Some Facts
The Diamond DA40 is a line of single-engine general aviation aircraft that has been manufactured for the global market by Diamond Aircraft Industries (DAI) since 2000. It was produced as a four-seat follow-on to the two-seat dedicated trainer aircraft the DA20. Variants of it are widely used as trainer aircraft due to its relatively forgiving flight characteristics and reliability; it was used as a trainer at the US Air Force Academy for a few years from 2009 to 2012. In addition, it is a popular 'first airplane' for pilots to consider purchasing, due to these same characteristics and because they are relatively widely available, having been in production for over two decades. Diamond aircraft are notable for having fully composite airframes, which give them a very strong and light structure, as well as lowering the maintenance cost and risk for the airframe itself. The DA40 is not considered a complex aircraft, because it has fixed landing gear; however, the glass cockpit version (using Garmin G1000 or G1000NXi systems) qualifies as a 'technologically advanced aircraft' (TAA) in the United States, which can be used to fulfill time requirements for more advanced certificates such as the commercial and ATP licenses.
There are several variants of the aircraft, which is named the 'Diamond Star.' Originally, there was just the DA40, which came with steam gauge instruments and once in production was provided with a tried-and-true general aviation engine, the four cylinder Lycoming IO360. The 'I' prefix of this O-360 family engine indicates that it includes fuel injection. The aircraft was available in fixed pitch or constant speed propeller versions.
Early in the 2000s, Diamond became one of the first GA manufacturers to offer a Diesel-powered aircraft, the DA40D or DA40-TDI. This is important in aviation because Diesels are simpler, not requiring an electric ignition system - meaning they theoretically can be made more reliable as well as cheaper to maintain. In addition, as 100LL avgas becomes less available (and more expensive) due to its environmental impact and limited demand, Diesel aircraft can burn the widely-available Jet-A fuels used by turboprops and turbine powered aircraft - and that fuel is actually much cheaper due to its wide demand and availability. In addition, the diesels are generally more efficient than the many-decades-old design of the Lycoming, thus burning less of the cheaper fuel - which means savings! This aircraft was termed the DA40D or DA40-TDI. Diamond continued to offer the avgas-powered Lycoming variant, which was then referred to as the 'DA40-180' as a reference to the 180 horsepower Lycoming. The DA40D was mostly different to the pilot in that instead of having separate throttle, mixture and propeller controls, it presented a single 'power' control which operated via FADEC.
The diesel version went through some variants - the original Thielert engines had significant problems, and Thielert was eventually bought by Continental, Lycoming's major competitor for piston aircraft engines. The diesel DA40 went on production hiatus, and then returned with a new engine, the 169 horsepower Austro AE300 - essentially an aviation-packaged version of a popular and massively used Mercedes automotive engine, made in Europe. It also came with a new name, the DA40-NG ('next generation').
The DA40-180, though, ended up with various additional versions. in approximately 2006, it was replaced with two models, the DA40-FP which continued the fixed-pitch offering, and the DA40-XL with a constant-speed prop, the PowerFlow exhaust and streamlining options. A year later, these were replaced again - the lower-cost DA40-FP was replaced with the DA40-CS, with a constant speed propeller but still with a limited options list for training and budget-conscious buyers. The XL was replaced with the XLS, which had a nicer interior and some additional options. That, in turn, was replaced in 2013 with the XLT, which added some interior options and a taller bubble canopy.
As of 2021, the Diamond DA40 is sold in two major variants, the DA40-NG and the DA40-XLT, which differ as to which engine they come with. There is a third package, the DA40 Tundra Star, which is a 'rough terrain' options package sold with the DA40-NG that deletes the fragile wheel streamlining trousers and comes with uprated landing gear and wheels. I don't believe you can get a DA40 new without a Garmin G1000 glass cockpit anymore.
This pilot's impression of the DA40-XLT
The DA40 is a very different experience from the Cessna 172s and 182s and Piper aircraft I have trained on previously. The closest to it I can say I have experience with is probably the Cessna 182SP that I flew in Australia as part of Outback Overflight. Both are Garmin G1000 aircraft; both have constant speed propellers and fixed landing gear. Both are four-seat. The biggest differences are the 230 HP six-cylinder engine and the high-wing configuration in the C182, vs. 180 HP four-cylinder low-wing in the Diamond. The slicker aerodynamics of the Diamond pretty much make up for the difference in horsepower, however.
The Diamond has a center stick control arrangement and a bubble canopy which hinges at the front. If like me you are a slightly immature aircraft nerd, this is coooool. The front seats don't move, instead the rudder pedal assembly moves back and forth electrically to adjust for pilot height. This can make for less intuitive pilot fit, but also removes the danger of sudden seat movements (no joke, Cessnas have ADs specifically around the locking mechanisms in the seat rails).
In flight, they are both very forgiving aircraft. However, the Diamond 'feels' much more agile and snappy, likely due to its low wing loading and its high aspect ratio. You can fly it with two fingers on the stick, with the rest of your hand braced on your leg, and pretty much the best way is to treat it like a motorcycle or a high performance car: instead of 'steering' it, just think 'go right' and...it'll turn just based on your unconscious bias. If you want it to turn faster, then sure, give it a very very light push. By comparison, the C172 and C182 are flying barns - you need to shove 'em around a little. This is likely partially due to the extremely narrow rear fuselage and empennage on the Diamond. The downside of that is that it has less rudder authority than the Cessnas, so slipping and correcting on takeoff take a leaden foot in the Diamond.
The visibility out of the DA40 is unbelievably better - the one-piece bubble canopy means a greater-than-180-degrees field of view out the front, and the wings are set far enough back that you can still look directly down from the cabin, unlike Pipers and other candybar wing aircraft. The downside to this? It's a greenhouse. Any direct sun and the cockpit starts getting hot, rapidly. Aftermarket sun shades and visors are the number one accessory for DA40s, and air conditioning systems are a popular factory option despite lowering your useful load by nearly 10%.
Diamond Aircraft Industries arose from a sailplane maker, and it shows. The DA40 will float FOREVER if you flare even a few knots over the POH recommended speed. Also, the flaps on the DA40 don't have nearly the effect of the 'barn doors' on the Cessnas, so more careful flying is required in the pattern or on the approach.