[RocketsNW] Parachute protection options

[kmcgoffin at worldaccessnet.com]

I've never spent the requisite long hours over cups of coffee mulling
every little detail to be knowledgeable about pistons.  I only used a
piston in one rocket, my L1 1/4 PML Patriot.  It makes sense to have a
rear skirt to catch a lot of the BP crud.  It makes sense to cup the
parachute in a forward skirt. (I always wondered why the parachute didn't
bind between the piston and body tube.)  I dunno.

I'm of the school of thought that pistons are best used in larger diameter
rockets that don't see many flights and which can be thoroughly cleaned
between each flight.  I'm not flying those unless I trip over a gold
nugget big enough to give me a hernia lugging it home...
+McG+


> Yeah, I suppose dual skirt pistons will work, but the via for the Kevlar
> lanyard is supposed to exit the piston face and it's unnecessary bulk to
> deal with if you have to reach even further to the skirt mouth for the
> attachment loop.
>
> The piston lanyard I use on 38/54mm is 1/4-inch tubular Kevlar - it can
> get torched hundred's of times w/o concern for fatigue / failure.  The
> ends are looped (thus the bulk concerns above).  Loops aren't sewn, but
> rather wrapped at their junction with Kevlar thread which further
> contributes to compact packing.  Think of a hangman's noose - where the
> coil thread wrap is then soaked with a thin laminating epoxy - it's
> exceedingly strong.
>
> Yeah, I know - different strokes...
>
> /Steve
>
> -----Original Message-----
> From: kmcgoffin at worldaccessnet.com [mailto:kmcgoffin at worldaccessnet.com]
>
> Sent: Friday, November 07, 2008 4:19 PM
> To: Steve Cutonilli
> Cc: kmcgoffin at worldaccessnet.com; 'Azinger, Fred'; rockets at rocketsnw.com
> Subject: RE: [RocketsNW] Parachute protection options
>
> Is there any law that says you can't put the piston skirt on both sides?
> +McG+
>
>
>> Naa - keep the skirt non-inverted that way the piston ID takes the BP
>> hit thus leaving the airframe contact surface clean for more reliable
>> function.  /Steve
>>
>> -----Original Message-----
>> From: rockets-bounces at rocketsnw.com
>> [mailto:rockets-bounces at rocketsnw.com] On Behalf Of
>> kmcgoffin at worldaccessnet.com
>> Sent: Tuesday, November 04, 2008 9:09 PM
>> To: Azinger, Fred
>> Cc: rockets at rocketsnw.com
>> Subject: Re: [RocketsNW] Parachute protection options
>>
>> Yup.  And with aluminum parts, don't forget the superlube.
>> +McG+
>>
>>
>>> Don't forget to "invert" the piston -- skirt forward.
>>> Think of an automobile piston on the power stroke....skirt away from
>> the
>>> charge...
>>> Yes -- when coefficients of expansions are matched, pistons work
> well.
>>>
>>>
>>> -----Original Message-----
>>> From: rockets-bounces at rocketsnw.com
>>> [mailto:rockets-bounces at rocketsnw.com] On Behalf Of
> Mfreptiles at aol.com
>>> Sent: Monday, November 03, 2008 8:35 PM
>>> To: rockets at rocketsnw.com
>>> Subject: Re: [RocketsNW] Parachute protection options
>>>
>>> I think Steve is on to something in certain situations.
>>>
>>> Taking Steve's advice, I've built a piston for my 38mm all aluminum
>>> rocket.
>>> The piston is machined aluminum and slides really smoothly within
> the
>>> aluminum airframe and won't bind because the piston skirt is several
>>> calibers long
>>> and the piston and airframe is the same material.  My  previous
>> problem
>>> was
>>> the bulk of the recovery gear wrapped with nomex.   Even then, my
>> kevlar
>>> harness
>>> was exposed to the ejection gasses and would  degrade after a few
>>> flights.
>>> With the piston, there is less bulk to pack,  and the harness above
>> the
>>> piston
>>> stays like new.  The kevlar harness  section below the piston will
>>> degrade,
>>> but since it is shorter, less $ to  replace.
>>>
>>> Now if you asked me if I believe in phenolic pistons in cardboard, or
>>> plastic airframes........forget it! :)
>>>
>>> Mike F.
>>>
>>>
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>>
>>
>>
>>
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