Speed Spitfire max speed...unknown?!

[Master_Ale_88]

Hi everybody,
Reading the Valiant publishing concerning the Spitfire Merlin powered versions I came to know about a special version of this legendary aircraft: the "Speed Spitfire". It was a modified version of the Mk. I Spitfire created in 1937 to beat the world top speed record. Unfortunately, this project turned out to be quite disappointing, since while remarkable steps were made towards increasing the Merlin engine power, german competitors such as the He 100 and the Me 109 R (or Me 209) ketp to increase the speed to be overtaken.
I became rather curious about this shiny, blue, Spit, but I can't find any futher information about it and, in particular, there is no apparent record of its maximum speed. This seems to be really absurd for an aircraft nicknamed as "Speed" Spitfire.
I would be really grateful if someone could kindly share any information about it.
Below there is a beautiful photograph of the Spitfire N.17 aka Speed Spitfire.
Thanks a lot in advance!

(source: Speed Spitfire N.17)

 

[fastmongrel]

I think it was recorded at 408mph/657kmh.

 

[pbehn]

As fastmongrel said it was recorded at 408MPH but at the time German planes were doing 470 MPH so work on it was stopped.

The Spitfire Society - Spitfire | The Spitfire Society

spitfire

www.spitfiresociety.org

323	Speed Spitfire	Modified Mk I for an attempt on the world speed record and first flew on 11 November 1938 and would eventually reach a top speed of 408mph. Unfortunately rival aircraft in Germany were approaching 470mph and the Speed Spitfire project lapsed.

 

[Master_Ale_88]

Thank you so much pbehn!

 

[pbehn]

Thank you so much pbehn!

I dont know anything about the speed Spitfire really but unless Supermarine were told to do it by the government, every hour spent was an hour wasted, around 1938 Supermarine almost lost the contract for Spitfires because they werent making nearly enough, messing about with a record breaking version wasnt in the plan. In any case the Mk IX that appeared only 4 years later was faster with all the wheels guns and armour of a fighting plane

 

[Master_Ale_88]

I dont know anything about the speed Spitfire really but unless Supermarine were told to do it by the government, every hour spent was an hour wasted, around 1938 Supermarine almost lost the contract for Spitfires because they werent making nearly enough, messing about with a record breaking version wasnt in the plan. In any case the Mk IX that appeared only 4 years later was faster with all the wheels guns and armour of a fighting plane

Yes, you're definitely right. In those years the engine development proceeded extremely fast. Therefore in a few years the developed hp on average were almost doubled!

 

[fastmongrel]

I have just reread the relevant chapter in my copy of The Spitfire story by Alfred Price.

Supermarine were going to remove the radiator and fit a boiling tank. The upper fuel tank was removed and a combined steam condenser and water tank was fitted. Steam was condensed but it couldn't have been condensed fast enough so excess steam was to be ejected from a jet at the bottom of the engine. The aircraft was expected to run out of water about the same time it ran out of its 60 Imperial gallons of fuel.

It was thought that between 430 and 450 mph could have been reached at 200 feet the record breaking altitude. As P pbehn said still not enough to make an attempt plus war was on the horizon.

 

[fastmongrel]

A modified version of a production fighter aircraft was never going to compare to a specially built record breaker. It was simply too big if you look at the Me209 record breaker it was tiny basically an engine with a pilot strapped to the back of the engine.

Messerschmitt Me 209 - Wikipedia

en.m.wikipedia.org

 

[special ed]

The Japanese Ki-78 was such a plane, an engine with a man. I would hope that a Japanese group build a replica for display.

 

[Deleted member 68059]

Hi everybody,
Reading the Valiant publishing concerning the Spitfire Merlin powered versions I came to know about a special version of this legendary aircraft: the "Speed Spitfire". It was a modified version of the Mk. I Spitfire created in 1937 to beat the world top speed record. Unfortunately, this project turned out to be quite disappointing, since while remarkable steps were made towards increasing the Merlin engine power, german competitors such as the He 100 and the Me 109 R (or Me 209) ketp to increase the speed to be overtaken.
I became rather curious about this shiny, blue, Spit, but I can't find any futher information about it and, in particular, there is no apparent record of its maximum speed. This seems to be really absurd for an aircraft nicknamed as "Speed" Spitfire.
I would be really grateful if someone could kindly share any information about it.
Below there is a beautiful photograph of the Spitfire N.17 aka Speed Spitfire.
Thanks a lot in advance!
View attachment 643186
(source: Speed Spitfire N.17)

There is a small amount in my book about it, but 408 mph (true) at 3000ft was the actual test result. Engine power was 1990 bhp at 3000rpm, this was reported on 30th may 1939. Prediction without a radiator was 425mph. Drag was 53.3lbs at 100ft sec (standard spitfire was 60.2lbs). It had a Watts four bladed fixed pitch propeller of 9.75ft dia, giving .832 relative Mach tip speed at 400mph, using the RAF 6 profile.

Proposals for an increase to 3200rpm and water injection were made but work stopped as war approached. It is very unlikely that a competitive speed could be reached when the engine had a deficit of about 25 percent in swept volume over the German engine. (Which was putting out nearly 2800bhp in the final record spec)

 

[gingerbob]

...unless Supermarine were told to do it by the government, every hour spent was an hour wasted, around 1938 Supermarine almost lost the contract for Spitfires because they werent making nearly enough, messing about with a record breaking version wasnt in the plan.

Of course they were told to do it, and therefore it WAS in the plan. Other development was also taking place. Yes, there were production problems, but that was true rather generally, even if the Spitfire was one of the more troubled types.

(By the way, I realize that this comment comes well behind the prior discussion!)

bob

 

[Daggerr]

There is a small amount in my book about it, but 408 mph (true) at 3000ft was the actual test result. Engine power was 1990 bhp at 3000rpm, this was reported on 30th may 1939. Prediction without a radiator was 425mph. Drag was 53.3lbs at 100ft sec (standard spitfire was 60.2lbs). It had a Watts four bladed fixed pitch propeller of 9.75ft dia, giving .832 relative Mach tip speed at 400mph, using the RAF 6 profile.

[........]

I have seen several times in books and websites that drag is reported for a speed of 100 ft/s, which is only 68 mph or 110 km/h.
That's the speed of a motor car, not a fighter plane that can fly about a factor 6 faster.

I know that drag increases with speed squared (for a given air density), but that is only so if the drag coefficient of the plane would be independent of speed, which I don't think is true as Reynolds and Mach numbers will be different at different speeds.
Measuring drag at 100 ft/s and then having to multiply this number by 36 to estimate drag at 600 ft/s seems rather primitive to me.

Does anybody here know why drag often was measured at only 100 ft/s ?

 

[pbehn]

I have seen several times in books and websites that drag is reported for a speed of 100 ft/s, which is only 68 mph or 110 km/h.
That's the speed of a motor car, not a fighter plane that can fly about a factor 6 faster.

I know that drag increases with speed squared (for a given air density), but that is only so if the drag coefficient of the plane would be independent of speed, which I don't think is true as Reynolds and Mach numbers will be different at different speeds.
Measuring drag at 100 ft/s and then having to multiply this number by 36 to estimate drag at 600 ft/s seems rather primitive to me.

Does anybody here know why drag often was measured at only 100 ft/s ?

As a guess I would think that is the fastest wind tunnel they had at the time.

 

[pbehn]

This tunnel which helped USA win the war according to the article operated at upto 120 MPH on a full size single seat fighter, it became operational in 1934.

https://www.theatlantic.com/technology/archive/2011/06/the-wind-tunnel-that-helped-win-world-war-ii/240277/

 

[muskeg13]

This tunnel which helped USA win the war according to the article operated at upto 120 MPH on a full size single seat fighter, it became operational in 1934.

https://www.theatlantic.com/technology/archive/2011/06/the-wind-tunnel-that-helped-win-world-war-ii/240277/

My father worked within a few hundred feet of the NACA/NASA Langley wind tunnels (there were several) for nearly 40 years, and a close friend who is about to retire was part of the team who operated this tunnel. Growing up 3.5 miles away in the 60s-80s, we could hear the tunnels roar when they were being operated.

 

[Deleted member 68059]

I have seen several times in books and websites that drag is reported for a speed of 100 ft/s, which is only 68 mph or 110 km/h.
That's the speed of a motor car, not a fighter plane that can fly about a factor 6 faster.

I know that drag increases with speed squared (for a given air density), but that is only so if the drag coefficient of the plane would be independent of speed, which I don't think is true as Reynolds and Mach numbers will be different at different speeds.
Measuring drag at 100 ft/s and then having to multiply this number by 36 to estimate drag at 600 ft/s seems rather primitive to me.

Does anybody here know why drag often was measured at only 100 ft/s ?

I`m only a stupid mechanical engineer, not a proper aerodynamicist, but I would think it would be useful to have a look at Reynolds at sea level and room temperature at 100f/s and then compare that with reynolds at 300mph at atmospheric conditions prevalent at say...30,000 feet

 

[Reluctant Poster]

I dont know anything about the speed Spitfire really but unless Supermarine were told to do it by the government, every hour spent was an hour wasted, around 1938 Supermarine almost lost the contract for Spitfires because they werent making nearly enough, messing about with a record breaking version wasnt in the plan. In any case the Mk IX that appeared only 4 years later was faster with all the wheels guns and armour of a fighting plane

I disagree. The work was done under an Air Ministry contract. In any event, the airframe mods weren't really that extensive. New windscreen, new wingtips, new engine mounts, flush rivets. The major mod was the new pressurized cooling system. The Speed Spitfire was the first Merlin powered aircraft to fly with the pressurized cooling system. The once through system was a later modification. In fact, Rolls Royce learned a lot about the capability of the Merlin and the whole experiment was worth it for that alone.

 

[Daggerr]

I`m only a stupid mechanical engineer, not a proper aerodynamicist, but I would think it would be useful to have a look at Reynolds at sea level and room temperature at 100f/s and then compare that with reynolds at 300mph at atmospheric conditions prevalent at say...30,000 feet

I`m only a stupid chemical engineer, not a proper aerodynamicist either, but familiar with Reynolds numbers in other situations.

Reynolds number is: speed times characteristic dimension divided by kinematic viscosity.

At 300 mph (440 ft/s) the speed is a factor 4.40 higher than at 100 ft/s.
At 30,000 ft altitude the kinematic viscosity of air is a factor 2.18 higher than at sea level.
So at 300 mph & 30,000 ft the Re number would be a factor 4.40 / 2.18 = 2.0 higher than at 100 ft/s & SL.

When the Speed Spitfire flew at 408 mph (598 ft/s) & 3,000 ft it's Re number was a factor 5.98 / 1.07 = 5.6 higher than at 100 ft/s & SL.

Moreover drag also depends on Angle of Attack (AoA), so in actual operation at different speed/altitude combinations, apart from differences in Re and Mach numbers, there will also be differences in AoA to obtain sufficient lift, but thereby affecting drag.

I guess pbehn could be right that in Britain the fastest full-size wind tunnel at that time operated at only 100 ft/s, although NACA managed 178 ft/s (120 mph) but I guess they had a bigger budget.

 

[pbehn]

I guess pbehn could be right that in Britain the fastest full-size wind tunnel at that time operated at only 100 ft/s, although NACA managed 178 ft/s (120 mph) but I guess they had a bigger budget.

I was sort of putting a time scale to the issue, the UK were commissioning tunnels through the 1930s. The Speed Spitfire was abandoned in 1938, that NACA tunnel was state of the art in 1934. The thing is everyone wanted to use wind tunnels, in UK or USA I doubt a racing plane would get priority over a military project unless orders came from very high up. Also it is easy to say "only 100 ft/sec". A hurricane force wind is 74 MPH and above, even these slow wind tunnels were recreating a hurricane force wind, but it has to be of known and reproducible speed, with smooth flow and precise measurements of forces need to be taken.
Development of UK wind tunnels is given here. Wind Tunnels - Farnborough Air Sciences Trust