Maximizing Throughput at Soft Airfields

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Research Questions

1. How can we best define the optimum cargo weight?
2. Does optimum landing weight equal the maximum aircraft landing weight?

Aircraft operations on soft fields are limited due to field rutting. Each subsequent aircraft pass, defined as one takeoff and one landing, increases field rutting until the field reaches a point where further aircraft operations are no longer permissible. The ability of aircraft to operate on soft fields is often expressed as a function of aircraft landing weight and the California Bearing Ratio (CBR) of the field (which measures the ability of the soil to resist compressive loads). Because soft fields can support only a limited number of takeoffs and landings, it is important to understand how to maximize the cargo throughput at these soft fields. The calculations in this document show that there exists an optimum landing weight that allows for maximum cargo delivery. This optimum landing weight is constant and independent of both aircraft ramp weight and field CBR. There is also is a maximum landing weight at which a given cargo requirement can be met. The author illustrates these calculations using the C-17A, which is one of the options being considered in the joint future theater airlift analysis of alternatives.

Key Findings

There Is an Optimum Landing Weight that Allows for Maximum Cargo Delivery

• This optimum landing weight, defined as the optimum cargo weight per sortie plus the ramp weight at the point of debarkation, is not necessarily the maximum aircraft landing weight.
• The optimum cargo weight is constant and independent of both aircraft ramp weight (landing weight minus cargo weight) and the California Bearing Ratio (CBR) of the field (which measures the ability the soil to resist compressive loads).
• The optimum cargo weight is independent of the return fuel load as well as the field CBR.
• By landing with a less-than-maximum payload, it is possible that more total cargo could be delivered.

There Is Also a Maximum Landing Weight at which a Given Cargo Requirement Can Be Met

• This maximum landing weight minimizes the number of missions that need to be flown while not exceeding the limits of the soft field.

• Chapter One

Introduction

• Chapter Two

Calculating Optimum Landing Weight

• Chapter Three

Boeing C-17A Analysis

• Chapter Four

Conclusions

Research conducted by

The research described in this report was sponsored by the United States Air Force and conducted by RAND Project AIR FORCE.

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