Embraer 2000nm 5 abreast

It is no secret that Embraer looks into building a CSeries rival with an own 5 abreast aircraft. But as Bombardier's CSeries will offer a maximum range of 2950nm and the wing is designed for that range, Embraer reportedly is looking for a range closer to 2000nm, but thinks about a little larger aircraft. Scott Hamilton wondered in a recent blog entry how Embraer could achieve to build a lighter aircraft, as Ronald Epstein, the BoA analyst suggested. Here is a quick explanation:
The CS300ER with a range of 2950nm has a MTOW of 139600lbf and a wing area of 1209sqft. What does that mean for an aircraft that is limited to  a range of 2000nm? First of all, you need less fuel and thus smaller fuel tanks, saving both emty weight and maximum take off weight. As you save maximum take off weight, you can make your wings smaller, as takeoff performance and cruise flight performance is dependent from the wing loading (takeoff mass/wing area). By that you further reduce the empty (and susequently) MTO weight. With the reduced takeoff (and cruise) mass the required takeoff (and cruise) thrusts are reduced (given that we can hold the lift/drag ratio constant), reduding fuel burn.
In reality, the lift/drag ratio will be a little worse with the smaller wing, unless you can realise the smaller wing with a higher aspect ratio, which requires a higher degree of technology.
The reduced thrust requirements could result in a smaller and lighter engine, further reducing weight and fuel burn.
For this exercise I kept engine weight and thust rating constant, as if Embraer would use the same engine as the CS300ER will get (PW1524G with 23.3klbf takeoff rating).
 I did a two-step exercise:
  1. I did let PIANO find the MTOW for a 2000nm CS300 with the same wing loading as the CS300ER has. Not only the wing was shortened by that, also the horizontal and vertical stabilizers were optimized for the lighter aircraft. This aircraft is shown as CS300 2000nm
  2. I then stretched the fuselage by 63", giving room for two additional rows or 10 passengers. This aircraft is shown in the graph as CS300+ 2000nm.
The results:
  1. The 2000nm CS300 burn 5% less fuel on a 500nm mission. Empty weight is reduced by about 8%, MTOW by almost 15%.
  2. The stretched 2000nm aircraft burns the same amount of fuel over a 500nm mission as the CS300ER, but carries 10 passenger more. This is a saving of 7% per seat (mile), which is one of the most important economic indicators in a high fuel price environment.

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