2010 Arrow Cowling

I was just on the Piper web site and noticed the cowling design. It appears the new Arrow, Archer, and Warrior have the older cowling design. Did they discontinue the Lopresti 2-hole type cowling? I was surprised to see this. I thought the Lopresti cowling reduced drag and provided higher cruise speeds. Can anyone shed any light on this?

Thank you.


  • I don't believe that the Warrior or Arrow ever had the Axial-Symentric cowel.

  • The axial symmetric inlet openings create a horrible loss in the diffusion ramps, resulting in less dynamic ram recovery to drive the flows across the face. The circular openings were copied from Stan Miley's research, but he used the shape only because the flow coefficients and losses were already known, thereby removing a couple of variables from his research. He repeated in his papers over and over that the shape should NOT be used on a horizontally opposed engine, but it got copied anyway. First by Sweringen, then by LoPresti who was a friend of Sweringen, then by Piper, copying LoPresti. The circular openings force a separation on the lower surface of the diffusion ramps.
  • Leigh, I'm not sure. I know Lopresti has cowls with the 2 "holes" as part of their speed mods for Arrows. Maybe the newer Arrow never went to that but I thought it did. As menitoned, the Archer and Saratoga uses the new design. Guess I'm surprised the Aroow doesn't. Maybe it never did.
  • Leigh, I have answered it before. The optimal shape would be a somewhat egg-shaped ovoid with the wide end outboard and inboard end far enough outboard to be clear of the area where the pressure inside the cowl is greater than that behind the prop (the area of reverse, forward flow). The key is to make the diffusion ramps as long as feasible while minimising the acute constriction on the bottom side of the inlet.
  • I really can't imagine why Sweringen ignored Miley's explicit warnings aginst the circlar openings when he 'emulated' Miley's work, but it sure did lead to a bunch of crappy cowls (though they are better than the originals).
  • Does anyone know why the android phone persists in replacing the word 'Miley' with 'Moody' over and over again? The keyboard patterns aren't even close to being similar.
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