Understanding and controlling jet blast
Jet blast is a phenomenon, which inevitably occurs in connection with jet or turbofan-driven aircraft. Simplified: They move because a mass of air is sucked into the intake, compressed by a high ratio, and then with the help of ignited fuel is accelerated and pushed out again.
The thrust achieved in this way is tremendous: If you have ever walked on the apron while an aircraft is taxiing past you, you will not only smell the burnt kerosene of the exhaust but also sense a breathtaking real storm of warm air. Plenty of videos impressingly show how even a full size pick-up with a weight of more than 4,000 lbs is simply blown away by the break-away thrust of a Boeing 747 preparing for taxi.
In other words: What is good and necessary to move an aircraft becomes a dangerous hazard for the aircraft environment during ground operations at an airport. This goes hand in hand with limited space available in the vicinity of aircraft stands at the terminal building where dozens of handling, supply and fuel vehicles compete for the available space.
The core problem
Jet blast is a highly energized hot air stream which can be best described as an artificial storm with enormous impact. Thus, the environment next to a turbofan engine exhaust becomes an area of imminent danger for airport personnel as well as for vehicles used for ground operations, for other aircraft in the vicinity or even for buildings. Thrust physically is a reaction force being described in Isaac Newtons second and third law of motion »If a system emits a mass in one direction, the accelerated mass imposes a force of equivalent size in the opposite direction«. The result achieved is called propulsion. The two engines of an Airbus A320 develop an idle thrust of 225 kN or 50,000 lbs altogether which equals almost 23 metrical tons. The idle thrust of the most powerful turbofan engine on the market is more than 500 kN or more than 50 metrical tons. One can easily imagine what it means to be exposed to that violent air masses in motion.
Strategies for dealing with jet blast
At airports with little traffic and a considerable apron area this problem can be handled by simply giving the aircraft enough space to maneuvre and blocking the affected vicinity for personnel and vehicles.
At most busy airports this is luxury: densely filled aircraft stands close to terminal buildings and busy schedules force the airport management to strive utmost efficiency regarding time and space available.
With the appearance of turbofan aircraft half a century ago engineers have understood that they have to shield man, vehicles or buildings and other protected areas of an airport from jet blast. This can be achieved by massive concrete or brick walls or by metal fences with a solid or a broken surface like fences made from mashed metal. With a solid surface both material and fundament must be very durable and deeply grounded. Mashed metal fences are a first step to a solution of the problem: with a greater overall surface per material used compared to a fence with a solid surface, a mashed metal fence is less vulnerable against jet blast and already disperses the jet blast directed against its surface at a considerable outcome. However, immediately behind the fence an air flow caused by the jet blast although already decelerated will still be sensible and a factor depending on the operational limits of the fence.
How blade deflectors make a difference
Amazingly, an array of blade deflectors made from metal or other heat resisting material can also help to break the fast and hot exhausts of a turbofan engine. Blade deflectors use basically the same principle like a mashed metal fence. But blade deflectors rather redirect than disperse the jet blast airflow. The deflected air streams kind of unite after their deflection thus creating a chimney effect. As a result, behind a blade deflector array the horizontal jet blast is entirely eliminated.
The blades used do not even necessarily have to overlap but can leave space between the single parts, thus providing a lighter construction method. The angle of the discrete metal elements determine a deflection of the air stream by up to 90 degrees, so that straight behind the fence the stream is broken and has no more hazardous side effects to the aircraft vicinity. The employment of jet blast deflectors thus helps to cope with challenges of high impact hazards in a space and time sensitive environment like an airport.
What Blast-Ex jet blast deflectors can do for you
Blast-Ex is a modular jet blast deflector system produced by RSB, a renown steel manufacturer in Germany. With decades of experience and being used by many airports all over Europe and in the Middle East, the system provides solutions tailored to the individual needs of an airport. With individual heights and dimensions, they might be installed on a permanent basis, as well as they could be used as portable devices for intermediate use like apron construction sites etc.
Planning, construction, building and installing can happen within a short timeframe at a reasonable price.