Matt,

Should be no problem since you will be using two ESCs (one for each motor) and a single timer. The K timer that Keith Renecle makes could be a problem. I think it could be attached to only one of the motor wires (to one of the motors) for governing but still control both motors. Maybe Keith will verify this. You should disconnect the BEC supply wire from one of the ESCs so that the timer is feed from only one of the ESCs.

I assume you are using a full fuselage. For running the wires, you should locate the ESCs in the fuselage near the battery (you are planning on one battery I assume). Short wires from battery to ESC is the rule and long wires from ESC to the motor. Therefore, you should run the three motor wires from the ESC in the fuselage to the motors via the wing. For my twin, I made a balsa tubes by wetting 1/32" balsa sheet and wrapping it around a dowel and then cementing the edges when it dried. You would need to build these into the wing during construction. I could pull the wires through the tube (kind of like pulling house wires through a conduit).

Using two batteries (one in each nacelle) would be a option if there is room. This would save the weight of the heavy ESC to motor wires in the wing and only the light timer wires would be required in the wing.

Hope this helps.

I think the only chance of success will be to use the Castle Phoenix in "Set RPM"  mode.  This is normally a good idea for twins anyway since there is always some small kv variance motor to motor and Set RPM will neutralize it.  This is not a perfect solution - because you will be operating in vastly different throttle regimes and the dynamic response of the motors & the governors will likely be different.  Castle recommends that you have the motor running at between 70% - 85% throttle setting for best governor performance, seriously doubt you can get BOTH motors in that range unless you are also using different props on each side - please don't go there. 

As for wiring I would opt for separate batteries (actually Castle recommended this to me) but one timer on a Y harness. The Y harness for a battery is HEAVY and adds nothing to the performance of the system.


Ya know Matt, if you are going through the time/cost/expense of building a twin, you REALLY ought to pony up for another motor to match one of the others

Guys,
Thank you for your thoughts.

I will use Keith Renecle advice: "using my timer system with twin motors requires two separate timers unfortunately. You can use a single switch that feeds both timers, but each esc will need it’s own timer. One larger battery will work fine for both motors and would most likely weigh less than two separate ones.

I will also get two identical motors as it makes everything easier.

At this moment I do not know which motors to choose but I would like to stay with Cobra.
Perhaps I should simply buy another 2826/10 or 2826/12 but which one is better?

I hope the answer will emerge when I size the plane starting from the diameter of the propellers.
These are three blade props similar in shape to the Mosquito props.

Cobra publishes the Motor Propeller Data and 2826/10 shows max. continuous power of 830 Watts on 5S LiPo and max. current = 45 Amps.
2826/12 shows 780 Watts on 5S LiPo and max. current 42 Amps.

Assumed span of the model: 65" (scale 1: 6.7 w/r to the actual airplane)
Corresponding, scale like prop. diameter: 12 " (3 blade).

It is important for me to keep the "scaled" prop. diameter.

Cobra 2826/10 (weight: 171 grams or 6.03 oz., KV=930) with MAS 10x5 with 3 blades on 5S, develops 787.5 Watts at 42.57 Amps.
Cobra assigned a yellow range to this setup therefore the prop can be used, but full throttle should be kept to short bursts. (80 to 100% power).    

There is no test data for 12" diameter 3 blade prop. but for sure the current will go up.

Not good.
 
2826/12 does not have the 3 blade prop. data at all.

3525/12, KV=650 shows on MAS 12x6x3 and 5S (18.5 V), 36.17 Amps, 669.2 Watts at 9,509 RPM  but this motor weights 8.92 oz.
5S battery ( one for two motors: 6000 mAH capacity ): ~26 oz. Cobra ESC: 40 Amps ( I have two already ) or 60 Amps: weight per one: ~2 oz.

2 Motors + Battery + 2 ESC + 2 props + wiring + harness + switch + 2 governors + spinners =~ 52 oz.

Painted structure with retractable landing gear: 46 oz. ( quite challenging at this size).

Total: 98 oz.

Decisions, decisions and more decisions.

Regards,
M

This sounds like a fairly large aeroplane .
Is it windy where you are .


 

Some fairly solid lines might be necesary . Some 2 Kilo ( 72 Oz. 0 planes could go out beyond 70 ft. easilly .
Might save you being towed down the field or pulled of your feet .

That said my little DeH88 ( 66 span ) is very light & neutral on the lines , so it aint necesarilly so . Though
it might pay to be prepared .

Any pictures ?