Hangar Door Design: Height / Width Issues

How many blades should a multi-blade hangar door design have?  What are the factors involved in making this decision?

Spec-Dor recently had to propose a three-blade hangar door where the client’s original contract drawings showed a four-blade design.  The reason was that with four blades, each blade was too narrow.

With a rolling door, it all comes down to the height-width ratio.  If the width is narrow and the height is tall, the centre of gravity is high.  This means the door is more susceptible to tipping over.

But how can a hangar door section tip over?  The answer is that the conditions for tipping are always present.  As with trucks or trains, it would be more economical if trucks were taller.  The truck would carry more cargo per voyage. The idea is good and would probably work well if there was no wind.  However, the tallest trucks we have on the roads today can be tipped over by unusually strong winds.

As with the truck, a tall thin hangar door section will work.  However, if an external force was to be applied, tipping can occur in the axis of the bottom rails. The external force required to tip the section will come from the energy input to move the section.

Imagine an external force applied to the edge of door section as in two men pushing a door.  Normally, the door would move with little or no resistance.  As they push the multi ton door structure, it increases in speed an energy.  Once the force is removed the door should slowly decelerate and come to a stop.  However, TWO things can go wrong:

1. An obstruction in the bottom rail, maybe a small pebble, will suddenly jam the door. The energy and momentum of the mass will want to continue forward. The door will rotate about one of its wheels and the upper door structure could impact the top guide rails.
2. The external force pushing the door section is applied for slightly too long a time. The door section is approaching the end of the door track at a too high a velocity and it hits the end of travel door bumper.  The door will rotate about the bumper and the upper door structure could impact the top guide rails.

In order to avoid these likely scenarios,  the simplest solution is to respect a width to heights ratio of less than 3.  The width should be calculated as the centre to centre distance between the wheels.  As a result, a door section of 4m in width and a centre to centre wheel distance of 3m, should be built no more than 9m high.

Now, if this ratio is too difficult to respect, then Spec-Dor can design a door system to work adequately while minimizing the consequences of tipping.  This solution would have to be based on probabilities and prevention and may include stronger top guides, minimizing building deflection, anti-lift top roller designs, bottom rail locks, electrical backup systems, and/or calibrated shock absorbing bumpers.  This solution would inevitably cost more with the increases coming from both the door supplier and the building supplier.

As with all aspects of construction today, insurance and liabilities seem to govern.  Spec-Dor believes that aircraft hangar door design should be simple and cost effective rather than complicated and risky.  Contact us today to get expert advice on your hangar door design requirements.