Hi Marius.
I'm not specifically familiar with the DA-42 (although I know what it looks like
), but a lot of both single and twin engined airplanes do have a minimum flight weight or mass restriction. I don't think it's always related to Vmca (a single is not so bothered), but rather to a certification design requirement.
In some cases (e.g., the Columbia 400 single), MFW varies with CG such that at 105 in. forward it's 2600 lbs but varies linearly to 2900 lbs at 112 in. aft.
Pretty sure this all as to do with flight load factors, representing the ratio of the aerodynamic force component (acting normal to the assumed longitudinal axis of the airplane) to the weight of the airplane. The manufacturer needs to prove the airplane meets ALL certification requirements between the MFW and the MGTOW.
minimum flight mass of 3329 lbs
Sorry, but I can't resist this: You might have written "minimum flight
WEIGHT of 3329 lbs", or "minimum flight
MASS of
1513 kg", but not mix them. The Diamond/Austrian/Canadian/European use of "mass" is more "correct" than the typical American usage of "weight" (an airplane's weight changes with altitude, but it's mass remains constant - fuel burn not considered)
Please take this as tongue-in-cheek, not an anal criticism on my part.
Someone else may "weigh" in here on the Vmca implications.
Cheers,
Tom