Spitfires and High Speed Roll Rate

[Krusty]

You're heaping a LOT of assumptions into this in-game testing.

A LOT of them.

And you're making a lot more to contend that something is faulty with the game (which definitely seems to be the tone you're using).

First off, the visual representation in-game is not always accurate. Take our mix-matched Typhoon. Take the old Spit9 as an example. The graphics of how long the aileron are may or may not be accurate. Heck the Bf109E slats didn't extend to the wingtips when it first came out, it doesn't mean they didn't function normally, it's just a graphics glitch.

As Brooke said, you have to look to the historic performances to compare the planes. You say "the same airframe" -- but it's not the same. The Spit9 is quite a bit different from the SpitVb. First thing that comes to mind is increased ammunition, different wing (C wing as opposed to B wing), and other changes around the length of the nose and the engine mounting. All of these and many other possible explanations can be the reason the roll rates are different between the V and the IX. If you want to debate the differences to find out why that's another discussion. This discussion seems more like a cry of foul.

[Anaxogoras]

You mean to tell me that these minor differences can account for the decrease in roll rate of nearly 66%?  Please explain how.

[dtango]

You mean to tell me that these minor differences can account for the decrease in roll rate of nearly 66%?  Please explain how.

Roll rate is not a one degree of freedom action.  You have to account for the effect of yaw and sideslip.    For instance roll rate can dramatically change depending on any yaw and sideslip of the aircraft.  I posted the following pic in the thread I referenced which shows just a couple of examples:



So first you need to figure out how to isolate your roll tests to be able to remove the effect of yaw and sideslip before you can even begin to evaluate the variables that affect the roll only in the roll axis.

Secondly even if we simplify only to the roll axis, there are a lot of variables involved as well and unless you can point out where your tests show that the FM violates the physics relationships it's at best a philosophical discussion.

Tango, XO
412th FS Braunco Mustangs

[Karnak]

Krusty,

The Spitfire Mk IX was a Spitfire Mk Vc with a Merlin 61 engine and resulting increased plumbing.

Other than somebody who posted the screen shots of the ailerons, none of us are talking about the AH Spitfires, we're talking about the real ones.  It so happens that the ailerons are graphically accurate in AH now. Before the Spits were updated the Mk XIV had ailerons the same length as the Mk IX, something I had commented on as being wrong when it was first added.

[BaldEagl]

Other than somebody who posted the screen shots of the ailerons, none of us are talking about the AH Spitfires, we're talking about the real ones. 

Are you saying that Anax went out and actually flew each Spit varient IRL to come up with his data?  I thought we were talking about AH Spits.

[Brooke]

The Spitfire Mk IX was a Spitfire Mk Vc with a Merlin 61 engine and resulting increased plumbing.

That's a quick summary, but didn't the IX have two radiators (one under each wing) while the V had one radiator?  I think so (not sure about it though).  Things like that might have an impact on roll rate.  With the different engine, was CG changed?  If not, did they move the wings a little forward or back then?  Did they change angle of incidence of the wings a tiny bit?  Did they change any washout or dihedral?  Who knows?  All these little things, which sources totally disregard when they summarize a new airplane type in one simple sentence, could cause changes in some aspect of handling.

I'd go by the flight-test data if it were available.

[SgtPappy]

Wing incidence on the Spitfire remained constant up until, and including to the Mk.XIX (and XX/a.k.a. Mk.IV). The wing design was virtually the same with the wing gaining slightly more weight. The washout, too, remained the same. Identical to K5054. The introduction of the IX pushed the CoG forward and the XIV did that moreso due to a steady increase in heavier wing structure, larger radiator/intercooler/oil cooler setup under the wings, armament and, most importantly, the bigger engines and propellers. The Mk.I had the CoG further back than any of the other marks.

As we saw, the Mk.I had fabric ailerons which ballooned at high speeds, reducing efficiency. The Mk.V was almost a Mk.I, and only had metal ailerons as a difference from a control surface point of view. The Mk.IX had its CoG placed more forward, and has a more powerful engine. The mK.VIII in the tests you chaps are looking at does have extended tips. Wing area of the said a/c has 40.1' wing span. The standard Spitfire wing span is 36' 10". In addition, the summary states that: "The smaller span ailerons combined with extended wing tip give the Spitfire VIII an inferior rate of roll."

At any rate, the less aileron there is the less roll there would likely be. Imagine putting the ailerons closer to the fuselage. The comparative lift/drop of one wing to the other will be very low and the plane won't roll effectively. Hence, the ailerons are near or at the wingtips. Chopping the outer part of the aileron is sort of like moving them closer to the fuselage by a small amount. The Mk.VIII, though similar to the Mk.IX in almost every respect, including CoG, rolls a little worse. The XIV rolls better (to the left) because of the torque. But was it tested rolling the other way? If anything, the CoG is probably the culprit for better roll of the Mk.XIV vs the VIII though they have the same ailerons.

EDIT: Try testing the planes flying at 400 mph and cutting their engines to eliminate torque. Or have I not paid attention.. has it been done already?

[Anaxogoras]

The mK.VIII in the tests you chaps are looking at does have extended tips. Wing area of the said a/c has 40.1' wing span. The standard Spitfire wing span is 36' 10". In addition, the summary states that: "The smaller span ailerons combined with extended wing tip give the Spitfire VIII an inferior rate of roll."

Ok, now we're getting somewhere.  Are you absolutely sure our Spit VIII has extended wing tips?  Visually the wingspan is the same as the other marks, but of course, looks can be deceiving.

Apparently, the extended wingtips were not popular:
"When I am asked which mark of Spitfire I consider the best from the flying point of view, I usually reply 'The Mark VIII with standard wingtips.' I hated the extended wingtips...They were of no practical value to the Mark VIII and simply reduced the aileron response and the rate of roll." - Jeffrey Quill

At any rate, the less aileron there is the less roll there would likely be. Imagine putting the ailerons closer to the fuselage. The comparative lift/drop of one wing to the other will be very low and the plane won't roll effectively. Hence, the ailerons are near or at the wingtips. Chopping the outer part of the aileron is sort of like moving them closer to the fuselage by a small amount. The Mk.VIII, though similar to the Mk.IX in almost every respect, including CoG, rolls a little worse. The XIV rolls better (to the left) because of the torque. But was it tested rolling the other way? If anything, the CoG is probably the culprit for better roll of the Mk.XIV vs the VIII though they have the same ailerons.

EDIT: Try testing the planes flying at 400 mph and cutting their engines to eliminate torque. Or have I not paid attention.. has it been done already?

I haven't tested the roll rate with the engine off with a stopwatch, but when I was experimenting it didn't seem to make much difference.  In the tests I did all rolls were in the same direction as the engine torque.

[Karnak]

That's a quick summary, but didn't the IX have two radiators (one under each wing) while the V had one radiator?

Yes, hence my comment about increased plumbing.

With the different engine, was CG changed?

The nose is longer as the supercharger needed more room., CG should be the same with added weight aft of center balancing the engine's greater weight and changed position.

If not, did they move the wings a little forward or back then?/quote]
No, the wings on all Spitfires through the Mk XIX are in the same position.  I don't know about the F.20 and on.

Did they change angle of incidence of the wings a tiny bit? Did they change any washout or dihedral?  Who knows?

If they did, they didn't note it anywhere I have ever seen.  I would be very surprised if the Mk IX's incidence, washout or dihedral were any different from the Mk V.  Even the Mk VIII which was intended as the final and ultimate Merlin Spitfire almost certainly had only internal changes to the wing, with the changed ailerons being the only obvious external difference.  Without evidence that they did those things I think it is best to work from a basis that they did not.

I'd go by the flight-test data if it were available.

There is almost no roll rate data available that provides specific numbers.  The NACA chart has a full span and clipped Spitfire in it, both Mk Vs I believe.  Other than that everything I have seen about Spitfire roll rates have been very general statements.

[Karnak]

Ok, now we're getting somewhere.  Are you absolutely sure our Spit VIII has extended wing tips?  Visually the wingspan is the same as the other marks, but of course, looks can be deceiving.

No, ours does not but seems to be modeled on tests of a Spitfire Mk VIII with extended wingtips.  Extended tips are easy to identify.  They are long and pointy.

Here is an image of a Spitfire with extended wings:

[Anaxogoras]

Ok, I'm willing to accept that the VIII has extended wingtips (what an awful version to model), even though they appear to be standard wingtips... But I'm still confused about the IX.  It has the same wing as the V.  Should moving the CoG forward with the heavier engine make such a difference?

Edit:

From HTC's webpage http://www2.hitechcreations.com/ahhelp/models/spit8.html

Supermarine Spitfire Mk VIII
Country of origin:    Britain
Crew:    Single-seat
Type:    Fighter/Attacker
Normal loaded weight:    7875 lbs.
Dimensions:    
Wing span 36'10"
Length 31'3½"
Height 12'7¾"
Internal fuel:    148 gallons
Armament:    Package 1
4) 303 cal Browning 350 rpg
2) 20 mm Hispano Mk II 120 rpg

Optional
1) 30 gallon slipper tank
1) 500 lb GP bomb

[dtango]

I don't know why you guys keep ignoring me .  You can't even begin an apples to apples comparison between different Spits until you have figured out how to null out yaw and sideslip out of you flight tests.  There's no point to even begin comparing until you do because your numbers aren't isolated to begin to even compare the specific variables you're trying to compare.  Good luck figuring a way to null those out because when you roll, you yaw and sideslip - when you yaw, you sideslip and roll, etc.

And that's just for starters .

Tango, XO
412th FS Braunco Mustangs

[Brooke]

But I'm still confused about the IX.  It has the same wing as the V. 

But two underwing radiators on the IX vs. one on the V.  Maybe that makes a huge difference.  It's possible.

[dtango]

But two underwing radiators on the IX vs. one on the V.  Maybe that makes a huge difference.  It's possible.

It does .  Because it affects Ixx - which of course affects roll.  And that's just one of many variables to worry about in just the one degree of freedom model of role.

Tango, XO
412th FS Braunco Mustangs

[SmokinLoon]

Why doesnt HTC step in here and comment on such things??? This is a legit topic (unlike many) with all sorts of theories and "truth" and a simple post from HTC would solve it, end of issue, no more discussion.