Spitfire as a diver

[tomo pauk]

How well it fared in dives? From what I can gather, it was slower than eg. Bf-109 to enter into dive pick up the speed (due to low wing loading?), but once in dive the thin wing was allowing for high speeds (only P-51 bettering it?).
I'm looking forward for a well informed input, so we (Me, at least) can have a full picture on this topic

 

[Aaron Brooks Wolters]

If I'm not mistaken the P-47 would outdo both the Mustang and Spitfire, but I could be wrong.

 

[tomo pauk]

IIRC the P-47 needed dive flaps to overcome compressibility effects; with those is was fine?

 

[Aaron Brooks Wolters]

Ok, I understand what your saying now. Makes sense. Your talking about maintaining control while in the dive and carrying speed also.

 

[tomo pauk]

Yes, something along those lines. I'm also interested about the roll abilities of the main combatants when in high-speed dive; for the Spitfire I'm interested most.

 

[Siegfried]

Spitfires supposedly could experience control reversal though I would like confirmation of that. Either way the relatively thin wing and essentially single spar design meant the early wings could twist opposit to aileron direction thus reducing roll rate. The Spitfire pilot might be able to deflect his ailerons with less effort than an Me 109 pilot but the wings countervailing twist could undo this, clipped wing versions aside.

Late war Me 109's could dive and remain in control to very high speeds. Dive problems had been traced to high mach latteral instabillity rudder horn overbalancing as early as 1942. The solution was a new taller tail which used a balance tab instead of a horn balance. These versions occaisionally outdived P-51's in the sense of regaining or retaining control at higher speeds.

Willy Messerschmitt made his name in aerodynamics via design of new wing sections that had excellent pitching characteristics.

Thw whole issue of diveing in combat seems to be a mixture of intial acceleration, mid dive acceleration, maximum speed of control.

 

[wuzak]

The Spitfire didn't have as good acceleration in the dive as many of its contemporaries. A combination of weight, drag and power, no doubt.

The XIV was nearly equal to the P-51

Early Spitfires had difficulty with control in the dive, which was largely solved by replacing the fabric covered control surfaces with all metal ones.

 

[davebender]

How well did a P-47 accelerate in a dive? We all know it could outdive anything if given enough time but is initital dive speed greater then the Me-109 or P-51?

 

[slaterat]

Tempest> P47 in a the dive

 

[Juha]

Hello Siegfried

the highest Mach number achieved in tests flights by German109 I'm aware was Mach 0.805.

It was achieved when in order to find the explanation of accidents in the front-line units the flight test unit of Messerschmitt made series of dive tests during spring 1943. The plane used was Bf109 F W.Nr. 9228. To reduce the risk of pilot over-compensation, the control movement was limited to 50% of the reference movement of the ailerons. For the first test flights the plane was in the standard condition of a 109F with G-wings, except for the movement limitation of the ailerons and the ejection seat. At this form the plane lost stability (at median centre of gravity) at speeds over Va=650 km/h ie IAS. Movements, starting at the vertical stabilizer;appeared around the yaw and longitudinal axes.
After this the stabilizer was changed to a larger one. Meaning the late production higher one. The elevator trim tab is enlarged in surface area by 100% compared to the original lower version. The horizontal stabilizer trim is limited in its upwards range of motion to +1°15 by a stop unit. With this new tail following speeds were achieved.
Maximum IAS Vamax = 737 km/h at 4.5 km, Maximum TAS Vwmax = 906 km/h at 5.8 km Maximum mach number = 0,805 at 7.0 km. This is the highest Mach number flown by a German 109 I'm aware. Bf 109K might well be capable to a bit higher max Mach number but was it ever tested flown in order to achieve that, I don't know.

Other max Mach numbers
P-51B: 0.84 and 0.82 for the P-51D
P-38: 0.65
P-47C: 0.69
the SpitfirePR XI was able to dive to 0.89 mach and make a full recovery. In combat trim this would probably be more like 0.83-0.85 for fighter versions.

And on roll rates, there isn't very much info on max roll rates of 109, but it seems that 109G max roll rate, 50lb stick force, was 85deg/sec at 425km/h (264mph)IAS. That means that it rolled clearly worse than metal aileron clipped wing Spit Mk V at all speeds and clearly worse than normal wing Spit Mk V up to say 410 km/h IAS. There wasn't so big difference between 410 – 520km/h (255-323mph)IAS between 109G and normal wing Spit Mk V. One must also remember that planes were individuals and at least Frise type ailerons used in Spits before Mk 21 were sensitive to rigging errors…

On the supposed control reversal of Spitfires, I cannot recall other claims but those of one ex-member of this board who at least had very strong pro-German and anti-British views. But it is true that Spit suffered reduced aileron effectiveness at high speeds because of wing twist but the theoretical control reversal speed seems to have been beyond speeds possible to be achievable by Spitfires in dives.

Juha

 

[Juha]

Hello Tomo
yes the initial dive acceleration of Spit was worse than that of contempory 109 but Spit had higher critical mach number but that was mostly only a theoretical advance.

Juha

 

[A4K]

Heard a long time ago from someone that there was a strict limit set on Spitfire dive speed due to fear of wing fatigue, and that a kiwi pilot once exceeded this limit, and had a wing shear off...(?)
I think this was a Mk.I during the battle of Britain, but can't be sure - anyone know anything about this incident (or indeed if it's true or not)?

 

[stona]

The Spitfire pilot might be able to deflect his ailerons with less effort than an Me 109 pilot

Actually the force required to achieve similar aileron deflection at similar speed is virtually the same. The configuration of the controls and pilot position meant that a Spitfire pilot could more easily bring greater force to bear on the controls. A Bf109 cockpit is VERY small,even compared to a Spitfire.
Cheers
Steve

 

[Tante Ju]

Actually the force required to achieve similar aileron deflection at similar speed is virtually the same. The configuration of the controls and pilot position meant that a Spitfire pilot could more easily bring greater force to bear on the controls. A Bf109 cockpit is VERY small,even compared to a Spitfire.
Cheers
Steve

This chart shows control force was much greater on Spitfire. But report also notes subjective feel of 109 control was more solid for pilots, because of different stick and control design :

More detailed aileron tests (measurement of stick forces and time to bank) were-made, and are described in section 5.2. These tests showed that, although the Me.109 ailerons felt much heavier than those of the Spitfire at speeds between 300 m.p.h. and 400 m.p.h., the aircraft could be made to bank at about the same rate as the Spitfire at these high airspeeds. The more " solid " feel of the Me.109 ailerons at high airspeeds is attributed to smaller stick travel (+/- 4 in. compared with +/- 8 in. on the Spitfire)., fairly rigid control circuit, and partly to the awkward seating position of the pilot. The matter is more fully discussed in section 5.2.

 

[stona]

Yep,I haven't looked at that reprt for ages! Maybe I should have said similar up to about 300mph

We shouldn't divert the thread into one about ailerons which is a complicated subject and only one facet of an aircraft's performance in a dive. Crucially the Spitfire ailerons,despite being much larger than those of the Bf109,did not FEEL as heavy at high speeds.

The report you quoted from was from late 1940 and refers to fabric covered ailerons on the Spitfire. The much improved metal ones were not introduced for nearly a year in July 1941.

Cheers
Steve

 

[Edgar Brooks]

Spitfires supposedly could experience control reversal though I would like confirmation of that..

In all of the hundreds of files, in the National Archives, I've never seen even the slightest hint of it.

Either way the relatively thin wing and essentially single spar design meant the early wings could twist opposit to aileron direction thus reducing roll rate

.
Can we get rid of this "single spar" nonsense, once and for all, please? The front spar was bolted to the firewall (frame 5,) and the rear spar (to which the flaps and ailerons were attached, and which went all the way out to the wingtip join) was bolted to frame 10.

The Spitfire pilot might be able to deflect his ailerons with less effort than an Me 109 pilot but the wings countervailing twist could undo this, clipped wing versions aside.

If the wing twisted, it buckled, and anything above 1/16", aft of the mainspar, meant a full inspection, and even the slightest damage to the l/e "D" box meant a replacement wing. Clipping the wings was done, at first, to speed up the roll rate, and had nothing to do with wing twisting. Later, it was done to stop wing damage when carrying bombs under the wings (Mark XVI.)

Late war Me 109's could dive and remain in control to very high speeds.

Not according to a Polish pilot, to whom I spoke about 30 years ago; he said that, in the 109 (which he flew post-war,) it was impossible to pull out of a dive in a straight line. You always ended up at right angles to your original line.
Returning to the "dive" question, in 1940 tests, it was found that the Spitfire I 109E, if they started together, at full throttle settings, then dived together, they were still dead level at the bottom of the dive.
The 109E wing was limited to a pressure of 640lb:sq.ft (according to a test report,) while the Spitfire V could take 700lb:sq. ft.
The Spitfire IX was limited to 450mph, in a dive, but that was caused by engine limitations, not the airframe; the Merlin could not be taken above 3000rpm, without severely shortening its life. In an emergency 3150 rpm was permitted, but only for 20 seconds.
The fastest known (and survived) dive speed, on a Spitfire, was achieved by S/Lr Martindale, in a P.R.XI, with a TAS of 606mph (Mach .89,) before his engine exploded, and the propeller disappeared. He retained control (and, no, his ailerons did not reverse,) and glided back to an engine-off landing. A month later, he again achieved almost 600 mph, when the supercharger burst, and the engine caught fire; again he managed to land it.

 

[davebender]

Why does this matter?

If the pursuing aircraft can remain within effective weapons range for a few seconds the aircraft in front is likely to become swiss cheese long before anyone achieves max Mach speed in the dive.

 

[stona]

Why does this matter?

Because the original poster asked how the Spitfire was as a diver and that is a first hand account of how a Spitfire MkI compared with a contemporary Bf109E.

The stability of the aircraft in the dive might be more relevant than distance in a combat situation anyway.

Cheers
Steve

 

[Edgar Brooks]

Why does this matter?

Because, as Steve says, the original enquirer wants to know how Spitfires were in dives; perhaps you'd care to explain how your contribution helps him in his quest?

 

[Siegfried]

In all of the hundreds of files, in the National Archives, I've never seen even the slightest hint of it.
.
Can we get rid of this "single spar" nonsense, once and for all, please? The front spar was bolted to the firewall (frame 5,) and the rear spar (to which the flaps and ailerons were attached, and which went all the way out to the wingtip join) was bolted to frame 10.

If the wing twisted, it buckled, and anything above 1/16", aft of the mainspar, meant a full inspection, and even the slightest damage to the l/e "D" box meant a replacement wing. Clipping the wings was done, at first, to speed up the roll rate, and had nothing to do with wing twisting. Later, it was done to stop wing damage when carrying bombs under the wings (Mark XVI.)

Not according to a Polish pilot, to whom I spoke about 30 years ago; he said that, in the 109 (which he flew post-war,) it was impossible to pull out of a dive in a straight line. You always ended up at right angles to your original line.
Returning to the "dive" question, in 1940 tests, it was found that the Spitfire I 109E, if they started together, at full throttle settings, then dived together, they were still dead level at the bottom of the dive.
The 109E wing was limited to a pressure of 640lb:sq.ft (according to a test report,) while the Spitfire V could take 700lb:sq. ft.
The Spitfire IX was limited to 450mph, in a dive, but that was caused by engine limitations, not the airframe; the Merlin could not be taken above 3000rpm, without severely shortening its life. In an emergency 3150 rpm was permitted, but only for 20 seconds.
The fastest known (and survived) dive speed, on a Spitfire, was achieved by S/Lr Martindale, in a P.R.XI, with a TAS of 606mph (Mach .89,) before his engine exploded, and the propeller disappeared. He retained control (and, no, his ailerons did not reverse,) and glided back to an engine-off landing. A month later, he again achieved almost 600 mph, when the supercharger burst, and the engine caught fire; again he managed to land it.

1 The theoretical ailerons reversal speed of the pre F.22 series was lower than most ww2 fighters, whether or not it actually was pushed to an actually reversal is another matter. It did cut into roll rate.

2 The Spitfire is regarded as a single spar aircraft. The "main spar" was formed with a D shaped torsion box that was formed by the skin between the main spar and the leading edge. (It was probably vestigial from the unsuccessfully Type 224 Goshawk steam cooling program). Stringers and a smaller spar to the rear of this D box carried little of the load and served mainly to hang of control surfaces and to finish of the wing. A two spar design would have two large spars with a box formed by the upper and lower skins.

3 Me 109F had a radically redesigned wing of both new cross section and planform as well as slats so Me 109E data can not be used as a proxy for Me 109F. Me 109G wings were strenghtened.

The Spitfire no doubt was a fast diver, though it seems to have been of limited tactical use and not exploited due to its relatively underdeveloped prop pitch control and range. One of the advantges of the Kommandogaraet of German fighters was that it properly integrated prop pitch with throttle. Constant speed props still needed feathering: not with the all in one control.

Spitfire V had a major dive problem develop around 1942 caused by weight and C of G shift that was eventually solved via bob weights.