I recently received a question about the effects of propeller thrust on aircraft stability and control (S&C). Within the aircraft design community, we know that power effects to S&C can be a significant engineering effort. Often, the quantification of these effects requires a powered wind tunnel test with a commensurate pricetag. With in the pilot community, we know that power -and especially propwash- significantly impacts (pun intended) the tail’s aerodynamic control power. There are jet aircraft (ex. YC-14, AV-8) using jet exhaust to provide lift and other reactions.<\/p>\n\n\n\n
One interesting historical case of a power induced dihedral is the Martin 2-0-2 prototype from the late 1940s. First, let’s discuss the theory. For a twin engine propeller aircraft, the natural design configuration is mounting the engines on nacelles mid-span and in front of the wing. <\/p>\n\n\n\n
![\"\"](\"https:\/\/charles-oneill.com\/blog\/wp-content\/uploads\/2020\/05\/power-induced-dihedral-image-300x121.png\")
<\/figure><\/div>\n\n\n\nWe also know that the propwash has a higher dynamic pressure resulting from the increased flow velocity. The propwash during a sideslip is thus non-symmetric across the wing panels (i.e. more outboard on the downwind panel and more inboard on the upwind panel). The asymmetric flow pattern will induce a roll moment into the sideslip. We call this an anhedral effect (i.e. a positive C_L_beta), which is usually detrimental to the aircraft’s flight dynamics.<\/p>\n\n\n\n
![\"\"](\"https:\/\/charles-oneill.com\/blog\/wp-content\/uploads\/2020\/05\/Martin_2-0-2_4563917854.jpg\")
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