Jump to content

109 sustained turn performance


Recommended Posts

4 minutos atrás, [TLC] MasterPooner disse:

OH MEU DEUS.

 

O ponto principal do Panthera era que as taxas citadas pelo JtD TINHAM A MESMA CARGA DE G.image.png

 

The question is: Why does the 109k4 even more powerful (1.98 ATA) fail to support more Gs?
Human error in the test or CLmax at the limit?

Edited by 3./JG15_Kampf
Link to post
Share on other sites
3 minutes ago, [TLC]MasterPooner said:

No....because if they are turning at the same G at the same speed it means he was not pulling max sustained G for one or both of the planes.

 

OR it means an increase in power doesn't improve the sustainable G/rate at the same speed ingame as it realistically should?? That's what he was saying:

 

"If the Bf109K-4 does indeed not gain anything from the extra power, it is worth looking into airscrew efficiency, as suggested earlier. Unless it stalls at this speed."

 

You would do yourself a massive favor if you actually read what others are writing before jumping to conclusions.

Edited by Panthera
  • Like 1
Link to post
Share on other sites
On 8/28/2020 at 8:45 AM, [TLC]MasterPooner said:

My response to JtD was to him looking at the 1.8 and 1.98ata 109s at the same speed with the same G load getting the same rate. Mathematically, its impossible for them to get different turn rates if these factors are the same. Read your own EM charts, you can see this happen.

 

JtD is correct. Increasing the power (strictly speaking thrust) while maintaining the same speed allows an increased load factor (and turn rate). Of course this is only possible within certain other constraints.

 

Nobody is denying that load factor, speed, and turn rate are kinematically interdependent. I don't know why you're assuming that the load factor must stay the same.

Edited by Mitthrawnuruodo
  • Upvote 3
Link to post
Share on other sites
3 hours ago, Panthera said:

 

OR it means an increase in power doesn't improve the sustainable G/rate at the same speed ingame as it realistically should?? That's what he was saying:

 

"If the Bf109K-4 does indeed not gain anything from the extra power, it is worth looking into airscrew efficiency, as suggested earlier. Unless it stalls at this speed."

No, because we know that is performs better in climbs and in level speed. It obviously has more thrust in game. It is therefore completely illogical to assume that it is the engines fault.  It it is even more obvious given the absurd methodology multiple people in this thread have been using to test turns, arbitrarily picking some random speed and then testing the planes. This will ruin the relative comparison regardless of which plane is getting the shaft due to that method. The reasonable conclusion drawn from him having the same G at the same speed is that the test was being done wrong, not that the K4 with DC engine magically lost all of its thrust.

 

Comparing at a arbitrary speed is ridiculous if you picked any two speeds other than the peak sustained turn speeds it skews the comparison:

P51D Fw190D9 Me109K4 stationary turn rate PAF PA49.JPG

3 hours ago, Mitthrawnuruodo said:

allows an increased load factor (and turn rate).

IF you use it.

  • Upvote 1
Link to post
Share on other sites

Presumably the easiest way to settle this and stop the argument is for other people to test the 1.8 vs 1.98 ata comparison in the game and see if they can indeed get a higher G and a faster turn with the latter. Question is how much higher difference should we expect, compared to the margin for measurement error? 

Edited by unreasonable
Link to post
Share on other sites

I did that several pages ago when this first came up. It was literally my first response to this.

22 hours ago, [TLC]MasterPooner said:

Dont do different speeds. Your turn on the edge of a stall until the plane settles to a sustained velocity and doesnt change. Randomly picking speeds gets us nowhere. :)

 

I just tested the K-4 50% fuel 1.98 ata.

 

19.9 degress per second for an 18.09 second turn. This is vs 18.65 seconds for the 1.8ata k4. 2.7G @265kph.

 

Edited by [TLC]MasterPooner
  • Thanks 1
  • Upvote 1
Link to post
Share on other sites
44 minutes ago, [TLC]MasterPooner said:

You need to read documents more carefully. TN1044 shows a mach number of .2 for the CL of 1.4. The P-51 in this chart is turning at a mach number of .23. We are in the right ballpark here. What is more, the P-51 tested at 25% fuel as in my tests unsurprisingly has a sustained turn speed at around 0.208 mach. Sustained turn speeds are "dog fighting" speeds.

 

1) Did you notice the high altitude comparison? The F6F is achieving a higher Clmax at the same mach (higher even) at 25,000 ft than the P-51 is at 5100 ft.

 

2) 280 km/h = 0.234 mach, 300 km/h = 0.24 mach, 370 km/h = 0.31 mach at SL (also mach increases relative to TAS with altitude),

 

3) At 0.24 mach the Clmax is listed as 1.34 for the P-51 at 5100 ft, power on.

 

Meanwhile the F6F reaches 1.35 at 0.35 mach and 25,100 ft, whilst at the same speed & altitude the P-51 reaches 1.12. (Both power on)   

 

What does this tell you?

 

Also note the following:

Vlu8flA.png

  • Upvote 1
Link to post
Share on other sites
1 hour ago, [TLC]MasterPooner said:

My response to JtD was to him looking at the 1.8 and 1.98ata 109s at the same speed with the same G load getting the same rate.

I was looking at 1.8 and 1.98 ata turning at the same speed and getting the same load and the same turn rate. Because in the test, the speed is fixed and turn time and g-load both are results. Which of course are related.

 

It's really difficult to misunderstand this.

Edited by JtD
Link to post
Share on other sites
3 hours ago, JtD said:

It's really difficult to misunderstand this.

Apparently not. It was manifestly obvious that the reason that test was showing all the same numbers was due to a testing error (G not being applied), not a magical loss of power from the 1.98ata plane. We know it has more power in game, and I posted my own tests demonstrating a difference in 1.98ata turn rates before you ever responded to me.

  • Upvote 2
Link to post
Share on other sites

I was not planning to participate any more in this thread but since there seems to be so much confusion about this measurement:

 

860687176_HomicideHankMe109K4turnratemeasurement.gif.e34d01ace4911915734712f6bd53f813.gif

 

The figure below shows that there is nothing wrong with the in-game modeling because of the same SL turn times at 280 Km/h IAS because that was just what was expected: Follow the 280 Km/h line up to where it intersects the turn rate curves in the figure below and lo and behold: The Me-109K4  has the SAME turn rate at this speed irrespective if the power setting is 1.8 or 1.98 ata.

 

1636577413_Me109K4180ata198ataSLfullfuel200819.gif.e3fb2c381cd2487e2ce50e4f7db057c3.gif

 

All propeller planes depending on power output have a "sweet spot" turn speed at which they achieve the best turn rate. As you can see it's slightly different depending on power setting and that is why in-game just as IRL you have to get to know your plane so you know at what speed this is depending on your power setting. I tried to explain this in this post and hopefully this added example above will help illustrate how this works.

 

  • Thanks 5
  • Upvote 2
Link to post
Share on other sites
22 hours ago, Aurora_Stealth said:

At higher speeds and higher altitudes (above 25,000 feet) - where the P-51 can utilise its low drag design to best effect (at high speeds / mach no's) or its superior engine power from its two stage supercharger, it can over come the Bf 109.

 

At high altitude you get high true air speed but from the aerodynamic standpoint you are fighting at LOW IAS speed so its basically the same as a low-speed turn fight at low altitude, except that you don't have the engine power. The Mach/true air speed relation of course decreases with altitude but you will never, ever get into high Mach power the region in a manoeuvring fight with propeller fighters, not so often even with modern jets. Turning and high mach numbers simply do not add up. Now unfortunately 605D also has more power output than the V-1650-7 at all altitudes and all boosts historically used by the USAAF. This is also true for higher altitudes although the difference is not breath taking to be relied on. 

 

Now, given that the P-51 is still pretty fast up there on account of its low drag design, and that everyone turns like a lame duck up there, what the 51 should do is teamwork and keeping the speed up, negating most of the 109s advantages in rooted in its higher power loading . 

  • Upvote 1
Link to post
Share on other sites

At 25,000 ft the Me-109K4 is far better than the P-51 when it comes to stationary turn rate: If fact I'm surprised no one has commented on that yet since it's pretty obvious in one of the old charts I posted years ago and that @[TLC]MasterPooner posted above. The curves for 8 km there is pretty much the same altitude (25,000ft = 7.6 Km) and as can be seen the K4 is way better at this altitude. Don't know how that is reflected in the game though? Maybe time for some high altitude testing? ;)

  • Like 1
  • Upvote 3
Link to post
Share on other sites

I think high alt does not get discussed much because it does not matter as much practically speaking. Maintaining precise level sustained turns at 20,000+ feet is rather difficult. Unless the difference is truly magnificent, like a P-40 or Yak-1 fighting a 109 or 51 at 20-35k, my observation from sims is that its not super critical to the outcome of most fights at high alt. Especially since in any high altitude fight where there is any negative PS, the use of flaps will provide a sustained rather than temporary advantage. In turns at sea level, use of flaps provides a momentary increase in turn rate at any speed greater than PS = 0 (except with fowler and slotted flaps, whose lift to drag ratios provide continued improvement at PS=0). So if a 109 or 51 drop flaps at SL at 225mph IAS, and if say the sustained turn speed with 10 degrees of flaps is 155mph, until either plane decelerates to 155mph the turn rate will be improved. Once both planes reach the new PS=0 speed, sustained turn rate will be worse than if flaps were up (you are all free to test this in any game with plain or split flaps). But if the turn fight happens at any altitude that is not SL, PS never reaches zero because both fighters will trade altitude for airspeed and PS will be negative. This is why I think most turn rate debates are always about a rate fight on the deck, since is the altitude where this really shows. Not that an advantage at 25,000ft is meaningless, just not nearly as damning as being out-rated on the deck.

  • Upvote 2
Link to post
Share on other sites

Interesting info about flap usage @[TLC]MasterPooner. However, the use of flaps in sims bugs me: I know this has been discussed a lot before but I think there is a reason that flaps are so seldom mentioned in combat reports: IRL they are not as good as they have been modeled in many games and while many swear they would never use them in-game so it's a non-issue I have seen the same persons post tracks in which they used them anyway so I guess they are not as "bad" in-game as some would have you believe........

  • Upvote 2
Link to post
Share on other sites
3 hours ago, Holtzauge said:

seldom mentioned in combat reports

I think it depends on the plane. Ive seen several accounts from 109 pilots claiming flaps were seldom used, although I have seen a few accounts of 109 flap usage from certain pilots. Ostensibly this is due to the highly impractical setup the 109s flaps use, requiring significant hand cranking that would prevent simultaneous use of the throttle and would probably be difficult at high speeds. On the other hand the flaps in a Mustang, 38, or 47 are all hydraulic and in the case of both the 51 and 38 they were specifically designed for combat in mind and there are numerous accounts of their use. Plus as for their general benefit, many modern jets automatically deploy leading or trailing edge flaps (or both) when turning.

 

image.thumb.png.e71054fbab40d42411bcab6a1c151c52.png

 

 

 

As for in game, this is just my personal experience, but based on interactions with people I have found people who are not using the flaps either do not do so because (as you said) they think it does not accomplish anything, or they dont use the correct settings. Ive run into several people who dont use the full-flaps down setting on the P-38 even when they are in a sea level rate fight on the deck and the speed is low enough to drop 100% flap. The other issue I think is related to the relationship I noted above, which is that the plain and split flaps do not maintain a rate benefit once PS drops down to 0 again from whatever speed they were deployed at. If anyone does a turn rate test with a Mustang in game, you will get a worse sustained rate in any PS=0 condition, and the same is true of every other split or plain flap design in the game (and any other game ive tested this in including DCS.)

 

Also this is an aside and is not in response to Holtzauge, but to anyone skeptical of the use of max flaps in combat, there are multiple accounts of FULL flaps being used on the P-51 in the above combat reports.

 

And also another note: Use of flaps provides a reduced turn radius regardless of PS. From what I can tell they are always useful in nose-to-nose radius fights such as a flat scissors.

 

Edited by [TLC]MasterPooner
Link to post
Share on other sites

Let me ask you all this:

 

If at 280 kmh, and 3 G, thrust equals the drag generated (aka you can sustain said 3 G at 280 kmh with no altitude loss), then what happens if you further increase thrust? 

 

I hope you can see where JtD is coming from after thinking about this. 

  • Like 1
Link to post
Share on other sites

S!

 

Just some info on the turn rates, from Finnish tests on a Bf109G. As it seems speeds vary on tests here. A 180deg turn at 1km altitude took 10s at starting speed of 450km/h and at end of turn speed was 380km/h. A full 360deg with same starting speed 450km/h took 18,0s with end speed of 330km/h. For a sustained 360deg turn it took 22,0sec at speed of 360km/h, 70deg bank angle and 3G.

Link to post
Share on other sites
3 hours ago, Panthera said:

Let me ask you all this:

 

If at 280 kmh, and 3 G, thrust equals the drag generated (aka you can sustain said 3 G at 280 kmh with no altitude loss), then what happens if you further increase thrust? 

 

I hope you can see where JtD is coming from after thinking about this. 

 

Thinking about this, which is all above my pay-grade: 

 

If you keep the same Gs, you must be keeping the same bank angle, and must be generating the same lift. So you are also generating the same centripetal force, which is what causes the turning.  This is all independent of thrust, assuming only that the thrust is sufficient to maintain 280kph and 3Gs.

 

So if you are at 3Gs and 280kph, at 1.8 ata, and then increase power to 1.98 but do not allow your speed to rise or bank angle to increase, how can you turn faster? Which I think is the message from MasterPooner's posts and also Holtzauge's diagram.

 

Alternately, if you want to allow speed or Gs to rise - but cannot do so at the higher power setting - then there may be an issue with the propeller already having reached some limit of efficiency, which I think was JtD's original point.

 

So I do not see any real conflict here, except about the issue of what the respective CLs should be for 109 and P-51. Or have I misunderstood?

 

   

Link to post
Share on other sites

I think the conflict was that he implied something (i.e. same g) which I didn't say or mean, which turned my true statement into a wrong one.

 

Unfortunately his response then left out the bit he implied, which made his reply wrong, as written and as understood by me.

 

I hope things have been clarified sufficiently by now (we have the exact two options spelled out by unreasonable) and the topic can move on, in particular as the 1.98 do improve the turn rate in game if you fly them both full throttle at 280.

 

Point worth moving into - what was the cl the Finns tested their 109G at? Sustained and maximum, first and second half turn?

Edited by JtD
  • Thanks 1
  • Upvote 1
Link to post
Share on other sites
7 hours ago, Panthera said:

If at 280 kmh, and 3 G, thrust equals the drag generated (aka you can sustain said 3 G at 280 kmh with no altitude loss), then what happens if you further increase thrust?

 

Depends.

 

If the turn was thrust limited, i.e. your wings could have produced more lift with higher AoA but the resulting drag would not have been able to be compensated by the given thrust, then increasing thrust will enable you to increase AoA and still keep going at the same speed, which according to the assumption that your wings were able to produce more lift when you'd further increase AoA, would make you turn tighter.

 

If your turn was lift limited, i.e. your wings could not produce any more lift when increasing AoA, but only drag would increase in such case (and probably lift would even decrease when you further increase AoA), then increasing thrust won't help a single bit if you'd keep turning at the same speed, because more thrust in such case would mean more drag, therefore more AoA, but according to the assumption that your wings could not produce any higher lift from further increasing AoA, it would not make you turn tighter, rather the contrary.

 

Therefore it all depends whether at the set speed you're "in front of" or "behind" the power curve.

 

:drinks:

Mike

Link to post
Share on other sites
6 hours ago, unreasonable said:

 

Thinking about this, which is all above my pay-grade: 

 

If you keep the same Gs, you must be keeping the same bank angle, and must be generating the same lift. So you are also generating the same centripetal force, which is what causes the turning.  This is all independent of thrust, assuming only that the thrust is sufficient to maintain 280kph and 3Gs.

 

Mhmm, but then what happens to your speed? 

 

A specific amount of thrust equals out the drag generated at a certain speed & lift coefficient (Ps=0). So if you increase thrust, but maintain the same bank angle and altitude, what happens? 

 

The answer is you keep gaining speed until you reach the next time drag & thrust reach equilibrium at a higher speed, G and rate. 

 

In other words if you got more thrust than what is generated in a level turn at Clmax (lift limit) and 280 kmh, then unless you deliberately stall your aircraft, you will accelerate until you reach the speed where drag again cancels out the thrust.

 

So if an aircraft which can maintain 3 G at 280 kmh with 10000 kgf of thrust (random no.), with no altitude loss, but now gets its thrust increased to 12000 kgf (new Ps=0 now equal to old Ps=+xxx), it will now actually be able to both maintain 3 G at 280  kmh AND climb at the same time. 

 

 

 

 

 

Edited by Panthera
Link to post
Share on other sites

I have no idea why you want to drag this out.

 

Do you think there is a generic problem with the FMs that affect all planes' turning behaviour? Or is it just a difference of opinion about the CLmax of the 109 and P-51?

 

 

 

 

 

Link to post
Share on other sites


It looks like there is some confusion and cross talking going here.

 

Turn rate in radians = the force of gravity * sqrt of the load factor squared -1 / Velocity of the turn.

 

Turn rate = g√(Nz^2-1 )/ Velocity
If we plug in the test conditions.
9.8 * √(2.8^2 - 1) / 280 kph
we convert to meters per second.
 9.8 * √ (2.8^2 - 1 )/ 77.77 = .33 radians. per second or 19.14 degrees

 

We get a turn rate of .33 radians a second, converted to degrees per second is 19.14  or a 360 turn time of 18 second.

 

If you turn at 280 kph with 2.8 g's you will always have a turn rate of 19.14 degrees per second regardless of the aircraft.

 

What Panth is trying to say is that more G should be available to 109 at 280 kph.

 

Which is why he is calling for a increased CL max. Increasing the Cl would increase the maximum sustained turn rate.
As Nz sustained =( Hp Available / W )* (L /Hp required). 

 

Since increasing the Cl, increases the lift, we can see that the sustained turn rate would increase if the Cl went up.


Though I don't think there is a great case to increase the Cl of the 109. Most of the data shows the same stall speed.  Since we can derive the Cl max from the stall speed, it's easy to check.
 
Stall Speed = √ W/ 1/2  Pressure * Wing Area * Cl max.
The British Test with pitot correction give the stall speed at 95.4 mph at 5580 lbs with a wing area of 174 sq feet. That would be with the slats down. So Cl Max with slats down is about 1.4
Stall  = W / Cl max * 1/2  air pressure * wing area.  
139.333 feet per second = Sqrt(5580 / (1/2 * (.00235)* 174 * (1.4)))
Given the G2 torp has a similar indicated stall speed the Cl max looks good.

 

The problem seems to be with the Mustang. Testing the stall speed at a known weight of  8002 Lbs. 10% fuel - 4 guns and no ammo. resulted in a stall speed of ~ 95 mph. yielding a Cl max of 1.46
140.79 = Sqrt(8002 / (1/2 * (.00237)* 233 * (1.46)))

 

Edited by Yak_Panther
Link to post
Share on other sites

Drag it out? 

 

There is obviously an issue. 

 

The main points raised so far is that the relative turn performance between the 67" Hg P-51 and 1.8ata K4 is incredibly different between IL2 and DCS. In DCS the 1.8ata K-4 performs substantially better than the 67" Hg P-51 in sustained turns (SL, 400 L fuel), as it should. Whilst in IL2 both aircraft are pretty much even, if not with a slight advantage to the P-51. 

 

31 minutes ago, Yak_Panther said:


It looks like there is some confusion and cross talking going here.

 

Turn rate in radians = the force of gravity * sqrt of the load factor squared -1 / Velocity of the turn.

 

Turn rate = g√(Nz^2-1 )/ Velocity
If we plug in the test conditions.
9.8 * √(2.8^2 - 1) / 280 kph
we convert to meters per second.
 9.8 * √ (2.8^2 - 1 )/ 77.77 = .33 radians. per second or 19.14 degrees

 

We get a turn rate of .33 radians a second, converted to degrees per second is 19.14  or a 360 turn time of 18 second.

 

If you turn at 280 kph with 2.8 g's you will always have a turn rate of 19.14 degrees per second regardless of the aircraft.

 

What Panth is trying to say is that more G should be available to 109 at 280 kph.

 

Which is why he is calling for a increased CL max. Increasing the Cl would increase the maximum sustained turn rate.
As Nz sustained =( Hp Available / W )* (L /Hp required). 

 

Since increasing the Cl, increases the lift, we can see that the sustained turn rate would increase if the Cl went up.


Though I don't think there is a great case to increase the Cl of the 109. Most of the data shows the same stall speed.  Since we can derive the Cl max from the stall speed, it's easy to check.
 
Stall Speed = √ W/ 1/2  Pressure * Wing Area * Cl max.
The British Test with pitot correction give the stall speed at 95.4 mph at 5580 lbs with a wing area of 174 sq feet. That would be with the slats down. So Cl Max with slats down is about 1.4
Stall  = W / Cl max * 1/2  air pressure * wing area.  
139.333 feet per second = Sqrt(5580 / (1/2 * (.00235)* 174 * (1.4)))
Given the G2 torp has a similar indicated stall speed the Cl max looks good.

 

The problem seems to be with the Mustang. Testing the stall speed at a known weight of  8002 Lbs. 10% fuel - 4 guns and no ammo. resulted in a stall speed of ~ 95 mph. yielding a Cl max of 1.46
140.79 = Sqrt(8002 / (1/2 * (.00237)* 233 * (1.46)))

 

 

The issue is wings level Clmax, i.e. low speed 1 G (& prop idle), is not going to be the same as the Clmax, power on, at dogfighting speeds

Edited by Panthera
  • Upvote 1
Link to post
Share on other sites
17 minutes ago, Yak_Panther said:

 


Though I don't think there is a great case to increase the Cl of the 109. Most of the data shows the same stall speed.  Since we can derive the Cl max from the stall speed, it's easy to check.
 
Stall Speed = √ W/ 1/2  Pressure * Wing Area * Cl max.
The British Test with pitot correction give the stall speed at 95.4 mph at 5580 lbs with a wing area of 174 sq feet. That would be with the slats down. So Cl Max with slats down is about 1.4
Stall  = W / Cl max * 1/2  air pressure * wing area.  
139.333 feet per second = Sqrt(5580 / (1/2 * (.00235)* 174 * (1.4)))
Given the G2 torp has a simialr indicated stall speed the Cl max looks good.

 

The problem seems to be with the Mustang. Testing the stall speed at a known weight of  8002 Lbs. 10% fuel - 4 guns and no ammo. resulted in a stall speed of ~ 95 mph. yielding a Cl max of 1.46
140.79 = Sqrt(8002 / (1/2 * (.00235)* 235 * (1.46)))

 

 

The minimum stall speed for the P-51 D in game is 99mph in flight configuration. That is from the tech specs page. If you assume that was at minimum operating weight it computes to a CLmax of 1.34   

 

Do the same for the 109 K and you get 1.39  (G14 1.39, G-6 1.38, G-4 1.26 (! possible typo?) G-2 1.37, F-4 1.38, F-2 1.38) So you can see that this pairing of speed and weight generates extremely consistent results for the 109s with the F and later wing, which is encouraging since they are very similar in wing and shape. This is also very close to the RAE test you mention on an E model (slightly different wing). So I agree that the game looks OK here.

 

According to Han, the data in the Tech Specs page is derived using a robot pilot to ensure consistency.  Presumably they can use it to see exactly at what speed lift is maximised without any loss of height. I think it is very difficult for us to test in game and identify the exact point of maximum lift to an equivalent level of precision. (TBH it must have been very difficult in RL too).  Given how sensitive the calculation is to even small changes in the stall speed,  I would rather stick to the Tech Specs data unless someone can prove it is clearly defective.

  • Upvote 1
Link to post
Share on other sites
1 hour ago, Panthera said:

Drag it out? 

 

There is obviously an issue. 

 

The main points raised so far is that the relative turn performance between the 67" Hg P-51 and 1.8ata K4 is incredibly different between IL2 and DCS. In DCS the 1.8ata K-4 performs substantially better than the 67" Hg P-51 in sustained turns (SL, 400 L fuel), as it should. Whilst in IL2 both aircraft are pretty much even, if not with a slight advantage to the P-51. 

 

 

The issue is wings level Clmax, i.e. low speed 1 G (& prop idle), is not going to be the same as the Clmax, power on, at dogfighting speeds

Cl is not effected by load factor.  The amount of Load factor available is effected by the Cl. The speed at which the propeller spins does effect the Cl. What term in the lift equation would you alter to compensate for propeller effects to derive the Cl for  a 5580 lb Bf-109 with a wing area of 174 ft^2?  What effects the increment of Cl to propeller effect? You seem to be saying that this increment is off, what data would you look for to prove your hypothesis and why? 

Edited by Yak_Panther
Link to post
Share on other sites

If Clmax was the same irrespective of speed and G load, then why do we have Clmax vs mach diagrams? ;)

 

As for what the exact Clmax should be at the respective speeds, power on, we don't have any exact figures for the 109. But we do have clmax vs mach figures for the P-51 vs aircraft using conventional profiles similar to that one the 109, and at the same altitude there is a marked difference. 

 

In short we can pretty safely assume that the 109's clmax between 0.2 to 0.5 mach is higher than that of the P-51.

 

It seems like this was taken into account for the FM in DCS, but not IL2. 

Edited by Panthera
  • Upvote 1
Link to post
Share on other sites

For reference, in a Bf109K calculation for a maximum performance turn at 6000m altitude, Messerschmitt uses a "cl = 1.13 ~ clmax". Speed in this turn where this cl applies is decreasing from ~160 m/s to ~130 m/s.

  • Thanks 1
Link to post
Share on other sites
4 hours ago, Panthera said:

If Clmax was the same irrespective of speed and G load, then why do we have Clmax vs mach diagrams? ;)

 

As for what the exact Clmax should be at the respective speeds, power on, we don't have any exact figures for the 109. But we do have clmax vs mach figures for the P-51 vs aircraft using conventional profiles similar to that one the 109, and at the same altitude there is a marked difference. 

 

In short we can pretty safely assume that the 109's clmax between 0.2 to 0.5 mach is higher than that of the P-51.

 

It seems like this was taken into account for the FM in DCS, but not IL2. 

I never said that Cl max isn't effected by speed. It is, do you know why?. How does load factor effect the lift equation? My point is you don't know what your talking about and are just guessing randomly. Your post proves that.

Link to post
Share on other sites

image.thumb.png.40a0c4b560d7a4c015ce775970103cb7.png

What about lift line (red) for Bf-109 and P-51? It is not distinguished between both on the chart. It shape depends on stall speed. The lower stall speed the more to the left and up line goes. This means more G’s in the slow speed turn up to maximum turn rate speed. What is stall speed for K-4 (with slots) and P-51 (clean)? I would expect majority of Bf-109 slots adventage is in this region of the chart. But I might be mistaken...

Edited by StaryMruk
Link to post
Share on other sites
15 hours ago, Yak_Panther said:

I never said that Cl max isn't effected by speed. It is, do you know why?. How does load factor effect the lift equation? My point is you don't know what your talking about and are just guessing randomly. Your post proves that.

 

You're not making much sense now. You're effectively trying to make a case that the Clmax is correct at 280 km/h based on a 1 G (prop idle) stall  speed measurement. Why would you do that if you already knew Clmax at 280 km/h (prop throttled) is going to be different? 

 

 

 

 

 

 

 

Link to post
Share on other sites
13 hours ago, StaryMruk said:

image.thumb.png.40a0c4b560d7a4c015ce775970103cb7.png

What about lift line (red) for Bf-109 and P-51? It is not distinguished between both on the chart. It shape depends on stall speed. The lower stall speed the more to the left and up line goes. This means more G’s in the slow speed turn up to maximum turn rate speed. What is stall speed for K-4 (with slots) and P-51 (clean)? I would expect majority of Bf-109 slots adventage is in this region of the chart. But I might be mistaken...

 

It is not distinguished on that chart because the chart is about the 109K-4, comparing BoX to DCS - and finding no measurable difference as things stand. It has nothing to do with the P-51.

 

You can find stall speeds in BoX in the Tech Specs page: 

 

Note that these always depend on the weight that you pick: for the P-51 D and 109 K-4, either plane could stall at a lower speed than the other, depending on the condition chosen. 

 

 

@Panthera I am curious to know if you think the 109K-4 and P-51 D 1G power off stall speed figures BoX is using, as in the Tech Specs, and the consequent calculated CLmax, are within an acceptably correct range, or not. If not, what should they be.  While we all understand that there are changes with speed, the developers presumably have to have some fixed points that they can compare to documentation.     

Edited by unreasonable
Link to post
Share on other sites

Just a sidenote:

Yes, prop wash increases CLmax on the affected portion of the wing.

Now... unfortunately that wing area is the inner portion of the wing - unless you'd be in a severe side-slip or your plane has a rather odd engine layout for a single engine aircraft.

That means that if you'd try to further increase the turn rate of a plane by using the increased CLmax from prop wash, leaving the wing's own CLmax area, then... yes, then you'll stall your outer wing sections, including ailerons.

Which as a result will cause a severe wing drop from the prop's torque effect.

 

:drinks:

Mike

Edited by SAS_Storebror
Link to post
Share on other sites

Right, but I think the idea is that the slats deal with that effect, at least partially, as does the washout on some other aircraft, including the P-51. So as the inner section stalls first, adding prop wash to that area can restore lift in that AoA range where the outer section is not yet stalled.

 

I do not think anyone is arguing that the mechanics as modelled in BoX are completely wrong, just about whether there is some quantitative error that produces a particular result, that a few people do not like,  but many others think is perfectly acceptable. (A familiar scenario ;) )

 

So there can only be any progress if the specific alleged error is identified, and those elements that appear not be be wrong are also acknowledged. Otherwise the game of whack a mole goes on indefinitely. 

Edited by unreasonable
Link to post
Share on other sites
4 hours ago, unreasonable said:

 

@Panthera I am curious to know if you think the 109K-4 and P-51 D 1G power off stall speed figures BoX is using, as in the Tech Specs, and the consequent calculated CLmax, are within an acceptably correct range, or not. If not, what should they be.  While we all understand that there are changes with speed, the developers presumably have to have some fixed points that they can compare to documentation.     

 

 

Well the landing speed I've seen for the real life K-4 was 150 km/h, so IL2's stall speed of 154 km/h gear & flaps down seems off, seeing as you don't land at, and certainly not below, stall speed. As for the gear & flaps up stall speed, I don't have a reference to compare it with, but in IL2 it appears very high.  

 

Now regarding the P-51 & power on Clmax, all I can say is that it should be around 1.3 @ 0.25 mach for the P-51 at low altitude, and as such most likely noticably higher for the Bf-109 at the same speed & altitude up until around 0.45 mach where the laminar flow profile resurges in Clmax. This is partly based on the direct comparison between the F6F & P-51B in NACA report TN1044, which shows the difference in Clmax vs mach we can expect between a fighter (F6F) using a similar conventional airfoil as the 109 (yet without slats), and one using the low drag type as on the P-51. And the difference is significant at the same altitude & speeds (flying speeds, mind you) where we have flight test figures for both. This in turn also checks out with what I've read others write regarding the F6F (& F4U) vs P-51B in USN testing, that is in terms of turning performance the disparity was significant despite a similar (F6F) to worse (F4U) wing loading than the P-51B. 

 

 

 

 

  • Thanks 1
Link to post
Share on other sites
47 minutes ago, Panthera said:

 

 

Well the landing speed I've seen for the real life K-4 was 150 km/h, so IL2's stall speed of 154 km/h gear & flaps down seems off, seeing as you don't land at, and certainly not below, stall speed. As for the gear & flaps up stall speed, I don't have a reference to compare it with, but in IL2 it appears very high.  

 

Now regarding the P-51 & power on Clmax, all I can say is that it should be around 1.3 @ 0.25 mach for the P-51 at low altitude, and as such most likely noticably higher for the Bf-109 at the same speed & altitude up until around 0.45 mach where the laminar flow profile resurges in Clmax. This is partly based on the direct comparison between the F6F & P-51B in NACA report TN1044, which shows the difference in Clmax vs mach we can expect between a fighter (F6F) using a similar conventional airfoil as the 109 (yet without slats), and one using the low drag type as on the P-51. And the difference is significant at the same altitude & speeds (flying speeds, mind you) where we have flight test figures for both. This in turn also checks out with what I've read others write regarding the F6F (& F4U) vs P-51B in USN testing, that is in terms of turning performance the disparity was significant despite a similar (F6F) to worse (F4U) wing loading than the P-51B. 

 

 

 

If it is not clear, we have to assume that this "150kph" is the pilot's IAS.  In BoX there is no instrument error - IAS=CAS, at high AoA and low speed the error is significant.  Which means that every quoted manual or test figure that did not explicitly take into account this fact is an unreliable guide. That is why all stall speeds in the Tech Specs are (or seem) higher than manuals and most tests.

 

I have yet to come across an exception in BoX FMs, except the initial release of the Tempest, where, I suspect, someone new to the job or just in a hurry worked towards the stall speeds from the Tempest manual. Which then generated the enormous CLmax. It has been changed now, but is still very high.  

 

Here is an example of a test done which did correct for this using a trailing pitot. You can see that the potential difference between a pilot's IAS and CAS can be very large at stall speeds, 20mph in this case.  

 

1197601356_RAE109test1.thumb.PNG.25d242a88705c5f07e52b6ba12036239.PNG503424397_RAEPECcurve.thumb.PNG.913833df44241ca173902319ac4c649f.PNG

 

 

The F&G up stall speed in BoX generates a 1.39 CLmax for the K4.  

 

As for the difference to a conventional airfoil for the P-51: the NACA TN 1044 chart that compares the P-51 with the F6F is at high altitude - indeed the P-51 data is for higher altitudes. Another aircraft with a conventional airfoil discussed in that report is the P39N. Here the lines are much more similar at the same altitude, so it is not at all clear that taking the F6F as your model of a conventional airfoiled plane is representative .

 

185919450_NACAgraph.thumb.JPG.f06c0e1f7da98c60c3f2ae5033748a5f.JPG

 

  

Edited by unreasonable
Link to post
Share on other sites

@unreasonable Keep in mind that the P-39 uses a symmetrical profile airfoil for most of the wing, and hence is going to produce a lower overall Clmax. By comparison the F6F uses the  high lift NACA 5 digit series profile (which is similar to the 2R1 of the 109,) from root to tip, and thus as we see in the same report also generates a significantly higher Clmax than the P-39 at the same speeds (until ~0.6 mach) & altitude:

s5RTIP1.png

 

That said the 1 G prop idle Clmax that they use for the aircraft in BoX might be correct, it's the power on Clmax at speed I'm curious about, esp. as compared with DCS for both aircraft.

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...