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Speed,Combat,Scale,Racing => Carrier => Topic started by: Jim Oliver on October 26, 2010, 08:15:21 PM
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About 25 years ago, someone modified CL engines to provide speed control by using a slide valve in the exhaust stack.
Anybody remember that? It may have been Bob Smurthwaite (spelling). I never had an engine modified like that, but saw some that were------seemed to work well, and lighter than an RC throttle. Just wondering why it is no longer used.......
Thanks,
Jim
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I dont believe it was Smurthwait. It was Bill Johnson, I am sure. What say you Heywood or Sawicki?
Wayne
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Could be.
Just wondering if the set up would be worth trying. Any known problems with it?
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I remember it being Bill Johnson.
The primary problem was the relatively close tolerance fit required on the exhaust slider to control the gas flow through the engine.
Some were used in conjunction with a fuel metering block to control the mixture with a fixed venturi. These were usually crankcase pressure setups.
Others were used with carburetor.
In both cases the motion of the exhaust valve was connected to the other control device.
Harry Higley published a system that added a crankcase pressure bleed to the metering block and exhaust slide system.
Exhaust baffles can work wonders helping some engines idle. A K&B 5.8 responds wonderfully to an exhaust baffle. The old ST C35 would idle in the 2500 - 3000 RPM range on 50% nitro fuel with a baffle for 30 - 40 seconds at a time and would come right up (Mag-3 or Mag-4 carb) when the throttle was advanced.
Without a baffle you may need to run the engine rich to get the desired idle speed.
The idle speed really only needs to be low enough that the model won't stay in the air at idle. It doesn't need to be super slow unless you have an airplane that just floats.
Dave
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Harry Higley did a mag article on constructing and installing a sliding exhaust valve/fuel meter - probably in Model Airplane News when he was the R&R columnist. I did follow that article and put one in some engine and it worked reasonably well, but it wasn't really worth the hassle. The fuel meter was required for pressure systems and was the real work-intensive part of it - either a complicated machine shop special that required a lathe to fabricate or a unit built up from brass tubing that was not very adjustable or otherwise user friendly. The introduction of fuel-metering (adjustable idle mixture) carbs for RC made the whole system somewhat unnecessary.
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I didn't remember any fuel metering device associated with this particular slide valve; but it's been a long time. I do remember Bill's metering device, and pics of one made of brass tubing.
The gadget I was asking about was just a slot cut through the exhaust stack and a flat metal piece with a somewhat tear-drop shaped opening that was moved by an arm on the J. Roberts bellcrank. The position of the flat slide could be changed, fore and aft wise; the hole in the slide was sized and shaped to progressively close off the exhaust stack as the trigger at the J. Roberts handle was moved.
Clear as mud??
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Jim,
You are describing the slide I was talking about. I did a couple of engines with them. The one that had a nice, close tolerance fit worked well with the carburetor on the engine. The one with the poor fit didn't have the desired fit.
I think Dick Perry may have done an article on the exhaust slides.
You may want to check with Tom Wilk. He may have the articles on his Carrier CD.
Dave
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Actually, everybody has a bit of the truth on this one.
Bob Smurthwaite did sell an exhaust blade as the J. Roberts "Vari-Speed" Throttle Control. It is shown on the plans for Vern Clements' Brewster Buffalo published in the July, 1960 issue of Model Airplane News. It was as described, a thin blade with an elongated teardrop opening. There was no fuel control. It is also shown on the plans for the Consolidated Dark Shark and the J. Roberts Mauler (Copyright 1960).
Bill Johnson, out of St. Louis, did manufacture the more involved system that included the fuel meter. It was very popular in the late 1960's. The St. Louis gang had things working pretty good in those days. I have a never used ST G40 with the complete Johnson set-up. (I'm at work right now ~ 7:37 AM EST ~ but will post a pic this evening).
There were a lot of home made knock-offs. I did one for my McCoy -60- Sterling Guardian. As Dave indicated, the fit was critical and some form of fuel control was also necessary. When the big bore Kavan carb arrived things got a lot better.
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Exhaust Throttle 1975 FM May p59 Julian, Gerald
Tom Wilk
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I asked about his because, if it works, it seems like a light, simple way to control speed. Guess if it was so good, we wouldn't have R/C throttles......
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I asked about his because, if it works, it seems like a light, simple way to control speed. Guess if it was so good, we wouldn't have R/C throttles......
The exhaust slide worked reasonably well for engines in a mild state of tune. Racing engines, especially with pressure were a different animal altogether. It's just that the carbs of the day had pretty small chokes and the Carrier guys wanted the power of the wide open venturi. So, the slide was an acceptable compromise.
Beyond that, it wasn't a commercially robust solution. The slot in the exhaust didn't lend itself to cost effective mass production and the slide was pretty vunerable in a crash. Remember, the market was really for R/C.
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Super Tigre G40 modified by Bill Johnson.
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Ah yes, the nostalgia of all this. Glad to have lived thru it because no one would believe it today.
Wayne
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Wayne,
Did you get my PM?
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Wayne,
Did you get my PM?
I did but my reply got bounced.
Send e-mail to wburan@zoominternet.net
Thanks
Wayne
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The zoominternet.net addy didn't work for me........ ???
Jim
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Organizing the shop I have been finding stuff I had forgot about. In one box was the original McCoy Redhead .60 I got off of Byron Meriwether with a Bill Johnson Metering system. That was my most succesful engine with a Sterling Gaurdian. Wound up 14th at 64 Grand Prairie NATS. No landing as has happened at a lot of NATS competition for me. In the same box was another McCoy Redhead .60 with an earlier version of Bill Johnsons metering system. This engine used to be used by Williard Adams. Got that one for $5.00 at an RC swap meet. Both engines were easy to run and set. Then I managed to get a Rossi .60 with metering system. It was not very consistant. Last carrier plane had a HB .60 throttle control engine with a perry pump on the back. It was fairly consistant also. Just never flew carrier that much. H^^
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Vern Clements was a good friend of AL Culver of Pocatello, Idaho, at the time I lived there.
Ty, You weren't by chance at one of the Prototype plants during that time were you... H^^ I went through there in the late 80's but alas was not actively flying at the time... I think I spent too much time either at the site HB~> or in the bars LL~