Can Vmg exceed the V of a jet exhaust?
Join Date: Aug 2001
Location: Dorset
Posts: 775
Likes: 0
Received 0 Likes
on
0 Posts
Mr Optimistic
I agree that most (but not all) of the rearward force on the nozzle is produced by the pressure in the jet pipe. But that does not mean that we cannot call it drag. Isn't Form drag caused by pressure acting on the forward facing surfaces of an aircraft?
I used the term DRAG because the force on the nozzle acts rearwards. If you prefer to use another word then you are free to specify one.
But the important point as far as this discussion goes is the fact that the force on the nozzle acts reawwards.
The pressure is actually acting on the forward facing surfaces of the nozzle. That's why it tends to push it rearwards.
Agrred, but does not answer the question.
Agreed, but still does not answer the question. IE. On what part of the engine does the thrust force that has been produced by accelearting gas through the nozzle act.
The nozzle would probably fly rearwards. The exception would be the a condi nozzle in which case the direction would depend on the relative magnitudes of the forward forces acting on that part of the nozzle downstream of the throat, and rearward acting forces on the part upstream of the throat. My vote would go for it flying reaward in most cases.
I do not agree.
I said that we don't neeed to consider a condi nozzle. You are correct that the pressure downstraem of the throat is greater than ambient. That is why it creates thrust on that part of the nozzle that is downstream of the throat.
Agreed. That "engineering factor" would include ensuring that the attachment of the nozzle was strong enough to stop it being torn off and thrown rearward.
But none of your post addresses the question at hand. On waht part of teh engien does the thrust caused by acceleration of air thropugh the nozzle actually act?
The high pressure in an engine or jet would tend to push the back end off: nothing to do with drag force on the nozzle surface,
I used the term DRAG because the force on the nozzle acts rearwards. If you prefer to use another word then you are free to specify one.
But the important point as far as this discussion goes is the fact that the force on the nozzle acts reawwards.
just pressure acting on the rear surface.
Nozzle turns pressure into flow speed.
Blow up a balloon, turn it around so it faces away from you and let go of the untied end. Would it fly away from you owing to drag over the aperture or into your face because of the thrust ?
Put a weak joint between the nozzle of a rocket motor and the case and see what happens (owing to the pressure inside the case) - from half a mile away that is.
And the adiabatic expansion or compression on flow through a cone would cause no discernable heating or cooling (convergent at subsonic speeds would in any case heat).
Don't need de laval nozzle theory here. NB look at most rocket plumes, they bulge out ie exit pressure is still above ambient. Small drag losses in a nozzle
I suspect are just accounted for by an 'engineering factor' in practice.
But none of your post addresses the question at hand. On waht part of teh engien does the thrust caused by acceleration of air thropugh the nozzle actually act?
pressure
For the balloon, if the thing is tied then the internal pressure acts equally in all directions on the inner surface. Open the back end and there is an unequal distribution. Same with rocket engine ie its the net force obtained by the pressure in the chamber. Only force causes acceleration but conservation of momentum or energy often gets the result easier, however it is always a net force.
In a turbojet, not sure but there is the bypass flow generating a differential pressure and the reaction force on the fan blades (as someone else said).
Had to do the pressure integration myself a generation ago, for a rocket.
That was at Caltech, btw. Applied Physics. Doesn't make me infallible however.
In a turbojet, not sure but there is the bypass flow generating a differential pressure and the reaction force on the fan blades (as someone else said).
Had to do the pressure integration myself a generation ago, for a rocket.
That was at Caltech, btw. Applied Physics. Doesn't make me infallible however.
Join Date: Aug 2001
Location: Dorset
Posts: 775
Likes: 0
Received 0 Likes
on
0 Posts
You are certainly right there ChristiaanJ.
There is no need to complicate the question with such things. In fact nothing useful will be achieved by doing so.
To simplfy the question as much as possible let's start by considering a metal cylinder which is closed at the front end and has a convergent propelling nozzle at the back end.
If the pressure in the cylinder is greater than that outside, then the air in the cylinder will be accelerated rearwards through the nozzle. This will produce a forward acting force which we conventionally call thrust.
But the force acting on the nozzle will be acting rearwards, so let's call it drag. Or if you prefer let's call it the Rearward Acting Force or RAF (a pretty appropriate abreviation really... the RAF always was a rearward acting force).
Now the thrust isn't pushing forward on the nozzle, so where exactly is it pushing forward?
If we can solve that one, then we can look at the slightly more complicated case of a zero by-pass jet engine where the front end of the jet pipe houses the exhaust unit and the turbines.
No maths required here, just a little bit of imagination and no emotion whatsoever (GRRRRRRR).
There is no need to complicate the question with such things. In fact nothing useful will be achieved by doing so.
To simplfy the question as much as possible let's start by considering a metal cylinder which is closed at the front end and has a convergent propelling nozzle at the back end.
If the pressure in the cylinder is greater than that outside, then the air in the cylinder will be accelerated rearwards through the nozzle. This will produce a forward acting force which we conventionally call thrust.
But the force acting on the nozzle will be acting rearwards, so let's call it drag. Or if you prefer let's call it the Rearward Acting Force or RAF (a pretty appropriate abreviation really... the RAF always was a rearward acting force).
Now the thrust isn't pushing forward on the nozzle, so where exactly is it pushing forward?
If we can solve that one, then we can look at the slightly more complicated case of a zero by-pass jet engine where the front end of the jet pipe houses the exhaust unit and the turbines.
No maths required here, just a little bit of imagination and no emotion whatsoever (GRRRRRRR).
sorry
...get a bit stressed when at work. Wish I could draw a picture but skills not good enough. Reason for adding in the rocket etc was that the same principles apply and thought it easier to picture. The pressure on the inside of the nozzle will be backwards (normal to wall ignoring friction), so if the nozzle broke it would fly backwards. However there is a hole in the nozzle. View the whole thing as a lump of dumb metal: it doesn't 'know' about the conservation of momentum, the only thing which affects it are the forces acting on its physical surfaces and all forces count.
Now release your grip on the cone a little bit and blow really hard until you no longer hold the nozzle.
If the nozzle is producing thrust it will force its way into your mouth.
It is producing thrust and pushing it and you backwards slightly.
But it will actually fly out and away from you.
Well yes, because of the pressure on the inside acting backwards. Because there is no front surface (where your mouth just was) there is no front surface on which the internal pressure can act so all forces are rearward. Same is true in a rocket nozzle except that there is a front surface of the whole chamber opposite the nozzle on which the pressure can act, so the force on the nozzle (and any back face) is indeed rearwards but then there is this hole (no metal so no force), imbalance = thrust.
This is because the aerodynamic force on the nozzle is drag acting downstream.
Conventionally drag infers force due to motion, motion gives shear, shear gives lateral force on surface. Its pressure which gives the overwhelming force.
So if the force on the nozzle is drag, how does it increase the thrust?
Need a way of having hole at the back while letting gas out while keeping internal pressure high at that all important front internal surface (where the pressure pushing forward on the wall acts).
Nozzle is a means to an end, net thrust is generated elsewhere.
Always pressure, - don't shout at me for introducing kitchenware as well as bypass engines- but if you have a cupboard with two doors, slamming one shut may pop the other open but its not the 'rush of air' which pushes, its the rush of air which decelerates on getting to the door which then increases in pressure until the pressure pushes the door.
Now release your grip on the cone a little bit and blow really hard until you no longer hold the nozzle.
If the nozzle is producing thrust it will force its way into your mouth.
It is producing thrust and pushing it and you backwards slightly.
But it will actually fly out and away from you.
Well yes, because of the pressure on the inside acting backwards. Because there is no front surface (where your mouth just was) there is no front surface on which the internal pressure can act so all forces are rearward. Same is true in a rocket nozzle except that there is a front surface of the whole chamber opposite the nozzle on which the pressure can act, so the force on the nozzle (and any back face) is indeed rearwards but then there is this hole (no metal so no force), imbalance = thrust.
This is because the aerodynamic force on the nozzle is drag acting downstream.
Conventionally drag infers force due to motion, motion gives shear, shear gives lateral force on surface. Its pressure which gives the overwhelming force.
So if the force on the nozzle is drag, how does it increase the thrust?
Need a way of having hole at the back while letting gas out while keeping internal pressure high at that all important front internal surface (where the pressure pushing forward on the wall acts).
Nozzle is a means to an end, net thrust is generated elsewhere.
Always pressure, - don't shout at me for introducing kitchenware as well as bypass engines- but if you have a cupboard with two doors, slamming one shut may pop the other open but its not the 'rush of air' which pushes, its the rush of air which decelerates on getting to the door which then increases in pressure until the pressure pushes the door.
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes
on
0 Posts
Keith,
Your 'cylinder' simplification takes us right back to this ancient picture (sorry, only a scribble on-the-fly)..
Where does the thrust come from? From the pressure/force on the left side, which is not compensated by an equivalent pressure/force on the right.
Now if this were a proper rocket, with a con-di nozzle, and enough chamber pressure for the throat to go Mach 1, you'd get some additional thrust from the expansion in the nozzle (why does the shuttle engine have those large bell nozzles? It does help ...).
CJ
Your 'cylinder' simplification takes us right back to this ancient picture (sorry, only a scribble on-the-fly)..
Where does the thrust come from? From the pressure/force on the left side, which is not compensated by an equivalent pressure/force on the right.
Now if this were a proper rocket, with a con-di nozzle, and enough chamber pressure for the throat to go Mach 1, you'd get some additional thrust from the expansion in the nozzle (why does the shuttle engine have those large bell nozzles? It does help ...).
CJ
CJ
nice picture, indeed so, but wanted to get to the main point of the pressure at the front acting on the wall so could then expand to pressure on the back of turbine blades pushing fwd, on back of arms when swimming, pushing fwd etc. Sorry I got a bit priggish, it isn't rare behaviour afraid.
Now if you ask a) what makes a 'good' nozzle and b) how do you know you have made a good one....don't know, tried looking for this myself some months ago co-incidentally (and failed).
Now if you ask a) what makes a 'good' nozzle and b) how do you know you have made a good one....don't know, tried looking for this myself some months ago co-incidentally (and failed).
Join Date: Dec 2007
Location: Pasadena
Posts: 633
Likes: 0
Received 0 Likes
on
0 Posts
Re: 47: Intake and turbine
I completely agree with the picture in 46. The uncompensated pressure on the left-hand wall of the balloon and the change in momentum of the escaping gas are equivalent ways to get the leftwards thrust force.
To try to draw a link to the ice-cream cone, if you were to snip off the balloon's blowing-end, it would be blown off to the right, because the air is trying to drag it to the right, and being slowed down in the process.
-
Now, the main point I wanted to make is about the general discussion about thrust from supersonic intakes and the thrust on turbine blades mentioned in 47.
The turbine extracts energy from the exhaust, slowing it down. This reduces the rearward momentum of the exhaust, requiring a forward force on the air, and Sir Isaac demands a rearward force on the turbine in reaction. The exhaust stream does not push the turbine into the engine, it tries to pull it off. You could also consider this a pressure drop from upstream of the turbine to downstream.
I think if you have `front of the combuster' instead of `the back of turbine blades' in the first paragraph of post 47 then the statement is true. When you're swimming you're accelerating water backwards with your arms: that's an analogy to your arm being a fan blade rather than a turbine blade.
-
For supersonic intakes, I don't think that the idea that they produce thrust is correct. In the intake the airflow is slowed to allow subsonic combustion. This is the same as the case for the turbine: the rearward momentum of the airflow is reduced, pushing the intake backwards. This typically happens, along with direction changes, at carefully-controlled shocks. Only by then burning fuel in the flow is it reaccelerated to ensure a net gain in rearward momentum through the whole engine, and thus a forward thrust. I can't see how any arrangement of components, ramps and shocks can extract thrust from slowing an airstream.
I suspect that if the J58's rotating core in an SR71 is producing drag at M3, then it must be providing mechanical power to a compressor to get enough airflow to the ramjet-like afterburner that actually provides the thrust.
To try to draw a link to the ice-cream cone, if you were to snip off the balloon's blowing-end, it would be blown off to the right, because the air is trying to drag it to the right, and being slowed down in the process.
-
Now, the main point I wanted to make is about the general discussion about thrust from supersonic intakes and the thrust on turbine blades mentioned in 47.
The turbine extracts energy from the exhaust, slowing it down. This reduces the rearward momentum of the exhaust, requiring a forward force on the air, and Sir Isaac demands a rearward force on the turbine in reaction. The exhaust stream does not push the turbine into the engine, it tries to pull it off. You could also consider this a pressure drop from upstream of the turbine to downstream.
I think if you have `front of the combuster' instead of `the back of turbine blades' in the first paragraph of post 47 then the statement is true. When you're swimming you're accelerating water backwards with your arms: that's an analogy to your arm being a fan blade rather than a turbine blade.
-
For supersonic intakes, I don't think that the idea that they produce thrust is correct. In the intake the airflow is slowed to allow subsonic combustion. This is the same as the case for the turbine: the rearward momentum of the airflow is reduced, pushing the intake backwards. This typically happens, along with direction changes, at carefully-controlled shocks. Only by then burning fuel in the flow is it reaccelerated to ensure a net gain in rearward momentum through the whole engine, and thus a forward thrust. I can't see how any arrangement of components, ramps and shocks can extract thrust from slowing an airstream.
I suspect that if the J58's rotating core in an SR71 is producing drag at M3, then it must be providing mechanical power to a compressor to get enough airflow to the ramjet-like afterburner that actually provides the thrust.
Last edited by awblain; 3rd Jul 2009 at 17:23.
Join Date: Sep 1998
Location: wherever
Age: 55
Posts: 1,616
Likes: 0
Received 0 Likes
on
0 Posts
Where is this darn force acting?
I agree with the nice balloon picture and made many an eggshell steam cart as a kid. I was told in my service days that the thrust was felt on all those parts that add energy to the gasses as they transit through the engine. I always have trouble with this when I see a Harrier in the hover as quite frankly the thrust is acting at 90 degrees to those previously mentioned parts. My mental picture now is of the thrust acting on the area of the Nozzle. not the surface but the hole as it were.
I agree with the nice balloon picture and made many an eggshell steam cart as a kid. I was told in my service days that the thrust was felt on all those parts that add energy to the gasses as they transit through the engine. I always have trouble with this when I see a Harrier in the hover as quite frankly the thrust is acting at 90 degrees to those previously mentioned parts. My mental picture now is of the thrust acting on the area of the Nozzle. not the surface but the hole as it were.
Join Date: Dec 2007
Location: Pasadena
Posts: 633
Likes: 0
Received 0 Likes
on
0 Posts
Harrier swivel nozzle?
In the four swivel nozzles the fan/turbine exhaust is turned ~90 degrees. Changing the momentum of the air from horizontal to vertical requires a force on the air pointing inboard at 45 degrees down from the horizontal. Sir Isaac arranges for an equal opposite force on the nozzle: 45 degrees up from the horizontal and outboard. Each nozzle supports about 1/4 of the aircraft weight in the hover, so the thrust acts up through the nozzle hinge with ~4000 lb of force, and also tries to rip each nozzle off the aircraft with ~4000 lb. I reckon you could probably get an insight from the force required to hold a sharply bent firehose steady.
Join Date: Aug 2001
Location: Dorset
Posts: 775
Likes: 0
Received 0 Likes
on
0 Posts
OK,
I think that most of us have now come to the conclusion that
A. The thrust force acts on the front of the chamber (in a simple rocket).
In a jet pipe it acts on the exhaust unit (which is just behind the rear
turbine), and on the rear face of the rear turbine.
B. The force on the nozzle acts rearwards.
Logically we can say that the resultant forward thrust is A minus B
This suggests that having the nozzle actually reduces the resultant thrust.
Which brings us to the real question.
Why don't we just remove the nozzle and get rid of the rearward acting force?
The above results suggest that this will give us more resultant thrust.
Once again, no heavy maths required (anyone who integrates will be excluded), just imagination and logical thought processes.
I think that most of us have now come to the conclusion that
A. The thrust force acts on the front of the chamber (in a simple rocket).
In a jet pipe it acts on the exhaust unit (which is just behind the rear
turbine), and on the rear face of the rear turbine.
B. The force on the nozzle acts rearwards.
Logically we can say that the resultant forward thrust is A minus B
This suggests that having the nozzle actually reduces the resultant thrust.
Which brings us to the real question.
Why don't we just remove the nozzle and get rid of the rearward acting force?
The above results suggest that this will give us more resultant thrust.
Once again, no heavy maths required (anyone who integrates will be excluded), just imagination and logical thought processes.
no nozzle = explosion
must be some measure of nozzle efficiency/effectiveness but no clear idea of it.
not the surface but the hole as it were.
To accelerate the body a force must act on the body. Application of 'control surfaces' often simplifies the maths but can mislead. The body doesn't 'know' what some parcel of ejected air is doing but remote parts of the air affect the air next to it which can be tracked back to the air next to the body and then to the body itself. Continuity. So in terms of whats happening at the hole, specifically 'no' but everything is connected to something else !.
On reflection, can't see that helping !
not the surface but the hole as it were.
To accelerate the body a force must act on the body. Application of 'control surfaces' often simplifies the maths but can mislead. The body doesn't 'know' what some parcel of ejected air is doing but remote parts of the air affect the air next to it which can be tracked back to the air next to the body and then to the body itself. Continuity. So in terms of whats happening at the hole, specifically 'no' but everything is connected to something else !.
On reflection, can't see that helping !
Join Date: Aug 2001
Location: Dorset
Posts: 775
Likes: 0
Received 0 Likes
on
0 Posts
When I say "Why don't we just remove the nozzle?" I don't mean "why not get rid of the exit hole". If we consider a typical jet pipe I mean "why not just leave it parallel"?
We have already established the fact that the thrust is caused by the increased pressure acting on the aft facing surfaces of the chamber.
The forward thrust is the Newton3 reaction to the rearward force that we have applied to the air in the jet pipe. It is the increased pressure in the jet pipe that is producing both the rearward acceleration of the air and the forward thrust. The increased pressure is tending to accelerate the air rearwards and accelerate the engine forwards.
The fact that the air gets accelerated rearward is (in a sense) just a by-product of the process.
The fact that we can use the eqaution T = mA to calculate the magnitude of the thrust does not mean that the acceleration actually causes the thrust. We could just as easily use the same equation to calculate the acceleration, but that does not mean that the thrust caused the acceleration, nor that the thrust and acceleration caused the mass.
I am not suggesting that getting rid of the nozzle would increase the thrust. It would not.
What I am doing is inviting readers to think about why we need the nozzle.
If
A. The thrust force acts on the front of the chamber (in a simple rocket).
In a jet pipe it acts on the exhaust unit (which is just behind the rear
turbine), and on the rear face of the rear turbine.
B. The force on the nozzle acts rearwards.
Logically we can say that the resultant forward thrust is A minus B
This suggests that having the nozzle actually reduces the resultant thrust.
Which brings us to the real question.
Why don't we just remove the nozzle and get rid of the rearward acting force?
The above results suggest that this will give us more resultant thrust.
We have already established the fact that the thrust is caused by the increased pressure acting on the aft facing surfaces of the chamber.
The forward thrust is the Newton3 reaction to the rearward force that we have applied to the air in the jet pipe. It is the increased pressure in the jet pipe that is producing both the rearward acceleration of the air and the forward thrust. The increased pressure is tending to accelerate the air rearwards and accelerate the engine forwards.
The fact that the air gets accelerated rearward is (in a sense) just a by-product of the process.
The fact that we can use the eqaution T = mA to calculate the magnitude of the thrust does not mean that the acceleration actually causes the thrust. We could just as easily use the same equation to calculate the acceleration, but that does not mean that the thrust caused the acceleration, nor that the thrust and acceleration caused the mass.
I am not suggesting that getting rid of the nozzle would increase the thrust. It would not.
What I am doing is inviting readers to think about why we need the nozzle.
If
A. The thrust force acts on the front of the chamber (in a simple rocket).
In a jet pipe it acts on the exhaust unit (which is just behind the rear
turbine), and on the rear face of the rear turbine.
B. The force on the nozzle acts rearwards.
Logically we can say that the resultant forward thrust is A minus B
This suggests that having the nozzle actually reduces the resultant thrust.
Which brings us to the real question.
Why don't we just remove the nozzle and get rid of the rearward acting force?
The above results suggest that this will give us more resultant thrust.
Join Date: Aug 1999
Location: England
Posts: 1,050
Likes: 0
Received 0 Likes
on
0 Posts
The fact that we can use the eqaution T = mA to calculate the magnitude of the thrust does not mean that the acceleration actually causes the thrust. We could just as easily use the same equation to calculate the acceleration, but that does not mean that the thrust caused the acceleration, nor that the thrust and acceleration caused the mass.
Join Date: Aug 2001
Location: Dorset
Posts: 775
Likes: 0
Received 0 Likes
on
0 Posts
It's amazing how often people think that F=MA implies the F is caused by A, rather than the other way round.
A runner on firm ground is clearly exerting a rearward force on the ground and the Newton3 reaction to that force is pushing him/her forward. But there is no detectable rearward acceleration of the ground.
The same runner on loose gravel is clearly accelerating some of the gravel rearwards, but he/she finds the going much more difficult. It requires much more effort to achieve the same speed.
This suggests that the rearward acceleration is actually an indication of the inefficiency of the propulsion process. It is.
Join Date: Aug 1999
Location: England
Posts: 1,050
Likes: 0
Received 0 Likes
on
0 Posts
<nod> Big M, small change in V, for efficiency.
Tie it into energy cost, 1/2mv^2 and pretty much everything about propulsive efficiency drops into place. Not to mention induced drag versus airspeed.
Trouble is, to really 'get' it, the student needs to be fluent with the conceptual differences between momentum and kinetic energy. Unfortunately many think that because they both have an M and a V in them they are basically interchangeable
pb
Tie it into energy cost, 1/2mv^2 and pretty much everything about propulsive efficiency drops into place. Not to mention induced drag versus airspeed.
Trouble is, to really 'get' it, the student needs to be fluent with the conceptual differences between momentum and kinetic energy. Unfortunately many think that because they both have an M and a V in them they are basically interchangeable
pb
gravel
..because the loose surface can't sustain as high a load so get skidding/slipping. Running on water is more difficult, only a couple of us have managed that.
harrier
...as for the harrier the upward force in hover must be on the nozzle surfaces. Do the nozzles have to rotate slightly past the vertical for a stationary hover ? (as I would expect a residual fwd thrust).
Join Date: Dec 2007
Location: Pasadena
Posts: 633
Likes: 0
Received 0 Likes
on
0 Posts
Re:51 why a nozzle?
Nozzles are necessary evils?
Rocket expansion nozzles lose a lot of thrust, but they are necessary to be able to gimbal the exhaust accurately and ensure control of the whole vehicle. Also, as stated by Mr Optimistic, straight release of the 1000 atmosphere through a 2-foot hole would be an explosion. Stable combustion requires a steady flow. Also, they reduce and control instabilities in the shear layer between the exhaust and air and prevent acoustic damage.
The likely 2:1 thrust loss I quoted previously for the shuttle main engine is much much more than in a jet engine. It might be 800,000lb, but acting over the 2.4-m wide, 3-m long nozzle, it's only a viscous force of ~ 6 lb / square in. The exhaust speeds and pressures in even a military engine are much less, and so is the jetpipe surface area, leading to a much smaller fractional loss.
Note to ChristiaanJ: I accept this is ignoring changes in internal energy in the gas from temperature-pressure-density, the careful manipulation of which can give an efficiency gain.
Rocket expansion nozzles lose a lot of thrust, but they are necessary to be able to gimbal the exhaust accurately and ensure control of the whole vehicle. Also, as stated by Mr Optimistic, straight release of the 1000 atmosphere through a 2-foot hole would be an explosion. Stable combustion requires a steady flow. Also, they reduce and control instabilities in the shear layer between the exhaust and air and prevent acoustic damage.
The likely 2:1 thrust loss I quoted previously for the shuttle main engine is much much more than in a jet engine. It might be 800,000lb, but acting over the 2.4-m wide, 3-m long nozzle, it's only a viscous force of ~ 6 lb / square in. The exhaust speeds and pressures in even a military engine are much less, and so is the jetpipe surface area, leading to a much smaller fractional loss.
Note to ChristiaanJ: I accept this is ignoring changes in internal energy in the gas from temperature-pressure-density, the careful manipulation of which can give an efficiency gain.
Last edited by awblain; 3rd Jul 2009 at 18:01. Reason: A bit simplistic - CJ
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by awblain
For supersonic intakes, I don't think that the idea that they produce thrust is correct...... I can't see how any arrangement of components, ramps and shocks can extract thrust from slowing an airstream.
I would suggest you dive a bit more into the relevant litterature....
On Concorde at Mach2, roughly a quarter of the thrust came from the intakes.
And this is no theoretical speculation..... to the structural engineers it was all hard fact, because those thrust forces had to be "led" from the intake structure into the wing structure and the rest of the airframe.....
CJ
Last edited by ChristiaanJ; 3rd Jul 2009 at 16:54. Reason: typo
