Which engine is this likely to be?

Awww, takes the fun out of it,  if you get all scientific on us. That's gotta make us think and stuff.
The steep Pitch(s) you've selected are....off the chart!!  I'm guessing it might be 1.20 Size Diesel.
as already mentioned, following the propeller size recommendations made by your engine manufacturer should always be your first point of reference. But there are generally recognised prop size ranges for each engine size and these are the sizes to choose if you're unsure about propeller selection.
The following propeller size chart (© Top Flight, reproduced with permission) is easy to use; select your engine displacement along the bottom scale, then follow the vertical line up to the shaded area to give the prop size range for that engine.
Propeller size chart
Although this chart is related to Top Flight's Power Point range of props, the size ranges suit all brands.
EP propeller sizes

It's no secret that matching a prop to an IC engine is fairly easy if you follow the general size recommendations outlined in the above chart, which have long been accepted in the hobby. Fitting an incorrect prop would mean the engine would still run, but your plane would perform poorly.
But with the advent of electric power (EP), propeller selection became a whole new minefield!
EP prop selection is much more critical because different combinations of motors, ESCs and battery packs can generate huge differences in operating speeds and loads.
As with IC, electric motor manufacturers give a specific propeller size range for their motors but it's more critical that the range must be adhered to. Over-propping can do irreversible damage to electric motors and ESCs, because an incorrect propeller will force the motor to work harder than it was designed to.
If you put an oversize prop on an IC engine, the engine will likely stall. No harm done. Put an oversize prop on an electric motor and the motor won't stall, it'll just keep on trying to turn the prop.
The motor will draw more and more current as it tries to keep up with its Kv rating - the number of revolutions per minute it has been designed to turn, per each volt fed into it. With too big a propeller, the motor will just keep working harder and harder to spin the extra load, until something (likely the ESC) overheats and catches fire.
Too small a propeller on an EP motor won't do any damage, but you won't get the required performance for your plane. The motor will draw less current and the plane will likely be seriously under-powered.
The only accurate way to know whether or not your EP propeller is resulting in the correct current draw through the ESC and motor is to use a Watt meter connected between battery pack and ESC, as the video below shows...



Number of propeller blades

A 3 bladed propellerThe majority of propellers used in the radio control flying hobby have two blades but props with three or even four blades are available.
Two-bladed propellers are commonly used because they are relatively efficient and easy and cheap to produce but sometimes an rc airplane will call for more blades, particularly where a scale look is required.
Adding more blades decreases the overall efficiency of the prop because each blade has to cut through more turbulent air from the preceding blade - in fact a single blade propeller is the most efficient but these are rarely (almost never!) seen in our hobby although they have been experimented with. Incidentally a single blade prop has to be balanced with a counterweight on the other side of the hub to the blade, otherwise the plane would shake itself to pieces as soon as the prop was turning!
If choosing a three or four bladed propeller the general rule of thumb is to decrease the prop diameter by an inch and increase the pitch by an inch, but on some models fuselage and ground clearance issues might dictate which propeller size you can and can't have on the model. As with everything, trial and error - and forums!
Well hopefully this page has given you an understanding of propellers used on rc airplanes, and an idea of how to select the right size propeller for your model.
Remember to follow your engine/motor manufacturer recommendations whenever you can, and use a Watt meter if you are going to experiment with different propeller sizes for EP rc planes.


The Chart did not copy and paste, my head hurts from all this reading....I need more pictures!!