Analysis of real life 109E performance for CloD

[camber]

Many posters have stated their preference for CloD FMs to be historically accurate. Personally, I don't believe that it is possible. It is not historically accurate to clone a single aircraft across a whole theatre of battle. Additionally, "average" historical performance, even compiled with the least possible bias and most technical knowledge is still imprecise, and subjective decisions then need to be made (by the devs) about how to set up aircraft performance in the simulation.

But that said, I wanted to attempt to answer the question...if I had the opportunity to set CloD 109E performance as historically accurate as I could, what would I set?

Real life 109 performance is somewhat controversial..this thread is a good indication and summary:

http://forum.1cpublishing.eu/showthr...=31450&page=19

The disagreement can be summarised as:

Position 1 (Fast guaranteed 109s): Messerchmitt guaranteed 500kmh on the deck and 572kmh max TAS for the 109E. The E1 prototype duplicates these figures theoretically once the actual flight tests are corrected for a measured engine deficiency of around 50PS.

Position 2 (Slow low 109s): Actual flight tests of production 109Es, both by Messerchmitt and by foreign governments on captured 109Es, indicate lower performance (primarily at low alt). Speeds are around 475kmh IAS/TAS on the deck and 560 kmh max TAS.

I support position 2, for reasons as follows.

Here is all the test data summarised. I am appending the data links at the end of the post. Most of this data is on "competing" websites (http://kurfurst.org and http://www.wwiiaircraftperformance.org). Most of it is on both, and it is exactly the same data..... however the interpretation is different. I will give kmh and mph figures, plus boost psi and ata.



Postion 1 (Fast guaranteed 109s) requires explanations to why all the 109E actual flight tests show lower performance than "guaranteed". A good start is assigning lower significance to tests on captured aircraft, as these may not operating at maxiumum efficiency (for various reasons). However this makes no real difference to the data set, as the flight tests (besides the E1 prototype) are all similar. The only exception is the Russian captured aircraft which appears to be a (low performance) outlier at low altitude, and can perhaps be discarded from consideration.

For test 1 (E1 prototype) the converted (theoretical) data appears reasonable. The engine power deficiency was measured on the test stand and used to provide a theoretical correction to actual flight data.

For tests 2 and 3, the suggested reason for low performance is that the results are not corrected for nominal DB601A output, as was done for the E1 prototype (http://kurfurst.org/Performance_test...MP16feb39.html). However this begs the question, why were multiple production 109Es failing in tests to reach their guaranteed performance because of underperforming DB601s? This seems an unlikely scenario, and rather a bone of contention between Messerchmitt and Daimler Benz!

For test 5, the explanation for underperformance relates to the function of the DB601 supercharger. The hydraulic supercharger coupling of the 109 was intensely interesting to the British and there is a couple of very good, detailed explanations of it's operation in the period press:

www.wwiiaircraftperformance.org/me109/DB-601A-Flight-7Nov40.pdf
http://www.flightglobal.com/pdfarchi...0-%200516.html

Both the DB601 and Merlin had the same problem...a supercharger powerful enough to allow high altitude performance would give so much overboost (unthrottled) at sea level to cause predetonation and engine damage. The Brits developed a boost controller that automatically throttled the supercharger inlet to avoid overboost. The Germans worked out an elegant hydraulic supercharger coupling that spun the supercharger impeller slower at sea level and faster at height.

The DB601 hydraulic coupling had two oil pumps which pumped oil into the engine to impeller junction. One pump operated continuously but insufficiently for efficient coupling, allowing slippage of about 30%. As altitude rose, a barometric control increased the action of the secondary oil pump, reducing slippage to the minimum possible, about 2%. The corresponding impeller ratios were 7.2:1 at sea level rising to 10.2:1 at FTH.

The continuously varied supercharger output accounts for the curved nature of the 109 speed vs alt curves (e.g test 4) Unfortunately some tests seem to omit data points in favor of straight lines, making it hard to assess whether the curves are characteristic of the hydraulic coupling or not (e.g test 5)

The (fast guaranteed 109s) explanation for the test 5 underperformance is based on the hypothesis that the hydraulic supercharger setup can be altered in tests to act a two speed supercharger, and the Swiss were testing in high altitude configuration at all altitudes including at ground level. As a consequence the high altitude speed is about right but the sea level speed is low (http://kurfurst.org/Performance_test...109E_J347.html)

This does not seem to be possible in light of the operation of the hydraulic coupling as explained in the references above. Manual operation of the variable oil pump (if possible) would have the following effects:

* If the variable oil pump is set to off, impeller slippage remains at 30%. Aircraft will perform normally at sea level, but boost will decay rapidly with altitude with consequent underperformance.
* If the variable oil pump is set to maximum, impeller slippage is held at 2%. The engine will be highly overboosted at sea level and will be unable to perform at all!

This also contradicts the idea that the test 1 (E1 prototype) performance is from a DB601 with hydraulic supercharger coupling manually manipulated to act as a two speed system. The data explicitly refers to a two speed system, so in the prototype it appears that the supercharger is an earlier direct and not hydraulic type.

The fact that the E1 prototype achieved higher sea level performance but similar maximum performance suggests that the hydraulic coupling had an efficiency penalty at low altitude as compared to a direct coupling. But the advantage of the hydraulic supercharger coupling in reducing pilot load in combat was probably considered an overriding factor.

I am not aware of other explanations of underperformance in the other actual 109E flight tests.

As to the Messerchmitt guaranteed performance, I am somewhat intrigued as it seems serial production 109s with hydraulic supercharger couplings did not meet it (at least at sea level). It would be nice to know the specific conditions (loading, boost etc) that went along with the guarantee, to assess what role it played.

So based on the above a reasonable (serial 109E with hydraulic supercharger) performance is based on the actual flight tests (minus the prototype):

475kmh IAS/TAS at SL 1.35ata 2400rpm
560 kmh TAS at 5000m 1.35ata 2400rpm top speed

1.35ata is 5 min combat limit. It is rather open to debate what effects sustained 1.35ata should have in the sim, what performance 1.45ata should give and whether it should work at all at height (historically it is a takeoff only boost after all).

camber

References for flight tests:

1 http://kurfurst.org/Performance_test...w_109V15a.html
2 http://www.wwiiaircraftperformance.o...109E1-1791.jpg
3 http://kurfurst.org/Performance_test...MP16feb39.html
4 http://kurfurst.org/Performance_test...formanceT.html
5 http://kurfurst.org/Performance_test...109E_J347.html
6 http://www.wwiiaircraftperformance.o...e-109E3-US.jpg
7 http://www.wwiiaircraftperformance.o...E3-Russian.jpg

[IvanK]

Some more grist for the mill

The source is AVIA 6/9352 RAE Performance tests on the bF110 and BF109E
In the UK National Archives

I personally do not think that any plane should be modelled after some specifications. However seeing the dispersion of the test results one wonders why the 109 can only do 450 kph (pre-patch) at sea level and from what I read will do only 467 kph with the new patch.

Seems completely arbitrary to set it to 467.

To my understanding IvanK's graph shows a 109 with Rolls Royce radiators (because the original ones were damaged during the forced landing of the 109?) and which is well below in altitude speed than the French test.

[fruitbat]

pffft, everyone knows the 109E climbed better than an Electric Lightning, turned better than an Albatross, and had super cruise.

[Ernst]

The criticism on the Me flight tests is valid. Then the same criticism should be applied on R.A.E tests of the spitfires and hurricanes too, right?

[von Brühl]

Originally Posted by 41Sqn_Stormcrow

I personally do not think that any plane should be modelled after some specifications. However seeing the dispersion of the test results one wonders why the 109 can only do 450 kph (pre-patch) at sea level and from what I read will do only 467 kph with the new patch.

Seems completely arbitrary to set it to 467.

To my understanding IvanK's graph shows a 109 with Rolls Royce radiators (because the original ones were damaged during the forced landing of the 109?) and which is well below in altitude speed than the French test.

Strange, I can only get 430kph level flight after the patch, anyone else confirm 467? I didn't see the 109s speed in the patch release notes, so thought it hadn't been fixed yet.

354mp/h also seems to agree with the Basic Flight Manual, Military Intellegence, Identification of German Aircraft published in 1942 by the War Department March 11, 1942 (page 16). It lists the 109Fs at 380mp/h.



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Even more reinforcement is the ranges, first I've seen comparative ranges in a time period specification. If it's top speed is truly 470kph, then 322mph in range would have to be diving, and it could hardly dive 540miles without starting in space!

[Kurfürst]

Originally Posted by IvanK

Some more grist for the mill

The source is AVIA 6/9352 RAE Performance tests on the bF110 and BF109E
In the UK National Archives

IMHO that graph illustrates how hopeless is it sometimes to come up with the 'correct' performance figures. All of these tests were performed with the same 109E-3, WNr 1304 by various establishments in varying power and aerodynamic conditions, and they all differ wildly.

[robtek]

I really dont understand this discussion, any 109 not meeting the guaranteed values from Messerschmitt was rejected by the Luftwaffe to be refurbished by Messerschmitt.

Each and every plane had a acception flight to prove it delivered the guaranteed values.

If there should be a deviation from the guaranteed values programmed in game, this deviation must be valid for ALL planes in this sim.

This just says that the 109 performance was quite certainly above the 500 kph minus 5% and would in no way exceed 500 kph plus 5%. But where should be the S/L speed be set for the 109 ingame?

The specification says NOTHING about average performance. The 500 kph is a fully theoretical value and was never meant to reflect real average performance.

I also highly doubt that the average 109 reached 500 kph and all tests indicate that it did not reach this value.

My guess is that the average speed at s/l was somewhere between 475 and 485 kph considering the flight tests.

If the average flight speed was 500 kph one should find flight tests showing individual 109s with speeds ABOVE 500 kph. I have never seen anything like that.

[robtek]

I've seen such a acceptance diagram from Meserschmitt 109's, but i don't know which series it was, anyway the general deviation was about 10 km/h below the guaranteed value, iirc. A few were above, the majority slightly below and five had to be refurbished because they've failed.
Found it: http://www.kurfurst.org/Performance_...catter_web.jpg