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During negative 'G' flight, the forces on the pilot (or pilots) will tend to push their legs up and away from the rudder pedals on your airplane. Needless to say, this is not conducive to making rudder pedal inputs!

Given that, if you are in negative 'G' flight in a suitable aircraft, and wish/need to make a rudder input during that negative 'G' maneuver, how do you do it? Do military and acro aircraft use any sort of special mechanism (such as foot pedal straps) to help the pilots keep their feet on the pedals during negative-'G' regimes?

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    $\begingroup$ Just like when your car goes over a hilltop or speed bump a bit quickly, your muscles don't just "relax" and go limp, ragdoll-like... extending your leg will still extend it. $\endgroup$ – SnakeDoc May 16 '17 at 17:45
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    $\begingroup$ In an aerobatic aircraft (and I believe fighters as well), you are strapped in by a 5-point harness which is designed to keep your body in place. Otherwise, during knife-edge maneuvers the pilot would "naturally" support his weight by pulling the stick to the side :P $\endgroup$ – kevin May 16 '17 at 17:45
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    $\begingroup$ Yes, there are straps for the feet on some aerobatic airplanes. Normally, my legs rest on the instrument panel cutout anyway, so the straps make not much of a difference. Once, when one strap get entangled with the battery cable and I had to fly with substantial rudder deflection until shortly before landing did I wish those straps away. $\endgroup$ – Peter Kämpf May 16 '17 at 18:31
  • $\begingroup$ @kevin -- yeah, but the 5 point harness can't stop the negative Gs from trying to force your legs into the bottom of the instrument panel... $\endgroup$ – UnrecognizedFallingObject May 16 '17 at 18:53
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    $\begingroup$ Much like gravity doesn't pull your legs down during normal positive-G flight and force you to have constant pressure on the rudder pedals, the muscles in your legs can be used under negative-G situations as well. Go ride the Hollywood Tower of Terror © at DisneyWorld© and keep your arms against the seat when you drop. You'll find that you can do so with minimal effort, though it wouldn't be as much fun... ;) $\endgroup$ – FreeMan May 16 '17 at 21:04
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The short answer is that at negative 2 G, the airframe limit for the A7-E, it took little effort to keep your feet on the rudder pedals.

In controlled flight there are aircraft limitations on both positive and negative G. I flew the A7-E for the US Navy and have some operational experience that might offer some context to the question.

I believe the positive G was limited to somewhere between 7-9 G. Can't quite remember the exact number, and it did depend on the external store configuration as well. Newer aircraft have higher G loading capabilities, although the human body has its own limit. Fitness and training can extend the pilots envelope to high G.

As mentioned negative G in the A7-E was limited to -2. There was no issue at these sorts of values keeping your feet on the rudder pedals. It is worth mentioning that the rudder is controlled by the AFCS (Automatic Flight Control System) system and so there is no real need to keep your feet on the pedals, although I did use them at times. Negative 2 G's was hard on the body, and a pilot would come back to the ship with bloodshot eyes after undergoing maneuvers that required this sort of thing.

I can think of 3 times that a pilot would find themselves in a negative G environment. I am not including standard acrobatic maneuvers, but more tactical situations. One, and this wasn't typical, was during training. At a high altitude you unloaded the aircraft to -2 G's and set a 45 degree dive. As the airspeed increased it entered an area on the IAS instrument that was no longer valid, and this was close to Mach. The goal was to observe the characteristics of the aircraft when it went supersonic. There was a gentle pitch down as you broke the sound barrier. I did this maneuver once, although I commonly practiced 45 degree dive bombing deliveries.

The second, and quite common, situation was a maneuver called a bug out. A bug out was used by a flight to engage other aircraft in air-to-air combat. It was at once a defensive and offensive maneuver. The lead called "Bug out. Bug out," and the flight went to -2 G's, unloading the aircraft, and giving up altitude for airspeed. As your adversary turned towards your 6-o'clock the flight would "Pitch back," and pulling positive G's, gaining altitude. Trading airspeed for altitude got the aircraft into slower flight where its turn rate could be maximized.

The bug out placed the aircraft immediately in free fall with military thrust applied. Rolling inverted and applying positive G's is like being in a turn in the sense that the positive G bleeds energy.

The third situation was a defensive maneuver. At low airspeed and with someone directly on your 6 o'clock the pilot might try to "jink." Jinking was a last ditch maneuver where the pilot randomly pulled maximum G, and then went full negative G. I used this against an F-14 in a fight, and afterwards the pilot came and told me he couldn't get a firing solution.

As for uncontrolled flight there is the flat spin which can exert substantial negative G on the pilot. If I remember correctly a flat spin had never been positively observed in an A7-E. It was postulated, however, that given asymmetric wing loading it might be possible. On the other hand the F-14 could enter a flat spin. Talking with pilots who had knowledge about this sort of flight I was told that the negative G could be large enough where it would not be possible to get your hands on the ejection handle, either low or high. Not sure about the feet :)

An interesting side note. At times a pilot will find themselves in a high g turn, grunting against the inflated g-suit, and fighting the encroaching tunnel vision. When I found myself here I would pull on the stick a bit more and watch my peripheral vision go dark (tunnel vision). A bit more g and the tunnel got even narrower, until it was like I was looking through a hole. Then I would ease the stick and watch the hole get bigger. Pull back and smaller. Kind of interesting.

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  • $\begingroup$ Thanks for serving! That last paragraph... Interesting mindset that wants to push to the limit of passing out and potentially killing yourself just for the "interesting" experience of watching the tunnel vision come & go... $\endgroup$ – FreeMan May 17 '17 at 15:31
  • $\begingroup$ If you needed to descend quickly would it be preferable to roll inverted first so any negative g's would act like positive g's to pilot and airframe? $\endgroup$ – TomMcW May 17 '17 at 17:28
  • $\begingroup$ @TomMcW Are you referring to using a Split S maneuver? $\endgroup$ – KorvinStarmast May 17 '17 at 17:50
  • $\begingroup$ @KorvinStarmast I have no idea what it might be called. Haven't looked at different maneuvers. So I presume the two (negative g's upright vs positive g's inverted) have different uses in combat $\endgroup$ – TomMcW May 17 '17 at 17:53
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I fly an aerobatic airplane. My G meter goes to -5 and I've pegged it before.

My plane (& most aerobatic planes I've seen) don't have foot straps.

During a negative G maneuver, it's pretty easy to push on both pedals at the same time thus bracing your legs against any tendency for them to slide off. It doesn't take much effort and I don't think about it while flying.

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  • $\begingroup$ I believe the negative G limitation on the A7-E was due to issues arising with fuel and engine oil. Not positive about this statement. I know our allowed time in inverted flight was due to this. This said, it always amazed me that our negative G limit was 2, and there was a fairly short time allowed for inverted flight. Another interesting limit is the number of aileron rolls you could do in a row (3 or 5 I think). This was due to flight instabilities. $\endgroup$ – Aaron May 17 '17 at 20:25

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