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  #111  
Old 03-25-2012, 08:29 AM
lostpilot28's Avatar
lostpilot28 lostpilot28 is offline
 
Join Date: Nov 2006
Location: Boise, ID
Posts: 1,095
Default

Quote:
Originally Posted by Omega232Devils View Post
Sorry Bob,
I still have a few more hours of break in on my overhauled cylinder before i feel comfortable running a test run. I am making two long flights this weekend and should be good for a test run mid to late next week! I am curious myself as I have had this fairing prepared for a few weeks now!

Dan
Hey Dan, eagerly anticipating your results on this! Any chance you've tested it yet? On a different thread, Dan, Ken and I are testing cowl pressures (upper and lower) and exit air temps. I'm considering adding this exit air fairing to the end of my testing to see if it helps lower the bottom cowl pressure.
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Boise, Idaho
RV-7A Flying!
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  #112  
Old 03-25-2012, 04:09 PM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default Done a lot of studying and have a semi-frozen plan

You know the comon expression that each RV is unique? Well there is one area of our RV-6A that is "uniquer" than most - the bottom center of the fuselage forward of the spar. I have spent quite a bit of time today going over the photos in the build albums to come up with the best way to do this.

My first choice was to install platenuts there and attach the center/keel fin with #8 flat hear screws. I have a dimple die that came with the pitot mast mount that works great and I would just remove the fin and install the screws flush if it didn't work out. The console is so integrated into every distributed system that it would be a MAJOR operation to remove it for the installation of platenuts on the floor/skin in that area.

I considered sheet metal screws which I know work great for inspection panels and other non structural applications but I don't consider them adequate for holding on pieces that are sticking out in the wind - not to mention the pointed ends of the screws going into an area that I can't inspect.

A central feature of my approach is going to be a central fin. I'm going to mount a 3/4"x3/4"x24" piece of angle to the fuselage with blind 1/8" rivets. The angle will have platenuts on it and the fin will be attached to it with #8 flathead screws. That way the fin can be replaced at will to experiment with different shapes sizes and thicknesses.

That is the key decision right now, the shroud/flow fences/fairing is generally established in my mind but this was the hard one. There is some freedom with the rest of it for now.

Bob Axsom
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  #113  
Old 03-26-2012, 05:56 AM
Bob Axsom Bob Axsom is offline
 
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Posts: 5,685
Default Worked all night on the center fin

It is ready to install but I need a little sleep. Should test fly today then move on to the fairing.

Bob Axsom
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  #114  
Old 03-26-2012, 02:54 PM
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Omega232Devils Omega232Devils is offline
 
Join Date: Jun 2011
Location: Catawba, NC
Posts: 319
Default Coming Soon

Sonny,
Let me appologize for the tardy response to posting test results. I have test flown the fairing, but haven't released the results as they were not what I was expecting, or what others here are expecting, so I was hoping to run another test run without the fairing to ensure I have a good baseline.

Waiting on a 70deg day in San Diego is normally not very difficult, but the weather has us all baffled here recently. I expect today or tomorrow I should get another run out and will post my results.

Dan
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RV-6A - N426JM - 180hp / C.S. / dual PMags
NC26 - Long Island Airpark, NC
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  #115  
Old 03-26-2012, 09:02 PM
Bob Axsom Bob Axsom is offline
 
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Posts: 5,685
Default Got the central fin installed




got the fin installed but ran out of daylight for the test - hopefully I'll get it done in the morning.

Bob Axsom
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  #116  
Old 03-27-2012, 10:28 AM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
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Default I flew the test this morning

183.8 kts was the final number which is 0.6kt less than the best speed I've ever seen so I'm considering it "no Change in speed" and I'll move on to the fairing.

Bob Axsom
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  #117  
Old 03-27-2012, 10:59 AM
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Ron Lee Ron Lee is offline
 
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Default

Bob, while speed improvement is good, can you state that cooling was impacted? I am assuming that CHT is the parameter to note.
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  #118  
Old 03-27-2012, 03:06 PM
Bob Axsom Bob Axsom is offline
 
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Default No noticeable cooling impact

EGTs ranged from 1296 to 1350, CHTs 347 to 354, oil 180.

Bob Axsom
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  #119  
Old 03-27-2012, 05:59 PM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default Next step

I went to the hangar and visualized a few different approaches recognizing the opening race of the season is 4 days away and I have some unique opportunities and irreversible decisions to deal with. I decided to mount two more angles on the fuselage bottom with plate nuts for adding the side flow fences whil maintaining flexibility in experimenting. The first flow fences are going to be rectangles just like the center fin and the they will be 0.090"x3"x22". I'm going to test fly the open bottom and most likely that is what I will race with Saturday at Sherman, Texas (GYI). With the experience I gained on the center fin I should be able to test the open fence configuration tomorrow.

Bob Axsom
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  #120  
Old 03-27-2012, 09:55 PM
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Omega232Devils Omega232Devils is offline
 
Join Date: Jun 2011
Location: Catawba, NC
Posts: 319
Default Exit Fairing Results!

Ok, first off again let me apologize for the tardy posting of the exit fairing results. I know this has been a 'Hot' thread with lots of anticipation.

I have a solid database from test flights before I overhauled my #2 cylinder, but I flew the exit fairing test run after the overhaul. The test flight did not produce the results I expected, so I thought it best to take another day to do a test flight without the fairing to ensure my baseline numbers were still accurate.

BLUF: (Bottom Line Up Front) My goal for the exhaust fairing was never speed, any speed gain was a bonus. My goal was to smooth the exit air, increasing the cooling flow and lower my CHTs.

I am open for questions regarding my test data or flight procedures. I try to keep as many perimeters the same as humanly possible. Nothing is perfect, but I think I have a solid base to make decisions with. All test flight profiles are flown exactly the same.

(FYI: 24/2400 numbers are climb numbers, all other MP/RPM is level flight cruise numbers)

Here is the the Baseline data: (WITHOUT Fairing!)


Here is the fairing data: (TWO test flights with Fairing ON!)


Fairing performance numbers: (Numbers in RED = Fairing produced BAD results / Numbers in GREEN = Fairing produced GOOD results!)



Results:
CHT: Overall average 13 degrees HOTTER. Climb CHT increase average: 14 degrees. Cruise CHT increase average: 12 degrees.
(WITH fairing, 1st cylinder hit 400 degrees at 1min 50 sec into flight. WITHOUT fairing after 9 min 50 sec hottest cylinder was at 392 deg.)
EGT: Overal average 16 degrees HOTTER. Climb EGT decrease average: 24 degrees. Cruise EGT increase average: 30 degrees.
Fuel: Rate of burn (Both climb and cruise) increased by almost 0.5gph.

As for the speed respect of the fairing, I would not take my opinion in choosing to add the fairing. I did not fly the 'speed profile' that is described in the forums using 3 or 4 legs and TAS etc. The speed data on my forms is strictly IAS and GS for my own kicks!

I would like to take the standard "5-7mph gain" that comes with any speed modification, but my opinion is there wasn't any noticeable speed increase.

There it is guys. I hope others have better luck with the fairing. It has worked great for Gary. I think the fact that I have an "A" model with anything and everything blocking the exit and causing massive exit flow turbulence has a lot to do with exit flow performance.

JMHO

Dan
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Dan Thompson
RV-6A - N426JM - 180hp / C.S. / dual PMags
NC26 - Long Island Airpark, NC

Last edited by Omega232Devils : 03-28-2012 at 10:46 AM. Reason: More defined CHT/EGT results!
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