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Speed,Combat,Scale,Racing => Carrier => Topic started by: david smith on April 02, 2014, 05:57:27 AM
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I know there is a way to use a bladder but I don't know how. I would like to use a pressure bladder on a Carrier plane but I don't know how to keep it from flooding on the low end. I have tried to lean the low speed needle but I can never make up the difference. I know it has been done before but I can't seem to find anything about it on the internet. Anybody have an idea?
David
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Dick Perry wrote about various pressure systems in an early MA Navy Carrier column. I found it in the MA archives by searching for "pen bladder". Unfortunately, the year is not shown on the page margin.
Basically he used a Super Tigre MAG carb and was able to adjust the fuel meter to work.
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Only way I can think of is the metering system like we used on the McCoy's & Rossi's on crank case pressure. The way they worked was they would cut the flow of fuel to the engine as you went into low speed. Worked great once set up. I think Bill Johnson down St Louis war developed it.
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Bill's system was designed to work with a wide open venturi. It used a custom made metering device fabricated from various sizes of brass tubing. The metering notch was the critical element.
Later carbs like the Kavan, S-T MAG, and Perry could do the job when adjusted right.
I copied the pages from MA but am having difficulty getting the file size small enough to post.
Update: I searched a different way. The article was in the APR 1976 issue. AMA members can log into the MA archives.
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Perhaps you could use an in-flight mixture control between the bladder and the carb to help limit the fuel getting to the carb at lower power settings. I don't know if this has ever been done, or how well it would work. It would function like the mechanical fuel meter of old, or at least I think it would. You would need to experiment with the various needle settings, and probably the amount that the in-flight mixture control actually moves (control arm length).
Conley Precision (the Perry carb people) makes an in-flight mixture control, # VP-IMC-05. Might be worth a try...
Bill Bischoff
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Chuck Herron had a system by which the model had both a bladder and a small carb connected to an open-vented hard tank. At the conclusion of the high speed the bladder fuel was dumped and the big venturi shut down. The model proceeded to fly low speed on the smaller suction carb.
Chuck was a great builder and machinist. I saw his stuff and marveled at the workmanship. Still, it has been said that the setup wasn't too reliable.
Art Adamisn has crankcase pressure system with a relief valve the dumped pressure at low speed. I guess he just couldn't open the throttle all the way once pressure was dumped.
Maybe this is good reason Profile is more popular.
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I've used hard tank pressure with a crankcase tap and the OS 4e carb. it worked fine. I am sure othe carbs would work. Never tried a bladder, but it seems to me that they would also work that way. Try the RC pylon guys to on RC Groups
John
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I used a bladder on my Webra Speed .61RR. Idle was fine. I was using a Wallick carb, which is just a large-bore aluminum Perry carb. So a Perry carb should work although you might have to modify the idle disc to have a narrower slit to deal with the higher pressure.
Pete
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If you are going to use a Perry carb they can be ordered in a pressure mode. That way the disc already has a very fine LS slit. If this is going to be used on a carrier plane wont the bladder have to be awfully BIG? I wonder how big Pete's is with that .61? Eric
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Fuel volume is a problem. When I used the bladder, the airplane was built in 1975 (old rules) and had developed a fuel-foaming problem. The bladder solved this. But in those days, low speeds, even later in the '70's, were not all that slow, so I got away with the limited fuel supply then. I can't imagine getting the 10+ ounces of fuel required into a bladder these days.
Pete
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Thanks for the input everyone. Eric it is for a carrier plane but it is for a nostalgia Class 1 so Im guessing I only need 3 oz or so.
Pete, I have some Perry carbs to play with so I will try some on a test stand.
David