Jet Propulsion?


#43

How about to get more thrust from a jet use an air pump to pump air through a hose down the mast and out into the impeller? Something like this maybe? 50w, 12v and 300lpm of air flow. We could even use the air flow to cool the esc and batteries before going down the mast. Maybe connect the air pump to an esc as well and optimise the air flow for the jet depending on rpm etc.


#44

The thrust from jets is the “exhaust” mass moving in one direction and the body in the opposite direction. The density of air being lower than water means it would have to be many times faster to have the same effect. Water is a great, heavy material to be used for thrust.


#45

Had the same idea in mind, but i will try it without additional air first, and then compare the thrust with and without added air.


#46

My simplistic thought process is that air being compressible unlike water will get compressed as it goes through the impeller and so as it goes out the jet it will want to expand giving more thrust. Also the air and water mix being compressible will allow the impeller to get up to speed faster with less torque. Maybe there is an optimal amount of air to give more power to an underwater jet?


#47

@surfsup, I like the idea of pumping air down to improve jet efficiency, I suggested that before too here. Jet dives run more efficient with a water/air mix, all jetskis benefit from this as the intake is so close to surface with lots of air bubbles. We don’t have that 4ft below. You should build a prototype, I am really curious how this would help :smile:


#48

Great minds think alike huh lol. I’d love to do a prototype to test but I think others will beat me to it. I have bruno’s magical 100kv inrunner so will be testing that first with a prop but I’ll probably be slow to even get that done as I have very little time at the moment. Bruno told me the motor was 85amp, 90v which sounded like it might work but I see he has told you its 65amp, 120v. I wonder which it actually is? I’m losing faith in this motor working as I’d hoped so will try a jet if it fails…