Twin Cessna Flyer Magazine Article

Twin Cessna Flyer Magazine Article

Since the subjective performance increase (especially in climb) seemed too good to be true, I went to and used the historic flight data to calculate as objectively as possible my average climb rates with and without strakes and Speed Covers. (Since there is no way of accurately estimating the winds aloft for each flight, I did not try to use this method to calculate average speed increases.) I always use the same cruise climb power setting (35 inches and 1900 RPM) and most of my flights are at about the same weight. I recognize that variations in temperature and other factors could have affected performance but the Flightaware data should provide some confirmation of my inflight measurements, subject to a margin of error. Based on my calculations, the average climb rate with strakes and Speed Covers below 20,000 feet increased by 233 fpm from 636 to 868 fpm, a 37% increase from the earlier flights. From 20,000 feet to 25,000 feet the average climb rate improved by 253 fpm from 393 fpm to 648 fpm, a 65% improvement from stock. (See table above.) Subjectively, the performance increase is consistent with how the plane feels: the effort to get up to the flight-levels seems greatly reduced, and the plane is more stable in yaw (especially when heavy). A quick calculation shows the improved climb rate is the rough equivalent of adding 5% more horsepower or 2 inches of MP. The strakes added stability and climb performance. The Speed Covers added more to the climb and cruise speeds. Given the cost of the modifications and the installation time, my opinion is that every 421C should have the Speed Covers. If there is money left in the budget, I am super pleased with the combined performance of both strakes and hubcaps, and recommend them both for speed and single engine safety margin. My expectations have been exceeded. The performance improvements allow the airplane to get up to the flight levels efficiently and fast, saving a lot of fuel and thus increasing the range.

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