"Arerodynamics of Gyroplanes"

kolibri282

Active member
Jean Claude,

as usual I am a bit confused since there is no sketch labeld 5 and in answer #5 there is no sketch. If you have a vector that has two non zero components it is of course rubbish to drop one of them. Please elaborate if this is the case.
PS: much of the confusion seems to lay in translation. Veullez vous, chère Jean Claude, svp attacher votre texte aussi en français, merci!
 
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kolibri282

Active member
Dans fig. 5 l'auteur essai d'expliquer comment la commande de l'autogir soit arracher du pilot par la force de trainé, la pousse n'as pas de bras de levier en ce cas es apparait pas.

Figure 5 explains how control is wrenched from the pilot by drag force, the thrust does not have a lever arm and therefore does not appear.
 
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Jean Claude

Junior Member
Juergen, Comme l'auteur, vous oubliez la portance. Ici la résultante rotor (RTV) n'a pas de bras de levier, mais la portance en a un.
La trainée n'est pas la cause qui tire le manche. Pas de trainée sans portance.
Juergen, as the author, you forget The Lift. Here, RTV has no lever arm, but the lift has!
Drag is not the cause that put the stick. No drag without lift.
 
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kolibri282

Active member
I didn't forget lift, I just set the lever arm to zero since it is very small anyway and the thrust would counteract the moment generated by the drag force so you err to the safe side. This is good engineering practice and probably more important in this case since we are considering a dynamic phenomenon where you can not be sure, whether the static formula for H force gives a good approximation. That way you get a safer estimate.
 

Jean Claude

Junior Member
I didn't forget lift, I just set the lever arm to zero since it is very small anyway
No very small. About 1/5 lever arm to Drag

the thrust would counteract the moment generated by the drag force .
The thrust or the lift? is not the same thing. Difference 10° is not negligible.

so you err to the safe side.
I did not say not to shift the axis of bearing. I said that the cause is not the ratio Lift / Drag. The real cause is the flapping angle, which can reach 8 degrees in certain flight conditions. The safety offset is therefore that indicated by Lovegrove, but for an entirely different reason.

Jean Claude
 

kolibri282

Active member
JC->The thrust or the lift? is not the same thing. Difference 10° is not negligible.
The cosine of 10° is 0.9848 the difference between lift and thrust is therefore 1.5%, that is why the so called small angle assumptions are almost invariably used in rotorwork since the errors in calculating the forces are usually much larger unless you use a numerical rotor model that takes into account a plethora of variables.
 

Jean Claude

Junior Member
Juergen, I agree with you: difference on value is negligible. But difference on the lever arm is basic, as shown in my sketch post #24
A good engineering practice is certainly having an understanding of basic phenomena and, better yet, secondary phenomena. Chuck thinks like me : "Rotor lift/drag ratio has nothing to do with it", contrary to the reasoning of Peter Lovegrave and yours.
 
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C. Beaty

Gold Supporter
Mr. Lovegrove also states that rotor drag increases with airspeed. That’s also backwards.

Cyclic flapping angle increases with airspeed.

So we now have a rotor-head and the machine which dangles from it, in beautiful balance. it will happily fly 'hands off' in that situation. If we want to fly faster and still 'hands off', the rotor drag may increase, so we will have too much effort trying to pull the torque-beam into the 'climb' mode. But, Hey , presto! we simply relax the tension on the trim spring with our inflight pitch trimmer, and its contribution to the rearward moment is reduced and the head system comes nicely back into balance.
 
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kolibri282

Active member
Most modern day trainee gyro pilots have experienced the brutality of the forces developed when they mess up their rotor starting and their little 22 foot (6.7 m) rotor decides to start flapping.
To me this sentence seems to state very clearly that the author sees flapping as the source of the rotor force component which the pilot has to control (or may no longer be able to control) or do I get the meaning of the sentence wrong?

He uses the term "Drag" for the force component in the negative x direction which is consistent with using lift for the upward component. If you carefully study the drawing you see that this "Drag" force is almost as large as the lift force and the resultant is not aligned with the axis of rotation but inclined backwards. So his "Drag" force includes the component of rotor flapping. I feel that the confusion comes from the fact that in rotor work "Drag" is not the inplane force component that is perpendicular to thrust but sums up all force contributions along the x axis. That inplane component of a rotor wich lays in the tip path plane is called H-force therefore the L/D ratio of the rotor alone is thrust devided by H-force (thrust/H-force).
 

Jean Claude

Junior Member
He was able to convince you with sketches false, and I could not convince you with sketches correct. Boo ... It's not fair ... My English is so bad ?
Jean Claude
 
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kolibri282

Active member
JC->My English is so bad?
Your sketches easily bridge any gap in comprehension that might occure due to the fact that we communicate via a lingua franca.
Thanks for your insisting on clarifying the matter!
 
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Resasi

Gold Supporter
Now I feel bad for obviously introducing someone who had it all ass-backwards.

I'm off for a beer.:eek:hwell:
 

C. Beaty

Gold Supporter
JC, your English is much superior to my machine translations of French to English.

When I use Google or Yahoo for translation: French in = gibberish out (Google says gibberish = charabia).

I expect the reverse is also true.
 
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Jean Claude

Junior Member
Thank you Chuck. With Google I can understand simple sentences. When they are more complicated, so I'm not always sure that the translation is your thoughts.
 
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