# Study of flight dynamics of a gyroplane in gliding flight

#### Jean Claude

##### Junior Member
Juergen
Of course, the result of JavaFoil confirms those of the DLR report because it is established on the same 2D false hypothesis.
I can not contain my laughs of the same reasoning (approved by H Dudda) if he had show the mast!

As I explained, neither the mast nor the tube representing the faired airframe does not have the infinite length that 2D reasoning assumes.
The error is gross.

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#### kolibri282

##### Super Member
Airplane design has been based on 2D data for a hundred years and thousands of successful aircraft have been designed using 2D profile data, so as a first approximation that gives you an idea of the order of magnitude of a problem 2D is perfectly ok. Of course there is an error but if you don't have anything better an engineer will be glad to use the data to come up with the best answer available and refine the model later, if need be. To me, as an engineer, a statement like "The error is gross" without offering at least a figure telling us what the order of magnitude of the error is sounds unprofessional. In engneering we dicuss figures not feelings.

#### Jean Claude

##### Junior Member
Juergen,
You know, like me, that an airplane wing is very long compared to its thickness (more 50 times), which makes the approximation of the 2D flow quite satisfying.
In the case of the gyroplane fuselage, the length is less than 2 times the thickness. Therefore It is unprofessional for an engineer to use a calculation method without checking the purview of application.

#### C. Beaty

##### Gold Supporter
As they say about computer projections; “Garbage in= Garbage out.”

#### kolibri282

##### Super Member
That's true, Chuck, but the first theorem of simulation states:"All models are wrong, some models are useful". We are all aware that only a fully fledged 3D CFD analysis would reveal the true fluid flow but that is also true for a propeller and those ones have been successfully modeled for a century with something as simple and far from the real flow as "actuator disk theory". So the question still is: do the shortcomings of the model, of which we are all aware, render the model completely useless or does the model still allow to gain some insight regarding gyro accidents in a crosswind?

#### C. Beaty

##### Gold Supporter
Juerqen, If Herr Duda’s hypothesis was to be taken seriously, gyros with full bodywork such as MTOs would be much too dangerous for average pilots to fly; they should only be flown by professional test pilots.

He talks about flow over the fuselage stalling the rotor; the only way a gyro rotor can be stalled is by removing the load*. Even in high speed flight where a substantial portion of the retreating blade is stalled, a correctly designed rotor will force the cyclic stick against its forward stop and cause a climb well before catastrophic stall is encountered.

*That’s a confusing statement; the rotor slows by removing the load and stalls when the load is reapplied.

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#### C. Beaty

##### Gold Supporter
I don't mean to imply that hiding a Bensen’s bare bones behind fiberglass boat panels is totally benign.

For satisfactory yaw stability, the center of pressure (CP) of the fuselage/vertical tail surfaces should trail the CG.

The CP can be approximated by balancing a cardboard cutout of the side view on a pencil point. This is technically the centroid of area but is close enough for an approximation of center of pressure.

#### Jean Claude

##### Junior Member
We must also keep in mind that with a left or right 45 degrees nose slip, the horizontal tailplane only receives a flow of 70%, and produces only half the force predicted for to oppose the HTL

#### C. Beaty

##### Gold Supporter
There are many design flaws totally unrelated to rotor stall that can kill you; yaw instability and HTL are only 2 of them.

The sad part of this is that Cierva had solved most of these problems in the 1930s; differential lift settings of the horizontal tailplane to cancel propeller torque roll, a balance between dorsal and belly fins to cancel throttle/yaw coupling and of course, CLT.

Unfortunately, modern gyroplane “designers” have, for the most part simply dolled up Bensens to look like something intended for space travel.

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