On Sun, 2008-11-30 at 22:01 -0500, Terry Leright wrote:
> Steve,
> The center plate was 3/16" thick. I kind of feel that was a big waste
> of perfectly good carbon plate though.
> If I did it over again the whole center would be foam or balsa.I
> drilled the plate to rid the fins of a little weight.
> These fins have such pointy tips I elected not to fight with bagging
> the tip to tip , rather I layed up 2 fins at a time ,
> poured 30 pounds of sand on them while they set up.I had a real mess
> going but it worked out well.
> Terry
>

Well, for what it's worth (probably not much), I ran your fin design
through FinSim. It can't handle your fin's internal structure, so I just
used a 3/16" flat plate as the fin. I tried aluminum (probably stiffer
than an equivalent plate of CF, but I don't know that for sure) and got
a flutter speed of around 1300mph. I tried G10, probably less stiff than
CF, and got a flutter speed of 760mph.

If I increase the thickness to 0.25", the aluminum flutter speed goes up
to 2000+mph, and the G10 goes to about 1200mph.

While that's not good news, I really would take FinSim's numbers with a
grain of salt, given your fin design. It absolutely is stiffer in
bending than a flat plate, and probably somewhat stiffer in torsion,
too, although maybe drilling all those holes reduced the torsional
stiffness (yet another experiment I need to run).  I also don't know
where CF rates in stiffness compared with aluminum. (If anyone has seen
any numbers on shear modulus or bending modulus for solid CF materials,
I'd love to hear about them.)

Finally, I don't know what FinSim does about aspect ratio. The calcs it
uses were originally based on airplane wings which had aspect ratios
above 7. Your aspect ratio is 0.5 and it is known that small aspect
ratios raise the flutter speed. There are known correction factors to
use when the aspect ratio is less than 7, but I don't think FinSim uses
them. So that, too, would tend to indicate that FinSim is
underestimating your true flutter speed.

Whatever you do, do *not* make the core of your fins out of balsa, foam,
or anything else that is less stiff than your facing material! When it
comes to stiffness, sandwich construction is almost never as stiff as a
plate made from the facing material. Sandwich construction is used to
*lighten* an assembly, or reduce its cost, while not sacrificing too
much *strength*. But with flutter, we're not talking about strength,
we're talking about *stiffness* and the core has a much larger influence
on stiffness than it does strength. When it comes to stiffness, floppy
core equals floppy fin (until the facing is so thick that it overwhelms
the core--see my report for details). You guys that are flying at these
speeds need all the stiffness you can muster and introducing a floppy
core is *not* the way to go, even if it does lighten things.

Please let me know what happens when you fly this thing...

--Steve

--- In CompositeRockets@yahoogroups.com, Steve Peterson
<steve_peterson@...> wrote:
>
> Sandwich construction is used to
> *lighten* an assembly, or reduce its cost, while not sacrificing too
> much *strength*.
> --Steve
>

Neither of these is the reason I use honeycomb core.
I feel the design of the sandwhich eliminates or at least damps some
of the harmonic oscilations.
I also feel it makes the fin stiffer.

OK, so I prove my design by flying it, not breaking it on the bench.
I find my way more exciting ;-)
2400MPH and counting...

Maybe I can push M4 and rip em off.


Robert

----- Original Message -----

From: Steve Peterson

To: CompositeRockets@yahoogroups.com

Sent: Monday, December 01, 2008 6:18 AM

Subject: Re: [CompositeRockets] Re: Jims Tutorial

On Sun, 2008-11-30 at 22:01 -0500, Terry Leright wrote:
> Steve,
> The center plate was 3/16" thick. I kind of feel that was a big waste
> of perfectly good carbon plate though.
> If I did it over again the whole center would be foam or balsa.I
> drilled the plate to rid the fins of a little weight.
> These fins have such pointy tips I elected not to fight with bagging
> the tip to tip , rather I layed up 2 fins at a time ,
> poured 30 pounds of sand on them while they set up.I had a real mess
> going but it worked out well.
> Terry
>

Well, for what it's worth (probably not much), I ran your fin design
through FinSim. It can't handle your fin's internal structure, so I just
used a 3/16" flat plate as the fin. I tried aluminum (probably stiffer
than an equivalent plate of CF, but I don't know that for sure) and got
a flutter speed of around 1300mph. I tried G10, probably less stiff than
CF, and got a flutter speed of 760mph.

If I increase the thickness to 0.25", the aluminum flutter speed goes up
to 2000+mph, and the G10 goes to about 1200mph.

While that's not good news, I really would take FinSim's numbers with a
grain of salt, given your fin design. It absolutely is stiffer in
bending than a flat plate, and probably somewhat stiffer in torsion,
too, although maybe drilling all those holes reduced the torsional
stiffness (yet another experiment I need to run). I also don't know
where CF rates in stiffness compared with aluminum. (If anyone has seen
any numbers on shear modulus or bending modulus for solid CF materials,
I'd love to hear about them.)

Finally, I don't know what FinSim does about aspect ratio. The calcs it
uses were originally based on airplane wings which had aspect ratios
above 7. Your aspect ratio is 0.5 and it is known that small aspect
ratios raise the flutter speed. There are known correction factors to
use when the aspect ratio is less than 7, but I don't think FinSim uses
them. So that, too, would tend to indicate that FinSim is
underestimating your true flutter speed.

Whatever you do, do *not* make the core of your fins out of balsa, foam,
or anything else that is less stiff than your facing material! When it
comes to stiffness, sandwich construction is almost never as stiff as a
plate made from the facing material. Sandwich construction is used to
*lighten* an assembly, or reduce its cost, while not sacrificing too
much *strength*. But with flutter, we're not talking about strength,
we're talking about *stiffness* and the core has a much larger influence
on stiffness than it does strength. When it comes to stiffness, floppy
core equals floppy fin (until the facing is so thick that it overwhelms
the core--see my report for details). You guys that are flying at these
speeds need all the stiffness you can muster and introducing a floppy
core is *not* the way to go, even if it does lighten things.

Please let me know what happens when you fly this thing...

--Steve

On Mon, 2008-12-01 at 12:50 +0000, Robert DeHate wrote:
> --- In CompositeRockets@yahoogroups.com, Steve Peterson
> <steve_peterson@...> wrote:
> >
> > Sandwich construction is used to
> > *lighten* an assembly, or reduce its cost, while not sacrificing too
> > much *strength*.
> > --Steve
> >
>
> Neither of these is the reason I use honeycomb core.
> I feel the design of the sandwhich eliminates or at least damps some
> of the harmonic oscilations.
> I also feel it makes the fin stiffer.

Before this goes too far, I should qualify my statement a bit. As I
point out in my report, for constructions *of equal thickness*, and
assuming (as is usually the case) that the core material has a lower
shear modulus than the facing material, then the sandwich will be less
stiff in torsion.

It is possible to make a sandwich stiffer than a solid assembly if you
increase the thickness (this makes up for the floppier core material).
Usually, however, increasing the thickness enough to achieve the desired
stiffness creates an unacceptable amount of drag. I have some examples
of increasing the thickness to achieve greater stiffness in my report.

So now we come to honeycomb and the shear modulus of a sandwich made
with it. Is it stiffer than solid CF? Maybe, maybe not--I haven't seen
any numbers on it. In the hobbiest world, people "test" stiffness by
testing it in bending by flexing it in their hands (thumbs in the middle
of the test piece). Rarely is torsional stiffness tested--unfortunately,
torsional stiffness is usually the controlling factor in flutter. So, to
my mind, we really don't know if honeycomb results in a more
flutter-resistant fin or not.

As to damping, all I can say is that according to the textbooks, it is
almost never clear what the effect of damping is on flutter. This is
completely counter-intuitive if your model is the usual resonance model
with an external forcing function. Unfortunately, that isn't what's
going on with flutter. Apparently there have been cases where increasing
the damping actually decreased the flutter speed. Go figure. And of
course, this assumes that honeycomb *does* actually increase the damping
of torsional oscillation.

--Steve (so many unknowns, so little time :-))

Just a few comments....

On Mon, 2008-12-01 at 08:52 -0500, Terry Leright wrote:
> Steve ,
> Thanks a million for running this simulation.

You're welcome. I hope I haven't caused you to lose any sleep over the
usability of your fins....the unknowns are great; I was just hoping for
a ballpark indication. Unfortunately, the ballpark is rather large :-)

> I would have thought that the core material didnt need to be there at
> all.Except for the fact that it gave me 3 walls to  attach  the fins
> to the airframe.
> Now that I think about it, suppose an airplane wing has a sheathed
> frame.

It does. But that frame is exquisitely designed to be very stiff both in
bending and torsion. To oversimplify greatly, they make a "box" of beams
inside the wing. We can do the same thing if we run *two* spars from
root to tip and space them as widely as we can and make them as deep as
we can. *Then* sheath the fin with a facing of CF (or whatever), making
sure the skin is securely attached to the spars. If you get the
dimensions right, then you *can* have an "empty" wing/fin that will be
torsionally rigid enough. But those dimensions have to be exactly right
and will probably result in a fin that is thicker than if it were
solid.

> Not that we're flying airplanes.

True, and thank the stars we aren't. The airplane designers have to
worry about all sorts of crap we don't. Like aelerons, engines hanging
from wings, fuel in wing tanks. Sandwich construction is more than
complicated enough, thank you :-)

> When you mention "flutter speed" I suspect your talking about when the
> fin starts to flutter.

Correct. Generally, but not always, the wing/fin falls apart almost
immediately. There are some cool videos of this process on YouTube.
Here's one of an R/C plane:

http://www.youtube.com/watch?v=nRit6tcNT4s

Then some other guys replicated it in wind tunnel:
http://www.youtube.com/watch?v=MlbYmqi5paE

Notice how quickly in both cases the wing falls apart--one second
nothing is happening, the next second it's toast.

On the other hand, it *is* possible to have a wing flutter and not fall
apart:
http://www.youtube.com/watch?v=kQI3AWpTWhM

Notice, however, that the plane's speed was not increasing very much if
at all--with the flapping, it was probably actually decreasing which
helped to keep things under control. In a  dive, the outcome would
likely have been different.

--Steve

----- Original Message -----

From: Steve Peterson

To: CompositeRockets@yahoogroups.com

Sent: Monday, December 01, 2008 9:45 AM

Subject: Re: [CompositeRockets] Re: Jims Tutorial

Just a few comments....

On Mon, 2008-12-01 at 08:52 -0500, Terry Leright wrote:
> Steve ,
> Thanks a million for running this simulation.

You're welcome. I hope I haven't caused you to lose any sleep over the
usability of your fins....the unknowns are great; I was just hoping for
a ballpark indication. Unfortunately, the ballpark is rather large :-)

> I would have thought that the core material didnt need to be there at
> all.Except for the fact that it gave me 3 walls to attach the fins
> to the airframe.
> Now that I think about it, suppose an airplane wing has a sheathed
> frame.

It does. But that frame is exquisitely designed to be very stiff both in
bending and torsion. To oversimplify greatly, they make a "box" of beams
inside the wing. We can do the same thing if we run *two* spars from
root to tip and space them as widely as we can and make them as deep as
we can. *Then* sheath the fin with a facing of CF (or whatever), making
sure the skin is securely attached to the spars. If you get the
dimensions right, then you *can* have an "empty" wing/fin that will be
torsionally rigid enough. But those dimensions have to be exactly right
and will probably result in a fin that is thicker than if it were
solid.

> Not that we're flying airplanes.

True, and thank the stars we aren't. The airplane designers have to
worry about all sorts of crap we don't. Like aelerons, engines hanging
from wings, fuel in wing tanks. Sandwich construction is more than
complicated enough, thank you :-)

> When you mention "flutter speed" I suspect your talking about when the
> fin starts to flutter.

Correct. Generally, but not always, the wing/fin falls apart almost
immediately. There are some cool videos of this process on YouTube.
Here's one of an R/C plane:

http://www.youtube.com/watch?v=nRit6tcNT4s

Then some other guys replicated it in wind tunnel:
http://www.youtube.com/watch?v=MlbYmqi5paE

Notice how quickly in both cases the wing falls apart--one second
nothing is happening, the next second it's toast.

On the other hand, it *is* possible to have a wing flutter and not fall
apart:
http://www.youtube.com/watch?v=kQI3AWpTWhM

Notice, however, that the plane's speed was not increasing very much if
at all--with the flapping, it was probably actually decreasing which
helped to keep things under control. In a dive, the outcome would
likely have been different.

--Steve

--- In CompositeRockets@yahoogroups.com, Steve Peterson
<steve_peterson@...> wrote:
>
> Before this goes too far, I should qualify my statement a bit. As I
> point out in my report, for constructions *of equal thickness*, and
> assuming (as is usually the case) that the core material has a lower
> shear modulus than the facing material, then the sandwich will be
less stiff in torsion.
>
> It is possible to make a sandwich stiffer than a solid assembly if you
> increase the thickness (this makes up for the floppier core material).
> --Steve (so many unknowns, so little time :-))
>

It seems obvious that thicker solid fins are stronger.
Of equal thickness is not really a practical comparison.
From the equation side of things yes calculating flutter or drag has a
high dependence upon thickness.
And it makes for a nice tidy calculation.

But in terms of practicality.
Lets look at the parts used.

Example:
I want to build a fin with 3 layers of carbon on each side.
I could simply make a fin with the 6layers of carbon and no core.
Or I can have a 1/8in core of honeycomb with 3 layers of carbon each
side.
The difference in drag is marginal between the two when you consider
all other unknowns.
But the core fin will be stronger and less prone to flutter.
And as far as technique this does not account for placing layers at
alternating 45deg angles.
We know this makes a stronger layup but how does that factor in?

You are correct, "so many unknowns"

Practically speaking of course,
Robert

On Mon, 2008-12-01 at 11:00 -0500, Terry Leright wrote:
> Steve ,
> This is a video of a freinds rocket. Seeing this was my introduction
> to fin flutter.You may have seen it.

Yes, many times! I did not mention it primarily because I figure
everyone on this list has already seen it multiple times (it having been
discussed extensively on other forums).

The end of the video certainly brings home how quickly the forces build
up--I counted about 8 oscillations before the fins came off.



--Steve

On Mon, 2008-12-01 at 16:25 +0000, Robert DeHate wrote:

> It seems obvious that thicker solid fins are stronger.
Stiffer...we're talking *stiffer* :-)

  And it wasn't obvious to me until I did the research, especially in
view of all the hype one reads about sandwich construction....
<snip>
> Example:
> I want to build a fin with 3 layers of carbon on each side.

Well, I'll grant you that some people approach it that way--that is,
start with the solution before they examine the requirements.

However, an engineering approach would be to ask "How strong does it
have to be? How stiff does it have to be? How much money am I willing to
spend? How thick can I make it and still be OK with drag? etc. etc." And
then to design/build to meet the constraints, possibly optimizing in one
or more directions.

In other words, what you come up with depends on the way you approach
the situation. Your example essentially asks "what's the stiffest fin I
can build with 3 layers of carbon on each side?" and the answer,
assuming that honeycomb is truly stiffer than solid fiberglass, is
sandwich the honeycomb between 3-layer CF facings. In short, the
*question* has determined the answer. Ask the question differently (in a
less constrained way) and maybe the answer changes.

(Just for the record, I have no opinion on whether honeycomb is stiffer
than solid fiberglass or solid CF--I just don't have the data either
way.)

> I could simply make a fin with the 6layers of carbon and no core.
> Or I can have a 1/8in core of honeycomb with 3 layers of carbon each
> side.
> The difference in drag is marginal between the two when you consider
> all other unknowns.

The FAI guys would probably disagree...

> But the core fin will be stronger and less prone to flutter.


Sure, but that's because you artifically constrained the solution by
assuming beforehand that you would use 6 layers of CF. That's exactly
the situation I described in the earlier post where I said "sandwich
constructions are used to lighten or reduce cost" but you said that's
not why you use honeycomb. Restricting yourself a priori to 6 layers of
CF is equivalent to saying "I'm not going to spend more than X dollars
on CF, so what's the stiffest fin I can build given that constraint?".
When that's your starting point, the answer is always sandwich
construction with the stiffest, thickest core you can find that meets
whatever other requirements you may have.

My point was that if the question is "what is the stiffest fin I can
possibly build?" you get a different answer, namely, "use the facing
material throughout". If you're going to compare two things, you have to
hold *something* constant. In my original example, I held thickness
constant in order to demonstrate a tradeoff. In your example, you held
"quantity of CF" constant to make a different point. My meta-point is
that which approach one chooses needs to be based on the requirements.

In general, you seem to be saying that a sandwich assembly has so few
penalties that it's always worth doing. That is, because the increase in
drag is minimal, and since you're going to use the 6 layers of CF
anyway, just go ahead and use the honeycomb. And I will agree that in
certain situations, that's the best answer.

However, I'm trying to get people to understand what the tradeoffs are
and to understand how those tradeoffs affect flutter.

My position has always been that the solution (design/construction)
needs to match the requirements. I suspect you agree with that; where I
think we may disagree is that you have a certain view of the
requirements (based on what you typically are trying to do) and I am
trying to be as inclusive as I can regarding *everyone's* potential
requirements.

> And as far as technique this does not account for placing layers at
> alternating 45deg angles.
> We know this makes a stronger layup but how does that factor in?

Yup, it's on the list of things to find out.

--Steve

Check out this report:

http://www.washingtonpost.com/wp-dyn/content/article/2008/11/29/AR2008112901914.\
html

"In a burst of activity meant to leave a lasting stamp on the federal
government, the Bush White House in the past month has approved 61 new
regulations on environmental, security, social and commercial matters
that by its own estimate will have an economic impact exceeding $1.9
billion annually. "

...

"The rules cover obscure as well as high-profile social and economic
issues: spelling out what kinds of records must be kept by sexually
explicit performers and publications, exempting hobbyists' rocket
motors from federal explosives controls, expanding the collection of
DNA samples from federal prisoners. "

Sounds too good to be true, does anyone have a reference to the rule
passed affecting rocketry?

Matt

Hi David,

It may be a red herring.  A friend wrote the reporter who submitted
this story, he was talking about the elimination of our motors
exemption, not the exemption of the motors.  :(

Matt

On Mon, Dec 1, 2008 at 12:30 PM, David <dwculp@...> wrote:
> Anyone have any other information???
>
> On Mon, Dec 1, 2008 at 1:56 PM, <Ez2cDave@...> wrote:
>>
>>
http://www.washingtonpost.com/wp-dyn/content/article/2008/11/29/AR2008112901914.\
html
>>
>> MORE SPECIFICALLY . . . ( Obviously, the part pertaining to Rocket Motors
>> )
>>
>> The rules cover obscure as well as high-profile social and economic
>> issues:
>> spelling out what kinds of records must be kept by sexually explicit
>> performers and publications, exempting hobbyists' rocket motors from
>> federal
>> explosives controls, expanding the collection of DNA samples from federal
>> prisoners.
>>
>> Dave Fitch
>>
>>
>> ________________________________
>> Life should be easier. So should your homepage. Try the NEW AOL.com.
>>
>

Hi David,

Here is the email chain to the reporter.  I don't think this is
definitive but it doesn't look good.

Matt

---------- Forwarded message ----------
From: Rick Dickinson <rtd@...>
Date: Mon, Dec 1, 2008 at 12:12 PM
Subject: Re: [ROC-chat] Fwd: [Tripoli-SD] Bush administration exempts
hobbyrocket motors fromfederal explosives control
To: ROC-CHAT <roc-chat@...>



On Mon, 01 Dec 2008 10:36:17 -0800, John Van Norman <yrockets@...>
wrote:
> We are looking at this and will get back to everyone--it sounds to
> good to be true--and everyone knows that old saying...
>
> John Van Norman
> VP, ROC BOD

It appears that our hopes were somewhat premature.  The mention of our
hobby in the article was based upon an apparent misreading of the old NPRM
removing the "PAD exemption" for rocket motors.

I wrote to the authors of the article, asking for clarification.  Here is
the reply I got from Jeff Smith at the Washington Post, and my response to
him:

========================

On Mon, 1 Dec 2008 14:05:09 -0500, Jeff Smith <smithj@...> wrote:
> it was a justice department regulatory change initiated and carried
> out by the alcohol, tobacco, and firearms section. it should have been
> published in the federal register by now. the draft regulation was
> known as 1140-AA24, Commerce in Explosives - Amended Definition of
> Propellant Actuated Device.

Ah, that's too bad, then.  I was afraid that this might be the change to
which the article referred.

Unfortunately, this change does not "[exempt] hobbyists' rocket motors from
federal explosives controls" -- it has the exact opposite effect.  It
eliminates an exemption, rather than granting one.

It has not yet been published in the Federal Register; the Agenda shows
Final Action scheduled for January 2009:
<a
href="http://www.regulations.gov/fdmspublic//component/main?main=UnifiedAgenda&a\
mp;agency=DOJ&pubperiod=200810&rin=1140-AA24"
target="_blank">http://www.regulations.gov/fdmspublic//component/main?main=Unifi\
edAgenda&agency=DOJ&pubperiod=200810&rin=1140-AA24</a>

Once the Final Rule's published in the Federal Register, it will eliminate
the possibility of exempting rocket motors from regulation by classifying
them as "Propellant Actuated Devices".  This is a tightening of already
over-burdensome regulations, not a grant of relief.

And, it's certainly nothing "new" that the Bush Administration is pushing
through at the last minute.  The Notice of Proposed Rulemaking for this
change came out over two years ago, and it was widely discussed (and
commented upon) at the time.

Thank you for taking the time to respond.  I appreciate the clarification,
even though it dashes my hope for unexpected regulatory relief.

Thanks again,

  - Rick Dickinson
   Director, Rocketry Organization of California


_______________________________________________
ROC-chat mailing list
ROC-chat@...
http://rocketeers.com/mailman/listinfo/roc-chat

--- In CompositeRockets@yahoogroups.com, Steve Peterson
<steve_peterson@...> wrote:
>
> On Mon, 2008-12-01 at 16:25 +0000, Robert DeHate wrote:
>
> > It seems obvious that thicker solid fins are stronger.
> Stiffer...we're talking *stiffer* :-)
>
>  And it wasn't obvious to me until I did the research, especially in
> view of all the hype one reads about sandwich construction....
> <snip>
> > Example:
> > I want to build a fin with 3 layers of carbon on each side.
>
> Well, I'll grant you that some people approach it that way--that is,
> start with the solution before they examine the requirements.
>
> However, an engineering approach would be to ask "How strong does it
> have to be? How stiff does it have to be? How much money am I
willing to
> spend? How thick can I make it and still be OK with drag? etc.
etc." And
> then to design/build to meet the constraints, possibly optimizing
in one
> or more directions.
>
> In other words, what you come up with depends on the way you
approach
> the situation. Your example essentially asks "what's the stiffest
fin I
> can build with 3 layers of carbon on each side?" and the answer,
> assuming that honeycomb is truly stiffer than solid fiberglass, is
> sandwich the honeycomb between 3-layer CF facings. In short, the
> *question* has determined the answer. Ask the question differently
(in a
> less constrained way) and maybe the answer changes.
>
> (Just for the record, I have no opinion on whether honeycomb is
stiffer
> than solid fiberglass or solid CF--I just don't have the data either
> way.)
>
> > I could simply make a fin with the 6layers of carbon and no core.
> > Or I can have a 1/8in core of honeycomb with 3 layers of carbon
each
> > side.
> > The difference in drag is marginal between the two when you
consider
> > all other unknowns.
>
> The FAI guys would probably disagree...
>
> > But the core fin will be stronger and less prone to flutter.
>
>
> Sure, but that's because you artifically constrained the solution by
> assuming beforehand that you would use 6 layers of CF. That's
exactly
> the situation I described in the earlier post where I said "sandwich
> constructions are used to lighten or reduce cost" but you said
that's
> not why you use honeycomb. Restricting yourself a priori to 6
layers of
> CF is equivalent to saying "I'm not going to spend more than X
dollars
> on CF, so what's the stiffest fin I can build given that
constraint?".
> When that's your starting point, the answer is always sandwich
> construction with the stiffest, thickest core you can find that
meets
> whatever other requirements you may have.
>
> My point was that if the question is "what is the stiffest fin I can
> possibly build?" you get a different answer, namely, "use the facing
> material throughout". If you're going to compare two things, you
have to
> hold *something* constant. In my original example, I held thickness
> constant in order to demonstrate a tradeoff. In your example, you
held
> "quantity of CF" constant to make a different point. My meta-point
is
> that which approach one chooses needs to be based on the
requirements.
>
> In general, you seem to be saying that a sandwich assembly has so
few
> penalties that it's always worth doing. That is, because the
increase in
> drag is minimal, and since you're going to use the 6 layers of CF
> anyway, just go ahead and use the honeycomb. And I will agree that
in
> certain situations, that's the best answer.
>
> However, I'm trying to get people to understand what the tradeoffs
are
> and to understand how those tradeoffs affect flutter.
>
> My position has always been that the solution (design/construction)
> needs to match the requirements. I suspect you agree with that;
where I
> think we may disagree is that you have a certain view of the
> requirements (based on what you typically are trying to do) and I am
> trying to be as inclusive as I can regarding *everyone's* potential
> requirements.
>
> > And as far as technique this does not account for placing layers
at
> > alternating 45deg angles.
> > We know this makes a stronger layup but how does that factor in?
>
> Yup, it's on the list of things to find out.
>
> --Steve
>

Exactly,
Sort of.
I do not believe a blanket statement that solid construction is best.
I also do not think sandwhich construction is always best.

You state:
"use the facing material throughout. that solid construction is
always best."

So don't waste your time trying to characterize anything but solid
construction.

Because we all know there is nothing new to be learned.
And old information is all there is to know.

Good luck with that.
Robert

On Mon, 2008-12-01 at 21:31 +0000, Robert DeHate wrote:

> Exactly,
> Sort of.
> I do not believe a blanket statement that solid construction is best.
> I also do not think sandwhich construction is always best.
>
> You state:
> "use the facing material throughout. that solid construction is
> always best."

Uh, Robert, I see where I said "...use the facing material throughout"
but it was in the context of "if you need the stiffest possible fin".

I don't see where I said "solid construction is always best". I did say
to Terry "whatever you do don't make your core out of balsa or foam" but
that was not a blanket statement to everyone or even to Terry. It was in
response to his musing about making a similar rocket but using
foam/balsa for a core, and I intended my answer to be read in that
context. My understanding of his situation is that he probably *does*
need the stiffest possible fin he can build while keeping thickness down
or even minimizing it, because he's already said he's concerned about
his 3/4" thickness.

What I'm saying is if the driving consideration is "stiffest possible
fin with the least thickness" then solid construction will turn out to
be the answer.

And if some other factor (weight, minimization of facing material [for
whatever reason: cost, availability, contest rules, self-imposed limit,
whatever]) is the driving factor, then sandwich construction turns out
to be the answer.

Different people will have different factors driving the decision.


--Steve

Steve just out of curiosity how many sandwich panel fin set have you
made and flown? What core did you use. Was it a high, medium or low
density closed cell foam. What was the compression strength, shear
Modula's, tensile strength and Modula's, What was it Thermal
conductivity or heat dissipation factor? What was you technique used
for construction? Did you use solid carbon bar stock for the core
edges. When you skinned the frame core what vacuum level did you
pull? Also what heat schedule did you use to cure and post cure them.
Also what was the fastest your sandwich panel fin set flew at? Mine
flew at 2332 fps is that close to what yours flew at.
I also had a 40 pound rocket fall from 22 thousand feet with no
chute. There was no damage to the sandwich panel fin set. Have you
ever had this happen to you?

Okay I know your not a big fan of sandwich panel fins so just tell
some history of the solid composite fins you made and flown. What was
you engineering criteria for the fins you made. After months of
equations and evaluating the exact strength to weight ratio for the
intended flight those must have been some pretty awesome fins. Do you
have any photo's you could share with us. As it seem that you are the
only one with the answers to make the perfect set of fins, I can't
wait to see the photos and hear about the flight.

If it sounds like I'm bitter it because I am. You have left the
impression that until you have it all figured out no one none of us
need to even make anything. People are shying away from experimenting
because you are so self assured that the only right way is Steve's
way.

I agree that the math is important so keep working on it, not saying
that it isn't. I just don't want everyone so polarized that
everything they experiment with makes them feel it is a total waste
of hobby time until you come up with the one true answer.

Mick


--- In CompositeRockets@yahoogroups.com, Steve Peterson
<steve_peterson@...> wrote:
>
> On Mon, 2008-12-01 at 21:31 +0000, Robert DeHate wrote:
>
> > Exactly,
> > Sort of.
> > I do not believe a blanket statement that solid construction is
best.
> > I also do not think sandwhich construction is always best.
> >
> > You state:
> > "use the facing material throughout. that solid construction is
> > always best."
>
> Uh, Robert, I see where I said "...use the facing material
throughout"
> but it was in the context of "if you need the stiffest possible
fin".
>
> I don't see where I said "solid construction is always best". I did
say
> to Terry "whatever you do don't make your core out of balsa or
foam" but
> that was not a blanket statement to everyone or even to Terry. It
was in
> response to his musing about making a similar rocket but using
> foam/balsa for a core, and I intended my answer to be read in that
> context. My understanding of his situation is that he probably
*does*
> need the stiffest possible fin he can build while keeping thickness
down
> or even minimizing it, because he's already said he's concerned
about
> his 3/4" thickness.
>
> What I'm saying is if the driving consideration is "stiffest
possible
> fin with the least thickness" then solid construction will turn out
to
> be the answer.
>
> And if some other factor (weight, minimization of facing material
[for
> whatever reason: cost, availability, contest rules, self-imposed
limit,
> whatever]) is the driving factor, then sandwich construction turns
out
> to be the answer.
>
> Different people will have different factors driving the decision.
>
>
> --Steve
>

----- Original Message -----

From: Steve Peterson

To: CompositeRockets@yahoogroups.com

Sent: Monday, December 01, 2008 4:59 PM

Subject: Re: [CompositeRockets] Re: Jims Tutorial

On Mon, 2008-12-01 at 21:31 +0000, Robert DeHate wrote:

> Exactly,
> Sort of.
> I do not believe a blanket statement that solid construction is best.
> I also do not think sandwhich construction is always best.
>
> You state:
> "use the facing material throughout. that solid construction is
> always best."

Uh, Robert, I see where I said "...use the facing material throughout"
but it was in the context of "if you need the stiffest possible fin".

I don't see where I said "solid construction is always best". I did say
to Terry "whatever you do don't make your core out of balsa or foam" but
that was not a blanket statement to everyone or even to Terry. It was in
response to his musing about making a similar rocket but using
foam/balsa for a core, and I intended my answer to be read in that
context. My understanding of his situation is that he probably *does*
need the stiffest possible fin he can build while keeping thickness down
or even minimizing it, because he's already said he's concerned about
his 3/4" thickness.

What I'm saying is if the driving consideration is "stiffest possible
fin with the least thickness" then solid construction will turn out to
be the answer.

And if some other factor (weight, minimization of facing material [for
whatever reason: cost, availability, contest rules, self-imposed limit,
whatever]) is the driving factor, then sandwich construction turns out
to be the answer.

Different people will have different factors driving the decision.

--Steve

Terry, Steve has described in very exacting mathematical terms with I
agree with whole heartedly about energy transfer from the outer skin
of one side of the fin to the other side through it's internal media.
Once this oscillatory motion starts it's hard to stop and the flutter
frequency will probably increase until the point of failure. I am
speculating or call it a theory that if you replace the solid core
with different media that has an osculation frequency that is
different than the outer skin it is possible to have this internal
media act as a dampener or at least a means of lessening the energy
transfer from one side to the other. So if you have a sandwich panel
capable of absorbing energy in a non liner fashion it is conceivably
possible that the internal media can cancel out the resonate
frequency of the parent material thus avoiding the energy transfer
through the solid core.
This is if it's still okay to have a unproven theory. There are so
many variable in fin flutter that it may never be mathematically
figured out. Some one may stumble on a cure from experimentation.

Mick

--- In CompositeRockets@yahoogroups.com, "Terry Leright"
<pyramid12@...> wrote:
>
> I didnt mean to get in the middle of this debate but I really
appreciate the extra time Steve and Robert
> Spent giving me last nights lessons, suggestions . This composite
material isnt cheap.
>  You can learn from the school of hard knocks or from more
experience.
> I guess I do a little of both.
> The material for this next ship is ordered and the fins, Im
thinking 3-4 layers of S-glass with 6 layers
> carbon on the sides. Solid plate fins.
> Thanks again,
> Terry
>
>   ----- Original Message -----
>   From: Steve Peterson
>   To: CompositeRockets@yahoogroups.com
>   Sent: Monday, December 01, 2008 4:59 PM
>   Subject: Re: [CompositeRockets] Re: Jims Tutorial
>
>
>   On Mon, 2008-12-01 at 21:31 +0000, Robert DeHate wrote:
>
>   > Exactly,
>   > Sort of.
>   > I do not believe a blanket statement that solid construction is
best.
>   > I also do not think sandwhich construction is always best.
>   >
>   > You state:
>   > "use the facing material throughout. that solid construction is
>   > always best."
>
>   Uh, Robert, I see where I said "...use the facing material
throughout"
>   but it was in the context of "if you need the stiffest possible
fin".
>
>   I don't see where I said "solid construction is always best". I
did say
>   to Terry "whatever you do don't make your core out of balsa or
foam" but
>   that was not a blanket statement to everyone or even to Terry. It
was in
>   response to his musing about making a similar rocket but using
>   foam/balsa for a core, and I intended my answer to be read in that
>   context. My understanding of his situation is that he probably
*does*
>   need the stiffest possible fin he can build while keeping
thickness down
>   or even minimizing it, because he's already said he's concerned
about
>   his 3/4" thickness.
>
>   What I'm saying is if the driving consideration is "stiffest
possible
>   fin with the least thickness" then solid construction will turn
out to
>   be the answer.
>
>   And if some other factor (weight, minimization of facing material
[for
>   whatever reason: cost, availability, contest rules, self-imposed
limit,
>   whatever]) is the driving factor, then sandwich construction
turns out
>   to be the answer.
>
>   Different people will have different factors driving the
decision.
>
>   --Steve
>

Steve I apologies for that post. Sooner or later I will learn not to
respond to post when I am so passionately charged up. I know you are
trying to help in a very professional engineering way. I just think
there is room for experimentation along with the science of it all.
More than once a problem has been solved through experimentation when
the math could not find the answer until after a successful theorized
experiment. I also know more times than not a well thought out
engineering approach has solved many problems also. What took me back
was that you were not giving any room for experimentation and that the
possibility of an un-mathematical solution could have have any worth in
this discussion.

So please except my apology for my outburst of emotion.

Mick

Steve makes the point that it is a harmonic resonance between
torsional and bending movements that cause the phenomenon.

As can be seen in Art's video it is the *amplitude* that increases to
failure.
It's easy to see why, those damn fins are marginal under regular power...

Unfortunately with a damping media, most if not all, of the energy
absorbed from flexing the fins will be turned into heat. A hot core
will not do much for the integrity of said fins.
The skins are coupled by their perimeters regardless, it's not just
the core acting on the other facing.

Once it gets to flexing it's already too late.
We need to model a fin that won't be subject to these forces within
the flight parameters it was designed for.

As I alluded to, that likely means one which has a frequency high
enough that it can't be excited to failure.(within reason)
The idea of changing the CG is intriguing and makes me want to
experiment with tungsten leading edges.

Thicker cores and a tapered beam section work to this end. But
aerodynamics plays a role in form too.
Look at a Nike fin. They are simple, solid and don't flex, but they
are heavy and have plenty of motor to push them.

It's an interesting conversation, let's not see it degrade into a
pissing contest.

-Jim



> Terry, Steve has described in very exacting mathematical terms with I
> agree with whole heartedly about energy transfer from the outer skin
> of one side of the fin to the other side through it's internal media.
> Once this oscillatory motion starts it's hard to stop and the flutter
> frequency will probably increase until the point of failure. I am
> speculating or call it a theory that if you replace the solid core
> with different media that has an osculation frequency that is
> different than the outer skin it is possible to have this internal
> media act as a dampener or at least a means of lessening the energy
> transfer from one side to the other. So if you have a sandwich panel
> capable of absorbing energy in a non liner fashion it is conceivably
> possible that the internal media can cancel out the resonate
> frequency of the parent material thus avoiding the energy transfer
> through the solid core.
> This is if it's still okay to have a unproven theory. There are so
> many variable in fin flutter that it may never be mathematically
> figured out. Some one may stumble on a cure from experimentation.
>
> Mick
>

----- Original Message -----

From: mickmkelly

To: CompositeRockets@yahoogroups.com

Sent: Monday, December 01, 2008 7:11 PM

Subject: [CompositeRockets] Re: Jims Tutorial

Terry, Steve has described in very exacting mathematical terms with I
agree with whole heartedly about energy transfer from the outer skin
of one side of the fin to the other side through it's internal media.
Once this oscillatory motion starts it's hard to stop and the flutter
frequency will probably increase until the point of failure. I am
speculating or call it a theory that if you replace the solid core
with different media that has an osculation frequency that is
different than the outer skin it is possible to have this internal
media act as a dampener or at least a means of lessening the energy
transfer from one side to the other. So if you have a sandwich panel
capable of absorbing energy in a non liner fashion it is conceivably
possible that the internal media can cancel out the resonate
frequency of the parent material thus avoiding the energy transfer
through the solid core.
This is if it's still okay to have a unproven theory. There are so
many variable in fin flutter that it may never be mathematically
figured out. Some one may stumble on a cure from experimentation.

Mick

--- In CompositeRockets@yahoogroups.com, "Terry Leright"
<pyramid12@...> wrote:
>
> I didnt mean to get in the middle of this debate but I really
appreciate the extra time Steve and Robert
> Spent giving me last nights lessons, suggestions . This composite
material isnt cheap.
> You can learn from the school of hard knocks or from more
experience.
> I guess I do a little of both.
> The material for this next ship is ordered and the fins, Im
thinking 3-4 layers of S-glass with 6 layers
> carbon on the sides. Solid plate fins.
> Thanks again,
> Terry
>
> ----- Original Message -----
> From: Steve Peterson
> To: CompositeRockets@yahoogroups.com
> Sent: Monday, December 01, 2008 4:59 PM
> Subject: Re: [CompositeRockets] Re: Jims Tutorial
>
>
> On Mon, 2008-12-01 at 21:31 +0000, Robert DeHate wrote:
>
> > Exactly,
> > Sort of.
> > I do not believe a blanket statement that solid construction is
best.
> > I also do not think sandwhich construction is always best.
> >
> > You state:
> > "use the facing material throughout. that solid construction is
> > always best."
>
> Uh, Robert, I see where I said "...use the facing material
throughout"
> but it was in the context of "if you need the stiffest possible
fin".
>
> I don't see where I said "solid construction is always best". I
did say
> to Terry "whatever you do don't make your core out of balsa or
foam" but
> that was not a blanket statement to everyone or even to Terry. It
was in
> response to his musing about making a similar rocket but using
> foam/balsa for a core, and I intended my answer to be read in that
> context. My understanding of his situation is that he probably
*does*
> need the stiffest possible fin he can build while keeping
thickness down
> or even minimizing it, because he's already said he's concerned
about
> his 3/4" thickness.
>
> What I'm saying is if the driving consideration is "stiffest
possible
> fin with the least thickness" then solid construction will turn
out to
> be the answer.
>
> And if some other factor (weight, minimization of facing material
[for
> whatever reason: cost, availability, contest rules, self-imposed
limit,
> whatever]) is the driving factor, then sandwich construction
turns out
> to be the answer.
>
> Different people will have different factors driving the
decision.
>
> --Steve
>

<snip>
> So please except my apology for my outburst of emotion.
>
> Mick

Mick,

From the sidelines....
It warms my heart to see anyone passionate about fabrication in this
day and age.
It seems to me everything has been reduced to formulae by now, and no
one is willing to take a hunch and run with it.
Innovation is key to progress.
I really look forward to seeing how your ideas pan out.

-Jim
>

On Tue, 2008-12-02 at 00:43 +0000, mickmkelly wrote:
> Steve I apologies for that post. Sooner or later I will learn not to
> respond to post when I am so passionately charged up. I know you are
> trying to help in a very professional engineering way. I just think
> there is room for experimentation along with the science of it all.
> More than once a problem has been solved through experimentation when
> the math could not find the answer until after a successful theorized
> experiment. I also know more times than not a well thought out
> engineering approach has solved many problems also. What took me back
> was that you were not giving any room for experimentation and that
> the
> possibility of an un-mathematical solution could have have any worth
> in
> this discussion.
>
> So please except my apology for my outburst of emotion.
>
> Mick
>

Apology warmly accepted.

I appreciate how a long discussion from a single point of view can start
to overwhelm other points of view, even if no one intends it to. As I
see you are fully aware, I'm just trying to shed some light on an isssue
and save people some time/effort if that is what they desire.

I'm pretty sure that everyone on this list is mature enough to challenge
my comments when they are in error or when people have contrary
evidence; that if they want to continue to build fins in a particular
manner, they will; that they know that just because theory says X
doesn't mean anyone has to do X.

I think we've had some good, concrete, vigorous discussions. People have
raised points, argued them, and learned. I include myself in that
category. Throughout, there have been no ad hominem attacks (rare for
lists as we all know).

A while back you asked about the health of the list; to me, vigorous
discussions like this are a sign that the list is indeed healthy. Thanks
for all your hard work to make it all happen.

--Steve

The reporters not only got the details wrong this has everything to do
with the NPRM that the ATF already put out about rocket motors NOT
being PAD's. This NPRM is scheduled for final ruling in Jan09. This
has been confirmed directly with the reporters (but not by me personally).

So while the report acts like there will be relief for us actually
they are reporting on something that is taking away something from us.

Jeff

--- In CompositeRockets@yahoogroups.com, "Lakestake Rocketry"
<lakestake@...> wrote:
>
> Check out this report:
>
>
http://www.washingtonpost.com/wp-dyn/content/article/2008/11/29/AR2008112901914.\
html
>
> "In a burst of activity meant to leave a lasting stamp on the federal
> government, the Bush White House in the past month has approved 61 new
> regulations on environmental, security, social and commercial matters
> that by its own estimate will have an economic impact exceeding $1.9
> billion annually. "
>
> ...
>
> "The rules cover obscure as well as high-profile social and economic
> issues: spelling out what kinds of records must be kept by sexually
> explicit performers and publications, exempting hobbyists' rocket
> motors from federal explosives controls, expanding the collection of
> DNA samples from federal prisoners. "
>
> Sounds too good to be true, does anyone have a reference to the rule
> passed affecting rocketry?
>
> Matt
>

--- In CompositeRockets@yahoogroups.com, "Terry Leright"
<pyramid12@...> wrote:
>
>> Starting with Jims tutorial .

Speaking of Jim's tutorial :-) ...

I've finished the airframe and the fins are tacked on. Not bad
progress for being about 4 weeks into the project. The airframe is
here:

http://tinyurl.com/5dyp9z

I was able to keep the epoxy to 48% by weight.  I don't think this is
too bad for a hand layup.

Jim

Well I have got some work done lately on my 38mm Carbon rocket called Kritter,
and its
starting to look really good (especially for my first try.) I have got two sides
done with the
tip2tip carbon and one to go, then its time to sand and shine :)

Most of my pictures are here...
http://web.mac.com/tennisace1/Site/Kritter.html

Once Kritter is done, I can start thinking about my L3 :D
~Jason B.

--- In CompositeRockets@yahoogroups.com, "jimjarvis50" <jim_jarvis@...> wrote:
>
> --- In CompositeRockets@yahoogroups.com, "Terry Leright"
> <pyramid12@> wrote:
> >
> >> Starting with Jims tutorial .
>
> Speaking of Jim's tutorial :-) ...
>
> I've finished the airframe and the fins are tacked on. Not bad
> progress for being about 4 weeks into the project. The airframe is
> here:
>
> http://tinyurl.com/5dyp9z
>
> I was able to keep the epoxy to 48% by weight.  I don't think this is
> too bad for a hand layup.
>
> Jim
>

Jason, that's looking good, and the nice thing is that I'll probably
get to see it fly!  I was wondering how long the mandrel was for your
tube - it looks reaaallly long.  And how are you planning to finish
the fins?

Jim

--- In CompositeRockets@yahoogroups.com, "jasonb429" <jasonb429@...>
wrote:
>
> Well I have got some work done lately on my 38mm Carbon rocket
called Kritter, and its
> starting to look really good (especially for my first try.) I have
got two sides done with the
> tip2tip carbon and one to go, then its time to sand and shine :)
>
> Most of my pictures are here...
> http://web.mac.com/tennisace1/Site/Kritter.html
>
> Once Kritter is done, I can start thinking about my L3 :D
> ~Jason B.
>
> --- In CompositeRockets@yahoogroups.com, "jimjarvis50"
<jim_jarvis@> wrote:
> >
> > --- In CompositeRockets@yahoogroups.com, "Terry Leright"
> > <pyramid12@> wrote:
> > >
> > >> Starting with Jims tutorial .
> >
> > Speaking of Jim's tutorial :-) ...
> >
> > I've finished the airframe and the fins are tacked on. Not bad
> > progress for being about 4 weeks into the project. The airframe
is
> > here:
> >
> > http://tinyurl.com/5dyp9z
> >
> > I was able to keep the epoxy to 48% by weight.  I don't think
this is
> > too bad for a hand layup.
> >
> > Jim
> >
>

Jim, the mandrel is 6ft, Its two PML full length couplers joined by a used 38mm
motor liner
with some tape so it was tight. It was hard keeping it straight so it would cure
straight.
And as for the fins, well im planning on sanding most of the peel ply out and
then putting
epoxy on and wiping it off to try to fill all the little holes, (like how you
descried to fill
scratches) then repeat till it looks decent then wet sand. Now I did have a
crease in my
peel ply so there is a line in the carbon, Is that bump just epoxy that i can
sand out, or is
it carbon??  As for the tip of the fin, well i have not decided how to finish
it. It wont ever
go over Mach 1.75 so I don't think there is any chance of delaminating, so i
will probably
just paint it to blend in.

Any comments or suggestions are always appreciated :)

~Jason B.



--- In CompositeRockets@yahoogroups.com, "jimjarvis50" <jim_jarvis@...> wrote:
>
> Jason, that's looking good, and the nice thing is that I'll probably
> get to see it fly!  I was wondering how long the mandrel was for your
> tube - it looks reaaallly long.  And how are you planning to finish
> the fins?
>
> Jim
>
> --- In CompositeRockets@yahoogroups.com, "jasonb429" <jasonb429@>
> wrote:
> >
> > Well I have got some work done lately on my 38mm Carbon rocket
> called Kritter, and its
> > starting to look really good (especially for my first try.) I have
> got two sides done with the
> > tip2tip carbon and one to go, then its time to sand and shine :)
> >
> > Most of my pictures are here...
> > http://web.mac.com/tennisace1/Site/Kritter.html
> >
> > Once Kritter is done, I can start thinking about my L3 :D
> > ~Jason B.
> >
> > --- In CompositeRockets@yahoogroups.com, "jimjarvis50"
> <jim_jarvis@> wrote:
> > >
> > > --- In CompositeRockets@yahoogroups.com, "Terry Leright"
> > > <pyramid12@> wrote:
> > > >
> > > >> Starting with Jims tutorial .
> > >
> > > Speaking of Jim's tutorial :-) ...
> > >
> > > I've finished the airframe and the fins are tacked on. Not bad
> > > progress for being about 4 weeks into the project. The airframe
> is
> > > here:
> > >
> > > http://tinyurl.com/5dyp9z
> > >
> > > I was able to keep the epoxy to 48% by weight.  I don't think
> this is
> > > too bad for a hand layup.
> > >
> > > Jim
> > >
> >
>

Wow, I'll bet you were glad to get the tube out!

I would suggest you just add epoxy over the peel ply and then sand.
If you try to sand on the peel ply surface, you'll get into the
carbon quickly.  And you get dust into the little holes that won't
come out.

I don't know about the crease.  Odds are it's carbon though.  Chicks
dig scars...

Jim

--- In CompositeRockets@yahoogroups.com, "jasonb429" <jasonb429@...>
wrote:
>
> Jim, the mandrel is 6ft, Its two PML full length couplers joined
by a used 38mm motor liner
> with some tape so it was tight. It was hard keeping it straight so
it would cure straight.
> And as for the fins, well im planning on sanding most of the peel
ply out and then putting
> epoxy on and wiping it off to try to fill all the little holes,
(like how you descried to fill
> scratches) then repeat till it looks decent then wet sand. Now I
did have a crease in my
> peel ply so there is a line in the carbon, Is that bump just epoxy
that i can sand out, or is
> it carbon??  As for the tip of the fin, well i have not decided
how to finish it. It wont ever
> go over Mach 1.75 so I don't think there is any chance of
delaminating, so i will probably
> just paint it to blend in.
>
> Any comments or suggestions are always appreciated :)
>
> ~Jason B.
>
>
>
> --- In CompositeRockets@yahoogroups.com, "jimjarvis50"
<jim_jarvis@> wrote:
> >
> > Jason, that's looking good, and the nice thing is that I'll
probably
> > get to see it fly!  I was wondering how long the mandrel was for
your
> > tube - it looks reaaallly long.  And how are you planning to
finish
> > the fins?
> >
> > Jim
> >
> > --- In CompositeRockets@yahoogroups.com, "jasonb429"
<jasonb429@>
> > wrote:
> > >
> > > Well I have got some work done lately on my 38mm Carbon rocket
> > called Kritter, and its
> > > starting to look really good (especially for my first try.) I
have
> > got two sides done with the
> > > tip2tip carbon and one to go, then its time to sand and
shine :)
> > >
> > > Most of my pictures are here...
> > > http://web.mac.com/tennisace1/Site/Kritter.html
> > >
> > > Once Kritter is done, I can start thinking about my L3 :D
> > > ~Jason B.
> > >
> > > --- In CompositeRockets@yahoogroups.com, "jimjarvis50"
> > <jim_jarvis@> wrote:
> > > >
> > > > --- In CompositeRockets@yahoogroups.com, "Terry Leright"
> > > > <pyramid12@> wrote:
> > > > >
> > > > >> Starting with Jims tutorial .
> > > >
> > > > Speaking of Jim's tutorial :-) ...
> > > >
> > > > I've finished the airframe and the fins are tacked on. Not
bad
> > > > progress for being about 4 weeks into the project. The
airframe
> > is
> > > > here:
> > > >
> > > > http://tinyurl.com/5dyp9z
> > > >
> > > > I was able to keep the epoxy to 48% by weight.  I don't
think
> > this is
> > > > too bad for a hand layup.
> > > >
> > > > Jim
> > > >
> > >
> >
>

Nah it wasn't too bad to get out, I used mylar and like 5 coats of wax.  Now my
first try,
well most of the mandrel is still in it, so im using it as a breaker bar in my
truck to get the
lug nuts off if I ever get a flat and it has saved me once so far :P

Scars?? what scars, i just see Character :D

~Jason B.


--- In CompositeRockets@yahoogroups.com, "jimjarvis50" <jim_jarvis@...> wrote:
>
> Wow, I'll bet you were glad to get the tube out!
>
> I would suggest you just add epoxy over the peel ply and then sand.
> If you try to sand on the peel ply surface, you'll get into the
> carbon quickly.  And you get dust into the little holes that won't
> come out.
>
> I don't know about the crease.  Odds are it's carbon though.  Chicks
> dig scars...
>
> Jim
>
> --- In CompositeRockets@yahoogroups.com, "jasonb429" <jasonb429@>
> wrote:
> >
> > Jim, the mandrel is 6ft, Its two PML full length couplers joined
> by a used 38mm motor liner
> > with some tape so it was tight. It was hard keeping it straight so
> it would cure straight.
> > And as for the fins, well im planning on sanding most of the peel
> ply out and then putting
> > epoxy on and wiping it off to try to fill all the little holes,
> (like how you descried to fill
> > scratches) then repeat till it looks decent then wet sand. Now I
> did have a crease in my
> > peel ply so there is a line in the carbon, Is that bump just epoxy
> that i can sand out, or is
> > it carbon??  As for the tip of the fin, well i have not decided
> how to finish it. It wont ever
> > go over Mach 1.75 so I don't think there is any chance of
> delaminating, so i will probably
> > just paint it to blend in.
> >
> > Any comments or suggestions are always appreciated :)
> >
> > ~Jason B.
> >
> >
> >
> > --- In CompositeRockets@yahoogroups.com, "jimjarvis50"
> <jim_jarvis@> wrote:
> > >
> > > Jason, that's looking good, and the nice thing is that I'll
> probably
> > > get to see it fly!  I was wondering how long the mandrel was for
> your
> > > tube - it looks reaaallly long.  And how are you planning to
> finish
> > > the fins?
> > >
> > > Jim
> > >
> > > --- In CompositeRockets@yahoogroups.com, "jasonb429"
> <jasonb429@>
> > > wrote:
> > > >
> > > > Well I have got some work done lately on my 38mm Carbon rocket
> > > called Kritter, and its
> > > > starting to look really good (especially for my first try.) I
> have
> > > got two sides done with the
> > > > tip2tip carbon and one to go, then its time to sand and
> shine :)
> > > >
> > > > Most of my pictures are here...
> > > > http://web.mac.com/tennisace1/Site/Kritter.html
> > > >
> > > > Once Kritter is done, I can start thinking about my L3 :D
> > > > ~Jason B.
> > > >
> > > > --- In CompositeRockets@yahoogroups.com, "jimjarvis50"
> > > <jim_jarvis@> wrote:
> > > > >
> > > > > --- In CompositeRockets@yahoogroups.com, "Terry Leright"
> > > > > <pyramid12@> wrote:
> > > > > >
> > > > > >> Starting with Jims tutorial .
> > > > >
> > > > > Speaking of Jim's tutorial :-) ...
> > > > >
> > > > > I've finished the airframe and the fins are tacked on. Not
> bad
> > > > > progress for being about 4 weeks into the project. The
> airframe
> > > is
> > > > > here:
> > > > >
> > > > > http://tinyurl.com/5dyp9z
> > > > >
> > > > > I was able to keep the epoxy to 48% by weight.  I don't
> think
> > > this is
> > > > > too bad for a hand layup.
> > > > >
> > > > > Jim
> > > > >
> > > >
> > >
> >
>

Jason,

Try letting the coupler cure in the mandrel in the "V" of a piece of
straight angle iron or similar.
Most hardware stores have a selection of extruded aluminum shapes.

The mandrel is 6ft, Its two PML full length couplers joined by a used
38mm motor liner
> with some tape so it was tight. It was hard keeping it straight so
it would cure straight.