Minnie-Magg drag mods for Level 2?

[Rschub]

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 !

Q1: I did not use the chute release on this flight because the air was dead calm, I had to re-arrange my chute harness to use the RNWS nosecone, and also in the interest of having one less thing to go wrong on the flight. Of, course, I knew my brilliant plan would work flawlessly. 8 seconds was right at apogee, although the rocket was arcing quite a bit. It looked exactly like one of my H225 flights, if that helps.

Q2: Not really that far, maybe 800 feet, just in the wrong direction. I did get to ride the golf cart back so that was a bonus. Everyone should get the chance to ride past the entire flight line with rocket held triumphantly overhead.

As far as calculating the drag, one of the goals of todays [rained out] flights was to install a flight computer and get some real altitude readings to compare.
I suppose one could sim the stock MM with the base drag hack to match the stock performance, then add more base drag until it matched the drag fin flight results. I think that there are so may aerodynamic things going on in this case that the sim would be useless, in other words, empirical results are what we are after, and making the sim match after the results are obtained is kinda pointless, at least to me.

Thanks for the congratulations, everyone!

 

[jmasterj]

I think that there are so may aerodynamic things going on in this case that the sim would be useless, in other words, empirical results are what we are after, and making the sim match after the results are obtained is kinda pointless, at least to me.

Are you never going to use the drag plates again? Seems like it would be useful to know the expected altitude in that case.

Great post, glad everything was successful in the end!

 

[Handeman]

Congrats on the L2!

Your flight sounds similar to my L3 cert flight back in '15. To this day, it's still the only chainsaw recovery I've had to do. It was recovered 4 days after it hung 80' in a pine tree. Fortunately we have a great landowner who's comment when told where it landed was, "Cut the tree down." We did.

Just a thought, but you might want to add some nose weight when you use those fin tabs. The only rocket I had that tended to veer off in unpredictable directions coming off the pad, even with 10:1 or higher TTW ratio, was a scratch built that turned out to have a much more marginal stability margin than what OR said. Adding 2 oz. of nose weight cured it of that and it was straight flights after that.

 

[Rschub]

Just a thought, but you might want to add some nose weight when you use those fin tabs

The tabs move the CP back, who knows how much. To be safe, I had 1.5 lbs of weight in the nose, the RNWS nosecone allows you to add variable weight to adjust for different motor sizes.
I had one full caliber of stability, the rocket weighed 7-8 lb at launch. I only had the one nose weight, which is sized for a different project.

Are you never going to use the drag plates again?

Yes I do plan on it.

Scott, at Dragon Rocketry made the drag plates for me and he also printed my design for an add-on electronics bay for the Macho-Magg.

Originally, I had a different supplier making this stuff, it was supposed to have been done a month age, so that I could have done some more testing.

Scott really came through, you should all buy lots of stuff from him!

I will use the ebay to do electronic eject with motor backup, this should take out the uncertainty of guessing at the delay, and give an exact number for the altitude.

I have a long term plan for using the drag plates, but in the interest of not angering the rocket gods, I must demur.

 

[ThirstyBarbarian]

Congratulations on your L2!

It sounds like the drag experiment was a success, even if the recovery was a bit of a “drag”. Do you think the odd launch angle had anything to do with the drag tabs? I could see how if the drag or weight were at all asymmetric, it could pull the rocket to one side.

 

[bad_idea]

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.
. . .
I thought I heard faint laughter.

Brilliant writing! Thanks for the entertaining read and the laughs, and congratulations on L2!

 

[Rschub]

As I mentioned in my first post in this topic, and someone else noted, the stock Minnie-Magg is prone to yoinking [yeeting?] off the pad in a random direction. There are several reasons for this that are inherent in the design of a stubby rocket.

The drag fins are a band-aid, if you will, to try to minimize the consequences of this behavior.

I did monitor the pads to see which ones were launching the straightest, unfortunately the one I wanted to use was taken when I got there because everyone else can walk faster than me. I will have a hard time coming up with a good solution to this problem. I will try plying the chainsaw/golf cart man with donuts next launch.

If I had just launched it normally it would have ended up deep in the tall trees, which start about 15 feet from the thorn trees. If I had used the chute release, it would have continued along the ballistic arc for longer and ended up again in the tall trees.

Since there was no wind, once the chute deployed it came basically straight down. Given the circumstances, the drag fins were not only a success, they were the only possible method of success.

This story is fairly typical of Tragedy. Here, the Tragic Hero's flaw was his determination to use the Minnie-Magg. He should have got a Doorknob.

 

[Rschub]

I flew the Minnie Magg today on a Loki I405. LOC suggests this motor will do about 2000 feet. With an av bay added and the drag fins on, computer 1 reported 863 feet and computer 2 reported 862 feet.
I didn't have the time to compare to a flight without the drag fins, it will have to be another day.
I did have my first DD flight which was completely successful, this was the main goal.
This flight was perfectly straight with no yeeting.

 

[kjhambrick]

I flew the minnie magg today on a Loki I405. LOC suggests this motor will do about 2000 feet. With an av bay added and the drag fins on, computer 1 reported 863 feet and computer 2 reported 862 feet.
I didn't have the time to compare to a flight without the drag fins, it will have to be another day.
I did have my first DD flight which was completely successful, this was the main goal.
This flight was perfectly straight with no yeeting.

@Rschub --

Your posts have been great for improving my impoverished vocabulary ...

So ... what is yeeting ?

EDIT: Oops ... never mind ... I see that you defined yeeting in your previous post.

Of course ! Yeeting is a synonym for yoinking !

-- kjh

 

[Rschub]

To be completely accurate, the 2 are not quite the same.

Yoink, or yoinked implies an outside force acting upon the object, usually inanimate.

Yeet, or yeeted implies an object with a self contained internal power source and possibly a mind of its own.

 

[kjhambrick]

To be completely accurate, the 2 are not quite the same.

Yoink, or yoinked implies an outside force acting upon the object, usually inanimate.

Yeet, or yeeted implies an object with a self contained internal power source and possibly a mind of its own.

Thank you, @Rschub !

Those flight modes are going into my glossary of terms along with TLAR

Yes, I've often wondered whether short, fat rockets might suffer from the relatively long lever-arm between the nozzle and the lower rail guide when they leave the rail at a lowish speed ...

It's hard to say ...

And to hijack your thread ... I've suffered both anomolies myself and sometimes it's hard to tell which is which ...

Most recently 'La Pequeña Vulcanita 34' coned VERY badly during the thrust phase due to either yoinking of yeeting.

Then her main did not eject at 700 feet and she trashed herself when her she landed on an asphalt road on a streamer.

I am not sure: Did she yeet because of her fins ? Or did she yoink because of off-center thrust (*) ?

I won't know until I fly her fin can again with a new av-bay and payload section design.

Thanks again !

-- kjh

(*) Hmmm ... would off-center thrust be catergorized as yoinking or yeeting ?

 

[Rschub]

Sometimes engineering terms can be difficult to understand. I will use them in a sentence.

The rocket immediately swerved off of its intended flight path. Technically correct.

The Rocket gods yoinked the rocket in the direction of the trees as soon as it cleared the rail.

The rocket yeeted toward the pond as if a dozen golden retrievers were chasing it.

(*) Hmmm ... would off-center thrust be catergorized as yoinking or yeeting ?

That depends on if you attribute the problems to the Rocket gods or some malevolent intelligence residing inside the rocket, because it can't be your fault.

That is the application for the "technically correct" language. I.E. The rocket swerved. The rocket coned, the rocket crashed, the LCO pushed the button, I am just standing here, etc..

I believe the proper terminology to describe your flight is suicided, or perhaps "took a dirt nap".

 

[Rschub]

Yes, I've often wondered whether short, fat rockets might suffer from the relatively long lever-arm between the nozzle and the lower rail guide when they leave the rail at a lowish speed ...

There was a rub mark on the nose cone when I used to mount my rail buttons flush with the body tube. I spaced them out about 1/4" to eliminate the rubbing, so there is obviously a rotational force acting around the top rail button. The I405 that I used has a much greater kick at the beginning of the thrust curve, so that would minimize the time the force has to act on the rocket, compared to the J270, and the airspeed will be higher at the end of the rail.

They launched a Sumo on an "N" motor yesterday and it went perfectly straight, so obviously there are solutions that work.

 

[Rschub]

I flew the Minnie Magg today on a Loki I405. LOC suggests this motor will do about 2000 feet. With an av bay added and the drag fins on, computer 1 reported 863 feet and computer 2 reported 862 feet.
I didn't have the time to compare to a flight without the drag fins, it will have to be another day.
I did have my first DD flight which was completely successful, this was the main goal.
This flight was perfectly straight with no yeeting.

To follow up on this, I launched today on the same motor without the drag fins and hit 1368 feet. I'll have to weigh this sucker, it must be a real pig.
On this flight the electronics performed correctly, but the 3 #2 shear pins broke loose at apogee and all the chutes came out. There was no wind so there was hardly any drift but I got a 4 inch zipper from the jerk at the top.
I was testing kevlar harnesses on this and the previous flight, they are much narrower than the 1/2 in straps I was using.
I am glad this happened here and not on my new rocket, I will do some kind of zipper proofing for it.
The good news is that the MM should be repairable.
It looks like the drag fins are not quite as effective as I had thought. The motor has a one second burn time so most of the time is coasting. I would need to do at least 2 other data points to get a good curve, so this is probably the end of the testing unless someone wants to supply the motors.
I am pretty happy about the results as it stands.