Quick Build 1/4 Patriot


Public Missiles 1/4 Patriot

The quick build Patriot is designed to help you get started in high power rocketry with a fun, easy to build high power rocket. The quick build techniques employed here remove the need for hours of sanding, painting and filleting that are typically required. This page will step you through the process of building this impressive high power rocket that will allow you to achieve level one and two NZRA high power certifications. Altimeter ejection is recommended because 'failure is not an option'.

The PML quarter patriot was chosen for many reasons. It's excellent value as it comes with fibreglass fins, parachute, shock cords, piston and the basic hardware. It's quantum tube is light and easy to cover with car vinyl removing the need for painting and sanding. 3d printed quick build fin blocks create a strong rocket that can handle 'J' motors without the need for 24 fillets and tip to tip fibreglass. The piston provides the best possible protection for your parachute and shock cord and will reliably separate your rocket at apogee with only .5gsm of black powder. The 1/4 group has never had a rocket fail to eject or suffer a piston jam.

Over the last two years 12 patriots have been built privately and 15 as part of a university course so the idea has taken off and many have contributed to the development of the 'quick build' project. See the Public Missiles 1/4 Patriot Group Facebook page here.


The Kit

The public missiles 1/4 Patriot kit is available in New Zealand from www.aerospaceducation.co.nz for $ 270 (Jan 2020) and overseas direct from www.publicmissiles.com. High shipping costs from USA means that purchasing in New Zealand is cheaper than buying direct.

The absolute minimum that you need in addition to the kit if you use 'motor ejection' is a method for retaining the motor which can be as simple as a couple of T nuts and brass clips made from picture hangars or preferably a screw on aluminium motor retainer which costs about $ 60. That will get you up and running with a rocket that in low wind conditions can be set to eject the parachute at apogee using the delay on the motor. Sadly in high wind conditions rockets are often damaged on their first flight due to the number of seconds to apogee being different from low wind conditions, the rocket arching over and ejecting at high speed with the shock cord then ripping the airframe. The solution and the step we recommend from day one is upgrading to an altimeter to reliably deploy your parachute at apogee. An altimeter also records your rockets flight allowing you to view graphs of it's performance. Altimeter ejection requires the addition of an altimeter, battery, altimeter board, cables and terminal block all of which are covered in the instructions below.

See Stuart Lloyd's video Quarter Scale PML Patriot Build and Launch Part 1- The Kit

Equipment

  • Tape measure with imperial and metric measurements

  • 1kg (10th gram accuracy) electronic scale .

  • Plastic shot glasses, $ 7 for 100 at supermarkets.

  • Lollipop sticks, 100 stick packs at the craft section of The Warehouse.

  • 1 sheet of 80,120, 400,600, 2000 grit wet and dry sand paper

  • Marine laminating epoxy such as West or NZ Fibreglass ($ 37 for 1/2 litre)

  • Isopropyl Alcohol, 1ltr $ 16

  • Epoxy wood sealer, $ 37 for 1ltr which would do 20+ rockets so best to share with another member of the 1/4 Patriot group.

  • Vinyl gloves to protect your hands from epoxy and surfaces to be glued from finger grease.

  • Masking tape

The combination of shot glasses and sticks allows you to make up small individual batches of glue. 30 minute and 5min epoxy are not suitable for the quick build blocks and the laminating epoxy will always be stronger as it penetrates better. Laminating epoxy is also a lot cheaper per liter than the 30 minute and 5 minute expoxies.

Terminology

Booster Airframe

Payload Airframe

Coupler

Payload & Piston Bulkhead

Seal all phenolic and plywood parts

Sand plywood and Phenolic parts

  • Sand the outside of the piston coupler tube until it is a loose fit into the airframe with 120 then 220 grit. You are are sanding the piston tube so that after adding the wood preserver the piston will not be too tight. (If you sand off too much now you can paint on a thin layer of laminating epoxy later on.

Paint phenolic and plywood parts to protect with two pot epoxy wood preserver. This stops the phenolic becoming furry and pealing. It also strengthens and protects the surfaces from water when cleaning up after a flight.

  • Apply wood preserver to all phenolic and plywood parts except the outside of the motor tube.

  • lightly coat the inside of the motor tube using a rag on a stick.

Bunker Workshop Video Part 2 - Wood Sealer

Prepare Air-frames for Vinyl Covering

Car vinyl is an ideal finishing material for PML quantum tube rockets as it removes the need to sand, fill, undercoat and paint tubes. It adds strength and is scratch resistant. Apply car vinyl to a shiny clean tube.

  • Prepare the airframes and fibreglass fins for vinyl covering by cleaning them with a hot strong detergent mix then rinse, dry and clean with Isopropyl Alcohol. From now on until the covering is on wear gloves handling the airframe.

  • Cut the vinyl with razor or scalpel using a long metal ruler so there is a 1cm overlap when rolled onto the tube lengthwise and sideways.

  • Some vinyl has a thin outer clear plastic cover, remove that now.

  • Draw a horizontal line down the tube with a long ruler and pencil

  • Fold down 1cm of the backing and apply to the line, try to minimise any pulling or stretching of the vinyl.

  • Slowly peal off the backing smoothing down the vinyl back and forth 1cm at a time. Ideally have one person support the end of the vinyl roll whilst you smooth back and forth. The less stretching and pulling the better.

  • White or light coloured vinyl will need two layers to block out the grey colour of the airframe tube.

  • Heavy duty vinyl is the easier to work with than thinner vinyl's. Heating and stretching is not recommended for vinyl on airframes but may be necessary for nosecones.

  • Bunker workshop method removes splits the airframe vinyl in two and removes the need to align the vinyl with a pencil line and covering fins now.

Bunker Workshop Video Vinyl Wrap Part 4

Maximum Strength Joints

A key to a long life for your Patriot is is sanding all parts that will be glued with 80 grit paper and cleaning with alcohol before gluing to 'key in' the epoxy to the tube.

Do not sand the inside of the main tube above the fin slots as you want a shiny smooth surface for the piston to slide in.

Lightly sand with 80 grit until the surfaces are scored as per photo. This will help the epoxy to adhere to the quantum tube. Your are scoring the surface only.

  • Inside the fincan up to 1cm past the fin slots

  • The outside of the motor tube

  • The top 1cm on the inside of the piston tube.

  • The bottom 1cm of the coupler tube where the payload bulkhead will be glued

  • The bottom 9cm inside of the payload airframe where the coupler will be glued in

  • The rectangle root area of the fibreglass fins that will be below the surface

Choose your Motor Retainer Method

Bunker Workshop

Aluminium retainer for extended motor tube

Aeropac Retainer for shorter motor tube extension

Harm-38 retainer, shortest motor tube extension

T-Nut and brass, aluminium or steel straps (Modified brass picture hooks pictured here)

Motor Tube Forward Centering Ring

Glue the motor tube centering ring (has slott for motor strap) to the top of the motor tube using a specifically designed spacer developed by Bunker Workshop called a Top Hat to ensure that the centering ring is at right angles to the tube and the correct distance from the end of the tube for your motor retainer. There are three Top Hat options

-Bunker Workshop motor retainer (To Hat available)

-Aero Pack motor retainer (Future Design)

-HARM motor retainer (Future Design 8mm)

  • Sand the inside of the centering rings for a snug fit to the motor tube. Dry fit the two centering rings. If the outside of the centering rings need sanding for a snug fit (not tight) to the airframe then roll them on a sheet of sandpaper to ensure you do not round the edges. *** alex need photo here

  • Glue the forward centering ring to the motor tube

Sanding centering rings so that the edges remain flat. Rings should be a firm but not tight fit so that they do not distort the airframe. If you take too much off paint the edges with epoxy and re-sand.

Bunker Workshop Top Hat fits on top of the motor tube to position the forward centering ring correctly for your specific motor retainer and to hold the ring square to the tube


Test fit the forward centering ring when glue is firm but not dry. Do not fit the rear centering ring until after you have built the finset.

Motor Strap

  • Pass the motor strap (the shorter black strap) through the notch in the forward centering ring 10cm down the motor tube.

  • Mark the centre position at the end of the strap with an x to ensure that the strip remains straight.

  • Align the strap and then soak the underside of the motor strap with glue.

  • You can use masking tape at the end to keep it straight whilst drying. You only want enough epoxy to glue the strap down as you don't want extra epoxy squeezing out of the sides of the strap interfering with the fins.

  • Check whilst drying and scrape off any excess glue.

  • You don't want any extra epoxy on the inside of the forward centering as that will stop the fins sitting tight to the centering ring and motor tube. (no fillet required on this joint)

Fincan Construction using Motor Blocks

Preparation

  • Before starting practice dry fitting the motor blocks and fins. The last fin block will be tight, insert the front of the last fin leaving the rear up and insert the fin block before dropping the rear of the fin.

  • Roll up the motor strap and insert into the motor tube to protect it from glue

  • Cover the fin area with masking tape and the rest of the air frame with plastic sandwich wrap.

  • Protect your table and floor from dripping epoxy

  • Have tissues or paper towels handy to clean up

  • Check that the inside of the airframe and root of the fins have been sanded

  • Check that the fin blocks are exactly the same length as the fins and if not cut or sand to fit

  • Check that the root of the fins have been sanded and cleaned with isopropyl alcohol.

Mix epoxy, coat inside airframe.

Mix up 40 (8g hardner/32g resin) of two pot laminating epoxy. Using a gloved hand apply a thin layer of laminating epoxy to the inside of the air-frame up to the forward end end of the fin slots. (Any further could leave glue inside the airframe to interfere with the piston)

Fins

Apply a thin layer of epoxy to the rectangular area at the root of the fins and lay on a plastic sheet ready to load. (this area should have been 80 grit sanded at the start of the project)

Epoxy fin blocks

Apply a thin layer of epoxy to the fin blocks and lay on plastic ready for the build. Insert the motor tube and rotate until the motor strap is half way between two fin slots.

Fitting blocks and fins

Lightly re-coat the first block and fit over the motor strap on the motor tube and then insert into the airframe between two fin slots. Then add second block, a fin, third block, a fin and then for the last block insert the block 1/4 way in and the fin front end in and work the two in bit by bit for a tight fit.

Thrust Ring

Push the fin blocks until they are flush with the fins and no further. Install the rear centering ring and push down onto the fins. Remove one glove, put your hand inside the air-frame and push the motor tube down so that it is flush with the top of the fins. Now cover the inside of the rear centering ring (thrust ring) with epoxy and push down on top of the fins. This should leave you with the required motor tube extension to suit your motor retainer.

Tension fins

Clean off any epoxy on the inside of the airframe above the forward centering ring and on the surface of the fins. Cover fin edges with rag or plastic Lightly strap the fins to hold them in place ensuring that they are providing even pressure to each fin. Don't apply too much tension. You only want enough vertical pressure to ensure that the the bottom of the fins maintain contact with the motor tube. If the straps are too tight they might pull the fins out of alignment.

Set aside to dry for 12 hours

Check that the fins are still in alignment and there is no epoxy inside the airframe and then stand the rocket on it's tail on a jar lid that will push on the rear centering ring and not the motor tube and leave to dry for at least 10 hours in hot weather and 18 hours in cold.

Piston

  • Using the Template provided

  • Drill 2 x 3mm holes for the terminal block

  • 2 x 2mm holes for the connection legs

  • 1 X 3mm hole for the lead return

  • Pass the quick connector cable through the lead return and up through the connection leg holes

  • Solder the terminal block legs using tape or heatshrink to cover the bare legs and cable.

  • Push the terminal block down but don't bolt down at this point

  • Pull the free end of the motor strap through the piston bulkhead

  • Slip the metal 'D' ring over the strap and feed back through the slot

  • Put the 2 x 3mm bolts through the terminal block and the bulkhead and trap the strap with the aluminium strip and screw down with 3mm nylock screws. Do not glue the strap to the piston.

  • Epoxy the piston bulkhead inside the piston body 30mm from the top

  • Add an epoxy fillet to both sides of the bulkhead

  • For extra protection from the black powder charges line the inside of the piston with aluminium tape from $ 2 shop or paint the inside of the piston with epoxy.


Payload Bulkplate and Coupler

  • Thread the nut onto the eyebolt as far as it will go

  • Push the bolt into the bulkhead hole

  • Add washer and but and tighten with wrench

  • Sand bulkhead to fit tight

  • Spread epoxy on bottom 13mm of coupler

  • Fit bulkhead with eyebolt on the outside 7mm inside the coupler (D)

  • Add a fillet on the inside and outside of the bulkhead

  • Mark line (E) half way down the coupler

  • Spread a layer of epoxy around the inside circumference of the payload airframe to a depth of 50mm. (this is so you don't end up epoxy outside the coupler.

  • With a slow twisting motion push the coupler into the payload airframe up to mark E

Vinyl Cover Fins

If you have the skills to spray paint you have the choice to paint or vinyl cover the fins. To cover with vinyl

  • Clean fins with isopropyl alcohol and cut vinyl about 4mm wider and taller than the fins.

  • Apply Vinyl to both sides of the fins and then with a razor cut the vinyl back to about 2mm short of the fin creating a temporary groove between the two sheets of vinyl

  • Run a bead of epoxy inside the groove using the sharp end of a bamboo BBQ spear and let it dry.

  • Razor cut the vinyl back to that bead of epoxy.

Fin Fillets

  • The two layers of vinyl covering help to stiffen the fins compared with painted fins.

  • The epoxied fin block set makes the fin can very rigid making it capable of handling J350 flights.

  • As a result you do not need the traditional fin fillets but it does pay to run a thin bead of epoxy in the join between fins and airframe to stop the vinyl pealing.


Rail Guides

  • Profile the supplied linear rail guides by putting 220 grit sandpaper on the airframe and sanding the guide down so that the bottom of the rail guide is the same profile as the airframe. You might want to spray paint the outside of the rail guides before fitting them but mask off the inside slot where it will fit on the rail.

  • Fit the rear rail guide supplied with the kit to the rear of the rocket equal distance between two fins. Drill holes 1/3 the size if the screw shaft. Use two self tapping counter sunk screws to screw through the air frame and fin blocks.

  • Fit the front rail guide by cutting the vinyl so that you can 80 grit sand and epoxy it onto the airframe inline with the rear guide. A long steel ruler or rod helps to ensure that both guides are in alignment.

Fit Your Motor Retainer

  • The New Zealand made Bunker Workshops retainer is available locally and is longer and is easier to fit hard up to the thrust ring (rear centering ring). In my experience it's not essential to use JB weld to fit a motor retainer on this size of rocket as the base of the retainer is never going to be heated enough to melt the epoxy.

  • 120 grit sand the inside of the motor retainer and motor tube.

  • Clean with isopropyl alcohol so there is no sign of grease (use gloves) and then use 24hr epoxy or JB Weld to glue the retainer to the motor tube. Apply weight to hold the parts tight for 12 hours.

Nosecone

  • Painted: You can spray paint the nosecone using plastic primer and then enamel spray paints. Experience has proven that standard undercoat/primer will not stick reliably to plastic. You need the same primer they use on car bumpers.

  • Un-painted white nosecone. Many people including myself fly unpainted nosecones. Wet sand off imperfections with 250 grit then 400 grit paper.

  • Vinyl: If you realy want a challenge then there are videos on Youtube to assist with the tricky job of applying vinyl to nosecones.

Piston and Coupler Fitting and Testing

Just Right

The payload coupler fit into the booster airframe should be tight enough that there is no 'slack' when you support the rocket from both ends but smooth enough that it ejects at apogee. Yes it's a compromise and as long as it passes the testing will be fine if not perfect. Sand the piston and coupler evenly using a rectangle cut from an icecream container and 220 sand paper to ensure that you don't sand 'flats' into the coupler.

Smooth As

Don't over sand. Sand evenly back and forth whilst rotating the tube a little at a time. Keep checking the fit after each rotation. If you over sand you will need to brush epoxy sealer or laminating epoxy and start again. Repeat the same with the piston.

Testing

Pack your parachute and shock cord and then blow hard down the motor tube to check if the parts are smooth enough fit to reliably deploy at apogee. Always clean out your booster air-frame and wipe down your piston and coupler before fitting as sand or dirt will effect the deployment.

Altimeter Bay

3d Printed Alt Bay Supports

  • 3d printed alt bay, fibreglass board and remove before flight switch, rod and flag are included in the add on kit.

  • Altimeter and battery options available from local suppliers here.

  • This fibreglass board has had black 4d carbon style vinyl applied



Fibreglass board

Cut fibreglass board to a height of XX and width of XX to fit the alt bay supports. The board and the alt bay support slide into the payload airframe and sit on top of the payload coupler.

Power Switch

Cut holes for the stereo headphone switch legs and glue to the board . Solder 2 X contacts on each side to the altimeter power switch and 1 X contact to switch on your camera or tracker. These spring switches have a much larger contact area than switches and are under significant pressure. Keep the switch dry and check the contacts are clean before flying.

Static Port/ Switch Access

With the board fitted measure down to the top of the board inside the airframe. Mark this out on a piece of paper that wraps around the air-frame and align. Then cut a 1mm hole and check if it's centered. Adjust and then drill a 6mm hole. This is more than large enough to act as the static port during flight.

Alternatively if you have a small high power magnet you can insert this into the power switch and detect the exact position using a small screw driver outside the airframe

Altimeter Recommendations

Many different altimeters are available. Members of the 1/4 Patriot group use these models and can help show you how to set them up and run.

  • Stratologger NZ$120 from local suppliers is simple and easy to use without a computer. Beeps out the altitude. If you want data as well you are better moving up to the Easymini as the USB dongle is expensive and the data low resolution. Will run off a 2 or 3 cell Lipo or 9v alkaline battery. Intermittently available due to limited manufacturing.

  • Easymini NZ$159 has built in USB connection, high resolution data collection and sophisticated flight analysis software. Will run off a small single cell lipo battery. You need to download the high resolution data after 2-3 flights.

  • Telemini NZ$ 270 has high resolution data and beacon tracking. Requires a radio receiver such as the TeleDongle NZ$ 191 or support of other NZRA members running the same equipment.


Quick Links

Two quick links are included in the add on hardware set

Shock Cord

Fold 5cm of the long shock cord over by 5cm and clamp leaving a 1cm loop then soak 4cm of the cor in expoxy and heat shrink in place. *** photo here


Retaining Nosecone

Drill 3mm hole through airframe into nosecone and use a single screw to retain the nosecone without weights and 2 screws with weight. Or use plastic rivets (not included)

Drill Hole for nosecone weights

Drill a hole in the nosecone base. Use a bolt to attach large nuts or lead weights to bring the center of gravity forward to at least 1 body diameter ahead of the center of pressure when the motor is loaded.

Finding Your Patriot

Once you are flying I motors and larger or if there are crop fields near by then it helps to use one of these methods to track your rocket. Using these methods no one in our 1/4 Patriot group has lost a rocket.

Video the landing or mark the direction by aligning your position with a distant point. Have another person guide you with a cellphone. Walk down the flight line with software on your phone or tablet that can draw your track on Google maps in real time (eg MotionX). Focus on that line and go a few extra paddocks than you expect if you don't see it first time then double back on a parallel track to your first line on the map

Use an altimeter with a built in GPS or a beacon tracker.

Beeline beacon trackers are the most reliable but it takes a skilled operator, yaghi antenna and radio to track the signal. Prices start at US$ 80 excluding freight.

Altus Metrum Telemini altimater and beacon tracking. NZ$ 270 including freight.

Altus Metrum GPS Altimeter + Beacon tracking. Prices start at NZ $ 509 including freight.

Beeline GPS and Satellite trackers provide high altitude and long range tracking. Prices start at US$ excluding freight

Build your own GPS tracker and groundstation.

If you are experienced at surface mount soldering then you can build a GPS transmitter and receiver dongle to plug into your laptop for around US$ 100 excluding shipping. You are on your own here but I hear that if built and operated correctly they work well. Transmitter weight, length required including antenna ****.

Cellphone network GPS Tracker

I have owned a similar tracker purchased in New Zealand 4 years ago and it's still going strong. The battery lasts for days. You call the tracker and after a minute it will reply with the position if it's within cellphone range. If it falls in a ditch or lands in the corn where it can't receive or transmit you will be out of luck. Weight is ****

Add on Hardware Kit

3mm screws and locknuts for terminal block through piston to aluminium strap

2 pin JST Connector Male/female, cut the clip off for quick release. Terminal block with aluminium strap stainless steel nuts and bolts. T-Nuts optional if you are making your own motor retainer.

2 x quick links and heat shrink for shock cord.

Yellow fibreglass board only cut to 97mm to work with pine alt bay supports. Will need trimming to work with 3d printed boards.

Add on 3D Printed Parts Kit

Bunker Workshop alt bay wings and fibreglass board

3d Printed Bunker Workshop Motor Blocks $ 40 for a set of four.

Chris's lightweight motor blocks $ 40 for a set of 4.

Michael's Alt Bay Supports

Rocket Stands

Bunker Workshop Single Bay

  • Built from imported parts and available in blue or grey

Bunker Workshop Double Bay

  • Built from imported parts and available in blue or grey

Parachute Packing

The Following Sections can only be accessed by NZRA Members

Ejection Charges

Ground Testing

Preparations Before Leaving for Launch Site

Preparations and checklist On Site Before going to launch pad

Preparations and checklist Before going to launch pad