Safety
It is believed by some that multirotor designs are the safer of the two options when it comes to flying around talent. The thinking being that the lesser of two evils is to be injured by 8 high rpm steak knives versus 2 medium rpm swords. This is a debate that has no real purpose. Both designs must be treated with the same respect when flown near people and property. To carry an equivalent weight camera package, both would have similar total weight and so would carry the same kinetic energy upon impact. If the risk advantage goes to the multirotor, due to less rotating mass, then the advantage goes to the single rotor platform in the event of a drive power failure due to this designs ability to still be guided during autorotation. Once again, such comparisons are pointless and safety must come from - the experience of the operator, the maintenance practices for the equipment, and well thought out risk mitigation planning for every shot.
The rig in the video below weighs approximately 20 lbs. and lost control with considerable force.
Vibration and Stability
A very common question is - which design provides smoother, steadier images? First let's discuss vibration. Further, lets define vibration as movement at fixed or semi periodic intervals (aka frequencies). In general it is a much simpler task to balance motors and fixed pitch propellers than drive shafts, gears and variable pitch rotors. This, more than any other reason, is why there are so few companies that can provide ultra smooth video from a single rotor machine. It is a very difficult undertaking that very few have all the technical/mechanical skills (and patience) to master. Can a single rotor design be built and balanced to the same relative vibration levels as a multirotor? Absolutely! The vibration frequency ranges are very different but in the end, if both are designed, built and balanced to exacting tolerances, the final product can be, for all intents and purposes, identical.
Regarding stability, there are two different, yet connected components that drive overall stability - one is the aircraft itself, with the second being the camera mount. If both operate smooth and stable, beautifully clean images result. If either is unstable, the other must absorb or dampen the unwanted motion. A perfect example is the current development of direct drive camera gimbals. These devices have both the speed and resolution to hide a multitude of sins being emanated from the aircraft airframe. Obviously, the smoother the airframe the better for camera and component life.
Within the next 12-24 months, it is reasonable to expect that a camera gimbal will be available that will provide near Cineflex quality for 10 -15 lb. cameras at a cost that is manageable for both top tier operators and insurance providers. This technology is already available for smaller cameras.
Flight Performance
In calm conditions, the flight performance is similar between the two arrangements. With electronic stability augmentation to assist the pilot, both have similar capabilities. In windy conditions however, the single rotor design wins hands down. This is due to the fact that a collective pitch rotor system is far more powerful and responsive to attitude changes when compared to multiple fixed pitch rotors. Think of this as driving a six speed performance sedan compared to a compact car with only third gear available. On top of this, the rotating mass of the larger rotors provides considerably more aerodynamic and gyroscopic stability than multirotors do. In general it is better to have an airframe/camera that never suffered from unwanted movement than one that did and had to have said movement removed through a correction in position.
Another significant difference is flying or descending at high speeds (above 55 mph) such as vehicle chase scenes. This is, once again, due to the advantages offered by a collective pitch rotor system used in single rotor designs over fixed pitch propellers on multicopters. A single rotor helicopter can descend at extremely high rates while still maintaining full control and camera stability. This is made possible because the helicopter is being flown rapidly downward using collective pitch with power verses simply falling through its own downwash which usually results in unstable/unusable footage.
The next area, and this one is perhaps the most significant one, is pilot orientation. This factor alone is perhaps the biggest single reason that single rotor designs continue to dominate close range aerial filming in big budget feature films. It is not a major problem to clearly differentiate the nose from the tail at significant distances with a single rotor; Not so with symmetrical shaped airframes. To get around this limitation, multirotor designs rely on flight control systems with complex flight algorithms and GPS return to home features. The problem here is currently these systems are frequently subject to malfunction, and this is the last thing one would want when carrying $50K + of camera kit/glass. Flying first person view (FPV) and navigation lighting are workarounds for the orientation issue however, at present, all indications are that FPV mode of flight will be prohibited or very heavily regulated in the future and will only be permitted in unpopulated areas. First and foremost is to only use a pilot with years of the right kind of experience and one that can fly well without reliance on autopilots .
One area where the multicopter does have a very significant advantage is yaw axis stability. A single rotor helicopter must have a perfectly tuned anti-torque system that immediately and accurately corrects for even the slightest change in applied motor torque. It must also be fast and accurate enough to correct for wind gusts at every possible angle. Since multirotors control of the yaw axis is by varying motor torque through an opposing number of motors, this is a much less of an issue for this design. For a single rotor design, much of this limitation can be reduced by having the camera gimbal automatically correct for sudden movements in the yaw axis using stabilization devices.
A multirotor is also significantly less risky to launch and retrieve by hand than a single rotor helicopter. This can open up numerous opportunities to obtain shots in very tight spaces and difficult terrain.
As is often said "there is a perfect tool for every job" and this certainly applies to aerial cinematography.
Cost
For most, making movies is a business endeavor, and so cost will always be a prime consideration. Currently the cost to build a rig capable of effectively carrying a Red Epic using a multiotor is roughly twice the cost of a single rotor design. You don't need to be a CPA to know that a lower initial investment, and the associated lower insurance costs, can result in a lower day rate being charged to the producer. This gap will likely narrow in the future, but for now, this is the current state.
