Tag: air tanker design

Awarded to CAL Poly, Pomona

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In 2015 the American Institute of Aeronautics and Astronautics (AIAA) Foundation held a Graduate Team Aircraft Design Competition open to undergraduate AIAA branches or at-large Student Members. They competed for prizes ranging from $500 for first place to $125 for third.

In October, 2016 the AIAA announced the three winners. The team that finished second represented Sharif University in Tehran, Iran, for their Anahita aircraft. On March 26 we wrote about the third place winning team. In a later article we will cover the team that took first place, but here we will describe the Sharif University entry in the competition.

The task from the AIAA was to design from the ground up a purpose-built large air tanker. Specifications for the aircraft included a crew of two pilots, 5,000 gallon retardant capacity, 2,500 nm ferry range, dash speed of 300 knots, and powered by turbofan or turboprop engines. Other criteria was a drop speed below 150 kt, stall speed of 90 kt, and takeoff from a Balanced Field Length of 5,000 ft. with an assumption of +35°F standard atmosphere at an altitude of 5,000 ft. above mean sea-level. In addition, fatigue stresses should be strongly considered.

Not being fluent in Persian, I looked up “Anahita”, the name the team gave their project, and found that it refers to an Iranian goddess associated with fertility, healing and wisdom.

Curiously, there was a fairly lengthy section in the team’s proposal discussing the feasibility of converting a 737 into an air tanker. The proposal was written in 2016, and in May, 2017 Coulson announced that they had purchased six 737-300s to convert them into 4,000-gallon “Fireliner” air tankers. Britt Coulson said they saw an opportunity when Southwest Airlines made a decision to replace their 737-300’s with the new 737-Max.

The students designed an aircraft with a high wing, “H” tail, and two turbofan engines under the wings. It would carry enough fuel for two sorties of three drops each.

The retardant tank would be cylindrical,  8.5 feet long with a diameter of 2.5 feet. My calculations determined it would only hold 312 gallons, far short of the 5,000 gallon requirement.

The students specified that the tank would be pressurized, “…so the drop operation will be more precise and there will be no splashing.” But there was no description of how that would be accomplished — with an onboard air compressor, a ground-based compressor, or another method.

The proposal mentioned that the aircraft could also carry cargo, and in another section, that the tank could be removed in minutes. There were no other details about cargo; presumably the tank would be removed to make it  multi-role capable. The document described the cargo door in a 737 but there was no mention of one in their purpose-built air tanker design.

The aircraft will have two pilots, and since it must be able to drop on its own without the need for a lead plane, the designers determined that an observer would be on board to monitor the fire. Extra windows cannot be installed in the cockpit because it would greatly increase structural fatigue. So for the observer to have an effective view of the fire area, five cameras will be embedded in the skin providing imagery to a Virtual Reality (VR) helmet worn by the observer, similar to the helmet worn by F-35 pilots. Two cameras would be in the nose, one in the middle, and two in the rear.

In order to determine the location of the drop, two infrared cameras would map the fire and, the students wrote, “…with the help of the geological data of the terrain and wind speed and direction, the fire behavior can be predicted by a computer and the optimal location of drop can be realized.”

Cost
They found an air tanker study that recommended an optimal number of 28 federal large air tankers. Based on production of 28, the unit cost would be approximately $279M. If 120 units were manufactured for worldwide use, the cost per unit would drop to $126M.

From the Conclusion section of the proposal
“It was realized that the 160-day contracts do not result in economical solutions to the LCC of Anahita, therefore, additional capability of performing alternate missions was considered. The 160 contracts per year were predicted to reach 208 by 2100, this indicates that the firefighting operation hours will increase in the future. Increase in the fleet was recommended in order to lower the unit cost, this was justified based on the increasing number of fires and 37 international agreements on forest fires between US and other countries, it was then indicated money for every player is guaranteed by Export Credit Loan, so foreign contractors could also be involved.”

You can download a copy of their proposal.

The designers:

In 2015 the American Institute of Aeronautics and Astronautics (AIAA) Foundation held a Graduate Team Aircraft Design Competition open to undergraduate AIAA branches or at-large Student Members. They competed for prizes ranging from $500 for first place to $125 for third. The task was to design from the ground up a purpose-built large air tanker. Specifications for the aircraft included a crew of two pilots, 5,000 gallon retardant capacity, 2,500 nm ferry range, dash speed of 300 knots, and powered by turbofan or turboprop engines. Other criteria was a drop speed below 150 kt, stall speed of 90 kt, and takeoff from a Balanced Field Length of 5,000 ft. with an assumption of +35°F standard atmosphere at an altitude of 5,000 ft. above mean sea-level. In addition, fatigue stresses should be strongly considered.

In October, 2016 the AIAA announced the three winners. Today we are writing about the third place contestant — in subsequent days we will cover the second and first place winners. Yes, even though we covered the initial announcement of the competition, we are a little late to the party to write about how it turned out. (No sense in rushing into these things.)

Receiving the award for third place was a 10-person group from California State Polytechnic University, Pomona, who called themselves the AeroTactic Company Team. You can download their very, very technical 65-page proposal.

The team’s FF-1 Rainbird aircraft design features an integrated retardant tank with a gravity-fed dispersal system. It is powered by two Rolls Royce Tay turbofan engines underneath the wings. Winglets increased the Rainbird’s lift to drag ratio by 5%, consequently increasing its fuel efficiency.

Their rational for choosing to have it piloted rather than unmanned, was,  “A piloted aircraft is more flexible to changing scenarios compared to a UAV. In addition, an unpiloted aircraft would cost more to maintain and to build due to the additional sensors, hardware, and software required.”

The high density payload combined with the low stall speed requirement drove the design of the aircraft to contain large wings and a small fuselage.

The two engines are attached to the wing’s leading edge, protruding past the wing in order to balance the aircraft for all loading configurations. It is capable of carrying enough fuel for four sorties and can reload the retardant within ten minutes.

The 5,000-gallon tank is located at the center of gravity of the aircraft, limiting CG shift while releasing its load. Their goal was for the fuselage to be as small as possible while still being long enough to maintain aircraft stability, hence the larger length of the tank relative to its other dimensions. The tank can be refilled from three fill ports simultaneously.

The group determined that for the aircraft to reach a fire 200 nm away in the least amount of time, 54 minutes, it should cruise at 20,000 feet at 245 kt.

The cockpit, but not the entire aircraft, would be pressurized and air conditioned. (Not all three of the student entries have pressurization.)

The aircraft will have two infrared cameras, priced at $4,200 each.

Cost
The graduate students assumed 200 units would be produced over the next 80 years with combined 20-year life spans covering 100 years. They estimated the research and development would cost $1.89 billion, including building and testing three aircraft. Total cost of production would be $89 billion, inflated to 2022 dollars (when delivery would begin). The flyaway cost for each unit was estimated at $45.3 million in 2022 dollars, including 10% profit. At 131 units, the program would break even in costs and begin to generate profit.

Below is an excerpt from the proposal:

“The cost comparison between the [students’] FF-1 and the C-130 and DC 10 was obtained through the analysis of depreciation, the costs associated with retrofitting an existing aircraft into an air tanker, and the limited life of the aircraft in the year 2022. The cost of retrofitting an air tanker was approximated to be $23.71 million, not to mention the installation of a retardant delivery system which is another $6.38 million. The cost for the both the C-130 and DC-10 were obtained from Military Aircraft. Table 17.5-1 exhibits the costs of the FF-1 configurations and the retrofitted competing aircraft.”

The table below shows how the design met the required specifications.

The American Institute of Aeronautics and Astronautics is conducting a competition for the design of a large air tanker open to undergraduate AIAA branches or at-large Student Members. They will be competing for prizes ranging from $500 for first place to $125 for third.

The purpose-built air tanker in this design competition will have a crew of two pilots, 5,000 gallon retardant capacity, 2,500 nm ferry range, dash speed of 300 knots, and will be powered by turbofan or turboprop engines.

The winners will be announced in August of 2016. It will be interesting to see what they come up with.

Thanks and a tip of the hat go out to bean.