Can I just add a small correction
Originally posted by Lefthanded_Rock_Thrower
VMCA is calculated is by the worst possible scenario, ie:
MTOW
Flap to T\O ( so retract flap, increase performance and decrease control ability )
Gear Up
live Eng to full pwr
Aft C of G ( rudder less effective )
Sea Level, critical engine failed
Failed Engine wind milling
VMCA is established in the required certification configuration (which may or may not be the absolute worst, depending on a number of factors, e.g. flap position).
The worst case from consideration of weight is the lightest weight (consistent with aft c.g.) as this provides the smallest weight component along the wings when banked at the maximum permitted 5 degree bank angle, which in turn permits the use of the minimum proverse sideslip to assist in trimming the aircraft.
It is not always necessary to consider the Sea Level thrust
if one is willing to schedule VMCA with altitude or temperature (which is permissible, and necessary to permit higher altitude operations in some cases).
VMCA
by definition occurs in the takeoff (second segment) configuration, so the issue of flap setting and landing gear position is defined, not left to determination of worst case. There is, of course, VMCL, which is a similar requirement in the approach/landing configuration.
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Any consideration of the flap effect must be very dependent on whether there are significant powered lift effects; on an aft mounted twin the engine/flap interference is not very significant - far more so is the engine/empennage effects.
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LRT and 'arm' - a further important consideration for aileron power is the need to be able to conduct the roll rate test for a VMCL manoeuvre, and also the dynamic VMC requirement which may be more demanding for the ailerons. (Depending on the degree of control cross-coupling, you may also find the aileron and rudder requirements cross contaminating, e.g. for a short tail arm with tall fin)