JGrc

My Feedback: (29)

I have some trouble trying to maintain sinc throught the range. I can adjust the top end or the idle, but I have a hard time with mid range which is most critical.

ANy advice on radio system or mechanical systems that would allow a good sinc?
Also, what would be the maximum allowed diffrence between engines without causing too much yaw?

Thanks,

JG

fancman

My Feedback: (16)

http://rcwarbirds.com/Techniques/techniguespage.htm#t2

evan-RCU

The important thing for a twin powered airplane is reliability. If you can get the two motors to idle reliable close to each other and to have a reasonable close midrange and a top end that both are running strong and reliable you are doing good. Most of your flying is done at half trottle and that's where you want you're best synch.

R8893

My Feedback: (20)

You could probably do it by using two channels and programming the slave channel to follow a non-linear response. I have done this to get flap travel to match very closely.

Or you could not worry about it. I have seen posts by Ed Moorman showing exactly how much difference a model will tolerate. It appears to me that the engines will self-synchronize in the air as the slow one windmills up a little and the strong one is dragged down. Currently flying a model with twin OS .52 4-strokes and one is almost 1000 rpm's stronger--other than a little pulling to one side in a loop it doesn't seem to effect flight.

Love the Hornet!! I've got to build another some day.
Chuck

eagledancer

add a twin-sync to your plane and problem cured

evan-RCU

NOT, you still have to make sure your engines are tuned correctly and reliable.

sledge_78

My Feedback: (24)

JGrc,

I have been flying a twin for over a year and find that most of what is said here so far is true. Let's put it into perspective. Reliable engines are key. I can't say enough about that point. If there is any doubt before take off, don't do it. Save the flight for another time when you are sure both engines are operating properly. As far as tunig both engines so they are synchronized, it would be wonderful if two different engines would perform equally by simply opening and closing the throttles, but they don't without some careful perseverance on your part. MY twin flys well and at full throttle they sound like they are in synch. If I back off the throttle the sound tells me that they are not match synched. They may be off by 200 rpm between full throttle and idle. It still flys the same and if it weren't for the sound I wouldn't know it. I bascally did two things when I set up the engines: 1) I tuned each engine separately to run at full throttle using the needle valve. This gave me confidence that each engine was not to lean or too rich. I wasn't forcing one engine to tune to the other. Although they do sound like they are in synch. 2) I set the linkage up for the throttle servos using the blank end of a drill bit. I set the first engine at 1/2 throttlw stuck the bit into the venturi so I could close the throttle until it touched the bit shaft. I noted the throttle position on the transmitter stick and then moved to engine #2. I set the transmitter stick at the noted position and adjusted the servo linkage until the throttle closed just touching the drill bit.

After doing this, I then knew that both throttles were going to open and close the same amount. I started each engine and tuned each one by itself to obtain the best running condition. I felt very comfotable that they were going to be reliable. I put a tach on each engine at various speeds and did find them off a little but not more that 200 rpm.

Finally, I have only heard good reports about using the Twin Synch and I am going to try one myself.

JGrc, make sure about the reliability of the engines, and enjoy your twin.

Sledge_78

DelRay

Sledge_78, nice tip on use of the blank end of a drill bit. I set my motors the same as you do, treating each one separately, and matching them very closely on high end, and usually within a couple of hundred rpm on the mid and idle.

evan-RCU

I do the drill bit trick too, works very well. I do it at idle and mid stick. I've only been flying twins for 20+ years though...

Boomerang1

I use the drill bit trick too. You will hardly ever be at idle except on the ground and with full throttle as long as both engines are slightly rich they will be happy and close enough to the same RPM anyway. The trick is to keep them both running. - John.

JGrc

My Feedback: (29)

Hi All,

Thanks for the input. I am using a Eclipse 7 radio and does not allow a 3 poit slave servo set up. I wil try Sledge's trick next.

JG

Thunderchild

Hello all,

I have just purchased my first twin and found this forum topic most interesting. Could you tell me please where I might find one of these "twin-syncs" you talk about please? Who is the manufacturer?

Cheers,

TC

Robby

My Feedback: (18)

RCSHOWCASE.COM is currently the only place to get the TwinSync..

http://www.rcshowcase.com/html/acces.../twinsync.html

BillS

Top RPM can be 500 to 800 different without affecting flight performance.

If one engine is slow spooling up on a tail dragger you are likely to be all over the runway before the airplane is in the air. Big engines on a tail dragger could be a handful.

If one engine is slow spooling up with tricycle gear the airplane will flat turn as the front wheel lifts off. One of my tricycle gear twins almost always headed straight for the big shade tree at lift off. The airplane and the tree had an agreement about a clean mess flight path but rarely consulted me.

My limited experience with Twinsync suggests it would be a good solution.

Bill

Robby

My Feedback: (18)

My extensive experience with Twinsync says you are correct..