Learning the V-speeds is a good way to become familiar with a new type of aircraft and this is how I started to study the DA42. Some values surprised me, both positively and negatively.

The rotation speed (Vr) is 72 knots. This is low, particularly when compared to high performance SEPs like the Saratoga or the Bonanza. As I did not yet study the take-off performance it’s hard to say if this is a good or bad surprise. The ground roll and take-off distances will be more interesting.

The speed for best angle of climb (Vx) and best rate of climb (Vy) are both defined at 79 knots. This is not really representative of the aerodynamics laws, but the AFM states:

“Vx is always less than Vy. For the DA 42 however, the actual  value of Vx would be below the minimum safe speed. The minimum airspeed for best angle of climb was therefore raised to the value of Vy.”

Please leave a comment if you know the definition of “minimum safe speed”. I honestly don’t know it yet but will ask my instructor.

The yellow arc (yellow tape on the G1000) starts at 155 knots and the never exceed speed is 194 knots. This is the worst surprise of all. These values are low compared to other light twins but also when compared to high performance SEPs. I knew this from the beginning of my training and it is no factor for me yet but if I were in position to invest half a million Euros now, this could be decisive.

The landing gear can be extended at speeds up to 194 knots and retracted up to 156 knots. This means that the gear can be extended at any time and I like it. Reducing speed after an high-speed approach is never easy and using the landing gear to speed down is not always possible because of such restrictions. I’ll have to publish an update of this topic later on, when I’ll know how efficient the landing gear is a speed-brake.

The two next speeds are very twin engine specific. Vmca is the minimum control speed with one engine out. The concept is quite simple: the increase in drag and imbalance caused by asymmetrical conditions is so important that it can’t be compensated if the speed falls down below Vmca – even with the other engine at full power. I’ll say more about it in a later post about asymmetrical flying, it’s sufficient for the time being to say that this speed is so critical that it’s represented by a red radial on classical air-speed indicators… In the case of the DA42, it is 68 knots, only four knots below the rotation speed. As Vmca is defined for gear-up conditions, this does not leaves a lot of options if an engine failure occurs right after take-off.

The concept of speed for the best rate of climb on one engine (Vyse) is also easy to understand. In the case of the DA42 it is 82 knots. Note that the “best rate of climb” does not means “good rate of climb” when it is on one engine. This speed is represented by a blue line on the airspeed indicator. As it is 10 knots above the rotation speed, the possibility of re-landing in case of engine failure immediately after take-off must be seriously envisaged, as long as the gear is still extended.

The final approach speed varies from 76 to 78 knots depending of the weight. “Varies” is probably not the right word, a span of two knots is not exactly wide. An adaptation of the final approach speed depending on weight is usual but most light aircraft don’t really require it. The DA40 is an exception – 5 to 7 knots adaptation is required – so I expected a much wider span for the DA42. Having a single value makes things easier, so this is definitely a good surprise.

Last but not least… Va, the maneuvering speed. As a reminder, this is the speed at which it is possible to use control’s full deflection without overstressing the airframe, and it’s a sound decision to slow down below Va in turbulence. This is always dependent of the weight, but for the DA42 the span ranges from 120 to 126 knots, which seems quite low.

I referred a lot to high-performance single engine aircraft in this post, and I know the PA32 Saratoga quite well. The list below compares the DA42 and the PA32:

I don’t have all the figures at hand, but a Beechcraft Baron 58 cruises at speeds typically around 195 to 200 knots… Not exactly something the DA42 can compete with.

The V-speeds of the DA42 are more like those of an high-performance single engine aircraft than other light twins. It climbs and approaches at roughly 80 knots, and can’t really sustain a climb on one engine. That being said, its fuel conumption and other performance factors must be taken in account when making a type decision. I’ll post more about performances when I’ll know more about this topic, so stay tuned to learn together with me about the DA42.