How close should a twin engine be synced - RC Groups
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Feb 23, 2013, 12:14 PM
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How close should a twin engine be synced

How close do I have to have a twin engine prop plane synced? Never done a twin so I'm not sure at what throttle setting should they be synced at. Also I see there are some really accurate laser opticals are these any good when compared to the standard light ones? I see that I can't select the three blade prop but I guess it wouldn't really matter if I am just trying to synch up engines
Thanks Jeff
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Feb 23, 2013, 03:23 PM
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I'm no expert but I have had a couple of twins and currently have one I like to fly. My advice is to tune each engine as best you can and do not try to match them. As long as the throttle linkage is the same they should be ok. I have watched a couple of club members go to extremes trying to match engines up and so far they have nothing but dead sticks and crashes for their efforts. Trouble starts when you start twisting needles to match the engines instead of just tuning the engines to run their best.
By laser opticals do you mean tachometers? Many of the small cheap ones work fine but the TNC is the best and most expensive at $95 but I just bought a new appearing one for $50. So they can be found cheaper once in a while. The glo-bee is junk but the H-9 and tower work ok. I have a near new H-9 to sell so pm me if your interested.It works great.
Feb 23, 2013, 04:46 PM
Hope to get out of life alive
kenh3497's Avatar
I was thinking there are now governors available for twins??? I know the heli guys are using governors to maintain a constant rotor speed.

Feb 23, 2013, 09:00 PM
Registered User
The way I see it tuning both engines to max could cause differental thrust problems...Just like in full scale twins, one engine will be the master. In our applications it will be the weak engine...tune the weakest of the two just like normal...then adjust the stronger engine to the weak one.
Remember in case of single engine, keep power as low as possible bank angle shallow and never turn into the dead engine
Feb 23, 2013, 09:39 PM
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earlwb's Avatar
Adjust each engine to run good by itself. They can be off quite a bit from each other and the plane will fly fine. Just a little aileron or maybe some rudder trim if it is way off. You want each engine to be happy, trying to sync them up or match them up just doesn't bode well for reliability. When guys try to match the engines up with each other is when they start having problems with engines cutting out on them in the air.

If a engine does quit in the air, just cut the throttle and land it like it is dead stick. Thus you won't wind up with a death spiral or roll into the ground. Some twins might let you increase the throttle a little bit to stretch a landing approach, but its better not to try. Now then there are some twins that do fairly well on one engine, but even then they are quite finicky and touchy and you could lose if you push it while flying on one engine.
Feb 23, 2013, 11:10 PM
hutchinstuff's Avatar
Troybuilt models sells a twin sync that will bring the one engine to idle if the other quits, I've heard its pretty neat, one of our club members has it on a beech 18...

I've got a coro twin running on AP 15s, and I use the throttle curve to match up the engines, pretty easy to do by the sound, you will know when they sync up. This also allows a person to just stop the throttle short on the weaker engine rather than messing with needles.
Feb 25, 2013, 11:21 AM
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Disarray's Avatar
I run a 4 engine Telemaster with 3 different types of engines(2-25 fxs, 1 25 la, and 1 25 gp). I can fly the plane on just the two 25 fxs and I have never tried to sync the motors. I just tune each motor for reliable performance and go from there. More important than sync is smooth transition. The 25 gp on this plane is very sketchy. It will lag behind the other motors and induce all kinds of adverse yaw until it catches up.

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