MILITARY AVIATION

Spec-Dor proposed a Bi-Parting Southern Hangar Door.  Southern design means that the tracks are completely outside the building.  This name derives from the fact that this solution can only be proposed in regions where there is never any snowfall as clearly, the tracks would become unusable.  This has the advantages that there is no pocket space required inside the building to accommodate the doors when they are open, and they can be moved completely to the side to allow use of 100% of the opening.

Hangar doors are liable to tipping if the height: width ratio is greater than 3.  (See our article Hangar Door Design: Height/Width Issues). Hence, a four-blade design was chosen so that each blade would be 10 metres wide by 25 metres high thus keeping the ratio to 2.5:1.

Unique hangar door safety issues resulted from the unusual height of the doors.  Each blade was considerably heavier than a typical hangar door blade, so the design had to consider the extra inertia and the energy needed to open and close the doors safely.

Dynamic Braking

The motors were designed to get the blades moving up to a speed of around 1foot per second.  In order to stop the heavy blades, a dynamic braking system was installed in addition to the standard disc braking system.  The dynamic braking system uses the regenerative properties of the motor to dissipate energy through a bank of resistors.  This dual-braking system allowed the doors to be stopped in the shortest possible distance.  The dynamic braking system parameters could be fine-tuned on site allowing optimum acceleration and deceleration to be achieved at installation time.

Non-Contact Proximity Switches

Usually, mechanical limit switches are installed on the top rails of a hangar door to determine the position of each blade and control the movement mechanism.  For this project, the limit switches would be 25 metres in the air – the equivalent of a 10 storey building!  This would make them difficult and dangerous to reach for maintenance.  
Hence, a system of non-contact proximity switches was devised to detect metal plates embedded in the bottom rails.  Each track had two proximity switches – one to begin the deceleration process and the other to stop the blade.  Non-contact switches were specified to meet the NFPA 409 requirements to maintain an explosion proof environment in the bottom 450mm of the doors.   This ensures that no sparks can be generated that may lead to ignition of any aviation fuel on the ground.

When the doors are reaching the fully closed position, they are automatically slowed down using the electromagnetic brake.  The door position is detected using end of travel limit switches.   Heavy duty floor bumpers are used to decelerate the blades to a complete stop without damage.

As an additional safety measure, end-stops were fitted at the end of the rails, sized according to the weight and speed of the doors.  Calibrated elastomer shock absorbers were installed, each with a diameter of 10 cm.  Many hangar door manufacturers do not include any shock absorbing features in their installations.

Designing airship hangar doors presented Spec-Dor with several challenges.  However, with more than 32 years of hangar door manufacturing experience, Spec-Dor had the expertise required to meet these challenges and deliver the best airship hangar door solution in terms of safety, reliability and maintainability.