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The following question is from the FAA PAR (Private Pilot, Airplane) exam :

The load factor on an airplane increases with :

(A) Any moderate change in pitch attitude, increase in weight, and steep turns.

(B) Increase in weight, an increase in power, and any moderate pitch changes.

(C) Increase in weight, steep turns, and abrupt changes in airplane attitude.

The correct answer is supposed to be (C).

All of the answers say that load factor increases with an increase in weight. However, load factor is inversely proportional to weight by definition.

What am I misunderstanding?

Edit: I think it is supposed to say "load" instead of "load factor" but it was not written that way.

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  • $\begingroup$ Weight is the force on a mass from acceleration. The aircraft mass is constant, so if the weight increases, it must be from an increase in acceleration. Load factor is the ratio between normal acceleration and gravitational acceleration, hence weight goes up with load factor. What surprises me is that the FAA does not confuse weight with mass, as they usually do in those exams. $\endgroup$
    – Peter Kämpf
    Commented May 7, 2019 at 10:47
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    $\begingroup$ @PeterKämpf The weight of an airplane does not change (appreciably) during flight maneuvers (e.g. steep turns). It is the force due to gravity, not the force due to acceleration. The load factor is 2g in a constant altitude 60 degree turn, so the pilot feels twice as heavy. However, his weight has not actually increased. $\endgroup$
    – simple jack
    Commented May 7, 2019 at 17:16
  • $\begingroup$ You are confusing weight with mass. What's your weight on the lunar surface? $\endgroup$
    – Peter Kämpf
    Commented May 8, 2019 at 15:28
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    $\begingroup$ No I’m not. I think you are confusing fictitious forces with weight. Are you saying that an airplane in a coordinated 60 degree constant-altitude turn literally becomes twice as heavy? $\endgroup$
    – simple jack
    Commented May 8, 2019 at 19:54
  • $\begingroup$ Yes, it has twice the weight and therefore needs twice the lift. Mass will stay constant, though. Which unit do you use for weight, and which for mass? $\endgroup$
    – Peter Kämpf
    Commented May 8, 2019 at 21:33

2 Answers 2

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I agree that this can be confusing.

The load factor is indeed inversely proportional to weight, unlike the load factor on an aeroplane, which might be thought of as the lift required divided by the certified MTOW for the category of operation (g limit). If the aircraft is in a steady 1 g flight at MTOW, the load factor to achieve this is one. Start turning in a steep bank and the load factor becomes two in relation to the design load factor of the aeroplane's structure. If you then reduce the weight of the aircraft to, say, half the MTOW, the load factor in 1 g flight is a half of the load factor the aircraft was designed for.

The load factor on an aeroplane differs from the abstract concept of load factor as it relates to the load imposed on the aircraft compared to the load imposed on the aircraft when operating at gross weight at 1 g.

I hope this helps.

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FAA exam questions are hopeless. Also there are several different definitions of load factor. The one that would appear to apply in this context ought to be invariant with weight, for any given G-loading. It's basically the same thing as the G-loading. Its the aerodynamic force divided by weight of aircraft plus contents. 1000 pound aircraft, generating 3000 pounds of force, has a load factor of 3.

On the other hand if we hold the aerodynamic force constant and we increase the weight then we decrease the G-load or load factor-- as the original question pointed out.

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