Sunday, October 22, 2017

Amateur manned multicopters. Flying cars are just around the corner.




Flying cars are just around the corner. Over the past several years there have been many examples of manned multicopter vehicles. Anyone that has several thousand dollars to spend on hobby aircraft parts and lots of free time can build a manned multicopter. Its not as complicated as one would expect. Someone can take hobby aircraft parts including electronic flight controllers and use them without much modification. Most of the manned multicopters use hobby parts meant for large scale model aircraft. Large high output brushless motors paired with large hobby propellers.




The biggest challenge with a manned multicopter is not lift, hobby motors and propellers are able to provide enough lift. Packing enough energy density into a power system to get a long flight is one of the biggest challenges. Building a manned multicopter becomes a balancing act, weight vs. lift vs. energy.
Increasing lift adds weight and uses more energy. Increasing energy adds weight and requires more lift. Increasing weight requires more lift. The props need enough power collectively to lift the vehicle and the passenger and power supply.




The power supply used for these type of experimental manned multicopters are usually an array of lithium based batteries. At the moment lithium based batteries provide the best energy density needed for a manned multicopter. The batteries are heavy and this means there is a limit to the amount of energy that can be carried onboard. Most of the experimental manned multicopters are only able to fly for 15-20 minutes max.

Some people have claimed that multicopters do not scale. One reason they cite is that larger props have too much momentum to be able to make the small changes in RPM needed for stable flight. Even the larger props are so light that this is not as much of a factor as some people think. There are a couple solutions to this anyway. One solution is to use many smaller propellers to gain enough cumulative lift. Other solutions people are working on are things like variable pitch props that change the amount of thrust instead of altering the RPMs of the rotor.



Battery technology is the limiting factor in this case. If there is a substantial breakthrough in consumer battery technology, then almost anyone could have a flying car. And they would not really cost too much looking at a minimalist build. Really light and strong modern materials like carbon fiber and ETFE can be used to further reduce the weight. For safety purposes someone could install a ballistic parachute commonly used on ultralight aircraft.

References:

https://en.wikipedia.org/wiki/ETFE
https://en.wikipedia.org/wiki/Carbon_fiber_reinforced_polymer
https://en.wikipedia.org/wiki/Ballistic_parachute










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