K-4 Flettners

[Kurfürst]

Originally posted by gripen
AFAIK only one Spitfire was tested with geared tab ailerons (Flettner tabs), late Spitfires and Tempests had spring tab ailerons which are quite bit different.

gripen

Hmm, when I said flettner on the spits, I meant that afaik the mkxiv had a double tab on the rudder, one working as flettner and the other as trim tab. Or was it combined? Certailnly I do not remember flettner tabs on the ailerons for wartime spits. Perhaps they were concerned of the wing flex issue.

agent 009, there`s a report on spitxiv vs. tempest v roll rate, it says the latter is better above 350mph. same is said in comparison of 109G2, though the report notes they were afraid to use the ailerons fully on the 109.

I have some roll reports for the tempest v with spring tabs, it`s pretty good at high speed - 80 deg/sec iirc at 350mph.

Back on flettners, it was perhaps because they were not so essential for the 109. all 109G vets I talked about are telling me about the ailerons remaining relatively light even in dives.. perhaps some help would be nice, as it`s clearly indicated by the drawings, manual and individual examples that they meant Flettners on the ailerons, but delays were accepted.

[justin_g]

I don't know if this quote refers to the exact same design of tab as seen fitted in the photos above, but here is a quote from Heinrich Beauvais regarding Flettner tabs on the 109's ailerons:

Flight controls

    One would have liked to have more effective ailerons, as well as lower control forces, at high speeds. I do not remember all the different methods tried to improve this, but the following two are still clear in my mind. One was designed by Blohm & Voss, adding a Flettner trim tab which resulted in a reduction of control forces: however, performance was not as smooth and effectiveness had not improved at all. A later form was the 'Keulenquerruder' (a shape of aileron tested at Memmingen in 1944) which had seemed promising, but had never been introduced. The rudder had no trim: it was 'ironed out' especially for the dive and produced fairly high aerodynamic forces during the climb. Nevertheless, it seemed the best of compomises: a spring to counteract the strong forces during the climb was considered, but never incorporated.

From "Test Pilots" by Wolfgang Späte(English language edition)

[MiloMorai]

justin,

your quote of Beauvais will be ignored.

One was designed by Blohm & Voss, adding a Flettner trim tab which resulted in a reduction of control forces: however, performance was not as smooth and effectiveness had not improved at al

[Kurfürst]

Flettner tab of course doesn`t improve aileron effectiveness.

Aileron effectiveness is an aerodynamic term and refers to the degree of roll rate achieved per degree of aileron deflection.

A Flettner tab reduces the force required to deflect the aileron, therefore it helps achiving more deflection at high speeds where stickforces could prevent deflecting the ailerons.

Therefore adding a Flettner improves roll rate at high speed by allowing higher aileron deflection angles and not by enchancing the roll rate per deflection angle (=aileron effectivness).

[Angus]

Well, Kurfie has it as I thought, - at high speed the aileons are more effective. 109 trying to be 190, hehe.
Anyway, this got stuck in my head:
"At a corrected speed of 770 kph (.75 Mach at the test altitude), Test pilot Willemsen was able to get the ailerons to travel to 2/3 of their available range (no approx. force required is mentioned), forces were the same to either side, and there was no overbalancing observed. "

That aircraft was then perhaps balanced (rudder trim) to something near that speed, or to high speed anyway, since otherwise it would roll better with the engine torque than against it.

The 109 was told to be delightfully balanced in the roll plane at low speeds, - did the Flettners simply trade that off to better performance at high speeds?

[Kurfürst]

Well, theoretically adding Flettners decreases the aileron surface and thus they should decrease roll rate at the same deflection... but this change is so small that it can be safely neglected.

The drawing of the 109K wing shows 504mm x 54mm Flettner area, total area of the aileron is 1465 x 298.... what`s that 1/3 x 1/6 = 1/18 decrease in area.. ~5%.

So if it`s linear and we take the 109`s roll rate of ca 90 deg/sec at 450 kph, it`s about 85degrees w. Flettner... you won`t notice the difference withing production standards, but the stickforce is even lighter and the roll can be initiated more quickly, more important imho than the peak roll rate for a sudden evasion.

[Angus]

Decreasing aileron surface is the drawback, right?
But the true effect is aerodynamic, at high speeds especially?
So, as with wing loading, large ailerons are most effective at rather low speeds, as low wing loading shines at lower speeds, right?
So, you trade off some low speed roll rate which for the 109 is :
A) A good deal, for it already has quite good roll characteristics at low speeds.
B)It badly needs better roll rate at high speeds and those can be aquired whith this method.

Basically emulating the 190 a bit, - which is the natural rollmaster of WW2.

[gripen]

Originally posted by Kurfürst

The drawing of the 109K wing shows 504mm x 54mm Flettner area, total area of the aileron is 1465 x 298.... what`s that 1/3 x 1/6 = 1/18 decrease in area.. ~5%.

Hm... Flettner area is away from the most effective area of the aileron ie the trailing edge.

gripen

[agent 009]

Tommy Hayes followed a 109 in his Mustang over Berlin in a high speed dive. The 109 veered away ( can't remember right or left ), & Hayes mentioned he couldn't follow. Hayes ended war with 10 kills & was no beginner. This from an interview from one of the big aviation mags. haven't got it at hand, but remember well this part.

Being over berlin, the wing tank full argument is out. This would tend to support the airelon still good at high speed for 109 thinking.

[Kurfürst]

Originally posted by gripen
Hm... Flettner area is away from the most effective area of the aileron ie the trailing edge.

gripen

If a Flettner is so bad gripen, why is used on so many planes, huh? I guess the gains more than outweight the losses.

[gripen]

Originally posted by Kurfürst
If a Flettner is so bad gripen, why is used on so many planes, huh? I guess the gains more than outweight the losses.

Please, don't put words to my mouth; I have not said if the geared tabs are good or bad. There were several planes with geared tabs in ailerons which worked well (say Fiat G. 50 and P-39) but apparently installation in the Bf 109 was not particularly succesfull (based on comment by Beauvais and the manual claim that the tabs were locked).

gripen

[MiloMorai]

Originally posted by Kurfürst
If a Flettner is so bad gripen, why is used on so many planes, huh? I guess the gains more than outweight the losses.

How many of each model of the 109 had operating aileron Flettners?

If they were as great, as you would like us all to believe, then why were only ~200 out of the ~1700 K-4s built have them? That is only ~12%.

gripen, comments by Beauvais will be ignored as it is in conflict with his uber German agenda.

[justin_g]

1. We still don't have any "official" reason for why the Flettners were locked(as per the K-4 manual). We need the document saying "Flettner tabs are to be locked because of reason X" if we want to know why they were locked, at the moment we are speculating based on anecdotes and guesswork...

Originally posted by Kurfürst
Well, theoretically adding Flettners decreases the aileron surface and thus they should decrease roll rate at the same deflection... but this change is so small that it can be safely neglected.

The drawing of the 109K wing shows 504mm x 54mm Flettner area, total area of the aileron is 1465 x 298.... what`s that 1/3 x 1/6 = 1/18 decrease in area.. ~5%.

So if it`s linear and we take the 109`s roll rate of ca 90 deg/sec at 450 kph, it`s about 85degrees w. Flettner... you won`t notice the difference withing production standards, but the stickforce is even lighter and the roll can be initiated more quickly, more important imho than the peak roll rate for a sudden evasion.

2. I can't find any exact figures for this type of tab, but I think that the reduction in roll rate at low speeds (where full aileron deflection can be reached) could be more than 5% with Flettner tabs. For example if you look at page 184 of NACA Report 868 there is a graph(figure 70) for the F6F with spring tabs, which shows about 13% loss of rollrate at 200mph(but at 400mph, the tabbed ailerons give 70% improvement!)

Although as you can see, the massive improvement in roll-rate at high speed is certainly worth the reduction at low speed.

[Kurfürst]

Originally posted by MiloMorai
How many of each model of the 109 had operating aileron Flettners?

If they were as great, as you would like us all to believe, then why were only ~200 out of the ~1700 K-4s built have them? That is only ~12%.

gripen, comments by Beauvais will be ignored as it is in conflict with his uber German agenda.

MiloMoron, you usual hysteria aside, can you tell us how you arrived at 'only' 12% figure ie. 200 109Ks having aileron Flettners?

Unfurtunately, I fail to see what`s an, what was the word 'uber German agenda' in discussion the various improvements done to an aircraft. One would think that to you, even mentioning that there were improvements done to German aircraft, gives you a heart attack and starts a berserker rage...You should really moderate yourself.

[Kurfürst]

Originally posted by justin_g
2. I can't find any exact figures for this type of tab, but I think that the reduction in roll rate at low speeds (where full aileron deflection can be reached) could be more than 5% with Flettner tabs. For example if you look at page 184 of NACA Report 868 there is a graph(figure 70) for the F6F with spring tabs, which shows about 13% loss of rollrate at 200mph(but at 400mph, the tabbed ailerons give 70% improvement!)

Although as you can see, the massive improvement in roll-rate at high speed is certainly worth the reduction at low speed.

I can very much agree with you about speculation and guesswork.. it would be nice to work with some hard data! One guesswork I can come up with is that probably the Nov 1944 trials with Flettners were in connection with the 109K, already in service, so perhaps they did not have enough data to know the effects, and were careful.

Have Beuvuais and Spaete more to say on the subject?

On point 2, what was the execution of the spring tabs and the type of ailerons on the F6F? As iirc gripen noted, spring tabs and flettners work differently, though from what I recall they are quite similiar (it`s been long time since I read 868 and I gotto run now) - therefore the effect may vary with ailron type, tab type and area...