Tagged: RTF Airplane

Aerodynamics

  • IntroductionAerodynamics is the study of forces and motion of objects through the air.

     

    Basic knowledge of theaero1
    aerodynamic principles
    is highly recommended
    before getting involved
    in building and/or flying
    model aircraft.
    • A model aircraft that is hanging still in air during strong winds may be subject
      to the same aerodynamic forces as a model aircraft that is flying fast during
      calm weather.
      The aerodynamic forces depend much on the air density.

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  • For example, if a glider glides 25 meters
    from a given altitude during low air density
    it may glide 40 meters during high density.


    The air density depends on the atmospheric pressure and on the air temperature.
    The air density increases with decreasing of the air temperature and/or with
    increasing of the atmospheric pressure.
    The air density decreases with increasing of the air temperature and/or with
    decreasing of the atmospheric pressure.
    A flying aircraft is subject to a pressure depending on the airspeed and the
    air density.
    This pressure increases exponentially with increasing of the airspeed.
    The aircraft’s resistance to the airflow (drag) depends on the shape of the
    fuselage and flying surfaces.
    An aircraft that is intended to fly fast has a thinner and different wing profile
    than one that is intended to fly slower.
    That’s why many aircraft change their wings’ profiles on landing approach
    by lowering the flaps located at the wings’ trailing edge and the slats at the
    leading edge in order to keep enough lifting force during the much lower
    landing speed.

    The wings’ profile of an aircraft is usually asymmetric, which makes the
    pressure on the wings’ upper side lower than the underside, causing the air on
    the wings upper side to accelerate downwards, thereby a lift force is created.

    The air always flows away from areas of higher pressure toward areas of lower
    pressure, thus the air over the wing top accelerates as it enters the lower
    pressure region (where the air curves toward the wing), whereas the air under
    the wing slows down as it enters the higher pressure region.
    So, one may also say that the wings create lift by reacting against the air flow,
    driving it downwards, producing downwash.
    The top of the wing is often the major lift contributor, usually producing twice as
    much lift as the bottom of the wing.

    The lift force of a symmetric profile is based on the airspeed and on a positive
    angle of attack to the airflow, which makes the air react as it was asymmetric.

    The following picture shows the airflow through two wing profiles.

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  • The uppermost profile has a lower angle of attack than the lowest one.
    When the air flows evenly through the surface is called a laminar flow.
    A too high angle of attack causes turbulence on the upper surface, which
    dramatically increases the air resistance (drag), this may cause the flow
    to separate from the upper surface resulting in an abrut reduction in lift,
    known as stall.Summarising:
    The aircraft generates lift by moving through the air.
    The wings have airfoil shaped profiles that create a pressure difference
    between upper and lower wing surfaces, with a high pressure region
    underneath and a low pressure region on top.
    The lift produced will be proportional to the size of the wings, the square
    of airspeed, the density of the surrounding air and the wing’s angle of
    attack to on-coming flow before reaching the stall angle.

    How does a glider generate the velocity needed for flight?
    The simple answer is that a glider trades altitude for velocity.
    It trades the potential energy difference from a higher altitude to a lower
    altitude to produce kinetic energy, which means velocity.
    Gliders are always descending relative to the air in which they are flying.

    How do gliders stay aloft for hours if they constantly descend?
    The gliders are designed to descend very slowly.
    If the pilot can locate a pocket of air that is rising faster than the
    glider is descending, the glider can actually gain altitude, increasing
    its potential energy.

    Pockets of rising air are called updrafts.
    Updrafts are found when the wind blowing at a hill or mountain rises to
    climb over it. (However, there may be a downdraft on the other side!)
    Updrafts can also be found over dark land masses that absorb more
    heat from the sun than light land masses.
    The heat from the ground heats the surrounding air, which causes the
    air to rise. The rising pockets of hot air are called thermals.

    Large gliding birds, such as owls and hawks, are often seen circling
    inside a thermal to gain altitude without flapping their wings.
    Gliders can do exactly the same thing.

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  • Wing Geometry Definitions
    A vertical cut through the wing parallel to flight’s direction (plan view) will show
    the cross-section of the wing.
    This side view (profile) is called Airfoil, and it has some geometry definitions
    of its own as shown on the picture below.

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      The longest straight line that can be drawn from the Airfoil’s leading edge to
      trailing edge is called the

Chord Line

      .
      The Chord Line cuts the airfoil into an upper surface and a lower surface.
      If we plot the points that lie halfway between the upper and lower surfaces,
      we obtain a curve called the

Mean Camber Line

      .
      For a symmetric airfoil (upper surface the same shape as the lower surface)
      the Mean Camber Line will fall on top of the Chord Line.
      But for an asymmetric airfoil, these are two separate lines. The maximum
      distance between these two lines is called the

Camber

      , which is a measure
      of the curvature of the airfoil (high camber means high curvature).
      Asymmetric airfoils are also known as cambered airfoils.
      The maximum distance between the upper and lower surfaces is called the

Thickness

      .
    Both Thickness and Camber are expressed as a percentage of Chord.

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      Airfoils can come with all kinds of combinations of camber and thickness
      distributions. They are designed for the condictions under which the plane is
      likely to be flown most of the time.
      NACA (the precursor of NASA) established a method of designating classes
      of airfoils and then wind tunnel tested the airfoils in order to provide
      lift coefficients and drag coefficients for designers.

Aspect Ratio

      is a measure of how long and slender a wing is from tip to tip.
      The Aspect Ratio of a wing is defined to be the square of the span divided
      by the wing area and is given the symbol

AR

      .
      The formula is simplified for a rectangular wing, as being the ratio of the span
    to the chord length as shown on the figure below.

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      Wing

Dihedral

      refers to the angle of wing panels as seen in the aircraft’s
      front view.
      Dihedral is added to the wings for roll stability; a wing with some Dihedral
      will naturally return to its original position if it is subject to a briefly slight
      roll displacement.
      Most large airliner wings are designed with Dihedral.
      On the contrary the highly maneuverable fighter planes have no Dihedral.
      In fact, some fighter aircraft have the wing tips lower than the roots, giving
      the aircraft a high roll rate.
    A negative Dihedral angle is called Anhedral.

  • Forces in FlightGravity, Lift, Thrust and Drag.

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  • Gravity is a force that is always directed toward the centre of the earth.
    The magnitude of the force depends on the mass of all the aircraft parts.
    The gravity is also called weight and is distributed throughout the aircraft.
    But we can think of it as collected and acting through a single point called
    the centre of gravity.
    In flight, the aircraft rotates about its centre of gravity, but the direction of the
    weight force always remains toward the centre of the earth.Lift is the force generated in order to overcome the weight, which makes the
    aircraft fly.
    This force is obtained by the motion of the aircraft through the air.

    Factors that affect lift:

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  • Lift force is therefore dependent on the density of the air r, the airspeed V,
    the type of airfoil and on the wing’s area according to the formula below:Lift Force = 0.5 * r * V2 * Wing’s Lift Coefficient * Wing Area

    Where the Lift Force is in Newton, Wing Area in m2 and the airspeed in m/s.
    The standard density of the air is 1.225kg/m3.

    The wing’s lift coefficient is a dimensionless number that depends on the airfoil
    type, the wings aspect ratio (AR), Reynolds Number and is proportional to the
    angle of attack (AoA) before reaching the stall angle.

    Thrust is the force generated by some kind of propulsion system.
    The magnitude of the thrust depends on many factors associated with the
    propulsion system used:

    – type of engine
    – number of engines
    – throttle setting
    – speed

    The direction of the force depends on how the engines are attached to
    the aircraft.

    The glider, however, has no engine to generate thrust. It uses the potential
    energy difference from a higher altitude to a lower altitude to produce kinetic
    energy, which means velocity.
    Gliders are always descending relative to the air in which they are flying.

    Drag is the aerodynamic force that opposes an aircraft’s motion through the air.

    Drag is generated by every part of the aircraft (even the engines).

    There are several sources of drag:

    One of them is the skin friction between the molecules of the air and the
    surface of the aircraft.
    The skin friction causes the air near the wing’s surface to slow down.
    This slowed down layer of air is called the boundary layer.
    The boundary layer builds up thicker when moving from the front of the airfoil
    toward the wing trailing edge.
    Another factor is called the Reynolds effect, which means that the slower we
    fly, the thicker the boundary layer becomes.

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  • Form drag is another source of drag.
    This one depends on the shape of the aircraft.
    As the air flows around the surfaces, the local airspeed and pressure changes.
    The component of the aerodynamic force on the wing that is opposed
    to the motion is the wing’s drag, while the component perpendicular to the
    motion is the wing’s lift.Induced drag is a sort of drag caused by the wing’s generation of lift.
    One cause of this drag is the flow near the wing tips being distorted as a result
    of the pressure difference between the top and the bottom of the wing, which in
    turn results in swirling vortices being formed at the wing tips.
    The induced drag is an indication of the amount of energy lost to the tip vortices.
    The swirling vortices cause downwash near the wing tips, which reduces the
    overall lift coefficient of the wing.

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  • The picture below shows the downwash caused by an aircraft.

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  • The Cessna Citation has just flown through a cloud.
    The downwash from the wing has pushed a trough into the cloud deck.
    The swirling flow from the tip vortices is also evident.The wing geometry (aspect ratio AR) also affects the amount of induced drag:
    Long wing with a small chord (high AR) has low induced drag, whereas a short
    wing with a large chord (low AR) has high-induced drag.
    For the same chord, the wing with a high AR has higher lift coefficient, but stalls
    at lower angle of attack (AoA) than the wing with a low AR.
    Also, aircraft with high AR wings are more sensitive to elevator control.

    The induced drag increases with increasing of the wing’s actual lift coefficient
    being generated and it’s proportional to the square of the angle of attack.
    And since a slower airspeed requires a higher angle of attack (AoA) to produce
    the same lift, the slower the airspeed is, the greater the induced drag will be.
    So, the induced drag is also inversely proportional to the square of the airspeed.

    In order to minimise tip vortices some designers design a special shape for
    the wing tips.
    With drooped or raised wing tips, the vortex is forced further out.

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  • However, this method will cause an increase in weight since they need to be
    added to the wing tip.An easier and lighter method is by cutting the wing tip at 45-degrees.
    With a small radius at the bottom and a relatively sharp top corner, the air from
    the secondary flow travels around the rounded bottom but can’t go around the
    sharp top corner and is pushed outward.

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  • There’s also the Interference drag, which is generated by the mixing of
    streamlines between one or more components, it accounts for 5 to 10%
    of the drag on an airplane.
    It can be reduced by proper fairing and filleting which allows the streamlines
    to meet gradually rather than abruptly.All drag that is not associated with the production of lift is defined as
    Parasitic drag.

    The graph below shows the induced and the parasitic drag versus airspeed.
    Total drag is the induced drag plus the parasitic drag.

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  • Since during constant speed and level flight the thrust is equal to the total drag
    the graph also shows how much thrust is needed at different level flight speeds.At take-off (just above the stall speed), a high AoA is needed to get enough lift
    which increases the total drag and also the thrust needed.
    As the speed increases, the AoA needed to get the same lift decreases and so
    does the total drag until the minimum drag speed is reached, above which the
    total drag starts increasing exponentially (and so does the thrust needed).
    The plane’s max level speed will be limited by the prop’s pitch speed or by the
    max thrust available, which altogether means by the max power available.

 

  • Stability ConceptsThe aircraft’s response to momentary disturbance is associated with its
    inherent degree of stability built in by the designer, in each of the three axes,
    and occurring without any reaction from the pilot.

    There is another condition affecting flight, which is the aircraft’s state of trim
    or equilibrium (where the net sum of all forces equals zero).
    Some aircraft can be trimmed by the pilot to fly ‘hands off’ for straight and
    level flight, for climb or for descent.

    Free flight models generally have to rely on the state of trim built in by the
    designer and adjusted by the rigger, while the remote controlled models have
    some form of trim devices which are adjustable during the flight.

    An aircraft’s stability is expressed in relation to each axis:
    lateral stability (stability in roll), directional stability (stability in yaw)
    and longitudinal stability (stability in pitch).
    Lateral and directional stabilities are inter-dependent.

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  • Stability may be defined as follows:
    – Positive stability: tends to return to original condition after a disturbance.
    – Negative stability: tends to increase the disturbance.
    – Neutral stability: remains at the new condition.
    Static stability: refers to the aircraft’s initial response to a disturbance.
    A statically unstable aircraft will uniformly depart from a condition of equilibrium.

    Dynamic stability: refers to the aircraft’s ability to damp out oscillations, which
    depends on how fast or how slow it responds to a disturbance.
    A dynamically unstable aircraft will (after a disturbance) start oscillating with
    increasing amplitude.
    A dynamically neutrally stable aircraft will continue oscillating after a disturbance
    but the amplitude of the oscillations will not change.

    So, a statically stable aircraft may be dynamically unstable.
    Dynamic instability may be prevented by an even distribution of weight inside the
    fuselage, avoiding too much weight concentration at the extremities or at the CG.
    Also, control surfaces’ max throws may affect the flight stability, since a too much
    control throw may cause instability, e.g. Pilot Induced Oscillations (PIO).

    Static stability is proportional to the stabiliser area and the tail moment.
    You get double static stability if you double the tail area or double the tail moment.
    Dynamic stability is also proportional to the stabiliser area but increases with the
    square of the tail moment, which means that you get four times the dynamic stability
    if you double the tail arm length.

    However, making the tail arm longer or encreasing the stabiliser area will move
    the mass of the aircraft towards the rear, which may also mean the need to make
    the nose longer in order to minimize the weight required to balance the aircraft…

    A totally stable aircraft will return, more or less immediately, to its trimmed state
    without pilot intervention.
    However, such an aircraft is rare and not much desirable. We usually want an
    aircraft just to be reasonably stable so it is easy to fly.
    If it is too stable, it tends to be sluggish in manoeuvring, exhibiting too slow
    response on the controls.

    Too much instability is also an undesirable characteristic, except where an
    extremely manoeuvrable aircraft is needed and the instability can be continually
    corrected by on-board ‘fly-by-wire’ computers rather than the pilot, such as a
    supersonic air superiority fighter.

    Lateral stability is achieved through dihedral, sweepback, keel effect and
    proper distribution of weight.
    The dihedral angle is the angle that each wing makes with the horizontal (see
    Wing Geometry).
    If a disturbance causes one wing to drop, the lower wing will receive more lift
    and the aircraft will roll back into the horizontal level.

    A sweptback wing is one in which the leading edge slopes backward.
    When a disturbance causes an aircraft with sweepback to slip or drop a wing,
    the low wing presents its leading edge at an angle more perpendicular to the
    relative airflow. As a result, the low wing acquires more lift and rises, restoring
    the aircraft to its original flight attitude.

    The keel effect occurs with high wing aircraft. These are laterally stable simply
    because the wings are attached in a high position on the fuselage, making the
    fuselage behave like a keel.
    When the aircraft is disturbed and one wing dips, the fuselage weight acts like
    a pendulum returning the aircraft to the horizontal level.

    The tail fin determines the directional stability.
    If a gust of wind strikes the aircraft from the right it will be in a slip and the fin
    will get an angle of attack causing the aircraft to yaw until the slip is eliminated.

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  • Longitudinal stability depends on the location of the centre of gravity, the
    stabiliser area and how far the stabiliser is placed from the main wing.
    Most aircraft would be completely unstable without the horizontal stabiliser.
    Non-symmetrical cambered airfoils have a higher lift coefficient, but they also
    have a negative pitching moment (Cm) tending to pitch nose-down, and thus
    being statically unstable, which requires the counter moment produced by the
    horizontal stabiliser to get adequate longitudinal stability.
    The stabiliser provides the same function in longitudinal stability as the fin does
    in directional stability.

    Symmetrical (zero camber) airfoils have normally a zero pitching moment,
    resulting in neutral stability, which means the aircraft goes wherever you point it.
    Reflexed airfoils (with trailing edge bent up) have a positive pitching moment
    making them naturally stable, they are often used with flying wings (without the
    horizontal stabiliser).

    It is of crucial importance that the aircraft’s Centre of Gravity (CG) is located
    at the right point, so that a stable and controllable flight can be achieved.
    In order to achieve a good longitudinal stability, the CG should be ahead of the
    Neutral Point (NP), which is the Aerodynamic Centre of the whole aircraft.
    NP is the position through which all the net lift increments act for a change in
    angle of attack.
    The major contributors are the main wing, stabiliser surfaces and fuselage.

    The bigger the stabiliser area in relationship to the wing area and the longer
    the tail moment arm relative to the wing chord, the farther aft the NP will be and
    the farther aft the CG may be, provided it’s kept ahead of the NP for stability.

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  • The angle of the fuselage to the direction of flight affects its drag, but has little
    effect on the pitch trim unless both the projected area of the fuselage and its
    angle to the direction of flight are quite large.
    A tail-heavy aircraft will be more unstable and susceptible to stall at low speed
    e. g. during the landing approach.
    A nose-heavy aircraft will be more difficult to takeoff from the ground and to
    gain altitude and will tend to drop its nose when the throttle is reduced. It also
    requires higher speed in order to land safely.

    The angle between the wing chord line and the stabiliser chord line is called
    the Longitudinal Dihedral (LD) or decalage.
    For a given centre of gravity, there is a LD angle that results in a certain
    trimmed flight speed and pitch attitude.
    If the LD angle is increased the plane will take on a more nose up pitch attitude,
    whereas with a decreased LD angle the plane will take on a more nose down
    pitch attitude.
    There is also the Angle of Incidence, which is the angle of a flying surface
    related to a common reference line drawn by the designer along the fuselage.
    The designer might want this reference line to be level when the plane is flying
    at level flight or when the fuselage is in it’s lowest drag position.
    The purpose of the reference line is to make it easier to set up the relationships
    among the thrust, the wing and the stabiliser incidence angles.
    Thus, the Longitudinal Dihedral and the Angle of Incidence are interdependent.

    Longitudinal stability is also improved if the stabiliser is situated so that it lies
    outside the influence of the main wing downwash.
    Stabilisers are therefore often staggered and mounted at a different height in
    order to improve their stabilising effectiveness.

    It has been found both experimentally and theoretically that, if the aerodynamic
    force is applied at a location 1/4 from the leading edge of a rectangular wing
    at subsonic speed, the magnitude of the aerodynamic moment remains nearly
    constant even when the angle of attack changes.
    This location is called the wing’s Aerodynamic Centre AC.
    (At supersonic speed, the aerodynamic centre is near 1/2 of the chord).

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  • In order to obtain a good Longitudinal Stability the Centre of Gravity CG
    should be close to the main wings’ Aerodynamic Centre AC.
    For wings with other than rectangular form (such as triangular, trapezoidal,
    compound, etc.) we have to find the Mean Aerodynamic Chord – MAC,
    which is the average for the whole wing.
    The MAC calculation requires rather complicated mathematics, so a simpler
    method called ‘Geometric Mean Chord’ GMC or ‘Standard Mean Chord’ SMC
    may be used as shown on the drawings below.
    MAC is only slightly bigger than GMC except for sharply tapered wings.
    Taper ratio = tip chord/root chord.

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  • To calculate MAC of a tapered wing, the following simplified equation
    may be used:
    MAC = root chord * 2/3 * ((1+T+T2)/(1+T))
    Where T is the wing’s taper ratio.
    The MAC distance from the center line may be calculated as follows:
    distance = half span * (1+2*T)/(3+3*T)

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  • For a delta wing the CG should be located 10% ahead of the geometrically
    calculated AC point as shown above.

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  • The MAC of an elliptical wing is 85% of the root chord and is located at 42.4% of
    the half wingspan from the root chord.
    Elliptical wing’s area = pi * wingspan * root chord/4
    The AC location for biplanes with positive stagger (top wing ahead of the bottom
    wing), is found according to the drawing below.

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  • For conventional designs (with main wing and horizontal stab) the CG location
    range is usually between 28% and 33% from the leading edge of the main
    wing’s MAC, which means between about 5% and 15% ahead of the aircraft’s
    Neutral Point NP.
    This is called the Static Margin, which is expressed as a percentage of MAC.
    When the static margin is zero (CG coincident with NP) the aircraft is considered
    “neutrally stable”.
    However, for conventional designs the static margin should be between 5% and
    15% of the MAC ahead of the NP.
    The CG location as described above is pretty close to the wing’s Aerodynamic
    Center AC because the lift due to the horizontal stab has only a slightly effect on
    the conventional R/C models.

    However, those figures may vary with other designs, as the NP location depends
    on the size of the main wing vs. the stab size and the distance between the main
    wing’s AC and the stab’s AC.
    The simplest way of locating the aircraft’s NP is by using the areas of the two
    horizontal lifting surfaces (main wing and stab) and locate the NP proportionately
    along the distance between the main wing’s AC point and the stab’s AC point.
    For example, the NP distance to the main wing’s AC point would be:
    D = L · (stab area) / (main wing area + stab area) as shown on the picture below:

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  • There are other factors, however, that make the simple formula above inaccurate.
    In case the two wings have different aspect ratios (different dCL/d-alpha) the NP
    will be closer to the one that has higher aspect ratio.
    Also, since the stab operates in disturbed air, the NP will be more forward than
    the simple formula predicts.
    The figure below shows a somewhat more complex formula to locate the NP but
    would give a more accurate result using the so called Tail Volume Ratio, Vbar.
    This formula gives the NP position as a percentage (%) of the wing’s MAC aft of
    the wing’s AC point.

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  • For those who are not so keen on formulas and calculations there is the
    Aircraft Center of Gravity Calculator, which automatically calculates the CG
    location as well as other usuful parameters based on the formula above.
    For Canards check the link below:
    Canard Center of Gravity Calculator

    For further equations on how to find the proper CG location with different wing
    shapes and design configurations including Canards, check here.

  • Stall and SpinOne of the first questions a pilot might ask, when converting to a new aircraft
    type, is “What’s the stall speed?”
    The reason for the enquiry is that usually, but not always, the approach speed
    chosen for landing is 1.3 times the stall speed.
    Stall is an undesirable phenomenon in which the aircraft wings produce an
    increased air resistance and decreased lift, which may cause an aircraft
    to crash.

    The stall occurs when the airflow separates from the upper wing surface.
    It happens when a plane is under too great an Angle of Attack (AoA).
    For light aircraft, without high-lift devices, the critical angle is usually around 16°.
    The picture below shows a stalled airfoil:

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  • Geometric Angle of Attack is the angle between the airfoil chord line and the
    direction of flight. The Angle of Attack is also known as Alpha.
    The angle of attack measured relative to zero coefficient of lift is called the
    Absolute Angle of Attack (Absolute AoA).
    There’s also the Pitch Angle, which is measured with respect to the horizon.
    For symmetric airfoils the Absolute AoA is equal to the Geometric AoA,
    whereas for asymmetric (cambered) airfoils these two angles are different, since
    these airfoils still produce lift at zero Geometric Angle of Attack as shown below.

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  • For airfoils of one family the symmetric airfoil stalls at a higher Geometric AoA
    compared with the cambered airfoil, however the cambered airfoil has higher
    lift coefficient and stalls at a higher Absolute AoA.
    As mentioned in the chapter Forces in Flight, the lift force is proportional to the
    density of the air r, the square of the airspeed V, the type of airfoil and to the
    wing’s area according to the formula:

    Lift force = 0.5 * r * V2 * wing’s lift coefficient * wing area

    Since lift coefficient is proportional to the angle of attack, the lower the airspeed
    the higher the angle of attack has to be in order to produce the same lift.

    Thus, stall may occur during take-off or landing, just when the airspeed is low:
    To keep altitude at low airspeed, the wing’s lift coefficient has to increase, and if
    a non-experienced pilot tries to lift the aircraft’s nose at a too low airspeed, it may
    exceed the critical angle of attack and stall occurs.
    If you’re flying near the stall speed and make a steep turn, the aircraft will stall.
    That’s because, if the aircraft stalls for instance at 20 knots in straight level flight,
    it will stall at 28.2 knots in a 60 degree banked turn.
    The rapid reduction in speed after passing the critical angle of attack means
    the wing is now unable to provide sufficient lift to totally balance weight and,
    in a normal stall, the aircraft starts to sink, but if one wing stalls before the
    other, that wing will drop, the plane falls out of the air. The ground waits below.

    Stalls may also occur at high airspeeds. If at max airspeed and full throttle the
    pilot suddenly applies excessive up elevator, the aircraft will rotate upwards,
    however, due to aircraft’s inertia, it may continue flying in the same direction
    but with the wings at an angle of attack that may exceed the stall angle.
    See an example here

    Stalling at high-speed gives a more dramatic effect than at low speed.
    This because the strong propeller wash causes one of the wings to stall first
    that combined with the high speed produces a snaproll followed by a spiral dive.
    This happens very fast causing the aircraft to dive at full throttle and unless
    there’s enough height for recovery, the crash will be inevitable.

    An aircraft with relatively low wing loading has a lower stall speed.
    (wing loading is the aircraft’s weight divided by the wing area)
    Since the airfoil also affects the stall speed and the max angle of attack, many
    aircraft are equipped with flaps (on the wing trailing edge), and some designs
    use slats (on the wing leading edge).
    Flaps increase the wing’s lift coefficient, but the simple ones may reduce the stall
    angle. Slats, on the other hand, increase the stall angle.

    Aircraft that are designed for Short Take-Off and Landing (STOL) use slots
    on the wing’s leading edge together with flaps on the trailing edge, which gives
    high lift coefficient and remarkable slow flying capabilities by allowing greater
    angle of attack without stalling.

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  •  Cruise                     Climb
    

    The leading edge slots may prevent the stall up to approximately 30 deg. angle
    of attack by picking up a lot of air from below, accelerating the air in the funnel
    shaped slot (venturi effect) and forcing the air around the leading edge onto the
    upper wing surface.

    The disadvantage of the slots and flaps is that they produce higher drag.
    Since the high lift coefficient is only needed when flying slowly (take-off, initial
    climb, final approach and landing) some designs use retractable devices,
    which closes at higher speeds to reduce drag.

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  • Such devices are seldom used in model aircraft (especially the smaller ones),
    mainly due to its complexity and also the increasing of wing loading, which
    may counter-act the increased lift obtained.
    The wing’s aspect ratio (AR) also affects the overall lif coefficient of the wing.
    For a given Re, the wing with higher AR (with long wingspan and small chord)
    reaches higher lift coefficient, but stalls at a lower angle of attack than the wing
    with low AR as shown below:

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  • However, for a given wing area, increasing the aspect ratio may result in a too
    small wing chord with a too low Re number, which may significantly reduce the lift
    coefficient. This is likely to occur with small indoor planes.
    Another method to improve an aircraft’s stall characteristics is by using wing
    washout, which refers to wings designed so that the outboard sections
    have a lower angle of attack than the inboard sections in all flight conditions.

aero32

  • The outboard sections (toward the wing tips) will reach the stalling angle
    after the inboard sections, thus allowing effective aileron control as the stall
    progresses. This is usually achieved by building a twist into the wing structure
    or by using a different airfoil in the outboard section.
    A similar effect is achieved by the use of flaps.
    The aileron drag is a further factor that may cause an aircraft to stall.
    When the pilot applies aileron to roll upright during low speed, the downward
    movement of the aileron on the lower wing might take an angle on that part of
    the wing past the critical stall angle. Thus that section of wing, rather than
    increasing lift and making the wing rise, will stall, lose lift and the aircraft
    instead of straightening up, will roll into a steeper bank and descend quickly.

    Also the wing with the down aileron often produces a larger drag, which may
    create a yaw motion in the opposite direction of the roll.
    This yaw motion partially counteracts the desired roll motion and is called
    the adverse yaw.

    Following configurations are often used to reduce aileron drag:
    – Differential ailerons where the down-going aileron moves through a smaller
    angle than the up-going.
    – Frise ailerons, where the leading edge of the up-going aileron protrudes
    below the wing’s under surface, increasing the drag on the down-going wing.
    – And the wing washout.

    Stall due to aileron drag is more likely to occur with flat bottom wings.
    Since differential ailerons will have the opposite effect when flying inverted,
    some aircraft with symmetrical airfoils designed for aerobatics don’t use
    this system.
    The picture below illustrates an example of a Frise aileron combined with
    differential up/down movement.

aero33

  • Another factor that affects the aircraft’s stall characteristics is the location of
    its centre of gravity CG.
    A tail-heavy aircraft is likely to be more unstable and susceptible to stall at low
    speed, e. g. during the landing approach.
    Downwind stall:
    For instance, a powered plane flying north with airspeed of 30 knots against a
    30 knots headwind has zero ground speed.
    If you turn 90 deg. left (west), the plane’s airspeed still is 30 knots but is now
    drifting 30 knots to the south resulting in 42 knots ground speed to the southwest.
    If the plane keeps turning south, the drift due to the wind is still 30 knots but now
    the ground speed becomes 30+30 = 60 knots, while the airspeed still is 30 knots.

    The pilot on the ground will see the ground speed but not the airspeed, and since
    the plane seems to move much faster flying downwind, the pilot may instinctively
    slow down the plane below the stall speed.
    This results in a pilot-induced stall due to the optical illusion of the plane’s higher
    ground speed when flying downwind.

    Recovering from a stall:

    In order to recover from a stall, the pilot has to reduce the angle of attack
    back to a low value. Despite the aircraft is already falling toward the ground,
    the pilot has to push the stick forward to get the nose even further down.
    This reduces the angle of attack and the drag, which increases the speed.

    After the aircraft gained speed and the airflow incidence on the wing becomes
    favourable, the pilot may pull back on his stick to increase the angle of attack
    again (within allowable range) restoring the lift.
    Since recovering from a stall involves some loss of height, the stall is most
    dangerous at low altitudes.

    Engine power can help reduce the loss of height, by increasing the velocity
    more quickly and also by helping to reattach the flow over the wing.
    How difficult it is to recover from a stall depends on the plane. Some full-size
    aircraft that are difficult to recover have stick shakers: the shaking stick alerts
    the pilot that a stall is imminent.

    Spin

    A worse version of a stall is called spin, in which the plane spirals down.
    A stall can develop into a spin through the exertion of a sidewise moment.
    Depending on the plane, (and where its CG is located) it may be more difficult
    or impossible to recover from a spin.
    Recovery requires good efficiency from the tail surfaces of the plane; typically
    recovery involves the use of the rudder to stop the spinning motion, in addition
    to the elevator to break the stall. However the wings might block the airflow to
    the tail.
    If the centre of gravity of the plane is too far back, it tends to make recovery
    much more difficult.

    Another circumstance that may cause loss of control is when a hinged control
    surface starts to flutter.
    Such flutter is harmless if it just vibrates slightly at certain airspeed (possibly
    giving a kind of buzzing sound), but ceases as soon as the airspeed drops.
    In some cases however, the flutter increases rapidly so that the model is no
    longer controllable.
    The pilot may not be aware of the cause and suspect radio interference instead.
    To reduce the flutter, the control linkages should not be loosely fitted and the
    push rods should be stiff.
    Long unbraced push rods can create flutter as vibration whips them around.
    In some difficult cases the control surface has to be balanced, so that its centre
    of mass (gravity) is ahead of the hinge line. It should be located at about 60-65%
    of the length of the control surface from its inner end:

aero34                                                                                                            Credits: http://adamone.rchomepage.com/  http:// 

Starfighter 104S RC Air Show 2015

Roger Knobel with his New Lockheed Aeritalia Starfighter F-104S ASA-M turbine Model
*Special Color per gil 82 anni del Gruppo 1918-2000
5° STORMO 23° Gruppo
C.I.O Veltri*
enjoy…  jet2 jet1

Red Line Remote Control http:// http://

The Top 10 facts about RC toys and RC vehicles!

RC-Vehicles-1  http://Red Line Remote Control

When it comes to RC toys, remote control toys, RC vehicles and remote control vehicles there are 10 really important things that everyone should know! This is especially the case if you are looking to buy a toy or vehicle for the first time or even if it’s just been a fair while since you last bought and you’re getting back into things.

The 10 things I’ve covered below are the best starting point to get a good understanding of the current state of the RC and remote control world including some of the common jargon and terminology used.

If there is anything else you think I’ve missed here that would also be great to have listed please feel free to leave me a comment below and perhaps we can later do a revised version of this post extending our list of 10 out to a top 20!

1. What is the real difference between ‘RC’ and ‘remote control’?

Now this is a very interesting one! Often when you read anything on the subject of remote controlled toys and vehicles you’ll either see the term ‘RC’ or just ‘remote control’ used. Often these terms are also used interchangeably (just like I do on this site).

So is there really a difference between what these two terms refer to?

To some degree this really comes down to who you ask. Just check out any of the forums on the internet and you’ll see there are even often some varying views within the community itself as to what the distinction really is.

Let’s start by looking at the term ‘RC‘. This is generally acknowledged to be short for ‘radio control’ and refers to the technical set up of the gadget in question which (keeping it relatively simple) is essentially:

  • A ‘transmitter’ which is the hand held controller you use to control the direction, movement etc of your gadget. When you move a joystick on push a button on your hand held controller effectively converts this movement into a message which is sent out as radio waves to your gadget.
  • A ‘receiver’ which sits inside your gadget to be controlled and receives the radio wave instructions sent from the transmitter.
  • A ‘servo’ (or even more than one servo) which is passed the instructions from the receiver and in response to these instructions will send an appropriate message to the motor (or motors) in your gadget.
  • A ‘motor’ (or even more than one motor) which once it receives is instructions from the servo takes action to put those instructions into effect e.g. makes your car race forward or backwards or turn left or right etc.

If you’re after a more in depth explanation of all these different components and how they interact on a more technical article then check this out

So in comparison to this very clear technical based understanding, what does ‘remote control’ actually mean? Now this is where a bit more disagreement often arises.

Unlike the very clear technical basis we have to define the term ‘RC’ when it comes to remote control we are much more looking at a descriptive term which on its most widely accepted meaning refers to any method of controlling a toy, vehicle or other gadget from a distance.

So this could refer to methods of control such as by wires, by infrared (as a lot of the cheaper models today use very effectively) or even arguable by RC as of course when you use an RC transmitter to operate a car you are still operating it from a distance.

So while all RC gadgets could be seen to be ‘remote control’ not all ‘remote control’ gadgets have the necessary technical make up to be considered ‘RC’ gadgets.

BUT increasingly people use the terms interchangeably (even I tend to on this site) and in all honesty it doesn’t really matter unless of course you are looking at buying and are really specifically after some of the advantages radio control may have over some of the other forms of remote control. In these cases make sure you do spend some time looking at the detail behind the name used to make sure you are really getting what you want.

2. Are RC Toys and RC Vehicles expensive?

Yes and no! The answer here really depends on what you are after.

The great thing we are seeing about some of the developments in new technology in the space (as I talk about further below) is that the range of toys, vehicles and gadgets is increasing not only in terms of the overall number available but also the previously existing boundaries are being pushed in terms of what is available to high end buyers as well as at a much more affordable entry level.

For example you can pick up a pretty impressive and fun little indoor RC helicopter for less than $30.        RC-Helicopter1 http://Red Line Remote Control

But at the very high end of things you can also spend into the thousands on a top of line nitro powered remote control car for competitive racing, particularly once you invest in the replacement parts and upgrades most people who get involved in competitive racing would consider necessary.

3. Are they just for kids?

In some cases definitely yes but in some cases definitely no!

You can of course get some great looking and very reasonably priced cars for kids of all ages that are great for safe indoor use. However at the other end of spectrum some of the high end modern nitro powered cars can hit 100 mph (and come with a price tag to match)! Definitely not a toy!

Similarly planes and other vehicles that can also achieve significant altitudes and velocity (such as some helicopters and drones) need to be used responsibility at all times and definitely wouldn’t fall into the toy category.

4. Is it a solo hobby?

Although when many people think of remote control vehicles they often associate it as a fairly solo pursuit there are in fact a number ways that is becoming more of a community focused pass time if you want to get involved in that way.

The internet has of course introduced a wide number of forums and social networking sites on which you can discuss all aspects of remote control toys and vehicles from maintenance, to new technology and even ‘vintage’ collectables. However there has also always been a strong club culture for real enthusiasts who want to get involved in competitive racing or just want to enjoy and show off their vehicles with others.

Today clubs for all types of vehicles are still strong and if anything recent years have seen resurgence in some areas, particularly as some of the more high performance and competition focused vehicles also come down in price.

5. Are remote toys and remote control vehicles easy to break?

Overall the higher end remote control toys and remote control vehicles are generally more robust these days than they have ever been, but the true answer to this really falls into parts.

Firstly all vehicles are of course generally designed for a specific purpose.

For example a remote control sailing boat is not going to go well in rougher waters and waves and also anRC car designed for on track racing will not cope well on a rough dirt track.

Using a remote control vehicle outside of its intended areas of use is not only going to increase the chances for breakages or permanent incapacitation but – let’s face it – it’s just not going to be as much fun if the performance of your vehicle will be hampered by the environment you’re trying to use it in.

Secondly, no matter how robust something is you need to be aware of its inherent limitations and also what maintenance it requires to keep it in the best condition. A higher end RC vehicle may be sturdier in the short term but its optimum performance and overall state of repair may deteriorate more noticeably overtime than a lower end vehicle if it’s not properly maintained.

So when choosing an RC vehicle think about how committed you really want to be to maintenance of the vehicle and also just how respectfully you are likely to treat it and tailor your purchase accordingly. This is a particularly important consideration when buying for kids!

6. Is the technology improving?

Definitely! The speed of motors, the robustness of the vehicles manufactured and of course the size and expense of the other component parts are also decreasing meaning that there are a lot more possibilities theses days when it comes to the purchase of (or building your own) RC vehicles in all price ranges.

At the lower end of the spectrum some of these technological advances have been especially seen in the greater quality of infrared and non ‘radio controlled’ RC vehicles (and most particularly those that fall into the ‘remote control toy’ category) that we’ve seen come onto the market in recent years.

The other really interesting development (I think!) in the space has also been the increasing emergence of iPhone and all the mobile phone and tablet controlled vehicles. These use a range of technologies from infrared ‘dongles’ that connect to your mobile device (like these ones do) to even blue tooth (like this one does) to control your vehicle.

7. Are there more to RC vehicles and RC toys than just cars, planes, boats and helicopters?

Yes! Yes! Yes! These days you can pretty much pick up any time of RC vehicle you can wish for. From tanks, jets, and submarines to even more exotic models like this one: http://Red Line Remote Control

8. Do all RC toys and RC vehicles run on batteries?

Although controllers will always use some form of batteries (whether standard off the shelf or more specific rechargeable ones), vehicles themselves can run on either batteries (in varying forms once again) or what is referred to as ‘nitro‘.

Nitro fuel is essentially just a methanol-based product that has had varying amounts of oil and nitromethane added. The type of nitro fuel you want to use depends on the type of vehicle your running (and also of course your budget!). Speciality nitro fuel can be purchased from all hobby shops and for the more intrepid amongst us you can in fact mix up your own!

Although less common than Nitro powered vehicles it is also possible to get vehicles which run on variations of more traditional gasoline.

Nitro and gas powered engines are generally only found in the more highline or competitive focused models. Definitely not something you want running inside your house!

9. Are old RC toys and RC vehicles able to be refurbished or updated?

This really depends on the model you have but for the ones which were more expensive when purchased generally you can update and up-spec them.

To some degree this will also depend on just how old the vehicle in question is and whether any newer parts can be substituted for the older materials.

There are however some fantastic examples out there of the refurbishment of older vehicles – check this out from the guys at IconicRC featuring a refurbished and modified Tamiya Hot Shot II 4WD Buggy (also actually the first car I had when I was 11!). http://Red Line Remote Control

10. Are the best ones only for use outdoors?

Although you can get some amazing RC toys and RC vehicles intended to be primarily used outdoors some of the developments in the whole RC space in recent times have most definitely benefitted what types of vehicles and toys you can run indoors.

From really fun and robust helicopters and drones to mini cars, iPhone controlled vehicles and even robots.

Whether you want something for indoors or outdoors these days you can be guaranteed to have a wide range of options to choose from!                                                                                                                                 Credits: http://www.myrctopia.com/

http:// http://

Ready to fly(RTF) Remote Control Airplane

RTF rc airplanes will be the very best strategy to get started in radio management flying if you happen to be not whatsoever bothered about building a model airplane, and just desire to fly one.

The abbreviation ‘RTF’ stands for Ready To Fly which suggests that you just, the consumer, will not need to do something to the design to get ready it for flight aside from set up the gear batteries that manage the radio and do some extremely standard last assembly function, like attaching the wing and tailplane for the fuselage. There may be no development involved in putting collectively an RTF plane.

RTF rc airplanes have launched a huge number of people towards the pastime of radio control flying, but it is only in much more recent a long time that they have become so widely available and have been priced reasonably. Immediately before the creation of RTFs these kinds of kitshad been the way in which to go but these deterred potential modelers who just wanted to fly and weren’t also thinking about the building facet of your hobby.

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