vmc
hello every one,
first you have vmcg(v min control ground) & vmca(v min control airborne).
the difference, except the obvious ground/airborne factor is : vmcg considers tire friction(NOT nosewheel steering) & vmca considers 5° bank towards the live engine to counteract with the lateral liftvector component the opposite yaw of the operating engine. altitude hold capability is not a factor. only directional rudder control/effectiveness is considered.
there is a physical(scientific) relationship between aircraft weight-takeoff speeds & takeoff distances: the lower the weights, the lower the t/o speeds & t/o distances & vice versa.
for uncontaminated rwy's & at very low weights the t/o speeds bump on the vmcg(function of airtemp & press altitude= density alt.). so FM states: you can still reduce the weight, but not the t/o speeds & related t/o distances.
the lowest zerofuel weight =simplified: basic weight + 2 crew +bags= dow,dry operating weight, this gives also the most aft zfw cg position & lowest arm for rudder effectiveness & highest vmcg/a.
of course, in order to fly it is advisable to add some fuel to the equation which will bring the t/o cg forward & improve directional control, with lower vmcg/a.
on contaminated rwy's you have to consider 3 factors:
1) sometimes large weight reductions cfr rwy contaminants
2) v1(mcg) limit weights
3) take the lowerweight of 1) or 2)
4) v1 adjustement(reduction) for actual weight, not below v1mcg
a last consideration: regulations stipulate config/thrustoutput of critical engine/weight parameters for vmc demonstrations.
vmca can only be demonsrated if above stall speed.( a job best left to the test pilots)
4 engine aircraft have a 2 engine out vmcland.
Last edited by blackmail; 30th Sep 2006 at 09:24.