Phantom vs XXX

[AnarchyZG]

1 hour ago, divinee said:

F-4 chart is without slats and with 4x sparrow and more than 7000lb of fuel.

My bad, doesn't say that in the chart and anyway I don't thing for sparrows on the belly make that much difference.

[divinee]

40 minutes ago, AnarchyZG said:

My bad, doesn't say that in the chart and anyway I don't thing for sparrows on the belly make that much difference.

No problem. Propably not aerodynamically because they are recessed but they weight about 500lb each. There is also charts for the slatted version in the first page of this topic posted by me and they give much better picture. Those charts are also with quite heavy fuel load so be carefull when reading those. Clean weight without fuel is somewhere around 32000lb for block 41.

Edited February 10, 2022 by divinee

[Dragon1-1]

You should remember that the MiG-23 was never the world's greatest dogfighter, even with all the aerodynamic improvements. The point of it is to come in screaming with wings fully back, launch its missiles and GTFO. It's a bit of an anomaly, since MiGs usually turn well. Every time the MiG-23 ended up evaluated against other aircraft, be it Constant Peg or the Russian trials with the captured F-5, it got its ass kicked. Its missiles were pretty mean, and it could go fast, but it was ultimately more of an interceptor than a fighter.

I'm still looking forward to the RAZBAM's take on it, but it's gonna require different tactics than, say, MiG-19, to make the most of it. 

[AnarchyZG]

I found this article which seems to be based on Soviet manual written after Israeli Syrian clash in 1982. Emphasis seems to be on F-15 and F-16 but they do mention F-4 as well

https://www.xairforces.net/analyses/mig-23.html

[Dragon1-1]

It pretty much lines up with what's been said above. Keep your speed up, don't turn too much, one pass and haul ass. MiG-23 was somewhat superior in BVR to its contemporaries (mostly due to the Sparrow being crap), but that's it. 

[F1GHTS-ON]

On 2/6/2022 at 7:44 AM, G.J.S said:

On FGR2 we would just go to min burner to clean up, stops a visual pick up. Not much point splitting throttles. Spey was A LOT cleaner than J-79’s, but would still give a trail, min burner under about 10 - 15 miles of a foe would deny the foe that telltale sign.

Would putting afterburner (even minimal) inside 10miles as you enter the merge, with post 1980's IR missiles with forward aspect capability be wise? I appreciate that the 9L/M is looking at the air friction generated heat, but...........

[G.J.S]

1 hour ago, F1GHTS-ON said:

Would putting afterburner (even minimal) inside 10miles as you enter the merge, with post 1980's IR missiles with forward aspect capability be wise? I appreciate that the 9L/M is looking at the air friction generated heat, but...........

Every move you make has a calculated risk.

Minimum burner is solely to deny a visual pickup. Why make it easier for your foe?

The ideal would be if your element/flight has a large-ish height split, to compound the enemies problems. A forward quarter heater can be dealt with by a sound and timely countermeasure deployment and evasive counters. If you expect to be shot at its not a surprise when it comes, and can be dealt with clearly and quickly because you have practiced many times before.

And - for the most part, those whom we expected to go against didn't have 9 Lima's or Mike  .

Edited February 20, 2022 by G.J.S

[Hummingbird]

On 2/10/2022 at 3:54 PM, AnarchyZG said:

Perhaps I'm misreading the data (note this is ML, not MLD)?
Seems pretty close to me in what is claimed by many to be the worst MiG-23 aspect (sustained turn), also note that F-4 chart seems to be clean F-4 while MiG-23ML chart is loaded with 2 R-23s (I'm guessing 7G is the structural limit with R-23s)

 

 

 

 

A 1973 Ps chart for the slatted F-4E for comparison:

As you can see the slatted F-4E achieves a higher STR at a ~2,000 lbs higher weight (e.g.: 5.3 G vs 4.9 G @ M 0.6  & 6.4 G vs 5.8 G @ M 0.7).

 

And here VN charts for comparison of ITR at equal weight (dated 1969 & 1973) between an F-4E with slats and an F-4J without (hard wing F-4 stalls at ~25 units AoA, the slatted F-4 @ ~30 units):

 

Edited March 22, 2022 by Hummingbird

[303_Kermit]

On 2/2/2022 at 4:21 PM, SgtPappy said:

Continuing from the other thread, the F-4J should certainly turn worse than the slatted F-4E. Unfortunately I don't think there are performance charts readily available for it nor the F-4D but I have found a couple of things (hopefully reputable) that should illustrate how much the slats improved things subsonically.

The information below comes from a Have Drill summary pdf I found and the F-4D charts below are pretty close to the hard-wing F-4E turn charts in TO 1F-4C-1. The D is a bit better because it's a lot lighter than the F-4E in the TO charts. Because they seem to be pretty close, I'd wager the F-4J (which is aerodynamically similar to the D and weighs similarly to the E) is not far off. See below.

F-4D vs MiG-17 at 20,000 ft from Have Drill Summary

 

Hard wing F-4E turn performance

 

Below are turn rate plots (in addition to info from their Vn diagrams for instantaneous turn rates) for the hard wing and slatted F-4E which have been directly taken from the TO manuals and overlaid. The difference in subsonic maneuverability is quite impressive. Note: Based on the weight charts at the top of the TO's, I realized that both hard and slatted wing F-4E charts (with AIM-7's only) have ~60% fuel.

Hard vs Slatted wing F-4E overlay

 

The Upper chart (sustained G turn) show 15,25°/s TRT at sea lvl by 575KCAS - the lower one (F-4E with slats vs F-4E without) - 20°/s at sea lvl by Ma=0,6. It's strange from 2 reasons:
1-st the difference is huge
2-nd Slats add Lift, but also a Drag - and a lot of it. Everyone who enjoyed a aerobatic in a plane with a slats on it may confirm - if slats jumped out at the beginning of the loop - the feeling is like someone pulled a handbrake - you won't make full loop. I'm sure that slats help a lot by instantaneous turn, but in a constant turn they bring no profit.

It make only sense if the lower chart (F-4E with slats vs F-4E without slats) shows  instantaneous turn capabilities.

With my best regards
303_Kermit

Edited May 23, 2022 by 303_Kermit

[Gambit21]

On 2/10/2022 at 6:00 PM, Dragon1-1 said:

You should remember that the MiG-23 was never the world's greatest dogfighter, even with all the aerodynamic improvements.

That's an understatement.

In the words of "Paco" Gesiler, "if you began an engagement with the MiG 23 on your 6,  you were offensive against that MiG. lol

That's when flying the F-15 or course.

 

 

Edited May 23, 2022 by Gambit21

[SgtPappy]

17 hours ago, 303_Kermit said:

The Upper chart (sustained G turn) show 15,25°/s TRT at sea lvl by 575KCAS - the lower one (F-4E with slats vs F-4E without) - 20°/s at sea lvl by Ma=0,6. It's strange from 2 reasons:
1-st the difference is huge
2-nd Slats add Lift, but also a Drag - and a lot of it. Everyone who enjoyed a aerobatic in a plane with a slats on it may confirm - if slats jumped out at the beginning of the loop - the feeling is like someone pulled a handbrake - you won't make full loop. I'm sure that slats help a lot by instantaneous turn, but in a constant turn they bring no profit.

It make only sense if the lower chart (F-4E with slats vs F-4E without slats) shows  instantaneous turn capabilities.

With my best regards
303_Kermit

 

The ITR in the lower excel-generated plot is a linear extrapolation from the data I have from the slatted F-4E manual. It may not be very accurate but I think it should be an OK estimate.

The sustained turn figures are directly from the manual. Manuals are also not perfect - a lot of data is calculated but should also give a rough idea of aircraft capabilities. The big jump in sustained G from these manuals however, imply that the difference was big enough to notice.

An aerobatic plane from an airshow probably won't have highly swept wings which is the main difference here as the drag created at high AoA flight has very different characteristics vs a straight or even moderately swept wing.

Early testing done on the F-86F sharp hard wing surprised engineers when, at high AoA, they saw turbulent flow that was reversing over the wing surface, indicating what would be a stall on a straight wing, yet the wing was not stalled - they realized they were looking at vortices created in part by strong spanwise flow which was providing lift at the cost of great drag.

Assuming the slats are scheduled correctly, they will decrease this drag that would otherwise be created at high AoA, turblent flow over a slatless swept wing. Of course the cost is complexity, weight, and - in the F-4's case - lots of profile and parasitic drag since the outer slats don't actually "retract". The Hornet and Viper have nice solutions which involve LE flaps on their very thin wings which cannot mount slats while using LERX/LEX to provide high AoA vortex lift. Meanwhile the Mirage uses slats on its highly swept wing.

Edited May 24, 2022 by SgtPappy

[303_Kermit]

21 hours ago, SgtPappy said:

An aerobatic plane from an airshow probably won't have highly swept wings which is the main difference here as the drag created at high AoA flight has very different characteristics vs a straight or even moderately swept wing.

 

Not exactly true. First Phantom posses a Wing with swept leading edge but it isn't called a "swept" wing. I've met with expressions like "cropped delta" and others, but to be honest - the solution was never used before or after. Phantom is unique.

If you want to learn something about low speed (subsonic) aerodynamics (in very simple language) I suggest a book made by eng. Roskam "Airplane design part III: Layout design of ...." Page 177, chapter "Effect of sweep on lift curve slope". For other aerodynamic literature i'm afraid there's higher mathematics needed (transformations opposite to la place transformations for a start) 

Unfortunately drag Isn't so simple as lift. First... because constants from Bernoulli equation aren't actually constant. Drag coefficient (in these case) depends on speed, humidity, and other factors. Drag force is even more complicated. Today we used to use CFD for such cases, but it's not always correct. 

Anyway - Drag of Swept wing has different nature in both cases (swept vs straight) true, but in straight wing slats work better - they're (much) more efficient. Swept wing makes many things more complicated. In subsonic speeds they give almost no advantage. My Professor used to say "if swept leading edge would be so brilliant in low speed airflow, Spitfire would have one".

There is a reason why Phantom II was nicknamed
"the triumph of thrust over aerodynamics."

 

21 hours ago, SgtPappy said:

Early testing done on the F-86F sharp hard wing surprised engineers when, at high AoA, they saw turbulent flow that was reversing over the wing surface, indicating what would be a stall on a straight wing, yet the wing was not stalled - they realized they were looking at vortices created in part by strong spanwise flow which was providing lift at the cost of great drag.

 

That was surprising 70 years ago. Reason is actually quite simple. You may find even videos on YT with explanation.

21 hours ago, SgtPappy said:

Assuming the slats are scheduled correctly, they will decrease this drag that would otherwise be created at high AoA, turblent flow over a slatless swept wing. Of course the cost is complexity, weight, and - in the F-4's case - lots of profile and parasitic drag since the outer slats don't actually "retract". The Hornet and Viper have nice solutions which involve LE flaps on their very thin wings which cannot mount slats while using LERX/LEX to provide high AoA vortex lift. Meanwhile the Mirage uses slats on its highly swept wing.

 

Rubbish. In almost every sentence. 

1. Slats never decrease drag, they usually improve Cd/Cl ratio. 

2. Slats used to work in laminar part of the flow. The point of changing the flow from laminar to turbulent may be actually calculated from the only known case of solution of Navier-Stockes equation (all other solutions are unknown). Usually it's first subject of Fluid Mechanics laboratory. 3-rd semester in my University. 

Back to the slats - Airflow through slats is usually laminar, true. It doesn't mean though, that the drag is lower. You're just changing one kind of drag to other ("friction drag" to "shape drag") usually (in these case ) summary drag is even bigger.

With my best regards
master engineer 303_Kermit 
 

 

Edited May 24, 2022 by 303_Kermit

[SgtPappy]

22 hours ago, 303_Kermit said:

If you want to learn something about low speed (subsonic) aerodynamics (in very simple language) I suggest a book made by eng. Roskam "Airplane design part III: Layout design of ...." Page 177, chapter "Effect of sweep on lift curve slope". For other aerodynamic literature i'm afraid there's higher mathematics needed (transformations opposite to la place transformations for a start) 

Thanks for the reading suggestion, I'll be sure to check it out. 

 

22 hours ago, 303_Kermit said:

Not exactly true. First Phantom posses a Wing with swept leading edge but it isn't called a "swept" wing. I've met with expressions like "cropped delta" and others, but to be honest - the solution was never used before or after. Phantom is unique.

Yes, though I feel the distinction may be a bit pedantic, the cropped delta is technically the right term, I meant swept leading edge. 

 

22 hours ago, 303_Kermit said:

That was surprising 70 years ago. Reason is actually quite simple. You may find even videos on YT with explanation.

Indeed, that was what I was implying - that it was surprising back then.

 

22 hours ago, 303_Kermit said:

Rubbish. In almost every sentence. 

1. Slats never decrease drag, they usually improve Cd/Cl ratio. 

2. Slats used to work in laminar part of the flow. The point of changing the flow from laminar to turbulent may be actually calculated from the only known case of solution of Navier-Stockes equation (all other solutions are unknown). Usually it's first subject of Fluid Mechanics laboratory. 3-rd semester in my University. 

Back to the slats - Airflow through slats is usually laminar, true. It doesn't mean though, that the drag is lower. You're just changing one kind of drag to other ("friction drag" to "shape drag") usually (in these case ) summary drag is even bigger.
 

I don't appreciate "rubbish" being thrown around, but I'll just take that as "it's the internet and people get mad a lot and resort to disrespectful language every now and then". You can just say I'm wrong. Trust me, I love learning and don't mind being corrected. But whatever, it's human nature and you sound like a decent person otherwise.

That said, I think there might be a misunderstanding here and I could have been clearer, apologies. Saying "drag decrease" was a poor choice of words. What I meant was that versus having a highly swept wing (or delta/cropped delta in this case) at high AoA with no slats, you get separation that would result in more drag at clean Clmax than the drag you have with slats at the same AoA (i.e. CL/CD is better with slats at high AoA, high Cl condition). Without slats, the aircraft would stall sooner so Cl is dropping while Cd isn't. With slats yes, of course Cd still goes up but you have access to higher Cl since the flow remains attached. Does that sound better? Can we have a discussion without insults?

For point #1, I'm not sure what you mean by "they improve Cd/Cl". Do you mean that Cd/Cl gets better = decreases or did you simply mean Cd/Cl increases (which would be a bad thing). What I was trying to say is that Cd/Cl would be even worse without slats.

For #2 what do you mean by slats "used to" to work in laminar flow? Do you mean they only operate in turbulent flow as a function of span, chord, AoA or something else?

When you look at the F-14 charts, you see a similar effect as seen in the F-4 charts - that slats can increase the sustained and instantaneous turn rate (maybe not always in other configurations) . The F-14 manuals show plots for the Tomcat with slats/flaps locked and another set for slats and maneuver flaps operating and all subsonic turn rates increase whether the wings are swept or not. If your original point was that slats should always produce enough drag such that sustained turns should be worse in general, then the Tomcat and Phantom plots imply that this is not true. There must be something more that is being missed.

 

Edited May 25, 2022 by SgtPappy

[Hummingbird]

Sgt. Pappy is correct. If the slats are engineered to only start opening at a certain AoA, then they will improve both the ITR & STR of the aircraft, you can observe this effect on the performance charts of basically all fighter aircraft so equipped.

To quote one of the conclusions from the F-4E slat testing program:

- "Thrust-limited turning performance data obtained during the test program indicate a significant increase above the performance demonstrated during F-4E Category II testing (reference 6). The F-4E Flight Manual for slat-equipped aircraft should be revised to indicate the sustained load factor capabilities demonstrated during this test program."

Why is this? A plain wing usually starts to experience a noticable increase in turbulent flow over the top surface starting around 10.5-11.5 deg AoA, hence most automatic LE slat/flap devices are designed to begin deploying in this AoA range. The effect is a smoothening of airflow over the top of the section and significantly increased critical AoA, resulting in a decrease in drag and thus increase in the L/D ratio (cl/cd). 

Simple illustration to showcase the effect:

https://imgur.com/uR1whTF

Now that being said, the L/D at clmax often decreases (i.e. L/D slope becomes less steep), but you don't fly at Clmax in a max sustainable turn anyway. Also if you're pulling Clmax you usually also desire a quicker loss in speed at the same time in order to reduce your radius as fast as possible. Hence why almost all modern fighter jets feature automatic LE slats/flaps.

 

Edited May 25, 2022 by Hummingbird

[303_Kermit]

Aerodnymics of Phantom is much more complicated. It's not the slats you shall concentrate on, but static vortex (I'm not sure about correct English name) - Very unique aerodynamic phenomena that appears on F-4 Phantom wing at certain AoA. That's the reason of very special characteristics. not the slats

Edited May 25, 2022 by 303_Kermit

[Hummingbird]

4 minutes ago, 303_Kermit said:

Aerodnymics of Phantom is much more complicated. It's not the slats you shall concentrate on, but static vortex (I'm not sure about correct English name) - Very unique aerodynamic phenomena that appears on F-4 Phantom wing at certain AoA. That's the reason of very special characteristics. not the slats

 

 No, read the F-4E slat testing program report. The thrust-limited sustainable load factor goes up in the subsonic speed range thanks to the addition of the slats.

Edited May 25, 2022 by Hummingbird

[303_Kermit]

"Thrust-limited turning performance" 

See there's the difference . For some of you turning performance is TRT+Cornering speed. In real life there's much more. One of the parameter is stability, next is lower vibrations (in Phantom very real problem), and there are much more. See also they mentioned "thrust limited" they didn't pusch it to the limits. TRT and cornering speed wasn't a subject of test... Probably. If I see rapport there is a chance I find some things you can't see in it.

Other case is, that when I use a word "Vortex " some of you think about Mirage or any other delta. It's not that "Vortex". The Vortex I mentioned has much to do with the slats. It also explains why in Phantom on high AoA smoke (if there is one) travels from trailing edge to the leading edge. As I mentioned Phantom is very specific plane. Slats can give you couple (3°-4°) extra AoA, they give some Cl (not as much in case of swept leading edge) but in case of Phantom there's more into it. Slats came to make Phantom a little bit less difficult to fly. Phantom could turn quite well with or without them, but he was even more difficult to fly than MiG-21. Adverse Yaw, buffeting, stick light when going subsonic from supersonic - name the problem, and be sure in some point Phantom has it. You can't explain Phantom just by sentence "yep - slats gave F-4 more maneuverability". It's huge underestimation. Go trough "Aircrew interview" channel there are at least 4 (maybe more) interviews with Phantoms Pilots. They all say how hard it was to push Phantom up to his limits. Charts are necessary of course, but you're scratching just the top of the iceberg not knowing that there's much more underwater. It's like that. Phantom isn't a flying brick, but it's a "pilots" plane. God damn difficult to fly. It's not the F-16,  he won't fly alone, you have to work hard for success. The point is not how high TRT Phantom may archive. The point is how long can you sustain a stable turn at corner speed without loosing control, or falling outside parameters. That is why slats came to Phantom

Edited May 26, 2022 by 303_Kermit

[SgtPappy]

1 hour ago, 303_Kermit said:

Other case is, that when I use a word "Vortex " some of you think about Mirage or any other delta. It's not that "Vortex". The Vortex I mentioned has much to do with the slats. It also explains why in Phantom on high AoA smoke (if there is one) travels from trailing edge to the leading edge. As I mentioned Phantom is very specific plane. Slats can give you couple (3°-4°) extra AoA, they give some Cl (not as much in case of swept leading edge) but in case of Phantom there's more into it. Slats came to make Phantom a little bit less difficult to fly. Phantom could turn quite well with or without them, but he was even more difficult to fly than MiG-21. Adverse Yaw, buffeting, stick light when going subsonic from supersonic - name the problem, and be sure in some point Phantom has it. You can't explain Phantom just by sentence "yep - slats gave F-4 more maneuverability". It's huge underestimation. Go trough "Aircrew interview" channel there are at least 4 (maybe more) interviews with Phantoms Pilots. They all say how hard it was to push Phantom up to his limits. Charts are necessary of course, but you're scratching just the top of the iceberg not knowing that there's much more underwater. It's like that. Phantom isn't a flying brick, but it's a "pilots" plane. God damn difficult to fly. It's not the F-16,  he won't fly alone, you have to work hard for success. The point is not how high TRT Phantom may archive. The point is how long can you sustain a stable turn at corner speed without loosing control, or falling outside parameters. That is why slats came to Phantom

That's all well and good - no one is disputing that there's more nuance to flying the F-4 but this was not the original point of discussion. You are changing the topic. The original argument you made was that it was odd that the F-4E with slats sustain a turn better since slats create extra drag especially when deployed. Everyone knows they make more drag. My rebuttal which you so kindly called rubbish before understanding what I was saying is that the extra drag does not cause a decrease in sustained turns for the F-4E; a point that is supported by flight test data specifically regarding the slat addition to the Phantom (which plainly show in figures 50 and 51 higher Cl/Cd ratios with slats extended at high Cl), the F-4E manual and the F-14 manual. With these three sources at least, we can surmise with little doubt that in general, the highest and realistically-achievable subsonic STR and max ITR increased with slats installed and extended - that's it. That's all I am saying. All the other stuff about aircraft dynamics - buffet, the reason why slats were installed, how hard the plane is to push to its limits - are not relevant to this particular discussion, but are good things to remember nonetheless. 

Reaching maximum instantaneous turn rate, one could argue is pushing to the limits but we've already agreed that this max turn rate is improved by slats:

1 hour ago, 303_Kermit said:

It make only sense if the lower chart (F-4E with slats vs F-4E without slats) shows  instantaneous turn capabilities.

 

 

1 hour ago, 303_Kermit said:

"Thrust-limited turning performance" 

See there's the difference . For some of you turning performance is TRT+Cornering speed. In real life there's much more. One of the parameter is stability, next is lower vibrations (in Phantom very real problem), and there are much more. See also they mentioned "thrust limited" they didn't pusch it to the limits. TRT and cornering speed wasn't a subject of test... Probably. If I see rapport there is a chance I find some things you can't see in it.

The thrust-limited performance of the F-4 is mentioned in the report, word for word that "Maximum afterburning thrust-limited turning performance tests were conducted at 10,000, 20,000 and 35,000 feet pressure altitude with loading 1. At the test altitude an acceleration was performed to a selected Mach number. The airplane was then banked into a turn at a constant altitude while sufficient normal load factor was attained to stabilize airspeed." Figure 50 shows they tested up to 6G at 10,000 ft. This 6G limit is shown in the F-4E-1 manual as the highest sustained G for the F-4E with 4xAIM-7s (and ~50-60% fuel based on the listed weight of 42,777 lbs). If that isn't the very definition of sustained turning, I'm not sure what else I am missing. 

Unless all three of these sources are incorrect/so erroneous such that they all lie about the improvement in maximum turn rates due to slats, then your point stating the slats should not improve sustained turn rate is not correct in the context of the F-4. Whether it was difficult to fly to this AoA or not is not relevant. Sure, we can surmise that the data and charts do not show the whole envelope of the F-4, but that's not what we're discussing... we're just looking at the most realistically achievable turn rates because anything past that is different from plane to plane and from pilot to pilot and isn't shown in the reference data (manuals) or the experimental data (slat report). 

Furthermore, anecdotes, though useful, are not data. Even if those interviews could be used as data, there are real Phantom pilots on these very forums posting in these exact threads who have spoken in favour of the Phantom's increased turn rates thanks to the slats and they also have mentioned the disadvantages associated with the extra drag that was present at all parts of the flight envelope. Like you said, you might be able to come over the top of a loop better in a hard-wing bird but that's a different maneuver than the sustained turns whose plots you questioned.

Before anyone asks "why the obsession with data? Flying a plane is more than data blah blah blah" well it's because data can be compared and reliably cross-referenced and most planes will probably fit that data with high confidence. There's probably even data out there about the aircraft stability, buffet "envelope" if you will, and all sorts of other things - but I doubt they will contradict the aforementioned sources. Anecdotes add context but will never replace verifiable data.

Edited May 26, 2022 by SgtPappy

[303_Kermit]

7 hours ago, SgtPappy said:

The thrust-limited performance of the F-4 is mentioned in the report, word for word that "Maximum afterburning thrust-limited turning performance tests were conducted at 10,000, 20,000 and 35,000 feet pressure altitude with loading 1. At the test altitude an acceleration was performed to a selected Mach number. The airplane was then banked into a turn at a constant altitude while sufficient normal load factor was attained to stabilize airspeed." Figure 50 shows they tested up to 6G at 10,000 ft. This 6G limit is shown in the F-4E-1 manual as the highest sustained G for the F-4E with 4xAIM-7s (and ~50-60% fuel based on the listed weight of 42,777 lbs). If that isn't the very definition of sustained turning, I'm not sure what else I am missing. 

Unless all three of these sources are incorrect/so erroneous such that they all lie about the improvement in maximum turn rates due to slats, then your point stating the slats should not improve sustained turn rate is not correct in the context of the F-4. Whether it was difficult to fly to this AoA or not is not relevant. Sure, we can surmise that the data and charts do not show the whole envelope of the F-4, but that's not what we're discussing... we're just looking at the most realistically achievable turn rates because anything past that is different from plane to plane and from pilot to pilot and isn't shown in the reference data (manuals) or the experimental data (slat report). 

 

Ok I try to explain . Sorry for putting crappy paintings, but I couldn't find anything more elegant in Internet. Sorry. Now One photo says 1000 words right? Lets try that. Two cases. First - Phantom without slats. No comments needed i think. Second - static Vortex. Consumes very little amount of energy from the airstream, under some conditions it works as a "Extra airfoil" - in simple words the airflow behaves like it's flowing around much bigger , thicker profile. The phenomena is stable, but appears and disappears quite rapidly. That is why you get STRT improvement.
 

[Hummingbird]

2 hours ago, 303_Kermit said:

Ok I try to explain . Sorry for putting crappy paintings, but I couldn't find anything more elegant in Internet. Sorry. Now One photo says 1000 words right? Lets try that. Two cases. First - Phantom without slats. No comments needed i think. Second - static Vortex. Consumes very little amount of energy from the airstream, under some conditions it works as a "Extra airfoil" - in simple words the airflow behaves like it's flowing around much bigger , thicker profile. The phenomena is stable, but appears and disappears quite rapidly. That is why you get STRT improvement.
 

 

Sorry but it's very evident based on your drawings that you've completely misunderstood how slats work.

Slats dont work by creating a vortice over the top of the wing, quite the contrary.

Slats work by delaying boundary layer seperation, i.e. they help maintain smooth airflow over the top of the airfoil along a much higher AoA range -> higher critical AoA (usually from ~15 to ~25 deg on a normal straight wing), Clmax and L/D at typical AoA during thrust limited sustainable turns.

https://images.app.goo.gl/ctFKB6VxYShw7uELA

https://images.app.goo.gl/HtTziaqKQMFfCoV49

Edited May 26, 2022 by Hummingbird

[303_Kermit]

1 hour ago, Hummingbird said:

 

Sorry but it's very evident based on your drawings that you've completely misunderstood how slats work.

Slats dont work by creating a vortice over the top of the wing, quite the contrary.

Slats work by delaying boundary layer seperation, i.e. they help maintain smooth airflow over the top of the airfoil along a much higher AoA range -> higher critical AoA (usually from ~15 to ~25 deg on a normal straight wing), Clmax and L/D at typical AoA during thrust limited sustainable turns.

https://images.app.goo.gl/ctFKB6VxYShw7uELA

https://images.app.goo.gl/HtTziaqKQMFfCoV49

 

I'm trying you to explain that slats in Phantom caused a Phenomena i described. It wasn't a original purpose of engineers - it was unexpected. I can reassure you I know how slats work, I know the Coanda effect, and what's more I can calculate a proper size of a slat opening, and other parameters necessary to construct a slated wing. I know that slats work only for some designed speed and angle of attack. The thing you can't understand is, that Phenomena I described was a byproduct - unexpected surprise for engineers. I'm not trying you to explain how slats work, because I expect you to know such basics. I assume that people here knows what Wikipedia is and I expect that very basic understanding of fluid mechanic is possessed. I'm explaining only things you won't find in Wiki.

With my best regards
303_Kermit

PS No slats can add you +25° to critical AoA. You went bit to far.

Edited May 26, 2022 by 303_Kermit

[SgtPappy]

4 hours ago, 303_Kermit said:

I'm trying you to explain that slats in Phantom caused a Phenomena i described. It wasn't a original purpose of engineers - it was unexpected. I can reassure you I know how slats work, I know the Coanda effect, and what's more I can calculate a proper size of a slat opening, and other parameters necessary to construct a slated wing. I know that slats work only for some designed speed and angle of attack. The thing you can't understand is, that Phenomena I described was a byproduct - unexpected surprise for engineers. I'm not trying you to explain how slats work, because I expect you to know such basics. I assume that people here knows what Wikipedia is and I expect that very basic understanding of fluid mechanic is possessed. I'm explaining only things you won't find in Wiki.

With my best regards
303_Kermit

PS No slats can add you +25° to critical AoA. You went bit to far.

 

Well, originally we were arguing about STR increase and slats but now we're talking about slat phenomena. So the discussion got a little muddy.

Do you have any papers on this phantom phenomenon? 

[303_Kermit]

I remember it was mentioned on "Plane Construction" workshops as curiosity. I can check my old pdf. ... some of them are 25 years old  It's a trip down memory lane for me. Anyway. maybe i didn't stated it clear enough - The phenomena lowers the drag. There are couple old cars with rubbish bodywork, but in spite of it - good Cx was archived, the reason was the same. I thought that connection between STRT and the Phenomena I described is quite easy to understand

[Hummingbird]

9 hours ago, 303_Kermit said:

I'm trying you to explain that slats in Phantom caused a Phenomena i described. It wasn't a original purpose of engineers - it was unexpected. I can reassure you I know how slats work, I know the Coanda effect, and what's more I can calculate a proper size of a slat opening, and other parameters necessary to construct a slated wing. I know that slats work only for some designed speed and angle of attack. The thing you can't understand is, that Phenomena I described was a byproduct - unexpected surprise for engineers. I'm not trying you to explain how slats work, because I expect you to know such basics. I assume that people here knows what Wikipedia is and I expect that very basic understanding of fluid mechanic is possessed. I'm explaining only things you won't find in Wiki.

With my best regards
303_Kermit

 

Do you have a source for this so called "unexpected phenomena" without a name on the Phantom?

So far I don't see it playing out on the actual Cl/Cd graphs for the F-4E in the report, instead they work exactly as I've described, I wonder why  

 

 

Also btw, automatic slats work in a range of AoA, not "a" single specific one. Also in general they're not speed dependant, and work entirely as a function of AoA, unless they're power assisted.

9 hours ago, 303_Kermit said:

PS No slats can add you +25° to critical AoA. You went bit to far.

 

You misinterpreted what was written.

I'll try again; Typically slats increase the critical AoA on a regular straight wing from a normal ~15 deg, to about ~25 deg. 

 

Edited May 27, 2022 by Hummingbird

[303_Kermit]

I shall wrote, that slats are constructed - means calculated for a specific AoA. You're catching a single words from what I write. English is not my first language. Well the point with the slats is, that Coanda effect which basically they use, needs specific parameter of airstream blowing through slat opening. Too much - and airflow won't "glue" to the upper surface. It blows it away. Too little - the same. That is why for slats - to "design" them (I hate these word), to calculate them - engineer needs a speed (usually it's a landing speed) , AoA, and of course prepared basic shape of a wing to calculate the reynolds number, because coanda effect strongly depends from it. That's what I meant.

Hummingbird. The drawings are very nice ( I mean the lower ones). I wish Airflow and Aerodnymics is so simple in real life.... You see. Most of "virtual airflow sim" or "virtual wind tunnel" use simplified aerodynamics. To calculate things they use assumption that the air has no viscosity, and no compressibility. Sometimes it's enough to become some rough estimation. Not in these time. 

Example? Just from angle of attack on your drawings I can say that the data on it are ment to describe Cl/AoA for Airfoil (with and without slat) - not for a wing. Because a shape of a wing makes the curves more "flat". Some wings has 25° critical AoA without slats. Others needs slats to rich such AoA. They both may even have the same airfoil, but work on different reynolds number.

 

Anyway... you asked why STRT is better with slats and I gave you explanation. Probably it's not as simple one as you may expect. 

CL/CD Chart - the one above, "Maximum Thrust - Combat configuration..." is interesting. With some additional data, one may use it to approximate STRT. Means, one may check if the chart CL/CD suits STRT chart. Some simplifications are needed, like a constant thrust in all speeds and AoA, or constant weight of a plane. Also as always in Aerodynamics it's necessary to calculate an error, but there are the ways to check if both data - CL/CD and STRT/TAS suit together. 

 

With my best regards
303_Kermit

Edited May 27, 2022 by 303_Kermit