I thought that the V-hackle dry fly was as stated, a V section trimmed out of the bottom of a hackled dry.
There is such a fly in the FOW archive - A Simple Dry/Emerger submitted by guess who.

If you want to tie a spinner pattern, there is quite an old technique from Roger Woolleys 'Modern Trout Fly Dressing' As follows:-


"On a bare hook wind on a good cock hackle for two or three turns as if for a plain hackled fly.
Take one, two hackle turns around the shank, tie down and trim away the surplus.
You now have a bare hook with a hackle wound around it, a hackle fly with no body.
Next, evenly divide the fibres of the hackle and stroke them into the position of the wings of
a Spent Gnat, at right angles with the hook shank.
Pressure between the thumb and forefinger will cause the fibres to remain in this position
until they are fixed by figure of eight tying. It is necessary to tie down the fibres for the wings
underneath as well as over the top of the hook shank so that the fibres stand out stiffly on
each side of the hook.
The figure of eight tying must be manipulated accordingly, tying the hackle fibres down on
the top of the hook first and then , turning the hook over, repeat the process on the under side of the hook.
The tying silk, in tying down the hackle fibres for a spent wing, also forms at the same time the thorax of the fly,
so care must be taken to use tying silk of the correct colours.
Do not get too many fibres for these wings, a bushy wing is neither needed nor desireable."