twinman

My Feedback: (2)

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.

warbirdz1

TwinMan......I can fully appreciate your method to keep throttles/Eng RPM sync'ed thru entire rpm range.......I have found using the gas engines (Used to have some glow twins some years back).....that by making each throttle mech geometry the same I get basically the same eng RPM through-out the entire rpm range.......I"NEVER" detune an engine to match the other....as a general rule by reducing power 1 or 2 clicks after getting up at cruise the rpms come in together ....the reason I dont detune is that might be the engine bringing me home......At T/O power 100 or 200 rpm wont make any significant difference.....on approach with the gear and flaps out I've found to be more critical for engine sync than T/O.....'ve also noted that temp/pressure changes can make each engine behave slighly different from the other as well......I use only one servo to drive both throttle linkages which also ensures good linear response.......one last thought....I also like installing an inflight shut-off(Controlled from the Tx) to shut-off both engines simultaneously in case a situation arises where one engine is stuck at a high power setting and the other at a low power setting(Mech failure of some sort).....gliders are easier to land than a "Pinwheel".........Bill....

twinman

My Feedback: (2)

warbirdz1 I full appreciate your ideas as they apply to gas engines. It is true that they are more reliable than glow engines.The tuning you refer to is for gas engines. I would never suggest peaking a twin engine glow powered plane.
Yes, using one servo for two engines is simplier, but it is also harder to set up, and as my other experiments show, (at least to me), using two servos ( one of each engine) allows greater flexiblity for aerobatic manuvers that a single engine can hardly match.
Wish there were a good way to shut down a glow engine in flight. There have been several times that would have been nice.
Ever fly around with one engine screaming due to linkage failure and holding the other to near idle until the other one runs out of fuel. Been there, done that!!!!!!!
Good Luck

warbirdz1

TwinMan.......Flying as you do mostly in the aerobatic realm of things adds yet another "Dimension" in flying.....I can see where problems arise that are more critical to your type of flying.....although warbirds have their elements to deal with as well....generally high wing loadings/inherent drag qualities.....twins make for a new approach to old aerodynamic and thrust related problems......what concerns me more than anything about a "Warbird" twin is their propensity to go upside down in a "Flash" (If not sooner.....also have first hand experience) after an engine failure .......If it happens up high...as its happened to me ...I was able to reduce power,push the nose down and roll it back to wings level.......but at a low altitude......forget-a-'bout-it.......most everything else is just plain good old stick time.....I flew a several duelists for several years and it was very good experience.....alot of single engine flying for learning purposes........Bill.......

crashnfix

My Feedback: (1)

Great information!

My first twin will be a Twin-Air. No retracts or flaps, so I will be able to try this mixing on my JR 652 6 channel. After spending some time trying to figure exactly how to adjust the slave, I guess I'll just have to wait until I finish the plane and do some trial and error. I understand the process you explained, now all I have to do is translate that to JR processes.

If there is anyone else who has had JR experience, a little help would be appreciated.

John

twinman

My Feedback: (2)

Reguarding the quick inverted snap roll...have had two other P-38's on glow......been there done that. Have two more now over 100". On the aerotech P-38 and the experimenting I did to control just what you are talking about, I installed two gyros. One on the rudders and a dual input output Hobbico. ( There are others!!) on the ailerons. It works with engine out.
Yes, the plane will yaw....slowly. But slow enough to react.
More of my two cents on this subject at the techniques page at rcwarbirds.com.
I do not claim to be an expert..experience is burn and learn!!
Just want others to avoid my mistakes.
Good Luck