Design of a Low-Cost Easy-to-Fly STOL Ultralight Aircraft in Composite Material

AR Wing aspect ratio. CLmax Maximum Lift coefficient of the aircraft with retracted flaps. CLmaxFF Maximum Lift coefficient of the aircraft with full flaps. CLmaxL Maximum Landing Lift coefficient of the aircraft. CLmaxTO Maximum Take Off Lift coefficient of the aircraft. RC, RCmax Maximum Rate of Climb. S Wing area. SLG, STOG Landing Ground run, Take Off Ground run. t Time. tmin Minimum time of climb to altitude z. V(RCmax) Speed at maximum Rate of Climb. Vmax, Vmin Maximum level speed, minimum level speed. Vs, VsFF Stalling speed flaps up, stalling speed flapsdown. WE Empty Weight. WTO Maximum Take Off Weight. P Power. z Altitude. , 0 Density, density at sea level.


Introduction
The class of Ultralight (ULM) and light aircraft in general has attracted by growing interest through Europe in recent years.Only in Italy in the last 5-6 years, at least 10 companies have started production of ULM aircraft.There is a very active market for this class, used to promote flight at all levels and for sports aircraft The maximum flight speed for ULM aircraft has been increased in recent years through the use of more powerful engines (100 hp instead of 64 or 80) and better aerodynamics.It is not surprising that a maximum level speed of about 280 km/h has been reached.Since the weight constraints are very strict, it is important to study ways to improve structural design, safety, flight qualities, aeroelastic behaviour and systems reliability, without raising costs.. Following the experience acquired in our department in designing light and ultralight aircraft, the design of a new composite ULM is being carried out at DPA.The design goals established for this new design were: 1) Short Take-Off and Landing (STOL) aircraft capable of taking off and landing from an uprepared runway within 40 m; 2) almost complete construction in composite material; 3) foldable wing, in order to make the ULM very easy to use, to put on a trailer and to hangar in a normal size garage; 4) wing with a retractable leading edge slat and slotted/fowler flaps; 5) maximum speed around 190-200 km/h at MTOW of 450 kg; 6) good flight and handling qualities, to be safely flown by inexperienced pilots; 7) low cost.

Market survey
All the analyzed aircraft are ULM (W TO = 450 kg = 4415 N) and equipped with an 80 hp (59.6 kW) engine; most of them are made of aluminium alloy with a high wing configuration, ensuring high stability and easy piloting.None satisfies all the above-mentioned design goals.In fact, the YUMA, the Savannah and the Zenair CH 701 are successful STOL aircraft made of aluminium alloy; however, their de-

Design of a Low-Cost Easy-to-Fly STOL Ultralight Aircraft in Composite Material
D. P. Coiro, A. de Marco, F. Nicolosi, N. Genito, S. Figliolia The paper deals with the design of an aircraft, starting from a market survey, the conceptual design loop and the preliminary choice of dimensions, and leading to the detailed design of efficient high-lift systems and a low-drag fuselage shape.sign is unattractive, and they have a fixed slat on the leading edge, which reduces maximum cruising speed.The Sky Arrow 450T and the REMOS G-3, on the contrary, are high cost "non-STOL" aircraft in composite materials, advanced ULM.They can easily by put onto a trailer, due to their removable or foldable wing.The main characteristics of the analyzed aircraft are shown in Table 1.Their main performance charac-teristics in terms of landing run versus maximum level speed at sea level are shown in Fig. 1.

Design point
The methodology followed during the design process is similar to that reported in [1], but it has been expressly modi-  ( Ip is defined as: In ( 4) P cr and P TO are respectively the power at cruising and take off, kv and kz are the speed and altitude factor (for a four-stroke engine kv = 1 and kz = s 1.22 ), j is the engine admission limit.The data scattering is probably due to limited reliability of the published data, and due to an unbiased difficulty in measuring the data: for example, slight differences in executed manouvres lead to great differences in measured data.
For this STOL aircraft, the main restrictions are maximum speed, take off and landing run, as shown in Fig. 5. Once these limitations have been reported in a graph relating power loading (W/P) TO and wing loading (W/S) TO , the resulting shaded area represents all the possible design point choices.Maximum power loading is fixed ( ( W/P) TO = 74 N/kW), because maximum take off weight (450 kg = 4415 N) and power ( 80 chosen, based on the criteria for keeping the wing area as small as possible (mainly for cost reasons) and using appropriate values of maximum take off and landing lift coefficient ((W/S) TO = 324 N/m 2 , S = 13.6 m 2 , C LmaxTO = 2.45, C LmaxL = 3.12).

Preliminary design
The conceptual loop is shown in Fig. 6 Chosen power loading (W/P) TO The design was accomplished using a code named AEREO [5], which has been developed in recent years at DPA to predict all aerodynamic characteristics in linear and non-linear conditions (high angles of attack) and all flight performances as well as dynamic behavior and flight qualities of propeller driven aircraft.The figures below report some aerodynamic characteristics (Figs.11, 12, 13 and 14) and performance characteristics (Fig. 15) of the aircraft calculated with AEREO code.Table 3 reports the main performances of the aircraft.Further optimization of the global configuration is in progress to improve the wing aero-structural behavior as well as the relative position of the wing and horizontal tail to minimize downwash and induced drag.

Conclusion
The preliminary design of a STOL ULM aircraft and numerical performance prediction has been shown.The aircraft shows acceptable performances that are consistent with the desired design goals.The predicted performances were ob-tained with AEREO code, which confirmed its usefulness as a fast and reliable design tool for propeller-driven aircraft.The parametric design and optimization loops have been highlighted.Detailed design and optimization of the high-lift system and three-dimensional aerodynamic analysis are in progress, while wind tunnel tests (high-lift airfoil, aircraft model) are planned in the near future.Fig. 14: Equilibrium horizontal all-movable tail deflection versus speed (center of gravity position is at 25 % of mean aerodynamic chord)

Fig. 1 :
Fig. 1: Landing ground run versus maximum level speed at sea level

C Lmax C LmaxFF
Technological challenges regarding the design of low-cost systems for flap/slat retraction and a simple wing folding system are highlighted.Aiming at an efficient optimization algorithm, we developed a new integration technique between CAD, aerodynamic and structural numerical calculation.Examples deriving from this new approach are presented.
(1) category: in particular, new statistical relations between take off ground run S TOG and Take Off Parameter for ULM TOP ULM(1), landing ground run S LG and landing stall speed V SL , power index Ip (3) and maximum speed at sea level V max have been calculated, as shown in Figs.2, 3 and 4. TOP ULM is defined as: 0.

Table 2 :
Main dimensions, weights and loadings