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<u>Engine Synchronization
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</u></div>If you are using a Y cable for throttles it is common practice to adjust your high needle valves to match engine RPM. Although this is the easy method for matched RPM, it can also spoil a good engine by leaning it out too much. REMINDER: A rich mixture not only delivers more lubrication, but the castor and synthetic lube is also carrying away a significant amount heat from the engine as it blows out with the exhaust. This is the main process for <u>internal</u> cooling in 2 and 4 stroke engines.
Even though these engines are identical and were broken in the same way at the same time, there are still significant differences between them. Because the rear engine is behind a firewall and its prop is moving air away from the engine instead of blowing at it, most likely, the rear engine runs at a higher temperature. And because the rear prop is spinning in the wake of the front prop, the rear engine runs with less torque. And in my plane, the rear exhaust configuration is much different than the front which results in increased resistance in the rear exhaust flow. So, higher temps, less torque and restricted exhaust flow, all combine to create quite a different environment for the rear engine.
A better way to match RPM is to have each engine running on its own channel (throttle – front, AUX – rear). You could mix throttle to AUX and use the mix parameters to match RPM. This way you can have each engine’s high and low needle settings set perfect for that engine and still get pretty close to synchronized RPM.
Or… You can use TwinSync!
Although a plane with a pusher / puller setup does not need to be synchronized, there is some special programming that Bill Wike (the manufacturer of TwinSync) can add to the control chip that improves performance for planes with in-line engines. I personally like the sound of engines running in perfect sync. And using TwinSync will take a lot of hassle out of trying to match your engine’s RPM.
The special programming that Bill Wike can install allows each engine to run at it’s own pace at any throttle position above 90%.
I’ll explain the TwinSync setup I have programmed for my plane:
The throttle channel is connected to the TwinSync and controls both engines. I am also using the TwinSync Glow Driver setup. This circuit connects in tandem with the TwinSync. It is programmed to switch on with an AUX channel (on my plane I am using the Gear channel to switch on glow drivers). You could, instead, set the glow drivers to turn on automatically below 3500 RPM. Synchronization is disabled below 3500 RPM which helps when starting the engines and lets each engine idle at it’s own pace. And as I mentioned before, at full throttle (anything above 90%) synchronization is disabled to allow each engine to run full out for maximum power. It is also programmed to NOT detect a dead stick. Since this plane will still fly with only one engine running there is no need to throttle down both engines to balance thrust like you would do for wing mounted engines.
Download the TwinSync manual at:
http://www.troybuiltmodels.com/items/WRCTWINSYNC.html
To get this special programming installed in your TwinSync <u>at no charge</u> mail the device (or, if you are handy with electronics, just send in the program chip) to: Bill Wike
$5.00 must be enclosed for return shipping.
Contact Bill to let him know what you want at:
http://www.rcuniverse.com/forum/m_4700596/tm.htm
<span style="font-size: large;">This is the end of my opening comments.</span>
I hope this helps some of you during your build of the Skymaster 337 from Nitroplanes.com
I am open for comments and suggestions. Since the Nitroplanes.com plans for this model are so minimal, the only way to get it right is for all of us to plan together! - This Forum Is the Manual –
Steve McCarthy