by Mike Reightley
Bend, Oregon—One of the most enjoyable aspects of being involved in the aircraft modifications business is getting the opportunity to work on a variety of interesting and challenging projects. When the request came along to develop a new fire tank and a stand-alone auxiliary hydraulic system for the Kaman model K-1200 or “K-Max” helicopter, it certainly fit the definition of both “interesting and challenging”. It goes without saying that it is a very unique helicopter and to develop an effective fire tank for it was going to require an equally unique approach. Billed by the manufacturer of the aircraft, Kaman Corporation, as the “Aerial Truck”, a state-of-the art fire tank would make an already versatile and excellent performing aircraft into a real aerial “Fire Truck”.
For some years, there had been discussions about tanking the K-Max to make it an attractive aircraft for working fires in the wild land-urban interface. A new tank program however is no small undertaking, so it had historically come down to what operator or group of operators were willing to step up and commit to a series of tanks to justify the engineering expense of the program. Operator commitments were made even more tenuous, since no specific fire contracts had been offered that asked for a tanked K-Max. In other words somebody was going to have to go out on a limb with the “if you build it, they will come” philosophy. One such operator was Superior Helicopter, LLC of Grants Pass, Oregon. Superior Helicopter, as the largest operator of K-Max helicopters in the world with at times up to five aircraft, has a reputation of being progressive-minded, promoting new markets and improvements to the aircraft. Superior’s mainstay is primarily in the heli-logging business, however, like similar operators of large helicopters, they look to augment their revenues with fire contracts during the summers.
Superior General Manager, Gary Jantzer and Assistant General Manager, Andy Mills did their homework on developing a marketable set of specifications for a tank. To take advantage of the capabilities of the aircraft and comfortably maintain a USFS tanker board Type 1 heli-tanker classification, a 700-gallon capacity tank was decided upon. Superior surveyed the known tank manufacturers for the project with one of the primary criteria in the tank specifications of having a hydraulic-powered snorkel system. The stand-alone auxiliary hydraulic system would power the fire tank as well as double for a substantial power source for logging grapples, tree saws, etc. Kawak Aviation Technologies, Inc. was well suited for this task, since we had just completed like-type programs for the Croman SH3H (Navy S61) fire tank, the Carson Helicopters S61 Fire King program and Los Angeles county’s Bell 412 aircraft. In addition, to the auxiliary hydraulic system we had designed and supplied the hydraulic portion of the door control system and provided the new high output hydraulic-driven snorkel pumps.
While not going into the program with the intent to contract the entire fire tank system, Superior requested that we be the lead contractor given the fact that we were going to be supplying the majority of critical components and we had a history of navigating successful programs through the FAA certification process. This was not the first time we had been asked to look at an entire fire tank program, however, this time the timing was right since we had spent the last couple years putting the building blocks in place for developing a state-of-the-art fire tank. Needless to say, this was a big vote of confidence in our abilities to have a notable customer like Superior on a high visibility program to give Kawak the nod.
The design challenges for installing a fire tank on this aircraft were many. The aircraft was built as a long line lifter with the load path being a single point at the cargo hook. With that, the c.g. envelope had a maximum range of 2.5” longitudinally and 1.25” laterally. The aircraft isn’t particularly fast at 100 knots, so only a minimum reduction in airspeed could be absorbed if the helicopter was to remain above the tanker board minimum specification of 90 knots. Between the rotor system and the shape of the aircraft, the helicopter is aerodynamically sensitive in a variety of ways, such that the tank shape had to be a major consideration. In addition, the tank had to be able to be installed or removed in less than an hour and refilled in 30 seconds.
Neil Loftsgard, Chief Engineer for Kawak, put the wheels in motion to figure out how to strap 700 gallons around this thing. He was intent on not having just another box under a helicopter, but a tank that was as impressive in its aesthetics as it was its function.
Given the ambitious time frame of five months for the development of the first article, the decision was made to utilize traditional aluminum rib and skin construction on the basic tank and carbon fiber on the fairings. Thanks to the use of a good solid modeling program, the weight and c.g. issues could be monitored as the tank was designed and constructed electronically. Weight was also a crucial item since the aircraft had a max gross takeoff weight of 6,500 pounds (under 7,000 kept the certification basis in Part 27). Kaman Corporation in a concurrent program, upped the gross weight of the aircraft to 7,000 pounds so that it could absorb the weight gain of the tank and still maintain fuel capacity.
As if we didn’t have enough on our plate, we intended to have the first article on display at the Helicopter International Association convention the first of February 2005. Temporary tooling was assembled and parts went through the first article conformity process. The first two pieces didn’t get attached together until Christmas Eve day. The next six weeks was a blur right up until the tank rolled out of the parking lot for Anaheim a few days before the convention.
Following the convention, the tank came back for wrap up which included the integration of the electronics and testing. To avoid testing in the middle of the winter and take an aircraft out of service, a framework to lift the tank and a Kaman supplied helicopter fuselage was constructed along with a 2,000-gallon catch tank. This allowed us to simulate a hovering helicopter over a pond, snorkel and dump water for calibration of the door system and general performance testing. The ensuing couple of months were spent completing the engineering package for FAA certification, as well as the separate STC for the auxiliary hydraulic system.
With the FAA test program three days away, the fire season quite literally took off like “wildfire”. Superior had three aircraft dispatched to fires around the west, including our test aircraft. A couple of weeks later however, we were able to pull everyone back together and complete the FAA flight tests. Superior Director of Maintenance “Reggie” Regimbal and his crew, along with aircraft Crew Chief Jeff Allen, had done an excellent job preparing the aircraft N267KA on short notice. Other than the expected “tweaking” here and there, the tank successfully passed all of the flight tests criteria. The drop pattern was exactly as we anticipated and the door control system worked flawlessly through the testing that consisted of roughly 100 drops in both company and FAA flight tests.
The result of nearly nine months of effort is the new “FIREMAX”, with 700-gallon capacity with foam injection system, 30-second refill capability, and a computerized constant flow door system with six different coverage levels from trailing drop that can last 45 seconds to full salvo.
Despite excellent results for our first complete tank program, the development doesn’t stop here. Tank two will incorporate a weight reduction program targeted to pull out 75 lbs. yielding a net weight of 625 lbs. for the total package. This reduction will come predominantly from a change in skin thickness from .050” to .040”. Kawak had to be conservative on the first article, until all of the dust had settled on the structural analysis.
The FIREMAX program represented the perfect collaboration between customer, manufacturers, the FAA, and a whole lot of people behind the scenes to bring about a successful result. I can’t say enough about working with the Superior group from management to woods crew, as well as the support we received throughout the program from the FAA. It was a professional effort by everyone involved. While the new FIREMAX tank may say Kawak Aviation Technologies on the side, it is the contribution of many that give the K-Max operator community an effective fire fighting tool and the public with a new aerial fire truck ready for service.