New HPR build, "Epiphany"

[josepher44]

After almost 2 years away from rocketry, finally getting some free time this summer has gotten me back into it. After some work with some older LPR/MPR kits, I have decided to embark on my first scratch built HPR project since returning, in preparation for turning 18 and the possibility of Level 2 opening up.

I have designed a much modified "replacement" to a rocket i built 2 years ago, dubbed Kid Speedy. It was a stubby 5.5 inch design, with a 5 motor cluster, consisting of a central 54mm and 4 29mm outboard motors. Unfortunately, an adapter failure lead to a rather disastrous maiden flight, crushing 2/3rds of the body and causing more minor damage throughout the fin can.

Partially to work with the parts I have on hand, and partially to prevent this build from becoming a complete redo of Kid Speedy's, I have redesigned nearly all of the rocket. The motor mount is still a 5 motor cluster, this time with the central mount scaled back to 38mm. The body has been completely redesigned. The new design stands 8.5 feet tall, with most of that being 3" tube. The lower 2 feet are 4", with a fiberglass-covered foam transition in between. Since the motor mount doesn't quite fit nicely in the 4" tube, the 29mm mounts will stick out a bit through precut slots, and be "capped off" by aerodynamic foam and fiberglass end caps.

Although I am waiting for most of the parts to come in, I have been able to start construction of some parts of the rocket, namely the centering rings and adjustable noseweight system. Couple pics of that, with more to come in a bit.

Finally, I have a couple of questions.

1. Once everything is epoxied together, will the large amounts of slots being cut in the booster still be a weak point, or will the motor mount hold everything together well enough? If not, what kind of reinforcement here would you reccomend? Would this be a good project to go with a foamed fincan?

2. For ease of access/wiring, I was planning on mounting at the very least airstarting electronics, and possibly deployment electronics as well, low down in the rocket, just below the transition. Will the presence of the transition, fins, and 29mm motor mounts create enough aerodynamic disturbance that this is a bad idea, or will they be fine down there?

And some pictures:

The remains of Kid Speedy (ow...):



Rocket modeled in Autodesk Inventor:



Motor mount, minus Aft centering ring:



Pile 'o Parts:



Cluster centering rings (AKA ninja stars of death) laid out on 3/8" birch plywood:



29mm holes cut out (all cutting was done with a dremel circle cutter)



Finished ring, pre-sanding:




Enjoy! More to follow

 

[Buckaroo]

WOW :eyepop: That's a pretty impressive design there! Good luck!

Since I'm a recent convert to the high power ranks (had my Level 1 for a couple months now) you can take this for what it's worth, no harm, no foul

With respect to the booster: My initial thought was that the motor mount should hold everything together fine... But then I started thinking. If you load up the biggest motor combination possible you're probably talking about something in the "K" impulse range, and more than likely supersonic speeds. With that in mind, I would say that some foam in the booster section would probably be a good idea, and you should probably think seriously about glassing the fins at least.

With respect to the electronics: If you're using any kind of barometric device then you definitely don't want to have your static ports below the transition, and from the looks of it, the fins will probably create some problems with that as well. If you're using g-switches and timers for the airstarts you could put those anywhere, but I'd definitely put any static ports a little higher up.

Good Luck Man! Looking forward to more of this build op:

 

[josepher44]

Thanks for the advice! The plan for airstarts was to use dual perfectflite Minitimers with built in G-Switches, so those will remain mounted below. As for reinforcement, after talking to a few people, tip to tip glass on fins is planned, as well as probably foaming the fincan.

Now, onto build progress. Until my big box of tubes and honeycomb comes in from Giant Leap, I can't do much on the fincan. However, I was able to nearly complete the adjustable noseweight system.

Here is how I build one of these:

Cut base off a plastic nosecone, in this case a giant leap 3"



Cut a 38mm tube so that when seated against the inside of the nose, it is flush with the base.



Cut out or get 2 centering rings, one sized to fit within the shoulder of the nose, one slightly smaller.



Install 2 T-nuts in the larger ring



Epoxy the smaller ring to the tube...



...then place epoxy on the end of the tube, and the outside of that ring, and slide the assembly into the nose



Finally, epoxy the larger ring onto the end of the tube, and into the nose cone shoulder



BBs or other weights can then be slid into the 38mm tube, using a lightweight plug to keep them in place. This is held in place by screwing a bulkhead onto the top of the centering ring at the base of the nosecone, using the installed T-nuts

I hope to get started on cutting fins and the booster tube in the next few days.

 

[Firefox]

That is a beautiful looking design you have there, certainly more exciting than three fins and a nosecone. As for your questions...

Finally, I have a couple of questions.

1. Once everything is epoxied together, will the large amounts of slots being cut in the booster still be a weak point, or will the motor mount hold everything together well enough? If not, what kind of reinforcement here would you reccomend? Would this be a good project to go with a foamed fincan?

2. For ease of access/wiring, I was planning on mounting at the very least airstarting electronics, and possibly deployment electronics as well, low down in the rocket, just below the transition. Will the presence of the transition, fins, and 29mm motor mounts create enough aerodynamic disturbance that this is a bad idea, or will they be fine down there?

1. Slots in your tube can be weak points, but only if improperly cut and taken care of. When you cut slots in your tube for TTW fin mounts, the idea is to make youe fincan assembly one piece. Follow this idea with your 29mm motor tubes and it is possible you may build a stronger fincan than just a tube and fins. To this end there are a few things you may want to consider.
First build your fincan outside of your body, and cut your TTW slots all the way to the base,then fill in the slots behind your fins, leaving the aft centering ring out until you have everything epoxied together (though you may want to use it to line everything up). This allows you to make sure your MMT to TTW fin mounts are well joined and also allows them to be glassed if you wish. Of course, because your fins are the full length of the airframe, you may only want to do TTW fin mounts for the widest parts of the fin and surface mount the rest. This technique worked very well on a 3.71:1 upscale of an Estes Guardian (which has huge fin area) that my brother L1'd on at NARAM 50 on an H128. We plan on flying it tomorrow on another H or perhaps even an I. Will report on the results tomorrow evening if all goes well.
Secondly, fill any space between your 38 and 29 mounts with a piece of balsa or basswood and put good epoxy or woodglue fillets on them. This, again, helps pull all your parts into one high strength piece. You may also want to do this with the fincan outside your main airframe as with the fins to make sure you have room to work on it and do a good job. Glass is an option, though I doubt you would need it.
Lastly, make sure that your bonds between the main airframe and 29mm mounts are strong, inside and out. These are very wide slots and may be a source of problems unless well bonded back into a single piece. I think I might be starting to sound like a broken record player here.

2. Any change in aerodynamic cross section will cause high and low pressure areas to form around the changes. Positioning a barometric altimeter anywhere but behind a straight section of tube or a smooth nosecone is just asking for trouble. If you want to easily access your electronics bay, put it in its own section of tubing and put everything on a sled that can easily be slid in and out of that section of tube. Alternatively, you can cut your tube to access the electronics bay through the side of the rocket instead of the end.

 

[Handeman]

Very cool design! I like the clusters.

A couple of things I noticed:

1. The adjustable weight nose cone is almost a must if you want to fly on the whole range of possible motors from single 38mm to max sized 5x cluster. Great design on that.
2. Since you are using 38mm & 4x29mm, even with the largest Aerotech cases, 38/1080 and 29/360 (it look like the 29/360s might not fit) you are still talking about 2520 Ns total. That is still only a large K. With the required nose weight increasing with motor weight, I would be shocked if you ever had to worry about getting near Mach or having to deal with any fin flutter issues.

I didn't catch what you are making the fins out of. Considering the above, my advice would be to keep the fin can as light as possible, you're going to have a lot of motor weight there already. To that end I don't think I would glass the fins, I would make them out of 1/4" or 5mm plywood (to handle the landings with all that casing weight) and bevel the leading and trailing edges to gain some aerodynamics.

As for electronics, I would put the timers in a door in the 4" tube, use the top of the transition as the top of a zipperless fin can, and put the altimeters in an electronics bay about mid point on the 3" tubing.

Just my :2:

Looking forward to the build and flight reports.

 

[josepher44]

Thanks for all the advice, I'm definitely going to go with the idea for strips of wood to hold all the tubes together.

Handeman, as pictured in the first post, 29/360 casings do not fit, and the design were updated a bit back to extend the 29mm tubes about an inch.

The fins are going to be made in 2 pieces, both out of Giant Leap's 1/4" Nomex Honeycomb material. The forward pieces will be surface mounted, while the larger, rear pieces will be mounted TTW. Just to be absolutely safe, the rear portion of the fins will be glassed tip to tip.

Your idea for the electronics basically covers the current plan.

 

[Firefox]

After a few discussions with two veteran HPR fliers, I've heard some good advice that may apply to your rocket.
Last friday, my brother and I flew our 2.34 Guardian upscale on a Cesseroni I350SS (IIRC). Unfortunately, this was just too much motor for the poor thing, and the rocket shredded in flight. After much discussion with the HPR fliers who witnessed the event, we came to a few conclusions.

1. Normal epoxy can break down over many flights around a motor mount due to the heat from the motor. Wood glue and JBWeld do not have his problem. This and having fillets on the centering rings and fin mounts that were too small were deemed to be the reason for the shred. Glass in just the MMT and fin fillets would have likely prevented the failure.

2. The eighth inch plywood fins were not the source of failure, even as the rocket approached mach. Even with the large area of the Guardian's fins, there was little fin flutter. Of the nine fins on the rocket, only one was torn from the airframe, and this one fin was almost completely intact, and the plywood had little to no loss in strength.

 

[patelldp]

2. The eighth inch plywood fins were not the source of failure, even as the rocket approached mach. Even with the large area of the Guardian's fins, there was little fin flutter. Of the nine fins on the rocket, only one was torn from the airframe, and this one fin was almost completely intact, and the plywood had little to no loss in strength.

I pretty much guarantee you that the 1/8" fins were the source of the failure. The shred of that design (big, goofy, swept fins) was most likely due to your large fin span. Also, an I350SS (almost a full I) in a 3" rocket is going to be a pretty kick-butt flight to begin with. Big motor, coupled with large fin span, complicated by very thin, un-reinforced fins, I guarantee that those sources of failure contributed to your shred. The fin is intact because the fin joint failed prior to structural failure of the plywood.

 

[josepher44]

Although the rest of the parts have not yet come in, I was able to get a bit more work done. Specifically, the 4" tube is now slotted!

First, I marked the tube using an estes-style tube wrap, and a piece of angle aluminum:


All slots were cut using a dremel cutoff wheel:


The finished tube!


Another, more interesting view:


The narrow, shorter cuts are for TTW fin mounts, and the long, wide cuts are for the 29mm mounts

 

[Pantherjon]

:y: I have been following this thread and knew the plans for the cut-outs and have read comments that said things should be fine structurally..But, man, thats a lot of tube cut out around the motor section!:y: Just a question and a comment..Will you have a bulkhead in front of the 29mm tubes? I think it may be a good idea for one..I also think it will do well to assemble the motor cluster to slide in the booster tube-is this your ultimate goal?Epoxy the 29mm motor tubes to the central 38mm tube, have a solid bulkhead in front of the 29mm tubes with a 38mm hole in the center(yeah, in reality a 38mm centering ring), then slide the finished assembly into the tube then when you attach the fins do fintip to fintip fiberglassing..

 

[josepher44]

Yeah, this was the step that I was worried would really justify my fears about the strength of the tube.

Yes, the entire cluster/fin assembly will be assembled outside of the tube, and yes there will be 2 38mm centering rings in front of the 29mm motor mounts (the 38mm mount is 18 inches, the 29s are 14.) These will serve partially to seal off the timer bay, and partially to support the motor mount with an intact body. In addition, the lowest section of 3 inch tube will extend down into the 4 inch section. The end of the tube, and the lowest 3" --> 4" centering ring, will be bonded with the top of the motor mount. This will help lock everything in the booster together, and give the motor mount a firm connection point that does not look like its gone through a bread slicer. Tip to tip fiberglass, which will not only bond the fins to the body but also the outer portion of the 29mm mounts to the body, will further help hold everything firmly together.

 

[DAllen]

The finished tube!

It's a broom!

-Dave

 

[DRAGON64]

It's a broom!

-Dave

Looks like a Partyfavor...

 

[josepher44]

Well after a, um, very, long hiatus from this project for the competitive robotics season, I'm back to work on this thing! First flights are scheduled for NERRF 6.

Onto pictures now...


29mm Motor mount tubes, and balsa strips. They are an inch longer than in the originally posted drawing, and now comfortably accommodate 29/360 cases.



Dry fitted motor mount. The balsa strips were slipped into the 1/4 inch gap between the central and outboard motor tubes, not to provide strength themselves, but to give the epoxy a place to "rest" on, to form solid fillets between the two tubes. This space was necissary to design in, to make the centering rings 1-piece.



After applying JB Weld (chosen for heat resistance, considering how much motor could be firing off at once in this thing). The forward and aft centering rings were removed as the epoxy set up, the forward to allow me to mount the recovery harness, and the aft to allow the placement of internal fillets later in the build.



A close up. Yes i know I'm messy...




Soon to come is the start of the forward E-Bay, and the fins

 

[redsox15]

looking good so far...keep the pictures coming!

Looking forward to seeing it fly at NERRF (im going as well)

Matt

 

[JDcluster]

Why must everyone over use JB Weld? It primary purpose is for bonding metal or 2 dissimilar materials, not paper or cardboard. Paper to paper or wood to wood bonding should be done with wood glue or epoxy.
Save your $$$$ for more rocket motors.
JB Weld will not save your rocket from a burn through, so why bother?


JD

 

[Handeman]

I tend to agree with JD about the JBWeld. It's probably extra expense and extra weight.

I was reading through the earlier posts and you mentioned getting all the electronics in the lower 4" section. Having the air start timers there might be good, but with the heavy fin can, I would suggest having the deployment electronics higher up to shift the CG forward without having to add weight to the nosecone or bigger fins.

 

[cjl]

Why must everyone over use JB Weld? It primary purpose is for bonding metal or 2 dissimilar materials, not paper or cardboard. Paper to paper or wood to wood bonding should be done with wood glue or epoxy.
Save your $$$$ for more rocket motors.
JB Weld will not save your rocket from a burn through, so why bother?


JD

I agree. It has a few legitimate uses (such as the attachment of an Aeropack retainer), but for normal motor mounts, it is both unnecessary and heavier than needed.

 

[Sailorbill]

Why must everyone over use JB Weld? It primary purpose is for bonding metal or 2 dissimilar materials, not paper or cardboard. Paper to paper or wood to wood bonding should be done with wood glue or epoxy.
Save your $$$$ for more rocket motors.
JB Weld will not save your rocket from a burn through, so why bother?


JD

I agree with JD, JB weld is expensive and not necessary. If you get high enough temps in your fin can to damage regular epoxy you will have more problems than than even the JB Weld can handle. :shock:

 

[TheAviator]

Just for comparison, the maximum case temperature for any HPR motor is 200 degrees Celsius. I have heard from the manufacturers that cases rarely if ever get close to that hot. With regards to your MMT, even the H97, which is one of the longest burn 29mm motors, barely gets too warm to handle, and was cool after about a minute out of the rocket. That means that the case may hit 50 C at max temp, no where near enough to break down normal epoxy.

 

[cjl]

Just for comparison, the maximum case temperature for any HPR motor is 200 degrees Celsius. I have heard from the manufacturers that cases rarely if ever get close to that hot. With regards to your MMT, even the H97, which is one of the longest burn 29mm motors, barely gets too warm to handle, and was cool after about a minute out of the rocket. That means that the case may hit 50 C at max temp, no where near enough to break down normal epoxy.

Plus the epoxy is bonded to the outside of the motor mount, and the motor is on the inside. The motor mount itself is likely paper, fiberglass, or phenolic, all of which are quite good thermal insulators, and therefore, the outside of the motor mount (where the bond is) will not even get as warm as the motor will.

 

[josepher44]

Thanks for the advice on the use of JB weld, its a bit late for this project, but i'll be sure to keep it in mind for my next one. On the disastrous flight in the first post, it was suggested to me that heat melted the epoxy of the thrust ring of my homemade motor adapter, leading to the failure. Hence, I didn't want to take any chances at all with this one.

Anyways, the fins are now cut and mounted!

Template laid out on Giant Leap's 1/4" Nomex Honeycomb material



Suiting up Cutting was done with a dremel cutoff wheel, with a vacuum to take in the majority of the fiberglass dust.



1 fin..



4 fins!



The fins were then stacked together, held together temporarily with CA, and sanded to match each other perfectly.

I've never had the eye/patience to line fins up well freehand. So for this build, i decided to try building a jig to hold the fins in place. Here it is laid out on 1/2 inch plywood



Cut out (with a hole saw and bandsaw) and slipped over the motor mount



Fins starting to go on. At this point, they are simply tacked on with CA



All 4 on the rocket. The alignment jig worked extremely well, and I highly recommend this technique.



And the alignment jig removed




The "flat" front bit of each fin will be covered by the forward fin-strips, to be mounted once this whole thing is inside the 4" tube.

Next up will be epoxy fillets on these fins, and the beginnings of the upper (avionics) e-bay

 

[redsox15]

looks great!

what do you plan on flying it on?


Matt

 

[UPscaler]

Very nice project you have going. This is a nice rocket! Might I suggest you certify L2 with the J350. Then to celebrate crank it up to full K power with all those outboards?

 

[josepher44]

First flight will be single-motor, on something 38/480 or 600.

Afterwords though, I am defiantly leaning towards making a Level 2 attempt with this thing, on a J350 or J420. If that goes well, I won't have the casings/funds available to do a full-power flight just yet, but would send it up on something along the lines of a I600, 2 H97s, and 2 G53s, airstarted in pairs, with a J570+4 I200s flight later in the year.

 

[UPscaler]

Should be a sweet launch no matter what it's on!

 

[josepher44]

Done with school, back to work!

Moving upward in the rocket, I've been doing some work on the Ebays. Here's the progress on the timer bay so far, with pictures of the altimiter mount soon to come.

Note: This is my first time doing anything remotely like this. Any comments/advice on my design and construction would be greatly appreciated!


The rest of the rings. The top ring will be used to cap off the motor mount, while the two others will be used to secure the 3" tube inside the 4" booster. There will be about 6 inches of "overlap" between tubes, from the top of the 38mm tube to the top of the 4" tube



Lower 3" section cut, to be capped off with anti-zipper construction eventually.



To make the timer bay, I decided to squeeze it into the section in which the 3" and 4" tubes overlap each other, by cutting a segment out of the 3" tube and covering it with a thin sheet of plywood.

Super-fancy tube marking guide (AKA, a carefully measured paper rectangle)



Tube cut with a dremel, with dry fitted centering rings. There is 5.5 inches of vertical space between rings.



Plate beveled to match inside of 3" tube



And dry-fitted



This piece will remain on the rocket at all times. A second plywood piece will hold all electrical components, and be bolted directly to the first, to allow for easy removal.

Electronics board cut out



Starting to build the custom battery mount.



More progress



And more. The battery snaps are exoxied to the plywood.



All parts test-fitted



T-nuts and clearance holes installed on permanent plate



And everything on the tube! Just barely fits inside the 4" tube. I had to remove the top cover of the batteries, and will be installing a similar, thinner piece.



More to come, including sealing off the top and bottom of the bay, wiring through the motor mount, and a way to make the batteries not fall out the back.

 

[josepher44]

And while I wait for some parts of the timer bay to dry, here's the forward Ebay so far.

I am using a perfectflite HiAlt 45k, with redundant batteries. Standard allthread "sled" setup.

Start of the electronics sled



Battery mount framework



Completed battery mount + brass tubing



Flip side, showing rotary switch and mount.



All parts mounted. The piece of angle aluminum is removable, to retain the batteries (since that picture, its been re-drilled for a snugger fit)



Coupler tube, with 3" band for power switch and atmosphere sampling holes



Lower bulkhead, with allthread (to be glued into the coupler)



Upper bulkhead, to be glued to the top of the electronics sled, and held on the top of the coupler by two nuts over the allthread



The whole bay together outside the coupler



Now, a question. The upper bulkhead fits very snugly in the coupler, but there still seem to be some tiny gaps through which gas could theoretically get into the bay. What are some good ways to create a "seal" between this bulkhead and the coupler?

 

[Pantherjon]

A small section of door seal gasket the same length as the inner circumference of the coupler..Measure down inside the coupler the thickness of the BH and glue the strip in(actually make the measurement 1/16" or so short of the thickness of the BH) then when you 'button it up' you will get some compression on the gasket to fill the gaps..

 

[josepher44]

Some miscellaneous progress today, mostly on the booster:

The timer bay rests above the motor mount. To allow for motor ejection to be used as a backup, I designed the timer bay so that it would not interfere with the path of the motor's ejection. But since these gasses will run "behind" the bay, the timer bay has to be effectively sealed off from the rest of the rocket.

Bottom and top seal plates cut off a scrap 3" centering ring



cut plates



bottom plate installed



and top one



3 basswood spars were glued around the 3" tube, to provide a bit more stability around the hatch area.



Looking down the top of the tube, when placed on top of fincan.



Next up was the booster bulkhead. I elected to use an anti-zipper design here. Here's the half inch bulkhead, with forged eyebolt and ejection gas vent holes.



And installed in the coupler.



After a hard lesson about storing reinforced phenolic airframes with 8 gigantic slots on the top of tall bookshelves, I decided to try out blue tube 2.0 for the re-made booster airframe. Its great stuff.



Put it all together and....



Hey, its starting to look like something!

After installing airstart conduits and cutting out the timer bay access hatch, all of this should be glued together sometime this week.