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Discover
Joined: 26 Feb 2007
Posts: 429
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 Posted: Thu Jul 07, 2011 9:05 am Post subject: Oil Cooler Setback |
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Hi Cliff,
I've experimented with airflow at the oil cooler on my Tiger. I found that it is not intuitive. That is the airflow there must be complicated. I have tried a deflector like Gary and others have used in front of the cooler. I have also spaced the cooler back in increments up to about 3/4". None of these provided better oil cooling than the factory location for me. The set back did not work at all and made the oil hotter. The deflector could be shaped to help but made the rear cylinder hotter.
I was quite "baffled" by these experiments as nothing seemed to work like I thought it would. I returned it to the factory position. I must say that changing one thing has a domino effect on the cooling of other things. Like I mentioned yesterday moving the front baffle on the front cylinders just a sixteenth of an inch up or down makes a big difference in CHT spreads. And I found it to be different in summer than in winter. So there are compromises. An easy way to experiment with this is to put aluminum tape in front of the cylinders just above the factory baffle. You can find the optimum position this way.
I would like to do what Gene Plazak has done and like a lot of RV builders do and use a plenum over the cylinders instead of the factory baffle system. Gary's baffles are a huge improvement over the factory baffles. but the whole concept of these type of baffles is lacking I think. A whole paradigm shift might be to use a plenum design. Plazak got his approved on a one time basis but it might be really hard to do that for an STC these days.
One example I'd like to try is the way Jabiru has tackled it as shown here: http://www.usjabiru.com/images/pdf/AirDuctInstall.pdf
Then there is the air exits that should be 7:1 like Dave Anders RV4 instead of 15:1 ramp slope like Tigers are.....
ned
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| Posted: Thu Jul 07, 2011 11:33 am Post subject: Oil Cooler Setback |
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I ran into Dave Anders in Visalia a number of years back. Trust me, I started thinking of ways to cut up the floor of the Tiger.
I also tried fooling with the oil cooler. That's how I came up with mounting it to the outside like on the Jaguar baffles.
The ramps in front of the cylinders "Like I mentioned yesterday moving the front baffle on the front cylinders just a sixteenth of an inch up or down makes a big difference in CHT spreads." are very dependent on angle of attack also. Setting one up to cool during climb hurts CHT spread in cruise and vise versa.
From: 923te <923te(at)att.net>
To: teamgrumman-list(at)matronics.com
Sent: Thu, July 7, 2011 10:03:57 AM
Subject: Re: Oil Cooler Setback
Hi Cliff,
I've experimented with airflow at the oil cooler on my Tiger. I found that it is not intuitive. That is the airflow there must be complicated. I have tried a deflector like Gary and others have used in front of the cooler. I have also spaced the cooler back in increments up to about 3/4". None of these provided better oil cooling than the factory location for me. The set back did not work at all and made the oil hotter. The deflector could be shaped to help but made the rear cylinder hotter.
I was quite "baffled" by these experiments as nothing seemed to work like I thought it would. I returned it to the factory position. I must say that changing one thing has a domino effect on the cooling of other things. Like I mentioned yesterday moving the front baffle on the front cylinders just a sixteenth of an inch up or down makes a big difference in CHT spreads. And I found it to be different in summer than in winter. So there are compromises. An easy way to experiment with this is to put aluminum tape in front of the cylinders just above the factory baffle. You can find the optimum position this way.
I would like to do what Gene Plazak has done and like a lot of RV builders do and use a plenum over the cylinders instead of the factory baffle system. Gary's baffles are a huge improvement over the factory baffles. but the whole concept of these type of baffles is lacking I think. A whole paradigm shift might be to use a plenum design. Plazak got his approved on a one time basis but it might be really hard to do that for an STC these days.
One example I'd like to try is the way Jabiru has tackled it as shown here: http://www.usjabiru.com/images/pdf/AirDuctInstall.pdf
Then there is the air exits that should be 7:1 like Dave Anders RV4 instead of 15:1 ramp slope like Tigers are.....
ned
[quote][b]
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Discover
Joined: 26 Feb 2007
Posts: 429
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| Posted: Thu Jul 07, 2011 12:36 pm Post subject: Oil Cooler Setback |
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Putting the exit ramp into the floor would be optimal. I was thinking that adding to the bottom with a fiberglass fairing might work. It would increase frontal area thus drag. Both the cowl and fuselage would have to be lowered with a fairing to get the proper NACA duct installed. I think it would be around 23" long
It would be great to place the exhaust into the NACA and try and get some "augmentor" effect...
It would be interesting to see which was geater, drag from increased frontal area or less cooling drag from a better NACA exit design.
[quote][b]
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