The First Successful Roadable Aircraft
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The First Successful Roadable Aircraft Imagine a vehicle that can take you Imagine being able to fly to virtually anywhere in the country in thousands of destinations which departure point to destination point in can’t be reached by any airline. times unheard of today. Imagine all this and you will find yourself in the world of the Pegasus, the world’s first modern “roadable aircraft”, a general aviation airplane with all the capabilities of the best four-place, single engine aircraft and with the added utility of having the family car with you at any flight destination. Imagine being able to fly your own plane Imagine being able to avoid high on vacation or business and not having rental costs of airport hangars to worry about being grounded overnight and tiedowns and parking lot fees due to weather or limited to certain for your car while on a flight away airports where rental cars are available. from home. Pegasus, the go anywhere, anytime vehicle that makes flying as unfettered as your imagination. AGATE Design_________________________________________________________Section 1.Executive Summary Section 1. Executive Summary 1.1. Introduction As today’s society becomes more demanding and its members become busier, convenience and reliability becomes more important. The Pegasus can provide both to the businessman as no craft could before. Its multipurpose role as both a plane and a car provide many advantages to its user, such as time and money savings, reliability, and the ability to always get to a destination. These are things that the commercial airlines, trains, buses, or a car alone cannot offer. If the goal of NASA’s Advanced General Aviation Transport Experiments (AGATE) Consortium and the Small Airplane Transportation System (SATS) is to make general aviation a viable alternative to current modes of transport, then they must look beyond the current vehicles being offered by the industry. These vehicles, while being safe, use 40 year old technology, are expensive, and do not offer the allure to young pilots that they once did. Figure 1.1-1 View of the Pegasus in flight 1 AGATE Design_________________________________________________________Section 1.Executive Summary The Pegasus (Figure 1.1-1) has state of the art technology incorporated into the user interfaces and structures. It has a newly designed, efficient, reliable propulsion system. It is designed to be the first successful roadable aircraft in the GA industry, which adds to its appeal to the younger generation who are always seeking something newer, faster, and better. The AGATE Consortium stresses safety, innovativeness, and user-friendliness. It also calls for designs that will help revitalize the general aviation (GA) industry and provide for more usage of this country’s small airports. The Pegasus meets and exceeds all these goals by providing a product that is versatile, yet affordable. It can even be used to fly to small airports where rental cars or taxi services are not available. The purpose of this vehicle is to exceed the performance of other GA craft on the market by providing the added bonus of door-to-door service. This added convenience will come at a small cost to the user. The price will be comparable to buying a small GA craft and a small, practical car. But, unlike buying both, the car is there when you need to get to the airport and when you land at the other end of the trip. The general arrangement drawing is shown in Figure 1.1-2. 2 AGATE Design_________________________________________________________Section 1.Executive Summary Figure 1.1-2 General Arrangement Drawing 3 AGATE Design_________________________________________________________Section 1.Executive Summary 1.2. Performance If the Pegasus is to succeed it must not only be “roadable” but it must be a viable alternative to existing general aviation aircraft by at least meeting their levels of performance. The performance data shown below reveals that the Pegasus is indeed able to match the performance of popular aviation vehicles such as the Cessna 182 and to excel in several categories. More detail on these performance figures and the assumptions behind them can be found in Appendix K. The cruise altitude used for the calculations was 3000 m (9843 ft) with an 80% power setting. Table 1.2-1 The Performance of the Pegasus Normal cruise speed at 3000 meters (9843 ft) 77 m/s 150 kts Maximum cruise speed at 3000 meters (9843 ft) 84 m/s 163 kts Sea Level take off ground distance 210 m 690 ft Sea Level take off with 15 meter (50 ft) obstacle clearance 280 m 920 ft Sea Level landing ground distance 230 m 755 ft Sea Level landing distance with 15 meter (50 ft) obstacle clearance 350 m 1148 ft Sea Level stall speed 28 m/s 55 kts Maximum rate of climb at sea level 445 m/min 1460 ft/min Range at normal cruise at 3000 meters (9843 ft) 1528 km 825 nmi Maximum range at 3000 meters (9843 ft) 1778 km 960 nmi Maximum endurance at 3000 meters (9843 ft) 9.5 hrs 9.5 hrs The power versus velocity curves for the Pegasus are shown below as Figures 1.2-1 and 1.2-2. It is seen from the above table and figures that the Pegasus is very competitive with existing GA aircraft and that there is no serious performance penalty associated with the vehicle’s ability to convert to an automobile for ground use. The on the road performance of the Pegasus is discussed in a later section of this summary report and in detail in Appendix M. 4 AGATE Design_________________________________________________________Section 1.Executive Summary 400000 350000 300000 250000 200000 Preq Pav, 100% Power (Watts) 150000 Pav, 80% 100000 50000 0 0 20 40 60 80 100 120 Velocity (m/s) Figure 1.2-1 Power vs. Velocity Curve for Sea Level 500000 450000 400000 350000 300000 250000 Preq Pav, 100% Power (Watts) 200000 Pav, 80% 150000 100000 50000 0 0 20 40 60 80 100 120 Velocity (m/s) Figure 1.2-2 Power vs. Velocity Curve for 3000 meters 5 AGATE Design_________________________________________________________Section 1.Executive Summary 1.3. Aerodynamics The design of a roadable aircraft presented some unique aerodynamic problems. The lifting surfaces had to be large enough to produce the required lift in the air yet small enough for safe driving on the road. The wing also had to be folded, retracted, or otherwise stored for road use. To find a solution to these issues, aerodynamic configurations not often used in the general aviation industry were examined. The solution included using extending wings. The design uses a low aspect ratio “inboard” wing with telescoping “outboard” wings. Several other uncommon features for increasing lift without increasing wing span were investigated including a Burnelli lifting body, a channel wing, and winglets. The final design used a combination of all these features. Figure 1.3-1 shows a top view of the Pegasus, displaying the lifting surfaces. 6 AGATE Design_________________________________________________________Section 1.Executive Summary Figure 1.3-1 The Top View of the Pegasus (dimensions in meters) Based on the performance parameters established for the design, the wing sizes and airfoil section were selected. To meet department of transportation (DOT) and European Community (EC) road requirements, the maximum span of the inboard wing was chosen to be 2.28 m (7.48 ft). A chord of 2.5 meters (8.202 ft) was selected for this inner wing, resulting in an area of 5.7 m2 (61.35 ft2). The telescoping wings each had a semi span of 3 meters (9.84 ft) with a chord of 1.75 m (5.74 ft). These sections total 10.5 m2 (113.02 ft2) in area, giving a total wing area of 16.2 m2 (174.4 ft2). The required size for the horizontal tail was 1.63 m2 (17.55 ft2), with a moment arm of 4 m (13.12 ft). The airfoil section selected for both the inboard and outboard sections is the NASA GA(W)-1 otherwise designated as NASA LS(1)-0417. Figure 1.3-2 shows the airfoil and figure 1.3-3 shows the lift curve slope for this airfoil. This is a 17% thick airfoil with a design lift 7 AGATE Design_________________________________________________________Section 1.Executive Summary coefficient of 0.4, and was designed for general aviation applications. This airfoil was selected for its smooth stall characteristics, a high stall incidence angle, and its high lift to drag ratio. Its large thickness was also useful in allowing retraction of the outboard wings into the inboard section. The maximum lift coefficient for the two dimensional airfoil section is approximately 2.0 with zero lift at –4 degrees angle of attack and a lift curve slope of 5.9. For the actual three dimensional airfoil, the maximum lift coefficient is about 1.8 with a lift curve slope of 4.9. The drag coefficient at zero drag for the Pegasus is 0.025, which compares well to today’s general aviation craft. 0.15 0.1 0.05 0 -0.05 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -0.1 Figure 1.3-2 The GA(W)-1 Airfoil Shape 2.5 2 1.5 1 Cl 0.5 0 -10 0 10 20 30 -0.5 -1 Angle of attack, degrees Figure 1.3-3 2-D Cl vs alpha for the GA(W)-1 8 AGATE Design_________________________________________________________Section 1.Executive Summary At a cruise speed of 77 m/s (150 kts), the aircraft’s ideal angle of attack is 0.06 degrees. Therefore, the inboard wing was mounted on the fuselage at 0.06 degrees so that the fuselage would remain level in cruise at altitude.