L3 Certification Build: 8" Upscale Frenzy

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After much cleaning of fiberglass parts I'm finally ready to start building the motor mount.

For epoxy I use Aeropoxy 6209. The motor tube is 36" (and yes it is only 75mm :y:). There will be four centering rings; two forward of the fins and two aft of the fins. The forward two rings will be epoxied to the motor tube first. The two aft rings will be added after the MMT is installed and internal fillets are done. This is the lower forward CR, which is positioned so that bottom of the CR will exactly line up with the top of the forward fin slot. Hopefully . . .

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What cutter are you using on your rotary? I've found that this guy cuts through fiberglass like butter.

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But if you have a way to keep the ultra saw straight, I bet it'll do a great job.

+1 not much beats that cutting disc for fin slots in either FG/CF or cardboard.

terryg the two cutting discs are nearly identical, only one fits the EZ-lock arbor the other has its own arbor.
 
Both forward CRs have now been epoxied to the motor tube. The upper forward CR is 1" plywood instead of fiberglass because it will be attached to the airframe with both screws and epoxy.

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Here is the motor mount all ready to be installed in the booster tube. The forward ends of the three allthread rods have welded eye nuts attached which are the attachment points for the recovery harness. I also put nuts on the allthread rods below the first CR and both above and below the second CR, and covered them with epoxy putty. This should help distribute forces across the CRs. For the remaining two CRs I will only be able to put nuts below the CRs.

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Here is the motor mount with the 3-point Y harness attached. Teddy at Onebadhawk.com made me this really nice Kevlar harness. Three attachment points is probably overkill but I had three allthread rods, so I decided to use all three of them.


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View from forward end after installing the motor mount. I installed it by applying epoxy to the inside of the tube in the area of the 2nd CR, then slid the MMT down the tube from the forward end. I slid it an inch past it's final location, then applied epoxy to the inside of the tube in the area of the 1st CR. Then I slid the MMT up to its final location and left it in a vertical position overnight for the epoxy to cure. The next day I applied a fillet to the forward side of the 1st CR. I will apply a fillet to the aft side of the 2nd CR before installing the fins.

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View from aft end . . .


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After recovering from LDRS I'm finally back to working on my L3 build...

I drilled and countersunk holes using the drill press, then screwed six 2" #10 stainless screws into the plywood forward centering ring. This was recommended by my L3 advisor. I will be removing the screws and will not put them back in until the rocket is finished and painted.

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Epoxied on the forward fins with Aeropoxy. One fin per day over the past 3 days.

Next step will be doing all the internal fillets on the forward fins before attaching the aft fins.

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Here is the motor mount with the 3-point Y harness attached. Teddy at Onebadhawk.com made me this really nice Kevlar harness. Three attachment points is probably overkill but I had three allthread rods, so I decided to use all three of them.

I typically install the harness by epoxying both ends of the kevlar strap to the MMT (CJ style). It's simple and works well, but the unfortunate side effect is that the booster section always comes down on an angle. With three fins you can't epoxy the strap on opposite (180 degrees) sides of the MMT because one of the fins is in the way. It's always offset to one side. Because of this, the booster section comes down on the same angle every time, and lands on the same part of the aft end of the body tube, and possibly the fin. It's not the end of the world, but that part of tube and fin get beat up more than the rest after multiple landings.

That 3 point harness will do a better job of bringing your booster section down straight and/or making the landing more random, evening out the little bits of damage from the landings.

Good looking build so far.
 
Really like your three point harness. It fully believe in redundant harnesses especially for apogee deployment on DD.
 
Finished doing internal fillets on the forward fins. I did the internal fillets on the forward fins before attaching the aft fins so that there is more room to work in the tube. I figure that there are 38 separate epoxy steps for the fins:

Attach 3 forward fins
6 internal fillets on forward fins to airframe
6 internal fillets on forward fins to motor tube
Fillets where forward fin tabs contact CR #2
Attach 3 aft fins
6 internal fillets on aft fins to airframe
6 internal fillets on aft fins to motor tube
Attach CR #3 and epoxy to bottom of aft fin tabs
6 external fillets on forward and aft fins

This is a slow process when you're using 12 hour epoxy. I can do 2 internal fillets at a time but that's still a lot of days of doing fillets.

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While waiting for fillets to dry I also started working on the nose cone. This is the inside of the completed nose cone shoulder tube, with fillets on the bulkhead and the U bolt attached. The small vent hole is to allow air to escape when I insert the shoulder into the nose cone.

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Next step: start attaching aft fins
 
I drilled and countersunk holes using the drill press, then screwed six 2" #10 stainless screws into the plywood forward centering ring. This was recommended by my L3 advisor. I will be removing the screws and will not put them back in until the rocket is finished and painted.

I started using this technique with my large 75mm 7.5" diameter rocket. I don't even have the MMT glued into the airframe. Just a thrust plate and lots of screws. The mechanical fastening works great. The glue and screws should be able to handle a metric butt-ton of stress.
 
Enjoying your build thread.

While I understand the "go larger/can always adapt down" points on the motor mount, being an economy minded flier myself, I completely agree with your decision on the 75mm.
(Hey, if anything you can look forward to a 98mm project after you get that L3 - gotta leave some future goals out there for ya).

(I understand you will be doing the L3 shoot in MD this fall - given Dave W. is your TAP. Will that be the maiden flight as well?).
 
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Yeah I may build a 98mm motor rocket some day but for now I'm sticking with 75mm. I just bought a 6 grain 75mm case from AMW a few weeks ago at LDRS.

I haven't decided yet if the first flight will be the L3 attempt at Higgs this fall. I was thinking about flying it on a big L motor first at Battlepark. I need at least 1600 N avg thrust to get 5:1 thrust ratio so there's not that many L motors I can fly it on. It sims at 3100 ft on a L2375 White Thunder.
 
I'll venture a guess...his TAP is Dave Weber at MDRA?

Correct.

I definitely plan to fly this at Battlepark this fall, either on a L motor before my L3 cert flight or on a M motor afterwards.
 
I love the Frenzy...sucker for split-fins in general, but this one is just drop-dead sexy. Looking forward to seeing how you finish it!
 
I'll be using a normal burrito style chute protector and not a deployment bag for the 120" FruityChutes main parachute. For the chute protector to work correctly it needs to be a snug fit in the tube to prevent the burrito from sliding down the tube and possibly unwrapping. So I will be putting this baffle in the long payload tube to hold the main chute up against the nose cone bulkhead. This is a CR with a bunch of 1 3/8" holes drilled in it.

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I'm starting to work on the av bay. Here's how I make ejection canisters from copper pipe tube couplers. For the base of the canister I make a bulkhead out of 1/8" plywood using the band saw and then finish it on the belt sander. Then I cover the bulkhead with a layer of epoxy. If a little epoxy seeps past the bulkhead it's not a problem because I hit the bottom with a sander after it's dry. Drill a mounting hole and it's ready to install using a #6 bolt. Total cost: about $1.

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Wow Nathan,,
I can't believe I missed this thread for all this time..
I guess I'm getting old..
What an super, unbelieveable meticulous build..
Quite honestly, that's no surprise from you..
Take your time with all those fillites and the 936 wait / cure times till the next set...
You just relish this time spent on this build...
No matter how long this build takes,,
you're going to have and fly this rocket for 100 times longer...
Take your time and enjoy it....

Your copper charge canisters...
I have always made my own charge canisters..
Out of a short of copper pipe with a copper pipe cap soldered on....
This is less time and trouble then what you did,,
and is infinitly stronger.....

Great build man.....

Teddy
 
Wow Nathan,,
I can't believe I missed this thread for all this time..
I guess I'm getting old..
What an super, unbelieveable meticulous build..
Great build man.....
Teddy

Only thing better than his builds - are the paint jobs....
Looking forward to that.
 
Any ideas on colors for paint yet??????????????

I have some ideas but I need to start working on the paint design soon. I'll try to do it in OpenRocket and I'll post a picture when I have something.
 
Hate to add to the pressure, but All of TRF is going to watch the Nathan paint job on this one! ;)
 
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