Wing breakage: 109 or Spitfire?

[claidemore]

How does beefing up a wing structurally increase aileron reversal speed?

 

[Juha]

Hello Kurfürst
Yes, the docu in question is Ribnitz'/DVL's The influence of the elastic properties of the wing on the rolling efficiency of Me 109-F2, which was found by Gripen some years ago from the Deutsches Museum, the title is of course translation of the German title. Yes, I know that you have the docu also. I also know who gave it to you. Tests were flown at 3000m. The Mach number given on x-axis with the km/h in some graphs, for ex in Abb. 18 and the roll rate hit the x-axis at bit over M 0.8 / a bit under 1000km/h at 3.000m. And it was you, (or at lest the writer had same pseudo name as you, same kind of info and attitude towards Bf 109 as you and same kind of attitude towards Spit as you and his behaviour was much like yours) who posted "The aileron reversal speed for the Me109 can be derived in FB 1951 and is around 611 mph while the Spitfire had only 510 mph (source avia report 6/10126 from the RAE)."

And thanks for the Material Command report, very interesting. Difficult to know the reason of so big difference between US and German data. All I can say as layman on technical matters that Ribnitz'/DVL's data is based on test flight program and had been so interesting that for ex. Kurt Tank had read it among others.

Yes, I'm welll aware of the beefing up of 109's wing in G-series.

Hello Claidemore
thickening of the skin and IIRC also reinforcing a few innermost ribs made the wing stiffer.

Juha

 

[drgondog]

Claidmore - the wing torses in high speed rolls. The dynamic pressure (Q) applied to the 'up' airleron, for example, creates a force on the aileron that is eccentric to the primary wing axis (visualize a vector parallel to the chord but above the mean chord line or longitudinal centroildal axis of the wing. That force, when translated to the wing does two things.

1.) it creates a vertical force on the aft/outer wing area which causes that wing to deflect downward

2.) it creates a horizontal force above the centroidal axis which causes the wing to twist about the centroidal axis.

It is the latter torsional force which will then tend to create a higher relative angle of attack, and hence increased lift on the wing - thereby counteracting the force imposed by the aileron in the rolling manuever.

So, stiffen the wing to resist the torsional load deflections or decrease the aileron area to decrease the applied Q load on the aileron.

As I looked at the diagram (VG-33) for the 109 wing it occurred to me that the leading edge must be a major part of the wing structure as the primary spar is at ~45% chord of the wing. The aerodynamic lift load vector is normalized close to 25-28% chord so a box beam should be created between the leading edge and the main spar to compensate for the huge inner wing cut out for the main gear.

In that region it would be analyzed as a horizontal "C" section beam with top skin and spar caps/leading edge in compression and bottom leading edge/bottom spar in tension for high g positive vertical loads.

If I'm wrong I would sure like to see the design analysis!

 

[Kurfürst]

urse translation of the German title. Yes, I know that you have the docu also. I also know who gave it to you. Tests were flown at 3000m. The Mach number given on x-axis with the km/h in some graphs, for ex in Abb. 18 and the roll rate hit the x-axis at bit over M 0.8 / a bit under 1000km/h at 3.000m.

...

Difficult to know the reason of so big difference between US and German data. All I can say as layman on technical matters that Ribnitz'/DVL's data is based on test flight program and had been so interesting that for ex. Kurt Tank had read it among others.

It simple to say why there's a difference between US data and German 'data' - there's no German data for aileron reversal in the DVL report...

I also have to note a few things regarding your comment 'roll rate hit the x-axis at bit over M 0.8 / a bit under 1000km/h at 3.000m' - I presume you did not see the actual roll rate graph no. 5 of the report. First of all, the roll curve doesn't hit the X axis (ie. roll rate=0) anywhere. The highest speeds for measured roll rates measured in the actual flight tests appear to be up to ca. 780 km/h at 6 degrees (less than half) deflection on the graph, where roll rate is given as ca. 0,82 radian. The highest extrapolated (calculated from actual measurements) roll rates/speed shown on the graph are 900 km/h and ca. 0,25 radian roll rate.

The zero roll rate was neither measured, nor calculated by the German DVL report. Layman estimations given the roll curves can be given (such as the ones I gave years before I become aware of the actual values), but those are just that, a layman's guess with a high degree of error vs. the US MatCom aileron reversal speed data, calculated from actual stress test.

In short, there's no contradiction between the two 'datasets' - there's just one set of data available from the 1944 MatCom report, posted before.

 

[Kurfürst]

Unfortunately you have chosen to present part of the paper that says what they are looking into not the piece that deals with the investigation. If this is the paper that I read in the entirety, the problem was associated to the change in the COG as new equipment was added to the Mk V which was easily fixed once the problem had been identified.

The report doesn't say any such thing. You don't have the report - you were asking for it just a couple of days ago - and you have made the above up.

 

[Juha]

Hello Kurfürst
Quote:" I presume you did not see the actual roll rate graph no. 5 of the report. First of all, the roll curve doesn't hit the X axis (ie. roll rate=0) anywhere."

In fact I have seen the Abb. 5 many times, but as I wrote I was talking on the Abb. 18, simply because I thought and still think that you got Your 611mph from there. And definitely the curve hits x-axis in that graph. And it isn't the only graph in which that happens.

Quote:"The highest speeds for measured roll rates measured in the actual flight tests appear to be up to ca. 780 km/h at 6 degrees (less than half) deflection on the graph, where roll rate is given as ca. 0,82 radian."

Yes, only that would say that that the speed was about 767km/h.

Juha

 

[claidemore]

Claidmore - the wing torses in high speed rolls. The dynamic pressure (Q) applied to the 'up' airleron, for example, creates a force on the aileron that is eccentric to the primary wing axis (visualize a vector parallel to the chord but above the mean chord line or longitudinal centroildal axis of the wing. That force, when translated to the wing does two things.

1.) it creates a vertical force on the aft/outer wing area which causes that wing to deflect downward

2.) it creates a horizontal force above the centroidal axis which causes the wing to twist about the centroidal axis.

It is the latter torsional force which will then tend to create a higher relative angle of attack, and hence increased lift on the wing - thereby counteracting the force imposed by the aileron in the rolling manuever.

So, stiffen the wing to resist the torsional load deflections or decrease the aileron area to decrease the applied Q load on the aileron.

Thank you! I'ts clear as mud now! lol.
Seriously, aileron reversal was something which I knew about, but had no clue as to what caused it, other than the situations (speeds) that it occured. I've got a glimmer of understanding now.

 

[Glider]

The report doesn't say any such thing. You don't have the report - you were asking for it just a couple of days ago - and you have made the above up.

I don't have it and have never claimed to have had it. I said that I had read a report on this topic and I also said, If this is the report that I have read. I am making nothing up and you really should read what people have written before getting your head down and charging into a brick wall.

You say that the report doesn't say any such thing then I am asking you to post what it does say. If you have the full report that you are quoting then please post the relevant summary as to the findings or better still the detail if practical. If its a file from the NA and if you have the source file or an internet link then post that and we might be able to find out what it does say. I would certainly put my memory in second place to an actual document

To show the page that says what its looking into and claim that is evidence is worthless. I am sure that I could find a report looking to see if the earth is flat, but it doesn't mean that the earth is flat.

 

[drgondog]

Thank you! I'ts clear as mud now! lol.
Seriously, aileron reversal was something which I knew about, but had no clue as to what caused it, other than the situations (speeds) that it occured. I've got a glimmer of understanding now.

Try this: Get a rectangular piece of plastic. That is the wing. Hold it one the left edge end in your left hand and visualize that as the wing root.

On the other end press the edge 'downward' from the center of the wing edge. The edge of the 'wing' simply deflects down but the edge angle of the plastic rectangle remains constant (angle of attack of leading edge does not change).

This would be a wing with a 'up aileron' and represent a torsionally stiff wing - it will bend slightly at the tip but not twist along the leading edge.

Now apply a twisting force on the right edge. The 'leading edge of the wing will twist relative to the root in your left hand. That increase the relative angle of attack of the wing tip in your right hand with respect to the 'root' in your left hand.

With that 'increase in AoA' the wing gains local increase in lift on outer wing, neutralizing the downward force imposed by the aileron.

 

[Soren]

It does matter which way he twists the tip though, you forgot to say that hehe If I was to twist the tip forward for example I'd decrease the AoA at the tip in relation to the root I know you know this, just couldn't resist pointing it out for Claidemore's sake.

 

[drgondog]

It does matter which way he twists the tip though, you forgot to say that hehe If I was to twist the tip forward for example I'd decrease the AoA at the tip in relation to the root I know you know this, just couldn't resist pointing it out for Claidemore's sake.

True- having said that I was leaning on Claidmore to remember the 'eccentric' load created by the aileron to cause the twist..

 

[Soren]

Copy that.

 

[claidemore]

Here is a part of a report on 109 dive limits (possibly the same one that Glider and Kurfurst were discussing earlier in this thread?). Note that it states specifically that dive limits are being reduced because of "continually recurring accidents caused by wing breakages".

It also mentions a bit later that these limitations include the 109G with it's 'strengthened' wing.

More complete info here: http://www.ww2aircraft.net/forum/aviation/bf-109-dive-rate-19817-6.html

Edit: My original posting about the report below not being in the context of piilots ignoring speed limitaitons was not well worded. I was in a hurry and had to get to work.
There are 4 subsections to the report, of which section 1 is shown below. All 4 sections deal with the same subject, "Reference 109 - wing breakages. The speed limitation reduction is in context of pilots ignoring the previous higher speed limits, but the subject of wing breakage, is not limited to that context. Basically the report covers permissible IAS, yawing, failure of a wing due to landing gear popping out of place, and paint on ailerons.

 

[Glider]

What I find interesting is the significant reduction in the limitations at altitude which for a fighter that is reckoned to be in its element higher up must have been a major limitation

 

[drgondog]

What I find interesting is the significant reduction in the limitations at altitude which for a fighter that is reckoned to be in its element higher up must have been a major limitation

Glider- those speeds are Indicated Airspeeds not True air speeds which are very much higher than IAS at 20K+ altitudes.

 

[Glider]

I was thinking of the before and after figures, 341 to 280 is by any standard, a drop.

 

[drgondog]

I was thinking of the before and after figures, 341 to 280 is by any standard, a drop.

you are correct - I should have asked what you were looking at.

 

[Soren]

And the Bf-109K had a max permissable dive speed of 850 km/h. So I'm thinking the document from 1942 has something to do with the landing gear popping out in dives and ripping the wing apart, cause the wing could clearly easily handle speeds up to 850 km/h. I don't believe any Spitfire ever had that high a permissable dive speed.

 

[Glider]

You could be right but we simply don't know. I admit that I have no idea what changes were made to the wing design of the 109K.

 

[VG-33]

Hi VG-33,
I did not find anything with Google search of "Ostolsawki" or "RDK" or "Kosminkov".
Can you give direct Amazon book links (ISBN number) or internet links.

Hi, did you try with Cyrillic letters?