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Old 08-19-2022, 08:56 AM
Freemasm Freemasm is offline
Join Date: Nov 2017
Location: Orlando
Posts: 903
Default Total? Dynamic? Static? Are you feeling it?

Happy Friday. Interesting Engine Cooling thread has me thinking about an often misunderstood application of a relatively simple relationship; Total, dynamic, and static pressure. Hopefully the Mods will allow this as it is applicable to our endeavors.

The first picture is the test set-up. A fan is drawing air through the test chamber. Like our flying aircraft, it is outside or basically an infinitely large room. Water is the fluid in the manometer tube. For us nerds that want to overcomplicate things, don't; Flow is not turbulent, no compressibility, ignore friction effects.

The second picture has the relevant parameters (?)

If VAF is similar to the undergrad engineering population; one third will get the answer, another third will be wrong initially and then get the correct solution, another third will tell me I'm an idiot.

Feel free to make assumptions. Are there enough listed parameters to determine water column height X? If so, what is it?
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Old 08-19-2022, 10:08 AM
D-Dubya D-Dubya is offline
Join Date: May 2009
Location: Beaumont, Texas
Posts: 215

Is this going to be on the final? It takes me back to engineering classes I took in the last century...oops, i think I had a little vomit in my mouth for just a second there.
David Welsh
Beaumont, TX
RV-7 N413WD
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Old 08-19-2022, 10:27 AM
Marc Bourget Marc Bourget is offline
Join Date: Apr 2009
Location: Stockton, California
Posts: 386

this presents the promise of a very interesting and informative thread.

Carry on!
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Old 08-19-2022, 05:24 PM
agent4573 agent4573 is online now
Join Date: Aug 2019
Location: Mountain view
Posts: 618

My answers: Pd = 3.78 psi. Ptotal can't be defined because you didn't give an altitude or temp. Assuming sea level on a standard day, that would make P static = 14.7 psi and P total equal to 18.5 psi. Manometer height is 10.7 inches (5.35 up, 5.35 down).

Other assumption: V amb = 0, so that Pamb = Pstatic
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Last edited by agent4573 : 08-19-2022 at 05:46 PM.
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Old 08-19-2022, 07:17 PM
RV8iator's Avatar
RV8iator RV8iator is offline
Join Date: Nov 2006
Location: Saint Simons Island , GA
Posts: 1,710
Default All I know

One thing certain is if pie are square, corn bread are round, or vice versa!
Jerry "Widget" Morris
RV 8, N8JL, 3,200+ hours on my 8.

VAF #818
Saint Simons Island, GA. KSSI
PIF 2007 - 2022

I just wish I could afford to live the way I do
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Old 08-20-2022, 08:14 AM
Freemasm Freemasm is offline
Join Date: Nov 2017
Location: Orlando
Posts: 903
Default No correct answer yet

Maybe question is below most VAFerís intellect to be worthy of their thoughts.

Maybe most are afraid they might be wrong to post an answer.

Maybe Iím the idiot and the whole question is just dumb.

The right answer will surprise (guessing) 2/3s of anyone that actually cares.

Anyone else?
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Old 08-20-2022, 09:02 AM
Norman CYYJ Norman CYYJ is offline
Join Date: Feb 2005
Location: Victoria B.C.
Posts: 1,514

I don't think that there is enough information presented. Eg. diameter of the entry and exit points and the diameter of the narrowest point. The real question should be how much Jack Daniels was consumed before publishing this question.
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Old 08-20-2022, 09:12 AM
74-07 74-07 is offline
Join Date: Dec 2016
Location: Greenville, SC
Posts: 722

Bad assumption

“VAF is similar to undergrad engineering students.”

My impression - we’re closer to pilots at happy hour.
RV-8 sold
RV-7 sold
RV-8 flying
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Old 08-21-2022, 01:19 AM
Cumulo Cumulo is offline
Join Date: Apr 2015
Location: KHMT
Posts: 111

X= 0 (no friction)

No math needed.
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Old 08-21-2022, 07:55 AM
Freemasm Freemasm is offline
Join Date: Nov 2017
Location: Orlando
Posts: 903
Default Cumulo is correct

The exercise is conceptual.

There were plenty of parameters available if needed. No energy is added to the system until the fan., so Pt is constant until that point.

The configuration in the pseudo test set up was chosen for its similarity to GA aircraft application

Thatís all Iíll say for now. Concepts canít be taught, only presented; a statement of mine that used to pi$$ off my math teacher wife until she reconciled it.

If you donít agree, thatís fine. If you have a question and donít want to post, PM me.

So, for those ~600 to now VAFers that bothered to read this (I realized most could care less), you know what third you fall into. Iíll say again, this concept applies to our EAB/GapA endeavors.

Cheers boys.
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