Flat hinges come in a variety of sizes for all types of model
airplanes. Only the smallest of model aircraft have surfaces that
are too thin for a flat hinge. Very thin surfaces use Monokote
hinges, sewn hinges or thin Mylar. There may be other ways of
hinging thin surfaces as well, but you would have to talk to someone who
is more familiar with micro-flight than I am.
This is a type of flat hinge that has a real pivot point - usually a
steel pin. At times when I use flat hinges, I almost always use the pinned
variety. I like using a hinge that is a real hinge rather than a
bendy piece of plastic.
If you look at any full-size aircraft, you will notice that the hinge
line is partially inset into the control surface. The only type of
hinge that allows this same setup in a model aircraft is a pinned hinge
(flat or Hinge Point).
I admit that in flight I can not tell the difference between a
pinned hinge and a non-pinned hinge, but I just feel better about using
real hinges, so I do.
Polypropylene Hinges (Also called Poly or "Live" Hinges)
These hinges are also excellent and very long lasting. They
almost always have a stamped hinge line.
The best ones available are made by Hayes. I use poly
hinges at times, but generally prefer Hinge Points or pinned hinges.
I still have some poly hinges in my shop, so I will use them eventually
because there is nothing wrong with them.
The good thing about poly hinges is that they last forever and tend to
be on the stiff side. This stiffness helps dampen flutter.
Before you install poly hinges, you should flex the
hinges back and forth many, many times to loosen them up. Most
experts agree that it is important that you pass the time spent loosening
the hinges by continuing to read all this site has to offer.
There are two things about poly hinges that I do not like. Due to
their stiffness, they tend to prevent the ends of the surface farthest
from the control horn from having the same amount of throw as the surface
has nearest the control horn. This behavior is most noticeable on
longer surfaces such as strip ailerons using torque rods near the wing
On the other hand, if a small amount of resistance from the hinge
prevents the surface from deflecting properly, then air loads in flight
will probably do the same thing even with a pinned hinge. In other
words, this is probably more of a problem with the control system than the
The second thing I do not like about poly hinges (and even more so with
CA hinges) is that they put the hinge line in front of the
leading edge of the control surface. Although there is nothing wrong
with this in practice, it is not really is not where the hinge line should
be. This is a direct assault on my anal-retentive nature so I fight
back with pinned hinges.
Nevertheless, poly hinges are good hinges and they
will provide good service.
CA (Cyanoacrylate) Hinges
These hinges are made for lazy people. (I wonder how many people
just got offended and went off to another web site). You know it's
true, so stop being offended and start using real hinges.
CA Hinges are made from a strip of Mylar with a piece of thin cloth or
paper laminated to each side of the Mylar. They are called CA hinges
because they are intended to be glued in place using cyanoacrylate. The
porous laminate is what the CA actually adheres to. However, epoxy
can also be used.
The only advantage CA hinges have over other types is that they are so
thin that you can shove a hobby knife into the surface and that is your
hinge slot. Other than that there are so many things wrong with them
that it is hard to remember them all.
The first thing that comes to mind is that they require you to
deliberately leave a larger gap between the flight and control surface
than would be necessary with any other type of hinge. This gap is
necessary to prevent these hinges from breaking.
The larger gap and the thin, flexible hinge material combine to allow the surfaces to flex up and down - sort of like what a
belly dancer does by panning her head side-to-side. Control surfaces
are not supposed to be able to move like that, but it is a fundamental and
defective property of CA hinges.
Second, and more importantly, CA hinges have the highest failure rate
of any type of hinge in the history of hinges. Some people will take
issue with my comments regarding these hinges stating they have never had
problems with them. I am sure many people have had good service from
remains that CA hinge failures are reported frequently,
to include everything from the laminate delaminating (followed by loss of
the control surface) to the hinges breaking. When other types of
hinges fail it is usually a building error - not a hinge
failure. For example, any hinge can pull out from the surface due to
I just do not like CA hinges and strongly suggest that you use any other
hinge instead. In fact, this is the only type of hinge I will
specifically not use.
I suggest that you always pin flat hinges for security. Do not
confuse pinning hinges with pinned hinges. Pinning refers to using a
toothpick or straight pin to secure the hinge to the flight or
control surface with the pin centered in each half of the hinge.
The proper way to do this is to glue in the hinges and attach the control surfaces per
usual. After the glue is set up, drill a 3/32" hole all the way
through the surface and the hinge.
Push a round toothpick through the hole and then use a single edge
razor blade to carefully trim off the excess. A drop of thin CA will
secure the hinge forever. You can either put a drop of fuel-proof paint
over it to match the covering or, if using iron-on covering, put a scrap
between two pieces of paper and use a hole punch to make dots that can be
ironed over the pins.
I kind of like how the pins look so I tend to leave them exposed.
I do not use straight pins because they are harder to trim nicely and
glue does not stick to them. However, I have used them in the past
and they never came out so they work fine. A hole does not need to
be drilled if using straight pins. Just push the pin through and
trim off the excess.
Many people say that they have installed flat hinges with glue and no
other reinforcement and have had no problems. I can say the same thing,
but I always use pins now. It is a little more work, a lot more security and one
less thing I have to worry about.
A pinned hinge will never pull out
without taking other parts with it. The choice is yours, but if you
ignore this advice, then you better be sure that you know how to glue a
hinge in properly.