Sonex Builders & Pilots Foundation

Lift Reserve Indicator

In our initial discussions with Sonex Aircraft, LLC while creating this foundation, the subject of Angle of Attack (AOA) indicators and Lift Reserve Indicators (LRI) came up. Sonex Aircraft, LLC expressed strong support for the installation and use of these safety devices. This discussion will focus on LRIs, as they are relatively easy to fabricate from scratch, install, and calibrate. An Angle of Attack indicator is not he same as an LRI, and is not discussed here. 

What is an LRI?

An LRI is a system used to measure the amount of lift being produced by a wing in any given situation, by comparing the static pressure to the dynamic pressure in a probe mounted in a fixed position under the wing. The device is used to maintain a safe margin from a stalling condition, and may be used in takeoff, landing, and while maneuvering at any attitude or angle.

When displayed on a simple pressure differential gauge with a modified face, the pilot knows the amount of lift reserve available at any given moment. The gauge is frequently mounted either on top of or near the top of the instrument panel, where it remains in the visual scan of the pilot. More sophisticated LRI and AOA systems may also be connected to an EFIS.

Why Install an LRI?

Installation and use of these devices is subject to the individual builder or pilot's implementation and use of the LRI. When taking off, landing, or maneuvering, an LRI provides visual indication of the lift being produced by the wing, regardless of angle of attack or bank. It simply measures differential pressure and provides feedback to the pilot about the lift being produced. As such, the system enhances safety as a visual aid to provide additional information to the pilot other than airspeed or visual angle of attack. 

For mormation about LRI systems, check out the following resources:

SBPF Member and President, Robbie Culver, wrote this article about LRI systems. Robbie also gives details about how he incorporated the system into his Sonex build.

Additional discussions about LRI systems may be found at:

The files used as reference by the author my be found at: