What is the true airspeed of the DA42?

Decoding the DA42’s True Airspeed: A Case Study at 17,000 Feet

The Diamond DA42, a twin-engine piston aircraft, is known for its efficiency and performance. However, understanding its true airspeed (TAS) requires more than simply looking at the indicated airspeed. Several factors, particularly altitude and wind, significantly influence this crucial flight parameter. This article examines a specific flight profile to illustrate this point.

At 17,000 feet, a DA42 was observed cruising at 190 knots true airspeed (TAS). This figure represents the aircraft’s speed relative to the surrounding air mass, unaffected by wind. Crucially, the aircraft consumed a combined 16 gallons of Jet-A per hour during this segment of the flight. This fuel burn rate is noteworthy, suggesting efficient operation at this altitude and speed.

However, the complete picture requires acknowledging the impact of atmospheric conditions. A significant tailwind of 39 knots was present during this flight. This tailwind component significantly boosted the aircraft’s ground speed – the speed relative to the ground – but did not affect its TAS. In other words, the aircraft’s forward progress relative to the ground was considerably faster than its actual speed through the air.

This example highlights the importance of distinguishing between true airspeed, indicated airspeed (IAS), and ground speed (GS). IAS is what the pilot sees on the airspeed indicator and is affected by air density. TAS corrects for the differences in air density at altitude, providing a more accurate representation of the aircraft’s speed through the air. Ground speed, on the other hand, incorporates the effects of wind, reflecting the aircraft’s progress over the earth’s surface.

The 190-knot TAS at 17,000 feet, coupled with the 16 gallons per hour fuel burn, provides a valuable data point for DA42 performance analysis. However, replicating this specific fuel consumption and TAS would depend on several variables including:

• Precise atmospheric conditions: Air temperature, pressure, and humidity all influence air density, impacting both TAS and fuel burn.
• Aircraft weight and balance: A heavier aircraft will require more power and consume more fuel at the same TAS.
• Pilot technique: Efficient piloting contributes to minimizing fuel consumption.

Therefore, while the observed 190-knot TAS at 17,000 feet with a 16-gallon-per-hour fuel burn is informative, it should not be interpreted as a guaranteed or consistent performance figure. It serves as a single data point illustrating the interplay between true airspeed, wind conditions, and fuel efficiency in a specific DA42 flight profile. Further analysis across a wider range of conditions would be necessary to build a comprehensive picture of the aircraft’s performance capabilities.