Request help with air stream force on plate problem.

[bobengr]

I am not a student. I earned a BSME 31 years ago, but I have not really practiced engineering for years. I've been doing mostly business software development during my career. I am working on a personal project and dusting off my engineering math skills.

I need to calculate the approximate force that a rectangular plate would experience when in an air stream. I'd appreciate it if someone would check my equation and math.

Given: PlateArea = 0.0110 ft2, AirDensity = 0.002683 slugs/ft3, AirSpeed = 146.667 ft/sec

Find: PlateForce

Equation: PlateForce = ((AirDensity) * (AirSpeed)**2 * (PlateArea))/2g, where g = 32.174 slugs-ft/lbf-sec2

Soln: PlateForce = ((0.002683 slugs/ft3) * (146.667 ft/sec)**2 * (0.0110 ft2))/(2*32.174 slugs-ft/lbf-sec2)

PlateForce = 0.010 lbf

I know this seems like a student problem, but I'll send you a photo of me and my gray hair if that helps

Thanks!

--Bob

 

[IRstuff]

I get just 1.25N, which is about 0.28lbf

TTFN
faq731-376

 

[bobengr]

Thanks IRstuff. My problem was the air density was wrong. At 0F the AirDensity = 0.0807 lbm/ft3.

I appreciate your help!

 

[SNORGY]

I would not be able to calculate anything if slugs were involved.
First thing I do is convert everything to metric, then solve the problem, then convert the units back.
Slugs are something you put salt on to get them out of your garden. Well, they don't leave on their own but they get easier to pick up.

Regards,

SNORGY.

 

[SNORGY]

There is pretty good treatment of this very problem in th study materials for the FE exam.


Regards,

SNORGY.

 

[rb1957]

no "g" ... force = p*A
p is dynamic pressure = 1/2*rho*v^2
rho is in slugs/ft^3

units work out slug/ft^3*(ft/sec)^2*ft^2 = slug*ft^4/ft^3/sec^2 = lbf

1 lbf = 1slug*1ft/sec^2 = 1lbm*g