Model Forum / Radio Controlled / Helicopters / November 2005

I can be sensitive in pitch attitude but I didn't find it to be as bad as
they make it out to be.  Even with those old mechanical gyros, it was more
than controllable.  Also, I wouldn't characterize it's yaw responses as
sluggish.  They're not as crisp as a standard tail rotor can be.  The deal
is, the model is relying on lift vectoring from the front and rear rotors to
start and stop the yaw motions.  That means that once you apply a yaw
command, the front and rear rotor planes tilt opposite each other
(differential roll cyclic) and the fuselage starts to accelerate in the
commanded directions.  Likewise, when you want to stop the rotation, the
rotor disks have to tilt the opposite direction and it takes a split second
for everything to decelerate and come to a stop.  Come to think of it,
having just tried to describe the process here in print, maybe sluggish
isn't that far off in terms of a descriptive word.  It's just that in actual
practice, it's not as bad as my description makes it out to be!  :-)

As for blade stalls?  I can't imagine the kind of control yanking it would
take on this model to induce one.  Even if it is possible, this isn't the
kind of model that should be flown that way.

Fly Safe,
Steve R.

And it does that with aplomb Kev. That's why they fit a gyro to the pitch,
but the old gyro's wren't quite up to the job. A nice new HH would probably
be a massive improvement though.

Still, it's be cool to

Best doing that with a BIG plastic bag filled with Oxy and a sniff of acet,
finished off with a taper of masking tape soaked in gasoline. Fit cat to
"balloon", fit taper to ballon, light taper and let go.

The heights gained are almost unimaginable if the taper's long enough and
the bang?? Wow. The cat's actually pleased to leave the area:-)

--
Beav
OMF#19
VN 750
Zed Thou

mail is beavis dot original at ntlworld dot com (with the obvious changes)

Well, that's the main issue, isn't it!  I was always conservative with this
bird, for what I consider to be obvious reasons!  :-)  I never let it get
moving too fast in any direction and thus, never had any "major" scares with
it.

About the only thing it did that was disconcerting was, when transitioning
from forward flight back to a hover and I'd power down for the approach, the
tail (rear rotor) would drop out and it would pitch nose up, drastically!!

The layout of the rear rotors controls is such that there is no direct
for/aft cyclic commands from the pilot.  The for/aft cyclic was rigged via
the geometry of the linkages to change with collective movement.
Supposedly, the rear rotors cyclic was neutral at a hover position.  Adding
collective above that point would feed forward cyclic.  Lowering it below
that point would feed aft cyclic to the rear rotor.  I "think" the combined
effect of lowering the collective and applying aft cyclic was what caused
the rear rotor to fall out, as it were.  The first natural response to this
was to feed hard forward cyclic.  This would help level the fuse but it
would also introduce a large differential collective between the for and aft
rotors.  What happens when you do that??  The torques no longer cancel each
other out so now the nose swings around and it's hard over on the yaw
control to keep that in line.  All of this resolved out when powering back
up  to hover but it sure got the pucker factor in the ozone in the mean
time.

My fix was to reposition the for/aft cyclic link on the large "L" collective
lever on the rear rotor.  The effect of this was to "greatly" reduce the
amount of for/aft cyclic change to the rear rotor with collective changes.
It still wasn't perfect but I think it helped a lot!

Fly Safe,
Steve R.