G-Loc, has it happened to you.

[BigEndBob]

http://aeromedical.org/Articles/g-loc.html
Any GA instructors ever suffered from this.
I think its something we probabaly disregard in GA, but i experienced tunnel vision only pulling 2G a few years ago.
Practising steep turns with student, first turn demo, i suddenly felt slightly unwell.
Student had a go, as he pulled into turn, the onset of tunnel vision started, like looking through a pair of binoculars or tubes, head began to flop, losing use of arms and could feel myself passing out.
Quickly told student to roll out although hard to speak.
Thought it would be a bit embarassing to pass out!
Only explaination, i had suffered from a cold a week before.
I mention this because its that time of year in the UK we all start suffering from colds, but don't do much flying due to the weather.

[Dan Winterland]

It's fairly unlikely you were close to g induced loss of consciousness at 2g. Most people's g threshold is far greater than that, however stranger things have happened.

The usual stages of g effects are grey out (colur perception decreasing leading to black and white vision, then tunnel vision (as a lack of oxygen makes you lose you peripheral vision) then blackout, then g-loc. Black out will normally preceed g-loc and you should be very conscious of the fact you have blacked out. However, these stages are different for everybody as are the individual's g tolerance which can vary due to phsyiology, previous exposure - and current health. Also, if you are doing the flying, your tolerance will be about 1g greater that anyone else on the aircraft.

I'm sure flying with a cold (or the after effects) will reduce g tolerance. Perhaps in your case it could be your cold also affected you inner ear and consequently your balance mecahnism which exacerbated the effects of g.
Also, GA aircraft generally don't have a g meter so it's hard to determine how much g you are pulling. If this was the case, perhaps it was more than 2g.

My only personal experience of g-loc was in a Chipmunk! Teaching maximum posssible rate turns (on a military syllabus) my student hadn't braced while I did the demo. He went out at a sustained 3g and suffered the classic symptoms being out for about 30 seconds and having no recollection of the event afterwards.

[das Uber Soldat]

I've had a few students become a bit unresponsive whilst demonstrating spinning, generally during the recovery, but nobody has really gone to sleep just yet. I'm surprised you felt those effects at a mere 2G's however.

[UAV689]

it is the sustained G which is the problem, most people do pass out at a sustained 3 g, it is quite possible when doing steep turns. especially if you are of ill health and i imagine smokers are at higher risk..

i have pulled 7g but only for a matter of 1-2 secs at the most, hence no blackout.

[Wombat35]

Hi,

As an ex mil pilot and current GA and Aerobatic instructor, you shouldn't experience GLOC in a non aerobatic aircraft if you are fit and well.

For most people GLOC starts around 3.5-4G sustained, if you don't make any effort to stain. Straining will generally increase your tolerance by 1G.

A simple strain would be tensing your legs and stomach to try and stop the rate of blood flow away from your head.

I would suggest that you were suffering from the effect of the cold and might of had some dizziness from you ears rather than your G tolerance, however it's a good lesson to learn just how a slight degradation in your health can have some interesting consequences.

Cheers

Wombat