November 1, 2013
As a pilot and airplane builder with an MIT degree in aerospace engineering and a career in the defense industry, I have been watching with interest the development of electric vehicles for three decades.
While I understand this article is intended as a glimpse at a possible future for aviation, I feel compelled to point out some technical shortfalls. The biggest issue, which I find to be encouraged by advocates of electric vehicles, is confusion of measurements. Energy is not measured in watts any more than it is measured in horsepower. Both are measures of power. Statements in the article such as “lead-acid batteries put out about 11 watts per pound” and “at 5,500 watts per pound, gasoline” are meaningless without also specifying the time. An ordinary lead-acid battery can easily exceed 100 watts per pound while cranking a starter, but will be dead in a matter of minutes. Power multiplied by time yields energy. For most of us in aviation, a more intuitive measure of energy would be horsepower-hours or horsepower-minutes. We all have a pretty good feel for what 100 horsepower can do when applied to our propellers for one hour.
Expressed in these terms, one pound of gasoline burned in my Lycoming O-360 will provide two horsepower-hours of usable mechanical energy to the propeller (less time at full rich, full power; more with careful leaning at cruise). One pound of the best lithium polymer battery performance claim I can find on the Internet, using the efficiency Yuneec claims for its new 81-horsepower motor on its website, will only provide 6.9 horsepower minutes. That’s 17.4 times more energy per pound from gasoline compared to the best battery I can find.
The example electric aircraft in the article are also so far removed from the proven practical GA archetype as to make fair comparisons impossible. Motorgliders and the very lightest LSAs and ultralights are good pioneering applications for electric propulsion because they need very low amounts of total energy with relatively high (but brief) peak powers—a perfect electric motor application. I might someday find myself experimenting with such a design, perhaps as a post-retirement project, but I certainly would not expect the resulting aircraft to be good for much more than a Saturday morning buzz around the patch or over to the neighboring airfield.
This technology is much further from being competitive to replace gasoline in everyday applications than any of the advocates would have us believe.
Before we get all rhapsodic about electricity and its environmental friendliness, we should acknowledge that the battery stores energy, it does not create it. If you follow the electric lines from your charging station, they will eventually lead you to a coal- or gas-powered generating plant. While the electric airplane does not generate any pollution here, it does generate it there. It may be that solar is the only truly clean energy, and it is so diffuse as to be of little real use. In the short run, I’m still hoping for a solution to the avgas problem. My Cherokee is calling and I must fly.
Rio Rancho, New Mexico
I read Dave Hirschman’s “Dogfight: ADS-B Abom-ination” article and I agree. Why can’t the FAA drop its signal blocking? They should broadcast all traffic information. I have Foreflight with Stratus 2 so I only receive glimpses of the complete traffic picture when there is an ADS-B Out aircraft nearby. To improve flight safety, I should always be receiving this traffic information.
At EAA AirVenture, I asked everyone I could find why the FAA does not broadcast all traffic information. The vendors say it is not a bandwidth issue, but a policy issue. The representatives at the FAA ADS-B display did know about the issue. Can we get AOPA to advocate for the FAA stop this data embargo? I think AOPA should use its organizational influence to help convince the FAA to broadcast all traffic information.
What might be forgotten in the debate is that ADS-B is a surveillance tool and the add-ons are just to sell the concept to U.S. general aviation. Ian Twombly might suggest that the main reason to go ADS-B is weather—I respectfully disagree. The only weakness in Hirschman’s argument is that I understand that one reason for the dual systems is a national imperative because of 1090 MHz (radar) congestion in some of the busy heavy-metal airspace corridors. In Australia, we have gone to only the international ADS-B standard 1090ES, which has added a safety benefit that the heaviest TCAS can see GA aircraft without needing translator stations. We don’t have radar congestion. I guess the U.S. has the sheer GA mass to allow it to go dual systems, and I also guess it is a great boon to avionics manufacturers—but for me, dual systems increases the chance of disaster.
Tom Haines might want to check his info source regarding the IO-520 power output he refers to in his article about the Bonanza G36 (“Classically Modern”).
I don’t believe any of the normally aspirated IO-520s used in the A36, V35B, and F33 were rated at 300 horsepower for takeoff. They were, I believe, rated at 285 horsepower both for takeoff and operation at full throttle and 2,700 rpm.
I think the two-blade propeller version did have an rpm limitation. The IO-550 is rated at 300 horsepower for both takeoff and continuous operation (again, full throttle and 2,700 rpm). It’s interesting that a lot of pilots still treat the full throttle and 2,700 rpm mode as though it were a power setting restricted to takeoff, and climb, using the old “25-squared” setting.
Yes, I’m aware that the POH recommends 25 squared, but this is not a limitation, and that 2,700 rpm is noisy. I reduce my rpm to 2,500 until clear of noise sensitive areas, and then it’s back to 2,700 until I reduce rpm for cruise. The throttle remains full forward until sometime during the descent, when I make a reduction to remain out of the yellow airspeed arc. It has served me well, and my IO-550 enjoys very cool cylinder head temperatures, both in climb and cruise.
Palos Verdes, California
The Aviators sounds interesting, and I will have to search it out on iTunes or Amazon! However, I am a bit perplexed on the perspective control lens used to turn what is a RV–8 (tandem seating) into a quoted “RV–7” on page 74—applied tongue in cheek and I enjoyed the article anyway!
Grand Haven, Michigan
Whoops, you’re right, Mr. Larsen. Thanks for keeping us honest.—Ed.
In “GA on TV,” the sidebar to The Aviators story, you neglected some earlier TV series that were produced around the period that Sky King was, and which used GA on a regular basis: Jungle Jim, who regularly flew around parts of Africa using a Republic RC–3 Seabee in the late 1950s; Steve Canyon, based on the comic strip character about a colonel in the United States Air Force from 1958-1960; Whirlybirds, late 1950s. Based on two pilots running a helicopter (Bell 47) charter operation; The New Bob Cummings Show. Bob was an avid pilot in real life and used his Taylor Aerocar in this 1961 series; 12 O’Clock High aired 1964-1967 about a B–17 bomber group during WWII.
These shows sparked the interest in flying for many a child. They did for me!
West Hartford, Connecticut
In “Test Pilot,” Question 8: When making a VFR, straight-out departure, a pilot should not make his first turn “whenever he wants” (erroneously indicated as the right answer). Pilot regrets the error.
We welcome your comments. Editor, AOPA Pilot, 421 Aviation Way, Frederick, Maryland 21701 or email ([email protected]). Letters may be edited for length and style before publication.
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