Hyfly III

(My L3 bird)

Components

Basic design(PDF file)

Flight computer

Construction Details
Items with links are done.

1) Cutout fins
2) Foam fins
3) Cut out CR's and drill holes for kevlar reinforcement
4) Mark alignment line on CR's and MMT for later alignment of holes
5) Apply CF and light Glass to fins, vacuum bag
6) Within 10hours of bagging, glue fins and lower two CR's in place and glass across fins and MMT, Verify MMT will have room below the aft CR for the motor retainer
7) Install MMT extention and glass upper section of tube
8) Adjust second CR ID. Verify CR location on MMT
9) Install Kevlar supports in bottom CR and feed through third CR
10) Make rail guide mounts. Install rail guide mount in CR3
11) Fiberglass 3 x 30in BT sections
12) Cut fin slots in BT
13) Install BT to fin unit verify fillets on second CR
14) Install Tube coupler into fin can
15) Feed Kevlar through second CR and glue CR in place
16) Verify position of CR1 and glue in position in second section of BT
17) Install second section of BT
18) Secure the screw eyes on the kevlar and verify length
19) Add fin fillets and fill gap from aft fin slot
20) Install aft rail guide mount and fillet the aft CR
21) Install the motor retainer

22) Additional mods...

Cutout fins:

The fins were cut from 1/4in 9ply Birch Aircraft grade plywood.
I cut the outline of the fins with the scroll saw by drawing the pattern on the wood and cutting on the line.
The lightening holes were then traced on these fins and cutout.
I first tried clamping the 3 fins together and cutting the hole with my rotozip cutter. It worked really well for the first cutout but was really loud. Because if this I cut a starter hole for each of the remaining cutouts with the rotozip then used my scroll saw to cut out each fin. This worked fine and was not as loud, but did take me longer.

Fin with lightening holes

I used two part poly expanding foam made by Evercoat
I started by laying out a piece of wax paper down on my bench.
I layed the fins out side by side and screwed them down to the bench because they were a little warped.
This slight warping will be fine because when I vacuum bag them they will have a weight on them to hold them flat till the epoxy cures.

I mixed up the foam and poured it into the openings in the fins

Pouring foam

Foam poured

I then waited for it to expand and fill the holes

Foam expanding

Foam expanded

I then used a hotwire to trim the foam flush with the wood

You can't see the Nichrome wire in this picture but its there

Fins trimmed before removing from bench

This worked great, I then sanded them with paper mounted to a wooden block.

The bottom had some voids in it so I foamed the bottom side and trimmed and sanded it.

Complete foamed fin

I cut the CR's from 1/4in plywood. I cut the inside and outside holes using my router hole cutting jig. Then I drilled out the holes for the kevlar using a 1/4in forstner bit followed by a 3/4in forstner bit where needed.

I then marked the CR's and MMT. I put a single mark down the length of the MMT and marked a single mark on all CR's. I also marked the fin locations on the two lower CR's as can be seen in the pictures to help with fin installation.

Completed centering rings

Apply CF and light Glass to fins, vacuum bag

I cut the carbon fiber and fiberglass to size. I also cut out the release fabric and breather to the proper size.
I layed out a sheet of plastic with the breather and release on it.
I put the fiberglass down, mixed up some epoxy and squeegied it around.
Then I layed down the CF and squeegied some epoxy on it.
I positioned the fins on the CF

Fins positioned on the Carbon Fiber

I folded the second layer of CF on top of the fins.
Mixed up more epoxy and squeegied it into the CF.
Applied the final layer of glass and epoxy then put the release fabric, breather and a sheet of plastic.

Fins with release

Fins with breather

I put duct tape around the edge of the plastic to seal it up.
Hooked up the vacuum pump and pumped it out.

Fins Bagged

I then placed a board on top of the fins to ensure that they would be flat.

Fins with board to press flat

After about 9 hours I removed the board and shut off the vacuum pump.
I removed the plastic and pealed off the release.
The fins looked pretty good, but there were a few wrinkles in the glass.
A leak must have developed in the bag.
This is OK because the CF layed down flat and the glass was just for finishing.

I cut the fins apart using a band saw.

They turned out quite nice and very ridgid.

Glue fins and lower two CR's in place and glass across fins and MMT

After trimming the fins with the band saw I used the disk sander to smooth out the sides of the fins so they would glue well to the MMT.

I positioned CR3 and CR4 on the line I previously marked.
I positioned the fins and tacked them in place with CA.

Once I had tacked all 3 fins in place I cut out fiberglass so it would go 3 inch up each fin and across the MMT.

I positioned this glass and applied epoxy to it and squeegied out any extra epoxy.

I let this dry. This made a very strong fin can.

Install MMT extention and glass upper section of tube

I need to extend the MMT to accomidate the long hybrid motors.
I also want to seal off the MMT so I don't have to seal the bottom of the electronics bay.

I took a standard LOC 4in BT and cut it to 22.5in long.
I then wrapped a coupler with plastic wrap and used it to join the motor tube to the extention.
I put one layer of fiberglass over this to glue them together and reinforce the standard tubing.

Extention glassed in place

I also added a fillet to CR3.

Fillet on CR3

Once the epoxy cured I trimmed the excess glass from the end and removed the coupler.

Due to a change in the design I had to cut new CR's for the upper rings.

I cut two new rings and sized their ID to match the motor tube.

Install Kevlar supports in bottom CR and feed through third CR

I used forged eyebolts and stainless nuts for the aft CR attachement of the Kevlar support

Hardware for aft Kevlar attachment

I attached the kelvar to it by feeding it back into its own weave.

Eyebolts with Kevlar attached

I then bolted them in place and fed the Kevlar through the hole in CR3.

Aft Kevlar attachment

I then pinned the nuts to the eyebolt threads with a punch so the nut cant move. When I install the Slimline motor retainer I will also put some JB weld on the threads.

Punched eyebolt

I cut the extra threaded part of the eyebolts off.

Eyebolt cut

Make rail guide mounts. Install rail guide mount in CR3

I decided to use Oak for the rail guide mounts. This choice was easy because I had it on hand.

I took the Oak 1x2 and cut 3 1.5in long pieces since I will use 3 rail guides.

I drilled a hole through it to accept a tee nut.

I rounded off one side of each to match the curve of the inside of the BT.

Rail guide mount showing curve

I installed a tee nut using 1/4in long nails to hold it

Tee nut mounted

I filled the tee nut and hole with Vasaline to keep any epoxy out when the BT is installed. I then put wood glue on it to attach it to CR3.

Rail guide mount ready to be mounted

Then I screwed it down to CR3

Rail guide mount, mounted

I glassed the 3 body tube sections with 4oz S-glass I got from Mr. Fiberglass.

The first thing I had to do was rig up a new rotisserie since I mounted my last one in the top of my paint booth.

I used a piece of electrical conduit and drilled a hole for a pin that goes through the motor shaft. I then built a variable power supply so I could control the speed of rotation.
I still had the piece of 2x4 that I used previously so I clamped that to one bench and the motor side to the other bench.

The left and right side of the rotisserie setup

I mounted the tubes to the rotisserie by first wrapping a towel around the shaft and taping it down.
I then slid over some 7.5in 54mm centering rings. The towel gave it just enough give to be able to tilt the rings so the tube went on easier.

The first step in glassing a LOC tube is to peal the outer glassine coating off.

Pealing off glassine layer

With the glassine removed the tube is ready for epoxy

Glassine removed

I then put a line of epoxy along the top edge of the tube and layed one edge of the glass into this.
I then slowly rolled the tube to a dry spot, with the glass wrapping the tube as I turned it, and poured on more epoxy and  squeegied it around.

Once I had all the glass on I made one more revolution to make sure there were no dry spots or extra epoxy.

The extra cloth can be seen at the ends of the tubes

I waited till the next morning and trimmed the extra glass from the ends with an exacto knife. This was easy since it was not fully cured yet.

I also decided to glass the inside of the coupler that will house the electronics.
I used a baloon inside the coupler to get a nice smooth inside.

Glassing coupler

I use my table saw to cut fin slots. I had to make a box to accept 7.5in BT sections so I made that out of 1/2in plywood.
I then put masking tape on my rip fence and mark the ends of the cut on it.

Cutting fin slot on table saw(saw is not running in this picture)

First pass for the first slot

Sometimes I use my dado blade to cut the finslots to the correct size in one cut. I decided to just use the standard blade for these so it took two passes for each slot.
They came out fine.

Install BT to fin unit verify fillets on second CR

I test mounted the BT several times before actually mounting it. In doing this it sometimes will fray on the inside of the tube so I put CA around the edge and sanded it smooth.

 
BT end CA'd

I then did yet another test fit of the tube to the fincan

BT test fit

Once I was happy with the fit I epoxied it in place.

I did this by mixing up some West systems epoxy and adding some milled fiberglass.
I put this inside the airframe just below the top of the fin slots.
I slid the airframe down till it was several inches from the aft CR and added more epoxy to the inside of the airframe then slid it down all the way.

I put a clamp at the rear of the airframe to keep the 3 sections against the aft CR

Hose clamp on rear of BT

I also decided to mount the bulkhead plate that seals off the MMT. I used a piece of hangar to keep it in position till the epoxy dried.

MMT bulkplate installed

BT installed

Install Tube coupler into fin can

To install the coupler into the lower BT I first used CA to harden just the edge of the coupler. This prevents it from pealing layers as you insert it. After sanding the CA'd edge I test fit it and it went in fine. With the coupler installed I put a line on it at this location.

I taped the kevlar supports out of the way against the MMT.

I mixed up some West systems slow epoxy and with a small brush brushed it inside the airfram where the coupler would go. I brushed it to within 1/2in of the edge but did not go to the edge as this makes it easier to insert the coupler.

I slipped the coupler down and turned it while sliding it down. I stopped when there was about an inch left to insert as evident from the line I made. I then brushed some epoxy onto the coupler up to the line to makeup for the epoxy I did not put on the BT.

Then I slipped it all the way in to the line and wiped off any excess epoxy with a paper towel/alcohol.

Coupler installed

Feed Kevlar through second CR and glue CR in place

I was concerned about getting epoxy on the kevlar supports because I would be gluing so close to it so I decided to use some tubular nylon as a sleave over the kevlar.

TN in place over kevlar

Once I had the nylon in place I slipped the cords through the holes in the CR being sure to keep the marked side on the side of the MMT with the line on it.

I mixed up some West systems slow epoxy and added plenty of milled fiberglass to make it thick. This will allow it to stay on the MMT/BT long enough for me to get the ring in position.

I put a generous amount of epoxy on the MMT and inside of the coupler. Lowering the ring in place I kept the kevlar tight so it would stay out of the epoxy. I then taped the kevlar down to the MMT to stay out of the way.

Ring in place with kevlar taped out of the way

Then I flipped the rocket over and stood it upside down so the epoxy would flow down and onto the CR.
I also place a heater near it so the epoxy would flow better.

Heating to help epoxy flow

After rotating the rocket several times I turned off the heater and let it dry overnight. The next day I applied a fillet to the top of the CR.

CR2 installed

Verify position of CR1 and glue in position in second section of BT 

I had some epoxy already mixed with filler from the CR2 fillet so I installed CR1 inside the upper BT section. I epoxied it in place 6in down from the end of the tube. I gave it a generous fillet on its bottom and none on the top.

I positioned and glued the BT in place. I made sure to put a generous amout of epoxy on the MMT so it would make for a nice fillet on the inside.

Secure the screw eyes on the kevlar and verify length

I tied the screw eyes onto the end of the kevlar because there was not enough room to use my normal technique. I used a figure eight knot followed by an overhand knot. These were followed by a couple tiewraps to make certain they would not slip. Using knots also allows me to adjust the length if needed.

Add fin fillets and fill gap from aft fin slot

I used the standard tape technique to mask off the fin slots and filled them with West Systems slow epoxy filled with milled glass.
I would normally not use glass but there was a bit of a gap and I wanted to fill it with something a bit stronger than microballoons.

I also filled the gap left at the end of the fin slots at the same time I was filleting the fins.
When I did two sets of fins I would fill the gap that was at the bottom by taping wax paper on the outside of the tube and filling the gap with the epoxy/filler mixture.

Install aft rail guide mount and fillet the aft CR

I installed the aft rail guide with epoxy and put a fillet around the outside edge between the CR and BT.

Aft rail guide mount installed

Install the motor retainer

I installed a 98mm Slimline motor retainer to hold the motor in. This I glued in with JB weld. I also mixed up enough to apply some to the nuts on the eyebolts holding the kelvar supports.

Assemble deployment bulkplate

I glued together two bulkplates, one that fit inside the coupler and one that just rested on top.
I then cut a piece of aluminum strip so it would strengthen the anchor points.

I drilled holes in the aluminum strip for the two u-bolts and two eyebolts that anchor to the fincan.
I also drilled a hole to mount the Tether that will reaf the chute till the altimeter tells it to deploy.

I mounted 4 terminal blocks for attachment of the e-matches and drilled small holes for the wires to pass that I will seal up later.

I mounted two PVC end caps that will contain the apogee charge, I might only use one charge well.

Here is the backside view after wiring.

Additional mods...

Strenghen aft end with kevlar

I decided to add kevlar to the aft end of the airframe to help it withstand landing forces. I used some 2in kevlar tape I had and West Systems epoxy.

Bulkhead extention

I decided to extend the lip of the bulkhead that is at the end of the kevlar. I did this because the kevlar can stretch a bit. I did feel good with the 1/4in lip provided by the 1/4in ply I was using so I cut a ring out of 3/8in ply and screwed it to the bottom of the existing plate. Now the lip is 1/2in wide, plenty.

Electronics bay

I decided to move the electronics placement. I moved them down the rocket so they are mounted to the MMT. This required me having to cut a hatch in the side of the airframe. I did this to make access to them easier. Also there was no good place to mount the switches for the electronics. I made a curved mount out of a 2x4 and epoxied it to the MMT.

Electronics bay opening I cut

One of the two mounts

Mount ready to glue in

I added a support to the bottom of the electronics mounting plate to support the 3 x 9V batteries durring boost.

I then glassed over this support to strengthen it.

Sled glassed

I had 3 pieces of electronics I wanted to install in this bay. I decided to go with 3 different technologies in a quest for redundancy that could withstand even system errors.

I used 2 types of altimeters. One runs off two 9V batteries like most standard altimeters. The other runs off a single AA battery. This gives a backup to the batteries used so if there is an issue with the 9V cells under acceleration the AA cell may overcome it. These were made by PICO alt

I also installed a magnetic apogee detector to function as a backup to the apogee charge.

Here is a completed view of the electronics bay.

Electronics bay

I installed coax connectors to use as power switches for each of the 4 batteries.

The two altimeters can be seen in the middle of the sled. I carved an oak block to secure the altimeters so that thier boards slid part way into this block. There is also a tunnel in the block for the wires. I then secured the altimeters with a piece of G10 formed to fit over both altimeters.

The 9V cells are butted against the block I glassed in place and secured with a brass strip that runs over all 3 and is anchored at both ends with machine screws that thread into Tee nuts. The AA cell has a block secured below it and is held down with zip ties. I decided to solder the wires to this battery to make the connection more secure. I installed a terminal block between the PICO-AD3 and this cell for attachment of the pre-soldered wires.
The wiring harness that leads to the charges can be seen running off the top right of the board secured with two zip ties.

This is a more detailed view of the electronics.

Electronics closup

Nosecone electronics

I was going to install the R/C backup electronics in the bay with the flight data recorder.
Concerned about interferience from the computer I decided to move the R/C gear to the nosecone.
This required that I cut the bottom off the NC, a job made easy with my recipricating saw.
I then fashoned a bulkplate with a hole in the center to hold a PML 2.5in tube.
I also installed tee nuts to hold the electronics in place.

Tube and plate

The bulk plate

Bulk plate installed

In the photo above you can see a 1/2in hole on the left side. I used that to pour in expanding foam.
I only put about 4in of foam in to lock the tube in place in the nosecone.

I drilled a hole through the base of the NC into the bay and glued a brass tube in place. This will be used to route the power wire and antenna outside of the NC.

I made a sled that would install into the bay using two bulkplates glued together. One fit inside the tube and the other didn't. To this I glued a plate to mount the electronics.
For electronics I used a standard FM R/C plane receiver. To this receiver I attached my custom circuit that senses 3 of the channels and controls two outputs. One of these channels is used as an arming signal that sounds a buzzer when armed.

Front side

Back side

Painting

I brushed on 3 coats of Rustoleum clean metal primer.

This filled the weave of the glass very well, and it sands good too.

I sanded this off and sprayed on a coat of Rustoleum clean metal primer.

Then I painted the whole rocket white. Then sprayed on several shades of blue.
I had delusions of painting the rocket to look like the Caribbean ocean. Well it came out looking more like sky.

Here is a shot of it squeezed into my paint booth. I had to let it dry then turn it because the fins span was too big.

In paint booth

Painting complete

Recovery harness

I took 5 feet of Kevlar and attached chain links to the ends. I made 4 of these, one for each end of the 1in TN I was using for the recovery harness.

I used a technique detailed here : http://www.geocities.com/rdh82000/Tips/kevlar.htm

This design was tested and the chain links broke before the Kevlar even thought of slipping. Thoes results can be seen here: http://home.sprynet.com/~monel/shock.htm

The test pieces broke at about 3000 pounds force. Thoes were made from chain links rated to 800lb so I used chain links rated to 1200lb for this project.

I looped the Kevlar over in the middle for attachment of the TN. I put a single tie wrap to keep the TN from sliding around on the Kevlar.

Connected to TN

Connected to bulk plate