Approved for public release 5/10/18, JSF18-362

F-35 Weapons Design Integration

II. F-35 Weapons Suite and General Arrangement

F-35 weapon requirements were defined by the F-35 Joint Program Office (JPO) in the Joint Contract Specification

(JCS). They were later refined during the Concept Definition and Design Research (CDDR) and Concept Development

Program (CDP) phases, prior to the System Development and Demonstration (SDD) production aircraft selection. The

initial weapons suite from the SDD contract contained effectively all stores in the U.S. and UK inventories, as well as

smart and older, unguided weapons. Early in the SDD program, we refined the weapons suite to eliminate some of the

older weapons that were becoming obsolete, such as: the AIM-120/B Advanced Medium-Range Air-to-Air Missile

(AMRAAM®), naval mines, current generations of the AGM-84 Harpoon anti-ship missile, and the AGM-88 High-

Speed Anti-Radiation Missile (HARM®).

1 Director, F-35 Systems Engineering, Mail Zone 6500, PO Box 748. 2 Senior Manager, F-35 Armament and Stores Management, Mail Zone 6421, PO Box 748. 3 GS-14, F-35 Weapons Integrated Product Team Lead, F-35 Joint Program Office.

Douglas M. Hayward,1 and Andrew K. Duff2

Lockheed Martin Aeronautics, Fort Worth, TX, 76101, United States of America

and

Charles Wagner3

F-35 Joint Program Office, Arlington, VA, 22202, United States of America

Tactical aircraft operations in a high-threat, hostile environment require an internal

weapon carriage capability that supports stealth operations while ensuring aircrew

survivability and mission success. Once the threats have been reduced, a multirole, increased

external carriage capability is then required to prosecute an expanded target set. The F-35

meets both roles with internal carriage of air-to-air and air-to-surface stores. It has a robust

external carriage capability of multirole stores, an internal 25-millimeter Gatling gun for the

F-35A, and a missionized 25-millimeter gun pod for the F-35B and F-35C. It also has a stores

management system designed to control current and future store interfaces. The F-35 weapon

carriage design is based on experience gained from developing our successful 4th Generation

F-16 and 5th Generation F-22 fighter aircraft. The design is highly common across the three

F-35 variants and provides interoperability and operational flexibility to the theater

commanders to engage a wide array of targets. This paper describes the weapons

requirements, design development, evolution, and trades performed to define and mature the

weapon carriage layout. It also details the associated systems required to load, carry, release,

and interface with F-35 weapons.

I. Introduction

HE design and integration of weapon carriage provisions on a stealth aircraft, such as the F-35, are a fundamentalT part of the overall aircraft design. As such, they must be considered during the earliest stages of configuration

development and layout. The weapons suite and carriage requirements are key drivers for both the fuselage and wing designs. Internal carriage affects fuselage sizing and structural arrangement, and external carriage affects wing load and flutter requirements. The weapons also define the interfaces required to employ the weapons, which drives system capabilities from a targeting, wiring, power, and computing perspective. The mass properties and resultant weapon inertias are drivers in the overall flight control system and impact control surface definitions. Even the landing gear design and placement are affected by ground clearances and center-of-gravity relationships. In spite of these design constraints, the system does not contradict the F-35 program’s pillars of affordability, lethality, survivability, and sustainability.

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Newer weapons, such as the Small Diameter Bomb (SDB) and Guided Bomb Unit (GBU) GBU-49 Enhanced

Paveway™ II munitions, were added to the requirements list. This keeps the F-35 weapons suite as modern, relevant,

and flexible as possible. The suite enables the F-35 to perform multirole missions, providing flexibility to the

operational commander to prosecute a wide variety of targets. Figure 1 shows the resultant internal and external

weapons suite.

Fig. 1 F-35 internal and external weapon carriage requirements.

In addition to the weapons the F-35 is required to carry, the JCS also included other specific requirements that

drove the weapons carriage arrangement and weapon station capacities, such as being able to carry external fuel tanks.

It also issued mixed parent and dual-carriage requirements for each service. Other influential factors were the variant-

dependent mission requirements, such as the F-35A’s need for an internal gun and the F-35B/C’s needs for a

missionized gun. Additional requirements focused on safety and flexibility, such as the requirement for MIL-STD-

1760 interfaces at all stations and the ability to safe the weapons systems from outside the cockpit. These design

requirements resulted in four internal and seven external weapon stations. Figure 2 shows the general arrangement of

the weapon carriage, and Fig. 3 shows the station type and weight capacities.

The commonality of the weapon carriage design across the three aircraft variants was maximized to reduce the

differences in the certification process and minimize cost. The internal weapon bays are common on the F-35A and

F-35C variants. These bays are capable of carrying one internal 2000-pound class store with one AIM-120C

AMRAAM missile in each bay. The F-35B bay is unique and capable of carrying one 1000-pound class store with

one AIM-120C missile in each bay. Air-to-ground or air-to-air stores are carried on adapters on the roof of the bays.

Each bay design includes a door-mounted AIM-120C station that rotates with the door to improve separation clearance

and loading access. The external wing stations are located on nearly common buttock line stations across all three

variants. The suspension and release equipment is common across all variants, with the addition of a unique 14-inch

bomb rack tailored to the 1000-pound class internal bays for the F-35B aircraft. The stores management system (SMS),

interfaces, safing features, and system operation are common.

Fig. 2 General weapon carriage arrangement.

Fig. 3 Weapon station capacity.

As part of the SDD program, a subset of these weapons and requirements was required to be fully certified. The

weapons in the subset needed to provide a warfighting capacity in time for each service’s declaration of initial

operational capability. The weapons and specific loadouts we certified during the SDD program are shown in Fig. 4.

The certification effort for these capabilities and specific loadouts to be fully certified was based on extensive analysis

and testing. The design was developed and validated using a combination of three-dimensional (3-D) design tools,

wind tunnel tests, and computational fluid dynamics analyses. The F-35’s preliminary layout and detail designs were

developed using a 3-D digital thread to ensure that all systems were effectively integrated and complete. Wind tunnel

testing formed the backbone of the validation tests and included 11 test entries with more than 3900 user-occupancy

hours and more than 1700 air-on hours. In these tests, we assessed the weapon bay design from both separation and

acoustic perspectives. We also defined performance requirements for the suspension and release equipment (S&RE)

and validated our separation models to support flight test continuation criteria. The weapon certification effort

culminated in the successful separation of 110 air-to-ground and 73 air-to-air stores during the flight test program.

The effort also led to 46 weapon delivery assessment (WDA) engagements in which the total end-to-end systems were

exercised to validate the overall air system employment’s accuracy. The details of the weapon separation and

certification efforts are described in Ref. [1].

Fig. 4 SDD certified weapon loadouts.

III. Internal Weapon Bay Design

The final F-35 configuration was heavily influenced by choices made with respect to the weapon bay design. From

a weapon arrangement standpoint, designers often discuss packing efficiencies associated with rotary, stacked, flat,

and tandem weapon bays. However, it is not until these arrangements are integrated into an aircraft concept that the

resultant system can be evaluated. As with all designs, a balance of competing requirements must be struck. From a

weapons standpoint, the final configuration must result in:

1) tight packaging solutions while also optimizing weapon loading,

2) open bay acoustic environment,

3) employment timelines,

4) station failure immunity,

5) separation risk, and

6) loadout flexibility.