Wing breakage: 109 or Spitfire?

[claidemore]

The 1942 document indicates to me that they knew they had a problem, but weren't sure exactly what it was. They addressed 3 likely causes, with a 4th cause added at the last minute by some braniac who was grasping at straws. Aileron paint?
One would think that lowering the dive speed limitations would have been counterproductive, instilling a lack of confidence in pilots. Unless; they were already losing confidence because of accidents attributed to wing breakage, real or imagined.
With regards to the landing gear popping open, the gear as i understand it is attached to the fuselage. (photos below, one from Axishistory website, the other I can't remember). I would assume then that a failure of the wing structure in that situation would be caused by forces on the wing from the empty wheel well?

 

[Soren]

Notice where the landing gear is attached Claidemore, if the landing gear was to rip itself loose and fall down during a 7 to 8 G pullout at 700 km/h then it would rip the wing root to shreds, causing a catastrophic wing failure. And since the air would emmidiately grab a hold on the landing gear as soon as it started to drop down it would rip it off before it could ever fully deploy, which means the gear would rip a large part of the wing to pieces.

 

[drgondog]

I have not previously read of any gear uplock issues with the 109 similar to P-51B-1 through -5 issues.

Having said this I agree with Soren that if any version of a 109 had a main gear pop out at 400+mph TAS that would be a recipe for catastrophic failure (or any other fighter).

Even if it didn't rip a wing it would create such a massive eccentric aerodynamic load on the fuselage that surely the rudder inputs to correct the resulting pitch and yaw would additionally stress the tail structure

 

[Glider]

The reality is that we are guessing. One thing struck me was whatever the reason for the wing failures and lowering of the VNE the problem seems to have been solved with the K version.

If it had been an uplock problem or something similar, wouldn't it have been identified somewhere between mid 42 and mid 44?

Kurfurst, you are the 109 guru do you know what the changes were in the design of the K wing?

 

[NZTyphoon]

Basically true. I don't think there was any great difference between the stress limits of the two airframes, nor that it is to be blamed on the airframe if the pilot does not adhere the operational limits of the airframe.

Secondly its a bit bizarre to argue that the German paper issued at the end of August 1942 is some sort of evidence that the Spitfire was less likely to be overstressed in dive, as you were already shown (several times) the British papers preceeding the German papers by a couple of months, and dealing with the very subject of

"several accidents to Spitfire V aircraft in service... attributed to excessive accelerations in pullouts from dives with consequent failure of the wing structure"

Firstly it is blatantly evident from the British paper that Spitfire wing structure failures occured and were a serious concern to the RAF the same time the LW became concerned about the same in the 109 (and I guess it is true for a couple of other airforces, which just become aware of the dangers at high Mach speed).

Secondly there's a difference - whereas the structural failures of the 109s were attributed to the pilots disobedience of the dive limits of their aircraft, the Spitfire wing failure accidents were attributed to a design aspect of the Spitfire, namely that the aircraft had a tendency to tighten up the turns in high speed dives, and overload itself... that was a fault of the design, not the pilot who flew it.



The Spitfire II Pilot's notes is very definietive about certain dangers stemming from the control characteristic of the aircraft (poor pitch stability, and overly sensitive elevator control). While indeed there are some generic limitations laid down in the manual which are valid for all aircraft, some are very specific to the Spitfire regardless how you blurr it.

The manual uses no uncertain terms that the aircraft has very sensitive controls, and it is easy to overload the design, and also notes that this could be easily done accidently, ie. due to unintenional movements of the pilot's hand in bumpy weather. Furthermore it makes clear warning not to trim the aircraft for level flight during dives because doing so exaggrevates the pilot's capacity to overload the airframe. Dives and bumpy weather are hardly ''extreme cases''...

The issue is simple to understand - the Spitfire had unusually low stick force stability, at about 4 lbs required to pull 1 G; the 109 was on the high side, at around 20 lbs/G.

Say a 109 and a Spitfire is a dogfight, both pilots pulling as much as possible on the stick, near their human limits, pulling 5 Gs... suddenly a blow of wind, a propeller from an aircraft or an AA shell exploding nearby shakes both aircraft and pilots, who accidentally pull another 20 lbs on the stick... the Spitfire is now pulling 10Gs all the sudden instead of 5, the 109 is now pulling 6Gs instead of 5...

Or you say you didn't see wing failure mention in context of other aircraft - say for example wing failures mentioned for Spitfire in documents you saw about a day before you wrote this? Or what way?

Firstly, the Spitfire V material was specifically discussing a serious of accidents which occured in 1942, when a number of Spitfire Vs crashed while diving. This problem was traced to bad loading of additional equipment on some squadrons which pushed the cg backwards; this was NOT an inherent problem of the Spitfire's design and these problems disappeared once the cg limits were adhered to. As a further measure bobweights had been introduced into the elevator control circuit and, according to Quill, the problem disappered. All the document submitted by Kurfurst proves is that the Spitfire, like most any other aircraft, reacted badly to having its cg pushed back beyond proper loading requirements, particularly when the airframe was highly stressed already.

Next the Spitfire II manual; this has been used time and again by Kurfurst to be representative of ALL Spitfires; as yet there has been nothing presented showing that in actual combat Spitfires were adversly affected by sudden gust loadings - has Kurfurst shown any evidence that such events during combat caused Spitfires to fall apart, to the glee (presumably) of the opposing pilot? Pure hypothesis on Kurfurst's part is not eveidence.

As it is there is evidence that throughout production Spitfires improved in respect of elevator control, particularly when the balance on the leading edge of the elevator was enlarged; eg: the PILOT'S NOTES for Spitfire Mark F.VII and Mark VII (A.P 1565G H - December 1943) say:
49. GENERAL FLYING
(i) Stability -On later aircraft fitted with horn balance elevators and large rudders there is a marked increase in longitudinal and directional stability, particularly at altitude.

If the Spitfire was truly such a bad aircraft to fly, as Kurfurst sometimes likes to maintain, I wonder why Cheif test pilots Quill and Henshaw kept their jobs?

 

[Kurfürst]

Firstly, the Spitfire V material was specifically discussing a serious of accidents which occured in 1942, when a number of Spitfire Vs crashed while diving. This problem was traced to bad loading of additional equipment on some squadrons which pushed the cg backwards; this was NOT an inherent problem of the Spitfire's design and these problems disappeared once the cg limits were adhered to.

Source with quoute please. If you wish to ignore the evidence, be my guest.

 

[Kurfürst]

The reality is that we are guessing. One thing struck me was whatever the reason for the wing failures and lowering of the VNE the problem seems to have been solved with the K version.

I don't think it was a particular problem with the airframe or any of it's particulars. I tend to believe that by 1942, the Luftwaffe, along with other airforces began to realize the dangers of high speed flight near the Mach number, and lowering the VNEs at high altitude reflected a trial and error approach - and guesswork. You can see the same stories with the high speed trials with Spitfires, P-47s, P-38s etc. Moreover pilots were reporting extremely high airspeeds - 1000 km/h and the like - from instrument readings, which were down to the unreliability of the pitots at those speeds. The designers probably thought that the pilots were approaching the speed of sound from those reports..

Its worth noting that the understanding of these effects were at their infancy - pilot manuals did not specifiy differentiated VNEs for altitude ranges, rather just a single, generic VNE; for example the early Bf 109E manual only specified 750 km/h with no altitude given, similiarly the early Spitfire I, II etc. manual only specified iirc 460 mph IAS, again no altitude given. Only later did altitude differentiated VNE limits began to appear, and they represented a degree of conservativeness or daring on the part of the manufacturer, based on a basic understanding that the speed of sound decreases with altitude considerably, therefore the VNE has to decrease with altitude too. At the time there was no firm understanding, or testing was available what happens to the aircraft suddenly when it reaches a magic barrier at around 0.75 Mach. The essential research was only done during wartime, and until then, it was essentially guesswork. I am sure Bill can add a lot more than that.

Another thing worth mentioning that the VNE has very little to do with the structural strenght of the fuselage or wings etc. Its not the air pressure or something like that that the wings can't stand up to, its the buffeting that tears it apart, and the vibration is largely function of things totally unrelated to the wing, rather how much free are the ailerons, elevator, stablisiers are aerodynamically designed and behave at high speed, how does the aircraft retains its stability characteristics at high speed. If it does not, or if the moving surfaces are badly designed (as the engineers designing them in the 1930s had no clue HOW to design such a device to be troublefree at high speeds, and it involved a fair bit of just getting lucky), the aircraft will simply tear itself apart no matter how well the wing could resist g-loads at lower speeds; Flutter for example will rip even the strongest wing apart, and its totally unrelated how ''strong'' the wing structure is..

If it had been an uplock problem or something similar, wouldn't it have been identified somewhere between mid 42 and mid 44?

Kurfurst, you are the 109 guru do you know what the changes were in the design of the K wing?

IMHO the VNE increase for the 109K merely showed increased confidence in the airplane (a lot of high speed trials were done in 1943-44, so they probably understood this area better by then). In 1943 they did tried to find out empirically the problems that may arise from diving at high speeds by making a 109F climb as high as it could, pushing the nose down in a vertical dive at full throttle, and substantially going over the nominal VNE in the process. Most importantly they confirmed that reports from pilots that they went over 1000 km/h were absurd, and was down to instrument errors, plus the usual symptoms of going near the Mach number in a WW2 fighter - aileron overbalance, compressibility being encountered and stick reversal etc.

If you look at the previous limits, you will notice that the limitation stayed the same from the F-2 to the G-10, despite the considerable aerodynamical difference that occured in the meantime, which strictly speaking surely effected the actual VNE of the aircraft, rather than the nominal VNE stated in the manuals. They probably didn't bother to update the limits until 109K model, and even that had probably more to do with aerodynamic changes (rembember both the main gear and the tailwheel had covers and was now fully retractable), rather than any structural change.

.

 

[Juha]

The test plane was a 109F with 109G wings, aileron movement was halved to reduce risk of overcompensation. Maybe explanation for higher dive speed for 109K was the fact that with the original low tail plane lost stability at speeds over 650km/h (IAS). After installation of the taller tail, used in late 109G-6s and later versions, speeds up to 737km/h (IAS) was reached.

Juha

 

[Glider]

Source with quoute please. If you wish to ignore the evidence, be my guest.

Kurfurst.
What evidence. I am still waiting for you to tell us what that report says, you remember the one, the one that was going to look into the impact of COG caused by the slight change in the design, the one that didn't mention accidents or investigation into accidents, the one you use as definitive evidence without any summary of the findings.

I admit that its only my memory, but my memory ties up well with what NZTyphoon has stated in his posting.

 

[Glider]

The test plane was a 109F with 109G wings, aileron movement was halved to reduce risk of overcompensation. Maybe explanation for higher dive speed for 109K was the fact that with the original low tail plane lost stability at speeds over 650km/h (IAS). After installation of the taller tail, used in late 109G-6s and later versions, speeds up to 737km/h (IAS) was reached.

Juha

That would make sense.

 

[Kurfürst]

Spitfire: The History: Amazon.co.uk: Eric B. Morgan, Edward Shacklady: Books deals in considerable detail with the diving accidents and structural failures occuring to the Spitfire Mk V.

It should be of interest for this thread:

 

[Kurfürst]

I am still waiting for you to tell us what that report says, you remember the one, the one that was going to look into the impact of COG caused by the slight change in the design, the one that didn't mention accidents or investigation into accidents, the one you use as definitive evidence without any summary of the findings.

The one posted is very definitive about investigating structural failures occured to Spitfire Mk Vs.
It definietely mentions accidents. Structural ones. With the Spitfire.

I don't know what your alleged report says, because I haven't seen it, because you have not been able to post it, and I don't think I've seen such report ever myself that would say things about a practice 'only concerning a couple of squadrons'' or a ''slight change in the design''.

Or are you saying that it is me who should provide the document which you claim to have seen/quoting etc, too? In other words, I am supposed to provide evidence to your own statements as well...? That would be odd..

I admit that its only my memory, but my memory ties up well with what NZTyphoon has stated in his posting.

Actually I am under the impression that you have seen no report at all, and only repeating the same claims NZTyphoon has made but failed to support despite numerous requests to him.

 

[Kurfürst]

The test plane was a 109F with 109G wings, aileron movement was halved to reduce risk of overcompensation. Maybe explanation for higher dive speed for 109K was the fact that with the original low tail plane lost stability at speeds over 650km/h (IAS). After installation of the taller tail, used in late 109G-6s and later versions, speeds up to 737km/h (IAS) was reached.

Juha

Actually there were several dives - aileron deflection was limited by half only final the last dive which reached the highest airspeed of 906 kph TAS / 737 kph IAS, after aileron overbalance was observed in previous dives reaching 850 to 890 kph TAS. Some 30 dives were performed in two months time.

An interesting detail is that the final dive that went 906 kph was made on the test pilot, Lukas Schmidt's own request, against the protest of several of his fellow engineers.

 

[Juha]

Of course there were several dives, a bit difficult to make only one dive if the tail was changed during the tests.

Quote:" aileron deflection was limited by half only final the last dive"

Really? Why then in Zustand der Maschine reads " Für die ersten Versuchsflüge befand sich die Maschine bis auf die Beschränkung der Querruderausschläge..."

That means that for the first tests flights a/c was standard 109F with wings of the G-model but aileron movement limitations (and an ejection seat, Germans were forefront in these).

Juha

 

[Glider]

The one posted is very definitive about investigating structural failures occured to Spitfire Mk Vs.
It definietely mentions accidents. Structural ones. With the Spitfire.

Where does it say this? The posting you have just done is not from a report

I don't know what your alleged report says, because I haven't seen it, because you have not been able to post it, and I don't think I've seen such report ever myself that would say things about a practice 'only concerning a couple of squadrons'' or a ''slight change in the design''.

I don't have it and I repeat never claimed to have it, only that I have read it in the past. the slight change in design is on the paper that you posted in post 37. The exact wording in para 4 is
The effect of flattening down the lip that existed in the rear edge of the elevator shrouds was investigated on the Spitfire VB.
Para 1 deals with the fact that they are going to look into several accidents to Spitfire V aircraft.

What we need to see is the summary of the findings of that paper. There are two known possibile issues
a) It is the firing of the guns that damaged the Oxygen feed to the pilot mentionind in the extract from the book. A modification to the oxygen feed was also mentioned in my posting of the Me109F thread.
b) It could be the COG problem mentioned by myself and NZ Typhoon.
c) It could be some major structural fault not mentioned by anyone
We don't know only you have the paper and for some reason you will not post the findings. As to why you will not post the findings I don't know. I can only think of two reasons
1) they agree with either A or B above
2) you don't have the rest of the paper

Or are you saying that it is me who should provide the document which you claim to have seen/quoting etc, too? In other words, I am supposed to provide evidence to your own statements as well...? That would be odd..

All we are asking you to do is to post the results of the paper that you say you have, to support your position. What exactly is wrong with that? As I have said if it is something else unknown then I will happily stand aside.
As for supplying supporting documents your track record is shall we say patchy (dare I mention the 100 octane). So support your position.

Actually I am under the impression that you have seen no report at all, and only repeating the same claims NZTyphoon has made but failed to support despite numerous requests to him.

One slight problem with that theory. I mentioned it first, its difficult for me to repat the claims that NZTyphoon has made, if I made them first.

 

[Kurfürst]

Of course there were several dives, a bit difficult to make only one dive if the tail was changed during the tests.

Quote:" aileron deflection was limited by half only final the last dive"

Really? Why then in Zustand der Maschine reads " Für die ersten Versuchsflüge befand sich die Maschine bis auf die Beschränkung der Querruderausschläge..."

That means that for the first tests flights a/c was standard 109F with wings of the G-model but aileron movement limitations (and an ejection seat, Germans were forefront in these).

Juha

Yes, REAALY dear Juha. Lukas Schmid is quoted by Radinger/Otto, and he makes it clear the first flight certainly did not have any aileron limitation - this was only added after a number of dives.

ie. first dive: "On 29 January all was ready, it was time to carry out the first diving flight."... later: "With the stabilizer trim now in order. I conducted a test flight to find a stabilizer position in which the elevator control force was manageable; this position was limited by a stop. As speed was increased — I was in the area between 850 and 890 kph — an aileron over-balance became apparent. Aileron deflection was subsequently limited by half, which certainly prevented a later crash." and then "Thus, I was able to carry
on, for I was by now curious to determine The terminal dive speed. I achieved this after peeling off into an 80° dive from an altitude of 10700 meters, reaching 906 kph and Mach 0.80 (see flight report)."

Your report only deals with one of these dives, the one that achieved 906 kph TAS, and describes the condition of the aircraft for that (final, I believe) test dive.

 

[Juha]

Now Flüge is plural of der Flug (flight) and maybe a look into Flugbericht Nr. 901/274 will confirm that during several flights, in fact during 14 flights, after tail was changed to taller one the movement of the ailerons was halved.

Juha

 

[Soren]

The test pilot himself made it pretty clear that the aileron movement was halvated first after having taken the a/c to both 850 and 890 km/h, in which speed regime the overbalance first became apparent. I really don't see how this can be misinterpreted.

 

[Juha]

Tests were made because "1. Klärung von Unfällen bei der Truppen (Ûberausgleich des Querruders und unzureichende Wirkung des Höhenruders bei hohen Mach'schen Zahlen.
…"
So it stands on the page one of the test report.

Ie. Because there had been accidents in front line units, suspected reason having been overcompensation of aileron controls and insufficient elevator authority at high mach numbers.
…

Juha

 

[NZTyphoon]

Source with quoute please. If you wish to ignore the evidence, be my guest.

Actually I am under the impression that you have seen no report at all, and only repeating the same claims NZTyphoon has made but failed to support despite numerous requests to him.

Numerous requests?? Since when has one sarcastic comment become "numerous requests" Funny how Kurfurst invariably and automatically provides ALL all of his scources and quotes on request ; however, to the point: Quill devotes an entire chapter to longitudinal stability (pages 229-241 Murray 1983) in his book "Spitfire a Test Pilot's Story" in which he goes into detail about the problems involving several Spitfire Vs which broke up in 1942; Quill describes the problem of Spitfire Vs breaking up; he then goes on to describe the solutions which were a): to ensure that when new equipment was added that the loading was kept within limits and b):the design of bobweights, which were added to the elevator circuit, as well as the modified elevators fitted to later Spitfire marks. After the bob-weights were fitted, and the loading sorted out, the problem disappeared.

Quill
"In general configuration the Mk I and Mk II production aeroplanes were almost identical to the prototype and so there was no problem with their stability." (231-232)

"The Mk III Spitfire did not go into production, but the success of the bobweight experiment in curing its instability...opened up the possibility of its use for later marks of Spitfire....which was just as well as we had to...respond to a nasty situation which developed in 1942.
The Mk V aircraft was...in full service with Fighter Command and,...a fair amount of additional operational equipment had gradually crept into the aircraft, most of it stowed within the fuselage. The aftmost acceptable position for the aircraft's centre of gravity had been fixed in the mormal course of flight testing by the firm and by the A AEE....Any rearward movement of the centre of gravity in service, for whatever reason, would begin to destabilise the aircraft. Therefore, for each sub-variant of the Mk V detailed instructions for the correct loading of the aircraft were issued to squadrons....However the importance of these loading instructions was not generally appreciated in squadrons and in the daily round of operational activity they tended to be disregarded." (pages 232-233 -Quill goes on to describe 65 Sqn's Spitfire Vbs which were found to be dangerously unstable)

"There was thus a real chance that, as of that moment, in almost every squadron in the Command Spitfires were flying in a dangerous state of instability....Up to that time there had been a distressing and increasing incidence of total structural failure of Spitfires in the air, which was causing great comcern in the MAP and especially at Supermarine." (pages234-235) Once the bobweights had been introduced and, in later marks, the modified mass balances on the elevators...it was statistically established that, as soon as the longitudinal stability of the Spitfire was thus brought under control, the problem of the unexplained breakings-up of aircraft in mid-air,...'softly and suddenly vanished away'." (page 238 )

What is interesting is that Quill points out that the majority of Spitfire Vs in service may have been dangerously unstable. If this was the case it is even more striking how few of them actually broke-up.

The report, one page of whick Kurfurst uses to imply that all Spitfires were inherently likely to break-up, is dated April-July 1942, and is one of those written during the investigations of the problems described by Geoffrey Quill.

X4266, according to Morgan and Shacklady, was originally a Mk I "11-4-42 hand(ling), stab(ility), recovery from dive and steep turns. Comp. trials with BM559..."

BM559 "hand stab characteristics recovering from dives. Steep turns to assess aeroelastically stresses. Comp trials with X4266 fitt (?) DeH and Rotol props. Trls with and without 6 1/2 intl wt in elevator system.

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.

No, Glider was not making this up - as Quill has described, the problems were caused by bad loading at squadron level, which led to problems of Spitfire Vs breaking up in a dive. It's very easy for Kurfurst to make all sorts of claims, based on selected pages (including a set of "Pilot's Notes", the provenence of which is unknown...), but I don't believe he had the experience of Quill in actually testing and approving the flight qualities of all marks of Spitfire.