Minnie-Magg build for L1 attempt

[Batjac]

I just finished painting my Minnie-Magg I built for my L1 attempt. The local club president recommended the Minnie-Magg, and after finding this Forum and reading, this seems like a good choice. The only deviation from the included instructions was to put about 7 ounces of weight in the nose cone. The advice I was given was that the rocket would fly without weight, but most club members put 4-8 ounces in the nose, so I put in 6 ounces plus the weight of the hardware to keep it in place.

I'm ready for final assembly, but have two questions. I tried doing forum searches, but got such varied results, that I figured I'd ask the questions directly. First, I am using a Jolly Logic AltimeterTwo. I planned to drill ahole in the tube just below the bottom of the nose cone shoulder, inline with the launch lugs. What size hole do I drill? Is 3/32" enough? Or do I need larger?

Second, the instructions say to loop the shock cord through the nose cone and secure to itself with the provided quick link, then attach the parachute to the quick link. Is this the best way to attach the parachute, or is there a better method of attachment?

I plan to convert the nosecone to an electronics bay later, but for the L1 attempt I want to keep things as simple as possible.

Thanks,
Mark

 

[crossfire]

What are you uesing for shock cord? I recommend putting chute about 2-3' below nose cone and tied off on the shock cord. What motor are you useing?

 

[John_461]

I don't think you need to drill a hole at all for an Altimeter 2. If you rocket is going to be reaching high altitudes quickly you'll need a vent hole in the booster tube to release the ground level pressure so the nose/payload section doesn't separate prematurely. I don't think a mini-magg quite fits that bill. On the other hand a 3/16-ish vent hole in the body tube won't hurt anything and may give you some peace of mind.

As for your parachute mount. I like to tie an overhand loop knot (pic attached) in the shock cord about 1/3 of the way down from the nose cone to keep the nose from banging into the rocket body and attach my parachutes to that. Swivels, quicklinks etc are optional. Secure the loose end to the nose cone with which ever knot you prefer. I use the over hand loop knot for this as well and secure the loose end to the rest of the shock cord with tape.

Good luck on your cert flight!

 

[Batjac]

Thanks for the replies, Guys. I forgot that the other deviation from the standard kit is using a Kevlar shock cord. I have a 15' length 1/4" tubular Kevlar shock cord instead of the included shock cord.

For the motor, I am going with the club president's recommendation of a H225 PR38-2G-WT. Looks like a good fit, and I try to always take advice given to me by the more experienced..

 

[Batjac]

I must say, LOC Precision gives you your money's worth. I pulled the shock cord from the package and unwound it in preparation for attachement to the rocket. I ordered the 15' length, but when I straightened it out it seemed much longer than that. So I pulled out my tape measure to see how long it was. It measures just about 20 1/2 feet. I checked the package to see if I got a different length than I thought I ordered, but the package says 15'. I guess LOC gives you a little extra to account for spoilage.

 

[Batjac]

Okay, now I'm concerned. I just weighed this ready to go, minus engine. I come up with a weight of 2,166 grams, or 76.1 ounces! I didn't think this would come out so heavy. I measured the c.g. at 22 9/16" back from the nose. I plugged the numbers into the trial version of Rocksim and got a caliber of 0.65 marginal. Using the above motor, it calculates an apogee of 1,293.69 feet, max velocity of 217.21 MPH, and max acceleration at 9.82 G's. I believe I heard somewhere that the desired velocity is 50 ft./sec leaving the launch rail. Rocksim says my rocket will leave the rail at 41 ft./sec. (Open Rocket has it at 44 ft./sec.)

Thoughts?

Mark

 

[thzero]

Well per the LOC basic rocksim file, it comes in at 68.1oz... so 76.1 isn't bad.

Are you using a rail? did you change the length of the rail? with a H255 and a 72" rail, I see an exit of 60fps using your 76.1oz.

 

[Batjac]

Ah, I did not see that the launch rail default is set to 36 inches. Thank you. I increased it to 72 inches. But, for some reason, after resetting the launch rail length the program keeps locking up when I try to run the launch simulation. Weird. Thank you for running the numbers for me.

And, if I hadn't added the 7 or so ounces in the nose, I guess I'd be at the LOC Rocksim file weight. Now I don't feel so bad.

Mark

edit: I just deleted the file and did it over. Now it's looking good. Thanks for the help.

 

[Five]

Where’s the pics? Pics are always a great idea.

 

[DaHabes]

FWIW, I did my L2 with my Minie Magg and a Jolly Logic Chute Release. Simple and easy.

 

[Batjac]

Where’s the pics? Pics are always a great idea.

Well, can’t say as there’s much to see. I’ve drawn up a bunch of graphics in Inkscape to cut with my Cricut Maker machine, but I learned a long time ago with my model planes and my full scale planes to not gussy them up until they’ve had a successful first flight. After the first flight I will prettify this model.

But, since you asked for it… Ladies and Gentlemen! I present for your viewing delight!

The Possum Rocket!!

https://postimages.org/] [/url]

 

[Batjac]

FWIW, I did my L2 with my Minie Magg and a Jolly Logic Chute Release. Simple and easy.

I've thought along those lines. As I'm recently retired, I gotta pinch the pennies where I can, so I may have to use this rocket for both certs. I have an idea for what I'd like to build for a L2 rocket, but we'll see when the time comes. With the price of motors, I'll probably use the Possum Rocket for both certs.

 

[crossfire]

Level 1 I would just bring chute out at the top.

 

[PSLimo]

Hi Batjac,

Great rocket choice for your level one cert flight.

You might want to add some anti zipper insurance with quarter inch kevlar on cardboard tubes with something like this

https://giantleaprocketry.com/products/large-fireball

 

[thzero]

Level 1 I would just bring chute out at the top.

Meh... use the JLCR.

 

[jmasterj]

Meh... use the JLCR.

Only reason I can think of not to is if you've never used it before. Otherwise go for it.

 

[jfdanjou]

What you can do with yer MiniMagg after crashin’ it….

 

[RocketRev]

Hello Batjac,

In my experience, the Loc Mini-Mag has always simmed out as marginally stable but flies great. One of my all time favorite kits. Its large diameter made it easy to see what I was trying to do when I built it. I'm on Mini-Mag #3 or #4 since 1991 when I got into this hobby. My last one flew with a Gnome sticking out of the end of the nose cone, but that's a whole 'nother story as they say.

The Mini-Mag's large base drag in relation to its diameter and length contribute to its stability.

Fly it!

Brad

 

[Batjac]

Well, I did my L1 cert flight today with the Tulsa Rocketry club. Everything went great. The weather even cooperated for my flight. It was stormy early this morning, a little windy before my flight, and a LOT windy just after my flight. But when it was my turn to launch my rocket, the wind died down and everything was perfect for the flight. It even came down about 25-30 yards from the launch pad so I didn't have much of a walk to retrieve it!





I used an H225-WT motor, and the Jolly Logic AltimeterTwo I put in it said the apogee was at 1,132 feet.

Mark

edit: Oh, I took Phil's advice and did my own version of the Fireball for zipper protection. I got a Kevlar sleeve off of Amazon, some insulating foam from WalMart, and some metal cable ties from Amazon. Worked great. With the added weight of the zipper protection and the AltimerTwo, the weight went up to 77.1 ounces without the motor.

I attached the parachute about 1/3 of the cord's length back from the nosecone with a quicklink using John's suggestion for looping the shock cord, and fixed the Kevlar chute protector just above the body tube so that the flapping cloth didn't touch the top of the body tube coming down.

 

[StreuB1]

Wonderful flight; cannot go wrong with the Minie Magg on a fast baby H.

As someone said above, rockets with a very low L/D ratio have something called base drag. Base drag will hold even BARELY stable rockets stable. The trick is fast burn high thrust motors. You need to get good velocity to generate that base drag before its off the rail to keep it stable.

With that added nose weight, you might want to jump up to the next size chute, that looked like it was coming in a little hot. Now if all you do is fly on beautiful grass, then you're likely fine.

The Minie Magg on an H242 is one of the old standbys for L1 certs. That H225 is nearly identical.

Great job, well done, and welcome to high power!

Now go put an I600 in it and send it.