Minnie-Magg drag mods for Level 2?

[Rschub]

I have flown my MM a lot since last year and learned a lot. I kinda over built it anticipating that I would fly it for my L2 flight. I passed the test last week so I need to fly something.

With a J motor, the MM will go to over 3000 feet. This is a problem because our site is fairly tight, and I have difficulty walking long distances, let alone climbing trees.

I do have a chute release that I always use to reduce drift, but I have had some funky off-angle launches.

I was inspired by this thread https://www.rocketryforum.com/threads/variable-drag-project.157027/ to add some more drag to limit altitude. This is what I came up with:



I am having them 3D printed now, my thoughts are these will at least triple the drag, move the CP rearward, and limit the flight to around 1000-1500 feet.

My question is, is this a "legal" configuration for a cert flight?

Any other helpful thoughts or comments are welcome.

 

[techrat]

I don't think those are going to do that much. I think you're better off finding a scrap of 8" (or larger) diameter tube, and making a Ring Fin. You'll need to sand down (or cut) the tips of the fins to square them up against the Ring and epoxy into place. Advantage is that it's hella-stable with that much fin area and it creates a butt-load of drag. Another thing you can do is add a pound of nose weight. Having to lift a useless payload also keeps the altitude down.

But the ultimate question is: Why are you trying to use a Minnie-Magg as a L2 rocket? I would think you're better off with something larger/heavier, but, buy another section of 5.5" tube and build a payload section at least. Make it a Maxi-Magg.

 

[3stoogesrocketry]

I have flown my MM a lot since last year and learned a lot. I kinda over built it anticipating that I would fly it for my L2 flight. I passed the test last week so I need to fly something.

With a J motor, the MM will go to over 3000 feet. This is a problem because our site is fairly tight, and I have difficulty walking long distances, let alone climbing trees.

I do have a chute release that I always use to reduce drift, but I have had some funky off-angle launches.

I was inspired by this thread https://www.rocketryforum.com/threads/variable-drag-project.157027/ to add some more drag to limit altitude. This is what I came up with:

View attachment 594925 View attachment 594926View attachment 594927View attachment 594928

I am having them 3D printed now, my thoughts are these will at least triple the drag, move the CP rearward, and limit the flight to around 1000-1500 feet.

My question is, is this a "legal" configuration for a cert flight?

Any other helpful thoughts or comments are welcome.

To build on what tech rate said , purchase a payload bay kit from Loc. Once it's built you can take a large bath towel and roll it up and put it inside the payload tube as ballast. Run your Sims again with a 18 inch or so long payload bay with a mass object of around a pound and see what the Sim does.

 

[Rschub]

making a Ring Fin.

You mean like this? Already thought about it.


The advantage of the 3D printed drag fins is that I only need to drill 3 3/8" holes to mount them, and they can be removed. And it already has a pound of nose weight.

The reason I am using it is because it is what I have.

Edit: The drag of one of those drag fins is easily more than the total drag of the entire stock Minnie-Magg.

 

[techrat]

The advantage of the 3D printed drag fins is that I only need to drill 3 3/8" holes to mount them, and they can be removed.

I would test that with the punchiest motor you can get while still L1 to make sure they don't just rip off the fins and/or rip themselves apart as the rocket flies up. Last month at Metra prefecture for TRA we had some kid try for his L2, and the rocket went up and the fins fluttered down as seperate pieces.

 

[Rschub]

I would test that with the punchiest motor you can get while still L1 to make sure they don't just rip off the fins and/or rip themselves apart as the rocket flies up. Last month at Metra prefecture for TRA we had some kid try for his L2, and the rocket went up and the fins fluttered down as seperate pieces.

Good point, I have an I345 in my motor box, I will be certifying with a single use J270.

My fins won't be fluttering down, the fin can was fiber glassed on the sections inside the body tube before installation.

 

[Steve Shannon]

If I were your certification witness I would allow the airbrakes you designed. One thing in particular that I like about them is that they’re YOUR solution.
In general I don’t like the addition of ballast. That introduces other issues.
I like the idea of a test flight.

 

[DragonRocketry]

Good point, I have an I345 in my motor box, I will be certifying with a single use J270.

My fins won't be fluttering down, the fin can was fiber glassed on the sections inside the body tube before installation.

I have a couple I600R's if you really want to test it out.

 

[kjhambrick]

@Rschub --

IANATRAL (*) but I don't see anything that would disallow air brakes.

They do disallow 'odd rocs':

Airframe – The rocket must be built by the flyer. The rocket shall display on the exterior identifying the calculated center of pressure. The rocket must be of “conventional rocket design.” “Odd Rockets” including flying pyramids, saucers, and flying spools, will not be allowed for any certification flight. The rocket may be either a kit or scratch-built. Scratch-built rockets may contain commercially built components.

but there is nothing odd about your airbrakes IMO, they're ingenius !

My only Qs are:

Q1: is there enough material behind your airbrake fasteners and is the material tough enough to prevent them tearing thru the fin material ?

I am with you, I want to fly more, walk less and you've come up with a kool solution

As others suggested, test it before your L2 flight ?

-- kjh

(*) IANATRAL - I Am Not A Tripoli Rocketry Association Lawyer so the final decision is up to your Prefect / TAP ...

 

[Rschub]

Q1: is there enough material behind your airbrake fasteners and is the material tough enough to prevent them tearing thru the fin material ?

The cutaway view shows an aluminum fully threaded standoff 3/8" dia. inserted through both the main fin and both sides of the drag fin. There is a generous edge distance from the hole in the plywood, so tear out forces of the bolt will be in the neighborhood of my excessive body weight. In addition, friction from the clamped sides will be the primary method of drag fin retention.
The material is still being discussed, I prefer a more flexible material to absorb any impact on landing, but my printer wants to use ABS, there will be a pretty good infill percentage in either case.
There will be a test flight!
I don't think I will get to the point of melting the material on any of these flights.
https://www.rocketryforum.com/threads/so-i-exceeded-the-limits-of-a-3d-printed-fin-can.167756/

 

[Buckeye]

I also like that you are adding drag, not mass, to reduce the altitude.

I would make something similar to a small fin alignment guide that would slide part way down the fins and wedge into place on the leading edge. Easy on/off, and potentially no fasteners needed.

 

[Rschub]

Just put a big rubber band around them to hold them on, Lol, I like it.

My original idea was to get cheap aluminum angles from the rocket store [Home Depot], cut them into 2" lengths and attach with wood screws.

Most people that heard this idea were..... not impressed, therefore I came up with this elegantly engineered alternative.

Apparently presentation is everything.

 

[jmasterj]

Just put a big rubber band around them to hold them on, Lol, I like it.

My original idea was to get cheap aluminum angles from the rocket store [Home Depot], cut them into 2" lengths and attach with wood screws.

Most people that heard this idea were..... not impressed, therefore I came up with this elegantly engineered alternative.

Apparently presentation is everything.

I like that aluminum angle idea! Keep it simple!

 

[kjhambrick]

Interesting stuff.

I wonder if OR or RockSim would sim close if you said your fins were X-inches thick ?

Where X is the mean thickness of the airbrake material purpendicular to your fin chords ?

Could be handy to know if the sims are close to the actual flight ...

-- kjh

p.s. Thanks for the link to the Variable Drag Project thread !

 

[Rschub]

TLAR is encoded into my DNA, so I have not worked with these sims yet.

 

[Tech 68]

Dirk Gates flew his and his late brother's upscale Sumo at LDRS 29 with similar "drag plates" on the aft edges of the fins to stay under the waiver with a full motor load-out.
They were perhaps 45 degrees to the fins, not perpendicular if I recall.

 

[ljwilley]

About it being legal, I have no idea why it would not be. You could use a kit, a scratch built rocket, or a modified kit for a cert as long as you built it yourself. No reason you can't add drag. It really is a good idea!!

 

[kjhambrick]

TLAR is encoded into my DNA, so I have not worked with these sims yet.

Sorry, @Rschub ...

I think I know what DNA is but what is TLAR ?

Thanks !

-- kjh

 

[Rschub]

That Looks About Right, an elegant weapon for a more civilized age.”

 

[kjhambrick]

Thanks @Rschub !

TLAR is a keeper !!

-- kjh

 

[Rschub]

Drag fins under construction:

 

[kjhambrick]

TLAR @Rschub ...

-- kjh

Actually ...

that is the KOOLEST idea I've seen or heard of in a long time

and your implementation is beautiful !

 

[techrat]

Drag fins under construction:

These are much more substantial looking than I had envisioned in my head. Should work well. Let us know how it goes.

 

[Rschub]

In Greek tragedy, those who struggle the most against their fate are those the least able to avoid it. The rocket gods are not Greek gods, but they must still be respected, mainly because they are fickle.



Today was the launch date, my supplier brought the drag fins and I installed them, everything fit perfectly. I proudly showed them to everyone that walked by and explained how they would lower the flight altitude and give me an easy walk, as planned. I will mention again that the purpose of this modification was to reduce the distance I had to walk, because I am a Lazy and Dangerous Rocket Scientist. I also decided that testing was for wimps and I would use the J270 and do the level 2 certification flight right then.

In due course the newly renamed "Macho Magg" was mounted on the pad and the button was pushed. The rocket leaped off the pad and roared skyward. The drag pads worked as predicted, the rocket got to about 1200 feet and the 8 second delay was just about perfect.

This was all too much for the rocket gods, so as the rocket was clearing the pad, a particularly mischievous one redirected the trajectory to a completely opposite direction.

All our pads aim left, because right is "abandon hope, all ye who enter here" territory. Every natural obstacle known to man, including cliffs, giant trees, thorn tree pastures and a rumored Bear Den are located that way. My rocket headed there. I clearly remember hearing from a bystander, "It's draggy, but not draggy enough"

One of the bonus features of this area is that anything landing there drops out of line of sight from the launch pad, so it's a treasure hunt from the beginning. Seasoned members of the club have been known to just shrug and write the rocket off immediately, but this was my certification flight, the rocket must return undamaged. I started walking.

I then met the most important person at the launch, a small child. "It fell right there, I saw it, follow me." We went into the underbrush. Through some miracle he led us directly to it, if you count about a half hour of thrashing around trying to find a way through a thicket of thorn trees as direct.



Other people were in the area, because the rocket gods didn't stop with me, so I asked the child to bring help, and he scampered off. I was alone, bleeding, sweating, my hip ached, and I wondered briefly how quickly it would be over with if a bear wandered by. Then I met the second most important person at the launch.

The man with the chainsaw.

I would like to say that I respect all god's creatures, that nature should be preserved, and that no trees were harmed during the recovery of my rocket.
But that would be a lie.


So, there you have it, experiment successful, rocket recovered undamaged, and the coveted level 2 certification obtained. Red badge of courage affixed indelibly upon my handiwork.

As I sat there in my chair, totally exhausted, sweating and bleeding, there was a launch.
It was a large rocket, it rose impossibly slowly, almost hovering, and finally accelerated skywards directly upward completely out of sight. We heard the event, the whistling descent, and saw the chute open as scheduled at 500 feet. The rocket landed barely 100 ft. from its launch pad.

I thought I heard faint laughter.

 

[Buckeye]

Well done. My stock Minie Magg often flew in odd directions.

What do you think is the Cd with wing tips attached?

 

[Rschub]

It has around 3 times the drag of the stock MM. It's supposed to do 3800 ft. or so on a "J"
Mine has usually gone pretty straight in the past, I am doing some more flights tomorrow, since I enjoy tempting fate.

 

[tsmith1315]

I proudly showed them to everyone that walked by and explained how they would lower the flight altitude and give me an easy walk, as planned.

The fatal mistakes are often disguised by zeal.

Great story, thanks so much for taking the time to tell it!

And congratulations on a well-earned L2 certification.

 

[kjhambrick]

Congratulations on your level 2 flight @Rschub !

Great launch report !

Macho Magg is a beautiful rocket -- your drag fin airbrakes look great.

And must say that I admire your devil-may-care J270 maiden voyage attitude and your 1200 / 3800 ft altitlude ratio is even more impressive

The gods giveth and gods taketh away: Thank the gods for the small child -- I had to blow up the photo of your rocket in the thorn tree to even kinda-sorta see it up there !

Two Qs ( for now ).

Q[1]: Did you pop the main at apogee ?

Q[2]: About how far, as the pegasus flies, was Macho Magg's thorn tree from the rail ?

Thanks for the report and congrats again !

-- kjh

 

[kjhambrick]

Well done. My stock Minie Magg often flew in odd directions.

What do you think is the Cd with wing tips attached?

@Rschub --

I wonder if you can back into the drag coefficient by back-calculating from the 1200 ft actual altitude ?

It would be interesting to see the numbers on how much your drag fin airbrakes affect the 'natural' CD of Macho Magg ...

-- kjh

 

[OzHybrid]

Congratulations.