Help: Need an aero calculation for safety issue.

[McRat]

I have a 30" x 30" rectangular window.

Assuming I am sliding sideways (worst case scenario), and the air stream is perpendicular to the window, and the window is only supported at the perimeter,

How much peak force is at the center point of the window?  How much distributed force is on the entire window?

I'm going to test the windows I make to twice the calculated force to measure deflection and perimeter attachment.

I took calculus 30 years ago, and forgot it all, and I never took fluids or aero.

Any help (or point me in the right direction) would be very appreciated.

[Captthundarr]

At what speed, temp, air density? will the window have a curve or bow in it? Just some fuel for the thinkers.

[McRat]

At what speed, temp, air density? will the window have a curve or bow in it? Just some fuel for the thinkers.

DOH!!!  215mph, Bonneville conditions (90°F - 9,000' DA).  Assume part is flat.

Wow, pretty sure my math is wrong.  I'm getting 480 PSI pressure.  Can't be.

[ol38y]

So Pat, I guess when you get to calculus, 30" X 30" is a rectangle? In algebra it's a square...    So, I got nuthin... 

[McRat]

So Pat, I guess when you get to calculus, 30" X 30" is a rectangle? In algebra it's a square...    So, I got nuthin...  

Algerbra? When my youngun graduarated from college, I was soo proud, I stood up and yelled, "That's my boy!!  He's real smart, he can even talk in algerbra!  Say something in algerbra sonny!!!  Say something!!"

He turned red, then said "Pi*R^2" ...

No wonder he turned red.  After 4 years and $100,000 he doesn't know pies are round!!!!    

A 30x30 rectangle is a square.  A square root is carrot who plays dungeons and dragons ...

[jl222]

I have a 30" x 30" rectangular window.

Assuming I am sliding sideways (worst case scenario), and the air stream is perpendicular to the window, and the window is only supported at the perimeter,

How much peak force is at the center point of the window?  How much distributed force is on the entire window?

I'm going to test the windows I make to twice the calculated force to measure deflection and perimeter attachment.

I took calculus 30 years ago, and forgot it all, and I never took fluids or aero.

Any help (or point me in the right direction) would be very appreciated.

  30'' X30''? buy a Ford My 98 crew cab is only 21''

  The 222 Camaro has the required Lexon [3/16'' but 1/4'' would have been better but tinted not available in 1/4'' and spun around 270mph no problem with window pushing in during spin but lots
of problems pushing out on other runs.
 We had one Pro-Stock type latch near front, with velcro at rear of window, had to add a brace down to door, still pulled out, then added extention on brace. No problem on last run but spun. We have now added another latch.
   Window is 16'' x 40'' tapers down to 7'' after 27''

           Good Luck JL222

[McRat]

Thanks!

[Jon]

30" X 30" = 900 square"

At 200mph you will have about 0.7psi (table I found only went up to 200 sorry)

900square" x 0.7psi = 630lb

You will have 630lbs of force pushing in the whole window at 200mph.


Cheers
jon

[hotrod]

I'm getting 480 PSI pressure.  Can't be.

That is too high. I don't have access to the info I need here at work but can look it up later. As I recall, Maximum dynamic pressure at 100 mph is about .5-.6 psi. This is the theoretical maximum ram boost you could get at 100 mph. That implies at 200 mph the dynamic pressure would max out around 2 psi tops (when the window was facing the direction of motion), so total dynamic pressure load on the entire 30x30 window could not exceed 1800 lbs (probably considerably less), since you never get more than about 60% dynamic pressure recovery in the real world without carefully designed ducting. I would say off the top of my head design load would probably be somewhere between 600 and 900 lbs at the moment he window was perfectly at right angles to the air stream flow.

I have a chart at home but can't find it on line that has actual dynamic pressures determined by NACA when bringing an air stream to a dead stop from those sort of sub sonic velocities. I will try to dig it up if no one finds better info sooner.

Looks like we posted at about the same time your chart confirms my recollections.

Larry

[WOODY@DDLLC]

McRat, you have 900 in² or 6.25 ft² of frontal area. Force is proportional to the velocity squared! Double the velocity 4X the force. (2²)

Use the attached calculator and give your flat plate a Cd of 1.00. Divide the lbf by the inches squared (900) and you have the psi which BTW is also the theoretical ram air psi but only at Cd 1.00. The lbf will surprise you but it is evenly distributed. If you build a sealed box around the plate and inflate to that psi you can measure your deflection directly. But remember the frame has to support the total force! 

Put in a Cd of 0.15 and you will have the force on a small streamliner - a whole lot less!! Notice the HP delta too!

Bonus: The calculator has a very nice coast down calculator, too! 

Thank these guys: http://www.precisionautoresearch.com/RDP/PAR37.htm

Larry's head is pretty close!