Decision is to take what we have already in the form of that 60-inch or 1500mm show-and-tell and make another that we can fit out as a working model. I had been scoping out propellers for this, when I realised that we could use what we had fixed to the mock-up... or at least one of them, because ideally we'd like one to swing in one direction and the other in the other.
Here then for your education and delectation: a primer on propellers.
First off, the direction in which single propellers swing as viewed from the cockpit is not standardised worldwide, those in the US being conventionally clockwise and the props in the UK having done the opposite. It's hard to know quite why, although it is worth bearing in mind that props during WW1 were swung by ground crew in the absence of electrical starters; and as they were raised on clocks, maybe there'd be fewer accidents if they stuck to the same hymn-sheet.
This did have real-world consequences, like for instance pilots from elsewhere being introduced to the Spitfire, applying the wrong rudder by way of correction during a take-off and departing off the side of the runway; the spiral efflux from a propeller impacts the tail-fin and applies a turn in one direction or the other dependent on the direction of that swirl.
Now as you may have noticed from your car ~ and I had one with a hand-crank as a back-up ~ that reciprocating or internal combustion engines run in one direction, unlike electrical motors which are easily reversed. Strictly speaking there have been two-stroke engines that could be set to run either way, but they've been a rarity.
Model aeroplanes however may have sprung up in a number of different countries, but the market and the money lay principally in the US and so these motors would run in one direction from the get-go. Accordingly, still to this day the market for the propellers available to the RC community tend to run principally in one direction.
You may have guessed by now that that direction follows conventionally practise at full-scale in the US viz. clockwise as viewed from the rear. This causes considerable problems when it comes to finding CW and CCW pairs to run on conventional types of aircraft, or indeed airboats like our own.
Not incidentally an issue in that wholly new arena of RC in the form of drones: these have generally been quadcopters from the outset, which require propellers sold in a pair that run in either direction. The problem however with these is that they have usually to be optimised for hovering flight, and thus have a much finer pitch than a pitch we would want on a fixed-wing aeroplane... or indeed boat.
Bear in mind at this juncture thar from the very earliest times, aircraft will have had 'pusher' propellers as well as 'tractor' propellers that pull. Nonetheless if you take a conventional RC combustion engine and face it backwards, the shaft is now turning in the opposite direction; so that the propeller has to be adapted accordingly so as not to pull the aircraft backwards but to push it forwards.
Push comes to shove, what that means is that you can take one of the pusher props in the picture above and fit it the wrong way round on a forward-facing motor and what you have is a CCW tractor as viewed from the rear... and easily complemented by a CW tractor (technically called a CCW, as ever viewed from the front as relating to models because that's the business end).
What this means for our own working five-foot prototype is that I ~ and as ever it is me who has to get the wallet out ~ just need a pair of 11x7 CCW model propellers to complement those above, and then we've a working pair and a pair of spares. By way of explanation, too, 11 is the diameter in pitch and 7 the number of inches the propeller would turn during one revolution were it to turn unrestricted in some or other dense medium like jello.
(It does not quite do that in air, but suffers 'slip' if this is indeed the correct term. It has been a while since I sat in an aerodynamics class, and I live with the trauma.)
Note the writing on the face of the propeller. This should always be readable by you as you bolt it to the drive-shaft, whether the prop is designed to be fitted to a motor up front or out back.
