A Tripoli Technical Advisory Panel Document
By Alan D. Davis TRA L3 #5935
In an effort to get this page to load fast I will be limiting any thumbnail images and provide a more detailed list of images for each phase of construction. Most all the rocket components arrvied from GiantLeap last week. After a quick inventory all was layed out for some photo op's prior to construction. Still waiting on the ScotGlas nosecone.
The main design for the fin can / motor mount was to construct the unit as a whole and then install the fin can into the booster section. This technique has been used on 2 previous rockets (Tethy's and original Phasar) with excellent results. However several construction obstacles where encountered during those previous attempts that were rectified in this project. The 1st was the ability to adhere the centering rings level on the motor mount. Usually centerings rings have some slight play which can easily cause the rings to become slightly cocked while the epoxy sets up. After some research on some other websites I found no acceptable techniques. A discussion with my fellow rocketeer, Mike (HugieBear) Hudgeons revealed the ultimate solution. Mike suggested a cut a 2-3 inch section of the top of the motor mount and slot the entire unit to slide over the existing motor mount tube and use as a support for the centering ring. Dude, he hit the jackpot for that solution. I cut a small section off the existing tube and slotted it on the trusty DeWalt chop saw. A note about chop saw's, I purchased a 10" DeWalt chop saw from Home Depot for the purpose of cutting body tubes, the only modification I've done is replace the existing blade with a metal cutoff blade, man you talk about some clean tube cutting! Anyway the problem was solved. The 6 centering rings where then tacked into place with some quick set epoxy. Once the fin can is installed into the booster tube then small holes will be drilled in between each centering ring and West Systems Epoxy will be injected with syringes to complete the centering ring fillets. Once the fillets have set-up then the booster will be inverted to inject the other side of the rings.
The next construction problem was the acurate alignment/installation of the 3 fins. The small problem was actually 3 individual problems, 1st anchoring the motor mount tube securely, 2nd establish a top dead center point and 3rd enusring the fins are perfectly vertical. The 1st problem was rectified by drilling 4 holes into my work desk area and having the ability to use bungee cords to secure the tube to the work surface. The 2nd problem was to find TDC (top dead center) affordably. Again a quick trip to the Home Depot to purchase 1 8oz plumb bob, what better way to find TDC than gravity. Again the plumb bob was attached directly overhead and centered on the aft centering ring. The 3rd problem was resolved by tacking the fins to the motor mount with quick set epoxy and using dual levels to insure the fins where plumb. After the fins where installed a measurement was made between the 3 fin tips and only a difference of 1/32" was discoverd between 2 of the fins. I am sure this is more than adequate for stable flight.
Once the fins where installed 1" Kevlar reinforcement tape was layed in the valleys between the fins and tube with an 8oz layer of fiberglass and Kevlar layered over the tube between the fins. As with the centering rings small holes will be drilled in the booster tube between the fins and injected with West Systems epoxy for the final fillets.
After all the reinforcements were installed the 75mm Aeropack was mounted to the aft centering ring with stainless steel screws and nuts.
Well now was the time to venture into my 1st attempt with working with Kevlar. I heard all the somewhat horror stories and unfortunately Ed from Giant Leap just introduced his Kevlar "socks" about 2 weeks after I placed my order with FibreGlast. Oh Well! So I will try to pass on any valuable information I gained during this foray. The primary thing I quickly learned with Kevlar is, this stuff is TOUGH to cut. Special shears are a MUST! After discovering this after my Kevlar arrived sent me on a journey to the local fabric store in hopes of finding the recommended pair which is the Ginger #8-NS-2. Well the fabric stored carried the Gingher brand of shears only by custom order. Since I was smart enough to actually bring my Kevlar into the store to "test" some shears a salesperson was quickly summoned for assistance. This was when I discovered there are not a lot of men in a fabric store with a bundle of Kevlar under their arm. Anyway the salesperson was really interested in the Kevlar and responded with the phrase: "isn't that what they make bullet proof vests from?" now we are having fun. She steered me to another brand of shears called Fiskars and we tried several different models with little success then we tried the "RAZOREDGED" model and we where off to the races! Great shears and only about $18.00.
Luckily my TAP member Derek Deville had worked with Kevlar before and gave me some great advice about working with it. The basic plan was to use 2 layers of the 5oz 17x17 5HS Kevlar followed by a finish wrap of 2oz fiberglass for finishing purposes. Derek had recommended using the preferred method allowing the layers to setup until tacky before applying the next layer as opposed to letting the layers completely cure. So I set aside the whole day for using this method which actually creates a chemical bond between the layers as opposed to a mechanical bond by having layers applied after they have cured. One good thing about these Texas summers is epoxy cures real fast in a 100 degree garage. Prior to applying the Kevlar the booster tube was prepped using 80 grit sandpaper and thoroughly cleaned. I mixed up some generous portions of the West System and started applying a layer directly to the tube. Once a tack coat was applied I started layering on the Kevlar being carefull not to stretch the fibers and to work the epoxy into the Kevlar. After the Kevlar was completely wrapped I went over the entire tube using a plastic squeegie and removed any excess resin. The Kevlar applied very nicely much like a heavier fibreglass, I had almost no buckling at all and actually enjoyed working with it. After this 1st layer was applied I set back and waited for the resin to start curing in preperation for the 2nd layer. Continued checking the "tackiness" until about 2 hours had passed and determined the tube was ready for lasyer 2. The next layer was applied in the exact same manor as layer 1 with the same great results. In conclusion I have to say many of the stories I heard about using Kevlar were a little exagerated. Yes it does take a little extra work and some special shears but I really loved the way it wet-up and applied.
Once the 2nd layer of Kevlar started setting-up the finish coat of 5oz fiberglass was applied. Again no surprises here it applied perfectly to the existing Kevlar with excellent results when completely cured. This tube feels indestructible!
On July 9 after the McGregor launch I prepped the upper airframe and booster extension section (12" since I can not fit all the required recovery in a standard 4' booster section) for the Kevlar laminates. This will give the booster section an overall length of 60". The upper airframe section is 36". Basically no suprises here during the Kevlar and fiberglass lay-ups with the same great results as the booster section.
Prior to installing the fin can the booster section had to reslotted due to the reinforcements. I was a little concerned about not being able to see the existing slots after applying the Kevlar but realized they showed up fairly well through the multiple layers of Kevlar. The slots were recreated using the trusty table saw and this time they were slotted all the way to the back of the tube to allow for installing the fin can.
Now it was time install the fin can and start injecting West Systems to create the reinforcing fillets for all the centering rings and fin joints. Prior to installing the fin can carefull measurements where done to show where each of the centering rings would be in the booster section. This would facilitate where to drill the holes to inject the West Systems. Marks where made on the outside and drilled with a 1/4" hole. These holes will later be filled in with a small piece of Kevlar. Next step was to create a very smooth fit for the fin can into the booster section. Some quick sanding was required to achieve that perfect slide into the booster.
I usually construct my recovery attachment modules as seperate components then epoxy the units in place in the body tubes and with this project the procedure would basically be the same.
The materials used to construct the booster section and forward airframe attachment modules are:
Building these components as unit then installing into the airframe is much easier than installing each component into the airframe.
After the bulkhead units were installed into the couplers small holes were drilled in the center of the couplers to allow for injecting the West Systems epoxy and creating the bulkhead fillets on both sides. The units are extremely strong and allow for a large area of distributing the shock load during deployment. One special note is the use of the regular eyebolts as opposed to either forged or welded. While these definitely offer some added margin of error it would still take over 400lbs. to even begin to straighten out the eyes. I believe if my deployment induces that much force to fail my eyebolts then the are some other serious problems going on that no eyebolt will solve. The extra section of coupler will be epoxied in place on top of the exposed bulkhead plates. A sufficient amount of West Systems will be poured on top of the exposed bulkhead while it is in the airframe and then the coupler section will be fitted into place to allow for extra reinforment not only to the attachment module but to the airframe tubing as well.
Section 7: Nosecone My goal here was mostly add some weight to the front of the PHASAR and add an attachment point of some kind just in case I use it on another future project. This was pretty straight forward for me, since the nosecone is a ScotGlas all I had to do was mix some West System up, pour into the nosecone and let cure. I estimate I added approximately 10oz. using this process. Next was to firm up the shoulder with some 1/2" Birch bulkhead plates and add an eyebolt in case I ever need to attach a recovery system to it. Again the design was just like the components in the recovery attachment modules with a 3/8" x 5" eyebolt running through both bulkheads which were spaced about 2" apart. Next all I had to do was sand the unit some to fit the slightly irregular shape on the inside of the shoulder and position inside the nosecone shoulder for epoxying. Also for improved fillets on the bulkheads I drilled 2 small holes between the plates for easy injection of West Systems and some really beefy fillets. After all was said and done I measured the distance from the nosecone rear bulkhead to the shoulder rest point and transferred this measurement to the forward airframe section of the PHASAR. I then drilled 3 3/16" holes through the airframe into the 1/2" bulkhead plates. Then I used 3 of the same inserts used by the BlackSky Aluminum Rail Guide buttons and attached the nosecone with 8/32 stainless steel machine screws.
Section 8: Coupler Reinforcement Since I was using standard phenolic couples I wanted to reinforce the inside area to withstand any zippering effect during deployment. I researched this area of reinformcent from several other individual websites and the best idea came from the Gate's Brother Website illustrating lining the inside of the coupler with Kevlar then Carbon Fiber while inflating a balloon inside the couple to expand the materials and compress the West Systems epoxy and cloth. The 1st layer was the Kevlar followed by a finish layer of 5.7oz carbon. This method produced a glass smooth interior lining plus added extreme strength to prevent a shock cord from zippering during deployment.
Construction
Section 1: Scenes from the Crime
Office: This is where the PHASAR 1st took shape.
RocketRoom: This is where the PHASAR indoor construction will take place.
Garage: This is where most of the PHASAR construction will take place.
Section 2: Da' Parts
Section 3: Fin Can / Motor Mount
Section 4: Airframe Reinforcement
