Today's Message Index:
----------------------
1. 12:21 AM - Don Dykins book (Remi Guerner)
2. 03:28 AM - Re: Don Dykins book (craig bastin)
3. 03:35 AM - Re: Don Dykins book (Mike Gregory)
4. 06:30 AM - Re: Don Dykins book (Mike Parkin)
5. 07:06 AM - Re: bowden cables, sliders (Jeff B)
6. 08:04 AM - Re: bowden cables, sliders (ALAN YERLY)
7. 12:16 PM - Re: Don Dykins book (craig bastin)
8. 04:14 PM - Re: Don Dykins book (Mike Parkin)
9. 07:20 PM - Epoxy Measuring - Balances vs Digital Scale vs Ratio Pump (Roger Lowe)
10. 08:37 PM - Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio Pump (jimpuglise@comcast.net)
11. 08:45 PM - Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio Pump (Keith Hickling)
12. 08:48 PM - Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio Pump (Fred Klein)
13. 10:38 PM - Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio Pump (Fred Klein)
14. 11:06 PM - Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio Pump (David DeFord)
15. 11:18 PM - Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio Pump (Greg Fuchs (FB))
Message 1
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Hi all,
I have just read Don Dykins book =AB Understanding the aerodynamics of
your Europa aircraft =BB and I am puzzled by what I read in the
"Prototype flight test performance" section.
Figure 1 on page 15 shows that you need more power to fly at a given
airspeed at altitude than at sea level. I first thought it was a typo,
but page 18 confirms this assertion: "more HP is required to fly at a
given speed at 10,000ft than at sea level".
The typical light aircraft cruises about 5 to 10 percent faster at
10000 ft than at sea level using the same power, and you can verify this
with your own Europa as well.
So Don Dykins is wrong. Unless he is talking about indicated airspeed.
In that case, talking about performance, this is nonsense.
I cannot believe someone who has contributed to the design of such a
wonderful aircraft can be so wrong. Am I missing something?
Please comment.
Remi Guerner
Message 2
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If you consider the fact that you need more power or a longer ground run to
take off at high temps or lower pressures (higher density altitude)
then Don's assertions are correct. Consider also that some aircraft were
supercharged during world war 2 only to delay the onset of "coffin corner"
and allow for a higher service ceiling. Well thats my 2 cents worth.
Craig
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com]On Behalf Of Remi Guerner
Sent: Wednesday, 30 January 2008 6:12 PM
To: Europa-List Digest Server
Subject: Europa-List: Don Dykins book
Hi all,
I have just read Don Dykins book Understanding the aerodynamics of your
Europa aircraft and I am puzzled by what I read in the Prototype flight
test performance section.
Figure 1 on page 15 shows that you need more power to fly at a given
airspeed at altitude than at sea level. I first thought it was a typo, but
page 18 confirms this assertion: more HP is required to fly at a given
speed at 10,000ft than at sea level.
The typical light aircraft cruises about 5 to 10 percent faster at 10000
ft than at sea level using the same power, and you can verify this with your
own Europa as well.
So Don Dykins is wrong. Unless he is talking about indicated airspeed. In
that case, talking about performance, this is nonsense.
I cannot believe someone who has contributed to the design of such a
wonderful aircraft can be so wrong. Am I missing something?
Please comment.
Remi Guerner
10:20 PM
Message 3
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Hello Remi,
Yes, the airspeed axis on page 15 Figure 1 is labelled "VEASKTS", standing
for Equivalent Airspeed in knots, which is a more technically precise term
than Indicated Airspeed for aerodynamicist's calculations. For practical
purposes, they may be treated as equal for the flight envelope of the
Europa.
The reason why you need more horsepower at altitude for a given IAS is that,
for a given efficiency, the engine is providing thrust to equal the same
drag (which is dependent on IAS) but the True Airspeed is greater, so the
actual distance moved in a given time is greater. Work = Force x Distance;
Power = Work/time. The engine is therefore having to do more work in a
given time at the same IAS at altitude, but this is more than offset by the
gain in TAS, so cruising at a given TAS requires less horsepower at
altitude.
I do not believe Don Dykins is wrong, and I do not agree that it is nonsense
to talk about performance in terms of indicated airspeed. As I understand
it, he is showing his calculations of aerodynamic performance and comparing
them with the results of flight tests, where IAS is measured.
It would be interesting to know how the latest VP propellers compare in
efficiency with his working assumption of 80%.
Best regards
Mike
_____
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Remi Guerner
Sent: 30 January 2008 08:12
Subject: Europa-List: Don Dykins book
Hi all,
I have just read Don Dykins book < Understanding the aerodynamics of your
Europa aircraft > and I am puzzled by what I read in the "Prototype flight
test performance" section.
Figure 1 on page 15 shows that you need more power to fly at a given
airspeed at altitude than at sea level. I first thought it was a typo, but
page 18 confirms this assertion: "more HP is required to fly at a given
speed at 10,000ft than at sea level".
The typical light aircraft cruises about 5 to 10 percent faster at 10000 ft
than at sea level using the same power, and you can verify this with your
own Europa as well.
So Don Dykins is wrong. Unless he is talking about indicated airspeed. In
that case, talking about performance, this is nonsense.
I cannot believe someone who has contributed to the design of such a
wonderful aircraft can be so wrong. Am I missing something?
Please comment.
Remi Guerner
Message 4
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| Subject: | Re: Don Dykins book |
Craig,
I am not sure that is correct. 'Coffin Corner' describes the area of
the flight envelope where stalling speed meets the critical mach no.
This is a problem with high flying aircraft such as the U2. I don't
think that extra power would help here.
regards,
Mike
do not archive.
----- Original Message -----
From: craig bastin
To: europa-list@matronics.com
Sent: Wednesday, January 30, 2008 11:24 AM
Subject: RE: Europa-List: Don Dykins book
If you consider the fact that you need more power or a longer ground
run to take off at high temps or lower pressures (higher density
altitude)
then Don's assertions are correct. Consider also that some aircraft
were supercharged during world war 2 only to delay the onset of "coffin
corner"
and allow for a higher service ceiling. Well thats my 2 cents worth.
Craig
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com]On Behalf Of Remi Guerner
Sent: Wednesday, 30 January 2008 6:12 PM
To: Europa-List Digest Server
Subject: Europa-List: Don Dykins book
Hi all,
I have just read Don Dykins book =AB Understanding the aerodynamics
of your Europa aircraft =BB and I am puzzled by what I read in the
"Prototype flight test performance" section.
Figure 1 on page 15 shows that you need more power to fly at a
given airspeed at altitude than at sea level. I first thought it was a
typo, but page 18 confirms this assertion: "more HP is required to fly
at a given speed at 10,000ft than at sea level".
The typical light aircraft cruises about 5 to 10 percent faster at
10000 ft than at sea level using the same power, and you can verify this
with your own Europa as well.
So Don Dykins is wrong. Unless he is talking about indicated
airspeed. In that case, talking about performance, this is nonsense.
I cannot believe someone who has contributed to the design of such a
wonderful aircraft can be so wrong. Am I missing something?
Please comment.
Remi Guerner
href="http://www.matronics.com/Navigator?Europa-List">http://www.matron
href="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
-------------------------------------------------------------------------
-----
30/01/2008 09:29
Message 5
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| Subject: | Re: bowden cables, sliders |
Jos,
When I added the heater door to Baby blue, I used a universal push/pull
(choke)cable assembly from Auto Zone. Works just fine...
Jeff - Baby Blue
363 hrs
josok wrote:
>
> Hi All,
> The ventilation-heating system has been installed. It should work, as far as
i can imagine. The difficult part for me is how to operate the selector valves.
I ordered some cables from ACS, but these are way to stiff to flex nicely into
the narrow spaces available. Bowden cables like in use on bicycles probably
should do the trick, but then i need some buttons or sliders on the other side.
I have no idea on what's available and from where. Anybody with some idea before
i start machining something from scratch?
>
> Regards,
>
> Jos Okhuijsen
>
>
>
>
>
>
> Visit - www.EuropaOwners.org
>
>
>
>
>
>
>
>
>
>
Message 6
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| Subject: | Re: bowden cables, sliders |
Jeff,
They are pricey, but I use part number A-700 Button Lodck Dash Control.
Red for heat and Black for cool if you have both. Usually the 6 foot is
OK.
I secure the .062 wire end with a Z bend and the spiral sleeve wrap with
a "cable safe" PN 05-16250 both available through Aircraft Spruce.
Bud Yerly
Custom Flight Creations
----- Original Message -----
From: Jeff B<mailto:topglock@cox.net>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Wednesday, January 30, 2008 10:02 AM
Subject: Re: Europa-List: bowden cables, sliders
<topglock@cox.net<mailto:topglock@cox.net>>
Jos,
When I added the heater door to Baby blue, I used a universal
push/pull
(choke)cable assembly from Auto Zone. Works just fine...
Jeff - Baby Blue
363 hrs
josok wrote:
<josok-e@ukolo.fi<mailto:josok-e@ukolo.fi>>
>
> Hi All,
> The ventilation-heating system has been installed. It should work,
as far as i can imagine. The difficult part for me is how to operate the
selector valves. I ordered some cables from ACS, but these are way to
stiff to flex nicely into the narrow spaces available. Bowden cables
like in use on bicycles probably should do the trick, but then i need
some buttons or sliders on the other side. I have no idea on what's
available and from where. Anybody with some idea before i start
machining something from scratch?
>
> Regards,
>
> Jos Okhuijsen
>
>
>
>
>
>
> Visit - www.EuropaOwners.org<http://www.europaowners.org/>
>
>
>
>
>
>
>
>
>
>
http://www.matronics.com/Navigator?Europa-List<http://www.matronics.com/N
avigator?Europa-List>
http://www.matronics.com/contribution<http://www.matronics.com/contributi
on>
Message 7
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Sure my use of the term "coffin corner" may not be correct, but it is a
simmilar situation is it not??
If the approach to coffin corner is caused by a lack of power rather than a
design limitation then it would be, wouldnt it? Say like trying to fly your
Europa with 60hp
at high altitude, you would end up in the same situation, can't go slower or
I'll stall, can't go faster not enough power. Some of the heavier 912ul
powered europa are flat out
at around 120kts arent they, yet the design is good for about 165-175 kts.
craig
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com]On Behalf Of Mike Parkin
Sent: Thursday, 31 January 2008 12:26 AM
To: europa-list@matronics.com
Subject: Re: Europa-List: Don Dykins book
Craig,
I am not sure that is correct. 'Coffin Corner' describes the area of the
flight envelope where stalling speed meets the critical mach no. This is a
problem with high flying aircraft such as the U2. I don't think that extra
power would help here.
regards,
Mike
do not archive.
----- Original Message -----
From: craig bastin
To: europa-list@matronics.com
Sent: Wednesday, January 30, 2008 11:24 AM
Subject: RE: Europa-List: Don Dykins book
If you consider the fact that you need more power or a longer ground run
to take off at high temps or lower pressures (higher density altitude)
then Don's assertions are correct. Consider also that some aircraft
were supercharged during world war 2 only to delay the onset of "coffin
corner"
and allow for a higher service ceiling. Well thats my 2 cents worth.
Craig
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com]On Behalf Of Remi Guerner
Sent: Wednesday, 30 January 2008 6:12 PM
To: Europa-List Digest Server
Subject: Europa-List: Don Dykins book
Hi all,
I have just read Don Dykins book Understanding the aerodynamics of
your Europa aircraft and I am puzzled by what I read in the Prototype
flight test performance section.
Figure 1 on page 15 shows that you need more power to fly at a given
airspeed at altitude than at sea level. I first thought it was a typo, but
page 18 confirms this assertion: more HP is required to fly at a given
speed at 10,000ft than at sea level.
The typical light aircraft cruises about 5 to 10 percent faster at
10000 ft than at sea level using the same power, and you can verify this
with your own Europa as well.
So Don Dykins is wrong. Unless he is talking about indicated airspeed.
In that case, talking about performance, this is nonsense.
I cannot believe someone who has contributed to the design of such a
wonderful aircraft can be so wrong. Am I missing something?
Please comment.
Remi Guerner
href="http://www.matronics.com/Navigator?Europa-List">http://www.matronhref
"http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
href="http://www.matronics.com/Navigator?Europa-List">http://www.matronhref
"http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
----------------------------------------------------------------------------
Release Date: 30/01/2008 09:29
10:20 PM
Message 8
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| Subject: | Re: Don Dykins book |
Craig,
What you are talking about is a stall - plain an simple. It is nothing
to do with the "Coffin Corner". Please see
http://en.wikipedia.org/wiki/Coffin_corner_(aviation)
regards,
Mike
----- Original Message -----
From: craig bastin
To: europa-list@matronics.com
Sent: Wednesday, January 30, 2008 7:45 PM
Subject: RE: Europa-List: Don Dykins book
Sure my use of the term "coffin corner" may not be correct, but it is
a simmilar situation is it not??
If the approach to coffin corner is caused by a lack of power rather
than a design limitation then it would be, wouldnt it? Say like trying
to fly your Europa with 60hp
at high altitude, you would end up in the same situation, can't go
slower or I'll stall, can't go faster not enough power. Some of the
heavier 912ul powered europa are flat out
at around 120kts arent they, yet the design is good for about 165-175
kts.
craig
Message 9
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| Subject: | Epoxy Measuring - Balances vs Digital Scale vs Ratio Pump |
Hi, I've purchased a partially complete Europa a little over a year ago and had
to put it storage until my garage/workshop was re-vamped in order to build the
kit. It is now to a point to where I can start moving my kit into it and start
working on it.
I have question about the different devices used to measure the epoxy and wondering
what most builders have done in the past. The cheapest of course is to make
the Europa mechanical balance which should be no problem (is it quick and easy
to use during a layup?) but I'm leaning towards either a Ohaus / Sartorius
digital scale with a resolution of 0.01gm (do I need that much precision or can
I get away with a lower cost 0.1gm unit?) OR a ratio pump like a Glenmarc Portionator
MBT-JR from A/S which is the most expensive of the all the options
(is it worth the cost for ease of use?).
I live in Canada so I will be using Aeropoxy resin (100:27 by weight or 3 to 1
by volume).
I would appreciable any feedback/experience that you have that would help me make
up my mind!
Thanks, Roger
Visit - www.EuropaOwners.org
Message 10
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| Subject: | Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio |
Pump
Roger-
I think you'll find that most people use a scale. I have an Ohaus which read to
1/100 of an ounce. Your mixing needs to be very precise and you will do it
often, so an easy to use and accurate scale is important. I throw a sheet of
plastic over it to protect it and put the cup on before it is turned on and use
bottles like ketchup is served in in restaurants to dispense epoxy and hardener.
If I go a bit over, a paper towel can be used to "wick" a little until it
is just right. I think the scale is a little over $ 100 but well worth it.
Jim Puglise, Punta Gorda, FL
-------------- Original message --------------
From: "Roger Lowe" <rlowe@speedway.ca>
>
> Hi, I've purchased a partially complete Europa a little over a year ago and had
> to put it storage until my garage/workshop was re-vamped in order to build the
> kit. It is now to a point to where I can start moving my kit into it and start
> working on it.
>
> I have question about the different devices used to measure the epoxy and
> wondering what most builders have done in the past. The cheapest of course is
to
> make the Europa mechanical balance which should be no problem (is it quick and
> easy to use during a layup?) but I'm leaning towards either a Ohaus / Sartorius
> digital scale with a resolution of 0.01gm (do I need that much precision or can
> I get away with a lower cost 0.1gm unit?) OR a ratio pump like a Glenmarc
> Portionator MBT-JR from A/S which is the most expensive of the all the options
> (is it worth the cost for ease of use?).
>
> I live in Canada so I will be using Aeropoxy resin (100:27 by weight or 3 to
1
> by volume).
>
> I would appreciable any feedback/experience that you have that would help me
> make up my mind!
>
> Thanks, Roger
>
>
>
>
>
>
> Visit - www.EuropaOwners.org
>
>
>
>
>
>
>
>
<html><body>
<DIV>Roger-</DIV>
<DIV> </DIV>
<DIV>I think you'll find that most people use a scale. I have an Ohaus which
read to 1/100 of an ounce. Your mixing needs to be very precise and
you will do it often, so an easy to use and accurate scale is important.
I throw a sheet of plastic over it to protect it and put the cup on before it
is turned on and use bottles like ketchup is served in in restaurants to dispense
epoxy and hardener. If I go a bit over, a paper towel can be used to
"wick" a little until it is just right. I think the scale is a little
over $ 100 but well worth it. </DIV>
<DIV> </DIV>
<DIV>Jim Puglise, Punta Gorda, FL </DIV>
<DIV> </DIV>
<BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px
solid">-------------- Original message -------------- <BR>From: "Roger Lowe"
<rlowe@speedway.ca> <BR><BR>> --> Europa-List message posted by:
"Roger Lowe" <RLOWE@SPEEDWAY.CA><BR>> <BR>> Hi, I've purchased a partially
complete Europa a little over a year ago and had <BR>> to put it storage
until my garage/workshop was re-vamped in order to build the <BR>> kit. It
is now to a point to where I can start moving my kit into it and start <BR>>
working on it. <BR>> <BR>> I have question about the different devices
used to measure the epoxy and <BR>> wondering what most builders have done
in the past. The cheapest of course is to <BR>> make the Europa mechanical
balance which should be no problem (is it quick and <BR>> easy to use during
a layup?) but I'm leaning towards either a Ohaus / Sartorius <BR>> digital
scale with a resolution of 0.01gm (do I need that
much
nd muc
<pre><b><font size=2 color="#000000" face="courier new,courier">
</b></font></pre></body></html>
Message 11
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| Subject: | Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio |
Pump
Roger,
I used the Europa balance, but modified by using 20 lb breaking strain nylon
fishing line as the pivot, rather than the nail as described in the manual.
The nylon line goes through the brass tube, and is stretched tight across
the frame. This was a suggestion from Dr Martin Armstrong, technical
director of SP systems (now Gurit) who make Ampreg resins. He pointed out
that if you use a nail for the pivot, the brass tube tries to roll on the
nail, resulting in a slight movement of the pivot point, and it also causes
significant friction, both resulting in inaccuracies.
I tested the balance against accurate pharmacy scales and found it was
accurate to less than 0.02 g when balancing a 100 g weight with a 25 g +-
small weights using the 4:1 ratio (ie 40 cm to 10 cm on the balance). In
practical terms, I can easily detect the effect of 1 drop of hardner when
nearly balanced. I expect that using digital scales would take longer, as
you have to accurately measure quantities of both resin and hardner, whereas
with the ratio balance you just pour roughly the amount of resin you want,
then add exactly the right amount of hardner. Having now got close to the
end, I have been amazed at the number of resin mixes needed - far more than
I initially envisaged - so any time saved here is significant.
I also always mixed the resin and hardner back and forward between the two
cups, rather than simply pouring the resin into the hardner as suggested and
then reusing the resin cup next time. I had thought, and Martin Armstrong
confirmed, that this can result in significant inaccuracies, depending how
long you spend draining the resin from the cup each time, as well as
allowing water (vapour) and CO2 into the residual resin in the cup.
I'll be interested to hear what others have found.
Regards,
Keith Hickling,
New Zealand.
Engine in, working on cowls.
----- Original Message -----
From: "Roger Lowe" <rlowe@speedway.ca>
Sent: Thursday, January 31, 2008 3:53 PM
Subject: Europa-List: Epoxy Measuring - Balances vs Digital Scale vs Ratio
Pump
>
> Hi, I've purchased a partially complete Europa a little over a year ago
> and had to put it storage until my garage/workshop was re-vamped in order
> to build the kit. It is now to a point to where I can start moving my kit
> into it and start working on it.
>
> I have question about the different devices used to measure the epoxy and
> wondering what most builders have done in the past. The cheapest of course
> is to make the Europa mechanical balance which should be no problem (is it
> quick and easy to use during a layup?) but I'm leaning towards either a
> Ohaus / Sartorius digital scale with a resolution of 0.01gm (do I need
> that much precision or can I get away with a lower cost 0.1gm unit?) OR a
> ratio pump like a Glenmarc Portionator MBT-JR from A/S which is the most
> expensive of the all the options (is it worth the cost for ease of use?).
>
> I live in Canada so I will be using Aeropoxy resin (100:27 by weight or 3
> to 1 by volume).
>
> I would appreciable any feedback/experience that you have that would help
> me make up my mind!
>
> Thanks, Roger
>
>
> Visit - www.EuropaOwners.org
>
>
>
Message 12
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| Subject: | Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio |
Pump
> The cheapest of course is to make the Europa mechanical balance which
> should be no problem
> (is it quick and easy to use during a layup?)
Roger,
I've used the standard balance design with, I believe, excellent
results. E04 will give you the proper lengths for Aeropoxy proportions.
I excercised some care in building mine to minimize friction. I find it
works like a charm.
I like the fact that I can pour out as much resin as I think I'll need
and easily match it up with the correct amount of hardener...the
balance registers to an accuracy (of say, a couple drops of hardener)
which I find astonishing.
Happy building...welcome to the list,
Fred
--
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.
Message 13
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| Subject: | Re: Epoxy Measuring - Balances vs Digital Scale vs Ratio |
Pump
Roger...one further thought re: my post.
I've not attempted to reuse resin cups as I found early on that as the
weight of the used but (somewhat) empty cup varied enough to upset the
balance point...rather than futzing w/ the location of the add on
balancing piece (I've used a large flat washer) every time I do a mix,
I zero out the balance w/ clean resin and hardener cups and once done,
it remains balanced.
Fred
On Wednesday, Jan 30, 2008, at 20:45 US/Pacific, Fred Klein wrote:
>
>> The cheapest of course is to make the Europa mechanical balance which
>> should be no problem
>
>> (is it quick and easy to use during a layup?)
>
> Roger,
>
> I've used the standard balance design with, I believe, excellent
> results. E04 will give you the proper lengths for Aeropoxy
> proportions. I excercised some care in building mine to minimize
> friction. I find it works like a charm.
>
> I like the fact that I can pour out as much resin as I think I'll need
> and easily match it up with the correct amount of hardener...the
> balance registers to an accuracy (of say, a couple drops of hardener)
> which I find astonishing.
>
> Happy building...welcome to the list,
>
> Fred
>
>
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Message 14
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| Subject: | Epoxy Measuring - Balances vs Digital Scale vs Ratio |
Pump
>
> Hi, I've purchased a partially complete Europa a little over
> a year ago and had to put it storage until my garage/workshop
> was re-vamped in order to build the kit. It is now to a point
> to where I can start moving my kit into it and start working on it.
>
> I have question about the different devices used to measure
> the epoxy and wondering what most builders have done in the
> past. The cheapest of course is to make the Europa mechanical
> balance which should be no problem (is it quick and easy to
> use during a layup?) but I'm leaning towards either a Ohaus /
> Sartorius digital scale with a resolution of 0.01gm (do I
> need that much precision or can I get away with a lower cost
> 0.1gm unit?) OR a ratio pump like a Glenmarc Portionator
> MBT-JR from A/S which is the most expensive of the all the
> options (is it worth the cost for ease of use?).
>
> I live in Canada so I will be using Aeropoxy resin (100:27 by
> weight or 3 to 1 by volume).
>
Roger,
You will find people who swear by each of these approaches, so I won't try
to tell you which is best. We used digital scales with 0.1 gram resolution
and found them to be quite satisfactory, though I wouldn't recommend less
resolution. Our original scale (an Ohaus Scout) died after a few years of
excellent service, and we have used a couple of cheaper models since. For a
staggering selection of scales, check out www.americanweigh.com.
Even the cheapest pocket-size scales would probably have good enough
accuracy, but you need a large enough weighing platform to hold your mixing
cups easily. (You will often be in a hurry when weighing epoxy, and spills
are a real pain.) Be sure that the scale stays on for long enough to zero
the cup weight, weigh the resin, and then weigh the hardener (even with some
interruptions) before it turns off to save its battery. Not a problem with
AC power, but some of the small scales with tiny batteries get in a hurry to
shut down.
Keep in mind that absolute accuracy is not needed for mixing applications,
only good linearity. This can be tested precisely even without accurate
calibration weights. Just weigh anything and note the result. Then replace
the first item with something else, and zero out the reading. Adding the
first item to the platform should result in exactly the same reading that
you got when weighing it by itself. The two objects together need only to
remain within the scale's range.
Remember also that you will frequently have to mix Redux/Araldite 420/???
with good precision, and it's ratio will be different from the layup epoxy,
so a mixing pump or fixed 100:27-ratio balance won't do this job. A digital
scale is a bit like the digital level or close-quarters drill that you buy
for one specific job, and then find that you use it for many other things.
Dave DeFord
N135TD
Message 15
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| Subject: | Epoxy Measuring - Balances vs Digital Scale vs Ratio |
Pump
-------------
Keith Hickling wrote:
"I expect that using digital scales would take longer, as you have to
accurately measure quantities of both resin and hardner, whereas with the
ratio balance you just pour roughly the amount of resin you want, then add
exactly the right amount of hardner. "
-------------
I have always used the digital scale. It is an Ohaus, with a resolution of
0.1 gram and does not suffer hysteresis inaccuracies like some do. Absolute
accuracy is not important, since the accuracy error will factor out in a
ratio, as long as repeatability is good. No need to bother with using the
sample weights that come with the scale to make it accurate.
With the scale, you never need 2 cups to mix the resin back and forth, and
only have to carefully measure the hardener. I put resin pumps on the
containers of hardener and resin, and leave them there(they can be obtained
from the local epoxy supply, such as Tap Plastics, or probably Aircraft
Spruce or Wicks), with a plastic bag over them when finished. Upon needing a
batch, just grab both out of the temperature-controlled storage area, pull
off the plastic bags, and start pumping. For example:
Epoxy:
Put a disposable cup onto the scale. Turn it on, and it will auto zero,
excluding the weight of the cup from the equation. Dump in whatever amount
of resin you feel like. It does not need to be measured, a wild-ass guess
will do, but write down the final amount of the weight of the resin.
Multiply this amount by 0.27 (Aeropoxy), and you have your hardener amount
to add. Add that number back to the initial amount of resin measured, and
you get the total amount of resin plus hardener needed. Simply pump hardener
into the same cup until you get close to the final amount, then go drop by
drop until you nail the reading to a tenth of a gram (resolution of the
scale), and you got it! Its very easy and takes almost no time, and no need
to mess around with pouring between the resin cup and hardener cup to use
all of the material -just keep a calculator handy, and a pencil to tap the
numbers to keep the calculator clean. Mix until you see a homogenous
mixture, and you are done. It took a little while to explain, but it goes
really fast. As a final check, keep a mixture lookup chart nearby and right
before adding the hardener, verify that the calculated hardener amount to
add is close to proper value.
Araldite:
Araldite won't pour, and needs to be scooped out with a Popsicle stick. It
will adhere grossly to the stick. Hence in this case, put the stick and the
cup on the scale before it zeros the value, to cancel out the weight of the
popsicle stick too. Make sure it is always in the cup during measurement.
Scoop out the araldite needed, and put the scooped amount along with the
stick, into the cup. The measurement reading taken will be for the araldite
only, since the stick was cancelled out. Make the calculation (multiply by
0.4, similar to the epoxy, above) Then pour in the hardener from a
ketchup-like bottle which has the ability to dispense from stream to drops,
depending on squeeze pressure (I purchased one from the local epoxy shop,
and it is similar). Verify calculated amount with the araldite mixture
lookup sheet (found on one of the web sites) to verify that the calculated
amount is close, then mix.
In the build manual, I write the resin amount measured, and hardener amount
to be mixed, along with the total amount of the two, which is the important
number, since you will add hardener until the total amount is achieved, then
write how close I actually got to the calculated total amount. Almost
always, the final resin + hardener measurement (actual) is the same as what
is calculated.
It is amazing how accurate the ratio scale can be if it is built properly,
like using the fishing line technique that Fred described. And it is
cheaper. For me though, the $100.00 digital scale which you can sometimes
find for 35 or 40 works really well, is fast, and if carefully done and
verified, will always make the proper ratio.
Have fun,
~Greg Fuchs
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