Letter from Chris Heintz

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Letter from Chris Heintz

May 10, 2007:

As the designer of the Zodiac CH 601 series of aircraft, I take it very personally when I hear of a fatal accident involving one of these aircraft, especially when it involves elements of an in-flight break up.

With the introduction of the Light Sport Aircraft rule, I personally re-calculated the entire Zodiac CH 601 XL design to confirm that it exceeded all minimum LSA design requirements. The structure of the design is comparable to the Alarus CH2000 FAR 23 certified aircraft (now certified in more than 20 countries). The present Zodiac XL S-LSA model is stressed to an ultimate +6/-3 g at 1,320 lbs.

Still, we have seen a disturbing number of accidents over the last year, including the most recent one on May 2, 2007 (NTSB Identification: DFW07LA102). Having evaluated the wreckage photos of a Zodiac crash in 2006, I am in the process of starting yet another complete set of structural load tests on a production airframe. This will be done at the Zenair Ltd factory in Canada. In order to make absolutely certain nothing is missed, an independent structural engineer will confirm the findings of these rigorous tests.

While I remain fully confident that my Zodiac XL design will again be found to be sound in every respect, it is important for builders and pilots of this popular airplane to have full confidence in the integrity of the aircraft. Findings of the tests will be communicated through this website.

Special note to Zodiac Pilots: The Zodiac aircraft has a large amount of elevator control. I designed this feature so that if a pilot improperly computes the C of G before flying, he/she will in most cases have enough elevator authority to safely return and land. Also, like most of my other aircraft designs, the Zodiac has excellent control authority at low speeds. It is critical that this extra controllability not be abused. Pushing the stick rapidly full forward at cruise speed - even briefly - can result in serious damage to the airframe. Caution must be exercised to not inadvertently push the stick rapidly to its limits ( i.e. while stretching, reaching into the rear baggage compartment, etc.). Remember also that, without a doubt, you will always have a more enjoyable flight if the weather is "severe clear".

Please continue to be safety-conscious whenever you fly. Always stay within the design limits of your aircraft and well within your own abilities as the pilot in command.

Chris Heintz.

Update: Photos of structural load testing performed by Zenair Ltd. (photos posted on June 18, 2007).

Update: March 2008 Update Letter from Chris Heintz

Update from Chris (July 2007):

"To 'certify' the CH601XL in the LSA category, a complete stress analysis was performed and confirmed for the positive loads be static tests. No permanent deformations were found at limit loads (i.e. +4 'g') and no failures at ultimate loads (i.e. +6 'g'). The bending deformations were in accordance with the analysis and the torsional deformations were barely measurable, removing the possibility wing or tail flutter.

Load testing the Zodiac XL by Zenair Ltd. (June 16, 2007)

"Recently, Zenair Ltd. also performed static tests of the negative loads on the wing, fuselage and horizontal tail (see photos) and the results were similar to the positive load tests: No permanent deformation at limit loads and no failure at ultimate 'g' loading. The bending and torsional deformations were very small (the torsional twist was practically zero!).

"I want to remind and reassure every owner, builder and pilot that not only is the main structure well in compliance with the ASTM standards, but also, 'accessories' such as the seat -belt attachments, battery installation, etc... were all static tested with very satisfactory results.

Owners should take note that the CH601XL has relatively light pitch control forces and that it is possible to exceed the positive (+6) and the negative (-3) ultimate load factors if forcing the controls in a very rough or sudden manner. Please be reasonable: the fact that the CH601XL can perform aerobatic maneuvers very well does not make it an aerobatic design."

A Brief Note from Zenith Aircraft Company:

We are pleased to report that our red and white factory demonstrator Zodiac XL (N9601Z) is now six years old and has logged over 1,000 hours. The aircraft has crisscrossed the United States dozens of times through all kinds of conditions. We fly well over 300 demo flights per year in this aircraft; that's over 1,800 passengers over the last 6 years. Additionally, over 15,000 people have taken a seat in this aircraft over the years at different shows and fly-ins, as well as at the factory. The plane flies as well today as it did when it was new; we feel very fortunate being the kit manufacturer for such a fine aircraft. The fact that our demo plane still looks and performs as well as it does is a testament to the design's integrity and robustness.

Zenair Ltd.
www.zenair.com
Light aircraft since 1974.