Cox Venom Piston Rod Reset Question

It may be that removing the tank-extender moved the engine back enough to cause your balance-issue.. especially on a short nose.

One thing you can try is obtaining a heavy hub-nut and use a stub-screw..



A weight comparison to a std. hub-nut..





It might be enough to tip the scale. You could also cut a pair of (.010") brass-sheet squares.. and attach/glue them to the front/tops of the pontoons. How about sourcing a pair of cast "model-ship cleats".. which would look kinda cool.

BTW.. I LOVE the model! To me; float-planes are the epitome of cool. Just something you don't see modelled "to fly" all that often. I presume that you're hand-launching? I don't think that the Venom has the testicular-fortitude to pull it off the water. Is there any way to incorporate beam-mounting rails through the firewall; that would be below and "clear" the Bee engine? Maybe tying-into the closest bulkhead? This would give you the option of running your Tee Dee's or Norvel by using aluminum bridge-plates for the correct spacing and thrust-line. It would also add somewhat-functional nose-weight to your current construction. You still have the finish-weight to consider too.

Landing on the water alone would be fun! I'm assuming that you have a pond nearby.. or near your flying-field. I'd love that! Model boats and amphibious model airplanes!

Assuming that the model will have a water-landing.. it would be good to have a recovery-craft to get it back to shore when the engine quits. A throttled engine would be cool for taxiing back to shore.. and you have a few options there.

Hi Scot, Not a bad 1st flight at all! I've done some bench-tests with that throttle-design (orig. Ace). It's nice to see you try it in flight. Ace recommends using a muffler to keep the top-end "hot" at low-idle. I wouldn't recommend a conventional muffler though.. because it will rob some power. It's a moot-point anyway.. seeing that you're planning a different engine/throttle configuration.

If you ever build a smaller model.. try using that throttle again. I achieved very good throttle response with mine and a much lower idle when using a minimally-restrictive homemade muffler, 6 x 3 prop and 25% Sig fuel. I have found that the engine's needle is best set for optimal rpm with the plunger fully-retracted from the backplate/venturi.

Here's a rather "candid" video I made several years ago..



You'll notice that the glow-driver is "on" throughout the run. I should have turned the driver off.. but neglected to. I have however, achieved similar results with it disconnected. I ran a small 1oz. Sullivan external tank with the feedline plumbed through a hole drilled in the Babe Bee's fuel tank. There are other ways to hold heat in the top-end for a more reliable low-idle.. than using a muffler. A "cowled-in" engine will run hotter.. and some modelers wrap a few turns of string/yarn around the upper cooling-fins when running in freezing weather. Just some things to think about/experiment with.

rscarawa wrote:Roddie
I saw your video about a month back and that is part of the reason I chose to test this configuration.

I agree that the motor needs to be kept hot but I think this design can be improved in the following ways.  First, the needle needs to be larger diameter.  The diameter of the BW motors venture is such that so much air still enters the motor with the needle in fully.  I am not sure why they made the needle so small but it could be so that it would work with other Bee motors with smaller venture systems.  If they can create a needle that closes the .07" venture, then I could get the motor to slow down much.  Still have a rich problem though.  How to fix that?  I think one might could fix this by utilizing SPI as a sort of air bleed system.  The slower a motor turns with SPI, the more air it should ingest in theory.  So start with a cylinder with SPI and close it off with cylinder shims.  As you want more leanness on the low end, remove the smaller shims to bleed a little air in.  Not saying this is perfect, but I think it would be an improvement over my current config.  But like you said, it is moot for the mean time as I need weight up front anyway.

thank you for your input.

Scot

Yes.. the BW venturi is approx. .082" as compared to .063" for the Babe Bee/Golden Bee that the Ace/Cooney throttle was actually designed for. The fuel-jet in the integral-tanked engine's backplate is directly inside and above the air-intake.. so with the "Bee's" smaller (.063") opening, there's close-to a 1:1 metering-ratio that can't be achieved with the .082" opening, using this throttle. With the smaller opening, you can actually set and use your throttle-servo "trim" to stop the engine by advancing the plunger into the backplate past the taper.

One of my Golden Bee's actually has the larger .082" venturi.. so I tried grinding a taper on the end of some .078" music-wire to test. It wasn't much of a test, because I hastily threw an engine together.. and the taper that I ground on the throttle-needle was crude. Also; the .078" (5/64") music-wire that I used is .004" smaller than the .082" opening. The design-clearance for the original plunger is .0005"/.001" which will fully-choke the air-intake when fully inserted past the taper. It deserves more testing.. because I believe it can be made to work just as well as the smaller-diameter set-up.

Play with it some more on a rainy-day.. Try swapping the backplate on your BW with a Babe Bee's for a bench-run. Power will be down some.. but I think you'll like the throttle-transition and lower idle-speeds a LOT more than what you've experienced with this throttle thus far.

Take into consideration that; when this throttle-concept was originally conceived/designed.. RC flight-systems were HEAVY. Adding a throttle-servo's weight in addition to the "then available" receiver battery-packs.. loaded into a 1/2A size model, wasn't a recipe for performance. Fast-forward to today.. and there's terrific nano-servos and receiver-batteries that weigh "ounces" less. The power-to-weight ratio of our little Cox glow-engines still rivals the comparable-size brushless-electric motors of today.. except; you get the added realism of having a "real" combustion-engine powering your airplane.