From NASA to L3, a short build thread

AndrewW

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So this story or a variation there of is probably not unique to me but this is my version of how I got here. By here I mean acquiring the tools, materials and knowledge to hopefully build a rocket to fly in an attempt to get my L3 certification.

So like many of you I played with ESTES kits back when I was young, almost 30 years ago. I was always interested in designing new rockets and I remember to this day how excited I was when I got my hands on the ESTES Designer Pack. I hardly ever got to fly any of the ones I built but much like today I think the thing I enjoy most about this hobby is building things with the actual flying being more of a validation of a job well done.

I also remember going to hobby shops where D motors were about as big as they came and talking with my friends about rumors that there may be even larger ones like E or Fs. But like many of you, girls, school and cars began to dominate my late teens and rocketry was forgotten.

Fast forward to 2016 and a conference for work takes me to Florida. I now have two young children of 4 and 2 and decide to take the family along with me to the conference, with the only free day I have I decide to take them out to Kennedy Space Center, a place I have always really wanted to visit.

So after a very enjoyable visit I got to thinking about the rockets of my youth and how I thought it would be fun to build a couple of them again with my son and maybe launch at the local school yard. So back at the hotel I got online and ordered an ESTES starter kit with the launch pad and two rockets, the Amazon and Crossfire. We built them in short order upon our return home and launched them a few days later. So I thought that was fun and got back on the old interweb machine and began looking for something a little bigger and it didn't take long for me to discover the world of High Power Rocketry.

In retrospect I think I was sold on just the name alone I mean come on High, Power and Rocketry those are three pretty cool things to put together into one hobby. But I didn't quite dive right in, I first found an ESTES Ventris for $20 and built that and started looking into motors for it. Needless to say I was super excited to see that not only could I buy E and F motors but that there motors up to O available. But initially I said this is crazy, to even spend $15 on a motor for a rocket that I will probably lose in the trees, it is just a waste of money. But before I even flew the Ventris I was already looking into my L1 cert and had purchased the 4" cardboard version of the Madcow DX3. I said that would be it, I would get my L1 cert to show that I could accomplish it and stop there because L2 and beyond just seemed just to out there for me.

So in September of 2016 I had my DX3 built and with my father and son we made the four hour drive out to URRG to try and get my L1. Before I flew the DX3 I figured I should get my feet wet first by flying the Ventris because up to this point I had only been flying low power stuff. Off to pads I went with my $20 rocket with a $15 motor and a $100 JL Alt3 in it and promptly got it stuck in one of the highest trees around. With this less than successful first MPR flight under my belt I hesitated to try my luck with the DX3 but finally decided that I drove four hours to get there I might as well give it a go.

With fear of losing another rocket to the trees I may have put a bit too much angle on the rod. It left the pad well on the I280DM and deployed near apogee albeit a bit far uprange. I initially thought I had successfully achieved my L1 but after a very long walk and finding that my rocket landed in a river I also discovered that I had zippered the air frame. I went home humbled and really decided that I wanted to learn more about this hobby and I wanted to do it well.

I got home and began to figure out what went wrong and how I could salvage the DX3. Before I had even gotten my L1 I had ordered a fiberglass kit for my L2. It was at this point that I realized that what had started as something for me and my son to do occasionally together for fun had turned into something that I was getting quite passionate about.

I got the DX3 together and got my L1 a month later at MDRA in MD followed by my L2 a month after that with a RW fiberglass Adventurer 3. Once again I said that is it, to spend over $100 let alone $300+ for on a motor that is completely useless after only a few seconds in pure lunacy. I had convinced myself that there would be plenty to do at L2 and I will likely not ever be able to justify the expense of a L3 attempt.

Well here I am two years later, I have travelled thousands of miles, burnt whole lot of APCP and generally had a whole lot of fun but I still want more. So now dropping $150 on a mid sized K seams completely reasonable and in my mind the next logical step is L3. Well that about sums up how I got here now onto the build.

I am going fairly conventional with the design of my L3 which is mostly based on a Performer 125 kit purchased from Ken at Performance Hobbies. I actually do like 3FNC rockets and this one in particular reminds me of the DX3 from my L1 cert. One of the things I enjoy most in life is refining my skills and knowledge in a particular subject so a couple of my goals for this project are to expand my knowledge of aerodynamics, develop some of my own electronics, and incorporate parts into the design fabricated on my newly acquired metal lathe.

I decided to go with a 5" kit as I found it to be a happy median between a 4" kit which on a M would seriously threaten our waivers here in the east and a 6" kit that I would hardly be able to fly on anything less than a mid size L. I have already fabricated most of the parts I need and started construction and will post some of the steps completed to date. I am hoping to have this done and fly it at URRF 5 at the end of June.

L3 3d view.jpg
 
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AndrewW

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My biggest deviation from the kit and a conventional design will be in the fin can area. I will be making the centering rings out of aluminum with what I am calling an integral fin carrier at each end. I am also making a thrust ring/motor retainer as well.
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Trueing up the 5-1/4” round stock
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Cutting to length
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Beginning to bore the center
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Machining the interior
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Final dimensioning
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Finished thrust ring
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How to turn 10lbs of AL into 10oz
 

AndrewW

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For the thrust rings I first machined a ring and the using a mill removed most of the aluminum just leaving a portion to be slotted which will help support the fins.

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Machining the ID and OD
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The forward CR with a lip to engage the end of the MM tube
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Layout of the fin carriers
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Removing the excess material
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Finishing the machining
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A finished CR
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Dry fit of MM assembly (29mm CTI 3G casing for reference)
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Thrust ring
 

jsdemar

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Nice lathe work!

To save on the time hogging out solid rounds, thick 6061 tube is available from Discount Steel online in large sizes.
 

neil_w

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This looks impressive. I always love seeing home-machined aluminum parts, even if it is far removed from anything I'll ever do.

One suggestion: that giant chunk of text in the first post is nigh unreadable without some paragraph breaks.
 

AndrewW

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Nice lathe work!

To save on the time hogging out solid rounds, thick 6061 tube is available from Discount Steel online in large sizes.

I usually do order tube from someplace like McMaster-Carr but it usually only comes in 1/2-1” sizes and in order to match the OD of the airframe I needed something a bit larger than 5”. So I found a 5.25”dia. X 5” solid round on eBay and made it work.
 

AndrewW

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This looks impressive. I always love seeing home-machined aluminum parts, even if it is far removed from anything I'll ever do.

One suggestion: that giant chunk of text in the first post is nigh unreadable without some paragraph breaks.

My apologies for the long run on paragraphs, I have always had a problem with that and it was late. I will try to clean it up a bit later.

Thanks
 

jsdemar

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I usually do order tube from someplace like McMaster-Carr but it usually only comes in 1/2-1” sizes and in order to match the OD of the airframe I needed something a bit larger than 5”. So I found a 5.25”dia. X 5” solid round on eBay and made it work.

I see, that's a unique size to find. 5" could work if the OD were built up with a 5" ID ring JBwelded to it.

I've used 6061 thick aluminum tube to make 3", and 4" motor closure retainers and nozzle holders.
For example:
3" OD, 2" ID: https://www.discountsteel.com/items/6061_Aluminum_Round_Tube.cfm?item_id=139&size_no=27#skus
4" OD, 3" ID: https://www.discountsteel.com/items/6061_Aluminum_Round_Tube.cfm?item_id=139&size_no=33#skus

Also, schedule 80 6" pipe is 6.625" OD and 5.76" ID. I've machine the ID of a ring of that to make a thrust ring on the OD of a 6" motor.
 

AndrewW

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I see, that's a unique size to find. 5" could work if the OD were built up with a 5" ID ring JBwelded to it.

That is an interesting idea and I will have to remember it.

The 5.25" round I got from ebay was only $25 and I still have half of it left so other than a whole lot of time and wasting a bunch of aluminum it worked for what I needed. I am still learning this stuff and I am definitely seeing the value in purchasing stock close to the dimensions of the finished part.
 

AndrewW

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Are you a machinist by trade or is this a hobby?

No I am learning as I go. My father had a Craftsman/Atlas lathe that was passed down to him from my grandfather. I started by making aluminum bulkheads out of scrap metal and I learned a lot by figuring out what didn't work. His machine was seldom used and had never been set up properly so spending time to align, adjust and fine tune things taught me a great deal. I just recently bought the same lathe as his for my shop and have been working on tuning up using what I have learned on his machine.
 

AndrewW

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Seeing as the milling machine I was using is up at my fathers house about an hour away and he didn’t have anything to make the 3/16” slot for the fins I tried to come up with something using the tools I had at home.

I decided to build a sled to be used on my table saw along with an abrasive blade. All the blades I could find where 1/8” thick so to make the slot the width I needed I set the sled up to first cut the outer edge and then used some 1/16” shim stock against the fence to widen the slot to 3/16”. The whole setup worked very well. I had to do a little bit of filing where the blade flexed at the bottom of the second cut but otherwise the slots where just about perfect.

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Marking the slots with a scribe

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The slotting sled

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The slotting sled

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Cleaning up the first ring

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Laying out the second ring

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Fit up

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The lower CR

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The upper CR

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The MM assembly
 

AndrewW

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In the past couple of days I got the MM completely assembled and installed in the airframe.

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The two CRs epoxied onto the motor tube. I have included the u bolts for anchor points if I want to use my 54mm CTI someday.

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Filling in the bevel on the lower CR

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The thrust ring installed which seats into the rear CR followed by an epoxy fillet.

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The completed assembly

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Applying epoxy for the from CR

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Installing the MM

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Pushing it home
 

Steve Shannon

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You’re doing beautiful work, but I have to ask: has an L3CC or TAP already signed off on the design and will a design with this much metal be allowed at the launch site where you intend to fly it?
 

AndrewW

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You’re doing beautiful work, but I have to ask: has an L3CC or TAP already signed off on the design and will a design with this much metal be allowed at the launch site where you intend to fly it?

I have received approval from both of my TAPs for the design.

The retainer/thrust ring actually have less mass than a commercial retainer and thrust ring combo. The two CRs are only slightly heavier than their equivalent FG CRs. I do appreciate the comment and will pass it by the clubs BOD to see if they approve.
 

Steve Shannon

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I have received approval from both of my TAPs for the design.

The retainer/thrust ring actually have less mass than a commercial retainer and thrust ring combo. The two CRs are only slightly heavier than their equivalent FG CRs. I do appreciate the comment and will pass it by the clubs BOD to see if they approve.

Thanks. It would be no problem at BALLS or my local launch site, but some launch sites have specific rules about the use of metal. I suspect that since your TAPs have already approved there should be no such concern, but I just hadn’t seen TAP approval mentioned above.
 

AndrewW

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Got a few more things done in the past couple of days. I know I have a problem when I am getting up at 4:30am to just epoxy one more thing as well as staying up well past 11pm each night to take advantage of the kids being in bed.

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Roughing up the root of the fins

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Applying epoxy to the root and the fin carrier contact area

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Verifying the fins are fully seated

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Checking the fins are all aligned and perpendicular to the airframe

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Injecting 21ml/fin root for internal fillets

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Making sure the epoxy flows evenly

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Verifying the epoxy is evenly distributed
 

AndrewW

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I was able to put a few more nights in on this. I am hoping to have it complete for URRF but at this point I am starting to have some doubts.

After completing all of the internal fillets I concentrated on getting the external ones done. These are by far the largest fillets I have ever made. I used Rocketpoxy and the results are not as good I have had with smaller airframes. So I will have to do a bit more sanding and fill my than I would have liked to. I also mostly finished up the retaining ring for the motor.

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Laying in the epoxy

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Pulling the fillet with a 3/4” pvc coupling

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Waiting to remove the tape

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Tapping the holes in the thrust ring for the retainer ring

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Drilling the mounting holes

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Finished retainer ring

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Retainer mounted with a 98mm to 75mm reducer
 

AndrewW

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So life got very busy around here for the past couple of months and I never got my project completed to fly at URRG. What little time I found during the summer I used to finish up my rocket for an attempt at the AUgust URRG Launch. So I never really finished this build thread but I am posting a video that I hope summarizes the project and the outcome:

Enjoy...

 

snrkl

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What are you using for telemetry overlay on the video, out of interest?
 
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