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