I decided to build a scale model for my level 3-certification flight. So to combine another one of my plans to build a scale V2 rocket I decided to build a 1/4 scale V2, this gives a V2 a little over 3.5Meters tall and 412mm in diameter.

 Overview of the Rocket 

The Rocket towas to use a single Aerotech M1315 for propulsion however due to forgetting to multiply the mass of the fins by 4 when doing the design the rocket came out too heave and the motor had to be upgraded to the M1939 .  The onboard BlackSky AltAcc was to trigger recovery, there was also a backup timer set to one second past the simulated apogee wired to a second (larger) deployment charge in case the AltAcc did not trigger the ejection charge.

The Original V2 Design

The Name A4 came from the rockets working name Aggregate-4 or translated Assembly number 4.

The V2/A4 was originally designed by the German Army Ordinance Department under the direction of General Wernher Von Braun and his engineers in Germany it was originally designated A4 until it was renamed for propaganda purposes Vergeltungswaffen 2 or vengeance weapon two and it became the V2.

 The first successful flight of a V2 took place on October 3rd 1942, following 3 earlier unsuccessful attempts test vehicle number V-4 made a perfect flight, it broke all previous rocket records for speed, altitude, endurance and distance.

 A total of approximately 4300 V2's were launched at an estimated cost of £35,700 each.  

For further information about the original V2 please look here.

 The following diagram shows the outline of the V2 with 1/4-scale measurements, these were used for this rocket.

Figure 1-Quarter Scale measurements

Diagrams

Here you can see the Rocksim 5.0 wire frame and solid rendering.

  Materials

Nose cone:                custom, 412mm x 1323.75mm fibreglass, custom tube, shaped styrofoam stock, ½”9ply Birch centring rings and bulkhead, 3 of Steel 43mm x M8 U bolt, Custom turned wooden nose tip block, ½”9ply Birch stringers.

Airframe:                    custom, 412mm x 1082.5mm, fibreglassed tube, ½” 9 ply birch stringers. Internal sealed tube for avionics with 4mm bulkheads.

Fin Can                       custom, 412mm - 260mm x 1103mm fibreglass, custom tube, shaped Styrofoam stock, ½” 9 ply birch centring rings, ½” 9 ply birch stringers, Steel 43mm x M8 U-bolt. 4 lengths of all thread with nuts, nylock nuts and sealing washers.

Motor tube:                manufactured, Aerotech 75mm motor mount tube, pheonelic.

Fins:                            custom, ½” 9 ply birch, fibreglass, Styrofoam stock.

Adhesives:                 WestSystems 5:1 Epoxy, slow hardener.

 Nose Cone Detailed Construction

The nose cone was constructed from a custom 250mm I/D 256mm O/D tube with a rear centring ring enlarging to 400mm, a mid centring ring enlarging to 412 mm and a forward centring ring reducing to a custom 138mm I/D 147mm O/D tube. This in turn had a bulkhead at the front that held a custom turned wooden nose tip via 4 21.5mm wooden dowels.

The scale nose cone drawing shows 3 of 4 dowels as does the diagram below these were be fixed into the nose cone tip by drilling holes into the tip block gluing the 21.5mm dowels into the holes and screwed diagonally for ensuring they are secure. The other ends of the dowels were in holes half the depth of the ply bulkhead, they are glued into these holes and bolted (used barrel connectors) from the opposite side of the bulkhead. The bolts were first placed through sealing washers to spread the load to ensure they did not pull through the bulkhead.

Between the rear and mid centring rings were wooden stringers to help strengthen the structure, these stringers were both glued and screwed between the two centring rings.

Three M8 U-bolts were bolted through the rear-centring ring as close to the centre as possible at 120^o to each other. These were  the attachment points for the recovery system. There were metal plates on the front side of the centring ring to stop the U-bolts from pulling through. The M8 U-bolts had both a standard Nut and a Nylock nut to ensure that the nuts did not come undone.

Inside the circle of the M8 U-bolts were 3 small U bolts that held on a 4mm ply disk that sealed off the nose cone area from ejection charge gasses. It is in this sealed off area that the parachute and majority of the shock cord was stored within. The edge of the centring ring had a bead of silicon rubber applied to help seal the nose cone area against the 4mm-ply disk. This is further detailed in the recovery section.

All joints used 30-minute epoxy and critical joints were reinforced with fibreglass tape, i.e. the rear-centring ring that had the recovery system U bolts attached to it.

The entire structure (apart from wooden tip) was covered with Styrofoam. The Styrofoam was then shaped on a lathe to give the nose cone and shoulder its shape. The whole structure was then be covered with 4 layers of 100g satin weave fibreglass.

West Systems Epoxy resin was used for the fibreglassing process as Polyester resins would melt the Styrofoam.

The process used for applying the fibreglass ensured that excess resin is not applied and maximised the strength of the finished product. Also stippling with a brush will damage the cloth. The process used is to use 125micron melinex polyester film as an envelope this envelope had the desired shape of the glass to be applied drawn on it with permanent marker. The fibreglass cloth was placed in the melinex envelope, catalysed epoxy resin was then be poured on top of the cloth and the envelope shut. A squeegee was then used to spread the epoxy resin through out the cloth this method expeled all of the air from the fibres of the cloth and also remove excess resin, the desired shape of the cloth can then be cut out through the melinex. The envelope would then be opened and the cloth applied to the nose cone.

  Not to scale

Tube and centring ring core with Turned Wooden Nose Tip.

In the above diagram the tubes are colour yellow and the wooden components are coloured blue.

Body Detailed Construction

The body tube were constructed from a custom 400mm I/D 412mm O/D tube covered in 4 layers of satin weave 100g/m fibreglass cloth. Fibreglass was applied as for the nose cone using the Melinex film to ensure the strongest finished product with minimal weight gain. On the inside four strips of 12mm x 48mm 9 ply birch was glassed into position these helped the longitudinal strength of the tube and pass the forces between fin can and nose cone. There was also a tube on the inside of the main tube this was used to house the recovery electronics, positioning the electronics at a level on the rocket where they are easily accessible while the rocket is on the launch pad. The position of the electronics was just in front of the center of gravity but low enough to be easily accessible.

Not to Scale

  Body tube with longitudinal stringers.

In the above diagram the 4 blue strips are the ply stringers to dissipate forces between nose cone and fin can so the longitudinal forces are not all taken by the tube alone. The rust colour tube is glassed to the inside of the main body tube and was used as the electronics bay, it was sealed at both ends by 4mm wooden bulkheads. Once the whole structure was glassed an access hatch was cut in the side of the main body, this allowed access to the electronics while on the launch pad. The access hatch was bolted into position so nuts were  glued onto the inside of the main tube witin the electronics bay thus ensuring the main tube stays sealed for ejection gases. Holes for electric matches for deployment charges were sealed inside and out by plumbers mate.

Tail Cone Detailed Construction

The tail cone was constructed from a custom 250mm I/D 256mm O/D tube with a front centring ring enlarging to 400mm, a mid centring ring enlarging to 412 mm.

This entire structure was covered with Styrofoam. The Styrofoam was then shaped on a lathe to give the tail cone and shoulder its shape. The whole structure was then covered with 4 layers of 100g/m satin weave fibreglass cloth again using the melinex envelope method described in the nose cone section above.

Not to scale

Tube and centring ring core.

In the above diagram the tubes are coloured yellow and the wooden components are coloured blue. The fin can and motor mount details are covered in following sections and mounted inside the above structure.

Fin Detailed Construction

The four fins were constructed from 12mm 9 ply birch, the fin shapes was cut out of the ply and lightening holes were cut into the fins, these holes were then filled with styrofoam. The whole structure was then covered with 3 layers of 100g/m satin weave fibreglass using the melinex envelope method as described earlier.  

Not to scale

Figure 7 12mm Birch Ply Fin shape

The slot at the front and rear of the TTW Fin mount had fibreglass tubes fitted through them holding all 4 fins tight to the motor mount. The slot in the middle of the fin mount was to accommodate the middle-centring ring on the motor mount tube. The other 2 centring ring at the front and rear of the fin had slots in them that the front and rear lugs on the fin mount sloted into also holding the fin securely in place.

Fin Can Detailed Construction

The Fin can was constructed of a 4" PML body tube  with three custom 12mm 9-ply birch centring rings over it. There were also 2 fibreglass tubes reinforced with wire that are used to assist in holding the fins into place

  Not to scale

12mm Birch ply centring rings

The top row shows the fore and aft centring rings, the bottom row shows the middle-centring ring.

     Not to scale

 Assembled Fin can

The above drawing shows the 4" motor mount in Yellow, The three centring rings now in Red along with a 250mm bulkhead at the front (not pictured previously) and the green is the wire reinforced fibreglass tubes. There are also ply strengthening stringers shown in blue and the all threaded rod shown in grey.

The wooden stringers and all threaded rods are only shown on one side each for clarity although there was stringers and threaded rod midway between all fins.

The mid centre-centring ring was first be epoxied to the 4" tube , then the fins were epoxied in place,  filleted and then fibreglassed to the 4" tube  and the centre-centring ring (the front and rear centring rings are used to hold the fins in alignement whilst the epoxy sets). The fibreglass rings were then epoxied on to the fins and the front centring ring was then epoxied into place (do not epoxy the rear one yet).

12mm 9 ply birch stringers were fixed between the centring rings 1/2 way between the fins. Also there was m6 all thread from the middle-centring ring through the front centring ring to beyond the motor mount tube. Where the All thread passes through each centring ring it had a large sealing washer placed either side of the centring ring and nuts to hold it firm, these nuts were epoxied to ensure they do not undo. Either end of the all thread had a nylock nut ensuring the rod remains held firm

A M8 U-bolt was fitted to the front bulkhead for recovery attachment, this had a metal plate on the rear of the bulkhead as reinforcement. The front bulkhead was not fitted until after the tail cone was fixed to the fin can.

The tail cone was then slotted from the rear so that it could be slipped over the front of the fin can and epoxied into place. Lastly the fin fillets were applied and the rear centring ring glued into place

The recovery attachment point was fixed into the front fin can bulkhead at the front of the tail cone shoulder. This bulkhead was fixed to the middle-centring ring via the M6 all thread and stringers. Metal plates were on the rear of all bulk heads/centring rings for strength of the recovery system. The M8 U-bolt had both a standard nut and a nylock nut to ensure that the nuts did not come undone.

Recovery Details

The recovery attachment points have already been discussed above. There was a climbing sting threaded to all of these via locking karabina's these slings were rated at 7 tonn. The slings were taped to hold them flat and stop the loop from opening and snapping shut at deployment. The sling attached to the fin can was covered in a nomex shock cord protector.

The opposite ends of the slings were attached to a 12-Meter length of Man rated climbing sling tape this was the main shock cord, All joints were tied and taped to ensure maximum strength and there was no ability of snagging parachute shroud lines.

The Parachute was be housed in a deployment bag held in the 254mm Nose cone tube this area was sealed off from the ejection charge bay in the main body by a 4mm-ply disk. This was be held in place by looping the shock cord from the fin can through 3 U-bolts that protrude through slots in the 4mm-ply disk, these 3  U-bolts were either side of the 254mm nose cone tube  on the rear centring ring of the nose cone shoulder.

The Parachute was stored in a deployment bag that was fixed into the forward tube in the nose cone. The apex of the Parachute was tied into the bottom of the deployment bag with thin thread that would snap once the parachute is fully deployed from the bag ensuring the shroud lines are taught making less chance of a shroud line becoming tangled. The shroud lines were fixed to the outside of the deployment bag with elastic bands these were to help in the taught deployment of the shroud lines. The neck of the deployment bag is sealed with thin thread that would be snapped with the deployment of the last length of shroud lines. This should ensure a snag free deployment of the parachute

There were 2 black powder charges as described below each sufficient on their own to deploy the recovery system. They were to be triggered by one of the two onboard electronics these being a BlackSky AltAcc  with the electric match wired to the main terminals so as to deploy the recovery system at apogee. The second system for backup was a BlackSky timer 2. This was set to deploy at 1 second past apogee with calculations  this was 17seconds after lift off.

 BP Calculations

The weight of black powder required to pressurise the body and nose cone cavity would be 64g as calculated by http://www.chmara.com/bt/rocketry/bpcalc.html this is approximately 2 35mm-film pots full. To reduce this to 34g it was decided to somehow seal the nose cone cavity from ejection gases; this was decided to be done with the aid of a 4mm-ply disk against the rear-centring ring of the nose cone. This lip would be sealed with a silicone rubber (bathroom sealant) gasket  and then sealed on the outside with masking tape. The main length of shock cord passed through a slot in the middle of this disk and the slot was sealed with epoxy.

The black power was inside film pots that had masking tapeto hold the lid on and an electric match inserted.

The Black powder charges were checked on ground simulations to ensure the charges were sufficient to eject the tail cone. This was done my wiring the charges as normal but not connecting to the electronics in the electronics bay but by connecting to the leads of a launch controller connected through the access hatch to the electronics bay and triggered from a save distance. These tests showed that only 17g of FFFF Black powder was required to blow the tail cone off.

Parachute Calculations

Using a total weight of 50Kg and a man rated parachute of 28ft would give a slow decent rate that should result in a safe recovery. These figures were checked by multiple means.

 Attachment points and shock cord

43mm Diameter U-bolts were used as anchorage points for the recovery harness. There were 3 U-bolts fixed to the rear nose cone centring ring there were metal plates on the front of this centring ring. To these were attached 30KN breaking strain 25mm nylon tape slings at 1.2M long  (rock climbing) these meet at a 30KN locking Karibiner (rock climbing). Also attached to this is a length of 25mm tubular nylon tape (rock climbing). This was of sufficient length to allow the fin can to pull the parachute all the way out of the nose cone before the tape pulls taught. It would also be long enough to allow the nose cone to hang clear under the fin can when under parachute, to allow the nose cone to land first slowing the landing speed for the more delicate fin can. This was approximately 32M long with the parachute fixed 10M from the Fin Can. The Parachute was fixed to the shock cord by another 30KN locking Karibiner. A 3rd locking Karibiner was used to fix the shock cord to a 4th 30KN breaking strain 25mm nylon tape slings at 1.2M long  (rock climbing).

Flight Results

Well on 1st July 2001 V0.5 flew. The motor came up to pressure instantly and the giant rocket leapt off the launch pad for an impressive and perfect boost. However things did not go as planned when the rocket reached apogee, there was no parachute deployment and the rocket laterally screamed back to the ground creating a 3ft deep crater.

Analysing the aftermath of the flight it can be determined that at least one set of electronics failed and hence the deployment charge did not go off. One ejection charge went off on impact and damage from this can bee seen on the exposed broken styrofoam of the nose cone. Also having had the data back from the ALTACC it did not record the flight but was armed I even have video of this. As to weather the timer's charge went off this is a matter we will not know some think it did some not as the timer had last minute repairs.

A lot was learnt from building this and a lot of fun had so back to the drawing board.