British Full-Scale Wind-Tunnel & Turbulence (i.e. why they thought the Beaufighter could do 370 mph)

[Zipper730]

I wonder if the origin of the 370 was when Bristol was asked how fast the Beaufighter would be and they said 317 (not 370) and it just went downhill from there. I have seen things like this happen several times during my time in industry.

Especially if it was a message that was dictated to somebody who typed it, or it was transmitted over either a wireless or telephone system.

This happened in 1940 or 41 when the P-40x was being tested and it was reported that it had reached 660 mph in the dive test - but it was actually 660 ft/sec which was 460 mph at the altitude it was reported to have achieved that speed.

That explains a lot, I was surprised where they got that number from (I thought they just made it up).

While I could understand why Curtiss had no inclination to correct them, I didn't know the maximum dive speed was 460 mph (I thought it was actually higher).

As I said, if could remember where I'd read it, I would have posted more information. At least I'm not going mad as Simon T remembers something similar!

Okay

 

[Simon Thomas]

Prof Melville Jones biography:

Bennett Melvill Jones. 28 January 1887 -- 31 October 1975 on JSTOR

Arnold Hall, Morien Morgan, Bennett Melvill Jones. 28 January 1887 -- 31 October 1975, Biographical Memoirs of Fellows of the Royal Society, Vol. 23 (Nov., 1977), pp. 252-282

www.jstor.org

Section 6 has good information of the history of turbulence & accuracy of tunnels in the U.K. in the 20's & 30's.

 

[Shortround6]

From the information in the link that EwenS provided it appears the Farnborough big wind tunnel was completed in 1935.
The Hawker Hurricane first flew in Nov 1935. It is quite possible that they checked out but how thoroughly?
It also appears that the big Farnborough tunnel was around 30 ft but offered a clear pathway of 24ft so it was not a full size wind tunnel for a complete airplane.
Does anyone one have a speed range on the Farnborough tunnel?

From Wiki on the Langley tunnel.

"It was a double-return tunnel capable of moving air at speeds up to 118 miles/hour (190 km/h) through its circuit. It had a 30 ft by 60 ft (9.1 m x 18.3 m) open throat, which is capable of testing aircraft with spans of 40 ft (12.2 m). The wind tunnel is a double-return, atmospheric pressure tunnel with two fans powered by 4,000 hp electric motors."

At the beginning of WW II there were twelve wind tunnels in the United States.

Year..............location....................shape....................throat size...............notes
1919.............Standford U.............round...................6 ft............................
1920.............Wright Feild............round...................5 ft...........................
1923..............Curtiss......................round...................7 ft............................
1925...........U of Michigan.........Octangal..............8 ft...........................
1925..........New York U................square..................9 ft..........................
1927............Langley......................round...................20ft..........................
1928............Langley......................round...................5ft...........................
1930............Langley....................rectangle.............. 7 X 10 ft................
1930............Cal tech....................round.....................10ft
1931.............Langley..................Rectangle.................-----...........Full size tunnel
1936............Langley....................round..................... 8 ft..............high speed tunnel
1937............MIT...........................elliptical.................10ft..............

By the end of the war there were about 40 wind tunnels in operation in the US.

 

[ThomasP]

Hey Simon Thomas,

re papers on dimensionless numbers in aeronautics

There are a bunch of NACA reports from the 20s-40s. They are heavy on the math in most cases and usually have pretty good descriptive explanations, which often gives some of the thinking of the times.

 

[MikeMeech]

Hi
The part work 'Aero Engineering' of the 1930s has a chapter on wind tunnels with various illustrations and information including the 24 feet one at the RAE, Farnborough:

The book 'British Aviation, Ominous Skies 1935-1939' by Harald Penrose, has a picture showing a Bristol Bulldog engine testbed undergoing tests:

While 'Forever Farnborough, Flying the Limits 1904-1996' by Peter J. Cooper, has an image with an early Hawker Hurricane I (fabric wings) in it on 23rd August 1939, trying to determine why performance deteriorated so rapidly in service after a few hours flying, going from 335 mph down to 300 mph (so presumably the wind tunnel could handle those speeds or an extrapolated calculation of it):

The book also mentions other wind tunnels there (page 59), including a mention of testing efficiency of aerofoil sections at speeds near the velocity of sound:

Of course aircraft designers would use models in wind tunnels to test our the aerodynamics of it, it would be a bit late in the day to test the design after it was built, except for clearing up problems that arose later.

Mike

 

[EwenS]

If you follow the links with the FAST site page I inserted in my post #14 there are some details for each of the preserved Farnborough wind tunnels. For simplicity here is the direct link.

Wind Tunnels - Farnborough Air Sciences Trust

airsciences.org.uk

 

[ThomasP]

Thanks for the answers everybody. I have been curious about this subject for a while but have never gotten up the steam to research it to any extent. The info and links you have provided are much appreciated.

 

[AMCKen]

@DarrenW , & @pbehn

f I recall a Canadian guy named Beverly Shenstone (I'd have hated to be a guy with the name Beverly...) who also noted that Supermarine's data was correct.

"It was at one time a common masculine given name"

Beverly (name) - Wikipedia

en.wikipedia.org

 

[elbmc1969]

I've been looking for an international history of wind tunnels, without success. I think that some of the problems the French had were due to being behind on wind tunnels for critical parts of the 1930s.

The Germans built later wind tunnels up in the mountains by dams, where they were able to use waterwheels to power to power the wind tunnels (if my understanding is correct--not hydroelectric turbines). You need a lot of power for a full-scale supersonic wind tunnel.

 

[elbmc1969]

Of course aircraft designers would use models in wind tunnels to test our the aerodynamics of it, it would be a bit late in the day to test the design after it was built, except for clearing up problems that arose later.

Cleanup was very, very important. The French were able to get much more speed out of the M.S.406 with aerodynamic refinements, a new radiator, and jet-effect exhausts. The resulting M.S.410 never went into service in meaningful numbers and conversions never really got off the ground.

 

[hermankeil]

@DarrenW , & @pbehn

I actually don't have a specific source (and I could be wrong), but I remember hearing something like this before. From what I remember, Supermarine didn't seem to be affected because they got most of their research data on race-planes they built and didn't listen to claims that a thick wing was desirable at high speeds. If I recall a Canadian guy named Beverly Shenstone (I'd have hated to be a guy with the name Beverly...) who also noted that Supermarine's data was correct.

I had two cousins, Shelby and Shirley, both guys. Used to wonder how they felt.

 

[Deleted member 68059]

From what I remember the full-scale wind-tunnel the British used had serious problems owing to turbulence forming within the tunnel, which appeared to obscure turbulence produced on aircraft models placed in the tunnel: While I assume they'd gotten the hang of correcting for the turbulence figures with various correction factors until they ended up in speed regimes where compressibility started to factor in more and more, and they hadn't developed the ability to correct for those properly.

I remember this led to a number of erroneous assumptions in aircraft designs: Namely the misguided belief that thick wings would work fine at high subsonic speeds, the Beaufighter would manage 370 mph, and the Typhoon would be able to pull off 460 mph.

I'm curious when this wind-tunnel was put into existence, when this problem was resolved and, why it took so long to resolve it?

Airframes, drgondog, S Shortround6 , wuzak

I have all the British Air Ministry type files on the Typhoon (actually Tornado at the time), as you can see the 460mph nonsense has nothing to do with the wings>

There is no doubt that early wind tunnels had severely degraded results due to being turbulent, this is expanded upon by Beverly Shenstone in the 1966 centenary edition of the Royal Aeronautical society journal.

Shenstone puts the very late survival of the biplane down to lack of understanding of wind tunnel turbulence. (i.e that tunnel experiments showed the bilplane to have very artificially low drag).

I cannot absolutely refute it, but I think in the case of major aircraft designed in the mid to late 1930`s in Britain, that it is very unlikely that this factor would have remained unknown. The papers Shenstone references were Shrenck (1928) and DeFrance (1933)

Someone would have to read the Hawker files to find a definitive answer on the specifics of Camm`s aerodynamics thinking. But I think its very clear that
the main reason for the failure to attain it was not wing section error. If Hawker are lying to Professor Potsan at the Air Ministry about that fact
in 1943, it is quite a brave lie - as anyone requesting the wing data with a slide rule and the basic data of the aircraft concerned could have shown it
to be nonsense!

 

[tomo pauk]

Someone would have to read the Hawker files to find a definitive answer on the specifics of Camm`s aerodynamics thinking. But I think its very clear that
the main reason for the failure to attain it was not wing section error. If Hawker are lying to Professor Potsan at the Air Ministry about that fact
in 1943, it is quite a brave lie - as anyone requesting the wing data with a slide rule and the basic data of the aircraft concerned could have shown it
to be nonsense!

Calum - is it stated anywhere in these papers how much the engine on the Typhoon was supposed to have horsepower, in order for the aircraft to attain 460+ mph?

 

[Zipper730]

D Deleted member 68059 ,

How much did the Typhoon grow?

 

[ThomasP]

Inquiring minds want to know.

 

[Deleted member 68059]

Not all data is to be had, but... this at least shows you that the estimates were heavily driven by power estimates. Look at the difference just projected from two engine choices.

You can also see at this point its a 12 x .303 gun aircraft.

(pencil scribbes are original)

Regarding the size originally envisaged I dont know, but I suspect from reading the file that this early speed esimate was little more than a rough
figure Hawker proposed based on the hoped for Sabre power in an updated fighter of approximate Spitfire/Hurricane size using more modern
design techniques. I think this was proposed before the air ministry specification was issued, and hence I think it is little more than Camm
saying "I can make a plane that goes that fast with that engine and has some guns".

 

[elbmc1969]

Regarding the size originally envisaged I dont know, but I suspect from reading the file that this early speed esimate was little more than a rough
figure Hawker proposed based on the hoped for Sabre power in an updated fighter of approximate Spitfire/Hurricane size using more modern
design techniques. I think this was proposed before the air ministry specification was issued, and hence I think it is little more than Camm
saying "I can make a plane that goes that fast with that engine and has some guns".
View attachment 666650

Those dimensions are with inches of the size of the production aircraft. Height is different, but that might be due to different ways of measuring height, or landing gear changes.

 

[Deleted member 68059]

Those dimensions are with inches of the size of the production aircraft. Height is different, but that might be due to different ways of measuring height, or landing gear changes.

Oh yes of course, I was being stupid and just glanced at it and thought it was the powerplant size in inches, didnt notice it was actually feet !

In that case the letter from Hawkers is just about true as those sizes (at least in height and length) are indeed less than those of a Hurricane.

 

[gingerbob]

On the subject of Typhoon vs Hurricane size, the comparison photos (model parts) in this thread might be of interest:

click here for Britmodeller thread

 

[Zipper730]

Far as I can figure, these seem to be the dimensions of all the aircraft in question (the Vulture engined design ended up as the Tornado): The height figures seem to be all over the place because there's the attitude of the plane in flight, the attitude of the plane with the prop up or down, at least I could deduce the Hurricane but the Tornado was based on Wikipedia as well as another online source which was in metric and converted to 14'7.9"