Radio Control Slope Soaring - 2009/12

116 MODEL AVIATION
SOMETIMES A FOAM sailplane crashes so hard that it looks for
all the world beyond repair. This is a sad event, and under the “You
only hurt the ones
you love” doctrine,
it’s sure to be a
model that you
really like to fly.
This happened to
me on a practice day
before the 2009
Midwest Slope
Challenge (MWSC)
at Wilson Lake,
Kansas, in May,
when I crashed my
60-inch-span Leading Edge Gliders (LEG) EPP-foam P-80 Shooting
Star—a favorite of mine for many months and a slope sailplane rated
“must have” by the New York Slope Dogs. I dorked it hard enough
to nearly tear the nose off of the model in a cartwheel landing.
[[email protected]]
Radio Control Slope Soaring Dave Garwood
Foam airframe repair after a bad crash
Also included in this column:
• Onboard battery care
• Updates at CR Aircraft,
Magnum Models, and SkyKing
RC products
A 120-inch-span DAW Ka6E soars in slope lift at Lucas Park, overlooking the Wilson Lake Dam, during the 2009 MWSC. Alex Paul
photo.
Mike Bailey shared his experience, helping Dave fix a shattered
slope jet. Mike inspires confidence and enthusiasm for the task.
Mike restored this LEG P-80, which the previous owner crashed
and discarded. Notice the covering’s subtle shade difference;
everything in front of the “F” in “FT-490” is fixed.
Dave’s LEG P-80 with its nose rebuilt. Dark lines intersecting “US
AIR FORCE” are flat carbon-fiber plate stiffeners. Notice the
external filament tape.
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December 2009 117
With a voltage below 4.8 volts “nominal” for a four-cell pack, it
needs to be charged. Red “recharge” LED is illuminated. Multiplebrand
cable ends are convenient in the field.
SuperTest measures battery-pack capacity. The pack reads “707
mAh 03/17/08.” This test will add “683 mAh 09/09/09” and can be
used with confidence; its measured capacity exceeds the rated 600
mAh capacity.
I brought much of the misery upon myself, by leaving off the
fuselage filament-tape reinforcement called for in the
manufacturer’s kit-building instructions. I did this to get a smoother
finish on the fuselage, and I outsmarted myself in an important
area: fuselage strength.
A 60-inch LEG warbird will most often survive a cartwheel
landing if it is built according to instructions, with strapping tape
on the outside of the fuselage.
So here I am, with my ultrasmooth-finish-fuselage P-80
Shooting Star battered and broken, but the damage seems confined
to the fuselage. It is torn open, bent at a 45° angle just in front of
the wing LE. The wing and tail parts are fine.
The fuselage’s open wounds show servos and fractured internal
carbon-fiber stiffening rods, reminding me of a compound fracture
from first-aid training. I’m thinking that a replacement fuselage will
be the minimum required, and certainly no more flying the airframe
on that trip.
Enter an old flying buddy, Mike Bailey of Wichita, Kansas, who
was full of confidence and brimming with ideas about how to fix
my shattered slope jet. He had recently repaired a similarly crashed
60-inch LEG P-80 that the owner had given up on and discarded.
Mike was flying the rebuilt model on the same slope at the same
time mine smacked the ground.
He assessed the damage to my Shooting Star’s broken fuselage,
and in a single workshop session, Mike performed the repairs that
got it flying again the next day. I was amazed and thankful.
I asked him what went through his head as he approached the
problem and how he made the series of decisions that led to
restoring the airframe to a strong and flyable condition. He taught
me the following.
1. Assess the situation. By reviewing the condition of each
damaged component, we can estimate the time, materials, and
techniques we will use to restore the parts to their original strength
and shape.
What is the condition of the radio-control gear? Prepare to
replace anything that needs to be. Are any spars or longerons
broken, and can they be spliced or do they need to be replaced?
Sometimes it’s easier to leave the broken stiffening parts in place
and add strength around them.
What’s the foam’s condition? If it has sustained a clean break, it
can be bonded with epoxy, Goop, or hot-melt glue. Crumbly foam
cannot be reglued; it must be cut out and replaced with new chunks.
It might be easier to remove a component, perform the repairs on it,
and reattach it to the airframe.
2. Figure out how it will go back together. Dry-fit the big pieces.
Pay careful attention to airframe alignment, and make note of where
foam is missing and must be replaced for strength and shape.
Make certain that the control-system components, including all
radio components and servos, function well. Is there a worn servo or a
tired receiver battery pack in a well-used airframe? This is an
opportunity to replace them.
3. Reassemble the broken parts. I like using hot glue to restore
foam that has clean breaks. For long cracks, I use Goop thinned
with toluene. Make sure you use this in a well-ventilated area.
Brush the thinned Goop in the cracks, tape it together, and let it
cure overnight.
On my Shooting Star, Mike glued some areas with hot glue. He
also removed some crumbly foam in places, replaced it with carved
chunks of new foam, and glued it in place with Goop.
To compensate for the rigidity lost at my model’s splintered
carbon-fiber-tube fuselage stiffeners, Mike inserted flat pieces of
impregnated carbon fiber near the surface of the fuselage,
extending fore and aft of the damaged area. The flat carbon-fiber
bars were installed with epoxy.
After a complete radio-function check, he applied strapping tape
and turned the fuselage back to me. It was prepared to cure
overnight and fly the next day and ready for me to re-cover when I
returned home.
4. Don’t be afraid to perform extensive repairs. You won’t
break it more. It won’t not fly. All top pilots have broken and fixed
airplanes, and most experienced pilots fly repaired airplanes.
It is usually cheaper and quicker to fix than to build new. So
even though it looks grim immediately after the damage occurs, the
repair route—even extensive repairs—is often the fastest and least
expensive way to get that model back into the air.
Many thanks, Mike. Again, I am impressed and appreciative.
Mike Bailey produces interesting EPP-foam electric-powered
models under the name Midwest Foam Planes and is known as
“Motorhead” on RCGroups.
On the topic of crashes and repairing their damage, I might as
well allocute to another crash—a “preventable” one that happened
during a May 2009 Kansas trip. The Dave’s Aircraft Works (DAW)
120-inch-span Schleicher Ka6E EPP-foam aerotow trainer is
popular at Wilson Lake. I believe I saw five of them in the air the
week I was there.
Shortly after one launch, my controls stopped responding. Not
too many things create that sinking feeling of doom as fast and as
hard as a receiver battery giving out during a flight. Okay,
launching with ailerons reversed brings its own brand of heartstopping
excitement and misery. The point is that both are
frequently preventable.
Preclude launching with ailerons reversed by performing a
thorough preflight inspection, paying particular attention to the control
surfaces’ actions. Are they correct and free? Holding onto each control
surface during the inspection and creating slight resistance with your
fingers is a good way to detect stripped servo gears.
To avoid dead battery packs during a flight, start with a
voltmeter—preferably one that will apply a test load. Do not fly
with a pack that drops to less than 1.2 volts per cell; it’s time to
recharge the pack.
When can this voltmeter be fooled? When a sagging pack has
been recently charged. The problem is that a freshly charged bad
12sig4.QXD_00MSTRPG.QXD 10/23/09 10:20 AM Page 117
pack can show an initial high voltage but
drop to an unsafe state much sooner than you
might be used to with fresh and known good
packs.
This is what happened with my Ka6E. I
charged the pack overnight, but the receiver
battery quit roughly three minutes into the
flight, and my 3-meter sailplane crashed out
of control.
To prevent this situation, use a batterycapacity
test meter. The Sirius SuperTest,
available from Peak Electronics, works for
me.
To use this meter, fully charge the four-,
five-, or eight-cell pack. Plug it into the test
instrument and select a discharge rate. When
fully discharged, the SuperTest will show the
electrical capacity drawn from the pack.
If the result meets or exceeds the pack’s
rated capacity, life is good. If the output is
lower, beware; you have a weak pack.
Checking any pack you use in a model once
a year or more often can confirm that it will
not let you down in the air, or it can identify
a pack that should be replaced.
Since my Ka6E had stripped three
servos and broken a pushrod in the crash, it
was unsuitable for a field repair. When I got
home and dug into the fuselage to remove
the battery pack and the stripped servo, I
found that the 9-year-old, 2000 mAh-rated
receiver pack was putting out 50 mAh. Yes,
50 milliamp-hours—barely enough for a
launch and a crash. So that crash was
preventable.
I have some news about the designers and
suppliers many of us know and love, in case
you have not been on RCGroups or have
not heard from another source.
CR Aircraft is back in business.
Legendary kits that Charlie Richardson
designed, including the Fun-1 one-design
racer (ODR), Turbo, Blazer, Renegade, and
Contender, are back in production.
This will be of interest to ODRs who
prefer fiberglass sailplanes. In Joe Chovan’s
capable hands, a vintage Fun-1 took second
place in the ODR competition at the 2009
MWSC.
Magnum Models has EPP-foam ODR
Duster kits ready to ship. Rick Stillman of
Colorado let me fly his Duster during the
2009 MWSC; it had been years since I had
flown a slope sailplane that was that much
fun. It was perfectly suited to my skills and
abilities, and I could not wipe the grin off of
my face while I was flying it.
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pack can show an initial high voltage but
drop to an unsafe state much sooner than you
might be used to with fresh and known good
packs.
This is what happened with my Ka6E. I
charged the pack overnight, but the receiver
battery quit roughly three minutes into the
flight, and my 3-meter sailplane crashed out
of control.
To prevent this situation, use a batterycapacity
test meter. The Sirius SuperTest,
available from Peak Electronics, works for
me.
To use this meter, fully charge the four-,
five-, or eight-cell pack. Plug it into the test
Look for a kit review and flight report
from me in the future. This will be of interest
to ODR fliers who prefer foam sailplanes.
Also of interest from Magnum Models is
the Cobra Hybrid ODR. In the capable hands
of Larry Blevins, a Cobra Hybrid won the
ODR at the 2009 MWSC.
SkyKing RC Products, which supplies
DAW kits and other “legacy” sailplane lines,
has announced that it will be producing a 2-
meter version of the DAW Ka6 by late 2009
and a new 3-meter Schweizer 2-33 for 2010.
The company has changed owners and moved
from Minnesota to South Dakota. See the
Web site for details and updates.
I did make the Wilson Lake spring trip again
this year. My 2009 MWSC coverage article is
scheduled for the December 2009 Flying
Models magazine. MA
Sources:
LEG
(785) 525-6263
www.leadingedgegliders.com
Midwest Foam Planes
www.midwestfoamplanes.com
RCGroups
www.rcgroups.com
Peak Electronics
(800) 532-0092
www.siriuselectronics.com
CR Aircraft
www.craircraft.com
Magnum Models
(865) 583-9241
www.magnumrcmodels.com
SkyKing RC Products
(605) 878-1880
www.skykingrcproducts.com
Ace Hobby
(866) 322-7121
www.acehobby.com
League of Silent Flight
www.silentflight.org