Letters

I am stumped by Dave Hirschman’s assumptions regarding the flight profile (“Efficiency: The Six-Minute Solution”). Everything seems right, except the descent. Granted, the simplest descent would be to simply reduce power, which would result in little or no speed change. 

But who does that? Am I the only one who rolls the trim wheel forward to get back speed lost in climb? Perhaps Hirschman did the power-reduction descent to standardize the parameters, but few of us are in danger of blowing through 250 knots in the descent, even with no power reduction. Granted, the power will increase in the richer air and require mixture and throttle adjustment, but hey, one reason we all got into aviation was to go faster.

Mike Heaton
AOPA 827263
Chester, New Hampshire

I read Dave Hirschman’s article and found his results to be vastly different than my experience. With that said, the difference in fuel burn and time would be so slight that I’m with him: I would climb for the smoother ride. Every airplane is different, but I’ve found that in my Mooney, I’m better off staying low for anything under 150 nautical miles (one hour). From there to about 450 nautical miles, it doesn’t really matter. Beyond about 450 nautical miles (three hours) it’s worth climbing.

I think the main error Hirschman made was his assumed fuel flow at cruise. There is no way you can cruise at the same speed at both altitudes and save two gallons per hour at 8,000 feet. If you were lucky, you might save 0.3 gph. Another error that probably does not make a significant difference is the assumed climb rate. I cannot imagine an airplane that can climb at 1,000 feet per minute but only cruise at 120 KTAS at 75-percent power and 9 gph.

I used book values from the POH for my Mooney M20J (201). In order to arrive at the destination at the same time I would have to spend about 83 minutes in cruise at 8,000 feet and would arrive with a measly 0.2 gallons less fuel. Total distance would be about 272 nm. To arrive at my destination with the same fuel I would have to spend about 131 minutes in cruise at 8,000 feet and would actually arrive about 90 seconds earlier with a total distance of about 398 nm.

Thanks for making me think.

Bob Patch
AOPA 7571653
Puyallup, Washington

Perfectly imperfect

Excellent article by Natalie Bingham Hoover (“Flying Life: Scars and Dents”). In a hobby like ours where the idea of perfection is often worshipped, it was refreshing to be reminded that the art and joy of flying is achieved through our necessary mishaps toward the ultimate goal of fun and safe competency. It reminded me of a fond memory of my dad, who was my aviation inspiration and owner of a 1955 Ford T-Bird. I was young and we were at a car show and I pointed out a T-Bird that was at least as nice and said, “Look Dad, there’s the first place one.” (His took ninth that show.) He smiled as we watched it being loaded on a chrome trailer and said, “Yeah, but ours is a convertible and we get to drive it all the way home while eating a ballpark hot dog.” And we did.

To scratches and dents—and even a little mustard on the seat.

David Underwood
AOPA 4416708
Nampa, Idaho

This is a test

It is true that there is no reduction in air pressure across a static port (“Test Pilot”). That is because the air flows straight across the port at a constant velocity. This has nothing to do with Bernoulli’s principle. (A static port is not a venturi.) Similarly, Bernoulli’s principle is not responsible for “lift.” (An airfoil is also not a venturi.) By Newton’s third law of motion, “for every action there is an equal and opposite reaction,” an airfoil forces air to curve downward and the reaction forces the airfoil upward.

Samuel Feldman
AOPA 565688
South Plainfield, New Jersey

As usual, “Test Pilot” was highly worthy. The one thing I’ll note, as someone who wrote central air data computer software for seven military jets, relates to the static source error question. The stated answer is amply true for subsonic and supersonic flight, but static pressure gets certifiably weird in the transonic regime, mainly about Mach 0.7 to 1.3. As speed increased in that range, the necessary error correction curves looked unpredictable except for an overall tendency to have the biggest errors near Mach 1.

The causes, of course, were the details of how localized shock waves formed on the airframe, and the peak magnitude of errors was surprisingly large, at least to me. In the B–1B and F–111, the Static Source Error Correction curve depended on five variables, only one being the measured static pressure. The other aircraft had conceptually similar static pressure corrections except for lacking dependence on wing sweep.

Paul Raveling
AOPA 562013
El Dorado Hills, California

Voice in your head

I just read Thomas A. Horne’s confessions in the article “On Instruments: An Approach to Remember” and appreciate his second (and third) guessing. Thanks for sharing—a good reminder to all of us to develop and listen to that “little voice” in the back of our head.

Todd Smith
AOPA 6341292
Creve Coeur, Missouri

Memories

I graduated from U.S. Air Force pilot training in January 1957. I was assigned to the 1739th Ferry Squadron at Amarillo Air Force Base, Texas. I had dreams of flying wonderful new multiengine aircraft to exciting destinations all over the world. After all my qualifications were complete, realism set in and my first mission in April was to ferry a C–47 from Sacramento to Tokyo. Once we got started, it only took us five days to deliver the aircraft with stops in Honolulu, Midway, Wake, and Iwo Jima. I went on to fly C–47s well over a thousand hours in rescue and reconnaissance. Today, I wouldn’t trade a single minute of that experience for anything, except for possibly a chance to fly one again, a feature article, or a new watch. Thanks for the nostalgia (“Pilot Briefing: Breitling DC–3 Wraps Up Its World Tour”).

Jim Rizor
AOPA 1203992
Henderson, Nevada