Institute of Technology
Charles Stark Draper Laboratory
FROM: Dunbar. C. Collins
DATE: 20 october 1972
SUBJECT: Demonstration of the French Thomson - CSF, All Weather Approach and Landing Monitor (TC-121) Heads Up Display
On September 25, 1972 a technical presentation and flight demonstration of the subject system was given to interested MIT personnel by Mr. G. Klopfstein, Engineer in Chief of a technical mission from Ecole Nationale Superieure De L'Aeronautique of France.
The mission crew has been demonstrating the system in a French Nord 262 twin-engine turbo prop for the past month to pilots/engineers of USAF, FAA, NASA, Pan American, and the like.
MIT attendees were:
J. Nevins* C. Collins* (Pilot A)
I. Johnson* J. Dunbar* (Pilot B)
M. Connelly* J. Allen*
G. Edmonds* B. DeWolf*
A. Chavlagon J. Sciegienny
N. Polner I. Levin
* Participated in flight demonstration
Technical Presentation (approx. 1 1/2 hours):
Mr. Klopfstein discussed the systems design philosophy, derived the desired display parameters and generally described the system’s hardware elements, performance capabilities and operating techniques. Unfortunately, time did not permit a detailed technical description or discuss ion of system performance. Mr. Klopfstein promised that this data would be transmitted to us. When it is it will be circulated to the interested parties.
This system presents a novel solution to the problem of displaying to a pilot, in a simple manner, all the necessary parameters for achieving trajectory control without exceeding the aircraft operational constraints.
It was shown that relatively few parameters, i.e., flight path angle, angle of attack and energy margin indication can provide more useful information than many parameters normally displayed (pitch attitude, rate of climb, RPM, power ratio, airspeed, etc.).
The advantages cited were simplicity and reliability which provide ease of training, safety during emergencies, improved cruise flight control and marked improvement in landing performances, i.e., a reduction in landing point dispersion from 600 meters to 60 meters in evaluation flights by a French test group.
Manual control with this system is reported to be as accurate as automatic control in all weather conditions in cruise, landing or taxi operations.
Some points resolved in the presentation were:
1. The primary inputs for trajectory control and energy management can be provided by a vertical gyro for pitch angle, a local angle of attack sensor (linear relationship to true a) and vehicle X, Z axis accelerometers. These are the elements of the CV91 visual guidance display. Fig. 1 shows the CV91
“black box”. The system reportedly sells for approx. $10 000. The VOR-Localizer capture function requires additional ILS inputs, radio altitude, heading and roll angle which are embodied in the TC121 display.
2. The system is self corrective for headwind component during final landing approach but a curved flight path trajectory results. This may be avoided by manual compensation (holding velocity vector up - runway for headwind) or by setting a console control to the value of the reported wind to bias the velocity vector marker.
3. Pilot induced oscillations are minimized in that flight path angle response to pitch inputs is a smooth first order curve.
4. The angle of attack display provides much better lift control than that achieved through an airspeed display. Angle of attack is measured more accurately than airspeed and also eye discrimination of 1/20° can be attained with the collimated display.
5. Minimum landing point dispersion and consistent touch-down velocity is best achieved with a two-slope trajectory, one of 2 – 3° and a final of 0,6 – 1.0°.
Operations oriented descriptions of the TC 121 and CV9l are contained in the Thomson - CSF brochures available from J. Nevins, Ext. 8-1347. Selected excerpts from these brochures are attached. A written transcript of the technical presentation has been promised to MIT.
Flight Demonstration (approx. 1 1/2 hours):
Two flights were made to enable the MIT pilots to evaluate the system and to provide a TV monitor of the TC12l pilots display for a number of observers.
A 20minute warm-up/alignment of the inertial system was required prior to the first flight and a 1 to 2 minute hold for realignment during the ramp stop, engines running, between flights.
The inertial system used for this demonstration is also used in French fighter aircraft and is classified.
Cockpit configuration of the system displays included:
a. A linear scale instrument, located in the cockpit, which displayed flight path angle and potential flight path angle markers against a calibrated pitch scale. (fig. 3)
b. A co-pilot station, glare shield mounted CV 91 visual guidance display (Fig. 3, shown in retracted position).
The CV 91 is used to facilitate visual approach on runways without glide path facilities.
The flight path marker is manually set to a desired flight path angle by means of a selector switch on the center console. There were no angle calibrations on the display, nor horizon. The size of the cross is a reference value.
c. A pilot station, overhead-mounted, all weather TC 121 Heads Up Display. This station was off limits to guest pilots due to possible collision of HEAD and HUD.
The procedure followed was to demonstrate the bas ic concepts of the system on the linear instrument and then to familiarize each pilot with the control-display response of the CV 91 from the co-pilot' s seat.
The pilot varied power, lowered flaps, dropped the gear and simulated engine failure to demonstrate ease of energy management.
In each case the lowering of gp marker supplied a simple, natural cue for response. i.e. increase power if available or lower g marker by pitching down until g and gp are aligned. The MIT pilots easily established climbs and descents at selected angles and adjusted power accordingly for energy equilibrium (T = D).
Although overshoot of power settings was noted on the display the changes in configuration and trajectory were accomplished with little airspeed variation (1 to 2 knots).
Pilot induced oscillations appeared minimal.
Control of velocity vector was simple and positive.
Angle of attack control by power management was also exercised and found to be easily performed.
The use of the velocity vector as an aiming device was also demonstrated during a descent through clouds by pointing it at a hole, and following through. The same principle can be applied in mountainous terrain.
An ILS approach and landing on Runway 11 was demonstrated by the pilot. Surface wind was approx. 240/15 Kt. Subsequent landings by MIT pilots were made on Runway 29.
The primary pilot tasks were:
1. Accomplish turn on to final approach
2. Establish glide path by holding velocity vector on the runway threshold (glide-path pre-set to 2 ½° )
3. Make heading corrections to align flight path with runway center line (strictly visual) .
4. Adjust power to approx. align gp and velocity vector,
5. Keep angle of attack within reasonable limits.
6. Cut power fully at pilots command (approx. 60 ft. altitude) and flare by pitching up to align velocity vector with far end of runway.
7. Maintain direction and velocity vector aim point until touchdown.
First approach (pilot B) was flared too early and touchdown was attempted by the standard method of “feeling for the runway”. The touch-and-go landing was completed by the pilot.
Two More approaches were made with the CV 91 used for both glide path and flare. Both touchdowns were smooth with landing point as targeted.
Pilot A then made 4 approaches and landings with consistently good results.
The system really facilitates the visual approach - there is no unnecessary jockeying of controls or preoccupation with altitude, airspeed, rate of descent, power setting, etc.
The aircraft was very stable.
Crosswind was no problem.
The CV 91 display brightness was adequate for the variations in background encountered, mainly cloudy with fair to poor visibility. Brightness is adjustable. The field of view, a 90 mm pupil, seemed adequate. There was no vibration and no appreciable obstruction of forward view.
The format is simple and easy to interpret.
Although we would have preferred to fly the TC l2l display to view the more complete symbology, we feel that the CV 91 flight adequately demonstrated the basic concepts.
It is suggested that altitude below 1000 feet be displayed digitally in 10s of feet similar to the flight path angle display on the TC121.
In summary, the system offers a number of advantages. It provides an on-board capability for making precision (visual) approaches to non-instrumental landing sites. It provides flight performance cues which do not exist in the ordinary flight director attitude displays.
It has particular value for off-nominal flight conditions, i.e. in the event of an engine failure the pilot has the cues to enable him to immediately assume the proper pitch attitude which will result in the best engine-out climb speed. It may have great value in application to the military tactical environment in a forward area where a minimum amount of navigational and landing aids would be available, It certainly is an excellent prototype flight test tool.
Prof. T. Sheridan
Prof. P. Whitaker
Prof. R. Curry