On this page, we at Training Technology International field some of your questions.  Please don't forget that, as a registered user, you can also post questions on our Forum which also allows other registered users to post their answers and comments.

Here's the first one.

• "We train Pilots and other Crewmembers on various rotary wing aircraft for military purposes and are trying to form standards similar to the FAA... The question I have is what is the standard for visual models? While integrated with the host computer how many moving models, e.g., trucks, planes, etc., should be seen in one screen?"

Fred Krajewski, Albuquerque, New Mexico

Answer:

There are two documents that define standards for commercial helicopter simulators; FAA Advisory Circular 120-63 "Helicopter Simulator Standards", and the European Joint Aviation Authorities (JAA) document JAR-STD 1H "Helicopter Full flight Simulators".

The referenced documents require visual systems to contain the following features:

Three specific airport models for use an operator's typical route flying procedures.
"Capability" to present ground and air hazards.
Sufficient scene content to conduct training scenarios in the operator's approved training program.
An "operator" in this context refers to commercial entities such as an airline or corporate operator of fixed or rotary wing aircraft.

Neither document specifies a minimum or maximum quantity of moving ground and air hazards that must be displayed in a visual scene.

Operators comply with the FAA/JAA requirements for moving models (e.g., trucks, planes, etc.) with a single airborne hazard that can be selected (by the instructor) to intrude on the host airplane from any direction or altitude. Ground hazards can be selected to appear at designated locations on the airport runways, taxiways or terminal ramps. The maximum number of moving ground objects that we have seen used in a current generation visual system is four (4), although we're sure more are possible.

Visual systems that we have seen on helicopter simulators contain many more moving ground objects than those found in a typical commercial simulator. However, we are not aware of any document describing a specified quantity of objects to appear simultaneously in a visual scene (database). Decisions on required quantity of objects and scene content are usually a determined by the user's training scenarios and capability of the visual system technology to meet the specified requirement.

Evans and Sutherland, a major visual system supplier, have a product called "Harmony" undergoing testing on a network of six helicopter simulators which can be operated together. It was due to the need to network the simulators that the initial demonstration was 350 models, the capability to demonstrate 500 models displayed simultaneously, or are selectable through a lesson plan menu, is now available.

- Joe DePaola & Murph Morrison
Managing Partners, Training Technology International

Another set of questions has been sent to us, this time from a simulator manufacturer. We feel that they have highlighted some areas that may cause others in the industry some concerns. Our answers are given but we invite you to raise any issues about them that you feel are important. Please note that although the questions posed relate to rotary wing aircraft, some aspects apply to both fixed and rotary wing types.

• Question 1 ~ For validation tests, it is quite common to get slight deviations in the trim/starting conditions with regard to the reference data which, although within tolerance, effectively reduce the allowable margin for the simulator responses. Might it be acceptable to offset the tolerance band so as to be centered in the actual trim/starting conditions during the test?

Answer ~ It is common to have some reference values offset at the start of a test but are you asking if you can offset the tolerance centre point for the whole plot so that would effectively mean instead of +/- 5% (or whatever) it becomes +8/-3% (or whatever)? That would be unacceptable in so much as we believe the tolerance is specific to a piece of A/C data at a specific time.

• Question 2 ~ Because of unavoidable differences between the sim tests and the real world (gusts, turbulence… that cannot be accurately characterized in the reference flight test data) an exact replication of all control inputs usually tends toward divergent behaviour even in a model otherwise perceived as fully representative by the pilots. Which tolerances/deviations might be acceptable for those control inputs not being the direct object of the validation test performed (i.e. lateral/directional for a longitudinal step response check)?

Answer ~ It might be because the A/C data is not detailed enough, meaning you either have not recorded enough parameters or the parameters do not have a high enough resolution to see exactly what the A/C is doing. Regardless, if the sim inputs are accurately following the A/C and the model is good, then the sim outputs should follow within tolerances. However, there are often differences between simulator tests and real world data due to wind velocity etc. as you state. Even with the correct control inputs the response can be divergent in long period tests. One testing method to overcome this is to use a closed loop feedback system to maintain the profile; deviations outside the tolerance parameters can be axplained as a note to the test result. See Vol I of RAeS Handbook for examples of these conditions & the explanations provided for the differences. The amount of acceptable deviation on the inputs we are afraid is down to "good engineering judgement". Any systematic error across multiple tests should be clearly explained (or justified) in a rationale. (We assume that you are discussing the parameters that are those mandated for the test in the Table of Validation and not those additional parameters listed in the RAeS Handbook, which are listed to assist in any fault analysis, and in which deviations might be acceptable).

• Question 3 ~ We developed and tuned the controls loading model to fully match the controls force/position measurements taken in a reference aircraft provided by the customer, but during subjective evaluation the pilots requested about 30% controls force increase. To readjust the model is an easy task but then we loose any objective reference. What would you suggest to handle this situation from a formal point of view?

Answer ~ You do not say in which flight control axis the control forces were too low, if it was the collective then the friction adjustment might not be representative, if it was the cyclic forces, which are normally very small, we suggest you might set up two files, one to data from the Fokker (target) plots and the other to those requested by the pilots and then run with the subjective pilot forces until you have had a significant number of pilots to comment on the forces. The normal situation is that the Fokker plots are taken without vibration and when there is vibration, as in the helicopter, then the running friction is lower and the hysteresis force loop smaller. Another issue is whether the pilots validating the results were true test pilots or those with significant experience on the aircraft type and that the a/c data was recorded correctly to provide the target values. It is not unusual for there to be variations between individual aircraft although a 30% difference is unlikely if the data aircraft had been properly maintained. We assume that the data was collected by yourselves or by contract and was not supplied by the aircraft manufacturer. In either case it would be wise to obtain additional data test cases in order to explain whether there was any discrepancy in their values. Having considered all of this and still being unable to resolve the issue, we would suggest that the matter be discussed with the Authority prior to submitting the QTG for validation and we cannot emphasis enough the need to discuss this issue with the relevant NAA ahead of time. A 30% change in control force would need some very careful explanation. Its more than likely that there's an error somewhere in the model and not necessarily in the control system.

Please send your questions to us or better still, post them on our Forum so that others can respond....