More on Performance
The projected performance of the Stratos 714 is based on a detailed performance model. In this section we review this performance model.
Much of our efforts over the past two years has been spent developing a detailed weight and performance model of the
aircraft. We have used only those analytic and empirical methods that are appropriate to this class of aircraft and these have been verified against existing designs or published data. The approach has been 'bottom-up' in the sense that weight of all major components and systems have been estimated and then summed to give the overall aircraft weight. As an additional check, 'top-down' weight estimates have also been made by comparison with the historical trends of similar aircraft. In both cases the approach has been conservative and the stratos weight targets are therefore achievable with standard composite materials and construction technique.
The Williams FJ44-3AP engine deck has been embedded in the performance model so the thrust, air and fuel flows come directly from Williams International test data. In doing so, we have been realistic in the estimation of intake pressure recovery, bleed air flows and mechanical power extraction, all of which impact the engine performance.
We have carried out a detailed trade study and have found the optimum stall speed for the Stratos aircraft to be 63 knots. As this is above 61 knots, the FAA will require demonstration of increased crashworthiness which will require additional fuselage structural weight. However, these are offset by savings in wing weight and, overall, 63 knots gives the best combination of weight, performance, field performance and low speed handling.
In Europe single engine aircraft are required to stall at 61 knots or below. EASA certified versions of the Stratos will have a slightly lower maximum takeoff weight to comply with this requirement.
Our performance model has been applied to existing aircraft and shown to give good estimates of their weights, cruise and field performance. The Stratos performance has also been analyzed independently by a reputable outside group and they have confirmed our performance projections to be realistic. We have very high confidence that we can achieve the design objectives.