The effect of 'clipping' Spitfire wings

[Kurfürst]

[Xjazz]

"How to m/fake a realistic document 101"

or

do you have a source?

[Kurfürst]

[Xjazz]

Ok, looks better now.

Anybody have that National Advisory Committee For Aeronautics report no. 868, page 166 chart picture, where clipped wing Spit V had much better Roll Rate than normal wing?

[Kurfürst]

And while we are that graph, anyone can confirm if that curve of an unspecified mark of Spitfire was coming from flight test, calculation etc.

The shape of the curve - sudden break at the top - clearly shows something is wrong. Apart from it does not match any other wartime roll data for the Spit..

[Nashwan]

Kurfurst/Isegrim knows very well where the Spitfire figures for the Naca chart come from, because we have been over this before on another board.

http://www.1jma.dk/topic.asp?TOPIC_ID=3624&whichpage=2

On that board, I'm Hop, Kurfurst is Barabarossa Isegrim.


To summarise the thread, I posted the figures for the Spitfire from NACA 868, Isegrim said they were from:

"later postwar Marks of Spitfires, ie. the NACA chart you are using as a basis is based on the Mk 21 Spitfire series which had reinforced and redesigned wings to cope with one of the two major flaws in the Spit`s design that attributed to it`s poor rate of roll at high speeds : severe wing twisting under force."

Note this is entirely made up, NACA 868 is based on tests of Spitfire Vs by the RAE.

I told Isegrim that, he responded with:

" Can you point towards this allegadly existing Spitfire V roll tests?

I have seen half a dozen Spitfire I, V, IX, VIII, XII roll tests, both clipped and unclipped, and none of them show similiar values.

Knowing your bias towards Spitfires, and your habit of claiming them to be the best in every area all the time, I think it`s quite clear that you made it up as a whole, and will be unable to support the claim with anything."

I then responded with the RAE chart for the Spitfire V, which is clearly the same data as NACA 868.
http://www.onpoi.net/ah/pics/users/282_1094123825_roll11.jpg

Isegrim, as is his way, didn't apologise for accusing me of making it up (the only made up bit was his claim the data was for the Spit 21). Instead he responded by trying to claim the RAE test was wrong:

" Interesting stuff, Hop, but it doesn`t agree with anything, let it be US or UK tests on Spitfire roll rate."

He then posted lots of other things, like tests done at 30 lbs stick force, roll acceleration test, instead of roll rate tests, etc.

Page 2 and 3 of the thread make good reading.

The shape of the curve - sudden break at the top - clearly shows something is wrong.

You made that claim in the thread as well, despite posting some NACA charts yourself which also featured the same peaks.

eg http://www.onpoi.net/ah/pics/users/715_1094126808_rollratespithurrip40p36.jpg

and

http://www.onpoi.net/ah/pics/users/715_1094128180_rolldataweb.jpg

In short, Isegrim wants to discount Naca 868 and the RAE charts on which it's based. To do so he claims that the peaks show the NACA/RAE chart are wrong, and yet the peaks on the other charts aren't evidence they are wrong.

As is typical with Isegrim, he ignores the direct test evidence when it suits him, and instead relies on secondary sources (eg he claims the chart at 30 lbs stick force gives better idea of roll rate at 50 lbs stick force than the actual 50 lbs stick force chart)

[Guppy35]

Agreed with Nashwan on this one.  You can always find a graph to show you what you want to see.

Regarding the clipped wings again and hopefully to put to rest this BS about loss of performance. From the RAF trials of a clipped Spit vs a Standard wing Spit.

"At all heights to 25,000 feet the rate of roll is considerably improved by the removal of the wingtips. The response to aileron movements is very quick and very crisp. Four dog-fights were carried out starting with the standard Spitfire on the tail of the clipped wing Spitfire. On two occasions the clipped wing Spitfire evaded so rapidly in the rolling plane that it was able to lose the standard Spitfire and reverse the positions in about 20 seconds. On the third occasion the clipped wing Spitfire was able to lose the standard Spitfire. The fourth occasion was at 25,000 feet and the standard Spitfire was able to keep the clipped wing Spitfire in sight.

The minimum turning circle of the clipped wing Spitfire at 20,000 feet has been increased by 55 feet . This slight increase does not detract in any way from the fighting qualities of the aeroplane..."

Quoting Jeffrey Quill, Supermarine Chief Test pilot on the clipped wing and Merlin 66 LFIX.

"Then at some in definate time in 1942, there seemed to be a change in the tactical philosophy on both sides. It was rather as if, by some sort of mutual tacit consent between enemies, it was realized that the band between 30,000 an 40,000 feet was a silly place in which to have an air battle, and the fighting tended to drop down into the more practical regions roughly between 15,000 and 25,000 feet. I remember how, at the time, this trend interested me very much indeed. It WAS CLEARLY REFLECTED in the LF MK IX(Merlin 66) with engine performance adjusted to the reduced height band.

IT WAS ALSO REFLECTED in the fact that, by removing the wingtips of the Spitfire, an improvement in lateral control could be achieved, but because it increased the wing loading and the span loading of the wing, an aerodynamic penalty was incurred at HIGH ALTITUDE. Such a proposition was unthinkable in 40/41 but in 1942/3 the idea was ENTHUSIASTICALLY adopted by squadrons in 11 group and the "clipped wing" Spitfire became a common sight in the sky."


Considering all SpitXII and XVI were delivered with clipped wings, as well as many Spit IXs, they must have found some benefit don't ya think?  They sure clipped a lot of LFVs and even some VIIIs and XIVs.

Dan/CorkyJr

[Toad]

Help me out here. In the early days of aviation, a lot of shade tree aeronautical engineers clipped various lengths of wing off of "standard" aircraft wings.

All those guys must have had an idea that something would get better, right? I mean they wouldn't clip the wing to achieve some aspect performance less than the orginal, would they?

Generally speaking, in my experience reading and talking to folks, clipping the wings is generally a techique for increasing roll rate (#1 reason) or increasing top speed or both.

I think it's very reasonable to expect a clipped wing Spit to have an increased roll rate. Most other airplanes that had wings clipped exhibited that performance gain. Further, you have documentation showing that is exactly what happened with the Spit.

What's the problem here?

[Guppy35]

Originally posted by Toad
Help me out here. In the early days of aviation, a lot of shade tree aeronautical engineers clipped various lengths of wing off of "standard" aircraft wings.

All those guys must have had an idea that something would get better, right? I mean they wouldn't clip the wing to achieve some aspect performance less than the orginal, would they?

Generally speaking, in my experience reading and talking to folks, clipping the wings is generally a techique for increasing roll rate (#1 reason) or increasing top speed or both.

I think it's very reasonable to expect a clipped wing Spit to have an increased roll rate. Most other airplanes that had wings clipped exhibited that performance gain. Further, you have documentation showing that is exactly what happened with the Spit.

What's the problem here?

Izzy/Kurfurst hates Spits with a passion

Dan/CorkyJr

[JB73]

my question is i can see roll rate increase...

but a decline in lift from less wing area, hence less climb, and wider turning radius because of an earlier stall.

how else can it physically be explained?

[Toad]

Yep, and if you read the docs, the clipped Spit had less wing area and a wider turning circle. However, the change was not a significant combat factor. Clipping didn't increase the turn radius much below 20k.

Basically, they optimised the wing for fighting below 20k. EVERYTHING in aviation is a trade-off. It's a rare airplane that doesn't get modified as the true nature of the mission becomes more specific and/or as the mission changes, or as technology advances.

Let me put it this way:

NA-73, Mustang I, P-51, P-51B, P-51C, P-51D, P-51K.

Changes in armament, engine, wing planform, canopies, drag reduction.... it's just normal evolution as the mission changed/evolved.

Clipping the Spit wing really wasn't any different.

[Karnak]

Originally posted by Guppy35
Izzy/Kurfurst hates Spits with a passion

Dan/CorkyJr

No, no.  It is we who are biased by our incredible loathing for the Bf109 and all things German.

[Guppy35]

Originally posted by Toad
Yep, and if you read the docs, the clipped Spit had less wing area and a wider turning circle. However, the change was not a significant combat factor. Clipping didn't increase the turn radius much below 20k.

Basically, they optimised the wing for fighting below 20k. EVERYTHING in aviation is a trade-off. It's a rare airplane that doesn't get modified as the true nature of the mission becomes more specific and/or as the mission changes, or as technology advances.

Let me put it this way:

NA-73, Mustang I, P-51, P-51B, P-51C, P-51D, P-51K.

Changes in armament, engine, wing planform, canopies, drag reduction.... it's just normal evolution as the mission changed/evolved.

Clipping the Spit wing really wasn't any different.

That's the key.  When the fights dropped to lower alts, the wing tips were not as much of a factor and the turning circle didn't change enough for it to be penalty enough to outweightthe increased roll rate, in particular with the 190 roll rate being so great.

Dan/CorkyJr

[Toad]

You know where they really DO have an argument?

In the modeling of the German 20mm rounds.

HT uses some pretty suspect data. Remember when Pyro posted the pic of all the ammo and the German 20mm is that little dinky round with fair velocity?

Well I found an ACTUAL photo of the REAL German 20mm Mauser 151/20 ammo.



I'm STILL waiting for it to be modeled correctly.

[Kev367th]

Lol nice Toad, bet the recoil was a beeatch.

Anyway back to clipped wings -
At the alts the combat was taking place at, clipped wings were more of an advantage, than disadvantage. OK they lost a little in turn, but gained in roll rate, exactly what they were designed to do.

Dan/Guppy35 has had a lot of contact with pilots who flew clipped wing Spits, so I'd go with him for impressions of how they flew.

In fact I remember reading somewhere that pilots absolutely loved the clipped wing Spit XVI.