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Here are the minimum performance specifications for a certified induction
heat system.
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Part 23 AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER
CATEGORY AIRPLANES
Sec. 23.1093
Induction system icing protection.
(a) Reciprocating engines. Each reciprocating engine air induction system
must have means to prevent and eliminate icing. Unless this is done by
other means, it must be shown that, in air free of visible moisture at a
temperature of 30° F.—
(1) Each airplane with sea level engines using conventional venturi
carburetors has a preheater that can provide a heat rise of 90° F. with
the engines at 75 percent of maximum continuous power;
(2) Each airplane with altitude engines using conventional venturi
carburetors has a preheater that can provide a heat rise of 120° F. with
the engines at 75 percent of maximum continuous power;
(3) Each airplane with altitude engines using fuel metering device tending
to prevent icing has a preheater that, with the engines at 60 percent of
maximum continuous power, can provide a heat rise of--
(i) 100° F.; or
(ii) 40° F., if a fluid deicing system meeting the requirements of Secs.
23.1095 through 23.1099 is installed;
(4) Each airplane with a sea level engine(s) using a fuel metering device
tending to prevent icing has a sheltered alternate source of air with a
preheat of not less than 60°F with the engines at 75 percent of maximum
continuous power;
(5) Each airplane with sea level or altitude engine(s) using fuel
injection systems having metering component on which impact ice may
accumulate has a preheater capable of providing a heat rise of 75° F. with
the engine is operating at 75 percent of its maximum continuous power; and
(6) Each airplane with sea level or altitude engine(s) using fuel
injection systems not having fuel metering components projecting into the
airstream on which ice may form, and introducing fuel into the air
induction system downstream of any components or other obstruction on
which ice produced by fuel evaporation may form, has a sheltered alternate
source of air with a preheat of not less than 60°F with the engines at 75
percent of maximum continuous power.
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These specifications are the result of extensive testing in response to
accidents. There is a large envelope of possible induction icing
conditions. A 50 degree temperature rise may be sufficient for 95% of
induction icing encounters, but surviving a few encounters does not prove
that you can survive the full range of possible encounters. My guess is
that many homebuilts are woefully inadequate in this department.
BILL HANNAHAN
WFHANNAHAN@YAHOO.COM
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