Kurfurst - nice to chat. I read about a test bed 109 on Nowarr's book that was designed to be a fighter bomber with wing hardpoint and a reinforced CL rack for a 550kg bomb.
Are you proposing this as a standard production G, around which fighter bomber groups were organized?
That was the G-1/R1 (500kg + 2 x 300 liter underwing droptanks). It was a long range FB model of which a handful was produced. The reason it did not see widespread service - apart from it's oddity - was probably that they had the FW 190, which was much more suited as a JaBo in any case. The 109G remained as a fighter, and on occasion a fighter bomber with a 250 kg bomb under the fuselage. It wasn't that much of a stuctural limitation, but a ground clearance issue; the 109K, which had longer tailwheel as standard, was cleared for the larger 500 kg bombs (and I suppose it stood true for the 109Gs which were having the long tailwheel).
The picture I've posted is a G-4/R3 variant, which was a standard variant, produced on smaller scale (80 or so as I recall, but there was also a G-6/R3 variant which production numbers I can't comment on. G-6 production is a mess), and it was used as a long range fighter recce, with the two droptanks under the wings and camera equipment in the fuselage. The engine cannon was retained, but in the MGs place extra oil capacity was built in. I am no expert on their operations, but they certainly operated in the Med and from Norway (one was shot down in a dive above Scapa Flow, described in Clostermann's book).
Given the above, I doubt it would present too much technical trouble to use the 109 wing to carry loads. You might recall it carried gondola weapons, and it was cleared for high loads under this condition, ie. manouvering dogfights.
Kurfurst - the Gondola would obviate the need to cut away and then reinforce the main spar internally - which would pose (solvable) problems that would add more weight than the gondolas.
Each gondola loaded put ca 120 kg under the fuselage, so given that and the fact that operational versions with about 250 kgs under each wings (i.e the long range FRs depicted with the droptanks) were used.
the 109 disintegrates so it wasn't uncommon.
on perhaps this thread or another one there was a discussion of 109 wings failing due to resonance - which I then doubted - but it was close to real issue. Nowarra mentioned the 109F tail failures due to resonance following removal of truss on E model - so that story seems true.
Yes, there were early 109F tail failures which I believe were rooted back to resonance from the engine at certain RPM. These were solved by adding external stiffeners to the tail section, and later internal ones.
Anyway, I don't quite see the point. The 109F had a new layout and was in the aerodynamic sense almost completely new airframe save for the centre section, so a few surpises at the time of the introduction were needed to be ironed out. Resonance also have absolutely nothing to do with actual structural strenght.
He also mentioned the cautions regarding extremely high G turns and dive recovery - causing 109F wing to fold at root.
I believe these statements root in British P/W interrogations about the new 109F. A P/W noted that two pilots, one of them being Balthasar snapped their wings on a 109F during high-G pulls in snaking dives. I presume Nowarra (who's rather old work is riddled with errors otherwise) simple repeated these Air Intelligence interrogations, being easy-to-find material. OTOH there's a lot of funny stuff in those A.I. reports, Me 209s etc.
In any case, the 109G wing was strenghtened, so maybe the F-wing was insufficently stressed - that I doubt, US measurements on it were quite positive. It was found to be satisfactory for flutter effects, and had a rather high aileron reversal point of 850 ?? To quote from the report (from March 1944) :
'
3. The analysis for flutter and aileron reversal indicate that the Me-109F is satisfactory from the flutter standpoint at speeds up the limit diving speed.
Did they state the Limit Diving Speed as 850mph -above- ??
4. The wing torsional rigidity of the Me-109E wing, which is practically identical with the Me-109F wing, compares favourably with that of a similiar high speed AAF pursuit plane.'
That's what made me look at the 109 wing from my personal airframe structural engineering background - to SPECULATE (not know for certain) on the design of the wing - as I stated above. If I saw the actual design analysis on how they compensated for the wheel well buried in 25% chord area and main spar behind that by more than a foot then I could be better informed... it also made sense that the 109 was never designed (exception on test a/c above) to carry heavy loads mid wing like all US fighters.
There's a French report describing in detail the 109E wing construction; to summerize it, the main spar only takes bending loads, whereas the box spar took the torsional loads.
That is classic wing design - but the main spar of 1he 109 is at approx 40MAC whereas the P-47 and P-51 and P-38 are at 25%MAC or where the aerodynamic center of lift is -- therefore no torque on the 'torque box' due to lift - which is not the case for the 109.. The 51 'torque box' starts with the 25% main spar, the 109 starts aft of CL as well as main spar
The report notes that the use of plating was rather thick (1-1.5mm), I guess Messerschmitt simply used heavy thickness skin at critical points, formed into a torsion box by 'false' ribs around the wheel well. In any case, combined torsional and bending loads were a sort of a common problem at the time, aircraft structure was usually not designed to resist both at one time (IIRC there's a NACA report mentioning that in regard of the P-47 as well)
The 109 had a box spar and a larger sizeable I-beam as a main spar to carry loads of the wings. The spar, the skin and ribs were reinforced multiple times during it's life. I have it documented in reports that this happened on the 109E, and on the 109G as well (which sported the new 109F wing).
All of those measures would be taken because of concern for both bending and torsional failures - there was no such design modification for a 51. Adding thickness to aluminum plate on top and bottom of spar adds 'effective cross section to spar caps' to take out more tension in bending as well as distributing shear loads.
As for the wing, Messerchmitt certainly did not like the idea of putting things into the wings. It was far from not being doable though. Galland even field-hacked his 109F, and put a 20mm Oerlikon FF into each wing. The Spanish post-war 109G airframes could cope with the rather sizable Hispano the Spanish built into the wings. Late war variants proposed as heavy fighter variants of the 109K saw both MK 108s and MG 151/20s alternatively built into wings.
I guess the the notion of the 109 wing not being able to cope with internal armaments stems from the fact that gondola weapons were used, an 'odd' solution. But in fact the gondolas did not add any more weight than an internal installation, and the (rather small) drag rise they gave was comparable to any internally mounted weapons of the era. Gondolas, as per Messerschmitt's datasheets, chopped off 8 km/h or about 5 mph from the top speed of the 109G at SL. Actually a bit less than Hispano installations in Spitfire wings. In other words, if Messerschmitt would have wanted to please the crowds 50 years later, and would have gone with an internal arrangement, he would have the same mount of performance loss. OTOH, the extremely heavy firepower (on par with a contemporary FW 190A) provided by the gondolas was seldom needed (the gondies themselves go back to late 1941), and being a complete unit, they could be easily mounted and dismounted when needed, they seem to me a rational design choice (and also complied well with the modular-designs the Germans preferred at that time, plus it spared the time to make changes in the wing design, and production lines).
Cut the long story short, I don't believe there was any extraordinary problem with the 109's wings structural strenght, nor do I believe that if they'd have wanted to have external stores under the wings it could not have been done in short order, given the similiar loads already carried by the 109 in production. If the 109G wing could carry a 250 kg worth droptank, it could certainly carry a 250 kg bomb, it was a matter of adding an extra rack under each wing in place of the underwing panel for the gondolas. Why it wasn't done? I dunno, but I suspect the FW 190 already took up that job.
What else was there catching my eye? Oh yes, if carrier stresses mean anything, there was a Bf 109T version meant for (never to come) carrier ops. Carrier-capability was probably one reason to have the U/C mounted on the fuselage, in any case it removed landing stresses from the wing structure and spar, and also gave a nice added bonus to maintaince and repair of the wing, which could be simply removed and replaced without disassamling the undercarriage. And no, the narrow undercarriage wasn't a root for the tendency to groundloop (the aircraft's relative real CoG on ground was), though it certainly made it more prone to the effects.
