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Building Tips and technical articles. => 1/2 A building. => Topic started by: Paul Smith on September 19, 2010, 06:43:11 PM
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I have a few in hand, but it looks like they've ALL been bored out for more boost.
I'm sure somebody recalls the original stock suction size.
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The stock size is .117" I.D.
Cheers, Paul
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Thanks, I'm trying to get at least one of my TeeDees to run on suction for a new scale project.
I'm looking at crankcase pressure as a fallback.
Bladder or pacifier is the ultimate fallback, by the pod wouldn't look so good on this plane.
Last night I designed and built a new TeeDee test stand and epoxied a venturi shut. Now, with this dimension in hand, I can redrill it.
At the same time, I made up a pressure back plate.
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I recall reading that all the TDs really wanted to run on pressure.
Not that I ever had the $$ for one when I was growing up.
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Could be true.
That's why I'm starting at .105", not the standard .117", to give it a fighting chance to draw fuel, and preparing the pressure fitting as a fallback.
They were only $7.95 back in my day, only a $2 bump from a Black Widow. You find a few now and again if you watch estate sales and club auctions, as in "here's $100, I'll take the whole box off your hands."
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I have a DO335 that started on suction. Couldn't get two TD's to run off of one tank. Never did try pressure. I converted it to two balloon tanks and it runs great. Ps it has a sure start piston and cylinder. Also the back TD has a LH crank. Picture is original tank setup that didn't work.
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I have never run a Tee Dee .049 on pressure. They are screamers on suction and 6X3 props.
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I'm assuming when were saying pressure , were talking about crankcase pressure. I had absolutely no luck whatsoever trying crankcase pressure. As soon as the plane was released from my hand it would quit. The only fix to that was using the stock size venturi. When I drilled them out they just wouldn't work. The other problem was extreme rpm differences which more or less resulted in sagging and overheating. I spent months trying to make this work. I finally gave up and went back to suction. I found that installing a uniflow pipe into the tank worked. I tried crankcase pressure from a backplate and also the carb body and neither worked successfully. I tried the one way valve which more or less resulted in extremely flooding the engine if you didn't get it started immediately. I would like to see this work as I have some small speed planes which I feel would benefit from this setup. Let us know what works Paul. Ken
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We'll see tomorrow, the epoxy is still drying on the new TeeDee test stand.
I got a new high RPM 1/2A starter, so I hope to run a lot of tests without wrecking my hand. I set up a backplate with a pressure fitting with a tiny pin hole. I know I need to keep the fuel line pinched (like a bladder) until the engine kicks in. I have years of experience with crankcase pressure, but it still doesn't always work. These little engines, especially the Cox brand have a lot of little secrets.
A bladder is the ultimate fall back, but I'd rather not have the pod on my plane.
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I got a new high RPM 1/2A starter, so I hope to run a lot of tests without wrecking my hand.
Does the TD feature a steel washer or other measure to prevent the crankcase from getting chewed up by the prop driver when you use a starter? The reedies were famous for getting rapidly trashed if you used a starter, unless you had a steel washer or a brass prop drive washer.
Here are some forensic pictures, to give you an idea. The one that I used with a starter is 8 mils shorter, and the end of the crank case is dished in. The prop drive washer (not shown) that came with the engine is similarly munged up, only it's dished out.
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Tee Dee .049s are more trouble than they're worth. I'll take a Medallion .049 at a 4k RPM loss any day.
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You poor guys. I find that Cox 1/2A's are some of the easiest to start. To me the Tee Dee's are the easiest to run/start. Like any engine you have to learn their idiosyncrocies. H^^
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Unless you are required to run .049, switch to the AP Wasp with Holuszko venturi (search, baby, search! lots of info in this forum). Perfect runs with balloon (floppy, NOT pressure, do a search for details) or better yet a uniflo tank. Same weight, more power, no hassles.
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I ran a few TeeDees today.
The .105" suction venturi worked fine. Only about a 500-to-800 RPM loss vs wide open and crankcase pressure. I'm set up for suction with the pressure tap plugged so I can upgrade if I need the revs. It's only scale. The new test stand worked great for cycling several units through in good time.
Surprisingly, my Black Widow squadron was a lot more healthy, a good omen for the logger.
I'll pass on the new wave engines. This is about utilizing what I've got.
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Wherer's the NV and spray ring??
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They were removed for downsizing.
It went OK.
Sprinklet holes plugged with ChapStick coated pins.
Filled with JB.
Drilled out to .107" (.010" undersize).
It ran very smoothly like this, and still plenty of power for scale.