Did this actually happen or is it just propaganda nonsense?

[marcos]

The engine mounts work practically the same with or without TVC. Yes, the angle makes a difference, but it's the same difference. You just don't see engines mounted at 90 degrees, while you may see nozzles positioned at such angles.

Nope.

 

The F-35 would need a lift fan even if the engine was rotated 90 degrees, unless it was also moved so that the thrust line was perfectly matched with the cg.

It might not be perfectly matched with the cg but rotating the engine about it's centre would move the thrust line a lot nearer the cg, but yes, it probably would still need a lift fan but at least you're seeing my point.

 

The loss of forward thrust though is essentially negligible. It's not small and marginal, it's basically zero. You don't trade 1 unit of forward thrust for 1 unit of thrust lift. It's more like 1:20 or possibly greater.

But it's more complicated than that because of the weight of the engine and the increase in drag.

 

The nozzles don't create additional drag directly. They only add weight directly. That weight is responsible for increased wing induced drag. The wing is often more efficient than the horizontal stabilizer though.

Maybe they do create additional drag. I don't think you can make that statement categorically. Changing control surfaces by small amount create drag, so maybe moving the nozzles will too.

 

Really though, the ACTIVE sort of proves that TVC works.

It seems that way but I think the gains are marginal.

 

There is no meaningful loss in forward thrust or TVC produced drag though. I'll get to the 9 g thing next.

The loss in forward thrust is small but the increase in drag is unmeasured as of yet.

 

Yes, the TVC weighs 9 times as much at 9 g, but it's still only X% of weight. That percent is all that matters. The TVC is only ever 9% of weight, so 1 g, 9 g, -50 g, 1000 g, the TVC has the same effect.

Except that in a conventional turn it might not be in play, so it's dead weight and if it were in play to reduce drag the required force and deflection normal to motion to cancel drag would be far higher and in such a direction that it creates a moment which opposes the turning direction, i.e. the opposite to the direction it moves in to tighten the turning circle in a energy reducing turn.

 

You only want to transport momentum to combat flow separation. If there is no threat of separation, you want laminar flow because of reduced drag.

 

The turbulence on a high speed body is not threat to separation, but it does cause additional drag.

 

Maybe you're confusing turbulent flow with turbulent air. The former produces disturbances and instabilities which are for the most part invisible to the plane. The latter is the kind of stuff that makes airliners rock around at altitude. The latter can causes separation, but the former doesn't really.

The latter is an extreme case of the former and the higher the speed the more extreme cases become.

 

I may have been confusing reduced separation with reduced drag for high speed lmainar flow. I don't think so, but I can't be arsed to check my notes. Turbulent flow at high speed sure doesn't seem like it would do any good for reducing separation.

 

But it's not. You can find a stall speed, but that's just calculating the speed at which the critical AoA will be exceeded in your current flight condition.

 

However, once you hit that stall speed, if you simply push the flight stick forward enough, you will never stall. However, no matter how fast you fly, pull the stick back while right on AoA crit, you stall.

I think you're just arguing for the sake of it now. Just calculating? Critical AoA is just calculating the other way. If you did a cobra in a MiG-29 at 1000mph, I'm sure the flow would separate too, even if the aircraft didn't, so an AoA that works at one speed doesn't work at another. Similarly take a small AoA that works at one speed and reduce the speed to 50knots, and the speed forces a critical AoA due to the change in flight path. Either we're trying to fly, or we're trying to crash. In the latter case, why worry about wings at all, a fuselage will do and it will never stall.

[marcos]

Stall warning are based on AoA. Basing them on speed would do no good. If your plane was banked but flying level, a speed based stall warning system set up for level flight would warn you after you stalled and started falling, which wouldn't be helpful.

Wrong and flawed argument. The warning is based on approaching the stall speed and if an AoA warning was based on passing the critical AoA, it would have the same affect that you mentioned.

 

Consider a case where there is no gravity, you will be able to avoid stall at any speed, but AoA still applies.

No gravity means there's no mass, therefore air can't be present because it has mass and would therefore create gravity unless the air is trapped between two bodies cancelling each others gravity. Flight would also be irrelevant and it may well be the case in this highly theoretically situation that too much speed and lift cause stall as the aircraft goes directly upwards. In any case you would still have to maintain level flight or the zero gravity situation would die. It's really a stupid example and I don't care to consider it but Re is still influenced by speed anyway.

[Exorcet]

It might not be perfectly matched with the cg but rotating the engine about it's centre would move the thrust line a lot nearer the cg, but yes, it probably would still need a lift fan but at least you're seeing my point.

Rotating the engine about the center is something else though. You need to rotate it so that the thrust line is in line with the TVC. So it would have to pivot at the nozzle.

 

 

But it's more complicated than that because of the weight of the engine and the increase in drag.

 

...

 

Maybe they do create additional drag. I don't think you can make that statement categorically. Changing control surfaces by small amount create drag, so maybe moving the nozzles will too.

The nozzles won't create additional drag because their job is to pressure match the jet flow to the ambient flow. The flow of gas from the engines serves to reduce drag on the nozzle.

 

It seems that way but I think the gains are marginal.

Determining how effective it would be is the hard part, I never tried to show that, just that it works.

 

 

Except that in a conventional turn it might not be in play, so it's dead weight and if it were in play to reduce drag the required force and deflection normal to motion to cancel drag would be far higher and in such a direction that it creates a moment which opposes the turning direction, i.e. the opposite to the direction it moves in to tighten the turning circle in a energy reducing turn.

Like I was saying before, tradeoffs. I was only arguing that TVC benefits cruise. Although thinking about it, there isn't much difference between a sustained turn and level flight. The difference is just AoA.

 

 

The latter is an extreme case of the former and the higher the speed the more extreme cases become.

By extreme, meaning the size of the eddies yes? If so I agree, but that is the fundamental difference. With flow over a wing, the eddies are small enough such that they blend into one net, smooth, direction. It the same way that air molecules going in random directions creation smooth laminar flow. However, in a turbulent patch of air, such as in a storm or in the wake of a plane much larger than yours, the eddies can be comparable in size to the aircraft itself.

 

 

I think you're just arguing for the sake of it now.

I assure you I'm not.

Just calculating? Critical AoA is just calculating the other way. If you did a cobra in a MiG-29 at 1000mph, I'm sure the flow would separate too, even if the aircraft didn't, so an AoA that works at one speed doesn't work at another. Similarly take a small AoA that works at one speed and reduce the speed to 50knots, and the speed forces a critical AoA due to the change in flight path. Either we're trying to fly, or we're trying to crash. In the latter case, why worry about wings at all, a fuselage will do and it will never stall.

A Cobra at 1000 mph would certainly involve stall. Even a Cobra at low speed does. The wing stalls, what doesn't are the horizontal stabs, they are fed by the LERX's.

 

The critical AoA is fairly constant, it is the limit at all speeds. The definition of stall is when the wing passes its crit AoA and experiences massive flow separation.

 

Wrong and flawed argument. The warning is based on approaching the stall speed and if an AoA warning was based on passing the critical AoA, it would have the same affect that you mentioned.

But how? The speed at which you reach critical AoA changes with bank. Critical AoA doesn't change.

 

 

No gravity means there's no mass, therefore air can't be present because it has mass and would therefore create gravity unless the air is trapped between two bodies cancelling each others gravity. Flight would also be irrelevant and it may well be the case in this highly theoretically situation that too much speed and lift cause stall as the aircraft goes directly upwards. In any case you would still have to maintain level flight or the zero gravity situation would die. It's really a stupid example and I don't care to consider it but Re is still influenced by speed anyway.

 

Then instead consider a plane being held up by a string. You can rotate it such that it will never stall at any speed, but no matter what it will stall at crit AoA.

[aaron886]

Not only do you not understand aerodynamics, you don't understand maths. I may as well try teach a monkey to write poetry.

Right.

 

I've done an MEng in Engineering with multiple aerodynamics modules

Well then if you actually do, I feel quite badly for whatever university you're reflecting upon. And I certainly hope I'm never stuck flying any aircraft you work on, because then I would fear for the safety of quite a number of people. I'm distinctly unimpressed. I'm sure you can punch numbers into MATLAB and program quad-rotor RC toys quite brilliantly, but your qualitative skills need help.

 

What you're doing is trying to de-couple the fundamental equations of lift from speed.

No, bud, I'm "de-coupling" lift equations from nothing. A common method for writing an equation for lift is (([rho]*v^2)/2)*Cl*A. (I don't take chances with parentheses.) Obviously, the entire equation is dependent upon Cl, a non-dimensional coefficient of lift. Look again at the graph of Cl vs a I posted a while back:

 

http://2.bp.blogspot.com/_pdCHfaZgNS8/R5djMfibZSI/AAAAAAAAAH0/EGz8P3LhiQU/s320/NACA%2B63415%2Blift%2Bcurve.gif

 

Lift can be lost irrespective of speed via the Cl factor, as a result of an excessive angle of attack. This is a stall. I can stall an airplane at cruising speed by artificially increasing the angle of attack past the critical angle. I do this from time to time. It's called an accelerated stall. There is another way to lose lift... it's called "going slow." This is reducing the v^2 factor of the lift equation. It is not a stall. An airplane at rest on the ground is not stalled... it's just not moving.

 

This is so simple and so fundamentally correct, if you cannot agree, you should not have your degree.

 

But how? The speed at which you reach critical AoA changes with bank. Critical AoA doesn't change.

Sometimes, the simplest question is the strongest argument. Please explain this one away using Reynolds number.

 

 

Bandying insults about the "absolute shit" I'm talking does you less credit than providing an intelligent explanation, Dr. Science. ;)

[marcos]

You say stall is dependent on AoA not speed, yet it can happen at a completely different AoA at high speed due to shock waves.

 

You say it's down to pressure gradient, but the local static pressure at any point is dependent on the local velocity.

 

Point the aircraft up and the speed in the direction the aircraft's nose is pointed reduces. This is just another take on the idea that AoA changes below a given stall speed because the aircraft is falling.

 

Re depends on V.

 

The original statement I countered said that stall was not related to velocity. I interpreted that as meaning that stall isn't related to velocity in any way. Clearly it is.

 

Son, what you're doing is taking a quote made by a lecturer to illustrate a specific point and trying to apply it literally on a general scale. Lecturer's will come out with all kinds of shit to illustrate a particular point, like the whole idea that an aircraft won't take off if put on a treadmill travelling at take-off speed in the opposing direction. The intention was to demonstrate that lift was dependent on velocity, but the statement is absolute bollocks when examined in the wider context.

 

Banking, turning, centripetal acceleration requiring a force to alter velocity.

 

Stick something in the way of airflow and drag is created. Hence nozzles pointing down into airstream, slight drag. How much? Don't know, but some. The effects of the jet recombining with slower air at a angle were not what I was talking about.

Edited September 5, 2012 by marcos

[marcos]

And I certainly hope I'm never stuck flying any aircraft you work on, because then I would fear for the safety of quite a number of people.

Since your preferred method of correcting stall is pointing the plane at the ground rather than altering velocity, I hope you don't either. I suggest a career in bagel production.

Edited September 5, 2012 by marcos

[marcos]

Blah, blah, blah

Basically, a few pages back, you read this thread and tried starting an argument on TV with me by agreeing with me because your reading comprehension sucked so immensely that you couldn't even fathom who was arguing what.

 

So as a suggestion, I'd work on fixing your literacy before moving on to aerodynamics.

[EtherealN]

I want everyone to re-read rule 1.2 before you continue posting.

 

http://forums.eagle.ru/rules.php#en

1.2. - Members must treat other with respect and tolerance. Material that is offensive, insulting or constitutes an attack against any individual or group will be subject to administrative actions.

[marcos]

 

The critical AoA is fairly constant

I thought this all conquering AoA was completely constant. Tell me now, what affects it?

 

For instance does higher mach not reduce the maximum lift a wing can produce and the AoA at which stall occurs? If so, then this statement:

 

Stall is also not related to speed.

 

is clearly wrong, and that's all I politely pointed out several pages back before umpteen pages of drivelsome crap. Unless you want to claim mach isn't related to speed. Sure altitude plays a part through temperature, but it is definitely related to velocity.

 

You need to be damn careful before arguing that anything in aerodynamics is not related to velocity and you fell for the trap. If I wanted to push a point I could even argue that something seemingly benign like aircraft dimensions are related to speed. In fact every item in the equation for Re is related to speed pushing the point further. Speed has a habbit of changing stuff that you wouldn't think could be affected by it. Even time and mass can be affected by speed pushing the point further still.

 

When you say that something isn't related to speed it means that any variations in speed have no impact on it in any circumstances. This is not the case, hence you are wrong irrelevant of how long you argue for. It was an easy battle analogous to proving a mathematical theory wrong simply by finding one single example where it doesn't apply. As a future tip, be very careful when making any statement of the kind x isn't related to y.

Edited September 5, 2012 by marcos

[marcos]

I want everyone to re-read rule 1.2 before you continue posting.

 

http://forums.eagle.ru/rules.php#en

1.2. - Members must treat other with respect and tolerance. Material that is offensive, insulting or constitutes an attack against any individual or group will be subject to administrative actions.

Sorry man, I didn't see that. The argument is over as far as I'm concerned. Cheers.:thumbup:

[Exorcet]

I thought this all conquering AoA was completely constant. Tell me now, what affects it?

Referring to this:

"*This doesn't contradict my statement that crit AoA is a function of Re. The crit AoA can be approximated as a constant over certain ranges of Re. While in reality, since Re changes between the two cases, the crit AoA could be off by something like .000001%, but this is for all intents and purposes the same. The difference in the speed at which you stall can be large."

 

There could also be a large change at certain Mach numbers due to shockwaves depending on the airfoil. At the other extreme, low Re lamiar flow greatly reduces AoA crit.

 

For instance does higher mach not reduce the maximum lift a wing can produce and the AoA at which stall occurs? If so, then this statement:

 

 

 

is clearly wrong, and that's all I politely pointed out several pages back before umpteen pages of drivelsome crap. Unless you want to claim mach isn't related to speed. Sure altitude plays a part through temperature, but it is definitely related to velocity.

Yes Mach is related to speed, but they are not the same. However I do agree that the critical AoA can change due to changes in Mach, though it should be essentially constant on either side of the Mach spectrum.

 

If your only argument involved that there could be a large change in AoA crit upon reaching a certain Mach number, we agree. However, your posts seem to imply that that stall is based on speed even at lower Mach numbers where there are no shocks.

 

EDIT see * below

 

When you say that something isn't related to speed it means that any variations in speed have no impact on it in any circumstances. This is not the case, hence you are wrong irrelevant of how long you argue for. It was an easy battle analogous to proving a mathematical theory wrong simply by finding one single example where it doesn't apply. As a future tip, be very careful when making any statement of the kind x isn't related to y.

But that's just it, AoA crit, the AoA at which the wing loses lift with increasing AoA, is not related to speed. You can correlate the two, but if you were just given a speed out of the blue and the speed at which the plane stalls in level flight and then asked if a plane was stalled was or not, you couldn't answer the question. If you were given the AoA, and AoA crit, you could very easily answer the question.

 

I guess what I need to know is, what is your definition of stall? The wing producing less lift than the weight of the plane, or the wing passing max cl?

 

We agree that you can put a velocity to a stall, but I don't think you can put a stall to a velocity.

 

I'm not trying to make myself any more correct by arguing for a long time. I just don't think your argument was totally correct, with all due respect.

 

 

* Going back, maybe this is where things went wrong. I read the following quote as "Flow separation (as in stall created by reaching AoA crit) changes with speed in both the low speed (subsonic) and high speed (trans/supersonic) regimes. Did you mean instead that it depends on what side of transonic you're on? If the latter, we agree.

Yes but flow separation depends on speed whether it's slow speed separation or transonic separation.

 

My reply was this, my comment on Re and pressure gradient referring to AoA crit within both regimes separate, not commenting on what happens when crossing from one to the other:

 

"It depends more on the Reynolds number and pressure gradient. You can pretty much make a wing stall free at any speed you want, but the AoA is a hard limitation that doesn't go away with modifying your wing design.

 

There isn't really a slow speed separation. Separation at low speed is caused by exceeding critical AoA. If you stay below critical AoA, your wing will never stall.

 

One way to look at it is like this, you can find a critical AoA for a wing, by itself, but not a stall speed. To find a stall speed, you need a plane. The stall speed would be the speed where the AoA required to generate the plane's weight in lift is above the critical AoA."

 

If I misread you, it's my mistake.

Edited September 5, 2012 by Exorcet

[marcos]

Yes Mach is related to speed, but they are not the same. However I do agree that the critical AoA can change due to changes in Mach

Therefore AoA is related to mach and mach is related to speed, so AoAcr is related to speed and stall is also related to speed. Pressure gradients - related to local static pressures, which are related to local speeds. Re changes with speed - therefore related. Case dismissed.

 

 

For any future responses refer to post 137 because I neither have the time nor inclination to repeat it, that is all.

Edited September 5, 2012 by marcos

[4c Hajduk Veljko]

So .... What is actual F-35 sustained turn rate? Climb rate? Anybody?

[aaron886]

Oh yeah sure I'll just go pull that off the Lockheed Martin website. :doh:

[Grimes]

Just watched the video, considering 60% of it is basically a montage of Flankers, I'm going to venture a guess that the video is at least 60% biased toward Flankers. ^_^

[GGTharos]

Let's see ... according to what has been said, 'slightly better than that of an F-16', along with some insane constant AoA. It might not be a bit surprise if the climb rate is similar to that of an F-15 depending on loadout, but I think in the full-of-fuel-and-a2g stuff configuration it will be more like that of an equivalently loaded f-16. The F-35 itself is pretty heavy - about as heavy as an F-15C empty, and loaded with full fuel it's the equivalent of an F-15C with a single tank of fuel. The thrust is a bit less.

 

In any case, just some barely educated guesswork :P

 

So .... What is actual F-35 sustained turn rate? Climb rate? Anybody?

[Exorcet]

Therefore AoA is related to mach and mach is related to speed, so AoAcr is related to speed and stall is also related to speed. Pressure gradients - related to local static pressures, which are related to local speeds. Re changes with speed - therefore related. Case dismissed.

 

 

For any future responses refer to post 137 because I neither have the time nor inclination to repeat it, that is all.

 

AoA crit is not related to speed. I didn't say that AoA crit varies continuously with Mach, but rather your being supersonic or subsonic mattered. It should be constant when in those regimes.

 

And despite the Mach and speed relation, it's a bit misleading that say that something depends on speed because it depends on Mach. They aren't the same thing. Mach .8 is not a set speed.

 

As for post 137

 

When you say that something isn't related to speed it means that any variations in speed have no impact on it in any circumstances.

No, we all know that incompressible flow isn't incompressible. Still, speed alone doesn't affect the critical AoA. It's Re that does. It might seem like a small difference, but it's a rather important distinction if you're trying to design an aircraft or carry out an experiment.

 

So .... What is actual F-35 sustained turn rate? Climb rate? Anybody?

 

I would put "F-16 like" as the lower bound. With the same fuel fraction, the F-35 is basically statically the same as the F-16, but it will have a less draggy profile when fitted for combat. Being heavier also means that weapon weight has less impact on performance.

[aaron886]

Marcos - I'm going to drop the whole issue after this with the expectation that we'll have a hard time keeping it civil per mod's request. I think we've both said some insulting things (albeit with varying levels of aggression,) so for that I at least will apologize.

 

Stalls at supersonic speeds "due to shock waves." It's generally called a shock stall or "mach tuck." It's also generally considered a condition separate from what is considered a "generic" stall. A shock stall is literally a separation bubble formed as a result of a particular propagation of a shock wave. Think of it as airflow being "shadowed" by the pressure gradient of the shock wave. Even in this condition, it's a bit naive to suggest that the stall is a result of airspeed, when the stall is a result of the shock wave artificially disturbing airflow. Many aircraft do not exhibit this characteristic at all when passing through transonic velocities, which draws a line quite nicely if you know what I mean.

 

One last situation I want to present, which might change your thought process with regard to flight attitude, airspeed, and their relationship to a stall. I couldn't find any examples on YouTube, but hopefully you've seen a video of an airfoil in a liquid-testing tunnel, in which oil streamlines are used in place of air. Even at incredibly low velocities, streamlines remain attached to the airfoil until disturbed by an increase in angle of attack. It's not a stall just because the local airflow is slow.

 

Banking, turning, centripetal acceleration requiring a force to alter velocity..

Nice little video example. I'd estimate a minimal loss of airspeed in that turn, still faaaarrrr above the published "stall speed" in a clean configuration. (Vs)

http://youtu.be/0rhcxGMoAEU

 

 

Back on-topic... lots of suggestions about the F-35. I was told by a couple of Canadian Hornet pilots (who know exactly what they're talking about, believe me,) that the F-35's performance would be a blend of the best qualities of the F/A-18 and F-16. Take that for what you will, but to me that's excellent news. There's not much need to up the standard of maneuverability and performance from those two aircraft combined.

Edited September 5, 2012 by aaron886

[marcos]

So .... What is actual F-35 sustained turn rate? Climb rate? Anybody?

The small wing area should actually help it in this department but good figures are probably not available right now. Performance specifications for even the most mundane military aircraft are often restricted. The actual figure will depend on fuel load, but somewhere near 60,000ft/min would be ball park.

Edited September 6, 2012 by marcos

[4c Hajduk Veljko]

So ... we don't have turn and climb rate data for F-35.

 

In that movie, at 1:00, it said that RAND corporation and US government prepared that report? I guess, they had appropriate data to work with. Who is RAND corporation anyway?

[GGTharos]

So ... we don't have turn and climb rate data for F-35.

 

No, but we do have reports of certain official goals being met, as well as pilot testimony and basic data. We know F-35's generally out-perform F-16's, plus what Aaron said.

 

In that movie, at 1:00, it said that RAND corporation and US government prepared that report? I guess, they had appropriate data to work with. Who is RAND corporation anyway?

A think-tank who don't have the data either. Saying it was 'prepared by the US govt' means nothing. If it said 'USAF' that would change things. It's the same thing where I live too - the gov't 'has opinions', but really a lot of these politicians have no clue whatsoever or they just don't care and they're talking without consulting the air force - it's all about politics and making one self look good (or just not knowing better).

 

Let's just say that this RAND study is old, tired, and well known. So is the YT poster known as 'PowerRussia', or whatever other similar nicknames he/she comes up with.

Edited September 6, 2012 by GGTharos

[aaron886]

So ... we don't have turn and climb rate data for F-35.

 

In that movie, at 1:00, it said that RAND corporation and US government prepared that report? I guess, they had appropriate data to work with. Who is RAND corporation anyway?

 

 

This link has been posted twice in this topic in response to RAND. It's going up again, unfortunately.

 

http://www.rand.org/news/press/2008/09/25.html

[4c Hajduk Veljko]

I see.

 

Sooner or later, we will get turn and climb rate. Then we will be able to compare. Now, everybody can speculate ...

[marcos]

50,000lbf and TWR >1 and 42.7m^2 wing area says climb rate will be respectable, at the very least, and probably good.

[aaron886]

Now, everybody can speculate ...

 

That's all it is, for now.