Am i trying to fly by pulling myself up by my hair? I'm currently trying to build a multi-rotor of my own, and am testing it when i noticed that the lift that i am supposed to be getting is wayy less than what i am expecting.
I have a rectangular body that is 12cm(width) by 26cm(length), and a motor attached with a (16 x 10) propeller mounted upright in the middle of it. I am doing lift/thrust testing by placing the body onto a weighing scale, and increasing the throttle, and by measuring how much the weight of the set-up decreases, i am thus able to measure the thrust i am getting from the motor.
From the manufacturer's specs provided, i am supposed to be getting a max thrust of 5000g(which seems suspiciously optimistic to me). HOWEVER, when i rev the throttle up to the max, i am only getting a thrust/lift of 550+ g, which is way less then what i should be getting (5kg).
Am i correct in thinking that when the propeller is spinning, wind is pushed downwards, so as to cause an upwards lift.However in my case, the wind that is pushed downwards comes into contact with my rectangular body, and as a result, pushes the entire set-up downwards.Therefore would i be correct in assuming that what little thrust i am getting is simply the result of the wind that is not coming into contact with the body?
If so, is there anyway i can mitigate the loss of thrust? I am thinking that one possible work-around would be to mount the motor & propeller upside down, on the bottom of the body so that when the motor spins, the wind caused by the propeller will not press down on the body?
I would appreciate any and all opinions and answers.
Thanks in advance!
 A: Well speaking of aerodynamics, you should know that ...


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*A propeller provides asymmetrical amounts of thrust at different points along its length, meaning that the surface near the center of the propeller provides less lift than the tips of the propeller. Check this helicopter image and notice that the propellers are tilted upwards. This quite simply is because the tips are moving faster because they have a larger distance to cover per turn. Now this means that the most thrust comes from roughly the outside 1/3rd of your half-propeller which from the dimensions you've given, extends outside the fuselages width and length. Leaving other factors like clearance from fuselage, intake drag, ... etc aside, I see no reason you shouldn't be getting a lot more than 500gr of lift, if your rotor/motor is indeed capable of delivering it.

*Lift is also related to the attack-angle (angle with the ground level) of the rotor blades and ofc the RPMs. Maximum lift force is at 45 deg but it will put the maximum strain on the blades so if your motor can adjust this angle you should start from 15deg and gradually (in steps of 5deg) move up to 45 to see how it goes BUT BE CAREFUL as the blades can break from the strain and hit or even KILL. You've been warned!
As you see, lift with propellers is not as simple as one might think but it is exciting nevertheless. Good luck ;-)
