- Nov 13, 2006
- Madrid, Spain
- ELA R-100 and Magni M24 autogyros
- Total Flight Time
- 628 gyro (Sept. 2020)
I read German well enough for simple, specially technical, texts. I find Kant impossible, but I'm able to read, and with delight, the discussions between Naphta and Settembrini in 'Zauberberg'. There was a time when I also spoke it fluently, but that was long ago...Very interesting paper Javier, it seems to support the view held by naca investigators, that it is sufficient to calculate the Fourier sieries for flapping up to second order. How did you come across a German report, do you speak the language? Actually the author makes things even more complicated by using fairly complicated dependent clauses, well them Germans, you know....;-)
Interesting, concept. Think I'll add this to see if the colleges would like to tackle it for us with an open source project??I can't help but believe some talented designer could eliminate 2-per in two bladed rotors. It occurs to me that if a two bladed rotor had TWO properly-phased universal joints and three rotational axes instead of the current two, a smooth two bladed rotor could exist.
The 'two per rev' vibration has nothing to do with the rotor head articulation, but is due to the fact that our semi-rigid rotors have two blades. Hence, in normal flight the relative wind strikes the blades 'full frontal' twice per revolution, and that 2/rev vibration disappears in vertical autorotation, when the horizontal velocity is zero...Now I have always been taught that a 2-bladed tetering rotor does not need lead/lag hinges and dampers because both blades speed up and slow down the same amount.
Really, if we take each rotating component of a 2-bladed rotor system and pigeon-hole it into ELLIPTICAL or CIRCULAR, we will quickly see that the rotor mast has a constant rotational velocity and all the components that rotate about an invisible tilted axis are always seeking a different rotational velocity due to their elliptical paths.
My thought is...this is why we just accept by faith that all 2-bladed rotors have an unavoidable 2-per-rev? The teter bolt or pin is constant velocity and rotates with the mast. The center of mass of each of the components that rotate about the invisible tilted axis (output) travels in an ellipse and at a varying rotational velocity. That difference "thumps" or transmits forces onto the teter bolt or pin into the body of the aircraft.
I can't help but believe some talented designer could eliminate 2-per in two bladed rotors. It occurs to me that if a two bladed rotor had TWO properly-phased universal joints and three rotational axes instead of the current two, a smooth two bladed rotor could exist.
I'll agree. It's really some of the components of the hub that follow an elliptical path and speed up and slow down. The blades do not belong in that group.Bryan,
Conventional studies choose to assume a constant rotation of the drive shaft instead of assuming a constant rotation of the blade in the tip plane .
This is a misleading point of view, because the rotating inertia of the shaft (and engine) is much lower than that of the blades.
It make sense that 3 or more blades are articulated in flapping if it impose to the others a different rotation via the shaft. Then,
their own inertias are fighting each other.
Doman's Rotor or Seesaw rotor does not do it
I believe that most pilots (and non-pilots) here wish to have a better understanding of the (aero)dynamics of rotorcraft, specially of gyros, and the rational, scientific answers given here by a few respected experts are highly valuable for most readers. In this forum, one learns a lot... Knowing the 'standard answers' for an exam may be important, but knowing the 'real', scientific answers is far more important...I'll agree. It's really some of the components of the hub that follow an elliptical path and speed up and slow down. The blades do not belong in that group.
My main gripe with this thread is, for decades...helicopter pilots have been taught rotor system aerodynamics in a certain way that may not pass muster scientifically when hairs are split, but it gives pilots a way of scuba diving in a cave called "Understanding Rotor System Aerodynamics" without stirring up the silt. This forum is not a scientific forum. It's a forum of recreational aviators who may very well be trying to pass an FAA Rotorcraft Written and those questions are not scientific either.