SD-27 in landing.

1.         Introduction

The SD 27 is a monoplane, middle-low wing, two seats, fixed landing gear training aeroplane. It is specifically for the needs of the civil primary training schools, surveillance operations and of the general aviation pilot. It has low acquisition and operation costs.

These are the main characteristics of the SD 27:

 •       a cabin that can accommodate 2 big adults in a comfortable side-by-side layout;

 •       allow the installation of electronic equipment and avionics suited for the goals;

 •       follows the requirements for certification under JAR-VLA (Joint Aviation Requirements - Very Light Aeroplane) as far as structural strength and flight qualities are concerned as well as the equipments;

      •       an accurate aerodynamic study to obtain good performance;

 •       to allow performing all the instructional maneuvers including spin.

The aircraft is designed and tested for loads factor of + 4,4 and - 1,76.

Three view-drawing

2.         Data

2.1.      Dimensions

•       Wing span                  10 m.

•       Length                        7,1 m.

•       Height                        3 m.

•       Wing chord                1,25 m.

•       Wing area                  12,5 m².

2.2.    Landing gear

•       tricycle

•       Shock absorber nose gear: leaf spring,

                     main gear: leaf spring.

•       Main wheels               500 - 5,  2,2 atm.

•       Nose wheel                400 - 5, 1,8 atm.

2.3.    Power plant

•       Engine                        ROTAX 912 A, 80 hp.

•       Fuel                           Gasoline, Avgas 100 LL.

•       Oil                             Synthetic oil for car, not aeronautical oil.

2.4     Propeller

•       Type                                      MTV-1-A/170-08, electrical  variable pitch

•       Diameter                                1,70 m

•       Propeller governor                  MT Propeller s/n P-210-A/2500.

 2.5.    Fuel tank

         •       Tank capacity                         80 liters.

         •       Utilisable                                78 liters.

•       Not utilisable                            2 liters.

 2.6.    Weights

         •       Empty weight                         420 kg

•       Maximum take off weight        620 kg

2.7.      Performance 

•       Max level speed                     105 kts

•       Cruise speed                          95 kts

•       Stall speed (flap up)                50 kts

•       Stall speed (flip down)            43 kts

•       Rate of climb (sea-level)         900 ft/min

3.         Structure

Most components of the Sivel SD 27, as you can see in fig. 1, are made in aluminium, except some parts that are made in composite. The framework is in welded steel tube recovered by composite.

Fig. 1

3.1.      Fuselage

 The engine is accommodated in the front fuselage, mounted on a cantilevered welded tubular steel frame. Access is provided by removable top and bottom cowlings.

The fuselage can be divided in other two different sections:

1.    The first section starts from the firewall to the fuel tank included. This section is the framework and, as we said before, it is made in welded steel tube. Here we have the cockpit. It is a generous size one, with very good visibility and a low noise level. There are one stick and a couple of rudder pedals for each occupant. The control brakes are mounted on the rudder pedals. The two seats are mounted side by side; the fuel tank is just behind them. Over the fuel tank there is the baggage compartment.

2.    The second section, the tail, starts from the framework, not included, to the end of the aeroplane. It is composed by 5 ribs, 4 spars made in aluminium. It is covered by aluminium. Inside there are the pulleys and the cables to control the rudder and the elevator; there are also the cables for the antenna, the anticollision beacon and the white navigation light. At the end of the tail there are the horizontal and vertical surfaces.

3.2       Wing

The SD 27 has a middle-low, rectangular wing. It is made by two half-wings. These are connected with the framework by three attachments, one for each spar: one main spar and two secondary spars. The half-wing is also composed by one aileron and one flap.

3.2.1.   Half-Wing

It is composed by one main spar, one secondary  front spar, one secondary rear spar and ten pressed ribs. It is recovered by aluminium. On the rear spar there are the attachments for the aileron and the flap. At the end of each half-wing there is one navigation light mounted in the composite wig-tip. All these parts are united by rivets.

3.2.2.   Flap

It is composed by one spar and nine ribs in aluminium. On the spar there are the attachments for the half-wing. It is recovered by aluminium and all the parts are united by rivets.

3.2.3.   Aileron

It is made by one spar and seven ribs in aluminium. On the spar are positioned the attachments for the half-wing. At the end of the aileron there is one counterweight. The aileron is recovered by aluminium and all the parts are united by rivets.

3.3.      Empennage

The empennage has a conventional design with one fin, one rudder, one stabiliser and one elevator. 

3.4.      Stabiliser

         It is formed by two spars and eight ribs in aluminium. On the rear spar there are three attachments for the  elevator. It is recovered by aluminium and all the parts are united by rivets.

 3.5.      Elevator

 It is composed by one spar and ten ribs in aluminium. On the spar there are the three attachments for the stabiliser. At the end of the elevator there are two tip made in composite. The elevator is recovered by aluminium and all the parts are united by rivets. 

3.5.1.   Trim 

It is positioned in the central zone of the elevator trailing edge. It is composed by one spar and six ribs in aluminium. At the end of the trim there are two counterweights. On the spar there are the three attachments for the elevator. The trim is recovered by aluminium and all the parts are united by rivets.

 3.6.      Fin

 It is composed by two spars and four ribs in aluminium. At the end of the two spars there are four attachments for the tail cone. On the rear spar there are also mounted the attachments for the rudder. There is a composite part on the top of the fin when there is the anticollision beacon. It is recovered by aluminium and all the parts are united by rivets.

 3.7.      Rudder 

It is composed by one spar and four ribs (on the higher one there is a counterweight) in aluminium. On the higher part of the spar there are the attachments for the fin; instead on the lower part there is the torque tube to control the rudder. It is recovered by aluminium and all the parts are united by rivets.

 3.8.      Landing gear

 It is a tricycle one formed by the nose landing gear and the main landing gear is just under the wing. The first one is connected with the firewall, instead the second is connected with the framework by attachments.

The brakes are on the two wheels of the main landing gear.

 4.        System

 4.1.      Electrical system

 It is composed by a generator that provides a direct current (DC) at 14 V and 18,5 A; and by a battery 12 V, 18,5 A. The aeroplane has also an external power supply system to start the engine. Every electrical circuit has a breaker to protect the avionics and all the system.

There is one main bus that energises the engine instrument, the auxiliary fuel pump, the propeller governor, and the turn and bank indicator.

Then there is an avionic bus which energises all the avionics.

There is also a secondary bus that energises the anticollision beacon and the navigation lights. 

4.2.      Flight controls

 All the control surfaces are controlled by stick and rudder pedals.

The elevator and the rudder are actuated by cables. The flaps are moved by push-pull rods. Instead the ailerons are driven by push-pull rods in the fuselage, and by cables in the wing.

Between the two seats there is the flap lever with the take-off and landing position marked. In this position there is also the trim tab to control the aeroplane around its pitch axis.

4.3.      fuel system

          This system is composed by an aluminium fuel tank (capacity 80 liters), a filter with its drain valve, a shut-off valve (for emergency situations) located inside the cabin, an electrical auxiliary fuel pump, a mechanical fuel pump mounted on the engine, one televel and a low fuel pressure light on the instrument panel.

4.4.    Instrument panel

          The SD 27 instrument panel is quite big, so a lot of instruments and avionics can be installed on.

          The engine instruments are mounted on the left: RPM indicator; cylinder head, oil and coolant fluid temperature indicator, oil pressure and MAP indicator; one televel, one voltmeter and one loadmeter. In the center there are radio and avionics equipment: one COM and NAV, VOR/ILS and transponder. On the right there are the flight instruments: airspeed indicator, a barometric altimeter, a vertical speed indicator, a artificial horizon, a directional gyro, a turn and bank indicator and a suction gauge. The compass is on the top of the panel, in central position (see figure n.2). On the right there is also the propeller control panel.

Fig. 2

4.5.    Engine

The SD 27 is equipped by a four cylinders in horizontal opposite position (boxer), four-stroke engine made by Rotax. It has two carburettors and a mixed air/water cool system: air for the cylinder and water for the cylinder heads.

          It has double ignition system without magnetos and has also an electric starter system.

          The propeller reduction gear, the fuel and vacuum pump and the generator are installed on the engine.

4.5.1.Engine data

4.6.    Propeller

          The SD 27 is equipped with two blades, variable pitch propeller made by MT-Propeller (Germany). An electrical system controls the pitch propeller, and the control is installed on the instrument panel, on the right.          

          The propeller can be used in manual or automatic position. So the pilot, using the first mode, can select the propeller pitch.

5.       Performance

5.1.    Take-off and landing distance

5.2.      Climb Performance

5.3.      Cruise speed

Conditions:

- Weight 620 kg

- No wind

- Altitude: 1500 ft

Conditions:

- Weight 620 kg

- No wind

- Altitude: 5000 ft

Conditions:

- Weight: 620 kg

- No wind

- Altitude: 10000 ft