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octagon

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octagon last won the day on August 6 2018

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About octagon

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  1. Somehow the Bee Gees fit the Robbie perfectly, awesome video.
  2. Sorry, butters, didn't mean to sound like it was a complaint or anything. Your explanation makes sense. I just have never seen an industry with this dynamic before, it's really strange to me.
  3. I don't understand the economics of this. An R-44 is worth around three quarters of a million dollars these days, how does it make economic sense to put the machine in the hands of a pilot who will accept $10/hour in wages? I guess there are highly skilled, experienced pilots who are retired and just want to fly?
  4. Sorry for two separate posts, but I think there is a size limit for attachments.
  5. Also, since LTE happens in high power, low airspeed environments it seems like it makes entering autorotation kind of a moot point, unless you are operating outside the shaded area of the height-velocity diagram. This seems extremely unlikely unless you're in a 500' hover or something.
  6. I hate to ruin a great thread with a stupid question, so apologies in advance. But I am puzzled by the effects of LTE. I read AC-90-95 and it makes perfect sense to me, intuitively. In that AC they make a special note that it's normal to operate in conditions that are conducive to LTE, and that the danger lies in not being prepared for it and allowing an uncommanded right yaw rate to develop into a loss of control situation. But the procedure they recommend also states that you may need to enter autorotation to stop the yaw. What I don't really grasp is how LTE can develop into a situation that can't be stabilized except by entering autorotation. I was thinking along the lines of what nearly retired was saying: with a right crosswind not only is there a right yaw moment due to weathercocking, but the airflow from the right also acts to decrease the angle of attack of the tail rotor blades. Both of these conditions require additional tail rotor pitch to counteract. And conversely, a left crosswind both induces a yaw to the left by weathercocking, and also increases the angle of attack of the tail rotor blades, both of which allow the pilot to use less left pedal. But when a right yaw is allowed to develop in a LTE situation the right yaw rate should act like a left crosswind as far as the tail rotor is concerned, making the tail rotor more efficient, and the higher the yaw rate the greater the gain in efficiency for the tail rotor. Additionally, it seems to me that with a significant yaw rate the tail rotor would not stay in vortex ring state, as it would be moving into fresh air constantly. This dynamic stability makes it seem to me that one can always recover from a runaway right yaw without entering autorotation, even in the fully developed case, given enough time. But there is also the issue of torque being lost to rotating the fuselage, which i'd imagine would result in a decreasing main rotor RPM relative to the air (obviously the governor would try to maintain NR relative to the fuselage but the fuselage itself is rotating in this case). It seems pretty obvious to me that the last thing anyone would ever want to do would be to pull pitch in an LTE situation where you have a fully developed right yaw, so you'd need to accept losing some altitude. Is this why so many crashes are caused by LTE, just not enough altitude for the pilot to recover? If so, I wonder how much altitude you'd need?
  7. Do all users require moderator approval to post in this forum? Is there anything I can do to apply for permission to post here without the delay of moderator approval? Not a big deal, I don't mind it, just curious.
  8. My understanding of the effect of dissymmetry of lift was that an imbalance between the advancing and retreating blades, for example as airspeed is increased, results in fore-and-aft tilting of the rotor disc (flap back), which is corrected by forward cyclic. The pilot increases pitch of the retreating blade relative to the advancing blade by applying forward cyclic, not right cyclic -- is that not correct? My understanding of the need for left cyclic when transitioning through ETL is due to an imbalance in lift production between the forward and aft halves of the rotor disc (inflow roll/transverse flow effect), which like the above case causes a response from the rotor disc 90 degrees later. I can't think of an effect that would require right cyclic as speed increases, and even more confusing is that it appears to be required at 90kt but not at 100kt...
  9. Figure 2-33 is very interesting, so I found a copy of FM 1-51 from 1974 and bought it online. Excellent purchase but unfortunately there is no in-depth explanation of that diagram in the FM. I'm wondering about the lateral displacement of the cyclic in the diagram. In a hover some left cyclic is needed to correct for the translating tendency caused by the tail rotor thrust, and at low forward airspeed left cyclic must also overcome the rolling tendency caused by the transverse flow effect, so that part seems straightforward. At higher speeds it seems reasonable that transverse flow effect is negligible and the vertical stabilizer reduces the need for tail rotor thrust, so left cyclic is no longer needed. But why is right cyclic needed at 90kt?
  10. Yeah, I realized just after posting that how silly an "overslung" hub would be. Like if you inverted the normal underslung hub so the tettering hinge was below the plane of the rotor disc. You'd basically have a flexible shaft then, and the "correction" applied when the blades flap would be in the wrong direction. The shaft would want to whip and the rotor would tend to whirl about the shaft axis pretty vigorously. I don't think you'd be able to fly a helicopter with a hub like that.
  11. https://patents.google.com/patent/US4580945A/en I am curious about the tradeoffs involved there. Not much info on "overslung" rotor systems.
  12. I really enjoy Mr. Schramm's explanation: The whole series of Helicycle engineering videos is pretty great.
  13. http://helicopterforum.verticalreference.com/topic/7512-r22-fuel-stick/
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