Support systems: Stabilizing aerials
Without stability an aerial is nothing more than an expensive toolbox; here's a look at the different stability systems on the market
By Robert Avsec
One of the most critical systems on today's aerial apparatus, regardless of type, is the vehicle's stabilization system. You know, the jacks or outriggers that keep the truck in its proper position, that is, vertical while we use the aerial device to accomplish emergency tasks.
The apparatus manufacturers are seriously committed to having the best stabilization systems on their apparatus because few things are worse for business than seeing one of their products in a non-vertical position in the news — or going viral on YouTube.
Apparatus manufacturers use several types of stabilizing systems.
- The A-frame style (sometimes referred to as the X style) has the stabilizer extending outward at a downward angle.
- The H-style has the outrigger extending horizontally and then down to the ground.
- The gull wing style is stored vertically and deploys downward.
- The under-slung style is part of the apparatus torque box and extends out horizontally and then down to the ground.
The H-style stabilizer is commonly used on apparatus manufactured by Pierce; Pierce also employs the A-frame style stabilizer on its Skyboom apparatus.
One advantage of the H style is its higher outrigger strength-to-weight ratio. This enables the designers to use lighter materials, such as high-strength steel, in the stabilizers.
Aerial apparatus equipped with an H-style system also enable the apparatus operator to deploy each stabilizer independently. This gives the operator a safe, effective and efficient means to operate the aerial when the situation calls for short-jacking the truck.
Because this style deploys horizontally and then down, it gives the operator a tool for avoiding a close curb or other obstacles.
X's and H's
Irregular, steep and sloped terrain present special challenges to the operator's placement and stabilization of an aerial device; the higher the stabilization device can lift the truck, the better. Today's X-style stabilizer systems can safely increase that lift to 20 inches.
Manufacturers are pretty consistent with their use of two rear outriggers as the stabilizers for a 75-foot aerial on a single rear axle. Some departments, where the aerial apparatus will often operate in steep or uneven terrain, may opt for an additional two stabilizers on the front of the rig as well.
For aerials greater than 75 feet, the OEMs typically recommend four of H-style stabilizers mounted fore and aft. This provides greater horizontal extension that in turn provides a better base for the operation.
Departments serving urban and densely populated suburban areas often need a smaller stabilizer footprint as their personnel face narrow streets, congested apartment parking lots, subdivision streets, etc. The OEMs typically employ the A-frame and under-slung stabilizers to meet the needs of those customers.
The under-slung style works particularly well in those types of situations because they're easy to set up — especially around obstructions. And because the steel structure is under the frame, they have a lower center of gravity. As a bonus, the under-slung accommodates an additional storage compartment over the jack leg.
Then there's the hybrid option that's a combination of stabilizers to create a system.
On a 100-foot mid-ship-mounted aerial, the manufacturer might use two jacks that drop straight down at the front and two of same at the rear. Then they would use a single set of under-slung stabilizers under the turntable. The operator can put the apparatus in a tight space and still get good stability and only have one set of extended outriggers, the under-slung.
Hitting the mark
Hitting their mark is an important task for an actor and the same goes for aerial apparatus operators (And there are no retakes on the fireground!). The apparatus OEMs understand this challenge and are working on placement systems that will help the operator of the apparatus with their jack placement.
Spartan's outrigger spotting system calculates the required distances necessary for correct positioning of the stabilizer footplate. It then directs a laser beam to that spot on the ground where the outrigger footplate will land. This enables the operator to quickly determine — before she deploys any of the apparatus's stabilizers — if there is enough space to deploy the outriggers.
Other systems include an automatic leveling system that lifts and levels the apparatus to a safe and proper operating posture.
Another is a ground-pressure sensing system within the stabilizer assembly that senses of ground-force pressure on the stabilizer. A minimum amount of pressure — typically around 4,000 pounds — must be satisfied to all outriggers before the system, which is connected to the aerial's interlock system, will provide power to operate the aerial.
Some aerials can operate without fully extending the jack on one side when necessary to avoid parked cars or other obstructions. This is known as short jacking, a term that can be used to describe any situation when the vehicle's full jack spread — defined as the distance between the centerlines of the side supporting jacks when fully extended — is not used.
Short jacking, while necessary in some situations, can result in decreased aerial stability if the operator attempts to use the aerial device over the short-jacked side.
Rosenbauer and KME are among the OEMs that have developed smart systems to reduce the potential for overturning the apparatus when operating the aerial device in the short-jacked position. These systems monitor the aerial device's active loading in real time and prevent the operator from extending the ladder or platform beyond acceptable limits.
The systems are designed to constantly calculate what is safe and prohibit the operator from putting the truck in an unsafe position.
Understand both the department's needs and the limitations and uses of each stabilizing system to get the most effective rig for your aerial buck.