The following is a quote from a textbook called "Fixed Wing Airworthiness", which nobody will recognise, because I won't finish writing it for at-least another 2 years....
>Requirements for VMCG and for control following an engine failure on the ground
VMCG is the minimum control speed on the ground, and is defined by the ability to maintain the runway centreline during take-off, within a given tolerance, in the event of failure of the most critical engine - which is again usually performed by shutting off fuel to an engine during a take-off run. The significance of VMCG is that above that speed, an aircraft may safely continue a take-off (assuming that sufficient thrust is available to do so) whilst below that speed, in order to remain on the runway, braking must be used and a take-off aborted. Obviously it is not the only consideration, but it is nonetheless one which must be determined, and taken into account when determining V1 - the take-off decision speed, which can never be less than VMCG (the other bound is obviously VR - the rotation speed, where in between V1 lies is a function of aircraft performance and runway length, surface and condition).
The method by which testing VMCG is carried out involves a series of take-offs, ideally into wind, with the critical engine deliberately being failed at a series of airspeeds, starting just below VR and reducing in small increments until the aircraft is unable to remain within the required distance of the runway centreline. The take-offs should be filmed from either behind or ahead of the aircraft, and in subsequent analysis of the take-off films, should determine at which engine failure speed speed adequate directional control on the runway can no-longer be maintained. Inevitably, the tests will be carried out at whatever is determined to be the most critical take-off configuration, with the worst case weight and CG conditions. Take-off trim is universally used.
Needless to say, this is a high risk exercise, which is normally carried out after all airborne minimum control speeds have been determined. The use of a very wide runway, with no significant obstructions to either side is essential, as is a very well briefed team on ever aspect of the trial. It is important in more complex aircraft to be particularly aware in VMCG tests of the flight control system - spoilers in particular can often lead to non-linear rolling moment with stick input characteristics, and may also lead to increased directional stability (weathercocking tendency) just when it is least wanted.
British Civil Airworthiness Standards Section K The quantity VMCG is not defined or used in BCAR Section K. If VMCG is required, the author recommends use of JAR-25.
Joint Airworthiness Requirements
JAR-23 The quantity VMCG is not defined or used in JAR-23. If VMCG is required, the author recommends use of JAR-25.
JAR-25 Propeller to take it’s natural position, with no pilot input to pitch setting MTOP Max. deviation from runway centreline: 30ft (9.1m), Roll Control only to be used to keep wings level whilst on the ground Max. Rudder force: 150 lbf; Nosewheel steering not permitted to be used in demonstration
Readers will note that in those standards which define a VMCG test, use of the nosewheel steering is not permitted. Conjecturing as to the reasoning behind the committees that drafted these standards, almost certainly this is to allow use of the nosewheel to counter crosswinds (which are not taken account of in these tests), but also readers mainly familiar with light aircraft, it is worth remembering that airliners usually have a separate “tiller” for control of the nosewheel steering, which is not connected to the rudder mechanism
G
N.B. Zeke, Pilots aren't expected to understand things. That's what Engineers are for.