The Whirlwind Project’s CAD man has worked out that the horizontal tail surface of the Whirlwind is a perfect NACA 63A-017 section. All well and good – EXCEPT that this section hadn’t been announced by NACA as a theoretical aerofoil until a year after the Whirlwind’s first flight.
The shapes of NACA 6-series aerofoils were derived mathematically to provide specific ‘optimum’ aerodynamic characteristics, and pioneered the concept of ‘laminar flow’ (Officially the first deliberate use of a laminar flow aerofoil was on the Mustang).
To have the exact same section appear on the tail of an aircraft designed before the research leading to this section was even published is either co-incidence (unlikely, as there were plenty of symetrical sections available at the time that could have been used ‘off the shelf’) or evidence of communication (or domestic research) way ahead of the official timeline.
Does anyone out there have specific knowledge of this particular period of aerofoil research, and can they enlighten us as to just what was going on in Somerset that put them apparently so far ahead of Langley?
Cheers,
Matt
By: Beermat - 16th February 2013 at 17:40
Hi Jeff
That’s a thought. We are waiting for the results of a 3 d scan of a wind tunnel model – it will be interesting to see if the profiles match..
Re the 5 digit Mainplane, that foil does fit with everything else we know, too. Funnilly enough I wa just thinking about trying a 5 digit naca foil with suffix modifiers to see if I can produce something similar to the tail section – that may be how the same numbers as the 63A-017 were generated. I wish I was better at maths! Can somebody tell me if this is feasible before I wear out another pencil?
By: Reckless Rat - 16th February 2013 at 12:26
Hi Matt,
I did wonder whether – being from the wind tunnel model – it might have been an experimental section to investigate the compressibility problems around the tail which resulted in the acorn, but I think that’s also too early?
Incidentally, I notice that Bingham has “…thin section wing of NACA 23017-08 section…” (pg 21) which is presumably the mainplane outboard of the nacelles. I’m sure you already have that, but I thought I’d mention it anyway in case it leads you in any particular direction!
Cheers,
Jeff
By: Beermat - 16th February 2013 at 10:30
Yes, to be fair what we are using are the scaled co-ordinates presented by the wind tunnel model plans, cross-checked with a small number of factory drawings of the tail acorn showing partial aerofoil. But the smoothed result happens to match to the point where the two plots drawn full-scale with 2mm lines overlay each other.
The naca plots were mathematically generated theoretical shapes, so could be called exact..
It is another section that matches with this degree of accuracy that I cannot find. But it existed in 1938, and would have been called something else. The 6 series were first documented in 1940.
By: HP111 - 16th February 2013 at 10:15
I am a bit suspicious of the term “is a perfect NACA 63A-017 section”. What exactly does this mean. Presumably, it is not stated what the section is in the relevant documents. Physical determination of the section will have its limits n accuracy and also the 63A-017 section itself would probably be calculated by “approximate” means. There must be a variety of sections that “match” within a degree of accuracy.
63A sections were being discussed in textbooks by 1949, so information was obviously available somewhat earlier.
By: Beermat - 15th February 2013 at 17:54
Indeed not! But I have exhausted the ‘usual suspects’ in trying to find a match. I’d be grateful for anything you find!
Great link. Here’s another for the hardcore: http://history.nasa.gov/SP-4305/ch4.htm
By: Rocketeer - 15th February 2013 at 17:42
I don’t think that NACA were necessarily the only sections used in UK! Would have to dig out my stuff…..some 20+ years since I looked at it!!!
see this
http://www.nasa.gov/centers/langley/news/factsheets/WWII.html
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February 15, 2013 at 5:36 pm