Why Red Flag exercises are not indicative of aircraft performance

[Hummingbird]

How can you turn around first if you turn slower ?

 

At no speed will the F-14 turn around slower, it's ITR is superior across the board.

 

So the answer to that question is: It doesn't turn slower.

[Hummingbird]

You have the measurement when it fully sweep out but not when it is fold back

 

Incorrect, I have both and have provided both. You really need to open your eyes now garrya, this is becoming ridiculous.

 

Clue: The F-14 won't be flying around at Mach 0.85 with fully unswept wings.

 

It's STR is something like 0.6 degrees/second at 50k feet as i remember

 

Which?

 

What does delta platform has to do with LERX here ? The thing on F-14 and F-15 arenot lerx and they are not used to create vortex when turning

 

Read my previous post. The vortex effect is there.

 

Not at all speed because at high speed it wing fold back , hence it no longer have the much superior CL like it does at slow speed

 

Yes it does, the lift curve chart I provided illustrate that clearly.

[Exorcet]

Still un convinced

Never saw an F-14 turn with this much vortex

It's not an exact science to measure LERX performance from condensation images. All you need to know is that the same mechanism present on the F-16 is also on the F-14. Highly swept wings produce more spanwise flow and tend to generate leading edge vortiecs.

 

And according to engineer i talked to , the big radius of the "LERX" on f-15 , F-14 just make the flow curve over instead of create the vortex

Yes, this is why the vortex is weaker on the F-14/F-15. Sharper edges increase the pressure gradient which creates stronger vortices. In rank of LERX vortex strength, the F-16 will most likely lead followed by F-14 and then F-15. Keep in mind that the F-14 has a larger LERX area to work with than the F-16 which means it's likely to generate more total lift force.

 

 

Going faster give your missiles more energy (range )does it not ?

This won't help you if you can't point the missile at the target.

 

[ame]

[/ame]

 

 

 

 

How can you turn around first if you turn slower ?

Because you don't have to turn as much. If you need to point at something inside your own turning circle, you need to turn through a large angle to reach it, if you can reach it at all. Corner speed will turn 180 degrees faster, but in a dogfight, you're trying to turn on a moving target.

 

 

 

 

 

9M can still be defeated by flares , and also F-15 , F-16 are fully able to use AIM-9X python-5 and HMD by now so i think if we gonna use missiles it practically the same between all fighter

If you're fired on and can't shoot back, you're at a disadvantage. Sure, flares can beat a 9M, but willingly going into a position where you're more likely to lose is not a good idea at all. You might win individual battles this way, but you'll lose the war to attrition over time.

 

Anyway, the whole missile thing was just an example. I was trying to point out that the best tactic will vary depending on the situation. Because of that, you can't really point to one thing, like corner speed, and say it's the best thing to use for every fight.

[garrya]

Look garrya, no'one is saying that the F-14 produces vortices as strong as those on the F-16, it obviously doesn't, but it does produce the effect.

 

Perhaps this will finally convince you:

 

From a NASA Flow Visualization Study of the F-14:

"The F-14 model was investigated to determine the vortex flow field development, vortex path, and vortex breakdown characteristics as a function of angle of attack and sideslip. Vortex flows were found to develop on the highly swept glove and on the upper surface of the forebody."

 

The above is exactly what we see on the picture posted earlier:

They did the exact ly same thing with the F-15 too with similar result

http://ntrs.nasa.gov/search.jsp?R=19790010115

[garrya]

At no speed will the F-14 turn around slower, it's ITR is superior across the board.

 

So the answer to that question is: It doesn't turn slower.

 

That not the question , excocet said turn radius help because you can turn around first , hence i said "how can you turn around quicker if you turn slower " ( because aircraft turn slower unless they are in their corner speed )

And F-14 will only have advantages of ITR at all speed if you ignore all glimit and what not

Edited January 10, 2016 by garrya

[Hummingbird]

They did the exact ly same thing with the F-15 too with similar result

 

Yes, but not with similar results. The difference is the strength of the vortices, the F-14 and esp. F-16 produce stronger and therefore more visible vortices.

[Hummingbird]

It's not an exact science to measure LERX performance from condensation images. All you need to know is that the same mechanism present on the F-16 is also on the F-14. Highly swept wings produce more spanwise flow and tend to generate leading edge vortiecs.

 

 

Yes, this is why the vortex is weaker on the F-14/F-15. Sharper edges increase the pressure gradient which creates stronger vortices. In rank of LERX vortex strength, the F-16 will most likely lead followed by F-14 and then F-15. Keep in mind that the F-14 has a larger LERX area to work with than the F-16 which means it's likely to generate more total lift force.

 

 

+1

 

More importantly this is exactly what we see realized on the lift charts.

 

Here's another picture:

 

What is important to note here is that these vortices show up on the F-14 before any form of condensation trails are visible anywhere else on airframe or wings, just as on the F-16, clearly illustrating that they are of quite a strong nature.

 

By comparison I cannot find any pictures of the F-15 showcasing this, I only notice a small vortice on the F-15 on pictures where the whole airframe is enveloped in condensation trails.

Edited January 10, 2016 by Hummingbird

[garrya]

Yes, but not with similar results. The difference is the strength of the vortices, the F-14 and esp. F-16 produce stronger and therefore more visible vortices.

 

I can see the F-16 have much bigger vortex but F-14 and F-15 look practically the same

[garrya]

. All you need to know is that the same mechanism present on the F-16 is also on the F-14. Highly swept wings produce more spanwise flow and tend to generate leading edge vortiecs.

Then in that case F-15 also have same mechanism and highly sweep wing does it not ?

.

Yes, this is why the vortex is weaker on the F-14/F-15. Sharper edges increase the pressure gradient which creates stronger vortices. In rank of LERX vortex strength, the F-16 will most likely lead followed by F-14 and then F-15. Keep in mind that the F-14 has a larger LERX area to work with than the F-16 which means it's likely to generate more total lift force.

Big it also have more weight to work again

 

 

 

. This won't help you if you can't point the missile at the target.

On head on pass from 10-15 km shouldnt it be very easy to point missiles at target ? ( since missiles get more energy from your speedt you can launch missiles from further distance )

 

 

 

 

.

Because you don't have to turn as much. If you need to point at something inside your own turning circle, you need to turn through a large angle to reach it, if you can reach it at all. Corner speed will turn 180 degrees faster, but in a dogfight, you're trying to turn on a moving target.

How about doing high yoyo instead ?

 

 

 

 

.

If you're fired on and can't shoot back, you're at a disadvantage. Sure, flares can beat a 9M, but willingly going into a position where you're more likely to lose is not a good idea at all. You might win individual battles this way, but you'll lose the war to attrition over time.

 

But wouldnt going slow (sacrifile energy for the turn ) also make you a really easy target incase target have wingman or if you miss the shot ?.

[Hummingbird]

According to the lift curves F-14 lost a lot of lift when it's wing start to fold back ( the line get much shallower )

 

1. When do you think the F-14's wings start to sweep back? (you'll be surprised)

 

2. The curve does not become much shallower, it becomes slightly shallower, so slightly that it STILL retains an ITR advantage over both the F-16 & esp. the F-15 which features no high lift devices.

 

At slow speed when the wing fully sweep out the f-14 may have superior lift to F-15 , F-16 , but that no longer the case when the wing

start to fold back , espesially in case of F-15 with much bigger wing area

 

False as already stated.

 

Furthermore comparing the wing area of 4th generation fighters in meaningless, what you want to be looking at is effective lifting area next you wanna look at the shape, planform and what high lift devices are provided, and in all these categories the F-14 is very much ahead. Only the F-16 approaches it with its LE maneuver flaps.

[garrya]

 

 

 

Which?

 

 

 

F-14A with wing gloves

[garrya]

1. When do you think the F-14's wings start to sweep back? (you'll be surprised)

That would depending on altitude it fly at

The curve does not become much shallower' date=' it becomes slightly shallower, [/quote']

The curve literally change from going up to going up at 0.4 -0.8 to going horizontal at 0.8-1 mach, going up and horizontal from 1 to 2 mach , after that it going down

so slightly that it STILL retains an ITR advantage over both the F-16 & esp. the F-15 which features no high lift devices.

F-15 have same curvy part as f-14 and It belly also provide lift ( enough to fly with 1 wing only )

 

False as already stated.

How could it be false ? F-15 main wing have bigger area and obviously you cannot have the same cl value when the wingbfold back and when it sweep out

Furthermore comparing the wing area of 4th generation fighters in meaningless, what you want to be looking at is effective lifting area next you wanna look at the shape, planform and what high lift devices are provided, and

You know the norminal wing area and CL value then you can estimate lift at certain speed , altitude

in all these categories the F-14 is very much ahead. Only the F-16 approaches it with its LE maneuver flaps.

F-16 have LERX and negative stability , F-15 also have lift from it belly so i wouldnt call the F-14 very much ahead in that regard

[Hummingbird]

That would depending on altitude it fly at

 

In other words you don't know, but I do and based on your comments it's waaay before you think.

 

Hint: It's nowhere near Mach 0.85.

 

 

The curve literally change from going up to going up at 0.4 -0.8 to going horizontal at 0.8-1 mach, going up and horizontal from 1 to 2 mach , after that it going down

 

And with that comment we can now positively confirm that you have not read the chart correctly.

 

Hint: You're describing the STR line.

 

F-15 have same curvy part as f-14 and It belly also provide lift ( enough to fly with 1 wing only )

 

Answer me this, what object do you think is more efficient at generating lift, object A or B?:

 

How could it be false ? F-15 main wing have bigger area and obviously you cannot have the same cl value when the wingbfold back and when it sweep out

 

*sigh* Are you aware that certain planforms & profiles provide a higher Cl at certain speeds than others?

 

F-16 have LERX and negative stability , F-15 also have lift from it belly so i wouldnt call the F-14 very much ahead in that regard

 

Negative stability doesn't increase lift, it increases responsiveness, there's a difference. And yes the F-15 produces lift from its fuselage, but nowhere near as efficiently as the F-14 which was designed specifically to enhance body lift.

Edited January 10, 2016 by Hummingbird

[Basher54321]

Negative stability doesn't increase lift, it increases responsiveness, there's a difference.

 

Not completely true.

 

Unlike on a stable design - if you move the CG back far enough, you get a "lifting tail" in most flight conditions. The F-16/22/35 are examples of this.

[Exorcet]

Then in that case F-15 also have same mechanism and highly sweep wing does it not ?

The F-15 only has relatively moderate wing sweep, and the fuselage fairings on either side of the inlet aren't wings at all. The glove vanes on the F-14 are highly swept and are significantly more wide than they are thick. This means the pressure difference from top to bottom is greater. It also means that it has better ability to turn the flow, ie direct it downward to produce lift.

 

All three aircraft will generate vortices, but the F-15 is going to have the weakest of the three. This should show itself in ITR charts (although it won't be the only thing to determine ITR of course).

 

Big it also have more weight to work again

Yes, we can look at ITR to determine which makes more lift/weight though.

 

 

 

 

On head on pass from 10-15 km shouldnt it be very easy to point missiles at target ? ( since missiles get more energy from your speedt you can launch missiles from further distance )

What if the plane pass right by each other? What if RoE restricts weapon use until visual ID?

 

I'm not saying that speed isn't useful. I'm just saying it's not the answer to everything.

 

 

 

 

 

How about doing high yoyo instead ?

Depends on the situation, like every other maneuver.

 

 

 

 

 

But wouldnt going slow (sacrifile energy for the turn ) also make you a really easy target incase target have wingman or if you miss the shot ?.

Sure, and that's something to think about in combat. Many v Many will make bleeding energy more risky, but it's going to be an option. Also, even if you miss, the target has to evade.

[Hummingbird]

Not completely true.

 

Unlike on a stable design - if you move the CG back far enough, you get a "lifting tail" in most flight conditions. The F-16/22/35 are examples of this.

 

Most 4th gen fighters gain lift from their horizontal stabs, the F-14 benefits more than usual from this as it sweeps back its wings moving the center of lift rearward in the process - which in turn also reduces trim drag.

 

The F-14 features enormous horizontal stabs btw, infact if I remember correctly they are the same size as the wings of an A-4 Shyhawk.

Edited January 11, 2016 by Hummingbird

[Basher54321]

Most 4th gen fighters gain lift from their horizontal stabs, the F-14 benefits more than usual from this as it sweeps back its wings moving the center of lift rearward in the process - which in turn also reduces trim drag.

 

 

 

Sorry should have been clearer - the difference is lifting in subsonic flight not supersonic flight (opposite of the F-15) so yes it does technically increase lift.

[garrya]

O

In other words you don't know, but I do and based on your comments it's waaay before you think.

 

Hint: It's nowhere near Mach 0.85.

Firstly different in altitude will make different in dynamics pressure at the same speed , mach 1 at sea level is quick , mach 1 at 60k feet is like a slug

So obviously the speed at which f-14 sweep its wing back is different depending on altitude , and I don't think F-14 fully fold it's wing back at speed lower than mach 0.85 ,10-15k feet

 

 

And with that comment we can now positively confirm that you have not read the chart correctly.

 

Hint: You're describing the STR line.

If we ignore all glimit in flight manual like you said then ITR line more or less have practically similar pattern with STR line in F-16 graph , unless F-14 some how get anti gravity device then I expect it to be similar

 

 

And you seem to be confused , no one say lift doesnot increase as you go faster , what Iam trying to say is even though lift does increase as F-14 go faster , it no longer produce as much more lift than F-15 and F-16 when it go fast , because it's wing have to fold back , let say F-14 have 1.5 times more ITR than F-16 at mach 0.5 then it need to produce 1.5 times more lift per kg weight than F-16 at that speed which could be possible because it's wing can fully sweep out , if it want maintain that ratio at mach 0.8 or mach 2 then it's wing need to produce exactly 1.5 times more lift per kg weight than F-16 at that speed too , very unlikely when youbfold back your wing

 

 

Answer me this, what object do you think is more efficient at generating lift, object A or B?:

Depending on AoA and speed , at AoA=0 , subsonic speed then obviously critical airfoil is better , at high supersonic then supersonic airfoil is a better design . At high AoA then both are practically the same

 

*sigh* Are you aware that certain planforms & profiles provide a higher Cl at certain speeds than others?

Yes obviously , that how F-14 get high ITR at low speed because its wing fully sweep out

And CL value isn't the only thing to consider , norminal wing area is important too ( before you talk about body lift and what not remember that all these are included in CL already )

CL is total lift on the airplane divided by dynamic pressure and a reference area. Dividing by a reference area is necessary to make the coefficient dimensionless. Any reference area will do the job, even if totally unrelated to lift, such as wetted area for a missile. Airplane engineers normally use nominal wing area as the reference area. That has led you to believe lift coefficient is for wing lift, and that is totally wrong. Lift coefficient is for total lift on the airplane.

 

Nominal wing area includes all the area between wing leading and trailing edges extended to the airplane centerline and the wing tips. So you can see there is significant fuselage area included in nominal wing area. But do not be confused into thinking lift coefficient includes only the lift on the nominal wing area. Again, lift coefficient includes ALL of the lift

Negative stability doesn't increase lift, it increases responsiveness, there's a difference.

Wrong , negative stability increase lift because the tail now increase lift instead of counter it

Pitch stability is mostly the result of the relative location of the center of gravity to the center of lift. A stable airplane has the CG forward of the lift center, while the opposite is true for an unstable airplane. For stable, added lift from increased AoA causes the nose to pitch down, reducing AoA and g. So to increase g, the tail must push down with enough positive pitch moment to overcome the negative pitch moment of lift aft of the CG. That down tail load must then be overcome by added wing/body lift (more AoA, drag, structural load in wing, weight) to get the desired g.

 

For the unstable airplane, wing/body lift is forward of the CG, so with increased AoA, the nose pitches up, increasing AoA and g. Left alone the airplane would pitch up out of control, with structural failure probable. So the horizontal tail, must push up to prevent that from happening and maintaining the desired AoA and g. The up load on the tail reduces the required wing/body lift (less AoA, drag, structural load on wing, weight) to reach a desired g. The unstable airplane is also truly a big deal in improving performance.

And yes the F-15 produces lift from its fuselage, but nowhere near as efficiently as the F-14 which was designed specifically to enhance body lift.

Well you don't know that , clearly F-15 design work well at altitude so it isn't as bad as you think in term of lift

Edited January 11, 2016 by garrya

[garrya]

Most 4th gen fighters gain lift from their horizontal stabs, the F-14 benefits more than usual from this as it sweeps back its wings moving the center of lift rearward in the process - which in turn also reduces trim drag.

 

The F-14 features enormous horizontal stabs btw, infact if I remember correctly they are the same size as the wings of an A-4 Shyhawk.

F-14 is not a negative stability design at dogfight speed , at high speed it is only slighty negative stability , unlike F-16which will practically pitch up and then fall down without FBW

 

[garrya]

The F-15 only has relatively moderate wing sweep,

Similar to mig-25 so I think that pretty high sweep

 

and the fuselage fairings on either side of the inlet aren't wings at all.

They can increase lift at AOA similar to F-15 belly , but of course it won't be like F-16 LERX

 

The glove vanes on the F-14 are highly swept and are significantly more wide than they are thick

Gloves vanes are deploy at supersonic for stability and F-14D don't have them anymore

 

 

All three aircraft will generate vortices, but the F-15 is going to have the weakest of the three.

I don't think we can really tell from pictures , there are too limited number of picture where F-15 , F-14 even produce even a small amount of vortex

This should show itself in ITR charts (although it won't be the only thing to determine ITR of course).

Which is quite hard because F-14 wing have different CL at different sweep angle

 

 

 

 

 

What if the plane pass right by each other?

Then high yoyo ?

I'm not saying that speed isn't useful. I'm just saying it's not the answer to everything.

Most of the time it better than going too slow and have no energy

 

 

 

 

 

 

Sure, and that's something to think about in combat. Many v Many will make bleeding energy more risky, but it's going to be an option. Also, even if you miss, the target has to evade.

I think the problem is nose point ing or Max ITR required you to either success or face really bad consequences , in game it OK because if you die you can start over , in real life most pilot would play it safe

[Hummingbird]

Sorry garrya but I can't help but find it amusing that you think I'm confused when you can't tell the difference between a lift curve and an ps=0 curve.

 

Anyway I'm done with the semantics, let's put the facts on table:

 

The F-14's wings start to sweep back at around Mach 0.45, a fact to which you were completely oblivious garrya.

 

At a speed of Mach 0.85 and at any altitude below 14,000 ft the F-14's wings are already at 55 deg sweep (50.5 deg >20 kft), and by Mach 0.94 they are fully swept at all altitudes.

 

So why the sudden notch on the lift curve at around Mach 0.85 at 35 kft? Simple, this is exactly the point where the wing sweep inhibits the actuation of the maneuver slats & flaps (50.5 deg sweep), i.e. the first point where the F-14's lift curve starts to become abit more shallow as it looses the benefits of its high lift LE & TE devices.

 

Regardless of this however the lift curve remains higher than that of the F-16 & F-15, and that only because of its lifting body design.

 

As an example at 35 kft and at a speed of Mach 1.0 (the point where the F-14's wings are already fully swept) the F-14's max instantanous load factor is 5.7 G's, where'as by comparison F-16C's max instantanous load factor at the same altitude and speed (DI = 50) is 5.5 G's. In short the F-14 maintains an ITR advantage even when its wings are fully swept.

 

A superior ITR can only be achieved in one way, and that is with a superior lift to weight ratio, thus the conclusion of the above can only be one thing: that the F-14 has this advantage across the entire speed range.

Edited January 11, 2016 by Hummingbird

[Basher54321]

 

As an example at 35 kft and at a speed of Mach 1.0 (the point where the F-14's wings are already fully swept) the F-14's max instantanous load factor is 5.7 G's, where'as by comparison F-16C's max instantanous load factor at the same altitude and speed (DI = 50) is 5.5 G's. In short the F-14 maintains an ITR advantage even when its wings are fully swept.

 

A superior ITR can only be achieved in one way, and that is with a superior lift to weight ratio, thus the conclusion of the above can only be one thing: that the F-14 has this advantage across the entire speed range.

 

 

 

A Max ITR 5.5Gs looks about right assuming the same 30 - 40k charts. Thing is though that load limit is still defined by the AOA limiter not L/W.

 

Due to the lack of air at M1.0 (~350KCAS), 35,000 ft it doesn't take much to hit the limits.

[Hummingbird]

A Max ITR 5.5Gs looks about right assuming the same 30 - 40k charts. Thing is though that load limit is still defined by the AOA limiter not L/W.

 

Due to the lack of air at M1.0 (~350KCAS), 35,000 ft it doesn't take much to hit the limits.

 

The AoA limiter is a limitation that's always there for the F-16 though, it had to have it due to that desire for negative stability.

 

In other words, eventhough they are two different things the AoA limiter on the F-16 affects the F-16's lift curve the same way that the F-14's gradual wing sweep affects its lift curve, preventing it from being even steeper.

 

That having been said the F-14 & F-16 designs both focus a lot more on lift enhancement than the F-15 design ever did, hence they are both better suited for the horizontal fight than the Eagle.

 

The F-16 is essentially a great blend between the F-14's horizontal capability and the F-15 vertical capability, which is what makes it one of the best dogfighters in US service. Clean very little can touch the Viper.

[Exorcet]

Similar to mig-25 so I think that pretty high sweep

It's not. The sweep of other aircraft has nothing to do with it, it's the sweep relative to vortex generation. It's besides the point though, I brought up sweep because it helps vortex generation, and the F-14's gloves are highly swept. The F-15 doesn't have a comparable LEXR surface, only the fuselage fairings. They won't produce the same amount of lift.

 

They can increase lift at AOA similar to F-15 belly , but of course it won't be like F-16 LERX

In raw lift generation, they will be inferior to the F-14 as well.

 

Gloves vanes are deploy at supersonic for stability and F-14D don't have them anymore

The D still has the gloves themselves, and what I said applies to them. The air will go for the easiest path. The stubby F-15 fairings don't give the air much of a reason to go around the side and form a vortex. They will probably also generate unsteady separation earlier than the F-14 or F-16 because they won't have as sharp a pressure gradient.

 

 

 

I don't think we can really tell from pictures , there are too limited number of picture where F-15 , F-14 even produce even a small amount of vortex

I'm not looking at pictures, I'm looking at the shapes themselves. That alone will give you a good idea of what they do and how they perform. Not perfect, but enough to have a decently accurate ranking.

 

Which is quite hard because F-14 wing have different CL at different sweep angle

This shows up in the ITR as long as the aircraft isn't artificially limited, so it's accounted for.

 

 

 

 

 

Then high yoyo ?

If the other plane can't point its nose up, why not.

 

Most of the time it better than going too slow and have no energy

"Most of the time" doesn't matter to specific situations though. What is best most of the time isn't best all the time.

 

 

 

 

 

 

I think the problem is nose point ing or Max ITR required you to either success or face really bad consequences , in game it OK because if you die you can start over , in real life most pilot would play it safe

And what is safest again depends on the situation. Rocketing past someone just to take a missile in the back isn't safe.

 

I think this has gone off track. I wasn't trying to counter your argument. I stepped in because it seemed like there was a deadlock and I thought it was from each side meaning something other than what the other thought.

[garrya]

It's not. The sweep of other aircraft has nothing to do with it, it's the sweep relative to vortex generation. It's besides the point though, I brought up sweep because it helps vortex generation, and the F-14's gloves are highly swept. The F-15 doesn't have a comparable LEXR surface, only the fuselage fairings. They won't produce the same amount of lift.

Neither the curve surface of F-14 or F-15 are called LERX or can achieve what F-16 LERX can

If you count the curvry part then I have to say F-15 LERX have very high sweep too

 

In raw lift generation, they will be inferior to the F-14 as well.

I doubt that , F-15 out performe both F-14 and F-16 at high altitude

 

 

The D still has the gloves themselves, and what I said applies to them. The air will go for the easiest path. The stubby F-15 fairings don't give the air much of a reason to go around the side and form a vortex. They will probably also generate unsteady separation earlier than the F-14 or F-16 because they won't have as sharp a pressure gradient.

 

 

Iam sure F-14D don't have the golves vane anymore

 

http://www.anft.net/f-14/f14-detail-glovevane.htm

 

I'm not looking at pictures, I'm looking at the shapes themselves. That alone will give you a good idea of what they do and how they perform. Not perfect, but enough to have a decently accurate ranking.

Iam skeptical of that , shape can sometime deceiving

Mig-25 look like a brick yet it fly higher and faster than all fighter

su-27 look sleek yet it is slower than F-15

 

 

This shows up in the ITR as long as the aircraft isn't artificially limited, so it's accounted for.

But then F-16 is AoA limited

 

 

 

 

 

 

 

And what is safest again depends on the situation. Rocketing past someone just to take a missile in the back isn't safe.

We probably should left missiles out of comparison since with modern HOBS missiles a few degree superior in tun rate is rather irrelevant