http://www.rolfwolf.de/daten/E4/Emil.html

Auszüge aus Flugzeugdatenblatt Bf 109 E-1, E-3 nach L.Dv.556/3

Höchstzulässige Horizontal-Bodengeschwindigkeit 485km/h

There is no such german tests of the production E-1. Only one test of the prototype V15a at supposed series condition and calculated projected output well before the E-1 was fully developed or out of production line.

Besides the agreement is much better with Holtzauge's calculation, the difference being less than 1,5%.

There is no official tests of production planes to fell of, I quess you are refering the tests of the prototype V15a again. The power output is actually not relevant because these were real production planes performing as delivered, no need to assume some kind of projected power.

All the tested production planes (Wnr. 1792, 1791, J347, 1304) had speeds within range of 18kmh and variation is less than 2%.

And please, don't reply with something on the prototype V15a again, it's a dead horse like the 100 octane discussion. If you have real tests on real production planes, then we have something to discuss.

There is allways chance of error regardless type of the test; error in timing, error on writing results, errors in calculation etc. If there is an error, it's likely in the outlier.

Where are the documents, rather than home made graphs and a translation?

http://www.wwiiaircraftperformance.o...dbookcurve.jpg

Data from the 109E-1/3 handbuch: Actual (wirklich) speed shows 450 km/h or 279 mph at sea level; indicated (anzeige) = 500 km/h 310 mph.

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

I did post some simultion 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? ;)

There is no single equation behind it and it's not a FEM program if that is what you mean. The C++ code is an extension of the code I wrote for my masters thesis (In Simula!) which was to access the influence of external stores like missiles etc on the performance of jet fighters. This meant I had to convert it to C++ and add some functions to handle prop performance and ram effect on engine. The prop function is dependant not only on advance ratio and density effects but also includes Mach effects due to prop tip speed. The same goes for the drag which rises steeply at typical dive Mach like 0.7 and upwards. Not much use in simulating dive performance otherwize. This shortcoming not to model compressibility effects is a major flaw in both IL2 and CloD IMHO.

Yes, the 498 Km/h SL figure for the V15s prototype does not make sense if you assume that the circa 570 Km/h figure at altitude is correct. I have simulated a number of different aircraft and usually it is enough with one data point with both power and speed and then you can with good correlation to historical data work out the others if you have the power/alt curve. This has worked for me on the Fw190A&D, Spitfire 1,5&9, P-51, P-47, Me109F, G and K etc and using the same principle yields around 475 not 500 Km/h at SL for the Me109E.

I also agree that unless some new data on series aircraft emerges that changes the matter, I'm going to stick with the 475 Km/h figure since I'm more inclined to believe the Rechlin reports on actual production aircraft for tuning my model rather than trusting some prototype data or a figure from a Baubeschribung from "circa 1939".

Finaly, Seeing Kurfurst's has been actively promoting the 500 Km/h story I never expected to convince him. My sole purpose with posting my chart was to provide an alternative analysis and in the end it's up to the readers what data they think is more credible and knowing the majority of users want historical not agenda driven performance I can only hope 1C will not be duped.

Pity we have not seen any.

A home made chart of which's maker even refuses to share the base data vs. properly flight tested, calibrated, corrected and guaranteed flight test data.

It is going to be a tough call I bet. :)

Yes, seeing the sniping is coming from someone with a documented history of always taking the inside envelope of any allied data and the outside envelope of any Me109 data I'm sure it will be a close call.

Over and out.

yep, it is.

by the way, isn't it peaceful here at the moment, shame its going to end soon......

Does anyone know the differences between the V15 and production E-3. I assume that 20mm guns, armour plate, self sealing fuel tanks, bullet resistant glass, were not included. Did the Germans install additional equipment to the 109 similar to Spit 1's compared to the Spit prototype, such as different radios, IFF, emergency equipment, bulges to accomodate the 20mm. All these things presumably would have impacted the performance to some degree.

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.

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.

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

Acquaintance may be too strong of a word? ;)

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

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

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

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

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. :evil:

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.

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 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)

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.

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

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

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?

I am

Great, so what's your explanation? I seem to have missed it.

Well, Mtt used exactly same rough calculation as Holtzauge to estimate the speed at different power. When the speed difference is around 10-15kmh, the changes in induced drag, propeller thrust and drag coefficient due to compressibility are so small that the error is less than 0.5kmh. That is certainly good enough, given that most data here is without compressibility corrections.

However, field is open for you interpretation, of course.

Thank you Kurfurst for the helpful reply and Holzauge for the extra calculation info.

This is a good point, made critical by the fact of having a single aircraft cloned exactly across the whole battle theatre is rather unhistorical really. My position is that the (may he exist) CloD FM czar should make a good faith attempt to find an "average" performing variant (which will always incorporate some subjective calls), then fiddle within plausible historical performance ranges to make CloD work best.

With the 109E, my position is that based on what flight testing/ etc. information is available, at 1.3ata the SL performance was around 475kmh. This close pass/fail performance on the Messerschmitt chart was however not an issue because the acceptance was based on an altitude performance test, where the typical 109E was close to the guaranteed average spec. I think we maybe overstate how important SL top speed was to the Luftwaffe of the time, as they were overwhelmingly interested in altitude performance, where the 109 performed inspiringly. In CloD however we like to chase each other just above the deck a lot more, I suspect.

I agree, the situation is a bit theoretical anyway because FM fine-tuning may not occur anyway in CloD. I do think (if we had to choose what was fixed) that it is better to have the aircraft end performance historical with wrong boost indications, rather than correct performance but for an unhistorical boost. Which brings us to the next point, about what boost the 109E SHOULD have:

This is a really interesting point. Googling back, I see the DB601Aa is a bit controversial in discussions going back a long way, in that is it just only an export version, or was it widely used in Luftwaffe 109s. As you say, CloD seems to have put a DB601Aa in every 109E on the channel coast, which seems an odd choice but not a demonstrably wrong one (like a Me262 Jumo jet engine would be :)). If I was CloD FM czar, I would consider re-engining all 109s to one of the DB601 A-1 variants and giving it 1.3 ata 475kmh/560kmh performance. If I stuck with the 1.35ata DB601Aa, I would increase speeds by an appropriate theoretically derived increment from the extra 0.05ata (e.g. using the formulae Holzauge provided), thus using the 1.3ata 109 data as a baseline.

Going on to the extra boost:

That seems reasonable to me, provided the 1.45ata FTH is reduced to the correct level (below 1.35ata FTH) for the supercharger capability. Right now in CloD the 1.45ata seems to be still working when around the 1.35ata FTH (without changing rpm). The one thing that concerns me is that I haven't read reports of 109 drivers reaching first for their clockwork boost buttons when in a sticky situation, in the same way RAF drivers went straight for the boost lever or tit.

Cheers,
camber

As for the Spitfire and Hurricane "get(ting) special treatment and are modelled in optimistic conditions?" While the British fighters are badly handicapped, what with engines blowing up after just a few minutes at higher boost settings, and badly under performing in other respects? Hardly "special treatment'', but there are some who don't mind.

Well I would hope that any adjustment of the Me109E would be coordinated with a corresponding adjustment of the Spitfire speed: So if the Me109 was raised to around 475 Km/h for the DB601A variant at 1.3 ata then I would expect the Spitfire to get approximately 283 Mph for +6.25 boost and 314 Mph for +12 boost.

BTW, doing a rough calculation for the DB601Aa for 1.35 ata would yield circa:

v=460 x (1045/910)^(1/3)= 482 Km/h

In addition, Cambers question is interesting: How many DB601Aa were there on the Channel front? Was it a mix of DB601A1 and Aa? If so what were the proportions?

Concerning which engine to model, even given a free choise, I'm not sure I would opt for the DB601Aa: If the Spitfire uses +12 boost the 109E is outclassed down low either with the DB601A1 or Aa. On the other hand the DB601A1 with "Neue Lader" has superior altitude performance while the Aa is outclassed on both accounts. So why give up the altitude advantage for a mere 7 Km/h more on the deck when the result is still far below the 505 Km/h the Spitfire will do on +12 boost?

Shikhov:
olefebvre (Butch2K) replies"

I don't believe the Luftwaffe intended to use the 601Aa in the 109 at first, it seems really associated with the introduction of bomb carrying 109. The reason being the increased power output of the take-off rating.

You correctly underlined the few differences between the Aa and the N, and indeed the differences are not that important. Keep in mind that the E-7 which was basically an E-4/B with droptank support was intended to use the DB601N at first. Yet the DB601N proved problem prone, and it's production was at first very slow. So i believe the introduction of the Aa on the /B and E-7 ac was a quick expedient to replace the DB601N until it proved reliable and could be really mass produced.

There were few 109 really equipped with DB601N engines, they simply did not provide any significant advantage at the time. With the introduction of the higher performance blower when the Friedrich entered production, then it provided an advantage.

Really did you read at least what I wrote on the last page?

(Edited on request).

Yes I did, assuming you are referring to this one. But it only states a few principles of aerodynamics, doesn't quantify them or provides a calculation illustrating that if this is taken into account, the numbers add up. I agree on the trend, but I doubt that they will account for the full difference.

Thank you for editing your post.

Well, the logical problem with Tomcat's argument on Holtzauge's calculation is that Mtt calculated that claimed 498km/h at sea level exactly same way as Holtzauge. So if we prove either of them seriously unaccurate, the other is just as unaccurate.

However, generally there is no steep rise on the Cd until mach numbers well over 0.6 so the error caused by compressibility is very small given the speed differerences around 15kmh talked here.

No Mig Sry but Mach nbr is the local mach, not the plane frwd speed.

At 15% thickness, the speed is in high subsonic when the plane is flying around 600kph.

At this local speed, drag effects are not linear and raise sharply.

Moreover, I think I was one of the first to put the dK/dt=SIGMA(P) eq around on forums. So don't nurse me with it. Thx in advance.

Remind simply that this give only the max speed any increase of pow will give to a plane. At high speed, this is not linear.

Generaly speeking:

Incompressible theo apply only for M<0.3
Btw M0.3 to 0.8 effecst are sharp and results vary btw 6% to 100%
Over 0.8, you hve shock waves and you need to apply according theo.

Of course many guys rely only on incompressible, simply because they never really to get into the others case :eek:

It's also much cheaper, computationally speaking, to use subsonic incompressible flow theory and then apply a linear compressiblity correction.

I imagine this is what IL2FB did, though I'd be surprised if their correction factor was at all realistic.

Hoerner gives 10% rise on Cd at mach 0.55 in his analysis on the Bf 109G, steep rise starts around mach 0,6. We are talking here about 15kmh speed differences around mach 0.4 (460-500kmh at sea level) so we can safely assume that there is less than 2% difference in the Cd due to compressibility and that causes much less than 1kmh error in the calculation.

I don't think that anyone is relying on incompressible theory here, just giving a quick estimate of speed change due to power change at good enough accuracy. You can, of course, point out that compressibility is not accounted (nor Cl, prop efficiency etc.) but can you prove that there are significant errors?

BTW that calculation method has been criticized earlier in this thread, actually well before Holtzauge used it and you posted your stuff.

@Mig

Always the same, always bragging ... When did I post my "stuff" ? Tell me.

If you gonna be insulting be precise, accurate and honest..

Your Holtzauge did not post detailed calculation or discuss his method. I pointed one source of error. Tht's it.

This is the basis in Sciences. Put it down and submit to what ppl think.

ANd you just hve to open a NACA chart to see the drag rise for the specific airfoil. You don't hve to pick bit of info here and there. It's free and available.

But, huh, tht's what hurt the dark internet genius as always.

And by the way, 10% of drag raise (outsourced from my memory) is equal to what a fully open rad will do on Seversky P-35.

Tht's not negligeable my dear and will certainly not impact the max speed for only 1km/h

Boring...

@Doggle : you are right of course

Post #516

Exactly the same calculation is used on the Mtt test on the prototype V15a to calculate speed at higher power at sealevel (blatt 5) posted several times here. I used the same calculation for demonstration on the post #448 and noted that it's a crude, unaccurate and partially wrong way to calculate it. However, it's good enough for small differences.

Yes, of course. But why do you complain about Holtzauge's calculation now but not about Mtt calculation which has been here much longer (or mine which was posted 3 weeks ago)?

Actually I'm refering tests of entire airframe, tunnel and flight tests. And yes, many are available. For Hoerner's Bf 109G analysis, get his Fluid Dynamics book. Some are freely available, here is one for few aircraft including Spitfire I. Below is also a Cd/mach number chart from that report attached, you can see that up to Mach 0.5-0,6 there is rather minimal drag rise due to compressibility.

Hoerner's number 10% is for entire speed range from mach 0.3 up to 0.55 ie speed changes 250-300kmh while we are talking here about 15kmh speed difference around mach 0.4, that means that drag rise is certainly certainly less than 2%, probably less than 1%.

No. Again lack of modesty in your assumption. Take a look on Youtube searching TcViP and related variables. You'll see that I posted that last time almost 3 years ago. Good Hunt :cool:

...Obviously you won't but that show you how personal arguments hve nothing to do on a forum. Even if that behavior seems rather popular Lol

Small diff... Yeah. But not small diff at max speed for this kind of plane !

All this story abt the 109E not reaching 500Kph is ridiculous. Juts like other big themes fairly popular here. Nothing new here so you can past those line.

Didn't I say local mach number ???? Again when your plane is traveling at Mach 0.5, your wing see a peak of high subsonic speed for a 15% airfoil section. Same with the fuselage, especially the bottle neck effect at the rear par. Yes, the 109 was very well streamlined but your calculation need to be repeatable to other type

Compare to what ?

Wil hve a look to your doc cited as refs. hoping that I won't lost my time wit another bunch of lifting line and alike theo.

If you are interested in the matter you shld read the books from Karman directly.~

A good one and easy to reach (amazon - very cheap):
Aerodynamics - Selected Topics in the Light of their Historical Development, Cornell University Press, Ithaca, 1954

The university of Warsaw hve also a very good list of PDF doc posted on theit website. Doing some Google searching you sld found it easily.

Well, I rely on what you have posted on this thread. At the post 519 you suggest that the calculation is ok "to estimate the time of accel from Stall speed to 200mph". But that is actually not true because the Cl and the hence Cd changes in large degree during acceleration as well as thrust. However, for a quick estimate for a small change as discused here, the calculation is good enough.

The testing of a whole airfame accounts all these and we know, based on Hoerner and other sources, that around Mach 0.4 the compressibility effects are minimal in the case of Bf 109G, there is no reason to believe that the Bf 109E is much different because the wing profiles are almost the same as well as the fuselage.

We can safely use the same rate of drag rise as given by Hoerner for assuming Cd change from 460 to 475kmh. And because the speed change is so small and we are around Mach 0.4, we can safely assume that the Cd rise is just a small fraction of that 10% given by Hoerner, probably less than 1%.

Ok 3 post and nothing new.

I hve been tricked liked that alrdy for hundred of pages. End of conv. for me.

Here is the link to the book I cited for the reader that would be interested to get a quick snap of what are aerodynamics forces, as told by a Jedi master:

http://www.amazon.com/Aerodynamics-H...+Topics+karman

Much better read than hanging here, sadly.. :evil:

May the Force (of flows) be with you.

If you were right, the Mach related drag increase on the 109E would happen only somewhere between 498 km/h and 537 km/h, as the top speed in first charger gear (537 km/h, 2150m, 1115 hp) and in second charger gear (575 km/h, 4850m, 1100hp) are in perfect agreement.

A plane doing 498km/h at 1018hp at sea level, should do around 555km/h at 1115hp at 2150m and 600km/h at 1100hp at 4850m, give or take a percent or two.

These figures happens to be pretty much spot on Bf 109F performance, which either means it did not suffer the E model Mach effects, or it means the problem with the data is elsewhere.

Google searching you sld found it easily
http://www.qmmv.info/12.jpg
http://www.qmmv.info/13.jpg
http://www.qmmv.info/14.jpg