109 sustained turn performance

[Panthera]

Hi guys,

 

I thought this might deserve its own thread after we discussed it at length here:

 

In summary the 109 seems to be suffering from excessive drag in turns, resulting in it not being able to turn with or better than other aircraft where it should easily be able to sustained (G14 & K4 vs P51 for example), which is in stark contrast to how it is said to compare in real life at similar engine power, or how it performs in other sims, like for example DCS where the difference between the K4 & P51 is quite significant; we're talking about a 0.6 G difference sustained at 200 kts.

 

I am not sure from where this extra drag originates from in IL2, but I have a hunch it once again stems from a misunderstanding of how the LE slats operate. Either way I believe the 109 FM deserves a revision to clear this up and get 109 to perform more realistically in this respect.

Edited August 15, 2020 by Panthera

[Cpt_Siddy]

What is the wing loading vs weight vs power?

 

What model, are slat drag involved?  (people think that slats are "free lift" at low speed, well kids, lift = drag, more lift = more drag)

 

109 is a compromise plane, made as small and light as possible, and it got fat and powerful as the models progressed. 

 

If anything, i think the low speed engine torque is underdeveloped on that plane, at low speed with MW50 on, the K4 and G-14 has waaay too small moment. 

[Panthera]

55 minutes ago, Cpt_Siddy said:

What is the wing loading vs weight vs power?

 

Well as mentioned in the other thread we can calculate the thrust required based on lift required, and doing this we can see that the K4 needs about 11% less thrust than the P-51 to maintain 3 G at 350 km/h at sea level under the same fuel load (400 Ltr). This difference will be a little bigger if we include the added fuselage drag at high AoA, as the P-51 is a physically larger aircraft, however getting an accurate figure here is a little tricky.

 

 

Example:

 

3 G at 350 km/h,  sea level.

 

K-4

Lift required = 98,907 newtons 

Cl required: Cl*((1.225*97.22^2)/2)*16.15 = 98,907  (Cl = 1.057)

Cd0 = 0.0213

Cdi @ Cl 1.057 = (Cl^2) / (pi * 6.09 * 0.85) = 0.0688

Cd = 0.0213 + 0.0688 = 0.0901

Total thrust required:

0.0901 * 16.15 * 0.5 * 1.225 * 97.22^2 = 8,423.9 newtons = 858 kgf

 

P-51

Lift required = 119,827 newtons
Cl required: Cl*((1.225*97.22^2)/2)*21.83 = 119,827 (Cl = 0.948)
Cd0 = 0.0161
Cdi @ Cl 0.948 = (Cl^2) / (pi * 5.82 * 0.85) = 0.0578
Cd = 0.0161 + 0.0578 = 0.0739
Total thrust required:
0.0739*21.83*0.5*1.225*97.22^2 = 9,339.3 newtons = 952 kgf

 

 

55 minutes ago, Cpt_Siddy said:

What model, are slat drag involved?  (people think that slats are "free lift" at low speed, well kids, lift = drag, more lift = more drag)

 

More lift = more drag, that is indeed a fact. However since we're not talking about instantaneous turn performance here, the extra lift the slats provide doesn't really matter, what really matters is lift required (& thus drag generated) vs the thrust available, which the above calculation serves to illustrate.

 

55 minutes ago, Cpt_Siddy said:

If anything, i think the low speed engine torque is underdeveloped on that plane, at low speed with MW50 on, the K4 and G-14 has waaay too small moment. 

 

I didn't really get the impression, to me it feels far more torquey than similar sized & powered aircraft ingame.

Edited August 15, 2020 by Panthera

[PainGod85]

The 109's LE slats deployed as a function of angle of attack. Pull hard enough and they will pop out at any speed, and at high speed, slat deployment naturally comes with a massive drag penalty as it substantially increases the airfoil's chord and therefore decreases the wing's aspect ratio.

[Panthera]

5 hours ago, PainGod85 said:

The 109's LE slats deployed as a function of angle of attack. Pull hard enough and they will pop out at any speed, and at high speed, slat deployment naturally comes with a massive drag penalty as it substantially increases the airfoil's chord and therefore decreases the wing's aspect ratio.

 

No, slat deployment does not come with a massive drag penalty, the only extra drag it will generate is that derived from the extra lift generated when needed, that is lift induced drag.

Also chord is not substantially increased, a slot in the wing is opened as a small airfoil is pushed forward (the slat), this causes a circulation effect that actually decreases drag by smoothing out the boundary layer over the main downstream airfoil and allowing it to reach a higher AoA before seperation occurs. 

 

Also rememeber that to decrease AR for the same span you have to increase wing area, which in turn reduces wing loading and thus required Cl and thus drag.

 

In short adding automatic LE slats to your wing actually provides nothing but positives from an aerodynamic point view, providing they're allowed to operate as intended ofcourse, which is where placement, design of the operating mechanism and maintenance comes in. The downside is complexity and an extra part that can fail, and when it does it can be potentially fatal, hence why a move towards powered devices was eventually taken, to reduce the chances of failure and give direct control over the slats should one fail (as in jam open or shut).

 

 

 

 

 

Edited August 16, 2020 by Panthera

[PainGod85]

8 hours ago, Panthera said:

 

No, slat deployment does not come with a massive drag penalty, the only extra drag it will generate is that derived from the extra lift generated when needed, that is lift induced drag.

Also chord is not substantially increased, a slot in the wing is opened as a small airfoil is pushed forward (the slat), this causes a circulation effect that actually decreases drag by smoothing out the boundary layer over the main downstream airfoil and allowing it to reach a higher AoA before seperation occurs. 

 

Also rememeber that to decrease AR for the same span you have to increase wing area, which in turn reduces wing loading and thus required Cl and thus drag.

 

In short adding automatic LE slats to your wing actually provides nothing but positives from an aerodynamic point view, providing they're allowed to operate as intended ofcourse, which is where placement, design of the operating mechanism and maintenance comes in. The downside is complexity and an extra part that can fail, and when it does it can be potentially fatal, hence why a move towards powered devices was eventually taken, to reduce the chances of failure and give direct control over the slats should one fail (as in jam open or shut).

 

The main effects of slats is pushing the airfoil beyond what would usually be its critical alpha, and giving the wing a better lift to drag ratio at those higher angles of attack. Extending slats on an as yet unstalled wing naturally comes with a drag penalty for the same lift.

 

 

Spoiler

 

[Aurora_Stealth]

Just to clarify, if the CLmax and Lift-to-Drag ratio is increased with slats when deployed at high AoA's (which it is), that means the amount of lift is going to be substantially higher than the amount of drag associated. I can't imagine they would agree to install a high lift device if it had such a detrimental effect on drag and thus performance in the way you are saying - that would negate its use in the first place.

 

That's not to say there isn't an effect on drag but its going to be pretty small compared to the benefit in lift. As Panthera mentioned - by re-circulating the airflow you are removing a source of drag (turbulence) from the boundary layer which is going to offset the additional induced drag from the extended aerofoil (slat) itself which is already integrated in the wing. This benefit does not only occur at airflow separation (stall) itself but also in the lead up to it and in any situation where the airflow over the wing starts to become disturbed / turbulent. After all, the slat is an optimised aerofoil, integrated in the wing as part of it's actual shape.

 

Playing devil's advocate - If it was really the case that it created significant or excessive drag, we would hear of many pilots noticing that they were losing energy at a visibly and much higher rate compared to their opposition in real life... yet with some exceptions (as always the case) the slats seem to have aided turning performance not hampered it. Unless of course the slats are not operating correctly (see that earlier linked thread), or otherwise deploying asymmetrically which is not normal operation.

[DD_Fenrir]

But you are also allowing an increase in AoA, thus you are presenting more of the underside of the airframe surface area to the oncoming airflow and creating more of an airbrake effect. 

 

Slats can be a very helpful device, but NOTHING in engineering - and particularly aerodynamics - is a free lunch; you always pay for benefits in one realm with degradations somewhere else.

 

I suspect that it's not one single item increasing drag but a combination of all these elements; it would also account for some 109 veterans describing egg shaped turns, loading the wing up and using the slats whilst approaching for a shot opportunity but then unloading as soon as practicable so a) as not to bleed too much speed and b) allow the airframe to accelerate to again.

[Cpt_Siddy]

21 minutes ago, DD_Fenrir said:

 

 

I suspect that it's not one single item increasing drag but a combination of all these elements; it would also account for some 109 veterans describing egg shaped turns, loading the wing up and using the slats whilst approaching for a shot opportunity but then unloading as soon as practicable so a) as not to bleed too much speed and b) allow the airframe to accelerate to again.

 

This, in dumb pursuit turn against Spit, you are going to lose because spit just have much more wing area than 109. 

 

109 is a compromise plane, not space unicorn magic.

 

Doing sustained horizontal with 109 against anything is just asking to get owned. 

[Aurora_Stealth]

Engineering is a compromise, and of course there is going to be loss of energy the higher the AoA you pull regardless of the aircraft - the leading edge slats simply enable you to achieve a higher AoA with this aircraft and wing design. Some aircraft can or cannot pull as high an AoA and wing area and wing loading plays its part - the compromise being that if you are able to pull tighter or achieve higher AoA you are also typically slowing down further. No controversial surprises there.

 

It's the choice of the pilot to pull back further on the stick and increase the AoA further; not necessarily a deficiency of the slats in being able to achieve that higher AoA.

 

Agree about bleeding speed but again its not necessarily the slats that are causing you to lose much of that speed themselves but the fact you are now pulling a higher AoA as an airframe in general. As you pull the aircraft tighter and tighter (which might otherwise not be possible without those slats) you are going to slow down further. The pilot still has to manage his aircraft's energy state and if you get too slow you can still stall, and yeah if you are below your optimal turning speed then it makes sense to let off some AoA and accelerate a little.

 

Can we please avoid the negative comments, no one is saying that the Spitfire won't out turn a Bf 109. This thread was a follow-on, after the fact that in-game the Mustang and Tempest, far heavier aircraft that are focused on high speed characteristics are outmanouvering aircraft at low speeds against aircraft known for having superior low speed characteristics i.e. Spitfire, Bf 109 etc on a regular basis. There's another thread discussing that general issue.

 

This thread was meant to address one perceived issue Panthera saw regarding the slats on the Bf 109.

 

The Spitfire can typically achieve slower speeds and tighter turns, but also has a harsher stall. Let's not go further into that as its going off-topic.

Edited August 16, 2020 by Aurora_Stealth

[unreasonable]

2 hours ago, Aurora_Stealth said:

 

 

Playing devil's advocate - If it was really the case that it created significant or excessive drag, we would hear of many pilots noticing that they were losing energy at a visibly and much higher rate compared to their opposition in real life... yet with some exceptions (as always the case) the slats seem to have aided turning performance not hampered it. Unless of course the slats are not operating correctly (see that earlier linked thread), or otherwise deploying asymmetrically which is not normal operation.

 

My understanding is that if the slats are operating as designed, they will always deploy asymmetrically unless the wings are level.  In any kind of turn or banking motion, the effective AoA of the wings is different. Additionally there will be some bank angle and turn combinations (ascending, descending) in which you could have a sustained turn with only one slat deployed. This is modelled in BoX, how accurately I have no idea.

 

No doubt this would cause no problems for a pilot experienced in their use, so I am not saying this is necessarily a disadvantage.

[Talon_]

Slats are designed as nothing more than a landing aid, confirmed by historical pilot accounts. One popping out before another in a high-AoA turn is a recipe for disaster, and one wing is always flying faster than another in a turn unless perfectly coordinated.

Edited August 16, 2020 by Talon_

[Panthera]

8 hours ago, PainGod85 said:

 

The main effects of slats is pushing the airfoil beyond what would usually be its critical alpha, and giving the wing a better lift to drag ratio at those higher angles of attack. Extending slats on an as yet unstalled wing naturally comes with a drag penalty for the same lift.

 

 

8 hours ago, PainGod85 said:

 

The main effects of slats is pushing the airfoil beyond what would usually be its critical alpha, and giving the wing a better lift to drag ratio at those higher angles of attack. Extending slats on an as yet unstalled wing naturally comes with a drag penalty for the same lift.

 

 

  Hide contents

 

 

 

You'd have done yourself a favour by checking the report said graph is from:

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.mdpi.com%2F2226-4310%2F3%2F4%2F39%2Fpdf&psig=AOvVaw3xqYZHQzXg9h6ZUzIl5ZdL&ust=1597681331511000&source=images&cd=vfe&ved=0CA0QjhxqFwoTCJjz3e6QoOsCFQAAAAAdAAAAABAM

 

Long story short: The graph is from a report concerning the characteristics of slats at very low reynolds numbers where they do not behave as they do as they do on aircraft (much higher reynolds numbers). The first clue is that the slats actually don't even increase the CLmax on those graphs, and that because of the very low reynolds number.

 

To quote the report:

"Abstract: One of the most commonly implemented devices for stall control on wings and airfoils is a
leading-edge slat. While functioning of slats at high Reynolds number is well documented, this is not
the case at the low Reynolds numbers common for small unmanned aerial vehicles. Consequently,
a low-speed wind tunnel investigation was undertaken to elucidate the performance of a slat at
Re = 250,000. Force balance measurements accompanied by surface flow visualization images are
presented. The slat extension and rotation was varied and documented. The results indicate that
for small slat extensions, slat rotation is deleterious to performance, but is required for larger slat
extensions for effective lift augmentation. Deployment of the slat was accompanied by a significant
drag penalty due to premature localized flow separation."

 

Here's what the effect looks like on a full sized aircraft (The extra drag is from the extra lift, that's it):

 

The genius part about the automatic LE slatted wing is that it acts like a plain airfoil in cruise condition, and then as the stagnation point moves sufficiently low as the plain profile nears its CLmax the slat pops out and reestablishes a smooth boundary layer over the downstream element.

 

Edited August 16, 2020 by Panthera

[JtD]

LE slats on the outer wing do little for improving turning performance, as the inner section will still stall and limit performance. The significant improvement is controllability.

 

Also, engine power doesn't translate 1:1 to thrust produced. Prop efficiency matters here, a lot, just as much as wing drag. So it might be worth looking into that as well.

[Panthera]

28 minutes ago, JtD said:

LE slats on the outer wing do little for improving turning performance, as the inner section will still stall and limit performance. The significant improvement is controllability.

 

In a power off condition that is true,  but not in a power on condition with a centrally mounted prop in tractor configuration, here the overall CLmax is noticably increased as the inner section is now energized by prop wash, allowing it to stay 'flying' for longer than an unslatted outer section. Thus with slats on the outer section you're able to reap the benefits of the increased lift generated over the inner section thanks to propwash.

 

It is for this same reason that automatic slats aren't full span on tractor configuration designs (unless the wing is mounted higher than the prop), as the high energy air from the prop would interfere with the free operation of the slats. 

 

Quote

Also, engine power doesn't translate 1:1 to thrust produced. Prop efficiency matters here, a lot, just as much as wing drag. So it might be worth looking into that as well.

 

True, however I don't think there will be much difference to be found here.

Edited August 16, 2020 by Panthera

[Aurora_Stealth]

1 hour ago, unreasonable said:

 

My understanding is that if the slats are operating as designed, they will always deploy asymmetrically unless the wings are level.  In any kind of turn or banking motion, the effective AoA of the wings is different. Additionally there will be some bank angle and turn combinations (ascending, descending) in which you could have a sustained turn with only one slat deployed. This is modelled in BoX, how accurately I have no idea.

 

No doubt this would cause no problems for a pilot experienced in their use, so I am not saying this is necessarily a disadvantage.

 

I believe they are independent in terms of their operation yeah (perhaps symmetrical is not the correct word - but they seem to operate well in unison) and ultimately act on air pressure and AoA yes, however they can vary in the amount they extend by - not just open/close.

 

So to put it simply - they should not be disturbing the axis of the aircraft in typical operation and this has been confirmed by modern day warbird pilots - including Airbus test pilots with hundreds of hours on them. The exceptions I'm aware of, are: inadvertent turbulence, prop wash (if chasing another aircraft closely) and you can get snatching or sticking if not properly maintained. You could well be right that in very specific circumstances or angles they can deploy, but we don't hear much about that from modern pilots - they seem to be pretty slick and unnoticeable in most flight conditions.

 

Sure, you can say the E models used a simpler design and were more prone to sticking / snatching and other effects but these were improved on later models.

 

I've read a few accounts where pilots were told to adjust into climbing and diving angles while in the turn to assist on getting angles, as a straight and level turn might not favour the Bf 109 - so I don't think it was an obstacle. The below video has some good footage of the E model in manoeuvres and it doesn't seem constrained at all by their operation.

 

 

At 4:14 you can see both slats open in coordination as bank angle increases, at varying degrees though yeah - not symmetrically (correction).

 

 

 

 

Edited August 16, 2020 by Aurora_Stealth

[Panthera]

51 minutes ago, Talon_ said:

Slats are designed as nothing more than a landing aid, confirmed by historical pilot accounts. One popping out before another in a high-AoA turn is a recipe for disaster, and one wing is always flying faster than another in a turn unless perfectly coordinated.

 

Sorry but this is simply not true.

[Panthera]

 

To qoute Mark Hanna:

 

[ZachariasX]

55 minutes ago, Panthera said:

Sorry but this is simply not true.

Once you understand that best sustained turn times are not flown at Clmax, this discussion will start to have value.

[Holtzauge]

According to theory Handley-Page type slats like on the 109 do not come out with a bang but creep out gradually as the lift coefficient (Cl) goes up. There have been tests done on the Me-109 slats as well and IIRC then they start to open up at Cl=0.9 and are fully out at around 1.3. You can find this info in Hoerner’s book on lift.

 

In addition to what Mark Hanna says I can add some new info I just got from Mikael Carlson who flies Hangar10’s Me-106G-6 and he says he does not even notice when the slats come out: No snatching, no disturbance in roll, no nothing which ties in nicely with theory because that is just how you expect them to work on paper. In addition I have a German WW2 report stashed away somewhere about Me-109 slat kinematics that says the same. Given the weight of evidence it’s simply amazing that people still insist that as a rule the Me-109 slats came out with a bang upsetting roll angles just because Eric Brown says so based on flying one captured specimen. I have no doubt they did that on the one example he flew but what is more likely, the aircraft he flew was not properly rigged or maintained or this is right and Mark Hanna, Mikael Carlson and theory is wrong?

 

Second, the drag added by slats in a tight turn is insignificant: A ballpark figure for the wings contribution to zero lift drag (Cdo) is about 35% and only a limited portion of the wing has slats so even if that goes up a significant amount  it only has a limited impact on Cdo. Now at best L/D Cdo is roughly the same as the induced drag (Cdi) but at higher lift coefficients (Cl) when the slats come out on a Me-109 at 0.9 and above the Cdi is totally dominant and Cdi is affected by span loading and not by slats so if the slats add some zero lift drag that does not matter because in a turn when the slats are out induced drag is everything.

[Panthera]

Yep, but infact in a turn the slats don't even add measurably to the Cd0 due to the circulation effect. 

 

Bottom line slats are merely there to increase the amount of lift available for the same given wing area, and in the case of automatic LE slats only when needed, and thus they don't come with any drag penalty, the drag produced being the direct result of the lift generated (lift induced drag).  So no free lunch, just a smarter method for increasing maximum available lift when needed, hence why they're so popular.

[Holtzauge]

32 minutes ago, Panthera said:

Yep, but infact in a turn the slats don't even add measurably to the Cd0 due to the circulation effect. 

 

Bottom line slats are merely there to increase the amount of lift available for the same given wing area, and in the case of automatic LE slats only when needed, and thus they don't come with any drag penalty, the drag produced being the direct result of the lift generated (lift induced drag).  So no free lunch, just a smarter method for increasing maximum available lift when needed, hence why they're so popular.

 

Can you explain why you think they don't add drag due to "the circulation effect"?  I would be surprised if they did not come with any drag penalty so I would appreciate if you could reference that statement.

 

In addition, most aircraft have washout to get decent stall charcateristics and the Me-109 does not, so slats are very much needed on the latter. I have never seen any reference to that the slats "are merely there to increase the amount of lift available for the same given wing area"? Source?

[Panthera]

2 hours ago, Holtzauge said:

 

Can you explain why you think they don't add drag due to "the circulation effect"?  I would be surprised if they did not come with any drag penalty so I would appreciate if you could reference that statement.

 

There is no measured drag penalty in relation to Cl compared with the plain wing, you can see this on Cl vs Cd graphs.  

 

 

Relevant papers:

https://commons.erau.edu/cgi/viewcontent.cgi?article=1300&context=edt

http://www.dept.aoe.vt.edu/~mason/Mason_f/HiLiftPresPt1.pdf

 

But obviously as the Cl increases beyond the Clmax of the plain wing, the induced drag (and thus total drag) also increases further. More lift  = more drag, this is inescapable.

 

Quote

In addition, most aircraft have washout to get decent stall charcateristics and the Me-109 does not, so slats are very much needed on the latter. 

 

Yes, the 109 utilizes slats in place of wash out, and it benefits from this by achieving a higher overall Clmax gain in the power on condition thanks to the outer section now being able to match the inner section which itself is kept flying further due to propwash. Where'as in the power off condition the slats ensure the root section stalls first, preventing wing drop and allowing for full aileron control up to and beyond the stall of root section - in other words, as the inner section stalls the aircraft starts to sink, but aileron control is keptuntil the slatted area itself later stalls.

 

As for slats being there to increase the amount of lift available for the same given wing area, this has always been the point of slats, to increase the CLmax of the covered area by allowing for an increased alpha to be reached before flow seperation.

Edited August 17, 2020 by Panthera

[Holtzauge]

The links you provide are for full span slats @Panthera and nobody as far as I know has contested that slats allow you to go to higher in alfa and get higher lift in that case.

 

However, the Me-109 has only part span slats that if you look closer coincide with the location of the ailerons and the problem I’m having is that you are making sweeping statements about the benefits of full span slats for Clmax and then applying that to the Me-109 like that was the intention of the designers when they put the slats on the Me-109 evidence for which is still missing as far as I can see. In addition, with the qualifier you now added ”this has always been the point of slats, to increase the CLmax of the covered area” then we are back to where we started and which no one is contesting. Also, If you look real close the drag is actually a little bit higher with slats out until the profile stalls but the effect is very small. But yes, that effect is minute and for sure I agree that the drag of slats is insignificant in this context and that was actually what I said earlier: the slat drag is irrelevant compared to the induced drag in a tight turn.

 

Returning to the Clmax at power on conditions: The Spitfire also gains a lot in Clmax in power on conditions in straight flight. There is actually a good report on Spitfire turn capability that quantifies this: Notes on the turning performance of the Spitfire as affected by flaps, RM 2349 by Morgan and Morris from 1941. In figure 10 of that report you can see that the Spitfire gets Clmax 1.8 in 1g full power conditions with no flap but in accelerated conditions (e.g. 3g) like in a turn it drops down almost to the same as in power off conditions.

 

The main problem as I see it with all this is that you are claiming that the slats mean that the Me-109 should be a whole lot better than the Spitfire and I think we could go on arguing about this for some time so why not instead try to put a number on how much better you think the Me-109 should be in terms of Clmax? The Spitfire has a power off Clmax of 1.36 and according to RM 2349 a Clmax of around 1.8 power on with no flaps at 1g.

 

The Me-109 has a power off Clmax of slightly over 1.4 and given that the Me-109 has slats on the outboard portions of the wing how much better should it in your opinion be than the Spitfire’s Clmax  in power on conditions? In BoX, what should be modeled as Clmax power on for the Me-109 at 1g, 2g, 3g and 4 g?

[[FAC]Ghost129er]

On 8/15/2020 at 8:47 PM, Panthera said:

I am not sure from where this extra drag originates from in IL2, but I have a hunch it once again stems from a misunderstanding of how the LE slats operate. Either way I believe the 109 FM deserves a revision to clear this up and get 109 to perform more realistically in this respect.

Does this including fixing the 109's OP Aldofium tail section made from the finest of invincible parts? :^)

[JaMz]

My head hurts....

[Panthera]

11 hours ago, Holtzauge said:

The links you provide are for full span slats @Panthera and nobody as far as I know has contested that slats allow you to go to higher in alfa and get higher lift in that case.

 

The links I provided as per the request to reference my statements regarding the circulation effect and that there is no real measurable increase in drag for the slatted area pr. Cl, infact for the automatic slat configuration it's identical to the plain airfoil (up until the plain airfoils stalls) as the slats don't start to pop out until around 75% of the way towards the critical AoA of the plain profile.

 

11 hours ago, Holtzauge said:

However, the Me-109 has only part span slats that if you look closer coincide with the location of the ailerons and the problem I’m having is that you are making sweeping statements about the benefits of full span slats for Clmax and then applying that to the Me-109 like that was the intention of the designers when they put the slats on the Me-109 evidence for which is still missing as far as I can see. In addition, with the qualifier you now added ”this has always been the point of slats, to increase the CLmax of the covered area” then we are back to where we started and which no one is contesting.

 

Yes, don't worry I am quite aware, and I am not assigning the 109 the benefits of full span slats.

 

What I am doing is highlighting the advantage of using slats over wash out on the overall lift produced by the wing in a power on condition for a propjob with a central tractor configuration where propwash substantially increases the lift generated on the inboard wing section. Such a configuration however also prevents the use of full span automatic LE slats for the same reason.

 

11 hours ago, Holtzauge said:

Also, If you look real close the drag is actually a little bit higher with slats out until the profile stalls but the effect is very small. But yes, that effect is minute and for sure I agree that the drag of slats is insignificant in this context and that was actually what I said earlier: the slat drag is irrelevant compared to the induced drag in a tight turn.

 

Yes very early along the AoA range you are right, however both graphs show results with the slots that are always open (across the AoA range). Automatic LE slats don't start to open until around 0.8-1.0 CL however, and thus act just like a regular profile until that point, and if you look at the graph you will see that the measured Cd is the actually the same from that point onward (until the plain profile stalls ofcourse). Hence why I say that, for automatic LE slats, in general there is no measured increase in Cd up until the point the plain profile stalls. Now after the plain profile stalls the Cd ofcourse increases further for the slatted profile, usually at the same gradient (until slatted profile itself stalls,) due to lift also increasing further, i.e. purely a Cdi increase. 

 

Side note:  -1.5% slot depth seems to be the closest to 109 configuration, so a very slight camber increase.

 

11 hours ago, Holtzauge said:

The main problem as I see it with all this is that you are claiming that the slats mean that the Me-109 should be a whole lot better than the Spitfire and I think we could go on arguing about this for some time so why not instead try to put a number on how much better you think the Me-109 should be in terms of Clmax? The Spitfire has a power off Clmax of 1.36 and according to RM 2349 a Clmax of around 1.8 power on with no flaps at 1g.

 

No no, not at all. Like I said earlier if I was to assign the benefits of full span slats to the 109 then yes it would be a whole lot better (up to 50+%), but the 109's slats only cover the outboard section (also well beyond the ailerons), and that because propwash would interfere with their operation in a power on condition otherwise. In such a configuration the gain the 109 accomplishes is only going to match the extra Cl the inboard section gains from propwash.

 

As for how much I think this gain would be, it's hard to put a number on it, esp. since the gain increases with increases in thrust, but considering the Spitfire lands around CLmax= 1.8 in the power on condition, then I would say maybe CLmax = ~2.00 for the 109. So not enough to offset the advantage in wing loading the Spitfire enjoys, esp. in the earlier versions, but enough that I'd agree skill would often be the deciding factor as Hanna says - esp. since riding the 109 close to stall would be easier thanks to the slats.

 

In summary the idea some people here keep repeating, that the slats were there purely to aid landing, simply isn't true. The slats were there to improve the handling and stalling characteristics of the aircraft, which is beneficial both during maneuvers and when on landing approach.

 

Hope that clears up any confusion as to what I'm actually saying

 

Edited August 17, 2020 by Panthera

[Panthera]

11 hours ago, Holtzauge said:

The Me-109 has a power off Clmax of slightly over 1.4 and given that the Me-109 has slats on the outboard portions of the wing how much better should it in your opinion be than the Spitfire’s Clmax  in power on conditions? In BoX, what should be modeled as Clmax power on for the Me-109 at 1g, 2g, 3g and 4 g?

 

If I remember correctly 1.48 was measured for a lower aspect ratio wing without slats right? 

 

 

 

[LColony_Kong]

On 8/15/2020 at 9:47 AM, Panthera said:

or how it performs in other sims, like for example DCS where the difference between the K4 & P51 is quite significant;

Other people are doing a better job than I could debunking that there is anything wrong with 109 turn performance in this sim, but this statement here is flat out false. I have spent a lot of time over the years testing turn performance at sea level in various sims from modern titles to stuff that is 20 years old. With the exception of 46 with was a joke FM wise, every single sim out there agrees with the current IL-2 modeling, especially with relative performance to other planes. Holtzauges charts have provided another source for this as well that is independent of sims.

 

Every single sim except 46 shows the spitfire to about 16 seconds. the P-51 is always about 19.5 and the 109 is always around 18.5 for turns at sea level at will power with equivalent fuel in terms of time of flight at full power setting.  Specifically, I cant imagine why you used DCS as an example because it is the same in that game as it is in Il2. The 109K and P-51D in DCS are about 1 second apart in sustained turns on the deck. The main difference between the two games is that IL-2 accurately models the G-suit advantages P-51 pilots would have, which makes the small different in turn performance between to two planes even more meaningless since by the time the fight dwindles down to sustained turn speeds the Mustang is usually far enough around the circle that it can keep its position by use of geometry etc. The other major factor here is that the Bf-109 has considerably more felt torque than the P-51 and woefully inadequate trim controls that make it much harder to fly to maximum performance even at sustained speeds.

 

This is not meant as gloating since I am hardly the only person that can do this, far from it in fact, but I can routinely stay with the 109 in turns in this OR DCS. No problem. The two planes are close enough in both sims that the skill gap between opponents is usually large enough that the better pilot (with regards to holding turns anyhow) will come out on top. When I fly the K-4 in il2 I have no trouble out-turning P-51s in sustained slow speed fights.

[Panthera]

11 minutes ago, [TLC]MasterPooner said:

Other people are doing a better job than I could debunking that there is anything wrong with 109 turn performance in this sim, but this statement here is flat out false. I have spent a lot of time over the years testing turn performance at sea level in various sims from modern titles to stuff that is 20 years old. With the exception of 46 with was a joke FM wise, every single sim out there agrees with the current IL-2 modeling, especially with relative performance to other planes. Holtzauges charts have provided another source for this as well that is independent of sims.

 

Every single sim except 46 shows the spitfire to about 16 seconds. the P-51 is always about 19.5 and the 109 is always around 18.5 for turns at sea level at will power with equivalent fuel in terms of time of flight at full power setting.  Specifically, I cant imagine why you used DCS as an example because it is the same in that game as it is in Il2. The 109K and P-51D in DCS are about 1 second apart in sustained turns on the deck. The main difference between the two games is that IL-2 accurately models the G-suit advantages P-51 pilots would have, which makes the small different in turn performance between to two planes even more meaningless since by the time the fight dwindles down to sustained turn speeds the Mustang is usually far enough around the circle that it can keep its position by use of geometry etc. The other major factor here is that the Bf-109 has considerably more felt torque than the P-51 and woefully inadequate trim controls that make it much harder to fly to maximum performance even at sustained speeds.

 

This is not meant as gloating since I am hardly the only person that can do this, far from it in fact, but I can routinely stay with the 109 in turns in this OR DCS. No problem. The two planes are close enough in both sims that the skill gap between opponents is usually large enough that the better pilot (with regards to holding turns anyhow) will come out on top. When I fly the K-4 in il2 I have no trouble out-turning P-51s in sustained slow speed fights.

 

Don't see the debunking you're talking about, but I tested the sustained turning performance in DCS not long ago and the difference is 0.6 G's in the K4's favour at 200 kts (sea level) when both are running the same fuel load, so I have to disagree. If you are able to match the K4 in turns in DCS with the P-51 then I have to honest and say the other pilot is not doing a very good job.

 

Tested it around the same time in IL2 and the difference is here the other way round, which is mysterious.

Edited August 18, 2020 by Panthera

[LColony_Kong]

4 hours ago, Panthera said:

 

Don't see the debunking you're talking about, but I tested the sustained turning performance in DCS not long ago and the difference is 0.6 G's in the K4's favour at 200 kts (sea level) when both are running the same fuel load, so I have to disagree. If you are able to match the K4 in turns in DCS with the P-51 then I have to honest and say the other pilot is not doing a very good job.

 

Tested it around the same time in IL2 and the difference is here the other way round, which is mysterious.

0.6g's? Same fuel load? Same speed? Your test basis is terrible. You have to compare them at fuel loads compensated for time available to fly, not "the same fuel load." A P-51 equivalent load to a 109 is about 25% fuel to a 109 carrying 50%. And the G's are meaningless since the two planes do not have the same sustained turn speed, radius, etc.

 

And your wrong about the til2 turn performance as well. They are slightly closer if you average the results in Il2 but the difference is small, and the 109 K4 is still the better turner even with the Mustang at only 25% fuel. At 67inches the Mustang is about 1 second worse in a sustained 360. With 150 octane its about 0.5 seconds.

 

If you are not getting these results in the games then you are simply not max performing the two planes. It is harder to max perform the 109 and this IS the reason that so many people complain that it supposedly cannot out turn the Mustang in this game (whether you think its not by a large enough margin is a different matter).  It has much strong felt torque which is exacerbated by the fact that you cannot apply trim to cancel it out.

 

The Mustang does not out turn the 109 in a sustained low speed fight in BOX even with 150 octane fuel and compensated fuel loads. And again, if you are not getting this result you are doing it wrong.

Edited August 18, 2020 by [TLC]MasterPooner

[Panthera]

6 hours ago, [TLC]MasterPooner said:

0.6g's? Same fuel load? Same speed? Your test basis is terrible. You have to compare them at fuel loads compensated for time available to fly, not "the same fuel load." A P-51 equivalent load to a 109 is about 25% fuel to a 109 carrying 50%. And the G's are meaningless since the two planes do not have the same sustained turn speed, radius, etc.

 

And your wrong about the til2 turn performance as well. They are slightly closer if you average the results in Il2 but the difference is small, and the 109 K4 is still the better turner even with the Mustang at only 25% fuel. At 67inches the Mustang is about 1 second worse in a sustained 360. With 150 octane its about 0.5 seconds.

 

If you are not getting these results in the games then you are simply not max performing the two planes. It is harder to max perform the 109 and this IS the reason that so many people complain that it supposedly cannot out turn the Mustang in this game (whether you think its not by a large enough margin is a different matter).  It has much strong felt torque which is exacerbated by the fact that you cannot apply trim to cancel it out.

 

The Mustang does not out turn the 109 in a sustained low speed fight in BOX even with 150 octane fuel and compensated fuel loads. And again, if you are not getting this result you are doing it wrong.

 

"You're wrong, I'm right"

 

Look instead of engaging in meaningless conjecture why not put up some actual numbers? Like how many G's can you sustain in either aircraft at specific speeds?

 

I can tell you that in DCS, at sea level, with both aircraft loaded with 400 liters of fuel, the K4 can sustain between 3.6-3.7 G's at 200 knots, where'as the P-51 can maintain 3.0-3.1 G's at the same speed.  Go test it out yourself. You can even put auto rudder on if you're afraid this isn't properly managed.

 

Now do the same test in IL2.

 

 

 

[Aurora_Stealth]

Frankly Pooner I've tried this in the K-4 for months on end online (not the quick dogfight servers before you ask), and can tell you categorically you will not out-turn a P-51 D using 150 octane in a turning contest where all other things are equal in BoX (except the settings you described of minimum fuel). If that P-51 is at that fuel load you almost always ending up in a disadvantageous situation (in this game) when flying the K-4. The exception is... if you play the silly little game of who has the best flap and pitch stabilizer position, more often than not the K-4 is on the losing side here as well - despite the Bf 109 meant to be having superior energy retention in maneuvers due to its high power-to-weight ratio and excellent low to medium speed acceleration (up to 350mph).

 

Sheriff did (another) excellent video a few months ago detailing how the P-51 operates and its strengths in-game. At 10:05 he compares the results of each major category including turn performance of the K-4 versus the P-51 D and comes to the same conclusion (the P-51 is a better turner than the K-4 at both low and high speeds). He is very talented with these sims, and frankly he confirms what a lot of other people experience which is the G-14 marginally out turns the P-51 at slower speeds but the K-4 does not.

 

This I'm afraid makes little or no sense to us - the P-51 is optimised for high speed flight.

 

If you are that certain about the K-4, please (and sincerely) do try this in a competitive online situation against a skilled player (Combat Box for example) - I'm not convinced and I know this is dubious. Below 300mph and at speeds around 250mph the Bf 109 is meant to have an advantage here as these were the speeds the Bf 109 was originally optimised for in the original design specification wheras the P-51 is optimised around higher speeds.

 

 

And 0:44 for the following video.

 

 

Edited August 18, 2020 by Aurora_Stealth

[Holtzauge]

15 hours ago, Panthera said:

 

The links I provided as per the request to reference my statements regarding the circulation effect and that there is no real measurable increase in drag for the slatted area pr. Cl, infact for the automatic slat configuration it's identical to the plain airfoil (up until the plain airfoils stalls) as the slats don't start to pop out until around 75% of the way towards the critical AoA of the plain profile.

 

 

Yes, don't worry I am quite aware, and I am not assigning the 109 the benefits of full span slats.

 

What I am doing is highlighting the advantage of using slats over wash out on the overall lift produced by the wing in a power on condition for a propjob with a central tractor configuration where propwash substantially increases the lift generated on the inboard wing section. Such a configuration however also prevents the use of full span automatic LE slats for the same reason.

 

 

Yes very early along the AoA range you are right, however both graphs show results with the slots that are always open (across the AoA range). Automatic LE slats don't start to open until around 0.8-1.0 CL however, and thus act just like a regular profile until that point, and if you look at the graph you will see that the measured Cd is the actually the same from that point onward (until the plain profile stalls ofcourse). Hence why I say that, for automatic LE slats, in general there is no measured increase in Cd up until the point the plain profile stalls. Now after the plain profile stalls the Cd ofcourse increases further for the slatted profile, usually at the same gradient (until slatted profile itself stalls,) due to lift also increasing further, i.e. purely a Cdi increase. 

 

Side note:  -1.5% slot depth seems to be the closest to 109 configuration, so a very slight camber increase.

 

 

No no, not at all. Like I said earlier if I was to assign the benefits of full span slats to the 109 then yes it would be a whole lot better (up to 50+%), but the 109's slats only cover the outboard section (also well beyond the ailerons), and that because propwash would interfere with their operation in a power on condition otherwise. In such a configuration the gain the 109 accomplishes is only going to match the extra Cl the inboard section gains from propwash.

 

As for how much I think this gain would be, it's hard to put a number on it, esp. since the gain increases with increases in thrust, but considering the Spitfire lands around CLmax= 1.8 in the power on condition, then I would say maybe CLmax = ~2.00 for the 109. So not enough to offset the advantage in wing loading the Spitfire enjoys, esp. in the earlier versions, but enough that I'd agree skill would often be the deciding factor as Hanna says - esp. since riding the 109 close to stall would be easier thanks to the slats.

 

In summary the idea some people here keep repeating, that the slats were there purely to aid landing, simply isn't true. The slats were there to improve the handling and stalling characteristics of the aircraft, which is beneficial both during maneuvers and when on landing approach.

 

Hope that clears up any confusion as to what I'm actually saying

 

 

15 hours ago, Panthera said:

 

If I remember correctly 1.48 was measured for a lower aspect ratio wing without slats right? 

 

 

 

 

Frankly @Panthera, how do you come up with Clmax=2 power on for Me-109? The way you framed it now looks more like a value you would like to see and something simply pulled out of a hat because I don’t see anything supporting that number at all. In addition, if I were to use your higher estimates on Clmax for the Me-109K4, I would get better than historical numbers not only for the K4 but for all Me-109 that I have modeled so no sale. Also cherry picking the highest number available for the Me-109 from the Chalais Meudon wind tunnel tests does not exactly strengthen your case: The results were 1.42, 1.45, 1.44, 1.42, 1.44, 1.48, 1.43 and 1.45. Taking the average of these we get instead 1.43 not 1.48 so picking the highest available number puts a dent in your credibility TBH. Thinking back I remember I have had this exact discussion back in 2014 in the DCS forum: A guy using the handle Hummingbird made a remarkably similar case to yours in this DCS thread.

 

One nice aspect of that discussion in DCS though, was that the DCS FM developer Yo-Yo participated in the debate and I would say that Yo-Yo and I landed very much on the same page regarding Hummingbird’s and Crumpp’s wish to jack up the Clmax for the Fw-190D9 and Me-109K4, as in no sale.

 

Attached below is a chart from that discussion which was done more to compare the Fw-190D9 and P-51D carrying the same fuel load so the Me-109K4 looks a bit better in that since it’s carrying a smaller fuel load. So in order to compare apples with apples, I  did another C++ simulation just now for SL conditions assuming the P-51 and Me-109K4 carry the same fuel load 290 l and for that I get the exact numbers  [TLC]MasterPooner mentioned above: For the 109 K4 18.48 s at 1.8 ata and for the P-51D 19.50 s at 67" boost.

 

And that about concludes it for me: This dead horse has suffered enough and while it is true that the P-51 is a lot worse than a Me-109 in a slow speed knife fight when hampered by a full or even half fuel load, my conclusion is that it is only a shade worse when compared on similar terms, i.e. the same fuel load.

 

 

Edited August 18, 2020 by Holtzauge

[Aurora_Stealth]

11 hours ago, Holtzauge said:

One nice aspect of that discussion in DCS though, was that the DCS FM developer Yo-Yo participated in the debate and I would say that Yo-Yo and I landed very much on the same page regarding Hummingbird’s and Crumpp’s wish to jack up the Clmax for the Fw-190D9 and Me-109K4, as in no sale.

 

It's a bit of a long shot to dismiss what is being said, when you just asked for a ball park figure.

 

So, how come we don't see the same situation in IL-2 as we do in DCS if what you are saying is true? how come the situation appears reversed to what experienced players are finding?

 

11 hours ago, HomicideHank said:

Ah, the good old Skip Holm video. Mandatory to post it at least once in every 109 FM discussion. You have to remember that these warbirds are flown at nowhere close to full throttle settings. Furthermore, the 2 guys being interviewed don't sound like the most trustworthy people either. They make some... questionable comments, like "109F will out-turn Spitfire V and Spit IX." And my favourite part of the video at 3:35: He's literally saying that the devs of the game are biased. :DD. The only thing we really learned from this video is that real warbird pilots can be wehraboos too.

 

Watch this video please. It's pure gold too http://www.youtube.com/watch?v=b69pO7538sE&t=1m36s "Skip says he can take on 5 or 6 Mustangs easy with it, if you wanna hang around for a fight."  :'D

 

 

I will absolutely be using evidence from an ex-USAF pilot with the world record number of combat hours, as well as an experienced Reno air race pilot and who has flown a long list of aircraft including warbirds and combat aircraft in his career. In fact you have just strengthened our case further by dismissing someone who is clearly very experienced on the matter - if not one of the best authorities we could have hoped for on the matter.

 

The real problem is - you haven't got a satisfactory answer to that have you. Unless you have over 1,000 hours on combat aircraft and compared these aircraft? the answer is no - before you attempt to twist that as well.

 

FYI - Here is a brief list of the other modern day pilots with stick time on both types... good luck confirming the P-51 can match the Bf-109 in a slow speed turn with them. Best of luck!

 

John Romain - ARCo
Charlie Brown (Ex-RAF)
Dave Southwood (Ex-RAF)
Rob Erdos
Klaus Plaza (Airbus Helicopters Chief Test Pilot)
Volker Bau (Airbus Helicopters Test Pilot)

Walter Eichorn
Rick Volker (Aerobatics)
Mike Spalding (Chief test pilot - Fighter Factory)

Ray Hanna (OFMC)
Mark Hanna (OFMC)

Mikael Carlson (Hangar 10)
Bud Granley

Edited August 18, 2020 by Aurora_Stealth

[Holtzauge]

1 hour ago, Aurora_Stealth said:

<snip> So, how come we don't see the same situation in IL-2 as we do in DCS if what you are saying is true? how come the situation appears reversed to what experienced players are finding?

 

Well if the Me-109K4 with 290 l fuel 1.8 ata is not out-turning the P-51D with 290 l fuel 67" boost in-game by about a 1 s then of course I'm on board: I just wrote that. However, as far as I understand that is being contested from both camps and IMHO a fair distribution of work could be that I do the simulations and maybe someone else who has a horse in this race could chip in and do some in-game flight trials? Honestly, there are a lot of opinions and statements being made in this thread but I have yet to see someone posting in-game turn rate numbers and tracks.

 

However, I see another issue with the current Me-109 FM: My impression is that it suffers too much drag when you go slow or alternatively when you pull high angles of attack and IMHO it seems like the Me-109 suffers more from this than it should but I have yet to figure out a good way to show that. To me it seems that if you go to slow in the Me-109 in-game and get "behind the curve" as in a low speed high angle of attack state, it takes more time and effort to get back energy than it should. I have discussed this with @ZachariasX (has from the Spitfire TR-9) who has the same opinion.

 

Edit: Just thought of a way to test this: Simply fly sustained turns at 1 Km with a full fuel load in the Me-109K4 starting at speed for best turn rate starting at say 300 Km/h IAS and then reduce in increments of 20 Km/h until you can't do a circle at all. Post the results here and I will do a chart comparing that to the C++ simulations. In this way we can see how induced drag has been modeled in-game when you get "behind the curve". It will of course take some time doing the in-game tests because I want to see at least 3-5 consistent turns holding altitude and  speed for each turn speed to get some level of statistical sampling. If this is to much work then by all means, continue the discussion without data. But if some of you could chip in and do the in-game flight tests then I will do the simulations and do the comparison.

Edited August 18, 2020 by Holtzauge

[Floppy_Sock]

Here's some data for sustained turn peformance:

 

BF 109K4 DB - Full emergency power, 50% fuel 

vs

P51 - 150 octane - Full power, 50% fuel

 

Substantial effort has been made to make this as accurate as possible - in game telemetry used to monitor and average pich / yaw rates to calculate true instantaneous horizontal turn rates.

Speed is recorded by hand once a steady state has been achieved. Unfortunately to get really good data, altitude and speed needs to be monitored through a telemetry output to be able to ensure P_s = 0, we cannot guarantee that but we try to maintain that as best as possible. Data is recorded when 20 seconds of constant speed, level, turns are achieved.

 

[Aurora_Stealth]

4 hours ago, Holtzauge said:

 

Well if the Me-109K4 with 290 l fuel 1.8 ata is not out-turning the P-51D with 290 l fuel 67" boost in-game by about a 1 s then of course I'm on board: I just wrote that. However, as far as I understand that is being contested from both camps and IMHO a fair distribution of work could be that I do the simulations and maybe someone else who has a horse in this race could chip in and do some in-game flight trials? Honestly, there are a lot of opinions and statements being made in this thread but I have yet to see someone posting in-game turn rate numbers and tracks.

 

However, I see another issue with the current Me-109 FM: My impression is that it suffers too much drag when you go slow or alternatively when you pull high angles of attack and IMHO it seems like the Me-109 suffers more from this than it should but I have yet to figure out a good way to show that. To me it seems that if you go to slow in the Me-109 in-game and get "behind the curve" as in a low speed high angle of attack state, it takes more time and effort to get back energy than it should. I have discussed this with @ZachariasX (has from the Spitfire TR-9) who has the same opinion.

 

Edit: Just thought of a way to test this: Simply fly sustained turns at 1 Km with a full fuel load in the Me-109K4 starting at speed for best turn rate starting at say 300 Km/h IAS and then reduce in increments of 20 Km/h until you can't do a circle at all. Post the results here and I will do a chart comparing that to the C++ simulations. In this way we can see how induced drag has been modeled in-game when you get "behind the curve". It will of course take some time doing the in-game tests because I want to see at least 3-5 consistent turns holding altitude and  speed for each turn speed to get some level of statistical sampling. If this is to much work then by all means, continue the discussion without data. But if some of you could chip in and do the in-game flight tests then I will do the simulations and do the comparison.

 

It sounds like we're on a similar page... in my book - one second is significant in turning time in a competitive situation. That is a subjective comment though so I acknowledge that - but its the difference between evasion/escape and being shot down.

 

I am a bit surprised things are nudged towards the P-51 considering there is a pretty strong consensus among modern pilots (there are others I haven't listed but I'll have to run through emails and check names and addresses) so I don't think there is an argument that the P-51 could out turn it when talking about lower speeds, even at low fuel loads.

 

In-game I'm quite sure (could still be wrong though - cannot rule it out without data) there is not a 1 second advantage to the K-4 although you are right to point out that I've not actually tested and quantified this, it does seem to be consistently disadvantageous to the K-4 which is what spurs this on.

 

Interesting, thanks for the background info - it is welcomed and appreciated.

 

I'll have a try doing some tests tonight.

 

p.s. Here's what IL-2 says from the spec sheet - between 24.0 and 24.2 seconds (depending on DB or DC engine) at 270 km/h at sea level, for reference.

 

Edited August 18, 2020 by Aurora_Stealth

[Holtzauge]

1 hour ago, Floppy_Sock said:

Here's some data for sustained turn peformance:

 

BF 109K4 DB - Full emergency power, 50% fuel 

vs

P51 - 150 octane - Full power, 50% fuel

 

Substantial effort has been made to make this as accurate as possible - in game telemetry used to monitor and average pich / yaw rates to calculate true instantaneous horizontal turn rates.

Speed is recorded by hand once a steady state has been achieved. Unfortunately to get really good data, altitude and speed needs to be monitored through a telemetry output to be able to ensure P_s = 0, we cannot guarantee that but we try to maintain that as best as possible. Data is recorded when 20 seconds of constant speed, level, turns are achieved.

 

 

Well if the 50% fuel in the chart above means 50% for both aircraft that means (in-game) 510 l for the P-51 and only 200 l for the Me-109K4 and in that case the difference should be bigger: Looks like they are about even in-game under those conditions while my simulation indicates about a 1 s advantage for the Me-109K4 with 290 l (i.e. 73% fuel) and the P-51D also with 290 l (i.e. 28% fuel). Don't have the time to simulate this right now but obviously I will get an advantage bigger than 1 s for the K4 in this case since the P-51 is hampered by a bigger fuel load. OTOH, the simulation I did earlier was assuming 1.8 ata for the K4 and 67" for the P-51 so it's not a 1:1 mapping then between in-game test and the simulations.

 

1 hour ago, Aurora_Stealth said:

I'll have a try doing some tests tonight.

 

Sounds good! If you do could you do it with 290 liters of fuel in both aircraft and 1.8 ata for the K4 and 67" boost for the P-51? Would simplify the comparison to the simulations.

 

Edit: I saw the IL2 specs you just added for the K4 and that 24 s at SL number has got to be a typo: I remembered there was something like that before as well for another aircraft in the aircraft descriptions and they updated it. However 24 s is the right number for the K4 at 3 Km altitude so that could have been it.

Edited August 18, 2020 by Holtzauge

[Floppy_Sock]

39 minutes ago, Holtzauge said:

 

Well if the 50% fuel in the chart above means 50% for both aircraft that means (in-game) 510 l for the P-51 and only 200 l for the Me-109K4 and in that case the difference should be bigger: Looks like they are about even in-game under those conditions while my simulation indicates about a 1 s advantage for the Me-109K4 with 290 l (i.e. 73% fuel) and the P-51D also with 290 l (i.e. 28% fuel). Don't have the time to simulate this right now but obviously I will get an advantage bigger than 1 s for the K4 in this case since the P-51 is hampered by a bigger fuel load. OTOH, the simulation I did earlier was assuming 1.8 ata for the K4 and 67" for the P-51 so it's not a 1:1 mapping then between in-game test and the simulations.

 

 

 

More data in more situations will come. The testing is slow and arduous because we don't have access to the necessary telemetry and need to record each data point by hand. We're just getting things rolling in terms of testing more thoroughly. This is the only data set I have on hand for those birds atm unfortunately. 

 

Can you shed some light on what your simulations entail. When you say simulation, are you actually simulating flow?

If so, can you provide some rough outline (the more detail the better):

Dimensionality, assumptions, method(finite difference, volume, element, collocation etc) 

 

Or are you using empirical coefficients - if so could you provide some of them and their references? I'm always hunting for more data. 

If the latter is the case, I'm quite curious since your data indicates that lift limit for the p51 is actually somewhat better, even at low mach number. This is somewhat contradictory to the data I've seen for the p51 (I don't mean to call you out here or claim you're making a mistake, more that I probably don't have good resources on hand.)

 

Thanks!

 

Edited August 18, 2020 by Floppy_Sock