HANDS ON
HOMEBUILDER’S HANDBOOK
Piano Hinges
How and where to use ’em
JACK DUECK
THE PIANO HINGE HAS many uses in amateur-built aircraft. On my wife’s and
my RV- 4 and RV-9A we have used piano hinges in numerous applications,
including cowling connectors, oil access doors, flap hinges, trim-tab hinges,
canopy hinges, seat-back hinges, hinge-pin safetying devices, and much more.
The piano hinge can be used in two ways: as a hinge and as a fastener (and
sometimes as both). If you use this versatile product as a hinge, you need to
keep a fairly straight hinge line. Over a long expanse, where the hinge is
bound to flex (as on an aileron), it is best to use separate sections of piano
hinge. If used as a fastener, the hinge line can bend quite substantially and
still work well as a quick disconnect device.
Piano hinges come in two types. The most common is the formed loop
and is designated as Mil Spec MS20257. The other is extruded aluminum and
is designated as MS20001. This hinge is stronger and is used in applications
where high strength is necessary. One application of this stronger hinge is in
the V-tail section on the Sonex Waiex. It is composed of either 2024-T4 or
7075-T6511; both are strong aluminum alloys and have been hardened by
heat treatment. While the formed loop (MS20257) is the weaker type, it still
finds many applications in our aircraft. However, you should never substitute
this hinge if the stronger extruded hinge is specified. A corrosion-resistant
stainless steel piano hinge is also available under the call-up of AN257C. It is
substantially heavier and consequently not often used.
Hinge pins should match the hinge loop diameter to avoid excessive play.
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Hinge pins should match the
hinge loop diameter to avoid
excessive play.
Formed loop piano hinge designated by MIL Spec MS20257
Extruded aluminum piano hinge
designated by MIL Spec MS2000
