Jeff,
I ‘ll share how poor the air distribution actually is for my two radiators. The attachment shows three tests with changes to guiding vane placements. The bottom measurements are what I’m flying now. I am turning the air 90 degrees right before the wedge entrance so that’s why the airspeed is so slow in that area. I don’t have enough room for a more graceful turn and didn’t find a better solution. I’m cooling 38” MP on a 95F day to pattern altitude with water temps around 215. Once power is reduced the water temp drops quickly. The core exit airspeed map shows what Charlie is point out.
If you can make a big change first try removed the exit wedge. I’ve been told we need 12” of clear space behind our heat exchangers . Dennis H. and I did some testing several years ago and I remember we observed a negative impact to airflow by placing a sheet of aluminum or cardboard at the core exit. We checked different distances but don’t remember if 12” was the magic number.
Good luck
Bobby
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Friday, May 15, 2015 10:43 PM
To: Rotary motors in aircraft
Subject: [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
|
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: |
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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