Straight talk about geared turbofans

February 2019

I found the article “High Gear” [October] to be one-sided in some parts and uninformed in others.

The article was one-sided in that it did not give enough attention to the serious issues experienced by the first GTF [geared turbofan] customers. There have been real issues for Lufthansa, for example, at their Frankfurt, Germany, hub and these issues have been painful. Also, the article made a brief reference to the non-geared CFM LEAP Engine, but it should have noted that the LEAP introduction into service was considerably smoother than that of the GTF. In addition, while some better efficiencies are associated with a lighter-loaded GTF low-pressure turbine, there are inherent losses associated with the gearbox. These losses are magnified as one goes to larger power plants like the one needed for a Boeing NMA (New Mid-Market Airplane). After numerous (10 to 20?) years of development on the geared fan, the fuel-saving-technology advantage has not been demonstrated for the GTF.

The article also provided an incomplete description of the GE90’s history, quoting someone calling the GE90 “an absolute pig, when introduced.” The GE90 indeed had a number of teething problems in the factory, but it turned out to be the most reliable high bypass engine in the field. The proof is in the fact that with the original version of the Boeing 777 aircraft, there were three competing power plants. The power plant of choice on all subsequent versions of the Boeing 777, including the new 777 X, has been the GE90.

M.J. Benzakein
AIAA fellow
New Albany, Ohio
Editor’s note: Benzakein was the chief engineer at General Electric Aircraft Engines for the GE90 engine program.