Hnefi
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- Jul 30, 2014
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I've seen this idea thrown around in a few non-dedicated build threads, so I figured I'd open my own discussion/build thread to ask a few questions and show some pictures as I'm building. Always loved the design of the Bullpup from when my older cousin used to send me pictures of his model rockets, and after doing a few stock Estes kits I want to make a slightly modified version of this bad boy that can handle a 24mm motor tube (BP motors only, I'll be cutting some of the tail cone so I can use a motor hook). My first kit mod/scratch build!!! :clap:
Done a good amount of reading on this mod so far, and there's quite a few people who have done it with success. Only issue seems to be dealing with the stability when you put that much weight far back. Using the stock RReviews rocksim file as a bse, I modded it for the updated tube, centering ring, etc etc, and had to use 100g of nose weight just to keep the stability at 1.1cal on an E9?? D12 shows 1.46cal and a fat C shows 2.83cal on my sim file. This is my first experience with openrocket, so I'm wondering if I did something wrong here.... But judging by what I'd read, it needs a TON of nose weight when you stuff it with a 24mm, so maybe it's not too far off.
So I figured, let's just stretch the body tube (IIRC it's a BT55) by a few inches. Re-built a 12" version and was able to cut 60g of nose weight AND increase the stability to 1.27cal on an E9, which is realistically the largest motor I'd EVER use for this guy. I live in the GTA and there's not a lot of green space in this city to launch model rockets in. Would you guys recommend just biting the bullet with the stock length and using fishing weights or something for the nose weight, or getting the longer tube??
Still trying to work on the recovery system. 36"x3" Mylar streamer (this is unrealistically huge, I don't think I could ever roll this well enough to fit it in a BT55) gives me an impact velocity of almost 11 m/s, or approx 35 fps. You guys recommend using a chute given that this rocket is going to weigh 85g dry? Given that I have small fields, I'd like to streamer it if possible, but you guys have a ton more experience than I do!
Posted my ORK files, would absolutely love a few more experienced eyes to glance over them since this is my first try!
View attachment estes_bullpup_24mm_extended.ork
View attachment estes_bullpup_24mm.ork
Done a good amount of reading on this mod so far, and there's quite a few people who have done it with success. Only issue seems to be dealing with the stability when you put that much weight far back. Using the stock RReviews rocksim file as a bse, I modded it for the updated tube, centering ring, etc etc, and had to use 100g of nose weight just to keep the stability at 1.1cal on an E9?? D12 shows 1.46cal and a fat C shows 2.83cal on my sim file. This is my first experience with openrocket, so I'm wondering if I did something wrong here.... But judging by what I'd read, it needs a TON of nose weight when you stuff it with a 24mm, so maybe it's not too far off.
So I figured, let's just stretch the body tube (IIRC it's a BT55) by a few inches. Re-built a 12" version and was able to cut 60g of nose weight AND increase the stability to 1.27cal on an E9, which is realistically the largest motor I'd EVER use for this guy. I live in the GTA and there's not a lot of green space in this city to launch model rockets in. Would you guys recommend just biting the bullet with the stock length and using fishing weights or something for the nose weight, or getting the longer tube??
Still trying to work on the recovery system. 36"x3" Mylar streamer (this is unrealistically huge, I don't think I could ever roll this well enough to fit it in a BT55) gives me an impact velocity of almost 11 m/s, or approx 35 fps. You guys recommend using a chute given that this rocket is going to weigh 85g dry? Given that I have small fields, I'd like to streamer it if possible, but you guys have a ton more experience than I do!
Posted my ORK files, would absolutely love a few more experienced eyes to glance over them since this is my first try!
View attachment estes_bullpup_24mm_extended.ork
View attachment estes_bullpup_24mm.ork