Spitfires and High Speed Roll Rate

[Anaxogoras]

Ok, we know most Spitfires don't roll well at 400mph+, but why are some mediocre and others terrible?  Here are some approximate times for completing a 360 degree roll at 400mph, starting with zero inertia.

Spitfire I:     19.83
Spitfire V:      5.47
Spitfire IX:     9.04
Spitfire VIII:  10.96
Spitfire XVI:    4.28
Spitfire XIV:    5.52

Now, my memory tells me the Spitfire I had fabric covered ailerons and the wing would bend instead of rolling the plane, so its abysmal roll is no mystery.  The Spitfire V (and Seafire) both roll decently at high speed, but then the IX is much worse, and the VIII is glacial.  The XVI is clearly the best, with the XIV less than a second behind it.

What's going on here?

[BaldEagl]

Were you rolling with or against tourqe?  If it was against, then as HP increases roll rate should decrease.  That would also explain the XIV being close to the XVI's clipped wing configuration because the engine turns the opposite direction of all the other Spits.

I'd be interested to see the data rolling the other way.

[Anaxogoras]

I made sure to roll with the torque, i.e. left, except for the XIV.

[Karnak]

Odd.

The Mk I should roll the worst due to fabric skinned ailerons, the Mk V, Mk VIII, Mk IX and Mk XIV should be too close to call all having metal skinned ailerons and full span wings and the Mk XVI should be best with metal skinned ailerons and clipped wings.

[bozon]

Didn't VIII had different ailrons? I vaguely recall something about making them narrower to reduce stick force.

[Brooke]

I suspect that HTC set it at whatever the real flight-test data said it was.

Real aircraft performance is subject to many, many variables.

[Charge]

"Real aircraft performance is subject to many, many variables."

I do agree but such variation defies logic. The change from fabric to metal cover was something that could increase the roll rate quite much and some versions had ailerons with different dimensions but I do not recall how that affected the roll rate. AFAIK the wing flexing was somewhat a problem until the new type of wing (in Mk21?) which was more rigid although initially that had some problems too, don't recall what exactly.

As Karnak said there should be a visible change in roll rates only from canvas to metal covered ailerons and full span to clipped. That if no dimension changes are modelled in ailerons or if there were no structural changes inside the wing.

I'm not sure if the propeller type could also affect the rolling moment to opposite side of rotation by increasing torque as in Mk V there was a wider blade propeller than in Mk1 and then again wide bladed five blade propellers in later models.

-C+

Ed. The relevant NACA report: http://aerade.cranfield.ac.uk/ara/1947/naca-report-868.pdf

[RTHolmes]

repeat the tests with no throttle during roll to eliminate prop effects?

I know some suspect that the VIII and IX roll rate is bad because its modelled on extended wing tips rather than standard tips. I did try to find this data on spitfireperformance.com but gave up after 40mins of looking

[Angus]

The VIII was supposed to be better than the IX AFAIK. Different stiffness of the wing as well as different ailerons and possibly different power transfer?

[Lusche]

Spitfire I:     19.83

And that's what makes the Hurricane I a much better fighter than the Spit I in AHII.. it rolls 2-3 times faster than the Spit. That's a decisive advantage.

[Anaxogoras]

repeat the tests with no throttle during roll to eliminate prop effects?

I know some suspect that the VIII and IX roll rate is bad because its modelled on extended wing tips rather than standard tips. I did try to find this data on spitfireperformance.com but gave up after 40mins of looking

I doubt that will make much difference.  The 109 series also has a lot of torque and there were no issues because of it.  The 109F-G-K all roll about the same through 400mph.  Only the F feels a bit lighter at 200mph than the others in terms of roll-acceleration.

The VIII and IX roll rate is actually better than the V at 200mph.  Here, let me put up all the numbers and you can see for yourselves.  Remember, the numbers are approximate and, in some cases, two aircraft that are very close might be the same if I had a more precise instrument than a stop-watch.

200mph
SpitI: 6.28
SpitV: 3.3
Seafire: 3
SpitIX: 2.71
SpitVIII: 2.88
SpitXVI: 1.92
SpitXIV: 2.72

300mph
SpitI: 8.97
SpitV: 3.37
Seafire: 3.21
SpitIX: 3.82
SpitVIII: 4.3
SpitXVI: 2.65
SpitXIV: 3.7

400mph
SpitI: 19.83
SpitV: 5.47
Seafire: 5.79
SpitIX: 9.04
SpitVIII: 10.96
SpitXVI: 4.28
SpitXIV: 8.71

I just noticed that the 400mph roll rate I listed for the SpitXIV last night was actually the Ta-152's.  My bad, I was tired.  But now the plot thickens: add the SpitXIV to the list of Spits that don't roll at high speed.

For my part, I just can't fathom why the RAF would transition from a fighter like the V, which rolls well enough at 400mph, to the IX and the VIII which roll like a stick in frozen poo.  The IX is supposed to be the same plane as the V except for a bigger engine; there should be almost zero difference in roll rate.  I guess I'm saying that I don't believe the flight model, and with more tests, if this roll-rate data holds up, I wouldn't be surprised to see something in an update or a patch after we submit it to HTC.

[Anaxogoras]

Here is a wikipedia quote that includes a citation:

All Mk VII and Mk VIII Spitfires had the following changes: The internal structure was strengthened and revised. On the wings the ailerons were reduced in span by 8.5 inches (220 mm) outboard of the outer hinges. There had been some instances of earlier models breaking up in the air in steep high speed dives, it was thought, because of aileron flutter.
-Air Ministry 1943, p.13.

Apparently some IXs had this change and others did not.

[Anaxogoras]

So far as I can see, our IX is a converted Vc.  The ailerons are exactly the same.

SpitV:


SpitIX:


SpitVIII:


SpitXIV:


As can be seen, all of our Spitfires have the same wingspan; there are no extended wingtips.  The VIII and XIV ailerons have smaller surface area than the V and IX, which begs the question as to why the IX rolls worse than the V at 400mph?

[RTHolmes]

some suspect that the roll rate data used to model the VIII was from extended-tip spits. just what i've heard...

early IXs were Vs with the new engine

[Bruv119]

for someone with a passion for luftwaffe planes this seems a little unhealthy obsession.  Is there anything you want to tell us gav.






(closet spit dweeb perhaps?)