Suction cup damaging canopy?

[benso...@gmail.com]

Ever known a suction cup mount (RAM) to mar or distort a canopy?

[uncl...@ix.netcom.com]

On Friday, September 2, 2016 at 11:02:16 PM UTC-4, benso...@gmail.com wrote:
> Ever known a suction cup mount (RAM) to mar or distort a canopy?

If surfaces are not clean eventually there will be a bit of dulling due to abrasion. There is not enough force in a cup the size commonly used to cause distortion.
UH

[David Hirst]

On Saturday, September 3, 2016 at 3:02:16 PM UTC+12, benso...@gmail.com wrote:
> Ever known a suction cup mount (RAM) to mar or distort a canopy?

It's not the suction cup that is likely to cause damage, it's whatever is attached to the cup that puts a twisting load onto that small section of canopy.

I had a heavy outlanding a few years back in a Discus (basically landed sideways and was lucky not to break the tail off) where the PDA/suction-cup caused the canopy to crack along the length of the mounting frame on that side. Yes, I admit that I never ran a 'control' experiment (by landing sideways without the PDA) and thus the evidence is circumstantial, but ever since then I've always mounted PDAs on the cockpit or instument panel.

You're probably OK with a small item on a short lever like a GoPro but I wouldn't trust anything heavier. Look along the outside of the canopy or look through it with polarizing sunglasses - if you can see any distortion then you're asking for trouble in the future.

My 2c.
DH
TX

[Oscar-Hotel-Mike]

Sorry for a bit of an aside on this topic but I dislike mounting anything to the canopy, frame or glass, as it could (maybe a big could) prevent the canopy from ejecting properly. Of course this would only happen if there is a power/data cable involved. Now I will admit that this would seem to be an unlikely event when a PDA/PNA has a USB connector which SHOULD release easily. It was probably more of an issue with the ubiquitous cradles holding Compaq PDAs of days gone by with surprisingly strong cabling. But if we have to eject we don't want anything hanging things up. Right?

[bumper]

On Friday, September 2, 2016 at 8:02:16 PM UTC-7, benso...@gmail.com wrote:
> Ever known a suction cup mount (RAM) to mar or distort a canopy?

I've seen localized crazing (numerous fine cracks) in the area covered by a suction cup on a plexiglas windshield. This on an aircraft parked long term on the ramp. I assume it was due to differential thermal expansion and stress. Using an IR spot thermometer, I measured the effect on the outside surface of static cling sunshades and a suction cup attached inside a Stemme canopy. Within just a few minutes in the sun, there was a rapidly increasing temperature differential on the outside surface between the uncovered area and where the items were attached.

The suction cup crazing might also have been caused by the outgassing of plasticizers or other chemicals in the suction cup not being compatible with a acrylic?

I removed the stuff. True, that ramp aircraft was an extreme case, but I didn't think it worth the risk, even short term.



bumper

[David Salmon]

At 02:08 04 September 2016, Oscar-Hotel-Mike wrote:
>Sorry for a bit of an aside on this topic but I dislike mounting anything

>t=

>o the canopy, frame or glass, as it could (maybe a big could) prevent the

>c=

>anopy from ejecting properly. Of course this would only happen if there

>is=

> a power/data cable involved. Now I will admit that this would seem to
be

>=

>an unlikely event when a PDA/PNA has a USB connector which SHOULD release

>e=

>asily. It was probably more of an issue with the ubiquitous cradles

>holdin=

>g Compaq PDAs of days gone by with surprisingly strong cabling. But if
we

>=

>have to eject we don't want anything hanging things up. Right?

If you go high in wave they can drop off.
Dave
>

[AS]

Tend to disagree! My new (used) glider shows a large (6"-8" dia.) circular distortion in the forward, flat part of the canopy, where a suction cup was attached - apparently over a longer period of time. Depending on the size of these cups, the force they can exert is considerable - certainly enough to stress and eventually distort the Plexiglas.
Assuming one can draw a 100% vacuum on the cup, a 8" (0.2m) diameter cup can exert over 3,000N (675lbs(f)!
Uli

[drguya...@gmail.com]

I have an LS8-18 and an SZD-59.
I use suction cups to mount the cameras on the canopies for more than five years.
I clean the canopy and the suction cup before mounting the suction cup.
I remove the suction cup at the end of each day of flying.
No damage.
No circular rings.
No crazing.
No distortion in the optics.
I apply my saliva to the rim of the suction cup before mounting.
No decay or periodontal disease has been detected, either.

[uncl...@ix.netcom.com]

So- like most answers, the issue is degree. I haven't seen a suction cup used that was more than 3 inches. I've used 1-1/2 inch cups for years. Go to 8 inches and, as Uli noted, it likely is a much different thing.
So the correct answer is "that depends".
CU
UH

[ND]

On Friday, September 2, 2016 at 11:02:16 PM UTC-4, benso...@gmail.com wrote:

> Ever known a suction cup mount (RAM) to mar or distort a canopy?

nope. do it.

[drguya...@gmail.com]

I think many are missing the significant differences between "suction cups."
A suction cup that is not supported by any structure would conform to the plexiglass shape and have a fairly uniform force on the plexiglass. A suction cup mount like those provided with GoPro cameras is significantly different in that there is a very stiff plastic backer so that when the cup is activated it is trying to pull the mounting surface into the stiff plastic backing which is relatively flat. Thus, the more the plexiglass surface is curved the greater the force to flatten the curve. Put this rigid suction cup mount on a curved piece of plexiglass and leave it in the hot sun and I can easily see distortion or cracking happening. The suction cups that are unsupported and use a small button in the center of the cup to be the mounting point will conform to the shape of the curved surface and have very little reshaping force.