gregj
Heliman
Location: Palos Verdes, Calif.
| > This is probably a silly idea but......
>
> With all this wind we have now, got me thinking of slope
> soaring. Do you think it would be possible to fly a heli off a hill,
> switch off the engine and have enough lift to keep it flying in
> autorotation?
>
Hi smudge,
I've been slope-soaring helis for a while here in Southern California.
It's a SERIOUSLY fun thing to do, not least because of the reactions from
observers.
I slope-soar a Hirobo Shuttle, and do it at a couple of strong slope soaring
sites overlooking the ocean in Palos Verdes. It takes a good bit of wind -
something like 12-14 knots. I find that it if there are white caps on the
ocean from the wind, it's probably strong enough to slope-soar the heli.
When I slope soar the heli, I remove the engine, canopy, 2 servos, tail
rotor, gas tank, gyro, etc. I.e., it's a really stripped down bird. Might
be better say what's there rather than what's not! Just 3 servos (collective,
2 cyclic servos), receiver, batteries, frame, head and blades, landing gear,
tail boom, and vertical stabilizer. (The latter for weathervaning
while flying).
I set up the collective to go from about -7 to +12.
To get the heli started, I stand at the edge of the slope and hold it
overhead with my left hand, gripping it by the top of the frame just behind
the main shaft.
I move the transmitter collective stick all the way down. (It is essential
to have a transmitter neck strap to do this, since you only have one hand
to manipulate the transmitter controls!) Slowly at first, the blades start
to turn. They gradually pick up speed. As they go faster, the angle of
attack the blades see decreases, and at some magic moment they unstall.
Then, the blades suddenly start going REALLY fast! I then use cyclic to level
the helicopter.
As the blades are cranking at their high speed, I move collective up.
It is easy to find the collective setting that maximizes lift; you can feel
the lift on the hand that is holding the helicopter. At this point, the
helicopter is straining hard against your hand, pulling upwards.
With your right hand on the cyclic stick, say a prayer (;-)) and release
the helicopter. It will shoot straight up maybe 30 or 40 feet. As it
does so, the blades will slow down, and reach a steady rate. At this
point, I take my left thumb off the collective entirely, and fly only
with cyclic. (I found the hard way that if the heli starts to settle it
is easy to subconsciously add in collective, and cross that threshold where
the blades will no longer keep turning. Lose head speed fast, come down
over the cliff line fast, ..., not good.)
As long as the wind hangs in there, you can stay up as long as you want.
You can use cyclic to fly back and forth along the ridge line. The
vertical stabilizer on the tail will ensure that the heli weathervanes, and
keeps going forward, nose into the direction of flight.
You can play the collective up and down a little, always making sure not
to push it too high and suddenly lose head speed. And, you can do a
"flare": pull back on the cyclic to expose more of the rotor disk to the
wind, and see the heli shoot up and somewhat back.
To land, I use cyclic to hover at altitude just behind the edge of the
cliff, and then use collective to slowly lower the heli. The goal is to
set the heli down on the ground at the edge of the cliff. But, it gets a
little dicey, because at some point you descend into the "shadow" of the
edge of the cliff and out of the wind. Expect a lot of "adventurous"
landings if you try this. But, the good news is that most crashes are
low-energy affairs and don't hurt the heli too much. Also, head balance
etc. seems much less critical doing this than flying with an engine.
Tail boom strike? No problem! Just bend that tail boom straight and
throw it off the cliff again! (The only thing the tail boom is doing is
holding the vertical stab; no tail rotor, etc.)
I think it would be really wild to try some aerobatics this way. The
ultimate would be to go inverted and slope soar back and forth along the
cliff inverted. Haven't done any of that though.
All in all, this is a lot of fun!
gregj |
