# Letters

0

## Big Brother Is My Copilot

I appreciate the sentiments expressed by Tom Wilson in his February 2019 column. Any information transmitted via ADS-B beyond position and velocity is not related to safety. The rest is an infringement on privacy, provides nothing more than a clear opportunity for abuse, and if the anecdotal evidence is correct, never deleted. It never fails to surprise me how as pilots we accept this.

—Walt Peters

## Air/Fuel Ratio Monitoring

I have a question about Figure 4 in Reinhard Metz’s article, “Adding Direct Air/Fuel Ratio Monitoring” in the March 2019 issue. Why the variations in the A/F ratio along the bottom axis? For example, the column width between 12.5 and 13 is 0.25. The column width between 14.7 and 16 is 0.65. Either the numbers are not correct or the scale of the graph has been distorted.

—George King

Reinhard Metz responds: Thanks for your attention to detail. However, the A/F numbers on the X-axis of Figure 4 are correct—they are just nonlinear as an artifact of the way the data was acquired and how Excel does X-Y graphs.

The data was generated by flying a constant altitude and manifold pressure, and varying the fuel flow in -gph (equally spaced) increments, and recording the corresponding A/F ratios, airspeeds, and EGTs. As a result, in Figures 2, 3, and 5, where the X-axis is fuel flow, the numbers are equally spaced. However, in Figure 4, where the X-axis is A/F, Excel simply plots the A/F numbers in sequential order, equally spaced. Since the A/F ratios corresponding to equally spaced fuel flows are not necessarily equally spaced, the X-axis ends up non-linear. The plotted data for each of these numbers is correct, and the graph smoothing is simply a second order interpolation applied by Excel.