Thoughts on the K-4 Manouverability

[Panthera]

5 hours ago, JtD said:

You're in fact getting about as much out of them as you're getting from conventional designs. They use a profile that reduces maximum lift by a bit, but design details were done well and manufacturing standards for the Mustang were extremely high, so the high qualitiy of the wing finish offsets much of the disadvantages of the profile shape.

I'm aware of clmax figures for the Bf109 in the range from 1.1 to 1.5, and for the P-51 I'm finding 1.2 to 1.45.

 

The manufacturing finish on the Mustangs wings weren't actually over the norm (and even if it was it probably wouldn't last a week in service), which is the reason the amount of laminar flow seen in mock up testing wasn't replicated by service aircraft. Biggest problem was/is that laminar profiles are more affected by surface roughness and bumps than the conventional types, whilst the wing paneling back then wasn't as strong as today. 

 

As for the Cl range for the 109 and P-51, the most common figure I've seen for the 109 is in the 1.45 range (1.48 is often qouted), however it's for unpowered flight, originating from windtunnel testing on a prototype with a shortened wing and no slats. So here we're missing effect of speed & propwash, the latter of which is maximized on an aircraft with outboard mounted slats covering the rest.

 

Thus we're better off looking at the figures derived from actual flight testing at representative speeds, and here the laminar profiles are shwon to be at a distinct disadvantage in Clmax compared to asymmetric conventional types (such as the NACA 230xx series which is very similar to the 109's 2R1), until around 0.5 mach where the laminar profile starts to come into its own - this is not the speed at which WW2 propjobs were dogfighting though.

 

Moving into the jet age however and the narrow/sharp leading edge and rearward positioned max thickness & camber start becoming ideal for fighter aircraft, esp. since now automatic leading & trailing edge devices can transform these values on demand, ensuring maximum effectiveness in both cruising and maneuvering flight.

 

 

 

 

 

 

Edited April 21, 2021 by Panthera

[JtD]

18 minutes ago, Panthera said:

The manufacturing finish on the Mustangs wings weren't actually over the norm, which is the reason the amount of laminar flow seen in mock up testing wasn't replicated by service aircraft.

 

The German evaluation for the Mustang wing clearly describes it as excellent and as superior to that typical for German manufacturing at the time. Now this is mostly done from a drag perspective, but still, in terms of surface quality, it was clearly better than contemporary aircraft (not only German ones). Just like that one, every analysis of the P-51 surface quality I've ever read attests above average to excellent finish. I have no idea why you are contesting this, care to share?

 

26 minutes ago, Panthera said:

As for the Cl range for the 109 and P-51, we have to look at those derived from flight testing at representative speeds, and here the laminar profiles are at a distinct disadvantage in Clmax compared to conventional types such as the NACA 230xx series (which is very similar to the 109's 2R1)

 

OK, what figures based on flight testing of the actual aircraft at representative speeds do you have, that allows you to reach that distinct conclusion?

[Panthera]

9 minutes ago, JtD said:

 

The German evaluation for the Mustang wing clearly describes it as excellent and as superior to that typical for German manufacturing at the time. Now this is mostly done from a drag perspective, but still, in terms of surface quality, it was clearly better than contemporary aircraft (not only German ones). Just like that one, every analysis of the P-51 surface quality I've ever read attests above average to excellent finish. I have no idea why you are contesting this, care to share?

 

 

OK, what figures based on flight testing of the actual aircraft at representative speeds do you have, that allows you to reach that distinct conclusion?

 

I haven't seen that German evaluation, but I have read about issues with surface roughness largely negating the effects sought after with the early laminar flow profile designs, and it came down to the paneling back then simply being far to susceptible to denting/deformation.

 

As for the flight testing figures, we have Cl vs mach charts for the P-51 & F6F which highlight the noticable difference in lift production vs speed between the two types of profiles these aircraft used:

 

 

 

 

Edited April 21, 2021 by Panthera

[JtD]

WRT surface quality of the P-51, a small snippet from a NACA report. Aircraft 1 is a p-51, 5 is a F4U and 6 an F6F. Wind tunnel testing at 60 mph.

 

[Aurora_Stealth]

44 minutes ago, JtD said:

 

The German evaluation for the Mustang wing clearly describes it as excellent and as superior to that typical for German manufacturing at the time. Now this is mostly done from a drag perspective, but still, in terms of surface quality, it was clearly better than contemporary aircraft (not only German ones). Just like that one, every analysis of the P-51 surface quality I've ever read attests above average to excellent finish. I have no idea why you are contesting this, care to share?

 

 

OK, what figures based on flight testing of the actual aircraft at representative speeds do you have, that allows you to reach that distinct conclusion?

 

I do remember reading some of the LW testing evaluations (was a while ago, think it may have been Hans Werner-Lerche), yes the P-51 was "unmistakable" in its aerodynamic efficiency and yes they recognised it had a very high attention to detail in terms of design and manufacturing with the flush rivetting and general surface quality being considered exceptional. The problem though is maintaining that surface quality in operational service, you still have exhaust fumes, dust from operating in field conditions and well - if you fly and maintain an aircraft in any kind of rough conditions its not going to remain in an ideal surface finish. That's ignoring the effects from accumulated in-service combat / surface damage (that could accumulate from things like patched bullet holes or debris etc) and that icing on these types of wings could and did in some accounts cause a catastrophic effect for pilots who flew the P-51 (such as when flying through clouds etc) which highlights this issue again. Just like with maintaining a car outside over time, you can of course just clean it rigorously - but the aircraft could be flown several sorties a day, and be flying for potentially six hours or more on a flight with the '51 and these guys were not only operating from the UK in ideal conditions. These aircraft were also in very high demand when they arrived, so relying on the aircraft to be in a perfect condition when they were being well used is a bit hopeful.

 

Obviously a wind tunnel is ideal conditions, which is where the LW confirmed their suspicions about the very high aerodynamic efficiency of the P-51.

 

So these issues in isolation may not seem significant but when seen in the broader context they are an undermining factor and this is specifically mentioned in the NASA/NACA conclusions.... its an aircraft that is relying a great deal on its aerodynamic efficiency with factors including surface finish playing a major role... so any degradation therefore has a pronounced effect on the aircraft's performance in comparison to others which may be using greater power output / thrust in the first place to achieve that given performance.

Edited April 21, 2021 by Aurora_Stealth

[JtD]

56 minutes ago, Panthera said:

As for the flight testing figures, we have Cl vs mach charts for the P-51 & F6F which highlight the noticable difference in lift production vs speed between the two types of profiles these aircraft used:

 

In these tests the P-51 achieved a clmax of 1.48 at Mach 0.175 at 13400ft. That's the maximum I see. Mach 0.25 - 0.3 might be a little more representative for turnfighting, and there the range is 1.1 to 1.32, depending on the test altitude. Unfortunately there's no comparable data for the F6F. And none at all for the Bf109.

 

21 minutes ago, Aurora_Stealth said:

The problem though is maintaining that surface quality in operational service, you still have exhaust fumes, dust from operating in field conditions and well - if you fly and maintain an aircraft in any kind of rough conditions its not going to remain in an ideal surface finish.

 

The quality of the P-51 surface is not about dust, it about panels and rivets actually being flush and airtight. This doesn't change when the aircraft gets dirty, even if it may change when you pull extremely high g's or produce a some rough landings. I'm willing to bet that the aircraft the Germans got to investigate weren't shipped in fresh from the factory, but had seen field service, and they still maintained these properties.

Edited April 21, 2021 by JtD

[Aurora_Stealth]

42 minutes ago, JtD said:

The quality of the P-51 surface is not about dust, it about panels and rivets actually being flush and airtight. This doesn't change when the aircraft gets dirty, even if it may change when you pull extremely high g's or produce a some rough landings. I'm willing to bet that the aircraft the Germans got to investigate weren't shipped in fresh from the factory, but had seen field service, and they still maintained these properties.

 

That's not how I interpret the below. A "sandlike" material sounds a lot like dust (in a thin layer) if you ask me.

 

 

Edited April 21, 2021 by Aurora_Stealth

[Bremspropeller]

That test shows how susceptable those early laminar'ish flow profiles were for any kind of leading-edge contamination (e.g. rain-droplets, icing, bugs, dents, scratches, any other kind of erosion, a $hitty paintjob, you name it).

 

Newer profiles can deal a lot better with those kinds of real-world factors.

 

Note the 661-212 unfortunately isn't represented in the graph, though.

 

 

[Dakpilot]

Two DC-4's that I flew regularly from dirt strips (neither of which were washed regularly and then only with plain water) had different finishes one painted and the other bare metal, the bare metal finish was much smoother - spent a lot of time on the wings fueling/oiling and pre flights - even though it probably had not had a polish in 20 years. 

 

Probably not very relevant but were P-51 wings polished Ali or paint? Paint quality is also important (having rollered/sprayed a number of A/C to various standards) 

 

Sure I recall some modern pilots who had flown both 109's and P-51's clearly saying that the P-51 was manufactured to a much higher standard, this was not regarding late war issues. 

 

Higher quality tolerances/manufacturing/paint etc will still out perform lower quality when both have some time on them, I would also hazard that allied aircraft got polished more often than axis simply based on resourses and manpower in latter half of the conflict 

 

Cheers, Dakpilot 

[JtD]

1 hour ago, Aurora_Stealth said:

That's not how I interpret the below. A "sandlike" material sounds a lot like dust (in a thin layer) if you ask me.

 

Fortunately, I don't have to, because NACA said what they mean in their data. The NACA standard roughness, which your chart also looks like, is 0.011 inch grain "considerably more than manufacturing tolerances or service deterioration but considerably less than accumulated mud, ice or combat damage". Here's another chart for comparison. It also shows that in terms of drag even tiny roughness has a large effect, whereas the effect on the maximum lift coefficient is more gradual.

 

However, as stated before, the high surface quality of the P-51 wing is not about surface roughness, it's about panels and rivets being flush and airtight.

 

[ZachariasX]

1 hour ago, Dakpilot said:

Probably not very relevant but were P-51 wings polished Ali or paint?

Wings are all pained and polished. There can be smaller panels covering the engine that are bare aluminum, but most of the airframe painted silver (or respective camo).

 

You can se ethis here on a Swedish AF Mustang (now museum exhibit):

 

 

Some screws are overpainted and some screws that are just replaced after the paint job was done. These are the tailwheel access panels. You can also see the paint leaking through on the green primer due to poor masking.

Edited April 21, 2021 by ZachariasX

[Mitthrawnuruodo]

15 hours ago, [Pb]Cybermat47 said:

I agree that there can’t really be an ‘official ruling’, but I don’t see why YouTube videos should be judged as inferior to books if both are made by professional historians who cite and analyse primary sources and peer-reviewed studies. 

 

Nothing wrong with videos. However, like any self-published work, they should be examined carefully, especially if the author isn't an established expert in a relevant field. As with forum posts, blogs, and enthusiast websites, there is zero oversight. Traditional books aren't infallible either, but ideally someone reviews them before deciding that publication is worth the risk.

Edited April 21, 2021 by Mitthrawnuruodo

[Panthera]

13 hours ago, JtD said:

 

In these tests the P-51 achieved a clmax of 1.48 at Mach 0.175 at 13400ft. That's the maximum I see. Mach 0.25 - 0.3 might be a little more representative for turnfighting, and there the range is 1.1 to 1.32, depending on the test altitude. Unfortunately there's no comparable data for the F6F. And none at all for the Bf109.

 

Yes, due in part to the effect of propwash which is stronger the slower you go. There is comparable data for the F6F (Fig.4, the page I referenced just shows the general difference), and here we again see the conventional type profile perform better below 0.5 mach. In other words aircraft with the NACA 230xx type profile will produce lift more efficiently below 0.5 mach than ones with the NA laminar profiles, and we see this demonstrated in comparisons between aircraft of similar W/L using these two types of profiles too (Navy comparison between F4U & P51B for example).

It is also considered when designing new profiles, the sharp leading edge and rearward placed position of max thickness & camber is only really beneficial if your aim is low drag at low AoAs and/or better high speed efficiency.

 

In low speed windtunnel testing the NACA 230 series usually achieves around 1.6 free flow.

Edited April 22, 2021 by Panthera

[JtD]

And yet, the actual aircraft equipped with NACA 230xx, at similar reynolds numbers in a wind tunnel, fail to achieve 1.4.

 

And no, the F6F chart in figure 4 is the same as in figure 14, there's no comparable data to the P-51. The chart ends at Mach 0.35 and does not allow to differentiate between Mach and Reynolds number effects.

[Yak_Panther]

 

If DCS is benchmark for accuracy for the 109. Then testing has already has proven that Il 2 is accurate, ie very close to the DCS 109 K4.

 

This show the specific excess power of both the DCS and Il 2 K-4 1.8 ata @ sea level are equal. Sustained turn rate is defined by  Specific Excess Power (Ps) is = (Trust-Drag)*V/Weight. The Sustained Rate line in these E-M charts is the Ps-0 line. That is 0 =  (Trust-Drag)*V/Weight

 

Since both of these curves match, we can conclude that both aircraft have the same total amount thrust and drag, including induced.

 

The instantaneous rate line is defined by, the Cl max at, either the structural limit, or the pilot limit. Since it is equal in both sims, we can conclude both aircraft have the same Cl max.

 

If the Lift, thrust and drag of Il2 K4 and the DCS K4 are the same, Then what specifically is wrong with the Il-2 K-4?

 

Both The DCS K4 and the Il2 K4. seem to have the same Cl max of 1.56 in a 2g turn and Cl max of ~ 1.4 in  a 1g powered off stall. both seem to have the same drag, including induced.

 

Flight testing of the I'l2 P-51,  Gives a CL max of ~ 1.5 at 2 g.  The spec sheets indicates the the 1 g power off Cl max is 1.38

Both the Il-2 K4 and the P-51 add 10% Cl from power on propeller effects. Which is pretty reasonable given which characteristics govern those effects. Propeller diameter, wing span, thrust coefficient, ect.

Source: https://reports.aerade.cranfield.ac.uk/handle/1826.2/3280

Shows ~ 10% increase in Cl max due to propeller effects.

 

Most of the turning advantage for P-51 comes from the G suit. Requiem captured in game data from the P-51 and The 190 D9 and created a set of EM diagrams comparing the two.   

Take the G suit away and the P-51's turning advantage shrinks considerably.

DCS doesn't model the G suit in the P-51. So the place in the envelope where the Il2 P-51 can out turn the K4 and the D9, Above the 6g line. Doesn't exists in DCS, which is probably why some people seem to think the DCS 109K4 turns better than the I2, when they both turn about the same. The difference between the sims is P-51's capabilities not the 109's.

 

The only thing I can think off that could be off in both sims is that 1 g Cl max is too low on the 109. The 1.4 Cl max of the 109 seems to based on 2 sources. The Chalais Meudon wind tunnel tests and the British test of the 109 E, RM 2361.

 

First lets deal with RAE report. The only thing that raises any eybrows is how they are computing the Cl max at various G loads.  They seem to be using the indicated speed and not the corrected speed in Calculation of 2g Cl max.  The RAE report gives the 2 g Cl max as 1.6 based on aircraft weight of 5600 Lbs * 2 g load factor at an alt of 12,000 ft. assuming as standard day and a speed of 150 mph. If you use the instrument corrected speed ~ the Cl max at 2 g goes to 2.36

 

But I don't think 2.36 is a realistic number given the airfoil. It's most likely that their instrument correction is wrong. The report notes that "

"Position error estimated from A.A.E.E. generalised curves as described in 5 2.74". So It's just a generalized position error estimate and the number of data points, 2, doesn't exactly instill a lot of confidence it's correct.

 

 

  It is interesting note that difference between 1 g stall Cl is  1.4  and 2g power 1.6 in this report is about 12%. Which is only 1% less than the difference in Il2's K4, 1.4 to 1.56 Cl's

 

The Chalais Meudon tests. Seems to report a Cl max of ~1.4 Though I can't seem to find a copy of the exact report. However Horner notes in his Book Fluid Dynamics Drag, that RE these test were conducted at a RE of 4 * 10^6, while the flying condition at top speed is ~ Re 2 * 10^7. So perhaps you could argue that Cl max power off, is a bit a low. Given the RAE  1 g stall was achieved at  95 mph, not accounting for the reynolds number might take away some CL. 

In the 109's case you maybe able to add another .05 Cl

The changes in Cl due renynolds number are called scaling effects.  This is from an RAE test on P-51. Don't take it as the end all be as when these test we're conducting this issues we're still being worked out. A lot of this testing was due to discrepancies between the RAE and NACA results. Both agencies were trying to account for the differences.

Source:https://reports.aerade.cranfield.ac.uk/handle/1826.2/3821

 

In this you can see the RAE beginning to investigate compressability, mach, and  the scale effects issues.  That were at the forefront aerodynamics in the late and post war period. https://reports.aerade.cranfield.ac.uk/handle/1826.2/3233

 

Here is a more modern take on scale effects.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a291964.pdf

 

If you haven't check out Horner's Fluid Dynamic Drag, it's worth the read.  Sighard F Hoerner, designed the Fi 156 Storch and conducted the drag analysis of the 109 G for Messerschmidt. He goes through the aircraft component by component and breaks down the drag penalty for everything, including the paint. The Surface roughness and imperfections account for 15% of the total drag. Going on he computes that if one were to clean up all the drag and were only left with the skin friction drag and the induced drag with a 1200 hp power plant the 109 would reach 800 kph. Despite the drag clean up the K-4 it still was a very draggy aircraft for it's time.

Edited April 22, 2021 by Yak_Panther
added image

[Aurora_Stealth]

1 hour ago, Yak_Panther said:

If DCS is benchmark for accuracy for the 109. Then testing has already has proven that Il 2 is accurate, ie very close to the DCS 109 K4.

 

This show the specific excess power of both the DCS and Il 2 K-4 1.8 ata @ sea level are equal. Sustained turn rate is defined by  Specific Excess Power (Ps) is = (Trust-Drag)*V/Weight. The Sustained Rate line in these E-M charts is the Ps-0 line. That is 0 =  (Trust-Drag)*V/Weight

 

Since both of these curves match, we can conclude that both aircraft have the same total amount thrust and drag, including induced.

 

The instantaneous rate line is defined by, the Cl max at, either the structural limit, or the pilot limit. Since it is equal in both sims, we can conclude both aircraft have the same Cl max.

 

If the Lift, thrust and drag of Il2 K4 and the DCS K4 are the same, Then what specifically is wrong with the Il-2 K-4?

 

Both The DCS K4 and the Il2 K4. seem to have the same Cl max of 1.56 in a 2g turn and Cl max of ~ 1.4 in  a 1g powered off stall. both seem to have the same drag, including induced.

 

Flight testing of the I'l2 P-51,  Gives a CL max of ~ 1.5 at 2 g.  The spec sheets indicates the the 1 g power off Cl max is 1.38

 

Both the Il-2 K4 and the P-51 add 10% Cl from power on propeller effects. Which is pretty reasonable given which characteristics govern those effects. Propeller diameter, wing span, thrust coefficient, ect.

 

Source: https://reports.aerade.cranfield.ac.uk/handle/1826.2/3280

Shows ~ 10% increase in Cl max due to propeller effects.

 

Most of the turning advantage for P-51 comes from the G suit. Requiem captured in game data from the P-51 and The 190 D9 and created a set of EM diagrams comparing the two.

 

Take the G suit away and the P-51's turning advantage shrinks considerably

DCS doesn't model the G suit in the P-51. So the place in the envelope where the Il2 P-51 can out turn the K4 and the D9, Above the 6g line. Doesn't exists in DCS, which is probably why some people seem to think the DCS 109K4 turns better than the I2, when they both turn about the same. The difference between the sims is P-51's capabilities not the 109's.

 

The only thing I can think off that could be off in both sims is that 1 g Cl max is too low on the 109. The 1.4 Cl max of the 109 seems to based on 2 sources. The Chalais Meudon wind tunnel tests and the British test of the 109 E, RM 2361.

 

First lets deal with RAE report. The only thing that raises any eybrows is how they are computing the Cl max at various G loads.  They seem to be using the indicated speed and not the corrected speed in Calculation of 2g Cl max.  The RAE report gives the 2 g Cl max as 1.6 based on aircraft weight of 5600 Lbs * 2 g load factor at an alt of 12,000 ft. assuming as standard day and a speed of 150 mph. If you use the instrument corrected speed ~ the Cl max at 2 g goes to 2.36

 

But I don't think 2.36 is a realistic number given the airfoil. It's most likely that their instrument correction is wrong. The report notes that "

"Position error estimated from A.A.E.E. generalised curves as described in 5 2.74". So It's just a generalized position error estimate and the number of data points, 2, doesn't exactly instill a lot of confidence it's correct.

  It is interesting note that difference between 1 g stall Cl is  1.4  and 2g power 1.6 in this report is about 12%. Which is only 1% less than the difference in Il2's K4, 1.4 to 1.56 Cl's

 

The Chalais Meudon tests. Seems to report a Cl max of ~1.4 Though I can't seem to find a copy of the exact report. However Horner notes in his Book Fluid Dynamics Drag, that RE these test were conducted at a RE of 4 * 10^6, while the flying condition at top speed is ~ Re 2 * 10^7. So perhaps you could argue that Cl max power off, is a bit a low. Given the RAE  1 g stall was achieved at  95 mph, not accounting for the reynolds number might take away some CL. 

In the 109's case you maybe able to add another .05 Cl

The changes in Cl due renynolds number are called scaling effects.  This is from an RAE test on P-51. Don't take it as the end all be as when these test we're conducting this issues we're still being worked out. A lot of this testing was due to discrepancies between the RAE and NACA results. Both agencies were trying to account for the differences.

Source:https://reports.aerade.cranfield.ac.uk/handle/1826.2/3821

 

In this you can see the RAE beginning to investigate compressability, mach, and  the scale effects issues.  That were at the forefront aerodynamics in the late and post war period. https://reports.aerade.cranfield.ac.uk/handle/1826.2/3233

 

Here is a more modern take on scale effects.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a291964.pdf

 

If you haven't check out Horner's Fluid Dynamic Drag, it's worth the read.  Sighard F Hoerner, designed the Fi 156 Storch and conducted the drag analysis of the 109 G for Messerschmidt. He goes through the aircraft component by component and breaks down the drag penalty for everything, including the paint. The Surface roughness and imperfections account for 15% of the total drag. Going on he computes that if one were to clean up all the drag and were only left with the skin friction drag and the induced drag with a 1200 hp power plant the 109 would reach 800 kph. Despite the drag clean up the K-4 it still was a very draggy aircraft for it's time.

 

Fantastic post btw (credit where its due - some interesting content).

 

Yeah I get your point - the P-51 pilot does receive a lot of help with the G-Suit.

 

Have to say, I wasn't aware that G-Suits weren't modelled in DCS and considering they have jets and some advanced features etc - I'm quite surprised. That does explain some of the differential, but like you alluded to and this does make sense to me - I still think there's another factor in there down to the aircraft themselves.

 

This is why I'm always very critical and very skeptical of other sides evaluating captured equipment, I agree the RAE figures are to be taken as general estimates not as a guideline - they do trip up in places (which is fine, they are not going to be as familiar as an actual manufacturer/operator is). I would have thought using IAS in a calculation like that to be a bit of a schoolboy error but its wartime circumstances etc I get it.

 

I have read Hoerner's analysis some time ago, but believe his analysis was of a Bf 109 G-6; which is absolutely fine and still very useful but it is one of the least refined, and highest drag variants of the aircraft. By comparison, its hard to say the Bf 109 F-4 or G-2 was poor aerodynamically for its time; but yeah new designs and advances in aerodynamics were making the aircraft look outdated later in the war. Looking again at drag due to surface roughness and imperfections though, its quite high.

 

Some really good stuff to read there, will have to read-up on the scaling - thanks again.

Edited April 22, 2021 by Aurora_Stealth

[JtD]

2 hours ago, Yak_Panther said:

First lets deal with RAE report. The only thing that raises any eybrows is how they are computing the Cl max at various G loads.  They seem to be using the indicated speed and not the corrected speed in Calculation of 2g Cl max.

 

How do you arrive at that conclusion? They say they are plotting the chart over "true air speed v" and "corrected air speed vi" and the lift coefficients correspond to these figures. If they were referring to the pilots speed indicator, they'd be using "A.S.I.". They also explicitely say in the report (in another paragraph) that they are using the "A.S.I. with the position error correction from figure 8" to arrive at the cl's.

 

Edit: I think I know what you were thinking. But then that would be an error on your side and the report would indeed be correct.

Edited April 22, 2021 by JtD

[gimpy117]

On 4/21/2021 at 6:57 AM, Panthera said:

 

The manufacturing finish on the Mustangs wings weren't actually over the norm (and even if it was it probably wouldn't last a week in service), which is the reason the amount of laminar flow seen in mock up testing wasn't replicated by service aircraft. Biggest problem was/is that laminar profiles are more affected by surface roughness and bumps than the conventional types, whilst the wing paneling back then wasn't as strong as today. 

look, if were gonna go into manufacturing problems with aircraft, I don't think it would be a good time for the late model 109's made in caves or wherever wasn't bombed yet...

 

aircraft are modeled as a perfect new example. 

Edited April 23, 2021 by gimpy117

[Panthera]

@Yak_Panther

The DCS & IL2 representations of the K4 & P51 have been tested and they are not the same, at all:

 

IL2 @ 370 km/h sea level:

P-51D, 400 L, 67" Hg: 3.4 G's sustained

109K-4, 400 L, 1.8ata: 3.3 G's sustained

109G14, 400 L, 1.8ata: 3.3 G's sustained

 

DCS for comparison:

 

DCS @ 370 km/h sea level:

P-51D, 400 L, 67" Hg: 3.0-3.1 G's sustained 

109K-4, 400 L, 1.8ata: 3.6-3.7 G's sustained

 

All of these figures are easy to test using the ingame G meters, and I've done them many times by now, so I know they're accurate - which makes it all the more curious why your doghouse plots show something different.

 

Furthermore on the doghouse plots you've generated you're incorrectly attributing a higher lift limit curve (instantanous rate) being due to a higher Clmax, which is not the case, esp. not when you're comparing a NACA 6 series laminar profile wing with a NACA 230 series conventional one at regular dogfighting speeds. A higher lift limit curve is the result of total lift vs weight, not just a lift coefficient.

Edited April 23, 2021 by Panthera

[Panthera]

On 4/22/2021 at 6:36 AM, JtD said:

And yet, the actual aircraft equipped with NACA 230xx, at similar reynolds numbers in a wind tunnel, fail to achieve 1.4.

 

Yes, in a windtunnel, where 1.5+ for the same aircraft was also achieved. However we need to add some more speed, power effects and service conditions to see the true difference, as shown in TN 1044 amongst others.

 

Also as I mentioned we see this reflected in the Navy comparisons between the F4U-1 and P-51B as well, where despite actually having a slightly lower wing loading the P-51 is found to be no match for the F4U-1 in a turning fight. The main reason for this appears rather clear when we look at the graphs in TN 1044, the conventional asymmetrical profile aerofoil is simply more efficient at generating lift at the speeds where dogfighting amongst propeller driven fighters occur. At very very low speeds (i.e. wind tunnel), and with perfect surfaces, there isn't always much of a difference, but once above ~0.175 mach the difference becomes telling.

 

It would be very hard to find any other reason as to why else the F4U was found so much better than the P-51 at turning if not for this.

Edited April 23, 2021 by Panthera

[JtD]

And yet, when NACA tested the stalling speeds of the XP-51 and the F4U in flight, they found a clmax of ~1.5 for the XP-51 and a clmax of ~1.4 for the F4U (gliding condition). Power on (cruising) they are both a 1.6. The XP-51 report shows time plots of turns up to 6g loads (flown at about 7500lbs load), resulting in lift coefficients of 1.3-1.4 utilized in these turns.

 

The Navy comparison I know between the F4U and a P-51B doesn't make a statement regarding turning fights. It simply says the F4U has superior speed, climb and horizontal maneuverability. So which one are you referring to?

 

In which wind tunnel did which 230 series equipped aircraft achieve a lift coefficient of more than 1.5 under what conditions?

[Panthera]

@JtD,

 

Well horizontal maneuverability refers to turning ability, and the F4U is remarked as decidedly superior in this respect, but in addition to this there are also the TAIC reports where the amount of turns the A6M requires to outturn specific American fighters is listed:

 

1 turn for P-51D Mustang

1 turn for P-38J Lightning

0.5~0.75 turn for P-47D Thunderbolt

3.5 turn for F4U-1D Corsair

3.5 turn for F6F-5 Hellcat

8 turn for FM-2 Wildcat

 

 

Edited April 23, 2021 by Panthera

[JtD]

But then these tests were separate between Navy and AAF, and where the Navy gives the number of turns to gain one turn, the Army gives the number of turns until the A6M gained an advantage (meaning a firing position on the tail or less than half a turn from opposing entries).

 

Just looked up the F4U-P51 report, they don't even say "horizontal" maneuverability. Just maneuverability. My bad. They also say it has a decidedly better take off, which isn't a horizontal turn. No other decidedlies in there.

Edited April 23, 2021 by JtD

[Panthera]

I believe we're dwelling on semantics now, as both reports indicate the F4U to be the superior turn fighter, the former down right stating it is everywhere superior to the P-51 in maneuverability, i.e. both in rolls and turns. That would not be the case if not for the higher lift provided by the conventional profile wing at the speeds where dogfighting in WW2 took place. 

 

More detailed reports on the difference between these profile types exist, but digging them all out is not something that tiggles my fancy atm I must admit. I do remember it being hammered into our heads early on during the  fluid dynamics courses when the development of laminar and later super critical airfoils was being lectured, where graphs similar to these were being shown:

 

 

Edited April 23, 2021 by Panthera

[JtD]

The comparison with the A6M doesn't give any indication about the relative performance of Navy and Army fighters, since the test procedures and criteria are not comparable. If you want to take any indication out of it, then you can compare the P-51 with the P-47 or P-38, both of which used conventional airfoils.

 

And WRT airfoil theory, yes, an (early) laminar design does not achieve maximum lift coefficients of conventional airfoils (at resonable air speeds). My whole point being that the wing manufacturing quality of the P-51 in comparison to that of a Bf109 will counter this advantage in practice to a considerable degree. And that's not comparing the results of trained workers in a state-of-the-art factory and slave labour in a cave, it's about design aspects and manufacturing technology.

As interesting as the relation of a P-51 to a F6F or F4U is, they still are no Bf109K. Mind you, by the sum of what's been quoted/stated/referred to by you and me in this topic, the P-51 and F6F are close in usuable cl max, even if you appear to disregard anything that doesn't agree with your opinion. There are wind tunnel tests that favour the P-51, NACA flight tests that show close proximity up to 200 mph / 4g turns, and incomplete data on Mach related effects that favour the F6F for most of the relevant speed range (but not so much the P-39, which also uses conventional airfoils, and for which there is more complete data).

On the bottom line, I don't see any reason to support a blanket statement that the P-51 in practice would have a considerably lower lift coefficient, mirroring that of the theoretical disadvantages of the airfoil.

[Aurora_Stealth]

1 hour ago, JtD said:

And WRT airfoil theory, yes, an (early) laminar design does not achieve maximum lift coefficients of conventional airfoils (at resonable air speeds). My whole point being that the wing manufacturing quality of the P-51 in comparison to that of a Bf109 will counter this advantage in practice to a considerable degree. And that's not comparing the results of trained workers in a state-of-the-art factory and slave labour in a cave, it's about design aspects and manufacturing technology.

 

As interesting as the relation of a P-51 to a F6F or F4U is, they still are no Bf109K. Mind you, by the sum of what's been quoted/stated/referred to by you and me in this topic, the P-51 and F6F are close in usuable cl max, even if you appear to disregard anything that doesn't agree with your opinion. There are wind tunnel tests that favour the P-51, NACA flight tests that show close proximity up to 200 mph / 4g turns, and incomplete data on Mach related effects that favour the F6F for most of the relevant speed range (but not so much the P-39, which also uses conventional airfoils, and for which there is more complete data).

 

On the bottom line, I don't see any reason to support a blanket statement that the P-51 in practice would have a considerably lower lift coefficient, mirroring that of the theoretical disadvantages of the airfoil.

 

Just to reiterate here - discussion of slave labour and quality control due to the deteriorating war conditions should not be used to downplay the Bf 109 from a design standpoint in this game. This is not a war or politics or factory simulator, this is a combat flight simulator so let's not go into all that - it's not part of the mission statement of the game.

 

We are trying to represent reasonable/normal in-service conditions at a frontline, not a replication of perfect out of the factory conditions and neither the kind or poor quality from a bombed factory, that includes omitting sabotage and slave labour etc. Those are factors well outside the player's control and should not be brought into the game - that may not be historically correct but a compromise has to be made there to make the game playable and opportunities equal to players.

 

If the Germans got the design of the aircraft so bad as you keep implying, how come the RAF, VVS, USAAF and others who studied Luftwaffe fighters (before the P-51 came along) were impressed with their construction and design methods such as with the Bf 109. And why did they remark especially about their construction techniques like overlapping the fuselage sections to create a very strong, consistent and high quality outer surface, and how they used flush riveting very early on and how they used low drag quick access latches all to minimise parasitic drag. The RAF by comparison was finding their aircraft were performing far below even their own spec's in 1942 and even wrote reports detailing it.

 

It seems like you're really doing your best to use the worst possible conditions to measure the Bf 109 (this could apply to all aircraft in the Luftwaffe in '44/'45)... but that should not reflect/denigrate its actual design, that's the war conditions. You then assume the very best factory and operational conditions to measure the P-51's design and assume this advantage always translates...

 

That's disingenuous, and the fact the reports state how difficult such advantages are to replicate with in-service conditions shows these advantages were actually much more limited in practice than you're letting on.

Edited April 23, 2021 by Aurora_Stealth

[unreasonable]

On 4/22/2021 at 3:51 PM, Yak_Panther said:

<snip>

 

The only thing I can think off that could be off in both sims is that 1 g Cl max is too low on the 109. The 1.4 Cl max of the 109 seems to based on 2 sources. The Chalais Meudon wind tunnel tests and the British test of the 109 E, RM 2361.

 

First lets deal with RAE report. The only thing that raises any eybrows is how they are computing the Cl max at various G loads.  They seem to be using the indicated speed and not the corrected speed in Calculation of 2g Cl max.  The RAE report gives the 2 g Cl max as 1.6 based on aircraft weight of 5600 Lbs * 2 g load factor at an alt of 12,000 ft. assuming as standard day and a speed of 150 mph. If you use the instrument corrected speed ~ the Cl max at 2 g goes to 2.36

 

But I don't think 2.36 is a realistic number given the airfoil. It's most likely that their instrument correction is wrong. The report notes that "

"Position error estimated from A.A.E.E. generalised curves as described in 5 2.74". So It's just a generalized position error estimate and the number of data points, 2, doesn't exactly instill a lot of confidence it's correct.

 

 

  It is interesting note that difference between 1 g stall Cl is  1.4  and 2g power 1.6 in this report is about 12%. Which is only 1% less than the difference in Il2's K4, 1.4 to 1.56 Cl's

 

<snip>

 

 

Quick comment on this section of the post: The RAE report is using the true airspeed to calculate Clmax, just as they should, not the indicated airspeed, (ASI in RAE terms), which is not on the first chart at all.  True Airspeed is clearly marked on the scale. 

 

From the top chart for the 2g stall boundry;

 

The Corrected airspeed (CAS) about 125mph

The true airspeed at 12,000ft is 150mph.  (Check with a TAS/CAS calculator).

 

From the PEC:

 

To get CAS of 125mph you would be reading ~115mph ASI, which is very near one of their empirical test results for PEC.

 

In short, there is nothing wrong with the RAE analysis. Quite how representative the aircraft was, conditions of the tests etc, is another matter, but AFAIK this is the only flight test we have which experimentally estimated PECs for any 109 at low speeds/high AoA.  

 

 

[JtD]

2 hours ago, Aurora_Stealth said:

(before the P-51 came along)

 

Exactly. Same way the German production methods and standards produced superior quality in the first half of the war, as can be seen in documents of the time, US (NAA) production methods and standards produced superior qualitiy in the last two years, most apparent with the P-51, as can be seen in documents of the time.

 

What I don't get is the refusal to accept that this is just as important as is fitting a bigger engine on a plane. Did you know they increased the top speed of the La-5 by roughly 60 kph by improving aerodynamic details? That's more than they got out of any other modification to that frame, including the change from the Ash-82 to the more powerful Ash-82FN. Do you think that flying a La-5 in 1942 that does near 600 on the deck would be reasonable? Asking, because in that strange world of yours, it all seems to be down to just 'production quality', which isn't supposed to be modelled in game.

Wonder why they employed engineers at all back in the day, who kept wasting years of their lifes on the development of technical details and the production methods to implement them... Apparently, it's the airfoil and the dust on it that matter, not the wing. Why again did they rework the wing for the K-4? Same airfoil as the G-6, getting just as dirty in field conditions, so it sure has exactly the same properties.

 

I also feel I'm getting lectured to not consider production quality after stating that I'm not considering production quality. That's sad.

[unreasonable]

@Aurora_Stealth "We are trying to represent reasonable/normal in-service conditions at a frontline, not a replication of perfect out of the factory conditions and neither the kind or poor quality from a bombed factory, that includes omitting sabotage and slave labour etc. Those are factors well outside the player's control and should not be brought into the game - that may not be historically correct but a compromise has to be made there to make the game playable and opportunities equal to players." 

 

(edit feature on this forum horrible.)

 

On the issue of the condition of planes in the sim: my clear impression from developers' posts has been that the planes are intended to be modelled as typical factory fresh: which I take to mean without defects due to sabotage, poor components, sloppy work etc, but with typical finish for their type. Wear and tear, dirt, dust or similar environmental effects from field conditions are explicitly excluded. If I have missed a developer post to the contrary I would like to see it.

 

While it might be cool in SP careers to have environmental effects according to the weather, nature of airfield etc, I doubt MP would stand for it.

Edited April 23, 2021 by unreasonable

[Aurora_Stealth]

1 hour ago, JtD said:

Exactly. Same way the German production methods and standards produced superior quality in the first half of the war, as can be seen in documents of the time, US (NAA) production methods and standards produced superior qualitiy in the last two years, most apparent with the P-51, as can be seen in documents of the time.

 

What I don't get is the refusal to accept that this is just as important as is fitting a bigger engine on a plane. Did you know they increased the top speed of the La-5 by roughly 60 kph by improving aerodynamic details? That's more than they got out of any other modification to that frame, including the change from the Ash-82 to the more powerful Ash-82FN. Do you think that flying a La-5 in 1942 that does near 600 on the deck would be reasonable? Asking, because in that strange world of yours, it all seems to be down to just 'production quality', which isn't supposed to be modelled in game.

 

Wonder why they employed engineers at all back in the day, who kept wasting years of their lifes on the development of technical details and the production methods to implement them... Apparently, it's the airfoil and the dust on it that matter, not the wing. Why again did they rework the wing for the K-4? Same airfoil as the G-6, getting just as dirty in field conditions, so it sure has exactly the same properties.

 

I also feel I'm getting lectured to not consider production quality after stating that I'm not considering production quality. That's sad.

 

Look, its importance depends on what you compare it to; I'm not interested (personally) in what comes fresh out of the factory on day 1 - its not relevant to me from a piloting perspective overall and I am questioning it.

 

Yes they put in a very special effort with the P-51 to make that standard of finish as high as possible (it was quite unique in that respect) - and that contributes greatly to the P-51's attainable high speed. It's the assumption that you would always maintain that minimal amount of drag and benefit while under normal in-service conditions that I find questionable and it is specifically mentioned in the NACA/NASA report - I'm pointing at it and you don't seem to acknowledge that could have been an undermining factor in the benefits you'd have had from it in-service.

 

I'm saying if the report questions directly how much value it actually brought in-service, then maybe that should be considered under "normal" conditions. Gosh - I'm such an unreasonable person for saying that. And as we all know, dust and average conditions have never been known to occur in frontline airfields lol.

 

About the La-5, like many aircraft and vehicles that were introduced in the Soviet Union - I'm sure initially it had a very crude finish, which would not be surprising considering the production / factory situation they went though. If you go from having a very crude finish to a very aerodynamically refined and carefully finished one... surprise, yes its going to show an unusually big improvement. Does this really need to be said, it doesn't mean I expect a crude finish to be reflected in-game because their factories were under threat - I do not run the factories; I fly the aircraft (under typical combat conditions) and that's what I'd like to see represented.

 

Wonder why they barely used laminar flow style wings on modern aircraft after the P-51 and Tempest then; wonder why they used paint and lacquer at all... and not bare metal? no need to use any paint because the panels were all perfectly aligned then? guess the P-51 was the only aircraft that used paint? guess I should start playing factory simulator 2021... because that's all more important than whether the aircraft was using a highly effective radiator design; or the fact that the laminar flow style wing was simply very low profile / low drag compared to the Bf 109's or maybe that just a better effort had been made on the surface quality than previously done on other US aircraft.

 

I'm saying that if conditions in-service meant that the aircraft was difficult / rarely maintained to such a high standard (outside of factory issues) - yes I think that should really be represented in-game. @unreasonable - this is my issue with that the given statement (cheers for clarifying) - its not typical condition in my opinion.

Edited April 23, 2021 by Aurora_Stealth

[JtD]

As already pointed out, I don't believe that a bit of dust causes the wing to crack or panels to spring open. Which would be necessary to deteriorate the relative benefits of the wings quality in terms of lift. Dust doesn't cause air leakage through joints and gaps. (The absence of which, as stated, is the quality that accounts for the relative benefits in terms of lift. I honestly have no idea why drag is so important to you, in a discussion about obtainable clmax.)

 

Anyway, I hope you don't injure yourself with all that guessing and wondering about irrelevant nonsense. And good luck finding your answers.

Edited April 23, 2021 by JtD

[Aurora_Stealth]

1 hour ago, JtD said:

As already pointed out, I don't believe that a bit of dust causes the wing to crack or panels to spring open. Which would be necessary to deteriorate the relative benefits of the wings quality in terms of lift. Dust doesn't cause air leakage through joints and gaps. (The absence of which, as stated, is the quality that accounts for the relative benefits in terms of lift. I honestly have no idea why drag is so important to you, in a discussion about obtainable clmax.)

 

Anyway, I hope you don't injure yourself with all that guessing and wondering about irrelevant nonsense. And good luck finding your answers.

 

I'm not saying anything so dramatic as the panels being sprung open or serious deformation or cracking. The original point was how much it could affect the actual Reynolds number when having a less than ideal surface condition and what that effect is on actual typical drag. This could be a potential issue when trying to estimate things like CLmax within a calculation and how much drag would be representative in actual flight testing compared to wind tunnels.

 

Conditions in a wind tunnel are not the same as in operational conditions and that is a potential factor here, relevant when trying to isolate accurately the actual CLmax of the aircraft.

 

The report is basically saying some of these theoretical advantages don't translate; and are only attainable under ideal conditions which were not realised.

[Panthera]

16 hours ago, JtD said:

The comparison with the A6M doesn't give any indication about the relative performance of Navy and Army fighters, since the test procedures and criteria are not comparable. If you want to take any indication out of it, then you can compare the P-51 with the P-47 or P-38, both of which used conventional airfoils.

 

And WRT airfoil theory, yes, an (early) laminar design does not achieve maximum lift coefficients of conventional airfoils (at resonable air speeds). My whole point being that the wing manufacturing quality of the P-51 in comparison to that of a Bf109 will counter this advantage in practice to a considerable degree. And that's not comparing the results of trained workers in a state-of-the-art factory and slave labour in a cave, it's about design aspects and manufacturing technology.

As interesting as the relation of a P-51 to a F6F or F4U is, they still are no Bf109K. Mind you, by the sum of what's been quoted/stated/referred to by you and me in this topic, the P-51 and F6F are close in usuable cl max, even if you appear to disregard anything that doesn't agree with your opinion. There are wind tunnel tests that favour the P-51, NACA flight tests that show close proximity up to 200 mph / 4g turns, and incomplete data on Mach related effects that favour the F6F for most of the relevant speed range (but not so much the P-39, which also uses conventional airfoils, and for which there is more complete data).

On the bottom line, I don't see any reason to support a blanket statement that the P-51 in practice would have a considerably lower lift coefficient, mirroring that of the theoretical disadvantages of the airfoil.

 

JtD the P39 uses a symmetrical profile, which in general produces a lower clmax than most asymmetrical ones, hence why it's closer, yet still produces more lift.  Meanwhile the P-38's clmax suffers from a larger part of its reference wing area taken up by nacelles, a drawback the twin engined aircraft all deal with.

 

Also I don't feel like I'm the one ignoring what doesn't agree with my opinion, on the contrary I am trying to explain why things are the way they are. Meanwhile IMO, even if I was to accept your reasoning regarding the TAIC reports, you're still ignoring the direct comparison made between the F4U and P51 by the Navy, which is incredibly clear cut in its conclusions if you ask me.

 

Finally, no the F4U & F6F are not the Bf109, however they share the use of a similar conventional profile wing, whilst they lack outboard slats. I brought them up to illustrate the known difference there is in lift generating efficiency between aircraft using common conventional profiles vs those using early low drag ones.

 

Like I said there are reports out there which go into greater detail on this, with data for a wider mach interval, and by the looks of things I'm convinced the DCS developers have access to these. Finally let me say that when comparing the aircraft between the sims, I've always had G-loc effects turned off in both, so that isn't affecting the results, which are wildly different (opposite infact), despite what Yak_Panther's doghouse plots suggest.

 

 

[JtD]

3 hours ago, Panthera said:

Also I don't feel like I'm the one ignoring what doesn't agree with my opinion, on the contrary I am trying to explain why things are the way they are.

 

That's good to know.

[unreasonable]

18 hours ago, Aurora_Stealth said:

 

 

I'm saying that if conditions in-service meant that the aircraft was difficult / rarely maintained to such a high standard (outside of factory issues) - yes I think that should really be represented in-game. @unreasonable - this is my issue with that the given statement (cheers for clarifying) - its not typical condition in my opinion.

 

That is your opinion on what the game should represent: others will have a different opinion. But this is irrelevant: it is not what the game actually tries to represent, which is undamaged, un-degraded factory fresh condition.

 

If you want to lobby for realistic degradation according to time in service, season, state of airfield, weather etc, you are free to do so, although I have no doubt this will not succeed. We have to judge the FM against it's stated standard, not some alternative standard you prefer.

 

FWIW I do not have a firm opinion on this P-51 vs K-4 issue, although I do know whose judgement I am inclined to trust, and it certainly does not include that of people who cannot read the scale of a graph, or give up-votes to posts by people incapable of same.

 

I am not surprised that JtD is getting short tempered in this thread: apart from being exceptionally knowledgeable on the technicalities and source data, he has produced many threads tried to see the data as it is without taking "sides", which is more than can be said for some. The personal attacks are unwarranted and reflect very badly on those making them. 

 

    

 

 

[LColony_Kong]

On 4/23/2021 at 12:48 AM, Panthera said:

so I know they're accurate

Well thats the best joke ive heard this entire thread. The only thing your flight tests between these games have ever demonstrated is that you dont know how to push either of these planes to the limits. The 67inch P-51 in il2 will not out turn a properly flown K-4 in a sustained turn fight.

 

Moreover, your turn tests you prize so highly are obviously wrong simply at face value. Neither the P-51 or the K4 in game can sustain anything close to 3.3-3.4G at their sustained corner speed, which is the only speed that matters in this conversation. Both planes turn best below 180mph at sea level in autumn conditions, at about 2.3-2.5G (400L). 3.4 G is absolutely absurd for either plane. We can even see this in the EM chart that was posted comparing DCS and Il2, which is at 200L (half your claimed fuel weight), and shows a sustained turn G of about 2.8.

 

 

[Aurora_Stealth]

3 hours ago, unreasonable said:

That is your opinion on what the game should represent: others will have a different opinion. But this is irrelevant: it is not what the game actually tries to represent, which is undamaged, un-degraded factory fresh condition.

 

If you want to lobby for realistic degradation according to time in service, season, state of airfield, weather etc, you are free to do so, although I have no doubt this will not succeed. We have to judge the FM against it's stated standard, not some alternative standard you prefer.

 

FWIW I do not have a firm opinion on this P-51 vs K-4 issue, although I do know whose judgement I am inclined to trust, and it certainly does not include that of people who cannot read the scale of a graph, or give up-votes to posts by people incapable of same.

 

I am not surprised that JtD is getting short tempered in this thread: apart from being exceptionally knowledgeable on the technicalities and source data, he has produced many threads tried to see the data as it is without taking "sides", which is more than can be said for some. The personal attacks are unwarranted and reflect very badly on those making them. 

 

It is... you're absolutely right, and I did try to make it clear that's my opinion (I am entitled to one - it is a forum after all, and this is a discussion). Also, people including myself do have very high expectations from the sim - including a very authentic performance; some of the margins are close between these aircraft and that does raise the stakes. My point was that performance may not always translate from ideal conditions you get from a wind tunnel and I was just trying to highlight that.

 

But yes - the sim has to work from something; its extremely difficult to verify historical data and compare it reliably. Overall I think the sim does a great job.

 

From my own point of view, I'm trying my best to keep a cool head; I am sorry if my comments are aggravating people including @JtD. I'm just trying to point in the direction of what I see as some undermining factors/variables and trying to use a bit of context to scrutinise these things. Appreciate that's very frustrating.

[HR_Zunzun]

6 hours ago, LColony_Red_Comet said:

Well thats the best joke ive heard this entire thread. The only thing your flight tests between these games have ever demonstrated is that you dont know how to push either of these planes to the limits. The 67inch P-51 in il2 will not out turn a properly flown K-4 in a sustained turn fight.

 

Moreover, your turn tests you prize so highly are obviously wrong simply at face value. Neither the P-51 or the K4 in game can sustain anything close to 3.3-3.4G at their sustained corner speed, which is the only speed that matters in this conversation. Both planes turn best below 180mph at sea level in autumn conditions, at about 2.3-2.5G (400L). 3.4 G is absolutely absurd for either plane. We can even see this in the EM chart that was posted comparing DCS and Il2, which is at 200L (half your claimed fuel weight), and shows a sustained turn G of about 2.8.

 

 

 

sustained corner speed? That sounds like an entelechy.

[ZachariasX]

2 hours ago, HR_Zunzun said:

That sounds like an entelechy.

As a result of forum idiosyncrasy.

[Yak_Panther]

On 4/23/2021 at 5:43 AM, unreasonable said:

From the top chart for the 2g stall boundry;

 

The Corrected airspeed (CAS) about 125mph

The true airspeed at 12,000ft is 150mph.  (Check with a TAS/CAS calculator).

 

From the PEC:

 

 

To get CAS of 125mph you would be reading ~115mph ASI, which is very near one of their empirical test results for PEC.

Vi corrected is 129 CAS. TAS is  = 161.

Pilots ASI is 118 CAS; TAS is =147.

The chart shows the conversion from TAS to CAS as  Vi= V*Sqrt of sigma. Where sigma is Pressure alt / Pressure sea level in Lbf^3.

Sigma =.053/.076 ~ .7

sqrt of .7 = .8

Vi = V * .8

Therefor: Vi / .8 = V

Vi 118/ .8 ~ 147 TAS.

The chart, Fig 17, is based off the Pilots ASI. Not the corrected indicated airspeed, CAS 129, from the trailing probe.

 If you compute the 2g stall speed at the conditions provide in the chart with the corrected CAS converted to TAS, 161 mph. The CL max comes to ~1.4. Which shows good agreement with the earlier stall tests in the report, Table 4.

 

In short, Table 4 is accurate, While the values of Cl Max in both the Spitfire and the 109  in  fig 17 are not accurate. 

It is Noted in the report that the Assumed Values of CL max are not derived from flight testing.

"The " stall boundary " depends on an estimate of CL max at full throttle. In the case of the Spitfire this has been measured in flight, while the Me.109 figures were based on the Spitfire results; tables of the assumed values of CL max are given in Fig. 17. CL max".

 

You can see that the author of this chart is using ASI in the Spitfire too.  He takes the 87 mph ASI stall speed and derives a Cl max of 1.87 based on the weight, 6000lbs . 

 

The 87 mph stall speed comes from Gates original work and many of the Spitfire flight tests conduct prior to this report. The flight tests of the era give a glide of 87 mph at that weight.

http://www.spitfireperformance.com/n3171.html

 

The method for creating these charts were formulated by Gates in his paper Notes on the Dog Fight, where he is also using ASI. 

http://www.wwiiaircraftperformance.org/Notes_on_the_Dogfight.pdf

The following equations we're used to derive them.

n g = normal acceleration

Vs = stall speed

V= Air speed

N = (V/Vs)^2 

 

Radius min = Stall Speed Vs^2/ g

R/Rmin = N / Sqrt(n^2-1)

Time of Turn = (2pi*Vs/ g)

Sec of the bank angle = n load factor, 

Cl = n/N*Cl Max

θ angle of limb in spiral - θ angle of climb in forward speed

Delta θ = θc-θ

= (1/Pi*A + K)* n^2 -1/ N * Cl Max

The Stall Boundary line is computed as n = N .

 

In short, I think the games value of Cl max for the 109 is correct. The 109 stall speed and Cl max as presented in Table 4 are correct. The "assumed values of Cl max" for the Spitfire and the 109 in figures 17 are not correct.

 

If anyone want's to compute ΔCl due to propeller effects. The simplified from of the equation for single engine aircraft is.

 

ΔCl = .5 *Ct*Clα*1(d/b)

Ct (coefficient of Thrust)=  T/q*So; 

So= D^2*pi/4

 d/b = propeller diameter(d) to wing span (b)

 

 

 

 

 

 

 

 

 

Edited April 25, 2021 by Yak_Panther
added a pic