FLYING A MODEL AUTOGYRO... What`s so different about it?

Most experienced,  long time modelers,  would find an autogyro fairly easy to fly once they understand how it responds/behaves.     An R/C helicopter flyer would adapt to an Autogyro fairly quick.    A new R/C flyer,  and even one with limited experience,  could find it difficult and frustrating.     However once you have experienced a successful flight the feeling is absolutely fantastic,  and more often than not the modeler goes on to experience different and more advanced versions of the model Autogyro.

This page is posted here as an aid to those fledgling GyroNuts about to attempt their very first R/C Autogyro flight.   Generally most of the comments pertain to models of the 'non-fixed-winged' design.    Regardless of the design,   the information will familiarize you with the flight characteristics of un-powered rotorcraft even though some models may have the assistance of a stubby wing.

GROUND HANDLING and LAUNCH

Before you fly,   be sure your rotor freely rotates,  and test it in a light breeze.     Face into the wind,   hold the model in one hand and pre-spin the rotor with the other hand.     Raise the nose high  (maybe 45-60 degrees)  and while facing the wind,  observe the rotation.     How quickly the rotor spins up rapidly will depend on the strength of the wind.    With very light breezes,  it may not accelerate much at all until you increase the effectiveness  (speed)  of the breeze by walking directly into the breeze while continuing to hold the model nose high.    You may even have to jog slowly.

  If the rotor still does not spin up,  you may have to slightly increase the negative incidence of the blades.     By the same reasoning,   if the rotor seems to spin-up almost too easily,  you may want to remove some negative incidence.    The more the negative incidence,   the quicker the spin-up,  but the rotor performance will suffer.    Ideally,  for maximum performance,   you would like to have zero or possibly a little positive incidence in the blades.    

Once you have noticed the rpm increasing,   now you will be looking for it to accelerate into an  "Autorotation"  condition,   which is necessary for the system to provide sufficient lift for flight.    Autorotation will be noticeable in a few different ways.     One,   you can see the blades really accelerate rather suddenly.    Two,  you can generally audibly  'hear'  the acceleration.     Three,   the increase in lift should remarkably increase.     If you don`t feel the increase in lift,  then the system may be inefficient and in-flight performace may be poor.

Flight  (full)  rpm must be present for launch or the model will normally roll into the retreating rotor blade,  since the lift will be higher on the advancing side at low rpm.     You cannot  (should not)  pull the model off the ground as you might be able to do with an airplane.     If the rotor is up to speed the model will want to lift off on its own.     If it has not lifted off as you approach the end of the field,   it is best to cut off the power and abort the attempt.    

Caution:   Do not rush the ground take-off.    Apply power slowly and allow the model to accelerate slowly!    Do not attempt a cross-wind takeoff,  unless you have a lateral tilting rotor and rudder control to assist.     Generally,  follow the rule of not taking off cross wind any time.

Actually hand launching of a small model  (less than four feet of rotor) is almost preferable for the first few flights.     One primary reason is that the model is closer to you at release and it is easier and quicker to see what correction is needed.   With a ground launch (ROG) the model may be just far enough away that you may have difficulty reacting quickly enough for a correction.     Small electric models are generally always hand launched,  simply because of the excess energy necessary to complete the ground launch.     If you are hand launching,   wait for autorotation and then  (and only then)   push the model forward and slightly upward.     If you release it too soon  (prior to autorotation)   it will most probably roll/turn in the direction of the retreating blades,  and drop rapidly.     If you throw or toss it too hard,  it may   nose up suddenly  [click] and/or sharply.     Under normal conditions,   the model should proceed forward in level flight,  enter a slight climb,   and possibly begin a slow right turn,   giving you sufficient time to gain full control with your transmitter.

IN FLIGHT

Limit bank/tilt angles to 30 degrees.     At bank angles between about 30 and 45 degrees,  extreme caution must be exercised or you may lose control.     If you exceed these angles,  the model may simply slide out of control and enter the deadly spiral turn.     The model will normally be flying in a one  "g"  condition,  and only use just enough elevator (aft tilt) pressure to hold level flight.    Do not attempt to push forward which will create a 'negative' g-force condition,  unloading the rotor.    These models are normally not sensitive in pitch/elevation,  and elevation is easy to control through the use of power rather than transmitter elevation control.    However they do generally react quickly to a roll/turn input.

Orientation is far more difficult with the Autogyro than a standard fixed wing model airplane.    One good flight technique is to -always- turn toward yourself whenever possible,  especially when the model is very far away.     With brightly colored rotor blade top surfaces,   the blades will then become visible when it is banked -toward- yourself and you will know what it is happening.     It is not uncommon for an R/C flyer to -relax- on the controls after initiating a turn.     This technique can present a problem with many gyros,  since the model will tend to -level out- with the lack of control pressure.     Apply the control pressure to begin the turn,  observe the attitude,  and continue to hold a miniumum of pressure to continue the turn.     Notice that this does not mean -continue to increase,  but simply hold what you have.

Picture a model airplane flying around with just the fuselage and tail showing,  and this is somewhat like the Autogyro in flight.     The limited profile of most autogyros will make it easy to become confused if you allow it to get very far away.    If you become confused and lose control,  reduce power (glow models) quickly and relax on the controls.     With electric models,  relax on the controls and use caution with power changes.     The larger relative propellor on many electrics have a very pronounced torque effect with large power changes.     Frequently,   with a relaxation of controls,   the model will attempt to level/right itself below the rotor.     This will hopefully give you the opportunity to re-orientate on the model and regain control.



"To tilt or not to tilt"
DIRECT ROTOR CONTROL (DC) versus NON-DC CONTROLLED MODELS

DC models utilize full servo control,  both lateral and pitch tilting of the rotor,  and generally do not utilize a rudder or elevator for flight control.     The advantage of DC is that control  (except yaw)  can be exercised at all airspeeds,   right down to zero speed,  including landing.     A non-DC model is fully controllable,  as long as it is above the minimum airspeed for rudder and elevator effectiveness.    A zero ground roll landing for a non-dc model can only be accomplished if you have some wind to retain rudder/elevator effectiveness.    

In flight a DC model may experience a horizontal  (flat)  rotation if permitted to slow to zero flight speed in light wind conditions without the aid of a rudder to counter the rotation.     Usually this will only happen if the nose is raised somewhat excessively relative to the slow forward speed.     Lateral DC tilting is highly effective.     Very little tilting will cause the model to react.     Pitch tilt,  while effective,  is not as 'sensitive' as lateral tilt.

Many of the non-pitch tilting models have the rotor placed high to clear the tail fin,  and for an added bit of stability.     However a higher placed rotor  (vertically)  than average may require the addtion of rudder control to accomplish a turn.     The lateral tilt simply "tilts" the model,  but it won`t turn until you add rudder.

Another type model is the one with  "Teeterbars",  a blade system where the blades are rigidly connected together at the center and "teeter" at the center shaft.     As one blade goes up,  the other goes down.    This configuration works,  and has been employed sucessfully with the "Whistler".    However, they just don`t seem to be nearly as efficient as the three or more bladed individually hinged rotors.     My Whistler flys,  but requires a much higher airspeed to maintain lift,  even though it also has a supplemental wing to support the craft.    It will not fly without the wing,  nor will it fly without the rotor,   at least mine won`t.     It will not hover in anything less than a relatively strong wind of at least 10 knots.

Other teeters I have watched,  and have been told about,  seem to behave the same,  and everyone I know of that has attempted the teeter system eventually abandoned it for the individually hinged system.     I don`t know if this is a result of poor design on the part of the modeler or simply a fact of teetering models?    Remember this is not to be compared with the teeter type rotor systems employing the helicopter/flybar.     They are converted helicopters,  not the style of pure autogyro we are speaking of,  and fly very different than the non-heli system.

Will a full sized autogyro perform aerobatics?    Yes,  to a degree.    A Pitcairn craft was known to have performed loops during exhibition shows.     Will the models perform aerobatics?   Yes.   Much better and easier than the full sized craft,  but certainly not nearly as smooth.    Depending on the type rotor system employed  (which will dictate the amount of forward airspeed necessary) ,  loops and rolls can be flown.     The same precautions as you would use with the average model airplanes are necessary.     Just obtain a little additional altitude and airspeed to insure recovery if you fail to execute the maneuver properly.    Caution:    If you intend to practice aerobatics,  it is advisable that you install slightly stronger servos, especially on the pitch control portion..     There is more stress/load on the pitch axis/servo than the lateral /roll servo.


And what happens if the engine quits?

Will this type model simply fall and destroy itself,  if so much depends on the engine to propel it forward ( thus maintaining flight capable rotor rpm),  and suddenly the engine fails?    

Well not really.... However it is certainly not like a model airplane where the craft usually will assume a decent glide angle and float in for a typical "dead stick" landing.    If your model has been properly balanced with the Center of Gravity just forward of the rotor shaft/spindle (or as prescribed for your particular model),  it will (should) assume a slightly nose down attitude under light or no wind conditions and descend nearly vertical like a "soft rock".   With D/C servo control you will have some degree of control over the general flying attitude and hopefully be able to "break" the rate of descent sufficiently to accomplish a soft landing.    With a rudder/elevator controlled model, you will not have nearly as much direct control over the attitude, however you should be able to lower the nose enough to accelerate sufficiently to be able to use the rudder and elevator to "break" the descent just prior to touchdown.    Again, this depends on the balance (hang angle) of the model.   Little or no hang angle ( relatively neutral CG ),   and you will have very little control over the descent.  With between 5 to 10 degrees of down hang, the model should give you a forward glide,  though rather steep,  and the opportunity to have some control effectiveness.

It may sound stupid to lower the nose during the latter portion of the descent thus increasing the rate of descent,  however this is one key to a successful soft landing.  The object is to gain sufficient airspeed to allow the aft tilting of the rotor and / or "up" elevator to raise the nose and reduce the rate of descent immediately prior to touchdown.   Timing of this is critical,  obviously..   Break the descent too early,  the model may drop the final foot or so tail first.  Break too late, and crunch!

It is good idea to actually practice engine failure landings.   Position the model with the nose pointed toward yourself,  slightly upwind ( but still over the landing field ) , at perhaps 200 to 300 feet of altitude.  Reduce the power to idle (tick over), and notice the degree of control you have...   Attempt to gain more control by lowering the nose ( this is where D/C really come s in handy )   and then break the descent for landing.   With initially using idle power,  you always have the opportunity to abort and try again.   Once you feel comfortable,  then actually stop the engine and prove to yourself that you can prevent a destructive landing.

IN SUMMARY

Most R/C modelers with some flying experience can fly a model autogyro,   if a degree of common sense and caution is exercised.     The rotor must be at full flying rpm   (into autorotation)   before the model will fly   ( non-fixed winged models ).     Orientation is difficult and tricky,   keep the model within a few hundred feet  ( 50-75 meters).     Limit bank angles to prevent loss of control.     Do not push down/negative control pressures   ( the model needs to fly at a slight positive 'g' pressure ).      Land before fuel is exhausted and with power applied    With engine failure attempt to gain sufficient airspeed to allow a breaking of the descent.   Please Note:  The electric models I have experience with utilize a much larger propellor  (geared motor)  and with power failure  (or a sudden closing of the throttle) the model may literally 'stop' flying and drop rapidly/unexpectedly due to the breaking effect of the large prop.   With this in mind limit initial electric model flights to a simple one minute circuit of the field and complete a landing, while noting any trim corrections required for the subsequent flight.    Cautiously extend the flight time of each subsequent flight but always land before battery power expiration.    A good idea is to ground test the system by timing the fully charged battery at full throttle and always land well before that time limit expires.

Jim Baxter,  April  2001  Technical page Rev..06-02-01.. jb