Canopy Pressure

[Dave Haller]

Need some help with my canopy. It was built by someone subcontracting with Mike Cook three years ago. It looks great and visabilty is very good out of it. The problem I have been experiencing is it pops open at about 150. We tried some re-adjustments in '07 and '08 but it kept coming open. Never did come apart or seperate, lexan stayed in tac. Someone out there said something about negative pressure. Can anyone explain what would cause it to jump the latch and pop open? I have two louvers in front of the windshield for air intake and one reverse louver above and behind the driver's head to let air out. I think I need to develope negative pressure inside the driver's compartment and am building positive causing the problem. Thanks for any ideas and help explaining what's going on.
Dave Haller #93

[SPARKY]

Dave can you post a picture?----remember----the reason we are required to have intake vents is an attempt to PRESSURErize the drivers compartment for fire saftey reasons---the highpressure air inside is just trying to feed the lowerpressure outside.  My guess is that something creates a lowpressure area somewhere outside you canopy...venting is allowed in lakesters--would just have to be sealed system.

[Rocky R]

We experienced this problem with the Ack Attack for the first time at the Shootout. On my final two runs the canopy opened both times in the measured mile. We have a huge hinge in front and a very sturdy latch on top. There are metal tongues on the side that slip under a frame section on each side. Still, at top speed there was enough negative pressure to pull the canopy open on the side and raise it a couple of inches. Hopefully Mike can add to this. All I know is it was a little unnerving having it pop open unexpectedly at speed.

[Dave Haller]

I'll get some pictures and post them.

[Dave Haller]

Been trying to get some posted but they are to big for the system.

[Peter Jack]

Dave:

I solved that problem by selecting each picture and e-mailing it to myself in the smallest format offered by windows. I then saved the resulting e-mailed pictures in a new folder and selected those to post. Worked like a charm.

Pete

[Dean Los Angeles]

If you have a windshield or canopy that is 40 x 25 you have 1000 square inches. I would suspect most are bigger, but for an example, 1000 sq in has 250 pounds of force if there is 1/4 psi differential between the two surfaces. That's not much pressure. A combination of a small negative pressure outside and a small positive pressure inside can place a huge amount of force on the Lexan.

More attach points to withstand the force are one option. Without instrumentation to read the pressure differential you won't know for sure what the force is that you are working against.

[Stainless1]

Dave, did you try taping over the intakes to see if that was a source of your problem.  It may not be that, but that is a way to eliminate one variable. 

[4-barrel Mike]

I shrank his pictures yesterday, but he hasn't been on since, so I'll post the ones he sent me.





Mike

[Dave Haller]

Sorry about the lack of response. Thanks Mike for posting. We had a family emergency yesterday with my daughter again. She continues to have heart problems at 15 but is a trooper. We were at the hospital most of the afternoon and evening. For those of you who don't know she has had two open heart surgeries and three other intrusive proceedures. She's a great kid. She was born in '93, thus my car number.
Thanks again and any ideas are much appreciated.
Dave Haller

[John Noonan]

Dave,

We wish you the best with your daughter.

John & Michelle

[1212FBGS]

when you say "opens" do the sides pop out? or does it lift off?
kent

[Glen]

Dave
Do you have any side view close up pictures wher it canopy joins the body area. Our prayers are with your great daughter. She was a great sport at the NW LSR banquet a couple of years ago.

[Richard Thomason]

Dave, so sorry to hear about your girl. Hope she is doing well now. As far as your canopy, from what little I know, with the squared off back portion, you are going to be generating a huge amount of lift. Only two ways to overcome it, one is to change the shape (which is a huge mystery in and of itself) the other is to have a much stronger latching mechanism. Talking about the force generated by air pressure, consider the emergency exit doors in a 767 aircraft. 34 inches by 52 inches equals 1768 square inches. At 10# air presure diferential from inside to outside, that means there is 17,689# pushing against that door. That is why there is no lock or security device on those emergency exit hatches. You can unlatch but you can't open them.

[4-barrel Mike]

Sorry about the lack of response. Thanks Mike for posting. We had a family emergency yesterday with my daughter again. She continues to have heart problems at 15 but is a trooper. We were at the hospital most of the afternoon and evening. For those of you who don't know she has had two open heart surgeries and three other intrusive proceedures. She's a great kid. She was born in '93, thus my car number.
Thanks again and any ideas are much appreciated.
Dave Haller

Glad to help, Dave.  Hope that your daughter is fine.

If you need more picture shrinkage, just send 'em.

Mike