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Thread: I have a few questions for you folks into RC Helicopters

  1. #1
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    Smile I have a few questions for you folks into RC Helicopters

    Q. How much lift does mone of these things get?
    Reason
    I want to make a robot that is somewhat pc based
    Q. Would adding more props one the same stem increase lift. (the stem would be the spinny thing that holds the props
    Reason
    I saw an airplane set up like this on the history channel


    I will ask more questions when I get some info

  2. #2
    My man uses Levitra. Peoples's Avatar
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    the osprey right? they decommissioned all of them in the military. I think the only reason for the use wasnt its increase in lift, but for vertical takeoff, then they would rotate forward and have the spead of an airplane
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  3. #3
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    No, this was a wing shaped airplane. But if it works for thrust it will work for lift?

  4. #4
    MySQL Error jcdillin's Avatar
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    do you want to have it fly like a plane or just act like a helicopter?
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  5. #5
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    Quote Originally Posted by jcdillin
    do you want to have it fly like a plane or just act like a helicopter?

    Eventualy both

  6. #6
    Maximum Bitrate EBFoxbat's Avatar
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    More props = more lift/thrust but...

    more props means mroe weights, slowing there spin meaning less lift. I suppose trial an error will let you know if there is a net gain or loss.

    I vote for a second motor with a second set of props.... what are you up to?
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  7. #7
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    You can buy ducted fan kits, which state the thrust amount for each unit. But you would need some big bastard ducts to lift a plane which is carrying a PC (based on a *light* 1kg laptop!)

  8. #8
    MySQL Error jcdillin's Avatar
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    I was actually planning to do this same thing at one time, my thoughts were to use a dual rotor design like army helicopters. Or something like this design for stability
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  9. #9
    MySQL Error Scouse Monkey's Avatar
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    My turn:

    If you simply add another rotor on top of an existing one you won't get an increase in overall lift as thrust is dependant on power. To increase the thrust of a rotor you change the angle of attack (incidence) and this angle is limited by blade stall but also to keep the rotor angular velocity high you need a power to overcome the drag of the high incidence.

    So if you add a second rotor you simply cannot use each blade as much as it can be and you will also have more balancing work.

    The dual rotor systems you see used (both in that vertical takeoff plane) and the Russian helicopter (see picture) with no tail rotor are counter-rotating as this cancels out the torque you get from using a single rotor so you don't need to have a tail rotor like a conventional helicopter. In this setup you need both rotors to have the same pitch to you get the same thrust and torque.

    This design makes it very compact as there is no dangerous tail rotor to hit things but is not as efficent per rotor as a single or side by side set up as the lower blades are int he wake of the upper blades making them slightly less efficient. The Chinnook system (fore and aft) also cancels out any torque so it doesnt need a tail rotor and also has the advantage of being able to accomodate a large change in the centre of mass along it's length which is why it is so useful but it cannot get certified for civil use because of the reliance of the gearbox inbetween the two rotors that stops them hitting each other which would destroy the aircraft.

    Going back to a single rotor system, if you fit a more powerful engine you could add a second set of blades but you would have to couple the control links etc and it is also likely you would have to increase the power of your tail rotor to maintain good control due to the increased thrust and therefore torque of the main rotor. But don'e expect 2x the power from doubling the blades but do expect a lot more vibration and less reliability.
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  10. #10
    Maximum Bitrate EBFoxbat's Avatar
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    Quote Originally Posted by Scouse Monkey
    if you fit a more powerful engine... it is also likely you would have to increase the power of your tail rotor to maintain good control due to the increased thrust and therefore torque of the main rotor.
    Good point

    If you double the wing (blade) area, you (slightly less than) double the lift. This is only true if the rotational speed of stem is kept the same. Most likely you would need a stronger motor to keep the same rotation speed because of the increase in mass it's trying to rotate.

    Simply adding more mass to the stem, spinning, means you'll have more rotational inertia that the tail rotor will need to overcome.

    I've never built an RC helicopter, but you do have other options, I just don't know how doable they are.

    1) Make the blades longer... more surface area=more lift... however it means more mass so you'd need a stronger motor.
    2) Add aditional blades on the same plane... 4 instead of 3 or 5 instead of 4... more surface area=more lift... however it means more mass so you'd need a stronger motor.
    3) Add an independent second motor and set of baldes... a la Chinnook . If you could regulate them some how to keep them rotating at the same speed, then you would have no net inertia causing rotation. Add a tail rotor and you could control rotation. And you would have one mean looking beast of a toy.
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