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OCR for page 174
174 APPENDIX C EMAS Calculations Appendix C provides the technical details of calcula- the EMAS bed. Thus, it was possible to estimate the speed tions supporting the EMAS sensitivity analysis discussed in profile for any setback, braking coefficient of friction, and Chapter 5. reverse thrust. Reverse thrust in such cases was simply taken as a lumped deceleration value. This value was varied to observe the sensitivity of the response and to determine the criticality C.1. Data of the assumed reverse thrust level. At 70 knots and lower, the The data for the EMAS performance calculations were reverse thrust contribution is generally minimal. Therefore, in obtained from the manufacturer. Specifically, the manufac- all comparative calculations, the standard assumption of zero turer conducted three simulations of an arrest using in-house reverse thrust was used. software. The three cases were distinguished by the type of A plot of exit speed with respect to stopping distance was aircraft used. The three types of aircraft were a CRJ 200 ER, obtained from a plot of the absorbed energy. That is, the force B737-800, and B747-400. For all cases, the exit speed was applied to the aircraft by braking, reverse thrust, and EMAS 70 knots; the compressive strength of the material was 60 psi; bed engagement was obtained from the resultant deceleration the setback was 35 ft; there was no reverse thrust; and there profile of the aircraft and its MTOW. This profile was then was a braking friction coefficient of 0.25. Given these initial numerically integrated to obtain the energy absorbed during conditions, the length of the bed was minimized. Plots of air- the arrest. For every quantity of absorbed energy there was a craft speed with respect to nose-gear travel were provided. corresponding stopping distance. The absorbed energy was set equal to the kinetic energy of the aircraft at its exit from the runway, as shown in Equation C-1. In order to extend C.2. Calculations the domain of exit speed to 80 knots, the steady-state por- C.2.1. Performance of an EMAS tion of the absorbed energy curve was linearly extended to an absorbed energy corresponding with 80-knot exit speed. The In order to characterize the performance of aircraft within resultant absorbed energy profile for the B737-800 is shown the EMAS bed, for each given design case, a total of 10 to 15 data in Figure C-2. Figure C-3 shows stopping distance with respect points were extracted from the manufacturer plots once the to exit speed for the three design aircraft. aircraft had entered the bed. That is, the initial point in the plots was the point at which the aircraft entered the bed. 1 2 L These extracted data points were plotted discretely and a mv = F ( x ) dx (Equation C-1) 2 0 polynomial trend line was fitted to the discrete data. The poly- nomial trend line was then used to generate points of aircraft m = mass of aircraft speed and aircraft travel in the bed for an arbitrary aircraft v = aircraft exit speed travel step. Elementary kinematic relations were applied over F(x) = instantaneous force applied to the aircraft as func- each travel step to obtain deceleration of the aircraft. The data tion of position with a trend line and extracted deceleration profile for the L = distance required to arrest the aircraft B737-800 are shown in Figure C-1 (a) and (b) respectively. Deceleration due to braking in the setback area and reverse For a given bed width and setback, the cost of an EMAS thrust during the arrest were added to the deceleration due to was calculated as a function of stopping distance, or, put
OCR for page 174
175 140 1.0 30 120 Data Poly. (Data) Deceleration [ft/s^2] 0.8 Deceleration [g's] 25 100 Speed [ft/s] 20 0.6 80 15 60 0.4 10 40 0.2 5 20 0 0.0 0 0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350 Bed Nose Gear Travel [ft] Bed Nose Gear Travel [ft] (a) (b) Figure C-1. (a) Speed and (b) deceleration profile of B737-800 in EMAS bed. Figure C-2. Energy vs. exit speed for B737-800. Figure C-3. Stopping distance vs. exit speed for three aircraft.
OCR for page 174
176 20 18 B737 5200.9 B737 Survey 16 B747 5200.9 14 B747 Survey Cost [$M] 12 CRJ200 5200.9 10 CRJ200 Survey 8 6 4 2 0 0 10 20 30 40 50 60 70 80 Exit Speed [kts] Figure C-4. Cost vs. exit speed for three aircraft. 20 18 B737 5200.9 B737 Survey 16 B747 5200.9 14 B747 Survey Cost ($M) 12 CRJ200 5200.9 10 CRJ200 Survey 8 6 4 2 0 0% 20% 40% 60% 80% 100% Cumulative Percentage of Occurrences Figure C-5. Cost vs. reliability for three aircraft using revised overrun probability curve. another way, minimum bed length. As discussed in Chap- speed to cumulative percentage of overrun occurrences. ter 5, design cost numbers are reported in FAA Order Therefore, for the three aircraft design cases, it was possible 5200.9 (29) and were obtained as part of the Survey of U.S. to generate several sets of curves where the paired param- Airport Operators (Chapter 3). Furthermore, as was also eters were either stopping distance, cost, exit speed, and reli- discussed in Section 4-4, DOT/FAA/CT-93/80 (5) and more ability. The resulting curves are shown in Figure C-4 through recent ACRP research (24) provided data for relating exit Figure C-8.
OCR for page 174
20 18 B737 5200.9 B737 Survey 16 B747 5200.9 14 B747 Survey 12 Cost ($M) CRJ200 5200.9 10 CRJ200 Survey 8 6 4 2 0 0% 20% 40% 60% 80% 100% Cumulative Percentage of Occurrences Figure C-6. Cost vs. reliability for three aircraft using CT-93/80 overrun probability curve. 800 B737 700 B747 600 Stopping Distance (ft) CRJ200 500 400 300 200 100 0 0% 20% 40% 60% 80% 100% Cumulative Percentage of Occurrences Figure C-7. Stopping distance vs. reliability for three aircraft using revised overrun probability curve. 800 B737 700 B747 600 CRJ200 Stopping Distance (ft) 500 400 300 200 100 0 0% 20% 40% 60% 80% 100% Cumulative Percentage of Occurrences Figure C-8. Stopping distance vs. reliability for three aircraft using CT-93/80 overrun probability curve.