What is Lomcevak?
Dave Johnson asks:
...He executed a Lomcevak...
Is there anywhere on the web people can read about maneuvers like this?
Or does anyone have a good book to recommend that I might find at the
library? I know what an Immelman is, but I don't have the foggiest what a
Lomcevak is...
Dave, a Lomcevak is a much-misunderstood class of negative-"g",
near-zero-airspeed maneuvers invented by the Czechs, where the gyroscopic
precession of the engine and propeller is used as an additional flight
control along with the three usual ones, aileron, elevator and rudder. Yup,
that's right, you can't do a true Lomcevak in a glider unless you bring
along some sort of VERY BIG gyroscope. In fact, it's very difficult to do a
true Lomcevak with any type of model, because the inertia of model
propeller relative to the inertia of the airframe is very low, in
comparison with full-scale aircraft. Although to many folks they look like
a totally out-of-control gyration, they are actually precision maneuvers,
with a specific definition of how they are supposed to look. However, they
are NOT in the Aresti aerobatic dictionary, which is probably just as well;
if they were, then they could be specified in compulsory sequences at
aerobatic contests.
There are a number of English translations of the Czech word "Lomcevak",
but the most popular I've heard is "the way your head feels the morning
after drinking too much plum brandy".
There are many variations of the Lomcevak, but they are generally divided
into five major categories:
The one most commonly seen, the "main" Lomcevak, is entered from upward
inverted flight. As the airspeed decays to near zero, the pilot initiates
an outside snap roll ("flick roll" for you Brits). The aircraft comes to
zero airspeed while rotating about all three axes, and proceeds to perform
three end-over-end negative "g" tumbles, each tumble 45 degrees to the
plane of the last. The maneuver ends when the aircraft begins falling with
enough speed for the airflow past the tail feathers to stop the tumbling.
There is another category similar to the "main", but entered from
knife-edge flight. This one is particularly violent.
The "cap" Lomcevak starts out much like a hammerhead turn, but as the
fuselage rotates to horizontal at the top, a combination of precession and
down elevator cause the aircraft to pivot about the wing in a perfect
pirhouette. The wing remains vertical during the maneuver.
In the last two categories, the "positive conic" and "negative conic", the
aircraft sweeps out the shape of a cone while pointed nose-upwards, with
the bottom of the wing tangent to the surface of the cone during the entire
maneuver. In the positive version, the nose is the apex of the cone, while
in the negative version the tail is the apex.
Lomcevaks are terribly disorienting but otherwise fairly gentle for the
pilot. The same CANNOT be said for the aircraft! All sorts of strange loads
appear on the airframe, ones that were probably never conceived of in most
aerostructures texts, such as high centrifugal forces on the wings. The
worst effects seem to be reserved for the engine mounts, crankshaft and
prop. There have been quite a few cases of major damage to these components
during Lomcevaks. The Yak 18 for example, experienced four crankshaft and
prop failures, and one where the engine was literally yanked off of the
firewall by the roots. Shortly after that, the "powers that be" in the
former USSR declared that anyone caught doing a Lomcevak in one of their
Yak 18's would get an immediate one-way ticket to Siberia!
Probably the best explanation of the Lomcevak (and where most of the above
comes from) is in the book "Aerobatics", by the great British aerobatic
champion Neil Williams. This is an excellent book, one of the best
available on the entire subject of aerobatics. It has an entire chapter on
Lomcevaks. Look for it in your public library, and I've also frequently
seen it in the bookstore at the U.S. Air Force Museum. If you're at all
interested in aerobatics, I recommend you pick up a copy!
Don Stackhouse @ DJ Aerotech
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