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

riacrato · Nov 14, 2012

I don't see how you arrive at that conclusion: This has absolutely nothing to do with whether or not you hate the Spitfire. I don't hate the Spitfire or the Bf 109 but they are designs where the majority of the torsional loads are carried by a single spar that is much stronger than the other(s), so they are from that point of view "single spar" wings. And that other designs with "true" multi-spar wings have certain advantages, including sometimes the roll rate, as well as certain disadvantages, is simply a fact.

tomo pauk · Nov 14, 2012

Well put.

bobbysocks · Nov 14, 2012

So with this "floating rib" construction...there is free play between the 2 halves if they are not attached, fixed, rivited together. i assume they are attached to the main spar and at the trailing edge or secondary fixture ( spar, etc ). i can also see how the placement of the "L" type supports on the upper and lower skins would aid in keeping the wing rigid. but with the 2 section rib like that there would have to be some tendancy for either the upper or lower part of the wing to "bow" outwards from the center of the rib to the edges or to slide slightly on each other....especially if one surface of the wing is subjected to negitive "G"s. what would be the advantages of that? and is that design used on any other ac or in use today?

Edgar Brooks · Nov 14, 2012

cimmex said:
With that logic the Bf109 wing would be a 3 spar design because it had a rear spar, a front spar where the slats were attached and of course the main spar. Nevertheless the common designation is a single spar wing.
cimmex

If Herr Messerschmitt said that the 109 had a three-spar wing, common courtesy would dictate that so should everybody else, and I would have no quarrel with that, since it was his design. Likewise, when it comes to R.J. Mitchell, I bow to his expertise.
In all this manipulation of the English language, with talk back-and-forth of "single-spar wings," perhaps it's time to remind you all exactly what the person, who started all this, actually said:-

The Spitfire with its single main spar suffered somewhat from this.

Not a hint of a secondary, auxiliary, rear, or afterthought spar do I see, there, and anyone who doesn't know the Spitfire would be forgiven for visualising a wing flapping around a single, albeit strong, bar of metal, and there remains a strong suspicion that this was exactly what was intended.

CobberKane · Nov 14, 2012

If I may change the subject by rudely returning to the original point of the thread...
How much of the 190s roll rate was attributable to concerntration of mass along the longitudonal axis? The more weight moves away from the centerline the more mass there is to accellerate in a roll - a real bugbear of twin ingine designs. The 190 mounted most of its firepower in the wing roots and nose, and later models did away with the outboard cannon all together. Where were the fuel tanks? Did Kurt Tank do a better job of mass centralisation than other contemporary desgners? This would seem to my uneducated opinion to be one of the primary determinants of roll-rate.

drgondog · Nov 14, 2012

You need look no further than the relative size of the ailerons

CobberKane · Nov 14, 2012

drgondog said:
You need look no further than the relative size of the ailerons

Really? So the fastest rolling aircraft in the ETO was the B-17?

Siegfried · Nov 15, 2012

CobberKane said:
If I may change the subject by rudely returning to the original point of the thread...
How much of the 190s roll rate was attributable to concerntration of mass along the longitudonal axis? The more weight moves away from the centerline the more mass there is to accellerate in a roll - a real bugbear of twin ingine designs. The 190 mounted most of its firepower in the wing roots and nose, and later models did away with the outboard cannon all together. Where were the fuel tanks? Did Kurt Tank do a better job of mass centralisation than other contemporary desgners? This would seem to my uneducated opinion to be one of the primary determinants of roll-rate.

Eric Brown reckoned the roll rate of the long nose versions was less than the radial version. I'm thinking it was caused by a kind of inertia coupling. An aircraft does not roll along its thrust or principle axis which is out of alignment with the flight axis but kind of lollops or nutates a little as it rolls. The longer the aircraft the more mass near the nose will tend to centrifuge out. It's only really supposed to be an issue on jets, a very serious one.

Wing span also an issue, given equal wing tip speed a short span aircraft will roll faster.

CobberKane · Nov 15, 2012

Siegfried said:
Eric Brown reckoned the roll rate of the long nose versions was less than the radial version. I'm thinking it was caused by a kind of inertia coupling. An aircraft does not roll along its thrust or principle axis which is out of alignment with the flight axis but kind of lollops or nutates a little as it rolls. The longer the aircraft the more mass near the nose will tend to centrifuge out. It's only really supposed to be an issue on jets, a very serious one.

Wing span also an issue, given equal wing tip speed a short span aircraft will roll faster.

Or maybe it was just weight. Increased weight close to the longitudonal axis will not slow down roll as much as displaced weight, but it will still have an effect.

bobbysocks · Nov 15, 2012

Siegfried said:
. The longer the aircraft the more mass near the nose will tend to centrifuge out. ....
Wing span also an issue, given equal wing tip speed a short span aircraft will roll faster.

the only way i can see the length of the ac being an issue is weight of the ac vs hp or torgue. equal lengths with different weights will spin on their axis ( roll ) at different speeds due to the torque needed to spin them. so a longer yet lighter span could spin ( roll ) faster than a shorter but heavier one?? next, is it the wing span. if you use equal wing tip speed as a meter, that would bias the shorter wing due to the distance need to be traveled. me and you will have a race...we will both go 60kph. i will go 60 km you go 80...who is gong to get there first? i would think it is more the total area of the wing...cubic displacement vs resistance..that would be the determining factor?? would a longer span roll worse than short a shorter span if the total surface are was less? also for roll rate the ratio of the aileron surface to the surface of the wing might come more into play. hence a long thin wing may have the same roll rate as a stubbier but wider shorter one. i honestly do not know..i am interested to find out .

Tante Ju · Nov 15, 2012

CobberKane said:
Really? So the fastest rolling aircraft in the ETO was the B-17?

Relative size - aileron area vs wing area. The total size of the aileron was 1,93 sq.m (I believe for one aileron..?), the total wing size was 18,30 sq. m. If I got it right it means the aileron area was no less 21% of the total wing area. Compare that to about 13% on the 109E and 15.5% on the Spitfire I. IIRC La-5 series had also a sizeable aileron area, and they rolled very well.

Also the gearing ratio was very good, the stick travel was the same as the 109's I believe, but the aileron's travelled +/- 17 degrees. That's about twice the gearing advantage for the pilot.

Ailerons were very well executed, Friese type (which helps stick forces), well sealed on the top.

Radial engine meant that the weight distribution in the rolling axis was even.

The wing structure was also rigid and seems to have resisted twisting forces well, so little reduction due to elasticity.

The wingtips were squared, which again helps the lift distribution to be at the extreme end of the wing for best effect. After all ailerons simply change the lift of both wings, that's why the plane rolls.

drgondog · Nov 15, 2012

CobberKane said:
Really? So the fastest rolling aircraft in the ETO was the B-17?

No. Tante Ju covered the 'obvious point' very well.

tomo pauk · Nov 15, 2012

Seems like Tante Ju answered the question from the thread's title, too.

CobberKane · Nov 15, 2012

tomo pauk said:
Seems like Tante Ju answered the question from the thread's title, too.

Sounds good to me. It makes sense that aileron and wing design would be the major factor in roll-rate, with weight and mass centralisation also being very important. Doubtless the !() did exceptionally well in both these areas. The Zero would be an interesting counterpoint here, as it was obviously light and also had large ailerons, but apparently rolled poorly at high speeds. I assume this was a function of the gearing of the controls mentioned, as beyond a certain point it would be impossible to move the ailerons against the airflow. Perhaps this was designed into the Zero in recognition that it was not rugged enough to withstand violent manouvers at high speed?

cimmex · Nov 16, 2012

I don't think that weight and mass centralisation is so important, never heard that the Fw190 rolled better when the outer wing guns were removed.
cimmex

Siegfried · Nov 16, 2012

Edgar Brooks said:
Mid-1940 two wings were tested to destruction, and found to resist a factor (G?) of 11-13 (when the design called for 8-10,) tested to an all-up weight of 6,200lbs; the test report is 17 pages, so there's no way that I can put it on here.
In February 1940, an instruction was issued, with regard to examination for skin wrinkling, after any "abnormal manouevres." Any wrinkling, at all, on the leading edge, forward of the mainspar, would lead to the wing being declared unserviceable, and due for replacement. Aft of the mainspar, between ribs 14-19, any wrinkle less than 1/10" (2.5mm) could be disregarded; any wrinkle deeper than that (or wrinkles of any depth in any other area of the wing) would necessitate examination of the wingroot bolts, and, if they were bent, wing and bolts were to be replaced.
There is a manual, on repairs, patching, etc., but it's umpteen pages long, and I've no idea if the rear spar is mentioned.

The concern for ensuring that overstressed Spitfire wings were wrinkle free on the leading edge but could tolerate with indifference 2.5mm wrinkles aft of the main spar is evidence again that the spitfire in concept is a single spar design.

A two spar aircraft is almost completely indifferent to the state of the leading edge skins and the leading edges can be penetrated by landing lights, pitot tubes, gun ports without any serious engineering.

I believe the Spitfire used no less than 4 bolts to attach the main spar. Evidence not only of the load this spar needed to carry but also of design to resist torsional loads.

Do a thought experiment; take an angle grinder to a spitfire and and cut from the trailing edge at the wing root to the main spar. The wings strength will be minimally effected even with loss of the rest secondary spar and continuity of the skin. Most of the lifting and torsional loads go through the front spar.

Do that to a two spar design and you've likely to loose the wing as you've lost the important rear spar and the thick upper skins that form a torsion box. Likewise cut into the leading edge of the Spitfire and a significant amount of strength has been lost.

tomo pauk · Nov 16, 2012

Siegfried said:
...

I believe the Spitfire used no less than 4 bolts to attach the main spar. Evidence not only of the load this spar needed to carry but also of design to resist torsional loads.

...

Main spas: 7 bolts per spar. 4 bolts per lower 'beam' (tube in tube construction; maybe people can remeber biology classes - the tube-in-tub 'construction' is applied by plants and bones); 3 bolts per upper 'beam'.
Here are photos:

http://www.ww2aircraft.net/forum/aviation/fw-190-roots-great-roll-rate-34677-3.html#post954157

For rear spars: 1 bolt.

Siegfried · Nov 16, 2012

CobberKane said:
Sounds good to me. It makes sense that aileron and wing design would be the major factor in roll-rate, with weight and mass centralisation also being very important. Doubtless the !() did exceptionally well in both these areas. The Zero would be an interesting counterpoint here, as it was obviously light and also had large ailerons, but apparently rolled poorly at high speeds. I assume this was a function of the gearing of the controls mentioned, as beyond a certain point it would be impossible to move the ailerons against the airflow. Perhaps this was designed into the Zero in recognition that it was not rugged enough to withstand violent manouvers at high speed?

Large ailerons are considered a disadvantage to roll rate at high speed due to pilot work load. The zero partially got around this by gearing the ailerons up when the undercarriage was extended. Aileron size and gearing is a complicated trade off it seems.

One obvious thing we've overlooked despite the photographs posted is the Fw 190s use of a carry through spars, there were no bolts and I imagine the lower wing skins were continuous across the fuselage.

Late war Hellcats and Corsairs received geared spring tabs on the ailerons. At low speed they reduced roll rate since the tabs acted against the ailerons. At high speed their effect in reducing pilot effort dominated and enormously increased aileron deflection and roll rate. Roll rate almost doubled.

The P-51A had a very poor roll rate, however because the laminar wing was relatively thick a sort of concertina bellows was put into the wing of the P-51B onwards that channelled high pressure air from the ailerons deflected side to the bellows and used it to relieve the pilots stick force for greater deflection. This is called internal balancing. A slow P-51B/C/D was easily out rolled by a Me 109 or Fw 190 however above 360mph it matched the Fw 190 and improved relatively from there as shock waves on the lip of the 190s frise ailerons impacted negatively.

That other laminar flow US fighter the P-63 king cobra had the fastest roll of any US fighter, presumably due to pressure balanced ailerons but possibly it had something to do with engine placement.

If hydraulic boost is available the bigger aileron is the better as pilot work load is no longer a factor.

drgondog · Nov 16, 2012

Siegfried said:
The concern for ensuring that overstressed Spitfire wings were wrinkle free on the leading edge but could tolerate with indifference 2.5mm wrinkles aft of the main spar is evidence again that the spitfire in concept is a single spar design.

A two spar aircraft is almost completely indifferent to the state of the leading edge skins and the leading edges can be penetrated by landing lights, pitot tubes, gun ports without any serious engineering.

I believe the Spitfire used no less than 4 bolts to attach the main spar. Evidence not only of the load this spar needed to carry but also of design to resist torsional loads.

These attach bolts if localized on a spar would seem to have zero importance for torsion resistance. Torsion on the wing about the Y axis (i,e tending to twist the main spar if it is the Only resistance to Torque as well as Bending) would impose intolerable loads on a closely set four bolt pattern. To resist torsion rotation in the wing/fuselage attach, there should be at least two structural load paths as far apart as possible to take the Moment My (Torque) into a positive Fz and negative Fz at the fuselage. Visualize a wing which is attached solely by a spar with no other connectivity from wing to fuselage - and try to imagine the sixe of that 'joint' which would have to take out a torque generated by a full deflection aileron a high speed?

Do a thought experiment; take an angle grinder to a spitfire and and cut from the trailing edge at the wing root to the main spar. The wings strength will be minimally effected even with loss of the rest secondary spar and continuity of the skin. Most of the lifting and torsional loads go through the front spar.

Lift - Yes. Torsion - No. Torsion/twist has to be transferred via a 'box' composed of at least two beams two ribs (or equivalent) and two shear panels connecting all four (2 beams plus two ribs). Having said this, the combination of a 'structural leading edge C section with thick enough skin attached to a main spar at 25% is a robust D section beam and serves as a 'box'

Do that to a two spar design and you've likely to loose the wing as you've lost the important rear spar and the thick upper skins that form a torsion box. Likewise cut into the leading edge of the Spitfire and a significant amount of strength has been lost.

The leading edge and main spar of a Spitfire Are violated with Cannon and Machine guns. Having said that penetrating a box of H or I section type spar in the center of the shear web is a fault that can be compensated for with suitable doublers to compensate for the loss of shear transfer from top to bottom cap in bending.

Milosh · Nov 16, 2012

One obvious thing we've overlooked despite the photographs posted is the Fw 190s use of a carry through spars, there were no bolts and I imagine the lower wing skins were continuous across the fuselage.

Nope the wing skins were no continuous from tip to tip. There was a large removable panel to give access to the fuel tanks. The rear spar was not 'carry through', it ended and was bolted to the fuselage.

http://www.albentley-drawings.com/images/FW190A6W.jpg

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

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