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Ram Air Drag Recovery Parametric Assessment
Use this tool to perform a conceptual analysis of the drag recovery potential of your ram air cooling duct as a function of the thermal energy transfered to the cooling airflow, flight conditions and ducted HX thermohydraulic performance. 
The drag recovery of the ram air cooling duct is expressed using the Thrust Ratio
TR = (Tn / Dg) - 1 ,
where Tn is the nozzle thrust and Dg is the gross drag of the duct. TR reflects the aerodynamic efficiency of a cooling duct: a TR value of zero implies a neutral impact of the ram air duct on the aircraft aerodynamics, while positive and negative values indicate net thrust or drag, respectively.- Step 1: Problem DefinitionDefine temperature offset from the international standard atm., assume an intake design MFR and estimate a duct-only total pressure ratio (often approaching unity).
- Step 2: Parametric AnalysisVary all parameters to display the thrust ratio (TR) of your duct as a function of the ram air temperature increase (x-axis).
- Step 3: GuidelinesFind optimal combinations of flight conditions and duct design parameters that, for a feasible (depending on your application) cooling flow temperature increase, minimizes drag or maximizes HX pressure drop for a given TR.
Remember!
- TR = 0No net drag
- TR < 0Duct introduces net drag!
- TR > 0Duct produces thrust!
Offset value from ISA
Assuming no HX
Design massflow rate ratio of intake
Adjust Parameters
Operating massflow rate ratio