G Tolerance

[Grob Queen]

As a PPL Student with 34 hours, I am starting 60 degree advanced turns. Would anyone have any ideas on how to "get" g tolerant please? I desperately need too!

Thanks!

[Rod1]

The more you do the better you will get. You can try tensing your stomach muscles which will help. Unusual to have an issue with steep turns though. How many have you done so far?

Rod1

[Grob Queen]

So far I have had two sessions - three weeks apart. Flown about 2 60' and 5 45' turns...and a few aeros (with friends as the P1)

[flybymike]

As a student I found that once established in a steep turn you become unaware of any G at all. To this day I only find short sharp bursts noticeable.
, or for example pulling out of a spin (which were compulsorily trained in my day)
Edit I wouldn't do aeros if you paid me...

[Ultranomad]

Grob Queen, are you sure your problems have to do with g? High g causes blackouts similar to the feelings you can get when suddenly standing up after a long rest or a hot bath, or suddenly stopping after a dash, but these are very unlikely for a healthy person experiencing a 2g overload (60° turn).
On the other hand, nausea is caused by Coriolis forces and/or a visually perceived rotation. You can train yourself to overcome it, but the first thing to do would be to eat the right kind of food before the flight: don't fly on an empty stomach, nor immediately after a hearty meal. Many pilots doing scenic flights recommend their passengers to eat protein-rich food (like steak and eggs).

[BackPacker]

I agree with Ultranomad.

The symptoms of too-high g-forces are loss of color vision (greyout), tunnel vision, blackout and eventually loss of consciousness (g-loc). These symptoms all occur because the brain, and in particular your eyes (which are most sensitive to this) do not get enough oxygen.

Oxygen is delivered to your brain by your blood. It's your blood pressure, generated by the heart, which pumps the blood upwards to your brain. Under normal circumstances, your heart is able to pump blood about one meter upwards (that's the reason that IV bags are hung relatively high). The vertical distance from your heart to your brain is about 25 centimeters. So a normally proportioned, normally fit adult should not suffer from any g effects until reaching, approximately, 4G.

There's a lot more science involved and there are several aerobatics books that cover this in a lot more detail, and with a lot more accuracy. But at 60 degrees bank angle you should only be pulling 2G and that's nowhere near enough to cause g effects. Even if you've done negative g's just before (which you have not). (Although if you go to 75 degrees angle of bank - just 15 degrees more - you need to pull 4G already and that might trigger g effects. But in a typical training spamcan, your cruise, full power and stall speeds are so that you will barely be able to sustain a 4G/75 degree steep turn for long enough for g effects to manifest itself.)

As Ultranomad says, it's probably nausea. You can get desensitized to this easily just by flying a lot, particularly steep turns and other unusual attitudes/aerobatics. There are also several exercises you can do on the ground. Here's a scientific paper on this subject:

http://medind.nic.in/iab/t07/s1/iabt07s1p37.pdf

And here's a site of a doctor that sells DVDs. Haven't seen those myself though (I stumbled on it searching for the link above), but it might be worth a look:

Motion Sickness (Travel Sickness, Air Sickness, Sea Sickness, Car Sickness, Cyber Sickness, Space Sickness) Causes, Symptoms, and Natural Prevention Information on PumaMethod.com

[Torque Tonight]

A 60 AoB turn is 2G. My granny could handle that without special training.

[FlyingSportsman]

Tense those buns!

[chevvron]

I once had a Hunter flight without a g-suit. We did a loop and pullled through at 5.5g, at which point I was greying out. I had previously had a Hawk flight where I experienced the workings of a g-suit, as it involved rapid changes of attitude between -3 and +4.5 g.
I have to admit I puked when we did a negative g barrel roll!

[Pilot DAR]

Grob, you've had some good explanations here. I would think it very unlikely that the G's you would experience in flight at the basic flight training stage, or in the aircraft type you are flying would be the least troublesome. Nothing you should be doing in that plane should be subjecting you to more than 2G, and this should be easily tolerated by any healthy person. Truly, if 2G is a medical problem for you, medical advice is in order.

For myself, back in the old Aerobat days, I found that 4+ was my limit as the passenger, and I could manage 5+ as the pilot. This seemed about the same for my buddy, as we entertained ourselves greying each other out one afternoon. Any maneuver exceeding 3G would be aerobatics, and I suggest that is not the type of flying you should be doing just yet, unless you are the passenger...

[I Love Flying]

Question: would having lower than normal blood pressure (not dangerously low, just lower than average) affect a pilot's/passenger's g-withstanding capability?

[BackPacker]

Yes.

In fact, the Royal Dutch Airforce instructor who taught the course on g exposure etc. (combined with the centrifuge session) noted that people with an unhealthy lifestyle and the resulting high blood pressure, were less susceptible to g effects than people who were really fit and healthy.

(On the other hand, the fit and healthy are more capable of performing the straining techniques that are required to keep the blood in your head, and are able to sustain these for a longer duration.)

And on a related note: I was once asked to fly aerobatics (LAROSA aerobatics, nothing serious, -1 to +4G maximum) with a girl who had a heart condition (leaky valves or something like that). I refused. And when I explained why, everybody understood and the issue was not pressed further.

[lopresto]

Grey/black/blu/strars/red vision... with a PPL aircraft.. well..

BTW... enjoy them

[I Love Flying]

(On the other hand, the fit and healthy are more capable of performing the straining techniques that are required to keep the blood in your head, and are able to sustain these for a longer duration.)

Please can you briefly explain these techniques in layman's terms to somebody who is yet to experience aerobatics (but rather fancies it one day, but who also has been told their blood pressure is slightly on the low side)...

[BackPacker]

Please can you briefly explain these techniques in layman's terms to somebody who is yet to experience aerobatics

As noted earlier, an introduction to aerobatics, up to Sportsman level, does not require exceeding -1 to +4G limits even when flying in competition. At +4G the worst you should encounter, even with low blood pressure (I've got that too) is mild symptoms and as the +4G is only sustained for maybe half a second, straining techniques are not really required.

Furthermore, straining techniques are not something you can learn from a book or PPRuNe post. You should practice them with a knowledgeable person present to tell you what you did wrong. Especially since if you apply them in the wrong order or at the wrong moment, you could actually be pushing blood away from your brain instead of pushing towards it.

Having said that, here's what I was taught during that Air Force centrifuge session. It's essentially two things that happen simultaneously. You tense all the muscles in your lower body up to your stomach, and you make sure to keep as much air pressure in your lungs as possible.

Muscles to tense are, from the bottom upwards:
- Toes: Feet flat on the floor, try to curl your toes against the soles of your shoes.
- Lower legs: Push your feet against the floor as if you are extending your feet.
- Upper legs: Try to clench your legs together, at the same time apply a counterforce. Also try to bend your legs, with the floor providing a counterforce.
- Buttocks: clench
- Stomach: clench

At the same time, inhale, block your breath and try to exhale (which you can't). Of course, you need to keep breathing so this is done with quick puffs after which you block/exhale again. (Some people advice you to grunt but really, the sound you make is irrelevant. What's important is to build up the air pressure in your lungs to assist your heart in pumping the blood upwards.)

A very common mistake is to let go of muscle tension as you exhale/puff, which is very dangerous as you can get g-loc very quickly under those circumstances. But you also need to make sure you time the application and amount of these straining techniques properly. If you overdo it, you may actually be more susceptible to g-loc.

The reason for the latter is that in your brain there's a little device (don't know the English word for it) that measures your blood pressure there. If the blood pressure is too low, it tenses the muscles around your arteries. If the blood pressure is too high, it releases the muscles around your arteries. But - and that's an important but - there is a delay of about ten seconds in this reaction.

So if you overdo the straining techniques, or apply them too early, the blood pressure in your brain will rise (since there's no, or not enough g force to counter it). That little device notices this, relaxes the muscles around your arteries to lower the pressure and as soon as the g force comes in, all blood will flow away because you've got no more counterforce to give.

Equally, if you go from, say, minus 3G to an immediate positive, say, 5G, it's extremely dangerous. Even more than going from 1 to 7G, say. This is because under negative G all the blood rushes to your head with rising blood pressure as a consequence. So all your arteries open up. If you then apply positive G all of a sudden, all the blood rushes away.

(The Air Force physician was really surprised to hear that some of the Advanced aerobatics pilots in our group did this. He considered the -3 to +5 situation far more dangerous than the +9 that F16 pilots need to sustain. As there's not a lot of reason to push negative G's in combat, it was something that he had never encountered. They also can't simulate this with their centrifuge.)

Once again, this is only skimming the surface of what's happening in your body and what you can do about it. The lecture we got from this Air Force physician took more than two hours and even after that lecture we did things wrong in the centrifuge - with several g-locs as a result. So please do not assume you can apply the perfect straining techniques just by reading the above text and some practicing in front of the mirror.

[I Love Flying]

Thanks for your reply Backpacker, that's understood. I was just interested to know what you were talking about really.

[Lunchmaster]

Interesting post. Having not flown aeros for more than a year I found myself feeling extremely rotten flying a Chipmunk last week.

Briefed as an aerobatic sortie with spinning, loops and barrel rolls I was flying the aircraft from the front seat with an experienced instructor in the back. Spinning was disorientating to say the least and it took me three attempts to nail the correct recovery technique with considerable height loss - good reminder in how essential it is to only begin aerobatics at a suitable height above the ground.

Next up were some loops. During the third loop I was happily watching the horizon reappear over my head when I found myself get the cold sweats and a dry mouth. Uh oh.

Moving on to barrel rolls and I was very, very queasy so called it a day and flew the aircraft back for an uneventful landing.

I was surprised my tolerance for aerobatics was not higher given previous experience. I'd eaten a decent breakfast, was rested and excited about the flight and well briefed about what to expect.

I don't think it was down to G tolerance but the onset of nausea was something I'd like to reduce or at least delay next time. Would using breathing and straining techniques have helped? Would the nausea be caused by G or just the mechanics of the inner ear?

Lunchmaster

[bsfish2003]

I have noticed that, if someone else is doing the steep turn, you feel the G. If you are doing it yourself you don't notice the G.

[B2N2]

Great post BackPacker
I was once balast weight on a serious aerobatic sortie in a glider, we went from -1.5 to +4.5, everything that we did prior was fine including inverted flight but this maneuver had me laying on the grass in the shade for a good part of the day.
With practice we could get to (briefly) +7 G's without passing out but vision would be completely gone. Never did develop a taste for negative maneuvers.
Hate them to this day.

As to the original poster;
Did you try the steep turns at the beginning or the end of your flights?
If it was at the end of your flights you may have been fatigued already.
Flight training at this stage of the. game is very exhausting, mentally and physically.
It is not unusual for an instructor to not recognize these symptoms and make the training flights too long.

[flyinkiwi]

I read one incident a few years back when a young and healthy CPL student went up with a fellow student to do some CPL revision after a heavy night out on the town and G-LOC'd doing a max rate turn in a 172. Fortunately the other student was flying at the time so they made it back in one piece. The incident report stated that fatigue, the lingering effects of alcohol consumption, dehydration and a lack of recent experience with sustained G maneuvers were contributing factors.