Types of Drone Airframes for Surveyors
There are three main types of survey drone airframes: small multi-rotors, large multi-rotors, and fixed-wings. Multi-rotors fly like helicopters: they take off and land vertically, can hover in place and make sharp right-angle turns. Fixed-wings fly more like airplanes, taking off and landing at a slope, needing to fly faster to stay aloft, and making large swooping turns. All three types are capable of being used as part of a drone survey program – with the right Standard Operating Procedures and data processing workflow – to produce final survey linework at 0.1’ vertical accuracy.
Small Multi-Rotor Airframes
Small multi-rotors weigh less than 5 pounds and are less than 1.5 feet in diameter. They usually have a built-in camera and are often sold as “pro-sumer,” or, in other words, high-end consumer or entry-level professional grade.
The biggest benefit of small multi-rotor drones is their simplicity. They are designed to be easy to use, but, more importantly, they are easy for staff to use on every project with minimal extra work. Small multi-rotors are also usually the most reliable airframes. Because their manufacturers are producing these drones at a large scale, they have been able to identify and resolve flaws that more boutique manufacturers often struggle with. For similar reasons, small multi-rotors are inexpensive. Using a low-cost drone means it’s less of a burden on the business, causing less pressure to maximize how much the drone is used, and making it easier to scale up the benefit to potentially even put one in every truck.
The primary drawback is a lack of flexibility. They are usually built as closed systems, and are not designed to swap out sensors or other components. Small multi-rotors are best considered as a specific tool for a specific job, rather than a “Swiss Army Knife.”
For most surveyors doing topographic or planimetric survey work, a small multi-rotor is going to be the right airframe choice. This is particularly true for surveyors just starting their drone program, or for larger companies looking to scale the benefits of drones to several teams. The drones’ low cost, ease of use, and reliability make them an excellent choice.
Large Multi-Rotor Airframes
Large multi-rotors usually weigh over 10 pounds and are 3 feet in diameter. They require some setup or assembly in the field due to their large size and, therefore, generally require more expertise to use effectively.
The two main benefits of large multi-rotors are their flexibility and increased range. Most large multi-rotors are designed to be able to carry a variety of sensors, meaning the sensor can be swapped out based on the specific needs of a job. Depending on the payload weight and power requirements, they also may have a larger range.
The main drawback of large multi-rotors is their reliability. These are more complex systems and are intrinsically more likely to have things go wrong. They require fairly complex custom building, and setup in the field is more complex as well. Given that the primary benefit of drones for most surveyors is time-savings – by enabling them to create linework faster in the office using drone-collected 3D models – any time the drone cannot be used on a job due to maintenance is negating that time-savings benefit. Particularly, if a third-party camera is used, the custom integration required is likely to cause challenges.
In addition, the range benefit of a larger multi-rotor can easily be negated if a larger sensor payload is used. Large multi-rotor airframes are also substantially more expensive than small multi-rotors – usually a minimum of five times the price when packaged with the sensor and support gear needed.
Large multi-rotors can be very beneficial for special-use-cases. For survey teams that are very experienced with the nuances of drone technology and frequently require the use of specialized sensors for unique project types, they are often the best choice.
Fixed-wing drones are typically about 3 feet in wingspan and can often be very light due to being constructed out of dense foam.
The primary benefit of fixed-wing airframes is their range. They are inherently much more efficient fliers than multi-rotors, and can fly for a longer time before requiring a battery change. For projects larger than 50 acres requiring good accuracy, this benefit can be substantial, as using a multi-rotor would often require so many battery swaps that they become inefficient.
Unfortunately, this benefit is usually negated by regulations. Today, it is required that a drone pilot actively watches the drone the entire time it’s flying. This is essential to avoid situations like emergency aircraft flying through. In most situations, operators will not be able to maintain line of sight for 50 acres, meaning they can’t take advantage of the entire range benefit of fixed-wing airframes.
In addition to this, fixed-wing aircraft have a handful of substantial drawbacks. The requirements to program take-off and landing patterns means that using the drone on projects is fairly complex. In addition, they tend to have short lifespans because they belly-land. They don’t have landing gear like an airplane, and instead just slide on their belly, which means they can quickly wear down.
Unlike multi-rotors, fixed-wing airframes must maintain a minimum speed to stay aloft. This means they have to fly high to minimize motion blur. And whereas most multi-rotors carry their sensor on a gimbal, which allows the camera to remain pointed straight down even as the drone turns or fights the wind, fixed-wings usually cannot carry a gimbal, which causes a higher frequency of unusable data due to blur or off-centered photos. Finally, fixed-wing airframes are quite expensive – usually twice the price of large multi-rotors with the sensor and support gear required.
For firms that regularly do very large survey projects of hundreds of acres or more and are rather proficient with drone operations, a fixed-wing aircraft may be the right choice. Working to get special waivers from the Federal Aviation Administration or using visual observers to effectively extend range of sight can help mitigate the line of sight limitations.
Choosing the Right Tool for the Job
There is no one right answer for every surveyor. For companies that are just starting out, a small multi-rotor is always our recommendation. Even for experienced firms, the small multi-rotor is likely to be their workhorse due to its simplicity and reliability. For firms that are very proficient with drone operations and have needs for specialized sensors, a large multi-rotor is a good investment to be used as a specialized tool. For experienced firms that do a lot of very large projects, a fixed-wing aircraft is a good choice.
Ultimately, when it comes to unmanned aerial systems, it’s up to each surveyor to choose the right tool or mix of tools for their business and types of projects.