Re: Disymmetry of lift.....


"The OTHER Kevin in San Diego" <skiddz "AT" adelphia "DOT" net> wrote in
message news:ojd2m1p39pf0dmeac8imna5f6lu27v2v4l@xxxxxxxxxx
> On Thu, 27 Oct 2005 18:20:47 GMT, "Steve R"
> <srhodes13@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
>>Probably 99% of the models I've flown are of the semi-rigid rotor type.
>>That includes, The Champion, Scout, X-Cells, Intrepids, Shuttle ZX's, and
>>most currently, my Freya. My first model was a Horizon and it was a
>>flybarless, rigid system with wood blades. The composite rotor blades we
>>have now, didn't exist back then. I've also flown Shuttles and mainly the
>>old Kyosho Concepts with the DDF heads that would be considered fully
>>articulated.
>
> Doesn't semi-rigid imply some sort of teetering or flapping hinge? I
> ran home at lunch to check out the Raptor rotorhead.. There's a
> LITTLE bit of up/down movement in "slop" of the blade grip's bearings,
> but not much...
>
The head axle, or cross shaft that holds the individual blade grips is
supported by a set of o-rings. It floats, to one degree or another and
allows a certain amount of flapping. If you grab each blade grip with each
hand and rock them back and forth in a "flapping" type motion, you should
see some flapping action within that cross shaft. The slop you mention
between the blade grips and it's bearings are just a Raptor trait. When the
rotor system is spun up, centrifugal force should pretty much take care of
that slop.

> Never seen a DDF head. Was it truly fully articulated with flapping
> and lead/lag hinges?
>
DDF = Duel Damped Flapping If you ever run into an orginal Kyosho Concept,
or the orginal Hirobo Shuttles, you'll find that each main blade grip was
mounted to it's own flapping hinge and is independant of the other blade.
It's the closest thing I've seen in the modeling world to emmunlating a
fully articulated full size rotor system.

>>Flapping, as I understand it, is the primary means whereby the rotor
>>system
>>compensates for dissymmetry of lift problems.
>
> Correct. Advancing blade has faster relative wind than the retreating
> blade (Assuming some sort of horizontal airflow across the rotor disc
> - we'll deal with forward flight only here for simplicity) and
> therefor creates more lift. This causes the advancing blade to want
> to fly "higher" than the retreating blade. This upward motion
> increases inflow and reduces the angle of attack, reducing lift.
> Conversely, the retreating blade's downward motion decreases inflow
> and the AoA is increased, increasing lift.
>
>>I've noted that the models do
>>show a "slight" shift in roll cyclic trim, rolling away from the advancing
>>side of the rotor disk after entering translational lift.
>
> This is actually transverse flow effect causing the roll. In full
> scale, you don't really feel the roll too much, but you definitely do
> on approach as your speed approaches 25-30 knots..
>
Oops, yeah, I think you're right. I hadn't run into the term "transverse
flow" in a long time. I remember a conversation a "long" time ago where the
speculation was that, considering the size of an average models rotor disk,
that transverse flow isn't as much of an issue as it would be in full size
birds. The colume of air coming over, and being accelerated by, the rotor
disk simply isn't there long enough to significantly change the velocity of
airflow between the leading edge of the disk and the trailing edge. What do
you think?
>
>
> My bro-in-law has an old X-Cell 60.. I'll take a drive over to his
> place and check it out. Kinda sounds like the fuel tube stuff was
> used as a sort of elastomeric damper to tame the flapping a bit..
>
Assuming it hasn't been upgraded. X-Cells don't use this system any more as
far as I know. It may still be used on the base level X-Cell 60. I tried
looking that up but didn't have much luck.

Fly Safe,
Steve R.


.

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