The thought just came across my mind and I simply cannot think of a good answer, especially not knowing much about the mechanics of it all.
In: Engineering
FYI, it’s not totally unheard of to have an airplane with propeller in the rear – see the Icon A5 for a modern example – [https://www.iconaircraft.com/](https://www.iconaircraft.com/)
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Having disturbed air entering the propeller on an aircraft creates a great deal of vibration. Escape in the air may also be more dangerous. There are lots of advantages to a tractor configuration!
Boats do not have a major issue of disturbed water entering their propellers because of the pressure profile around the hull. Also the speed, fluid density and viscosity regime results in a much smaller boundary layer of fluid. Basically a propeller on the back of a boat is pretty much operating in free stream, unlike one on the back of a ‘plane.
In both cases the propeller is actually more efficient when mounted on the rear. This is because the inlet cone on a propeller is much wider then the exaust cone so the hull of the craft is not so much in the way. However the problem that aircraft face is the issue of weight distribution. For stability reasons you need the weight of a craft in the front of the drag. The best example of this is an arrow or a dart which is very stable because it have a heavy point in one end and a tail for stability in the back. Airplanes are designed with the same principle. But in order to do this they need the heavy engines far in the front. Aircraft that use a pusher propeller therefore have to run a long prop shaft through the entire length of the tail of the aircraft. Some boats does have a very similar configuration but because they do not have to fly they usually have much smaller engines and propellers compared to the size of their ship. So they can easily get away with running a small propeller shaft along the keel of the ship to a center mounted engine.
There is also another reason which is why even aircraft with wing mounted engines usually have the propellers in front of the wings. It has to do with low speed control. A big issue with low speed flying is that you do not get enough airflow over the control surfaces to be able to control the aircraft. One solution is to put the control surfaces in the blast of the propellers which gives them more airspeed. And because there are control surfaces on the wings you therefore need to put the propellers in front of the wings. Ships do the same thing but with a slightly different configuration. They put the rudder behind the propeller but the rest of the ship is still in front of it. If you look at some more extreme aircraft designs you do sometimes find this with pusher propellers as well. But cutting out parts of the wing or hull of the aircraft in order to place the propeller in front of the airfoils but behind the rest of the structure is often counter productive.
This is how I would explain to a 5yo. It’s a speed problem. Things pulled from the front can go faster without falling over and things pushed from behind are more likely to fall over when moving quickly. Because a plane is a lot faster than a boat it needs the puller in front and a boat is a lot slower so it gets help turning when the pusher is at the back.
I skipped a lot of other factors for the sake of getting to the cookies and milk faster.
Not exactly an explanation, but the plane the Icon a5 has it’s propellor on the back! So not every plans Is necessarily like that
I haven’t seen this mentioned yet, but if you put a propeller on the front of a boat, you would be standing/sitting in the propeller wash for your entire journey, which would probably get old very quickly and make it very difficult to hold your beer.
I haven’t seen it mentioned yet… To lift the nose up for takeoff, the tail has to be lowered very close to the ground. That greatly limits the size of the propeller you can mount behind the main landing gear.
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