scott@opus.UUCP (Scott Wiesner) (11/12/84)
What is the "correct" procedure to get out of a flat spin? I only work
with models, but the theory's all the same I'm sure.
While flying last weekend, a friend and I decided to play around with
"snap" manuevers. My friend has a fast "pattern" plane, complete with
retractable landing gear. He would pull vertical, keep the power on,
and pull full up and full left rudder. The plane did a couple of violent
snap rolls, and then started tumbling as it lost all it's airspeed. It
was really wild to watch, so we talked about it a little, and the next
time, he threw in some down elevator as the plane started to tumble.
He was still at full throttle, and were hoping to see it tumble forward
(lomchevack?). Well, all of a sudden, the plane was in a very flat spin.
I would estimate the nose was only about 20 degrees down. The spin rate
was about 1.5 rotations per second I think. Still at full throttle, and
giving right rudder and down elevator did absolutely nothing. The spin
started about 150 feet up, so there wasn't much time to try a lot of things.
When it was obvious nothing would help, he chopped the throttle, and watched
it helicopter in. The decent was quite slow, so it was like a bad dream in
slow motion. As soon as it hit, we ran out to the plane, and discovered
there was NO DAMAGE! He had left the gear retracted, and the plane hit in
fairly high weeds. All he could find was a small scratch on the bottom of
the wing which he said was probably already there.
Is there anything he could have done to get out of the spin? Another thing
I wonder about is whether he would have been able to pull out in time assuming
he had gotten the spin stopped.
--
Scott Wiesner
{allegra, ucbvax, cornell}!nbires!scottkiessig@idi.UUCP (Rick Kiessig) (11/14/84)
From "Aerobatics" by Neil Williams:
"If we look at the flat spin from inside a Zlin 526,
we will see that it can be entered from any position which
will permit a normal spin. If we first establish a normal
spin to the right, and wait for it to stablise, we will note
that it is faster than the left hand spin [the prop on the
Zlin goes to the right -- RK], with the nose a little higher,
about 50 to 60 degrees, and we have about 5 to 10 degrees
of bank to the right. If we now apply full left aileron,
still keeping the stick back, the nose will come up to about
45 to 40 degrees, with a faster rotation and less bank. If
we now apply full power, the nose comes up dramatically
to about 10 degrees below the horizon, and we really start
to rotate, but the vertical decent has now slowed. To complete
the requirements for the flat spin, still with full power
and full aileron, push the stick fully forward! By now the
nose will be on or above the horizon in a fully developed flat
spin in the best sense of the term. The reason for this
forward stick is thought to be that it blanks off the fin
and rudder, which are now moving so fast that they are
tending to slow the spin.
"To recover, as one would expect, one merely reverses
the operation. Stick back, throttle closed, ailerons neutral,
and when the aircraft stablises full left rudder and stick
forward. It will take up to 2.5 turns to stop, and it will
feel longer, so don't panic; just give the recovery action
time to work."
End of quote
You can also enter a flat spin directly, like from the
top of a slow outside loop, which sounds more like what happened
to the RC plane referred to in the original article.
You can also do this manuever inverted.
The lomcovak: There are five different kinds. The
"Main Lomcovak", "Cap Lomcovak", "Positive Conic Lomcovak",
"Negative Conic Lomcovak" and another one which is initiated
from sliding knife flight in a 45 degree climb. This last
one is interesting to watch because the plane will actually
go upwards, backwards! The conics make the plane look like
a kids toy top spinning around - positive is with the prop
staying relatively still, and negative is for the tail staying
still. Cap and Main are too hard to describe without drawing
a picture. All of them are gyroscopic manuevers, though;
made possible by the gyroscopic forces of the engine and
prop. As such, the throttle is a critical element of control.
Again, from "Aerobatics":
"The 'main' lomcovak is entered from a climb which
is slightly over the vertical, the level speed before the
climb having been as described above [biplane: max. straight
and level speed, monoplane: 85% of max. S&L speed -- RK].
If the propeller turns anticlockwise as seem from the cockpit,
the inverted flick roll [i.e. snap roll -- RK] is initiated
with left rudder, and stick forward and to the right. At this
point the flightpath precesses owing to engine/propeller
gyroscopic forces, and the aeroplane reaches a state where
all the rotation is about the lateral axis in a forwards
direction, this axis being vertical with respect the the earth.
"A this point one has the option of leaving full power
on and continuing with the 'main' lomcovak, with the lateral
axis itself precessing after the first turn until it is again
horizontal; alternatively, one can use the throttle to acheive
a 'cap' lomcovak. In the first case, if the entry has been
fast in terms of control application, it can produce three
complete turns; the last being a forward loop on the spot
with nil airspeed. It can also cause damage to the aircraft,
so I personally restrict it to two turns, by entering the
figure more gently. One can also finish up in an inadvertant
tailslide, with fully deflected controls.
"By leaving full power on, a steady roll around the
longitudinal axis of the aeroplane can be maintained: this
is not due to the ailerons because airspeed is almost zero.
In the case of the 'cap' lomcovak, the intention is to make
a forward loop of 360 deg. with the lateral axis vertical to
the earth; therefore the engine is used smoothly as an
extra aerodynamic control to prevent any further roll
around the 'A' axis once the 'B' axis is perpendicular.
Since the rotational force for the complete manoeuvre comes
from the engine, throttling down will slow the pitch rate
almost to zero, and this should be reached after one
complete rotation.
"In our aircraft as described above the right wing
will be towards the ground. The stick is pulled fully back
and left full rudder is applied: this initiates a sideslip
to the right, just enough so that when the rudder is reversed
and power applied, one exits in the same manner as from a stall
turn to the right. If this rudder reversal technique is
not used, the aeroplane will roll onto its back and sink
out of control."
End of quote
Well, you get the idea. I'd be interested in hearing
from anyone who has a chance to play with any of these moves
using RC equipment.
--
Rick Kiessig
{decvax, ucbvax}!sun!idi!kiessig
{akgua, allegra, amd, burl, cbosgd, decwrl, dual, ihnp4}!idi!kiessig
Phone: 408-996-2399marcum@rhino.UUCP (Alan M. Marcum) (11/15/84)
In many aircraft, flat spins are unrecoverable without, for
example, a "spin chute" (a parachute, usually beneath the tail,
used for breaking unrecoverable attitudes). Sammy Mason's
_Stalls, Spins, and Safety_ provides interesting insights into
the dynamics of spins, inverted spins, and flat spins.
The observation of little damage has been found in other flat
spin incidents. Because of the speeds and attitude of the plane,
the energy of the impact can be absorbed by the airframe. The
plane ends up being squashed, but the occupants don't.
--
Alan M. Marcum Fortune Systems, Redwood City, California
...!{ihnp4, ucbvax!amd, hpda, sri-unix, harpo}!fortune!rhino!marcumron@brl-tgr.ARPA (Ron Natalie <ron>) (11/16/84)
He Gad, you nearly gave me a heart attack. If you are going to post things to net.aviation like this, please be sure to state that you are talking about RC planes. -Ron
lgl@cbosgd.UUCP (Lionel Lynch) (11/24/84)
In article <5811@brl-tgr.ARPA> ron@brl-tgr.ARPA (Ron Natalie <ron>) writes: >He Gad, you nearly gave me a heart attack. If you are going to >post things to net.aviation like this, please be sure to state >that you are talking about RC planes. > >-Ron <HELLO> Yup! you really had me going there for awhile! This would have been interesting material for a novel especially since you lived to talk about it. Has anyone experienced this first-hand?? -Lionel (cbosgd!lgl)