Converting the Aircraft Jetstream 31 into a Firefighting Jet - Case Study Example

Converting the aircraft Jetstream 31 into a firefighting jet Converting the aircraft Jetstream 31 into a firefighting jet Jetstream 31 is a small aircraft that is designed to carry a maximum of 21 passengers (cabin crew included). That is, 2 crew members and 19 passengers. Before converting this aircraft into firefighting jet by removing the passenger seats and replacing them with a water tank, it is important that the basic features of this aircraft are understood. These features will important in the calculation of the capacity of the water tank, center of gravity (COG) and maximum take-off weight among others. The features are shown in the figures below. Figure 1: Side view of jetstream 31 Figure 3: 19 passenger seats arrangement in jetstream 31cabin Specifications of the Jetstream31 The specifications of this aircraft are shown in the table below. These specifications will be important in the calculation of the parameters mentioned during the conversion of the Jetstream 31 from being a passenger aircraft to a firefighting aircraft. Table 1: Specifications of Jetstream 31 Description Specification Maximum take-off weight 15,212 lb or 7,059 kg Maximum Landing Weight 14,900 lb or 6,759 kg Maximum Zero Fuel Weight 14,300 lb / 6,486 kg Operating Empty Weight 10,200 lb / 4,626 kg Maximum Payload 4,100 lb / 1,860 kg Maximum Fuel Capacity 3,024 lb / 1,372 kg Engine 2 x Honeywell TPE331-10 Takeoff Rating per Engine 940 shp Diameter 106 in / 2.69 m Overall Length 47 ft 1.5 in / 14.36 m Overall Height 17 ft 8 in / 5.38 m Overall Wingspan 52 ft 0 in / 15.85 m Cabin Length 24 ft 3 in / 7.39 m Cabin Height 5 ft 11.5 in / 1.8 m Cabin Width 6 ft 1 in / 1.85 m Cabin Volume 600 ft3 / 16.99 m3 Typical Baggage Volume 150 ft3 / 4.25 m3 Maximum Cruise Speed 255 kt Maximum Cabin Differential 5.5 psi Maximum Cruise Altitude 25,000 ft Range with 60% Load Factor 856 nm Center of gravity of the firefighting Jetsteam 31 In order that the stability of the converted aircraft is not comprised it is important that its stability is investigated. When the aircraft is suspended in air the magnitudes of tail-heavy and nose-heavy moments must be equal for it to be stable. Consider the figure below, Moments: a) Aircraft empty weight moment Aircraft empty weight (weight of the aircraft excluding crew members, payload and usable fuel) = 9990 pounds or 4531.4 Kg Arm of the aircraft empty weight = 216 inches or 5.4864 meters Moment associated with the aircraft empty weight, Therefore, b) Usable Fuel weight moment. Usable fuel assumed to be carried by the aircraft = 700 kg Arm of the Fuel weight, = 216 inches or 5.4864 meters Moment associated with the Usable Fuel weight, Therefore, c) Crew Weight moment Two crew members and assuming each is 90Kg in weight. Therefore, Weight of crew members = 180 kg Arm of the crew members’ weight (From the figure above), = 140 inches or 3.556 meters Therefore, d) Evaluating stability of the aircraft with fuel tank full but without the retardant tank Weight Moment Position of center of gravity (COG) of the aircraft after removal of seats with crew inside, fuel tank full, but without the retardant tank, From the above diagram the allowed center of gravity of the aircraft should between 5.422 to 5.778 m from the center of gravity datum. Therefore, the aircraft was very stable before addition of retardant tank. e) Retardant Tank Capacity Maximum allowed tank weight = Maximum takeoff weight-Ramp Weight Maximum take-off weight = 7059Kg (From table 1) Therefore, Maximum retardant weight = 1, 648 Kg Capacity of the retardant tank in liters is calculated below in case the retardant to be used is water. Tank capacity in liters, Therefore, But, Density of water = 1000kg/m3 Therefore, But, 1000 liters = 1m3 Therefore capacity of the tank in liters can be calculated as follows; 435.36 gallons It is important to note that if the aircraft is to carry water as the fire retardant, the water must not be more than 435.36 gallons or 1648 liters. The capacity of tank may, however, change if the retardant to be used is not water. However, the weight of the retardant must not exceed to maximum payload allowed. Arm of the tank’s weight is not known, and is assigned x meters from the datum. This value determines the location of tank in the aircraft in order to maintain stability of the aircraft. Position of the retardant tank so as to maintain the COG of the aircraft For stability to be maintained, Therefore, x = arm of the retardant tank. Position of the tank from the plane’s datum Therefore, the center of gravity of the retardant tank must be 6.1825 from the aircraft’s center of gravity datum. Overall center of gravity of aircraft if the aircraft is loaded with fuel and retardant, and is ready to take off Moments Moment due to aircraft empty weight, Moment due to Usage fuel weight, Moment due to crew members, Moment due to the weight of the fire retardant, Retardant weight to be carried by the aircraft, = 1648 kg Arm of the fire retardant weight, = 6.1825 meters Therefore, Total moment, Weights Weight of aircraft empty weight =  Weight of Usage fuel weight = 700Kg Crew members’ weight = 180Kg Weight of the fire retardant = 1648Kg The new center of gravity of the loaded aircraft The allowable center of gravity (COG) range is between 5.422 to 5.778 m from the aircraft’s center of gravity datum. Therefore, placing the retardant tank 6.1825 from the aircraft’s center of gravity datum does not make the aircraft unstable since the overall center of gravity (5.6m) falls within the allowable limits (5.422 to 5.778 m). Evaluation of the take-off weight The total weight of the loaded aircraft if the aircraft is loaded with maximum fire retardant weight is as calculated below Weight of aircraft empty weight =  Weight of Usage fuel weight = 700Kg Crew members’ weight = 180Kg Weight of the fire retardant = 1648Kg Prescribed maximum take-off weight for Jetstream 31 is 7059Kgs (check table 1). Therefore, the take-off weight of the converted aircraft if loaded with maximum retardant weight is within the required limit. Jetstream 31 fuselage modification steps (methods) Aircraft fuselage is amongst the most important sections of an aircraft. It is the main body or structure of an aircraft. This is the structure that gives an aircraft space for cargo, aircraft accessories, personnel, passengers and controls among others. In addition, other important structures that are supported by the fuselage include: wings, landing gear, power plant and stabilizers among others. Since it is the fuselage that provides space for cargo, accessories, crew, passengers and controls, most modifications will be done on it. These modifications include: cutting of gaping door, modification of the plane floor, fixing of hardware for securing the retardant tank in position in order to avoid movement of the retardant tank during flight. The gaping door will be used for the removal of seats and fixing the retardant tank. Conversion of this aircraft into a firefighting aircraft will involve seven main steps. First step is construction of the retardant tank. Based on the calculated tank capacity, the retardant tank is constructed using plastic as the raw material. Plastic is normally light and cheap compared to other materials such as steel and aluminum. The second step can be done concurrently with step one. Based on the dimensions of the tank, the existing door may be widened in order to allow the tank to pass through. Widening the door is preferred to cutting a new opening on the fuselage since the interference of the former with the stability of the fuselage will be minimal. Widening the existing door does not involve cutting the aircrafts framework and stringers, but the fuselage skin that falls within the stringers and frames will be cut. This helps in maintaining the stability of the aircraft fuselage. This will also assist in keeping the cost of modification (cost of converting the jetstream 31 passenger jet to firefighter jet) as low as possible. The third step is to remove the seats. The nineteen (19) passenger seats are removed in order to create space for the retardant tank. After the removal of the seats, the floor frame of the aircraft is stabbed using ball bearings; tie down tracks and rollers in order to easily move the seats. Step four is to drive a van that will be used to transport the removed seats away from the fuselage. The van is aligned alongside the opened gaping door in order to receive the pallets containing the seats in specific groups using two hydraulically operated levels. The pallets containing the removed seats are rolled out of the aircraft into the awaiting van. The fifth step is disconnection of the water quick action coupling and gallery. Electric cables in the cabin are also removed. These equipment (Electric cables, water quick action coupling and gallery among others) are also then loaded into the waiting van. The van is then driven away. Step five is modification of the fuselage. The fuselage of the empty aircraft is then modified to accommodate the retardant tank; these modifications include floor, fixing securing devices, and installing full length cabin liners on the fuselage among others. After the fuselage has been modified, the retardant tank is loaded into a van to be transported to the aircraft. This truck uses the hydraulic lifts and motorized belts to help in the movement of retardant tank pallets into the opened gaping door, and into the ball bearing floor. Finally, the retardant tank pallets are rolled in, and towed into position and secured into place using the fixed securing devices. Cost Evaluation Converting jetstream 31 into a fire fighting aircraft is a project, and should follow “aircraft modification life cycle”. This cycle is divided into five typical steps namely: “feasibility, definition, execution, completion and finally operation. For converting jetstream 31 into a fire fighting aircraft project the steps can be divided into two main categories namely bidding phase (includes: feasibility study and definition) and execution, also known as realization phase (includes: execution and termination steps of the project). The bidding phase of the project which includes feasibility studies and project definition will not account for much money in this project; the cost of this project phase may account to 5 percent of the total project cost. This is due to fact that the main activities being carried out in this phase include defining the scope of project (in this case conversion of jetstream 31 into a fire fighting aircraft) and making bids for the project, which do not cost much. The project phase also involves declaring the winning bidder, and the tender is finally awarded. Project execution phase is the most important phase in this aircraft conversion project and accounts to most of the project costs (about 95 percent of the total). This phase of the project may involve the following: designing, fabrication and installation, and handing over. Designing may involve determination of important parameters of the project (may involve the calculation shown above; determination of shifts of center of gravity, take off weights, retardant tank capacity, and tank location among others). The fabrication and installation phase involves conversion of the design from paper or computer to real modification of the aircraft. Finally, the completion step involves handing over the modified aircraft to the owners. Table 2: Cost breakdown Project phase Task to be carried out Estimated cost Definition and feasibility Planning and Bidding $2000 Execution Design $6500 Fabrication and installation (Labor, raw materials and equipment among others) $20000 Completion Miscellaneous and completion operations $5000 Table 3: Summarized estimated costs Project phase Estimated cost (X 100) Percentange commulative values of percentage Fabrication and installation $200 60% 60% Design $65 19.40% 79.10% Miscellaneous and completion $50 15% 94% Planning and Bidding $20 6% 100% TOTAL $335 100%   Figure 4: Pareto cost evaluation chart Read More