Quadcopter VS Helicopter – Why not Scale Up, Full Size Drone

Comparing Helicopter with Quadcopter

Quadcopters and other multicopters are getting popular in RC hobby and scientific research. One of the main reasons might be the simple mechanical structure.

Regular helicopters have 1 big motor and a small tail motor, while quadcopters have four motors. Many small size quadcopters seem pretty agile and easy to control, in fact they are generally less stable than an helicopters. Quadcopters and other multicopters are also LESS efficient.

helicopter-quadcopter

Can quadcopter be scaled up to carry out tasks like full size helicopters, for transportation for example?

Mechanical Simplicity

On a traditional helicopter the propeller blade spins at a constant speed. Changing thrust is achieved by adjusting the propeller pitch mechanically. This pitch mechanism is complex and expensive. Other movement (e.g. Yaw) is achieved by the small tail rotor.

Roll_Pitch_Yaw

Quadcopters has four motors which uses four fixed pitch propellers. Mechanically this is very simple compared to what the helicopter has. Along with the compact electric motors powered directly by battery, the simplicity makes small size model quadcopters more popular in RC hobby. But when it comes to full size aircraft, things gets more complicated in the  such as whether to have four engines in quadcopter.

Here is a picture of the helicopter blade pitch mechanism.

helicopter-pitch-propeller-change

A small quadcopter motor with its fixed-pitch propeller.

quadcopter-motor-propeller

Stability

Quadcopters are less stable than helicopters. That’s right! They might seem pretty stable in many small hobby models, but that’s the Flight controller and speed controller doing all the stabilization for the pilot. It would be extremely hard to fly a quadcopter without the asistance.

Flight controllers are getting better and better it’s amazing how well it’s working. It leads to the misunderstanding that quadcopters are more stable than helicopters by nature.
For the quadcopter to maintain balance, each individual motors must adjust speed to change thrust. If motors on one side are spinning faster, it will generate more thrusts and the quad will tilt to the other side. Because quadcopter relies on changing the speed of the propellers to make yaw, roll and pitch movements (3 dimension movements), how fast it can change the motor RPM (rotation per minute) determines how agile the quadcopter is.

Apart from the electronic speed controller, this is also very much depends on the inertia of the propellers. As you can imagine, generally the bigger and heavier the props, the harder it is to slow down or speed up. Therefore that contributes to the less agile and unresponsive characteristics of a large quadcopter. Just like stopping a bicycle is easier than stopping a train. :)

Efficiency

As mentioned, when quadcopter is making movements, the rotation speed of the propellers and motors need to change. Helicopters’s varying-pitch propeller mechanism is a more efficient solution, because it takes more energy to slow down / speed up propellers than keeping the motor and propeller at a constant speed.

Basically, to be more controllable and stable, the more frequent the motors change speed, and therefore the less efficient it will get. This is why you don’t get much flight time out of a quadcopter generally.

Finally The larger your rotor disk is, the less energy wasted in moving the mass of air. You also don’t have air flow interference from adjacent rotors / propellers in helicopters. This is why long flight time quads tend to use large propellers. (But again, they are less agile)

Safety

When disaster happens such as loss of power or motor failure, quadcopters might spin around or flip sideway, because the quadcopter can only be balanced effectively when all four motors are working. On the other hand, helicopters tend to just glide down to the ground vertically.

Conclusion

Although quadcopters are less stable and efficient than helicopters, they are more suitable to be made in small form factor. they are more mechanically simple and also cheaper to make. When they are scaled up, the disadvantage becomes more significant too.

13 thoughts on “Quadcopter VS Helicopter – Why not Scale Up, Full Size Drone

  1. Rohan

    What will happened if 2 propeller are placed in right angle to any 2 propeller out of 4 propeller of quad copters.
    Like 🚁 helicopter but in such a way so it will push or pull coming air.

    Reply
  2. Oliver Thompson-Yates

    Full scale helicopters DO NOT have a smaller motor to drive the tail, the tails are shaft driven.

    Reply
  3. vicky loknar

    as i consier, if we use the fan blade type structure on front side of the drone and when the drone moves forward it automatically rotates the fan blades and the energy produced by the rotation( just like our wind turbine energy ) is used to charged the batteries………what u say guys

    Reply
    1. Oscar Post author

      that’s just resistance and it would slow down the drone, to go at the same speed you will have to go faster and use more energy in the end, as the regenerative energy efficiency is lower than 100%.

      Reply
  4. xxx

    The efficiency argument / reasoning maybe true in other respect but I don’t buy the acceleration/deceleration argument in relation to efficiency. Surely acceleration needs energy but that energy is not lost, instead it is stored in the rotor as kinetic energy . And it is not lost in deceleration like in a car, it is not like there were brakes to convert the rotational energy to heat.

    Reply
  5. Adigo

    Aditionally the larger rotor is more fuel-efficient. A heli lave cca 35% more flight-time! Lust because the propellers are larger (you know: more grams/W the larger the propeller is)

    Reply
  6. Ilia

    Nice article!

    I still can’t understand how big quadrocopters builders for human transportation sole problem with autorotation. One of four engines fail – you are dead. Helicopter has advantage: if engine fail you can land easily (I did it in R44 by myself!).
    Why nobody is looking for that problem and building E-hangs and other big quads?

    Reply
    1. jairaj shetty

      E-hang will never see commercial deployment. Rather a helium filled UFO type things with passengers dangling like fruits would be the air taxi of the future. You see , everything is gentle here. you crash gently, you move slowly etc. Did I hear “woah thats so safe here ” ?

      Reply
  7. Dave

    You would not have to rely sole on batteries for a scaled-up quad to replace a helicopter. A small gas engine would run a generator to charge the systems batteries like how train engines work. Also, to make it safer you would want six or eight motors so if one fails it’s not a lost issue. The nice thing you can do with it is install a ballistic chute system because the blades could be out far enough so as not to interfere with the chute. It has been tried many times on helicopters and even so far as using ballistic bolts that hold the rotor on to try jettison the rotor, so the ballistic chute could deploy. Personally, I think it is the way it will end up going. Also pound for pound the multi rotor can lift much more.

    Reply
  8. Ben

    Respectfully disagree. Helicopters have how many moving parts versus 4 moving parts in a quadcopter? The controllers are getting better and so is the battery technology. No it will not be perfect but way less variables. Also, training time and ease of use and when you get autonomy… This, folks, is the future. Probably not quads but definitely multirotor.

    Reply
  9. Bruce Tuggle

    Like all newer technology, something else will show up. So, it may not be a quad, maybe the main rotor will be mounted on top like the helicopter, and the stabilizer blade will be two on the sides or front/back or over the main blade, or none at all. Since it hasn’t happened yet, it is anybody’s guess.

    Reply
  10. Brian

    Well done, I appreciate your explanation.
    It’s interesting to see folks like Larry Page are still bullish on the idea despite greater chance of catastrophic failure, lack of efficiency, battery limitations, etc. Perhaps it’s just about hype or maybe they see enough upside given the relative simplicity and cost-savings potential of a scaled-up multi-rotor.

    Reply
  11. ALFALFASPROUT69

    Amazing write up, and really cleared up my question.. I guess we may never really see full size Quadcopters.

    Reply

Leave a Reply

Your email address will not be published. Required fields are marked *

For prompt technical support, please use our forum IntoFPV.com. I check blog comments weekly.