The GRETSS** history : 1983 - 1993

The GRETSS**, a new team

1983 - 1993

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[Parathon'air] [PLQMTM] [Ibex] [Résolution] [Marie-Antoinette] [Storig] [Minifarad] [Horus] [Promethée] [Arcadia] [Fox]

PARATHON'AIR (1983 -1984 François, Simon, Jeff, Papy)

mise au point de la télem au Ruchard

In August 1983 three new members of the club had participated (François, Simon & Michel) in a summer camp for experimental rocket building where they had developed a rocket recovered by an "umbrella" (PARAZIT). Although the electronic had worked perfectly, the mechanical construction lacked strength.

As a result of this experience the PARATHON'AIR came into being.

The club was strengthened with the Jeff & Papy & so the club GRETSS* became GRETSS**.

A bambi was chosen as the motor to simplify construction & since it was well adapted to the size of the project. The only negative point was that launch accelerations were in the region of 20G, requiring a very solid construction.

Parathon'air at the Ruchard with Papy (center in white), Gretss ' and Jean-L'ouille

The project incorporated 2 innovations for a rocket of this size:

An umbrella like aerobrake was used as a recovery system in the place of a normal transversally deployed parachute. At peak altitude 4 plates attached to the side of the rocket opened, acting as a breaking system for the rocket (an improved version of the system used in PARAZIT). A pyrotechnic system was used to initiated opening of the system with the airflow over the rocket leading to full deployment.

Principe de la récupération par parapluie

A telemetry system was used to follow the flight events (start of umbrella opening, end of opening & locking of each plate, initiation of pyrotechnic commands). Since 16 channels were needed it was very difficult to achieve this with an analogue system. Therefore, an electronic system was used. At the time I had an Apple IIe (it still works too!). This gave me the idea to use a 6502 & 6522 chip to perform telemetry functions. Also the opening of the umbrella was controlled by a microprocessor (this is now prohibited by ANSTJ, a sequencer / timer must be used to command deployment of the recovery system).

With a 3.5kg lift off weight, 63mm diameter & 1.4m length a peak altitude of 1200m after 13 seconds was calculated.

The launch took place at the Ruchard military camp. Despite a nominal lift off a gust of wind flattened the trajectory. As a result of this the rocket developed a much higher horizontal velocity than desired. So after 13 seconds when the umbrella was deployed the rocket experienced a very sharp deceleration & shock. This caused the telemetry system (which had functioned perfectly up to this point) to reset, resulting in no useful data being returned after this point. Additionally, the umbrella was seriously damaged during deployment & failed to decelerate the rocket sufficiently. As a result, Parathon'air impacted far from the launch site & was never found

PLQMTM (1982 - 1985)

PLQMTM (Plus Lourd Que Moi Tu Meurs) fût la première d'une longue série de navettes réalisée par le GRETSS**.

L'idée de base était de construire un engin dont la récupération ne poserait pas de problème (cf. PLEONASME2 et L'APLUBEL). Les navettes étant alors à la mode (on parlait beaucoup du Space Shuttle et déjà d'Hermès) et permettant en théorie de ramener l'engin à l'endroit désiré, le club décida (en même temps que le CAC ) de se lancer dans l'étude d'un tel engin.

Comme vous pouvez le constater sur le schéma, PLQMTM est composée de 2 parties distinctes qui se séparent à culmination :

Un planeur (de couleur rouge, pour ceux qui ne l'aurait pas reconnu) qui doit redescendre tout seul en vol plané télécommandé.
Un propulseur chamois et des ailerons pour la stabilité de l'ensemble en phase ascensionnelle.

Ce choix (qui s'avéra mauvais en fin de compte) vint d'une remarque toute simple : Pour voler en phase ascendante, une fusée doit avoir une marge statique comprise entre 1 et 3, alors que celle d'un planeur doit être quasiment nulle. Il paraissait alors logique de faire un planeur correctement équilibré et de lui adjoindre un étage propulseur munis d'énormes ailerons pour faire redescendre le centre de poussée.

En théorie, cela peut fonctionner, mais cela pose de très gros problèmes de réalisation. Il est très délicat de fixer des ailerons de 60 cm de coté (en balsa et fibre de verre) sur une virole de 10 cm en aluminium, et je ne parle pas des performances d'une telle configuration.

De plus, cette navette employait des techniques de constructions adaptées aux fusées (tube PVC, structure des ailes en bois et aluminium), mais inadaptées pour un planeur. Le résultat fût un engin très lourd (plus de 14 Kg, d'où son nom) et très fragile.

Le tir eu lieu en août 1985 au Ruchard et la navette se disloqua en fin de propulsion. Le pilote n'eut pas l'occasion de tester les réactions de l'engin en vol.

Une maquette animée par un micro-propulseur a été réalisée pour valider la stabilité en vol.

Elle se trouve sur une rampe spéciale avec Jeff au centre et Sakapus à droite

IBEX (1985 - 1986 Jeff, Simon, Gretss ', Michel)

After Parathon'air and PLQMTM a simple & reliable project was developed & again a Bambi was chosen for propulsion.

Technical data:

80mm diameter in aluminium & porteuse. Although the original weight was planned to be around 3.5kg, the final lift off weight was around 4.8kg which is very heavy for a bambi
Recovery by a transversally separated parachute activated by a PPUK (Pyrotechnic activated system). This system was subsequently used in many of the clubs projects.
A streamer released at maximum altitude .
Printed circuit boards mounted in polystyrene boxes.

2 telemetry channels using IRIG encoding :

A commercial acceleration sensor (+/- 25g)
A vibration measuring system using a flexible blade mounted between two fixed plates.

A sequencer / timer (using a 4060 chip) to activate the PPUK igniter.

IBEX décollera le 24 août 1985 à 16 heures du camp militaire de Mourmelon.

En 11 secondes, la fusée arrive à culmination (800 mètres). Mais pas de parachute. Que se passe-t-il ? Après de longues secondes d'attente (la minuterie s'était déréglée), le parachute sort enfin et la banderole est libérée. La PPUK est donc qualifiée et pourra être installée dans d'autres projets.

La télémesure subit elle quelques problèmes.

La courbe d'accélération est inexploitable sans qu'on est pu en trouver la cause (dérive du codeur IRIG, bambi à poussée inversible). Comme le dit le concepteur de cette télémesure, "Mort à l'analogique, vive le numérique"
La mesure de vibration est elle aussi inexploitable, le capteur ne mesurant pas grand chose.
Enfin, la télémesure s'est arrêtée 11 secondes après l'ouverture du parachute à cause de l'arrachage de l'antenne dard.

Bref, ce n'est pas la gloire !

Mais l'objectif premier a été atteint, le club a tiré une fusée en 1986 et il n'est toujours pas mort.

RESOLUTION (1986 François, Jeff)

A 1/2 scale model of a proposed experimental rocket boost glider (Storig), to test the stability & aerodynamic properties of the larger vehicle.

The objectives of resolution were two fold:

Verify stability of the Storig design during boost & glide phases of flight
Test construction techniques for Storig

Technical data

85cm span, in the form of a double delta, using a NACA 0006 airfoil and 1.050kg all up weight

Wings constructed from Polystyrene foam & balsa, covered with Solarfilm. Glass fibre body tube, with wooden nose cone.

No active guidance system, but a timer was used to move the elevators at the end of the boost phase of the flight. The timer activated a pyrotechnic device which released a elastic cord leading to elevator deployment

200m maximum altitude after 4 seconds of flight

Specially constructed 3m (10ft) launch ramp

Resolution was flown twice (first flight (in 7 photo) with a dik-dik, second with a Koudou). The boost glider functioned perfectly, with a stable flight gliding in concentric circles.

It will be relaunched a third time in Mourmelon. (August 1991) painted in black, powered by a Koudou. But this time, a remote control was embeded.

Based on this success the development of Storig was started.

MARIE-ANTOINETTE (1987 Freluquet, JFK and Manu)

It was the first rocket of this new team. Because of lack of documentation, I can't explain a lot about it.

If I remember correctly, Marie-Antoinette was powered by an Isard and carried 2 telemetry chanels.

Elle fit un vol balistique car la vis de sécurité qui maintient la fusée en une seule partie (au cas ou les goupilles sortiraient prématurément) n'a jamais été enlevée. La fusée est partie avec, les goupilles sont sans doute sorties à culmination, mais la fusée ne s'est jamais séparée.

STORIG (1984 - 1988)

en cours de rédaction

An elegant experimental rocket boost glider 2.42m long, with a double delta planform. This was propelled by a Chamois motor & radio controlled from the ground .

Storig was launched on 27 August 1988 at Mourmelon.

Sadly, Storig broke up at the end of the propulsive phase after 2.5 seconds of flight due to aerodynamic / structural overload.

MINIFARAD (1989 Simon and Papy)

A small but original design, built from condenser tubes. The objective of this design was to miniaturise many of the systems found in experimental rockets to fit into a mini rocket propelled by a Koudou (A G/H class motor).

Technical data:

30cm long x 50mm diameter, weighing 800g.
Transversally separated parachute compartment using a pyrotechnic device.
An electronic timer sequencer, with green, orange & red LED's to indicate the state of the sequencer.

Maximum altitude of 500m after 8 seconds of flight (August 1989 launch at Mourmelon)

HORUS (1990 - 1991 Miloux tout seul)

A day when Miloux was out of beer, he had an idea.Generally, when he's out of beer, he bougth some new bottles. But this day, he decided to realize all alone its own rocket

More mechanic than electronic, he decided to carry 4 IRIG chanels in an Isard :

Static pressure measurement (Altitude determination).
Dynamic pressure measurement (Airspeed determination).
Internal temperature measurement.
Acceleration measurement, using a sensor found in a cupboard at the club!.
.An LED display to indicate the state of the battery charge (with a UAA 180)

Construction from PVC tube, 1.9m long by a 63mm diameter. 4.7kg lift off weight.Recovery by a parachute deployed by sequencer / pyrotechnic device

Horus was launched at Mourmelon using an Isard motor & reached a peak altitude of 1800m after 18 seconds of flight. At this point the parachute opened & the rocket descended slowly to earth during 2m20seconds.

Unfortunately only acceleration & temperature data could be decoded due to a shift in transmitter frequency during launch (caused by a potentiometer coming loose)..

ARCADIA (1991 Michel)

Début 1991, Michel décide aussi de faire une navette propulsée par un Koudou.

Arcadia se caractérise par une aile trapézoïdale associée à un profil porteur. Elle dispose aussi de trois ailerons arrières disposés à 120°. Des maquettes en micro-fusée démontreront la bonne stabilité de l'engin en vol plané.

Sa structure est faite de styro entoilé de fibre de verre. C'est à la fois léger et solide.

Une télécommande permet d'actionner les 2 gouvernes placées en bas des ailes.

Elle sera tirée en août 1991 lors d'une campagne régionale à Stutzheim (comme ça s'éternue, à 15 Km de Strasbourg) sous les caméras de FR3 national (résultat, 2 minutes de reportage diffusés diffusé dans "une pêche d'enfer")

Le vol de cette mini navette ne sera pas aussi concluant que celui de ses maquettes. Peut après le départ, elle dévie de sa trajectoire et se met sur le dos. Ne disposant que de gouvernes sur les ailes, le pilote (JFK) ne pourra malgré tout ses efforts et sa superbe radiocommande la remettre dans le droit chemin. Elle finira par s'écraser tristement au sol.

ARCADIA et PROMETHEE IV sur l'aire de lancement peut avant le départ

PROMETHEE IV(1991 JFK)

en cours de rédaction

FOX (1992 - 1993 François, Hervé, Florent)

This rocket was built by Francois & two other students as technical project for their studies. The key features of this rocket were a pneumatic gyroscope, to measure the rotation rate of the rocket & very fine construction.

1550mm long, with a maximum diameter of 120mm. Total weight of 12kg.

Chamois motor, giving a maximum altitude of 1200m after 16s.

Parachute deployed by a pyrotechnic system with transversal separation.

Moulded conical nose & boatail sections joined to a central aluminium section. The moulds used to make these sections were fabricated using a programmable lathe.

A fantastic surface finish / paint job.

No external screws

Description of the gyroscope system:

General principle:

The gyroscope was invented by Foucault in 1852 to demonstrate the rotation of the earth & the laws of pendulum motion.

Any body which has a rapid rotation rate can be considered as a gyroscope. The properties of a gyroscope are due to an angular momentum caused by centrifugal force in the rotating mass.

If the gyroscope is not subject to a prolonged force it will maintain the same axis of rotation in space.

However, if a continuous substantial force is applied to the gyro one of two things will happen depending on whether the axis of rotation is constrained or not.

If the gyroscope is forced to follow the direction of the applied force it will react at right angles to the direction of the applied forcet.
If the axis of the gyroscope is allowed orientate freely, the axis of rotation will progressively orientate (precess) to that of the applied force. The rate of this change in orientation depends on the rotation rate of the gyro.

Choice of method for spinning of gyroscope:

To measure the rotation of the rocket around its axis during flight to maximum altitude the gyro must turn at a very high rotation rate (30,000 rpm or more) to give an accurate measurement.

Therefore, three different methods of spinning up the gyro were studied :

Wire spun gyro. A wire was wound around gyro wheel & attached to the launch ramp. At launch the wire, still attached to the pad spins up the gyro. With this system it is possible to obtain the desired rotation speed, but the system is not very practical. It cannot be tested before flight & there is always the risk that the system might jam during launch damaging the rocket.
Electrically spun gyro. An electric motor spins the gyro. This system was tested in Callisto (Michel & Papy), but was found to be very unreliable. The vibration of the motor disturbed the axis of rotation too much & the system was very complex & heavy.
Air spun gyro. Just prior to launch a high pressure air jet is applied tangentially to the gyro wheel until the gyro reaches the desired spin rate. After the air jet is cut off the gyro continues to rotate due to its inertia. With a 100m/s air stream it is possible to obtain rotation rates in excess of 60,000rpm. It was this system which was selected for the project.

Using the air gyro system it was possible to spin a 20mm gyro wheel up to 60,000rpm (the rotation limit of the bearings) using a 6 bar air supply flowing through a 1.6mm needle which acted on a series of blades on the edge of the gyro.30 seconds after the air flow was cut the rotation rate was still greater than 30,000rpm.

On the launch ramp air was supplied to the gyro through an umbilical up to a few seconds before launch, when the umbilical was retracted using a pyrotechnic device.

A low mechanical resistance potentiometer was used to measure rotation of the gyro through 360 degrees. Rotation rate data was to be downlinked using an IRIG encoded telemetry system & a transmitter provided (IBIS) by ANSTJ.

After 2 years of effort, Fox was ready for flight at the annual CNES / ANSTJ launch campaign in August 1993. The rocket had passed all safety tests with flying colours, but was finally not launched due to a logistical problem during the launch campaign!