Safety Comes First - 2012/02

92 MODEL AVIATION
MIKE POWELL and I had an email
exchange with a few holes in it. Mike
mentioned an incident where a propeller
hub was hand-drilled with the wrong bolt
pattern (maybe more than once), filled with
epoxy, and redrilled to correctly fit the
engine.
Dave Gee | Safety Comes First [email protected]
Don’t mess with perfection
that a new propeller is a bargain compared
to the risk of using one that has been
damaged or compromised.
Mike said the lesson is to never attempt
to repair a propeller, and to use a drill press
and drill guide when making holes in a
propeller hub. The electric-power pilots
used to be more casual about this than the
“gassies,” but the current power of some
electric systems is just amazing. Shortcuts
should not be used when it comes to
propellers.
I’m always glad to get emails from readers.
Some have great topic ideas, others have
scary near-miss stories, and a few take me
to task for goofing up.
My son, Jeff, was the first of many to
send me an Internet link to some video
footage of an amazing test flight. The “evolo”
vehicle is similar to those multirotored
RC model helicopters, with electric
motors on the ends of crossed booms. Such
a configuration is unstable except for a
computer that keeps everything right side
up.
Models of this type have been on the
market for years, but Thomas Senkel, the
constructor and test pilot of the machine,
thought bigger was better. He made a large,
cross-boom rig and put four big motor
propeller assemblies on each arm. The rig is
essentially 16 large, powerful model
airplane electric-powered propeller
assemblies on booms.
Also included in this column:
• Drilled-out propeller hub
• Radio-controlled, manned
helicopter
• Safety issue or consumer
dispute?
• Young pilots use aerodynamics
As you might guess, since you’re
reading about it in the safety column, the
propeller failed and shards flew
everywhere. I didn’t bother to track down
this story for verification, since I know it
has happened to others throughout the
years. There may be a proper and safe way
to redrill a propeller hub, but that isn’t it.
Some modelers think nothing of drilling
or altering a propeller hub, but they
wouldn’t just cut away part of the landing
gear or wing mount or rotor shaft, which
are usually under less stress than the
propeller.
I’m no engineer, but I know it is a bad
idea to weaken or alter such a critical
airframe component. Someone likely did
stress calculations on that hub and I’m not
going to cut a bunch of material away and
then see if it is still strong enough! And
despite my legendary cheapness, I think
Another “Monster Hangar”
build team with their oddball
effort: a Wright biplane. Is
that Dave Gee in the back
row? Will Woods photo.
Below: Okay, it’s a little blurry, but here is
proof that the biplane glider flies. Woods
photo.
Right: These middle school
students salvaged glider parts
to create their own design,
learning about aerodynamics
as they worked. Woods photo.
02sig3.QXD_00MSTRPG.QXD 12/16/11 1:55 PM Page 92The landing gear is a giant, inflated
rubber ball strapped underneath the rig. If
you’re more than 40 years old, you’ll
recognize it as a Hoppity Hop bouncing
toy. Younger folks call it a Pilates exercise
ball. Either way, it’s a clever way to absorb
landing forces.
The video shows this big contraption
taking off, hovering, and landing under
radio control. Pretty cool! Then, it gets
interesting, because a man climbs into a
chair on the center of the machine, and
someone hands him the transmitter! The
rotors start whirling and once again, the
entire thing rises into the air, with a human
pilot sitting amidst all of the spinning
propeller blades, flying himself by radio
control. Talk about First Person View!
People sent me the link because of the
apparent danger to the pilot. He sits in the
same rotational plane as all those blades.
Onboard computers maintain flight
stability, since no human pilot could
possibly keep such a machine on an even
keel. This is certainly not the first aircraft to
depend on computers for safe flight, but the
concept is still a bit hard to accept for some
of us old Free Flighters who are
accustomed to models with built-in
stability.
I’m not sure if this all really relates to
aeromodeling, but I do think the pilot had
nerves of steel to fly that rig. It certainly
looked risky to be surrounded by so many
whirling propellers. One false move or
computer glitch and he would experience a
real Ginsu [knife] moment.
Of course, since this story doesn’t really
involve modeling, a responsible columnist
would never take up valuable space in the
magazine to discuss it. Oops.
Some subjects don’t really belong here, but
there are gray areas. Readers sometimes
email me about problems they have with
hobby products, and they want me to put
pressure on manufacturers to resolve things
in their favor. The matter is often pitched as
a safety issue that affects everyone, but
more often it is a business dispute.
In nearly every case, the manufacturer is
eager to quickly solve any problems with
the product. By the time I hear about an
issue, it usually has been corrected.
Warning everyone about a problem that
was resolved long ago does no good, and
the out-of-date information would be in
print for years.
Although it disappoints those readers,
it’s not my job to get embroiled in
consumer disputes. I’m just a safety
advocate. The fact is that our models are
inherently dangerous. Most have a spinning
airscrew on the nose, and only our care and
vigilance keep us safe. An incident rarely
can be blamed on equipment failure;
accidents are nearly always caused by pilot
error. That’s a reason for staying vigilant as
we have fun with our aircraft.
Remember a few paragraphs ago when I
ranted about altering model airframe
components? There’s a time and place for
everything, because I have a story about
doing something similar.
I work with an active student model
airplane club at Luther Burbank Middle
School in Burbank, California. The club is
full of inquisitive, sharp kids. Local adult
modelers mentor the school-age members
and provide them with a program of
lectures, building sessions, and flying
meets.
It’s a big advantage to learn how and
why a model flies as you progress from
simple gliders to complex models of all
types. Too many adults miss out on these
basics when entering the sport. Sometimes
they pay a price by crashing models that
cannot be repaired. Don’t underestimate the
value of understanding the construction and
operation of your machine!
The best evidence of this is those
popular videos showing RC airplanes
crashing, one after another, with musical
accompaniment. A large percentage of the
models seem to be out of balance, mainly
tail-heavy.
After a few months of meetings, any kid
in the model airplane club can identify that
problem and ask why the pilot in the video
didn’t balance the aircraft before test-flying
it. Of course, being young, they also enjoy
seeing the crashes.
They love to construct their own models
and fly them in the schoolyard and in the
gym. As the middle school kids progress
each year, they consistently ask to “build
something.” This warms my heart, since it
seems to be a vanishing part of
aeromodeling. I am sad to see such an
enjoyable segment of the hobby disappear
among model airplane enthusiasts.
As the school year progresses—and
there have been lessons on aerodynamics
and flight-trimming models—the students
build more complex airplanes. After the
basics are mastered, we schedule a session
of Monster Hangar, one of their favorite
activities. The adult mentors bring bags of
salvaged and new balsa glider parts for the
youngsters to combine and modify into
whatever flying machines they can imagine.
Kids can be open-minded about aircraft
design. Any configuration seems worth a
try, and they want to know why something
will or won’t fly. My crew wanted to make
“something like the Wright brothers’
plane,” despite the fact that this
configuration is fragile, hard to launch, and
fairly unstable in flight. They wanted to
know what angles and sizes were best for
the control surfaces, and then away they
went!
The designers/builders work in teams,
with adult supervision of the CA glue and
tools. Too many children have never built
anything with their hands, and this is a
golden opportunity to help them develop
some skill by letting them measure, cut, and
sand the balsa parts. They are attentive and
use great care with hobby tools.
These little gliders became important to
them and were heavily decorated with felttip
pens and signed by all who helped. No
multimillion-dollar airliner prototype ever
got a more serious rollout than these
oddball gliders, with each team admiring
and worrying about the creations of rival
crews.
Finally, it was time to test-fly the weird
flying machines to determine a winner. The
photos show the results of this session, with
beaming kids, strange models, and a
triumphant test-flight of the “Wrong Stuff”
glider, as it was named by the builders. MA