Howler

Not to be confused with the Howler, a Filipino siren of the same name.

ACA Howler
An early ACA Howler, located in Cologne, MN. It is the last active Howler, and remains in service as of August 2024. Photo credit to Minneapolis Aviation.
Company	Alerting Communicators of America
Produced	1972-1989
Type	Rotational Electromechanical
Sound output	123 dB @ 100 ft
Frequency	60 Hz
Horsepower	10 hp
Voltage	208-240/480 V AC 1 or 3 ph
Preceded by	ACA Allertor 125
Succeeded by	ACA Penetrator
Documentation	Product sheet

The Howler is a rotational mechanical siren that was produced by Alerting Communicators of America in the 1970s and 80s, as an attempt to produce a cheaper rotating siren that did not have the same issues that the larger Allertor 125 had. Unfortunately, it was completely overshadowed by the Allertor and later the Penetrator-10 which led to this siren selling few units despite its long production run.

History and design

A 1987 ACA Howler, privately owned by RamFett. Note the slightly different projector design compared to Cologne's.

The Howler was introduced in 1972, the same year that the Allertor 125 received its third generation redesign. It was found that the Allertor was prone to letting water into the projector drum which would then get trapped and freeze, which led to the rotor getting frozen stuck and burning out the motor. ACA decided to develop a new projector and intake design that would intake and output from the same area, and would not suffer from the same icing problems as the Allertor. The Howler was ACA's first siren with this horn design. The Howler is essentially a rotational version of the Screamer S-10, using the exact same rotor and stator from the Screamer S-10. Because of this, the Howler is quite a bit smaller than the Allertor and Penetrator sirens, with an 18 inch rotor. Like all of ACA's other sirens, the Howler is made of fibreglass to prevent corrosion. The siren came exclusively in 9/12 port dual tone, driven by a dual sided 10 hp AC motor, and it was available in either single or three phase power, with a decibel rating of 123 dB at 100 ft. Despite 8-port S-10s being available, no 8-port Howlers are known to have existed.

The motor cover is offset from the horn, rotor and stator, as can be seen here,

Like the Screamer S-10, the rotor and stator of the Howler are directional, meaning that if the rotor is spinning the wrong way, the siren's sound output will be severely reduced. The Howler uses a compact belt-driven rotator, with a belt connecting the motor to a large pulley wheel connected to a gearbox, which then drives another horizontal belt that pulls the entire siren unit around its stationary base. On some units, this horizontal belt is a chain instead. The siren's collector rings are located right below this belt/chain. A large conical intake is attached to the stator by 4 bolts, with a projector horn focusing the beam of sound in one direction. The horn and intake are very similar to what would be used in the later Penetrator series. Originally, the horn bolted onto the rear of the stator (as can be seen on Cologne, MN's unit), but in the mid 1980s, the horn was redesigned to match the Penetrator's horn, bolting onto the outer ring of the stator. The siren's motor cover is offset, meaning the siren does not sit on the middle of its base and the horn and rotor/stator are not attached to the middle of the motor cover.

RamFett's Howler with the motor cover removed, showing the belt driven pulley connected to the motor which drives the rotator mechanism.

The Howler's slip rings, brushes, gear reduction drive, and lower rotator belt.

The Howler was not a very successful siren. The Howler was seldom advertised compared to ACA's other sirens, and the fact that it ran on the Screamer platform meant that it was outperformed by the Allertor 125, which gave much better performance despite the potential for icing issues. The Penetrator series would be introduced in 1980, and with it the Penetrator-10 was introduced, which not only outperformed the Howler, but also solved the Allertor's problems by using a very similar one-piece projector as the Howler. The Howler also suffered the same problem as Federal's 500 series sirens, where the rotator belts often wore out or loosened over time, causing the rotator to slip or fail completely. If the siren was not tested regularly, the belts could also dry rot or become stiff, leading to the rotator working poorly or failing. With the Penetrator-10 rendering its purpose obsolete, sales dwindled. It was still sold alongside the Penetrator series as a smaller, cheaper option, before it would finally be discontinued in 1989.

Today, there are very few Howlers left. Fort Worth, TX, had an entire system of these before the system was upgraded, and the majority of remaining units are in small towns in MN. One unit was destroyed by lightning in Macon, GA, leaving only a single Howler left in service in Cologne, MN. This siren has been long due for replacement, but as of August 2024 it is still active and in service despite worsening rotator issues. Every other surviving Howler is either in private possession or abandoned in place.