In the wake of the sad crash of ET-302, I am reading on multiple sources that

the 737 Max's "engine is a bit further forward and a bit higher in relation to the wing, compared to the previous version of the plane. That affects the balance of the plane"

(from the BBC)

Is there data available on how much these "bit further forward" and "bit higher" amount to?

In particular, to minimize misunderstandings, it would be ideal to know how much the CoG of the engines has moved w.r.t. the neutral point.

  • $\begingroup$ Without a better answer, you could try and estimate it using the scale drawings from the public Airplane Characteristics for Airport Planning manuals: boeing.com/commercial/airports/plan_manuals.page $\endgroup$ – Cpt Reynolds Mar 11 at 12:30
  • $\begingroup$ Comparing the -800NG (boeing.com/resources/boeingdotcom/commercial/airports/acaps/… page 39) and Max 8(boeing.com/resources/boeingdotcom/commercial/airports/acaps/… page 2-11), does not seem to be any significant change. $\endgroup$ – DeepSpace Mar 11 at 13:07
  • $\begingroup$ @DeepSpace I wouldn't know how to determine that from those figures, since the numbers are given w.r.t. something that changed for sure (the fuselage is longer, so the nose is further ahead) and the outlines are not required to be exactly to scale, I think. $\endgroup$ – Federico Mar 11 at 13:10
  • $\begingroup$ @Federico There are scale drawings at the very end of the manuals... $\endgroup$ – Cpt Reynolds Mar 11 at 13:27
  • $\begingroup$ @CptReynolds not really reliable if we are trying to determine changes in the centimetre range, right? $\endgroup$ – Federico Mar 11 at 13:28

The Boeing 737-800 and 737 MAX 8 both have the exact same fuselage length of $ 39.47 \, \mathrm{m} $, so I chose these two models for comparison.

Boeing publishes CAD drawings for all aircraft models. I used the two CAD files for the 800 and MAX 8 to compare the engine size and location:

737-800 737 MAX 8

Since I do not know the units used in the CAD files, I used the known total fuselage length to scale the numbers:

  • Distance from the nose to the front of the engine nacelle:

$$ \text{737-800:} \; 13.544 \, \mathrm{m} \; , \; \; \text{737 MAX 8:} \; 13.180 \, \mathrm{m} $$

  • Length of the engine nacelle including exhaust:

$$ \text{737-800:} \; 5.075 \, \mathrm{m} \; , \; \; \text{737 MAX 8:} \; 5.345 \, \mathrm{m} $$

  • Diameter of the engine nacelle:

$$ \text{737-800:} \; 1.978 \, \mathrm{m} \; , \; \; \text{737 MAX 8:} \; 2.407 \, \mathrm{m} $$

  • Distance from the top of the engine nacelle to the bottom of the fuselage:

$$ \text{737-800:} \; 1.359 \, \mathrm{m} \; , \; \; \text{737 MAX 8:} \; 1.554 \, \mathrm{m} $$

Based on these measurements, the new engine nacelles are $ 270 \, \mathrm{mm} $ longer and have a $ 429 \, \mathrm{mm} $ larger diameter. They start $ 364 \, \mathrm{mm} $ further forwards and the top is $ 195 \, \mathrm{mm} $ higher.

Therefore, the center (geometric, not necessarily center of gravity) of the engines has moved $ 229 \, \mathrm{mm} $ forwards and $ 19 \, \mathrm{mm} $ downwards. While the geometric center may have moved downwards, the center of gravity probably moved upwards because the old nacelle was not symmetric (flattened at the bottom).

  • $\begingroup$ The dimensions given are in inches. $\endgroup$ – fooot Aug 25 at 16:32
  • $\begingroup$ From the drawings it looks like the radome is a bit more elongated in the MAX version, as well as the tail cone. I'll accept these numbers for the moment anyway. $\endgroup$ – Federico Aug 26 at 5:47

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