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motorgliders as towplanes
Ah, chemistry; I never did that either. Shoulda tried Wikipedia first; was
sure it was some sort of shortened up slang. Thanks. At 15:13 16 March 2009, Bruce wrote: monomer Dimer Trimer .... Nyal Williams wrote: I know this is not alt.usage.english, but what is the etymology of this word? Is it slang? Jargon? Engineer language? Is it Di-mer or Dim-er or dimer... something or other? I'm just a poor musicologist trying to figure stuff out. At 14:27 16 March 2009, Bruce wrote: Sorry Nyal - excessive vocab use. Dimer == related pair of. In this case two vortices - one off each wingtip that interact to create a roughly symmetrical "geared disk" shape behind the wing. With the downward part of the vortex from each wingtip merging with the downward flow from the other. If you drive behind a (modern / streamlined not SUV) car in the rain or snow you can see the dimer it creates. Formula one and Nascar rear wings also create impressive examples... Nyal Williams wrote: Help; what is "dimer" ? At 14:09 15 March 2009, Bruce wrote: Paul There is a large scale vortex dimer operating behind any aircraft, and particularly behind high wing loading, heavy short winged things like Pawnees. The wake we fly above in high tow is the turbulent propeller wake, but we would have to be impossibly high and/or far back to avoid the downward moving centre section of the dimer. I saw a picture using smoke trails that demonstrates the scale and power of this some years back - http://www.nasa.gov/audience/forstud...ry/Vortex.html There is a more impressive video at http://www.youtube.com/watch?v=uy0hgG2pkUs&NR=1 So - given that you are flying in a field of air that has a significant downward component, maybe you do have a higher angle of attack on the wings. Bottom line is that even in the smooth air above the propwash you are still in air affected by the tug. Bruce sisu1a wrote: Agreed. My money is on the towplane wake. I put my monies on the elevator authority/AoA ratio. We fly above the wing wake (USA...) in most cases, in relatively clean air, but sometimes in the clean air below it. Box the wake, it will tell you where it is and where it isn't... But typically glider's noses, on tow, are unnaturally high (and thus AoA is higher...) for a given airspeed, in addition to being more forcefully held there, both effects of course due to the rope's pull. The elevator is the same size whether on tow or free flight though, so the authority it can exert against the countering forces is proportionately lower than in free flight... The fix is the same regardless of why though- more speed... please! (wings rocking in vain...) -Paul |
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