# Why does reverse thrust work? **URL:** \ **Category:** Factual Questions\ **Created:** [January 10, 2013, 4:38pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758 "2013-01-10T16:38:48Z")\ **Posts on this page:** 20\ **Page:** 12
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [January 22, 2013, 7:40am UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/221 "2013-01-22T07:40:32Z")
> [@virtually\_yours](#): > > This probably doesn’t pertain to this but I want to correct something I stated earlier (remembering my old flight ground school days). I’m surprised the pilots in here didn’t pick up on it, maybe I was correct where the turbo fan was concerned unless they are cambered also… I couldn’t imagine them not being .. But The propeller does not really go forward by corkscrewing (as a screw does in wood) through the air though that is the result, it is the camber on the blade that is the same as the camber on the wing that creates a low pressure on the front of the blade and that is what _pulls_ the aircraft forward. hope I didn’t step in it again,bracing for impact. > vyVY Without wanting to open another can of worms, the camber is not required for the creation of lift for a wing or thrust for a propeller. What IS required is an angle of attack between the wing/propeller blade and the relative airflow. A flat wing will work but a cambered wing is more efficient. The same goes for a prop. You are correct that a propeller works the same as a wing does, you are also correct that there is a low pressure area in front of the prop and on top of the wing. That is not the whole story though. The wing works by accelerating air downward. As with the engine, the lift force can be calculated by the equation F=MA, where F is lift, M is the air mass, and A is the acceleration of the air mass. This next point is important, the lift force can ALSO be calculated by measuring the pressure differential around the wing. Hand in hand with the acceleration of air downward there is also low pressure above the wing and high pressure below it. If you choose to think of it as the wing creating low pressure above and high pressure below, you may, you can also think of it as the wing accelerating the air downward, both ways are equally correct. Please don’t let yourself get suckered into an argument between those two correct ways of conceptualising lift. On a related note, there are two popular but incorrect layman explanations for lift. One says that the air is deflected downward, and the other says that the air travelling over the wing must travel faster than the air travelling below because it has further to travel and that this creates low pressure above the wing (equal transit time theory.) Both of these explanations are similar to the explanations I’ve outlined earlier, but they are both flawed in key areas. The deflection explanation completely ignores the very important part the upper surface of the wing plays in the creation of lift. The “equal transit time” explanation says the air molecules travelling over the wing must reach the trailing edge at the same time as their “partner” air molecules travelling below the wing. This is wrong and if the upper air only travelled fast enough to achieve equal transit time there would not be enough of a pressure differential to create lift. Some links for further study from NASA: [Incorrect theory 1](http://www.grc.nasa.gov/WWW/k-12/airplane/wrong1.html) [Incorrect theory 2](http://www.grc.nasa.gov/WWW/k-12/airplane/wrong2.html) [Correct theory](http://www.grc.nasa.gov/WWW/k-12/airplane/lift1.html) I’d suggest you start another thread if you want to get further into propeller and wing theory. ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 22, 2013, 2:48pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/222 "2013-01-22T14:48:27Z")
> [@Richard\_Pearse](#): > > Without wanting to open another can of worms, the camber is not required for the creation of lift for a wing or thrust for a propeller. What IS required is an angle of attack between the wing/propeller blade and the relative airflow. A flat wing will work but a cambered wing is more efficient. The same goes for a prop. I have no prob with this . I see fans and computer fans. I was correcting my statement the kind of disregarded the camber on the prop.. > [@Richard\_Pearse](#): > > You are correct that a propeller works the same as a wing does, you are also correct that there is a low pressure area in front of the prop and on top of the wing. That is not the whole story though. The wing works by accelerating air downward. uh oh _acceleration_ I’m not touching this one.. > [@Richard\_Pearse](#): > > On a related note, there are two popular but incorrect layman explanations for lift. One says that the air is deflected downward, and the other says that the air travelling over the wing must travel faster than the air travelling below because it has further to travel and that this creates low pressure above the wing (equal transit time theory.) Both of these explanations are similar to the explanations I’ve outlined earlier, but they are both flawed in key areas. The deflection explanation completely ignores the very important part the upper surface of the wing plays in the creation of lift. The “equal transit time” explanation says the air molecules travelling over the wing must reach the trailing edge at the same time as their “partner” air molecules travelling below the wing. This is wrong and if the upper air only travelled fast enough to achieve equal transit time there would not be enough of a pressure differential to create lift. That’s not what I understand. I understand that the air over the top of the wing tries to make it to the back of the wing at the same time as the air underneath but is unable to do it. So this creates a low pressure or type of vacuum so to speak. The only thing left to try and fill the vacuum is the top surface of the wing. so as the air tries to make it down over the camber the wing tries to go up to fill the _space_..If that’s wrong well I will have to try and get deeper into what is happening.like you said, in another thread.. With your correct theory diagram [Correct theory](http://www.grc.nasa.gov/WWW/k-12/airplane/lift1.html)I use 'newton analogy" If I whittle away the aircraft and leave the wings would the wing still have lift.. I have to conclude yes..maybe I am reading the diagram wrong.. vyVY ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [January 22, 2013, 3:27pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/223 "2013-01-22T15:27:47Z")
> [@virtually\_yours](#): > > I thought to myself where is the speeding up in this, so I just accepted that they were using the word acceleration for two different meanings one for speeding up and the other for change in velocity direction. I couldn’t understand how if I am driving along at 10 mph and take a left at 10 mph that I am somehow _speeding up_. So I figured that it meant two different things. When you use brakes or throttle to adjust the magnitude of your velocity, you are accelerating in a direction _parallel_ to your current path of travel. When you drive around a turn, you are changing the _direction_ of your velocity without changing the magnitude. This requires you to accelerate in a direction _perpendicular_ to your path of travel. The magnitude of that lateral acceleration is proportional to the square of your speed, and inversely proportional to the radius of the turn: a = V[sup]2[/sup]/R Just as your tires will skid if you step on the brakes or gas too hard (too much acceleration), they will also skid if you go around a turn too fast (too much acceleration). That’s a big clue that changes in direction of travel do indeed require acceleration, which in turn requires the tires to exert traction force against the road. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [January 22, 2013, 3:33pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/224 "2013-01-22T15:33:04Z")
> [@virtually\_yours](#): > > That’s not what I understand. I understand that the air over the top of the wing tries to make it to the back of the wing at the same time as the air underneath but is unable to do it. This is wrong - see incorrect explanation #1. It’s a common belief, but wrong. Did you follow and read the link? ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 22, 2013, 4:42pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/225 "2013-01-22T16:42:07Z")
> [@Telemark](#): > > This is wrong - see incorrect explanation #1. It’s a common belief, but wrong. Did you follow and read the link? yeah.. I’ll go back over it again.. cant get the plugins to install. will try iE vyVY ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 22, 2013, 4:43pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/226 "2013-01-22T16:43:29Z")
> [@Machine\_Elf](#): > > When you use brakes or throttle to adjust the magnitude of your velocity, you are accelerating in a direction _parallel_ to your current path of travel. When you drive around a turn, you are changing the _direction_ of your velocity without changing the magnitude. This requires you to accelerate in a direction _perpendicular_ to your path of travel. The magnitude of that lateral acceleration is proportional to the square of your speed, and inversely proportional to the radius of the turn: > > a = V[sup]2[/sup]/R > > Just as your tires will skid if you step on the brakes or gas too hard (too much acceleration), they will also skid if you go around a turn too fast (too much acceleration). That’s a big clue that changes in direction of travel do indeed require acceleration, which in turn requires the tires to exert traction force against the road. Does centrifugal force have anything to do with this (acceleration) or it is a different entity? vyVY ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 22, 2013, 4:59pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/227 "2013-01-22T16:59:59Z")
> [@Telemark](#): > > This is wrong - see incorrect explanation #1. It’s a common belief, but wrong. Did you follow and read the link? With all respect a wing doesn’t look like that.. The wing in that simulation has symmetrical sides top and bottom.. I have preflighted enough aircraft to know the underside looks much different than the topside. Not saying the theory is wrong, just saying what I see. use the paper in your hand example. blow only over the back of the paper and it will start to rise.. no action on the bottom part vyVY ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 22, 2013, 5:38pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/228 "2013-01-22T17:38:41Z")
And btw the article says that it is basically correct :_{The upper flow is faster and from Bernoulli’s equation the pressure is lower. The difference in pressure across the airfoil produces the lift.} As we have seen in Experiment #1, this part of the theory is correct. In fact, this theory is very appealing because many parts of the theory are correct._ It seems at one point they are saying correct and at another point saying not… (head spinning) vyVY ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [January 22, 2013, 5:56pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/229 "2013-01-22T17:56:31Z")
> [@virtually\_yours](#): > > Does centrifugal force have anything to do with this (acceleration) or it is a different entity? > vyVY Centrifugal force is the force that accelerates you toward the center of the curve. It’s the lateral acceleration we’re now talking about, multipled by the mass of the object which is being accelerated: F = m \* a = m\* V[sup]2[/sup]/R > [@virtually yours](#): > > With all respect a wing doesn’t look like that.. The wing in that simulation has symmetrical sides top and bottom. It is true that most wings do not use symmetric airfoils; instead they use asymmetric airfoils, which are optimized to provide lift most efficiently over a particular range of angles of attack. However, some planes _do_ use symmetric airfoils, which are less efficient but are able to generate lift over a much wider range of angles of attack. This is most commonly used on aerobatic planes, where maneuverability is much more important (and fuel economy much less important) than long-haul commercial airliners. for either airfoil type, the theory of operation is the same: faster flow/lower pressure on top, slower flow/higher pressure on bottom. ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [January 22, 2013, 5:57pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/230 "2013-01-22T17:57:32Z")
> [@virtually\_yours](#): > > With all respect a wing doesn’t look like that.. The wing in that simulation has symmetrical sides top and bottom.. I have preflighted enough aircraft to know the underside looks much different than the topside. > Not saying the theory is wrong, just saying what I see. use the paper in your hand example. blow only over the back of the paper and it will start to rise.. no action on the bottom part > vyVY The shape of the wing affects its efficiency and various other parameters. It is not necessary that a wing be asymmetric - in fact, plenty of planes fly with symmetric wing s(e.g. acrobatic planes), and even planes with asymmetric wings can fly upside down (which would be impossible if the asymmetry of the wing was crucial for lift). Aerodynamics is very complicated. There are approximately 4 different ways to analyze airflow around a wing, all equivalent in the end. Fundamentally, the angle and shape of the wing relative to the oncoming air acts to produce a low pressure region above the wing, and a high pressure region below it. This pressure imbalance causes lift. Note that what actually, physically keeps the wing aloft are the collisions (pressure) from the gas molecules below the wing, and the relative lack of such collisions from the gas molecules above the wing. ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 22, 2013, 7:59pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/231 "2013-01-22T19:59:09Z")
> [@Absolute](#): > > The shape of the wing affects its efficiency and various other parameters. It is not necessary that a wing be asymmetric - in fact, plenty of planes fly with symmetric wing s(e.g. acrobatic planes), and even planes with asymmetric wings can fly upside down (which would be impossible if the asymmetry of the wing was crucial for lift). I disagree. I am a pilot. Remember level flight is balanced. If the plane at a given power setting wants to climb you push the nose towards the ground until it stops climbing, hence level flight. upside down is the same principle but opposite to the ground: Upside down you are still flying through the air, the aircraft doesn’t know up or down, so if you see the ground getting closer you push forward on the yolk hence pushing the nose of the aircraft away from the ground climbing upside down gaining altitude. > [@Absolute](#): > > Aerodynamics is very complicated. There are approximately 4 different ways to analyze airflow around a wing, all equivalent in the end. Fundamentally, the angle and shape of the wing relative to the oncoming air acts to produce a low pressure region above the wing, and a high pressure region below it. This pressure imbalance causes lift. Note that what actually, physically keeps the wing aloft are the collisions (pressure) from the gas molecules below the wing, and the relative lack of such collisions from the gas molecules above the wing. respectfully I disagree, use the paper in your hands example. Let it fold over like an airfoil and blow only over the top, the paper will rise without any any air blowing from your mouth under the paper. Now we agree that there is a lack of air molecules on top of the wing under the air flying up over the camber and hence there is low pressure there. Whether the plane is being sucked up, or pushed up, or one more than the other, or both, may or may not be debatable.. My layman mind sees the low pressure as a big syringe, if I put it a few inches from the top of the wing and suck hard anything near is trying to be sucked up in there; air and the metal on the wing.. use the same piece of paper, lay it flat in your hand start sucking air in your mouth and get closer; the paper jumps to your mouth before your mouth touches it.. that’s what I see vyvY ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [January 22, 2013, 8:16pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/232 "2013-01-22T20:16:10Z")
> [@virtually\_yours](#): > > I disagree. I am a pilot. Remember level flight is balanced. If the plane at a given power setting wants to climb you push the nose towards the ground until it stops climbing, hence level flight. upside down is the same principle but opposite to the ground: Upside down you are still flying through the air, the aircraft doesn’t know up or down, so if you see the ground getting closer you push forward on the yolk hence pushing the nose of the aircraft away from the ground climbing upside down gaining altitude. I am also a pilot. 😃 The amount of lift the wing generates varies with speed and angle of attack. Higher angles of attack generate more lift (up to the point of the stall). When you trim the nose down you reduce the angle of attack, until lift is equal to the weight of the plane and it maintains altitude. When you are upside down in level flight, the orientation of the lift force created must be reversed. Rather than generating lift towards the top of the plane, it must generate lift towards the bottom of the plane, in order to oppose the force of gravity and keep the plane from losing altitude. If the asymmetry of the wing was required to generate lift, then the lift generated would always be towards the top of the wing. And when you turned the plane upside down, the top of the wings would now be pointing down, and it would plummet to the Earth. This does not happen - therefore, the asymmetry of the wing is not required for lift. > [@](#): > > respectfully I disagree, use the paper in your hands example. Let it fold over like an airfoil and blow only over the top, the paper will rise without any any air blowing from your mouth under the paper. Yes, because the movement of air over the top lowers the pressure, relative to the bottom. That’s all that matters. > [@](#): > > Now we agree that there is a lack of air molecules on top of the wing under the air flying up over the camber and hence there is low pressure there. Whether the plane is being sucked up, or pushed up, or one more than the other, or both, may or may not be debatable.. > My layman mind sees the low pressure as a big syringe, if I put it a few inches from the top of the wing and suck hard anything near is trying to be sucked up in there; air and the metal on the wing.. > use the same piece of paper, lay it flat in your hand start sucking air in your mouth and get closer; the paper jumps to your mouth before your mouth touches it.. > that’s what I see > vyvY Yes, well, that’s the problem. “Suction” is an illusory force. What happens when you create low pressure is that the surrounding regions of high pressure try to expand into the region of low pressure. There is no force in nature that attracts things to a vacuum. It is the pressure of the surrounding atmosphere trying to expand into the vacuum that creates that illusion. There is no sucking force. There is only the force of the atmosphere trying to reach the region that has been “sucked”. Fundamentally, physically, the atmosphere pushes on the bottom of the wing more than it pushes on the top of the wing, and that keeps the wing aloft. ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 22, 2013, 8:42pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/233 "2013-01-22T20:42:33Z")
> [@Absolute](#): > > I am also a pilot. 😃 > > The amount of lift the wing generates varies with speed and angle of attack. Higher angles of attack generate more lift (up to the point of the stall). When you trim the nose down you reduce the angle of attack, until lift is equal to the weight of the plane and it maintains altitude. > > When you are upside down in level flight, the orientation of the lift force created must be reversed. Rather than generating lift towards the top of the plane, it must generate lift towards the bottom of the plane, in order to oppose the force of gravity and keep the plane from losing altitude. > > If the asymmetry of the wing was required to generate lift, then the lift generated would always be towards the top of the wing. And when you turned the plane upside down, the top of the wings would now be pointing down, and it would plummet to the Earth. This does not happen - therefore, the asymmetry of the wing is not required for lift. Well I’ve seen regular aircraft doing barrel rolls and regular rolls close to the ground they don’t plummet.. maybe something else is going on? > [@Absolute](#): > > Yes, because the movement of air over the top lowers the pressure, relative to the bottom. That’s all that matters. > > Yes, well, that’s the problem. “Suction” is an illusory force. What happens when you create low pressure is that the surrounding regions of high pressure try to expand into the region of low pressure. There is no force in nature that attracts things to a vacuum. It is the pressure of the surrounding atmosphere trying to expand into the vacuum that creates that illusion. > > There is no sucking force. There is only the force of the atmosphere trying to reach the region that has been “sucked”. Fundamentally, physically, the atmosphere pushes on the bottom of the wing more than it pushes on the top of the wing, and that keeps the wing aloft. Agreed. you are right. In other words it is trying to equalize. I assume it’s because of the _weight_ or pressure of the air finding the path of least resistance? vyVY ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [January 22, 2013, 8:47pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/234 "2013-01-22T20:47:53Z")
> [@virtually\_yours](#): > > Well I’ve seen regular aircraft doing barrel rolls and regular rolls close to the ground they don’t plummet.. maybe something else is going on? That’s my point. An airplane of any kind can fly upside down regardless of the shape of the wing - even though most wings are asymmetric. The asymmetry of the wing simply makes it more efficient at producing lift in one direction, and less efficient in the other. It is not _required_ to produce lift. ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 22, 2013, 10:10pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/235 "2013-01-22T22:10:12Z")
> [@Absolute](#): > > That’s my point. An airplane of any kind can fly upside down regardless of the shape of the wing - even though most wings are asymmetric. The asymmetry of the wing simply makes it more efficient at producing lift in one direction, and less efficient in the other. It is not _required_ to produce lift. Another crack at this: at 10,000 ft I push the nose down directly at the ground. gravity is there not affecting but I am still flying, the wings are not stalled so to speak. no gravity acting on the bottom or top of the plane but I don’t start going in the direction of the top of the wings, because I push the yolk to counteract it. Same way if I pulled up and went straight up at the sky, The air is still flowing over the wings the plane is flying, there is no gravity at my feet or head so I should shoot backwards but I don’t , I can counteract that with the yolk if necessary using the air.. So I see it as the same thing upside down, use the attitude of the nose to fly the plane. Don’t know if this is relevant to the point, I’m think I’m losing it (the point) somewhere probably, but thought i would mention it all the same vyVY ---
**Author:** ![AdamF](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/adamf/32/6246_2.png) [@AdamF](https://boards.straightdope.com/u/AdamF)\ **Post date:** [January 23, 2013, 5:47pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/236 "2013-01-23T17:47:56Z")
I didn’t realize that there was a controversy… Lift is most certainly produced by the difference in air pressure between the top and bottom surface of the wing. However, there are different ways to produce the pressure difference. One way is to take a wing with symmetric profile and fly it at positive angle of attack. Second way is to use a wing with asymmetric profile and fly it at zero angle of attack. And third way is to blow a air over the upper surface. Planes usually combine the first and second approach, because that is more efficient. ---
**Author:** ![AdamF](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/adamf/32/6246_2.png) [@AdamF](https://boards.straightdope.com/u/AdamF)\ **Post date:** [January 23, 2013, 6:00pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/237 "2013-01-23T18:00:04Z")
> [@virtually\_yours](#): > > Adam I don’t know if you read the previous posts but it is proved that in the engine it is the combustion that provides the heat that gets the molecules in motion that act on the aircraft to move it.. I am perfectly aware of how a jet engine conceptually works. The problem is that all models are by necessity an approximation of what actually occurs. The most common simplification is that the air flow speed through the engine is constant. In practice, this is not true. Air passing through an axial compressor will slow down, while radial compressor tends speed it up. Air certainly accelerates somewhat when it is rapidly heated up in the combustion chamber and then it slows down while passing through a turbine. Yet to the first order of approximation, the net change in speed is zero. However, I would be very interested in knowing what the actual values are and I have trouble finding anything about it. > [@virtually\_yours](#): > > The _inner_ part of the fan provides the air needed for the exact fuel air ratio to burn, too much air,well you know what will happen, but there is a bypass for scenarios like that Bypass ratio is entirely about decreasing the specific fuel consumption (or increasing specific impulse) of the engine and nothing to do with fuel/air ratios. No jet engine can run at stoichiometric conditions anyway - it would melt the turbine. Therefore, all jets run on a lean mixture (when comparing the core air flow to fuel flow - local conditions at any point in the combustion chamber can be very different). ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [January 23, 2013, 8:56pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/238 "2013-01-23T20:56:18Z")
> [@virtually\_yours](#): > > Another crack at this: at 10,000 ft I push the nose down directly at the ground. gravity is there not affecting but I am still flying, the wings are not stalled so to speak. no gravity acting on the bottom or top of the plane but I don’t start going in the direction of the top of the wings, because I push the yolk to counteract it. Same way if I pulled up and went straight up at the sky, The air is still flowing over the wings the plane is flying, there is no gravity at my feet or head so I should shoot backwards but I don’t… :dubious: You say you’re a pilot, but you don’t understand the importance of [angle of attack?](http://en.wikipedia.org/wiki/Angle_of_attack) AoA will be different in level flight vs. a vertical climb; in the latter case, the AoA will be such that the wings produce zero lift. > [@](#): > > I can counteract that with the yolk if necessary using the air.. So I see it as the same thing upside down, use the attitude of the nose to fly the plane. Exactly. You adjust the pitch of the aircraft to achieve the AoA necessary to get the wings to produce whatever amount of lift you want. This is true regardless of whether the aircraft is inverted or not. The whole point is that this is true regardless of whether the aircraft is fitted with a symmetric airfoil or an assymetric one. ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 24, 2013, 9:56pm UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/239 "2013-01-24T21:56:12Z")
> [@Machine\_Elf](#): > > :dubious: > > You say you’re a pilot, but you don’t understand the importance of [angle of attack?](http://en.wikipedia.org/wiki/Angle_of_attack) AoA will be different in level flight vs. a vertical climb; in the latter case, the AoA will be such that the wings produce zero lift. Actually my scenario was to try and show a no gravity situation.. and the plane would still fly.. imagine how newton did if the earth was whittled away and the plane was flying in a box of air, angle of attack now? > [@Machine\_Elf](#): > > Exactly. You adjust the pitch of the aircraft to achieve the AoA necessary to get the wings to produce whatever amount of lift you want. This is true regardless of whether the aircraft is inverted or not. The whole point is that this is true regardless of whether the aircraft is fitted with a symmetric airfoil or an assymetric one. ooops By absolute, I just reread this: _ **When you are upside down in level flight, the orientation of the lift force created must be reversed. Rather than generating lift towards the top of the plane, it must generate lift towards the bottom of the plane, in order to oppose the force of gravity and keep the plane from losing altitude.** _\* I had misread it earlier thinking it was a refutation,thats why I wrote what I wrote I see now it is saying the same thing as me..vyVY ---
**Author:** ![virtually\_yours](https://avatars.discourse-cdn.com/v4/letter/v/a587f6/32.png) [@virtually\_yours](https://boards.straightdope.com/u/virtually_yours)\ **Post date:** [January 25, 2013, 1:28am UTC](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758/240 "2013-01-25T01:28:08Z")
On the vacuum issue let me know what is happening here: A glass vacuumed sealed tube on wheels. You break one end, if moves in the direction of the break. what and where is the action? thanks vyVY [Previous page](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758.md?page=11) [Next page](https://boards.straightdope.com/t/why-does-reverse-thrust-work/646758.md?page=13)