The Apache tail rotor is, as you note, actually a pair of stacked tow-bladed
teetering rotors. There have been claims that the unusual blade spacing
you're asking about was intended to reduce noise. While the spacing may
give some noise benefit, the real reason for the orientation is simple: it
was how the blades would fit. If you look at an Apache tail closely you
will see that if you tried to orient the outboard rotor at 90 degs from the
inboard rotor, the pitch links for the outboard rotor would interfere with
the inboard blades. (The interference geometry is largely a result of the
skewed teeter hinge, which is needed to get the desired pitch-flap coupling.
This pitch-flap coupling reduces the flapping of the tail rotor in rotor
flight.)



"Tim" wrote in message
...
Hi,

Please can anyone explain to me what the tail rotor on the AH64 Apache is
all about? I see that the two pairs of blades are actually in different
planes and only at about 30degrees spacing.

What's the thinking behind this?

(I'm into radio controlled helicopters and considering how/whether to
replicate this on a model)

Thanks,

Tim


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