Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Anaxogoras on January 15, 2009, 12:02:52 AM
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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?
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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.
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I made sure to roll with the torque, i.e. left, except for the XIV.
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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.
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Didn't VIII had different ailrons? I vaguely recall something about making them narrower to reduce stick force.
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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.
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"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
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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 :rolleyes:
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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?
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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.
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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 :rolleyes:
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. :o 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.
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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.
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So far as I can see, our IX is a converted Vc. The ailerons are exactly the same.
SpitV:
(http://farm4.static.flickr.com/3395/3198635563_29014d447b_o.png)
SpitIX:
(http://farm4.static.flickr.com/3322/3199481004_c23fe452cc_o.png)
SpitVIII:
(http://farm4.static.flickr.com/3519/3199481110_737a0b5884_o.png)
SpitXIV:
(http://farm4.static.flickr.com/3468/3198635789_6346b1da02_o.png)
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?
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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 :)
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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?)
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(who isnt ;))
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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?)
:rofl Bruv. It's a long story, but I just finished testing the roll rate of our fighters at 200, 300, and 400mph and the Spitfire data stuck out like an infected toe. I'm only bringing this to light because I want our Spitfires to perform their best when I shoot them down. :aok
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lol gavagai.
I would expect the VIII to be similar to the XIV because the spit14 is essentially a spit VIII, with a griffon thrown in.
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lol gavagai.
I would expect the VIII to be similar to the XIV because the spit14 is essentially a spit VIII, with a griffon thrown in.
It seems like our IX rolls like the VIII and XIV even though in appearance it has the wing of the V.
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I recall that the VIII had different ailerons etc to eliminate flutter and such. Bear in mind that it appeared later than the IX due to the IX being hurried in while the VIII was finished.
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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.
Guys, just to clarify the terminology, it's not wing flexure (bending) , but torsional stiffness that affects high speed roll-rate. Once you stiffen the aileron attachment points (stiffer rear spar?) and control cable mounts (cable stretch is also an issue), the only real way to significantly increase the wing's torsional stiffness (provided the external dimensions are fixed) would be to increase the aluminum skin thickness or go to steel. No way Supermarine went to steel, and I doubt they made any significant increase in wing skin thickness.
So I think you're right to suspect there's something fishy here.
just my .02 :salute
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I've never read anything that suggested the shorter ailerons on the Mk VIII or Mk XIV reduced the roll rate.
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What Quill has on the VIII, ailerons and vs the IX:
"It also featured ailerons on which the the long overhang outboard of the outer hinge was shortened in order to increase the stiffness of the aileron structure. "
Later..
"The Mk VIII however was by far the better aeroplane"
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:rofl Bruv. It's a long story, but I just finished testing the roll rate of our fighters at 200, 300, and 400mph and the Spitfire data stuck out like an infected toe. I'm only bringing this to light because I want our Spitfires to perform their best when I shoot them down. :aok
If you want them rolling better you have my full support. ;)
Knock yourself out trying :aok
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Just read up a bit more.
They changed the aileron hinges again on the Mk 21. Piano hinges that time and a wing 47% stiffer. Resulted in much better roll rate.
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The only thing that matters is whether the performance in AH matches the flight-test data.
All of this arguing about what should or shouldn't be based on how big the ailerons look in the game, whether the wing is clipped or not, etc., is all just a philosphical discussion. You can't guess the roll rate based on such things -- there are too many other things that matter. In the end, you have to look up what the real plane actually did in flight testing and have the in-game plane match that.
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true, shame that most of the RAFs test data seems to concentrate in detail on speed/climbrate at different alts/weights/boost/gearing/props. theres barely any mention of roll rate except comments like "not much different". the only thing I found for the VIII was along the lines of "the shorter ailerons dont seem to reduce roll rate." The only rate/speed graph I found was a ?V vs 109 comparison. :(
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The only thing that matters is whether the performance in AH matches the flight-test data.
All of this arguing about what should or shouldn't be based on how big the ailerons look in the game, whether the wing is clipped or not, etc., is all just a philosphical discussion. You can't guess the roll rate based on such things -- there are too many other things that matter. In the end, you have to look up what the real plane actually did in flight testing and have the in-game plane match that.
Thank you Brooke ;).
On top of Brooke's comments, rolling unfortunately does not occur in one degree-of-freedom. Roll, yaw, and sideslip are coupled so they affect one another. Until you can isolate all that on top of all the other variables you have to consider in just the roll axis it's kind of meaningless.
Here is some more general info regarding rolling:
http://bbs.hitechcreations.com/smf/index.php/topic,253393.msg3138691.html#msg3138691
Tango, XO
412th FS Braunco Mustangs
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... add in the fact that roll rate is like turn rate - instantanious and sustained rates are different - and its quite a hard thing to quantify. knowing the time to roll 360deg doesnt have much relation to ACM, 90deg might be a more useful measure.
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The only thing that matters is whether the performance in AH matches the flight-test data.
All of this arguing about what should or shouldn't be based on how big the ailerons look in the game, whether the wing is clipped or not, etc., is all just a philosphical discussion. You can't guess the roll rate based on such things -- there are too many other things that matter. In the end, you have to look up what the real plane actually did in flight testing and have the in-game plane match that.
Naturally, but if test data said that the IX rolled far worse than the V at 400mph, would you believe it? I hope not. It's a better explanation that the test data was flawed than that the same airframe yielded far different results depending its designation. That the latter explanation is absurd is known a priori.
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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.
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You mean to tell me that these minor differences can account for the decrease in roll rate of nearly 66%? Please explain how.
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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:
(http://thetongsweb.net/images/roll_types.jpg)
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
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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.
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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.
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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.
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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?
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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.
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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.
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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:
(http://www.luchtoorlog.be/img/spit_v/hf.jpg)
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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 (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
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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
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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.
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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
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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.
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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
We appreciate your input tango. Generally you like to pop into these threads and throw out the most abstract analysis possible and hope that we deduce the more specific point you have in mind. That's probably not going to happen. ;)
Let me ask you a question: Does your above statement imply that I cannot reach the judgment that one spitfire outrolls another, unless I "null out" yaw and slip with the scientific precision of an engineer? Please give me some specifics. I think I understand your point, but it would seem to be applicable to cases where the roll rates are very close, not where they are drastically different. For example, I don't need to null out yaw and sideslip to know that the 109F outrolls the 109E at 400mph. The former rolls without too much difficulty, and the latter almost doesn't roll at all!
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dtango,
Because your argument is basically that we can't know anything or even guess at anything or even use historical test results unless we know everything. It isn't useful unless we want to just stick our heads in the sand and play know-nothings.
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Why not compare to archival footage? It always seemed to me that our Spit Is rolled way slower than archival footage of Spit Is peeling off. Of course it is not possible to estimate airspeed from movies but for movie footage you could guess they are going between max cruise and military.
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We appreciate your input tango. Generally you like to pop into these threads and throw out the most abstract analysis possible and hope that we deduce the more specific point you have in mind. That's probably not going to happen. ;)
Let me ask you a question: Does your above statement imply that I cannot reach the judgment that one spitfire outrolls another, unless I "null out" yaw and slip with the scientific precision of an engineer? Please give me some specifics. I think I understand your point, but it would seem to be applicable to cases where the roll rates are very close, not where they are drastically different. For example, I don't need to null out yaw and sideslip to know that the 109F outrolls the 109E at 400mph. The former rolls without too much difficulty, and the latter almost doesn't roll at all!
Geez, even I have to agree with you on this one. Who really cares about what forces are acting on what. The question is when you crank the ailerons all the way in one direction or the other does the thing roll at a rate consistant with what it did in real life or not but as Brooke already brought up, the only way to know is to have hard data on real life roll rates.
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Why not compare to archival footage? It always seemed to me that our Spit Is rolled way slower than archival footage of Spit Is peeling off. Of course it is not possible to estimate airspeed from movies but for movie footage you could guess they are going between max cruise and military.
Now that was an idea. Really!
Should of course be testable in RL, still lots of Spits around. I've seen a Mk I in the air, but think there is only one. But V and IX's are by the bundles...
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Gavagai:
I have no issue with doing that test and saying one out-rolls the other. But that's as much as you'll be able to deduce from the way it's tested.
But if we want to now try to analyze WHY one out-rolls the other and HOW that's CORRECT or INCORRECT then we're going to have to do a lot more in the testing and analysis to figure that out. From your tests results we are not able to make conclusions of the nature that people are making conclusions about. Examine the dynamics involved then you'll understand why. I'm sorry I have neither the time or energy to explain the physics. I and others have explained just SOME of it before in this thread that I already referenced. Here it is again if you want to glance at it.
http://bbs.hitechcreations.com/smf/index.php/topic,253393.0.html
The easier alternative is to do what Brooke suggests. Look for real flight tests to compare to. Even there you need to understand the way the've done the tests and the dynamics they are isolating.
dtango,
Because your argument is basically that we can't know anything or even guess at anything or even use historical test results unless we know everything. It isn't useful unless we want to just stick our heads in the sand and play know-nothings.
Karnak - that's not what my argument is at all :).
Tango, XO
412th FS Braunco Mustangs
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Gavagai:
I have no issue with doing that test and saying one out-rolls the other. But that's as much as you'll be able to deduce from the way it's tested.
But if we want to now try to analyze WHY one out-rolls the other and HOW that's CORRECT or INCORRECT then we're going to have to do a lot more in the testing and analysis to figure that out. From your tests results we are not able to make conclusions of the nature that people are making conclusions about.
Fair enough. I think that for the rest of us, because the IX and V were nearly the same airframe, we are extremely skeptical. For my part, after testing all of the roll rates of all of our aircraft, there is nothing comparable to the V and IX. The 109F-K are too close for my stopwatch to measure the difference (despite becoming heavier, having redesigned v-stabs, redesigned cowlings, etc.). The 190 series shows little change, and the same is true of the P-47D series, the Yaks; even the Hurricane IID doesn't roll much worse than the Mk I or IIC. So here I am, I observe all these examples of consistency despite small changes in weight distribution, oil cooler placement, weapon loadouts etc., and then I get to the Spitfire V and IX and they are drastically different at 400mph. So yeah, I am skeptical, and because of the consistency across small changes in our other aircraft the burden of proof is on those who say the V and IX should be so different.
Now, I don't believe you're saying they should be different. You're right that we need test data to be sure. Let's come full circle and agree that there is reason for HTC to check their numbers. Need I remind everyone of how much some of their flight models have changed over the years? We had the Spitfire V and IX in Warbirds and they almost rolled the same. Check out http://www.rdrop.com/users/hoofj/wbroll.htm (http://www.rdrop.com/users/hoofj/wbroll.htm) Hoof's numbers are also for one 360 degree roll.
Roll rates: 150 200 250 300 350 400
SpitV 4.6s 3.6s 4.1s 5.1s 7.1s 10.4s
SpitIX 5.0s 3.7s 4.2s 5.4s 7.9s 11.4s
So the same person, HT, modeled those Spits and they rolled about the same. The difference is that the Spit V rolls much better at 400mph than it did then!
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Finding real period test results would help. Knowing that the Mk VIII's roll rate is based on extended wingtips it makes more sense that it lags behind the others but the IX's roll rate gives me pause!
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Gavagai:
I understand your logic. However you and others have made too many aerodynamic assumptions.
For starters are you sure you removed the effect of yaw or sideslip from your roll tests between the Spit V and Spit IX? Because yaw and sideslip will change your roll performance.
For grins let's say that you have and assume we can simplify the analysis just to one degree of freedom. The following is the general equation for estimating roll rate in the one degree of freedom case:
(http://thetongsweb.net/images/roll_rate_eq1.jpg)
It covers both the roll accleration and steady state roll. It's already been mentioned that the Spit IX has two radiators vs. the Spit V's one. Why does a small thing like that matter? Because the roll transient time constant 1/T, which determines roll accleration is impacted by the rolling moment of inertia (Ixx). Here's the equation for 1/T:
(http://thetongsweb.net/images/roll_rate_eq2.jpg)
where:
Q = dynamic pressure (.5*air_density*velocity^2)
S = wing surface area
b = wing span
Clp = coefficient of rolling moment due to rolling
Ixx = rolling moment of inertia
V = velocity
The 2 radiators under each wing increases the rolling moment of inertia. Increase the moment of inertia reduces 1/T which reduces roll acceleration.
And that's just one variable. There are others. Roll performance is complicated and there are more details to be considered that can affect it than the factors folks have brought up in this thread.
Why do the WB roll rates differ from AH for the Spit V and IX? Beats the heck outta me :).
Should HTC look the AH Spit V and Spit IX numbers? Sure thing.
Is there something wrong? Maybe / Maybe Not, but I sure the heck can't tell from speculating from your data points and the simple factors that people have thrown out so far for why it is wrong because we're totally ignoring other key aerodynamic factors as well.
Tango, XO
412th FS Braunco Mustangs
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I can see why the Spit IX's roll acceleration would be slower based on your clear explanation of the second formula. I am still studying the link you gave in this thread, so I'm not going to ask you for help with the first formula yet. ;)
On the other hand, roll acceleration rates are minimally responsible for the different rates I measured. Suppose I had nulled out yaw and side slip, and suppose that we weren't interested in roll acceleration, but only roll rate. What sort of changes in the Spitfire IX impact roll rate alone?
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Ah yes. Thanks Tango for another great page of explanations :aok The math behind turning page is also favourite'd.
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Anaxo, - the load would. Or rather/also the weight distribution.
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Anaxo, - the load would. Or rather/also the weight distribution.
Like the 109/p47/190/hurricane/yak series? :P
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Gavagai:
I understand your logic. However you and others have made too many aerodynamic assumptions.
For starters are you sure you removed the effect of yaw or sideslip from your roll tests between the Spit V and Spit IX? Because yaw and sideslip will change your roll performance.
For grins let's say that you have and assume we can simplify the analysis just to one degree of freedom. The following is the general equation for estimating roll rate in the one degree of freedom case:
(http://thetongsweb.net/images/roll_rate_eq1.jpg)
It covers both the roll accleration and steady state roll. It's already been mentioned that the Spit IX has two radiators vs. the Spit V's one. Why does a small thing like that matter? Because the roll transient time constant 1/T, which determines roll accleration is impacted by the rolling moment of inertia (Ixx). Here's the equation for 1/T:
(http://thetongsweb.net/images/roll_rate_eq2.jpg)
where:
Q = dynamic pressure (.5*air_density*velocity^2)
S = wing surface area
b = wing span
Clp = coefficient of rolling moment due to rolling
Ixx = rolling moment of inertia
V = velocity
The 2 radiators under each wing increases the rolling moment of inertia. Increase the moment of inertia reduces 1/T which reduces roll acceleration.
And that's just one variable. There are others. Roll performance is complicated and there are more details to be considered that can affect it than the factors folks have brought up in this thread.
Why do the WB roll rates differ from AH for the Spit V and IX? Beats the heck outta me :).
Should HTC look the AH Spit V and Spit IX numbers? Sure thing.
Is there something wrong? Maybe / Maybe Not, but I sure the heck can't tell from speculating from your data points and the simple factors that people have thrown out so far for why it is wrong because we're totally ignoring other key aerodynamic factors as well.
Tango, XO
412th FS Braunco Mustangs
I am so retarded :O
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Like the 109/p47/190/hurricane/yak series? :P
Not sure what you're getting at, but look at the difference when wing tanks are full/empty for instance.
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Not sure what you're getting at, but look at the difference when wing tanks are full/empty for instance.
I'm getting at the fact that all of those aircraft underwent changes in weight and weight distribution without the effects we observe in the transition from the V to IX.
It's also possible that the V rolls too well. Look at the old numbers from Warbirds. Back then HT had the Spit V rolling much more slowly at 400mph.
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The V should AFAIK roll slightly better than the IX, - it's all muscle powered and the aircraft is lighter.
The V had a very delicate C.o.G. by the way. While that had a very big effect on pitch, I am not sure on roll.
The IX would be more nose heavy.
With a flick-roll, the V would definately be swifter than the IX, however a Mk I would be even swifter while being unmoveable at speeds where the other ones could still roll...