Author Topic: Ventilation Inlet Location  (Read 6026 times)

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Offline flyingwaldo

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Ventilation Inlet Location
« on: August 02, 2009, 09:01:51 AM »
My builder put an inlet under the strake and tight to the fuselage.  The inlet shape is just a slot and grabs no air.  I'd planned on replacing it with a small NACA inlet but wondered if that area isn't good for an inlet due to air flow??  The plenum it feeds is inside the strake with a nice eyeball outlet so I was hoping to salvage that structure. 
Thanks for any input!

Offline Hmanvel

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Re: Ventilation Inlet Location
« Reply #1 on: August 02, 2009, 05:27:38 PM »
Under the canard seems to be a good place to grab air, at least with a NACA style inlet.  Works on my Defiant, along with others. 
Harry Manvel
Defiant N2HM
PTK / Pontiac, MI

Offline Bill James

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Re: Ventilation Inlet Location
« Reply #2 on: August 03, 2009, 06:13:20 PM »
A few thoughts of analysis-
It would be unusual for a cabin opening to be doing nothing.
Is it in the front or back seat area?
A friend had two identical forward facing air inlets fore and aft on the fuselage side. Air came in the forward one and went out the aft one (going frontward).
It sounds like the only "known" is that it doesnt have a forward facing scoop, and that it is assumed to be an inlet. It might be surprising to confirm what it is actually doing in flight with a string, in climb and cruise and descent, probably all the same.
Assuming there is another "inlet", tape this one closed and see how the other inlet works (with no exit).
A cabin inlet needs an outlet. Since it doesnt have a scoop, it may be functioning as a needed exit, in either area. A flush slot can create low pressure, creating an outlet.

I have two inlets, one in the front seat on the leading edge of the strake, and the inlet for the back seat is under the strake/fuselage corner with a 5/8 inch forward facing opening, faired back along the corner about three inches.

They are both robust inlets-- because of an excellent exit on the opposite fuselage side under the aft armrest. A slot exit as you describe would work there, but i made it an aft facing NACA to give folks something to point at and say "That wont work."    :)Oil flow and string flow shows it to work interestingly well. The location under the armrest results in no exit noise for the back seater.

During Oshkosh lunch Nick Ugilini described several interesting and useful results from pressure testing his LEZ cabin using an airspeed indicator. His bottom line was that it is significantly pressurized, showing 68 mph of pressure at one point. If flyingwaldo can further describe the slot, I hope you can chime in Nick.
Bill James, Fort Worth VariEze N95BJ
Downdraft Plenums, QuickCowls
There was supposed to be anhedral?
ATP, Society of Flight Test Engineers

Offline flyingwaldo

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Re: Ventilation Inlet Location
« Reply #3 on: August 05, 2009, 02:21:08 PM »
Thanks Bill.  I oil flowed the area and get good flow across the inlet but nothing comes up in it.  With the eyeball open or closed it makes no difference to the input from the NACA in front of the canopy so appears not to be acting as an outlet.  I have plenty of leaks around the back of the canopy (which will get fixed some day) so don't have need for an outlet yet.
Have made a mold of a good NACA design and will lay up one to try in that area in lieu of the slot.
Thanks again.
Waldo

Offline GNorman

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Re: Ventilation Inlet Location
« Reply #4 on: February 26, 2013, 08:28:30 AM »
I have the extended strakes that go forward up to the panel. I was considering putting slotted inlet air vents on the leading edge but not sure of two things:
1) Does this location chill your arm while flying high?
2) Is a small NACA scoop under the canard still a better place considering air volume and less rain in your face?

Offline flyingwaldo

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Re: Ventilation Inlet Location
« Reply #5 on: February 26, 2013, 09:21:43 AM »
Boy, is this an old thread!  I found that it was the slot that didn't work.  Mine is under the strake and feeds a nice little plenum just behind my seat in the strake.  As soon as I cut out the slot and replaced it with a small NACA scoop made from a mold cut directly off the full size dimensions in the Bingelis book - it blows out the GIB.  When the time comes I'll replace my plans vent in front of the canopy with one in the front corner of the arm space if I can make a proper plenum to make it work correctly.  Will be on the side of cockpit and have an eyeball inside like the rear, a common installation I've seen.

Offline BruceHughes

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Re: Ventilation Inlet Location
« Reply #6 on: February 27, 2013, 11:47:27 AM »
Are you guys that cut holes here and there, checking the plans for the underlying structure?
There is absolutely NO way that I would cut holes in the leading edge of the strakes.   
I don't have my plans with me so I cannot look .  It just seems scary.   Debbie Iwatate
published a pamphlet with 4 or 5 mods that she and others developed.  I suggest that
you find one of those (I don't know if she is still selling them).  She has nice plans for
an inlet in the NOSE.  Maybe one of aeronautical engineers will post on this "home in the
leading edge" idea.   SCARY!

Bruce Hughes   :)