Understanding Load Factor
Load factor is a numerical value representing the ratio of lift to weight. Later in this lesson we will look at how to do a simple calculation to determine this number. But first, let’s take a look at what load factor is.
Load factor indicates how much additional force your drone is pushing against to maintain flight, compared to solely hovering in the air. Factors like wind or flight manuevers like sharp turns will increase the load factor.
When your drone is flying straight and level with just its base weight, the load factor is 0. It’s like cruising on a flat road with no extra stress or strain pushing against your car to work harder to move.
On the other hand, when you turn your UA, it banks, or tilts to the side. As the UA banks, the demands and stresses on it increase, making it feel more strained and overloaded. This increased stress is quantified by the load factor, which measures how much more lift the drone needs compared to its normal weight to maintain stable flight.
As the bank angle increases during a turn, the load factor goes up because the drone needs more lift to stay aloft and prevent dropping altitude. The steeper the bank, the more lift is required to counteract the increased force on the drone.
Impacts on Load Factor
Environment: Wind Gusts & Turbulent Air
When flying a drone, gusty winds and turbulence can disrupt smooth airflow around the propellers, causing fluctuations in lift and an increased load factor.
Fluctuating Lift: Sudden changes in airflow from gusts can cause the drone’s lift to fluctuate, making it feel like it’s being pushed up or down unpredictably.
Increased Load Factor: Gusty winds and turbulence cause the load factor to spike, meaning the drone experiences more force on its wings than usual. This extra force can strain the drone’s structure and impact its performance.
Performance and Stability: As the load factor changes, the drone’s stability can suffer. The drone might wobble, lose altitude, or become harder to control, especially with strong or frequent gusts. Turbulent air, due to wind gusts, weather conditions, or obstacles, disrupts the smooth flow of air and exacerbates these issues.
Maneuvers: Steep Climbs & Turns
Steep Climbs: When climbing steeply, the propellers work harder, increasing the load factor and making the drone feel heavier.
Sharp Turns: During sharp turns, the drone banks and the centripetal force increases stress on the propellers, raising the load factor and potentially affecting smoothness and stability.
Payloads: Maximum Load Factor
Every drone is designed with a maximum load factor it can safely handle.
This value represents the highest level of stress that the drone’s structure can withstand without being damaged. The maximum load factor varies depending on the drone’s design, weight, and intended use. It’s an essential limit that operators must not exceed to ensure the drone’s integrity and safety during flight.
Flying a small UA near its maximum allowable weight can lead to shorter endurance, decreased maneuverability, and reduced speed.
Calculating UAS Load Requirements for Turns
To ensure your UAS can handle the forces during a turn, you’ll need to perform a simple calculation involving two key numbers: your UAS’s weight and the load factor from the below FAA chart. This number determines if the drone can handle the turn without exceeding its maximum weight capacity.
The chart, which includes different bank angles (e.g., 30°, 60°, and 80°), provides the load factors you need. On exam day, you’ll receive a printed version of this chart and a calculator. Here’s how to use these resources for your calculation:
FAA Load Factor Chart:
- X-Axis: Bank Angle (degrees) – Displays the angle at which the drone is banked during a turn.
- Y-Axis: Load Factor – Represents the multiple of the drone’s weight that the drone effectively experiences at different angles.
Be Aware: Load Factor Significantly Increases at 45°-50° Bank Angles
The load factor rises sharply around a 45°-50° bank angle.
At these steeper angles, the forces needed to keep the sUAS in the air increase quickly.
Essentially, the sUAS and its components start to feel much heavier. This is because the sUAS needs significantly more lift to maintain altitude while turning, and this need grows rapidly as the bank angle steepens.
Calculation Practice
Question You have Sample questions, above, then more questions here, then Practice questions, then the quiz. Too many question sections ! 🙂
When operating an unmanned airplane, the remote pilot should consider that the load factor on the wings may be increased any time:
A. the CG is shifted rearward to the aft CG limit.
B. the airplane is subjected to maneuvers other than straight-and-level flight.
C. the gross weight is reduced.
B. the airplane is subjected to maneuvers other than straight-and-level flight.
Explanation:
When an unmanned airplane (or any aircraft) is subjected to maneuvers other than straight-and-level flight, such as turns, climbs, or descents, the load factor on the wings increases. This is because these maneuvers require the wings to generate additional lift to counteract the increased gravitational forces acting on the aircraft. As the load factor increases, so does the stress on the wings and other structural components of the aircraft. Therefore, it’s important for remote pilots to consider the effects of load factor when maneuvering the aircraft to ensure safe operation.
Question
The importance and use of performance data to predict the effect on the aircraft’s performance of an sUAS. When operating an unmanned airplane, the remote pilot should consider that the load factor on the wings may be increased any time:
A. the CG is shifted rearward to the aft CG limit. [This wouldn’t increase load factor. If the airplane uses an elevator for pitch, this would actually DECREASE load factor.]
B. the airplane is subjected to maneuvers other than straight and level flight.
C. the gross weight is reduced. [Gross weight reduction would DECREASE load factor.]
Answer: B. the airplane is subjected to maneuvers other than straight and level flight.
Question
The importance and use of performance data to predict the effect on the aircraft’s performance of an sUAS. (Refer to FAA-CT-8080-2H, Figure 2.) If an unmanned airplane weighs 33 pounds, what approximate weight would the airplane structure be required to support during a 30° banked turn while maintaining altitude?
A.34 pounds.
B. 47 pounds.
C. 38 pounds.
Answer: C
[Explanation: In a turn of 30 degrees of bank and while maintaining level flight (no altitude loss because you slightly pitched up), you will have a 1.154 load factor. This means that in this turn you will be feeling like you are pulling 1.154 G’s. 33 pounds x 1.154 = 38.082 pounds.
Practice Quiz
quiz title is Payload Shifts, but that’s not part of this section.
question 4, it’s 57.57 pounds, so wouldn’t it need to support 58? 57 wouldn’t be enough?
question 6 the correct answer isn’t one of the options. It’s 46.41 pounds
