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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 '19 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 '19 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 '19 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 '19 at 16:49
  • $\begingroup$ An example of use is given in this answer. When the MFW is not satisfied fuel ballast must be used. $\endgroup$
    – mins
    Oct 13 at 12:44
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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), zero cargo, with minimum crew.

The minimum weight at which the airplane can fly. You may also have maximum zero fuel weight, maximum landing weight, maximum takeoff weight, and maximum taxi weight.

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  • $\begingroup$ In other words, the least the airplane can weigh when ready to fly (briefly). $\endgroup$
    – Zeiss Ikon
    Oct 11 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 at 19:44
  • $\begingroup$ In many cases, minimum weight is unreachable in any sort of normal configurations. $\endgroup$
    – busdriver
    Oct 12 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 at 17:00
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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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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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