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Pressure Test, Need Help Setting Up A manometer.

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LAN_403

Patrick

Mon Aug 26 2013, 05:19AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

that's interesting, they use that method for solar collection templates.

your math talent and skill greatly exceeds my own, and im grateful for your help, but ill use hot wire and foam to make my templates. but the greater question I have is what exact dimensions should I use for a 10" dia, 20.1 m/s flow through a Y tall duct, for max efficiency at sea level in a hover.

your comment on the upper curve not being as consequential as a lower parabola has me rethinking everything.

what im going to try next:

Andy

Mon Aug 26 2013, 06:26AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

What pressure reading did you get for the center of the duct?

Patrick

Mon Aug 26 2013, 06:32AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Andy wrote ...

What pressure reading did you get for the center of the duct?

I haven't finished any ducts yet, but i may cut 3 or 4 straight shrouds tomarrow.

are you meaning pressure between the red and green arrows here?

I just don't know if the parabola is to much or not enough in the above pic.

Andy

Mon Aug 26 2013, 06:39AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

The blue one and another away from the duct.

The blue one should high pressure than atmosphere, the green one should be local atmosphere, with the pressure from the blue one, you can workout if you double or triple the area of the exhaust

Patrick

Mon Aug 26 2013, 06:44AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Andy wrote ...

The blue one and another away from the duct.

when I get a duct fully functional ill measure using the manometer from an array of tubes along the red blue and green locations.

but the local pressure, and exhaust pressure difference should be zero right? this way I get maximum thrust coupling to the atmosphere, right? (a difference in exhaust pressure means force and energy wasted...)

your following quote fascinates me:

Andy wrote ...

Chamber to nozzle area ratio
inf
3.5
2.0
1.0
Throat Pressure %
100
99
96
81
Thrust Reduction %
0
1.5
5.0
19.5
If the pipe doesn't have a expansion nozzle, it will loss 20% of power, any more than 4 times the area is a waste.

your suggesting I widen the exhaust diameter greatly...As it is shown now, its a throat to exhaust area of 1.21 times... your suggesting upto but less than 4 times the area...

.

Andy

Mon Aug 26 2013, 07:08AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

If the pressure is at the blue is 4atm, the diameter of the blue section, the green section will have to be four times the area, if 8atm, then four times the area, that is for the expansion, then you lose alittle from not being equal to the local pressure, the air pulls away from the walls or it sticks to the walls and creates turbulence at the tip.

EDIT
My bad, "Chamber to nozzle area ratio"

Edit
It is throat to exhaust Rt = 1.0 and R2 = 5.0, were did you get the 1.21 value?

Patrick

Mon Aug 26 2013, 08:06AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Andy wrote ...
... were did you get the 1.21 value?

this duct is 1.21 as shown. 96/79 = 1.21

Patrick

Tue Aug 27 2013, 04:16PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Andy, ill build the duct ive illustrated, then make pressure measurements so we'll have some real numbers to look at.

Patrick

Sun Sept 01 2013, 09:40PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

ok ive got a styrofoam mold made, i can make many test articles now Andy.

here are the pics for the 6" smaller tail duct:

this mold will be covered in polyethylene sheets, then sprayed with wax to be slippery, and then epoxy or fiberglass will be wrapped around it to make the final part.

Patrick

Mon Sept 02 2013, 07:23PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I was up till 2am after a full work day, and learned some valuable lessons.

first, the fiberglass just didnt stay wide when a wrapped it circumferentially around the mold. it got longer and narrower.

second, when i put short strips vetically, they did stay better in close contact with the mold.

third, i may need to use the "lost foam" method, making the need for aerodynamic simulation a must. As the difficulty of making all this is very high, so i need to be sure im getting the best airflow for all this effort.

I was hoping to reuse the mold many times to make spare parts, as since crashes are bound to happen with autonomous flight in office spaces.

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