Will's Cert 3 recovery subsystem

This project uses dual-deployment. The rocket separates into two halves, retained by nylon webbing, at apogee. It uses only a 36" drogue parachute until 1000' AGL. The perigee charges then deploy the recovery system from the forward compartment. My review team recommended the use of separate parachutes for the nosecone and for the rest of the rocket.

The lower airframe and avionics bay are recovered by a RocketMan R14 parachute. This is pushed out of the payload bay last but is not contained in a deploy bag, so it will open immediately. It retains the deploy bag leaving the 15' parachute attached to the nose cone.

At apogee the redundant charges shear the four #4 nylon screws and separate the lower airframe from the avionics bay and nosecone. These two pieces are attached together with about 50' of nylon webbing. There is a 36" parachute attached to the webbing. The nose is heavy enough that it might "streamline", and not properly "tumble", without the drogue parachute. Nomex parachute and line protectors are used.

At 1000' the perigee charges shear the four #4 nylon screws holding the nose cone to the upper recovery bay. The nose cone has its own 15' parachute which is housed in a deploy bag. The deploy bag is retained by the avionics bay. The avionics bay and lower airframe are recovered by a RocketMan R14 parachute which is protected from the ejection charges by a fireproof cloth.

Parachute sizing

The nosecone by itself weighs about 31 pounds. Ed Rowe has kindly loaned me a 15' parachute for the nosecone. The Descent Rate Calculator page at AeroCon gives a descent rate of 14 ft/sec.

The rest of the rocket weighs about 15 pounds. (This weight is TBD awaiting final assembly.) The RocketMan R14 parachute is rated for 20 to 35 pounds and yields descent rates from 15 to 20 feet per second.

Rocket Drift

The manufacturer recommends launching this rocket in winds of less than 5 MPH (or 7.3 ft/sec). At 15 ft/sec sink rate the rocket would take 67 seconds to reach the ground. The maximum expected drift would be about 500 feet.

Ejection charge sizing

Apogee

The apogee recovery bay is about 7" deep and about 10" across. The MissileWorks B.P. formula is: grams of B.P. = Compartment Diameter (inches) * Compartment Diameter (inches) * Compartment Length (inches) * 0.006 which yields a charge of 4.2 grams.

This ejection charge calculator says that charge would generate 15 PSI and handle 21 shear pins. They recommend 8 to 15 PSI. A 2.27 gram charge generates 8 PSI.

A three gram charge will be tested.

Perigee

The perigee recovery bay is about 15" deep and about 10" across. The MissileWorks estimate is 9 grams. The info-central calculator recommends 4.86 grams for 8 PSI up to 9.12 grams for 15 PSI.

A six gram charge will be tested.

Tracking

Although there should be little drift it seems wise to incorporate some tracking technology into this project. A BeeLine DF transmitter will be included in the payload bay and one attached to the nosecone recovery harness. Pratt Hobbies MicroBeacons will be used to provide a sound source for close-in aural tracking.

Last revised 2005-10-26.

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