Backyard Ballistics (tm)

Periwinkle's Pride - Hybrid Bash
Content Copright 2001, 2002, 2003 by Private Data, LLC

Hybrid Bash

Periwinkle pre bash
Stock Periwinkle
Periwinkle with bash payload bay test fit
Hybrid Bashed Periwinkle
Periwinkle re-bash
Hybrid Bashed Periwinkle - rebuilt after her coresample flight.

Mike with Periwinkle with PP J-140

Mike with Perwinkle re-bashed with extension and loaded with Propulsion Polymers J-140. Check out the launch report below for some great video of that launch.

I wanted to build a new rocket with and for all my new toys - RockSim 6.0 and a Propulsion Polymers motor set. After the CFO (wife) put the brakes on ordering new rocket parts, I decided to consider bashing Periwinkle.

The small motor tube, the H70, would essentially fit, and would just need electronics for deployment. But, I wanted to also get my L2 certification this spring. The L2 would require the J-140 tube and that tube is 34" long - nearly as long as the 36" body tube of Periwinkle. Even the I-140 at 24" leaves no room for electronics AND the chute, and that for single deployment.

And did I mention that I also really didn't want to change Periwinkle, visibly, at all. She looks great , she flies great, and I'd rather work around, if possible, than taint and modify. This with a target for a later build specifically for the longer of these motors.

The "traditional" anti-zipper retrofits.This was a non starter as it would require the coupler tubing to be structurally attached to the main body tube. I didn't want to epoxy this, and I didn't want to screw it in.

The traditional dual deploy designs also didn't quite match up to Periwinkle. Basically, the motors leave no room for electronics bays, which are often embedded in the descending coupler.

So, to bash periwinkle, I would need an upper payload tube, and this tube would have contain  the coupler and house the streamer and all it's components, the electronics, and the main parachute and it's components. I would need a removable upper motor support to properly support the longer motors. I would need a vent tube channel through the fin can area.

Hybris motor upper motor support The upper motor support was easy in principle and construction. It consists of a 2" (or so) section of  2.5" coupler tubing, with two 2.5-1.5 centering rings (I had CRs not CCRs). Centered within was a 6" (or so) piece of 38mm motor mount tubing. The longer motor mount tubing serves to offset the 2.5" portion well down inside the body tube. This is necessary to accomodate the 4" of coupler that will slip in from the payload tube.

Since the upper motor support is non structural, I made a slot in the CRs to allow the nylon strap to pass through. I also added a couple loops of kevlar thread to allow both retrieval of the mount via hook and also to secure to the motor top to prevent ejection from forcing the mount down into the body tube rather than forcing the paylod section off.

The Payload tube is more involved. It's relatively simple, but must contain both deployments and an embedded electronics bay. I did not want the break the body again, so the electronics bay would need to be embedded yet removable.

I had hoped I could keep the extension short, but that was not to be the case.  I had hoped for 18" and she ended up about 26". I needed to build the Electronics Bay first.

I had never built an electronics bay before. I had read up on them on RocketryOnline, Info Central, and many other sites. This seemed a bit unique as the bay went into the middle, yet the tube was small, making post-build wiring problematic. And the hole for the altimiter would be a large opening in the relatively small body tube. I discussed this with Doug Pratt and he said "6 of 6-32 bolts".

So I built the bottom of the bay with a double outer thickness to accomodate the bolts without compromising the strength. with 6 I likely would have been OK with a single thickness provided I nailed the CR exactly in the center. My specific combination, aside from strength, was driven by what was on hand.

I built a center-mount plate with a full length allthread with threaded couplers. This is strong. I had the RRC2 to test fit with, and I knew the battery mount would be close, but as it turns out, it's very tight. I either need to shave the mount or recess the RRC2 into the mounting plate (perhaps a RRC2 sized slot with back supports - all I need is 1/8" extra.

I also wanted an outside-rocket arming switch. You can see it's installation. This is and remains a pain. The alignment requirements for a removable bay with a switch, means any amount of error or slop and the switch doesn't align with the coupler tube or the body tube. I may permanently epoxy the plate to the lower bulkheads to facilitate easier and more accurate installation.

Not strictly necessary, but to facilitate an axis of electronics bay alignment and also provide some strength, the lower coupler tubing is extended the full distance up to the electronics bay bottom. This provides a firm and strong seating base with the only axis of alignment left being rotational.

I inserted the externally assembled bay into the tube. With careful measurements, I marked off 6 holes that should be evenly spaced and also nail the center of my built up bulkhead. I then pre-drilled a hole, inserted a screw, and completed all 6, inserting a screw each time (this serves to guarantee absolute alignment). Next time I will make one of the 6 significantly off to make determining the exact alingment very determinstic later (as your marked and as-drilled holes will be off slightly).

With this done, I marked off the switch hold and made that cutout. As this was done separately ,and with the e-bay done first (bad move, always drill IN first, and through everything,  and reference from that - besides, mistakes inside don't show), anyways, I made and trimmed the switch cutout. I also made two more altimiter vents at 120 degree invervals. These are inside out drilled and align perfectly even though they're small (1/16").

This sounds too easy. It wasn't it was tedious. But with lesson learned and a bay under my belt, the next ones will be better and also be built faster.

Chutes? Did I leave enough room? The bash would be several pounds heavier, 4.5 heavier for 6.5lbs total. I knew I'd need a bigger chute but not how much bigger. And my RockSim was "shooting low" due to a 20lb estimate for the rocket weight. I tracked this down to an incorrect streamer, but not before I'd made allowances, but otherwise cut the payload tube.

RockSim was saying about 54", and that with computations normalized the the orignal PML sim (mostly factoring out the supposed RockSim penchant for over-sizing chutes). Will a 54 fit? Too late to order ahead from Ken. Hope? Pray.

Visiting with Ken at the launch, we were having difficulties finding the 54 he thought he had. But when I mentioned my space concern AND the descent rate concern, we looked at the 58 as too big (physically too big) and the 48, 50 too small (descent rate). Not finding any 54s Ken remembered seeing a special "thin mil" 58, (Giant Leap) from an abandoned special order. We found that and it's a 'beaut. Very thin, and it will fit. Thanks Ken! Thanks Giant Leap! Saved!. Lesson: Always size your chute with RockSim till it's close, then size it physically with recovery cord before cutting your tubes!

For a drogue I selected an 18" chute per RockSim computations. This also from Giant Leap not PML (again, mostly availability - I didn't need X-thin for this chute).

Recovery is otherwise with Pratt Hobbies Kevlar, 20 feet for each stage.

Venting the motors. The hybrid motors require a N2O tank vent and the Propulsion Polymers vent from the top. I did not have the body tube length to vent up and out (it would interfere with the coupler on the long motors). So I had to go down. Down is problematic during setup, but this rocket's already getting involved (consider ejection charges on the embedded electronics bay). If I only went down some, it could interfere with using the shorter H-70 motor, and that left, essentially, out the bottom of the rocket. For that, I aligned some tape, hoping to avoid the fins and the recovery strap. I also wanted to be away from the rail to give a wider viewing angle, for venting, no matter how the rocket positioned on the rail. To make fising easier I chose to retrofit a 8" (or so) length of brass tubing through the fin can area. This will still be difficult to hit, so I plan on using a 36" length of music wire to facilitate threading the vent tubing through the fin can area as well as through the upper motor mount. This is small enough it should not vent too much ejection charge gases  (esp on a standard motor).

rail button installation tools and glue Rail buttons. I needed to attach a launch lug on the payload section. The regular 1/4" lugs on the main body were also too small for for a rocket this long and of this power range. I was discussing plaement of a 3/8" or 1/2" lug on the upper section, and alongside the smaller ones (dual use!) this with Doug, and he kept saying "rail buttons". Convinced, I ordered rail buttons from and (less necessary) a rail from McMaster-Carr per the instructions on

marking an laying out rail buttons These were a bit more problematic to retrofit, and also as I wanted to preserve the piston deploy of the original kit (for standard motors at least). I chose to offset mount them to 3/16" slices of 1/2" phenolic rod I had handy. I drilled and tapped these for the 6-32 screws.

Installed rail buttons with glue drying I carefully marked out the holes with taped angle iron (to protect the finish), drilled pilot/alignment holes, and chipped the paint away. I also scored well into the QT to give the cement some bite. I used masking tape to facilitate fillets without messing up the paint job. These were glued on with Plastic Weld glue (several brands, from JbWeld, LocTite, ...) which was a test over epoxy. It worked well. (I find Plastic Weld fantastic for gluing tough to glue plastics - but it sets quickly so mix just enough at a time for one button).

For recovery harness, I had the local shoe repair bar-tack all the recovery strapping and now the rocket, in any configuration, assembles with screw links.

Dual Deploy Recovery

I had built an altimeter bay for the upper section and then core sampled her. So I rebuilt the upper and here's the new alimeter bay. I added a Magnetic Apogee Sensor as backup for apogee deployment. It's the upper bay; the lower is the new bay I built at the same time for the Bullpuppy.

Altimeter bays

Top shot; Periwnkle with RRC2 and MAD for backup; Bullpuppy with PerfectFlite Mini-Alt altimeter

Altimeter bays

Bottom shot;

Launch Reports

04/27/2003 - Battle Park, Culpepper VA

This day was a valiant but failed attempt at launching my hybrid bash. Read the launch report of the eventual conventional Periwinkle launch here.

6/2003 - Whitakers, NC

I certified TRA L2 at this launch! I planned to certify L2 with the Periwinkle Bash and my Propulsion Polymers J-160. But luck was not with me and the the HyperTek equipment was in Greensboro and Doug couldn't make it with the HyperTek to PP/Ratt adapter. Bill Shamblin had his equipment - but was having difficulty getting a N2O fill from his supplier.

Fortunately a Cesaroni J285 and case were made available and I was able to launch and obtain my certification with a picture perfect flight and recovery. I want to thank all that helped and particularly Kelly Mercer and Ed Row. Both were all around helps and I borrowed a Walston Transmitter from Ed - and a good thing as I landed in the corn field -  a field that had eaten several rockets already. Kelly helped me as well with a throrough checkout and especially with recovery - he helped me manage both the Walston receiver, electric fences, cornfields, and recovery all while I had a very hot, tired, 4 year old on my back.

This was an interesting weekend. I took my time with the L2 written exam. Partly as it was hot, partly as we were all chatting, partly as I wanted to ace it after barely flunking it twice at Battle Park (I forgot to study the Safety half at all!) I aced it!

I took my time putting the rocket together. This as I had many firsts coming together and I also don't have much time at home that isn't post midnight (due to kids). I also needed to score some parts from Ken. I kept working through my list as Kelly patiently occasionally asked "are you ready yet?" :)

I finally got her ready near 5pm - but, unfortunately a big storm was rolling in. While we all hoped it would clear - it didn't. In fact, we got an inch or two and all ended up huddled in the big tent, holding it down. The LSO shelter was trashed as was anything else not staked down. Needless to say I didn't launch that day. But I DID get some of that pig that they bbq'd. Yum!

I talked my wife into my returning Sunday. Getting the L2 was key to having more freedom to fly the hybrids on my own - and as I'd found - hybrid equipment and gas availability is never a given so I needed the L2 to be able fly whenever, whereever (as hybrids require L2 to operate at this time). I also wanted to start playing with EX motors and this also was an enabler. As part of the deal, I returned with my 4yr old son. This was a mistake.

It was clear, but very hot on Sunday. My son doesn't do well in hot nor in the sun (for long), and for nearly the whole time I had to carry him or walk very slowly. This in itself made it take all afternoon to launch his Estes twice and mine once. But my only real goal was the L2 shot and I told everybody, including my son (continously), that we're going home after that. And it was all worth it!

Here are some great pictures:

Whitakers line with me in the near foreground

Chatting with Bill Shamblin at the Pig Pickin. I was trying to fly and cert and all they could do was think about that pig. Yum!

Gratuitous shot of me with the pad in the background

Distracted by some APCP going up

Periwinkle on the pads - photo by Dave Morey

Periwinkle going up - beautiful launch photo by Dave Morey

Periwinkle coming down - into the corn - photo by Dave Morey

7/26/2003 - Whitakers, NC

I attended the sport launch day (Saturday the 26th). My main goal was to get at least *one* hybrid shot off on Periwinkle. I don't care which motor nor which configuration - just to get one hybrid shot off and have it be successfull.

Due to hybrid GSE availability issues I decided to make my own. I am building out my own N2O tank/manifold/solenoid assembly as well as my own controllers for the same. It will be tough to pull everything together in a fully assembled manner - but I will arrange for some combination of it and other's equipment to be there so that I can launch.

I am also building my own RDF transmitter and receiver. The Walston I borrowed works great but I had already bought parts to build up Pete's setup. I hope to have it together for this launch - and that will be timely as the club's receiver may not make it back from LDRS. Having something is very desirable as Periwinkle was difficult enough to find the the corn on my L2 cert flight and that with the Walston. That corn had already eaten a couple other nice rockets that day.

As it turns out, I went to load up the J-160 motor, but found I didn't have the right floating injector (only the 3/16ths will do). I spent the rest of the afternoon trying to cheese somethign together, including fruitless runs to the hardware store. In the end I didn't get a launch.

Unfortunately, while digging around at home, I found the injector. It was in the I-140 tube - and I'd had it all along at the launch. ack!

11/2003 - November 2003, MDRA Higgs Dairy Farm

I had Periwinkle loaded with the Propulsion Polymers J-160 motor. It was a cold day, in the 40s. I had also upped the ejection charges. Unfortunately I think the combination of these lead to my unsuccessfull recovery. But first things first.

I set up my GSE on a far pad, loaded up Periwinkle, and launched her. This was a first on many fronts - my first hybrid flight and all by myself on all my own equipment. I was proving many things this time!

The boost was great - a very impressive launch, boost, and coast. Sims predicted about 6,000 ft or more.

Unfortunately, she remained ballistic and coresampled into a farmer's field. Forensics indicate that the ejection charges blew, but that the apogee charge blew out the middle and jammed the separation keeping her ballistic. The nose cone was just to the side of the "hollow point hole" and was flattened on its side. Indicating the main charge blew, but with a ballistic rocket, didn't have time to do anything.

Interestingly, the lower section, being essentially all motor, acted as a pile driver on the upper section, destroying everything, but protecting the lower section save for an inertia separated motor mount ring. The RRC2X looks repairable with just the connectors ripped off. The remainder a total loss, including the RDF TX and the parachute.

1/3/3004 - Battle Park, VA

I skipped Whitakers December launch to spend the time re-building Periwinkle and building up the BullPuppy for the RATT H-70. This was a successfull launch of  the re-built Periwinkle on the Propulsion Polymers I-160 motor. Click here to view that full launch report.

5/22/3004 - Whitakers, NC

I had a good launch day. I fired Periwinke with the body extension with the Propulsion Polymers J-140 (that now fits). She really ripped off the pad like a bat out of hell. Here's a good picture of me, Here's a good picture of her coming down under chute, and do check out the video here.

I also got two shots off on my Bullpuppy Intergalactic Noxious Space Explorer with the RATT H-70 motor. As usual, clouds rolled in, and everybody packed up. I was re-prepping the Bullpuppy during that and finished prepping her as the launch equipment, except what I was going to need, was torn down. As you can imagine, I was the last flight of the day.