DVL data on Bf 109 roll rates

[LRRP22]

Originally posted by Kurf�rst
You should read the first graph BTW, the thick line (ymax=15) shows the roll rate at 15degrees stick deflection in radians.

Isegrim,

Wouldn't the measured performance data provide a more accurate picture than the calculated data?

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[Kurfürst]

It isn`t calculated, it`s extrapolated from measured data for max deflection.

[LRRP22]

Originally posted by Kurf�rst
It isn`t calculated, it`s extrapolated from measured data for max deflection.

Ah, okay.  Any ideas why max deflection wasn't measured?

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[Kurfürst]

IIRC the test plane had to be given back or it was destroyed, something like that. The report is concentrating on theoretical study about wing flexing effecting roll rate, via a practical example, so it wasnt the main thing - I guess the 109F roll rate wasnt someting new to them in 1944. DVL was (is) the German equivalent of NACA.

[Knegel]

Originally posted by Kurfürst
Out of curiosity, how did you convert TAS to IAS, with what variables?

I am still not sure if this is IAS or TAS.
It`s pretty hard to be sure given the rought Mach/kph scale, and that it`s quite effected by tempereture, humidty and altitude...

Simply there`s too much margin for error.

Hi,

here is a nice true airspeed calculator: http://www.csgnetwork.com/tasinfocalc.html

Its for sure TAS! Look to 600km/h (lower picture), its close to Mach 0,5. If the km/h would be in IAS, it would be 708km/h TAS, but thats a 'bit' more than mach 0,5 (Mach1 in air is roundabout  1220km/h, depending to the temperature).

Greetings, Knegel

[gripen]

Originally posted by Kurfürst
I guess another myth died today.

Hm... The data actually confirms what is allready known about the aileron characters of the Bf 109 ie the forces and effectiveness are normal at low speeds but at high speeds the forces are very high.

At 3000 m (about 10k) the TAS value is roughly 20% higher than IAS value depending on conditions. As an example 400 mph IAS is about 770 km/h TAS. If some body want's to make comparison with the NACA data, the speed should be converted to IAS and mph and stick force should be converted to 50 lbs.

Also it should be noted that the calculated peak roll rate of this particular plane was about 80 deg/s  when elasticity of the wing and linkage was counted.

gripen

[niklas]

charts are for an 109F2. Would be interesting to know whether later wings were stiffer.

In any case the 109 can hold it´s own against contempory fighters, comparing this chart to NACA chart for example

niklas

[Angus]

Later wings of the 109 went stiffer I think,- so less twisting.
As the engines went more powerful, rolling into the torque would also become heavier.
As you would not trim the plane at any speed to balance the torque (outside trim), there is a certain speed where the aircraft rolls rougly equally into both directions. So, with ultimate power/speed it will need a boot on the rudder to keep it level, and to apply more force in one direction, and less in the other.
The airscrew pumping out 1000-2000 hp will definately give some aid or trouble to a human arm working to haul a 2-3 tonne aircraft from one side to the other.
So is the chart an avrage figure, - or isn't there so much difference between left and right at all?
Just me....

[Squire]

Well, the 109F-4 wont do 400 TAS at 10k in level flight, but...

Took up a 109F-4, 10k, 400 TAS (from a 2k dive), rolls 180 degress in @ 2-3 seconds.

So if somebody could let me know what all the fuss is about later, that would be cool. The film does not show fractions of seconds, so you have to guesstimate.

Go ahead and see for yourselves.

Has to be a myth 1st before it can die. Personally I have never heard of the 109 being unable to roll well at 400mph at a low alt like 10k. A6M5 Zero maybe...

[Angus]

Just the 109E model had problems rolling at high speed AFAIK.
At really high speeds all controls grew heavy on later models, but all in HArmony.  

[Squire]

Upon seeing some of the other charts it would seem that you need a set value of stick force pounds to compare properly, but like I say, the 109F-4 rolls very nicely from my tests. Maybe somebody else can do a better analysis.

[Charge]

"but the metal aileroned Spitfires easily roll better then the Bf109s"

I wonder where that claim comes from?
Hmm, which of them suffered more of wing flexing?
Did the Brits manage to build a large and rigid wing?
Small wing is more rigid and that is what was an advantage in German fighters. But then again the wingloading was high.

Wing flexing works against roll rate, U know....

-C+

[Nashwan]

Originally posted by gripen
Also it should be noted that the calculated peak roll rate of this particular plane was about 80 deg/s when elasticity of the wing and linkage was counted.

Do you mean the highest line on the chart,  the extrapolated one that peaks at 1.6 rad, about 90 degrees, doesn't take account of wing flexing?

[justin_g]

Charge: Karnak was talking about the aircraft as they perform in AH, not any real life data.

[Karnak]

Originally posted by justin_g
Charge: Karnak was talking about the aircraft as they perform in AH, not any real life data.

I was, but Allied tests from WWII found the same thing.  The metal aileroned Spits handily outrolled the captured Bf109s in their tests.  The question is, were those Bf109s in good enough condition to make the tests valid?  The fabric aileroned Spits (Mk I, Mk II, early Mk V) rolled very much worse than the metal aileroned Spits and there was little to choose between a Bf109E and Spit I in the roll.  Both had serious defiencies in that area.  The Bf109F and metel aileroned Spitfires both improved roll performance over their predecessors, however the both still had problems at higher speeds.

The wing twisting that Charge was refering to is something that plagued the Spitfire until the wing was redesigned in the Spitfire F.21.  That was mostly a problem at higher speeds though and at lower speeds the Spitfire's roll rate was unimpeded.  You can feel the model of this in AH when the Spit's roll rate goes to crap above 350mph to the point where you can't really roll at all at 500mph or above.