THE WORKSHOP

• Choosing a bottle

• Making the rocket First Stage propulsor  

• Making a nose cone

• Making a simple parachute

• Parachute Level 2 

• Making a tube launcher

• Simple plug launcher

• Different types of launching systems.

• Multi-Stage Rockets

• Design and development 

• Design Creativity, 'Brain -Storming' and lateral thinking.

There are a lot of fizzy drink bottles that you can find in any supermarket. PETE plastic bottles come in a large variety of shapes and sizes. 

• Initially I would advise taking a good quality 1 litre PETE bottle that has no corrugations or stiffening ribs.
• Next carefully remove all the labels by leaving the bottle to soak in water overnight. 
• Then closely inspect the bottle for any moulding blemishes or dents that could reduce the capability of the bottle to hold pressure.
• New 75ml bottle from Badoit March 2007

Note: Some of our best water rockets are made from 1000ml Badoit bottles. 

          So this new addition of the 75ml bottle could produce some 

          interesting flights and  a potential new second stage.

• Never use glass bottles or metal canisters.

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The following procedure is not difficult but accuracy is very important to guarantee good stable flight trajectory later on.

• Take a clean dry good quality PETE bottle and use a 25mm paper strip long enough to pass around the circumference of the main cylinder of the bottle. 

• Mark a line at one end across the 25mm and use two short strips of sticky tape to locate the strip around the circumference. Then mark a second line where the strip overlaps.

•   Remove the strip and measure the distance between the two marks. Dividing it into as many parts as you want fins. Then draw lines across the paper strip at these positions.

• If you want 4 fins then the distance will be divided into 4, 3 fins 3 etc.

• Now re-stick the paper strip in place around the circumference of the bottle and transfer the marks to the bottle.

• If you intend to make a few rockets it is useful to make up a little pattern from the paper strip that makes this marking out simpler in future. Note: An example of this can be seen in the photograph where a cone section from a similar bottle has been cut and marked up with the positions so that they can be transferred easily. By just sliding the cone/pattern over the neck of the bottle and transferrering the markings to the bottle using a black felt pen.

• To make the bottle more stable I find it helps to partially fill the bottle with water.
• Then take a very fine wet and dry Grade1000 and lightly abrade the surface where the fins will be bonded.
• During bonding the chemical linking that takes place occurs at the molecular scale. That is microscopic. 
• It is very important that the surface to be bonded is clean, free from dirt, grease and will allow the adhesive to wet the two surfaces to be bonded.
• more about surface preparation

• Detailed adhesive specifications can be supplied on request courtesy ICI Permabond.

· Rapid air cured 2 part expoxy.

· Hot melt.

· Toughened adhesive systems.

· Polyurethane sealants.

• Most adhesive systems have accompanying application and (health and safety) instructions read them.

• Always avoid skin contact when handling adhesives and wash yours hands thoroughly afterwards. Use thin disposable gloves if you have them available. 

For our demonstration rocket we will use an air cured 2part epoxy that cures in 90secs. 

• Mix the two components in sufficient quantity to bond one fin at a time.
• Apply the adhesive to the fin edge that comes into contact with the bottle. Position on the bottle and remove to see if there are any points on the surface of the bottle that are without adhesive. Apply more adhesive as necessary and reposition and hold the fin in place checking alignment and trim.
• Repeat for the other fins.

Note it is not advised to use urethane sealants other than in compression areas in the nose cone module where impact loadings are experienced. Ideally a toughened adhesive system should be used.

• After every flight and any impact always check bonded joints for any signs of discolouration or damage.
• If in any doubt remake the bonded joint.

Note: This depends on the reliability of your rocket recovery system/parachute

If everybody is honest it is rarely 100%.

• Using the neck of the bottle as a datum mark and trim the base of the fins to guarantee a common ground datum.
• Turn the rocket over placing it upright on a flat horizontal surface and it should stand vertically.

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We use two No.14( 18.4*2.7mm) tap  'O' rings. On the external threaded neck of the bottle. Making the neck a piston fit inside the tulip cup of the launcher tube.

Replace the 'O' rings when they become worn or begin to show signs of cracking.

Making a nose Cone or Coiffe.  

A simple and basic nose cone can be manufactured simply from a block of polystyrene foam recovered from some discarded packaging.

• Cut a cube block of foam with a side length equal to the rocket diameter.

• Mark the centre point on the top and bottom faces of the cube. 

• Place the end of the rocket bottle onto the bottom centre and draw round the circumference with a felt tip pen.

• Now mark out the rough cone form shape on the 4 side faces. Then remove the top corners of the cube with a saw blade and start to produce the rough cone shape using some medium grade sandpaper.

• Keep turning the cone whilst sanding to help keep the form shape symmetrical.

• To finish lightly sand using a finer grade of wet and dry paper.

• Then simply attach to the top of the rocket using some wide (20mm) sticky tape or masking tape.

This type of nose cone will avoid a lot of the impact damage to either the landing site or the rocket.

It is advised to manufacture a couple of spare nose cones to speed up replacing damaged nose cones or replacing lost or damaged rockets.

• Manufacturing a modular nose cone.

A modular system means that you can change the module from one rocket to another or replace it with a nose module carrying a larger parachute.

Specialised modules can be built later to carry cameras or measuring instrumentation to record flight data.

As an introduction I have chosen one of our designs that has proved tough and reliable.

 

The ‘Aerocoiffe’©

This particular design is for using with a Badoit1L based rocket which is a safe platform from which to start experimenting.

• Materials list:

Manufacturing Procedure for modular nose cone Capsule:

• Take the Aix bottle and measure down 45mm below the blue top collar and mark with a fine black felt tip pen a ring around the bottles circumference.
• Take a craft knife or a good pair of scissors and roughly cut out the nose cone cutting below the line.
• Then re-cut accurately too the 45mm line . Removing any ragged edges with some fine 1000 grade wet and dry paper.
• Next remove the bottom 45mm from the 1L Badoit bottle using a similar technique used above marking out with a felt pen and removing the module base.
• Mark out and remove a taper locating ring from the cone part of the Badoit bottle.
• Measure up 15mm from the base of the cone section and mark a ring for the baseline. 
• Then mark out a second line 35mm above the base of the cone section of the bottle. This will leave you with a taper ring of 20mm. For subsequent manufacture making a cone template to quickly mark out the base line of the taper collar speeds up marking out and controls repeatability.

• Remove any rough edges and 

• apply a thin bead of polyurethane sealant to the inside of the base of the taper ring 

• bond to the top of the jar lid. 

• Position the ring concentrically with the exterior of the lid 

• remove any excess sealant before leaving it to dry. 12 hr. (over night)

• Take the ‘Shock plate’ locally clean the underside of the lid 

• bond it to the module base cut from the bottom of the Badoit bottle using spots of polyurethane sealant.

• Leave to dry 12hr( over night).

• Take the nose module base and drill a hole in the centre that passes through the lid and the plastic base to take the shock cords of the parachute.

• Now drill out 6 holes just inside the taper ring directly above each of the bottle base indents.

I use small pilot holes then drill them out to the larger final size.

These are the launch pressure equalisation holes.

Localised Aerodynamic turbulence causes a drop in pressure within the capsule that keeps the nose cone in place until the velocity of the rocket has reduced near the top of its flight.

• Clean any surplus sealant from the nose module base taper and test the fit of the Aix nose to the taper.

It should not be either too tight or too slack. Allowing the nose cone to fall away when the base module is tipped.

• Depending on the balance mass requirements of your rocket cut the nose mass length to suit and place in the nose of the capsule.
•  Refer to determination of rocket center of mass.

• Attach your parachute by passing the shock cords through the center hole of the shock plate and sticking the ends to the under side of the base. 
• Coil the parachute cords carefully onto the base as shown then pinch the parachute at its center and pull lightly on the cords to form a folded umbrella shape before fold the parachute canopy in a zig-zag starting at the base and working towards the center point. Stand the folded zig-zag upright at the center of the base-plate and replace the nose cone.
• When packed correctly the nose cone should fit easily onto the shock plate and not be held up by the folded parachute.

• Test the nose cone assembly on the tilt table to determine the separation angle and assess the best method for packing the parachute and cord system. 

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For higher acceleration loads we use a double taper cone.

This stiffens the lower lip of the the nose cone and controls the cone release.

This is done by selecting the cone band that smoothly fits over the shock plate collar. Then bonding it inside the open end of the nose cone using polyurethane sealant.

We use the same collar arrangement for locating intermediary stages and modules.

Links: Good nose cone design

          Nose Cone separation

          Recovery systems 

Making a parachute is relatively easy.

Our main objective is to recover the rocket without damage so a parachute system that is reliable is essential.

• Deciding what size of parachute is the ideal for specific situations or competitions needs a little more overall attention to total nose cone module specification and design.

• Refer to section on good nose cone/coiffe design. The controlling factors are nose cone packing volume, nose cone separation angle, payload mass of the parachute assembly and the affect on overall rocket performance.

• The ideal is to match the size of the parachute to the rocket mass and rate of fall required. Rate of  fall calculation Excel spreadsheet

For larger rockets or longer decent times you will need a larger diameter than for smaller rockets or minimum recovery time.

Here we will take a parachute that has been developed for the rocket nose cone above made earlier.

• Materials required

• Take the thin bin liner and cut along the bottom seam and down one side and open flat on the floor or a protected table top.

• Take a tape measure and mark where the centre would be for a 60cm diameter parachute canopy.

• Take the felt tip pen and attach some of the cord to give a swept radius of 30cms. (Ref photo1422)

• Slowly and only pressing lightly on the felt pen mark out the circumference of the 60cm diameter circle onto the sheet.

• Next take a sharp pair of scissors and cut out the canopy. Putting the waste material aside for future use.
• Fold the circular disc into half then quarters and finally in half again to divide the disc into eight parts.

• Run your finger down the folds to form a crease then reopen the parachute to reveal the eight points on the circumference where the cords will be attached. Then take the pen and mark where folds reach the edge of the parachute. 

•  Cut 4 parachute cords twice the diameter of the parachute in length. In this case 120cms long. Seal the ends with a lighter flame to prevent fraying.

•  Attach each in turn to the shock ring. This is done by folding the cord in two and passing the loop through the ring and re-passing the free ends through the loop as shown.

•  Secure the knot with a simple knot to stop the cord loop from slipping and varying the cord lengths.

• To attach the free ends to the parachute take each end in turn and loop the cord around a 20mm wide strip of duck tape.

• Fold the parachute over and stick to the outside of the canopy as shown

• Smooth the tape down and seal the outer cord loop with a short length of sellotape.

• To make the attaching shock cord cut a 250 mm length of thicker cord and attach to the ring as before.

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• Alternative parachute canopy materials;
• Silk. Light weight silk
• Nylon
• Polyamide

• msc Explorer 1 © :

          High pressure tested fully brazed tube launcher system with coaxial release 

         collar.

         Quick release water coupling and safety pressure dump valve.

         Compressed air coupling using threaded adapter with high pressure       

         flexible extension.

         Multiple adapters for changing from standard tyre valve thread to micro   

         bore plastic tube push lock fittings

         Instructions for manufacture are being prepared.

          Materials list spreadsheet with costs. Click here.

          For schools, colleges and universities we are able to supply launchers

          and flight data loggers.

          Contact us for details. Contact us

Two sizes of PVC tube 40mm and 32mm outside diameter OD.

These are used to manufacture the slide release collar.

Copper tube 16mm OD

This is where the neck of the bottle will fit inside with the flange resting on the top of the 28mm outlet throat.

16mm olive compression fitting to 1/2inch female. 

Use white teflon thread tape to seal the threads.

Note:1/2inch or whatever the ball valve fitting requires.

This 18mm double compression fitting has two rubber clamping seal rings. Which we need to hold the 10 black cable ties in place.

Note:

This replaces the adjustable hose clips which we had found to be unreliable when they stripped. Making the launcher unsafe.

The head of the adjusting screw caused the release mechanism to be offset and  not  aligned with axis of the launch tube. Causing the release to be uneven.

Cut three lengths of 16mm copper tube

L = 450mm

L = 90mm

L = 70mm

Lightly file square the tube ends and clean with some fine emery paper removing any  grease from the surface before silver brazing.

Allow to cool and then slide the modified 18mm compression fitting over the end  of long length and slide to the bottom before brazing the 16 to 28mm adapter to the top of the free end.

Note: Brazing can be replaced by bonding the joints using a toughened engineering  two part epoxy adhesive and placing in an oven at 80C for the cure time of the adhesive.

Grip length adjustment is achieved using a cut off bottle neck inserted into the launcher release throat. Slide each cable tie by pulling on the free end until it clamps the top of the bottle neck flange and repeat for all the cable ties in turn working around the circumference.

Potential movement under pressure is avoided by locking the double compression fixing at the step joint  created at the interface between the the 28mm adapter and the 16mm copper tube.

This shoulder stops the fitting sliding up.

Alternatively use a good quality stainless steel 'Norma'  adjustable hose clip. Clamped between the compression fitting and the shoulder. Here the hose clamp is no longer required to take any major  loading .It  provides a compressive stop between the shoulder and the top of the compression fitting.

Then  slide over the larger 40mm OD  PVC  locking tube.

The lower end of which is located axially by a smaller 32mm OD tube passing  inside and acting as a guide.

Readjust and tighten. Recording the test date on a sticker prominently displayed on outside of the launcher tube.

Retest and adjust at the start of every season/academic year.

Using the packing blocks either side of the launcher tube base.  Clamp it in position using the vise of a mini Black and Decker work bench. Or equivalent.

We install this on top of a leveled concrete slab . So no matter where the launch site is you always have stable platform from which to launch.

To set the launcher tube vertical we use the liquid level in the rocket bottle as a spirit level. Adjusting the inclination axis of the tube to obtain the desired inclination before final clamping.

1* Car tyre or bicycle inner tube pressure valve.

1* Cider bottle cork

Flexible extension to connect tyre pump to the pressure valve.

A good tyre pump with a pressure gauge incoporated.

A drill of the same diameter as the tyre valve stem..

Urethane sealant Sika flex.

Masking tape

• Take the cork and check that it is a tight fit in the neck of the bottle.
• Measure the diameter of the tyre valve stem and drill a hole of the same diameter through the center of the cork.
• Clean the external surface of the valve stem to remove any dirt or grease.
• Take a short strip of masking tape and seal the valve aperture and threaded portion of the valve stem. To prevent any sealant getting into the valve.
• Apply a film of urethane sealent to both the interior of the hole in the cork and the exterior of the valve stem.
• Then fit the valve into the cork with the threaded valve end towards the outside end of the plug. Leave the sealant to dry before removing the masking tape. 
• Couple the valve up to a tyre pump and check that air freely passes through the valve.
• To pressure test the plug. Take the bottle you intend to use for your rocket and fill it with water. Then insert the pressure plug you have just made into the neck of the bottle.
• Stand the bottle outside on a level surface and connect the valve to a tyre pump.
• Pump and check for leaks.
• Continue to pump and make a note of the pressure at which the plug is forced out of the bottle neck. Try to keep the release pressure at less than 4bar to start with.
• This will allow you to get the launching procedure together before you try to increase the launch pressure. Normally 7bar will give you a satisfying launch.

Note: The plug being ejected from the bottle  is what will eventually release the  rocket.

• Check the clearance height required below the rocket to enable both the plug and the flexible tube extension from the pump to pass.
• Make the rocket fins so that they hold the rocket vertically with enough space below the bottle neck /nozzle for the plug to release.
• The only problem with plug launchers is that you can not determine exactly when they will launch. So it can be a bit difficult trying to get a good video. Plus you need a flat and level launch site.
• With young children around it is always better  and safer launching from a elevated launch platform. Say from  the top of a white plastic garden table. Some stable surface that is above head height.

Different types of launching systems

Our Development of the plug launcher .

To obtain a better seal and a longer plug life we found several ways of replacing the cork with drilled out tap washers and rubber panel grommets.

• Take the car tyre valve and slide a drilled out coin or washer down the valve so that it blocks at the base taper of the valve.
• Now drill out some 22mm rubber tap washers and slide them in a stack of three down the valve stem.
•  Now install the compression washer at the top which can be used to press the plug into the neck of the bottle.
• To install the pressure plug into the neck of the bottle use the following procedure.
• Fill the bottle with the volume of water you require for the launch.
• Then insert the lower end of the plug into the bottle.  Push the plug into the neck of the bottle using a length of tube that has an external diameter to suit the size of compression washer used for the top of the plug.
• Carry the rocket to the launch site and install the pump with the flexible pressure tube. Setting the rocket to the vertical. Install the parachute module onto the top of the rocket and group the flight crew upwind of the launch site. Before starting to increase the internal pressure. Start to pump and continue to pump until the rocket launches.

Mk3 plug

This is a little more sophisticated and uses the clamping nut on the bicycle tyre valve to clamp the rubber piston made up from rubber grommets.

Which expands the rubber piston diameter once it is inside the neck of the bottle

• Take a bicycle tyre valve cut from an old inner tube and install the reaction washer at its base. Made from a stainless steel washer that has  a diameter smaller than the neck of the bottle.
• Then take two rubber grommets of 22mm OD that are used to protect electrical cables as they pass though steel panels. 
• Then cut a short length of rubber fuel pipe that is 1.5 times  in length the thickness of one grommet,  Choose a diameter that will just fit inside the internal diameter of the grommet and will fit over the bicycle valve stem. This short length of rubber tube packs out the small diameter of the valve stem and axially  locates the grommet against the walls of the bottle neck.
• Now place the top compression washer onto of the two rubber grommets followed by the clamping nut. Note that the clamping washer needs to have a central hole that is just large enough for the valve to pass through.
• Further improvements on piston sealing can be gained by inserting 'O' rings into the groves of the panel grommets of the correct diameter.

This simplifies the procedure to install the plug into the neck of the bottle. With the final expansion of the seal being done by tightening the clamping nut using a small spanner.

In the image the smaller diameter bicycle valve plugs are the 2nd and 3rd from the left. Click on the photograph to obtain a larger image.

• msc  Explorer 2 © 

          As above but with refined pneumatic release actuator.

• 'Spider' ©  Ultra lightweight high pressure launcher system.

Inter-stage release as the first stage finishes and the second takes over are  important in guaranting the continued progress and the acceleration of the remaining

rocket mass

Spider interstage release ©  September2003

This allows for the different stages to be charged independent

What is the optimum mass ration for multistage rockets.?

Optimum Two stage water rocket calculation Excel

The inter-stage tube is rejected with the first stage

Contact us for details. Contact us

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Fin shock loading at launch.

Normal loading conditions will require the fins to support a simple compressive load made up from the mass of the rocket prior to launch.

 At launch the water jet force assumes the responsibility for this mass propelling the rocket into the atmosphere.

Subsequently the loading on the fins becomes that introduced by the flight dynamics of the rocket.

Flow induced dynamic 'Flutter' is to be avoided at the high initial flight velocities

The main role of the fin  surface is to stablise the direction of flight and avoid any major derive/deviation from the intended flight path.

Exceptional fin loading occurs when the rocket explodes on the launch pad. With the direction of energy thrust being reversed.

The adjacent photograph shows the compression shear stress marks that resulted.

This type of compressive shear can also be induced when multistage rockets fall back to Earth immediately after launch due to insufficient initial thrust force being generated at launch. With the initial rocket mass M1 of the subsequent unused stages trying to crumple the fin panels as they impact the ground.

" Great things are not done by impulse, but a series of small things brought together".
Vincent Van Gogh

Ironic quotation which says that success is the result of assembling many  simple existing systems or ideas in a new original way.

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Understanding the need for rocket development and failure analysis

Getting the water rocket design and development team to sit down and analyse why things did not work as planned is an integral part of any project.

To understand that even the best engineers and scientists get it wrong sometimes is therefore a very healthy exercise.

Whether your project is  family or college based. 

Organise a de briefing meeting to discuss what went wrong.

Analyse videos and get everybodies observations on the event. Before any conclusions are made.

Do not believe in what your computer simulation tells you.

Invariably what happens in the real world will be different. For all soughts of reasons.

Practical experience is invaluable to develop a reliable launcher and flight programme.

Detailed analysis of failure can identify multiple causes that improve future reliability.

The soviet Semoirika/Soyuz is a classic example.

The Worlds most legendary launcher. Is based on minute detective work required to uncover the problems during its conception and development.

Heres a link that will help.

Design Creativity, 'Brain -Storming' and lateral thinking.

         Using the water rocket project to introduce lateral thinking and creativity.

         http://www.edwdebono.com/debono/selfi.htm