Jabiru Aircraft
Pty Ltd
Installation Manual
Jabiru 3300 Aircraft Engine
REVISION
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Dated : 1
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Dec 2016
Page: 51 of 56
Figure 58. Cowl Outlet Geometry
Figure 59. Outlet Restriction Caused By Flange On Lower Firewall
12.6
Cooling System Testing & Evaluation
For new installations (new designs rather than new aircraft of a known type) the pressure drop across both
Ram air ducts must be checked.
The following is a guide to evaluating an engine installation to see if it meets minimum cooling requirements.
The easiest way to measure the air pressure drop across the engine and oil cooler is using a U tube
manometer using water. It is basically a piece of clear tube
bent into a “U” and half filled with water (if the
water is hard to see add a bit of food colouring).
For ram-air duct pressure, connect one side of U to a static port inside the ram air duct and the other to a
static probe inside the cowl near the outlet. For the pressure drop across the oil cooler plumb a static probe
against the front of the cooler and a static probe inside the cowl near the outlet. The further the probe is in
front of the cooler the less the static pressure that will be measured, so place the probe no more than 5mm
in front of the cooler and parallel to it.
Using multiple U-tubes several measurements can be taken in one flight.
Details of a typical static probe are shown in Figure 60.
Note that probes must be fitted in the same place each time to ensure you get consistent measurements.
Some hints.
Usually the most critical situation for cooling is climb however this is not always true, so check all situations.
The change in air temperature is approximately the same as the change in engine temp. For example if you
did all your testing in 15°C and you want to flying in up to 35°C weather, in 35°C all your engine temps will be
approximately 20°C higher. Check you have sufficient margin for all conditions you plan to fly in.
Fuselage cut away to give deeper & larger cowl outlet
