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This has been puzzling for quite a long time.

Every action movie or military documentary features helicopters with no door or with open doors and yet people inside look like they couldn't care less. Apparently they're not falling out...

Why is it so?

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    $\begingroup$ uhm, last time I checked gravity was still working in the up/down direction, not sidewise. $\endgroup$ – Federico Jun 12 '15 at 11:42
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    $\begingroup$ @Federico Yet I'm sure you know what I meant ;) $\endgroup$ – Cedric H. Jun 12 '15 at 11:42
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    $\begingroup$ @CedricH. - ever driven a car with your windows open, top down or, something with detachable (or no doors) like some of the old school jeeps? Did it seem like you were in danger of falling/getting sucked out? Same thing applies to flying helicopeter/airplanes with doors and/or windows open. $\endgroup$ – habu Jun 12 '15 at 12:13
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    $\begingroup$ My bicycle and my motorbike don't have doors either yet I feel perfectly comfortable riding them. Maybe doors aren't needed to prevent you from falling off / out $\endgroup$ – DeltaLima Jun 12 '15 at 12:16
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    $\begingroup$ cars don't lean into the turn so the turn vector forces the passenger towards the door. in a heli or a motorcycle, the passenger is forced into the seat. $\endgroup$ – rbp Jun 13 '15 at 13:17

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Aircraft, fixed-wing or rotorcraft, have limited capability to produce a sideways force, so they simply can't throw you out.

It is a matter of physics. Inertial forces (gravity and centrifugal force) act on you and the aircraft the same, so they won't make you move relative to the aircraft. The only force between you and the seat is caused by the aerodynamic forces. And the wing or rotor can only produce significant force vertically, and some torque with help of control surfaces. But for lateral force there is only drag of the fuselage and the vertical stabilizer and, in most helicopters, anti-torque rotor, which don't produce that much force unless there is really bad turbulence or in some cases if the handling is really bad.

When aircraft turns, it banks to be able to produce the necessary side force, so the resulting force is still mostly straight to the floor.

Of course the other reason is that all aircraft and helicopters have seat-belts and the people sitting by open door usually have them on—except for skydivers, who have the parachute on already, and rescue divers who are tied to the winch instead.

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    $\begingroup$ So basically it is harder for my dog to stay stable when he's in the back of my car than it would be for someone in a helicopter? $\endgroup$ – Cedric H. Jun 12 '15 at 12:55
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    $\begingroup$ That's not completely true, you can fall out of a helicopter if the handling is rough enough. It's happened to soldiers before. $\endgroup$ – GdD Jun 12 '15 at 12:57
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    $\begingroup$ @CedricH.: Most of the time, yes. $\endgroup$ – Jan Hudec Jun 12 '15 at 13:02
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    $\begingroup$ That seems very plausible Cederic H. The road can apply a lot of sideways force to your car in a turn through friction with the tyres. There's nothing equivalent to push a helicopter sideways. $\endgroup$ – bdsl Jun 12 '15 at 14:46
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    $\begingroup$ It's also worth noting that a human sitting correctly in a seat (with their back against the backrest) has a fair amount of contact with that seat and so is held, in part, in place by friction. $\endgroup$ – Dancrumb Jun 12 '15 at 16:49
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The reason that the occupants are so calm about being in an open helicopter are because they are strapped in. There are many configurations that open helicopters can have, some with seats and some not. The seats are generally removable, connecting to points on the floor. Occupants in the back have 2 options for strapping in, the first is your typical seat belt, the other is known as a "monkey harness", which is a harness that goes around your shoulders and waist and can be clipped to points in the floor. Door gunners usually preferred harnesses because it allowed much more freedom of movement so they could fire at more angles.

Remember also that these people were used to it as well. I'm sure most of them were bricking it big-time their first few trips no matter how well they were strapped in. Also, I suppose when you're about to be shot at falling out may frighten you less than it may otherwise.

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    $\begingroup$ @Cedric Everything looks easier on TV than in real life :) $\endgroup$ – Hanky Panky Jun 15 '15 at 7:23
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I taught sport skydiving for 10 years, and I have sat half-out of the open door of an aircraft, no seatbelt, hundreds of times while the aircraft makes 45 degree banks toward the open door side. It's a bit odd seeing the airport above the wingtip.

Unless the plane is in a spin or otherwise spectacularly out of control, the forces are largely perpendicular to the floor of the aircraft. At no time have I ever felt like I was going to fall out, and actually getting out is difficult enough that we spend an hour or more practicing it on the ground.

You asked about helicopters specifically - they are less able to produce cross-fuselage forces than fixed-wing planes. Look at the rotor, then the thin post connecting the rotor hub to the fuselage. It's not that thick and thus cannot produce enough force to toss someone out the door.

Heavy turbulence could bounce you around to the point where falling out is possible. Not guaranteed, just possible if you bounce in that direction. But at low speeds and clear weather it's unlikely to the point where sitting down is adequate. Standing and moving around with an open door is common, but the 1 inch strap that is plenty strong enough to hold you up is very hard to see, especially on TV.

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    $\begingroup$ @SteveJessop sounds like Tyler flies in a turbulent area, and/or needs to work on his technique (he certainly needs to work on his harness - they do NOT "pop open"). We used Cessnas in the prairies. $\endgroup$ – paul Jun 12 '15 at 23:10
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    $\begingroup$ @SteveJessop Tyler apprears to be a fixed wing pilot who does not recognise that helicopters are very different. I have heard it said on this site several times that in flight, "helicopters fly just like fixed wings". They don't. Many people think that because you can generate a certain force in a fixed wing, that you must therefore be able to generate the same force in a fixed wing. This is a fallacy and does nothing to help discussions such as this one. $\endgroup$ – Simon Jun 24 '15 at 6:59
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Consider for a moment what would have to happen for you to fall out. That would have to happen either through gravity, or inertia.

Some rough over-the-thumb rationalizing (and keep in mind that I'm not a pilot, let alone a helicopter pilot -- just some basic physics applying here):

Gravity. The helicopter would have bank at a significant angle, and at the same time not have enough centripetal force (which would press you into your seat via inertia, as during a "normal" bank). For example, if the pilot forces the copter into a bank and then zeroes out on the collective. However, that same gravity will act on the chopper as well... uncomfortable low-g conditions, yes, and you probably would want to grab hold of something, but you don't get ripped out of your seat immediately.

Inertia. The helicopter would have to make a sudden lateral movement, so you get jerked out of your seat. However, as others have pointed out already, a helicopter does not have a way to induce sudden lateral movements of that magnitude. So, no dice.

Once we start considering outside forces -- turbulence, high winds, blasts from ordonance fired at you -- you probably had enough sense to strap yourself in.

Many of the movies you've been seeing will be picturing helicopters operating in Vietnam, Iraq, Afghanistan, Somalia... see a pattern here? Those are hot climates we're talking about. So, given that the usual chopper ride is unlikely to toss you out of the door, why shouldn't people enjoy a bit of a breeze? ;-)

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  • $\begingroup$ There's another physical aspect that can cause people to fall out: pressure loss in an aircraft with a pressurised cabin. $\endgroup$ – gerrit Jun 12 '15 at 15:47
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    $\begingroup$ If you're flying in a chopper with the doors open, @gerrit then you've already lost pressurization... $\endgroup$ – FreeMan Jun 12 '15 at 16:00
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    $\begingroup$ The point most people don't get, and it's simple physics, is that in a turn, you are constantly accelerating. The opposing force to that acceleration is what keeps you in place. $\endgroup$ – Simon Jun 12 '15 at 19:08
  • $\begingroup$ @FreeMan What I'm getting is at is if people expect to be blown out just because the door opens, that's probably because they are thinking of spectacular pictures of passenger airlines where the door suddenly blows open. $\endgroup$ – gerrit Jun 13 '15 at 17:45
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    $\begingroup$ @gerrit: At the altitudes helicopters are usually operating, decompression is not an issue. (I don't know if helicopters even can achieve altitudes where it would become a problem...) $\endgroup$ – DevSolar Jun 13 '15 at 18:33
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I don't fly helicopters, but I can tell you that in fixed wing aircraft you always strap in. I assume helicopters are the same.

If a plane has no doors and you are not strapped in, you will have an excellent chance of falling out. I would assume the same is true for helicopters. Some of the other answerers have talked about centrifugal forces or whatever. In reality what happens is that gusts hit you and knock you around all the time. You don't notice the gusts in big aircraft like Airbuses, but in a small aircraft it can be like being inside of a barrel rolling down a mountain. You definitely do not want to be unsecured at any time in flight, especially with a door open.

Once I was getting towed in a glider and my harness popped open. In about 2 seconds my left foot was sticking straight up, wedged against the bubble canopy and my right knee was in my face. I was upside down. Meanwhile, the glider is moving around like Pirates of the Caribbean and the tow pilot is wondering, "What the hell is he doing?" I had to wedge myself against the sides of the glider and instrument panel like Jackie Chan to get the harness buckled again.

Of course, the knuckleball motion of a gusted aircraft can be an advantage sometimes, such as when you need to deal with an unruly passenger. Just unbuckle his harness when he isn't looking, kick his door open and he will be singing "Free Falling" by Tom Petty in no time :-) Just kidding, of course, don't do that.

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    $\begingroup$ I have flown helicopters often with doors off, and although I strap in, it has nothing to do with me "falling" from the aircraft. I have never felt significant force other than perpendicular to the Z axis. Indeed, it's quite possible to roll on 45 degrees of bank and lean out of the door. I would need to shove off the aircraft to "fall out". You say "centrifugal force or whatever" as if it doesn't exist. It does. It's the apparent (or fictitious) force in a rotating frame which opposes centripetal force. The craft experiences little lateral resistance so does not produce lateral force. $\endgroup$ – Simon Jun 12 '15 at 19:06
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    $\begingroup$ What on earth was going on it that glider, in a tow, to generate the amount of G you describe? $\endgroup$ – Simon Jun 12 '15 at 19:07
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    $\begingroup$ @Simon Try doing an aero tow on a gusty day in a two-seater without wearing a harness. Might be an educational experience for you. $\endgroup$ – Tyler Durden Jun 12 '15 at 19:34
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    $\begingroup$ @romkyns Well, the OP asked about helicopters, the discussion is about helicopters and helicopters don't have rudder pedals :) $\endgroup$ – Simon Jun 14 '15 at 5:39
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    $\begingroup$ @romkyns What fixed wing pilots really struggle with is how a helicopter works. The fuselage hangs under the rotor like a pendulum. It takes a long time for it to move in response to the disc moving and it moves much more slowly and heavily damped. To produce that kind of violence would likely tear off the rotor or chop off the tail before you induced enough lateral force to eject someone. $\endgroup$ – Simon Jun 14 '15 at 16:54
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You don't fall, even in the turns because of the the direction of the body acceleration is toward the helicopter floor, including when the pilot turns. So the body is maintained with a force towards the floor, never towards the open door.

On my first ride out to the jungle (Vietnam), I looked for a seat. There weren't any. I was instructed to just sit on the side with feet hanging out. The first ride was interesting, but they soon became routine. The pilot could turn sideways and this force would hold you in. Sometimes we flew so low I thought my feet were touching the treetops.

I think about this 40 some years later. Would I sit on the side again without being strapped in ? I don't think so.

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  • $\begingroup$ That's what I meant by saying the force would hold you in. I am assuming centrifugal force held you in on turns and gravity in level flight. $\endgroup$ – Joseph J Kopac Jul 5 '15 at 16:51
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To fall out of a helicopter, your center of gravity would have to lie outside of the aircraft. Because helicopters tend to bank smoothly when they accelerate, your center of gravity stays within the aircraft. Unless the aircraft were struck by another object, it is unlikely you would ever experience a significant lateral force while flying in a helicopter.

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    $\begingroup$ LOL, try this: ask your passenger to take off his harness, open the door and stand in front of the door, then do a heavy, sudden skid to the side opposite the door and see what happens to your passenger's "center of gravity". $\endgroup$ – Tyler Durden Jun 12 '15 at 20:14
  • $\begingroup$ I think the ultimate answer lies in the fact that helicopters banks when turning and the resulting force is not purely lateral (as would happen in a car). $\endgroup$ – Cedric H. Jun 12 '15 at 22:21
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    $\begingroup$ @TylerDurden You are a self-confessed "non helicopter driver". I am a helicopter driver. it is not possible in a helicopter to generate significant lateral force no matter what you do. the fuselage is effectively a pendulum hanging beneath the head. If you make a rapid lateral control input, the disc will respond quickly, and violently, but the fuselage experiences a much delayed, much smaller and highly damped reaction. I have been in military helicopters being flown as aggressively as it gets. Manoeuvres with that kind of violence would almost certainly result in catastrophic damage. $\endgroup$ – Simon Jun 13 '15 at 6:18
  • $\begingroup$ I'd be curious to see accelerometer/axis logs for various helicopter maneuvers, and see just how much lateral force an occupant actually experiences. With regards to Tyler's hypothetical, the scenario he presents is one where the occupant is deliberately placing their center of gravity in a precarious location, and then deliberately accelerating the vehicle in a direction intended to push the occupant's cog outside of the vehicle. I didn't say it was impossible to fall out of a helicopter, just that it is unlikely, for the reasons I provided. $\endgroup$ – Byron Jones Jun 13 '15 at 18:07
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    $\begingroup$ @ByronJones The seat of my pants is a pretty good accelerometer and my brain a fairly decent log. I've been in military helicopters in combat manoeuvring and in "normal" helicopters doing aggressive manoeuvring (torque turns, falling leaf, rapid reversals) and so on. In none of that experience did my accelerometer log significant lateral force nor did I ever get forced towards a door. The forces are almost entirely vertical pushing you into or pulling you up from your seat. $\endgroup$ – Simon Jun 24 '15 at 7:03
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The helicopter is basically suspended from its main rotor, so you are sitting in the equivalent of a large swing/ride and pulled towards its floor. Suspended monorails with the ability to lean into curves can likewise look precariously wobbly from the outside while appearing perfectly stable for the inside passengers who don't feel the outside forces exactly because the craft is able to follow them, compensating their effect on the load.

The amount of jerk you can put on a heli by controlling the main blades is limited. You'll probably cause more problems by switching on and off auxiliary means of propulsion. However, those don't make for the dramatic dives, banks and turns in movies.

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    $\begingroup$ I like the analogy of suspended monorails. It helps to explain the pendulum effect of the fuselage. $\endgroup$ – Simon Jun 24 '15 at 7:06
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If you mean when the helicopter banks then all the people are either strapped into their seats like your car seat belt as all the people above have mentioned or because the have a cord attached to their jacket. (The cord part is what I saw in a documentary on the Discovery Channel).

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  • $\begingroup$ You seem to be implicitly comparing to cornering in a car. In a car, turns are achieved my the tyres applying a horizontal force to the road, so you feel an opposite (centrifugal) force pushing you outwards. However, aircraft turn by banking. In a banked into the turn, the forces felt by the passengers are primarily towards the floor. $\endgroup$ – David Richerby Jun 10 '17 at 13:31
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Are you expecting them to fly out of the helicopter because in movies, when the plane/spaceship/whatever door is opened, people get sucked out?

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If so, that effect is real (though perhaps exaggerated), but it's not caused by the craft's movement. It's caused by the depressurization of the room.

The inside has high pressure, while the outside has low pressure. When a door opens, the high pressure inside-air moves towards the outside, exerting a force on anything it meets (in the same way that the wind pulls you during a nasty storm). However, the effect dies down quickly as the pressure equalizes.

In a helicopter with open sides, that pressurization never happens to begin with, so there is no depressurization to pull the passengers out.

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  • $\begingroup$ And what about the high speed relative wind? $\endgroup$ – Mageek Jun 14 '15 at 14:31
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    $\begingroup$ @Mageek Just like in a car, the relative-wind caused by the movement of the helicopter is parallel to that movement, so unless you're sticking your head out the door you'd feel very little of it on the inside. $\endgroup$ – BlueRaja - Danny Pflughoeft Jun 14 '15 at 16:17
  • $\begingroup$ @Mageek. You never feel the relative wind inside. By definition, it's impossible since it is relative to the direction of flight. $\endgroup$ – Simon Jun 14 '15 at 16:55
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    $\begingroup$ This doesn't answer the question which state a context of "Flying in a helicopter with open doors" $\endgroup$ – mins Jun 27 '17 at 20:46
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    $\begingroup$ No the OP doesn't indicate anything about opening the door quickly in flight. In addition a helicopter usually flies close to the ground where pressure differential would not exist. The OP just wonders why being on an instable vehicle with door open seems not bother occupants. $\endgroup$ – mins Jun 27 '17 at 20:58
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Might not be relevant but here in the UK, I have been in helicopters on Search and Rescue training and missions in the mountains and you will always be belted in, whether it is by ground entry or winched up. The winchman will be attached by leash and harness as he is usually hanging around or out of the door.

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Actually seat belts in helicopters and airplanes aren't really to keep you in the plane, rather, they are to keep you from losing control if turbulence happens to throw you against the ceiling and/or knock you out. Helicopters usually avoid negative G forces as it does bad things to the rotor system, so becoming airborne is less likely, but still possible. These forces could cause you to levitate and if the turbulence is also of a sidewards component, the helicopter could travel sideways while you are airborne. Guess what?

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  • $\begingroup$ Why was this downvoted? There is nothing incorrect in this answer. $\endgroup$ – Simon Feb 23 '17 at 7:44
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People aren't falling because the cabin isn't pressurised. If you would try to open the door in mid-air of your average passenger æroplane cruising in the upper troposphere, you would be not amused. People would be sucked out. But helicopters usually don't fly at altitudes where pressure is a problem, so there is no cabin pressurisation, so there is no outward force due to an open door.

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  • $\begingroup$ If you tried to open the door of a passenger airliner during cruise, you'd be unamused because you'd be physically unable to do so (the pressure differential holds the door closed) and because you'd be restrained by your fellow passengers and the cabin crew, and arrested on landing. $\endgroup$ – David Richerby Jun 10 '17 at 13:26
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As an "Airmobile" infantryman (101st), I rode in Blackhawks countless times, sometimes in a seat belted in, but usually not. Maybe because we were only in the Blackhawk to get out of it -- rappelling, fast-roping, helocasting. I don't know if we ever had the doors closed -- can't think of a time, anyway. I have thought of this before, looking back, and wondered why we never seemed concerned about sitting in the door with our legs dangling out. I'm guessing that the scientific explanations offered above are the reason why. But I can tell you, it's not just Hollywood. We really did sit in or around the open door and never seemed to think twice about it.

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  • $\begingroup$ While this is good anecdotal information, it is more of a comment than an answer. $\endgroup$ – OSUZorba Mar 23 at 2:42
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Take a bucket of water with a handle. Start swinging it in a pendulum motion until it has enough swing to actually go around at the same constant speed. Not a drop of water will be spilled. #Pendulumeffect

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  • $\begingroup$ please consider expanding your answer $\endgroup$ – Federico Jun 10 '17 at 10:29
  • $\begingroup$ Sitting in a helicopter in no way resembles sitting in a bucket being whirled around somebody's head. And this has nothing to do with pendulums once the bucket is rotating. $\endgroup$ – David Richerby Jun 10 '17 at 13:23

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