The use of small drones for FPV and autonomous mapping is becoming more and more popular, especially as the popularity of FPV drones and the availability of parts increase. This article discusses several considerations regarding whether an aircraft is suitable for use as a drone and, if so, how to choose the right type.
Multicopter vs Airplane
What advantages can an airplane offer over a multicopter? While a multicopter is great for fun FPV/autonomous flight, its payload and flight time are still limited because the rotors must be constantly spinning (and thus expending energy) to fight gravity and keep the drone in the air. Airplanes, on the other hand, use their wings to create lift. So which type is best? Apart from the electronics such as transmitter, receiver, FPV equipment, flight controller, the following features seem to be the most relevant to answer the question:
- Capable of taking off and landing vertically, as well as hovering in place.
- They don’t require a lot of space to fly and are essentially “omni-directional” capable of changing direction and speed very quickly.
- The thrust generated by the propellers is what keeps the ship in the air.
- Less intuitive in flight given that the craft can change orientation and fly in almost any direction, and gimbals can easily cause disorientation.
- “Medium sized” multicopters ranging from 400mm to 600mm in diameter are the most common and typically cost between US$200 and US$1,000 for a (configured) ready-to-fly rig.
- Despite the fact that multicopters have significantly fewer moving parts than helicopters, almost any malfunction of the quadcopter leads to an accident.
- Launched by hand, runway or catapult and usually lands on relatively flat grass or runway.
- A large open space is required to fly, as the maneuverability of the aircraft is limited (i.e. always moving forward).
- Wings create lift.
- Higher load capacity.
- Foam models can be forgiving in the event of an accident and most can be restored/repaired.
- Models with a wingspan of 500mm to 1.8m are the most common for hobby use, and a complete set typically costs between US$200 and US$1,000.
- In the event of an engine failure, it is still possible to land without damaging the aircraft.
VTOL (vertical takeoff and landing)
- Designs include wings and propellers (not many commercial/production products at the moment).
- The controls are still quite difficult to transition from vertical to horizontal flight.
- Designs are very different from winged quadcopters or using/extending the support arms (arms) of a drone to include wing profiles.
- Will not be discussed further in this article.
- Launch location: Due to the ever-present possibility of causing injury or damage to persons or property, UAVs/UAVs are prohibited from being launched over buildings, in densely populated areas or in crowded areas. Airplanes ideally require large open areas, while multicopters can be operated in more limited spaces. If you don’t have open space to fly, it’s best to use a small multicopter.
- Application: A multicopter is more than ever suitable for aerial photography / FPV. Cartography and long-range flights are best done by aircraft.
- Interest: This should be one of the biggest considerations when choosing one type of drone more than another.
- Budget: The most common multicopter (500mm) is likely to be slightly more expensive than a comparable aircraft (with a ≈1.5m wingspan), but not by much. How prepared are you to lose the drone due to a sudden crash or loss of control causing it to fly out of control?
- Flight time: An average mid-sized quadcopter will stay in the air for 10–15 minutes (although some manufacturers may increase this time to 30–40 minutes), while an average mid-sized electric aircraft will provide about 20–60 minutes + minutes at ” normal use (i.e. not full throttle), but in both cases there are many different factors to consider.
- Flight controller: Not all controllers are capable of controlling all types of aircraft. Before choosing one of the many, make sure that the type of aircraft you are interested in is supported by the flight controller (if you intended to use one). How to set up the flight controller will not be considered in this article.
Common Types of UAV/Drone Wing
There are many different airframes used to build drones, but some designs are much more common than others. As more and more manufacturers start producing custom aero frames for standalone use, unnecessary details such as cockpit layouts that were commonly found on RC planes in the past are disappearing.
Delta Wing (Delta Wing / Flying Wing)
The flying wing is by far the simplest (and possibly the most popular) design. A simple/rudimentary frame can be made using inexpensive expanded polypropylene foam (EPP) and a basic Klein-Fogleman (Kline-Fogleman or KFm) airfoil. They classically have only two control surfaces, which means that all turns are rolled. The propeller is usually at the back (which allows the camera to be mounted from the front), but it flies just the same with the motor located in the center or in the front, provided the center of gravity is correct. An excellent design for its simplicity and tends to fly at high speeds.
If you want to stay in the air for as long as possible (i.e. the longest flight time), this design is the best choice. It typically has a medium to high wing, and the tail is often T or V shaped. All of the frames shown here can be used for fun flying (or more), however if you want to keep your drone in the air for as long as possible you need to consider a large winged aircraft and this is where gliders excel. They are not designed to be the fastest (rather the slowest) and carry the largest payload (they should be as light as possible), but a good design can stay in the air for many hours. Almost all propellers are mounted on the front, so in cases where a camera is required, it is usually mounted on the bottom/belly of the fuselage.
The design is built on a pusher power plant, the propeller of which is installed just behind the wings, and the tail support, so as not to interfere, is located a little lower. The wing is usually trapezoidal or rectangular. An alternative design uses two beams (one on each side of the propeller, “Twin Boom” type) to support the tail. For the size of the fuselage, the design is a compromise between a large winged glider and a conventional aircraft. The fact that the main rotor is at the rear means that the front can be equipped with a camera (unobstructed view). The sufficiently high rotor position facilitates manual launching, and the propeller in a normal landing (with or without landing gear) will never touch the ground. Such designs are generally good for maximum payload, decent speed and flight time, and offer the most versatility.
Conventional RC aircraft are still frequently repurposed for use as drones, with designs ranging from Mustangs (Sport) to Piper Cubs (Trainer). Almost all have a front mounted propeller (puller or puller). The wings usually have a straight leading/trailing edge (rectangular), but for fighter aircraft copies the wing may be more trapezoidal. Such designs are most commonly used because they are the most common and easily available RC aircraft. Unfortunately, the aircraft are not suitable for modification and include aesthetic elements that are not needed when used as a UAV. In addition, this is not the most convenient design in terms of choosing an unobstructed place to install the camera. Most are based on a tree that does not forgive accidents.
Several custom designs are available, one of which is the “Drak” (almost inverted delta). This particular design has wings in an almost forward swept position, and a propeller at the rear. The advantages and disadvantages vary depending on the model, although their unique appearance often attracts a lot of attention.
So how big should your plane be? A criterion that predetermines the future mode of transportation, which is often referred to even before application. Planes are (almost) always larger than multicopters, and since the space you plan to fly may not be near your home or business, transportation will most often need to be done by car. Because of this, the frame size for this type of drone tends to be limited to 2 meters (wing span), and in most cases the wings must be removable. If the flying wing cannot have detachable wings, then the span will be less than 1.2 meters so that they can be easily placed on the back seat of the vehicle. Classically, standard size RC planes have a wingspan of 0.5 – 2m, so the availability of parts for this size (motor, ESC, battery, servos, etc.) is very good.
The second question you could ask yourself is how long the plane should stay in the air. If you are planning to remote control an aircraft, it is worth considering that after about 20–30 minutes of flying, most people get tired physically/mentally and try to complete the flight. For long-term flights, it is recommended to consider a glider with a wingspan of at least 2 meters (with a small payload).
And the third consideration, of course, is the potential application. In the list of common ones: FPV flight, mapping, as well as fully autonomous flight using sensors. For autonomous flight, you need a flight controller with GPS, and it is also possible to add sensors.
Designing a custom aircraft is rarely a priority for those who just want to get airborne for FPV or autonomous flight, as it usually requires either serious research or relevant knowledge of aerodynamics. For this reason, frames designed specifically for FPV/UAV are becoming more and more popular. However, given the widespread popularity of conventional RC aircraft, many enthusiasts are still turning to existing RC models (not necessarily scale models) and adapting them for FPV/offline use.
RTF (Ready to Fly) — such a kit includes everything you need to use the product for its intended purpose, and, as a rule, it includes a fully assembled frame (wings can be dismantled for a more compact delivery) with pre-installed working stuffing (motor, ESC, servos, flaps etc.), as well as transmitter and receiver, battery and charger. Usually you connect the fuselage to the wing (or wings), charge, install and connect the battery, and you are ready to fly. This is the fastest way to get into the air, but at the same time, such kits do not allow a subsequent upgrade.
BNF (Bind and Fly) – the drone is delivered almost completely assembled (wings can be dismantled for a more compact delivery). The kit does not include a receiver/transmitter. The assembly is very fast considering that all parts are already mounted/assembled. You will need to connect the receiver to the servos and power plant, install the battery and check the CG (Center of Gravity / Center of Gravity), and then go through the pre-flight launch checklist, calibrate. Please note that you may need to adjust your control equipment for this UAV model. This is the second fastest way to get airborne.
PNF (Plug and Fly) — the aircraft is mostly fully assembled (wings can be dismantled for a more compact delivery). The kit includes ESC, propellers and servos. Kit does not include transmitter, receiver, battery or charger. It will be necessary to connect the receiver to the servos and power plant, select and install the battery (check CG), and then go through the pre-flight start-up checklist, calibrate. Please note that you may need to adjust your control equipment for this UAV model.
PNP (Plug and Play) – same as PNF kit.
ARF (Almost Ready to Fly) — products in this configuration usually include a frame and some hardware. Supplied partially assembled with virtually all parts/components of the frame needed to assemble it. Some bonding may be required. The user needs to choose their own transmitter, receiver, motor, ESC, propeller and servos as they are not included.
KIT — These days KIT planes include build plans, but it will be a long time before a plane is worth flying. It is recommended that you have some piloting experience before flying a KIT aircraft, as one crash (usually on the first flight) can result in many hours of UAV recovery.
DIY (Do It Yourself / DIY or built from scratch) — which, speaking of aircraft, usually means a completely non-standard design, which, perhaps, was designed by the pilot. It is usually necessary for the designer to select all suitable components, and assembly is often a trial and error process.
There are many different materials used to build the frame, wings and tail of RC Aircraft/Drones. While manned aircraft often use fiberglass, aluminum, and even carbon fiber, drone manufacturers have yet to use these materials in small craft. Below are the most common materials you will find in the industry:
EPO (Expanded PolyOlefin) This type of foam is lighter, stiffer and more durable than expanded polystyrene (EPS). In the manufacture of molds allows you to achieve a fairly smooth surface. In the event of an accident, such foam is compressed, and if the force is excessive, the weakest points will be subject to destruction. As a rule, parts made of EPO remain intact, and if the accident is not serious, the affected elements can be subsequently glued.
EPP (Expanded PolyPropylene) — This type of foam is flexible and resilient, and although slightly heavier than EPO, it is virtually indestructible (for practical purposes).
EPS (Expanded PolyStyrene/Expanded Polystyrene) – This type of foam is commonly used as a packaging material for televisions, electrical appliances, in the manufacture of helmets, inside ice boxes, and for road and home construction. EPS contains about 95–98% air.
Balsa Wood (Balsa, balsa, balsa wood, chrome) – In the past, most RC aircraft used balsa as their base material. It is an incredibly light yet remarkably tough and easy to work wood, ideal for frames, wings and tails. Incredible care and time must be invested during construction, and even the slightest impact can cause serious damage to the frame (more serious crashes result in complete destruction).
blown plastic The plastic blow molding process involves a closed die into which semi-molten plastic is blown and then cooled to retain its shape. The output is a solid hollow shell. Blow molded plastic is most often used to create the fuselage (as opposed to the wings), after manufacturing, the user must make the appropriate cutouts. Blow molds/parts may also include pre-cut balsa as reinforcement. Blow molded plastic can withstand small force impacts and tends to dent rather than shatter.
Vacuum plastic (Vacuumed Plastic) — the process of vacuum forming sheets involves heating a thin plastic sheet to such an extent that it becomes flexible, but not completely melted, and placing it on a male matrix; as long as it remains flexible, the air between the die and the sheet is removed (i.e. deflated), which causes the sheet to take its shape. The plastic cools down and a three-dimensional shape is carved out of the surrounding material. There are many different types of plastics that can be vacuum formed and their properties can vary. Polycarbonate is a good compromise between weight and impact resistance.
Corrugated Plastic – while few aircraft use it for the fuselage or wings, it is often used to stiffen doors or where flat surfaces are required. Corrugated plastic looks like corrugated cardboard, but is made of plastic. It is very crash and impact resistant, easy to work with without any special tools and very smooth (aerodynamic).
What material is better?
So what material to choose for the aircraft? The vast majority of the FPV community uses EPO foam because:
- Compared to balsa, it takes exponentially less time to assemble, and therefore rises into the air faster.
- Relatively light compared to other materials and decently stiff*and at the same time can be easily modified / cut.
- “Forgiving”, in the sense that it is able to withstand accidents and low-strength impacts, and can also be re-glued many times; and fly again.
- Good quality; Foam models are quite expensive, as the designer needs to offset the cost of construction, prototypes, and mold, and the cost of the frame is usually proportional to its size.
- Does not require the use of special tools such as a heated laminating iron.
- Most complete frames include the basic components required (balsa models often require additional purchase of overlaminate, most hardware, and more).
* Foam models are rarely stiff enough on their own, and in order to withstand the forces exerted on the wings in flight, the latter require additional reinforcement in the form of “spars” (long and thin rods, usually made of fiberglass or carbon fiber) to increase rigidity. These spars usually need to be glued in various strategic places, both above and below the wing (glued into pre-cut channels). The size of foam models tends to limit only practicality, which is why it is quite rare to see models with a wingspan of more than 2m.
- Foam: It is important to note that not every adhesive can be used to glue foam, as some of the existing ones can corrode and destroy the material. The most common adhesives used to bond EPO foam are “Goop” (brand name) and “Gorilla Glue” (brand name). Goop is clear and has a thick consistency as well as excellent bonding. Gorilla Glue — requires a little water to activate, the initial consistency is thick. After contact with water, it foams up to about 400% of its original size and has a yellow color. Gorilla glue can be cut off in places where it is not desired, but it is necessary to prevent the glue from leaking into areas where it should not be (for example, using masking tape), and after application, the parts to be fastened must be motionless while the glue expands and hardens. The foam is usually cut with a sharp knife, a soldering gun (as opposed to a soldering iron), or a heated wire. A hand saw tends to tear the foam and leave a very rough surface. Foam planes are more often white, rarely black, and even less often gray or other colors. Customizing the appearance consists of adding color or patterns that can be done using special paint, laminate or vinyl. Please note that not all paints are suitable for painting foam, some can destroy it.
- Balsa: Cyanoacrylate glue is most often used to bond balsa wood — usually a viscous liquid (almost like water), provides a very strong bond between the glued surfaces. Once the frame is ready, it needs to be laminated (a plastic sheet with heat-activated adhesive on one side) to create an aerodynamic surface. The laminating film is heated/applied with a laminating iron, resulting in a dense/hard surface. Laminate is only suitable for gluing to balsa wood — it cannot be used to create three-dimensional shapes.
- Composites: it is still rare to see composite materials used to build small aircraft (carbon fiber). These parts are epoxy based (or a special bonding agent) and are more difficult to cut by hand, often requiring a CNC router. Creating 3D shapes is also quite a complex process. Typically, aircraft use composites for reinforcement.
- The aircraft power plant consists of a motor, a propeller (propeller), an ESC and a battery. Choosing the right parts for a frame shouldn’t be a “guess” and it’s best to see if the frame manufacturer has any recommendations for motor, propeller or range for a given payload.
- These days, most enthusiasts lean towards electric motors over fuels (such as kerosene) due to the lowest cost of ownership and ease of use. Solar energy is rarely used because the power that solar provides, compared to the added weight of solar panels (which are used to charge batteries), is still not profitable.
- Choose a motor/propeller combination capable of providing the required thrust for your airframe, which has a specific load. Some airframe manufacturers offer a number of ideas about thrust requirements based on their own experiments, which should give a general idea of the required range.
- Insufficient power to the aircraft can cause it to become unstable or crash. An overloaded aircraft can be completely unstable in flight. Considering that almost all of the technology used to build drones comes from the radio control industry, there is ample information available on choosing the right thrust and servos for various applications.
- Center of Mass: The center of mass is the point around which the frame can be placed so that the weight is the same on all sides. Center of lift/momentum factor. This is the point where all the lift generated by the wings and control surfaces is summed up, usually at the highest point in the airfoil. It is desirable that the center of mass corresponds to the center of lift.
- Runway launch/landing: To use a runway, a drone needs wheels, and the runway needs to be as flat and perfectly paved as possible.
- Manual start: There are two main types of hand launches: underhand or overhead. The swing method is similar to launching a disc (or throwing rocks across the water) where the operator is trying to get the drone up to its maximum speed using angular velocity. Alternatively, there is an overhead method where the operator launches the aircraft up (best to have a second operator/assistant do this).
- Launch by catapult: To accelerate the drone as quickly as possible, the catapult uses one of several different methods: a woven rubber cable (bungee cable / bandy), a winch, or even compressed air. Catapults are not easy to transport and require additional investment and diagnostics.
- Hand grip: catching a small drone by hand is not difficult, provided that the propeller does not rotate, but, anyway, the method requires some skill.
- Landing: The most commonly used landing method is skid landing on a fairly level surface such as grass. This method is relevant because fewer and fewer drones have landing gear (and the runway is inaccessible), forcing the aircraft to simply land on any possible plane. Usually before the flight, the pilot finds a suitable place to land. Ideally the aircraft should have replaceable skid plates due to gradual wear.
- Network “capture”: Although this landing method is most often used by the military for small drones, the use of a net to catch a drone is very effective where other landing methods are difficult. That being said, setting up a networked system takes time, and for most enthusiasts, it is preferable to use other types of fit.