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Level 2 cert thread - scratch built

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NateLowrie

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Time to redo my Level 2. I did my level 2 originally back in 2007, but stopped rocketry when I moved back east in 2008 until this year. I was going to build a new rocket for my L2, but LDRS coming to my new home field of MDRA next year has pushed up my time table for everything. So, I am turning to the rocket I originally did my L2 in, which I am renaming "Youthful Indiscretion" partly because back then I made so many mistakes with this rocket, which you will be seeing me correct shortly.

Attached is the Rocksim I had to redo for this rocket. Fin can is 48" long with a 36" 54mm MM. 2 bay style DD with a 24" drogue in the lower bay and a 60" flare chute in the upper bay. So, my working list for this rocket:
  • Fix the fins. They got some pretty gnarly ships from being drug through the desert due to a stupid choice of materials.
  • Construct the altimeters. I will be running 2 eggtimer TRS units each with a WIFI switch and a 1200mah 2S lipo.
  • Construct the AV bay. I have the coupler, the bulkheads, and the all threads, but no bay. If memory serves correctly I used to take an ill fitting wood plank, mount an ARTS2 to it and cross my fingers. Not this time...
  • Install shear pins in the nose. I friction fit the nose the last few times I flew it and had at least 2 failures with the nose popped off and the main deployed at apogee.
  • Redo the ground testing and develop a launch checklist.

Note, almost all of this has been done. I am retroactively posting pics here.

View attachment Youthful Indescretion.rkt
 

NateLowrie

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Here's some shots of the fin damage. The core of the fins are a kelvar honeycomb with layers of fiberglass on each side. Giant Leap sold it years ago and I am not sure if it's even available. The fins are TTW. When I originally, constructed it, I used West Systems epoxy with microballons for the intneral and external fillets. Where I made the mistake was putting balsa edging on it to get a bevel. I did 2 layers of tip to tip glass over the whole fin including the balsa. Everything held up good for 3 flights until it got dragged across the NM desert and split the edges.

You can see the damage in the pictures. It's all along the balsa beveled edge. The tip to tip glass on the root is intact. After batting around ideas with David McGregor at the last MDRA launch, we decided the easiest thing to do was to cut the balsa completely off and use epoxy to create a round leading and trailing edge. The fins would be slightly smaller but it doesn't affect stability.

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neond7

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If it was my bird I would fill in the damaged areas with thickened epoxy, use a finishing sander to shape it all smooth, and put a layer of 3oz glass across the fins. Weight addition would be very minimal.
 

NateLowrie

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Here's the Av Bay. The original coupler was a 3.9" coupler 8" long. I drew up an av bay in Solidworks last week and cut it out on the CNC. Standard 1/4" plywood, nothing fancy. I just needed something quick and dirty. I glued the av bay with wood glue after some dry fitting and changes.

I ran into 2 problems:
  1. The Av Bay coupler was 7 and 13/16, not 8". :facepalm: Shame on me for not measuring.
  2. I forgot about the U-Bolt nuts and bar on the backsides of the bulkheads.

So, after some manual cutting and reconfiguring of positions I now have a finished sled with an altimeter stack on each side. I know it's far from ideal to have the antennas in the bay with the allthread, but after talking with Chris it should be fine for the altitudes I am going with this rocket. You can see the stack in the last few shots. Still left to do:
  1. wire strain relief
  2. redo the charge terminals on the bulkheads. The old terminals were badly corroded so I just junked them.

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NateLowrie

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If it was my bird I would fill in the damaged areas with thickened epoxy, use a finishing sander to shape it all smooth, and put a layer of 3oz glass across the fins. Weight addition would be very minimal.
I had definitely considered that, but I was concerned the remaining balsa would split. It was easier to just cut it off and use epoxy with faring compound as a thicker to create a round edge. I have already done the fin repair. I'll post pics when I get home and can take some.
 

Nathan

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Nate's L2 attempt on Sunday didn't go well. It appeared that apogee deployment charge blew off the motor retainer. The rocket came down ballistic and was completely destroyed. Here are a couple of pics of his flight before things started going badly . . .



 

Bat-mite

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Nathan, I am not following you (my fault, not yours, I'm sure). How could a deployment charge blow off the motor retainer? And even if it did, why didn't the main charge still deploy the main, even if it was at high speed? Or was it single deployment?
 

NateLowrie

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First, it was good to meet Bat Mite and see the other Nathan. I've attached the root cause analysis report I prepared. What it came down to was I didn't not complete the last step of arming both egg timer TRS altimeters :facepalm::facepalm: and as a result both were not really armed and the apogee charges never fired. So, the flight was doomed from the start.

Nathan, from the video I have of the ascent and impact, it looks like the slimline separated from the fin can when the impact hit the ground. The forward 5.5 feet of rocket crumpled and buried itself in the ground. The fin can managed to survive with the exception of the forward coupler and the slim line adapter. I'll cut 6" off it and install a new coupler and redo the motor retention.

As far as the upper bays go, the chutes and shock cords are salvagable. The TRS units both cracked in half and both lipos are gone. The WiFi switches may be salvageable.

View attachment Root Cause Failure Analysis.pdf
 

Bat-mite

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I didn't know EggTimers were so complicated. Man, with an RRC2+, Adept22, or StratologgerCF, all you do is turn on the switch.

Sorry it didn't go well. Are you looking at August?
 

dixontj93060

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Nice to see someone doing a postmortem like this. I thought I was the only one :).
 

NateLowrie

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I didn't know EggTimers were so complicated. Man, with an RRC2+, Adept22, or StratologgerCF, all you do is turn on the switch.

Sorry it didn't go well. Are you looking at August?
The eggtimer TRS systems are the most complicated eggtimer unit because of the telemetry downlink. Even then, the arming sequence is only a few steps:
  1. Turn on LCD Receiver. Wait for it to power up and say "Waiting for Sync".
  2. Turn on the altimeter by turn on you switch.
  3. Wait for the altimeter to sync to the LCD receiver. The customized name of the altimeter appears on the receiver and the altimeter stops beeping.
  4. Select the "Start a Flight" entry from the LCD receiver menu and hold down the button for 7+ seconds.
  5. Verify the settings are correct on the screen and hold down button for 7+ seconds to arm. Confirm the altimeter emits a warbling buzzer sound.
I just missed step 5.

Also, note that the Eggtimer Quark functions exactly like the RRC2+, Adept22, or StratologgerCF in that you only need to turn the switch. The eggtimer Quantum is a little different in that you arm it by connecting to it with the wifi on your phone and going to a web page it serves to arm it (read: you don't have to climb a ladder/tower...)

As far as a redo goes, I would love to do it in August but I have a prior commitment that weekend (though I may see when Tripoli Pittsburgh is flying next and do it with them in August). Either way, I will be out at the sod farm in September.

Nice to see someone doing a postmortem like this. I thought I was the only one :).
If I don't I drive myself insane. Now I just need proper SOPs onsite with a checker at the pad.
 

BDB

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  1. Select the "Start a Flight" entry from the LCD receiver menu and hold down the button for 7+ seconds.
  2. Verify the settings are correct on the screen and hold down button for 7+ seconds to arm. Confirm the altimeter emits a warbling buzzer sound.
I just missed step 5.
I did the same thing a couple months ago. I was so mad at myself, I could barely sleep that night.
 

NateLowrie

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I bet you'll never forget step 5 again!
Never again... Though I am diversifying my altimeters. I will be ordering a stratologger CF along with another TRS and an eggtimer quark. I think for now I'll use the quark and the straologger CF just because they are simpler to arm and operate.

I did the same thing a couple months ago. I was so mad at myself, I could barely sleep that night.
Did you core sample your rocket too? My solution is going to be a small checklist card stored in a pouch on the underside of the receiver box in addition to a step on the master checklist for verbal confirmation of the warble tone.
 

BDB

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Luckily, mine came down horizontally, so I just snapped one fin. That was my "shakedown" flight to practice DD before my L2 attempt. You can see the damage here.

I actually have the repair nearly complete now. Just waiting for some less humid days to paint. I'm hoping to fly it again in August, and I will definitely use a checklist next time.
 

NateLowrie

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Postmortem, the following survived the ballistic descent and burial into the dirt.
  • The fin can is intact expect for a) the slim line adapter broke loose when it hit the dirt and b) the forward coupler broke off at the body tube connection.
  • The 2 wifi switches survived
  • The shock cord, both chutes, and recovery harnesses survived.
  • The charge wells survived.

So, now we rebuild. I could take the surviving fin can and rebuild the upper half. I may do that eventually, but I decided to just build a new airframe.

I have done the preliminary rocksim for the rebuild of my Level 2 cert rocket. I picked up a RW 4" Patriot kit from AMW at the last launch. It's one of the few with the metal tip on the patriot nose. Rob and Gloria gave me a good deal on it. I plan on modifying it somewhat heavily. I've attached the rocksim file for reference.

Modifications to the kit:

  • Fin can
    • Bevel fins to 10 degrees.
    • TTW Interior fillets done by epoxy w/ chopped fiberglass injection into a hole next to the fin slot.
    • Exterior fillets done with epoxy w/ chopped fiberglass
    • Tip to Tip glass with 3oz glass
  • Recovery
    • I don't like the single long tube. I could attach an eyebolt to the top centering ring, but I a) wouldn't be able to get a hand into the tube down that far to change shock cords if need be and b) it limits the kit to motor ejection which is not desirable either. So, I won't do that. I don't want to cut the tube either.
    • My solution is to add a coupler that houses an AvBay and a 24in recovery bay.
    • The av bay with hold dual altimeters of different brands that are simpler units. I am looking at a Stratologger CF and Quark for now.
    • Dual Deploy will be done with an ARRD used to release the main. The sequence is detailed below (Note, the body tube is hidden).
    • The av bay will be a custom machined G10 sled with G10 centering rings done on the CNC in my shop.
    • I am not sure yet whether I was to permanently bond the coupler and lower av bay ring with epoxy to the fin can or have it be completely removable and attach it with screws. Any thoughts here would be helpful.

[SUP](Note: Images are not mine. I grabbed them from a place on the net I don't recall some time ago. They illustrate the concept well so I am borrowing them.)[/SUP]


This is the packed configuration. The charges for the drogue will be positioned above the main chute. I am going to epoxy 2 tubes on opposite sides of the AvBay to act as charge cannons for the ejection charges. This will allow me to release the BP charge above the main and ensure the main doesn't snag on any wires coming out.

rec1.jpg


The drogue charges will blow the drogue and it's shock cord out.



rec2.jpg
The drogue shock cord is connected to the ARRD and keeps the main chute in the body tube.



rec3.jpg

At 500', the ARRD releases and the drogue pulls the main free of the body tube and out of the deployment bag.



rec4.jpg

The nosecone and bag come in on the drogue chute. The rest of the rocket comes in the main.



rec5.jpg

I like this recovery setup because:

  1. it stands the least chance of the main chute getting tangled
  2. you only need to split the rocket in one place.
  3. If the main does fail to deploy, chances are good the booster will land on the motor mount which would help prevent some fin can damage.

I've used this setup before though that was a long time ago with 2 ARTS2 altimeters. It functions well and is compact. I can fit the chute setup in 12" of 4" tube for a 10-14 lb rocket and 30" of 4" tube for a 40 lb rocket.
 

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thomas

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I will use the same recovery method in my L3 project. I will not use the ARRD but two spacetec SRM2 for redundancy.
I will glue the coupler in, because it will avoid the parachutes schock forces on the screws.
But some engineers told me that screws would also be fine.
Screwing the coupler in makes it easier to build the AV-bay. I ended up with additional threaded rods to have a removable AV-bay.
 

John Beans

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If you ever feel like scaling it down a bit, you could always pick a baby J motor with motor eject, add a Chute Release for delayed deployment, and ease your building effort and stress on cert day a bit.
Maybe not as fun as a more complicated rocket, but that doesn't have to all happen on cert day, right?
 

NateLowrie

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If you ever feel like scaling it down a bit, you could always pick a baby J motor with motor eject, add a Chute Release for delayed deployment, and ease your building effort and stress on cert day a bit.
Maybe not as fun as a more complicated rocket, but that doesn't have to all happen on cert day, right?
John, I had really considered that. I have a MadCow Super Batray that I could do that to now if I want too. Robert DeHate and I talked about that at length. I ultimately decided to do it this way because my Level 3 project will use the same recovery setup and this an opportunity to prove out the setup and take care of any hiccups. As far as the build goes, really the only additional complexity is the Av-Bay build out, which shouldn't be that complicated.

At some point I will pickup a chute release as it looks like it'll function really well for some of the airframes I'll have in mind. Thanks for chiming in. Keep the suggestions coming!
 

John Beans

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I've always thought that there's two schools of thought for cert flights:

1. Keep it simple
2. Do something interesting

Maybe it's time to add a third:

3. Combined L2 and L3 platform.

I tend to be a #2 (I like something interesting for motivation).
I think the reason I've never considered #3 is that my rockets never last that long.
 

NateLowrie

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I've always thought that there's two schools of thought for cert flights:

1. Keep it simple
2. Do something interesting

Maybe it's time to add a third:

3. Combined L2 and L3 platform.

I tend to be a #2 (I like something interesting for motivation).
I think the reason I've never considered #3 is that my rockets never last that long.

I guess it all depends on your goals. I had intended to build a set of 54mm and 98mm rockets to be robust research platforms I can use to prove out individual systems and research motors for eventual high altitude flights. The recovery setup with the ARRD is one of those systems. The fact that they are cert rockets doesn't really bother me as much as it would if I was doing this for the first time.
 

Tonimus

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  1. Turn on LCD Receiver. Wait for it to power up and say "Waiting for Sync".
  2. Turn on the altimeter by turn on you switch.
  3. Wait for the altimeter to sync to the LCD receiver. The customized name of the altimeter appears on the receiver and the altimeter stops beeping.
  4. Select the "Start a Flight" entry from the LCD receiver menu and hold down the button for 7+ seconds.
  5. Verify the settings are correct on the screen and hold down button for 7+ seconds to arm. Confirm the altimeter emits a warbling buzzer sound.
I just missed step 5.

I did the same thing a couple months ago. I was so mad at myself, I could barely sleep that night.
I too, have done the same. Thankfully I was using motor backup, and still had a safe recovery, albeit under drogue.
 

NateLowrie

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Well, I am back with the rebuild. As mentioned before, I picked up a Rocketry Warehouse Patriot collection of parts that passes for a kit at the last launch from AMW. I am not going to be building it in the stock configuration. I am going to be adding a av-bay and 24" section for recovery components. I have a bunch of pictures for the build and haven't had time to write everything up. So, here we go.

Step 1) Bevel the fins. They are 3/32" G10. I don't like to leave the stock edge, so it's time to bevel. Knowing that I also have to do the Formula 200 fins, I build a jig for beveling the fins on the router.
IMG_7252.jpg IMG_7251.jpg

Here's the basic jig. It sets the fin at a 10 deg angle relative to a straight router bit. You just set the fin against the fence and clamp down. I didn't get a shot of the Patriot fins, but I did get a shot of the Formula 200 fins on the jig. Note, in the future a split fence would really help this process be more accurate at the ends.


IMG_7253.jpg IMG_7192.jpg

Fins came out good.

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NateLowrie

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First order of business is marking the things that need marked. I inserted the coupler into the backend and marked 4 lines for where the PEM nuts are going. Then I did the same thing with the nosecone to mark the shear pin locations (2) on opposite sides.
IMG_7260.jpg IMG_7261.jpg

Next up is gluing the centering rings to the motor mount and assuring proper spacing. The rings need to be tight up against the fins to get a good grip. What I did was put enough epoxy on the motor tube to tack the back ring. Then I slipped the aeropack retainer on end and used it's machined edge to ensure the centering was mounted flat. Between the fin slots I put a bit of a fillet on the inside edge of the centering ring, taking care not to get any where the fins are going. The epoxy was mixed with milled FG at a 1:2 weight ratio to get a consistency like peanut butter. After the epoxy set on back ring, I slid the forward centering ring on and tacked it in place. Then I took the fins and positioned them between the rings. I clamped the fins between the centering rings so the forward centering ring would set up perfectly positioned to encapsulate the fins. After the epoxy set I went back and did internal fillets in between the fin on the inside edge of the forward ring. Unfortunately, I didn't get any pictures of this process.:facepalm:

Next up is dry fitting all the parts together and that's were I ran into issues. The fin slots were 10 thou smaller than the fins. :( Sanding 10 thou on a fin slot is a real pain in the butt... Half hour later, I got all the slots sanded out and a mess of fiberglass. After that fiasco, I marked the locations of the epoxy injection holes and drilled them out with a 1/8". I am using a luer-lock tip on the string and don't need the holes as big as normal. I cleaned up the back side with sandpaper to remove the burrs.

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Finally I installed the motor mount into the airframe. I used Epoxy mixed with milled fiberglass again. The fillets on the outside of the centering rings will use 1/4" chopped FG.
IMG_7262.jpg
 

NateLowrie

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Time to fillet the top centering ring. It's a long way down the body tube, so I made up a system to deliver the epoxy.

[video=youtube_share;-kJFk4ym9Uc]http://youtu.be/-kJFk4ym9Uc[/video]

Here's the result.

IMG_7272.jpg
 

NateLowrie

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Next step was the fins. I made a fin alignment jig based off of the design here: http://www.rocketryforum.com/showthread.php?9694-Homemade-Fin-Alignment-Guide It works great although I did make a few modifications. I did not make a stand of it as I find it works better just strapped you the body tube on top. I used bungie cords to pull everything down. I also found it much more convenient to use a 30 degree edge instead of the 45 degrees. It sits better on the tube. Note, the reason its so big is I wanted to size it to be able to handle the Formula 200 fins.

The fins went on super straight and it turned out well.

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IMG_7287.jpg IMG_7285.jpg IMG_7278.jpg
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NateLowrie

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Time for Epoxy injection.

I mixed 15 grams of US Composites thin epoxy and mixed in 15 grams of 1/32" milled fiberglass. Mixed thoroughly for 5 minutes and loaded 10ml into a syringe. Note the syringe has a piece of 3/16 heat shrink tubing attached to the end of it. The tubing shrinks down to 3/32 after heating. The two reasons to do this are 1) to only need to drill a 1/8" hole and 2) I am able to get the tubing right down to the fillet to inject it.

After injectioning 10ml on each side I will tilt forward and backward for 4 seconds each to spread the epoxy. Then, I put a board across the fins and pop a bubble level on top to level both directions.

Note, I can clean the syringe up and generally use it for all of the internal fillets and top centering ring. After the last fillet it gets thrown in the trash.

IMG_7294.jpgIMG_7293.jpgIMG_7295.jpg
 

NateLowrie

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Shot of the Ebay sled with the mounting done. I have a Stratologger CF and a Eggtimer Quark. Both are powered with 9V batteries and MissileWorks screw switches. The screw switches are mounted on the sides of the board to be perfectly inline with the vent holes.

The av-bay is a Madcow removable av-bay. Note that the picture on the Madcow site showed a 2 sided sled so I was surprised to get a one sided sled. Mike apologized for the confusion and offered to ship me the ABS version as compensation, but I wouldn't have been able to build and wire it in time.
IMG_7305.jpgIMG_7304.jpg
 

NateLowrie

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Was putting the finishing touches on things last night and I ran into 2 problems.
  1. I need to redo the battery mounts on the sled. They are too close to the edges and are interfering with the mount. That wasn't readily apparent until I put the sled on the bulkheads. Easily fixable but somewhat aggravating. This is what happens when you don't design in CAD.
  2. I was assembling the ARRD for the deployment ground testing and noticed the O-Ring was the wrong size. It's about 1/4" to big for the groove. I checked the manual but the size isn't in there. Anyone know the correct size? If not, I'll measure the groove when I get home and size off of that.
 

NateLowrie

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I got into contact with RattWorks and they helped me out with the ARRD. For future reference, there are 2 O-rings on the product:
  • The piston requires a Buna-N quad seal o-ring (aka X-Ring, double seal o-ring, or Quattro profile) that is 1in OD and 1/16in thickness
  • The base requires a Buna-N standard o-ring that 1 1/16in OD and 1/16in thickness.

I got 2 to the base o-rings with the package and no quad seal o-ring.
 
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