scope:

INTRODUCTION

This leaflet was previously issued as Leaflet 600/1 of DEF STAN 00-970 Issue 1 and gives information related to 2.1.1 to 2.1.27.

The flying qualities of an aeroplane are intended to embrace those stability and control characteristics which govern the ease and precision with which a mission may be carried out and those characteristics which have substantial effects on flight safety. The Contractor should bear in mind that the ease of control may be affected by such factors as the pilot's seat installation, view, the form of guidance provided, the instrument display, the weapon aiming system. It is important therefore that any simulation or flight test assessments should be carried out with an overall installation that is as representative as possible of production aeroplanes.

Clearly, as these qualities become progressively degraded by failure (which may occur in the structural, mechanical or avionics systems) the probability that the mission will fail due to deficient flying qualities will be increasing, while further degradation may lead to impaired flight safety. The definition of acceptable rates of mission failure due to deficiencies in flying qualities will be the responsibility of the Aeroplane Project Director and will be set out afresh in each new case. To offer the best chance of success for an important mission the Aeroplane Project Director will require a high standard of flying qualities; thus the definition process will usually involve compromise between success rate on the one hand and cost or complexity on the other.

In the present state of knowledge, it is not possible to frame general requirements for flying qualities based solely on numerical values for the parameters involved. Although such an approach might be possible within a particular simple class of aeroplane, the large variety of aeroplane configurations and the diversity of missions to be covered within some classes make it too restrictive and unreliable for general use. In several instances, therefore, terms such as 'piloting difficulties' or 'undesirable' are used in the requirements. The final interpretation of these and other similar terms (where there is no associated Acceptable Means of Compliance) will be by agreement with the Aeroplane Project Director. Where numerical values are attributed to the parameters used in framing the requirements, compliance with these values will not necessarily lead to the desired levels of flying qualities being achieved.

The numerical requirements are generally stated in terms of a linear mathematical description of the aeroplane. Certain factors, for example flight control system non-linearities and higher order characteristics or aerodynamic non-linearities, can cause the aeroplane response to differ significantly from that of the linear model. The contractor shall define equivalent classical systems which have responses most closely matching those of the actual aeroplane. Then those numerical requirements which are stated in terms of linear system parameters (such as frequency, damping ratio and time constant) shall apply to the equivalent system rather than to any particular modes of the actual system. The Aeroplane Project Director shall be the judge of the adequacy of the response match between equivalent and actual aeroplane.

The requirements of Part 6 are intended to apply not only to a particular test aeroplane but also to all aeroplanes of the type. A number of the components that go to make up a complete aeroplane are subject to tolerance. The effects of some of these tolerances can be eliminated during normal production flight testing. However, it may be necessary to change components in Service and it is unacceptable that there should have to be special selection of components or lengthy checking procedures. The Contractor should therefore attempt to ensure that aeroplane behaviour is not significantly affected by the full range of tolerance of particular components of the system. In appropriate cases, flight tests may be necessary at such limits of tolerance.

The proper use of flight simulator facilities permits a flexible approach to the optimisation of the flying qualities of a projected aeroplane in many of its flight phases. The flexibility is reflected in the requirements and leaflets of Part 6 on the assumption that piloted flight simulator techniques will be used where appropriate during the design of any aeroplane in which special problems in flying qualities may occur. It is therefore important that appropriate test pilots nominated by the Aeroplane Project Director should participate throughout in the use of simulators.

The requirements and leaflets of Part 6 are based on the US document MIIL-F-8785C dated 5 November 1980 and MEL-F-83300 dated 31 December 1970 (Military Specification: Flying Qualities of Piloted Airplanes) and the associated explanatory information in Ref 1. Although there are a few major departures, the requirements of Part 6 are consistent with the US requirements in most cases and, where applicable, the corresponding paragraphs of Ref 1 are quoted in the leaflets.

DEMONSTRATION OF COMPLIANCE

As far as possible, Acceptable Means of Compliance are specified using parameters that can be directly measured in flight tests and in these, cases the Demonstration of Compliance may often be derived directly.

However, flight testing is expensive and sometimes dangerous. To indicate the likely ease of meeting the requirements, and the more critical areas of the flight envelope, analysis, calculation, model or other tests and simulation should be used. Only after these exploratory investigations have been made for a particular aeroplane can a schedule of minimum flight tests to demonstrate compliance be made.

Compliance with some requirements cannot readily be determined quantitatively by flight testing; for example, some dynamic stability requirements, and requirements related to theoretical turbulence models. In these cases, compliance can be shown by theoretical calculation or simulation, by agreement with the Aeroplane Project Director, provided that the data used is derived as far as possible from flight testing and provided that some back-up qualitative flying is done; for example, some flying must be done in real turbulence.

SPECIFICATION OF MISSIONS (LEAFLET 600/6)

The Aeroplane Specification should define the entire spectrum of intended operational use and consideration should be given to the variations of useful load, flight time, speed and altitude, in the specification of missions. For the purpose of requirements 'missions' are intended to include operational flights, aborted flights (e.g, flights in which the aeroplane returns with the weapons unused) and training flights.

In its definition of the training missions to be considered, the Aeroplane Specification will take account of practical constrains which would not always be relevant to wartime operations. For instance, in training (and in peacetime flying generally), experience of asymmetric stores complements is likely to be more frequent and to cover wider combinations because it may more often be necessary to carry out further attacks or to return to base with partially expended loads; in such circumstances, however, it is reasonable to be less demanding in respect of the associated flight envelopes because the performance required will be less than that required for wartime operations.

STATEMENT OF REQUIREMENTS

Each of the requirements of Part 6, other than those for performance given in Chapter 606, is stated, where appropriate, in terms of the following:

The type of aeroplane - Class

The flying task - Flight Phase

How good the flying qualities must be - Level

Combination of these groupings would permit 36 different values for each flying qualities requirement, even after combining the flight phases into 4 categories. Seldom will such a fine breakdown be required, nor will there be sufficient information available to make such fine discriminations. Thus, in most cases, the 36 possible values have been combined to some extent, but not necessarily in the same pattern for all requirements. In other cases, different or additional breakdowns are required, eg a specific flight phase.

The performance requirements of Chapter 606 are stated in the terms of Groups determined by levels of safety and in particular by the extent to which the aeroplane is required to survive an engine failure. For each Group three standards of performance are specified: the Normal Operating Standard (NOS), with the highest degree of safety, which is the standard normally used; and the Reduced, and Military Operating Standard (ROS and MOS) which would apply when the urgency of the mission justified greater risks or penalties (See para 2.3 below).