Good read, Allen.
James, I would have to disagree on the performance aspect.
Now someone smart (like with credentials, not just a smart ass) jump in and
correct me if I'm wrong, but the way I understand it, shape alone will dictate
drag, regardless of what the innards are. To agree with Mike, from much earlier
in this thread, the heavier the material, the less volume it occupies, which
means you can move the CG farther forward of the CP with less material than
with a less dense material. I've stabilized many a short or goofy rocket with
ballast. Just don't get too top-heavy, otherwise coning could occur - then drag
could come into the argument due to lateral movement.
I think the most important thing is to find out what President Trump thinks is
the best solution. Maybe he can make rocketry great again.
Best,
Troy Monroe Stacey
-------------------
On Jan 30, 2017, at 10:16 PM, James Dougherty <jafrado@xxxxxxxxx> wrote:
Yes, good point. Doesn't help for safety.
My point to Richard earlier is that it doesn't help for performance either.
All that extra volume in Airframe and nosecone loaded up with cat litter
would just translate to drag.
On Mon, Jan 30, 2017 at 8:12 PM, Allen Farrington <allen.farrington@xxxxxx>
wrote:
No need to do an experiment...we have everything we need to "first order"...
Two identical nose cones, let's say 4", 5:1 conical. Total internal volume =
0.00138 m^3, mass of cone itself is 0.2 kg.
Each nose cone contains the same mass of material, lead or sand.
For packed dry sand, the max amount of mass we can get in there: 2.3kg
For lead, we can easily get 2.3kg in the cone...it holds about 15kg.
Let's say that it falls from high enough to reach a terminal velocity of 90
m/s.
So when this cone hits something, it has KE=1/2mV^2 or 10.125 kJ of energy.
If it hits something hard, then it'll stop in 0.1 seconds (generous) and
ignoring bounce, it'll dissipate nearly 100,000 Watts in that 0.1 seconds.
That's enough to melt things...
Trust me on this, I've seen a nylon parachute completely melted in this type
of collision.
Now at this speed and energy, before the shell of the cone is destroyed, it
and the lead or packed sand has already penetrated together. As long as
structural integrity of cone is greater than packed sand, it'll penetrate as
a block.
So, Richard, sand doesn't buy you anything over lead for this case. Mass is
Mass and at these energies, things happen so fast that you'd be injured all
the same. It's a stark reminder that the recent death from a falling
nosecone/rocket was an unweighted, plastic nose. It doesn't take much if the
hit is in the right spot, sadly.
Is this what you had in mind?
Allen
Sent from my iPad
On Jan 30, 2017, at 5:52 PM, R Dierking <applerocketry@xxxxxxxxxxx> wrote:
I am a little surprised that no one has even suggested a little experiment
to impact test solid vs something like sand.
Keep in mind that one of the major reasons this topic kept going was
momentum. It didn’t have much time to slow down or ‘go away.’ (Be nice
David.)
I tried to quickly respond to questions as they came up, and the initial
topic didn’t go in many directions.
Richard Dierking
From: Wedge Oldham
Sent: Monday, January 30, 2017 5:45 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Prohibiting Metal for Nose Weight
If mass isn't mass; then it doesn't matter.
Seriously; the nose cone of my Nike Hercules came in ballistic in
Amarillo. It weighed 42 pounds; and fell from 12,000 feet.
Is there a non-metal material that would have made this safer?
Sent from my iPhone
On Jan 30, 2017, at 5:10 PM, Troy Monroe Stacey <tstacey001@xxxxxxxxxxxx>
wrote:
Clearly, the real debate is:
If mass is/isn't mass.
Best,
Troy Monroe Stacey
-------------------
On Jan 30, 2017, at 4:29 PM, Adrian P. Bailey <adrian@xxxxxxxxxxxxxxx>
wrote:
So, did the lakebed dry a little while we were chatting?<
It must have, with all the hot air… ;)
From: roc-chat-bounce@xxxxxxxxxxxxx
[mailto:roc-chat-bounce@xxxxxxxxxxxxx] On Behalf Of R Dierking
Sent: Monday, January 30, 2017 3:22 PM
To: Michael Klett <xsive.guy@xxxxxxxxx>; ROC Chat <roc-chat@xxxxxxxxxxxxx>
Subject: [roc-chat] Re: Prohibiting Metal for Nose Weight
Ok, might be a little off-topic. But, this kind of thing
(discussion/consideration/thinking out of the box), is not only
interesting, but necessary. Otherwise, it goes like, incident, rule,
incident, rule. How much fun would that be. Or, how about, let’s do the
same damn thing all the time.
Remember, some people were discussing the current condition of the
lakebed and it’s not even February. Sorry, but come on guys! You all
have been going to the lakebed enough times to know this is kind of
pointless now.
OK, I’m a pain. I’m actually being nice. I have hundreds of these topic
things. 😊
One thing that I know, when you bring something up that flies in the face
of established dogma, watch out! And, the reasons people will stand on
to defend; OMG.
For example, I once said that it was dangerous launching one rocket after
another without knowing the fate of the previous rocket. And, people
said, “what about the line of people waiting!” So, I replied, I have a
bow, not a powerful one, but I will stand by the low power pads, and
shoot one straight as possible into the air, and then immediately fire
another. “You can’t do that!” “That’s dangerous!”
I’m accumulated a list of things. But, I don’t keep track.
So, did the lakebed dry a little while we were chatting?
From: R Dierking
Sent: Monday, January 30, 2017 3:07 PM
To: Michael Klett; ROC Chat
Subject: [roc-chat] Re: Prohibiting Metal for Nose Weight
Not taking feathers. Considering the differences between pieces of metal
material and particles of other solid materials. Or, even water.
From: Michael Klett
Sent: Monday, January 30, 2017 2:49 PM
To: ROC Chat
Subject: [roc-chat] Re: Prohibiting Metal for Nose Weight
Yes, they weight the same but their volume can be very different. If the
volume difference is significant (lead vs. feathers) you may need more
weight to counteract the location of the CG of the weight.
On Mon, Jan 30, 2017 at 2:37 PM, David Smith <davew6dps@xxxxxxxxx> wrote:
Mike,
An ounce of BBs weighs the same as an ounce of sand.
Mass is Mass.
Dave
On Mon, Jan 30, 2017 at 2:34 PM, Michael Klett <xsive.guy@xxxxxxxxx>
wrote:
No, mass is not mass. If I needed 4 oz of weight at the tip I would need
a pound at the middle (depending the length of the rocket, placement of
CP an CG etc. The point is the lever arm.) With lead I can get really
close to the tip. With feathers I'd need a lot more volume and the cg of
the mass would not be near the tip so I'd need perhaps a pound of
feathers to be equivalent to the 4 oz in moving the rocket's CG. The
length of distance between the center of Mass of the rocket without the
weight and the center of mass of the added weight determines how much
weight you need to add. At the tip "less is more".
But to your other point. Once I add the epoxy to keep the sand in place
it in fact becomes "trash" on the playa because of the epoxy. And if
I've used the epoxy and things come apart a 4 oz blob of sand/epoxy is
going to hurt just as much (probably) as a 4 oz blob of lead/epoxy.
Sorry, I don't see any benefit to changing materials currently. Although
I must admit your idea of using water for ballast on the way up and
letting it drain out on the way down to reduce weight at landing has
always fascinated me.
Thanks,
Mike
On Mon, Jan 30, 2017 at 2:19 PM, R Dierking <applerocketry@xxxxxxxxxxx>
wrote:
Sorry Mike. I believe you have not considered other things and went to
what you knew first.
Yes, mass is mass. I don’t think anyone needs a high density material
for nose weight. It’s just not that critical.
However, it would probably be impossible for me to convince anyone that
insists on metal material. But, what the heck, I’m trying anyway.
Richard
From: Michael Klett
Sent: Monday, January 30, 2017 2:15 PM
To: ROC Chat
Subject: [roc-chat] Re: Prohibiting Metal for Nose Weight
Richard,
My ballast of choice is lead BBs. They seem safely captured in epoxy. I
would also argue that by using lead they occupy less volume so I can get
the center of the mass of the BBs further in to the tip of the nose cone
and so I need less weight. Less weight is safer. If I tried to put the
weight in the AvBay for instance, I'd need a lot more weight to balance
the rocket and the additional weight would reduce the safety some.
Thanks,
Michael
On Mon, Jan 30, 2017 at 2:05 PM, R Dierking <applerocketry@xxxxxxxxxxx>
wrote:
Then why do even people with model rockets use metal?
The RSO wouldn’t want someone with an aluminum nose cone on a HP rocket
but accepts rockets with a nose containing bolts or lean shot. And,
having taken a nose apart that had bb’s set in 5 minute epoxy, the epoxy
cracks and releases the bb’s.
From: Allen Farrington
Sent: Monday, January 30, 2017 1:59 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Prohibiting Metal for Nose Weight
Tripoli has an official statement on using metal...you can find it on
their website here:
http://www.tripoli.org/Portals/1/Documents/Safety%20Code/Metal%20in%20Rocket%20Construction%20v2.0.pdf
Allen
Sent from my iPad
On Jan 30, 2017, at 1:50 PM, R Dierking <applerocketry@xxxxxxxxxxx> wrote:
Next time the NAR and TRA safety rules are revised, there should be
something about what kind of nose weight should be used or how about
shouldn’t be used.
Don’t the codes already say something about minimizing the use of metal?
Why add it? There’s no good reason why metal has to be used; there are
other things that would work fine.
And, just to get ahead of the one response that’s going to ask if a
rocket with other types of weight could hurt someone just as bad. Yes, I
realize that. But, again, if you think through the various failure
scenarios, metal (bolts, lead shot, bb’s, what ever…) is a poor choice
for nose weight.
What other things could be used? Things that would be even better for
both safety and performance.
Richard Dierking
--
Justice shall flourish in his time, and fullness of peace for ever.
Psalm 72
--
Justice shall flourish in his time, and fullness of peace for ever.
Psalm 72
--
David P Smith
NAR 78668, L2
Amateur Extra, W6DPS
--
Justice shall flourish in his time, and fullness of peace for ever.
Psalm 72
