Date: October 30, 1992
Subject: High Performance Amateur-Built Aeroplanes
This advisory material is published to provide advice and information on certain characteristics associated with the design of amateur-built aeroplanes, particularly high performance amateur-built aeroplanes.
2. Reference Airworthiness Standards
Chapter 549 of the Airworthiness Manual, section 549.103(a)(2).
3. Background And Discussion
Transport Canada had, until 1990, imposed a wing-loading limit of 65 kg/m2 (13.2 psf) on amateur-built aeroplanes without flaps and 100 kg/m2 (20.4 psf) with flaps. These wing loading criteria were created to provide a maximum stalling/landing speed that the average light-plane pilot could cope with. This maximum was based upon the maximum stalling speed (Vso) of 61 knots contained in the United States Federal Airworthiness Requirements (FAR) Part 23 for single-engine and multi-engine normal category aeroplanes under 2723 kg (6,000 lbs.). This limit was derived from basic aerodynamics, relating Vso, Clmax and wing-loading for typical light aeroplanes of the 1940's and 1950's.
In recent years, with the progress of aircraft technology, increased demands for higher performance (higher airspeeds), and consequent availability of advanced modern technology kit-built aeroplanes, many newer designs are available which may attain significantly higher lift coefficients in the landing configuration. Consequently, these advanced aeroplanes may have wing-loadings exceeding the above-mentioned limits, but their stalling/landing speeds may be 61 knots or less. The possibility of flutter and divergence on these advanced high-performance aeroplanes is more prevalent than on slower, less advanced types and has led to fatal accidents in the past.
Amateur-built aeroplanes with a wing-loading exceeding 65 kg/m2 (13.2 psf) without flaps, or 100 kg/m2 (20.4 psf) with flaps, are defined as high-performance amateur-built aeroplanes. (ref. Personnel Licensing Handbook, Vol.I, Part II, Chapter 4, and Chapter 549 of the Airworthiness Manual, section 549.103)
Although flutter and divergence can occur at any airspeed, high performance aeroplanes are more prone to this than lower performance aeroplanes. This is due to several factors including: higher airspeeds and aerodynamic loads, less tendency for "over-design", and increased use of non-traditional methods of construction and materials affecting structural stiffness with the potential for displaying unusual failure modes. Therefore, amateur-builders and owners are cautioned to be aware of the potential for flutter and divergence with particular attention to the following:
- an aeroplane with a relatively clean aerodynamic design,
- an aeroplane where non-traditional construction techniques and methods are employed,
- an aeroplane with a stalling speed exceeding 61 knots or a wing-loading exceeding 65 kg/m2 (13.3 psf) without flaps or 100 kg/m2 (20.4 psf) with flaps,
- an aeroplane employing any of the following:
- pusher powerplant(s);
- canard geometry;
- T,V,X,H or any other unusual tail configuration;
- external pods or stores mounted to wings or other major aerodynamic surfaces;
- fuel tanks outboard of the 50% semi-span;
- tabs which do not meet irreversibility criteria;
- spring tabs;
- all-moveable tails (i.e. stabilators);
- slender boom or twin boom fuselages;
- multiple articulated control surfaces;
- wing spoilers;
- leading edge devices such as slots, etc.; or
- - geared tabs (servo or anti-servo).
6. Reference Material
- AMA 549.101 (paragraph 6) (August 15, 1987)
- FAA Advisory Circular (AC) 23.629-1A (October 23, 1985)
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