Suction mounts on a canopy
db
device on it (G96) to fall off the canopy every half an hour or so?!
The canopy is new, surface is perfectly clean, almost flat (blanik's canopy
starboard side), tried two diferent suction mounts, one with light PDA
device mounted but the result is the same - it is always falling off the
canopy!
Mal
eg while as high up as possible.
Clint
dangers of cracking canopies was pointed out.
Clinton
LAK 12
Paul Remde
Have you tried the RAM-B-224 suction cup mounts that I sell? They work
great for me and I've sold hundreds of them to glider pilots around the
world. If you clean the canopy and wet the suction cup it should never fall
off. I use mine to hold an iPAQ hx4700 with large battery and CF GPS with
no problems. It has withstood the 4Gs of a loop and the bumps of a landing
on a grass runway in a Ventus with no shock absorber and the tire pumped up
to a high pressure - very bumpy.
It should hold your large Garmin fine as well.
If you have tried that suction cup without success then you may have
received a defective one that could be replaced free of charge.
You can see details here:
http://www.cumulus-soaring.com/ram.htm
Good Soaring,
Paul Remde
Cumulus Soaring, Inc.
http://www.cumulus-soaring.com
"db" <tulip...@yahoo.com> wrote in message
news:eviacc$bi$1...@ss408.t-com.hr...
Paul Remde
Good point! I sell a suction cup from RAM called a RAP-224-1 that pulls a
hard vacuum when you rotate the locking ring. I don't recommend it for use
on glider canopies because it pulls the canopy out of shape - which could
cause crazing or other damage in the long run. I would never use one on a
glider canopy, but it works well on glass windows in cars.
Paul Remde
Cumulus Soaring, Inc.
http://www.cumulus-soaring.com
"Clint" <cb...@webmail.co.za> wrote in message
news:1176291400.6...@d57g2000hsg.googlegroups.com...
flying_monkey
> Hi,
>
> Have you tried the RAM-B-224 suction cup mounts that I sell? They work
> great for me and I've sold hundreds of them to glider pilots around the
> world. If you clean the canopy and wet the suction cup it should never fall
> off. I use mine to hold an iPAQ hx4700 with large battery and CF GPS with
> no problems. It has withstood the 4Gs of a loop and the bumps of a landing
> on a grass runway in a Ventus with no shock absorber and the tire pumped up
> to a high pressure - very bumpy.
>
> It should hold your large Garmin fine as well.
>
> If you have tried that suction cup without success then you may have
> received a defective one that could be replaced free of charge.
>
> You can see details here:http://www.cumulus-soaring.com/ram.htm
>
> Good Soaring,
>
> Paul Remde
> Cumulus Soaring, Inc.http://www.cumulus-soaring.com
>
>
> news:eviacc$bi$1...@ss408.t-com.hr...
>
> > Is there any trick how to prevent suction mount with a relative heavy gps
> > device on it (G96) to fall off the canopy every half an hour or so?!
> > The canopy is new, surface is perfectly clean, almost flat (blanik's
> > canopy starboard side), tried two diferent suction mounts, one with light
> > PDA device mounted but the result is the same - it is always falling off
> > the canopy!
Just to reinforce what Paul says, I bought that suction cup mount from
him. It holds my Axim just fine. It never comes off. I hate to say
this, but I usually lick around the edge, then stick it on. But I
have to remember to clean the inside of the canopy _really_ well, or
my partner gives me such a ration of s**t that I can hardly stand it.
"There's no reason to ever touch the canopy." Well, sometimes, ya
gotta.
In my truck, I use the same Axim for navigation, and there I have a
smaller suction cup with a toggle lever on it that holds for weeks at
a time, but eventually falls off. Paul's suction cup is much better.
Ed
Ed
Andreas Alin
> "There's no reason to ever touch the canopy."
Well, not if you fly ASW 15. I have to touch it after each landing... no
way to get out without touching. ;(
Andreas
Bernie
device? You've got me worried now ..........
fred....@gmail.com
experience reinforces this. I can't explain why, but try water
instead of spit. Fred
Paul Remde
I doubt it would crack a canopy. My fear (founded or unfounded) is that the
localized deformation of the canopy would lead to internal crazing -
especially in extremely hot or cold conditions.
I just wouldn't want to risk a $2000 to $5000 glider canopy.
Paul Remde
"Bernie" <berni...@bigfoot.com> wrote in message
news:1176333055....@p77g2000hsh.googlegroups.com...
db
>pressure eg while as high up as possible.
Well, seems this works fine, I have just tried this technique on a 3.5 hours
flight up to 7000 feet.
Suction mount fell off after 30 minutes of flight (after being attached on
the ground), but it didn't fell off after being attached on 7000 feet!
I'll try water instead of spit next time.
John Scott
from my Camelback to wet the cup before attaching. I try to make sure I
press down all around the cup and squeeze out as much air as possible. I'm
also attaching to the lower edge of a 1-26 canopy, so there is not a lot of
curvature at the point of attachment. I've installed it at 7000' and flown
to 18,000 and back without it coming off, including flights of 5+ hours. I
generally have to pull on the edge of the cup and peel it off to remove it.
John Scott
<fred....@gmail.com> wrote in message
news:1176339981.8...@o5g2000hsb.googlegroups.com...
Simon Taylor
I'd reason that the most pressure the atmosphere can
exert on the outside of the canopy, even with a true
vacuum in the suction cup, is atmospheric pressure
- about 1kg/cm^2. A fingertip has about 1cm^2 of area,
so to gain a feel for the scale of what we're talking
about, try pressing down on kitchen scales with one
finger until the scale reads 1kg ( 2.2lb / 35oz / 5.47
standard Hungarian apples). Not inconsiderable, but
(I would have thought) not enough to risk damage of
any kind.
To test this theory more thoroughly, you could try
wandering over to a glider on the flight line and exerting
the same pressure with a finger on the canopy. I'd
wager no localised distortions will be inflicted -
at least, not on the canopy.
Simon
PS As a disclaimer: My entire knowledge of physics
is based upon observations I made watching hollywood
movies.
PPS Steven Seagal movies.
At 01:48 12 April 2007, Paul Remde wrote:
>Hi Bernie,
>
>I doubt it would crack a canopy. My fear (founded
>or unfounded) is that the
>localized deformation of the canopy would lead to internal
>crazing -
>especially in extremely hot or cold conditions.
>
>I just wouldn't want to risk a $2000 to $5000 glider
>canopy.
>
>Paul Remde
>
>'Bernie' wrote in message
Paul Remde
I don't think the issue is how much pressure the outside air pressure can
put upon the outside of the canopy. The issue is that the suction cup is
shaped like a ... well... a cup. It has enough force to pull the canopy to
form to the shape of the inside of the cup. That causes local stresses on
the canopy. It may or may not be a visible deformation.
Paul Remde
"Simon Taylor" <REMOVE_TO_REPLY...@gmail.com> wrote in message
news:587dmmF...@mid.individual.net...
bumper
the suction cup will get a lot hotter than the surrounding canopy. This will
cause thermal stress as well.
bumper
"Paul Remde" <pa...@remde.us> wrote in message
news:MqxTh.50146$oV.12792@attbi_s21...
Simon Taylor
As I understand it there will be no pulling force acting
on the inside of the canopy. This is admittedly counter-intuitive
to anyone who tried the following bored-in-science-lab
experiment; if we place a pipette against our skin
and release the nipple, our skin feels as if it is
being pulled towards the low pressure. In fact the
higher pressure inside our flesh is pushing our flexible
skin towards the low pressure area.
Back to gliding, which always tends to distance itself
from the world of skin and nipples, this does imply
that any minute pockets of trapped air in the canopy
might pull- sorry, might cause the very insidemost
parts of the canopy to be PUSHED in towards the low
pressure within the suction cup, potentially damaging
the canopy. However, I presume such pockets don't exist;
there would be visible depressions in the canopy where
these pockets had cooled after the forming of the canopy,
and any such pockets would be just/almost as prone
to deforming the canopy during a high wave flight.
Without the existance of air pockets, I reckon the
situation would be just as I described before - complete
with disclaimer..
Simon
Matt Herron Jr.
canopy by a suction cup is due to the differential in pressure on one
side of the plex vs. the other. trapped air bubbles in the plex would
not have an effect. air pressure at sea level is about 14.7 PSI.
Assuming the suction cup pulled a perfect vacuum (unlikely) and it had
a diameter of 2", then the maximum possible force would be:
Pi*D*14.7=92.4 lbs of force. Not insignificant. Another way to look
at this is that it would require 95 lbs of force to pull the suction
cup off the canopy.
At 6000' atmospheric pressure drops to about 12 psi, yielding 75lbs of
force. Still pretty high. Note that deflection of the canopy in this
area would be pretty small, but stress internal to the material would
be high. Low temperatures, UV exposure, etc would exacerbate the
issue.
In reality, a suction cup probably doesn't come anywhere close to
pulling a perfect vacuum, so the numbers would be much lower, but I
couldn't guess how much. I can't offer any analysis on skin/nipple
distances.
Matt (jr)
On Apr 13, 4:03 am, Simon Taylor
<REMOVE_TO_REPLY.simon.taylor...@gmail.com> wrote:
> Back to gliding, which always tends to distance itself
> from the world of skin and nipples, this does imply
> that any minute pockets of trapped air in the canopy
> might pull- sorry, might cause the very insidemost
> parts of the canopy to be PUSHED in towards the low
> pressure within the suction cup, potentially damaging
> the canopy. However, I presume such pockets don't exist;
> there would be visible depressions in the canopy where
> these pockets had cooled after the forming of the canopy,
> and any such pockets would be just/almost as prone
> to deforming the canopy during a high wave flight.
>
> Without the existance of air pockets, I reckon the
> situation would be just as I described before - complete
> with disclaimer..
>
John Wilton
"Matt Herron Jr." <ma...@digitalshorts.com> wrote in message
news:1176617793.6...@o5g2000hsb.googlegroups.com...
Martin Gregorie
> Why is the maximum possible force Pi*D*14.7 ?
>
atmospheric pressure at sea level.
--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
Ed Winchester
> John Wilton wrote:
>
>> Why is the maximum possible force Pi*D*14.7 ?
>>
> Physics 101. Area of the suction cup in sq. in. multiplied by
> atmospheric pressure at sea level.
>
>
I'm not a physicist, but I think you're looking at this problem all
wrong. Which is rigid, the canopy or the suction cup? The suction cup
which Paul was recommending earlier is soft rubber. So the deformation
is there. The only force on the canopy is that caused by the
deformation of the rubber, plus the torque or weight applied to the mount.
I happen to have that suction cup in my hand right now, and I estimate
that it takes about 10 pounds of force to compress it. Then, after
compression, that same 10 pounds is trying to spring back, but is being
prevented by the vacuum. This load is continuously applied as a bending
load trying to deform a disk of plexiglass the size of the cup.
Plexiglass is pretty stiff, I've never seen any deformation of the
canopy when the cup is on. I'm certain that at no time is the stress
greater than when you apply the cup. If one were to put their hand on
the outside of the canopy at the same time to provide counter pressure,
that stress could be reduced to almost nil. That cup is 4 inches in
diameter, or 2 inches radius. The release force would be 2*2*3.14*14.7,
or about 185 pounds, assuming the suction was perfect. Now, my Dell
Axim which I use this way weighs about 1/2 pound, and when hooked to the
cup, it has a moment arm of about 6 inches with the mount I bought from
Paul. That's 1/2 pound * 1/2 foot, or 1/4 foot pound of torque being
applied to the mount. And, I don't think that is increasing the overall
force exerted, it's just redistributing the 10 pounds of compression
force over the disk area.
And if you put the suction cup on properly, there is almost no air
inside there, certainly less than 10%, so it is probably 90% of a
perfect vacuum. Now, it you tried to pull the suction cup straight off,
that would apply the maximum force to the canopy, and as the cup started
to pull off, the volume inside would try to increase, making the vacuum
even greater. But if you remove it by pulling the little tab, then it's
released with almost no force because the vacuum is broken.
The bottom line for me in this is that I think I'd be most careful when
installing and removing the cup. I won't worry too much about the loads
it applies in use.
Ed
Martin Gregorie
> Martin Gregorie wrote:
>> John Wilton wrote:
>>
>>> Why is the maximum possible force Pi*D*14.7 ?
>>>
>> Physics 101. Area of the suction cup in sq. in. multiplied by
>> atmospheric pressure at sea level.
>>
>>
> John, the formula for area is Pi*r*r. Pi*d is circumference.
>
possible force that can be exerted is the pressure per unit area times
the area, is still valid.
This is the highest force that can be applied if you try to pull the cup
straight off the canopy without twisting it, sliding it, or lifting its
edge.
> I happen to have that suction cup in my hand right now, and I estimate
> that it takes about 10 pounds of force to compress it. Then, after
> compression, that same 10 pounds is trying to spring back, but is being
> prevented by the vacuum.
>
Quite true unless you pull on it at right angles to the panel.
> That cup is 4 inches in
> diameter, or 2 inches radius. The release force would be 2*2*3.14*14.7,
> or about 185 pounds, assuming the suction was perfect. Now, my Dell
> Axim which I use this way weighs about 1/2 pound, and when hooked to the
> cup, it has a moment arm of about 6 inches with the mount I bought from
> Paul. That's 1/2 pound * 1/2 foot, or 1/4 foot pound of torque being
> applied to the mount. And, I don't think that is increasing the overall
> force exerted, it's just redistributing the 10 pounds of compression
> force over the disk area.
>
I'd restate that a bit. The Axim is applying a downward force of 1/2 lb
at the end of a 6 inch lever, so that is, as you say, 1/4 foot-lb. But,
that is being resisted by a counterbalancing torque thats conventionally
represented as a point force acting at the center of the cup at the end
of a lever that is pivoted at the cup's lower edge: visualize the cup
peeling off the canopy: it cones unstuck and detached by swinging round
its lowest edge. This is also a 1/4 foot-lb, but the lever is only 2
inches, so the outward force on the cup is 1.5 pounds weight. Higher
than your estimate, but still tiny compared with the force needed to
detach the cup.
> The bottom line for me in this is that I think I'd be most careful when
> installing and removing the cup. I won't worry too much about the loads
> it applies in use.
>
Agreed.