Viwanda light aeroplane, kenya.

From my private study, I have categorized a typical project in to the following to ease design and fabrication

 

1 The Power plant( Engines), reduction system and propeller ( some times called the firewall forward components )

2 Landing gear ( wheel system) 

3 Control surfaces ( flaps, ailerons, elevator, rudder etc)

4 Remote control when applicable

5 Basic Instruments

6 Center of gravity Balancing along the wing chord. tail areas/volume  calculation

7 Electrical system

8 instruments

9 The framework/ fuselage

10 Materials.

 

 

  1.ENGINE TYPES AND PROPELLERS

Aircraft engines will almost always be Jet engines for large aircraft, turbo prop engines for medium size aircraft and Piston engines for light aircraft. Jet and turbo prop engines are variants of a general type referred to as gas turbine engines with three main components. 

 

 

 

 

 

Compressor,(axial or radial) Combustor, Turbine( axial or radial). radial is also referred to as centrifugal.

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Jet engines today are mostly fan jets where ahead of the compressor stages is a large fan that provides bypass air at the design bypas ratio. this  is powered by a free turbine.This byass air stream does not go through the combustor and provides a lot of thrust.

 

 

 

 

 

 

 

The compressor is in form of discs alternating from spinning compressor discs and stationery diff-user vane disc. Again the turbines too have a similar design alternating between spinning turbine disc and stationary expansion vane discs.

In turbo props the emerging jet stream powers free turbines which via reducing gear box rotate propellers.

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Since my projects are for very light aircraft the discussion will be restricted to piston engine type such as the rotax  100 hp engine below

 

 

 

 

 

 

 

 

 For light air crafts with a gross of below 600 kgs.Most of engines in this category are manufactured by Rotax bombardier and Continental motors and many others .Some  people use auto conversions too to cut cost. Honda and zuzuki are popular

Piston engines can be direct drive or with reduction drive of either gear or belt types.

Re- drive engines are more efficient since they spin larger propellers at lower speeds.

 

My engine for some time has been the single cylinder  Hirth F33 as  mounted  below .28 hp at 6500 rpm 2.5 ratio reduction drive. drives 60 inch x 28  2 blade prop or  59 x 24 3 blade.

 

 

 

 

 

 

 

 

PROPELLERS are discussed in a separate page.

2. LANDING GEAR

 Are either tricycle or conventional tail wheel type. In tricycle type the plane is level to the ground  in parked attitude. While in tricycle type its inclined. The distinction is the position of the main wheels with respect to the center of gravity. tricycle type have main wheels behind CG. while conventional have main wheels fore of CG.

3 WINGS.

These are dealt with in a different menu page.

 

4 . CONTROL SURFACES

 Comprises of rudder/vertical stabilizer

 Elevator/ horizontal stabilizer

Ailerons, flaps

Rudder controls yaw, Elevator controls pitch up and down,and Ailerons control roll. full flaps down  help in landing approaches. Light flaps down helps in shortening takeoff. Flaps up are used in a cruise. flaps generally affects climb rate negatively.

Control authority is needed at low speeds. This can be affected by center of gravity positioning along the wing chord. too fore positioning means reduced elevator authority or the size of the elevator. rudder authority is also important ad again size matters. too small vertical surfaces will imply sluggish yaw control

Some light aircraft eliminate the need for separate flaps and ailerons and combine them into flaperons.

 

5. REMOTE CONTROL

This comprises of transmitter, receiver and heavy duty linear servos and associated wiring.

 

6 . BASIC INSTRUMENTS

 Altimeter

 Air speed indicator

 Compass

THE PITOTS

 This picks up the static pressure and the pitot pressure. the difference is used by the instruments to measure the airspeed.at the back of the Air speed indicator there are two pipes the P and  S which the two pressures are fed.

 

 

 

 

 

 

      Theory                                           As mounted on typical aircraft               My home made

 

 7 .BALANCING  This is discussed in the WINGS menu page

 

11. THE FUSELAGE

  This need be lightest possible with correct dimensions to seat comfortably. cabin height of 42 inches is comfortable for most peoples height.microlights can be open cockpit without doors and the body need not be covered fully to save weight.

 

12 MATERIALS.

Generally stainless steel hollow tubes are strong easily welded  but are heavy. Aluminum is light and difficult to weld in an informal workshop and is expensive in Kenya. Capability to weld aluminum has been acquired now. For wings one can use aluminum sheets 0.3mm or aircraft fabric. Fabric can be used to cover frames too. Fabric is cloth and deteriorates with heat and moisture.

 

THE TAIL AREA ( EMPENAGE)

This consists of the Vertical stabilizer, the rudder. the horizontal stabilizer and the elevator.Trim tabs could be there for some designs.

 

DESIGN GUIDELINES

The utility of the plane dictates the choice of parameters . e.g wing area, engine propeller, choice of landing gear

a bush plane demands a stronger landing gear and STOL capabilities to clear obstacles. and a propeller pitched for climb.

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WING LOADING.

For small engines( 28-40 hp) with high power loading of 6-7 the planes are slow at around 50 Mph. Very low wing loading is used. 1.6- 2.0  kg per square feet.

The lower the power loading the then a higher wing loading is used. all these can be calculated using the lift equation and assuming a cruise cl of 0.5. for engines with 80-120 hp with power loading of 4 then wing loading as high as 3kg /square feet  can be used.

A  speedy cruiser even when powered with same engine will have smaller wing area less drag and more streamlined. Its propeller also has higher pitch and less diameter.

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For light aircraft of gross weight below 500 kg and seating maximum two people.

 

General simplified design guides for light designs with engines not exceeding 120 Hp .

*What use for the aircraft do you want and whats is the gross weight it should have. whats the desired cruise speed.

*Choose an engine for that.

Work around the power of  the engine in HPs of the power plant you have.

* Choose a wing airfoils shape with known data for the intended use of the aircraft.

*Calculate the Wing area depending on the cruise possible with your engine. A light wing  with an area of 130-160 square feet can work for nearly the range of power from 40-100 hp.

* Choose a propeller with correct pitch and diameter for your cruise at cruise engine RPM and power.

* cruise coefficient of lift is generally around 0.4. use that to calculate your wing area

Lift ={cl x density of air at the location x square of speed x Wing area }/ 2.

For STOL  wings with slats  its safe to assume that cl will be 2.0 at stall and for others cl will be 1.3.  Lift will be gross weight . Density of air is approx 1.2 kg/ m3 depending on altitude and temperature . Working out the speed gives the stall speed. Maintain metric units all through,

 

 A ROUGH GUIDE.

28 Hp can cruise at max 55 MPH at gross of 224 kg   HIRTH, KAWASAKI) single place

40 HP >>> 65 MPH   280 kg   ROTAX, HIRTH, HKS   single place

65 HP>>>>>  75 MPH  400 kg  ( ROTAX, HIRTH, OTHERS )  single place but well designed with a generous wing can take two place . this engined powered the famous piper J 3.

80 HP >>>>>85 MPH   450 kg   (ROTAX, JABILU, OTHERS)  Two place

100 HP>>>> 100 MPH  500 kg    (ROTAX, JABILU, LYCOMING, OTHERS )  Two place

150 HP 200 MPH 1000kg    4 place

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OTHERS.

Some dihedral helps in stability. This includes longitudinal dihedral .

The P factor. This is a tendency of a plane to fly of course due to spinning prop.To counter this the engine is angled slightly off center line 2 degrees.