Optimum Structural Design of Light Float for Small Seaplane

Takeshi KAGAWA and Katsumi HIRAOKA School of Engineering, Tokai University, Hiratsuka, Kanagawa, 259-1292, Japan

Ryoji ORIHARA IVIS Engineering Solutions,Inc., Bunkyo, Tokyo, 113-0033, Japan

Keiichi ITO Hiyoh Aircraft Manufacturing and Development, Shinagawa, Tokyo, 142-0041, Japan

and

Yuuji AOKI Flying Boat Development Cooperative Association, Japan

Using the structural analysis software NASTRAN and the structural optimization software HyperSizer, optimum structural design of the float for an ultra-light seaplane is carried out. Since the mass of an ultra-light seaplane is less than 225kg, it is needed to reduce the mass of the float. Length of the model float is 4m, and the support positions to seaplane are 1.2m and 2.2m or 1.2m 1.7m and 2.7m from bow of the float. Our goal is to reduce the mass of the float with support bars to less than 14kg by changing the materials, thickness of the plates, and the internal structure. Optimum structure of the float was designed from viewpoints of the mass and the margin of safety. Pressure distributions that were calculated by experimentally obtained equations at landing on the surface of the water were used for the structural design. In the present study, the materials, thickness of the plates, and the internal structure of the float are widely investigated and the method of the optimum structure of the float for an ultra-light seaplane is explained.

I. Introduction he airplane has promoted long range since it flew at the first time. Promotion of long range needs to improve performance of aerodynamics from the external structure. Also it needs to be lower mileage and mass of

airplane by changing materials and inner structure. Since oil price is so high in these days, lowering mileage is required more than before.

Until now, optimum structural design has been carried out by experience. But we can accomplish it now easier than before by using NASTRAN and HyperSizer. HyperSizer chooses a material and the structure from a lot of the pattern by calculation. It is very quick and efficient. We design light float for small seaplane applying these software from viewpoints of the mass and the margin of safety. Our goal is to reduce the mass of the float with support bars less than 14kg by changing the materials, thickness of the plates, and the internal structure.

II. Ultra light seaplane Although license is not required to fly ultra light seaplane, there are some regulations as follows: 1. Body mass for single seat; less than 180kg, 2. Body mass for double seats; less than 225kg, 3. Area of wing; more than 10m2, 4. Velocity of the stall; less than 65km/h, 5. Maximum velocity of leveling flight; less than 185km/h, 6. Thrust device; propeller, 7. Landing gear; wheel, sled, float etc., 8. Capacity of fuel; less than 30litters, 9. Required equipment; airspeed indicator and altitude indicator.

T

48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference<br> 15th23 - 26 April 2007, Honolulu, Hawaii

AIAA 2007-2294

Copyright © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

We choose the following ultra light plane in order to design optimum structure of the float.

[Mass of plane] 1. Body 225kg 2. Crews (2) 154kg 3. Cargoes 20kg 4. Fuel (30 litters) 21kg

Total 420kg [Design Velocity] 1. Stall velocity 65km/h 2. Max.velocity 185km/h

Fig.1 Ultra light seaplane.

III. Model of the float As a float model, we use the following specifications: [SPECIFICATIONS OF SINGLE FLOAT] 1. Length 4.0m 2. Max. Width 0.45m 3. Max. Height 0.58m 4. Displacing volume 520litters [SUPPORT POSITION] 1. In case of two positions: 1.2m and 2.2m from bow of the float. 2. In case of three positions: 1.2m, 1.7m and 2.7m from bow of the float.

[LOAD CONDITION] Approximate pressure values of three parts of float at simulated watering moment. 1. Front (1.2m from bow); 39200Pa 2. Middle (from 1.2m to 2.2m); 43120Pa 3. Rear (from 2.2m to 4.0m); 39200Pa [MATERIALS] 1. A12024 2. Rohacell 110Wf (110.72 kg/m³) foam materials 3. Rohacell IG 711G (7.0584 kg/m³) foam materials

Fig.2 Model of the float.

IV. Summary of design and procedures

Fig.3 How to connect NASTRAN and HyperSizer.

HyperSizer

Selection of optimum structure of float element

NASTRAN

Calculation of float deformations and stress of each element

Deformations and stress of each element Repeating of calculation until convergence of mass

Optimum thickness; 2mm

Optimum thickness; 5mm

V. Result and comment V-1 Result The structural optimization results are as follows: In case of two support positions 1. Case of 9 components Mass 5.72kg

Max. margin of safety 2.756 Number of plate thickness 9

2. Case of 14 components Mass 5.18kg

Max. margin of safety 2.889 Number of plate thickness 10

3. Case of 17 components Mass 5.03kg

Max. margin of safety 2.889 Number of plate thickness 11

4. Case of 33 components Mass 4.23kg

Max. margin of safety 0.9135 Number of plate thickness 9

In case of three support positions 1. Case of 9 components Mass 5.13kg

Max. margin of safety 16.93 Number of plate thickness 14

2. Case of 14 components Mass 4.04kg

Max. margin of safety 4.110 Number of plate thickness 9

3. Case of 17 components Mass 3.99kg

Max. margin of safety 3.221 Number of plate thickness 7

4. Case of 33 components Mass 3.47kg

Max. margin of safety 2.120 Number of plate thickness 9

V-2 Comment

Fig.4 Panel structure of small components.

Fig.5 Panel structure of large components.

As shown in Fig.4, in case of small components, optimum thickness of left plate is designed to be 5mm and that of right plate is 2mm. On the other hand, as shown in Fig. 5, in case of large component, thickness of right plate is designed to be equal to that of left plate 5mm. Setting component smaller leads to optimum strength structure of

Optimum thickness; 5mm

Perfect binding Pressure(strong) Pressure(weak)

Although 2mm plate thickness is enough, HyperSizer designs 5mm plate.

Pressure(strong)

Pressure(weak) Perfect binding

each part. On the other hand, setting component larger comes to structure with unnecessary strength. Hence, we can see how mass depends on number of component. Following figures show relation between mass and number of components.

Fig.6 2 support position

3.03.54.04.55.05.56.0

Mas

s[kg

]

Number of component9 １４ 17 33

4.23 kg

5.03 kg5.18 kg

5.72 kg

Fig.7 3 support position

3.03.54.04.55.05.56.0

Number of componentM

ass[

kg]

339 14 17

3.47 kg

3.99 kg4.04 kg

5.13 kg

Fig.8 In case of 14 components

3.03.54.04.55.05.56.0

Number of support position

Mas

s[kg

]

4.04[kg]

5.18[kg]

2 3

We can understand that more number of components leads to less mass. In the range of component numbers 9 to14, each component decreases mass by 0.108kg, and in the range 14 to 17 it decreases 0.05kg, and in the range of 17 to 33, it also decreases mass by 0.05kg. It is clear that increase of components is most effective in the range 9 to14. It is same in case of three support positions. Concerning easiness and cost of building plane, it is not always acceptable to increase number of components. Increase number of component means increase of number of parts and joints. We, hence, come to conclusion that in this case the number of component 14 is most desirable. With regard to number of support positions, Fig. 8 shows that increase of support positions 2from 3 decreases mass by 1.14 kg. Increase of support positions certainly leads to increase of supporting bars at least by 3 and building cost. To appeal benefit of ultra light plane “Easy flight without license”, it is essential to lower sales price as much as possible. We come to conclusion that the float of 2 support positions and 14 components is the most desirable for this ultra-light plane.