The most right way to choice engine is to select type ones on your rest models. If you can handle all type of engine you will use any type ones but if you use one type motor only I strongly recommend using the same type motor. Twin or multi is not suit to learn new type motors.
I prefer glow 4 - strokes engines due its sound.
If you have problem with glow fuel your choice will be limited petrol or electric engines. The batteries can be post everywhere without problems now.
If it’s not matter for you what kind of engine to use I’ll give follow classification.
For me only one choice – all working engines should produce enough thrust for wanted type of fly. Usually models are overpowered slightly. I think you have to follow such rule in case of twin also. If you design scale transport model, you don’t want to do loops, rolls, you want to fly circles – select appropriate engines. It will be model with trainer’s power. If you design PE-3 or Lighting – any fighter or as me sport aerobatic model and you want the model will able to make some pattern maneuvers you have to select engines with power equivalent to pattern models.
For example you design model with wingspan 1600-1700 mm.
If it is scale transport with power of trainer model it is 40 – 50 size. For such model will be enough two 20-25 size 2 strokes or 30-35 size 4 strokes engines or electric equivalent.
If it is fighter or sport model it will be 60-90 size. In this case the engines have to be more powerful and bigger. 30-46 2 strokes or 60 - 70 4 strokes.
In the first view the power never is a lot of but more power – more weight – more speed – more difficult to control in normal and especially in emergency situations.
Let’s look one more aspect of overpowered model but especially according twin or multi engine models. Overpowered engine will produce more thrust to turn the plane if one engine stops. The time of decision decreases. The lover power that slower will develop emergency situation and you will more chances to save model.
Therefore I do not recommend installing too powerful engines on twin or multi.
If you can turn engine properly you’ll not have any problem turning engines on twin or multi. Turn full throttle and idle for each engine separately. Don’t miss the vertical test. Then you achieve properly turn of engines separately you need to turn theirs together. Your further actions will be depending of what kind of radio you have.
If you have modern computerize radio and you can make independent moving throttle servos and you will have trim responsible on all those channels and you will able to cut off all engines from one switch or from one trimmer it will be enough for safety fly.
If your radio can’t provide above described functions you can take Y link or made yourself one to connect all throttle servos in one throttle channel.
You further actions will depend of what more important for you idle or high speed of engines.
If you make a scale model likely the idle speed will be more important for you. If you have sport model high speed will be more important probably. As you have decided what more important you mechanically turn the length of rod to achieve wanted throttle position on wanted mode. The opposite mode has to be turned with trimmer, T.A. according worst engine in case of idle or than the first pushrod riches limit of moving in case of high speed mode.
That’s all. I think that it was more difficult to describe as to do in real situation. As you start to turn you’ll make it easy. It should be done only one time. After that you can forget it about.
Speed controller has to be calibrated and install to brake mode. Why brake mode?
Let’s return to the chart with shadows and add free rotated propeller. The rotated propeller will shade some wing area decreasing lift additionally. The braking from propeller will produce additional turning level.
