Fix It - Don’t “86” It-2012/04

If you fly long enough, eventually one of your
models will meet the ground in an unscheduled
landing. One of my club’s best fliers says, “All aircraft
have an expiration date, some earlier than others.”
Often the airplane will be mostly confetti and
unfixable, but frequently a few hours’ work may
restore it to its previous beauty and usefulness.
Always gather all the parts and pieces after a crash
and take them home. You may need them later so
that they can be glued back in place, or you can use
them for reference. The field maintenance crew
will appreciate it. Who wants their flying field
littered with yesterday’s misfortunes?
When you are ready to tackle the project,
lay the parts out on your workbench and
evaluate the damage. What is broken, bent,
or missing? What parts can be glued back
together or in place, and which ones are
destroyed?
A quick evaluation of the airplane’s damage shows some of the
internal bulkheads were broken and the front edge of the wing’s
center section was crushed.
The lower sheeting, battery tray, and F-2 bulkhead were broken
loose or shattered and required replacement.
It’s a good idea to
strip the covering off the
damaged areas to look
for split wood and allow
you better access to the
interior. If internal parts
are broken or out of place,
remove enough covering or
sheeting to permit access
for accurate reinstallation
or replacement.
Fuselage Repair
If it’s a glow- or gas-powered
aircraft, is the wood oil soaked in the
areas that need repair? If the airplane
was properly prepared for flying, the
wood in the engine compartment was
painted or coated with thinned epoxy,
so it should be relatively oil free.
If the fuel tank was ruptured,
fuel could have spilled in the tank
compartment. It probably saturated
any exposed bare wood. When you
need to make repairs or do other work
in a fuel- or oil-soaked area, there
are a number of ways to prepare the
contaminated areas.
One recommended method is using
K2r Spotlifter to remove oily residue.
It comes in a 5-ounce can that sprays
Do a thorough evaluation of the damage to
determine if repair is feasible. In this case,
the airplane was readily repairable.
The lower front fuselage sheeting
was removed and the area sanded
smooth. Loose splinters were
removed from the firewall and F-2
bulkhead areas.
The firewall, lower part of the F-2 bulkhead, and
landing gear block were carefully aligned and
epoxied in place.
The extent of the wing’s LE damage was more
apparent after the covering was removed. Broken
parts were removed and the edges trimmed
smooth.
Photos by the author
on the product like a gel and dries to a
white powder. It pulls the oil and fuel
out of the wood.
Use an old toothbrush to remove the
white powder after it has dried. It takes
roughly 10 minutes for the product to
dry to powder. If the first application
doesn’t remove the oily residue to
your satisfaction, do it again. K2r is
available at True Value Hardware, Ace
Hardware, and other hardware stores
and home centers.
If the firewall is damaged beyond
use, make a new one from a piece of
plywood. If it’s useable, check to make
sure it will fit back in the space from
which it came. Trim away any splinters
or broken pieces.
Align the firewall and epoxy it in
place, making sure it is exactly where
it was before the crash. If there’s any
doubt about the strength of the joints,
add a small strip of fiberglass cloth on
each side of the back of the firewall,
overlapping onto the fuselage sides,
and saturate with epoxy.
Repair or replace any other damaged
formers and reinstall them using CA or
epoxy, whichever was used originally.
Fiberglass reinforcement shouldn’t be
necessary in those locations.
Reinstall any wing-mounting blocks
that may have broken loose. They
should fit right back into the locations
from which they came. Epoxy is
preferred for this application, but CA
can be used.
If it’s a glow-powered airplane,
reinstall the throttle linkage. If there
is a battery-carrying shelf, reinstall it
using CA or epoxy. Be sure to reinstall
all of the blind nuts in the firewall and
landing gear mounting block. Check
the fit and reinstall the landing gear
mounting block using epoxy.
Don’t forget to replace any
protective materials you may be using
behind the firewall. The airplane
shown in the photographs has a 3/4-
inch piece of Styrofoam between the
firewall and battery. Install the motor
and any other components that may
present an access problem later.
You can sand the areas where the
lower front balsa sheeting will be
installed to remove any irregularities
before its installation. In this instance,
the corners needed to be rounded,
so Sig Bond aliphatic glue was used
because of its easy sanding properties.
If one or more holes were provided for
cooling air egress before, cut new ones.
Hobbico HobbyLite or any filler can
be used to fill gaps or irregularities,
then sand all of the exposed wood
smooth.
Wing Repair
Carefully cut and remove the
covering from the damaged area(s).
Remove the damaged wood and trim
the edges straight. Trim the skin even
with the edges of the ribs. Don’t try to
trim the skin to the centers of the ribs;
they’re probably glued well enough
that it would be difficult to achieve a
straight edge.
Copy the profile of the exposed
ribs and make a template of the same
thickness. Cut partial ribs then fit and
glue them in place on the exposed
sides of the existing ribs. These partial
ribs are to hold replacement sections
of sheeting.
Check to ensure that the wingmounting
pin or pins are solidly
mounted and glue them again if
necessary. Cut and add pieces of balsa
LE stock if required and sand them to
match the rest of the LE.
Trim and fit pieces of sheet balsa
as needed to fill the holes. The new
sheeting should fit on the partial ribs
and be flush with the surrounding
sheeting. Apply HobbyLite to any low
places or irregularities and sand flush
to match the surrounding sheeting.
Fit the wing on the fuselage. Check
to ensure the mounting screws are
aligned with the holes and everything
fits as it did before the crash.
Re-cover the Repaired Areas
If the airplane is an ARF or RTF
and has sticky-back covering, the best
results will probably be realized by recovering
the entire panel, but patches
will be satisfactory if you can match
the color and it’s carefully applied.
If compound contours are to be
covered, apply MonoKote or other
material in the usual manner with
a hot sealing iron. MonoKote Trim
Solvent is useful for patching flat areas
of iron-on coverings and will adhere to
most of them.
Apply a light film of solvent to
the surrounding covering with a soft
Four sub-ribs were made to match the wing’s LE sheeted
area. This airplane was scratch-built, so rib templates were
available.
Sub-ribs were installed to support
replacement sheeting. New LE stock
was installed to replace the broken
parts. CA is a good adhesive for this
application.
After the damaged area was fixed and the
wing re-covered, it was as good as new.
After installing the propeller and spinner, check
the motor, all controls, and the CG before flight.
cloth or paper towel. Cut the patch
approximately 1/4 inch large to overlap
the edges. Carefully lay the patch in
place, avoiding wrinkles.
Squeegee the patch smooth around
the edges and work out any bubbles.
Wipe off any excess solvent and let
it set for 24 hours before using. No
heat is necessary; heating may actually
cause wrinkles. Repaint any bare wood,
any areas that may be exposed to fuel,
and those that look bad.
Finishing
Install the landing gear, propeller,
spinner, etc., and check all controls to
ensure proper operation. Be sure to
reconfirm the CG because repairs may
have affected the weight.
Now you’re ready to charge up
and go fly! You’ve saved the model
and hopefully learned a bit about
building.
—Walt Wilson
[email protected]
Sources:
K2r
(203) 732 4479
www.k2rbrands.com
Sig Bond
(800) 247-5008
www.sigmfg.com
HobbyLite
(800) 637-7660
www.hobbico.com
MonoKote
(800) 637-7660
www.monokote.com
The battery tray was reinstalled along with a new piece of foam
behind the firewall for battery protection. The aircraft received a
light sanding before installing sheeting.
After installing new balsa sheeting, the corners were sanded to
the original contours. Install the motor and ESC if access might be
difficult later.