#### Jean Fourcade

##### Newbie

Dear all,

I have been involved in gyroplane between 1995 and 2004, building and flying a Dominator and studying flight mechanics of this very special aircraft. Then I was interested in other activities.

Few years ago I got interested again in gyroplane, looking on internet, and I was very surprised to read on Tervamaki web site a page concerning gyroplane stability where he speaks about “thrust line psychosis” and concludes that the work of the Glasgow university was a misconceptions on gyroplane longitudinal stability. Tervamaki oppose to the work of Glasgow university a paper from Prof. Laine and the way it is presented make think that there were some mistake on Hounston’s work.

Now this page has changed. The word “misconception” is no more used but there is still a remark (we don’t know from whom) which says that Houston reports have done damage to the evolution of safer gyroplanes.

The current trend concerning the design of autogyros seems to be : ok, we know that in HTL gyro the rotor thrust line goes in front of the CoM but this not a problem because it can be compensate by an adequate horizontal stab !

For instance, eddie , on a recent post said :

Personally, I disagree with this point of view because LTL gyro are, by far, the more stable and safer gyro you can design. Of course, such a scientific opinion has to be proven.

The Studies of the longitudinal stability of rotary wing aircraft and especially computation of long period mode (phugoid) are not simple. As I know there is no free software that everybody can use to compute such modes and I thought it will be a good idea to try to make one. The GyroKit library is a Java library which was developed for that purpose. The library is not finish yet but it is time to speak about it. This library is distributed under the http://www.cecill.info licence which gives you access to all sources code. The library can be found on my web site here.

The library includes also some programs and the first one developed is the GyroRotor which purpose is to compute aerodynamic characteristics (force and torque, flapping and torsional deflection coefficients) of a rotor in uniform translation and rotation.

The following figure shows an example where data are the one from the Kelett KD-1 rotor. For more details see the user manual of the program that provides you description of input/output parameters of the software.

The next figure shows the results of a simulation where the aircraft speed is 97.68 km/h, rotor incidence 7.079 degrees and blade pitch 5.5 degrees. One interesting result is the twist of the blade which value at 3/4 radius is -1.35 degrees.

Within the library you will find the "applications" package which contains the KD1.java class and the R22.java class.

The KD1.java class compares the results of the GyroRotor program with the data measures in flight as given by the NACA report 600. The two following figures show the flapping coefficient (a0, a1, b1, a2, b2) and the Fourrier coefficients of the blade twist (u0, u1, u2, v1, v2).

The next figure shows the twist of the two bigger coefficients (u0 which is the mean coefficient and v1 the first sine component) along blade radius.

The R22.java class computes the power diagram of the R22 helicopter. The curves shows are compared to the R22 user manual.

The GyroRotor program computes also blade angle of attack distribution. The following figure shows aoa distribution for the R22 helicopter at full speed.

Finally, the GyroRotor program computes also the rotor derivatives with respect to rotor disc frame or body-fixed frame. As the rotor program takes into account the blade twist, it allows computing for instance the effect of twist on Mq derivative.

I will be back on that point on a future post.

Be aware that this program has not been intensively used and that there may be some bugs.

Remarks are welcome.

Jean Fourcade

I have been involved in gyroplane between 1995 and 2004, building and flying a Dominator and studying flight mechanics of this very special aircraft. Then I was interested in other activities.

Few years ago I got interested again in gyroplane, looking on internet, and I was very surprised to read on Tervamaki web site a page concerning gyroplane stability where he speaks about “thrust line psychosis” and concludes that the work of the Glasgow university was a misconceptions on gyroplane longitudinal stability. Tervamaki oppose to the work of Glasgow university a paper from Prof. Laine and the way it is presented make think that there were some mistake on Hounston’s work.

Now this page has changed. The word “misconception” is no more used but there is still a remark (we don’t know from whom) which says that Houston reports have done damage to the evolution of safer gyroplanes.

The current trend concerning the design of autogyros seems to be : ok, we know that in HTL gyro the rotor thrust line goes in front of the CoM but this not a problem because it can be compensate by an adequate horizontal stab !

For instance, eddie , on a recent post said :

eddie said:The thrustline was never the problem of instability,it was the lack of a horziontal stab.The knee jerk reaction was to lower the thrust line. Which with time the horz stab has proven to be the fix. the high rise gyro will become a thing of the past as the new euro gyro is more attractive and flys just fine. Its called progress, some approve and some don"t.

Personally, I disagree with this point of view because LTL gyro are, by far, the more stable and safer gyro you can design. Of course, such a scientific opinion has to be proven.

The Studies of the longitudinal stability of rotary wing aircraft and especially computation of long period mode (phugoid) are not simple. As I know there is no free software that everybody can use to compute such modes and I thought it will be a good idea to try to make one. The GyroKit library is a Java library which was developed for that purpose. The library is not finish yet but it is time to speak about it. This library is distributed under the http://www.cecill.info licence which gives you access to all sources code. The library can be found on my web site here.

The library includes also some programs and the first one developed is the GyroRotor which purpose is to compute aerodynamic characteristics (force and torque, flapping and torsional deflection coefficients) of a rotor in uniform translation and rotation.

The following figure shows an example where data are the one from the Kelett KD-1 rotor. For more details see the user manual of the program that provides you description of input/output parameters of the software.

The next figure shows the results of a simulation where the aircraft speed is 97.68 km/h, rotor incidence 7.079 degrees and blade pitch 5.5 degrees. One interesting result is the twist of the blade which value at 3/4 radius is -1.35 degrees.

Within the library you will find the "applications" package which contains the KD1.java class and the R22.java class.

The KD1.java class compares the results of the GyroRotor program with the data measures in flight as given by the NACA report 600. The two following figures show the flapping coefficient (a0, a1, b1, a2, b2) and the Fourrier coefficients of the blade twist (u0, u1, u2, v1, v2).

The next figure shows the twist of the two bigger coefficients (u0 which is the mean coefficient and v1 the first sine component) along blade radius.

The R22.java class computes the power diagram of the R22 helicopter. The curves shows are compared to the R22 user manual.

The GyroRotor program computes also blade angle of attack distribution. The following figure shows aoa distribution for the R22 helicopter at full speed.

Finally, the GyroRotor program computes also the rotor derivatives with respect to rotor disc frame or body-fixed frame. As the rotor program takes into account the blade twist, it allows computing for instance the effect of twist on Mq derivative.

I will be back on that point on a future post.

Be aware that this program has not been intensively used and that there may be some bugs.

Remarks are welcome.

Jean Fourcade

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