KestreL

A new 54mm minimum diameter kit from 3 Dogs Rocketry. This rocket was designed with the Cesaroni K300 (P54-6GXL motor) in mind with the newly certified boat tail aft closure. I will be getting my HAM license so I can put a tracker in this puppy and actually find it after it’s launched.

I received the kit today (3-31-10) and it looks fantastic. This will be my first all fiberglass rocket and I’m very excited to build it. My plan of attack is to first model all the components in CAD down to the fastener (McMaster-Carr has step models of most of their fasteners) to have a virtual integration before I even mix some epoxy. I’m primarily doing this for the electronics bay so I can make sure everything fits well. I can even route all the harnessing with a module in my software. Then once I’m done with the design I can order the exact parts needed.

Construction

As with most things preparation is key, all surfaces to be bonded are sanded with 60 grit sandpaper and then cleaned with acetone to ensure proper bonding between components.

First off is the booster section and fin can. The tip-to-tip fin reinforcement will be done using a similar method outlined by Jim Jarvis shown here. The fins were tacked in the booster tube after inserting a 54mm motor case wrapped with a plastic film (provided with the kit). The handy dandy fin alignment tool also provided with the kit ensures perfectly aligned fins, which is pretty awesome.

Fin Fillets

JB Weld is used for the primary fin fillets as it is very strong and handles higher temperatures pretty well. I vigorously slide a steel washer back in forth in the joint to “score” a line to tape off for the fillets. After the tape is in place I pour the epoxy and then run the same washer over the joint to provide a smooth and evenly distributed fillet. Aeropoxy will then be used for the secondary fillets with a slightly larger radius washer using the same process.  This makes the layup easier as the bends won’t be as sharp. I will be using three layers of 5oz carbon fiber on each side.

Tip-to-Tip Carbon Fiber Fin Reinforcement

Vacuuming bagging is the way to go, however, I’ve had pretty good luck with hand layups using peel ply and some cheap tools. I start out by carefully creating a template with a sheet of paper so that I can cut out the carbon fiber to fit the tip-to-tip joint. You can make a sloppy layup that is plenty strong or you can make one that is strong and also looks fantastic. I will be showing you how to do something in between…or hopefully closer to the latter.

If you really want to make this look good, you’re going to have to spend of a lot of preparation time here. This is definitely the most crucial and challenging step of the construction.  You will have to make several small slits in the carbon fiber (and peel ply, purchased from aircraft spruce item number 01-1482) in the areas above and below the fins to make the transitions to the airframe as smooth as possible. Again, I’m following a similar technique explained by Jim Jarvis and spray the areas I will be cutting lightly with 3M spray glue to keep the ends from fraying.

I first spread the epoxy with a small brush over the entire area of the joint. Next I place the sheets of carbon fiber over the wetted joint and use enough epoxy so that fiber is completely saturated. The peel ply (that is also slit in the appropriate areas) is then placed over the carbon fiber, and with a small foam roller I evenly distribute the epoxy below and above it. The roller can be purchased at home depot for a few bucks and trust me this cheap tool makes a big difference. I’ve done this process without the roller and the end product tends to come out wavey and non-uniform.

As the epoxy starts to setup, you want to trim and removes the excess carbon. You can do this after it has dried but it is much more difficult, especially the areas where the carbon meets from joint to join. I then lightly sand the surface with some 100 grit and then 320 grit sand paper. You don’t want to sand too much of the carbon down but rather smooth the surface. In some areas where the carbon overlaps you need to grind it down a bit, but just the bare minimum. Next I thinned some epoxy with some acetone and proceeded to rub a very very fine layer over the fin can using a soft lint free cloth. Do this in a well lit area and look at the reflection to spot out the areas you need to wipe down. I repeated this process of lightly sanding with 320 grit and then polishing until I got a finish that made me happy.

Payload Section

The payload bay include the electronics bay ( the coupler) and nose cone assembly. The electronics bay is held into place with three #4 fasteners using captive nuts from McMaster Carr (item #94648A320). The nuts are low profile and work great with the fiberglass tubing. All you need to do is drill the appropriate sized hole in the material and compress the knurled portion of the nut into the hole until its seated properly. The nuts are pretty secure but I add a small bit of epoxy when installing them for good measure.

I think I will be using set screws (show in pictures below, mcmaster item #92311A106) instead of a typical pan screw to further reduce drag, although I dont think regular pan screws would raise the drag coefficient that much. I matched drilled the coupler to the airframe for these inserts first using a 1/16″ bit, and then opened them up to the desired sizes. If using the socket set screws you shouldn’t drill the holes in the airframe with too much slop, I think I used a 7/64″ bit.

The nose cone will be housing a Big Red Bee tracking beacon so I can actually find the thing after its launched. For shock cord attachment I used some Kevlar tied in a loop with the ends soaked in epoxy to bond to the inside of the cone. Four 6-32 coupling nuts were then bonded radially 90 degrees apart near the top of the cone to secure the nosecone bulkhead with the mounting hardware for the tracking beacon.

Flight

The KestreL flew at Balls 19 to 24,366′ on a CTI K300 out of my homemade launch tower for a perfect flight!

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  1. #1 by John Wilke on April 7, 2010 - 5:02 pm

    NICE!!!! Looks like you are doing a superb job and I can’t wait to hear your additional comments. So far so good!

  2. #2 by Joel Schiff on April 7, 2010 - 9:45 pm

    Please keep up the posts as I’m just putting the fins on my own newly arrived KestreL and would like to see how you handle some of the other aspects.

  3. #3 by Joel Schiff on April 7, 2010 - 10:51 pm

    Actually, the fin guide is a real treat and even a guy with two left hands got them on perfectly. All kits should have one just like this one.

  4. #4 by James on April 8, 2010 - 1:42 am

    More content coming over the next few days, stayed tuned!

  5. #5 by John Wilke on April 12, 2010 - 10:07 pm

    YES! very, very nice. Gosh, it looks a lot better than mine! Wanna trade?

    Keep up the good work!

  6. #6 by James on April 13, 2010 - 2:22 am

    Thanks John, just added another picture with the second polished layer. A few more and this will look awesome!

  7. #7 by Andrew Hamilton on April 13, 2010 - 3:32 am

    That CF looks great James! Thanks for documenting the build process. I’ve just received my KestreL today and the more build info I can reference the better!

  8. #8 by Jim Jarvis on April 13, 2010 - 10:24 am

    This is starting to look pretty good! And I’ll bet you’ve noticed how friggin stiff the fins are! When you’re done, I’d love to get your feedback on the method and the decisions you made along the way.

  9. #9 by James on April 13, 2010 - 10:40 am

    Andrew, so far i’m quite pleased with the way its turning out. Let me know if you have any other questions.

    Thanks Jim, yeah the fins are incredibly stiff! I plan on giving a summary of the build after I finish that will include thoughts on the kit itself and the build process. Much thanks to your guide as it has been quite helpful.

  10. #10 by Steve on April 27, 2010 - 9:55 pm

    Looks great. I haven’t started my build yet but am planning on making it similar to yours. Are the polished pictures shown above after all three layers of carbon? Where did you buy the carbon cloth. Do you have a project finish weight?

  11. #11 by John Wilke on April 30, 2010 - 11:14 pm

    WOW!…. will you build mine?? That is way very cool….

  12. #12 by James on May 3, 2010 - 12:05 am

    Thanks John!

    Steve,
    The polished pictures are after all the layers of cloth, i purchased the carbon from aircraft spruce.

    I have been so busy with some other projects i had to put the Kestrel on hold…so i dont have a finished weight. I hope to resume construction this week and work on the electronics bay.

  13. #13 by John Wilke on May 11, 2010 - 1:48 am

    Finished weight should come in 40-46 oz (or thereabouts). That is with recovery, electronics, etc. My last one was right at 48 oz, but I overdid some things :-)

  14. #14 by Phillip Babcock on May 12, 2010 - 8:45 pm

    Your build thread is excellent. I am in the process of building my own Kestrel. I wanted to know the part numbers for the fasteners and broach nuts you ordered. I was planning on using plastic rivets but I like your idea much better. Thanks

  15. #15 by James on May 13, 2010 - 1:46 am

    Thanks Phillip, I just updated the paragraph with the mcmaster item numbers.

  16. #16 by Joel Schiff on May 13, 2010 - 11:00 pm

    So are you doing just a single separation at apogee and if so is it altimeter based?

  17. #17 by James on May 13, 2010 - 11:44 pm

    No, I will be doing dual deployment using a featherweight raven. I like the raven since it has four programmable pyro channels…for a typical dual deployment flight I use all four channels, with a primary and main ematch for each event (with a 1.5 second delay). The Raven is also very small.

  18. #18 by Phillip Babcock on May 14, 2010 - 1:32 am

    Thanks you for posting the item numbers. How did you secure the broach nuts into the fiberglass airframe?

  19. #19 by James on May 14, 2010 - 12:01 pm

    Philip, I’m not sure if you’re familiar with captive nuts but you basically press fit them into a hole. See the picture here: http://images.grainger.com/B307_43/images/products/250×250/1TTC5_AS01.JPG

    I typically just line the nut up with the hole, then tighten a screw in it. This presses the nut into place and works pretty well. I additionally put a very small dab of JB weld on the broach end to make sure it stays there.

  20. #20 by Steve on August 14, 2010 - 11:38 pm

    James, Have you made any progress lately?

  21. #21 by James on August 15, 2010 - 8:08 pm

    Steve :

    James, Have you made any progress lately?

    Steve,

    I’m pretty much finished minus the paint job, which, probably wont happen before I launch. I’ll try to put up some pictures in the next week or two. How is your build going?

  22. #22 by Steve on August 18, 2010 - 10:41 pm

    James :

    Steve :
    James, Have you made any progress lately?

    Steve,
    I’m pretty much finished minus the paint job, which, probably wont happen before I launch. I’ll try to put up some pictures in the next week or two. How is your build going?

    I am just getting started. I believe mine will be about 9″ shorter than stock and I also cut the fins down about 3/8″. Should go pretty high.

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