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  1. #1

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    Control twin engine rpm?

    How does it work when use two engine aircraft? How to control the speed (rpm) of both engines?
    Is there any equipment (regulator) which control the revolution of both engines which can keep the rpm exactley same (synchronized) on both engine?
    Or, is it just control with one servo on each carburetor (connected to same channel) and do the manual adjustment (what is possible) before flying?

    Is there any electronic eqipment which can be attached and control the carburetors on both engine for sync rpm)?

    Just curious




  2. #2

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    RE: Control twin engine rpm?

    ww.emsjomar.com: twin engine sync system.

    Requires installation of small magnets on spinner backplates, and sensors to read RPM. One engine is designated as master, the throttle servo to the other second one adjusts it's RPM accordingly. I have used the system, works well, but engines should be of good quality and well broken in.
    Tell Mark I sent you. Eloy

  3. #3
    TooLow's Avatar
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    RE: Control twin engine rpm?

    There is an electronic goodie called a Twin Sync thAT takes a tach reading from one engine and matches the other electronically. All read by a hall sensor on the engines. I have flown twins for years and beleive in the KISS theory. Set them close and 1or2 clicks rich and fly them. Most of the time I tune the motors by ear till they sinc then fly. Even tho most motors are new they seem to have one that runs slower than the other. Tune the rpm's to that motor and dont try to peak them both out. Dont be afraid of twins- - - they just take twice as much fuel as a single
    Nosen Cessna 310 Club #1 Co-founder
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  4. #4
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    RE: Control twin engine rpm?

    There is nothing better than:

    http://www.troybuiltmodels.com/items/WRCTWINSYNC.html


    Here are the features:
    The TwinSync Synchronizer allows twin engine airplanes to keep the engines running at the same RPM and produce that unique sound when engines are synchronized in flight. The TwinSync does NOT operate on the Master/Slave principal and has a very fast reaction time to engine speed changescommanded or otherwiseNO lag in maintaing sync.

    Engine RPM information is supplied by easily installed Hall Effect Sensors.

    The TwinSync has a unique safety feature that brings the running engine immediately to idle in the event that one engine stops with no change in throttle stick.

    This feature prevents loss of control when one engine stops while flying the model. The pilot can regain control of the idling engine by simply moving the throttle stick to idle. Control is then returned to the throttle stick and the pilot has full control.

    The TwinSync has another safety feature to kill both engines if the loss of transmitter signal is detected on a FM radio system. This feature operates similar to how PCM transmitters and receivers operate. If a PCM radio is used with the TwinSync it will operate as normal and the TwinSync has no impact on PCM failsafe operation.

    The TwinSync has several additional modes of operation adding capabilities beyond just keeping the engines synchronized. These modes are detailed in the TwinSync manual.
    You won\'t find Nirvanna if you don\'t have any nerve ...

  5. #5
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    RE: Control twin engine rpm?

    Tune each engine as if it were the only one on the plane, and go fly....a few hundred RPM difference will not be noticeable in flight
    All I ask is for a chance to prove that money can\'t make me happy......

  6. #6

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    RE: Control twin engine rpm?

    Try this link for more info and questions to designer.
    http://www.rcuniverse.com/forum/m_4700596/tm.htm

    Ken

  7. #7

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    RE: Control twin engine rpm?

    I use a JR X9303 transmitter and a separate channel for each engine servo. This transmitter, as well as others, have a throttle curve for each engine(dual engine). By adjusting each throttle curve, you can attain nearly identical rpm on both engines at all throttle positions. If you can use the transmitter, it is a lot simpler than adding another system on board you plane. The synch systems do throttle back the running engine when an engine fails so as not to have a severe assymetric thrust condition. However, several of my engine failures have been during takeoff. I was able to continue flying with the single engine. The synch systems would require you to reduce the throttle positon and then advance the throttle to get power back on the good engine. I'm sure, though, that there are advantages to the using a synch system.
    UltraSport Brotherhood #17

  8. #8
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    RE: Control twin engine rpm?

    Or if you want to keep it simple use one servo per engine and Y the servos to thottle channel. I have done this quite successfully on quite a few twins one three, two four and one six engined airplanes.

    John

    \"Keep your controllines tight\"

  9. #9

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    RE: Control twin engine rpm?

    Thanks, This is my first twin, very exciting I must say. I am almost done with my twin. I have 2 x O 25FXs. I was figuring out how to 'syncronize them'. I am doing it the simple way. 2 separate throttle servos and then a Y to the throttle channel. I tried it yesterday and putting trim down to kill the engines I see one of them dies first than the other, my new idea is to adjust the throttle linkages in both until they die almost at the same time (I guess it is very difficult to make align them to die together exactly at the same time)..... is it the way to go???

    After that, I am planning to tun both engines separated, then, whichever that has more RPM, to rich it slightly to be close to the one with less RPM.... am I correct doing all that????

    Thanks!

  10. #10
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    RE: Control twin engine rpm?

    Hi matador and the answer is yes and yes sounds like you have a good plan.

    All my mutis are set up with a Y or custom soldered harness to the throttle channel and I alway make an access port over the throttle servo then the pushrod is make up of thin piano wire with a solderon threads and a plastic clevis at the engine but adjustments are never made here.

    On the throttle arm use an easyjust and adjustments can be made rapidly at the field without turning the airplane over even with my underwing tubs.

    Adjusting manually a twin is a peice of cake a little more time consuming on my four and sixer but works perfectly

    These pictures of my Oxy Moron twin engine glider and my kit bashed Champion Lancer you can see the access holes where the adjusters are easily accessable at all times.

    John
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    \"Keep your controllines tight\"

  11. #11

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    RE: Control twin engine rpm?

    On my OS 25FXs I had to use an Z in the throttle arm because there is no room for the clevis due to the fuselage structure of my twin (c160). So, I gotta do all the adjustments on the servo arm...... which if I undertand right it is the way to do it, as you say, to adjust from the servo arm, I have the easy adjust nuts that you have, that way is easy to push/pull the throttle.... I'll see tomorrow how it goes, I want to have it ready tomorrow to do the maiden on saturday, a friend of mine who is experienced in planes is gonna do it for me!

    The only thing I do not like of my plane is that servos are down the cowls and you can not adjust if the wing is on! unless you flip the whole plane, which makes hard an easy adjustment on the field and needs lots of pacience! (which I do not have most of the times)

  12. #12
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    RE: Control twin engine rpm?

    The 25FX has a metal throttle arm so I suggest you get rid of those Z bends at first opportunity. If there is no room for a plastic clevis or ball joint with plastic cup then you need to make room! Never use metal to metal at this critical juncture. Metal to metal due to vibration here can and will at some unknown point as the Z bends wears the hole bigger produce stray RF noise (interferance).

    Good luck on the maiden

    John
    \"Keep your controllines tight\"

  13. #13

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    RE: Control twin engine rpm?


    yes, I had heard about it, but I am using Spektrum 2.4Gz, would I have the same problem with that????? somebody told me no... I was thinking about refilling the Z and throttle arm hole with epoxy or silicon.....

  14. #14
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    RE: Control twin engine rpm?

    Can,t say I have a fair number of aircraft on 2.4 and a whole bunch more on 72 so I just do it right in the first place and never have the problem but can say a lot of my students have had the problem on 72 and they never beleve me untill it happens to them.

    John
    \"Keep your controllines tight\"

  15. #15

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    RE: Control twin engine rpm?

    I see... there is really no space in the tiny cowls of the C160 to put clevis in the throttle arm, the manual (6pages) shows they do but I have different sizes of clevis and none of them fit, the space is so reduced that if I put it, when I close the throttle arm then the clevis is binding either with the engine or the cowls. I am sorry I can not take pictures but I do not have a camera

    I am going to carefully refill the hole and Z with silicon to prevent as much as I can the rubbing between metals, but you are right. I'll order online different sizes of clevis until I find one that fits. But for now, I want to do the maiden this sunday and I want to believe that it should be fine with the spektrum 2.4ghz, interference should not be an issue....

  16. #16
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    RE: Control twin engine rpm?

    A dremel tool with a sanding drum will do wonders on making room. Folks bring airplanes to me all the time with things like a tiny hole in the cowl to stick a scew driver in to adjust the main needle with or no access at all for midrange adjustments. No way to pinch a fuel line for pinch tunning.

    A dremel will do wonders and to me accessability is always makes the differance in a successful airplane.

    John
    \"Keep your controllines tight\"

  17. #17

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    RE: Control twin engine rpm?

    Use a helli ball link (thunder tiger raptor) on the inside of the throttle arm, that should fit.

  18. #18

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    RE: Control twin engine rpm?

    metal to metal contact generates rf noise as long as we use radios rf noise can be a problem no mater what band/freq.

  19. #19

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    RE: Control twin engine rpm?

    As said above, get the both running reliably (setting them up individually) and if the bottom, middle & top throttle rpms are somewhere near each other then you will be fine. I always tune the engines to peak and then a few clicks rich for reliability. Done this on many twins and fours. Its not important to sync them, I have done quite a few different multi's now that I mostly do it by the engine sounds these days.

    Reliability is 100 times more important then syncing rpm's!

  20. #20
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    RE: Control twin engine rpm?


    ORIGINAL: awood12345

    As said above, get the both running reliably (setting them up individually) and if the bottom, middle & top throttle rpms are somewhere near each other then you will be fine. I always tune the engines to peak and then a few clicks rich for reliability. Done this on many twins and fours. Its not important to sync them, I have done quite a few different multi's now that I mostly do it by the engine sounds these days.

    Reliability is 100 times more important then syncing rpm's!
    I agree 100%. Forget having the motors sync in perfect harmony. It sounds great but that is as far as it goes andcan cause a flying disaster.
    Steve
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  21. #21
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    RE: Control twin engine rpm?

    Over the past 5 years or so, my buddy, Flaps Laffert, and I have built 25 twins. I have test flown several more for other club member, The main thing we have learned is engine reliability above all else. I can say from vast experience that a few hundred rpm difference is a whole lot better than 10,000 rpm difference. That being said, I prefer OS 2-strokes. I have found them to be thebest running engines in pairs and I have tried, Thunder Tiger, GMS and Evolution of various sizes.

    I do have a twin with OS .25FXs and they run excellent. It's a delta and I use Jett tuned mufflers on the 25s.

    As the man from Florida said, the JR 9303 has a twin program with 2 throttle curves and that's why I bought one.

    The next best thing is a JR Matchbox or a SmartFly Equalizer. These let you program 2 servos together on the same channel. I used these on twins until I got the 9303.

    Third best I have found is mixing 2 channels.

    My last choice is 1 channel and flex rods or belcranks. Given the technology available today, I wouldn't do this.

    To make everything easier to set with 2 servos, turn on your radio on and put the throttle at half power, straight up. Check the servo arms. They ought to be 90 degrees to the servo case. If not adjust by moving the arm, then using sub trim for the last little bit.

    Next open your carbs all the way and see if the throttle arms are the same angle. Also do this at idle. You might need to loosen the nut and re-position the throttle arm.

    SEt the carbs half way open and hook up the pushrods or adjust them. If you are good at half way and both the throttle arms and servo arms are at matching angles, most of your adjustment is done. The idles should be about the same opening. Full throttle can be a little off and not hurt anything.

    As someone else has already said, I recommend you tune the engines separately. Crank one, set to max and back off 300-500 rpm. Shut down. Crank the other, set it the same way. Hold the nose up and do those checks, just don't set them too lean. You have to back off a little more than you do on a single or one will invariable lean out. Refuel, crank both, don't let your buddies adjust either engine and fly. Check both engines for a little smoke trail at the first of the flight. That's a rich 2-stroke setting and it's what you want.

    If the plane does anything weird in flight, come back to idle and get the plane right side up. Then add back half power and see what happens. You probably have one out. Hold some rudder and land.
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    Ed Moorman, AMA 553, Former R/C Report Fun Aerobatics Columnist. 76 and up to my old tricks!

  22. #22
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    RE: Control twin engine rpm?


    [quote]ORIGINAL: Ed_Moorman

    My last choice is 1 channel and flex rods or belcranks. Given the technology available today, I wouldn't do this.
    [quote]




    I agree with you Ed and no I would not do that either however you left out my First Choice and that is one channel and however many servos are needed (up to six in my case).


    When done properly with EZjusts on the servo arms and external access to those servo arms It all becomes a piece of cakethat I illustrated in post #10. Besides simplifing the rites of passage for many new multi pilots a simple Y harness is a no brainer for most and and anything more than that is no problem for most of us with a soldering iron. I have proven that it works very well up to six engines. KISS does continue to work and some would argue that it works best for newbies.

    John

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    \"Keep your controllines tight\"


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