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

[Zipper730]

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 , W wuzak

 

[pbehn]

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 , W wuzak

Where did you get your information from?

 

[SaparotRob]

Grumman.

 

[pbehn]

Grumman.

They ignored all advice about blue paint.

 

[DarrenW]

Hey Zipper do you happen to have the number of the report which states this information? Just curious and not questioning what you claimed.

 

[Zipper730]

DarrenW , & P 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.

 

[pbehn]

DarrenW , & P 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.

The Beaufighter was a direct development of the Beaufort Torpedo attack aircraft. Almost everything about it was known apart from how much extra weight had to be put in it and how much power the engines it would have produced.

 

[ThomasP]

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.

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. 460 mph was the max rated dive speed that the pilots test flew the aircraft to during acceptance trials. But the reporters heard the speed was 660 and they ran with it. Curtiss saw no reason to correct them.

 

[FLYBOYJ]

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. 460 mph was the max rated dive speed that the pilots test flew the aircraft to during acceptance trials. But the reporters heard the speed was 660 and they ran with it. Curtiss saw no reason to correct them.

Just like the F-35 program costing $1.7 Trillion and the press said that was the cost of one aircraft!

 

[Shortround6]

DarrenW , & P 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.

There are few hiccups to the racing plane story.

Quite a few airplanes from WW I and 1920s used thin wing sections.
But then with external bracing they weren't worried about the wing having enough strength to support itself.
The trick with the Spitfire wing was that it not only thin, it was able to keep from folding up or flapping around like a flag on a windy day.
The wing on the S6B was also only about 145 sq ft.

The other thing was that the thin wing sections that had been used in WW I and the 1920s had vicious stall characteristics, they didn't mush or just drop the nose, they quit flying altogether at stalling speed. They were also responsible for Handley Page becoming a wealthy man
Handley Page and his partner were licensing the slats/slot to many countries to reduce the landing accidents from these bad stalling aircraft.
The thicker wings promised gentler stalls and a strong wing without excessive weight.

Now please note that the Supermarine used an NACA 18 airfoil on the Supermarine 224 fighter prototype, at least at the root. And the 224 failed to meet the landing requirement by 10mph.

 

[ThomasP]

Question: Did the UK have a relatively high speed wind tunnel (say 400-450 mph) prior to the decisions made re the Hurricane/Spitfire/Typhoon/etc?

 

[Snautzer01]

I have a few wind tunnel reports spitfire vb spitfull. In there is also noted the way they measured. If intrest i can u.l. them.

 

[ThomasP]

Please do!

 

[EwenS]

You will find some history here about the Farnborough wind tunnels.

Wind Tunnel Buildings - Farnborough Air Sciences Trust

airsciences.org.uk

For comparison details of the NACA full scale tunnel at Langley

NASA - NASA Langley's 30- by 60-Foot Tunnel

I recall reading somewhere recently (and now of course can't find it!) that Hawker relied on data from NACA when choosing the wing section of either the Hurricane or Typhoon. Problem was that data turned out to be flawed and the wing section ended up thicker than it needed to be.

 

[ThomasP]

Thanks EwenS

 

[Simon Thomas]

Part of the issue the UK had was they were using wind speed in mph in the wind tunnels. This led to scaling errors on the small scaled aerofoils. This is why Sidney Camm got sold a pup with the Hurricane aerofoil. (EwanS - I have read the same article, but I also can't recall the name!)

Some time in the early-mid 30's they moved to measuring the speed in Reynold's number and the wind tunnel data improved significantly. (It would be interesting to dig further into the whole dimensionless numbers in aeronautics - does anyone know of any good papers?)

Prof Melville Jones used full scale testing and figured out that the boundary layer transition point was different from that found in the wind tunnel. Jacobs saw this during a visit to the UK, and was able to add this piece of the puzzle on his way to developing laminar flow aerofoils.

 

[Zipper730]

I recall reading somewhere recently (and now of course can't find it!) that Hawker relied on data from NACA when choosing the wing section of either the Hurricane or Typhoon. Problem was that data turned out to be flawed and the wing section ended up thicker than it needed to be.

What caused the data to turn out flawed?

Part of the issue the UK had was they were using wind speed in mph in the wind tunnels. This led to scaling errors on the small scaled aerofoils. This is why Sidney Camm got sold a pup with the Hurricane aerofoil. (EwanS - I have read the same article, but I also can't recall the name!)

That explains some things, as reynolds numbers going up often require a sharper airfoil. That ended up affecting the DC-8 years later (though if I recall, the problem was viscosity effects instead of inertial effects).

Some time in the early-mid 30's they moved to measuring the speed in Reynold's number and the wind tunnel data improved significantly.

I'm surprised that didn't affect the Typhoon design.

Prof Melville Jones used full scale testing and figured out that the boundary layer transition point was different from that found in the wind tunnel. Jacobs saw this during a visit to the UK, and was able to add this piece of the puzzle on his way to developing laminar flow aerofoils.

Is Paul Melville Jones American or Canadian (you mentioned a visit to the UK)? When did he discover this?

 

[don4331]

Given Formula 1 teams in 21st century still have issues getting their wind tunnels to provide data which correctly corresponds data on the track, it shouldn't be surprising that they had issues almost 100 years ago.

From what I've read the Langley Variable Density Tunnel (VDT) was the advantage NACA had. By increasing pressure, the VDT was able to increase density, so small scaled models more closely matched the full size plane.

Flaw in the data is they weren't operating at high enough speeds and when airflow reached trans-sonic speeds drag increased exponentially.

 

[don4331]

DarrenW , & P 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.

Beverly (At least its better than being a guy named Sue) left Junkers with latest German airfoil information and went to NACA where he traded that information for the latest US (4 digit series) data. Then he went to Hawkers and walked out of interview with Sidney Camm over misunderstanding on airfoils. He then took that combined NACA and German information to Supermarine - which explains why the Spitfire has NACA 4 digit airfoils, while everything else British has RAE airfoils.

 

[EwenS]

What caused the data to turn out flawed?

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!