This paper examines the effects of fitting various Jet-flap configurations to an AV8-B “Harrier II” Baseline aircraft using two NASA developed computer codes. The first code was written for this particular study but will not be published in this report. This code predicts the ground roll of an AV8-B with a partial span jet-flap, a full span jet-flap, a partial span internally blown-flap, and a full span internally blown-flap as well as the Baseline configuration. The second code used was a mission performance estimation routine called ACSYNT (Aircraft Synthesis) and is presently available to US companies and universities. This code models each configuration on a standard mission so that the relative merits may be determined.