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Posted By: Hal Brown
Date Posted: May 18, 2009
Description: This is a frame from a lucky video I made of a Hurricane taking off from the Military Aviation Museum. The spiral track of the prop blade tips is probably condensed vapor--it had just rained and was going to rain again, so the air was very humid. I've seen vapor trails coming off of wings before, but never from a prop. The video is in the File Cabinet.
Date Taken: May 18, 2009
Place Taken: Military Aviation Museum, near Virginia Beach, VA
Owner: Don Maxwell
File Name: Picture_44.jpg   - Photo HTML
Full size     - <img src="/show.php?splash=SZS370000h">
Medium    - <img src="/show.php?splash=SZS370000m">
Thumbnail - <img src="/show.php?splash=SZS370000s">
Category: 23, Max Pix
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Read what others had to say:

Dan Nickens - May 18,2009   Viewers  | Reply
    Beauty, Don! And thanks for all the other fine photos of the fly in.     
  
Don Maxwell - May 18,2009   Viewers  | Reply
    I forgot to mention that they said this was to be the first ANNUAL show: <a href="http://www.militaryaviationmuseum.org/events_airshow.html">http://www.militaryaviationmuseum.org/events_airshow.html</a><br /><br />I didn't notice until too late that for this weekend only they allowed GA airplanes to land on their runway.<br /><br />Here's the poster for 2009: <a href="http://www.militaryaviationmuseum.org/source/images/media/Va%20Beach%20Airshow.jpg">http://www.militaryaviationmuseum.org/source/images/media/Va<br>%20Beach%20Airshow.jpg</a><br /><br />I'm looking forward to 2010.     
  
Chris Vernon-Jarvis - May 19,2009   Viewers  | Reply
    I think the condensation trails on any aircraft are fascinating. It was years before I understood just how quickly the condensation forms and dissolves, just see a flyby by a Buccaneer (the RNAS version!) with its high wing loading. Last Jan we went to Las Vegas and on take off from Vancouver there were wonderful patterns around the engine intakes and the leading edge.<br /><br />What is interesting in the picture is how widely spaced and even the spirals are.     
  
Eric Batterman - May 19,2009   Viewers  | Reply
    This is what I see when I look out the window...<img src="inline/20053-gremlin.jpg" alt="gremlin"><!-- >'"><br><font color=red size=6>' or &gt; missing in user HTML. Please fix the HTML.</font> -->      Attachments:  

gremlin.jpg
gremlin

    
  
Don Maxwell - May 19,2009   Viewers  | Reply
    Find a brick.     
  
Don Maxwell - May 19,2009   Viewers  | Reply
    I grew up seeing condensation trails in comic books and thought they were just the artists' way of suggesting speed. Had no idea they were real. Then a relative took me to the Cleveland Air Races when I was 12, and I saw them streaming off the wings of the Thompson Trophy racers as they rolled almost knife-edge and pulled around the final pylon, right in front of the grandstand. The condensation trails, the sound of those big engines, and all--amazing, astonishing!     
  
Don Maxwell - May 19,2009   Viewers  | Reply
    At first I thought these spiral condensation trails were a digital camera artifact. If you watch the video, you'll see how the camera 'slowed' the prop drastically. And some digital photos of very fast motion look bizarre because the sensor is scanned one line at a time, so the image may be wildly distorted. Prop blades on SeaReys, for example, sometimes look like cubist boomerangs. But it turned out to be the real thing.<br /><br />I think. I saw the phenomenon only through the camera, and I didn't hear anyone remark about it at the time. It's possible that they might not have been visible to the naked human eye. But the camera 'sees' into the near-infrared. (You can make a video of a tv remote's infra-red LED.) So it's possible that NObody saw these trails.<br /><br />It might be possible to calculate the various speeds here, and the prop pitch. The prop has three blades, each maybe--what?--5 feet long? And in this frame (and in the video) the engine must have been turning well above 3000 rpm, maybe closer to 3500. So the blade tip speed was probably close to Mach 1. I'm not sure at what airspeed a Hurricane's tail will come up on takeoff--50 knots, maybe? The camera (a Canon still cam with 640x480 video) was running at 30 frames per second, but I don't know what the actual scan rate is, other than that it repeats 30 times per second. Well, that's about as far as I go today.     
  
Chris Vernon-Jarvis - May 19,2009   Viewers  | Reply
    You can see the shutter speed in the length of the actual prop tips (The yellow flashes) Assuming all three blades are making the spirals you could estimate the pitch against the fuselage length.Say about a quarter of the fuselage, maybe seven of eight feet, however that varies during the take off. Obviously forward motion starts as zero and at 250 knots would be far longer and then there is the actual variable pitch to think about. Probably too many variables for a simple mind.<br /><br />One thing I have noticed with the Merlin is how it sounds different in a Spitfire. With all the other aircraft it was in it sounds loud and throaty but in a Spitfire it seems you can almost hear the mechanical parts individually and it is, perhaps, more crackly departing. Maybe something to do with the closeness of the cowl or the sleekness of the airframe. I don't hold any particular brief for the Spitfire, as an effective weapon it probably cost far more to build than was sensible but it maybe made up for that as a morale builder. Sometimes, in war, the intangibles are as important as the tangibles.     
  
Don Maxwell - May 19,2009   Viewers  | Reply
    For those with too much time on their hands, I've posted a slo-mo version of the video in File Cabinet.     


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