Level 3 Build - Rocketry Warehouse Terminator

I plan on foaming the Fin can on my T5. I did this on my RW all american and it worked great.

Sanding fun. 150 grit then 340 grit on the bevels. 60 grit on the fin roots to make sure I get a good bond. I'll be doing this for a while.

EeebeeE said:

A question:

What is the benefit of using threaded rods to hold CRs together. I don't see it, but I know people who swear by them. I am trying to determine if I need to do that because it will make a process to do internal fillets very difficult.

For my internal fillets, I want to tack the fins into the slots using 15 minute epoxy. I will temporarily fit the CRs in place, then temporarily slide the MT in place. Then I will glue the fins...only at the slots. When they are aligned and glued in place, I will slide out the MT, take out the CRs. and have a lot more free space to apply Rocket Poxy internal and external fillets. When that is complete, I will then glue CRs and MT into place. I will repeat the process for the tailcone fins.

Having threaded rods would make it difficult to effectively do this. Do I really need them?

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I had never even considered using threaded rod like that. I used plenty of strong epoxy in the fin area, no issues at all.

watermelonman said:

I had never even considered using threaded rod like that. I used plenty of strong epoxy in the fin area, no issues at all.

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As long as you have a strong bond to the walls and a good bead of RocketPoxy around the CR's I don't see how they would come out. But I've known L3 CCs who practically demand them.

EeebeeE said:

As long as you have a strong bond to the walls and a good bead of RocketPoxy around the CR's I don't see how they would come out. But I've known L3 CCs who practically demand them.

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Yeesh, probably the same guys who demand 18 or however many switches too.

For the record I landed my L3 project on drogue. Not for the certification flight, obviously, but still. It held together, and flew again without repair.

Someone correct me if I'm wrong, but I believe the majority of the thrust is on the thrust plate (hence the name), which is often the aft CR. The other CRs just keep the motor centered (hence the name again). I really like Mike Crupe's idea of a stepped thrust plate that fits half inside the booster, and half butts up against the booster. Two-part foam in the fin can before you put the thrust plate on holds the fins in there pretty much ... forever.

Anyway, as long as your thrust plate is firmly affixed and can take the force of the motor, then I don't see a need to allthread the CRs together. Good sanding and good epoxy win the day.

On large rockets with heavy boosters (or boosters with heavy motor hardware), I use threaded rods between the rings to distribute the separation forces on the booster during apogee and main deployment. With just an eyebolt in the top ring you are depending on that one ring to support the load. With the rods, the load is transferred to all the rings the rod passes through as long as nuts are applied at each location. Without the rods, I'm sure some of the load is being transferred through the motor mount tube but you're relying on epoxy connections vs. steel or aluminum.

I had to cut off 1" of the boat tail because it was too narrow for the retainer. Now I'm thinking that the CR for the boattail could be mounted on the surface of the boattail with a small buildup of FG behind it, and it could act as a thrustplate. I would create a bevel with my Dremel so it could sink into the boattail and sit flush. The boattail is FG and it is 1/8" thick, so there is room to bevel it out.

The photo should give you a sense of what I mean, but the motor tube of course would be flush with the CR.

Scott S said:

On large rockets with heavy boosters (or boosters with heavy motor hardware), I use threaded rods between the rings to distribute the separation forces on the booster during apogee and main deployment. With just an eyebolt in the top ring you are depending on that one ring to support the load. With the rods, the load is transferred to all the rings the rod passes through as long as nuts are applied at each location. Without the rods, I'm sure some of the load is being transferred through the motor mount tube but you're relying on epoxy connections vs. steel or aluminum.

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That makes sense. I'll have to think about this some more.

Scott S said:

On large rockets with heavy boosters (or boosters with heavy motor hardware), I use threaded rods between the rings to distribute the separation forces on the booster during apogee and main deployment. With just an eyebolt in the top ring you are depending on that one ring to support the load. With the rods, the load is transferred to all the rings the rod passes through as long as nuts are applied at each location. Without the rods, I'm sure some of the load is being transferred through the motor mount tube but you're relying on epoxy connections vs. steel or aluminum.

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Good point. I was totally thinking thrust and not recovery stress.

In lieu of threaded rod, glue a Y-harness to your motor mount. Use 1in flat Kevlar strap [4500 lb.].

Light weight..proven. I have used them on 8in diam. rockets with 6in motor mounts weighing 150 lbs.
Top of this page, there is a sticky about building a 3in DarkStar with details on how to do. Just scale it up.
Harness should be designed to barely stick out of fin-can & recovery gear attached to it.

Ps if you have room in your added weight situation.....toss in a six-pack or some booze. Kill 2 birds with one stone & something to celebrate with after recovery!!!! LOL

EeebeeE said:

I had to cut off 1" of the boat tail because it was too narrow for the retainer.

View attachment 279834

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I used a RA75P retainer, didn't shorten boat tail, fits well and look like it designed for it.

robbdm said:

I used a RA75P retainer, didn't shorten boat tail, fits well and look like it designed for it.

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Nice! That's exactly what I want mine to look like.

robbdm said:

I used a RA75P retainer, didn't shorten boat tail, fits well and look like it designed for it.

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Pretty cool, but I am on a budget. I already have a flanged retainer, which is why I decided to cut the tailcone by 1". This is what mine should look like. Not as streamlined as yours, but close.

robbdm said:

I used a RA75P retainer, didn't shorten boat tail, fits well and look like it designed for it.

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Pretty cool, but I am on a budget. I already have a flanged retainer, which is why I decided to cut the tailcone by 1". This is what mine should look like. Not as streamlined as yours, but close.

View attachment 279964

Opted to go with threaded rods. So I drilled 3 1/4" holes. The rods will sit between the fins. Found a 3/8" u-bolt that could handle 6,000 PSI at Lowes. ice thing is that it is pretty long, so I can extend it forward enough that I can reach it from the forward end of the motor assembly. The reach inside the airframe to the shock cord is now about 21", and I should be able to reach in there to tighten a quick link. The u-bolt is 3/8" and is capable of 6,000 PSI of stress, so I should be OK.

I would lower the u bolt some. More thread on the the inside.

The u-bolt will hold but will the CR hold? You might want to also install a kevlar Y harness glued to MMT.

The three holes on the CR are for threaded rods. I decided to go with them. Between them the glue joints of the fin roots, and the bead of glue around the CR's, everything should hold in place. The U-Bold will straddle one of the fins, so there will be additional glue in place right at the base of the U-Bolt. Also, It doesn't make a difference in the hold if it is threaded all the way down or not. If the nut gives way, it will give completely away and will strip before the bolt does. The most likely scenario however is that the CR will break, because its shear strength is not as strong as the U-Bolt's. THis U-Bolt is 3/8" stainless steel, rated at 6,000 PSI. It is without doubt the strongest part of the recovery system.

With that in mind, I kept the U-Bold long for three reasons:

1. Reaching inside to connect the quick link. requires a 24" reach to the CR, which is the limit of my arms. So having the U-Bolt stick up about 3" makes it easier to attach and detach the shock cord.

2.The motor tube is right there. I want it to extend forward by a half-inch or so to get a good bead of glue around it. That would also make it more difficult to attach and detach the shock cord. Structural integrity is critical, but so also is functionality.

3. Without the motor tube in the way, even if I use a longer motor case, I will have room for a larger and stronger quick link. I was concerned that only a 1/4" link would fit (800 PSI strength) between the airframe and the MT. Now a 5/16" can, and that is about 2x as strong. My shock cords can handle 1,500 PSI, so I want every part of the recovery system to be about that strong. Doesn't make to have that strong of shock cords if your quick links can't handle the pressure.

Next steps.

To understand how this is done, I should line-item how the fincan gets assembled.

1. Add threaded rods to forward CR.
2. Glue forward CR into place.
3. Glue Boattail CR in place.
4. Dry fit Aft CR.
5. Slide, but not glue motor tube into place.
6. Dry fit boattail into place
7. Tape boat tail into place to ensure tight fit.
8. Glue forward fins in place only at fin slots.
9. Glue aft fins into place.
10. Remove boat tail.
11. Remove aft CR and motor tube.
12. Glue internal and external fillets on fins.
13. Glue motortube into place.
14. Glue boattail into place.
15. Fill aft area around motor tube with FG and epoxy.
16. Cut off excess Motor tube.
17. Sand and finish. then add Aeropack flange retainer system.

Makes a lot more steps, but there will be a lot better glue connections as a result.

So here are first steps photos of gluing the forward CR with threaded rods into position, then gluing the first fin into place. The first photo is a dry fit to determine where nuts should go onto CR. when it is glued into place.

View attachment Terminator 5 Level 3 Cert..ork

Evan,

I think you may have entered in the mass of only one fin for each fin set? I'm not sure, but I am in the process of making my cert package for my L3 attempt, and I made my own OR. I have added a whole lot of little things to my OR file, such as eyebolts, nuts, and washers. A little overkill for an OR file probably, but I wanted to make sure I did a good job. Getting to the point, my Terminator sims to 9,500 feet, without the added weight of epoxy. I'm not sure how much epoxy I'll end up using, but usually I overdo it a bit haha. If I use 1kg of epoxy, my Terminator sims to under 9k. I'm dealing with the same 10k waiver restriction because my local field's waiver is only 10k too. Anyway, I've attached my OR file to this post (hopefully if I attached it right!). I've used your mass for nosecone and the fin lower airframe section because I can't measure anything over 1kg accurately.

Anyway, can someone take a look and tell me what you think? Advice? Suggestions?

You might consider a second U-bolt, opposite the one you have, and use the previous suggestion of a Y harness between them. This will accomplish several things...

The "extended" position of the single U-bolt gives it a large moment of leverage. Hit it with the forces some of these things see, and it will try to bend. That's when you're gonna bust that c/r. I had a 4" project once that pulled the threads out of the nut on a 5/16" quick link, and pulled the link out straight. Nasty.

It spreads the load. Only half as much force on each one is less likely to bust out that c/r. Also, putting it opposite the current U-bolt, it will straddle one of your thru rods. Stronger than the moment of leverage that you have putting it farther from the thru rod.

Once you reach in and attach the Y harness with quick links, top of the Y harness sticks out the top of the booster tube. Easier to attach and remove the main harness as needed for transport and/or prep.

Edit: Ever consider attaching the main harness to the forward closure of your motor? A cast eye-bolt, jam-nutted to the forward closure, will be the strongest point in the entire bird, and eliminate the need to reach inside to attach the harness. Just drop the end thru the mmt, attach, and slide in the motor. Bingo.

Talk to your L3CC/TAP about all of this.

BTW... My sig doesn't say it, but I am a former L3CC. Gave it up due to health issues.

Just reweighed my aft fins. Checked against the specs and they were right. Made some adjustments to other components as well.

BTW, Open Rocket has you add fins as a set with a combined weight for all of them. The forward fin weigh 33 oz. The aft weigh 21. When I initially added the threaded rods as a cluster set of in inner tubes I calculated the combined weight as well, but just discovered that the program calculates each mass individually instead of the set as the program does with the fins. So it was way overstating that weight. That error was corrected.

Right now, the booster section has the airframe, CRs, Forward fins, CRs, boat tail, U-bolt, and threaded rods in place, and it weighs 157.6 oz. (9 lbs. 13.6 oz.) Some of those components are not glued in and I do not yet have the fillets done, so probably about 6 oz. or so needs to be added on top of that.

My sim, with smooth paint and airfoiled fins (bevels on the fear fins facing aft) currently shows 16,808’ altitude on an M2245.

This is the latest version of the OR file with weights and lengths adjusted accordingly. I will continue to make these weight adjustments as I build, although I will run up against the limit of my scale once the aft fins are in place, so I will have to rely on estimates from this point forward on the booster.

View attachment RW Terminator 011816.ork

cherokeej said:

You might consider a second U-bolt, opposite the one you have, and use the previous suggestion of a Y harness between them. This will accomplish several things...

The "extended" position of the single U-bolt gives it a large moment of leverage. Hit it with the forces some of these things see, and it will try to bend. That's when you're gonna bust that c/r. I had a 4" project once that pulled the threads out of the nut on a 5/16" quick link, and pulled the link out straight. Nasty...

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That's a good thought, however I cannot make the change now that everything is glued in place. Also consider the following points.

1: I had thought about that as well, but the U-bolt base is 24" inside the 5" airframe. The maximum angle that it can be bent to is about 12 degrees. (Sin (5/24)=.20683 = 12 degrees.) because at that point the shock cord will be against the airframe on the opposite side. Actually it is less than 12 degrees...more like about 9-10. The bulk of the force will still be pulling out, vs. pulling laterally, until the airframe zippers, which is hard to do with filament-wound G12 FG. If the U-Bolt was not in so deep and the airframe was a wider diameter, there would be a greater chance of this happening, because I would be approaching a 30-degree bend angle where the lateral forces would be close to equal the pulling force.
2: The plate on the back side of the U-bolt will be glued to a finroot, and the CR will also be glued to the motor tube with a solid bead on the forward side. RocketPoxy has a shear strength of 14,000+ PSI. The combination of the stainless washers and backplate on that area takes both sides to within 1/16" or so of the edges of the CRs, where the strength of the glue bond should be the dominate resistance. The tensile and flexural strength of G10-FR4 1/16" sheet is 10,000 and 23,000 PSI respectively. I also opted to add in threaded rods although their combined strength is about 7,500 PSI, which is weaker than the glue bond. Since the bond, G10, and U-Bolt are all greater than 6,000 PSI, and since the shock cord is rated to break 2,000 PSI and quick links are approx. 2,000 PSI, then hypothetically, those should fail first.

Famous last words...I really think what I have will hold.

Now tacking aft fin set into place on the boat tail. A line has been drawn on the other side to show proper alignment of the two sets. Once this is done, I will take the two sections apart and start applying internal and external fillets.

Hmm... Well thats interesting... I'm not sure maybe your forward fins have a different mass than mine? Mine weigh 399 grams each for a 3 fin set weight of 1197 grams. I just reweighed them. In your OR, you have the 3 fin set weighing 936 grams. For the aft fins, mine weigh 225.7 grams each for a combined 3 fin set weight of 677.1 grams. You have 621 grams as the weight of the rear 3 fin set. Could our number be this far off from each other's? My fins are black. Could this be it? But then for your Boattail, you have a weight of 493 grams where as I have 428 grams. It's weird haha. Could my scale be off? lol

This is a new kit and the boat tail is a brand new part. However mine should be a little lighter if anything because I cut off the last inch to accommodate my flange retainer. There could be variations, but I'm not sure by 10%. It could be my scale is the bad one as well.

After I tack the fins in place I will be able to take the assemblies apart and weigh them. I will factor in another 6-8 oz. of glue and be able to come up with a pretty good estimation of a total weight. We'll see what it comes out to.

EeebeeE said:

This is a new kit and the boat tail is a brand new part. However mine should be a little lighter if anything because I cut off the last inch to accommodate my flange retainer. There could be variations, but I'm not sure by 10%. It could be my scale is the bad one as well.

After I tack the fins in place I will be able to take the assemblies apart and weigh them. I will factor in another 6-8 oz. of glue and be able to come up with a pretty good estimation of a total weight. We'll see what it comes out to.

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Alright cool. Hope your build continues to go well! I can't wait to start building mine! I look forward to following this build thread!

I did think I noticed that you used a freeform fin set. Did you trace these fins and are they pretty exact? If so, they actually seem a bit smaller than mine, so that may account for the difference. But that would be weird, since it is a kit.

I don't know, but I just thought I would say something just to make sure one of us wasn't doing something wrong. I wouldn't want to have had the right weights and have not said anything, or you have the right weights and me be too ignorant and think you're wrong and then I end up being wrong. Better to raise question I think!

At the time I bought this they had not yet done a Rocksim file so I used a ruler and measured the X-Y coordinates. They could be off slightly, but not too much. I think I will need to check my scale and see if it is accurate.

Fins have been tacked into place with 15-minute epoxy. Now the whole thing comes apart and the motor tube is removed so I have plenty of room to use RocketPoxy and make internal and external fillets.