Mike's Level 3 Project
I'm scheming for a L3 certification.
Preferably with a Hybrid. Why a hybrid? Partly because I can get a
motor and a reload for the cost of one solid "M" reload without the
motor case. So it's less expensive. I'm also comitted to showing those
in the area that Hybrids are a viable alternative for all sizes of
rockets, including the big ones. In that light I'd like to do a Hybrid
L3 as well as at some point some large experimental hybrid motor work
The current motor I'm thinking of is the RATT L/M-900 motor combo. The
only other contenders are the HyperTek 98mm M motors, An advantage of
the RATT is the per-flight costs are cheaper, largely due to the
simpler and less costly grain (a slightly milled pipe insert) vs the
more expensive HyperTek reloads, which are specially cast motor/thrust
chamber assemblies. The HyperTek also has higher thrust profiles than
the RATT, allowing for more weight flexibility in the rocket design.
A disadvantage of the RATT is the lower average thrust and only one
thrust profile, at average 900ns. It's also very long at 78" for the M
assembly due to the 64mm tube. So we're looking at a 30 (preferable) to
40 (marginal in winds) rocket. The Hypertek at 98mm is only about 40"
long so for my target 6" rocket can be about 38" shorter, allowing for
an easier build to weight.
The overall design I like and want to
build to is an AGM-78, commonly known as a Standard Arm. There is a
nice 6" design starting point RockSim file on EMRR. The long strakes
may also allow for lighter construction of the BT as it naturally
Ideally, I can also fly my EX solids in this motor. Offhand, I'd like
to be able to accomodate at leasta a Baby M solid and that of average
to low average thrust (say the AT M1319 as a max average thrust to
design for). But the primary design is for the hybrids, so I will
sacrifice the higher end of solids for solid L/M hybrid flights in my
design. And get that approved by my TAP :)
The shortest length Hybrid MMT would, I think, be about 40" long 98mm
for the smallest HyperTek M. Starting with that I would already have to
lengthen the "starting point" AGM-78 mmt by about 15" or so. And maybe
upsize the chutes, requiring uplengthed payload bay ...
With that as a new baseline, I could also fly at least fly a 30" 75mm
Loki Baby M motor, so I'm in range of my solids compatibility.
Aside from a 40" HyperTek in 98mm, I'm also considering the RATT Works
L/M-900 motor combo. It's a 64mm (2.5") motor so is 42" long for the L
and 78" long for the M configuration. If I designed for this
combination I would build the rocket as a stretched AGM-78 with a 42"
75mm MMT for L hybrid and M solids flights and have an attachable
booster extension (semi-scale to the AGM-78 booster), that would
provide the length to accomodate the 78" long M tube for M flights. The
only disadvantge here is that the rocket that would accomodate a M
HyperTek would only accomodate an L RATT. With the RATT L & M
having the same average thrust, I'd need to conserve weight to allow
for the booster weight and still stay under design weight.
For the RATT Works L/M-900 I'm told that a 30 lb loaded rocket is great
and that 40lbs will work on calm days. I'd prefer to not worry about
calm days at Whitakers. And with a 13 lb loaded motor for the RATT,
that leaves only a 17lb budget for the rest of the rocket. With the
RATT that must acccomodate the extra 36" of booster extension.
I am otherwise told, not by my TAP, but by others that fly the RATT
L/M, that straight up PML 6" BT is more than adequeate for the thrust
and wouldn't need to be strengthened for that reason. So I could
consider skipping glassing the BT. I'm also told that many fly the RATT
L/M in 4" rockets to further help keep weight down. That seems to yield
rockets about 12' long.
The RATT would also be flyable anywhere. Since I mostly fly at
Whitakers, that's less of an issue, but still exists. Even though
Whitakers has GSE, I might need the drop down stem mods for the M, so
that would be an additional cost.
So I'm not sure about the motor. The HyperTek allows me to build one
rocket, and a shorter one at that, but at the expense of higher
Once nice advantage of the AGM-78 is the already designed in strakes.
While they add weight, they do stiffen the rocket and would allow more
flexibility in what I built up for the body tube (perhaps one less wrap
of fiberglass or CF).
I'm considering "true composite
construction" which mean fins, for example, will be surface mounted to
the airframe, not TTW. For "true composite airframes" (as I'm told by
Dave Triano of Shadow Aero), cutting your composite structure weakens,
but proper surface mounting is actually stronger. Emphasis on "proper".
I think the strakes will go a long way towards any "first time
composite" issues wrt strengthening, esp as single piece fins.
The challenge then is transferring motor force to the body ... but I'm
getting ahead ... as that's assuming the motor inserts are full rocket
I have a new page on Composite Structure Evaluations - Composite
Two stage? Not for the L3 cert flight,
but with some careful design, It could be built in such a way as to be
the sustainer ... hmm ...
Current intentions are a Tether pyrotechnic recovery device and a
"Control" flight computer, both from Defy Gravity.
Ed Rowe's SpinalTap
Excuse Me L3 project
A Hybrid with composite construction. Good for tips Dave Albertaw (
also on composite group ) http://www.cadvision.com/albertaw/Home.htm
David Cox's website
for his Juggernaut L3 project. He uses a lot of composite
construction in manners I was considering.
Devy Gravity may now be at http://22.214.171.124/defygravity/products.html
BlackSky AARD http://www.?.com
Composite Rocket Component
There's the rocket motor parts testing guy has some strength numbers on
his site, and also provided me with some weight tradeoffs.
Google Search on carbon fibre: http://www.google.com/search?q=L3+carbon+fiber+body+tube&sourceid=mozilla-search&start=0&start=0&ie=utf-8&oe=utf-8
John Coker's "Generic Rocket" ... 6" fibered airframe; similar specs
(mine might be heavier due to agm fins). http://www.jcrocket.com/generic.shtml
He's also got good How
To Pages Including vacuum bagging amongst other things.
Purple Rein on the Star Rocketry site.
Nike-Ajax - long and thin, "with
booster"; other rockets with Nike booster candidates (esp as Nike was
seemingly a popular booster.
Dave's Level 3 Certification Project - perhaps his
documentation - I like this format - lots of detail
http://www.strapworks.com - all
kids of strapping (not a rocketry specific site, but useful products)
fin flutter www.info-central.org/design_finflutter.shtml
Phasar L3 and construction.