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Aircraft/Characteristic Diamond Star DA-40 Diamond Star DA-42
Span 11.94m 13.42m
Wing area 13.54 m² 16.29 m²
Max Occupants 4 4
$Va$ 108 KIAS 126 KIAS
$Vno$ 129 KIAS 155 KIAS
$Vne$ 178 KIAS 194 KIAS
Max Take-off Power 180 HP 2×180 HP
Max Continuous Power 160 HP 2×160 HP
Max Fuel in one wing 25 US gal 26 US gal
MTOW 1200kgs 1785kgs
MLW 1150kgs 1700kgs
Max Altitude 16,400ft 18,000ft

Source: Internet Source: Internet

My questions are:

  1. Is the 50% increase in MTOW the only benifit of DA-42?

  2. Despite having twice the power, there is not much difference in the cruising speed of the two aircraft. Why is that?

  3. DA-42 has two engines - shouldn't that increase the fuel consumption and thus decrease the range?

  4. Why was DA-42 introduced much later than DA-40, despite having such similar performance?

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In regards to your questions:

1: like all twin engine airplanes, the benefit of a second engine is in a increased maximum takeoff weight, better, climbing ability, higher cruise speeds (combined with the retractable gear), and potentially offer greater redundancy. The DA-42 is also turbo-diesel powered, giving superior high altitude performance and climbing abilities on hot days and/or high field elevations and operates on JET-A fuel as opposed to AvGas. It’s also equipped with some additional systems, such as optional onboard WX radar.

2: The DA-42 is a solid 30 KTAS faster than the DA-40, and this really opens up above 10,000 ft, where the normally aspirated DA-40 lags.

3: Your onboard fuel stats are incorrect; while the capacities of the wing tanks are similar, the DA-42 also has two auxiliary tanks at 18 USG per side. This fuel must be manually transferred by pump to the main tanks for use by the engines. And the Austro engines in the DA-42 are very efficient burning about 8 gal/hr @ 95% power and 5-6 gal/hr @ 65% power. An IO-360 will consume around 10-11 gph for a high speed cruise. Given the 20-30 kt cruise speed difference for a given power setting plus the extra fuel, I’m not surprised at all that a DA-42 has longer legs than a DA-40.

4: Different markets and Diamond was apparently not interested in manufacturing twins when the DA-40 was developed.

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  • $\begingroup$ The difference in efficiency is in major part because they are diesels: diesels in general have about 30% better fuel efficiency (their main disadvantage for aviation is they are heavier for the same power). $\endgroup$
    – Jan Hudec
    Jan 1, 2023 at 1:25
  • $\begingroup$ There are DA-40's which have the exact same engine as DA-42's. DA-40's can be equipped with both the IO-360 and the AE300. $\endgroup$ Jan 1, 2023 at 6:56
  • $\begingroup$ Yes, modern variants of the DA-40 now use the Astro turbo diesel engines. They (the DA-40NG) still don’t match the performance of the DA-42. $\endgroup$ Jan 1, 2023 at 7:41

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