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  #31  
Old 08-16-2022, 06:01 AM
maxmirot maxmirot is offline
 
Join Date: Feb 2022
Location: Hereford
Posts: 98
Default

I am lost without a picture or drawing of these ducts
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  #32  
Old 08-16-2022, 06:44 AM
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BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,850
Default Great start with data!

Pete, please do plot the upper plenum pressure vs airspeed to assess the recovery. Just shooting from the hip(looking at your data), and your comment about leakage, it seems that the by pass leakage may be at the root of the issue.

Let's say the baffles are all sealed pretty well, it appears you have some wraps on the inside of the barrels to about midway. Then the restrictions are inlets, fins/leakages, then exit. With stock inlets and exit, that leaves looking at where the flow goes from the inlets. If a lot of air bypasses the fins (upper plenum) it does two things, chokes the exit with excess mass flow, and lowers the upper pressure as there is no resistance against which to build that dynamic pressure.

While it is also possible that you could have such poor diffusion (recovery of dynamic pressure) in the inlet-to-plenum transition, the fact that your lower cowl pressures rise that much indicates (to me) that it is leakage/by-pass air that is currently dominant factor. More precise information on the expected dynamic pressure is a good step to solidify the situation.

Now - there is another seldom discussed restriction between the upper chamber/cowl/plenum and lower cowl. That is the opening(s) at the bottom of the heads and barrels. If everything else (bypass wise) is perfect, this can result in lower mass flows. Vans baffles/instructions/drawings/ don't address this as it is typically a design feature and the opening is controlled by proper installation and fitting so they are snug. If one made baffles from scratch, this might be a variable to be controlled, and in Sam James baffle instructions for making baffles it is specified. Typically it would manifest itself in a cylinder to cylinder temperature imbalance but is usually overridden by other issues, like front dams, and blockage of #3 and#2 casting limitations. OK now I am down in the weeds, but important to know the effect exists.
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  #33  
Old 08-16-2022, 09:11 PM
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petehowell petehowell is offline
 
Join Date: Jan 2005
Location: MN
Posts: 2,336
Default Take 2!

Now that I is more smart, I gots more datas. Tapped the static system. Flew big squares, used Ottopilot. Used the Manometer function that averages readings over time to get a better result. Used Test Pilot Sheet to verify speeds flown. Despite what Andi says, i can be trained.

This is what I had time to get tonight. Let me know if this looks correct.

(Upper cowl press - aircraft static press) / calculated freestream dynamic press = Cp

Over 0.8 is good. I fall short........more work to do. Thanks Dan, Bill and others.

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Pete

Amateur Plane - RV-9A N789PH - 2650+ Hrs
Amateur Radio - KD0CVN
Doggies Delivered - 25+
St. Paul, MN

Last edited by petehowell : 08-17-2022 at 10:20 AM.
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  #34  
Old 08-17-2022, 11:02 AM
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DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 11,091
Default

Andi is right, as usual. Nice work!

Quick review says it's valid. Are you using the common piccolo setup from the white paper?

What Bill said. Pressure recovery is only one part of the puzzle, and changes to other parts can affect pressure recovery. Put another way, good pressure recovery doesn't guarantee good cooling, but it's hard to get good cooling without it.
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Last edited by DanH : 08-18-2022 at 09:21 AM.
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  #35  
Old 08-17-2022, 11:16 AM
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petehowell petehowell is offline
 
Join Date: Jan 2005
Location: MN
Posts: 2,336
Default Std Setup

Yes sir! - piccolos from your diagrams in the same locations - made them in the kitchen - got some side eye when she got home......

I'll make some plans for a winter project to improve things.

Quote:
Originally Posted by DanH View Post
Andi is right, as usual. Nice work!

Quick review says it's valid. Are you using the common piccolo setup from the white paper?

What Bill said. Pressure recovery is only one part of the puzzle, and changes to other parts can affect pressure recovery. Put another way, good pressure recovery doesn't guarantee good cooling, but it's hard to get good cooling without it.
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Pete

Amateur Plane - RV-9A N789PH - 2650+ Hrs
Amateur Radio - KD0CVN
Doggies Delivered - 25+
St. Paul, MN
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  #36  
Old 08-17-2022, 05:01 PM
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BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,850
Default Sorry a little confused.

I am missing something, Pete. The chart says pressure differential - is that upper to lower or upper to static?

Maybe a terminology thing. I would call upper pressure referencing static port "Upper pressure" and differential upper-lower.

I typically reference static on one side of the manometer, attache upper tube, then lower tube then lower to static side for differential. All while stacking pennies, watching the traffic monitor, and recording URL time. Then go back and do my get my detailed airspeed averages from recorded garmin data.

The cockpit is full of stuff (as is my head at the time) so I use a board with velcro and tape to attach the digital manometer and secure the tubes from writhing around like snakes looking for a place to hide. This way the labeled tubes are swapped so as to prevent vertigo.
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  #37  
Old 08-17-2022, 05:11 PM
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petehowell petehowell is offline
 
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Location: MN
Posts: 2,336
Default

Hi Bill,

Upper vs static in the chart (in the red cells) is the diff b/t the upper cowl pressure and the line I tapped into the static system. I just compared them across the manometer using the average reading over time function. Lower cowl pressure was not used for this set of data.

I agree the cockpit was busy!


Quote:
Originally Posted by BillL View Post
I am missing something, Pete. The chart says pressure differential - is that upper to lower or upper to static?

Maybe a terminology thing. I would call upper pressure referencing static port "Upper pressure" and differential upper-lower.

I typically reference static on one side of the manometer, attache upper tube, then lower tube then lower to static side for differential. All while stacking pennies, watching the traffic monitor, and recording URL time. Then go back and do my get my detailed airspeed averages from recorded garmin data.

The cockpit is full of stuff (as is my head at the time) so I use a board with velcro and tape to attach the digital manometer and secure the tubes from writhing around like snakes looking for a place to hide. This way the labeled tubes are swapped so as to prevent vertigo.
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Pete

Amateur Plane - RV-9A N789PH - 2650+ Hrs
Amateur Radio - KD0CVN
Doggies Delivered - 25+
St. Paul, MN
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  #38  
Old 08-17-2022, 05:26 PM
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BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,850
Default Bad Bill . . . . :o

Quote:
Originally Posted by petehowell View Post
Hi Bill,

Upper vs static in the chart (in the red cells) is the diff b/t the upper cowl pressure and the line I tapped into the static system. I just compared them across the manometer using the average reading over time function. Lower cowl pressure was not used for this set of data.

I agree the cockpit was busy!
Excellent, I fixated on the differential and missed the big red label "upper vs static"

Looks pretty stable over the speed range.
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  #39  
Old 08-18-2022, 07:55 AM
Jerry Fischer Jerry Fischer is offline
 
Join Date: May 2007
Location: Winder Ga
Posts: 970
Default I concur

Great work Pete.
From a retired Quality Engineer
6 Sigma Black Belt
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  #40  
Old 08-18-2022, 08:37 AM
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petehowell petehowell is offline
 
Join Date: Jan 2005
Location: MN
Posts: 2,336
Default Thanks

Thanks Jerry - took me two tries and I had expert help! I get there eventually....

Quote:
Originally Posted by Jerry Fischer View Post
Great work Pete.
From a retired Quality Engineer
6 Sigma Black Belt
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Amateur Plane - RV-9A N789PH - 2650+ Hrs
Amateur Radio - KD0CVN
Doggies Delivered - 25+
St. Paul, MN
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