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General Need Help With A 2kg Plane And A High Kv Motor Will It Fly

Discussion in 'Airplanes' started by Nikhil Rathore, Oct 17, 2017.

?

Will it fly.

  1. Yes

    0 vote(s)
    0.0%
  2. No

    0 vote(s)
    0.0%
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  1. Nikhil Rathore

    Nikhil Rathore New Member

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    Hi everyone my self Nikhil and I am from India I am 17 years old I am building a maker trainer by lucas weakley and I am new to rc but in India it is very difficult to find a depron so i made it with different type of foam is it stiff enough but with all electronics it weights around 2kg but I have a NTM PROPDRIVE 2836 3000KV motor at 4s lipo on a 4.75x4.75 and a 60a hobbyking esc prop this setup can give around 1.4 kg of thrust .I know now I can't handlaunch it but my question is if I use a long runway then will it work I mean will it fly or I have to change the motor and prop?
     
  2. Tony

    Tony Administrator Staff Member

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    That is a very high KV for a trainer. I highly suggest a 1000kv motor around 350 watts and weighing about 60 grams. Use that to spin a 10x6 prop. But, will it fly, anything will fly if you give it enough power, and with a 4s setup that you are talking about, you may have enough power, but will that small prop get around the fuse, that was my first thought. And yes, if the motor can pull the plane along, you can take it off on the ground. Shouldn't need a long runway for this plane, it's pretty good at getting in the air.
     
  3. rdsok

    rdsok Well-Known Member

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    It would be very unlikely.... not to mention you've got the wrong kind of motor for a larger plane like that.

    When designing an airframe and selecting the motor for it... You must take into account more factors than just the weight of the plane. The wing span, the area of the wing, the type of airfoil and several other factors need to be taken into account to properly select a motor ( or engine ).

    For a larger plane like that... you'll want around a 750kv motor capable of about 900w with about a 14" prop and likely use 4s batteries... Something like this hacker motor as far as specs ( based on just weight ) A40-10S V2 14 pole - Hacker Motor USA
     
  4. Nikhil Rathore

    Nikhil Rathore New Member

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    First of all thank you Tony sir and rdsok sir for replying I know that it is my fault that I have chosen a high kv motor and I may need to buy a new motor for this plane it is a kind of difficult for me to buy because in India these brushless motor and esc are very difficult to find but for now i just wanted to know will it take off or not because many of my WhatsApp friend told me that prop will be stalled with this motor and I need a bungee launcher this makes me very sad because I can't afford to have a frequent change in motor as I belong to a middle class family . Specs of this model are:-
    WINGSPAN (length):-50inchs
    WINGSPAN (breadth):-5.3inchs excluding the control surface
    Airfoil shape wing
    With a internal spar
     

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  5. rdsok

    rdsok Well-Known Member

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    The type of airfoil is called a Clark Y .... there are different types, each differ in performance. That is a good basic airfoil used on many trainers.

    I wasn't offering to try to calculate the amount of lift for you... I was saying there were other factors that need to be taken into account so you would know that it takes more than you initially were thinking about. That way you could learn from this. Your previous motor prop combination will not work properly in my opinion.

    A motor and prop between the range that Tony mentioned at the very least... and the one I mentioned at the very most, is what you should be looking for. You need a prop that is long enough to provide wind ( and therefore lift ) across the wings during take-off and flight. Since your motor you currently have spins so fast ( high kv ), it can't "swing" a long prop without burning up. So be patient and when you find and can afford another motor, get one more like what you need so you don't hurt your plane by using the wrong equipment.
     
  6. Nikhil Rathore

    Nikhil Rathore New Member

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    Ok understood sir but according to calculation minimum take off speed is 51kmph and that is huge so I thought that a faster motor will handle this job. One more question what is prop stall I have heard about wing stall it means the wing loose all it's lift but what is prop stall?
    ACTUALLY MY FATHER IS IN INDIAN AIR FORCE SO HE TOLD ME ABOUT THE MIN TAKE OFF SPEED OF PLANE
    !!AND SORRY FOR ASKING SUCH FOOLISH QUESTIONS!!
     
  7. rdsok

    rdsok Well-Known Member

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    Prop stall is just like wing stall. The difference is a prop is an airfoil that rotates instead of going straight through the air, so when it doesn't get enough air going across it, it stalls ( does not produce thrust ).

    These types of questions you are asking just take time to grasp and understand. There is a big difference in ignorance, stupidity and foolishness.... An ignorant person has yet to learn, a stupid person can not learn and a foolish person will not listen to learn.
     
  8. Nikhil Rathore

    Nikhil Rathore New Member

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    And is it important to have thrust of motor more than the aircraft's weight to fly" for example a ntm propdrive 2836 3000kv with 4.75x4.75 prop on 4s produce 1.4 of thrust will it be enough to fly a 2kg weighted aircraft?
     
  9. rdsok

    rdsok Well-Known Member

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    I don't believe it is enough.... which has been said before.

    That is much to small of a prop to get enough air over that size of a wingspan... not to mention that the width of the fuselage would block air getting to the prop ( if it's a pusher prop ) or getting to the wing if the motor is mounted in front.
     
  10. Smoggie

    Smoggie Well-Known Member

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    Your plane is going to be really hard if not impossible to fly at that weight. Even if you have enough power and thrust it's really far too heavy to be a trainer. The wing loading it up around what you would expect for a racer. I suppose that if you have all the parts then you have nothing to loose in giving it a try but even if you can get it to fly it would fly very fast and be extremely hard to control, the very opposite of what you need for a trainer.

    I think your best plan is to use the building of this plane as valuable experience and now build another using the correct materials and built much lighter.
     
  11. Smoggie

    Smoggie Well-Known Member

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    Virginius E Clark must turning over in his grave to have his airfoil's name so applied :rolleyes:

    Nakhil, your airfoil would probably work ok if the plane was much lighter, but for best performance you should make the radius of the nose of the airfoil much smaller. This is a real Clark-Y airfoil which is a very good airfoil for a trainer, try to aim for a shape like this:
    629358.jpg
    But dont sweat on this too much. For a trainer almost any airfoil will work acceptably well providing the model is light enough. Even flat plate wings work ok.
     
  12. Imzzaudae

    Imzzaudae New Member

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  13. Nikhil Rathore

    Nikhil Rathore New Member

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    For getting off from the ground and to get reasonable climb rate we need static thrust should be at least 1/3 of aircraft's weight and according to a online calculator I got a static thrust of around 2200 grams but according to above rule it should be around 666.6 grams.
     

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  14. Smoggie

    Smoggie Well-Known Member

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    There are a few possible problems:

    • First; you dont actually know what the static thrust is. I'm guessing you are basing your figure on claims for the motor rather than actual measurement?
    • Second; the 1/3rd rule is just a average figure based on a typical model. You model has a much higher wing loading than average so will need to fly much faster so will need more thrust than the average plane.
    • Third; your biggest problem is not thrust but weight. The problem of being overweight cannot be solved by adding more thrust. Even if the plane can be made to fly it will be very hard too fly because it will need to fly so fast, this makes it unsuitable for a trainer.
     
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