3 questions to answer before buying an aerial
Knowing the capabilities and limitations of the different configurations are key to getting the right rig
By Robert Avsec
The aerial apparatus has come a long way since it was first introduced in the early 20th century. That evolution has left fire departments with serious choices: rear-mount or mid-ship-mounted aerial device, ladder or platform — or ladder platform.
The decision to purchase an aerial apparatus is a complex one that should begin with getting the answers to a three basic questions.
- What tactical operations do you expect to conduct using this piece of equipment?
- Where do you forecast that those tactical operations will take place?
- Where will the truck be housed?
The typical mid-ship-mounted ladder or platform will have a lower overall travel height because the ladder does not extend over the cab. Take a good look at the mid-ship option if your department has station doors with restricted height, lots of low-hanging trees and power lines, and low bridges or train trestles.
When it comes to the apparatus fitting into the station, make sure it will fit into more than one station in your department so that you have short-term or long-term housing options. Also, look at neighboring jurisdictions that you have mutual- or automatic-aid agreements so that your aerial apparatus doesn't wind up parked outside in cold weather during a station fill in assignment.
The mid-ship option is popular for those departments that want a platform on the working end of the aerial device. The platform does not hang over the cab in the driver's line of sight as it is with rear-mounted aerials.
This overhang can be somewhat intimidating, especially for inexperienced drivers. And it makes it more difficult to size up the incident scene, that is, to see overhead obstructions or see traffic signals.
The rear-mounted does have some features that make it more tactically desirable than a mid-ship aerial, especially if a department doesn't have an overall height concern in its station or its response area.
A rear-mounted aerial is capable of getting down to zero degrees elevation above the cab while a mid-ship is capable of about 8 degrees.
A rear-mounted aerial can provide a 200-degree rotation below grade off the sides and back of the vehicle a mid-ship is limited to 45 degrees on the left and 45 degrees on the right because the turntable is in the middle of the truck.
Because it's low around the entire rear of the apparatus, the rear-mounted performs well in that scrub zone. These aerials can go from zero to -6 degrees and rotate 270 degrees around the back of the truck, whereas a mid-ship can only go low over the side of the truck.
The typical rear-mounted aerial has more storage space for ground ladders and equipment because the turntable and body are higher.
Three vs. five sections
The number of sections used in the design and construction of an aerial device are important. The mid-ship aerials have four or five telescoping sections, while rear-mounted aerials usually have three sections. More, and shorter, sections in the mid-ship aerial mean:
- More maneuverability in congested area.
- Ability to place the ladder tip or platform closer to the ground or lower on the face of a building when buildings are closely spaced on the fireground.
- Reduced space required to swing and rotate the aerial past trees, electric lines, and buildings.
The five-section ladder design used in the mid-ship aerial typically makes it heavier than similar rear-mounted aerials with only three ladder sections. Mid-ship aerials also have higher initial costs because of the increased number of sections and the parts and labor associated with those sections — they run about $80,000 to $100,000 more.
The number of telescoping sections also influences the waterway flow. For a mid-ship aerial platform, the rated water flows are less because water must flow through five ladder sections, meaning the friction loss is higher. For example, a rear-mounted platform might provide 3,000 gpm; a comparable mid-ship's maximum flow rate would be 1,500 gpm.
Aerial apparatus are an important part of any department's fire protection plan. By looking first at what you want and need from an aerial you'll have greater success picking the type that's best for your community.