Scratch Diablo Original Design / Scratch Built
Scratch - Diablo {Scratch}
Contributed by Aris Simsarian
| Construction Rating: | starstarstarstarstar |
| Flight Rating: | starstarstar_borderstar_borderstar_border |
| Overall Rating: | starstarstarstar_borderstar_border |
| Published: | 2012-01-25 |
| Manufacturer: | Scratch |
Brief
The scratch build is a 4-inch diameter rocket. The nose cone is provided by What's Up Hobbies and is fiberglass. The body tubes I purchased through Giant Leap Rocketry.
Originally, I planned to purchase a 48" long Dyna-Wind body tube cut into two sections, where one was 26" long and the other was 22". However, due to what they had available, the order was changed to two 36" long tubes, one cut 28" long and the other cut to 22" long.
The fins were custom designed by me by use of Rocksim 9 and were cut out of .188" thick fiberglass by Public Missiles. Each of the three fins cost $28.67. The rest of the components were purchased from Giant Leap Rocketry, including the three centering rings, multiple bulkplates, and the motor mount tube.
My goal in building this rocket, was to incorporate an anti-zipper design by attaching the coupler assembly to the booster airframe portion.
Components
- 3-.188" thick G10 Fiberglass fins
- 1-28" long Dyna-wind body tube
- 1-22" long Dyna-wind body tube
- 1-8" long phenolic coupler
- 3-coupler sized bulkheads
- 3-Nose cone sized bulkheads
- 2-large U-Bolts
- 3-3.9" to 2.125" Centering Rings
- 1-54mm Aeropack motor retainer
- 1-36"MMT (cut to 24")
- 30 minute epoxy
- 15 minute epoxy
- 4oz fiberglass cloth
- Bondo- Fiberglass resing and hardner (from Home Depot)
- 4" wide by 22" long Nose cone (fiberglass and Hollow)
Construction
I ordered the fin slots to be the same width as the fins themselves. The fins obviously did not fit and therefore I had to widen them. By use of a dremel, I widened them carefully until they could slide in. Next I lined up the bulkheads in a vice and a clamp to drill holes in them for the antizipper design.
I drilled a 3/4" hole in the center of the three bulkheads and eight 1/4" ones around that. I had to use multiple 3/16" bulkheads because the holes drilled into the wood weakens them. The thickness increase provides structural strength. I attached one of my dad's wide u-bolts that is slightly smaller in diameter than the bulkhead itself. This is to spread the load over the entire bulkhead. As said on the Vastaas rocketry page, if you use an eye-bolt, the center of the bulkhead could be ripped out if the deployment is too fast.
The antizipper design needs to be very strong because the point is to be able to deploy a 'chute high velocities. I epoxied the bulkhead assembly using a generous amount of 15-minute epoxy and was very careful that none of the epoxy went into the holes I had previously drilled. Also, I fiberglassed the inside of the already strong phenolic coupler for stiffness and strength.
The motor mount assembly contained three 3/16" centering rings, and one 36" long 54mm MMT. The booster section of the rocket is 28" long, but the coupler protruding from it adds another 4 inches and therefore is 32" in length. I wanted the MMT to be on the long side so the gases from the motor ejection when I use that will have less space to pressurize. To do that I cut the MMT to 24" long, leaving only a 4" by 8" area within the coupler assembly to be filled with gasses. The rocket will have the space to accomodate a 54/852 motor up to a Cesaroni 54mm L.
I glued two centering rings as one at the forward end about 2" from the tip of the MMT and the other one just in front of the end of the TTW fin tabs to add support to them. For added strength I fiberglassed the exterior of the MMT on the portion not coming in contact with the TTW fin tabs. I left the rear centering ring un-glued, but drilled two small holes in each side of it. This way, when I glue the fins in, I can pull off the centering ring and add internal fillets.
I glued the couple in using 30-minute epoxy due to it being the highest strength in shop-grade epoxy.
The fins were the widest I could purchase through the custom ordering process at Public Missiles. I used 15-minute epoxy to tack them down onto the MMT. I wiped clean any areas on the body tube where the epoxy was using a wet paper towel. I paid close attention to the fins for the 15 minutes and used my eyes to do the adjusting for the majority of the time. However I did utilize a right-edge to be more exact. I let each fin dry for about two hours before I rotated the airframe to place the next one.
I used 30-minute epoxy to create the external fillets. I mixed about 7/8 of an ounce of epoxy in one of the cheap little mixing cups you can get at Smart & Final. Then I used a syringe to suck out the right amount of epoxy for each fillet. I did only two at a time to prevent sagging. To evenly spread the epoxy, I rotated the airframe up and down and side to side. This is described in more detail in the article from info-central which I employed on my rocket.
Even though I left the aft centering ring off to do internal fillets, I called an expert telling him that my goal was to eventually launch an Aerotech K-1050W and a Cesaroni L-1030 R and he said that they were unnecessary. Instead I added epandable foam to the internal structure.
The nose cone is 24" long total but has 20" exposed. It is fiberglass and was purchased through What's up Hobbies. I needed to sand the seams on either side to ensure everything was smooth. The nose cone shoulder was an extremely tight fit with the Dyna-wind body tube so in order for the nose cone to actually fit in the rocket I had to peel a layer or phenolic off the inside of the body tube and sand the nose can down a lot. becuase of the anit-zipper design, The nose cone does not come off during flight and therefore does not need to slide on and off easily. It is actually preferable if it is a tight fit becuase the rocket will separate at the coupler.
The aft centering ring I glued on last but after I painted because I only had one day of sun to paint for a week. After epoxying the aft CR on the MMT, I used JB-Weld to secure an aeropack retainer for the motor.
Using a door stop, I drew a straight line to line up my conformal rail buttons I purchased from Giant Leap Rocketry.
The anti-zipper design I used is directly from these links:
Finishing
The Dyna-wind tubing I purchased had a very insignificant seam where the fiberglass was wrapped. However, there were many bumps along the seam that I needed to sand off. Afer sanding the bumps, I used elmer's wood filler a little at a time and kneaded the filler in wet hands. This way I could shape it to hide any imperfections and to make the fillets look flawless. The wood filler came in handy filling any little cracks. I used dark red primer in two coats for the enitre rocket. For the top coat, I used glossy black for the booster section and apple red for the nose cone and payload section. To cover the coupler on the booster from paint, I used an old 4inch coupler and cut it down the center. That way I could wrap it around the booster section's coupler and tape the gap along the center. I did 2 coats of paint for the rocket.
Flight
Its maiden flight was at ROCstock 2011 on November 12. I loaded up J800T-14 (blue thunder) motor and had it signed off by Wedge Oldham. I just turned 16 and therefore cannot achieve a level 2 certification. He has been signing all my flight cardsfor almost 2 years because the majority of the time I Launch J-L motors. I filled the pan with 3grams of BP and asked for a signature so that I could fly the motor. The launch even though windy, barely windcocked and sped through the clouds. We could hear the Ejection charge's pop even though there was no visual on it. The rocket separated in 3 parts instead of 2 however they were all connected. The Nose cone popped off even though that was not the plan. The rocket came down wwithout a parachute. Here is why; there was too much ejection charge (I did not do any ground testing and therefore I estimated and estimated poorly). Consequentially, the ejection charge instead of passing through the coupler bulkheads, blew out the sides of the coupler itself. Therefore little gas overpressurized the upper airframe and caused the chute to remain in the payload section. The nose cone was obviously not on tight enough and might have been knocked loose from a violent deployment. If there was a violent deployment though, I would not have been able to see it due to clouds. Even though the rocket was not under chute, the only damage it sustained was to the booster section. The coupler was obviously destroyed but also, the airframe cracked in two places perpendicular to the fin slots. The fins were ok and only one came off (after yanking it out). I will pull out the other two fins when I find time and rebuild the bottom section. Next flight will be with electronics which I have used before. The replacement costs for the booster section will be around 100$.
Also when looking at a slow-motion video from the ground of the launch, I noticed tat te rocket wobbled some and therefore did no go straight up. The fins I have concluded were to small (specifically the span) for a straight and stable flight. I have since Purchased new fins (pml C-03 fins .1875" thick). I will post a rebuild review for this rocket.
Recovery
Parachute did not come out so....it did not work correctly.
Summary
First scratch built and a learning experience for me.
Sponsored Ads
 |
 |