# L3 Brainstorming

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#### MitchR

##### Air Defender
So for those of you that remember my first attempt, here begins the thoughts and ideas for attempt 2. My first round was at Southern Thunder 2007 where I flew my "Lactose Intolerant" - a modified Big Nuke 3E, on an M1297. She screamed to 10,500ft and had a flawless flight, that is until the main chute snagged on a sheer pin that didn't sheer right because I put a bigger chute protector in at the last minute (stupid mistake, I know) and changed the entire dynamic of my deployment setup. That rocket is repairable and will be seen flying again, however, I'm wanting to do a much lower, slower flight this time around.

I'm toying with ideas right now and have always enjoyed thoughts provided by this forum.

I want the largest diameter within reasonable cost, so far 10" seems to be the ticket. I'm leaning towards a 10" Bullpup or an upscale SA-14 Archer (two of my favorites). Any thoughts or ideas for a low altitude L3. I'd like to be in the 1500-3000ft range.

#### cjl

##### Well-Known Member
Well, for low alt, you'll want heavy and high thrust (fairly short burn), so something in the 10" and quite heavy (>50lbs) would work well to keep the altitude down. The Aerotech M1500G is an example of the type of motor I'm suggesting - 350lbs of thrust off the pad, and 3.5 second burntime. That would give a safe liftoff all the way up to around a 70lb rocket or so, but burns short enough to stay pretty low.

As far as the rocket design, that's of course up to you, but I really like the idea of the SA-14 Archer.

#### C.O.B.H.C.

##### Well-Known Member
My friend Erik did his L3 with a 10" Polecat Aerospace Bull Pup that weighted in at 80 pounds at lift off on a M1419W and only got 4,500 feet.

#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
Depending on your inclination in terms of making your own nosecones... You could always build something out of 16" sonotube and make yourself a nosecone for it.

It has the benefit of being incredibly inexpensive, relative to standard rocketry products.

-Kevin

#### bobkrech

##### Well-Known Member
I agree with Troj. A 16" Fat Boy type 3FNC weighing 55 pound on a CTI M2500 will go to about 2500'. 16" sonotube airframe, cheap blue foam built-up NC, 17' mil-spec flare chute, 3/8" plywood fins and bulkheads.

Bob

#### rrobe99999

##### Well-Known Member
Hey Mitch,
You sound like the new guy from the SEARS launch last Sat. This is Russ, the guy W/ the Sat V. It was fun meeting you. Thanks for all the help with recovery. I'm glad to see that you are thinking of a big build to fly with us.

#### AHansom

##### Well-Known Member
The 10" Bullpup should be able to be controlled to a 4000' or less flight. Aerotech is offering 25% discount on a M-1297 used for Level 3 certification

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#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
Bullpups are cool rockets; just watch the CP/CG -- it's short and stubby, and those forward fins can cause issues.

A friend did his L3 on a 7.5" one, and if I remember correctly, it took 50+ pounds of nose weight to keep it stable.

More weight = more issues on recovery.

-Kevin

#### sailmike

##### Well-Known Member
How about the 10" Thumper? What kind of altitude would this see?

I like the idea of using sonotube. Just add a couple layers of 5 ish oz fiberglass and it's good to go. But I don't know of anybody who sells that around Northridge.

Mike

#### Pantherjon

##### Well-Known Member
Should be able to get sonotube at any Lowes or Home Depot..Or Quickrete tubes can serve the purpose as well I would think...I have seen quite a few of those tubes in the local Lowes here, even had a couple in the 24" diameter!

#### bobkrech

##### Well-Known Member
How about the 10" Thumper? What kind of altitude would this see?

I like the idea of using sonotube. Just add a couple layers of 5 ish oz fiberglass and it's good to go. But I don't know of anybody who sells that around Northridge.

Mike
A 30 something pound 10" Thumper on a 7500 NS M would get about 4150', not 3000'. (Used wrong diameter in sim.)

Sonotube doesn't need glass for strength because it's plenty strong for holding concrete. A wrap of glass will make it look prettier though.

Bob

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#### AHansom

##### Well-Known Member
I did my level three with a 10" Thumper. On the pad ready to go the weight was just shy of 50 lbs. Using a Aerotech M-1850 it almost got to 6000'. I am not sure but I think the Bullpup might even take some more nose weight than the Thumper does. I only needed five lbs in the nose to get one caliber seperation of the CG & CP. Even at 6000' it's a big rocket and was very easy to visualy track.

#### MitchR

##### Air Defender
Ah, I'm enjoying the feedback guys thanks! A few things to add to the discussion, particularly regarding CG/CP relationships.

I cannot think of any complications, but wouldnt it make sense to just extend the 10" Bullpup by about 24"? This would make a roughly 10' tall Bullpup. An extended Thumper for that matter! This is what I did with my Big Nuke 3E in order to accomodate the M without having to add crazy amounts of nose weight.

I called a fiberglass company regarding 16" tubing. http://www.smithfibercast.com/ some heavy stuff but great quality! The nosecone would be the time consuming part but that'd be fun. Sonotube is the cheapest option still I think in regards to the custom build.

The above suggestions with the mil chute, cheap bulkheads, sonotube and custom nosecone is by far the cheap way to go. =D

#### AHansom

##### Well-Known Member
Extending a rocket is a way to get the CG forward although 24 on a bullpup it wont bring the CG that far forward. What it will do is give the weight in the nose more leverage so you will need less It all depends on the style of rocket you like. It might look cool but I am not sure it would still look like a Bullpup if it was streched 24".

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#### Kaycee

##### Well-Known Member
Welcome back, Mitch!

I knew you couldn't stay away for very long.

#### MitchR

##### Air Defender
Welcome back, Mitch!

I knew you couldn't stay away for very long.
Thanks Kaycee! I just needed some recoop time, now it's plotting time. haha =)

##### Well-Known Member
Kevin,

How did that flyer build his Bullpup? I find it hard to believe that 50 lbs was what was needed. Was he planning to fly it on really large motors? Or more likely, overbuilt the aft end? I think GaryT posted here about his 7.5" weighing less than 30 lbs dry. Sounds to me like less fault of the design and more of the builder.

#### tazzdevl1

##### Well-Known Member
Hey Mitch,
You sound like the new guy from the SEARS launch last Sat. This is Russ, the guy W/ the Sat V. It was fun meeting you. Thanks for all the help with recovery. I'm glad to see that you are thinking of a big build to fly with us.
And this is Cliff from SEARS. Nice meeting you Saturday. Welcome back.

Cliff

#### AHansom

WOW 50# of ballast in a 7.5" rocket. The lead alone would cost more than a M motor. I checked on Cabela's website and 50 16oz. fishing sinkers cost $400.00 + shipping Last edited: #### troj ##### Wielder Of the Skillet Of Harsh Discipline, Potent WOW 50# of ballast in a 7.5" rocket. The lead alone would cost more than a M motor. I checked on Cabela's website and 50 16oz. fishing sinkers cost$400.00 + shipping
Fishing sinkers is one of the most expensive ways to do it.

Lead shot is way cheaper -- well under $100. Some work at the local scrap yard and you can do it even cheaper. -Kevin #### Peartree ##### Cyborg Rocketeer Staff member Administrator Global Mod Or talk to a local guy who does tires or body work. The ones I know always have a bucket full of old lead tire weights laying around. #### cjl ##### Well-Known Member Fishing sinkers is one of the most expensive ways to do it. Lead shot is way cheaper -- well under$100.

Some work at the local scrap yard and you can do it even cheaper.

-Kevin
Agreed - I filled my L2 4" Amraam's nose with 10lb of lead shot - it wasn't that expensive.

#### GaryT

##### Well-Known Member
There is no way a 7.5" Polecat Bullpup will need 50# of nose weight? Mine flew at RG6 on an M1297W to 5879' with 6#'s of nose weight and it flew perfectly strait, In the short fat birds you don't really need a full caliper between the CP & CG, 1/2 to 3/4 will work fine. Mine was 42lbs on the pad, I tend to build heavy as well.

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#### MitchR

##### Air Defender
There is no way a 7.5" Polecat Bullpup will need 50# of nose weight? I just flew mine at RG6 on an M1297W to 5879' with 6#'s of nose weight and it flew perfectly strait, In the short fat birds you don't need a full caliper between the CP & CG, 1/2 to 3/4 will work fine. Mine was 42lbs on the pad, I tend to build heavy as well.

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Great looking flight on your Bullpup there Gary, like it a lot =)