DVL data on Bf 109 roll rates

[gripen]

Originally posted by Knegel
Of course we have! Look to the Stickforce/alerondeflection and pb/2V curve, for ecxample.

The charts show simply that at low speeds roll rate is about that what it should be. When the speed rise, the roll rate curve starts show unlogical shape ie the stick force decrease about 40% for given roll rate when the speed increases. Basicly the shape of the curve speaks about problems (stretch or something else) not about properly made mainteance.

Originally posted by Knegel
Who care who realy made this tests, on the 50lb datasheat i can read NACA, and i was talking about this tests.

No one understands you if it's unclear what test you mean.

Originally posted by Knegel
Aha, so there are more datas regarding the Spitfire in the 50lb comparison??

As has been told earlier, these come from RAE tests on Spitfire I, which have basicly same wing and same aileron movement.

Originally posted by Knegel
The testers gave a clarification why the curve look that strange, later spits had a different leverage setup.

The testers simply tell the results, the leverage change is your speculation.

Originally posted by Knegel
Once you say they found at least 0,5° variation(aleron deflection) and then you say the linear lines are not bad??

I have no idea what you are trying to argue.

Originally posted by Knegel
Wake up, 60mph smaler speed of max stickdeflection!!

I wonder if you have missed all written so far in this thread; I'm looking for sensible explanation and I can't find any sense from your writings.

I can see from the graphs that the problem existed only with combined high stick forces and large deflections. The stretch fits well here because it happens due to high stick forces and the differential linkage fits also well here because it explains the problems in high deflections.

gripen

[Knegel]

Hi,

so you use Spit1 datas, where the alerons was different and maybe the linkage too, to explain the 50lb curve?? Nothing to add here.

I dont know what you did learn, but a stretched linkage result in smaler aleron deflection, so far so good, but also in a higher speed of max stickdeflection. There is NO way that a strech can result into a decreased speed of max stickdeflection.

My assumption is same logical, like if conclude out of the weight and performence datas of the 109E and 109G, that the 109G must have had more thrust.

Thats not a speculation, thats basic knowlege of the physical law, in our case knowledge of the leverage law.  
 
If there would be a unexpected high strech, specialy the differential linkage would keep the leverage relative high, therfor the speed of max stick deflection would increase even more, but the tests show a decreased speed of max stick deflection.

A to extreme differential linkage, where smal aleron deflection need very smal stickforces but high aleron deflection need much much more stickforces explain the testresults (5 times higher stick force to aquire full delfection than half deflection). This also explain the strange curve.

Greetings, Knegel

[gripen]

Originally posted by Knegel

so you use Spit1 datas, where the alerons was different and maybe the linkage too, to explain the 50lb curve?? Nothing to add here.

The aileron movements and areas are the same. If there is a difference (increased rigidity or something), it would make Spitfire V roll relatively better.

Originally posted by Knegel
I dont know what you did learn, but a stretched linkage result in smaler aleron deflection, so far so good, but also in a higher speed of max stickdeflection. There is NO way that a strech can result into a decreased speed of max stickdeflection.

Actually it can if the control force is wasted to bend or stretch something inside linkage instead moving the ailerons. And the change of the relative movement of the ailerons can also change forces for given mean deflection.

Note that NACA did not actually record position of the ailerons during flight (only stick position) and they actually claim flexibility in the aileron control system.

Originally posted by Knegel
Thats not a speculation, thats basic knowlege of the physical law, in our case knowledge of the leverage law.  

Actually assuming changed leverage (or geometry) is speculation because many other things can have same effect ie progressively increasing control force. There is evidence on poor condition of the plane but no direct evidence on changed geometry.

Note that NACA claim almost linear rise of the aileron effectiveness just like RAE measurements up to about 250 mph EAS

Originally posted by Knegel
A to extreme differential linkage, where smal aleron deflection need very smal stickforces but high aleron deflection need much much more stickforces explain the testresults (5 times higher stick force to aquire full delfection than half deflection). This also explain the strange curve.

Now you are mixing the aileron differential to the aileron expotential which are completely different things. If there had been purpose built expotential in the aileron circuit, also the effectiveness curve would have been expotential. But in reality it was linear.

gripen

[niklas]

Originally posted by Knegel
Niklas,

the Spit5a rollcurve show a speed of max stick deflection only up to 130-140MPH, above this speed the stick deflection isnt constant!
Knegel

I know. Isnīt it interesting that though a reduced stick deflection the rollrate still increases linar?

Well actually you can observe at 140mph in my chart a little spike, so tendency below that speed seems to be progressive with speed.

Maybe a reduced stick deflection has a strange effect for the spitfire: it produced less aileron forces, thus less tension/bending,  maybe also less wing twist, after all the loss due to the reduced stick deflection is not proportional to the stick deflection.

Unfortunatly it is not said whether the deflection in the chart is aileron deflection or stick deflection (the text mention aileron deflection) and when itīs aileron deflection, whether aileron elasticity etc. is taken into consideration.

In any case this characteristic raises the question whether the peak in other aircraft curves is the 50lb limit or whether they reached also the force limit earlier

EDIT: Maybe the cause for the progressive tendency up to 140mph is the high AoA of the aircraft at low speeds. It seems to get more efficient when flying at a more flat AoA, what shouldnīt be a surprise. The Naca chart begins at 160mph, thus this progressive speed range is not visible. Maybe other aircraft would show the same characteristics. But below 160mph rollrate isnīt of great importance for dogfighting anyway. Furthermore the reduced stabillity of the whole machine at these low speeds probably donīt allow correct measurments without influence of slip etc.

EDIT2: Added RAF (naca868) curve to the table.


niklas

[gripen]

Originally posted by niklas

Unfortunatly it is not said whether the deflection in the chart is aileron deflection or stick deflection (the text mention aileron deflection) and when itīs aileron deflection, whether aileron elasticity etc. is taken into consideration.

The NACA report on Spitfire V explains the the issue quite directly in the page 4:

"The instrument recording the angular position of the three control surfaces was attached to the control linkages near the cockpit. Tests made on the ground showed that errors in the recorded angles due to stretch in the control system were small enough to be negligible in the case of the elevator and rudder controls. A slight amount of flexibility was noticeable in the aileron system but, inasmuch as no simple means was avalable for determining the error introduced, no correction was applied to the recorded aileron angles."

The RAE comparison claims device named "rat" used for recording aileron angles. Probably the same device is described in the Spitfire I report:

"A standard RAE control movement recorded was used to measure the aileron displacement. It was fitted in the wing and connected to the aileron control system at the aileron end, thus making correction for the cable stretch unnecessary."

In addition tested plane was fitted with camera for "continuous photographic record of a well defined line painted chordwise on the wing at the mid aileron position". That data was used for determining wing twist.

Edit: The RAE report on P-51B describes yet another device:

"Aileron Angle A Desynn transmitting instrument was mounted on each wing and linked directly to the inboard end of each aileron respectively."

gripen

[niklas]

ok, ok.  i only read quickly over the test result phrase for my judgment... have better things to do currently instead of reading through x pages of outdated stuff...

niklas

[gripen]

Well, the notable thing is that they claim "slight amount of flexibility" apparently with no particular load on aileron circuit. That supports Tuck's opinion on that plane.

gripen

[niklas]

Iīd say: This Spit example demonstrates very well the difference between a factory fresh, well prepared and adjusted, "best case" aircraft and a service condition aircraft.
Furthermore it shows very well how few importance a test of a single aircraft alone has. A single machine simply can not speak for a whole series!

So, coming back to AH, what is modelled: The "best case" spitfire rollrate and the worst case service condition fw-190 rollrate, because it is MENTIONED in the RAF test report that 2 other 190 had lighter ailerons what would result in a higher rollrate at med to high speeds. BAH!

Oh, in case of the 109, what about the influence of this single tested 109E, oh....


niklas

[gripen]

Originally posted by niklas
Iīd say: This Spit example demonstrates very well the difference between a factory fresh, well prepared and adjusted, "best case" aircraft and a service condition aircraft.

I'd say that the NACA tested Spitfire V was poorly maintained.

Originally posted by niklas
Furthermore it shows very well how few importance a test of a single aircraft alone has. A single machine simply can not speak for a whole series!

RAAF tested Spitfire V did roughly same or better than RAE tested with normal wing.

Originally posted by niklas
So, coming back to AH, what is modelled: The "best case" spitfire rollrate and the worst case service condition fw-190 rollrate, because it is MENTIONED in the RAF test report that 2 other 190 had lighter ailerons what would result in a higher rollrate at med to high speeds. BAH!

The results RAE measured with that tested plane (PE882) were still very good and it ailerons might have been within normal variation.

gripen

[Crumpp]

The results RAE measured with that tested plane (PE882) were still very good and it ailerons might have been within normal variation.

Gripen,

The deflection was within normal variation.  However the ailerons were out of adjustment.  We can cross reference the Fiesler Force Gauge limits as stated in the regulations with the forces, altitude and airspeed given in RAE 1231.  These will shows that RAE 1231's FW190A4 exhibited forces that were out of the range limits.  They were close but still out of specification.  The Luftwaffe manual gives a clear range, accounting for the natural variation of Frise type ailerons.  The RAE chalked up the difference in feel between the FW190's as this natural variation.  It was a mistake.

If the FW190 tested by the RAE had been in front of a Luftwaffe maintenance crew, and they were shown the data, work would have started adjusting the ailerons.

 It adjusts the amount of gap between the aileron/wing and how much of the Frise horn is in the slipstream.

Not surprising as the Luftwaffe had difficulty maintaining adjustment.  It is rather silly to expect a foreign service unfamiliar with the design to be able to do it.

All the best,

Crumpp

[gripen]

Originally posted by Crumpp
The deflection was within normal variation.  As stated before, simply look in the aileron adjustment regulations and you can see RAE 1231 represents an FW 190 with out of adjustment ailerons.  Adjustment had nothing to do with aileron deflection.  It adjust's the amount of gap between the aileron/wing and how much of the Frise horn is in the slipstream.

Hm... I did not mean deflection (which is within tolerances) but stick force and for stick forces I don't know any reference value to compare with. AFAIK it's not known which ailerons (of at least three types you listed) the tested plane had.

gripen

[Crumpp]

Hm... I did not mean deflection (which is within tolerances) but stick force and for stick forces I don't know any reference value to compare with. AFAIK it's not known which ailerons (of at least three types you listed) the tested plane had.

The regulations are the same for all three as are the force tolerances.

Get a copy of the regulations, they are listed there.

They have been posted in several threads.

All the best,

Crumpp

[gripen]

Hm... I have no idea what regulations you are talking about. Could you simply list what should have been the aileron deflection at given speed and stick force (or what ever yard stick they used for regulations)?

gripen

[Crumpp]

The range is 10-14kg at 8 degrees of aileron deflection with a speed of 400mph at 10,000 feet.  The forces exhibited must be with 1 Kg for each aileron.

At that speed with properly adjusted ailerons a reduction of forces in the first centimeter of travel is normal but cannot be less than 1Kg.  Otherwise the pilot will experience trouble holding the ailerons steady and may experience a knocking of the stick.

All the best,

Crumpp

[justin_g]

is that 400mph IAS or TAS?