twinman
Posts: 1628
Joined: 1/19/2002
From: Katy, TX, USA
Status: offline
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OK, so a few of you are still complaining that you cannot get the engines to come up together. Yes, there are electronic sycronizers, but you may have the ability to do this already at your finger tips.
I use the Futaba 8UAPS and 9CAPS eight and nine channel radios. OK, not don't start complaining that JR, Hitech, Airtronics, or whatever is better. I cannot comment on that arguement. Started with this and am too old to change now.
The Super Version of the 8 channel has seven mixes. The last two added with the Super Version, have an interesting feature that allows you to map the response on the control curve of one channel that is mixed into another channel. The control curve of the mix can be set along five points on the stick movement. With this feature you can match two engines together on the acceleration curve. You did mix the rudder into the two engines and putting the engines on separate channels to allow individual adjustment, didn't you?
Well, I sometimes still have problems with the two engines coming up together. For normal flight this is not necessary, but I am progressing into more aerobatic work with twins, so additional experimentation is reqired.
OK SO I NEED A LIFE!! TWINS DO THIS TO YOU!!!
As the engines are already mixed together, all that is required is to get one (The right engine) to be the slave of the other (The left engine) and get them to come up in RPM together. I have previously stated that you should use matched engines, (not new and old) but even matched engines have performance differences. Yes, you can go crazy and use a tach the whole way, but if you listen for the harmonic on the two engines running together, you will be very close.
Now, the big safety message. DO NOT DO THIS WITHOUT SECURING THE PLANE!!!! You will be running the engines up and down, and adjusting the radio, for periods of time and you CANNOT DO THIS WITH ONE HAND!!!
First, get the engines properly adjusted as noted in previous posts. It is absolutely necesary to have the master engine (the left engine (the left engine should be on channel 3 for futaba and the right engine should be on channel 8)) reliable and ready to transition reliably. Always set the stronger engine down to the weaker engine, never the other way around. Both should be slightly rich- more so than you would do for a single engine plane. Remember, reliability is the key for suvivability on multi-engine planes. Shut the engines down, as the next step is accomplished without the engines running.
Start at the idle position and get the engine's visual carburator openings to match idle speeds based upon the first or last of the five position settings according to how you initially set up the mix of the two engines. ( For some instances, this maybe position five or position one on the mix). Once you have adjusted the values of the idle speed, set the values of the high speed position (the extreme opposite position (I.E. If idle was position 1 full throttle will be position 5). Each position of the five is completely independent of the others so misadjusting the idle postion will not require a readjustment of the other four positions. However, because of this, you will have to have the throttle in the correct postion to adjust each phase (I.E. If you are adjusting idle you must have the throttle set to idle). After idle and full throttle is set, make postion 3 of the opening of one carburator, match the other carburator opening at half throttle setting. It is critical to do this part next, because you will simply put positions 2 and 4 at a point that makes the engines sync (audibly or with a tach). The position of 2 and 4 may not be exactly between 1&3 or 3&5. It may vary according to the engine performance curves. Once you have set them up where they look similary in the carburator opening, from idle to full throttle movement, it is time to start them and test them.
Tie the airplane down so you can operate the engines without fear of the plane getting away. Always stand behind a plane while the engine is running. Start with idle, make the engines match here first, using the mix. If you do not have enough throw in the mix use the ATV (This changes the servo travel) function and if you must, the subtrim also. Remember that Subtrim adjustments affect all the postions. Next, move to the full throttle adjustments, advance the throttle to full and make the slaved engine match the RPM of the master engine. If you do not have enough throw in the mix, use the ATV function for the right engine. Next, check that half throttle is equal. Make the other two Joystick positions (2&4) match next. Finally confirm that the throttle response is linear, and if it is not, adjust postions 2 or 4 (and maybe 3, but only if it is necesary) to make the engine response linear. You adjust only these two (points 2 and 4, and maybe three) because postions 1, 5 are set to make top and low end adjustments.
The engines are now mapped for equal response. In the future, all engine mixture adjustments must be done at idle and full throttle as was done before you started to map the engine response.
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Mapping the engines for linear response - 
