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Ace throttle experiment for Cox Babe Bee Empty Ace throttle experiment for Cox Babe Bee

Post  roddie Thu Oct 05, 2017 6:46 pm

For some time now.. (decades actually..) I've been eager to try the Ace venturi-throttle designed for the Babe Bee engine while using a larger than standard-diameter propeller. I’ve experienced decent performance running 6" diameter props of varying pitches while using the Ace throttle on the Cox Babe Bee.

Years ago.. I built a self-designed 1/2A C/L biplane powered by a Babe Bee engine. One day, I decided to try bushing the hub of an 8 x 3 “Zinger” wood-prop to see if the engine would “swing-it”. It did.. albeit with a narrow margin of a needle-setting to obtain a two-stroke operation. The exhaust-note/sound was like “scale-music”.. that you’d have to hear to believe. I’d always launched my 1/2A C/L models “R.O.G.” via a pin-stooge.. and this biplane model had no problem getting airborne (off a grass field..) for “roundy-rounds” with the 8" prop.. although I never attempted any aerobatics.

This experiment is to see if and how the Babe Bee engine will respond to the Ace venturi throttle for possible-use in very lightweight 1/2A RC scale-models of the golden-age. Triplanes, Biplanes.. and early monoplane designs.. that lumbered-around the sky’s in the early 1900’s. Not the “speed-demons” of later years.

RC flight can be less demanding on a model-engine than C/L flight is. Untethered; the model is free to “float” where it wants.. unhampered.

For this reason.. I think it’s worth an experiment to see just how viable a Cox .049 Babe engine might be, for “true” 1/2A-scale applications. I already know that a healthy engine will run in a two-stroke mode with a 1”:1’ scale propeller. If it can be throttled-down and possibly “idle”… it would be the ultimate in scale-realism.
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Post  roddie Sat Oct 07, 2017 2:29 pm

With some modeling-motivation watching Rusty's latest "Stunt Hangar" video-hangout show; I managed to put together a set-up for attempting to throttle a Babe Bee using the Ace/Cooney venturi-throttle.. with a larger than standard propeller.

I had three old Babe Bee's to choose from; all of which were modified for an external fuel-feed. I picked one that seemed to have better compression than the other two.. and pulled its tank to check the reed, and replace the venturi-gasket.

The reed is the copper 4-pointed star type.. which I prefer to use on the older Tanked Bee's.. so I checked its function by blowing and sucking on the front of the reed-housing with my mouth.. to find the valve to be functioning properly.  Smile  

The needle was a candidate for sealing with some fuel-tubing.. (there was notable "play" in the threads) so I did that, omitting its spring. As I recollect; running the planned 8" prop years ago, resulted in a narrow needle adjustment-window to achieve firing on every stroke.. so I figured that a reliable seal would definitely be in order for tuning within this power-band.

Ace throttle experiment for Cox Babe Bee Dsc04915

You'll notice that the tank-bowl has a hole drilled for the installation of a rubber-grommet. This helps to both; anchor and protect the fuel-line from pulling-off the nipple inside.. and from abrading on the tank-bowl due to vibration. A snug-fit of the line through the grommet is in order here. When reassembling the tank and back-plate; the fuel-line is "tugged-through" the rubber grommet until the slack is taken-up.. and the fuel-line takes a smooth 90 degree turn out through the side of the tank-bowl. I've had good success with this method.. and have applied it to several Babe Bee engines over the years, to increase their run-time on the bench for experiments.. just like this one.

Recapping the Ace/Cooney design; its needle/plunger (.062" music-wire)  moves in and out of the engine's air-intake by removing the small mesh-screen from the Bee engine's backplate. The Cox Bee engine is unique; in that its "fuel-jet" is located just inside the air-intake-tube, unlike a conventional "spray-bar". Because of this; the throttle's tapered-plunger actually meters both the "fuel and air" when it enters the venturi.. (albeit crudely..) rather than "choking-off only the air.

The radial engine-mount (firewall) is drilled-out for the "plunger" to pass through. This guide-hole for the plunger is exactly on-center with both; the engine's case-screws and mounting-lugs.. so it's as easy as drawing an "X" through the engine mounting-holes on the firewall, to accurately locate the guide-hole. This can then be drilled-through with a 1/16" drill-bit.

My Bee engine mounts for this throttle-design are made of PVC using a CAD program.. but that was just a matter of convenience. I made a lot of parts that way when I had access to a CNC router machine. A firewall-mount with guide-hole can easily be made with hand-tools.

Here's my set-up..

Ace throttle experiment for Cox Babe Bee Dsc04916

An RC servo would normally actuate the throttle.. but this experiment is to see whether the engine will swing this propeller "initially" with a wide-open throttle. If it does.. then the throttle will be closed to see if the engine can be idled-down.. and remain running.

I tied a string to the throttle-needle so I don't lose it.. in case it inadvertently falls-out of the guide during the tests.

The prop is a wooden "Zinger" 8 x 4 with bushed-hub to fit the Bee's 5-40 prop-screw. I couldn't find my 8 x 3... so the bigger pitch might be too much for the engine.

The engine cylinder is a slit-exhaust type typical of the later product-engines (dual-bypass). The glow-plug is a standard one.. and fuel will be Sig "Champion 25".

Stay tuned.........
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Post  roddie Sat Oct 07, 2017 6:13 pm

Well... I have a vid for ya'll... but it's not the quality that you're used to here.. Laughing Actually; it's pretty bad.. but I did prove that the Babe Bee will run with an 8 x 4 prop.. and can be throttled-down using the Ace/Cooney style venturi-throttle.

https://www.youtube.com/watch?v=yytMAFLLxcs



Low-idle requires a glow-driver assist. I had taken some tach-readings before my wife shot the vid. The useful throttling-range was approx. between 2K-6.5K. 2K operation was fairly consistent. The lowest tach-reading was 1.6K before the engine started "loading-up".

The muffler is one of my homemade designs.. and was equipped with dual pipes drilled-out for maximum-flow. A muffler-pressure line can be seen hanging below.. but was not used.

I have a Zinger 8 x 3 woody somewhere.. but couldn't find it. I did run a Rev-Up 7 x 2.8 which developed much higher revs.. and good low-idle #'s... but still required juice to the plug to sustain.

The Ace instructions recommend using a muffler to keep the plug-lit (head hot) at low idle speeds. My muffler didn't really handle this task; having full-flow pipes installed. I hope to be able to get consistent low-idle speeds without a glow-driver assist.

I only tested the one standard Cox glow-head using one gasket.. and my fuel is pretty old.


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Post  fit90 Sat Oct 07, 2017 8:24 pm

Outstanding!! That is so cool to see a babe bee idling at such a low speed! A couple of things you might want to try are a merlin/insert type plug in the "hot" heat range and lots of head gaskets. I hope you are able to fly that on an R/C model some day.
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Post  roddie Sun Oct 08, 2017 12:54 am

fit90 wrote:Outstanding!! That is so cool to see a babe bee idling at such a low speed! A couple of things you might want to try are a merlin/insert type plug in the "hot" heat range and lots of head gaskets. I hope you are able to fly that on an R/C model some day.

Thanks Bob, I'll have to try that. It would be great to achieve low idle-speeds without needing the glow-driver on.
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Post  getback Sun Oct 08, 2017 9:37 am

Cool stuff !! Thats a big prop for that little bee but doesn't seem to have a problem with it for what it is , as Bob said a hott drop in may give some better results (without the glow driver ) maybe try a idle bar plug ? Keep us updated This Site Rocks! Thumbs Up
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Post  roddie Sun Oct 08, 2017 12:29 pm

getback wrote:Cool stuff !! Thats a big prop for that little bee but doesn't seem to have a problem with it for what it is , as Bob said a hott drop in may give some better results (without the glow driver ) maybe try a idle bar plug ? Keep us updated This Site Rocks! Thumbs Up

Thanks Eric. It is kinda' cool messing-around with this throttle. I neglected to check this cylinder for SPI.. and it's hard to tell with the slit-exhaust port-style as opposed to the open-type. I'm falling-short on providing complete data. Rolling Eyes

I wanted to conduct some more tests today.. but the weather has turned wet and windy. One of the tests I want to conduct is running a flywheel mounted with the propeller. I made a bunch of various types of flywheels on the CNC router years ago.

Ace throttle experiment for Cox Babe Bee Dsc04917

The pieces were all cut with a 1/8" endmill. The hub-holes are exactly on-center. They're programmed as "drill-points".. and being 1/8" diameter; they fit the Cox's 5-40 prop-screw perfectly.. which helps with balancing. Materials are PVC, aluminum and acrylic. Some were also designed for possible marine use. Lots of different combinations of weights to try.

Ace throttle experiment for Cox Babe Bee Dsc04918
Ace throttle experiment for Cox Babe Bee Dsc04919
Ace throttle experiment for Cox Babe Bee Dsc04920
Ace throttle experiment for Cox Babe Bee Dsc04921

I may be wasting my time in the application of "flyweight" on the crankshaft to correct the low-speed loss of ignition without a glow-driver assist. I may end-up trying the running of a flywheel alone.. without the "cooling-action" of an aero-propeller. Maybe a "reduction in compression" is the key? I'd rather not retain "excess-heat" in the upper-cylinder during high-rpm operation.. if that can be avoided.

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