The main idea for this rocket is to keep it simple, straight-forward and strong. The only departure from this plan is the dual-deploy. This is a trade-off on risk verses walk. I'm tempted to install a GPSFlight unit and then run just a single-deploy of a main at apogee. This would probably result in 3-5 miles down-range landing. This would be OK by the rules and not an issue with the GPS tracking.....just low "style" points.
The rocket is your basic three-fin, conical nose cone, with standard dual deploy recovery. It has a 75mm motor mount inside it's 3.9" body. Fincan construction will be "through-the-wall" with generous fiber-filled-epoxy fillets and 2-part foam filling between the centering rings. All exterior parts parts are fiberglass while bulkheads and centering rings are birch ply and the motor mount is phenolic. Flight avionics duty is handled by a single FC-877 recording altimeter. This unit is mach-immune and very flexible. It's four pyro outputs provide for a primary and backup charge for both parachutes. Recovery depends on Rocketman chutes and custom harnesses.
I purchased most all of the fiberglass parts from Curtis @ Performance Rocketry The man does very nice work - highly recommended. Below is a picture of the main raw parts. I didn't include everything, just the basics. Also pictured is a true bundle of joy....we did a group purchase of FC-877 altimeters. Here is a photo of the case of six!
In order to get something going, I decided to start the electronics bay (EBay). Since this is a common component in all my rockets and I build them all the same (for the most part). This one is slightly different in that I'm attempting to use a single all-thread instead of the usual two.
Below are a few shots of the EBay under construction:
The
first photo on the left shows how I've squeezed the central all-thread and it's
wing-nut into the center of the U-Bolt. This leaves more room on the end surfaces
for the terminal block and ejection-charge holders. I like the single thread
design, but I worry about it unscrewing due to any rotation during recovery.
I added the giant (1500# rating) swivels to avoid this and also added some features
to the aluminum avionics tray that will lock the two ends together.
The white section in the photos below is a custom tray to hold the avionics and the pyro battery. I make a template using Visio, print it out and spray-mount it to a sheet of 0.04" aluminum. Then I use a Rotex punch, a mill and bending brake to form all the details. The result is a nice tray that firmly holds the FC-877 and the extra battery. The big holes that are visible along the sides are used for wire-ties to strap in the batteries. I make these trays for all my EBays and they work very well. Once I have the Visio template, it takes me only about an hour to make a tray.
In the photo to the left, you can see the double-wall section of the Ebay. I build my EBays so that they have a small portion that is part of the external body. This allows a clean way to expose controls to the outside as well as the vent holes. It also provides double-wall construction in the area where I need to cut holes...so that the necessary holes don't compromise the structural strength of the unit. The only down-side that I see to this type of construction is that the Ebay becomes part of the rocket's paint scheme...makes moving complete EBays weird. Also, some people also don't like that you end up with two seams on the rocket which will generate a bit more drag. The machined rectangles are where the switches are going to be mounted. I don't mess with mounting hardware, I just glue them in. You need to be careful not to get glue in the switch - I've glued a few in the process of perfecting my technique. You can see all three vent holes, including the one on the back side by looking through the switch opening.
This is a photo of the backside of the Ebay tray. Notice that the single all-thread location makes for a secure battery for the FC-877. It blocks in the main battery very well, but I'll still put a wire-tie around it for flights. The pyro battery is shown in position but without wire-ties to secure it. It is tucked into a holder bent into the tray so that it is firmly secured by metal on four sides, with wire ties finishing the job
.
Shown
here is a close up of the Ebay switches. These are 4PDT switches made by Switchcraft.
I bought a bag of these at surplus for 25 cents each. They have worked reliably
in all my rockets. I wire all four Pyro charges to one switch and use the second
switch to control battery power.
The pyro switch is wired so that main and delay charges are staggered across the contacts. The switch either connects each pyro to the FC-877 or disconnects and shorts the EMatch. I wire ALL pyro connections as full two-wire circuits. There is no attempt to save on wiring by [abusing] the common circuit ground. Fully wiring all circuits removes any notion of polarity and the assumption that all avionics, now and in the future, will have a common ground for one leg of the pyro outputs. This eliminates all the polarity sensitive wiring except where the pyro-battery connects to the FC-877. All other circuits are polarity agnostic for safety reasons....less to worry about. Color coded (stranded and double-tinned) ribbon wire is used throughout so that signals can be easily traced from the FC-877, through the switches and out to the terminal blocks. This way this is no confusion as to which set of terminal-block contacts connects to which pyro channel.
The power switch uses two sets of contact per battery. I use multiple or staggered contacts so that any momentary switch contact failures caused by vibration or G-loading, will probably not effect both set of contacts simultaneously.
The next step is to add a big glob of epoxy to insulate and strengthen the wiring and then glue the switches into place. The photo below on the right are all the parts that go into the EBay except missing are another 9V battery and a couple of nylon wire ties.
And here is the finished Ebay. You can see that everything on the bulkheads is bolted down and epoxied over. I used two different size PVC pipe caps for ejection charge holders so it would be obvious while loading which is for the main and for the larger backup charge. All that remains to do is glue up the holes where wires exit the top and bottom bulkheads. Then install the batteries with wire-ties and run a pyro test. Then it is ready to program and fly - after painting of course. The whole unit, with both batteries, weighs in at 1,092 grams.
Below are two photos from the finished Ebay. The one photo shows the labels on the EBay switches. The second photo is showing the hair-pin I installed in the ends of the all-thread. I was still somewhat worried about parachute rotation unscrewing the single EBay all-thread, so I came upon this idea. This should withstand plenty of twisting force. A few people have asked about these terminal blocks getting shorted by the swivel or other metal parts. I avoid this by putting duct tape over the terminal block after it is wired....its a step in my checklist.
Next is to machine the fins. I've decided to use 0.20" thick FR-4 material as I want the extra strength for a certification flight. Normally I would use well-sealed aircraft-grade birch plywood, but this is about survival.
The construction will be through-the-wall, but with tight spacing's. I use fiberglass filled epoxy for the fillets both inside and out. The fins will be capture top and bottom by ply centering rings. The narrow space between the centering rings where the fins mount will be filled with two-part expanding foam. The fin root tabs are drilled so that when I foam the fin can they help cross-link the fins in place. I used a milling machine to put the airfoil surface on the trailing edge.
Then I used the mill to cut the fin slots and drill the holes for the rail buttons. No "Gambler effect" here!
Here is a few shots of a dry fit of the motor section and a picture of the third fin being glued in place:
Below is a picture of all the parts (except the recovery) before starting to glue the motor section. Weights for all these parts were taken and will be plugged back into Rocsim. That's my Kosdon 75/6000 motor at the top of the picture. The motor section is sized to take a 41"long "N" motor.
Check out the teaser photos that Dave Proffitt sent me of in-progress glimpse of the painted nosecone. And this is not even the finished coats so the gloss will be higher! The man knows how to lay down paint! I can't wait to see the whole thing!
Below is a picture Dave took when I went to pick up the rocket. It was shot about 9:20PM, so the lighting is pretty bad. I will shoot more when the sun comes out - wanted to get this posted now!
The sun was only out for a short time today, but I manage to grab a few quick shots. Looks even better in the sunlight!
Here is an export from Rocsim 6:
Here is a copy of the TRA data capture form:
Here is a copy of Wiring Diagram
Here is a copy of the Check List
Here is a copy of the Parts List
The flight was made at Brothers, Oregon on June 26th, 2004.
Flight Data was right on the money -
My latest rocsim predicted: 14705 ft; Max V=1246ft/s;
15.8G; 29.28s to apogee
Flight results showed: 14460 ft. Max V= 1249ft/s; 14.1G; 31.24s to apogee
The rocket was recovered in perfect condition.
Here is a picture of me with the rocket on the pad.
