Hmmm .... every case of whiplash I treated over the years followed a vehicle rear end impact where the recipient occupant's head went back then whiplashed forward. Of course they were all relatively minor injuries since all cars have head restraints nowadays that absorb some of the energy and also limit the initial backwards extension of the neck.

If you want to protect your neck in a glider front end impact you would need something like an F1 style HANS device - although in a typical glider serious accident there is little point given the likely state of the rest of your body.