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Scarab 54 vs Wild Thang Jr build challenge

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Mr G

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This is a reboot of the "Scarab 54 vs Punisher Sport build challenge" after a number of commenters preferred to see two builds with more similar kits. Go to http://www.rocketryforum.com/showth...nisher-Sport-build-challenge&highlight=scarab for the rest of that story leading up to now. The thread is now under the HPR section as both kits are set up for 38mm motors.

This story starts with the recent arrival of a Wildman Wild Thang Jr kit. After cleaning the fiberglass parts with warm water and dish soap, they were set up next to the blue Scarab parts for comparison.
IMG_7402.jpg
First off, the Wild Thang was not the same as what is shown on the Wildman website - the tubing was red, not green! There is something about the color red that evokes a sense of speed, daring and a certain cachet - like with a red Ferrari. And the nose cone was not polycarbonate but filament wound with a metal tip! So the Wildman has been making subtle upgrades to this kit to the benefit of the customer.

You can see that tube lengths vary between kits with the Wild Thang coming out several inches taller. Both boosters and sustainers are thin wall as well as the Wild Thang motor mount. The Scarab had been ordered from Rocketry Warehouse some time ago and did not come with a vent band although it had the other eBay parts. After explaining the oddity to MadCow Rocketry - who is now the source for the kit - Mike said he would send me a blue vent band. That's awfully kind of him considering I did not buy the kit from Madcow.
 

Banzai88

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OK, this is worth watching.
 

patelldp

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That's a welcome upgrade to the Wildman kit...dumping the poly cone in favor of reintroducing the FWFG cone without a price increase.
 
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Mr G

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The Scarab fins are 1/16" while the Wild Thang fins are 3/32".
View attachment 298375View attachment 298376
A thirty-secondth of an inch thickness may not seem like much but there is a certain heft to the Wild Thang fins that is quite apparent. Performing a hand calibrated five pound stress test resulted in the following deformations:
View attachment 298377View attachment 298378
With a big motor, on the way up at close to or just over Mach 1, the 1/6" fins might flutter. And they would not be as strong hitting something hard on landing if with a small high descent rate parachute. No worries with the 3/32" fins. The shape may also be a factor as the Wild Thang fins taper in to the booster tube on both ends whereas the Scarab fins protrude below and out from the bottom of the booster tube.
 

crossfire

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Just build 1 av-bay coupler and use it on both rocket if it will fit.
 

Mr G

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The Wild Thang kit came with some hardware.
IMG_7407.jpg
A long 1/4" welded eyebolt for the nosecone plus two shorter ones for the e-bay will more than handle any gyrations during deployment and recovery. First time I've seen quick links in a kit - and they look like the high strength 1/8" stainless steel ones at that! You know its a Wildman kit focused on high performance when it includes rivets and shear pins - a sure sign of expected high speed flight.

There was no hardware included in the Rocketry Warehouse kit.
 

CzTeacherMan

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Will you be painting the red tube on the Jr or just clear coat? With clear, that red turns translucent candy-apple red and really pops in the sun. Highly recommended. If you do, I use black primer on the black parts to even out the color.
 

blackjack2564

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The Wild Thang kit came with some hardware.
View attachment 298381
A long 1/4" welded eyebolt for the nosecone plus two shorter ones for the e-bay will more than handle any gyrations during deployment and recovery. First time I've seen quick links in a kit - and they look like the high strength 1/8" stainless steel ones at that! You know its a Wildman kit focused on high performance when it includes rivets and shear pins - a sure sign of expected high speed flight.

There was no hardware included in the Rocketry Warehouse kit.
All the E-bolts are also stainless. The long is for replacing the screw holding tip on. Replace with the E-bolt and you can make a dual-deploy av-bay out of the NC, hook up recovery to it and stuff the chute in cone. Stick it fincan for flying big motors Dual deploy....very versatile rocket.

Just fit the av-bay & vent band to cone first, it will then fit in either payload or NC... now you can fly rocket in short or long version.

DSCN5794.jpg
 

CzTeacherMan

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All the E-bolts are also stainless. The long is for replacing the screw holding tip on. Replace with the E-bolt and you can make a dual-deploy av-bay out of the NC, hook up recovery to it and stuff the chute in cone. Stick it fincan for flying big motors Dual deploy....very versatile rocket.

Just fit the av-bay & vent band to cone first, it will then fit in either payload or NC... now you can fly rocket in short or long version.

View attachment 298396
Brilliant! ... I need to buy a new nosecone. LoL
 

Mr G

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The thought was that with smooth colored fiberglass, it obviated the need for filling spirals, sanding, shooting primer, sanding, painting, sanding, coating again, etc. that is required of cardboard kits. But bringing out the translucence of the colored tubing with clear coat is worth consideration.
 

Mr G

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Another package showed up today - a vent band for the Scarab. Thanks Mike at Madcow! No questions, no cost - he just sent it because I asked. Can't beat that kind of understanding and service.
IMG_7419.jpg
As it is black - matching the nosecone and fins - maybe this rocket's nickname will end up being "Black & Blue."
 

Mr G

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Question -
The Wild Thang's thin wall fiberglass motor mount is a different diameter than the existing Aeropack retainers. It is clearly small compared to both the 38P and 38L retainers. What is the acceptable gap between motor mount and retainer?
 

Mr G

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Thanks, Tom - didn't know about a 38L2. Just ordered one from Wildman.
 

watermelonman

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I filled the gap with JB Weld. It is not perfect but remember that many retain motors with masking tape.
 

Banzai88

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I filled the gap with JB Weld. It is not perfect but remember that many retain motors with masking tape.
I've done this. I wrapped my motor case with wax paper and inserted it into the tube while the JB weld was curing so that it would center up things perfectly.
 

Mr G

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There was the thought for a while about filling the void between the thin wall tube and the retainer as suggested. That would have been a quick solution that, as long as everything was aligned properly, would have worked fine. I erred on the side of caution and simplicity, ordering the retainer body that would slip on the tube with tolerances prescribed by the professionals.

A few launches ago, it was discovered that an Aero Pack 38/29 adapter was missing the aluminum ring at the end that holds the motor in place. As a last resort, out came the masking tape. I was picking gooey little strips of tape off the motor for a long time - at least as long as it took to clean the burnt propellant off the 29/240 case and closures. Maybe that was a motivator for just getting the right part for the application.
 

Mr G

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Crazy Jim's builds show epoxying the shock cord on both sides of the motor mount tube, ending up with a loop at the top of the booster tube. With double the line, is there a case for 1/8" over 1/4" Kevlar shock cord? Obviously, the 1/8" is lighter and smaller. Any preference with one or the other?
 

CzTeacherMan

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Crazy Jim's builds show epoxying the shock cord on both sides of the motor mount tube, ending up with a loop at the top of the booster tube. With double the line, is there a case for 1/8" over 1/4" Kevlar shock cord? Obviously, the 1/8" is lighter and smaller. Any preference with one or the other?
You're talking about the y-harness, and that is the part permanently installed, I always go with the 1/4". It'll last longer than the 1/8". Haven't found a limit to the 1/8", but fit something you'll be unable to replace without major rocket surgery, why not use the one that lasts longer? As for the shock cord itself, you can use the 1/8" since it can be replaced if necessary.
...
Times when it will matter:
-pulling a rocket out of a tree by the shock cord
-after years and years of ejection blasts
-less than optimal ejections
 

Mr G

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IMG_7514.jpg
Carving out a notch on either side of the forward centering ring. Both the Scarab centering rings would not fit over the motor mount tube and had to be sanded down before they would slide on. Hopefully Madcow will remedy this with future kits.
IMG_7515.jpg

IMG_7518.jpg
After the first ham-fisted mess (the blue one) masking tape was applied to either side to keep excess epoxy from landing where a fin may be placed. You can see a small piece of masking tape holding the shock cord back until after application of the first layer of epoxy. You may also see a black dot near then end of the tape as a guide for the cord length and position.

IMG_7519.jpg
The Bob Smith 30-minute epoxy started to heat up and cure way too soon. It melted the plastic cup and turned into a big blob before the last piece of shock cord could be encapsulated.
IMG_7523.jpg
 

Nick@JET

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That has happened to me too, started smoking even, you can feel it starting to set when stirring it...it's done, mix again. I think with mine I just eyeballed the hardener and used too much. Now I just use a paper plate to spread it out more. Also have switched to west and RocketPoxy . Bob smith has just always been quick and easy, but there are stronger epoxies out there. Popped a fin on my 4" MAC VTS-6 on a soft landing and I'm kinda done with BS on large rockets - seems brittle to me (but it could be user error on my part too).

It happens, you can always power sand and start over, or just sand with 100 grit and go right over it no worries.
 
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CzTeacherMan

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View attachment 299203
Carving out a notch on either side of the forward centering ring. Both the Scarab centering rings would not fit over the motor mount tube and had to be sanded down before they would slide on. Hopefully Madcow will remedy this with future kits.
View attachment 299202

View attachment 299201
After the first ham-fisted mess (the blue one) masking tape was applied to either side to keep excess epoxy from landing where a fin may be placed. You can see a small piece of masking tape holding the shock cord back until after application of the first layer of epoxy. You may also see a black dot near then end of the tape as a guide for the cord length and position.

View attachment 299200
The Bob Smith 30-minute epoxy started to heat up and cure way too soon. It melted the plastic cup and turned into a big blob before the last piece of shock cord could be encapsulated.
View attachment 299199
That has happened to me too, started smoking even, you can feel it starting to set when stirring it...it's done, mix again. I think with mine I just eyeballed the hardener and used too much. Now I just use a paper plate to spread it out more. Also have switched to west and RocketPoxy . Bob smith has just always been quick and easy, but there are stronger epoxies out there. Popped a fin on my 4" MAC VTS-6 on a soft landing and I'm kinda done with BS on large rockets - seems brittle to me (but it could be user error on my part too).

It happens, you can always power sand and start over, or just sand with 100 grit and go right over it no worries.
Bob Smith epoxy is really not a great choice for fiberglass rocket building.
The heat and clump effect is due to the large amount of epoxy you're mixing. For the BS epoxies, the more you mix, the faster it sets up because heat speeds up the setting process, and there's a critical mass where it gets a little warm which speeds up the set, which heats it up more, which speeds up the set, which heats it up more...... Etc etc etc and bam, you get this liquid that turns super hot and sets quickly.
That's not the reason Bob Smith isn't great, just explains why that happened.
RocketPoxy is the best all around epoxy for this size rocket, IMO. I usually use RocketPoxy, JB weld in places, West sometimes, and Proline 4500 occasionally. Different epoxies for various applications. Proline and JB weld have higher heat resistance so I use them for "on the MMT" applications. RocketPoxy is great for general purpose and filleting. I bought a gallon of West, and it's thin viscosity with the optional filler makes it versatile for various purposes, fantastic for doing lots of vary large fillets, like on my L3 rocket (5 fins with about 12" root edges).
 
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patelldp

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Bob Smith epoxy is really not a great choice for HPR rocket building.
Meh. Sure, it's not as strong as others, but in most cases it's available locally and is more than adequate for the job. Most non-FG materials can even safely use wood glue.

I usually use RocketPoxy, JB weld in places, West sometimes, and Proline 4500 occasionally. Different epoxies for various applications. Proline and JB weld have higher heat resistance so I use them for "on the MMT" applications.
This is one of the biggest misperceptions in rocketry. No certified motors are to exceed 200C per NAR, so you don't need a high Tg epoxy unless you're bonding directly to the motor. I guarantee that no one has seen a motor mount fail due to heat soak of the epoxy permitting the motor tube to fly freely.

JB Qwick "appears" to have a Tg 150C. Regular JB Weld "appears" to have a Tg of 260C. I was unable to find any reputable data sheets that cover this similar to what is provided with Loctite and other adhesives. I have my doubts about that capability as there have been posts on the forum that you can remove an Aeropack from a motor mount using...you guessed it...heat.
 

watermelonman

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I have large, high power rockets built with nothing but Bob Smith. However I never use it on fiberglass, except maybe a vent band or two.

It is more about the materials being bonded, than the power of the motor or size of the rocket.
 

CzTeacherMan

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I have large, high power rockets built with nothing but Bob Smith. However I never use it on fiberglass, except maybe a vent band or two.

It is more about the materials being bonded, than the power of the motor or size of the rocket.
Agreed. And corrected.
 

Mr G

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IMG_7537.jpg
Before attaching the fins, rail button placement is marked and drilled. Compared to cardboard, fiberglass is tough stuff so no need for reinforcement, just drill and screw in.


IMG_7536.jpg
The screws on hand were just a tad too long so a washer was added under the rail button. The tip should just push against the motor mount tube which will help secure the screw.


IMG_7538.jpg
Fin guides were printed out from payload bay.com after entering booster tube diameter and fin thickness and width. The paper was then taped down to some scrap 1/4" foam board. The fin and tube areas were cut out using an Xacto knife.
 

Mr G

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IMG_7551.jpg
It appears that some of the fin tab sticks up above the outside diameter of the booster tube. In fact, it sits flush with a 29mm motor tube installed indicating that the Wild Thang Jr may have been originally set up for a smaller diameter motor.

The hole drilled out for the rail button pulled up the fiberglass just a bit. I'm tempted to put a dot of super glue on it to keep it from fraying.
 

Mr G

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While cleaning the fiberglass I noticed a few small dark patches on the inside of the Wild Thang booster tube. I tried using alcohol and then an Xacto knife to remove them with no luck. Tim said he didn't know what they were from. Does anyone else know?

IMG_7526.jpg IMG_7528.jpg
 
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