EDO’s AVEL Missile Ejection System: Extending the Raptor’s Claws
EDO Corporation has been awarded a not-to-exceed, $17.2 million contract from Lockheed Martin Aeronautics Company for continued production of its LAU-142/A AMRAAM Vertical Ejection Launcher (AVEL, pron. “ayy-vell”) for the F-22 Raptor. This latest order covers production for up to 24 Lot-6 aircraft, each of which is equipped with 6 AVEL launchers. Production Lot-6 will bring the total number of F-22 aircraft under order to 131, all of which are equipped with the AVEL. These aircraft are slated for delivery to the Air Force in 2008.
EDO’s original AMRAAM Eject Launcher (AEL) for the YF-22 demonstrator was developed during the 1980s, and used a “trapeze” approach. The system was designed to maximize the F-22’s punch by giving it the ability to store its missiles in stealth-friendly internal bays. Nor would the launcher use explosives to achieve missile separation, as conventional launchers do. The new launchers had to:
- Hold AIM-120C AMRAAM missiles securely within the bay as the aircraft undertakes maneuvers up to 9G.
- Safely control and eject them fast enough to penetrate the air boundary layer as they make the transition from the quiet weapon bay to the fast-moving airflow outside airflow field. This means ejecting the missile at the precise angle and velocity needed to optimize its guidance, all without interfering with the aircraft’s maneuvers at supersonic speeds.
- Minimize the time that the F-22’s stealth is compromised by having open bay doors.
- Offer outstanding maintainability and reliability; the F-22’s launcher would be significantly more complex than classic pylons or recessed fairings, but no aircraft cannot afford to have its armament carriage as a point of failure.
AEL was based on the idea that the F-22 would carry 2 missiles in each of its two underside bays, and the general belief was that the launcher would have to impart forward momentum as the missile exited the aircraft in order to work properly. But during DEMVAL (Demonstration and validation) testing, the 412th Test Squadron at Edwards AFB discovered that horizontal momentum was not essential.
This was an important opportunity. The force and stress tolerance required of a trapeze design meant that it was heavy, and less maintenance-friendly than it could be. If its functions weren’t absolutely necessary, the trapeze design needed to change. Once the F-22 contract was awarded, therefore, work began on a new launcher: the LAU-142A AVEL AMRAAM Vertical Eject Launcher. The critical timeframe was the 1991-1993 period between the F-22 contract award and the Preliminary Design Review, as the test team rethought the system with the aim of fitting more missiles in each bay. This was just one of the changes made to the original YF-22 design, but the potential to increase the plane’s full-stealth AMRAAM load by 50% could turn a minor part into a major program win.
Still, this re-design was going to be challenging. Understanding the missile’s dynamic loading is critical to the design of the launcher, which had to take place long before the F-22 had flown. Building a representative test fixture to apply (static) loads over the entire missile surface, instrumenting the launcher to measure the loads, then running multiple build-and-test iterations, would have been both time and cost prohibitive. Worse, the accuracy of the results would still have been in question without the ability to analyze dynamic loading.
As part of that rethink, therefore, EDO engineers turned to software. MSC Software’s MSC.Adams virtual prototyping tool was used to develop the structural and dynamic models, cutting development times and cost considerably. Predictive analysis was used in simulation for structural integrity and analytical performance, avoiding multiple build/ re-build cycles. A total of 223 critical load conditions were applied to the model to account for the impact of air, inertial, and oscillatory forces under a wide range of different flight conditions. For each load case, Nicolas DeSimini, Senior Staff Engineer for EDO ran the virtual prototype through 15 time steps designed to simulate the missile launch and separation from the aircraft. See full case study.
Throughout, Edwards Air force Base personnel and other members of the Integrated Product Team continued to play important roles, making design suggestions and assisting with evaluations.
The design evolved as they evolved toward the concept of a mostly aluminum pneumatic/hydraulic ejector mechanism using a six-bar linkage. The mechanism folds up like a scissors in the stowed position. During ejection it is stroked 9 inches by the pneumatic actuator, at which point it develops the required end of stroke velocity to safely separate the missile from the aircraft. The AVEL ejects the missile out of the bay at more than 25 feet per second with a force of 40G at peak acceleration, and the entire process from start to the closing of the bay door takes 3 seconds. See this video for an example.
In the end EDO, Edwards’ 412th Test Squadron, and the other stakeholders involved in AVEL delivered a launcher to the Lockheed-led F-22 team that allows the Raptor to carry 3 missiles in each internal weapons bay – while shrinking the bay itself and reducing the aircraft’s weight by 264 pounds. Thrust:weight is a critical ratio for any fighter, and improvements are always welcome; meanwhile, stealth compatible weapons capacity had been increased by 50% to six AMRAAM missiles.
Note that the F-22’s side bays, which feature launchers for AIM-9X Sidewinder missiles, are not made by EDO but by another company under contract to Lockheed.
“The AVEL is an example of the type of highly-engineered technology that is central to our growth strategy,” said EDO Corp. CEO James M. Smith.
In addition to the new F-22 platform, EDO provides aircraft-armament equipment for the F-15, F-16, and F/A-18. The company is also developing ejection systems for the Navy’s new P-8A Multi-mission Maritime Aircraft, as well as an internal weapons launcher for the F-35 Joint Strike Fighter (the “Pneumatic LAU-120”) which remains in development. It will face different loading than the F-22’s AVEL, as it must be able to handle much heavier ordnance. Nevertheless, EDO told DID that the Pneumatic LAU-120 has benefited significantly from work done on AVEL, and that simulation software remains a very important part of their design process.