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Brian-Tampa

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Hello,
I was thinking of purchasing a 4" Black Fly kit from MAC Performance.
Their site does not have the correct RockSim file for this rocket in the 4" version. (.rkt file format)
They do have the file for the 3" version which I downloaded and loaded into RockSim.
The file is showing .33 margin for this model empty. This is severely understable.
CP = 26.6951"
CG = 25.6278"
Margin= 1.0673"

I have yet to find the correct RockSim file for the 4" Black Fly so I am hoping somebody can help me.

I have several questions regarding the 3" Black Fly RockSim file that I downloaded:

1. With this margin being so low empty, when a motor is installed won't the CG most likely move behind the CP?
2. To prevent this an awful lot of nose weight will be required to pull the CG forward far enough to be stable.
3. If there is anybody out there that has built the 4" Black Fly, what was the CG and CG empty?
4. Did you have to add nose weight to achieve an acceptable margin? And how much?
5. Does anybody have the correct Rocksim file for the 4" Black Fly? (.rkt format)

I know this may seem like a lot of questions, but I really like the 4" Black Fly and want to build it.
I was just really disturbed to see the margin on the 3" version so low.

Any help would be GREATLY appreciated!!

Thanks
Brian
 

mpitfield

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When I get home I can send you a file. As far as the stability margin, that is normal for shorter or squat style rockets. A lot of them require nose-weight and are inherently unstable. YMMV. It really depends on your build and motor choices. You can decide to use permanent nose-weight or removable, adjustable. I will share my choices later.
 

Brian3325

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I built my 4 inch Black Fly mostly stock. I did go with duel deploy with the main in the nosecone. My empty cg is at 26 inches from the nose and cp is calculated at 34.68 inches. I'm using Rocksim. First flight was on a J415, perfect straight up flight.
 

Brian-Tampa

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When I get home I can send you a file. As far as the stability margin, that is normal for shorter or squat style rockets. A lot of them require nose-weight and are inherently unstable. YMMV. It really depends on your build and motor choices. You can decide to use permanent nose-weight or removable, adjustable. I will share my choices later.
Michael,
I really appreciate your input and advice on the Black Fly.
Looking forward to see that RockSim file and any further input you might have.
Best Regards,
Brian
 

Brian-Tampa

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I built my 4 inch Black Fly mostly stock. I did go with duel deploy with the main in the nosecone. My empty cg is at 26 inches from the nose and cp is calculated at 34.68 inches. I'm using Rocksim. First flight was on a J415, perfect straight up flight.
Brian,
Thanks for the input.
Dual deploy might be the way to go on this build. Putting the main in the nose would put some much needed weight in the nose and pull the CG forward.
I''ll have to play with the RockSim file once I get it from Michael and see what I need in the nose weightwise to get a decent margin of stability and then work backwards.

Best Regards,

Brian
 

gfunk

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Here's my sim file. I saved this from Open Rocket, so your mileage may vary.

Heck of a rocket, definitely put the main in the NC and DD it. Get the upgraded WM NC, and expect to need a little nose weight.

My favorite rocket in the fleet, for sure. It will handle any motor you can cram in there! I really enjoyed the K2050ST, but I think the K1275R was still my favorite.
 

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Brian-Tampa

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gfunk,
I can't thank you enough for the sim file for the Black Fly.
Now I know how to proceed.
Thanks even more for the flight video, I've watched it 3 times. That has to be one of the best flights I have ever seen.
Gives me some incentive. LOL

Best Regards,
Brian
 

DeepOvertone

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IMG_0525.jpg


My dual deploy 4” black fly. It flies great. Got my L2 on it. Flew on a J270 for my L2 and an I364FJ on its second flight. I have sim files for it as built. Let me know if you’re interested.
 

mpitfield

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I see George beat me to it. Below is my RS and FWIW my OR file. Keep in mind that the CG and Mass are overridden in both files. The number I used is based on my completed build mass, fully loaded, minus the motor. Also, IMO, the 4" BlackFly with the Wildman FWFG nosecone is better suited for a HED dual deploy config. That doesn't mean that you can't fly single deploy and keep it simple; it is up to you.

While deciding, keep in mind that the mass of the AV bay and additional recovery gear in the nosecone, and the FWFG nosecone helps to offset the noseweight you may need.

My advice is to sim up every motor you think you may want to fly, leave the nosecone accessible, build her, do an actual weigh-in and measure your CG. At that point, you can decide if you want to add, as well as how to add any additional nose-weight.

Here is a pic of my 4". I used an Aeropack Tailcone retainer, which is removed in this pic so it can fit on the stand.
IMG_20200201_160208__01.jpg
 

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Brian-Tampa

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I would like to thank everybody on their input on the 4" Black Fly.
I now know how to proceed regarding nose weight.
The feedback on this forum is great.
Thanks again!
 

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