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

[tomo pauk]

The Fw-190 was acclaimed as the plane with a great rate of roll. Why was it able to achieve that?

 

[spicmart]

Sturdier, stiffer wings compared to other contemporaries; rod controlled ailerons that have no fabric but metal cover; small wing area. These are some things that come to mind.

 

[Siegfried]

The Fw 190 had two spars that meant that the wing didn't twist from aileron forces which tended to cause control reversal from aeroelastic twist. The Spitfire with its single main spar suffered somewhat from this.

The wing tips were quite thin which reduced stiffening at high speed.

Friese ailerons reduced aerodynamic forces.

 

[drgondog]

The FW 190 Did suffer twist/aeroelastic torsion in high G/High AoA manuevers. Two features contributed to this.
1. Large effective ailerons
2. Zero washout from 80% semi span to tip. At normal increasing AoA the lift Distribution was primarilt on the inner 40% (like a level wing approach/stall). But under high G/High AoA, the outer panel started to bend/twist and the lift distribution was shifted from inboard to outboard and the wing, then tended to stall completely at the high AoA rather than Inboard ----> Outboard progression .

Gross, P. "Die Entwickland Tragwerkkonstruction Fw 190 -Bericht 176 der Lillenthall-Gesellshaft 2 Tiel, January, 1944"

 

[Siegfried]

Of course all aircraft have aero-elasticity, in the case of the Fw 190 the twin spar wing box ensured relatively high torsional rigidity and therefore a high theoretical reversal speed; this being the speed the aileron imposed forces would roll the aircraft in the opposit direction.

However there was a downside in that under high g the wing would twist so as to increase the angle of attack and therefore induce a premature tip stall with limited warning. Recovery was however immediate as the wing returned to shape. A single spar wing might twist so as to reduce AOA and so did no suffer from this issue.

Ta 152 had a new wing structure, at least in the Ta 152h aileron control might be maintained post stall due to high 3 degree washout. There may have been other issues such as inertia cross coupling since the long nosed version lost roll rate.

Thanks for the citation.

Several US aircraft had good roll rates. P40, the P63, P51B onwards (only at high speed). High P47 roll rate was a myth.

The thick laminar flow wings allowed a stiff structure and internal pressure balancing to reduce pilot forces.

 

[GregP]

I think the Fw 190 also had great aileron gap seals, making the air flow over the aileron, rather than around it, better than other fighters.

Gap seals are a BIG factor in roll rate.

 

[CobberKane]

USN tests found that the Hellcat and Corsair could both roll with the 190, although they noted that the the 190 was more nuetral and easily controlled

 

[Siegfried]

USN tests found that the Hellcat and Corsair could both roll with the 190, although they noted that the the 190 was more nuetral and easily controlled

If it is the test I am thinking of it also noted that during high speed turns that the Fw 190s aileron Flutter was so severe that the vibration started to push the pilot into unconsciousness.

This was in no way normal and indicates improperly rigged ailerons, which were a hard to setup due to the 190s pushrod system. Hence I would argue that the comparisons are not valid.

Late war Corsairs and Hellcats received geared spring tabs that improved high speed roll rate at the expense of low speed.

 

[FLYBOYJ]

If it is the test I am thinking of it also noted that during high speed turns that the Fw 190s aileron Flutter was so severe that the vibration started to push the pilot into unconsciousness.This was in no way normal and indicates improperly rigged ailerons, which were a hard to setup due to the 190s pushrod system. Hence I would argue that the comparisons are not valid.

Late war Corsairs and Hellcats received geared spring tabs that improved high speed roll rate at the expense of low speed.

With regards to rigging ailerons (and this is across the board) improperly rigged ailerons (deflection angles) will not flutter, rather give you varied turn rates and may cause the aircraft to fly "one wing low." Aileron flutter is usually associated with improper balance or "play" within in the control circuit (in the case of cables, under tension, in the case of pushrods, loose or worn rod end bearings).

As far as the statement about "pushing the pilot into a state of unconsciousness." I'd like to see that report - if true; I think this statement is a bit exaggerated. If you're flying an aircraft that is experiencing aileron flutter that hard that you're blacking out, chances are other parts of the aircraft already self destructed.

 

[Thorlifter]

Very interesting thread. I only understand about 25% of it, but it's very interesting. I'm not trying to hijack the thread but was just wondering if WWI planes experienced the same effects. My complete guess is yes, but at a reduced effect due to much lower speeds.

 

[drgondog]

Of course all aircraft have aero-elasticity, in the case of the Fw 190 the twin spar wing box ensured relatively high torsional rigidity and therefore a high theoretical reversal speed; this being the speed the aileron imposed forces would roll the aircraft in the opposit direction.

No particular design philosophy guarantees high torsional rigidity. True a twin spar box is a sound approach, but depending on the mass distribution, Spar spanwise moment of inertia qualities and the surface skin thikness - such design may not have better torsional rigity of say a single main spar design with reinforced leading edge and aft spar upon which the flap is attched.

If the main spar is located along the airfoil station where the pressure centroid/Center of Lift is located - then more 'pure' bending occurs until the COP is re-located by adverse pressure gradient which typically happens near stall.

Net - net Absent the actual drawings combined with the aero team supplied loads and the structures team stress analysis, not a lot can be stated unequivocably?

However there was a downside in that under high g the wing would twist so as to increase the angle of attack and therefore induce a premature tip stall with limited warning. Recovery was however immediate as the wing returned to shape. A single spar wing might twist so as to reduce AOA and so did no suffer from this issue.

Maybe review the comments above before making such a bold statement. Virtually ALL WWII fighters had a combination of at least one primary spar, and one secondary in the form of the ~80% chord location of flap (i.e 109), and usually a fairly stiff leading edge. Any equipment spar shear web structure (like a big ass cannon barrel near the root) has to be accounted for with very serious scrutiny.

Ta 152 had a new wing structure, at least in the Ta 152h aileron control might be maintained post stall due to high 3 degree washout. There may have been other issues such as inertia cross coupling since the long nosed version lost roll rate.

Thanks for the citation.

Several US aircraft had good roll rates. P40, the P63, P51B onwards (only at high speed). High P47 roll rate was a myth.

The thick laminar flow wings allowed a stiff structure and internal pressure balancing to reduce pilot forces.

"High P-47 roll rate is a myth" If referring to NACA 868 it only illustrates the P-47C-1. Even so it was superior to all then existant USN and USAAF fighters except for P-63, XP-51 (<320mph) and P-40.

A 'thick wing' in context of max T greater than comparable wing sections for a 'thinner wing' in absolute dimensions does offer some advantages on increased spar section Moment of intertia versus comparable 'shorter' beam with same web and cap material thickness. Note that the 'thinner' Spitfire wing had nearly the same absolute 'thickness' 'tallness', etc as the Mustang but the Spit spar was at ~ 25% chord and the P-51 was closer to 40% -

The Spit wing was 'thinner' (in ration to T/C) simply because the chord was so much greater than the P-51.

 

[drgondog]

One other note about flutter. Even if properly rigged, resonance may occur at different flight speeds - causing the control surface to flutter.

 

[GregP]

I have never seen any report claiming the Hellcat and Corsair could roll with an Fw 190, but have seen MANY rep[orts claiming the Fw 190 was superior at roll to everything it came against.

Maybe a link to the report in question so we can read it?

 

[FLYBOYJ]

One other note about flutter. Even if properly rigged, resonance may occur at different flight speeds - causing the control surface to flutter.

True Bill, but I think for the most case this will be more like a "buzz" at the stick.

 

[MikeGazdik]

Did the FW190 roll well at certain speeds, such as in the Zero only at lower speeds, or was across the board? I understand the Mustang rolled well at speed, and have read the Thunderbolt too. From reading I know the Corsair rolled well, but was it also across the the speed envelope? I knew the P-40 rolled well. Its news to me the P-63 rolled well, but I'm good with that!

 

[drgondog]

Did the FW190 roll well at certain speeds, such as in the Zero only at lower speeds, or was across the board? I understand the Mustang rolled well at speed, and have read the Thunderbolt too. From reading I know the Corsair rolled well, but was it also across the the speed envelope? I knew the P-40 rolled well. Its news to me the P-63 rolled well, but I'm good with that!

Google "NACA 868" to get a 1943 persective regarding comparisons..

 

[Edgar Brooks]

The Fw 190 had two spars that meant that the wing didn't twist from aileron forces which tended to cause control reversal from aeroelastic twist. The Spitfire with its single main spar suffered somewhat from this.
Friese ailerons reduced aerodynamic forces.

How many more times must we refute this nonsense; the Spitfire had a mainspar, attached to frame 5 (the firewall,) and a rear spar (to which the flaps and ailerons were attached) attached to frame 10 (the former under the pilot's seat.) It also had Frise ailerons, and the early Mk.I, with fabric-covered ailerons, had an aileron reversal speed (calculated and corrected in 1942) of Mach .74

 

[cimmex]

Didn't all WWII planes had a rear spar to attach the flaps and ailerons? Please name a plane with a single spar wing. The Spanish Buchon which is currently going restoration at Meier Motors in Germany had a two spar wing or when you count the rear and front spar also then it is a four spar wing.
Cimmex

 

[Tante Ju]

The rear is only an auxilary spar on both the Spitfire and the 109. It isn't really capable of transversing loads. On the Spitfire the front, relatively thick D-seck of the wing - a legacy of the early evaporative cooling - and the main (centre) spar formed a D-shaped box, which was probably while the design had a tendency for wing flexing under aileron load. The 109 had a box spar design, where the main spar and the thick skin of the wing formed a torsion box.

 

[FLYBOYJ]