Giant Leap Rocketrys new Mariah 38 kit review

ClayD said:

all-thread is not a rod. it has compression points. its failure in tension is at the compression point . It will almost always be in line with the thread cut and certainly not at 45degrees.

In tension, the shear load is drasticly reduced.... so to tighten an allthread, and then place some form of shear, (tightening a nut, and then loosening it.. over and over) fatiges the all thread...any other shear load, landing on the nose cone.. could also cause a failure.

any anomolies in the alloy cause hard spots and softspots, all of this can be the week point.

I could snap the head of a bolt far easier than shearing one....

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All thread in tension doesn't have any compression points. In addition, it can be approximated as a rod with reasonable accuracy. Also, shear and fatigue are two different things.

Basically, aluminum all thread is stronger in tension than it is in shear. It's true that 4-40 aluminum won't be terribly strong no matter what, but it can definitely hold more load in tension.

cjl said:

All thread in tension doesn't have any compression points. In addition, it can be approximated as a rod with reasonable accuracy. Also, shear and fatigue are two different things.

Basically, aluminum all thread is stronger in tension than it is in shear. It's true that 4-40 aluminum won't be terribly strong no matter what, but it can definitely hold more load in tension.

Click to expand...

That is why all structural building connections use bolts in shear (ductile threaded shanks). And, the same in shear load for a bolt, when is in tension for a moment connection you increase the size of the bolt to the next size.

You can treat all thread in a rod if you use the smallest diameter, and that it will fail inline with the threads. the tension loads will direct on the threads.., tensioning the all thread to any level, will ultimately remove any resistance to a shear load, which can happen in this application.
So a threaded rod used in tention has far more and weaker failure points, than a 4-40 screw, only in shear....

Not to mention you could put (2) 4-40 screws in at less weight than 6" all thread, and is even by your standards stronger.

fatigue and shear are completely different, but failure is still a failure...


What would the optimum mass be on a j-570 for the mariah?

I made some mods to my Mariah build to achieve 3 things:

1. House Big Red Bee in nose cone and make it easily accessible
2. House Raven altimeter in breadbox with secure but removable attachment
3. Shorten overall length by 2" for improved performance which I achieve by upgrading to an even more compact Fruity Chute

I'm happy to share more info if anyone's interested.

troj said:

The only method I know is brute force, and I think this is the method RockSim uses.

Adjust weight up or down by a bit, and see how your altitude changes. That tells you the direction you need to move, then move in gross steps in that direction, rerunning the sim, until you get the max altitude dropping again. Now you have it bracketed. Keep doing smaller steps in between, until you get a final number.

-Kevin

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Nah...there is an easier way. Run a sim with the motor you want to use and then select that simulation. Then it's Simulation > Predict Optimal Mass > Start Simulations > Plot Graph.

:cyclops:

DAllen said:

Nah...there is an easier way. Run a sim with the motor you want to use and then select that simulation. Then it's Simulation > Predict Optimal Mass > Start Simulations > Plot Graph.

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True, though RockSim seems to use brute force for you.

....though it is much easier to let the computer do all the work.

-Kevin

cwbullet said:

Guys,

I am trying to think of a way to make the nose cone removable without shear pins. I thought of a screw on method, but that may add too much cost. Maybe an estes type plastic retainer?

Chuck

Click to expand...

Me Too!!

This is what I came up with.

I'm using a 6/32 Stainless Steel machine screw. about 1 1/4" screwed up through the bulkhead in the av-bay to the nosecone, where I installed another bulkhead in the nose that has a 6/32 "T" nut in it.
Not much more weight in my book. But, I ran optimal mass in RockSim to get Aprox. 68 oz. with a J-570 to achieve maximum altitude.

JDcluster said:

They need a HP version of Rocksim. This Engine ejection thing kills me, as I just want to pull my hair out trying to workaround it!
At least make it so that you can turn off any motor ejection timing for staged rockets without having to pay $1000+ for the commercial version.


JD

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huh? Just "engine delay sec -> none" and then choose "flight events" for your DD setpoints....

cbrarick said:

huh? Just "engine delay sec -> none" and then choose "flight events" for your DD setpoints....

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I believe JD was commenting on two-stage setup, not dual deploy, but just as easy; set your engine delay to 0 sec, then set sustainer ignition time.

konoctipirate said:

I made some mods to my Mariah build to achieve 3 things:

1. House Big Red Bee in nose cone and make it easily accessible
2. House Raven altimeter in breadbox with secure but removable attachment
3. Shorten overall length by 2" for improved performance which I achieve by upgrading to an even more compact Fruity Chute

I'm happy to share more info if anyone's interested.

Click to expand...

I'll bite...lets have a look at your setup. I have a bag of parts, a new Raven and looking to place a tracker (BRB, TLA, or ?) in the nose.


Chris

Here's some updates on the Mariah series:

1) The Mariah-54 and Mariah-75 are progressing nicely, but slower than expected. It's the busy season and we're buried with orders. I don't want to give specific release dates, because they'll probably be wrong.

2) We are developing an internal motor retention system for these kits so that an external slimline will not be needed. The Mariah-54 and 75 internal retention systems are fairly straight forward. The challenge, however, with the Mariah-38 is room -- adding an internal retainer reduces space for the longer motors. More on this later.

3) We will be coming out with a minor construction update of the Mariah-38. Think of it as Mariah-38, version 1.0001. More details later.

thanks,

Ed
Giant Leap Rocketry, Inc.

Is the internal motor brand specific ? Or universal ?

I will be in for a 54 and 75. I like the new kits. Fantastic build.

I'm almost done with my build and I want to give credit to Kent and GLR.
It's one thing to get a rocket with some new thoughts and design elements to bend your head. Even better is a design that still allows some modifications. I've really enjoyed this build and the 25 pages of instructions that caused me to think "how could I make this even better?".

I made 3 mods to the GLR instructions:

1. Permanent mount in bread box and fiber glass sled that mounts to it with Raven and LiPo battery. Note: this also required changes to where bread box access hole and static port is drilled

2. Detachable nose cone from breadbox so transmitter can be inserted in nose cone.

3. Reduced overall length by 2" for performance improvement by cutting off 2" from top of main airframe, chute cannon AND the glue stick.

Mod #1: Raven and Sled Mount
Raven mounted on sled which attaches securely to inside of breadbox

I built a small fiber glass sled. The Raven mounts on the top side. The lipo battery and screw switch mounts on the reverse. The lipo battery is epoxied onto the sled.

The sled mounts are attached with epoxy to the inside of the bread box, opposite the opening. Each sled mount has a threaded insert. The glass sled then attaches to the two mounts.
Between each sled mount is some padding which the lipo battery rests snugly against.

The whole breadbox internal sleeve rotates nicely to shut the Raven away. One note: the static port which will also function as the whole to access the screw switch is 180 degrees away from what the instructions indicate.

Mod #2: Removable breadbox for transmitter capsule access in nose cone

Instead of epoxying the breadbox into the short piece of airframe, I wanted the nose cone to be accessible so I could house my Big Red Bee. I discovered that standard orange pill containers are very close to 38mm in diameter. I cut off about half an inch from the top and drilled a hole in the bottom so that the antenna could stick up into the nose cone. The pill capsule then inserts into the nose cone.

The breadbox is attached to the nose cone section (nose cone + pill capsule + short airframe piece all epoxied together) with machine screws which screw, through recessed holes, into threaded inserts which can be inserted into the pre-existing bulkhead at the forward end of the breadbox outer tube.

Mod #3: 2" reduction in length
This required cutting the main airframe by 2", cutting the chute cannon by 2" and reducing length of included glue stick by same 2". There are some other instruction mods required to make this work.

How did I reduce overall length by 2": By using a Fruity Chute rather than standard chute. This requires less space. As it turns out, and other parts of this thread indicate, reducing length helps performance but, for the bigger 38mm motors, increasing weight helps more!

I'll share pics of this later. I've already tested the Fruity Chute and reduced compartment requirements which made me brave enough to hack off the 2". I'll show some comparison pics later.

Capsule for Big Red Bee Transmitter...

And to finalize the first set of pics of mods, here's the picture into the nose cone of the pill capsule which will hold the Big Red Bee. I knew there was a rocketry reason for the daily blood pressure tablets.

I am using Duplicolor metallic paints for the finish. Have finessed the heck out of the finish on the nose cone and body today and I love the look of this paint.

I'll share some pictures of the completed rocket soon.

Hey Ed,

If you develop internal motor retention for CTI, I'm all ears. Gene Engelgau (Mr. Fruity Chutes) has a mechamism for Aerotech which is cool and could be applied to the Mariah.

I'm especially interested in internal retention for CTI.

Then again, the older I get the more I'm embracing KISS so friction fit is increasingly appealing to me.

Martin

Martin,

I build mine by the instructions, but i bought another one to modify. You have made it the way i wanted. Thanks for sharing.

I appreciate all the kind words you all have been saying about the Mariah. But the facts are that I contributed only three things to the design:

a. names (Mariah, Shotgun Tube and Breadbox)
b. fin shape
c. rotating breadbox door

The bulk of the concept came from Ed and he is the one who deserves the credit, not me. When he first sent me his drawings, I was so far in the dark it made no sense to me. He had to walk me through it before it became clear.

Kent/GLR

Thanks everyone for the ideas. I have never posted on a forum before and only just logged in and found the replies so clearly I need to log on more often. I would like to do a rocksim for my J570 and then probably go with a tight friction fit with a couple of spots of superglue. I always fly with a Beeline GPS or TX onbaord because we fly in farmland with rocket munching crops so a tracker and Yagi antenna are a very good investment.

Duplicolor anodized metallic paint which turned out really well after a weekend of sanding and spot puttying ...

Out with the LUNAR gang at Snow Ranch yesterday, my Mariah38 made its maiden flight on an H123 skidmark. Perfectly straight boost and great flight. Pictures attached.

For those working on this kit (and if you're not, go order one now), here's an observation and a tip...

1. Rocksim

My flight sim'd at 3,800'. Actual altitude: 4,750'
This means the J570 is likely to push this rocket to 13,000' or higher.

2. How NOT to pop the main at apogee...

I exchanged emails with Kent about an additional flight prep tip...
"You want to be certain the 1/8" shockcord has no "slack" under the parachute. Put the slack on top of the chute-under the step cap."

If you don't do this, the main will be pulled out when the rocket separates at apogee.

Martin,

We were far past 13K in tests with the J570. Did you have your altimeter hooked up correctly for the apogee ejection?

Kent/GLR

Hey Kent,

Yes, my deployment problems were due to me getting my altimeter wiring wrong. I wired the accelerometer and barometric apogee channels on the Raven. So, with motor ejection backup too, I managed to have 3 charges go off at apogee and none at main.

Fortunately no major harm apart from a longer than anticipated walk to location that my tracker led me to.

Martin

does anybody have any flight pics or videos out there yet? what motors are you flying and whats the altitudes you are acheiving?

I finally got a chance to lay my hands on a Mariah 38 this weekend, and it's a pretty darned slick design! There are lots of little things to this kit that add up to a whole bunch of "that's pretty darned slick!" It's well thought out, and well designed, and the nice thing is that the way it goes together, it's not something that you have to be worried is going to jam up or wear out after just a few flights.

-Kevin

Kevin,
Did you see Jays J510 flight sunday morning or did you make the same mistake that i did and blink when it came out of the tower? It still amazes me just how hard the mariah 38 accelerates on a J570 or a J510

cmcain said:

Did you see Jays J510 flight sunday morning or did you make the same mistake that i did and blink when it came out of the tower? It still amazes me just how hard the mariah 38 accelerates on a J570 or a J510

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I actually managed to follow it, which surprised the heck out of me! That thing just flat-out moves

Personally, I think there ought to be a law against paint jobs as nice as his. :wink:

-Kevin

Someone flew a Mariah on a J510? Anyone know the altitude?

a good guess is somewhere in the neighborhood of 13000'-15000' the main deployment charge was just barely visible. i do know for a fact that the j570 pushes one to almost 13000'

Rocking paint job!

cmcain said:

a good guess is somewhere in the neighborhood of 13000'-15000' the main deployment charge was just barely visible. i do know for a fact that the j570 pushes one to almost 13000'

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That low? That's odd - I would have guessed higher than that (assuming a tower launch). I would have thought 15k with the 570, and 17-18k on the 510, but that's just a guess.