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I spent several hours yesterday working on the inlet plenum. First the pinch was removed and reprofiled with a gentle slope. Then I decided to divide the airflow front and back
by adding a divide vane. I simply cut a notch on both sides of the plenum, slipped in a sheet of aluminum and glassed over the seams. Also added some foam core on the inside to aid the back half of the core ... see attached photos. Still have to examine
the outlet diffuser (or none) and/or cowl flap, plus check cowling to see if any inlet area is being wasted.
Jeff
From: Bill Bradburry [flyrotary@lancaironline.net]
Sent: May 16, 2015 9:18 AM
Subject: RE: [FlyRotary] Re: Return to Flight - 2
Jeff,
One other thing that I just noticed. I was looking at your photo to see what you were saying about the oil pan clearance as regards
the pinch and I happened to see that you have a double pass radiator and the inlet/outlet are on the rear of the radiator. That means that you can have an air pocket in the forward radiator tank and if large enough it could also be in the cooling area. There
are several ways you can address this if you can not/don’t want to turn the radiator around, you can install a bleed hose in the forward tank and take it to the bottom of your swirl tank. Or just to get the air out after a fill, you could raise the tail of
the plane between runs to let the air rise to the swirl tank. That might take several tries.
I am putting most of my money on addressing the pinch.
Bill
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Saturday, May 16, 2015 7:26 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Return to Flight - 2
Thanks for the replies guys; all good points to consider and I'll try to address your comments.
Yes, I could remove the outlet plenum but the radiator air would now combine with oil cooler air and pressure inside the cowl, right now it"s isolated.
The right nostril feeds my stock Mazda oil cooler; left nostril feeds a Fluidyne - having extra oil cooling there is a possibility to scavenge more air for the radiator.
Yes, the pinch IS a problem and is there mainly because of the oil pan behind it; also thought the pinch (or downward turning vane) would help the front portion of core.
I have a manometer that was used on previous setup - just clear plastic tubing with red food coloring - it's difficult to do 1 step at a time because I'm using a test pilot - need to make best efforts even it means combining solutions.
No, I haven't done any flow testing and yes I should.
Back to the drawing board ... will post when more results available.
Thanks again ... Jeff
From:
Charlie England [flyrotary@lancaironline.net]
Sent: May 15, 2015 10:42 PM
Subject: Re: [FlyRotary] Re: Return to Flight - 2
Hi Jeff,
First, a caution: I'm a long way from flying, so this is untested in flight.
But I did a similar thing to what Bobby said, and used a leaf blower to pressurize my rad plenum. I used a thread on a stick to check outflow from the rad core. Looking at the drawing of your wedge plenum, I'd bet that almost all the air is coming out the last
5 or 8 inches of the core. Before I made mine, I asked Tracy about his RV-8 plenum. He said to pinch the back down tight; that he had to stuff open cell foam in the back of his to even the flow, so I did (I thought). He happened to be here as I was getting
ready to glass the mold, and commented that it was probably too thick at the rear. (It was *much* tighter than your drawing shows.) Sure enough, when I checked flow, all the air came through the rear of the core. To get even flow from front to back, I re-shaped
the inside of the wedge until the last couple of inches almost touch the core.
Also, in order to spread flow across the core (side to side, perpendicular to the inlet flow), I had to install a turning vane in the inlet duct. For reference, I'm building an RV-7 with a Sam James cowl made for a Lyc; not the rotary cowl with a chin inlet
for the rad. So my ~4.5" round inlet transitions to more or less rectangular cross section with slightly increased area where it arrives at the front edge of the core. Then it's a concave wedge, pinching down to almost a knife edge at the back end of the core.
No idea if it will actually cool, but I do know that the airflow coming out of the core is pretty evenly balanced when using the leaf blower to push air through it.
Pics below. The trailing edge is a lot thinner than it looks, because there's 'filler' on the inside to thin the wedge.
FWIW...
Charlie
http://s1155.photobucket.com/user/rv7charlie/media/1d6b1e19.jpg.html
http://s1155.photobucket.com/user/rv7charlie/media/slobovia12a_zps3194777e.jpg.html
http://s1155.photobucket.com/user/rv7charlie/media/pdrop2012_zpscbc0ae13.jpg.html
http://s1155.photobucket.com/user/rv7charlie/media/4seatback_zps033399e2.jpg.html
http://s1155.photobucket.com/user/rv7charlie/media/Slobovia14_zps413ea84e.jpg.html
On 5/15/2015 2:17 PM, Jeff Whaley wrote:
Actually I don’t have any really good pictures because I took it apart … but attached is a side-view after removal of the inlet
diffuser on top and also a sketch of approximate scale and shape of what I tried to make, (I don’t have a damper plate or cowl flap yet). The top shape isn’t quite right; needs to be pinched more at the rear, also am considering a turning vane to direct more
air through the front half. Trying to make air bend 90 degrees twice isn’t easy but I chose this orientation because of the desire to add a damper at the output for winter operations. I could drop the rear of radiator and bring air in through the bottom,
spilling out over the engine but would lose the ability to have a damper – I don’t like the idea of inlet dampers. On top of it all, my climb speed is usually only 90 mph; I don’t have the ability to get extra pressure from increased airspeed. P.S. the
radiator is the Griffin 2-58185-X, same as several other installs on this list.
The top plenum was out in the SUV; hopefully more attachments in next post …
Jeff
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Sorry to hear that Jeff. My apologies if you have already posted pictures of the your installation and the diffuser, but could you post some
now?
Dave Leonard
On Fri, May 15, 2015 at 8:19 AM, Jeff Whaley <flyrotary@lancaironline.net>
wrote:
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From:
Jeff Whaley
Sent: Friday, May 15, 2015 11:19 AM
To: 'Bobby J. Hughes'
Subject: Return to Flight - 2
Well, the second flight occurred last night with same results as before; one short low-level circuit due to insufficient cooling
… looks like Al Wick made the correct prediction.
There are 3 things I can try with the current configuration: 1) Increase inlet area 2) Increase outlet area (adjustable cowl
flap) 3) Re-profile the pinched diffuser. I will do all 3 and see what happens.
If all of the above show remarkable improvement then repositioning the radiator is the only alternative.
Jeff
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