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3 Answers

Confusion about load factor

Asked by: 2218 views Aerodynamics

When we talk about load factor and limit load factors, are we only referring to stresses in the vertical axis? Does the aircraft experience any side-loading during flight that a pilot should be concerned about? 

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3 Answers



  1. RobA61 on Jul 26, 2020

    The biggest side-loading issue to worry about is when you’re on the ground. Crosswind takeoffs/landings performed improperly or taxiing too fast in turns can add too much side-load to the aircraft. In flight, vertical load limits come into play because gravity and weight act in the vertical direction. If you accelerate too much in the vertical (against gravity) you may exceed load limits (excess force). There isn’t a force acting against the acceleration in the horizontal per-se (such as gravity does in the vertical)

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  2. Mark Kolber on Jul 28, 2020

    I would go with load factor having a very specific FAA definition, right from FAR 1.1:

    “Load factor means the ratio of a specified load to the total weight of the aircraft. The specified load is expressed in terms of any of the following: aerodynamic forces, inertia forces, or ground or water reactions.”

    Whole the definition might suggest more, as used in just about every aeronautical text I am familiar with, it’s actual usage is lift vs weight. Side load obviously imparts a “load” and it’s definitely a “factor”, but I have not seen the term used that way.

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  3. Brian on Sep 08, 2020

    “When we talk about load factor and limit load factors, are we only referring to stresses in the vertical axis?“

    No, load factor is associated and tested for on all axis as per part 23 and 25. However, the axis most referred to by pilots is the longitudinal (Pitch).

    Limit load factor is a point that, if exceeded, could result in deformation, bending, etc. but, will not break. Separation of parts occurs at ultimate load factor. And the Vn, Vg, or whatever it’s called this week (also found in part 23/25 for pitch limit load testing) refers to pitch limitations relative to speed. When can you be aggressive, when should you be gentle? This diagram explains when. *This diagram is subject to the same limitations as Va: New Airframe, Coordinated Pull/Push, and Progressive test.

    “Does the aircraft experience any side-loading during flight…”

    A great deal. It’s even caused accidents. Think rapid alternating use of rudder while changing pitch…tail falls off. Side loads can be imposed that break the airplane. Mother Nature on a typical day won’t cause side loading sufficient to damage the aircraft if it were flying along pilotless. Pilots on the other hand…just ask any mechanic about pilots ability to discover ways to break things that nobody could have possibly imagined. 🙂

    “…that a pilot should be concerned about?”

    Quite a few things, but here is a short list:

    Knowing that Va and the Vn diagram are a symmetrical and progressive stress tests performed on a brand new aircraft. If you’re banking, uncoordinated, or snap pull (sharp wrist motion used to snap stall an aircraft) then Va does not protect you from tearing off parts. So bring spares if you’re in doubt.

    Rudder tests are a single full scale deflection in one direction. Deliberate full extension and rapid left/right is not tested, especially if coupled with pitch changes. Remember, roll wings level and yoke held firmly in a neutral (trimmed) position. Ride the waves and keep the greedy side down.

    There is much to learn from these 3 questions. Well asked and please check out Aerodynamics for Naval Aviators (AFNA) Chapter 4 on stability. It will give you loads more questions and answers.

    Good day and great to see so many still around here posting. Hope all are well as we navigate this uncharted terrain!

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