BD Tyrannosaur Build

So it's about time this thing gets started. I bought the Tyrannosaur by Binder Design over a month ago, but I have been swamped with other crap that I had to do. Every night I've been dreaming (literally) about this rocket. This will be by first HPR build, so I'm pretty nervous. I want to document this build because I can't find much on this forum about the Tyrannosaur and because I would love the insight from this community as the build progresses.

So here are the obligatory pictures of the parts and of the dry-fit:



I can tell you that thus far I've been very impressed by the kit and by Binder Design, as a whole. The parts appear to be high quality (though I don't have much of a point of comparison), and Mike was really helpful through the whole purchasing process. The best part of this kit is the detailed instructions--they should be very helpful for a HPR newbie like me.

I agree that Mike is very helpful when it comes to supporting his products. The instructions are top notch, and the quality of the parts are too.

I wouldn't be surprised at all if he'll weigh in on anything you might have an issue with.

Thats a helluva good comibnation you have there Binder and Loki :headbang:

My friend built this kit. Its big ...7 feet I think or slightly taller??

@ Afterburners: It's a really tall rocket. With the electronics bay it should be 7' 5".

I spent a few hours this afternoon beveling fins using a finishing sander (100 grit). This is going to take a while. I may run out to get some 60 grit pads for the sander to speed the process up tomorrow.

So here is my first question....the instructions call for cutting out the tabs between the fins and then mounting the fins to the motor mount. The airframe would then have to be patched with Bondo. It seems to me that this would ensure that the fins are secured to the motor mount but that the airframe would be weakened. I'm also concerned about the patching step; it seems analogous to repairing a hole in a wall--and I suck at drywall.

I've seen others on this forum attaching fins by drilling small holes near the fin slots and injecting epoxy with a syringe. Do you guys have some advice about this step? I'm hoping to start attaching fins tomorrow night.

BDB said:

@ Afterburners: It's a really tall rocket. With the electronics bay it should be 7' 5".

I spent a few hours this afternoon beveling fins using a finishing sander (100 grit). This is going to take a while. I may run out to get some 60 grit pads for the sander to speed the process up tomorrow.

So here is my first question....the instructions call for cutting out the tabs between the fins and then mounting the fins to the motor mount. The airframe would then have to be patched with Bondo. It seems to me that this would ensure that the fins are secured to the motor mount but that the airframe would be weakened. I'm also concerned about the patching step; it seems analogous to repairing a hole in a wall--and I suck at drywall.

I've seen others on this forum attaching fins by drilling small holes near the fin slots and injecting epoxy with a syringe. Do you guys have some advice about this step? I'm hoping to start attaching fins tomorrow night.

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Thats the method I use, the injected fillets. However, I have recently learned of a method for making "fin pockets" basically its just a thin wood dam applied to the motor tube on each side of the fin allowing the mmt to be fully assembled and slid into place then some epoxy placed into the pocket that has been created and the fin inserted. I am planning to use this method for my L3 rocket.

The way the aft ring is mounted it is a double ring so the thickness of the two rings fills in that gap. At least that's how I remember it.

The trick to the injection holes is to drill them inside the radius of your intended external fillet. Way inside. I saw a build thread where the builder didn't drill next to the fin, but instead, before the fin was installed, cut short slots perpendicular to the fin slot. These were short, so they would be well inside the radius of the external fillet. Just be sure they are big enough for your syringe.

AfterBurners said:

The way the aft ring is mounted it is a double ring so the thickness of the two rings fills in that gap. At least that's how I remember it.

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Correct, and if you save the paper tabs you cut out of the airframe, you just tack them back on, problem solved. There will be no Bondo needed, if there were a need for it, the instructions would say so.

Regarding the other advice offered, these individuals have likely not built a newer Binder Design kit. These kits go together much differently than your standard rocket kit. They don't need injection for internal fillets because the whole fin assembly slides out of the rocket and you can get to everything real easy. One centering ring goes between the fin sets to fill that gap and if you save the tabs you cut out, same as the ones at the rear, you just tack them back on to the exposed ring surface to fill the tab holes.

Just follow the directions, it is really that simple. Binder Design kits are well engineered and I spend about a month putting together each instruction set. The only thing I might suggest doing differently than the instructions is to use a good wood glue for all paper/wood bonds instead of epoxy.

We are the only HPR kit manufacturer to utilize the "modular fin can" assembly process in our instructions.

BDB said:

So here is my first question....the instructions call for cutting out the tabs between the fins and then mounting the fins to the motor mount.

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Please read the instructions more carefully. The fins are tacked to the motor tube first. After they are set up, then the tabs are cut and the whole assembly is slid out and all fillets are applied. Save the tabs for tacking back on to the rings later to fill those small gaps.

Thanks Mike. I wasn't thinking of how the rings will support the tabs after they are inserted. I'll give the modular fin can method a shot tomorrow.

See... What did I say? Thanks for proving me right Mike!

BDB said:

Thanks Mike. I wasn't thinking of how the rings will support the tabs after they are inserted. I'll give the modular fin can method a shot tomorrow.

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Glad to help. If you have anything else you are unsure of, hit up our e-mail and we'll get it figured out.

Binder Design said:

Correct, and if you save the paper tabs you cut out of the airframe, you just tack them back on, problem solved. There will be no Bondo needed, if there were a need for it, the instructions would say so.

Regarding the other advice offered, these individuals have likely not built a newer Binder Design kit. These kits go together much differently than your standard rocket kit. They don't need injection for internal fillets because the whole fin assembly slides out of the rocket and you can get to everything real easy. One centering ring goes between the fin sets to fill that gap and if you save the tabs you cut out, same as the ones at the rear, you just tack them back on to the exposed ring surface to fill the tab holes.

Just follow the directions, it is really that simple. Binder Design kits are well engineered and I spend about a month putting together each instruction set. The only thing I might suggest doing differently than the instructions is to use a good wood glue for all paper/wood bonds instead of epoxy.

We are the only HPR kit manufacturer to utilize the "modular fin can" assembly process in our instructions.

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I agree with you on the wood glue. I see no need for epoxy when gluing these types of materials together. Why people use epoxy for wood and paper materials is beyond me. The rocket looses it's performance because of the increase in weight. I just don't get it. Fiberglass, plastic, carbon fiber yeah use epoxy

BDB said:

Thanks Mike. I wasn't thinking of how the rings will support the tabs after they are inserted. I'll give the modular fin can method a shot tomorrow.

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Please take (and share) lots of pics of the assembly to help us visualize how the modular fin can works. I'm sure I understand how it works, I just want to confirm my ideas.

AfterBurners said:

I agree with you on the wood glue. I see no need for epoxy when gluing these types of materials together. Why people use epoxy for wood and paper materials is beyond me. The rocket looses it's performance because of the increase in weight. I just don't get it. Fiberglass, plastic, carbon fiber yeah use epoxy

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The only reason our instructions call for use of epoxy is because it provides a faster build and gets the flier comfortable with using it so that when the time comes for L3 or composite bonding it is not a new thing to them. All of our newer kits use construction techniques that can be transferred to L3 rockets. In fact, we do have a couple of L3 capable kits in the works that will teach composite layup in the instructions.

But yeah, wood glue is the ticket for a strong, light build for wood and paper materials.

This rocket is on my VERY short list when I move up to a 54mm mount. I will be watching with great interest!

Things are progressing slower than I expected. I had hoped to make considerable progress over the long weekend. But I ended up working a bunch at another house. (Crappy landlord stuff ruined my vacation.) I finally finished beveling the fins tonight.

I started by marking guidelines 1/4" away from the edges that I intended to sand. I then rounded the edges using a mouse sander with 50 grit paper. It was pretty cool watching the lines appear from the plywood. I used them as a guide, trying to make it look like the lines on a contour map. I will probably sand everything once more by hand with 120 grit paper, but I'm relatively happy with how they turned out.



My goal is not performance with this kit. (That is what the Mongoose 54, my next HPR build, is for.) I just want to familiarize myself with HPR techniques and earn my L1. I just rounded the fins, but I am planning to use 30 min epoxy throughout, just so I can familiarize myself with it. I'm also considering tip-to-tip fiberglassing for the fins. I doubt this is necessary, though the instructions mention that it might be a good idea if I ever wanted to fly it on K motor. We'll see about that when the time comes.

The other rocketry-related activity that I accomplished this weekend was assembling an Eggfinder RX. I'm just posting a picture here because I'm a little proud of it. Those were by far the smallest components that I have ever soldered.

BDB said:

I'm also considering tip-to-tip fiberglassing for the fins. I doubt this is necessary, though the instructions mention that it might be a good idea if I ever wanted to fly it on K motor.

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No need to glass. K's are no problem. I have to update our instructions. That's in our instruction template from when we were using 5 ply 3/16". This 1/4" 12 ply will take an M with no glass on the fins.

Finally had some time to build last night. I'm always paranoid about my fin alignment, so I attempted to construct a guide from an old piece of hardboard that I had in my garage. I copied the alignment guide from the back of the instructions, glued it to the hardboard, extended the fin lines by tracing around the root edges of the actual fins and then cut it out with a jig saw. It came out ok, though I have to shim the tube in a few places to make sure that it is centered in the guide. Now that I'm finished with the first set of fins, I think I probably could have done just as well by sighting down the fin can like the instructions describe.



I had previously glued the thrust ring to the motor mount tube and the aft centering ring to it. Trying to follow the instructions to the letter, I tacked a centering ring ~1/4" from the front of the motor mount. After sanding the rings a little and roughing up the surface of the MMT, I was able to get the motor mount to fit into the slotted air frame, but the CA didn't hold the front CR on very well. It snapped free as I inserted the MMT. I just stuck a pencil through the fin slots and worked it towards the front of the MMT because it was only there to hold the MMT straight while the fins were attached--it was going to come back out in a little while anyway. I also had to increase the length and width of the slots in the air frame by about 1/16" with a Dremel to get the fins to slide in. (Even then, it was still a little tight. Maybe I should have sanded the fins a little more.)



Next I mixed up a little bit of 5 min epoxy (The instructions called for 15 min, but I only had 5 and 30 min stuff.) and used it to secure the root edge of the fin to the motor mount tube, being careful to not drip any glue that could accidentally adhere the air frame to the fin. This worked quite well, though I should have probably sanded the slots just a little more to allow the fins to slide a little better. My hack-job fin alignment guide worked pretty well too.



After letting the epoxy cure for ~ 15 min, I rotated the air frame 120 deg and repeated the procedure. Later I discovered that I did tack the body tube to the fin in one small spot, but it was easily freed with my knife blade. Overall the process worked well. Like I said earlier, my alignment guide worked well, but I suspect that you could do nearly as well by just putting the printed guide on the floor and sighting down the tube.

Now for the part that made me lose sleep (literally). I cut small tabs out of the airframe to extend the slots to the end of the tube. This worked fine using a sharp Exacto blade. Per Mike's instructions, I saved the little tabs in a Ziplock bag for later. It took a little wiggling, but I then slid the MMT and the fins out of the back of the airframe. Because the front CR was already loose, I had to reach in and pull it out separately.



Then disaster struck! Well not really, but I did gasp when one of my fins snapped off as I pulled the fin can out of the airframe. The instructions say that the fins are only supposed to be tacked into place at this point--the internal fillets are what really provide the strength. But apparently one of the fins had not made good enough contact with the MMT. While this sucks, it's best that I caught it now. Honestly, if I hadn't pulled out the fin can, I would have never known that I had a poor quality bond. I just scrapped the epoxy off the MMT and the fin's root edge, applied fresh epoxy and then re-inserted the fin can into the airframe. I used 30 min epoxy this time to make sure that the sucker formed a strong bond, and I let it sit overnight. (I'm just using the Bob Smith brand of epoxy for now. I ordered some Rocketpoxy on Black Friday, but it hasn't arrived yet.)



The next morning (after dreaming about fillets) I woke up early to ostensibly help my daughter study for a history test. Luckily I was able to multi-task, so while quizzing her on Chinese history (Amazing what they teach now; I'm sure I was never taught that stuff.) I pulled the fin can out again and started the fillets. I slid the CR that had been previously sanded to fit into the airframe to the front of the fins and attached it using a thick fillet of 30 min epoxy. I then systematically applied the internal fillets. One of the fins, the one that had previously broke off, was attached a little worse than the others. This was evident because the epoxy for the fillets leaked through a few gaps in the root edge and ended up on the other side of the fin. I used some blue painters tape on the back side of the fin (opposite the side I was filleting) to keep the epoxy from running through these small gaps. The other fins were fine. I hope that one doesn't come back to bite me.



Thanks for reading this lengthy post. I'll work on the front fins later this week.

Now for one question...I've never worked with this kind of phenolic tubing before. As I was working last night I realized that the spirals in the tubing are pretty large. Do I need to fill them with wood filler or bondo or can I get by with a high fill primer at the end? Thanks.

I believe Binder uses a Loc type cardboard airframe which is not phenolic, treat it the same way you would Estes tubing for filling the grooves either primer and spot and glazing putty or CWF.

You are right--this is LOC-type tubing. Being a HPR newb, I apparently don't know what phenolic is yet. I just thought this stuff sure looked better than Estes stuff.

It is most definitely better. When you get to larger diameters, the walls have to be thicker and the tolerances have to be closer. Not to mention, Estes tubing would never hold up to the speed and pressure a full HPR motor would put on it.

Kruegon said:

It is most definitely better. When you get to larger diameters, the walls have to thicker and the tolerances have to be closer. Not to mention, Estes tubing would never hold up to the speed and pressure a full HPR motor would put on it.

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A stock build Loc Magnum 3E will take an M class motor when built stock, nothing fancy but it will do it. Binder Design's rockets will probably do a M just fine as well, but that's Mike Fisher's call, he knows the capabilities of his designs better than any of us and he uses the best quality parts in his rockets.. Someday I will own a couple of his rockets for my fleet and the Tyrannosuar, Velociraptor, and Excel DD are on that list.

Last night I started building the avionics bay. It went together quickly and painlessly. I'm planning to fly with full dual deploy and an Eggfinder TRS for my L1 cert flight, which probably won't happen until the early spring. Eventually, I hope to mount a GoPro too.



Between now and then, I want to take my time building and finishing this thing. (Though my wife is getting sick of it occupying the dining room table.) I have some ambitious ideas about the paint job, but it is already too cold to paint here in New England, plus I don't want to jinx the finish by telling you guys just yet.

Overall, I'm glad I bought the avionics bay kit from Binder Design. Not to sound too much like a commercial, but it includes nearly everything that I need, even an arming switch, which is really helpful for a noob like me. I will just need to find something to use for a sled and some PVC caps or centrifuge tubes to use for the charges.


So now for two questions....

1) Vent holes for the altimeter. I've seen others discussing this on the forum, but I don't know what the consensus is. How many holes and what size to I need?

2) I'm steadily heading towards installing the recovery gear. The kit came with a nylon harness, but I know that most people here use kevlar. What are the pros and cons of kevlar over nylon?

Thanks.

BDB said:

Last night I started building the avionics bay. It went together quickly and painlessly. I'm planning to fly with full dual deploy and an Eggfinder TRS for my L1 cert flight, which probably won't happen until the early spring. Eventually, I hope to mount a GoPro too.

View attachment 277529

Between now and then, I want to take my time building and finishing this thing. (Though my wife is getting sick of it occupying the dining room table.) I have some ambitious ideas about the paint job, but it is already too cold to paint here in New England, plus I don't want to jinx the finish by telling you guys just yet.

Overall, I'm glad I bought the avionics bay kit from Binder Design. Not to sound too much like a commercial, but it includes nearly everything that I need, even an arming switch, which is really helpful for a noob like me. I will just need to find something to use for a sled and some PVC caps or centrifuge tubes to use for the charges.


So now for two questions....

1) Vent holes for the altimeter. I've seen others discussing this on the forum, but I don't know what the consensus is. How many holes and what size to I need?

2) I'm steadily heading towards installing the recovery gear. The kit came with a nylon harness, but I know that most people here use kevlar. What are the pros and cons of kevlar over nylon?

Thanks.

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1) I prefer an odd number of holes usually 3 or equal and in line with my fins, size is dependant on the size of the Av-Bay and what your altimeter recommends, if no recommendations then I use https://www.vernk.com/AltimeterPortSizing.htm Usually I make one of the holes slightly larger to allow access to my altimeters switch.


2) As for the difference between kevlar and nylon, the nylon will require more protection than kevlar from the heat of the ejection charge, lots of people use a kevlar sleeve over the first few feet of the nylon harnesses or even tape will protect it from the charge. Kevlar is more flame/heat resistant therefore mostly I don't add any additional protection to the kevlar harness beyond using a hand full of dog barf on top the ejection charge and under the chute protector. I when possible wrap my chute protector around the chute and as much harness as I can, since kevlar harnesses will still wear out sooner or later. Nylon has better shock absorbing because it has a small amount of stretch, Kevlar has little stretch therefore you may want to z-fold and tape the harness to prevent shocks to the recovery system (I would do this anyways for nylon or kevlar). Kevlar is also stronger for a given size so a 1" wide nylon can be replaced by a 1/2" wide kevlar of the same length and it will pack into a smaller area, I use a 1/4" Tubular Kevlar Harness on my 3" Frenzy XL clone that weighs 6.5lbs loaded with no issues. Checkout OneBadHawk's harnesses and recommendations, Teddy knows his harnesses.

rharshberger said:

A stock build Loc Magnum 3E will take an M class motor when built stock, nothing fancy but it will do it. Binder Design's rockets will probably do a M just fine as well, but that's Mike Fisher's call,

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The fins will do M without glass, the airframe would need double wall with couplers or a wrap or two of glass. I've seen them go up on L's with stock airframe but I wouldn't suggest putting an M in a stock build. Even the L is pushing it. For liability reasons, I recommend K as maximum for the stock version.

Binder Design said:

The fins will do M without glass, the airframe would need double wall with couplers or a wrap or two of glass. I've seen them go up on L's with stock airframe but I wouldn't suggest putting an M in a stock build. Even the L is pushing it. For liability reasons, I recommend K as maximum for the stock version.

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Thanks Mike that's good to know.

BDB said:

I also had to increase the length and width of the slots in the air frame by about 1/16" with a Dremel to get the fins to slide in. (Even then, it was still a little tight. Maybe I should have sanded the fins a little more.)

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My apologies. We're still fine tuning our CNC slotting process and getting better at it with every tube. I'd rather send them out a bit tight than with gaps. Thanks for letting me know about this, I'll check my machining files.

@Mike Thanks. It wasn't a problem at all. The only complaining came from my wife who didn't like the sound of the Dremel resonating through the tube.