Fw-190: the roots of the great roll rate?

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drgondog said:
You're thinking like a structures engineer that took the time to emphasize the "do not poke holes here' instructions to Maintainers.. lol
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A couple of stories you guys would appreciate. When I first hied on at Northrop there were quite a few "old heads" that I enjoyed talking to. One told me a story about the F-89. He was in charge of installing electrical wiring. On arriving at the aircraft, manufacturing had forgot to provide electrical runs in the bulk head. His solution? Electric drill, which provided the runs. Another story occurred during the early manufacturing of the F-5. The aft fuselage, which contained the vertical and horizontal stabilizers were mounted to the main fuselage by bolts. At that station, there were two experienced assemblers that had been there for years and all went well. One day one was on vacation and one was sick. When the replacement crew started to assemble the next aircraft, the mounting holes did not line up. The manufacturing line stopped. On examining the other fuselage sections in the line, none lined up. When the sick guy returned, they asked him about it. Oh yeah, its been that way for years, we just took a larger drill bit, drilled them out and put in a slightly larger bolts, no problems? After great consternation and analysis, after all quite a few F-5a had been built that way, it was determined that the change they made had no impact on structural integrity.
 
the Polikarpov I-16 had a hellacious fast roll rate iirc. i was trying to find a wing/spar diagram just to compare but seems to be difficult to find...
 
FW-190 parts, not Flugwerk. These are part of the White 1 build. The FW-190 has a different construction method than conventional period wings. The top and bottom skins are one piece, while the ribs are riveted in halves to the top and bottom skin.


flaps

wings skins and a few ribs attached

close up of an original FW wing with the "floating ribs"


unfinished skin

new ribs
 
Jim - great shots. Beautiful design both for approach and producability. Now if Kurt was still around we could ask him why zero twist on leading edge for last 20% of semi span. Off the top, it may have reduced induced drag a tiny amount, but created the issues with high AoA/asymmetrical stall.
 
Floating Ribs?? someone explain this to me...surely both halves of the rib were rivited together..correct? but i can see where that would be a stiff wing..
 
The ribs are not riveted together, only to the outer skin, which is why we called them "floating ribs". If you look closely at the photograph the ribs are not riveted together. The aluminum sections of wing skins gets progressively thinner from the inboard sections to the tip. There is a lower, for lack of a better term "strap", that is formed to the dihedral of the wing and crosses the center section to about midway out each wing panel. The stringers attached to the skin also vary in thickness and conform to the differences in thickness of the wing skin. It's by no means simple, and from a restoration point of view a nightmare. I watched John build up the skin, then the jig and the ribs. I can't speak for the twist or washout but he was working with all the known available drawings to build the jig. It's a massive undertaking in today's terms, but I am sure that during the war it was a fairly quick way to build a wing.

Jim
 
jimh said:
FW-190 parts, not Flugwerk. These are part of the White 1 build. The FW-190 has a different construction method than conventional period wings. The top and bottom skins are one piece, while the ribs are riveted in halves to the top and bottom skin.
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Precisely,

As your photos show the FW 190 is clearly a two spar design with a box like structure formed by relatively heavy upper and lower skins between the two spars. (forward spar and rear spar)

In the Spitfire the main spar is near the quarter chord point with a torsion 'box' like structure formed between the leading edge and the main spar. The leading edge skins purpose is to provide substantial stiffness in the torsional axis. The Center of lift of most traditional wing is at the quarter chord point and this is also where there is the main spar.

A look at an image of the chordwise lift distribution of a wing will show that almost 75% of the lift comes from within +/- 25% of this quarter chord point so the final 66% of the wing aft of the spar needs to transmit little of the lift to the main spar and can be a relatively light structure and thinner guage metal.

In a pure single spar design ribs will be present and it is to these ribs that the airlerons and flaps are attached. Many aircraft of course also receive stringers along the wing and it would seem natural to close of rear of the wing with a small secondary spar which can add some strength. The Spitfire aileron hinges still attached to the ribs and the secondary(rear) spar carried little load and the wings can certainly function if the entire structure rear of the main spar including the skins and rear spar was damaged. The relatively thin non structural leading edge skins of a two spar wing can more easily be cut ot for gun ports, landing lights etc.

Me 109 also had a single spar but it was completely different, more at the 40% of chord point with elaborate detours around objects like the undercarriage and it looks like the upper and lower skins were an important part of the structure. The aircraft had excellent roll rate but this reduced at high speed due to aileron stiffening. The Spitfires roll rate reduced at speed due to wing twist even after all metal Friese airlerons were fitted. Its worth noting that the 109 and 190 retained fabric covered ailerons.
Mk 22 spitfires received a new wing structure and modified planform.

I suppose one could argue that the presence of a much smaller secondary spar at the rear of the wing made the Spitfire a hybrid design though I think this disguises the point that the Spitire roll rate was substantially determined by the wings structure and its aeroelelastic properties ie relatively low torsional stiffness were more that of a single spar design than a two spar design.
 
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You can twist, turn, (even do handstands) as much as you wish, but the fact remains that the Spitfire had a rear spar which was (as rigidly as possible) bolted to the fuselage frame 10, and went out as far as the wingtip; it had ribs which were fixed to the front and (non-existant) rear spars; it had overlapping skins rivetted (sometimes double-rivetted) to the spars and wing ribs. There are no wing ribs, in the vicinity of the ailerons, aft of the (non-existant) rear spar, since the permissible gap between the aileron nose (before it is covered) and the (non-existant) spar and aileron shroud is .15" - .25", so there's no room for any ribs. Also, the aileron hinges are bolted directly onto the (non-existant) rear spar, not the (definitely non-existant) wing ribs. It seems that all of this concentration on the rate of roll is designed to cover up the fact that the Spitfire could turn inside the 190 the 109, a manouevre which will do more to keep its pilot alive than rolling.
 
Yeah right, Fw 190 was clearly helpless against Spitfire MkIX in 1943 and shot down "in droves"
 
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