Suction cup mounts at altitude...

[Shadrach]

Greetings Ladies and Gents,

I have finally become relatively comfortable with my BK AV8OR and its shortcomings. However, I am noticing that the suction cup windscreen mount gives up when climbing through DAs around 11,500ft.  One would think that simply reattaching it at the higher DA would cement it in place...but so far this is not the case.  

Does anyone have any tricks or tips to solve or minimize this issue? 

[AndyFromCB]

Quote: Shadrach

Greetings Ladies and Gents,

I have finally become relatively comfortable with my BK AV8OR and its shortcomings. However, I am noticing that the suction cup windscreen mount gives up climbing through DAs around 11,500ft.  One would think that simply reattaching it at the lower DA would cement it in place...but so far this is not the case.  

Does anyone have any tricks or tips to solve or minimize this issue? 

[xftrplt]

Quote: Shadrach

...climbing through DAs around 11,500ft.  One would think that simply reattaching it at the higher DA would cement it in place...but so far this is not the case.

[Shadrach]

Quote: xftrplt

...and one would be wrong.  It's air pressure that presses the suction cup to the surface.   At 11,500', you've got less than 70% of SL pressure.  A larger cup may help by giving more surface area to counter the lower force per square inch.

[xftrplt]

Quote: Shadrach

...and one would be wrong.  It's air pressure that presses the suction cup to the surface.   At 11,500', you've got less than 70% of SL pressure.  A larger cup may help by giving more surface area to counter the lower force per square inch.

[sleepingsquirrel]

Quote: xftrplt

[Shadrach]

Quote: xftrplt

Respectfully, I'm not sure you do.

There can be absolutely no air inside the cup, and it will still have <70% of the available adhesion at FL115 than at SL.  Air density has absolutely nothing to due with it; it's purely a function of ambient air pressure.

[carusoam]

Ross,

I am with Dick on this one.  Pressure differential is key here.  Even though some "unusable" area is created by your expanding bubble, the "usable" area of your rubber suction cup has a lessened effect because nothing (or much less) is pressing to get in...  Or else re-setting the suction cup at altitude should work, right?

I could be wrong, keep bringing valid arguments, I may switch sides.

Otherwise go with the super Velcro.  Cessna pilots don't seem to have this problem....?

 

Best regards,

-a-

[sleepingsquirrel]

I think that air pressure is what holds the thing to a surface, 90% . 10 % is the gecko lizard adhesion effect.

[xftrplt]

If you've taken offense, I meant none but was addressing your OP, below:

"One would think that simply reattaching it at the higher DA would cement it in place...but so far this is not the case."

That's my point.  At altitude, you can push the cup again to expel the air that has expanded, but it still won't support the weight because of the lower ambient absolute pressure.  That's why I suggested a larger vacuum cup.

I hope I've made myself (or at least the physics) clear.  If not, I apologize a priori.

[xftrplt]

What the hell.  The Squirrel is right...or maybe it's just FM.

[carusoam]

So far I'm still with Dick,  but squirrel does bring sticky saliva juice to the front...

-a-

 

It seems my Garmin portable's antenna would not stay attached to the windshield either....

Apparently we are not supposed to fly above 5,000' according to the portables manufacurers...

[orangemtl]

I suggest nails. They are indifferent to ambient air pressure.

[Piloto]

[Piloto]

Dick is very right on his explanation about air pressure holding the suction cup in place. Velcro on the other hand does not rely on ambient pressure but on mechanical linkage. The only weak link on Velcro is the adhesive itself. With time and heat it has a tendency to come off.

Jos

[xftrplt]

PS:  Yes, I'm well aware of the effects of altitude on sealed containers, having been on numerous chamber rides, carried water bottles in my G-suit for years, and opened sealed crew meals for another twenty.

[jetdriven]

Yep, you got it right Dick. I don't open the yogurt in the crew meals at altitude after a few instances.

[Shadrach]

[Shadrach]

[Shadrach]

[Shadrach]

Quote: jetdriven

Yep, you got it right Dick. I don't open the yogurt in the crew meals at altitude after a few instances.

[Hank]

Quote: jetdriven

Yep, you got it right Dick. I don't open the yogurt in the crew meals at altitude after a few instances.

[xftrplt]

Ross,

For sure, the horse is dead.  And, at the risk of admittedly hijacking this (dead) thread, I have a question:

Flying in to HGR from the west, I've noticed, about 10m to the west, what appears to be a SAM site (I've made a few lowish passes) embedded in the top of the mountain.  My RHAW didn't light up, so I snapped some pics.  Do the locals at HGR know about this?  There are no restrictions around it.  (I've seen another similar site near Charlottesville.  Any info?

[N601RX]

Here are some larger suction cups.  You can get them from www.mcmaster.com.

 

Rubber Suction Cups

With Male Thread

Great as nonslip feet for office machines and other items. All have a molded-in machine screw with male threads (except for 53535A33, which has an untapped hole). All suction cups are made of black rubber (except for 53535A45, which is gray). Maximum temperature is 200° F.

Warning! Never exceed capacities. Never use to lift people or items over people.

Cup Dia.	Load Cap., lbs.	(A)	Screw Size	(	Pkg. Qty.		Per Pkg.
1"	2.5	5/16"	8-32	1/4"	10	53535A11	$6.81
1"	2.5	5/16"	8-32	3/8"	10	53535A22	7.66
1 1/4"	3	1 1/8"	9/32"	__	10	53535A33	6.76
1 3/8"	3	1/2"	8-32	1/4"	10	53535A12	7.24
1 3/8"	3	1/2"	8-32	3/8"	10	53535A25	9.47
1 1/2"	3.5	5/8"	8-32	3/8"	12	53535A23	12.63
3 1/8"	30	1 17/32"	1/4"-20	3/8"	4	53535A45	9.32
3 3/4"	50	1 3/8"	5/16"-18	5/8"	1	53535A46	5.16

[Shadrach]

Quote: xftrplt

Ross,

For sure, the horse is dead.  And, at the risk of admittedly hijacking this (dead) thread, I have a question:

Flying in to HGR from the west, I've noticed, about 10m to the west, what appears to be a SAM site (I've made a few lowish passes) embedded in the top of the mountain.  My RHAW didn't light up, so I snapped some pics.  Do the locals at HGR know about this?  There are no restrictions around it.  (I've seen another similar site near Charlottesville.  Any info?