Thoughts on the K-4 Manouverability

[Panthera]

On 3/31/2021 at 12:39 AM, gimpy117 said:

I also wanna throw out, are we also taking extra wing slat drag into account? there's no such thing as free lift... 

 

There is no "extra drag" added by automatic slats. Lift induced drag (Cdi) depends on lift required. 

 

In other words, more lift means more lift induced drag, however a lighter aircraft equals less lift needed* which in turn equals less lift induced drag generated. 

 

*Automatic leading edge slats will deploy and increase lift only when needed.

 

 

Edited April 1, 2021 by Panthera

[QB.Shallot]

@Panthera

Tell me if I'm missing something here, but didn't you just agree with gimpys point in a round about way?

 

Slats generate more lift at appropriate speeds. 

Lift results in induced drag.

More lift=more induced drag. 

Thus, when slats deploy, they provide more lift, and more induced drag. 

 

I'm not saying it sways the argument either way, but the presumption that slats generate more induced drag is correct.

 

As to your citing of the report on the 51's radius of turn, a report made literally a month later on the same model of Mustang stated "The airplane has a fairly short radius of turn and an excellent rate of roll." Unless a test is directly comparative, I wouldn't draw too many conclusions, and I certainly wouldn't use DCS as a reference source. 

 

While IL2 might not nail every aircrafts performance right on the nose, the fact that we have the entire 109 line modeled offers very good insight into the performance evolution of the aircraft. Early 109G's can and will out turn Mustangs, with the heaviest of the entire 109 series, the 109K, being the boatiest of the bunch. It makes perfect sense to me, and shifts in CG might also be the culprit for its worse turn.

[JtD]

Gimpy sounded as if the slats as such create drag ("extra wing slat drag"). Wing slat drag doesn't exist as such. Besides that, the idea behind them is the creation of extra lift. Other ways of achieving the extra lift could be a larger wing, deployment of flaps, a different airfoil or wing shape and so on. Slats don't create more drag than any comparable means of increasing lift. So I think Patheras comment on that is more than fair.

 

However, the main point of the slats on the Bf109 is to maintain lateral control at high angles of attack, not to significantly increase overall lift. In that case, slats basically don't cause any extra drag, as they only allow you to fly your aircraft to the limit without worrying about aileron reversal or any of that tricky stalling/spinning stuff.

Edited April 1, 2021 by JtD

[Bremspropeller]

Careful when discussing direct and global net-effects:

 

Grumpy is correct, when assuming opening a slat-gap and forcing air through it (energizing the boundary layer), that there is no free lunch.

However, we're talking about the entire airplane and not just profile-aerodynamics here, so we have to consider other things, too, to get the whole equation.

 

First, the slats are just a different kind of VG. That is they'll achieve a positive net effect in some area of operation over the basic wing, while coming with drawbacks in another (cruise, climb, fast flying) sector. The advantage of slats over the common VG is that the slat can be retracted and will be flush with the basic wing (except when otherwise, which will not be discussed here). This comes with little aerodynamic drawbacks, but will come with additional weight and systems-complexity over the "dumb" VG.

It should be easy to see that energizing the boundary layer and keeping the flow attached will at least partially set-off the additional drag of the slat (by reducing pressure drag), if it's done right.

 

But there's more:

The slat will have the center of pressure move forward, unloading the tail and thus lessen trim-drag - as opposed to dropping a notch of flaps and having to counter the rearward-shifting CoP by a higher load on the tail.

 

5 hours ago, QB.Shallot said:

Thus, when slats deploy, they provide more lift, and more induced drag. 

 

That's generally correct, but you'll have to look at L/D over AoA, not just total drag. At higher AoA the L/D of a VG or slatted wing will be better than the basic wing (if done right). And, as said before, there's other things globally going on on the airplane, so just discussing wing-aero is not the complete picture.

[QB.Shallot]

@JtD @Bremspropeller

Thank you both for clarifying the impact of slats on the 109's (and other aircrafts) performance. Certainly something I'll have to learn more about.

Just to make sure I'm translating this to a 5 year olds level of understanding properly, would it be fair to say "While leading edge slats in isolation do generate additional drag, their impact on the aircrafts performance (as a whole) is one of the more efficient ways of augmenting controllability at low speeds"?

 

In regards to the threads subject, the whole 109 vs 51 turn issue is a bit of a pickle. Sadly the test data of the 109G that the allies captured seems to be in poor practice, as they reportedly eased off the turn to avoid slat deployment. As such, they evaluated it as a worse turner than the 190.

 

For in game performance, I haven't gathered any tracks on the matter, so most of this is anecdotal, but the 109G14/K ability to maintain a higher AoA at mid-low speeds compared to the Mustang does allow it to stick with it in a turn for long enough to get a good bead on the target. The problem is that after the initial turn, it seems like the 109s ability to hold this angle starts to bite back, and its lateral control starts to suffer until it wallows around and has to break off the turn.

 

By contrast the P-51 doesn't have any control issues besides its fatal tip stall. If the 51 driver can 'ride the whistle' for long enough, he'll find the 109 pilot will eventually have to break off. However, a Mustang player pulling too hard will have much more fatal results than the 109 player, with the aircraft loosing all lateral stability and eating dirt shortly after.

 

Like I said before, with IL2 offering us the entire 109 line up to compare the performance of the various variants, it seems reasonable that the 109K, the heaviest of the bunch, would suffer the most in this regard. Meanwhile the G6/14 being able to compete handily with the 51s turn. I will say that the 109K seems markedly worse of a seemingly moderate increase in weight, but I feel like it (once again, pure conjecture, and thus not useful) has to do with how center of gravity is handled within IL2.

[Bremspropeller]

56 minutes ago, QB.Shallot said:

Just to make sure I'm translating this to a 5 year olds level of understanding properly, would it be fair to say "While leading edge slats in isolation do generate additional drag, their impact on the aircrafts performance (as a whole) is one of the more efficient ways of augmenting controllability at low speeds"?

 

 

I think it's pretty hard to generalise - you'll have to plot L/D over AoA for slats in and slats out. In the high AoA-range, there will be a point, where slats-out will give you a benefit in terms of overall drag. Certainly beyond the point, where Cl_max of the clean wing is reached.

The 109 is special, as it doesn't have the entire wing slatted, but just the section ahead of the ailerons (ensuring proper roll-control through to the stall-break). Ideally, the stall will progress root-to-tip. Here it would be interesting to know whether that is also assured by wing-geometry (e.g. washout or selection of different profile-sections), or just by the slats alone. JtD or Panthera probably have more knowledge on this.

 

Arguing that the slats don't add drag, because drag is dependant on Cl alone is wrong. "Slats-out" adds energy to the boundary layer, which isn't free; it has to come somewhere (=> drag). Also, "slats out" changes your L/D polar, as it changes profile-geometry. It also changes wing-area.

 

Another interesting but unrelated detail on the 109 is the wingroot cooler-door, which might be counter-productive to generating lift, when open. Is there a known schedule, possibly in relation to TE flap-angle? I think I have seen a diagram before - somewhere.

It would kinda blow, if the upper door opened (say in a prolonged slow-speed, high power engagement) and dumped some vital lift just when you could need it...

 

 

Edited April 1, 2021 by Bremspropeller

[Panthera]

10 hours ago, JtD said:

However, the main point of the slats on the Bf109 is to maintain lateral control at high angles of attack, not to significantly increase overall lift. In that case, slats basically don't cause any extra drag, as they only allow you to fly your aircraft to the limit without worrying about aileron reversal or any of that tricky stalling/spinning stuff.

 

 

Speaking of the 109 (and other propjobs with a similar central tractor setup) that's the case in a power off/idle situation, like when coming in to land (this is why 109 pilots talk of the aircraft not dropping a wing and instead "sinking", with full lateral control retained, if stalled power off/idle in level flight), however in a power on situation propwash is energizing the inner section of the wing, locally raising the Clmax & as well as the critical AoA relative to free stream. As such adding slats, instead of wash-out, to the outer wing section allows this area to match the energized inner section in both critical AoA & lift during power on flight conditions, which in turn results in a net increase in max lift.

(You don't see full span automatic slats on such propjobs for the same reason, as the powerful propwash right infront of the inner section would interfere with their operation. Meanwhile on jets, which lack propwash energizing any part the wing, full span slats are used.)

 

Thus whilst wash out is a simpler and lighter solution to maintaining laterally control near the stall, it doesn't come with this added benefit of a net increase in lift, as here the outer section is merely twisted downward so as to constantly be at a lower AoA than the inner section, thus delaying wing tip stall.  

 

2 hours ago, Bremspropeller said:

 

 

I think it's pretty hard to generalise - you'll have to plot L/D over AoA for slats in and slats out. In the high AoA-range, there will be a point, where slats-out will give you a benefit in terms of overall drag. Certainly beyond the point, where Cl_max of the clean wing is reached.

The 109 is special, as it doesn't have the entire wing slatted, but just the section ahead of the ailerons (ensuring proper roll-control through to the stall-break). Ideally, the stall will progress root-to-tip. Here it would be interesting to know whether that is also assured by wing-geometry (e.g. washout or selection of different profile-sections), or just by the slats alone. JtD or Panthera probably have more knowledge on this.

 

Arguing that the slats don't add drag, because drag is dependant on Cl alone is wrong. "Slats-out" adds energy to the boundary layer, which isn't free; it has to come somewhere (=> drag). Also, "slats out" changes your L/D polar, as it changes profile-geometry. It also changes wing-area.

 

Another interesting but unrelated detail on the 109 is the wingroot cooler-door, which might be counter-productive to generating lift, when open. Is there a known schedule, possibly in relation to TE flap-angle? I think I have seen a diagram before - somewhere.

It would kinda blow, if the upper door opened (say in a prolonged slow-speed, high power engagement) and dumped some vital lift just when you could need it...

 

 

 

 

There is no measured drag penalty in relation to Cl for automatic slats as compared with the plain wing, you can see this on Cl vs Cd graphs.  It simply extends the lift curve further along the AoA range. (Note: automatic LE slats usually start to deploy around 11 deg AoA on common wing profiles)

 

 

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. But that's the genius part about the automatic slats, they only deploy to reenergize the boundary layer and increase the lift when needed.

 

As for the 109 radiator flaps, there are two of them, the lower one deflects down and increases wing camber (like a flap) when opening.

Edited April 1, 2021 by Panthera

[Bremspropeller]

36 minutes ago, Panthera said:

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

 

The plain wing outperforms the slotted wing in terms of L/D right up to the point where flow-separation (pressure drag) finally spoils the party - somewhere around 10-12 degrees. That's where the energised boundary layer's impact overcomes it's negative impact.

 

39 minutes ago, Panthera said:

As for the 109 radiator flaps, there are two of them, the lower one deflects down and increases wing camber (like a flap) when opening.

 

That might offset the lift-penalty, but again it costs L/D. I'm sure it worked well enogh, but it is a bummer-design.

[Panthera]

14 minutes ago, Bremspropeller said:

The plain wing outperforms the slotted wing in terms of L/D right up to the point where flow-separation (pressure drag) finally spoils the party - somewhere around 10-12 degrees. That's where the energised boundary layer's impact overcomes it's negative impact.

 

Infact it's very close to the same even before that point, but that's the beauty of the automatic LE slats, they don't open until around the 11 deg AoA, where'as the above shows the graph for a constantly open slot.

 

Quote

That might offset the lift-penalty, but again it costs L/D. I'm sure it worked well enogh, but it is a bummer-design.

 

Can't say for sure without knowing the schedule of the system. But obviously it will add drag when it open, as did every other radiator design, Spitfire, P-51 etc.. So design wise I don't see it as a bummer compared to the rest.

Edited April 1, 2021 by Panthera

[ZachariasX]

1 hour ago, Panthera said:

As for the 109 radiator flaps, there are two of them, the lower one deflects down and increases wing camber (like a flap) when opening.

But that would change the trim of the airplane, rather tedious if you have automatic flaps. The upper flaps, didn‘t they move up to offset the camber induced by the opening of the lower flap?

 

Btw., the inlet flap was variable as well.

[Bremspropeller]

1 hour ago, Panthera said:

Infact it's very close to the same even before that point, but that's the beauty of the automatic LE slats, they don't open until around the 11 deg AoA, where'as the above shows the graph for a constantly open slot.

 

That really depends on the data-set.

If you take, for example, the 1932 paper and use 5° AoA, you'll get a 0.1 increase in Cl (some 15%-ish difference) with the clean wing for basicly the same drag (too close to tell). The CFD is a little more in favor of the slots and shows a less clear loss compared to the clean wing, but still an evident advantage up to around 10 degrees.

 

1 hour ago, Panthera said:

But obviously it will add drag when it open, as did every other radiator design, Spitfire, P-51 etc.. So design wise I don't see it as a bummer compared to the rest.

 

Neither the Spitfire, nor the P-51 use cooler-doors that impact the suction-side of the wing, so their design is a little more elegant if you ask me.

[Panthera]

 

Quote

That really depends on the data-set.

If you take, for example, the 1932 paper and use 5° AoA, you'll get a 0.1 increase in Cl (some 15%-ish difference) with the clean wing for basicly the same drag (too close to tell). The CFD is a little more in favor of the slots and shows a less clear loss compared to the clean wing, but still an evident advantage up to around 10 degrees.

 

Well that's why I also included the latter, as it's for a 3D finite wing of a relevant AR, and thus a little more accurate. But again, the slats do not deploy until around 11 degrees AoA, so we're really focusing on irrelevant details at this point.

 

1 hour ago, Bremspropeller said:

Neither the Spitfire, nor the P-51 use cooler-doors that impact the suction-side of the wing, so their design is a little more elegant if you ask me.

 

Doesn't really matter as you've got one going the other way, also the adjustable lip should mean less radiator flap deflection is necessary for the same cooling effect, and thus less drag in that regard. Thus in the end I don't believe the 109's radiator design brought any negatives that the other designs didn't (MTT certainly found it an improvement over the older design on the Emil which was more similar to that on the Spitfire), so I don't really think it's an area worth given too much attention to.

 

Edited April 1, 2021 by Panthera

[Bremspropeller]

1 hour ago, Panthera said:

Well that's why I also included the latter, as it's for a 3D finite wing of a relevant AR, and thus a little more accurate. But again, the slats do not deploy until around 11 degrees AoA, so we're really focusing on irrelevant details at this point.

 

Are we? Let's zoom in a bit. There's supposedly "no extra drag", remember?

 

For the sake of discussion, let's say the wing stalls at 15° sharp.

The clean wing manages to (slightly) outperform any slotted wing in terms of drag right up to the stall. Not by much, but it does.

 

 

 

 

In fact, the clean wing is only bested in drag beyond it's stall. The two slots which are beating it beyond that are underperforming in lift, compared to the other two slots.

The 1%c slot manages to just about match the clean wing's drag beyond it's stall AoA, but it's always just above the clean wing's drag up to about 22° AoA.

It shows that the additional interference-drag of the slot doesn't really outweigh the clean wing's flow-separation, until significantly beyond the plain wing's critical AoA.

 

 

Meanwhile in the lift-department:

 

The best performing 1%c slot only manages to get a better L/D ratio beyond 12-ish degrees, where the clean wing is already in flow-separation.

 

The takeaway:

The optimised slat does not come with "free lift", but it attains a significantly improved L/D beyond the point of flow-separation of the clean wing.

All of that is bought in the lift-department and for the amount of cost (drag), it's a good deal.

 

2 hours ago, Panthera said:

Doesn't really matter as you've got one going the other way, also the adjustable lip should mean less radiator flap deflection is necessary for the same cooling effect, and thus less drag in that regard. Thus in the end I don't believe the 109's radiator design brought any negatives that the other designs didn't (MTT certainly found it an improvement over the older design on the Emil which was more similar to that on the Spitfire), so I don't really think it's an area worth given too much attention to.

 

I don't expect it a major deal-breaker (even Mtt would have come up with a better design), but it's certainly not helping on the aircraft that has the smallest wing between the Spitfire, Mustang and 109 to begin with.

 

 

[Panthera]

Bremspropeller, again you're forgetting that automatic slats don't start to deploy until around the 11 deg AoA, where the L/D is practically identical between the plain wing and the slatted one (the 109 uses a slat design that is about 1% deep), and from 10 deg AoA onward they're practically the same in drag. At ~15 deg AoA the plain wing stalls, whilst the slatted wing is starting to beat it in lift already at 12.5 deg AoA.

 

In short no'one is arguing that fixed slots, like found on the Me163 for example, don't add "extra drag", but the automatic LE slats do not as they do not actually deploy until stagnation point is low enough on the LE that the plain wing is becoming worse.

[Bremspropeller]

I'm not disagreeing on the L/D argument (I have written that several posts before) - I'm just being pendantic about the slots opening not creating extra drag, which isn't true.

 

 

 

[Aurora_Stealth]

Just a quick FYI - spoke briefly with Greg, from Greg's Airplane's and Automobiles youtube channel (great channel - can thoroughly recommend it). He does some excellent breakdowns on the performance and capabilities of various WW2 aircraft and how they stack up. The really good thing is he takes you through the calculations and data and explains precisely what's going on in the charts etc and why things are occurring and giving a certain result.

 

He's planning on addressing the turning performance question for the Bf 109 G / K versus the P-51 Mustang at some point in future and has had a few requests about it.

 

He gave a brief initial response: "As a general rule, the 109 has the edge there, but not by much and not at 25,000 feet".

 

Which is... what I'd expect, assuming the Mustang has used up a good chunk of its fuel reserves before engaging.

 

It's also worth saying, for the sake of a reminder... that the modern day TF-51 (Two seater P-51) does not compare accurately as it is considerably down on weight due to the removal of its weighty armament (lightening the wings considerably) and also does not have the rear fuel tank. While this could be argued with many of the warbirds, it has a particularly large differential on this airframe due to the number of guns and equipment weight.

 

Below is a little snippet to set some expectations.

 

 

Cheers,

[QB.Shallot]

@Aurora_Stealth Do you know if the test you included an image of was performed with the P-38 having deployed its combat flaps? Seeing as the P-38 was able to out turn a Bf-109 and the P-51 is not too far behind in performance on that table, the P-51 being a close match for the 109 seems reasonable. I'll also note that in the 1-circle, where radius is key, the 109 will slap the 51's cheeks with consistency. 

 

But the table does only tackle radius, and not rate. Noteworthy because most complaints about the P-51s turn lie in its performance in the 2 circle fight, where rate of turn will be the key factor. Where the 109 will have the initial lead, the 51 can sustain a slightly lower rate longer, until the 109 will wallow and have to start lagging behind. 

 

I guess all I can say is I hope Greg lays down some hot hot data to clear the air. 

Edited April 19, 2021 by QB.Shallot

[gimpy117]

On 4/15/2021 at 10:07 AM, Aurora_Stealth said:

Just a quick FYI - spoke briefly with Greg, from Greg's Airplane's and Automobiles youtube channel (great channel - can thoroughly recommend it). He does some excellent breakdowns on the performance and capabilities of various WW2 aircraft and how they stack up. The really good thing is he takes you through the calculations and data and explains precisely what's going on in the charts etc and why things are occurring and giving a certain result.

 

He's planning on addressing the turning performance question for the Bf 109 G / K versus the P-51 Mustang at some point in future and has had a few requests about it.

 

He gave a brief initial response: "As a general rule, the 109 has the edge there, but not by much and not at 25,000 feet".

 

Which is... what I'd expect, assuming the Mustang has used up a good chunk of its fuel reserves before engaging.

 

It's also worth saying, for the sake of a reminder... that the modern day TF-51 (Two seater P-51) does not compare accurately as it is considerably down on weight due to the removal of its weighty armament (lightening the wings considerably) and also does not have the rear fuel tank. While this could be argued with many of the warbirds, it has a particularly large differential on this airframe due to the number of guns and equipment weight.

 

Below is a little snippet to set some expectations.

 

 

Cheers,

are hydraulic boosted controls molded? 

[Aurora_Stealth]

On 4/17/2021 at 1:50 AM, QB.Shallot said:

@Aurora_Stealth Do you know if the test you included an image of was performed with the P-38 having deployed its combat flaps? Seeing as the P-38 was able to out turn a Bf-109 and the P-51 is not too far behind in performance on that table, the P-51 being a close match for the 109 seems reasonable. I'll also note that in the 2-circle, where radius is key, the 109 will slap the 51's cheeks with consistency. 

 

But the table does only tackle radius, and not rate. Noteworthy because most complaints about the P-51s turn lie in its performance in the 2 circle fight, where rate of turn will be the key factor. Where the 109 will have the initial lead, the 51 can sustain a slightly lower rate longer, until the 109 will wallow and have to start lagging behind. 

 

I guess all I can say is I hope Greg lays down some hot hot data to clear the air. 

 

@QB.Shallot

 

I'm trying to find a specific statement from that test, I've seen a caveat in these test reports saying "Radio antenna in place, gun openings covered, wheels up, wing flaps neutral" but that was for speed testing. I'll let you know if I find more. The P-51 Pilot Manual does however specify 20 degrees of wing flap extension for a minimum radius and max sustained rate turn.

 

Same here, I'm hoping Greg will address all that for us.

 

The flaps seem to be essential for the P-51 and P-38, but also I suspect G-forces are playing a role in the prolonged, sustained turning battle where a G-suit may be the difference between gaining and not.

 

What I found most surprising was that the P-38 J @ 15,000 lbs weight is turning a bit better than a P-51 B @ 9,000 lbs. This illustrates nicely what I've been trying to get at regarding the wing design, you're not getting a great deal of lift with those high speed wings on the Mustang... it seems to be the price of achieving that very low drag.

 

It should also be noted that the P-51 tested was the lighter 'B' variant of the Mustang, so the 'D' will have a little bit more drag (bubble canopy) and a higher loaded weight; including notably in the wings from the additional armament.

 

@gimpy117

 

Yes it does, from the IL-2 notes for the P-38 J-25:

 

"The aircraft is equipped with hydraulic aileron actuators, making their operation and good roll performance at high speeds possible. The actuators are turned on using a special valve on the left side of the cockpit and require at least 1200 psi pressure in the hydraulic system, so they should be turned off if there is only one engine running. In the sim, they are turned on and off automatically."

 

Not having the aileron boost would be a significant disadvantage for earlier variants though (not in-game) when rolling into a turn, and especially in a rolling scissors I'd say.

 

Cheers,

Edited April 19, 2021 by Aurora_Stealth

[Panthera]

On 4/17/2021 at 2:50 AM, QB.Shallot said:

@Aurora_Stealth Do you know if the test you included an image of was performed with the P-38 having deployed its combat flaps? Seeing as the P-38 was able to out turn a Bf-109 and the P-51 is not too far behind in performance on that table, the P-51 being a close match for the 109 seems reasonable. I'll also note that in the 1-circle, where radius is key, the 109 will slap the 51's cheeks with consistency. 

 

But the table does only tackle radius, and not rate. Noteworthy because most complaints about the P-51s turn lie in its performance in the 2 circle fight, where rate of turn will be the key factor. Where the 109 will have the initial lead, the 51 can sustain a slightly lower rate longer, until the 109 will wallow and have to start lagging behind. 

 

I guess all I can say is I hope Greg lays down some hot hot data to clear the air. 

 

 

I don't think it's reasonable to expect the P-38 to be able to outturn the 109, at least not sustained. Instantaneous with the use of the fowler flaps, that's possible however. I know there are reports by P-38 pilots who claim they could outturn 109's, even Zero's infact, but pilot testimony is as mentioned a very tricky subject. LW pilots for example found the P-38 to be the easiest of the Allied fighters to combat, with prominent figures such as Adolf Galland not having much in terms of nice things to say about it.

 

 

On 4/15/2021 at 4:07 PM, Aurora_Stealth said:

Just a quick FYI - spoke briefly with Greg, from Greg's Airplane's and Automobiles youtube channel (great channel - can thoroughly recommend it). He does some excellent breakdowns on the performance and capabilities of various WW2 aircraft and how they stack up. The really good thing is he takes you through the calculations and data and explains precisely what's going on in the charts etc and why things are occurring and giving a certain result.

 

He's planning on addressing the turning performance question for the Bf 109 G / K versus the P-51 Mustang at some point in future and has had a few requests about it.

 

He gave a brief initial response: "As a general rule, the 109 has the edge there, but not by much and not at 25,000 feet".

 

Which is... what I'd expect, assuming the Mustang has used up a good chunk of its fuel reserves before engaging.

 

In terms of the 109 G6 vs P-51, I would agree with Greg, they're going to be close. But not when it comes to the 109 G10,14 or K4, they really are going to be noticably better turners than the P-51, also up high. You see this reflected in DCS as well.

 

 

Edited April 19, 2021 by Panthera

[-=PHX=-SuperEtendard]

To properly evaluate the turning capabilities of the planes we would need an EM diagram, because you could have different situations at different altitudes and speeds, one plane might out turn the other at 350 km/h, but then it might be the other way around at 220 km/h, and this extended across different altitudes. Also the instantaneous turning profiles might be different, in the case of prop planes structural limits wouldn't be reached, it would be more dependant on the elevator authority and wether or not it reaches critical angle of attack in a high speed pull.



 

Edited April 19, 2021 by -=PHX=-SuperEtendard

[QB.Shallot]

@Panthera Making the claim that "LW pilots for example found the P-38 to be the easiest of the Allied fighters to combat, with prominent figures such as Adolf Galland not having much in terms of nice things to say about it." is very, very disingenuous. Opinion of the P-38 are highly mixed depending on theater of encounter, timeframe and expectations of the encountering pilot. Doubly so when they only secured a kill on said airframe once, (yes, Mr. Galland) 

 

Meanwhile..."could turn inside us with ease and they could go from level flight to climb almost instantaneously. We lost quite a few pilots who tried to make an attack and then pull up... One cardinal rule we never forgot was: avoid fighting the P-38 head on. That was suicide."

-Franz Stigler 

 

If you want to contest the 38s turn, that's fine, but I'm not going to spend too much time defending what seem to be a generally accepted notion. As for all your other assumptions, particularly about turn at altitude, I'm happy to wait for an official ruling by Greg. 

Edited April 20, 2021 by QB.Shallot

[JtD]

The "official ruling" by a youtube broadcaster. Wow. And I thought the internet was bad 20 years ago.

[Bremspropeller]

I wouldn't put too much credibility into Galland. By the time the P-38 had matured a little bit (and it's pilots becoming a little less green), he was flying an Oak Desk Mk III.

The only P-38 he seems to have claimed was when he was flying the 262, in April '45.

[Aurora_Stealth]

Yep, the early P-38's without aileron boost, and reaching compressibility early in the dive (without the brake flaps) would have been lackluster; but these shortcomings were addressed with the J-25 variant (which we do have in-game). So it depends when/which model you compare. By the time these issues were addressed though, the P-51 was already on the scene - and was preferable for other reasons.

 

The snippet I attached earlier shows you that quite dramatic difference in roll rate @ 400mph.

[Panthera]

4 hours ago, Bremspropeller said:

I wouldn't put too much credibility into Galland. By the time the P-38 had matured a little bit (and it's pilots becoming a little less green), he was flying an Oak Desk Mk III.

The only P-38 he seems to have claimed was when he was flying the 262, in April '45.

 

As I recall he was summing up the opinion of the pilots under him, and not basing it on his own experience. But again it's pilot testimony, and certainly not what I base my opinion on.

 

To get an idea of where the truth lies we can take a quick look at the physical properties of the airframes:

 

P-38L vs Bf-109K4

Weight: 7,938 kg vs 3,362 kg

Power: 1600 hp x2 vs 1825 hp 

Wing span: 15.85 m vs 9.92 m

Wing area: 30.43 sq.m. vs 16.05 sq.m.

_________________________

Wing loading = 262 kg/sq.m. vs 209 kg/sq.m.

Span loading = 500 kg/m vs 338 kg/m

Power to weight = 0.4 hp/kg vs 0.54 hp/kg

 

 

Edited April 20, 2021 by Panthera

[Bremspropeller]

15 minutes ago, Panthera said:

As I recall he was summing up the opinion of the pilots under him, and not basing it on his own experience. But again it's pilot testimony, and certainly not what I base my opinion on.

 

And those testimonies are mostly resultant from times when green P-38F/G/H groups with airplanes less than optimal were struggling with very experienced Luftwaffe units.

No matter if ETO or MTO.

 

It should be noted that a P-38L at max gross can fly multiple times the distance of the Bf109K-4. It could also almost carry an empty 109 and drop it on target.

Maybe one should take a P-38 with the amount of gas that would give it a range similar to a K-4.

And then there's the maneuvering flaps.

 

The actual picture is a lot less clear-cut.

[Panthera]

4 minutes ago, Bremspropeller said:

And those testimonies are mostly resultant from times when green P-38F/G/H groups with airplanes less than optimal were struggling with very experienced Luftwaffe units.

No matter if ETO or MTO.

 

That's an opinion, but based on the physical properties of the aircraft it wasn't really suited for dogfighting the single seaters.

 

Quote

 

It should be noted that a P-38L at max gross can fly multiple times the distance of the Bf109K-4. It could also almost carry an empty 109 and drop it on target.

Maybe one should take a P-38 with the amount of gas that would give it a range similar to a K-4.

And then there's the maneuvering flaps.

 

 

Keep in mind that the single seaters have flaps as well, and as you can see the difference wasn't even that great between the P-38 and P-51, the latter of which is a noticably worse turner than the 109.

 

What would a combat ready P-38L with 900 L of fuel (added 100 L to account for the extra drag), weigh? 

Edited April 20, 2021 by Panthera

[Bremspropeller]

8 minutes ago, Panthera said:

That's an opinion, but based on the physical properties of the aircraft it wasn't really suited for dogfighting the single seaters.

 

Actual dogfighting isn't what we're seeing on Berloga.

It's a quick bounce. The P-38 (pre boosted ailerons, pre dive flaps) could do those just fine. The additional weight makes for better zooming potential.

The early P-38 fights much like an early P-47, with the exception of prolonged dives.

 

What really hampered the P-38 was technical issues, not so much performance limitations.

 

Warren Bodie mentions a 3450HP 5min WEP setting for the P-38L airplanes post October '44 - that's 1725HP per side.

Haven't been able to dig up any more specific numbers, though.

 

10 minutes ago, Panthera said:

Keep in mind that the single seaters have flaps as well, and as you can see the difference wasn't even that great between the P-38 and P-51, the latter of which is a noticably worse turner than the 109.

 

The P-38 has Fowler flaps, which also enlargen the wing-area. Again, the story is just a little bit more complicated.

 

21 minutes ago, Panthera said:

What would a combat ready P-38L with 900 L of fuel (added 100 L to account for the extra drag), weigh? 

 

Why does it have additional drag? L/Dmax for the P-38 is quoted as 13.5 on wiki. Does the 109 perform better?

The P-38 pilot actually has better fuel-flow control and can squeeze more range out of the engine.

I don't have specific numbers or weight-tables in my manual. A wild-a$$-guess will be our best initial shot, so just take twice the gas of the 109.

 

0.75kg/l (using the middle value for AVGAS 100LL) density for the Bf 109 gives us (with 400l capacity) 300kg of fuel weight.

Hence the P-38 usues roughly 600kg as a WAG.

 

Note:

A six-tank P-38 has 416 US gallons of internal fuel aboard - at 6lbs/gal that's 2496lbs (let's say 2500).

That's (x 0.4536) 1134kg total gas - let's assume 1150kg*.

____

* All depends on roundings, temperature and conversions.

416*3.78*0.75= 1179kg

[QB.Shallot]

9 hours ago, JtD said:

The "official ruling" by a youtube broadcaster. Wow. And I thought the internet was bad 20 years ago.

Credibility of content is not by virtue of the medium, but by the professionalism of the creator. Gregs videos are the best and most well researched pieces you'll find discussing period appropriate aircraft short of a peer reviewed paper. He goes into incredible detail, explaining how and why he draws the conclusions he does, and always references professional sources for any hard figures that he pulls.

 

His content is superior to any TV program, documentary, or book (short of an aeronautical engineering textbook) that I've had the pleasure of viewing when it comes to discussing the aircrafts performance in it's historical context.

 

@BremspropellerIIRC it's mach limitation really got in the way at higher altitudes where it was doing its escort work as well. Tactical units performed admirably though. Makes sense to me that Galland gather pilot accounts from dealing with the 38's in an anti bomber capacity would make note of poor maneuverability considering that the word carries a much wider scope than just addressing its turn rate (something I'm not familiar with how it'd fluctuate with altitude for the 38).

Edited April 20, 2021 by QB.Shallot

[Cybermat47]

9 hours ago, JtD said:

The "official ruling" by a youtube broadcaster. Wow. And I thought the internet was bad 20 years ago.

What’s wrong with uploading informative videos to YouTube? Take this video for example. It was created by a professional historian who specialises in WWII military aviation, and uses a primary source as its basis.

 

I’d hardly dismiss it as nonsense simply based on the medium used to convey the information.

[Panthera]

1 hour ago, Bremspropeller said:

The P-38 has Fowler flaps, which also enlargen the wing-area. Again, the story is just a little bit more complicated.

 

It does, and yes fowler flaps generate more lift than regular or split flaps, however you musn't forget that the single engined have the option of flaps too, and often used it.

 

Quote

 

Why does it have additional drag? L/Dmax for the P-38 is quoted as 13.5 on wiki. Does the 109 perform better?

 

 

Much bigger & heavier airframe = more total drag to overcome. 

 

Size matters a lot when it comes to fuel consumption. As for the wiki figure, I can't find a source for it.

 

But we can also stick with a simple double up, so 800 L which is about 600 kg as you state. What would a fully combat ready P-38L then weigh? 

 

If we assume 7,938 kg is the fully fueled & armed clean weight of the P-38L, and the total internal fuel capacity is 1,574 liters (416 gallons), then we can subtract 974 liters to arrive at 600. Avgas usually has a density of 0.71 kg pr. liter, so we subtract 974*0.71 (691 kg) from the 7,938 kg total, arriving at 7,247 kg.

 

Then the numnbers look as follows:

Weight: 7,247 kg

Power: 1600 hp x2  (1725 hp x2)

Wing area: 30.43 sq.m.

Wing span: 15.85 m

____________________________________

Wing loading = 238 kg/sq.m.

Span loading = 457 kg/m

Power to weight = 0.44 hp/kg (0.47 hp/hp)

 

 

Again not bad for a twin engined aircraft, but it's still not up there with most of the single engined fighters. 

 

PS: Can see I accidently called the single engined fighters "single seaters" in my previous post, which the P-38 ofcourse is also, so disregard that brain fart  

Edited April 20, 2021 by Panthera

[unreasonable]

52 minutes ago, [Pb]Cybermat47 said:

I’d hardly dismiss it as nonsense simply based on the medium used to convey the information.

 

 Did anyone say that Greg's videos are nonsense? I do not think there is anything wrong with using a different medium - and I agree Greg's videos are usually interesting and well presented. (Although his voice is awful....)

 

The nonsense is in calling his take on events an "official ruling", as though it would trump any other view. It is just his opinion, there are plenty of people here just as well informed, capable of forming their own. (Not including me, on technical issues, BTW).  

[ZachariasX]

59 minutes ago, QB.Shallot said:

IIRC it's mach limitation really got in the way at higher altitudes where it was doing its escort work as well.

Yes, true. It has one of the lowest critical Mach numbers. It has so because the inner wing profile was chosen to hold a lot of gas. Kelly Johnson didn't really put too much consideration into that fact. Almost nobody did in the 1930's. Besides pilots not being really trained in making optimal use of superchargers, it was mainly that the cockpit of the Lightning is drafty and tha pilot has a very bad time high up. They never had to fly that high in the Pacific, there it was not that much of an issue.

 

It always amazes me (in general) how much disregard people give to basic creature comfort. It really doesn't matter if you are shot down or die in an accident. Dead is dead.

 

59 minutes ago, [Pb]Cybermat47 said:

What’s wrong with uploading informative videos to YouTube?

Nothing. But taking such as an "official ruling" is a bad decision you make in life.

[Cybermat47]

15 minutes ago, unreasonable said:

The nonsense is in calling his take on events an "official ruling", as though it would trump any other view.

True, but I would say that that applies to any medium, not just YouTube. 

[Bremspropeller]

36 minutes ago, Panthera said:

Size matters a lot when it comes to fuel consumption. As for the wiki figure, I can't find a source for it.

 

You can't just extrapolate without running the numbers.

Especially since the 109 uses a highly automated engine-control setup that leaves very little FF tweaking-control up to the pilot.

 

L/D Source:

https://www.hq.nasa.gov/pao/History/SP-468/app-a2.htm

 

48 minutes ago, Panthera said:

It does, and yes fowler flaps generate more lift than regular or split flaps, however you musn't forget that the single engined have the option of flaps too, and often used it.

 

Depends:

 

1) The Fowlers, again, don't just increase CL, but also increase wing-area, so their net-effect is greater.

2) We know that some pilots played around with flaps, but most probably didn't. There's no anecdotal mention of Luftwaffe pilots using flaps often. Some did, most didn't.

 

Again: Most dogfights were over after the initial bounce.

 

 

39 minutes ago, Panthera said:

Then the numnbers look as follows:

Weight: 7,247 kg

Power: 1600 hp x2  (1725 hp x2)

Wing area: 30.43 sq.m.

Wing span: 15.85 m

____________________________________

Wing loading = 238 kg/sq.m.

Span loading = 457 kg/m

Power to weight = 0.44 hp/kg (0.47 hp/hp)

 

Which basicly halves the initial wing-loading delta to the K-4.

And that's without using flaps.

 

46 minutes ago, Panthera said:

Again not bad for a twin engined aircraft, but it's still not up there with the single engined fighters. 

 

It's close enough to be effective.

Especially when considering all the other strengths of the airplane, like range, endurance and the possibility of carrying up to 4000lbs of ordnance.

The 109 with the tall tail finally got around to carrying a 500kg bomb, but had barely enough fuel to bomb it's own airfield.

 

FWIW:

The second generation high performance twins (e.g. Ta 154, Hornet, Tigercat) were right up there with the singles.

[JtD]

13 hours ago, [Pb]Cybermat47 said:

True, but I would say that that applies to any medium, not just YouTube.

 

There can be no "official ruling" and if there was, it would be extremely complex and cover a series of well researched books. Which if made into video, would need more time on screen that GoT in its entirety, with an equally disappointing finale.

 

---

A bit on the subject:

On 4/19/2021 at 11:51 AM, Aurora_Stealth said:

you're not getting a great deal of lift with those high speed wings on the Mustang

 

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.

[Cybermat47]

1 hour ago, JtD said:

 

There can be no "official ruling" and if there was, it would be extremely complex and cover a series of well researched books. Which if made into video, would need more time on screen that GoT in its entirety, with an equally disappointing finale.

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. 

[JtD]

Videos, as a trend, are presentations, while books (or written things) can be fact collections. Wikipedia doesn't come as a youtube video for a reason, even if indiviual articles could be well presented there. With complex technical and historical things there are limits, and therefore all you'll get from Greg will be his (possibly well educated) opinion. Not a processible collection of facts and an explanation of physics that permits you to reach your own conclusion.

I take it some people see flight physics of historical aircraft as a black box, some information goes in, something happens in there, and then some result comes out. For those, videos are great. Because they present input and output. For those who care about what happens in that black box, know all sorts of input and know all sorts of output, videos mostly are a waste of time.

 

In the particular case of a Bf109K compared to a P-51D in terms of sustained turning performance, the only proper answer will be "it depends" anyway. What game changing, previously unknown information could a video presentation possibly add in this case, if you've already dug through thousands of pages of original sources to come to a conclusion like that?

[Aurora_Stealth]

2 hours ago, JtD said:

In the particular case of a Bf109K compared to a P-51D in terms of sustained turning performance, the only proper answer will be "it depends" anyway. What game changing, previously unknown information could a video presentation possibly add in this case, if you've already dug through thousands of pages of original sources to come to a conclusion like that?

 

Regarding youtube etc, some people just prefer a different medium to communicate information but that doesn't mean the approach and content in a video can't be scientific. Sometimes primary source data is obscure and hard to come by, and calculating things theoretically and using charts to cross-check is one way of dealing with this issue.

 

I understand what you're saying and don't question that the team does the best it can (I know they do), but if thousands of pages of verified information were actually backing this up clearly - and not anecdotally; I could also say... why then is the Tempest flight model so contradictory when it comes to turning performance and why is that difference so large. That's a different discussion but it makes a point.

 

I'd suggest because reliable information is hard to come by and often imperfect, certain assumptions are made - and gaps in information are filled in.

 

It's also not a coincidence to me (just my opinion) that the aircraft with questionable turning performance in-game both use the "laminar flow" style of aerofoils (Tempest, P-51). This denotes to me flawed assumptions on what their limitations are. These limitations are very clearly concluded about in literature such as NASA's Quest for Performance which summarises clearly the timeline of progress and development in aerodynamics including the NACA research. There are good reasons why these types of aerofoils were not used much afterwards in modern aircraft designs. Even today, Airbus... which has trialed these types of laminar flow style wings in project BLADE "Breakthrough Laminar Aircraft Demonstrator in Europe" is still trying to incorporate them on a modern airliner - this is 80 years on.

 

I agree, it will depend - the biggest factor to me however is differentiating the turn performance between the lower and higher speeds, the two aircraft shouldn't be so comparable when co-energy at the far ends of the speed envelope as the airframes are optimised differently. They would however likely converge half way up the speed envelope. Altitude would also play a factor as would the type of engine as they would be optimised for different heights V1650-3 / V1650-7 and DB 605 DB / DC etc.

 

But again, I'd like Greg to spell things out here and perhaps show this on an E-chart and support with some calculations.

Edited April 21, 2021 by Aurora_Stealth