system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:why are plane propellers in the front and submarine propellers in the back?
gpt
For planes having the props in front:

1. The weight of the engine in the front helps to balance the airframe versus the aerodynamic center for stability

2. Less chance of connecting with the tarmac on rotation

3. During takeoff the air coming from the props moves over the wings. This is faster than the speed of the aircraft. By putting the props in front you get an added bonus to lift, meaning shorter roll or higher weight

4. Your prop is acting in "clean" air, increasing the efficiency of taking power from the engine and putting it into moving air. If at the back, the air is more turbulent because it's moving over the plane first

Reasons this isn't a big deal for subs:

1. Balance is achieved through more components, so one big mass is less influential

2. Subs don't rotate, they usually bring the nose up and sweep up

3. Subs don't need extra lift over their drive planes

4. The viscosity of water is so much higher than air, and the velocity of subs is so much slower, that the water is marginally more disturbed than ambient

And for subs, silence is key. You want your prop wash to not hit anything or the cavitation bubbles that form on the tips of the prop will make more noise than they already do

There are likely more nuances, but those are the big hitters, imho.