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In the Aircraft Flight Manual of the Bombardier CRJ700, the Minimum Flight Weight is listed as 42,000lbs. What is the meaning of Minimum Flight Weight?

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    $\begingroup$ Welcome, Takeshi. Could it be that "What is the meaning of Minimum Flight Weight" is a better title to your question? $\endgroup$ May 18, 2019 at 11:29
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    $\begingroup$ Do you simply want to know the definition of this phrase and how to ensure its complied with, or do you want to know why the limitation exists? $\endgroup$
    – nexus_2006
    May 19, 2019 at 14:10
  • $\begingroup$ Thank you for your comment. I'd like to know the definition and why the limitation of the weight. If flight with less than this weight, how harmful is it to operating the aircraft? $\endgroup$
    – Takeshi
    May 20, 2019 at 1:14
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    $\begingroup$ Could it possibly be the case that if the aircraft is below the minimum flight weight, then if it encounters a strong vertical or horizontal gust that generates X pounds of additional lift, the resulting acceleration will be so strong that heavy items with lots of inertia such as batteries, engines, etc might be ripped loose from their mountings? In other words the airspeed - G-load envelope is only valid down to a certain minimum weight and the specified maneuvering speed etc does not adequately protect the plane in turbulence, or if the pilot makes rough control inputs, below that weight? $\endgroup$ May 25, 2019 at 16:49
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    $\begingroup$ An example of use is given in this answer. When the MFW is not satisfied fuel ballast must be used. $\endgroup$
    – mins
    Oct 13, 2021 at 12:44

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After little digging found EASA Part 25/FAR 25.25 (same text):

CS 25.25 Weight Limits

(b) Minimum weight. The minimum weight (the lowest weight at which compliance with each applicable requirement of this CS–25 is shown) must be established so that it is not less than –

  1. The lowest weight selected by the applicant;

  2. The design minimum weight (the lowest weight at which compliance with each structural loading condition of this CS–25 is shown); or

  3. The lowest weight at which compliance with each applicable flight requirement is shown.

So the aircraft has to meet all of its structural and performance design criteria at all approved weights. As you can see from the wording, the chapter it self is quite ambiguous and includes the entire regulation within its scope. This would include for example controllability and gust limits etc. For example, aircraft being too light would lose its controllability in engine failure or might overstress in sudden gust.

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  • $\begingroup$ Which is not to say that an aircraft would be dangerous if flown under-weight (although it might well) but that the aircraft has been designed and tested to operate safely at this weight. $\endgroup$
    – Frog
    May 9, 2022 at 2:08
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For purposes of determining minimum design weight: it is the empty weight + installed equipment + crew + full oil + MINIMUM (not “undrainable” or “unusable” fuel). Minimum fuel for these calculations can be determined by the manufacturer, or, for modern aircraft it is the amount of fuel used in 1/2 hour at METO power setting, or for older (CAR certified) aircraft, it is 1/12 gallon per max horsepower. See CAR 4a.37(c).

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  • $\begingroup$ So it's not a limitation? But see "On the A310 freighter there is a 'Minimum Flight Weight' ie the take-off weight of the aircraft must be at or above this weight to depart.". From aviation.stackexchange.com/a/66487/34686 . $\endgroup$ Apr 28, 2022 at 20:29
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This is the weight in an operational condition(with engine oil, hydraulic fluid, unusable fuel in the tanks[maybe also with a specific usable amount like 30 minutes], and some other misc items), with minimum crew. With sufficient ballast, if necessary, to keep the center of mass position and total mass within the design requirements for safe handling characteristics.

In different words, the minimum weight at which the airplane is allowed to fly, with consideration for required equipment, the required position for center of mass, and performance limits. As an example, by requiring a certain minimum weight there will be more inertia and it may be possible for the aircraft to be certified for more severe wind conditions.

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  • $\begingroup$ In other words, the least the airplane can weigh when ready to fly (briefly). $\endgroup$
    – Zeiss Ikon
    Oct 11, 2021 at 18:32
  • $\begingroup$ Now that I consider the exact words, there may be two meanings. What I described is the minimum operational weight. It is possible the minimum flight weight is a limit on calculated weight and balance, there are a few transport category aircraft which cannot fly at minimum operational weight for flight control reasons and must have some ballast added if there is no cargo. $\endgroup$
    – Max Power
    Oct 11, 2021 at 19:44
  • $\begingroup$ In many cases, minimum weight is unreachable in any sort of normal configurations. $\endgroup$
    – busdriver
    Oct 12, 2021 at 6:55
  • $\begingroup$ The question is concerning the definition of specific terminology, this is not a slang or lay-speak use of minimum weight. The minimum weight in question is inherently reachable by the definition of the parameters. $\endgroup$
    – Max Power
    Oct 12, 2021 at 17:00
  • $\begingroup$ So it's not a limitation? But see "On the A310 freighter there is a 'Minimum Flight Weight' ie the take-off weight of the aircraft must be at or above this weight to depart.". From aviation.stackexchange.com/a/66487/34686 . $\endgroup$ Apr 28, 2022 at 20:29
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The Bombardier CRJ 700 is a has two rear jet engines with a T tail and a long forward fuselage. It's MTOW is around 75,000 lbs, allowing for around 33,000 lb combinations of passengers, cargo, and fuel. The 42,000 lb "minimum weight" (also listed as 44,000 lbs) would be a useful tool to determine safe loading of the aircraft.

But one other criteria for loading is Center of Gravity. Many CG diagrams look like a lopsided rectangle, especially for the utility category. Heavier loads favor more rearward placement. It occurred to me that some aircraft actually require a brace to keep the tail from dropping when completely unloaded.

So, "minimum weight" (for safe flying) may be different from "empty weight" because empty CG is too far aft. Further reading into the CRJ 700 POH with attention to CG charts may be in order.

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