The Rocket Doc
Mad Rocket Dog
("Hesagooboy")
I've done a number of black powder clusters over the past two years.
Photo, Maurice "Moe" Bertrand
Eruption
But none have been perchlorate motors. Having certified Level 3, I felt it was time to plan one. I decided not to go small with prototypes. I wanted a rocket that was at least 7 inches in diameter and about 11 feet long. It would have a central 54mm surrounded by four 38mm motors. As my friend Dwain Desbien always says, "Go big or go home." Life is too short for little rockets. But there's always a place for them.
I want to first confirm in a test flight that a central 54mm small K (K660 CTI) by itself will get the rocket off the pad safely to at least 3500'. In a second flight, I would air start four 38mm motors one second after launch with the central 54mm K660. After that, I would have many motor options. I have to count on these motors all igniting. So, I'll be using Cesaroni only because I just can't count on Aerotechs to pressurize in a predictable way. The PerfectFlite minitimer3 should be perfect for the airstarts. The miniTimer3 comes with the G switch already on the board.
I like the hatch arrangement (Level 3). It allows for easy access to all of the electronics and no external switches. I'm using a Spherachute 168", 12.9" spill hole for 13.5 ft/sec descent for the main and a Rocketman 48" drogue at 46 ft/sec descent. Planning began in January and the build began on February 2, 2011.
January 2-15, 2011
Plans
RockSim Basic Design
Thrust curve with the planned motors
Thrust curve with the L1030RL alone
Main Parachute Calculation Drogue Parachute Calculation
3-D View
Plans
RockSim Basic Design
Thrust curve with the planned motors
Thrust curve with the L1030RL alone
Main Parachute Calculation Drogue Parachute Calculation
3-D View
I started with the standard scratch parts:
Sonotube 7.5" x 48" (Polyester, Epoxy Resin coated) without doubler tubes
3/8" aircraft birch ply for bulkheads and fins will be fiber-glassed
One 54mm and four 38mm motor Kraft phenolic motor tubes
February 2, 2011
The Sonotube's outer and inner skins are peels off. I have filled the spirals of the upper and lower airframes with Bondo, then sanding after drying overnight. The three motor mount centering rings are cut (Dremel Circle Cutter) and test fitted around the central 54mm motor tube.
February 18, 2011
Preparing the centering rings for the four 38mm motor tube cuts. I have cut the hatch from the aft end of the upper airframe. The right hand picture is of the bulkheads for the e-bay. There are sitting on the e-bay/coupler. That is slid into the aft end of the upper airframe. It creates the liner for the e-bay and a shelf for the hatch. It projects 8 inches from the aft upper airframe to create the coupler to the lower airframe. Here, I have saturated the coupler portion with ultra thin CA. This really helps to strengthen the whole coupler. It's easy to sand down to a perfect fit into the lower airframe.
Here's the airframe coupler test fitted into the upper airframe. I have to polyester/epoxy "sock" the upper airframe before I can make this permanent.
February 21-28, 2011
Nosecone
3D Plan
What I have done here is start with the nosecone coupler. Below is the doubled coupler and one of Moe Bertrand's old cone built with a technique originally developed by Bob Henninger. That cone is foam with a central cardboard tube to center the foam rings and to stabilize them after epoxying. Note the plugged plastic funnel in the cone. I made a cone tip by pouring epoxy into it. When it hardens, I remove the tip and sand it to fit the contour of the cone. A 5/16" hole is drilled into the tip and a 5/16" all thread is epoxied into it. The tip with thread will later be epoxied to the ring on the top of the cone. Later, the all thread will run the length of the cone and coupler.
I then sand the cone tip for a clean fit:
The removable aft bulkplate (not epoxied!) is fitted flush to the coupler with a hole drilled for the 5/16" all threat. It sits on a recessed epoxied centering ring that will hold a length of ~54mm mailing tube that will eventually contain lead ballast as needed for proper balance. You can see that the removable aft bulkplate becomes the cap for the ballast compartment. Holes are drilled symmetrically through the aft bulkplate and centering ring. Screws to blind nuts will hold the plate in place. (This, of course, has to be done now before the forward ring is epoxied into the coupler.) The forward part of the coupler is prepared the same way. Only the forward centering ring is epoxied flush to the edge of the coupler (below). Not shown is the bulkplate that is epoxied to this ring. The diameter of that plate (with a centered 5/16" hole) is just sufficient to provide a lip so that the cone can sit on the upper airframe.
After epoxied is applied between the foam rings on Moe's cone, the base of the cone is epoxied to the forward bulkplate. With the cone set up, the all thread that runs from the nose tip through the aft bulkplate is tightened gently with a washer and eye nut. The tightened thread acts as an internal clamp to hold everything tight and lined up until cured. After a night of curing, you end up with cone and coupler below perfectly fitted into the upper airframe.
Later, the cone is coated with Elmer's Wood Filler and sanded smooth. A Giant Leap 5" polyester sock is pulled over the cone and soaked in West Systems epoxy resin.
February 24 and 28, 2011
Motor Mount
3D Plan
I went ahead and cut four 38mm symmetrical holes in each of the centering rings. The basic fit is below right, That middle centering ring will later be equidistant from the end rings.
March 4
Airframe epoxy resin
Here I have stretched the Giant Leap large diameter polyester sock over the upper frame and saturated it with West Systems 105/206 resin. The rotisserie is running during this process. The thickness of resin is pretty even but the time it's cured. However, you have to trim the sock from the hatch area with an industrial blade just when the resin starts to harden but not when it's cured.
Once the upper airframe resin has cured, the airframe coupler is finally epoxied in. I have already fitted the hatch and identified the screw locations. There are blind nuts behind all the screws. I then cut out the shelf for the attach and temporarily screw the hatch on. The forward edge of the coupler will become the shelf for the removable forward e-bay bulkhead. The aft e-bay bulkhead is permanently epoxied into the aft end of the coupler recessed several inches.
March 13-15, 2011
Fin slots and aft e-bay bulkhead
Just because I wanted to now, I cut four 3/8". Later the slots will be extended all the way through so that the entire motor mount can be slid into the airframe.
But below and right, I epoxied the aft e-bay bulkhead into the airframe coupler after adding black powder holders and terminal strips. The holders are made of 1.5" PVC end caps. These are screwed into blind nuts so that I can replace them should I ever need to. The caps are filled with enough epoxy to cover the screws. The terminal strip on the right is for the primary and secondary igniter wires. The strip on the left is for the igniter wiring to the air-started 38mm motors. I only really needed four terminals, two for each pair of wires to the igniters for opposite motors. But back up terminals are useful. You never know what else you might try to do in the future. Not shown is the identical treatment of the forward e-bay bulkhead. Notice that I cut a ring of doubler from the aft bulkhead to the airframe tip. It just helps to strengthen the edges for when they hit the ground under full chute. It's usually a slow hit, but I want little or damage. I'll epoxy this in later.
April 16-18, 2011
Lower airframe epoxy resin
When I first drew the sock over the lower airframe, it was so tight that the fin slots narrowed. This was correct by used a few more rotisserie rings spaced evenly under the slots. The polyester/resin treatment was good.
May 12-23, 2011
Motor Mount
I cut fins from the birch ply stock consistent with the RockSim plan. The were sanded to round on all the fin edges and smooth on the fin sides. What I decided to do was attach the fins to the 54mm motor tube right next to (touching) a 38mm tube. You can see below that the fin placement allows for the chute harness u-bolts, the 3/8" aluminum conduits for the air-start igniter wires and later the bulkhead mounted 1515 rail buttons. As I added each fin to a custom fit, I simply tacked them in place with extra thick CA. Any alignment error could be relatively easily fixed. Later, I'll apply a bead of slow cure (30 minute) hobby epoxy to all the internal contact points.
After a little more than 3 months, I just had to see what it might look like with just two fins. I have sanded the upper airframe resin and coated it with 3 layers of gray automotive filler/primer and sanding in between. You really have to do this for a good finish, because the sock texture is difficult to fill.The coat shown is the first white primer coat. When I sand, high and low points are easily seen (high points are gray). The nosecone has not been polyester/epoxy coated yet (polyester and West 106/205 epoxy resin). I put a layer of Bondo over the foam layers. It has been primed with automotive filler/primer. After the first round of sanding, low points are corrected with Elmer's Wood Filler until the cone is as symmetrical as possible. I'm not done with it yet. I'll have to go back later and correct some asymmetries with filler even after the sock. In the pictures below, I have extended two fin slots to the end of the lower airframe and tested the fit of the motor mount.
February 24, 2011
Motor Mount with four fins test fitted into the lower airframe.
It is a very good fit. Notice the forward points of the fins. The gaps will be filled with Squadron putty before fiber-glassing all the fins.
Confirming the motor mount fit before permanently installing. All of the internal contact points have already been filleted with 30 minute slow cure hobby epoxy. Here, I'm just confirming the tightness of the the airframe contact with the aft centering ring. This is a great fit, so just a load of rubber bands need to be used to hold it together after internal epoxying. Notice the extended slot cuts to accommodate the motor mount. I'll have to fill them later.
To epoxy the motor mount into the lower airframe, I used a mixture of West 105/206 and Sticky Stuff 1/8" chopped strand fiberglass. I poured a few ounces into each compartment as I pushed the mount in. This produces rock solid internal fillets. I also chose to do this because I could not use internal foam with this kind of mount. The level on the top of the can is to make sure the epoxy spreads evenly to create good fillets at the internal centering rings/airframe contact points.
Nosecone
May 28-June 2, 2011
Here's my follow up from May 5. I'm just trying to get the foam filled and more asymmetry corrected with wood filler patches. I'm using Elmer's because it's easy to sand. Here is the cone basically finished with it's automotive filler/primer and ready for the sock..
Forward and aft e-bay bulkhead preparation
Aft e-bay airframe doubler
May 28, 2011
I want to reinforce the part of the airframe at the aft e-bay because it is an area that will hit the ground. The hit is somewhat gentle because the fin can hits first under full chute. Still, I want this part of the frame doubled. I made a custom piece to fit. I use 30 minute slow cure hobby epoxy for the final fit.
Finished doubler below. The doubler seam is filled with hobby epoxy. I also treated the edges of the airframe with ultrathin CA. I finished the edges off by adding a ring of 5 minute hobby epoxy. This fills and gaps and hardens the edge for the landing. I'm getting the aft e-bay bulkhead ready for wiring. The red wires on the left are for the Primary and Secondary drogue igniters. The green/red and black/red are for the airstart motor igniters. The green/green and green/black are back-ups or for other uses in the future. The forward e-bay bulkhead is being prepared for wiring. Both terminal strips are wired though only one with its two igniter wires will be used for the main chute. The opposite strip is a back-up.
Drogue chute and air start igniters wires are in the left picture and main chute igniters are in the right.
Drogue and air start igniter wires screwed into the terminals and epoxy coated and on the right, the main chute igniter wires.
Sonotube 7.5" x 48" (Polyester, Epoxy Resin coated) without doubler tubes
3/8" aircraft birch ply for bulkheads and fins will be fiber-glassed
One 54mm and four 38mm motor Kraft phenolic motor tubes
February 2, 2011
The Sonotube's outer and inner skins are peels off. I have filled the spirals of the upper and lower airframes with Bondo, then sanding after drying overnight. The three motor mount centering rings are cut (Dremel Circle Cutter) and test fitted around the central 54mm motor tube.
February 18, 2011
Preparing the centering rings for the four 38mm motor tube cuts. I have cut the hatch from the aft end of the upper airframe. The right hand picture is of the bulkheads for the e-bay. There are sitting on the e-bay/coupler. That is slid into the aft end of the upper airframe. It creates the liner for the e-bay and a shelf for the hatch. It projects 8 inches from the aft upper airframe to create the coupler to the lower airframe. Here, I have saturated the coupler portion with ultra thin CA. This really helps to strengthen the whole coupler. It's easy to sand down to a perfect fit into the lower airframe.
Here's the airframe coupler test fitted into the upper airframe. I have to polyester/epoxy "sock" the upper airframe before I can make this permanent.
February 21-28, 2011
Nosecone
3D Plan
What I have done here is start with the nosecone coupler. Below is the doubled coupler and one of Moe Bertrand's old cone built with a technique originally developed by Bob Henninger. That cone is foam with a central cardboard tube to center the foam rings and to stabilize them after epoxying. Note the plugged plastic funnel in the cone. I made a cone tip by pouring epoxy into it. When it hardens, I remove the tip and sand it to fit the contour of the cone. A 5/16" hole is drilled into the tip and a 5/16" all thread is epoxied into it. The tip with thread will later be epoxied to the ring on the top of the cone. Later, the all thread will run the length of the cone and coupler.
I then sand the cone tip for a clean fit:
The removable aft bulkplate (not epoxied!) is fitted flush to the coupler with a hole drilled for the 5/16" all threat. It sits on a recessed epoxied centering ring that will hold a length of ~54mm mailing tube that will eventually contain lead ballast as needed for proper balance. You can see that the removable aft bulkplate becomes the cap for the ballast compartment. Holes are drilled symmetrically through the aft bulkplate and centering ring. Screws to blind nuts will hold the plate in place. (This, of course, has to be done now before the forward ring is epoxied into the coupler.) The forward part of the coupler is prepared the same way. Only the forward centering ring is epoxied flush to the edge of the coupler (below). Not shown is the bulkplate that is epoxied to this ring. The diameter of that plate (with a centered 5/16" hole) is just sufficient to provide a lip so that the cone can sit on the upper airframe.
After epoxied is applied between the foam rings on Moe's cone, the base of the cone is epoxied to the forward bulkplate. With the cone set up, the all thread that runs from the nose tip through the aft bulkplate is tightened gently with a washer and eye nut. The tightened thread acts as an internal clamp to hold everything tight and lined up until cured. After a night of curing, you end up with cone and coupler below perfectly fitted into the upper airframe.
Later, the cone is coated with Elmer's Wood Filler and sanded smooth. A Giant Leap 5" polyester sock is pulled over the cone and soaked in West Systems epoxy resin.
February 24 and 28, 2011
Motor Mount
3D Plan
I went ahead and cut four 38mm symmetrical holes in each of the centering rings. The basic fit is below right, That middle centering ring will later be equidistant from the end rings.
March 4
Airframe epoxy resin
Here I have stretched the Giant Leap large diameter polyester sock over the upper frame and saturated it with West Systems 105/206 resin. The rotisserie is running during this process. The thickness of resin is pretty even but the time it's cured. However, you have to trim the sock from the hatch area with an industrial blade just when the resin starts to harden but not when it's cured.
Once the upper airframe resin has cured, the airframe coupler is finally epoxied in. I have already fitted the hatch and identified the screw locations. There are blind nuts behind all the screws. I then cut out the shelf for the attach and temporarily screw the hatch on. The forward edge of the coupler will become the shelf for the removable forward e-bay bulkhead. The aft e-bay bulkhead is permanently epoxied into the aft end of the coupler recessed several inches.
March 13-15, 2011
Fin slots and aft e-bay bulkhead
Just because I wanted to now, I cut four 3/8". Later the slots will be extended all the way through so that the entire motor mount can be slid into the airframe.
But below and right, I epoxied the aft e-bay bulkhead into the airframe coupler after adding black powder holders and terminal strips. The holders are made of 1.5" PVC end caps. These are screwed into blind nuts so that I can replace them should I ever need to. The caps are filled with enough epoxy to cover the screws. The terminal strip on the right is for the primary and secondary igniter wires. The strip on the left is for the igniter wiring to the air-started 38mm motors. I only really needed four terminals, two for each pair of wires to the igniters for opposite motors. But back up terminals are useful. You never know what else you might try to do in the future. Not shown is the identical treatment of the forward e-bay bulkhead. Notice that I cut a ring of doubler from the aft bulkhead to the airframe tip. It just helps to strengthen the edges for when they hit the ground under full chute. It's usually a slow hit, but I want little or damage. I'll epoxy this in later.
April 16-18, 2011
Lower airframe epoxy resin
When I first drew the sock over the lower airframe, it was so tight that the fin slots narrowed. This was correct by used a few more rotisserie rings spaced evenly under the slots. The polyester/resin treatment was good.
May 12-23, 2011
Motor Mount
I cut fins from the birch ply stock consistent with the RockSim plan. The were sanded to round on all the fin edges and smooth on the fin sides. What I decided to do was attach the fins to the 54mm motor tube right next to (touching) a 38mm tube. You can see below that the fin placement allows for the chute harness u-bolts, the 3/8" aluminum conduits for the air-start igniter wires and later the bulkhead mounted 1515 rail buttons. As I added each fin to a custom fit, I simply tacked them in place with extra thick CA. Any alignment error could be relatively easily fixed. Later, I'll apply a bead of slow cure (30 minute) hobby epoxy to all the internal contact points.
After a little more than 3 months, I just had to see what it might look like with just two fins. I have sanded the upper airframe resin and coated it with 3 layers of gray automotive filler/primer and sanding in between. You really have to do this for a good finish, because the sock texture is difficult to fill.The coat shown is the first white primer coat. When I sand, high and low points are easily seen (high points are gray). The nosecone has not been polyester/epoxy coated yet (polyester and West 106/205 epoxy resin). I put a layer of Bondo over the foam layers. It has been primed with automotive filler/primer. After the first round of sanding, low points are corrected with Elmer's Wood Filler until the cone is as symmetrical as possible. I'm not done with it yet. I'll have to go back later and correct some asymmetries with filler even after the sock. In the pictures below, I have extended two fin slots to the end of the lower airframe and tested the fit of the motor mount.
February 24, 2011
Motor Mount with four fins test fitted into the lower airframe.
It is a very good fit. Notice the forward points of the fins. The gaps will be filled with Squadron putty before fiber-glassing all the fins.
Confirming the motor mount fit before permanently installing. All of the internal contact points have already been filleted with 30 minute slow cure hobby epoxy. Here, I'm just confirming the tightness of the the airframe contact with the aft centering ring. This is a great fit, so just a load of rubber bands need to be used to hold it together after internal epoxying. Notice the extended slot cuts to accommodate the motor mount. I'll have to fill them later.
To epoxy the motor mount into the lower airframe, I used a mixture of West 105/206 and Sticky Stuff 1/8" chopped strand fiberglass. I poured a few ounces into each compartment as I pushed the mount in. This produces rock solid internal fillets. I also chose to do this because I could not use internal foam with this kind of mount. The level on the top of the can is to make sure the epoxy spreads evenly to create good fillets at the internal centering rings/airframe contact points.
Nosecone
May 28-June 2, 2011
Here's my follow up from May 5. I'm just trying to get the foam filled and more asymmetry corrected with wood filler patches. I'm using Elmer's because it's easy to sand. Here is the cone basically finished with it's automotive filler/primer and ready for the sock..
Forward and aft e-bay bulkhead preparation
Aft e-bay airframe doubler
May 28, 2011
I want to reinforce the part of the airframe at the aft e-bay because it is an area that will hit the ground. The hit is somewhat gentle because the fin can hits first under full chute. Still, I want this part of the frame doubled. I made a custom piece to fit. I use 30 minute slow cure hobby epoxy for the final fit.
Finished doubler below. The doubler seam is filled with hobby epoxy. I also treated the edges of the airframe with ultrathin CA. I finished the edges off by adding a ring of 5 minute hobby epoxy. This fills and gaps and hardens the edge for the landing. I'm getting the aft e-bay bulkhead ready for wiring. The red wires on the left are for the Primary and Secondary drogue igniters. The green/red and black/red are for the airstart motor igniters. The green/green and green/black are back-ups or for other uses in the future. The forward e-bay bulkhead is being prepared for wiring. Both terminal strips are wired though only one with its two igniter wires will be used for the main chute. The opposite strip is a back-up.
Drogue chute and air start igniters wires are in the left picture and main chute igniters are in the right.
Drogue and air start igniter wires screwed into the terminals and epoxy coated and on the right, the main chute igniter wires.
Some Details
Setting up the BoosterVision video camera
June 20, 2011
Mounting the video camera to the upper airframe for the view over the hatch cover and what will be through the fins.
The view down the lug line of the upper airframe. I mounted the upper rail button (1515) through the e-bay. It's nearer to the expected launch CG there rather than the forward centering ring of the motor mount. Epoxy putty is inside. It's drilled and tapped for the button screw.
E-Bay Ports, Airframe Vents
June 21-22, 2011
All holes are treated with ultra-thin CA
Here's the equation provided by Missile Works for the RRC2-mini for volumes greater than 100 cubic inches. How about five ports in a ring around the bay excluding the hatch cover itself:
Bay Volume = radius X radius X length X 3.14
3.75 x .375 x 21 x 3.14= 927.28
Single Vent Diameter = 2 x SQRT ( volume/6397.71))
2 x SQRT (927.28/6397.71)= .761
Single Vent Area = ( Single Vent Diameter/2 ) X ( Single Vent Diameter/2 ) X 3.14
(.761/2) x (.761/2) x 3.14= .455
Multi Vent Diameter = 2 x SQRT ( ( Single Vent Area / # of holes ) / 3.14)
2 x SQRT (.455/5)/3.14= .34 inches
So, each of 5 vents is ~1/3". Below are airframe vent holes.
Filling in the Fin Slits
June 22-23, 2011
I used custom fitted airframe material to fit each of the fin slots. I filled with Squadron putty and sanded. I sprayed with automotive filler/primer and sanded again.
Motor Retention
I’m using LOC heavy duty z-clips for motor retention.
The photos show a 38mm with one clip and the central 54mm with two. You can’t tell from the pic angle, but the clip doesn’t obstruct the nozzle. I think this setup should hold them in. During ground testing I plug the motor tubes internally with rubber stoppers. Maybe I should leave them in (except the central 54mm as it runs the entire length of the tube plus some.) Wires for the motor igniters exit the aft centering ring through the aluminum conduits.
Fin fiber-glassing
June 24-26, 2011
I used Squadron putty for gaps at the forward ends of the fins and created small fillets along the length of each fin/airframe. That gives me a nice epoxy fillet that I just have to sand lightly later. The rail button is removed and the hole filled with Vaseline to protect the threads. Two fin saddles at a time are then fitted with 2 oz satin fiberglass and saturated with 105/206 West epoxy resin. Some would say that the 2 oz fiberglass is just too light for this application. But, the motor mount is internal strong with fiber-glassed reinforced fillets. The rocket is not expected to fly any faster than mach .6 so I don't expect flutter. The lower airframe is already polyester epoxy coated. I don't want to add even more weight to the can. So, this is for some additional external strengthening and great fillets. The overlap is cut with a utility blade when the fiberglass is curing but not too hard.
Fiberglass Fin Filleting
Here I've set up the fins for a 10mm wide fillet using Vern Knowle's technique. I've mixed a batch of West Systems 105/206 resin with 1/8' chopped strand fiberglass from Sticky Stuff in Glendale, AZ. (Two squirts of the West and two teaspoons of the fiberglass seems to work well.)
Here, I've completed all fillet sanding initially with a circular file, then 150 grit paper. Any irregularities were filled with Squadron putty filler again and sanded with 150 grit, then 220 grit paper. The last coating of automotive filler/primer was sprayed on. After final ground testing, I'll do the final sanding and preparation for paint.
The Nose Cone
June 22-23, 2011
Using the Giant Leap polyester sock, West Systems 106/205 epoxy resin. I use insulated 22 gauge wire to hold the sock tightly on the cone. It's easy to remove later. Note the nose tip. All that wrinkle has to be cut away after an overnight cure. The cuts have to filled with Bondo and carefully sanded to tip shape. By the way, that's the small sized sock.
Not too bad.
Cone automotive filler/primer and sanding.
June 25, 2011
This work is tedious. But the cone needs to be symmetrical. Ground testing usually gets me some scrapes and small dents. They can be repaired before final painting. I've always had this thing about tight seams (right). These are created by filling the seam with Squadron putty. While it's still wet, I run a #11 blade all around the interface. I pull the parts apart and let the putty cure.
Starting the Electronics Sled
June 22- July 9, 2011
This is pretty straight forward and similar to the setup for my L3 cert. The 1/8" birch ply is cut to 5" x 15". 3/8" pieces of birch are run along the outside length of the board. I run 15" of 5/16" copper tube at the inside junction of the board and birch length and epoxy it in with good fillets. The tubes allow for the use of the sled in a traditional "LOC style" e-bay with or without a central all thread. 3 1/2 " inches from each end is devoted to the battery boxes, then I position the components before fitting in. I'll allow some space for additional auxiliary rotary switches to accommodate things like GPS transmitters or whatever later. I have to space the components for easy reach through the hatch (about 4" x 8" of access).
Battery box for a pair of 9V batteries for the altimeters.
Then the board with everything but the electronics on the top side. Test fit in the hatch with battery boxes hidden making just the electronics visible and accessible.
Closeup. I can rotate the board to easily connect wiring to the terminal strip. But, I need a good way to hold the board in place for launch so that it doesn't rotate around the all thread (and maybe break some wires). Four screws through the airframe around the hatch to nearly touch the board above and below each battery box. It can't move.
Finished and tested:
So here is what the whole setup looks like. Complete.
PerfectFlite Timers (miniTimer 3G) and Ground Testing
June 28, 2011
Per their website, "This timer can be used for ignition of sustainer motors in multistage rockets and ignition of air-
I put together this quick and easy board to test the timers for airstarts. I screwed the leads of two homemade low amp igniters in parallel into the terminals (RocketFlite MagFire ematch). Each igniter has a resistance of 1.5-1.6 ohms. I set the timer for 2 seconds. With the rig hanging from the fishing string in the "on-the-pad" orientation (aft end down), I turned on the slide switch (on the left on the board). The beep tones confirmed my programming and continuity. Swinging the over my head ignited the two e-matches simultaneously. I tried it a coupler of times. I think I have confidence the my airstart ignitions should work.
Ground Testing
Calculating deployment charges
June 29, 2011
Since the nose cone's build is now complete except for final sanding and painting, it's the best time for ground testing the black powder charges that will separate the rocket components at apogee and for main deployment. If the nose cone or airframe is scraped up, when I'm satisfied with the testing, I can go on to final filling, priming again and painted. I use Verne Knowles method to calculate (estimate) charge size. Here is the concept directly from his website:
"The parachute deployment system on all high power rockets should be ground tested before the rocket is flown for the first time! This means estimating how much ejection charge is needed and then trying it out while the rocket is still safe and sound on the ground. This seems really obvious but I have seen many people skip this step and end up having serious damage done to their rocket when the recovery system failed. Of course I have also seen some folks use way too much black powder too! I guess those particular rockets were doomed to be blown apart anyway, be it on the ground or in the air!
I also feel that the ground test should be done with the rocket configured the same way as it will be for flight. I pack the parachute and recovery harness exactly the same as I would for launch. The amount of black powder can then be adjusted until the desired forcefulness of the separation is achieved. I tend to go for a "reasonably forceful ejection" but not so much that parts translate across the ground to the end of the recovery harness. I don't really have a good way to quantify it, but I would rather error on the side of slightly too strong rather than slightly too weak.
As a starting point for the ground test I use the chart below to estimate how many grams of black powder are likely to be needed. This is just an estimate! I'll get to the details later, but for now let me say this table assumes 15 psi for body tubes 5.38 inches or less in diameter. It assumes 350 pounds of separation force for body tubes larger than 5.38 inches. Remember this table is for generating an initial estimate. "Your mileage may vary." Many factors will influence the situation. Ground test it!
|
Body Tube Inside Diameter |
Estimated Ejection Charge Size |
| 1.53 inch | 0.5 grams per 36 inches of length |
| 2.15 inch | 1 gram per 36 inches of length |
| 2.56 inch | 1 gram per 25 inches of length |
| 3.00 inch | 1 gram per 18 inches of length |
| 3.90 inch | 1 gram per 11 inches of length |
| 5.38 inch | 1 gram per 6 inches of length |
| 6.00 inch | 1 gram per 6 inches of length |
| 7.51 inch | 1 gram per 6 inches of length |
From this table:
For my main compartment:
The 7.625' diameter and length of 24" = 4gms
For my drogue compartment
Diameter is 7.625, length is 14"
The 7.625 diameter and length of 14" = 2.33gms
Ground Testing
July 17, 2011
Because there are no motors in the rocket, I made plugs for the motor tubes. The are simply routed bisquits that fit tightly into the aft end of the tubes in the drogue compartment that are not permanent. So, when the the charge goes off in that compartment, you know that all the pressure is in the compartment and not flying out the tubes. The central bisquit is removed for launch because the central L1030 protrudes. The others will stay in place. In the future, some or all of them can be removed for motor charges to deploy a parachute for when this will become a booster for a two stage rocket.
For the central 54mm tubes. This one is a tight fit, so the eye bolt lets me pull it out easily
For the outboard 38mm tubes
Drogue separation
3.0gms Elephant Black Powder
Pretty pathetic. Try again next week with 4.0gms.
Main separation
4.0gms Elephant Black Powder
Perfect! I'll duplicate this next week.
Finishing the ground testing
July 23, 2011
4 gms of Elephant black powder for the main to duplicate last week's testing. I packed the chute too tightly, but this had the same force as last week. It pulled the rocket a foot or so. So I think this is fine for the launch.
4gms for the drogue compartment.
Test #1
Hmmmm.... better than last week.
Test #2, 4gms
This will work. 4gms for each compartment.
So, the planning began in January and the build and final ground testing was complete in 6 3/4 months. The date for launch is scheduled for August 13 at Rainbow Valley, AZ. The alternate date is September 10. It will take me another two weeks to paint.
Finishing
August 5-7
7 Months
Here’s my finished Mad Rocket Dog “Hesagooboy” ready to fly this Saturday August 13, 2011 at Rainbow Valley, AZ. The nose cone is one of Maurice "Moe" Bertrand's original foam test cones modified for this rocket. All electronics and ejection charges have been tested. The anti-zipper harnesses have a pool noodle wrapped in yellow duct tape, heat resistant foil duct tape and then regular flexible duct tape. The hatch pic shows a pretty custom fit. The screws are painted red to disappear. Only the four outer screws are visible in black. I discovered that on my L3 flight, the electronics sled rotated about 45 degrees around the central all thread. This time, with battery boxes at both ends of the sled, 2 inch screws hold the whole sled in place. The screws don’t go into the sled, they just wedge the b-boxes. The video cam is mounted. The view is right over the hatch and down the fins. I’ll have a lot to set up, so I’ll be out pretty early Saturday.
Drogue anti-zipper harness Main anti-zipper harness
Flight Performance
August 13, 2011
Rainbow Valley, AZ
All photos by Maurice "Moe" Bertrand
Flight Data:
Ignition and launch
All outboard motors ignited
Here is the booster for the Mad Rocket Dog "Whatagooboy" two-stage rocket due around February 2012
August 13, 2011
Rainbow Valley, AZ
All photos by Maurice "Moe" Bertrand
Flight Data:
Flight data:
Altimeter A
Actual Predicted
Altitude: 5440’ 5840’
Peak
velocity:
810ft/sec
691
ft/sec
Time
to apogee: 20secs
19.7 secs
Altimeter B
Altitude: 5427’
Peak velocity: 810ft/sec
Time to apogee: 20secs
Average altitude: 5434ft
Ignition and launch
All outboard motors ignited
Here is the booster for the Mad Rocket Dog "Whatagooboy" two-stage rocket due around February 2012
