More Questions about coning forces & rotor noise!!

On Fri, 05 Mar 2004 04:52:00 GMT, (John) wrote:

When you do an auto rotation from a power on cruse condition you drop
the collective and at THE SAME TIME move the cyclic back and to the
right to reload the rotor system for the new rotor airflow condition.
If you do the transition correctly you NEVER unload the rotor system.
If you do NOT move the cyclic when you drop the collective then yes
you will unload the rotor and you will loose rotor RPM rapidly because
the airflow has to flow up through the rotor in an auto rotation and
it will not do this until the rotor is tilted back to allow this.

We did dozens of entries to autorotation during a couple of Test Pilot
School Exercises with an instrumented aircraft (Gazelle). From the
instrumentation data gathered it was very clear that the aircraft
would enter autorotation very nicely if no longitudinal control input
was made as the collective was lowered.

I remember wondering a bit why this was the case (although I am an
engineer, and not a RW pilot myself, I had read your explanation above
in a number of texts) and making a couple of quick calculations;
When the collective is promptly lowered, the momentary low load factor
will very quickly result in a downward speed component of the
aircraft. This will of course then generate the flow up through the
rotor. ( If you do a 0g lever drop, which is not awfully aggressive,
you will obtain a 2000fpm rate of descent in about a second, from high
school math, right?) At least this was how I explained this to myself
then.

I do not know, what is the exact procedure for the entry to
autorotation in the British military, but the way the exercises were
conducted was to use cyclic to keep the aircraft attitude steady
during the entry (or in a few instances to do nothing with the cyclic
during power chop and entry to auto to observe the engine failure
cues). No deliberate back cyclic was applied in order to retain load
factor.

Mikko

(Disclaimer: The above is mostly my own observations. Please keep
doing your entries to auto as you have been trained and as your flight
manual tells you to.



The coning may flop around some during the power to auto transition
but when a steady auto is established the cone angle is very nearly
the same as at hover because the horizonal and vertical forces on the
blades are almost the same. There is some difference in where the
center of lift is verses span distance on the blades between an auto
and powered flight but this also varies with the amount of twist built
into the blades.
John


On 2 Mar 2004 05:30:47 -0800, (Eric D)
wrote:

If you start a descent from cruse by reducing pitch and maintaining
rotor speed, what happens to coning forces as compared to cruse?

I have noticed that during a decent in a R22 that you can get a
"Wop-Wop" noise from the main rotor blades. Changing cyclic or
increasing rotor speed a very small amount can make it go away, or at
least not heard from the cockpit. Can someone explain what is
occurring and why?

Thanks,

Eric D