I tend to agree with those who think this design increases structural weight compared to typical t-prop configuration: high wing with engines.
However, depending on the mission profile targeted, lowest weight != lowest fuel burn.
Here are some advantages of the proposed layout i've thought of:
1) Optimized wing: The design allows the wing to be thinner and better optimized aerodynamically. Tprop engines on wings create quite a bit of drag from the prop wash and plyon integration. I believe this hasn't been an area of focus due to relatively short stage lengths and fundamental efficiency advantage tprops have over jets. While there hasn't been much optimization in this area on tprops, in the turbofan space there has been a lot of research has gone into optimum engine/wing/pylon placement. I wager there is a net drag reduction with the props in the back on little engine mounts.
2) Wing-body integration: High wing design creates a major hurdle with body integration. Most classic designs stick the wing above the body, which creates a discontinuity along the top of the fuse. This has pretty high drag impact and is very difficult to optimize. Sticking it through the fuse interferes with cabin space and creates a section without adequate headroom -- not an option. Low wing designs are difficult due to engine placement on wing needing to be high, which is not feasible due to efficiency loss. Low wing with under wing mount engines and using very tall landing gears is an option, but such gear is and mount area is, frankly, unfeasible due to weight using conventional materials, and too-expensive to produce using advanced or rare high performance materials. The proposed layout eliminates all of these concerns; i.e. low wing placement with classical wingbox not affecting cabin space, and standard landing gear to minimize weight/costs.
3) Cabin noise and vibration: As others have alluded to, the cabin noise will be significantly less on this layout compared to classical wing mounted engines. However, I think there is a good chance that cabin vibration is significantly lower as well. This is not something often discussed, but classical tprops produce a lot of vibrations that amplify the perceived noise level. A lot of this is caused by prop wash over the wing. With this design, I think these can be minimized. I will note, the natural frequency will be different due to the placement at the back and they may have to be careful with resonance scenarios.
4) Most tprops use T-tails to keep it out of the prop wash. I don't think that's a big deal here. Hstab will need to be larger, however, due to the shorter distance to wing.
1) Weight: Additional structural weight is required. This may be offset some depending on material selection and operating ceiling. For example, if the mission profile calls for a ceiling of FL35 for storm/mountain routing comfort, the additional hoop stress structure needed by this may already be sufficient to carry the longitude stresses required by the rear mount, so it may not actually end up being much more weight.
2) Runway performance: Rather than tail strike, it looks like the props will touch ground before the tail does. Prop strike is a bigger deal than tail strike, and additional margins will be needed here. I can see runway performance being closer to turbofan type requirements, rather than conventional tprops, which may reduce the addressable market.
3) I'm still not convinced the USA public will accept it, and it's the largest single market.
4) Are there enough synergies with E2 program? Those subsystems are optimized for longer flights and are likely too expensive for this mission profile??
I wonder how much weight savings would exist for a wing and wingbox which do not have to support either engines or landing gear. I could see that being enough to offset weight gains at the rear.
As to TP acceptance in the USA, I could see this design doing better. I feel like the negative connotations are uniformly based around designs with wing-mounted props. It’s partly the snazzy livery Embraer designed in this artistic rendering, but to me the craft has a very modern look to it; very different from a DH8, Q400, B1900, ATR72/42, or almost any other TP in regular commercial US service within the last 40+ years.
Engines typically reduce
the weight of wing spars + wing skin, not increase it. This is because they provide reverse bending relief along the span.
Similar story with the landing gear. The loads from it are high and the lightest place to attach them is in the wingbox. Otherwise, you'll have to carry heavy structure from the wingbox to the mounting point, and that'll be on a moment arm magnifying the force. Further, for center of lift of the wings is near where the center of gravity should be on the ground. The gear cannot be too far forward otherwise it'll tip on it's tail. And any further you move the gear back increases the load on the nose landing gear, further increasing weight and decreasing break ability. I'm confident the gear will fold into the main wing box.This is the only logical way to approach a wheeled landing gear (floats/pontoon's introduce some alternative concepts).
I'm not sure how much the WBF (wing body flaring) is random work by a graphics person doing a mockup vs representative of their actual engineering concepts. WBF has been an area of great research and improvement over the past 20 years.
If this design is representative, they may have found clever low-drag solution to prevent turbulent air from reaching the props (one of the major problems of rear props, especially at some AOA's). This increases drag and noise. Could be one of those "critical enablers" for success of the design concept. Biggest one is the engine/vstab/tailcone integration which someone else indicated previously. If they get that wrong, this thing is DOA. If they get it right, this could become the eureka moment for tprops moving forward.
Regarding the wing: the mock up looks pretty similar to some Cessna's Citation wings. I imagine it'll have good laminar flow characteristics and have a great lift-drag ratio. As I stated earlier, lightest isn't always most efficient, and they may have come across a combination where the drag improvement of the wing more than offsets the structure weight penalty. Classical tprop wings are not highly optimized aerodynamically, and certainly not for fast (ish) cruise speeds. I'm not convinced this thing needs to be Q400 fast, but it cannot be ATR slow and cover 800nm sectors.