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# Maximizing Throughput at Soft Airfields

Christopher A. Mouton
Copyright Date: 2013
Published by: RAND Corporation
Pages: 26
https://www.jstor.org/stable/10.7249/j.ctt5hhszc

## Table of Contents

1. Front Matter
(pp. i-ii)
2. Preface
(pp. iii-iii)
3. Table of Contents
(pp. iv-iv)
4. Figures
(pp. v-v)
5. Table
(pp. vi-vi)
6. Summary
(pp. vii-ix)
7. Acknowledgments
(pp. x-x)
8. Nomenclature
(pp. xi-xi)
9. 1. Introduction
(pp. 1-2)

The number of passes an aircraft can make on a soft field is limited because rutting of the field occurs with each successive pass. Eventually, absent resurfacing, this rutting will reach a point where further aircraft operations are no longer permissible. The maximum number of passes an aircraft can make is commonly described as a function of the California Bearing Ratio (CBR) of the field and the weight of the aircraft.

In many situations, CBR is not the best predictor of maximum passes; however, it is frequently used because of the relative ease with which it can be measured and...

10. 2. Calculating Optimum Landing Weight
(pp. 3-6)

Performance charts for aircraft designed to operate on soft fields, such as the C-17A and C-130J, often present a table relating the maximum number of passes that aircraft can achieve as a function of the weight of the aircraft and the CBR of the field. These charts assume that there is no runway resurfacing during operations, which could drastically increase the total number of passes. It was found that these performance data could be fit with an equation of the form

\${P^{\max }} = aCB{R^b}{e^{ - c{W_L}}},\$(1)

where\${P^{\max }}\$is the maximum number of passes and\${W_L}\$is the landing weight. The coefficients a,...

11. 3. Boeing C-17A Analysis
(pp. 7-13)

CBR data were sampled from the figure entitled “Runway Weight Bearing Capacity on Unpaved Runways Using CBR Rating with Standard Tire Pressures” from the C-17 Technical Description and Planning Guide, based on a 32-percent mean aerodynamic chord center-of-gravity limit, at landing weights of 280,000 1b, 300,000 1b, 350,000 1b, 400,000 1b, and 447,000 1b, and for 50, 100, and 300 passes.⁵ In particular, a pass is defined as one takeoff and one landing. Using the form for the maximum number of passes, as given in Equation 1,

\${P^{\max }} = aCB{R^b}{e^{ - c{W_L}}},\$(15)

we can solve for the three coefficients using the 15 data...

12. 4. Conclusions
(pp. 14-14)

Based on the preceding analysis, we derive several important observations and calculations regarding aircraft operations on soft fields.

First, we show that for a given fixed ramp weight, there exists an optimum landing weight and that this optimum landing weight is not equal to the maximum aircraft landing weight. This optimum landing weight can also be expressed as an optimum cargo weight, and this optimum cargo weight is found to be independent of both field CBR and aircraft ramp weight. In fact, for the C-17A with a ramp weight of 315,000 1b, the optimum landing weight is less than the...

13. References
(pp. 15-15)