That is a standard assumption in aircraft performance for power producers. It assumes a good propeller design.

The data listed below is peak efficiency which is a small part of the advance ratio curve. When you average out the entire curve, it comes out to ~.8 for a well designed propeller.

Crumpp your Spitfire V 109 acceleration chart is I presume 1G flight ?

Yes

Thanks!

Ok then its straight line running not sustained turn performance. So wrt your comment :

"If the Bf-109E3 maintains his trim speed of 400 kph, he is tough customer for a Spitfire to deal with." I respectfully disagree. Obviously I prefer to accept the RAE's views rather than yours.

WRT the sustained turn performance based on RAE computation at 12000ft, 400Kmh/248mph (TAS). The Spitfire can sustain 2.95G giving an approximate sustained turn rate of around 14.0 deg sec. The 109 on the other hand can sustain only 2.3G giving an approximate turn rate of 10.5deg sec.

So according to the RAE The Spit at 12,000ft/400Kmh TAS has 0.65G sustained G advantage over the 109 and 3.5 deg sec sustained turn rate advantage. Thats a nose position advantage of just on 119degrees in a single 360 degree turn. Sustained turn radius wise the Spitfire is around 526ft smaller to boot. So based on RAE calculations the 109 is not so "tough a customer at 400Kmh" in any turn fight.

A 109 Pilot in this engagement is just going to watch the Spitfire translate aft in his canopy until he ends up nose in lead with guns firing. Best option for the 109 (imo) is as soon as he sees the aft translation back through his 3/9 line to ease off on the G (maybe holding the bank on for deception) extend (using his superior 1G Ps) then transition into a climb, get the separation he needs and come back into the fight at a later point..... and that sort of thing is exactly what the good On line 109 drivers do.

Ties in with the Historical record and what we see On line every day.

Well IvanK, had RAE chosen the lowest available speed and max lift coefficient values for the Spitfire and the highest available speed and max lift coefficient values for the 109, at the altitude which is most favorable for the 109, their results would have agreed with Crumpp's :)

Ironic mode off: Why waste time with obviously deeply biased stuff? Just google with keywords: Crumpp Spitfire calculation. You will get thousands of hits from the several sim forums over the past few years, I think he has produced enough text and calculations for several books.

Apparantly, you can't even read your own tables..

Column 12, "Airscrew effiency" from flight results, at 18 000 feet:

Rotol RA 611 0.924 = 0,800
Rotol RA 621 0.920 = 0,805
Rotol RA 600 0.911 = 0,785
Rotol RA 640 0.940 = 0,800

... besides the fact that NZTypoon has reading comprehension problems, there's also the fact that the above values are only true for 18 000 feet altitude and max. speed level flight of about 365 mph.


Instead, RAE has picked the lowest available speed and max lift coefficient values for the 109 and the highest available speed and max lift coefficient values for the Spitfire, and so they have arrived at the results they did.

What all people seem to forget that the results in all these calculations are deeply rooted in the source base data, and since there is a great deal incertainity in those, the results tend to diverge quite a bit.

I just recalled I still have my near three year old turn performance estimate spreadsheet. I attached it, so anyone interested can produce charts to their likings. I've added some 109 E and Spitfire I data, feel free to use your own data sets. If you have any questions, just ask.

Thanks, this is very usuful.

I fooled around with the specs a bit, with best/worst case data in bost cases, but interestingly the tables keep showing that the 109E is evening things out in turn and then having an advantage at and above around 400 km/h.

Math is just too impartial I guess.

The only way to change that would be using 100 octane performance for the Spitfire I, giving it a level speed similar to the 109. Or go to high altitude, were Spitfire and 109 are always fairly close in terms of speed. Other than that, 30ish extra km/h is quite a bit.