Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Ex-jazz on March 11, 2011, 03:34:57 PM
-
Hi
(edit)
This all about the prop driven aerobatic planes.
Everybody knows, the aerobatics pilots can make a insane +/-G's peaks.
I'm curious about how much the +/- G's they really can make and how long time they can go on?
Also, how they are 'feeling' those extreme +/- G loads in visually and audible?
And from what point the G-breathing/grunting starts?
Thanks
-
google is wonderfull.
http://www.aerobatics.org.uk/repeats/g_forces.htm
http://en.wikipedia.org/wiki/G-force
http://www.ncbi.nlm.nih.gov/pubmed/3675463
-
I've had some training in an Extra 300 L. Rated at +/- 10Gs. Pulled +6/-4 with no problem.
-
google is wonderfull.
http://www.aerobatics.org.uk/repeats/g_forces.htm
http://en.wikipedia.org/wiki/G-force
http://www.ncbi.nlm.nih.gov/pubmed/3675463
And answered very few of his questions....
The limit is often quoted at 12 G's but they are limited to that by the rules quite often, I know the Red Bull Air Race is one case.
Strip
-
Watched some red bull racing on tv, and they had g loads displayed. over 9 was very common for the duration of the turns (approx 3-6 seconds), and a few pilots were pulling over 10 for the same duration.
As for the raw physiology...
As soon as the eyes lose blood pressure, visual acuity begins to decrease. Grayout and visual blackout can occur nearly instantaneously, even if the pilot is still conscious.
The brain has enough oxygen stored up to permit approx 3 seconds of consciousness after a loss of blood pressure and/or blood flow. This is true even if the pilot can't see, because the eyes are affected first.
There is a "rebound" effect after the first G onset, at approximately 5-6 seconds after the Gs begin. If a proper anti-G strain is done for the first 5-6 seconds, the body adapts and automatically helps with the strain. If the strain is not sufficient to get to this state, then gloc will probably occur, somewhere between 3 and 5 seconds after the initial G onset.
Fatigue takes hold after 10-15 seconds, so a second risk of gloc occurs when the fatigue impact is felt after somewhere around 10-15 seconds.
I've seen (on tv) a couple of red bull racers gloc while flying the course, right around 9 to 9.5 Gs. In all cases they rolled partially wings level before passing out entirely, resulting in "bounce-and-go" impacts that left the planes damaged but flyable.
As for myself, my sustained G tolerance has hovered between 6 and 7 Gs with a G-suit, meaning I can hold 6 to 7 Gs as long as necessary without having to relax the turn. My upper tolerance for Gs has never been tested since the planes I flew were not rated over 9 Gs, and I was able to handle 9 Gs during break turns. In the centrifuge, I tolerated a sustained 7.5 Gs without loss of vision or ability to manipulate the flight controls. Without a G suit, I found it fairly easy to sustain somewhere around 5 Gs for extended periods of time while still being able to talk/instruct, and fly precise maneuvers relative to another aircraft. Without the G-suit I also had no problem sustaining approx 6.5 Gs for a minimum of 15 seconds, however above 6 Gs without a G suit I found it difficult to talk and 6.5 Gs was fairly fatiguing.
And I'm just a fighter pilot, not a red bull racer or professional aerobatic pilot. Those pilots train for even higher sustained G loads. For all of us that pull lots of Gs routinely, one constant factor is that we have all gone through fairly rigorous training to build up our tolerance for Gs.
-
Without any G training at all I have been at +4/-3 with no gloc effects at all. Not very impressive, I know, just thought you would be interested in a total rookie's tolerance. I was a little bit dizzy after the tumbles that switched from possitive to negative G. It was the switches from + to - G that encouraged me throw up a little into my mouth and had to spit in the bag :D
-
Redbull air races are capable of going 11+ G's and quite a few of them approach the 12 G limit.
9 G's is a Sunday picnic to some of them.....
Strip
-
the red bull guys do wear pressure suits though.
-
In advanced aerobatics, you usually pull +9 -6 if you want to get good scores. The thing about prop aerobatic airplanes is that they can't maintain high Gs for long, as they lack the power to maintain the speed. So when we are talking +9 means +9 for a second or two, and then it rapidly decreases.
Worst situations are going from several inverted figures and then loading 9G. In those cases you really have to grunt in order to avoid G-loc. Tumbles are not high in G, just disorienting.
Never had G-loc myself, just lost color and a couple of times some kind of sparkles that went away soon.
Daniel
-
The sparkles or "seeing stars" from lack of oxygen I've seen and like Cyrano said going from sustained negative G's to positive G's can have the strongest effects at least it does on me. Not flying aerobatics as much as I'd like these days when I do as a rule I don't go from any sustained negative G's to back to anything close to significant positive (more than +4) without a short delay between maneuvers or figures.
The sparkles I'm sure we've all seen at one point or another and the various levels of hypoxia training there are you can receive can actually show some of the similar effects of what's being talked about. As you lose oxygen your color vision decreases which you might not notice until it comes back. It's eye opening so to speak to see as you're in a hypoxic state and then go onto 100% oxygen to see some of the color snap back so quickly.
-
Hi
Thank you for your highly informative feedback.
Is the plane vibrating under the high G's and causing a pilots head 'shake'?
How about audible feedback?
Is the high alpha causing a turbulent 'rumbling' and /or plane structure 'creaking' sounds?
I try to understand these G-force caused physical phenomenons little bit better, to be able to make a necessary G-effect code for the BGE_AiRace game/sim.
Just in case, the yt-link about the related project:
http://www.youtube.com/watch?v=ZKyOM7rMN-k&hd=1
(edit)
"Over 13 g, Bonhomme Disqualified at Porto Red Bull Air Race"
http://www.youtube.com/watch?v=TSNi4yeSwn8
-
The G limits depend on the airplane, so does the time the airplane can pull them for. Planes typically can pull more instant Gs than constant.
The amount of Gs the pilot can pull depends on the person. A trained pilot (trained in pulling Gs not flying) would obviously be able to pull more Gs than an untrained one. An average person can pull about +6Gs (don't remember how many negative). A small person can pull more Gs than a large person. Also don't forget that a lot of pilots that have to pull a lot of Gs use G-suets.
With extreme Gs you would loose your peripheral vision and color vision (you can play around with that it's a lot of fun). Then as you continue to pull more Gs you would be able to see less and less. If you keep that up you G LOC (Gravity-induced Loss Of Consciousness) and hopefully you don't hit the ground. The "G-breathing" that you mentioned is the L1 maneuver, under extreme Gs you would want to flex the muscles in your legs in order to push the blood up to your brain. That is also exactly how the G-suet works, squeezes on your less therefore pushes the blood up.
As far as I know the computer in modern fighters limits the amount of Gs they can pull because the actually airplane can pull more Gs than the pilot. Don't quote me on this but I believe when you eject you experience 36Gs.
-
Don't quote me on this but I believe when you eject you experience 36Gs.
That number is WAY high. About 3 times more than you'd actually experience if memory serves.
My legs work hard but you really feel it in your abdominal muscles (at least I do) after a flight especially after a hiatus from aerobatic flight which sadly these days most are months apart. :(
-
That number is WAY high. About 3 times more than you'd actually experience if memory serves.
That's why I said don't quote me. ;)
Logically it does seem very high, but that is the number I remember. My memory might be wrong, or the sours might be wrong. However your pulling those Gs for a very short time so it might be right. I don't know for a fact.
-
Some of the older designs pulled around 20 Gs, the newer designs are quoted as 12-14 G's from what I have been privileged to look at.
Strip
-
Eagl has it right. He knows.
I myself know that I go out like a light bulb at 7.5G, and yep even with a G-suit.
That being said, our fighter pilots (and yours too) are able to keep flying and fighting at 7.5 G. For how long...you'd have to ask eagl, but I can tell you that the guys I flew with were able to keep their head up and in the fight at over 7G. This is not a sustained loading though.
It is important to know that the high G experienced by most fighter pilots are not sustained very long at those high numbers. Neither are they sustained very long by aerobatic pilots.
At any rate the ability of the aircraft surpassed the ability of the pilot years ago.
cheers,
RTR
-
Nice read ...
-
:rofl
(http://i252.photobucket.com/albums/hh32/bobmic111/th_stuntplane.jpg) (http://s252.photobucket.com/albums/hh32/bobmic111/?action=view¤t=stuntplane.mp4)
-
eeewwwwww :rofl
-
:rofl
(http://i252.photobucket.com/albums/hh32/bobmic111/th_stuntplane.jpg) (http://s252.photobucket.com/albums/hh32/bobmic111/?action=view¤t=stuntplane.mp4)
Negative Gs are not fun, and I could never understand why someone would take unprepared passengers on board for such a flight.
-
to laugh when they puke...duh
-
to laugh when they puke...duh
Sure the video is funny, but I'm trying to figure out why did they do it originally.