Missile Fin Actuator – Case study

Missile Fin Actuator – Smaller, Lighter and More Powerful

Another defence industry triumph from OTM

Missile Fin ActuatorA leading international defence manufacturer faced the kind of problem that could have been tailor-made to showcase the skills and expertise that have kept OTM at the forefront of actuator design and manufacture for over 50 years.

The issue, to do with its surface to air missile, was one of space and environment. The only space available to house the missile fin control actuator was between the outer skin of the missile and the rocket motor. In addition, the unit had to weigh less than 2.75 kg, deliver an output torque of 50 Nm, a bending moment of 230Nm and had to be able to do all this at a temperature of 120°C

After trying unsuccessfully for three years to solve this problem they called on OTM. We saw the kind of challenge that has been the hallmark of our success for many years. High powered actuators working in limited spaces, harsh environmental conditions and under strict weight restrictions are our forte.

The first thing we did was break with convention. The actuator on a missile fin usually operates in-line with the motor. This was not possible given the space constraints we were working with. So, we turned the actuator through 90 degrees to operate at right angles to the body of the missile. Like we said, not conventional but it achieved the necessary result.

This was a breakthrough in itself but out of this solution came the next problem. Ordinarily, the required shelf-life of an actuator in this application is 25 to 30 years. That’s all well and good so long as the unit can be exercised on a regular basis which means running it every so often to make sure it is still operational.

However, the unique nature of this application meant that the actuator could not be accessed once installed without major dis-assembly of the missile, which means it simply can’t be exercised in the usual way. This unit, therefore, was required to have a shelf-life of 10 years, which is the service period of the missile, but with no exercise other than electronic test sequences to make sure they are functioning correctly.

At OTM, we were more than confident in our ability to produce an actuator unit that possesses the capability to last 10 years without being exercised, but this presents new problems. Since the unit can’t be accessed between service intervals, it cannot rely on traditional lubricants. Conventional lubricants separate over time making their use impractical. Having met the challenge in building the actuator, we also had to go to great lengths to source a lubricant that we could impregnate the gears with and that would stay active for 10 years. And, we did it because overcoming difficult problems and challenges are what we do at OTM.

We are extremely proud of what we managed to overcome through solving this problem. Everything we have talked about here was a feat of engineering for sure. But it also highlighted the unique partnership we have with our clients. Halfway through the process the customer changed the communication protocol for the missile which involved complete re-design of the electronics and the software. This was an excellent example of the flexibility OTM has always exhibited in its client relationships. We go the extra mile to get under the skin of the client’s business to meet their exact needs and adapt quickly to their changing requirements.

The actuator installation has  been flight tested and is in pre-production qualification. It is ITAR free and meets the size and weight specification that the client struggled so hard to accomplish before OTM were involved. The very nature of aerospace applications means that size and weight are always at a premium. We genuinely believe that this is why this industry and OTM are such a good match. No other bespoke design company could meet the requirements of this project and we proved once again that we could succeed where others had persistently failed.