Item by item discussion of analysis
Item 3: Initial weight estimates are made using statistically derived equations which have are based on collected data from similar vehicles already in existence. “All The World’s Aircraft,” by William Jane, is the predominant reference for this type of data and was used for this task. We also searched manufacturers’ specifications listed on the internet and reviewed 30 years of Sport Aviation magazine’s pilot reports on 2 and 4-seat amphibians. We also made detailed measurements on a local Grumman Albatross which was available to us. The end result was an estimate of gross weight equal to 3554 pounds. This is similar to the Sea Wind, which was adopted as the main competitor and the comparison benchmark.
Data on different amphibian/sea plane designs was collected to form an initial weight estimate curve fit equation.
The following table of Amphibian Weights lists the selected amphibians and their corresponding characteristics.
Amphibian Weights
The spreadsheet below shows the details of the weight calculation. The payload was chosen as four occupants weighing an average of 165 pounds each, with 100 pounds of baggage. The often used FAA suggestion of 170 pounds per person is easily entered as an alternate value. Fuel weight estimation uses the Breguet range equation and is additionally based on the following mission profile:
Warm up & takeoff -> Climb -> Cruise (1215 nm) -> Loiter 20min -> Land. Empty weight is estimated from the statistical data in the table above, which is plotted below in Figure 1 and then has an equation generated from curve fitting the plotted trend. The variables A and C in
Table 1 are the mathematical representation of the curve shown on
Figure 1, which illustrates the trend in empty weight fraction (empty weight/gross weight) versus gross weight. Again, the end result was a calculated gross weight equal to 3554 pounds, shown in the shaded area at the bottom of Table 1. Functional versions of all Excel spreadsheets will be emailed to the sponsor if the sponsor so desires.
Table 1: "Conceptual Weight Sizing"
Figure 1
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