Though not shown here, an analysis of local Cp data was done (similar to that of Figure 11) and again, aside from the front lip, no significant areas of interference drag were identified.
[20.] Tesch, G., Demuth, R., Adams, N., "A New Approach to Analyzing Cooling and Interference Drag," SAE Technical Paper 2010-01-0286, 2010, doi:10.4271/2010-01-0286.
There are three types of parasitic drag: form drag (from blunt, non-lift producing surfaces), interference drag
(from mixing air flows) and skin friction.
OThere is an aerodynamic phenomena called interference drag
that occurs when two lifting surfaces intersect.
They reduce interference drag
and could bring fuel savings of up to 3.5% but that, says Airbus's John Leahy, is about as far as it goes with airframe improvements.
Wing drag was calculated as the sum of zero-lift drag, induced drag, wave drag, profile drag and interference drag
. For the fuselage and tailplane, only zero-lift drag was considered.
The P-51 external tank is mounted close to the wing, and as a retired aerodynamic engineer Ill bet that the interference drag
between the tank and wing is greater than the P-47 pylon installation.
Pratt & Whitney, along with Motoren-und Turbinen-Union (MTU) of Munich, West Germany, and Fiat Avio of Turin, Italy, has been addressing the key technologies of acoustics, interference drag, nacelle and variable-pitch fan design, and gear systems.
Installing an engine that is as much as 50 percent larger in diameter than a conventional turbofan of the same thrust requires careful integration of the wing, pylon, and nacelle such that the performance benefits are not lost to increased interference drag.
A joint test program was conducted in 1987 by Pratt & Whitney, MTU, British Aerospace, and Messerschmitt-Bolkow-Blohm (MBB) to investigate wing, pylon, and nacelle interference drag. A series of flow-through nacelles was designed that simulated bypass ratios between 10:1 and 24:1.
Because air flow that would have otherwise entered the grille must be diverted elsewhere in the closed grille condition, the external surfaces play a large role in the cooling drag term, this phenomena is called interference drag. Interference drag, depending on the vehicle, can occur on any of the external vehicle surfaces and can interact with external air flow patterns .
Several methods (not considering interference drag) to mitigate cooling drag have been discussed in the literature, these include: grille opening optimization, cooling fan/shroud optimization, active grille shutters (AGS), and heat exchanger ducting [8, 9, 10, 11, 12, 13, 14].