1/3 SCALE PATRIOT BUILT BY DAVE THOMSON Pictured right is myself (Dave Thomson) with my 1/3 scale Patriot rocket which flew at on 4 single use Areotech 'G' motors at the 'SERFS' Yatesbury meeting in September 1997. The rocket was originaly designed to fly on 19 x D12 Estes motors. It flew once on this configuration. See bottom of page for images. The rocket is a 1/3 scale model of a US Army Patriot missile. The motors are 2xG80-7W Aerotech motors for the first stage and 2xG40-4 Aerotech motors (air started ) for the second stage. The rocket has an inertia timer (built by myself) that arms the system on launch and then fires the second stage after 1 to 10 seconds (adjustable by potentiometer on board). Unfortunately for the first flight I forgot to turn on the arm switch for the second stage. The original design was to fly on 19xD12-3 Estes motors. The rocket flew once on this configuration and is covered in the motor mount section below. STAGING TIMER my home-made staging unit uses 555 timers and an inertia switch. The timer circuit consists of two 555 timers. One timer is looking at the inertia switch and waiting for it to be closed for a pre-set time. This pre-set time can be varied (by onboard potentiometer) but is normally set to around 1 second or slightly more. If the 'closed time is less than 1 second then the second timer will not be enabled. This means that if after arming the system it is dropped or knocked then the system will not 'go off'. A vertical launch will provide enough 'G' force to keep the switch closed long enough for the second timer to be enabled. When the second timer is enabled then it closes an output relay to the second stage motor ignitor after another pre-set time which may be varied by onboard potentiometer. This output to the relay will stay energised for another pre-set time during flight to ensure that the ignitor starts the second stage. The system will not re-arm during parachute deployment or landing due to the inertia switch requiring to be closed for more that 1 second. Image left shows the timer being set for flight. It is mounted within the nosecone and cables to the ignitors are run through the external conduits to the motors at the base. ROCKET CONSTRUCTION BODY TUBE The body of the rocket is made from 120mm diameter A0 size drawing storage tubes. These are similar in weight to phenolic tubing but cost nothing! They are not as durable or as strong but are acceptable never the less. The worst part of making any rocket is to hide the spiral wound paper markings on the outer tube wall. Lots of careful rubbing and filling is required. I coat the outside with a slightly watered down PVA glue when complete to seal and strengthen the tube ready fro final coating. Gloss undercoat is brushed on and left to dry between rubbing down with a medium paper. around 4 to 5 coats are required to give a good smooth spiral free finish. The top coat is sprayed on lightly with car touch-up spray cans. One tip I learnt during making of my aircraft during applying different colours is after masking the area to be coated to then give the edges around the masking tap a light coat of the same colour and letting it dry before putting on the other colour. This gives a nice clean edge to adjacent colours (no furry edges!). The second stage cabling is run through the external scale conduit to the base of the rocket. This conduit is small section rectangular plastic conduit available from B&Q. The cables are very lightly twisted together in line at the nose cone joint and a small piece of masking tape used to prevent shorts. The wires easily separate when the nose cone is blown off. NOSE CONE The most difficult part of a rocket to make is the nosecone. Commercially available nosecones do not fit the tubes I use. So I decided to make my own. It is a lot of work but it means that you can make it whatever size and shape you want. It is more satisfying also to know that you have make every part. The nosecone started life out as a 2inch thick sheet of polystyrene. This was cut into a number of circles that reduced down in diameter to simulate the basic shape required. These where then mounted on a central axis of M12 screwed rod with large ply washers at either end. The pieces were PVA glued together before the pieces where tightened up and left to dry. Next I made a basic home-made lathe . This used a standard drill as one end of the lathe into which on end of the screwed rod would be placed. The other end had a pillow block bearing to hold the screwed rod. These were mounted onto a wooden frame work which also had a wrist rest to steady tools against. The nose cone was turned at the drills slowest speed (only 2 speed) and a hacksaw was used to get the rough shape. When stopped the finish is very rough but very quickly comes to a smooth finish with rough and then medium sandpaper. Once the nosecone is smooth and the correct shape then it is covered with layers of fine fibreglass and PVA glue (thinned down). Normal epoxy resin cannot be used as it melts the foam. When dry this is then turned and smoothed. The surface is then coated with a thin layer of car body filler and turned and smoothed. This process is done a few times to get the smoothest finish. A number of coats of gloss under coat is then used to smooth out any final irregularities. The nosecone has a large payload area that holds the timer and other equipment. An end plate is used to keep equipment in and doubles up as a shock cord mounting. The shock cord is 5mm diameter round cord available from B&Q. The other end of the cord is mounted onto a large shaped wooden block down inside the body tube that is glued and screwed in place. The shock cord can easily be examined or replaced if found to be damaged. MOTOR MOUNT TYPE 1 Not having access at that time (1995 )to high powered motors I was limited to clustering Estes 'D' motors. I concluded that 19 x D12 motors would fit into the base of the body tube and should provide enough thrust to get it off the ground a few hundred feet. If D12-3 motors where used then this short delay and plenty of ejection charge should pop the nose cone and deploy the chute's. Image left shows the 19xD12 cluster motor mount in my camera rocket. It can be interchanged between different rockets of the sma body tube. The motor mount was made of two thick layers of perspex to the same diameter as the inside of the airframe tube. The 19 motors where arranged in a 'cake' and tapped together. The two layers of perspex then had 19 holes cut out in each to allow for exhaust and ejection charge gases. The whole assembly was held together by a number of M4 threaded rod that passed between the motors and through the plates. Mounting brackets where fixed to the M4 stud to mount the motor mount to the airframe. The ignition of the motors was by standard Estes ignitors wired in parallel. A wiring nightmare I can tell you!! But it did fly once at a THRUST meeting in Tamworth in England. Here are the pictures to prove it. Unfortunately only 13 of the 19 actually ignited. Lack of current gave slow ignition. The rocket rose slowly on a wide but short flame (lots of smoke) to a rather low altitude before a good apogee deployment, but one of the chute's was tangled and a fin was broken on landing. TYPE 2 The motor mount is made of two layers of thin ply separated by four 32mm high temperature waste pipe tubes (available from B&Q) some 12 inches long. The surfaces of which are roughened up before fixing into place with epoxy. The motor mount is removable and interchangeable by having strong fixings that go through the body of the rocket onto brackets which are part of the motor mount. An end stop in the tube is also given for extra security. Image left shows the Patriot loaded with 4xG motors (2xG80-7 and 2xG40-4) FINS Fins are made of thick coloured perspex. These are cut to shape and have tabs to pass through the body of the rocket. Epoxy beads are run along the length of the fins on each side. This design is to now be modified as my camera rocket. This is a bolt-on design. Click here to goto that page. RECOVERY SYSTEM The Patriot uses two large ripstop nylon parachutes of homemade design and construction. The Patriot loaded with 19xD12-3 motors at the May 1997 'THRUST' meeting. Rocket struggles off the pad on most of the motors. LOTS of smoke! Deployment is ok but one fin is damaged on landing. 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