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Sonex Submits Sport Pilot NPRM Comments

May 3, 2002. Oshkosh, WI


Sonex,ltd Comments Released today on Sport Pilot NPRM:

Sonex,ltd submitted the following comments to the FAA today regarding the Light, Sport Aircraft NPRM:

1. Eliminate the Maximum Speed in level flight with maximum continuous power (Vh) of 115 knots [FAR Part 1; Definitions and Abbreviations]
Sonex recommends the elimination of the Maximum Speed in level flight. The top speed of the Light, Sport Aircraft is naturally limited by the other definitions, most notably the maximum stalling speed (Vso) of 39 knots CAS and the maximum stalling speed without the use of lift-enhancing\ devices (Vs1) of 44 knots CAS.

The Maximum Speed Limit (Vh) of 115 knots greatly reduces design efficiency and adds nothing to the safe operation of the "Light, Sport" Aircraft.

The current Sonex Airframe, which was designed to optimize the Ultralight Aircraft Requirements of Europe and Canada, has been designed to be used with 3 engine options all operating at a gross weight of 1100 lbs. The first two are rated at 80hp and translate to performance that fits perfectly into the Sport Pilot Proposal in its current form. The third engine option is rated at 120hp, which puts the Sonex top speed out of the Maximum Speed in level flight as it is currently defined.

Sonex,ltd believes most sport pilots and light, sport aircraft will be operated out of short, grass strips sometimes with obstacles at the approaches and often at high density altitudes. Regardless of whether the 80 hp or 120 hp engine is fitted to the Sonex, the low speed handling is identical. This means the pilot skill required to operate either model is the same and that more power is available if it is needed with the larger engine. With the standard Sonex Propeller, the additional power the 120 hp engine provides translates to a 50% increase in climb performance along with an increased cruise speed of 130.32 knots (150 mph) and top speed of 147.7 knots (170 mph).

Many Sport Aircraft, with the engine at less than full power, can be accelerated to speeds well in excess of Vh by simply dropping the nose. The ability to increase kinetic energy will always be there, and is limited only by the Vne of a particular aircraft.

If adopted as is, Sonex, ltd will be fitting flat-pitch propellers to the larger engine option to meet the Maximum Speed Limit. Unfortunately, this will dramatically reduce the cruise performance and greatly reduces the efficiency of the Sonex design (higher fuel burn rates). We don't believe there's a pilot who flys today that hasn't been in a situation where a little extra power (as in the 120hp engine option) that would have been welcome to get them up over trees or out of a grass strip faster.

In conclusion, the Maximum Speed requirement does not enhance safety and penalizes design efficiency.

2. Eliminate the 87-knot Vh speed limit for student sport pilots. [SFAR 89, Sections 35(e), 65, 73, 83, and 121-(3)(iv), Section 135(c)]
Sonex believes this special speed limit for Student Pilots will provide for less safe aircraft to be operated by Student Pilots.

In order to meet this requirement, "Light, Sport" optimized designs like the Sonex will be forced to use the smallest horsepower engines, reducing the available power to the Student Pilot and making accidents on short grass strips with obstacles more likely.

The only effect this part of the proposal has is to reduce the level of safety for student pilots and makes them less prepared for operating standard "Light, Sport" Aircraft.

How to make a comment:
If you share a similar view with Sonex on the top speed requirement, we\ highly encourage you to send a comment to the FAA. At this late date, there are two ways to submit your thoughts. We encourage all builders to add to or change our comment in any way they wish.
1. Electronically: EAA has set up an electronic submission form at:
2. Fax: Prepare your letter and fax it to the Docket Office at 202-493-2251. Only one copy needs to be faxed. Make sure your comments include your name, address, phone number/e-mail address.

Further instructions are available on the EAA's Sport Pilot Web Site at:

Sonex,ltd is very excited about this proposal and will continue to tout the Sonex as the class-optimized "Light, Sport" Aircraft.

FMI: Contact Jeremy Monnett, Sonex General Manager at the numbers or e-mail below.
Tel: 920.231.8297
Fax: 920.426.8333

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