SV build progress
 

Things are going very nicely with my Estes SV #2001 build. I started in earnest on the build about 9 days ago. I have been taking my time and never rushing a decision that might benefit from some added research or further deliberation.

In prep for this build, I read every build blog on any of the various versions of the model I could find (a real goldmine of info) as well as reading a huge amount of the building techniques on this forum (many great tips). I also downloaded and read thru the old K-36 instructions as well as the Apogee SV. I asked the forum for input on several items. I was determined to incorporate the collective wisdom and insights that had accumulated over the many years starting with the K-36.

I have been documenting the build in pics and words and will create a running set of posts highlighting the changes I made to the stock build.

The list of mods on this build are considerable, but they all started with my desire to fly on a 5 engine cluster as it just seemed appropriate to stay true to the actual SV. I also desired the ability to fly different engine configurations, so an interchangeable engine core was on the list. I drew on the old K-36 interchangeable engine design, the TMRK design, on Rocket Babe's cluster/stage designs and my own thoughts. The final design may be viewed as overkill, but it is robust and flexible.

The entire build uses 30 minute epoxy and thin CA as adhesives. I also used thin CA as a "paint" strengthen many areas.

In researching clustered engine mounts, it became apparent very quickly that most of the kits were built around the BT-80 tube. As I clearly had the space for an internal BT-80 tube that simplified things a bit. I ordered up a 5 engine cluster (center 24mm, 4 outboard 18mm), a 3 engine 24mm cluster, a 4 engine 18mm cluster and a 29mm single engine kit. My original thought was to house each engine core in its own housing, but I then realized there was no need, they could share the same housing.

Another design feature I wanted was for all the engine cores to function with an aft thrust ring design rather than one located forward in the BT-80 tube. You may question my decision to house the engine cores inside a BT-80 coupler. That decision was based on the fact that I had concerns about the robustness of the thin walled BT-80 tube against the ejection pressures of the clusters/ larger single engines and about longer term scorching. I already had decided to incorporate a removable baffle section and the BT-80 tube would require a coupler to create the desired length, so it was a small leap to simply line the entirety of the BT-80 tube with removable sections. Yes, this added some weight, but the offsetting structural integrity improvements and the ability to replace if necessary, scorched sections as needed far outweighed the weight penalty. I intend to fly this bird often and for a very long time.

I built all the engine kits with fillets of epoxy on both sides of the CRs. Nothing outside a standard build. The engine cluster kits came from jonrocket.com and the 29mm kit from unclemikesrocketshack.com. The only mod to the kits was to reduce the forward centering ring diameter so as to allow it to slip inside a BT-80 coupler tube. The kit CRs were all .125 thin ply. The aft CR was left stock to act as the thrust ring for the engines. With the exception of the 29mm core, the actual engines in each core use the standard forward thrust/stop ring and retainer hook design. The 29mm uses a retainer cap system and no forward thrust ring.

To add strength and ease of removal to the 4" BT-80 couplers used to line the BT-80 tube, I painted them with thin CA. Then I sanded the exterior and repeated with more CA until I had a glassy exterior. The interior I only roughly sanded after strengthening with CA. I also CAed/painted/sanded the aft interior section of the BT-80 tube for added strength and integrity around the opening.

The finished BT-80 inserts slide in with a smooth, almost buttery feel and while there is a friction fit, they are removable. To totally line the BT-80 tube required 6 of the BT-80 couplers, one for the engine core, one spacer, one for the baffle, one to couple the 2 sections of BT-80 tubing and one at the top. I painted the interior of the couplers above the baffle with a thin coating of JB Weld for its heat resistance properties.

The baffle's origin was a kit from uncle mike's. The baffles are made of LetraMax which has superior heat handling properties. The original design used 2 baffles, one with a ring of holes near the center and the other with the perimeter ringed with holes. I modified it with 2 additional LetraMax BT-80 to BT-50 CRs located at the aft-most location and above the internal perimeter ringed baffle. The top baffle is the one with the ring of holes near the center. To build the baffle, I first epoxied the BT-80 to BT-50 CR to the bottom of the BT-80 coupler from the inside. The CR has the same diameter as the coupler, so this ring also benefits from the strength of the coupler edge when faced with the ejection blast. I then placed the first internal baffle and tacked it in place using a few small drops of CA, then a nice solid fillet of epoxy. Note all the fillets are located on the side opposite the ejection blast. I then added in another CR, using the same technique, whose diameter had been sanded to fit into the BT-80 coupler. Finally I installed the top baffle just down from the top of the BT-80 coupler so as to allow room for a solid fillet of epoxy. How will the baffle hold up longer term, no clue, but it is removable for cleaning and replaceable if necessary.

More build details will follow....

david

I predict you are going to need a LOT of noseweight due to the mass of all that epoxy and CA not to mention the added stuffer tube and plywood as well.
It will still fly well on a single 29mm F50/F52 though. probably really well on a G64W/G80T/G78G.

I think you'll do fine and I like that you're putting so much thought into this. Obviously you're enjoying building very much and with this kit you should be. :)

Verna
http://www.vernarockets.com
http://www.amazon.com/dp/B00HHJHOK6
http://www.amazon.com/dp/B00O14ET8K
http://www.amazon.com/dp/B01CX1UPCG

center of gravity
 

I am actually way beyond what I have posted. Today was just the first time I took time to collect my notes/pics and post.

I have the entire rocket minus the paper wraps, plastic/balsa details and paint completed. You are correct that I have added in weight, but with everything stacked including chutes and the 5 engine cluster core, but no actual engines, the CG is running about 1.5" FORWARD of the CP with NO additional nose weight. Yes, I will be adding nose weight as, with engines installed, I want the CG around 4" forward of the CP.

I started by building out the stock Estes BT-50 engine core and finding the CG of just the BT-101 with it dry fitted at the recommended 3 3/8" from aft location. As I built out the flight core, I used the original Estes core data as my reference and while I would have been happy with even neutral stability before adding nose weight, I was really delighted when I did the complete SV, as built, CG test. I have included a provision to easily adjust the nose weight in my design.

As for engines, I have run the calculations using various engining profiles and I have found several that look really good (i.e. around 5 thrust to weight, between 150-200ft burnout, around 500ft apogee with coast time running around 4.5 seconds.) These are all clustered approaches.

I have done a few calculation runs with smaller F and G engines and they are not promising. As you pointed out, I will likely need to move to the larger F/G end of the spectrum.

Such is life outside the Estes box.

Yes,I AM having a good time!
 

Verna,
Thanks for the ongoing encouragement.

david

Looking forward for more pictures and details!

:D Your enthusiasm is contagious. The 2001 kit is my favorite version and I agree with you, it should be done as a 5 engine cluster at a minimum.

I'm looking forward to seeing some launch photos!

Verna
http://www.vernarockets.com
http://www.amazon.com/dp/B00HHJHOK6
http://www.amazon.com/dp/B00O14ET8K
http://www.amazon.com/dp/B01CX1UPCG

The only Estes SV I have in flying shape/built is a 2001 that I have a permanent single 29mm mount in.
I fly it mostly adaped-down to 24mm on RMS24 F24's

moving right along
 

With the engine core build well underway it is time to move on to the actual BT-80 core.

For starters, I ran into the total lack of commercially available BT-101 to BT-80 CRs in ply or balsa. I contacted BMS and they no longer do custom work. I considered cutting my own from .125 stock, but it would be so much nicer if precut. In the end, it was a compromise. BMS offered to cut me BT-101 to BT-50 (a stock size) in .125 lite ply (non stock for this size). Between my scrollsaw and sandpaper wrapped around a BT-80 coupler tube I had my BT-101 to BT-80 CRs in .125 lite ply.

I had decided to go with an internal launch tube, so I clamped 6 of the CRs together and drilled a 5/16th hole thru them. I also drilled a 1/8" hole opposite the launch tube for the fishing leader that I planned to use as the shock line from the base to the top of the BT-101 section.

Before I started in with the epoxy, I dry fitted the CRs to the BT-80 on 6" centers and made sure that the the removable cores of the BT-80 would slide in and out as a sanity check.

At the base of the BT-80 tube I crafted a small block of basswood curved to fit the BT-80 tube and to match the curve of the BT-101 with a coupler installed. I drilled the block for a small steel eyebolt. After screwing in the eyebolt, I then CAed the block against the BT-80 tube just forward of the aft end of the BT-80 tube by ,250", the thickness of at CR and a .125 ply reinforcing ring. You might note in the 3rd pic the Eagle Claw double latched hook. I also applied CA to the eyebolt block in general for strength. Note the pic of the eyebolt block with the CR is to show the fit, it was NOT affixed in that pic. I crafted a couple more smaller blocks of basswood to act, along with the eyebolt block as gussets between the BT-80 and the bottom CR, installing them in the same relative vertical position on the BT-80 tube. I then applied a fillet of epoxy along the top and sides of the blocks adjacent to the BT-80 for additional strength. Later in the build, I will epoxy the bottom of the blocks to the aft CR.

As the bottom CR also has to provide a means to retain the removable engine core, I modified a couple of 10-24 pronged T-nuts by grinding them down slightly to fit the available space. I then epoxied them over the 3/16" holes that I had drilled thru the aft CR. Once this CR is epoxied to the BT-101 wall with fillets on both sides as well as being epoxied to the basswood blocks on the BT-80 tube and to the BT-80 tube itself, there is WAY more than adequate structural integrity for the engine core retainer as well as the shock line.

Before I epoxied the aft-most CR, I dry fitted a short length of BT-101 coupler to function as a reinforcing ring at the 3 1/2" mark (i.e. 3 3/8 + .125" CR) and marked the location in pencil. I then used CA to secure the reinforcing ring as well as painting it for strength. The ring is a bit of belt and suspenders, but with a significant portions of the lift off thrust transferring thru this bottom CR I wanted to make sure that it was supported.

Then I dry fitted 4 CRs, using the 5/16" aluminum launch tube for alignment, at approximately 6" intervals along the BT-80 tube. I epoxied the two center most CRs with fillets on both sides (no pics, pretty standard stuff). The BT-80 tube is actually two segments with the lower segment being 18" and the upper segment being shorter. I did CA a BT-80 coupler to the aft end of the upper segment but did NOT attach it permanently to the lower tube (explanation to follow later).

Once the center CR epoxy cured, I threaded the fishing leader lines thru the holes and hooked them to the eyebolt at the aft end of the BT-80 tube.

At this point, I switched away from the lower section for the time being

david

moving upstage
 

Before I could really go any forward with the lower section build I needed to have alignment with the upper section so that I could orient the internal launch tube to exit in the solid black section of the 2nd to 3rd interstage, so this is where the build picks up.

Going into the 3rd stage/SLA/SM build I wanted to enhance the structural integrity to better withstand the rigors of recovery (ejection blast, landing).

For starters, I elected well before commencing the build that I would use the Moldin' Oldies resin cast Apollo/LEM & shirt/fins to eliminate those damage prone elements of the original Estes design. After locating a wonderfully detailed 3D printed version of the Apollo/LES, I have elected to use that for display and not bother with the Estes versions

Back to the build.
Continuing with .125 thin ply CRs. I built the 2nd to 3rd stage transition. I needed the thin ply to support the section of launch tube that will reside in that section. To close the aft end, I epoxied a BT-101, .125" thin ply bulkhead (note the bulkhead was designed to fit inside a coupler). Yes, I know, more weight, but this is forward of the CG. In my build process, I inadvertently grabbed a couple of my BT-101 to BT-80 CR lacking the launch tube hole, an oversight that did not hit me until after the fact. Not a big oversight and one I could easily correct later.

Rather then using the Estes string design for the aft chute harness attachment point, I took a heavy paper clip, formed a "U" and epoxied it into place (i.e. similar to the Estes upper attachment design).

I CA reinforced the BT-101 coupler used in the transition. I then epoxied the bulkhead/CR and the forward centering ring to the BT-101 coupler using interior fillets. This made a very robust piston against the ejection gases with virtually no potential for damage. Once the epoxy cured, I then applied a fillet to the CR ID of the bulkhead/CR and inserted the 3rd stage BT-80 tube. Once that epoxy cured, I applied a fillet of epoxy at the top BT-80 CR.

I pretty much made the BT-80 to BT-58 transition per Estes instructions other than using epoxy. I did make a slight mistake in the construction by extending the BT-58 tube just slightly past the aft end of the transition so that I could get a good epoxy fillet. Of course that came back to haunt me a bit later, but as you will read, I turned that lemon into some lemonade.

With the upper section cores made, I turned my attention to the foundation wraps. I did the roll/glue tab/hold/smooth process. The glue joint turned out about a good as you can get and easily made perfect later.

The inherent weakness of the paper foundation wraps concerned me. I had read on an Apogee SV build about using paper-thin carbon fiber to reinforced the interior of the wraps. A bit of research led me to Sollier Composites and an 8g/sq meter carbon fiber product they call carbon veil. The stuff is WAY thinning than typical paper and incredibly strong even before application. Using copies of the foundation wraps as templates, I cut the carbon fiber. Starting with the SLA wrap, I trimming the carbon fiber until I had a perfect interior fit. Then I started to attach from the top with CA, only to discover that as the CA cured, the carbon fiber ever so slightly shrank. I cut a few relief lines to relax the carbon fiber layer and continued with the CA. To ensure that the SLA foundation wrap cured in a perfect circle without risking it sticking to the BT-58 core, I used an extra paper BT-80 to BT-58 CR at the bottom temporarily.

I did the lower wrap similarly, but initially only spot CAed it into place. As I did the spot attachment, I gently pushed the carbon fiber against the previous spot welds to build in a tiny bit of scrunch for the shrinkage once I fully CAed the carbon fiber against the paper. This worked MUCH better, no shrinkage issue when I followed up with a solid painting of CA.

After allowing the foundation wraps to cure overnight, I applied a couple of layers of CA over the outside to allow me to get a glass like exterior as well as sanding the seam line until it was totally smooth. With the carbon fiber backing the wraps and the CA exterior paint coats, I was able to sand the seams more than I would have been comfortable doing otherwise. With the wraps finished, I used them to establish a reference line on the upper section relative to the lower chute harness attachment point.

I am VERY pleased wth the carbon fiber reinforcement modification.