Nowadaysaircraft operators and fire-fighting authorities take for granted capabilities that up until a few years ago didn’t exist. In this article, we look at how aircraft capability has evolved from the early simple mechanical “pull the lever” designs, to today’s computer-controlled “drop by wire” firegate systems equipped with advanced telemetry and data gathering capability.

The SEAT revolution began with Leland Snow, the legendary developer of the Air Tractor series of aircraft. In the early 1990s, he had the vision to create a low-cost 800-gallon fire-bomber based on his hugely successful AT-502 crop-duster. He and the design team at Air Tractor began work on the much larger airframe and powerplant design that would become the equally successful AT-802. Leland was an engineer’s engineer. His tools were pencil, slide rule, protractor, and paper. But like all geniuses, he knew the limits of his capability and was wise enough to ask a local company, Spectra Technologies, to computerize the fire gate.

Pictured is the pilot interface module on board the 10 Tanker Air Carrier DC-10. Photo by Trotter Controls

A team led by Professor Robert L Woods took on the task, and a young Victor Trotter was selected to develop the controls and hydraulics designs. A fundamental objective was to improve the efficiency of the material’s delivery from the hopper, and thus the constant flow FRDS GEN I system was born. By 2006, more than 150 AT-802F firebombers had been delivered with the first generation Air Tractor gate and were in service worldwide. It was time to move on, and Leland asked a new company, Trotter Controls, to apply state of the art and newly available micro-processors to the fire-fighting challenge.

A lateral thinking Victor Trotter patented a new hydraulic valve control method, which allowed the new FRDS GEN II system to utilize multiple redundant cost-effective and rugged directional valves in place of a single fault-prone servo valve. Additionally, adding advanced self-diagnostic features to the system as well as enhanced flow control capability. Since then, more than 200 FRDS GEN II systems have shipped worldwide, many being upgraded from the original GEN I systems. Interestingly, more than 30 years after their inception, several GEN I systems are still in service and are finally at the end of their operating life (support for GEN I systems was discontinued as of Q1, 2020).

Trotter Controls has provided worldwide service and support for the Air Tractor fleet since the inception of the GEN I system. Several employees involved with the first GEN I system at Spectra Technologies are still building and supporting systems worldwide. For many years, Australia’s National Aerial Firefighting Centre (NAFC) has been a pioneer of fire-fighting performance analysis, continuing its hunger for additional data.

In 2014, recognizing that this would become a worldwide trend, Trotter Controls began developing a firegate telemetry system that could be used on a variety of fixed-wing and rotary aircraft. By 2016, the DataVault product was ready for deployment. Four aircraft successfully demonstrated its capability to collect and deliver data from Air Tractor GEN I / GEN II systems as well as other gates. Conceived as the telemetry and control equivalent of a “Swiss Army Knife,” DataVault can read sensors, control valves, interact with the pilot and send satellite messages. Since the controller can communicate with peripherals via virtually any standard protocol, DataVault is easily expanded and can deploy in a myriad of aviation applications.

Since its inception, more than 100 DataVault telemetry systems have been installed worldwide in a variety of roles on fixed-wing and rotary aircraft of all sizes. The most significant example of innovation is 10Tankers’ DC10 fleet. The highly capable DC-10 airframe has three independent tanks with a total volume above 10,000 gallons. Still, by 2015, its aging control system was no longer able to meet the extremely stringent IAB specifications for VLAT aircraft.

In addition to fixed wing, Trotter Controls products are also used in helicopters such as this Helimax CH-47. Photo by Trotter Controls.

Trotter Controls worked with the 10Tanker engineering team to produce a state-of-the-art constant flow system using a variant of the FRDS GEN II controller hardware to control the flow rate from each firegate. A Master Controller, together with a network of DataVaults, determines the gate configuration needed to achieve the commanded coverage level and split. The retardant can be delivered using each gate in sequence, or all three gates together. The system is so accurate that it can provide a 10,000-gallon payload in 8 equal drops of 1,250 gallons each.

The upgrade has been very well received by 10 Tankers’ customers and has dramatically enhanced the aircraft’s performance during operations in the USA, Chile, and Australia. At the smaller end of the scale, the Trotter team, in collaboration with Air Tractor, set about re-designing the successful FRDS GEN II system from the ground up. Victor Trotter saw that the power available from today’s ultra-efficient electric motors, customarily used for vehicle propulsion, would be more than capable of controlling the flow of fluid from the AT-802 tank.

The GenIII all-electric Firegate pictured is fitted to the Dauntless Air Air Tractor AT-802. Image by Trotter Controls.

This meant the weighty hydraulic power unit, valve manifold, and accumulator. All associated plumbing could be removed from the legacy FRDS and be replaced by a 15lb motor, gearbox, and a DataVault based control system. In another example of innovation, a single torque tube opens and closes the bomb bay style doors. Thus reducing obstruction of the flow path through the gate considerably over the dual torque tube design common throughout the industry and reduces component count and weight.

Taking electric motor and DataVault control technology to new limits, Trotter Controls worked with Airborne Suppression Technologies to create a ground-breaking constant-flow, carbon fiber tank for CH-47 aircraft. Working with Bart Brainerd, Trotter Controls also created an all-electric, DataVault controlled firegate for Brainerd’s fleet of UH-60 Firehawks. These systems both received STC’s and will be operating over fires in the US this season.

Considerable advancements in flow compensation have been made during the evolutionary development process since tank flow rates are now compensated for aircraft speed, maneuvering G’s, as well as the level of fluid in the tank to maintain constant coverage of retardant on the ground. By way of comparison, a system without G’s compensation would flow 41% too much liquid during a one G maneuver, thus wasting retardants and reducing the covered ground line. The technology’s driving goal has always focused on maximizing the ground line (length of the pattern on the ground) that can be protected using the least amount of retardant possible.

In addition to the all-electric applications, Trotter is currently developing hydraulically controlled firegates using the DataVault controls platform for various other airframes. The advances in performance, weight, and data gathering capability are serving to increase the effectiveness of the aircraft and improve the ability to coordinate authorities to manage fire operations.