap time. Nobody can give you the absolute optimum combination but yourself.
My goal is to give you a safe starting combination. But even with that approach the first flights with all due caution.
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I routinely set up this type of reed valve to run on bladder pressure. You get the dual benefit of being able to drill out the Venturi for maximum performance and still get consistent fuel draw. I am not able to get any significant performance gain with the tee dee cylinder over the #1 black widow, but that's just my experience.
Jim
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That is a sweet plane! Very nice!
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I routinely set up this type of reed valve to run on bladder pressure. You get the dual benefit of being able to drill out the Venturi for maximum performance and still get consistent fuel draw. I am not able to get any significant performance gain with the tee dee cylinder over the #1 black widow, but that's just my experience.
Jim
That white backplate could very possibly already have the 128tpi fine thread needle you need for bladder pressure. Some of the white ones came with that NV, as did the red postage stamp backplate from the black Stuka. That's a great looking plane, good work, Gary.
Rusty
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Thats a nice looking model that I think is about the right size...are you using a separate fuel tank to give enough flight time ??
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Jim, he's using one of the "product engines" that came in the Cox RTF models. They have a plastic backplate/reed retainer, but no tank.