When do I need shear pins?
Jerry O'Sullivan
Is there a "rule of thumb" for the use of shear pins (body dia, mass, etc)?
Thanks,
Jerry
Dean Roth
> Is there a "rule of thumb" for the use of shear pins (body dia, mass, etc)?
Use them to keep the nose cone on during descent when you use
two-stage recovery.
I recommend #2 nylon screws. They are hard to find. They are sold
by McMaster-Carr www.mcmaster.com . I used to use styrene rod,
but found that it would sometimes break before the ejection
charge fired.
Shear pins can also be used to keep the fin can and recovery
(payload) sections connected during coast to apogee if the
coupler is loose.
--
Dean Roth
dean _ roth at yahoo dot com
TSmith1315
Do shear pins require a substantial increase in the ejection charge in order
to snap them?
Tim Smith
TRA #4907 L2
Dean Roth
> Do shear pins require a substantial increase in the ejection charge in order
> to snap them?
I and the people that I fly with that use #2 nylon screws have not
increased the size of the ejection charge.
--
dean_roth at yahoo dot com
NOTE: Modify the return address to reply via email.
Jerry O'Sullivan
What I wondered was, at what size rocket do you feel they're necessary. For
example, I've flown 1.9 and 2.6" dia relatively light rockets with 2 stage
recovery several times with no problem.
My upcoming L2 project is a bit larger and heavier however - 4" and about
6lbs without motor and I'm concerned the additional mass will increase the
chance of early main deployment.
Thanks again,
Jerry
Dean Roth wrote in message <3803922F...@spamless.com>...
Jerome Craig
I think you were at the last MD Tripoli launch when I did my Level 2 with a
9lb Mini Magg.
(10/2 - 10/3). I use enough masking tape so that I can pick the rocket up and
carry it around
by the nose cone. I also have a 1/4" vent hole in the body tube, just below the
bottom of the
nose cone. I've not had any problems.
Jerome Craig
David Wakarchuk
I would use shear pins on any rocket where you need a little extra piece of
mind to know everything will stay in place until the proper time. I would
routinely use 1/16" styrene rod on almost any high performance rocket. For
example I use two set of 3 shear pins each on a 2.6" phenolic airframe. One
set to hold the nosecone on a vented payload bay that releases a polypropylene
streamer at apogee and another set to secure the fin can to the electronics bay
which releases the main chute for dual deployment. I have flown this rocket
with motors between an I65 and a K490 motor. I wouldn't even dream of flying
this rocket without the shear pins.
I do find that styrene 1/16" shear pins are very resitant to forces along the
axis of the airframe, while even a slight twist will easily break them. This
can prove to be annoying at times.
David Wakarchuk
CAR S53 TRA 1192
dave thedens
It is not a matter of mass, body dia, or such but a matter of inconvenience.
For instance, with my Lil' Moose at 4" dia it flys to 5K with a J5jo. It is
not to bad if the main comes out early. However, with Squirrel, the same 4"
diam on a L330 which flys to 11K, it would be a bad day if the R9 came out
too soon.
dave
Jerry O'Sullivan <mailto:erie...@erols.com> wrote in message
news:7tvusa$hs0$1...@autumn.news.rcn.net...
>Hi,
>
>Is there a "rule of thumb" for the use of shear pins (body dia, mass, etc)?
>
>Thanks,
>
>Jerry
>
>
Juerg Thuering
>
> Hi,
>
> Is there a "rule of thumb" for the use of shear pins (body dia, mass, etc)?
>
> Thanks,
>
> Jerry
Jerry
Quite frankly: allways!
Shearpins is one of the few clean solutions to hold it together,
friction fit always is sort of gambling.
Shearpins on the other side are quite predictable and give you
repeatable results.
I use shearpins on all of my high power rockets.
Juerg
TRA Switzerland
Juerg Thuering
>
> Jerry,
>
> I think you were at the last MD Tripoli launch when I did my Level 2 with a
> 9lb Mini Magg.
> (10/2 - 10/3). I use enough masking tape so that I can pick the rocket up and
> carry it around
> by the nose cone. I also have a 1/4" vent hole in the body tube, just below the
> bottom of the
> nose cone. I've not had any problems.
>
> Jerome Craig
Jerome
The problem of friction fit is that it depends on minimal tollerances!
If you happen to paint the body tube black and the nose cone white, the
sun will heat your body tube, it will possibly expand more than the
(white) nose cone and your friction fit is gone!
This happens also if you don't use different colours, just because of
different thermal expansion of tube and nose cone material.
Shear pins on the other hand allways shear of on (more or less) the same
load.
Juerg
TRA Switzerland
Juerg Thuering
> Do shear pins require a substantial increase in the ejection charge in order
> to snap them?
It depends on how many and how strong pins are used.
If you configure it for a normal strengt (you can just lift the rocket
holding it on the nose cone only but more load would not be supported),
you don't need more charge.
Static testing on the ground is a good idea anyway.
The nice thing: Once tested you know it works because the next time the
pins will fail under the same load (charge).
Juerg
TRA Switzerland
InMphsTim
From: "dave thedens" dave_t...@am.exch.hp.com
Date: Wed, 13 October 1999 01:12 PM EDT
Message-id: <7u2epr$fn9$1...@hpbs1500.boi.hp.com>
>>
Does anyone know if High Power or Sport Rocketry mags have written anything on
shear use and how to install them ?? InMphsTim @ aol.com Thanxs
Andrew Waddell
something in there about it.
--
Andrew D. Waddell
PML Online Support Rep
TRA 2043 L2/NAR 52875 L2
Email: ADWa...@home.com
PML: www.publicmissiles.com
InMphsTim <inmp...@aol.com> wrote in message
news:19991024094451...@ng-xa1.aol.com...
Dean Roth
>
> Does anyone know if High Power or Sport Rocketry mags have written anything on
> shear use and how to install them ?? InMphsTim @ aol.com Thanxs
HPR and Sport Rocketry do not write articles. Someone like you
or me must write whatever is published, and then submit it for
publication.
Dean's Guide to Installing and Using Shear Pins
-----------------------------------------------
1. Buy #2 nylon screws, 3/8" or 1/2" long. They can be hard to
find. They can be mail ordered from McMaster-Carr
www.mcmaster.com - about $6 for 100 screws plus about $3 shipping.
2. Insert nose cone into airframe.
3. Drill one or more 5/64" holes through the airframe and through
the nose cone's shoulder, about 1" below the top of the
airframe, or midway in the nose cone's shoulder if 1" is too
below the shoulder's midpoint. If more than one hole is used
equally space them around the airframe.
2.6" diameter airframe 1 hole
3-4" diameter airframe 2-3 holes, typically 2
4-6" diameter airframe 3-6 holes, typically 3 or 4
The number of holes depends upon the nose cone's mass
and the mass of the stuff behind it and how easily the
stuff (parachute, bridle, etc.) slides in the airframe.
Don't overdo it. More is not necessarily better. You
don't want to permanently attach the nose cone to the airframe.
If the airframe is plain cardboard then reinforce the
hole(s) with a drop of CA. Fiberglass and phenolic
airframes should not need reinforcement.
4. Find a screwdriver that fits the #2 nylon screw.
5. Turn the screw into the airframe and nose cone.
6. My experience has been that whatever ejection charge size has
worked should continue to work. However, a ground test
prior to the first flight using shear pins may be desired.
7. After a flight remove the portion of the screw that's still
in the airframe, and poke the piece in the nose cone into
the cone.
Alan Gorecki
rockets 4" and above if you use dual deployment. I use two in my 4" Hawk Mountain
Bad Attitude and three in my six inch Proteus. A good shear pin is the PML rivets
used in their old CPR system. The PML rivet is a two part system. Separate the
rivet from the holder and you're ready to go.
Alan
InMphsTim wrote:
> << Subject: Re: When do I need shear pins?
> From: "dave thedens" dave_t...@am.exch.hp.com
> Date: Wed, 13 October 1999 01:12 PM EDT
> Message-id: <7u2epr$fn9$1...@hpbs1500.boi.hp.com>
> >>
>
Chris Taylor Jr.
want the NC any tighter :-)
hehe
--
-----
Trust me you can Mail me without Mods
Chris
http://www.nerys.com/rocketry/
http://www.nerys.com/myjeep/