48
$\begingroup$

I have always wondered about this one.

Pulling high G-forces is, I assume, the most physical challenge the pilot of a high performance fighter aircraft needs to be able to sustain without blacking out or worse. Indeed, in most countries in the world would-be fighter pilots cannot qualify for jet-jockey status without first passing the dreaded centrifuge test.

Further, modern jets can in fact pull much higher G-forces than the pilot without damage to the aircraft. Indeed, I read somewhere once that one of the issues with auto-missile-avoidance systems is that the aircraft is limited to performing maneuvers that the pilot can withstand.

As I understand it, the issue with high-G turns is that the blood is drained or driven from the body to the lower (and upper when undergoing high negative-G) extremities of the body resulting in starvation of the brain and consequent blackouts or even embolism in the negative-G case.

I realize pilots wear tight G-suits which have air pumped into them to restrict the amount of blood that can accumulate in their lower extremities, but that doesn't reduce the stress on the heart trying to pump blood up to the head.

Fighter pilot in seated position

It seams rather obvious to me that much of the issue with high-G is caused by the seated position of the pilot. It is an established fact that the more vertical you are the harder it is to withstand G-forces.

Why then are modern jets not designed with the pilot in a more reclined position? For example, the position used by Formula-1 race car drivers:

F1 driver in reclining position

Don't get me wrong, I understand F-1 drivers do not need to withstand the same kind of sustained vertical forces that a fighter pilot does, however the legs-up reclined position seems to be far more practical for a high-G environment.

I do realize that the whole ejector-seat mechanism would need to be redesigned to eject the pilot differently, and that the pilot's ability to see behind himself would be compromised without technical aids, but surely the increased turn rates and lower profile cockpit would outweigh those issues.

NOTE: I have seen other posts on using the head first "prone" position, including this stack-exchange link but nothing on reclined.

ADDITION: Found this image of a Foka-5 glider pilot position too... note how wonderfully streamlined it is.

Glider pilot in reclinet position

$\endgroup$
  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – casey Aug 5 '17 at 2:19
47
$\begingroup$

Fighter pilots are far more reclined than you might think.

But seat angles are limited by the need for good visibility. Pilots frequently need to look to down-and-sideways, down-and-forward, and towards their back-quarters. These are angles that your F-1 Driver couldn't possibly see.

Also, High-G maneuvers are quite rare. Most modern military planning is about making sure pilots are never even in a position where they need to evade a missile or dog-fight another plane.

$\endgroup$
  • 9
    $\begingroup$ The helmet / camera systems are not available on most airplanes. The F-22 might be the only plane that has a fully-featured system. The F-18 was created in 1983 (when digital cameras and advanced processing was completely unheard of). $\endgroup$ – abelenky Jun 5 '17 at 12:38
  • 8
    $\begingroup$ I believe the F-35 is still under development. When complete, it should have a full head-mounted display system, but nothing on that project has gone according to plan. $\endgroup$ – abelenky Jun 5 '17 at 14:47
  • 23
    $\begingroup$ Pilots look over their shoulder for such mundane things as: "How far away is that runway?" "Which town/road/landmark am I passing?" and "Did my bomb just hit the target?" $\endgroup$ – abelenky Jun 5 '17 at 15:12
  • 4
    $\begingroup$ As a note about camera vision systems, the F-22 doesn't have one. It also doesn't have a helmet mounted display required to use one. The F-35 does have one, it's fully functional and has an operational HMD. The camera system is called AN/AAQ-37 Distributed Aperture System (DAS), if you do a quick google you'll find plenty of demonstration videos. $\endgroup$ – ww602 Jun 6 '17 at 13:03
  • 2
    $\begingroup$ @Obsidian If the electronics fail in a modern fighter jet the pilot can only hope that they can eject manually, because they certainly couldn't fly it anymore. And the chances of just the display failing without reason seems negligible. $\endgroup$ – Voo Jun 6 '17 at 16:47
37
$\begingroup$

The F-16 in fact has a relatively large recline (compared to other fighters). From the main F-16 Wikipedia

The F-16's ACES II zero/zero ejection seat is reclined at an unusual tilt-back angle of 30°; most fighters have a tilted seat at 13–15°. The tilted seat can accommodate taller pilots and increases G-force tolerance; however it has been associated with reports of neck ache, possibly caused by incorrect head-rest usage. Subsequent U.S. fighters have adopted more modest tilt-back angles of 20°. Albano, J. J. and J. B. Stanford. "Prevention of Minor Neck Injuries in F-16 Pilots". Aviation, Space and Environmental Medicine Issue 69, 1998, pp. 1193–1199.

From this archived DTIC Article from 1962 it appears to confirm a lot of what the other answers said. As noted in the comments this in regards to the prone position and not a reclined position. From the summary page:

The prone position of the pilot in high-speed airplanes has certain advantages (higher g-tolerance of the pilot, reduction of drag due to decrease of frontal area, improved instrument visibility) and drawbacks (narrowing of field of vision, decrease of visual acuity, aggravation of claustrophobic tendencies, discomfort encountered in this abnormal position).

Spacecraft routinely have their pilots in the reclined position but their main objective is a fairly narrow scope compared to a fighter pilot. It seems the wrap-up answer is that other positions are useful in the context of the specific mission of a given platform but for military aircraft it doesn't seem to offer an advantage.

$\endgroup$
  • $\begingroup$ Note that specific article quote is about prone positions, whereas the OP's question is specifically about supine positioning (as in the F1 and glider examples). The article does explicitly distinguish prone and supine. Prone crew positions are rare in actual aircraft, except maybe some WWII bomb aimers, and the Wright brothers... $\endgroup$ – Michael MacAskill Jun 6 '17 at 0:21
  • $\begingroup$ Note that prone != reclined. Prone means on your stomach - and spacecraft rarely have their pilots in the prone position. The two common ones I know of for spacecraft is seated (reclined or otherwise) or standing (like the lunar lander). $\endgroup$ – slebetman Jun 6 '17 at 5:40
  • $\begingroup$ A prone flying position was tested on a Meteor aircraft diseno-art.com/encyclopedia/strange_vehicles/… $\endgroup$ – Adrian Jun 6 '17 at 8:12
  • $\begingroup$ thanks, edited to address the comments. I thought of this last night as I'd routinely hear prone in reference to a laying down rifleman not a reclining rifleman (which seems a lot more comfortable though probably harder to point down the battlefield) $\endgroup$ – Bageletas Jun 6 '17 at 12:18
8
$\begingroup$

A pilot position as reclined as pictured would have the pilot upside down with blood rushing to the head whenever the plane is in a steep fast climb such as takeoff and many dogfight maneuvers.

Probably not a great position for maintaining orientation and consciousness.
It feels natural to move forward while seated upright.
Even climbing vertically is a similar G sensation pressing you into your seat. But people are not accustomed to being dragged skyward by the feet.

A very critical device in a F1 car that allows for that extremely reclined position is the HANS head and neck restraint system. Without it, the inertia of a helmeted head would carry the head forward causing grave injury in a crash, and to a lesser extent during hard braking. The reclined position starts you out closer to the limit of your safe range of motion. HANS prevents you from reaching that limit, but it also prevents you from looking down. That can be a useful skill if you are the type of pilot that likes to.. uh... land. A HANS type device isn't required in the glider pictured because it lacks the capability to rapidly accelerate or decelerate, thus leaving the pilot free to look around.

$\endgroup$
  • 2
    $\begingroup$ is slomobile a sock puppet of user22253? Looks like they have same avatar. BTW interesting answer $\endgroup$ – Peter M. Jun 5 '17 at 21:33
  • 1
    $\begingroup$ Probably, he created a named account, but either didn't know how to convert the existing account or something went wrong. @slomobile, you can ask a moderator (or maybe a Stack Exchange employee) to merge the two accounts if you care about your existing rep points. $\endgroup$ – Jörg W Mittag Jun 5 '17 at 23:27
  • 3
    $\begingroup$ "A very critical device in a F1 car that allows for that extremely reclined position is the HANS head and neck restraint system." Not true. The HANS system is to prevent injury. It didn't existed before 2003. But pilot seating has been very low for a long time. $\endgroup$ – roel Jun 6 '17 at 10:01
  • 2
    $\begingroup$ Re "It feels natural to move forward while seated upright." I don't think so. At least there are many individual differences. I feel much more comfortable in the semi-reclined posture of sports cars or gliders than in the bolt-upright posture of SUVs or my Cherokee. $\endgroup$ – jamesqf Jun 6 '17 at 18:42
  • 1
    $\begingroup$ @jamesqf - I wasn't referring to the G-force, but the actual angle of climb. If a C-172 was climbing at a leisurely rate, but the pilot were reclined, his feet would be at or above his head with the F1 seating position. This would lead to the blood pooling in the head and the resulting discomfort, etc. This is the exact opposite of what fighter pilots experience with the current seating position when doing high positive G maneuvers and the blood pools in the lower extremities (hence the use of a G-suit). Probably easier to have a g-suit acting on the legs than the head. ;) $\endgroup$ – FreeMan Jun 8 '17 at 19:55
4
$\begingroup$

This question is pretty similar to this one but you provide a slightly different position so there may be some variances. Some things to consider,

  • In the F1 like case, blood would still have the ability to pool in the gluteal region as well as the feet since they are lower than the head.
  • In the more reclined, feet forward position one would need to have the instrument panel over their legs (and a significant amount of it) lest it be quite far and possibly out of reach. This could potential cause a problem in an ejection scenario.

A good, practical example of this position is the Bede Jet a not so popular kit plane famously flown by James Bond.

$\endgroup$
  • $\begingroup$ Yup, issue 2 I assumed more side panel controls including side joy-stick... i.e. a wider cockpit vs tall. Not insurmountable though. Issue 1 true, but still I would think less of an issue than seated, but I could be wrong. $\endgroup$ – Trevor_G Jun 5 '17 at 12:48
  • $\begingroup$ the controls are not whats in the way, its the instrument panel aircraft instrumentation require physical input along with the control surfaces they are not just things to look at. $\endgroup$ – Dave Jun 5 '17 at 13:03
  • $\begingroup$ Yes I know, but they could also, just as easily, all be at arm reach left and right of the pilot. $\endgroup$ – Trevor_G Jun 5 '17 at 13:05
  • $\begingroup$ They could be to the side, @Trevor, but there's only so much space available exclusively to the side in a cockpit and still within the pilot's reach when pulling high Gs. The other advantage to having controls in front of the pilot instead of to the side is minimum time with eyes inside the cockpit to ensure that the right switch is being operated and/or confirming switch settings. $\endgroup$ – FreeMan Jun 8 '17 at 14:24
  • $\begingroup$ Bede Jet not so popular? :) You may not be aware of this, but some 40 years later there are companies still producing them and they have a waiting list. The most well known is bd-micro.com $\endgroup$ – Juan Jimenez Oct 21 '17 at 22:35
4
$\begingroup$

The Recline was to get the seat in the jet... that is the primary reason. On long ferry missions not much pressure is on your sit bones and back.

G tolerance and endurance is about hitting the gym.. not really the 30 degrees of recline :)

Also ejection out of the jet.. which can be career ending... your knees have to clear that dash on the way out... so they had to make sure the seat gets you clear of the suns-shield /dash and the vertical tall as you are fired toward it... 

$\endgroup$
  • $\begingroup$ Yes I realize the classic ejection method would not work..but if you are going to redesign the entire cockpit that would all be part and parcel of it. See my latest comment on the main question. $\endgroup$ – Trevor_G Jun 6 '17 at 19:18
  • 1
    $\begingroup$ Ahh ok.. Well the B1 has a ejection pod... the Su-27 series as well as the MiG 29 series as well as the F-35 have auto eject systems on the jets. In the Case of the 27-35 the Ekron determines when the jet is not viable and pushes the pilot out.. the F35 uses a similar system but it is because the eject angle is critical due to the the way the cockpit opens $\endgroup$ – 007 Jun 6 '17 at 19:28
  • 1
    $\begingroup$ Cockpit design back during the Fighter Mafia days was a brutal process... Engineers want one thing, the Military leadership wanted something else... Stuff like in cockpit fuel shut off and breakers can be placed in places that make no sense... so a lot of factors go into it.. also when you are being shot at you don't want any buttons or switches in areas that will degrade the jet or it's system... that's why some stuff is places in odd spots... $\endgroup$ – 007 Jun 6 '17 at 19:34
  • $\begingroup$ Yup..always the way,,, $\endgroup$ – Trevor_G Jun 6 '17 at 19:34
  • 1
    $\begingroup$ yeah.... the good old days of the single role fighter are gone... if you compare the the A-7 Corsair II to the F-16 you can really see how early block F16 air to ground mode is almost a direct software copy of the A7. $\endgroup$ – 007 Jun 6 '17 at 20:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.