still spinning my wheels..

Literally and figuratively. I actually tried to bench-run an engine today in my workshop. It was an experiment that I could have prepared better for.. but I didn't want to tear down a Babe Bee. I had one RTR with a needed hex drive-plate for my "flywheel encased cam-style starter-spring" test . The back-plate screen already removed for testing the Ace venturi throttle with the flywheel.  This arrangement is being tested for a marine application running a 1" surface-prop.  

I mounted the starter-spring and cam then fitted the hollowed-out PVC custom-made flywheel using a 5-40 stud/spinner-hub and custom 3/4" x .080" thick aluminum washer-plate. Mounted the engine on a custom PVC fixture having a guide for the venturi-plunger/needle (Ace design.. the same one used in my throttle vid). Dug out a "Sandblaster" heat-sink (Cox P/N 1970) and tighten it on.

This Bee like a few others I have, has been fitted with an external fuel pick-up. I have used the little 1oz. Sullivan clunk-tanks with success on the bench.. but today I opted for one the small tin speed tanks that I built.






As usual.. I'm thinking way outside the box..   I fuel-up through the uniflow-vent with the needle open until fuel flowed through the line to the engine. Good.. maybe it will start without an exhaust prime? I connect my Cox glow-clip coming from the glow-driver in my power-panel. I proceed to wind-back the flywheel and release.. repeat.. repeat.. Nope.. exhaust-prime needed. Fires off the prime.. Good! Several repeats of this process until she started to draw fuel.. but wouldn't run long enough to get a decent needle-setting. Starting was hard.. and I found that the only way to get fuel out of the tank was to choke the venturi with the "Ace" needle.. which did work.. but I'd only get "pops" because of the lack of air.

One thing that concerned me was over-revving the engine... so most of the cranking was done with a very rich needle.. and the Ace plunger inserted into the guide. The tank is suspect.. because it hasn't seen much testing. I didn't want to use a lot of fuel if I didn't have to.. being indoors. Just a "thimble's worth" basically. I tried uni-flow-only vent.. then opened-up the fill-vent which seemed to improve starting.. but not draw. I also didn't have much time before my wife got home..  

I did confirm that the custom flywheel; wound-back using fingers-thumb isn't a great method for starting the engine.. (not a cold one anyway) It also requires mounting the engine a little higher in the hull for clearance.. as compared to a Dumas flywheel.

My intention was to avoid needing a belt to start the engine.. and possibly achieve a higher throttled rpm than I might when using the heavy Dumas-style flywheel which is designed for w.o.t. operation.    

I made smaller PVC flywheels that fit back-over the round drive-plate, that could be used with a friction-wheel electric-starter.



These may need to be weighted for inertia.. but I may have that covered in the way of the alum. fender-washers that I made.

The Dumas boat kits designed for the Cox .049 recommend their 1" plastic "submerged-style" prop, flywheel and running hardware.



Some parts not shown here..



I did a search for 1" dia. "surface-drive" props.. and came up with replacement props and drive for the Aqua-craft "Reef-Racer" boat which is sold by Tower Hobbies. It's a 15"L. x 5.3" beam model.



The prop is a 1"D x 1.58"P nylon with drive-dog threaded for a 3mm solid-steel shaft.

Set of two replacement props.. $5.00



Shaft and stuffing-tube.. $10.00



I looked at a variety of couplers.. and should be able to make a surface drive for my rigger.. without needing to build a strut for the transom. I have a couple of Graupner rudders that should mount over the shaft exit-point.. and extend far enough back to clear the prop. If not I can make an extension-block.

This is that rudder. I like the design in that it will pivot "up" if it strikes an object floating in the water.. and also can be "tamed" as far as the authority in which it applies it's force in turning.



This boat (Dumas "Short Stuff") flipped on it's maiden with the rudder in the position shown. Tilting it back on subsequent tests prevented this. By tilting-back to around 45 degrees.. I could carve deep turns at full-throttle without flipping it. There will be a different turning dynamic with an out-rigger as compared to a Vee-hull though.

It's going to take more time than I put in today to get the engine running "out of the water"... but it's a start.