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07-18-2017, 05:44 PM
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Join Date: Jan 2005
Location: Tampa, FL
Posts: 2,861
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Quote:
Originally Posted by DanH
On the mounting screw. Here the screw point is just above my left index finger.
Of course, the washer spaces the tin away from the head at the black rectangle as well as the no-fin depth area in the red circle. Airflow at the black rectangle is just a leak. That's why I referred you to how to make a bypass duct instead.

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OK that explains the right rear (#5 in my case). What's the solution for the left rear (#6) as there's no onto cylinder mounting screw used on that side. I'm just looking for a temp setup to run some tests with the idea that the permanent solution are the ducts.
__________________
Todd "I drink and know things" Stovall
PP ASEL-IA
RV-10 N728TT - Flying!
WAR EAGLE!
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07-18-2017, 06:08 PM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by Auburntsts
OK that explains the right rear (#5 in my case). What's the solution for the left rear (#6) as there's no onto cylinder mounting screw used on that side. I'm just looking for a temp setup to run some tests with the idea that the permanent solution are the ducts.
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Look at your head - that restriction is only on one side. So - -it is only front left and aft right head that is affected by the baffles.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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07-20-2017, 07:50 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by N941WR
Yes Dan, but... if the cut only slants forward an inch, what is the speed loss? 2 knots, maybe 3? Well worth the tradeoff, if all else fails. Also, IL looks better than adding louvers or a lip and simpler than adding a cowl flap.
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Bill R. asked an interesting question. Although it's hard to precisely quantify in terms of speed loss, it can be quantified in terms of exit area increase. Knowing how much you actually opened the exit is important, because it offers some realistic expectation about additional cooling.
For five angles of cut (see the diagram below) the multiples of original exit area are:
10 deg 1.0154
20 deg 1.0642
30 deg 1.1547
40 deg 1.3054
45 deg 1.4142
What this little trig exercise tells us is that you'll need some significant cut angle to actually increase area very much. For example, assume the existing RV-6 cowl exit is 6" high (I'm guessing, don't have one handy). Cutting it back 1" would be a cut angle a fuzz less than 10 degrees, so the area multiplier would be 1.0154, or only about 1.5% larger than stock...which would not make any measurable difference in speed or cooling.
IF you elect to cut the exit for more area, you'll probably want to choose 30, 40, or 45 degree cuts. For an exit originally 6" high, those angles would mean cutting forward roughly 3.5", 5", or 6", for an area increase of 15%, 30%, or 41% respectively.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 09-03-2018 at 07:27 AM.
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05-27-2018, 12:40 AM
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Join Date: Feb 2007
Location: Mpumalanga, South Africa
Posts: 1,065
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Here's what I have done so far:
I removed the 2006 oil cooler and fitted the larger 2007. I then made an L-shaped plate which I temporarily fitted with RTV over the oil cooler outlet in the rear baffle. I covered about 30% of the hole and bent the "L" to about 45 deg so as to guide (hopefully) air over the No6 cylinder.
This was partially successful. The oil temperature remains normal. The No6 CHT dropped by about 15F but that still leaves it 15-20F above the No5 which is the next highest (that is about 15-20 higher than the front 4 cylinders). The boroscope on my annual check confirmed that No6 was running a little warmer but everything looked normal.
So, if I go full chat in race trim and lean to around 19gph (about best power), the number 5 gets to just over 400 and the No6 goes to about 420. I'm not going to do that! I need 21gph to keep the number 6 at around 400 - which I can live with.
I am going to take the cowls off again and check once more the sealing on the lower baffles but I am convinced there is nothing wrong on the top side.
I have one more thought. Would it help to put a slightly larger injector on the No6? I cruise LOP and have a GAMI spread around 0.3 and other than going flat out, my CHTs are fine even if No6 is a little higher than I would like - so I am not sure I actually want to screw with any of this.
__________________
Paul
Mercy Air, White River FAWV
RV-10 ZU-IIZ - "Zeus"
Building Bearhawk Bravo - RV-18 not available
2019 Donation Made
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05-27-2018, 05:39 AM
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Join Date: Jan 2010
Location: Florida
Posts: 267
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Quote:
Originally Posted by aerhed
My current rv10 will climb full throttle, 90kts all day and never hit 400. Bone stock cowl, baffles, louvers. Gear slot extended maybe 2 1/2 inches. They should all do this. If one can't, then something is being missed.
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Actual Repeat Offendrer, I would very much like to see some photos of your baffles installtion next time you open the cowl. Although, I don?t have the same issue, I do go over 400 deg in climb, summer of winter. Thanks.
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05-27-2018, 07:43 AM
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Join Date: Sep 2009
Location: St. Louis, MO
Posts: 1,788
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I struggle at times in the summer heat with CHTs that will hit 400 in the climb if I don?t reduce power and keep the airspeed up to 125. Most recently I made a mod to the heating system which helped significantly. I blocked off the right side 2? exit at the rear of the baffle that supplies air to the right heat muff. I then put a splitter in the line coming from the left side forward air supply for the left heat muff and routed it to the right side. My CHTs have come down around 10 degrees with this mod.
There is still more than enough heat coming in with this mod
__________________
Bill Peyton
RV-10 - 1125 hrs
N37CP
First Flight Oct 2012
Aviation Partners, LLC
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05-27-2018, 09:16 AM
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Join Date: Feb 2007
Location: Mpumalanga, South Africa
Posts: 1,065
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I might try that - I already have the front intake feeding both hot air outlets. I have kept the rear baffle vent connected for potential use as a vent to keep tunnel temps down if required. However, there doesn't seem to be an issue there.
__________________
Paul
Mercy Air, White River FAWV
RV-10 ZU-IIZ - "Zeus"
Building Bearhawk Bravo - RV-18 not available
2019 Donation Made
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09-03-2018, 11:33 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by paul330
One thing I can't agree with is that the oil duct doesn't "steal" air. The argument that the pressure equalizes I don't think holds water. Since the air is a moving compressible fluid, the pressure is going to be different all over the baffles, so air going through the duct can for sure cause a lower pressure (and therefore less cooling) over the no 6 cylinder.
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Returning to a thread from a few months ago....
It's a common belief that an oil cooler inlet somehow steals air from the adjacent rear cylinder, causing it to exhibit a high CHT. I've suggested it does not do so, based on some previous observation of CHT with changes in oil cooler air supply location. I've also said that measuring static pressure at various points within the upper plenum space would tell a lot.
As it happens, I recently rigged my plenum with pressure taps at each FI nozzle location, a story for another time. In the context of stolen air, I thought everyone might like to see the reality.
Below you can see the pressure taps on the #1 and #3 nozzles. They are simple aquarium bubble rocks, the goal being to record static pressure, not dynamic. The taps on #2 and #4 are similar, but note they are on the forward facing part of the head, where the conversion of dynamic pressure to static is a little higher, rather than on the rear facing part like 1 and 3.
Key point here is the location of the #3 tap, immediately in front of the oil cooler duct inlet:
And the numbers, at three altitudes, with three speeds at each altitude:
Note that #3 pressures are not significantly different, and in fact are just a bit higher than those recorded for the #1 nozzle well forward of the oil cooler intake.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 09-07-2018 at 12:09 PM.
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09-07-2018, 09:10 AM
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Join Date: Jan 2017
Location: Lake Stevens, WA
Posts: 8
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Dan, I agree with your conclusion, but I’m not sure your pressure taps prove the point. It seems you should have bottom deck taps as well, so you can see the pressure drop over each cylinder and over the oil cooler and, perhaps, test both with and without the oil cooler path blocked.
The notion that the oil cooler path “steals” air from the adjacent cylinder is presumably based on a flawed presumption that there is a static supply of cooling air (i.e., if it didn’t go over the cooler it would have gone over #3). In reality, the cooling air will travel through the path of least resistance, which appears to many as that 4” scat tube behind #3, but if one takes that simplistic approach to its logical conclusion, he’d convince himself that NONE of the available cooling air goes over the cylinders. Obviously, the scat tube isn’t the end of the story. The air must get through the oil cooler and then out the exit area (along with the other air in the exit area that came over the cylinders or through baffle leaks).
Your pressure readings show us that the static pressure in the top deck is reasonably uniform regardless of the location. What they don’t show is the pressure drop over each cylinder and the oil cooler. The pressure drop at each location is directly related to the speed and volume of cooling air, so it seems that would be better evidence to support your conclusion, particularly if shown with the oil cooler path both open and blocked.
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09-07-2018, 10:37 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by sbrault
Your pressure readings show us that the static pressure in the top deck is reasonably uniform regardless of the location.
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Correct.
Quote:
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What they don?t show is the pressure drop over each cylinder and the oil cooler.
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Cylinder and cooler delta would be useless in this context. A second round of upper deck measurements with the cooler duct entrance blocked might be illustrative.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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