Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Karnak on November 18, 2005, 04:48:29 PM
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I did some quick and dirty tests, which I cannot ensure are acurate, and it seems that the Spit VIII rolls notable slower than either the Spit IX or Spit XIV.
Test method:
Take off with full fuel.
Climb to 500ft.
Reach speed of 310mph.
Trim to neutral.
Roll 360 degrees right without rudder inputs, record time.
Roll 360 degrees left without rudder inputs, record time.
Note: Timing had to be done by counting and so is not precise.
Spitfire Mk IX:
Right: 5 seconds
Left: 5.5 seconds
Spitfire Mk VIII:
Right: 6 seconds
Left: 6.5 seconds
Spitfire Mk XIV:
Right: 5 seconds
Left: 5 seconds
Note: The Spit XIV was harder to test due to it's greater engine power, keeping it at 310mph was problematic.
Now, if I have not grossly mistimed these rolls it seems that the Mk VIII rolls slower than the others. Why so?
It has shortened ailerons, but the reduced surface area should allow for higher deflection for the same stick force, ending with approximately the same roll force being generate by the ailerons as the larger ailerons on the Mk IX at a lesser degree of deflection. In addition the Mk XIV also has shortened ailerons.
It also has fuel in the wings unlike the Mk IX. I don't know how this would affect the roll rate, but the Mk XIV also has fuel in the wings.
I have also not read of any difference in roll rate between the Mk VIII and Mk IX. The Mk XIV had a similar roll rate to the IX, but favoring the oposite direction due to the Griffon rotating the prop in the oposite direction.
So, are my timings just off or is there something going on here?
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Higher aileron deflection is not a good thing. In fact, it can be a very bad thing, with the upward aileron pretending to be a spoiler, and the lower one a drag rudder.
I would think that the travel of the ailerons was not adjusted with the shorter span surfaces, in order to prevent the above mentioned nastyness. But without rigging instructions or mfr's data I can't tell you for certain.
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Originally posted by Tails
Higher aileron deflection is not a good thing. In fact, it can be a very bad thing, with the upward aileron pretending to be a spoiler, and the lower one a drag rudder.
I would think that the travel of the ailerons was not adjusted with the shorter span surfaces, in order to prevent the above mentioned nastyness. But without rigging instructions or mfr's data I can't tell you for certain.
I wasn't thinking that the travel would have been increased. By the time a Spitfire is going 300mph the pilot can no longer get full deflection out of the ailerons as the pressure on them is too high given the way a Spitfire is layed out. With less surface area there would be less pressure and thus the pilot would be able to deflect the ailerons closer to full deflection.
I would fully expect the Mk VIII and Mk XIV to have a reduced roll rate at speeds where full deflection of the ailerons can be obtained, but that is below 220mph as I recall. Maybe below 180mph. By 300mph the pilot simply is not going to get max aileron deflection.
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Originally posted by Karnak
I wasn't thinking that the travel would have been increased. By the time a Spitfire is going 300mph the pilot can no longer get full deflection out of the ailerons as the pressure on them is too high given the way a Spitfire is layed out. With less surface area there would be less pressure and thus the pilot would be able to deflect the ailerons closer to full deflection.
I would fully expect the Mk VIII and Mk XIV to have a reduced roll rate at speeds where full deflection of the ailerons can be obtained, but that is below 220mph as I recall. Maybe below 180mph. By 300mph the pilot simply is not going to get max aileron deflection.
Ok, I see what you're saying here.
The pilot would be able to get more deflection out of the ailerons if they had shorter span, certainly. The problem is that the shorter span ailerons would have reduced authority compared to the longer ones. So, on a good day, they may even out at high speeds. Or, the short-span surfaces may have LESS authority at higher speeds.
I have no practical experience with Supermarine products, so I'm just going by theory here :D
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You've got it. It may be correct as it is, but I've never heard that the roll rate dropped.
I'm asking for an explanation is all. That could be "It is correct because of X and Y and Z." It could be "Oops, it should be the same." It could be "Jeez Karnak, can't you even keep time for less than 7 seconds. It is the same and you botched the tests."
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Depending on the design of the aileron, it could be the short span surface is capable of deflecting too much at high speeds, leading to the problems I described. The aileron acting less as an aileron and more like a drag rudder. Does the Spit8 yaw more than the others in a high speed roll, with neutral rudder? If so, that may be what's happening.
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I'm not sure, but keep in mind these are the exact same ailerons as the Mk XIV has. They also aren't much shorter, less than a foot off the outer ends.
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Odd, really, especially the relative perf of the VIII/XIV.
For what it's worth :
Alex Henshaw, chief test pilot at the Castle Bomwich Spitfire factory.
"I loved the Spitfire in all of her many versions. But I have to admit that the later Marks, although they were faster than the earlier ones, were also much heavier and so did not handle so well. You did not have such positive control over them. One test of manouverability was to throw the Spitfire into a flick roll and see how many times she rolled. With the Mark II or the Mark V one got two and a half rolls but the Mark IX was heavier and you got only one and a half. With the later and still heavier versions one got even less.The essence of aircraft design is compromise, and an improvement at one end of the performance envelope is rarely achieved without a deterioration somewhere else."
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Manoeuvrability
5......... There was nothing to choose between either aircraft as regards turning circles at any height; whether on offensive or defensive manoeuvres neither could make any impression on the other. In rate of roll, however, the Spitfire IX was considerably better especially at low altitude. A number of full rolls through 360 degrees were timed by the same pilot flying each aircraft in turn and although quanitative tests are difficult to produce, it appeared that there was often more than 1.5 seconds superiority for the Mark IX over the Mark VIII. The Mark VIII feels fairly light on the ailerons but at high speeds it becomes very heavy, and so this new combination of extended wing and small aileron cannot be considered satisfactory.
CONCLUSIONS
7......... There is no difference in performance between the Spitfire VIII and Spitfire IX with Merlin 63 engines, except that with the extended wing tips the Spitifre VIII is performing a little bit better at high altitude.
8......... The smaller span ailerons combined with extended wing tip give the Spitfire VIII an inferior rate of roll.
Spitfire Mk VIII Testing (http://www.spitfireperformance.com/spit8tac.html)
The above tests were F.IX and F.VIII both with Merlin 63.
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There could be other things to factor in that will deteriorate roll rate. Weigth distrobution being one of them, and I'm not talking about just in the wings. Anything outside the axis of rotation will slow down an aircraft's roll rate and other facets of manuverability.
Like I said, I'm not familiar enough with Supermarine products to be able to say for certain what could cause the differences in roll rate. I just know a bit of theory.
EDIT: *Reads Bruno's post* Extended wing tips. That will do it right there.
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Spitfire roll rates in degrees per second, based upon one 360 degree roll.
Air speed: 300 mph
Altitude: 2,000 feet.
Fuel: 50%
Stopwatch used to measure. Average of three tests.
Mk.VIII
Right = 68 degrees
Left = 74 degrees
Mk.IX
Right = 78 degrees
Left = 81 degrees
Mk.XIV
Right = 78 degrees
Left = 82 degrees
Mk.XVI
Right = 112 degrees
Left = 116 degrees
For comparison:
Fw 190A-5
Right = 125 degrees
Left = 131 degrees
F4U-1
Right = 97 degrees
Left = 100 degrees
My regards,
Widewing
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I was wondering about this myself.
Not knowing anything about it historically, I'm going by simple physics. In that case one must differentiate between limitation due to "force applied on stick" and limitation due to plane design.
The force needed to be applied on the stick for max deflection really depends not only on aerodynamics of the ailron but also much on the mechanics of the control wires and levers. Simply having a longer stick as a lever will require less force applied by the pilot (although longer deflection of the stick).
If max deflection is achieved, we turn to aerodynamics. Roll is done by uneven lift of the wings. On the rising wing, the aileron increases the angle of attack, but the rolling motion reduces back the effective angle of attack - the longer the wing the more severe this effect since the roll speed is roll rate times the distance from roll axis. The decending wing has the same effect in the other direction. So roll rate will depend both on area and maximum angle of attack of the aileron section and the distance from roll axis - the shorter the wing, the better. Parts of the wing not in the aleron section just hinder roll due to the effective angle of attack. Another consideration is torque of the engine which will make rolling in one direction faster than the other.
clipping the spit wing eliminate the part that hinder roll the most - the most far from the axis that is not part of the aileron section. 8 and 14 have almost the same wing I believe (save the weapons) so I'm not sure why the difference.
Bozon
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Bruno,
The Spit VIII in that test had extended wing tips. Most, such as the one in AH, had standard wing tips. Of course the extended wing Spit VIII will roll worse. It is the oposite of clipping the wings.
Just to clarify, the test Bruno posted does not have anything to do with our Spit VIII. The extended tips refered to by the test are the long, pointed wings you can sometimes find on Spits. The rounded tip wings like we have are standard wings and the squared wings as on the Mk XVI are clipped.
So that test is refering to a different wing shape.
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The extended wing tips alone don't account for the IXs better roll rate entirely.
If you read what I quoted:
The smaller span ailerons combined with extended wing tip give the Spitfire VIII an inferior rate of roll.
Your test show a 1 sec roll advantage for the the IX. The test I linked says:
it appeared that there was often more than 1.5 seconds superiority for the Mark IX over the Mark VIII.
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Given how much the clipped wings increased the roll rate of the Spitfire I am not prepared to assume that the extended wings only very slightly reduced the roll rate.
From the Mk XIV testing when compared with the Mk IX:
Rate of Roll
19. Rate of roll is very much the same.
Remember, the Mk XIV has the same shortened ailerons as the Mk VIII.
Spitfire XIV AFDU Tactical Trials (http://www.spitfireperformance.com/spit14afdu.html)
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Originally posted by Karnak
Given how much the clipped wings increased the roll rate of the Spitfire I am not prepared to assume that the extended wings only very slightly reduced the roll rate.
So give every bit of the increase in the VIIIs roll rate above 1 sec to the extended wing tips in that test. Thus the 1 sec you are left with matches up with AH, doesn't it?
Which was kinda my point...
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19. Rate of roll is very much the same.
That is not a scientific conclusion, its an opinion.
Very much the same = exactly the same?
Slighly worse?
Slightly better?
etc...
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Originally posted by Bruno
So give every bit of the increase in the VIIIs roll rate above 1 sec to the extended wing tips in that test. Thus the 1 sec you are left with matches up with AH, doesn't it?
Which was kinda my point...
So you're suggesting that shortening the ailerons by about 8 inches would add a full second to the roll time and then extending the wing tips only .5 seconds? That is hard to believe. And it doesn't match the effect of clipping the wings..
Neither the text you posted or mine is scientific. Yours was more detailed, but for the wrong wings. Very much the same sounds like it would be very close, not 10 degrees per second slower. That would be "19. Rate of roll is similar." at best. 10 degrees per second is not slight.
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No what I am suggesting is that the shortened ailerons did have an effect on the roll rate, whether it be 1 sec or .5 it doesn't matter. Let's say its .5 sec, so what? The roll rate of the VIII and the IX weren't the 'same'.
The conclusion:
The smaller span ailerons combined with extended wing tip give the Spitfire VIII an inferior rate of roll.
That inferior roll rate reached '1.5 seconds superiority for the Mark IX over the Mark VIII.'
The shortened ailerons impacted roll rate. If you claim that 10 degree per sec is too much, then prove it. If you are going to argue over +/- .5 sec of roll then I chalk that right up there with those old threads about how the the 'A8 is 4 mph to slow otd' and Ram's 'the A-5 is 12 mph to slow'.
EDIT:
Also, it should be noted that the A-5 max roll rate of just 131 degrees (left) is considerably slower then it should be. Far in access of the 10 degrees we talking about here with the VIII.
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And I am saying that you can base very little to nothing on that one off hand comment based on a wing that we aren't even discussing.
What should the Fw190A-5's roll rate be at 300mph? Keep in mind that Widewing's test was not of sustained roll rate. Widewing's test was not at all of the max roll rate. Isn't there supposed to be a 190 FM revision coming in any case?
The Spits are supposed to be done now, so if this is an issue and if it is to be addressed it needs to be addressed now. I am still open to it being correct, but I'd like to see something that actually backs that up.
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Originally posted by Karnak
What should the Fw190A-5's roll rate be at 300mph? Keep in mind that Widewing's test was not of sustained roll rate. Widewing's test was not at all of the max roll rate. Isn't there supposed to be a 190 FM revision coming in any case?
My roll rate tests were done for a single revolution as this is more realistic of combat. A single roll will include delays associated with resistance to rolling (overcoming inertia). 300 mph was used simply as a common baseline, without regard to determining best roll speeds for each type.
As to the 190A-5 being slower than it should be, it really isn't. In fact, it is very close to NACA's test data for a 190A-4. However, the 190's best roll rate is attained below 300 mph, as this speed is on the backside of the roll curve. I tested the 190A-5 at slightly lower speeds and it was considerable faster. Ideally, the best speed for the 190 is around 280 mph. I tested at 290 and 280 just to verify the curve seen below. All numbers rounded to closest non-fractional, either up or down.
290 mph, 2,000 feet, 50% fuel:
Right: 137 degrees
Left: 140 degrees
280 mph, 2,000 feet, 50% fuel:
Right: 140 degrees
Left: 144 degrees
(http://home.att.net/~ww2aviation/P-38rollchart.JPG)
My regards,
Widewing
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I tested the Spitfire Mk.VIII for roll at various speeds beginning at 150 mph and in increments of 50 mph up to 400 mph.
2,000 feet, 50% fuel
150 mph:
Right: 65 degrees
Left: 72 degrees
200 mph:
Right: 85 degrees
Left: 93 degrees
250 mph:
Right: 79 degrees
Left: 87 degrees
300 mph:
Right: 68 degrees
Left: 74 degrees
350 mph:
Right: 52 degrees
Left: 54 degrees
400 mph:
Right: 36 degrees
Left: 37 degrees
Note that as speeds increase, the Mk.VIII suffers from increasing pitch-up when rolling and that requires elevator input to minimize, likely effecting times recorded, and thus rate of roll measurement will have an increased error.
My regards,
Widewing
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In fact, it is very close to NACA's test data for a 190A-4.
The NACA simply copied the data from the RAE 1231 test of a captured FW-190G series.
In that test the forces exhibited and the behavior of the aircraft do not match the calibration charts found in the aileron adjustment regulations.
Even the test pilot noted something was wrong.
There are several threads which showed the documentation.
The NACA curves and RAE 1231 represent an FW190 with ailerons out of adjustment and are a very good measurement of "at least" performance. They certainly do not represent average or best performance.
All the best,
Crumpp
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Originally posted by Crumpp
The NACA simply copied the data from the RAE 1231 test of a captured FW-190G series.
In that test the forces exhibited and the behavior of the aircraft do not match the calibration charts found in the aileron adjustment regulations.
Even the test pilot noted something was wrong.
There are several threads which showed the documentation.
The NACA curves and RAE 1231 represent an FW190 with ailerons out of adjustment and are a very good measurement of "at least" performance. They certainly do not represent average or best performance.
All the best,
Crumpp
Is this the data you are referring to in NACA report 868?
(http://home.att.net/~c.c.jordan/NACARollData.jpg)
My regards,
Widewing
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Yep
You want the whole report?
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Originally posted by Crumpp
Yep
You want the whole report?
I have it, but thanks anyway...
Gotta tell ya, that Typhoon rolls like a fat man sleeping on a 2x4....
My regards,
Widewing
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Gotta tell ya, that Typhoon rolls like a fat man sleeping on a 2x4....
Yeah, from what I understand the Typhoon had a problem with the wing design nullifying much of the aileron input.
You have to love that Napier Sabre though.
All the best,
Crumpp
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Here's a little input.
For Kurfurst:
The quote from Henshaw regards a FLICK roll, not actual roll rate and this has been pointed out to you at least 2 times before.
Then the second thing. The aileron control was improved on the Mk VIII to increase stiffness It has something to do with the hinges. It's in Quill's book and I can find it - in fact I posted it a couple of weeks back.
The third thing was posted somewhere above but is needed to be kept awake. Our Mk VIII does NOT have the extended wing.
If anything the VIII should probably roll better than the Mk IX.
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The quote from Henshaw regards a FLICK roll, not actual roll rate and this has been pointed out to you at least 2 times before.
I think this is one of the things AH does not model well. All the aircraft have computer precision rolls based on their roll rate not the ADM standard.
Some aircraft simply did not begin to respond to aileron input as fast as others even though their roll rates where very similar. This is why you do not see "agility" as a very important characteristic for a fight in Aces High. In reality it was much more important than sustained turning ability for air to air combat.
All the best,
Crumpp
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If the roll rate, say doing a half roll ends up at the same time, how can this be a big factor?
One aircraft starting the roll a bit more crisply, the other (given that it does the half roll in the same speed) catching it.
:huh
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If the roll rate, say doing a half roll ends up at the same time, how can this be a big factor?
If you look at the ADM standard Angus some aircraft are simply quicker to begin a roll from the moment the pilot move the stick.
After the ailerons move then roll rate takes over.
All the best,
Crumpp
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The Mk VIII had different hinges on the ailerons to allow crisper control.
Did the 190 have rods or cables BTW?
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Originally posted by Angus
The Mk VIII had different hinges on the ailerons to allow crisper control.
Did the 190 have rods or cables BTW?
Interesting. This kind of goes to Crump's statements about agility in the two big Luftwaffe threads right now. If so it could indicate that the SPits I, V, IX, XVI and Seafire should have a bit of a slower start in regards to rolling whereas the VIII and XIV would be a bit more agile, to use Crump's words.
Now, what evidence of this do you have?
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Originally posted by Angus
The Mk VIII had different hinges on the ailerons to allow crisper control.
Do you have any details of that or what perfromance change it may or may not yielded? I was unable to find any improvement anyway, not MkVIII roll, comparisions (there's one but that's with longspan wings amd its poorer), but the XIV (=heavier VIII airframe) was compared to the IX, the conclusion was that 'Rate of roll [of the XIV/VIII is very much the same [as the IX]'.
Did the 190 have rods or cables BTW? [/B]
Both 109 and 190 had control rods actuating the ailerons.
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One thing about cables vs rods. They make no difference in a freshly tuned aircraft. Cables will lose their effectiveness much faster and to a much larger degree though.
As AH models factory fresh aircraft it is a non-issue. In ToD, where I understand you keep your aircraft for a long time, it should be modeled as in that case the difference would be significant.
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From what I can find, the short span ailerons on the VIII were added at the same time as the wing was strengthened. There had been a number of accidents where earlier Spits were lost in high speed dives where aileron flutter was considered as the reason for the accident.
The shortened ailerons were to reduce the possibilty of aileron flutter. Nothing seems to indicate there was a reduction in performance because of it.
They were introduced on the high alt Spitfire VII first and were also on the Spit XIV but interestingly not on the Spitfire PR19 which was the recce version of the Spit XIV.
As far as AH is concerned, I've been bouncing between the IX and XVI and I don't know that I don't like the IX a bit better. It just feels 'smoother' and in fights against XVIs, even down low, I've been able to knock em down.
Nothing to back that up numbers wise, just the feel of the IX vs the XVI.
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AFAIK, there are three major things that affect the attainable roll-rate: Wintip design in relation to aileron position, torsional rigidity of the wing, and aileron stiffness. The aileron has to be stiff both of its surface and its structure, any deformation eats its effectiviness.
Then there are pressure matters and venting but those are found in detail in NACA 868.
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