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Old 11-12-2018, 12:38 PM   #11
DD_Fenrir
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And yet another source, comparing Mustang roll rate and stick forces with an unspecified Spitfire, shows a stick force of 24lb at 300mph to obtain a 45 degree/sec roll rate for the Spitfire...

You're assuming a great deal shredder and piling assumption on assumption to conclude ED have miscalculated their Spitfire FM.

The NACA Spitfire used is a Mk.Va with 8x .303s - a lot of these were simply re-engined Spitfire Mk.I, or at the very least very early production Mk.V. In either case they would still have had fabric ailerons when initially converted/built.

You assume because of chronology that the airframe would have had metal ailerons; a reasonable assumption but it does not take into account whether or not the airframe had any operational RAF time (in which case it could well have had the metals fitted as an operational expediency as many units chased down metal ailerons for retro-fit at squadron level as pace of production of metal ailerons struggled to meet demand).

Alternatively, many airframes did not go straight to a unit from production/refit but were instead supplied to Maintenance or Storage units so as to provide a ready reserve for loss replacement.

Right having typed all that out I discovered the following:

Serial number: W3119

Built as Mk.Va, at Supermarines Eastleigh Works first flew on 22nd April 1941. Sent straight to 39 Maintenance Unit on 25th April 1941, it was sent to Wright Field, Dayton, Ohio during July of 1941, then to NACA at Langley Field in December the same year.

Given the above, I would suggest it is far more likely that W3119 was not equipped with metal covered ailerons.

Furthermore, I have found this quote on an old Ubiforum post, referencing a paper by Joe Smith (the designer at Supermarine who succeeded Mitchell and the man responsible for the design changes from the Mk.I forwards); I do not yet have the paper itself, though I am trying to source to corroborate whether the information presented has been accurately reproduced.

Quote:
These Spitfire roll rate data were taken from THE DEVELOPMENT OF THE SPITFIRE AND SEAFIRE - 706th lecture delivered before the Royal Aeronautical Society (19 Dec 1946) by J. Smith (chief designer for Supermarine during the war).

Herewith follows the roll rate graph values, as closely as I can approximate them:

All data are give for "full aileron or 50 lb stick force" - I suppose whichever limit was achieved first.

All air speeds are given as "equivalent air speed". Not sure what is meant by this term; I'm guessing that it means indicated airspeed.

Spitfire V / fabric covered frise ailerons:
90 deg/sec @ 170 mph (lowest speed graphed)
75 deg/sec @ 200 mph
55 deg/sec @ 250 mph
40 deg/sec @ 300 mph
27 deg/sec @ 350 mph
20 deg/sec @ 380 mph (end of graphed values)

Spitfire Mk V / metal covered frise ailerons
85 deg/sec @ 150 mph
105 deg/sec @ 200 mph
90 deg/sec @ 250 mph
75 deg/sec @ 300 mph
60 deg/sec @ 350 mph
40 deg/sec @ 400 mph

Spitfire Mk V / plain ailerons with tabs
65 deg/sec @ 180 mph
75 deg/sec @ 200 mph
95 deg/sec @ 250 mph
118 deg/sec @ 300 mph
90 deg/sec @ 350 mph
70 deg/sec @ 400 mph

The explanatory text which accompanied the graphs follows:

"Careful analysis over a long period of time on various marks of Spitfire had revealed fairly wide variations in aileron section and in the position of the ailerons relative to the wings. These differences resulted in inconsistent aileron characteristics, and it was felt that ailerons of a type which would be simple to manufacture and which would be less sensitive to manufacturing tolerances were necessary.

Quantitative data obtained from flight trials on a Spitfire Mark V with plain ailerons fitted with a balance tab had previously indicated that aileron properties comparable with those of a metal-covered Frise type could be achieved, with a reduction in drag due to the elimination of the gap. Ailerons of this type with area increased to 6 per cent of the total wing area, as against 5 per cent on earlier marks, were fitted to the stiffer Mark 21 wing and gave a high rate of roll with reasonable stick forces at high speeds."


Smith then goes on to show a graph of stick efforts required to "apply 1/4 aileron at various speeds.

Spitfire V / fabric covered frise ailerons
8 lbs @ 200 mph
16 lbs @ 250 mph
27 lbs @ 300 mph
43 lbs @ 350 mph
57 lbs @ 375 mph (end of graphed values)

Spitfire V / plain ailerons with tabs
7 lbs @ 200 mph
9 lbs @ 250 mph
13 lbs @ 300 mph
18 lbs @ 350 mph
24 lbs @ 400 mph

Spitfire V / metal covered frise ailerons
4 lbs @ 200 mph
5 lbs @ 250 mph
7 lbs @ 300 mph
9 lbs @ 350 mph
12 lbs @ 400 mph

Smith elsewhere mentions in passing some roll rate values for other Spitfire Marks, to wit -

Spitfire I - 14 deg/sec @ 400 mph
Seafire 47 - 68 deg/sec @ 400 mph


Hope this helps.
As can be seen there is some correlation between the figures presented for the Mk.Va NACA airframe and those figures as noted above for Mk.V airframe with fabric covered ailerons.

Last edited by DD_Fenrir; 11-12-2018 at 02:00 PM.
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Old 11-14-2018, 02:47 PM   #12
shreddersa
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Quote:
Originally Posted by DD_Fenrir View Post
And yet another source, comparing Mustang roll rate and stick forces with an unspecified Spitfire, shows a stick force of 24lb at 300mph to obtain a 45 degree/sec roll rate for the Spitfire...

You're assuming a great deal shredder and piling assumption on assumption to conclude ED have miscalculated their Spitfire FM.

The NACA Spitfire used is a Mk.Va with 8x .303s - a lot of these were simply re-engined Spitfire Mk.I, or at the very least very early production Mk.V. In either case they would still have had fabric ailerons when initially converted/built.

You assume because of chronology that the airframe would have had metal ailerons; a reasonable assumption but it does not take into account whether or not the airframe had any operational RAF time (in which case it could well have had the metals fitted as an operational expediency as many units chased down metal ailerons for retro-fit at squadron level as pace of production of metal ailerons struggled to meet demand).

Alternatively, many airframes did not go straight to a unit from production/refit but were instead supplied to Maintenance or Storage units so as to provide a ready reserve for loss replacement.

Right having typed all that out I discovered the following:

Serial number: W3119

Built as Mk.Va, at Supermarines Eastleigh Works first flew on 22nd April 1941. Sent straight to 39 Maintenance Unit on 25th April 1941, it was sent to Wright Field, Dayton, Ohio during July of 1941, then to NACA at Langley Field in December the same year.

Given the above, I would suggest it is far more likely that W3119 was not equipped with metal covered ailerons.

Furthermore, I have found this quote on an old Ubiforum post, referencing a paper by Joe Smith (the designer at Supermarine who succeeded Mitchell and the man responsible for the design changes from the Mk.I forwards); I do not yet have the paper itself, though I am trying to source to corroborate whether the information presented has been accurately reproduced.



As can be seen there is some correlation between the figures presented for the Mk.Va NACA airframe and those figures as noted above for Mk.V airframe with fabric covered ailerons.
Very interesting info and very valuable, thank you DD! I will have a good look at the figures and see how they might be incorporated. It would indeed mean that for the IX the forces are overstated. That's a bit of a relief really as it means I can go for weaker springs and less forces are induced in the system overall. Currently the FF provides the following results:
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Old 11-15-2018, 12:03 PM   #13
shreddersa
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Quote:
Originally Posted by DD_Fenrir View Post
You're assuming a great deal shredder and piling assumption on assumption to conclude ED have miscalculated their Spitfire FM.
...........
You assume because of chronology that the airframe would have had metal ailerons; a reasonable assumption but it does not take into account whether or not the airframe had any operational RAF time (in which case it could well have had the metals fitted as an operational expediency as many units chased down metal ailerons for retro-fit at squadron level as pace of production of metal ailerons struggled to meet demand).

...........

Right having typed all that out I discovered the following:

Serial number: W3119

Built as Mk.Va, at Supermarines Eastleigh Works first flew on 22nd April 1941. Sent straight to 39 Maintenance Unit on 25th April 1941, it was sent to Wright Field, Dayton, Ohio during July of 1941, then to NACA at Langley Field in December the same year.

Given the above, I would suggest it is far more likely that W3119 was not equipped with metal covered ailerons.

..........
Hi DD, I regret that you too are working on assumptions. I went through the NACA L-334 report again which formed the basis of my force calculations. It states explicitly on page 2 and again on page 12 that the ailerons were metal covered.

All that said, I would dearly love to get hold of the lecture notes by Smith to better understand the context of the figures you present.

It's all a very interesting journey!
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Old 11-15-2018, 12:32 PM   #14
DD_Fenrir
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Looks like I need to go back to the opticians! Good find.

Well, I stand corrected.

I will put a caveat though, in that the NACA figures do seem on the high side in comparison to those quoted from the Smith paper, and in general given the anecdotal evidence of the lighter control afforded by metal ailerons.

Quote:
All that said, I would dearly love to get hold of the lecture notes by Smith...
Me too! Without it we are having to rely on someone else's interpretation of graphs and assume they are correct...
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Old 11-15-2018, 12:38 PM   #15
shreddersa
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Quote:
Originally Posted by DD_Fenrir View Post
Looks like I need to go back to the opticians! Good find.

Well, I stand corrected.

I will put a caveat though, in that the NACA figures do seem on the high side in comparison to those quoted from the Smith paper, and in general given the anecdotal evidence of the lighter control afforded by metal ailerons.



Me too! Without it we are having to rely on someone else's interpretation of graphs and assume they are correct...
I saw the Smith paper on Cambridge University Press. However, to fork out GBP25 for a paper published in 1947 (should be free and in public domain after 70 years) is a bit rough. So I will work on the figures I can get. These all seem to corroborate the NACA tests as far as I can see. I will compile a set of what I have and publish it here.
Cheers,
Roel
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