DVL data on Bf 109 roll rates

[gripen]

Originally posted by Knegel

what i find to be very strange is that they assume a absolute rigid linkage.
Up tp 60lb stickforce the alreron deflection increase absolute linear with the stickforce(double stickforce = double alerondeflection).

The report claims directly:

"Stick forces for various aileron angles and speeds are given in Fig. 4 where it will be seen that the stick force is roughly proportional to the aileron angle applied, and also follows the 'speed squared law'; there is thus no increase of -Kb2 with speed. This is probably due to the fact that an effort has been made to cut distortion to a minimum, both by using a small rib spacing and by employing a push-pull rod control circuit. The latter is effective mainly by reducing the variation of the upfloat of the ailerons with speed, from 200 mph ASI to 400 mph ASI the upfloat (measured on starboard aileron) was sensibly constant at 1 deg."

And:

"(iv) -Kb2 for the ailerons is -0,11, and does not vary apprediably over the speed range 200 mph to 400 mph EAS or angular range +-10 deg."

The elasticity of the linkage is there and it was measured to be very small ( 1 deg upfloat would mean 0,5 deg for mean aileron deflection assuming upfloat). Notable thing is that FW specification for the aileron movement was 18 deg up and down so the elasticity was actually about same amount as production variation or measurement error.

It should be noted that even the DVL report on the Bf 109F-2 is a bit strange in this respect; the claimed average deflection in the report is 17,5 deg ( ie 23 deg up and 12 deg down) and the measured average deflection with no load was about 15,5 deg. The manufacturers specified average deflection was 17 deg ie 22,7 up and 11,3 down.

In the case of the Spitfire I the report gives the stretch for used stick force range and the loss of aileron movement with 50 lbs stick force was about 2 deg:



Generally you can spend the rest of your life nit picking the data but IMHO that is not purpose of this thread.

gripen

[Knegel]

Hi,

the DLV test dont clain that the 109F had 23 deg up and 12 deg (17,5°) down aleron variation, thats the max range for the measuring instrument.
I only found a max displayed aleron deflection of 15,5°(very slow speed).
With the same stickvariation the 109F lost roundabout 2,7° aleron deflection due to a soft linkage.  

If , like you say, the by the manufacturers specified average deflection was 17 deg, we can assume a loose/worn linkage.

Actually i wonder why they made such tests with a outdated plane in 1944 anyway.

I find it very usefull to discuss this tests to get a better idea of the testresults.  

Greetings, Knegel

[Crumpp]

Notable thing is that FW specification for the aileron movement was 18 deg up and down so the elasticity was actually about same amount as production variation or measurement error.

The specification for FW190 aileron movement is 17 degrees (+-2 degrees).



If you check the aileron adjustment regulation for the FW190 and cross reference for the speed and altitude given in RAE1231 it is easy to see that the ailerons were out of adjustment.   The stick forces are simply out of range and would not have passed the Fiesler Force meter checks.  This is not a linkage adjustment and does not effect the amount of aileron movement.

It adjust the amount of space between the aileron and wing.  In otherwords the aerodynamic balance of the Frise ailerion.  With the adjustment block full forward, you still get 17 degrees of aileron movement.

The adjusting blocks attach to the mounting blocks of the aileron.

Additionally the FW-190 mounted 3 types of ailerons with different hinge axis.





So even though the RAE test pilots noticed something was up with the aircraft:



We can cetainly say that RAE 1231 represents the "at least" performance of an FW190A4 with ailerons in need of adjustment.

Of which aileron type, we do not know.

All the best,

Crumpp

[gripen]

Originally posted by Knegel

the DLV test dont clain that the 109F had 23 deg up and 12 deg (17,5°) down aleron variation, thats the max range for the measuring instrument.

Ah, that's my error, the chart says "gerät", you are correct.

Anyway, the Mtt documentation gives following specs for the ailerons of the Bf 109F:



I have not found tolerances for the 109F but the K had tolerance +1 and -2 up and +- 1 deg 30' down, so apparently 15,5 deg is within normal tolerances.

Originally posted by Knegel

I only found a max displayed aleron deflection of 15,5°(very slow speed).

Hm... let's have look to the chart:



It shows 15,5 deg at zero speed ie no dynamic pressure.

Originally posted by Knegel

With the same stickvariation the 109F lost roundabout 2,7° aleron deflection due to a soft linkage.  

Is there a reason to think that it's not a normal value?

Originally posted by Knegel
If , like you say, the by the manufacturers specified average deflection was 17 deg, we can assume a loose/worn linkage.

Well, you can assume what ever you want but the chart shows logical linear elasticity of the linkage just like Spitfire I chart. In addition, the roll rate chart shows typical logical curve for the frise type aileron and the roll rate values are very close to calculated values in the test. At least I don't see signs of loose or worn linkage nor other problems with structure.

Originally posted by Knegel
Actually i wonder why they made such tests with a outdated plane in 1944 anyway.

That should have been asked from DVL but I don't see a reason why the tested aircraft should not have been in normal condition.

Originally posted by Crumpp
The specification for FW190 aileron movement is 17 degrees (+-2 degrees).

The manual gives +-17 so you are right. I have two separate sources claiming +-18 degrees like chart below (for the A-5), anyway, that's within normal tolerance:

Originally posted by Crumpp
So even though the RAE test pilots noticed something was up with the aircraft:

That has been pointed out several times during this thread and actually I have quoted that in this BBS before you were even member here.

gripen

[Knegel]

Hi,

quote:
--------------------------------------------------------------------------------
Originally posted by gripen

Is there a reason to think that it's not a normal value?

--------------------------------------------------------------------------------

I dont say its not normal, rather i find the assumption of a rigid linkage for the FW190 and Spitfire not normal. At least the FW190 curve got calculated with a rigid linkage.

The soft BF109F2 linkage start to show significant decreasing results above 200mph IAS, with full aleron deflection, but specialy here the picture dont show test results for the FW190. Is there another picture, with testresults with full alerondeflection and/or max stickforces?  

If i see the exact linear max stick deflection roll curve of the Spitfire(normal wing), the Spit wing and linkage must have been absolut rigid.

[gripen]

Originally posted by Knegel

I dont say its not normal, rather i find the assumption of a rigid linkage for the FW190 and Spitfire not normal. At least the FW190 curve got calculated with a rigid linkage.

I don't see such assumption in the RAE reports. Given the claimed 1 deg upfloat in the case of the Fw 190, such small elasticity (smaller than normal production variation) is difficult to see from the graphs and also difficult to calculate out from the rough charts. They measured it and I don't see a reason why they should have not included it.

Originally posted by Knegel
The soft BF109F2 linkage start to show significant decreasing results above 200mph IAS, with full aleron deflection,

Actually the full aileron deflection curve is a calculation and the full stick deflection curve is a calculation as well.

Originally posted by Knegel
but specialy here the picture dont show test results for the FW190. Is there another picture, with testresults with full alerondeflection and/or max stickforces?  

It shows test points and upfloat was measured as noted in the report. You have got the all the data I have on these tests and the field is open for your own search. These tests are so far the best instrumented and documented data I have found (since early nineties). But there might be better stuff out there, so why don't you just start start digging instead nit picking?

Originally posted by Knegel
If i see the exact linear max stick deflection roll curve of the Spitfire(normal wing), the Spit wing and linkage must have been absolut rigid.

The Spitfire V reached the force limit at so slow speed that bending is not particularly visible; there appear to be some bending but the Fig.6 is rough anyway. And based on measurements on the Spitfire I, the Spitfire seem to have a somewhat more rigid aileron linkage than Bf 109F.

We do know that:

"This course has been adopted in Fig.6 which shows the results obtained for the F.W.190, Mustang, Typhoon, and Spitfire V (metal covered ailerons) with both standard and clipped wings. On all these aircraft instrumental records of rolling performance have been obtained at the R.A.E, similar to those under discussion for the Fw 190."

So all these planes were tested same way and the elasticity (wing and linkage) was measured and I don't see a reason why these should have not been included to the curves.

gripen

[Knegel]

Oh,

you have problems to believe that the SpitVa wing and linkage was normal standard, but you dont have problems to believe that the Spit in the NACA comparison have absolute rigid wings and linkage up to 207mph and that the FW190 had a absolute rigid linkage as well??

"I don't see such assumption in the RAE reports. Given the claimed 1 deg upfloat in the case of the Fw 190, such small elasticity (smaller than normal production variation) is difficult to see from the graphs and also difficult to calculate out from the rough charts. They measured it and I don't see a reason why they should have not included it."

Yes, they claimed this, but made tests mainly only with around 5°(+/-3°) alerondeflection. Nevertheless they did insert a linear line, and calculated the 50lb roll performence out of the roll result with smal alerondeflection and the aleron effectiveness.

With only5° initial aleron deflection(4,5° constant stickdeflection) the Me109F2 also only lost roundabout 0,8° between 200 and 400mph IAS.
With 12,2° initial aleron deflection(11,8° constant stickdeflection), the different was already 2°!!

And also very important to know is that the softness of the linkage have most influence below 200mph!!

And even if we believe the testers, and the FW190 was that stiff all over, a 0,5° reduction of alerondeflection would let decrease the max roll rate to 157°/sec!!

You can call this nit picking, but i saw already many so called test results, where the testers made mistakes(one very nice, well known, is the RAE turnperformence comparison, 109E3 vs Spit1, where the result was calculated only by the wingload).

If we wanna get a credible conclusion out of all tests, we need to understand how the testers got the results and if they made mistakes.

We are not in a church, we can understand this tests and we can see mistakes. To believe results like they are, without to understand the used procedure, dont seems to be logical to me.

Iam gathering flight tests, but as you know, there are only a few roll performence tests available. I already was in some german museums, but dont found more than i already had.

Greetings, Knegel

[gripen]

Originally posted by Knegel

you have problems to believe that the SpitVa wing and linkage was normal standard,

As noted several times the NACA test on Spitfire V shows unlogical shape of the roll rate curve.

 

Originally posted by Knegel
but you dont have problems to believe that the Spit in the NACA comparison have absolute rigid wings

No, as pointed out above several times with RAE data and quote, the conclusion by NACA was simply wrong. Besides NACA choosed to use RAE data for their later works.

Originally posted by Knegel
and linkage up to 207mph and that the FW190 had a absolute rigid linkage as well??

No, as pointed out several times above the report clearly states that upfloat was measured.

Originally posted by Knegel
Yes, they claimed this, but made tests mainly only with around 5°(+/-3°) alerondeflection.

No, as pointed out above, the measurement range was roughly from 2,5 to 14 deg.

Originally posted by Knegel
And even if we believe the testers, and the FW190 was that stiff all over, a 0,5° reduction of alerondeflection would let decrease the max roll rate to 157°/sec!!

At least I can't read the grahs with such accuracy that I can find reliably  5 deg differences ( note that I have used pretty much allways rough values during this thread).

Originally posted by Knegel
You can call this nit picking, but i saw already many so called test results, where the testers made mistakes(one very nice, well known, is the RAE turnperformence comparison, 109E3 vs Spit1, where the result was calculated only by the wingload).

I have not seen such RAE test, the RAE report on the AE479 contains flight tested Clmax data which was used for comparison calculations. Maybe you should start a new thread on that topic?

Originally posted by Knegel
Iam gathering flight tests, but as you know, there are only a few roll performence tests available. I already was in some german museums, but dont found more than i already had.

Happy hunting! Hopefully you have enjoyd the stuff I gave to you.

gripen

[niklas]

Originally posted by gripen
As noted several times the NACA test on Spitfire V shows unlogical shape of the roll rate curve.

gripen

I disagree. In case you think there happened too much elasticity: Remember the chart is for 6000ft only. Density in 6k is higher than in 10k, so stress on the ailerons is higher, thus more tension.

Does a plane roll faster or slower at lower alt? I expect at least a faster roll acceleration, in case of banking tests i expect it to roll faster after all.

It only looks so strange because high stickforces are reached already at verly low speeds. Normally you would expect a decrease of rollrate when max. stickforce is reached to achieve max. deflection, the SpitV in this test was able to roll still a bit faster when reducing stick deflection due to force limit. But the same can be observed in the naca868 chart (F6F-3, or P47-C being at the peak).

When the constant rollrate curves in fig.28 reach a minimum, then there is the point reached where a further increase of speed will result in an decrease of rollrate, when a max. constant  stickforce is given. This is for high stick deflection somewhere between 190-220mph and fits nicely to the RAF Measurement


niklas

[gripen]

Originally posted by niklas
I disagree. In case you think there happened too much elasticity: Remember the chart is for 6000ft only. Density in 6k is higher than in 10k, so stress on the ailerons is higher, thus more tension.

Feel free to disagree but my speculation is based on assumption that the elasticity might change the leverage to the worse direction.

Originally posted by niklas
Normally you would expect a decrease of rollrate when max. stickforce is reached to achieve max. deflection, the SpitV in this test was able to roll still a bit faster when reducing stick deflection due to force limit. But the same can be observed in the naca868 chart (F6F-3, or P47-C being at the peak).

The shape of the curve is completely different if compared to the RAE measurements.

Originally posted by niklas
When the constant rollrate curves in fig.28 reach a minimum, then there is the point reached where a further increase of speed will result in an decrease of rollrate, when a max. constant  stickforce is given. This is for high stick deflection somewhere between 190-220mph and fits nicely to the RAF Measurement

Hm... deflection is not particularly high at 190-220 mph IAS with 50 lbs, the right roll about 1,2 rad/s at 200 mph IAS ie about 69 deg/s (using Spitfire I charts, separate for left and right) which means roughly 60% deflection and the left roll might be around 1,3 rad/s ie 75 deg/s which means roughly 75% deflection. The RAE data gives full deflection at 200 mph IAS at 10k ie 105 deg/s and the fig. 28 indicates that full deflection would have needed around 80-100 lbs at 6k. I don't see a good fit here, density difference between 6k (about 1,02 kg/m3) and 10k (about 0,9 kg/m3) does not explain the difference. At higher speeds the curve seem to come close RAAF data ie at low deflections there appear to be better fit and also the fig. 28 seem to give normal shape of the roll rate curve at low deflections.

Anyway, feel free to believe what ever data you prefer.

gripen

[Knegel]

Originally posted by gripen
As noted several times the NACA test on Spitfire V shows unlogical shape of the roll rate curve.
gripen

Who say that the shape is unlogical? Its different to later Spits, but it show a similar shape like many other planes(F6F, F4F, P47). And as i pointed out before, it looks like a different leverage(geometry of linkage).

Originally posted by gripen
No, as pointed out above several times with RAE data and quote, the conclusion by NACA was simply wrong. Besides NACA choosed to use RAE data for their later works.
gripen

Conclusions and testresults are two different pair of shoes. We have measured curves for both spits, the conclusion that the wing was rigid was probably wrong, but not the measured curve.

Originally posted by gripen
No, as pointed out several times above the report clearly states that upfloat was measured.

Originally posted by gripen
No, as pointed out above, the measurement range was roughly from 2,5 to 14 deg.
gripen

Yes, but they only have 1 measured point at 14° and 1 at roundabout 11°, all over they display only 30 points, most of them are with around 5°(+-3) aleron deflection.
There is no way to get results with high aleron deflection out of the testresults!

Originally posted by gripen
At least I can't read the grahs with such accuracy that I can find reliably  5 deg differences ( note that I have used pretty much allways rough values during this thread).
gripen

We dont need to calculate to see that they dont took the 'soft' linkage into account, we see a absolute linear behaviour in their 'Stickforce/aleron' graphic, growing up from the zero point.  

Originally posted by gripen
I have not seen such RAE test, the RAE report on the AE479 contains flight tested Clmax data which was used for comparison calculations. Maybe you should start a new thread on that topic?
gripen

Compare the results of the resulting calculated min radius with the wingload relation and you will see it fit. The Clmax relations for sure vary much from the wingloadrelations.
http://mitglied.lycos.de/luftwaffe1/Carson/Carson.html
You can open a new theatre if u want, i dont see the need.
 

Originally posted by gripen
Happy hunting! Hopefully you have enjoyd the stuff I gave to you.

gripen

For sure i enjoy it, same like the discussian with you! Thank you very much!

Greetings, Knegel

[gripen]

Originally posted by Knegel
Who say that the shape is unlogical? Its different to later Spits, but it show a similar shape like many other planes(F6F, F4F, P47). And as i pointed out before, it looks like a different leverage(geometry of linkage).

Hm... no other plane shows roughly 40% stick force decrease for given rate of roll when the speed increases. The P47 curve show slightly increased (say 1-2%) roll rate after the force limit is reached before it starts to decrease. The curves of the F4F and F6F seem to show just the wing twist because the original curves were for 30 lbs stick force, it should be also noted that F6F curve is for spring tab ailerons.

Notable thing is that none of the many RAE measurements on Spitfire with various type of ailerons nor RAAF measurements show this kind of curve.

Originally posted by Knegel
Conclusions and testresults are two different pair of shoes. We have measured curves for both spits, the conclusion that the wing was rigid was probably wrong, but not the measured curve.

I wonder why you just keep repeating that rigid wing argument? Only source which claims rigid wing is NACA report on Spitfire V and that claim is errorneous as pointed out several times. All RAE data mentioned here assumes wing twist which is calculated from the tested roll rates. If the RAE data had been derived from rigid wing values, the roll rate curve would have shown well over 120 deg/s at 200 mph EAS.

Note also that in the RAE reports the curve for the rigid wing is calculated from the measured results so there is simply no logic in your argument.

Originally posted by Knegel
Yes, but they only have 1 measured point at 14° and 1 at roundabout 11°, all over they display only 30 points, most of them are with around 5°(+-3) aleron deflection.
There is no way to get results with high aleron deflection out of the testresults!

There is a simple way, just the same as used by DVL, values can be extrapolated with good enoug accuracy.

Originally posted by Knegel
We dont need to calculate to see that they dont took the 'soft' linkage into account, we see a absolute linear behaviour in their 'Stickforce/aleron' graphic, growing up from the zero point.  

The results show roughly linear increase of stick force  (despite the scatter) so linear assumption is not far off. You can test it your self, just fit the lines to data.

Originally posted by Knegel

Compare the results of the resulting calculated min radius with the wingload relation and you will see it fit. The Clmax relations for sure vary much from the wingloadrelations.

I wonder what do you mean, the RAE results are based on measured Clmax data (flight tested for both planes with similar instrumentation) not just wingloading. Please, read the report and open a new thread if you like to argue.

gripen

[Knegel]

Originally posted by gripen
Hm... no other plane shows roughly 40% stick force decrease for given rate of roll when the speed increases. The P47 curve show slightly increased (say 1-2%) roll rate after the force limit is reached before it starts to decrease. The curves of the F4F and F6F seem to show just the wing twist because the original curves were for 30 lbs stick force, it should be also noted that F6F curve is for spring tab ailerons.

Notable thing is that none of the many RAE measurements on Spitfire with various type of ailerons nor RAAF measurements show this kind of curve.
gripen

Yes, no other Spit did show this curve cause they had a other leverage(linkage geometry) so they didnt show this curve, cause the point of max stick deflection was at much higher speeds. Its also possible that they made other, aerodynamical variations on the alerons on later Spitfires, to arcive a other performence. The SpitVa test state why the stickforce decrease with increasing roll speed.

Originally posted by gripen
I wonder why you just keep repeating that rigid wing argument? Only source which claims rigid wing is NACA report on Spitfire V and that claim is errorneous as pointed out several times. All RAE data mentioned here assumes wing twist which is calculated from the tested roll rates. If the RAE data had been derived from rigid wing values, the roll rate curve would have shown well over 120 deg/s at 200 mph EAS.

Note also that in the RAE reports the curve for the rigid wing is calculated from the measured results so there is simply no logic in your argument.

In this case i didnt repead anything, i just was telling that the wrong conclusion, regarding the rigid wing, dont make the measurement wrong.

Originally posted by gripen
There is a simple way, just the same as used by DVL, values can be extrapolated with good enoug accuracy.

The DVL made roundabout 50 testpoints only for 11,8° stick deflection, 50 points for 7,6° stick deflection and roundabout same number of measured points for 4,5° stickdeflection. From this resulting directly measured lines its not difficult to calculate the 15° stickdeflection results! If the DLV would have had only the 4,5° stickdeflection results, they dont would have been able to know what happen at higher aleron deflections!

Originally posted by gripen
The results show roughly linear increase of stick force  (despite the scatter) so linear assumption is not far off. You can test it your self, just fit the lines to data.

 
I dont know where do you see this, the test results are in most cases far away from the concluded line, we even could assume lines.


This entry fit in the same way to the measured points like the assumed linear entry´s.

Originally posted by gripen
I wonder what do you mean, the RAE results are based on measured Clmax data (flight tested for both planes with similar instrumentation) not just wingloading. Please, read the report and open a new thread if you like to argue.

gripen

Strange, so the CLmax of the Spit and 109E was the same, what a odd luck.

Greetings, Knegel

[hitech]

Im trying to think why cable stretch would have any impact on roll rate.

The only time I can see it change the roll rate , is if the stick is limited by full throw and not by force. If it is just limited by stick force then the same force would still be at the ailaron no mater how much the cable streatches, only the stick would move slightly further. But the angle of the ailaron would still be the same.


HiTech

[Kurfürst]

I don't think it's cable stretch either. Altough in gripen's world it's possible that even metal connect rods - like on the 190, 109 or P-47 - would stretch, for the rest of us it seems quite unlikely - even the NACA report that gripen appearantly didn't read before qouting from it states that calbe stretch is not really a factor for fighter sized aircraft, rather more of an issue with bombers etc.

I'd believe though the reason for more limited deflection is the wing twist. If the wing bents a bit, the distance the rod has to cover between the aileron and the stick will change, and this may well effect the amount of aileron deflection vs. stick deflection.