Spit/109 sea level speed comparisons in 1.08 beta patch

[NZtyphoon]

Originally Posted by Kurfürst

Pity we have not seen any.

None from Kurfurst either, but we do have the power curves from the 109E handbook which give 470 km/h at sea level, which is far more realistic than the treasured 493 km/h.

[ACE-OF-ACES]

Originally Posted by Holtzauge

Had a look at your site and it looks promising! Will be even more interesting when you add some more aircraft.

Thanks!

The IL-2 section only shows about 10 planes now, but I have the data for the 600+ planes.. I just have not bothered to upload it for now while working on the CoD portion. The biggest difference being in the CoD portion I will have the real world data plotable right along side the in game data that will allow all to see just how well the in game data matches the real world data.

Originally Posted by Holtzauge

I can certainly do some simulations if there are some particular scenarios you would like to see and yes, the output is in text format that I copy to Excel to produce the charts.

Cool!

In that as you well know, there are a lot of real world data sheets missing for specific planes! Would be nice to have your results as another sanity check

Originally Posted by Holtzauge

I did post some simulation results a few years back about Fw190 dive and compressibility effects which unfortunately came to the attention of a certain Herr Crumpp whom I believe is a mutual aquaintence?

Acquaintance may be too strong of a word?

[camber]

After reading through this thread and the last big thread on this issue:

http://forum.1cpublishing.eu/showthread.php?t=32259

I am still in the camp of the typical 109E doing around 475kmh at SL and 560kmh TAS top speed. IMO it is too much argument work to make the available flight tests match the 500kmh deck speed for series 109Es, as opposed to allowing that the aircraft were actually around the pass/fail level at SL (but OK at alt).

One thing that was brought up in the last thread, that the aircraft would be "failed" and sent back to Messerschmitt if they did <475kmh at SL. However, the 109G acceptance plot posted in this thread shows testing at a single altitude that varies but is closer to FTH than SL. It makes sense to me that acceptance tests would not be based on a full speed vs alt test regime, and especially not an actual test of the 109 belting along at sea level (a bit difficult to arrange except in CloD). So a 109 doing 470kmh at SL could still pass.

The other thing is considering 1.3ata vs 1.35ata. If the actual limit was 5 mins 1.3ata without the takeoff boost, I don't see that the fact the CloD 109s show 1.35ata suggests they should be made faster than historical (although we are getting toward hair splitting). Instead the CloD boost indication should be fixed or ignored. In the same way if the CloD Spit boost gauge showed +14psi, I wouldn't expect it to be made faster than historical to match the gauge.

One thing I really find interesting for 109s is combat use of the 1 minute takeoff boost. Whether or not it actually works except close to SL really depends on how it is designed...similarly to difference between the actual Spit II gated takeoff boost (will decay quickly with alt) and red tab combat boost (will work at any alt the supercharger is capable of delivering it).

Right now the 1.45ata works even up to FTH (odd), which seems very unlikely. But in real life it should certainly work if you are chasing or being chased low over the channel, but I have not seen a combat report or memoir that confirms this.

With that all said, I would be happy with 500kmh SL 109s if that gave the best and most fulfilling online CloD for both red and blue (with red FM fixed too)

camber

[bugmenot]

Originally Posted by NZtyphoon

Where are the documents

Bf 109 E, LDv 556/3, Flugzeug-Handbuch
http://www.luftfahrt-archiv-hafner.de/messerschmitt.htm

[Holtzauge]

Originally Posted by camber

After reading through this thread and the last big thread on this issue:

http://forum.1cpublishing.eu/showthread.php?t=32259

I am still in the camp of the typical 109E doing around 475kmh at SL and 560kmh TAS top speed. IMO it is too much argument work to make the available flight tests match the 500kmh deck speed for series 109Es, as opposed to allowing that the aircraft were actually around the pass/fail level at SL (but OK at alt).

One thing that was brought up in the last thread, that the aircraft would be "failed" and sent back to Messerschmitt if they did <475kmh at SL. However, the 109G acceptance plot posted in this thread shows testing at a single altitude that varies but is closer to FTH than SL. It makes sense to me that acceptance tests would not be based on a full speed vs alt test regime, and especially not an actual test of the 109 belting along at sea level (a bit difficult to arrange except in CloD). So a 109 doing 470kmh at SL could still pass.

The other thing is considering 1.3ata vs 1.35ata. If the actual limit was 5 mins 1.3ata without the takeoff boost, I don't see that the fact the CloD 109s show 1.35ata suggests they should be made faster than historical (although we are getting toward hair splitting). Instead the CloD boost indication should be fixed or ignored. In the same way if the CloD Spit boost gauge showed +14psi, I wouldn't expect it to be made faster than historical to match the gauge.

One thing I really find interesting for 109s is combat use of the 1 minute takeoff boost. Whether or not it actually works except close to SL really depends on how it is designed...similarly to difference between the actual Spit II gated takeoff boost (will decay quickly with alt) and red tab combat boost (will work at any alt the supercharger is capable of delivering it).

Right now the 1.45ata works even up to FTH (odd), which seems very unlikely. But in real life it should certainly work if you are chasing or being chased low over the channel, but I have not seen a combat report or memoir that confirms this.

With that all said, I would be happy with 500kmh SL 109s if that gave the best and most fulfilling online CloD for both red and blue (with red FM fixed too)

camber

Did not read your excellent compilation in post#1 until now but I think it does a good job of summing up the situation so thanks for the info!

Some additional thoughts on the Me109E speed issue: First of all that 1.35 and not 1.3 ata was displayed in the CloD was news and also that take-off boost as high as 1.45 ata was usable at altitude. Wonder why they modelled it like that? Is there some data indicating that this was the case? Most data I have seen list Dauerleistung 1.15 ata, Steig und Kampffleistung 1.23 ata and then the 1.3 and 1.4 ata Startleistung boosts. Anyway, it just struck me that there is an alternative way of accessing Me109E sea level speed at 1.3 ata boost:

If one assumes that the Steig und Kampffleistung figure of 460 Km/h according to datenblatt L. Dv 556/3 at 1.23 ata boost is correct then one can use this to estimate the ballpark figure for 1.3 ata. Assuming that the prop efficiency is about the same and that the drag coefficients are fairly constant ( I think this is reasonable given that the induced drag is not a major factor at top speed and that if anything, the Cdo should go up somewhat due to compressibility effects) one could calculate this:

Assuming 910 Ps at 1.23 ata and 990 Ps at 1.3 ata (From datenblatt L.Dv 556/3)

Solving for speed at 1.3 ata:

v=460 x (990/910)^(1/3)= 473 Km/h

So if we assume that the speed figure of 460 Km/h at Steig und Kampffleistung is correct then this would lend further credence to the 475 Km/h figure at 1.3 ata.

Interestingly, using the same principle for the Spitfire Mk1 at +6.25 and +12 boost is spot on compared to the chart figure of 314 mph at +12 boost:

Assuming 885 hp and a top speed of 283 mph at +6.25 boost this then gives for +12 boost assuming 1201 hp:

v=283 x (1201/885)^(1/3)= 313 mph

[TomcatViP]

The 1/3 coeff i s good (came from dEc/dt=SUM(P)). Seems at least this went trough the mind of the bloggers.

However at high speed (and we will talk abt what is high speed), drag does nit increase linearly, but rather as a square function at the rate of the maximum local speed on the extrados of the wing (I am taking into account wing drag only) which is already significantly higher than the plane frwd speed.

To be rigorous also, at speed higher than Mach0.3, you'll need to make the conversion btw local press, ro and speed. The relation btw the Power and the speed is not true anymore if you don't add a term in ^2 to reflect the wet surface and the viscous drag effect.

So there is no linear relation btw speed and power, hence no guess work on the estimate gain in speed. A close look at a pressure plot of any airfoil will give you a hint. Usually an honest guy will use this equation in reverse, to have an idea of what is the ABSOLUTE MINIMUM of POWER you'll need for any increase of speed.

[Kurfürst]

Originally Posted by camber

I am still in the camp of the typical 109E doing around 475kmh at SL and 560kmh TAS top speed. IMO it is too much argument work to make the available flight tests match the 500kmh deck speed for series 109Es, as opposed to allowing that the aircraft were actually around the pass/fail level at SL (but OK at alt).

My view is that other POV, which simply wants to ignore the official specs and ignore test results in favour of uncorrected (engine powers not corrected) tests with very little detail (only very rough and extrapolated figures), with a differing engine fitting running at less boost and less power makes much less sense.

While there's a simply and logical explanation as to why how the V15a/official specs relate to the other tests, which is supported by the results themselves, the other way is simply to ignore a few tests in favour for the lowest possible values anyone can find.

Curiously, the most loud supporters of this agenda are the same people who want RAF planes modelled after the highest possible results, and ignore all but the most favourable data.

One thing that was brought up in the last thread, that the aircraft would be "failed" and sent back to Messerschmitt if they did <475kmh at SL. However, the 109G acceptance plot posted in this thread shows testing at a single altitude that varies but is closer to FTH than SL. It makes sense to me that acceptance tests would not be based on a full speed vs alt test regime, and especially not an actual test of the 109 belting along at sea level (a bit difficult to arrange except in CloD). So a 109 doing 470kmh at SL could still pass.

Yes of course there were a lot of 109E's that just passed the minimum specs and were still accepted into service. So were Spitfires and Hurricanes. So why should be 109Es modelled after the worst possible specs instead of the nominal/guaranteed/tested and confirmed specs, while Spitfires and Hurricanes get special treatment and are modelled in optimistic conditions? Especially as the CLOD engine models wear of the airframe, so worn/badly manufactured planes and the scatter in performance can be easily modelled...?

The other thing is considering 1.3ata vs 1.35ata. If the actual limit was 5 mins 1.3ata without the takeoff boost, I don't see that the fact the CloD 109s show 1.35ata suggests they should be made faster than historical (although we are getting toward hair splitting). Instead the CloD boost indication should be fixed or ignored. In the same way if the CloD Spit boost gauge showed +14psi, I wouldn't expect it to be made faster than historical to match the gauge.

The Spitfire II analouge is limping, since it essentially says that if the performance doesn't match the engine outputs, decrease the engine output until it matches the wrong speed. It's akin to say that if Spitfire speeds do not match the +12 performance levels, but they match the + 6 1/4 boost, simple set the gauge to show 6 1/4 (which is unfortunately the current situation in the sim). Moreover the Spitfire I / II had only one type of engine fitted (M III or XII).

The Me 109E in contrast had at least four fitting and used during the Battle of Britain, with different boost and outputs.

The DB 601A-1 with the old type supercharger, 1.30 ata for five min and 990 PS, and 1.40 ata for 1 min and 1100 PS. Rated altitude being 4000m.

The DB 601A-1 with the new type supercharger, 1.30 ata for five min and 990 PS, and 1.40 ata for 1 min and 1100 PS. Rated altitude being 4500m.

The DB 601Aa with the old type supercharger, 1.35 ata for five min and 1045 PS, and 1.45 ata for 1 min and 1175 PS. Rated altitude being 3700m (altitude output was otherwise very much like the DB 601A-1 / old s/c, though it is an open question wheter the new s/c was fitted to the Aa as well. So far no evidence to that though.)
This is the type we have in the sim.

The DB 601N, 1.35 ata for five min and 1175 PS. Rated altitude being 4800m. (there was a second type of 601N, mounted in one in the 109F had better supercharger and IIRC 5200 m rated altitude)

Therefore, it is pointless to compare our 601Aa equipped Emils performance (1.35ata) to real life tests of DB 601A-1 equipped Emils at 1.3ata. It should of course match the real life DB 601Aa at 1.35ata (V-15a, Baubeschreibung "5%" specs, Swiss trials of serial no. 2404)

One thing I really find interesting for 109s is combat use of the 1 minute takeoff boost. Whether or not it actually works except close to SL really depends on how it is designed...similarly to difference between the actual Spit II gated takeoff boost (will decay quickly with alt) and red tab combat boost (will work at any alt the supercharger is capable of delivering it).

Right now the 1.45ata works even up to FTH (odd), which seems very unlikely. But in real life it should certainly work if you are chasing or being chased low over the channel, but I have not seen a combat report or memoir that confirms this.

The 109's 1-min Startleistung of 1.45ata worked different from the Spit II gated boost: like the Spitfire I, it had an automatic boost control which maintained 1.45ata up to near rated altitude. The primary difference was, evidenced from the DB 601Aa power curves is that just above the 1st supercharger speed, the power output with the 1 min rating suddenly dropped quickly, and although it still brought some very marginal power increase.

This, along with the description of device makes it clear that the system employed a sort of fixed charge enrichment, providing a very rich mixture ratio to boost power for takeoff and low level. It was probably fixed for an optimum at supercharging ratio in the 1st gear of the engine, which became unsuitable as altitude increased to provide reasonable increase and there was no automatic mixture compensation for the 1-min rating. It could still be used up to near FTH, up to where the supercharger was phyisically capable delivering 1.45ata (I would guess - ca 3400-3500m in case of the 601Aa)but the decription notes that it only leads to increased fuel consumption and strain with very little increase in output. The manuals prescribe it's use only for takeoff, but its also evident from the warnings that there is no physical difficulty in using it any other time.

So there's not much wrong with the 1-min rating being usable up to FTH, what is wrong is how it's modelled. At low altitudes, it should bring a MUCH more noticable boost in power than currently, given that it boosts the engine by 110-130 HP, but above ca. 1.5 km it should amount next to nothing (with fuel consumption still being sky high).

Hope this helps.

[Holtzauge]

Originally Posted by TomcatViP

The 1/3 coeff i s good (came from dEc/dt=SUM(P)). Seems at least this went trough the mind of the bloggers.

However at high speed (and we will talk abt what is high speed), drag does nit increase linearly, but rather as a square function at the rate of the maximum local speed on the extrados of the wing (I am taking into account wing drag only) which is already significantly higher than the plane frwd speed.

To be rigorous also, at speed higher than Mach0.3, you'll need to make the conversion btw local press, ro and speed. The relation btw the Power and the speed is not true anymore if you don't add a term in ^2 to reflect the wet surface and the viscous drag effect.

So there is no linear relation btw speed and power, hence no guess work on the estimate gain in speed. A close look at a pressure plot of any airfoil will give you a hint. Usually an honest guy will use this equation in reverse, to have an idea of what is the ABSOLUTE MINIMUM of POWER you'll need for any increase of speed.

Sorry if I jumped over some steps: I'm not saying there is a 1/3 linear relationship between power and speed. Actually it's to the power of 3. In addition I agree that drag does not go up linearly but by the square. I'm only assuming the coefficients as constant, not the drag.

Thrust :T=(P x n)/v

Drag: D=0.5 * ra*v^2*(Cdo+Cdi)*S

This gives: P/v^3=0.5 * ra*(Cdo+Cdi)*S*1/n

Where n is prop efficiency, ra is density, Cdo and Cdi drag coefficients and S wing area. Since these are assumed to remain constant I substitute this with constant K

Therefore P/v^3=K in both cases

So entering the numbers we get:

910/460^3=990/v^3

Solving this for v we get:

v=460 x (990/910)^(1/3)= 473 Km/h

[TomcatViP]

no again. Sry. But you are in inviscid and incompressible.

Those eq are valid only bellow Mach 0.3. Btw 0.3 and O.6, this can do a nice guess-estimate if you had a coeff. Above 0.6, you can't rely on this way for calculating perfs.

Remind that 0.X is the LOCAL maxima of speed.

Thx however for the details you pushed here.

REM: If you had used your calculation to estimate the time of accel from Stall speed to 200mph, I won't have said anything (if you have added a coef in 2Pi*Alpha). Or the cruise speed (WWII).

~S

[JtD]

OK Tomcat, if he's got it all wrong, then why does it work reasonably well with about all other WW2 aircraft in the same speed league? He's clearly got a point, 500 at sea level and 575 at 5000 m don't add up with the power levels given. Personally I'd be most curious to have that sorted, preferably to a point where the test results make sense.

Can you guys try to be constructive and solve that problem?