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Old 22nd Sep 2022, 23:47
  #26 (permalink)  
fdr
 
Join Date: Jun 2001
Location: 3rd Rock, #29B
Posts: 2,956
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strakes

Strakes can be applied in varying means for varying outcomes.
  • On a tail boom, a longitudinal strake on the opposite side to the anti-torque direction of thrust provides a local flow that gives lateral force. (vertical flow oriented VGs on the opposite side improve that outcome considerably)
  • On a chipmunk or tigermoth, they alter the spin characteristics when applied as extensions to the horizontal stab.
  • On the KingAir, Learjet etc they are applied so as to improve lateral directional stability. They can also reduce total drag, as they can cause reorientation of the flow that has considerable separation otherwise at the rear of the fuselage on most aircraft.
  • The Q-400 implementation gives flow cahnges around the body of the aircraft otherwise influenced by the wake of the propellers.
  • Strakes were added to the belly of the Harrier and reduced the thrust required to hover.
  • A series of strakes were trialled on the C-17 to reduce drag.
  • Strakes on various cargo aircraft are applied to control flow particularly when airdrop operations are being conducted.
  • Strakes were added to the DC-9-51 and other variants of the long beach cable companies toy. They are in an area of upwash around the lower forward fuselage, which increases the upwash at higher AOAs.
  • Strakes have been evaluated on various "slender bodies at high AOA" that happen to end up with asymmetric shedding of vortex structures coming off the nose cone, that cause nose slice and consequent roll off at very high AOA.
The downside with strakes is they can be overly effective in lateral directional stability, and that gets to be a problem with normal control authority. While they can reduce drag, particularly the lower angled types, for longitudinal stability they will mostly interact with the stabiliser when it is a variable stab, and can have an adverse drag count change.
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