AOPA Pilot Magazine - February 2011 - 22

LETTERS
Suppose I increase my speed to 115 knots. At this speed I will burn an extra 1.125 gallons of fuel and speed up my trip by 32.026 minutes. In other words I am spending 17.56 cents for each minute I save. (I’m assuming $5/gal). Is this worth it? Suppose I increase my speed even more to 132.2 knots. (This is the mythical magic 1.316 factor computed by Carson.) In that case I will almost double the amount of time saved (59.179 minutes); however, I will burn an extra 4.008 gallons. In other words I’ve now spent 33.86 cents for each minute saved (nearly double the cost per minute at my 115-knot speed). As I continue to increase my power setting, the cost per minute of time saved continues to increase. This cost increase happens smoothly from the minimum drag speed (99.7 knots) and so it is difficult to point to any particular point as being optimal unless you factor in your particular time and financial constraints. What about the typical renter pilot who is renting the airplane wet via the Hobbs meter? His minimum cost is to fly the airplane as fast as possible, even if that overheats the engine—leading to

a much shorter engine life. The Carson speed has no significance in this situation. The pilot will also be motivated to taxi as fast as possible without making the probability of an accident excessively high, another reason why some of the more intelligent operations shy away from this wet rental model. Now if you are renting dry, then there will be an optimum speed to fly to minimize cost, but you can’t calculate it the way Carson does. In fact, you would have to know the relative cost of the hourly rental compared with the fuel cost before you could make such a calculation. And what about the typical aircraft owner? My opinion is that the engine wear for the two flights (at 115 knots and 132.2 knots in my example) is actually the same despite the fact that the higher-speed flight saves 27 minutes. Unless it is just for bragging rights, the pilot doesn’t really care about the speed. He really cares about how much time he can save. If you look at it in terms of how much time you save versus how much you spend to save it, I think you will see that the Carson speed is no magic bullet. Paul Mennen, AOPA 856519 Sunnyvale, California

Cross-country in a Cub I found the article “Cross-Country in a Cub” (December 2010 AOPA Pilot) very interesting. The author/pilot brought the trip alive for me in his text. I commend him for his efforts. However, I do have a problem with the opening picture on page 75 that (per the caption) shows the Grand Canyon. At no point in the article does the author state he flew over the Grand Canyon. The map of his route of flight on page 76 does not show the route of flight anywhere near the Grand Canyon. You did the author and your readers a disservice. Don Hagedorn, AOPA 670814 Columbia, South Carolina Our editors need to get out more—the photo shown is the Moab Valley in Utah. No one is pointing fingers, but some editor must have been in the eggnog early and mistakenly labeled the photo as the Grand Canyon. AOPA Pilot regrets the error. Head of the class I thank you for your article “Head of the Class” regarding the training of future young aviators (December 2010 AOPA Pilot). My son attends Marine Military Academy (MMA) in Harlingen, Texas, and

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AOPA Pilot Magazine - February 2011

Table of Contents for the Digital Edition of AOPA Pilot Magazine - February 2011