Arapahoe-J - Successful L2 Cert!

Darn you... Now I really want one!

Looks like Semroc still has some 5.25" Ogive Nosecones (BNC-60VD V-2 Scale: Drilled) available (I just picked up two, and it looks like there are 7 left). Based on the BT-60 based .rkt file I found, those should work. I'm thinking a PNC-60RL or PNC-60AH may work for the tailcone.

K'Tesh said:

Darn you... Now I really want one!

Looks like Semroc still has some 5.25" Ogive Nosecones (BNC-60VD V-2 Scale: Drilled) available (I just picked up two, and it looks like there are 7 left). Based on the BT-60 based .rkt file I found, those should work. I'm thinking a PNC-60RL or PNC-60AH may work for the tailcone.

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It is just too cool of a design, everyone should have one. I think that excelsior sells the plan pack along with the decals. Would take the guesswork out of it anyhow.

Cl(VII) said:

It is just too cool of a design, everyone should have one. I think that excelsior sells the plan pack along with the decals. Would take the guesswork out of it anyhow.

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The only part that has me stumped (not really, just pondering...) is figuring out how to get the printed fin templates to fit the boat tail (and look good). The rest looks like a simplified version of my two stage Velociraptor downscale.

I'm thinking for the strakes I'll add ttw fin tabs to keep them aligned properly.

Perhaps someone can steer me towards the image/thread I'm looking for.

I'm sure that I saw an image of one with a fairing that covered an engine hook (vs friction fit or an exposed engine hook). Now that I'm gathering resources to attempt one myself, I'd like another look at it. Problem is, I can't find it for the life of me.

Any help here would be appreciated.

Thanks!
Jim

[EDIT] Found a thread over on YORF, but I'm sure I saw a better image of the finished product.

Some progress has been going on, but an serious case of incredibly busy has slowed progress. However, the fins are tacked on, and here is how we arrived at that...

I glass all fins, partly for ease of finishing, but mostly because I love building rockets, however I HATE repairing rockets. I don't want a rocket where the fin breaks and I have to repair it, so if the fin breaks I expect the rocket to be a heap of confetti. Also, these things are huge and could use the reinforcement I think.

I am in the progress of upgrading my composite materials from LHS style to more serious stuff. The change for this project was ZPoxy to US Composites laminating epoxy. The cloth is the Hobbico 5oz from the LHS. I layed the fins out of wax paper, and mixed up a 4 oz batch of epoxy. The pot life is said to be between 20-25 min...it kicked at 23, so spot on. Fortunately I finished laminating at 22 m 45 s. It was about 80 F is the garage, so I should have used a water bath for the epoxy cup, but I didn't think it would take 20+ minutes to get things good. Anyhow, I laminated both sides, added a second sheet of wax paper, and sandwiched the whole thing between some hardboard under some power tools and bricks for weight. Most of this isn;t pictured because of limited time and epoxy hands (gloves).

The setup:


Now with ZPoxy wax paper peels right off, but with the good stuff not so much (fortunately I ordered some peel ply for my next attempt). To get the wax paper off the fins a great deal of time was spent scraping with fingernail, rubbing down with mineral spirits, and gentle sanding. Better epoxy calls for appropriate materials apparently. Also, this is indeed better epoxy. It is far less brittle than ZPoxy when cured, and doesn't chip when sanded at the edges, even if you catch it on the belt. I'm impressed.

Now this makeshift laminating method will leave you with an imperfect surface that is difficult to fill on the rocket, so I choose to take care of most of the imperfections now. As such the entire fin gets a coat of Bondo spot and glazing putty, and once dry it is sanded down with a palm sander being careful not to dig down to the glass. Once done, the edges were rounded using the belt sander, and a little and a little hand sanding at the larger curves. This went better than expected as there are no long flat edges on this the entire process was done on the edge of the belt, and was very freehand in nature.



The slots were then widened out to fit each fin snugly. The fins were also fitted to each slot by removing the excess tab length, and final shaping of the aft tip on the belt sander. And the step from the boat tail to the tube was blended with a couple cycles of bondo. It isn't perfect, but will need to wait until primer is applied to get much better. The fin tabs were roughed up using a sanding drum on the Dremel to prepare them for epoxy. The fins were then tacked in place with 5 min epoxy, which brings me up to date. Seeing the fin can together all I could think is this rocket is going to be really big (by my standards at least). Internal fillets next, these are going to take some time.

Looking Good!

Slow progress, but it's hard to get excited about internal fillets.

I use a kludged together syringe and 5 mL pipet. This requires drilling out the Leur-lock threads from the syringe, snapping the pipet tip off, and some electrical tape to keep the whole thing together (probably doesn't need it, pretty tight fit without). I then mixed up some Aeropoxy and milled fiberglass, loaded that in the back of the syringe and put in the plunger. This works great, and my lab buys pipets and syringes by the thousands I don't have to worry about cleaning them.



Now the internals to the MM were done on three straight nights, but I also wanted to seal up the crack along the fins and reinforce the plastic boat tail- fin connection. For this I used US Composites laminating resin. Sure it's not really for this, but it fills the cracks due to its low viscosity, and did definitely add strength. I tried to work some fiberglass strips into these filets, but I just couldn't do it down in the boat tail, so I gave up on that. To keep the epoxy from flowing through the cracks I sealed it up with masking tape prior to pouring epoxy. Once the epoxy was just getting leathery I removed the tape, and cleaned up and stray stuff with alcohol. These took 3 non consecutive nights to complete.



In all I think it is more than strong enough for my needs.

Rail button holding, fin sandwich CR is next.

The extra ring was cut into slices and two of these glued to the next CR with some leftover Aeropoxy from some filet or another. These were held with a clamp for drying giving me a big target to hit for the rail button insert later.



This ring was then epoxied in place with the rail button block aft.



Next the coupler needed epoxied in place, but the coupler fit is extremely loose. To ensure a straight coupler masking tape spacers were applied. These are 4 layers thick which gives you an idea about how loose the coupler is. The coupler was then epoxied in place. I also took this opportunity to attach the shock cord anchor, so I epoxied a Y-harness of 1/2" 5000# tubular Kevlar in place...overkill, yes. I wrapped the MM over the harness with fiberglass to give some extra hold to the attachment.



I decided to do a double thickness coupler because I overbuild things. I could give you all my reasons, but in the end it comes down to I overbuild...it's a compulsion...like ellipses. I cut a 3" section of coupler and split out enough to let it fit. I then set the final CR at the top of the MM, and epoxied in the internal coupler at the same time.



That brings me more or less up to date. The fin can currently weighs 3 lb 1 oz. Yep, overbuilding has consequences.

K'Tesh said:

Darn you... Now I really want one!

Looks like Semroc still has some 5.25" Ogive Nosecones (BNC-60VD V-2 Scale: Drilled) available (I just picked up two, and it looks like there are 7 left). Based on the BT-60 based .rkt file I found, those should work. I'm thinking a PNC-60RL or PNC-60AH may work for the tailcone.

Click to expand...

Hey K'tesh, need a good drool? I'm personally proud of this one. Flew like a champion. Can't wait to see how CI's turns out. Samb said it best, these are sexy rockets.

Gary Byrum said:

Hey K'tesh, need a good drool? I'm personally proud of this one. Flew like a champion. Can't wait to see how CI's turns out. Samb said it best, these are sexy rockets.

View attachment 245943

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GB... You're right to be proud of that one...

Gary Byrum said:

Hey K'tesh, need a good drool? I'm personally proud of this one. Flew like a champion. Can't wait to see how CI's turns out. Samb said it best, these are sexy rockets.

View attachment 245943

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Very nice. I like how the red black came out.

Cl(VII) said:

Very nice. I like how the red black came out.

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Thanks. It's Duplicolor, Dark Cherry Met. I'm not a big fan of Duplicolor because it dries very brittle, but the shade was killer. The fins on both my Arapahoe's are balsa, and honestly, they're a real bear when you have to sand the root edge down to the tip to fit the boat tail nicely. It's so brittle down there. Neither of my boat tail or fin templates matched up very well because of the imperfect curves sanded on the boat tails. I turned both of them myself which is why they weren't exact. That's when my tenacity kicks in...lol

Starting to turn into a rocket. The main work has been getting all of the 16 holes that needed drilled into this rocket in place.

The first step was extending all lines from the fin can onto the air frame. This was easily accomplished with a piece of aluminum angle, which meant it was time for shear pin holes 3 each fore and aft.

To do this the fin can and airframe had to actually fit together. The coupler is ridiculously undersized, so three full wraps of heavy aluminum tape was used to get a nice fit and ensure centering. At this point the holes were drilled one at a time with the shear pins being inserted along the way to hold everything in place. The same was then done for the NC. These holes were placed in line with the large fins.


That took a lot of tape to make fit!

The insert for the aft rail button was also installed by drilling out the hole and carefully threading in the insert. I don't have one of those cool tools from doghouse rocketry for this, so I just put a couple nuts on a screw, thread that into the insert and tighten down the entire thing...works great, and the screw backs out fine when done.



The electronics bay for this rocket is fully removable to allow for easy setup. Therefore I have to hold it in there somehow. I decided to put a bracing ring of coupler aft of the bay for extra strength and to make it easier to line up the screws that will hold it in place by ensuring the proper depth. To this end a 1.5" piece of coupler was glued in place with Aeropoxy being sure to keep excess off the top edge, so the electronics bay will seat evenly.

Next I need a way to hold that bay in place and to retain the top rail button. I am using 8-32 screws for everything on this build so it is all standard and therefore easier. I made backing blocks from 1/4" Basswood by laying some sandpaper on the inside of the coupler and sanding the curvature into a long strip, then cutting them to length. Countersunk holes were drilled to accommodate the profile of the T-nuts, and these were glued in place with 5 min epoxy. The backing block for the rail button was rounded on the fore and aft ends to ensure no parachute snagging.



The rail button block was carefully smeared with 5 min epoxy and held in place with a screw while it set.



The electronic bay had to also be shimmed for a good fit with the airframe, so a triple thick payer of aluminum tape was applied fore and aft to provide a good seal against ejection gasses, and to help ensure there is no play in the internal to external vent hole alignment. The electronics bay was then slid into place and a single retaining hole was drilled. The bay was removed and a backing block attached with 5 min epoxy again held in place with a screw until set. The bay was then returned to the airframe, and held in alignment with a screw. The remaining holes for the retaining screws were drilled, and the backing block attachment completed. The bay was returned to the airframe, held in place with screws and (3) 3/16" vent holes were drilled. All holes for the electronics bay were drilled on the aft fin lines.



The remaining fore and aft compartment vent holes were drilled on the rail button line.



I have now exhausted all of the delaying activities, and I am going to have to do external fillets next. I plan to ground test my charges before the final strake fins are attached. They don't weigh much and shouldn't influence the deployment charge size, so I since they are surface mounted I'd prefer to keep them from being damaged in ground testing.

Extremely nice build thread. I have one of these planned and have all the parts, including decals. When I get to it, this will be a nice reference.

dixontj93060 said:

Extremely nice build thread. I have one of these planned and have all the parts, including decals. When I get to it, this will be a nice reference.

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Thanks very much. I look forward to seeing what you build as well. I have to ask, what diameter?

Cl(VII) said:

Thanks very much. I look forward to seeing what you build as well. I have to ask, what diameter?

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The same, 4".

External Fillets

Pretty straight forward stuff. I'm using Aeropoxy structural thickened with a generous portion of microballoons. I've heard this weakens the fillets, but the structural duty was handled with the internal fillets, so I went for convenience. A lot of microballoons was needed as the curvature of the boat tail ensures that there is no such thing as level, so the stuff needed to be thick. I use the widely employed method of taping off the fillet and pulling it clean with a curved item. I use a scoopula which gives me about a 5 mm fillet which is a nice aesthetic size, and for a rocket like this aesthetics is clearly the goal.

Ground Testing

It was beautiful today, so me and one of the short people took advantage of that to do some ground testing.

I made a couple 16' shock cords out of 1/2" diameter 5000# tubular Kevlar with two loops spaced about 1.5 ft from opposite ends. This is so the parachute is pulled from the Nomex by the fleeing parts on ejection...no intact burritos for me.

I refer to Vern Knowles ejection charge table, and up that about 20% for a first try. If you haven't looked a Vern's site you are missing out, lots of great resources there. Anyhow, the Main compartment is 10" so that would be ~0.9 g on the chart, so I went with 1.1 g...forceful, but not too frisky. The Drogue compartment is about 17" long plus the MM (which for this test was stuffed with a Slimline 38-54 adapter and an 38/360 AT case with a plugged forward closure, so basically sealed). The drogue compartment and empty MM volume suggested ~1.7 g, so I went with 1.8g because I didn't want to ruffle any of my neighbors. I let the neighbors next door know I was about to test charges as I was basically between our houses...they came out to watch. 1.8g gave a good ejection throwing everything free, but didn't fully extend the shock cord, this is surely because of sliding across the grass. I think I will use 2.0 g for flights though, the shock cords can surely take the stress. Now like a fool, I switched the chutes that go in the two sections, but those charges have plenty of frisky to handle that relatively insignificant change. Note: both events broke three 2-56 shear pins cleanly.

[video=youtube;nsUjyIEhVxs]https://www.youtube.com/watch?v=nsUjyIEhVxs[/video]

Do you have a rocksim or openrocket file?

qquake2k said:

I love ground testing!

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I do too, and my 3 year old who was pushing the button really enjoyed it. One of my neighbors who came out to watch the drogue test didn't really think about what testing charges entailed. My guess is she hasn't jumped that high in a couple decades.

Cl(VII) said:

I do too, and my 3 year old who was pushing the button really enjoyed it. One of my neighbors who came out to watch the drogue test didn't really think about what testing charges entailed. My guess is she hasn't jumped that high in a couple decades.

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:lol:

cwbullet said:

Do you have a rocksim or openrocket file?

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Yep, attached. It isn't perfect, and the real weights haven't been put in, but it gives the idea.

View attachment Arapahoe-J.ork

Cl(VII) said:

I do too, and my 3 year old who was pushing the button really enjoyed it. One of my neighbors who came out to watch the drogue test didn't really think about what testing charges entailed. My guess is she hasn't jumped that high in a couple decades.

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Isn't scaring old ladies mentioned in the safety code somewhere ? :wink:

samb said:

Isn't scaring old ladies mentioned in the safety code somewhere ? :wink:

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Considering I knocked on their door, and told them "if you hear what sounds like a small cannon don't worry that's just us" I considered her properly warned. They are really nice people, her husband has come to several launches with us and she wants to come out to one too, so she took the startle well. Also, they are comfortable with a mad scientist living next door. Which is a good thing, considering I do science experiments in the driveway with the boys...many of which are quite vigorous and/or loud.

Besides they have to be nice to me now, we always send Thanksgiving leftovers over and they want to be nice or no Cranberry/Cherry Pie this year. :no:

Cl(VII) said:

Considering I knocked on their door, and told them "if you hear what sounds like a small cannon don't worry that's just us" I considered her properly warned. They are really nice people, her husband has come to several launches with us and she wants to come out to one too, so she took the startle well. Also, they are comfortable with a mad scientist living next door. Which is a good thing, considering I do science experiments in the driveway with the boys...many of which are quite vigorous and/or loud.

Besides they have to be nice to me now, we always send Thanksgiving leftovers over and they want to be nice or no Cranberry/Cherry Pie this year. :no:

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Ha, very good. I figured you were a "well known" disturber of the peace. I can imagine you as the Doc Brown of the neighborhood in a few years !

Cl(VII) said:

Yep, attached. It isn't perfect, and the real weights haven't been put in, but it gives the idea.

View attachment 247427

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Thanks.

Stretch run! Modification of Tracker bay.

I recently received my EggFinders from Connor who assembled them, great service and totally worth it. I've been trying to figure out the best way to attach these and keep metal away from the antenna. I settled on cutting a 2" wide sled that goes to the tip out of 1/4" plywood. This was attached by modifying the removable bulkhead to use a U-bolt instead of an eyebolt. The eyebolt hole was plugged with a piece of dowel, and sanded smooth. Angle brackets were made out of aluminum angle, and the sandwiched between and held with two 8-32 screws...every screw possible in the project is 8-32 to make things less frustrating in the field.



I have multiple length antenna for the EggFinder with the longer being higher gain. To provide enough room for the longest antenna the aluminum brackets need a slot cut to allow for lower mounting of the EggFinder. I'm not in love with the clearances mounting this way, so the holes are there if I need them, but I will try my middle sized antenna first. The mounting holes for the Eggfinder are backed by PEM nuts. The antenna is additionally supported by a zip tie, and a 850 mAh 2S LiPo is zip-tied to the sled opposite the altimeter. This battery should give me 5-6 hours to find my rocket, and doubles as a nice 54g piece of nose weight.



Incidentally with only a 3 satellite signal the GPS is off by about 50 ft for my kitchen table. A minute later it had 5 satellites, and was within 10 ft. Nice product!

These are the last pieces that need to be attached for the rocket to be complete...very exciting, at least for me.

The Strakes have been clamped to my bench for over 2 months (to keep the little buggers from warping), just waiting for their moment. First the angled edge was rounded over on the belt sander, and everywhere else (except the bonding edge) got a quick polish with 320 grit to smooth it out some. Next the three with the most warping were taped together and cut to give the short fin can section of the strakes.



The long strakes were attached to the body tube first. To do this the strake centerline was bracketed by reference lines running the length of the airframe slightly over 1/4" apart. This is need for two reasons; one, the fin will obscure the center line and comes to the aft edge of the airframe, so there is no reference aft; two, the Magnaframe need roughed up significantly for anything to stick (I really prefer Blue tube, but I think I've already mentioned that) which destroys the centerline anyhow. The strakes were attached with 5 minute epoxy, which is more than strong enough. How do I know you ask, oh you know what I did. Yep, I attached the first two strakes flush with the forward end, i.e. backwards. ARRRRRRRRRRRRRGGGGGGGGGGGGGGGGHHHHHHHHHHHHHHHHHHHH! Much careful Xacto work, prying, cursing, and a Margarita resulted in the salvaging of the strakes with very minimal airframe damage. The strakes were then attached right way around.



The airframe and fincan were pinned together and the aft strakes aligned with the calibrated eyeball to the front strakes. Again 5 minute epoxy did the bonding work. No pics of this part.