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CULTURAL PARADIGM:

 

- “Gyros can handle high winds”

 

                                    - Greg Gremminger

 

It is our hope that we can help more gyro pilots make safer decisions about how they fly their gyro – especially about flying in windier conditions.  Toward that goal, to perhaps provide more and better background information to make better decisions, I would like to expand on an issue that may not be well-enough understood or respected.

 

Sometimes there are long-promoted cultural paradigms that promote poor decisions.  It is an often-heard statement: “Gyro's can fly in high winds.”   This may be our most dangerous paradigm about gyros.   While it is true that a rotor is much less sensitive to turbulent wind because of its effectively very high “wing loading,” it is an improper conclusion that the entire gyro would therefore safely handle gusty winds.  Whether a gyro is safe to fly in gusty winds or not is a factor of the aerodynamic stability characteristics of the AIRFRAME – the rest of the gyro – the dynamic response of that airframe to a disturbance (wind gust or g-load). 

 

The presumption that a gyro can handle gusty winds must be highly qualified as to the characteristics of THAT particular gyro and the skill of the gyro pilot to control THAT particular gyro

 

While it may be true that a rotor is much less sensitive (than a wing) to wind turbulence, it is not always true that the gyro, itself, is therefore insensitive to the wind or safe to be flown in gusty winds.  The rotor is a very powerful “wing,” and can respond very quickly and powerfully to cyclic inputs.  Any “un-commanded” cyclic inputs from improper pitch responses of the airframe can dramatically amplify those improper airframe movements and further aggravate the gyro response.

 

Whether a gyro is stable and safe to fly in gusty winds depends in large measure on the aerodynamic stability of the AIRFRAME – the response of the airframe to wind or g-load disturbances.  An airframe which responds in the wrong or divergent direction to wind or g-load transients can readily couple improper direction, un-commanded cyclic inputs into the rotor.  It would take a pilot, very highly skilled in that particular gyro, to “dampen,” prevent, or correct these un-commanded rotor cyclic inputs.  That pilot control reaction must be of proper timing and amplitude to prevent rapid divergent or oscillatory response of the whole gyro.  On some gyro configurations, these airframe divergent responses can occur at a rate that would be very difficult, if not impossible, for even the most skilled pilot to properly react to and correct.  In many cases on such gyros, the pilot’s reactive response would likely be of such improper timing (“phase”) so as to actually amplify or “resonate” the disastrous divergent response of the gyro/pilot system – Pilot Induced Oscillations (PIO) or Bunt-Over.

 

Gyros can, however, with proper aerodynamic stability design, be very much less sensitive to wind turbulence or even pilot commanded disturbances.  A gyro, whose airframe is aerodynamically configured to respond in pitch in the proper direction and at the proper rate, will couple those un-commanded stabilizing cyclic inputs to the rotor.  The rotor will then cause the whole gyro to respond in the stabilizing or corrective direction to dampen or prevent divergent or oscillatory response of the whole gyro – without pilot input, and without exciting improper pilot reaction.  These un-commanded rotor cyclic inputs themselves, on a well-stabilized gyro, will then reduce or prevent any improper divergent or oscillatory gyro response.

 

A horizontal stabilizer is the most important component of a stabilized airframe.  Although, a horizontal stabilizer, alone, does not necessarily assure a properly stabilized gyro, it is probably not possible to properly stabilize a gyro without one.  A stabilized airframe, which responds in pitch in the proper direction and rate, is not wholly the function of the horizontal stabilizer.  The horizontal stabilizer must be properly designed to “balance” other aerodynamic and inertial factors of the airframe.

 

It is not a simple matter to determine if proper gyro stabilization and insensitivity to gusty winds is present in a particular gyro.  Certainly the presence of a very large horizontal stabilizer, placed well aft on the airframe is a good indication.  Also, a propeller thrustline and an airframe or fuselage Center of Drag relatively well-aligned with the Center of Gravity (CG) of the airframe is a good indication.  But, often, a subjective determination can be misleading – good or bad!  Probably the best indication that a gyro MAY fly safer in gusty wind conditions would be the accident record of similar configuration gyros – do your research and make your decisions accordingly - of what to fly in what winds by a pilot of your skills and experience!

 

It would be well for all gyro pilots to exercise a high degree of caution in any gyro that has “questionable” historic safety in turbulent wind. But, don’t assume anything.  The insidious nature of PIO and other pitch-related issues is that they are not readily apparent, and in fact are deceptively unapparent for many gyros that might seem to be “stable” when flown in typical mild conditions.  The dangerous responses of a particular gyro may not be apparent until just the right conditions are present, and only after it is too late!

 

Have a safe Day!


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