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Recovery Systems
Piston, Ring and StrapThe booster section recovery system was somewhat complicated by the removable motor can, since recovery straps are typically bonded to the motor mount assembly due to the strength of the motor mount and its integration with the airframe. Figure 13 shows my solution. I used a standard PML 7.5" piston assembly, and bonded the recovery strap to a piece of 7.5" coupler. The bond of the recovery strap was then reinforced with a fiberglass overlay to ensure it stayed bonded to the coupler.  | | Figure 13 - Ejection Piston, Piston Strap, and Strap Mounting Ring |
The coupler ring with strap was then slid deep into the airframe just above the motor thrust ring. Since it was such a tight fit to the airframe (which is very good), the only bonding technique I could use was to dribble thin CA around both the upper and lower joints. I used nearly an entire small bottle of the CA, so I’m sure it has wicked deep down into the interface between the coupler and the airframe. While the thin CA was still wet, I then applied some medium CA as well, hoping the capillary action of the thin CA wetting the surfaces would assist in pulling in the medium CA. For the coupler ring to fail, it would have to "cock" at an angle in the airframe, which is essentially impossible, especially with the bond to the airframe. Even so, I also glassed over the ring to the ID of the airframe. The key stress point in the system is the bonding of the strap to the ring itself. On the 12", I will make the coupler section longer to have a very large bond joint to the coupler. Cable Harness and Reinforcing  | | Figure 14 - Upper Section Recovery Cable Harness; Recovery Mode |
The upper section presented its own challenges due to the desire to recover the upper section somewhat "nose up" to prevent damage to the LES assembly upon landing. I decided to upgrade the 1/100 Saturn V concept of a harness/sling arrangement to meet the strength requirements of this model. See Figure 14 for the "as in recovery" view of the cable harness. The cable itself is 3/16" aircraft-grade steel cable. It has been joined at various places using aluminum ferrules designed specifically for this purpose. The ferrules were put in place, then clamped as tightly as possible in a bench vise. Each "gripping point" of the ferrule was then peened on both sides with a dull center punch. As final insurance, each ferrule/cable joint was CA’d to get the CA to wick into the interface between the cable and ferrule.  | | Figure 15 - Upper Recovery Harness Attachment Bulkplate |
The 1/100th Saturn V design has a wire ring that comes out the side of the SM; the recovery harness is clipped, via a snap swivel, to that wire ring. I upgraded this design by using a hobby plywood "bulkplate" inside the 3.0" tubing, to which I attached a large T-nut which passed through a large OD fender washer to help distribute the load further over the bulkplate. (See Figure 15) The 3.0" tubing has a hole through it into which the T-nut threaded portion protrudes. This allows attachment of the cable harness upper eyebolt. Figure 14 shows this. After attachment of the bulkplate/T-nut assembly to the ID of the 3.0" tubing, I then used medium CA and accelerator around the T-nut threaded portion protruding into the airframe. This was to ensure a seal for the next step, in which I built a "dam" on the lower section of the bulkplate to the airframe, then stood the upper section on end and filled the void between the airframe and bulkplate with epoxy. This was to ensure the load from the cable would be applied to the maximum amount of the 3.0" airframe as possible, to help prevent tearing the mounting out of the airframe in case of high-speed deployment. This area could be improved by carefully sanding the bulkplate to the exact shape of the ID of the 3.0" airframe, sort of a half-moon shape.  | | Figure 16 - Lower Cable Harness Attachment Details |
The lower mounting of the cable harness assembly was relatively simple. I used a T-nut on the back side of the bulkplate on the bottom of the upper section with an eyebolt through it. The bottom of the cable harness is attached to this eyebolt by a Kwiklink. (See Figure 16) In retrospect, I would have liked to have used a larger eyebolt and T-nut. The current arrangement has performed well, but I’d prefer a larger one. To help ease my concern about the size of the eyebolt I had used, I added a "backup" eyebolt to the bottom of the upper section. I used an expanding eyebolt that is inserted in a hole, then is turned to make the plastic portion expand into a sort of "flower petal" arrangement. The upper harness is passed through this safety eyebolt, then the kwiklink is attached, then the kwiklink is attached to the main eyebolt and screwed closed. In this way, if the lower eyebolt failed, neither the kwiklink or the lower eyebolt can pass through the eye of the safety eyebolt, so some form of recovery system attachment is ensured. The same is true of the upper eyebolt section. Even if the bulkplate tears through the 3.0" tubing, the harness is still attached at the bottom, so though recovery will not be "nose up" as intended, the recovery system still stays attached. The only failure mode of the recovery harness that would allow total detachment would be tearing of the upper bulkplate from the airframe and failure of both lower eyebolts and/or bulkplates. Parachutes On the first flight, I used a PML 54" parachute for the upper section, and a PML 72" chute for the lower. These proved to be sufficient. However, there was a break in one of the fin shrouds on the booster section after landing. This was due to the booster taking a bit of a wind push just before touchdown, and the booster landing essentially on one fin. After repair of the shroud, I did two thing to help prevent the situation. One, I moved up to an 82" parachute for the booster second flight. I also injected expandable foam into the inside of the shrouds. (See Shrouds and Transitions for more details on the foam usage). Spacecraft and LES The spacecraft itself is a pouring casting of urethane which was then machined into shape. The shoulder of the spacecraft fits inside the 3.0" tubing about 1.5". As mentioned previously, the spacecraft has been drilled and tapped for threaded rod for the addition of bronze nose weight discs. To allow easy removal of the spacecraft/LES assembly to change weight discs, the shoulder of the assembly was drilled and tapped to accept a retaining screw through the 3.0" tubing.  | | Figure 17 - Spacecraft and LES/Tower Detail |
The LES (Launch Escape System) and tower was entirely scratchbuilt from various sizes of dowel. See Figure 17 for detail view. There is nothing in particular to tell here...just careful measuring, sanding, and patience. The LES assembly was built entirely with CA to allow quick retention of parts in position. Attachment to the spacecraft is simply through angled mounting blocks CA’d to the spacecraft. The LES is another area where "sport scale" came into play. The actual LES tower legs splay outward as it reaches down toward the spacecraft; mine has straight legs. After two flights, the tower has broken off on landing each time. Even though the recovery harness allows for "tower up" recovery, upon landing the upper section of course eventually lays down entirely. It seems to tip forward upon landing (probably due to the one 13 oz. nose weight disc I fly as "insurance" for stability), and this snaps the tower off. It has always broken the escape rocket itself from the tower assembly, which is very easy to reattach with CA. If you build a Saturn V, either make the tower/LES assembly absolutely indestructible, or make a built-in "snap point" where it will break and easily be reattached. Altimeter Bay  | | Figure 18 - Self Contained Altimeter Bay Assembly |
The Saturn V project uses an ALTS25 altimeter for primary deployment (and a backup deployment). This was done because the possibility for premature ejection due to motor delay inconsistencies was just too high for 5 motors. The use of an altimeter eliminates the need to select a correct delay time before launch, and also doesn’t require the use of a "pretty close" delay grain if the timing needed doesn’t fall into the standard delay times available. I built a self-contained altimeter bay based upon the article in the November 1997 High Power Rocketry Magazine. (See Figure 18) My bay using an ALTS25 required some modification from what was described in the article, which used an ALTS2. This was due to the wiring connector on the ALTS25 being in a different orientation than the ALTS2. The basic design is very similar, however. I won’t describe the specific alterations, as any experienced builder will see the interference and find their own solution.  | | Figure 19 - Altimeter Bay Mounting & Pressure Port Holes on Airframe |
The altimeter bay is designed such that it can be easily installed and removed from any rocket. The rocket to use the altimeter bay only has to have 3 holes drilled, 2 for the bay mounting screws and one for the pressure port. See Figure 19 for these holes in the side of the Saturn V. One consideration in mounting the altimeter bay is the pressure port should be on a smooth area of the rocket with little to no exterior protrusions above the pressure port. This is to ensure a non-turbulent airflow to the pressure port. The Saturn V has many exterior details, so I was forced to pick the lesser of about 5 evils in selecting a position for the altimeter pressure port. The first flight went well, so the position I picked was apparently turbulence-free to the ALTS25. The bay is made from 38mm tubing and couplers. Both ends of the bay are removable for removal and installation of the altimeter. Each end cap is sealed with an O-ring, primarily to seal the bay from extraneous pressure that might interfere with the pressure reading. The O-rings also protect the ALTS25 from black powder blast residue on deployment. The screw mounts for the bay and the pressure port are also sealed to the side of the airframe with o-rings and rubber flat washers.  | | Figure 20 - Sealing Rings for Mounting Screws & Pressure Port |
One end cap contains a female RC car connector that leads to the ON/OFF wiring to the ALTS25. See Figure 21.  | | Figure 21 - Interconnect for Phone Jack Safing Switch |
Upon installation this is connected to wiring from a normally-closed phone jack on the side of the rocket. The phone jack is held to an open position by a phone plug inserted during prep of the altimeter bay and the rest of the rocket. This allows the ALTS25 to be turned on only when ready to go at the pad, by pulling out the phone plug and closing the circuit. The other end cap has two of the same female connectors. (See Figure 22) These connect to the primary and secondary deployment flashbulbs. I have also attached two PML EC-LES ejection canisters to the side of the altimeter bay. These canisters are used with the Robby’s Rockets Loadable Ejection System (LES), and hold the black powder and flashbulbs for deployment. They hold about 4 grams each of BP with the flashbulb installed. They are pointed somewhat toward the center of the airframe as shown in Figure 18.  | | Figure 22 - Altimeter Bay Connectors for Ejection Charge Ignition |
Shrouds and Transitions The fin shrouds and transition pieces were made from 0.020" and 0.030" styrene sheet. Styrene was selected because it is readily available, bonds well with common hobby solvents, and takes paint well. I used the transitions tool in VCP to create the templates for the transitions. The fin shrouds were done by taking a fin shroud portion I had from the 1/100th Saturn and tracing its outline. I then ran that drawing through my scanner, and enlarged it properly to fit 1/52 scale. This printout was then used as a template to draw out the fin shroud on the styrene. The shrouds were made from the 0.020" styrene, mostly because the 0.030" was too stiff to bend nicely in the curve needed. The styrene was cut with scissors; the pass-through hole for the fin itself was done by measuring and trial and error. The fin cutout from the 1/100th could not be directly scaled because the 1/100th fins were oversized by about 35% for stability. Once the correct size fin pass-through was made, I used that first styrene piece as a template for the rest. Due to minor variations in each fin, I recommend cutting the pass-throughs a bit small and shaving to fit as needed with an Xacto knife. Once each shroud was determined to fit correctly on the fin, the lower "half-moon" portion of the shroud was attached. A template was created for these half-moons (called "shroud lowers" from now on) by the same "scan and scale-up" method. The shroud lowers were made from 1/8" hobby plywood. I considered a number of different ways to attach the shroud lowers to the shrouds, and finally settled on a method using CA and accelerator. I had determined when test-fitting the shrouds to the fins that attachment of the shroud lowers first would greatly aid in attaching the shrouds to the airframe with the correct semi-conical shape. To attach the shroud lowers, I began with the shroud laying flat on the table and what would be the bottom edge of the shroud facing me. I put a spot of medium CA on the outboard edge of where the lower would attach. See * on Figure 23. I then put the matching portion of the shroud lower on the CA, allowed a couple of seconds for the CA to soak into the wood, then hit it with accelerator. I then placed another dot of CA on the shroud styrene a bit further around the lower edge, rolled the shroud lower into it, and again hit it with the accelerator. With careful progress, I had eventually rolled the shroud lower all the way onto the shroud.  | | Figure 23 - Shroud Lowers |
After the shroud lower was attached, I ran a bead of medium CA both on the inside and outside of edge of the joint. At this point the shrouds were ready to be attached to the airframe. Using the same "scan and scale-up" method described earlier, I made a template of the fin shroud marking guide from the 1/100 model. Using that guide I marked the intended final position of the shroud on the airframe. The next part requires an assistant: I discovered that I needed to squeeze the shroud into position, then have my wife put a dot of medium CA on and hit it with accelerator, much like attaching the shroud lowers. It is important to hold the shroud in the correct position, and also to hold it tight to the airframe so the capillary action pulls the CA into the bonding area between the shroud and the airframe. After "tack-welding" the shrouds to the airframe, I ran a bead of medium CA completely around the joint of the shrouds to the airframe. After the shrouds with the lower half-moons were attached, I then custom-fit strengthening pieces of 1/4" basswood between the bottom of the fin inside the shroud to the shroud lower half-moon of wood. This was done to strengthen the shroud lower to the fin assembly to provide better strength on landing, since the shroud lowers are the first thing to hit the ground. Finally, the opening of the side of the shroud toward the center of the rocket needed to be closed. I used 3/32" heavy posterboard. I held a strip of it in position to the shroud, then tacked it with CA. I then ran CA completely around the perimeter of the strip; once it had set, I used an Xacto blade to trim the excess. The shroud lowers, the posterboard covers, and the base of the motor can were then covered with a thick metallic tape with a strong adhesive backing to help prevent degradation due to heat and flame "roiling" in the bottom of the rocket due to base drag turbulence. As noted in the Parachutes section, one of the fin shrouds broke on booster section landing on the first flight. To help stiffen the fin/shroud assembly I used an expanding foam product inside the shrouds. I used a minimal-expanding foam, as opposed to the usual type called triple-expanding. I drilled two holes in the shroud lowers for inserting the foam can tip as well as for bleed holes to allow the excess foam to come out. Be aware that the foam, even the minimally-expanding type, does indeed expand substantially! Be prepared for the foam to weep out of the holes for hours as the expanding process slows and stops. Also, the foam will stick to absolutely ANYTHING. This super-adhesive nature of the foam is actually beneficial in many instances, and is beneficial in this usage. The foam not only provides a filler to the shroud area for stiffness, but also bonds the shroud to the fins and gussets, to the airframe, to the shroud lowers, etc. Wear latex or plastic gloves when using it and be sure to consider that when setting up for the overflow. One last item: I have seen some reports online that expanding foam can "reactivate" and begin expanding again with exposure to the sun. Apparently there’s a two-part expanding epoxy material that is readily available in better hobby stores. Though I experienced no problems with the foam reactivating, good judgement would suggest using the expanding epoxy product for this application. The transitions were made with standard shroud construction techniques. The shroud pattern was made using VCP software, then that pattern was transferred to the styrene sheet, except for the glue tab. The styrene is too thick for a glue tab through a slot as in a paper shroud. Instead, I cut a strip of styrene and glued it to the inside of the transition. The length of the internal strip is important; it must be as long as it can possibly be without interfering with the fit of the transitions to the airframe. Even so, plan for plenty of filling and sanding of the butt joint of the transition where it comes together. Use only as much cement as is necessary to get a good bond, or softening and distortion of the styrene will taken place, ruining the part and requiring you to start over. Make sure you use a plastic cement that is specifically designed for styrene parts. I recommend a liquid cement with a brush applicator, as opposed to a gel type glue such as Testor’s Model Airplane Cement. Using liquid, you can get the transition formed properly with the internal strip in position, then weight or clamp everything in place. Once all the parts are positioned, use the brush applicator along the edges of the internal strip and the cement will wick underneath and join the parts. After applying the cement, allow the parts to sit weighted and undisturbed overnight! The cement will take quite a while to set completely and for the styrene to re-harden; if disturbed early the joint will fail as some point or another and the part will be ruined. Do not use CA for the internal strip bond, as it apparently somewhat attacks the styrene causing it to crack easily. Due to the bending of the styrene, once a crack starts it propagates quickly. Use CA very sparingly with styrene sheet! The transitions were built off the airframes. When the cement had set overnight, I then slipped them over the airframe and into position. CA was used around the perimeters of each joint to the airframe. About the only hints I can give you for the transition part of the project is to practice on scraps first, and be prepared to ruin a part or two before you get the hang of it. It ain’t easy!
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