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  #21  
Old 03-22-2009, 11:03 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
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<< the only opening into zone 3 from zone 1 is through the oil cooler and baffle seal leaks>>

Ahhhh. I assumed your oil cooler outlet was ducted to the zone 2 plenum, and knew nothing about the 1/4" x 7" slot exit.

<<Before I added the horizontal baffles zone 2 had a gross leakage path to zone 3 up around the valve covers past the upper plenum over the baffling below and aft of the engine>>

Better ask; how did you determine the flow was from 2 into 3, and not 3 into 2?

......Below the fuselage the curved center lower cowl baffle is mounted with screws and is held off below the fuselage by four AN960-10 washers giving a pressure vent of 1/4" x ~7" to dump the oil cooler air .......Experimentally increasing the opening this by 1/16" (another washer added to each mounting point) decreased the speed slightly so it is not static in there.>>

Interesting. Not static is no surprise. Was this experiment before or after adding the horizontal seals to isolate 2 and 3?
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  #22  
Old 03-22-2009, 03:20 PM
Bob Axsom Bob Axsom is offline
 
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Posts: 5,685
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Quote:
Originally Posted by DanH;311196

<<Before I added the horizontal baffles zone 2 had a gross leakage path to zone 3 up around the valve covers past the upper plenum over the baffling below and aft of the engine>>

Better ask; how did you determine the flow was from 2 into 3, and not 3 into 2?

[I didn't actually. The idea to add the horizontal baffle was based on a SWAG that the isolation might have an effect. I really had no insight into how it would affect performance - strictly an experimental cut and try. I felt I should try it before pulling out the complex lower cowl baffle assembly. Many small iregular shaped plates are required to form the curved part of the baffle and seal everything passing through it - engine mount, nosegear fuel line, primer lines, CHT & EGT sensor wires, starter and alternator wires, mixture, throttle and Carb heat controls etc.

......Below the fuselage the curved center lower cowl baffle is mounted with screws and is held off below the fuselage by four AN960-10 washers giving a pressure vent of 1/4" x ~7" to dump the oil cooler air .......Experimentally increasing the opening this by 1/16" (another washer added to each mounting point) decreased the speed slightly so it is not static in there.>>

Interesting. Not static is no surprise. Was this experiment before or after adding the horizontal seals to isolate 2 and 3?
It was after the horizontal seals were added. My assumption is the vent size is controlling the pressure in zone 3 and effectively limiting the air flow through the oil cooler. The change was small but I don't want to give up anything. I have thought about reducing the size but so far I have been content - the oil temperature could be higher though. In my last test the oil temperature was 200 and it is usually no higher than 180 - that observation is nagging at my brain a little bit. Everything is connected and oil temperature is a parameter of interest in cooling drag experiments. I have rationalized explanations but for now I will just monitor it and when I can get some free time from my three page spring chore activities, reinstall the old experimental inlet plugs fly a test and decide what to do from there.

Bob Axsom

Last edited by Bob Axsom : 03-22-2009 at 03:25 PM. Reason: Typos
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  #23  
Old 03-25-2009, 02:50 PM
Bob Axsom Bob Axsom is offline
 
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Posts: 5,685
Default Test with inlet plugs installed

Some time ago I developed som inlet plugs for our RV-6A and the results were not impressive. I decided I would reinstall them and fly a test with the plugs and lower forward baffle in place. Before I reinstalled them I cut away a fiberglass web I had applied across the depression in the leading edge between the spinner and the inlet to test the effect on speed - it was bad - and sanded a smooth recession back in this area.



Here are the numbers for today's test.

20 second interval speeds for each track:
360 - 192, 191, 192, 192, 192
120 - 174, 174, 174, 175, 175
240 - 178, 178, 179, 179, 178

I plugged 191.8, 174.4 and 178.4 into the National Test Pilot School spread sheet and learned the wind was 10.4 kts out of 166.8 deg. True airspeed is 181.7 kts

EGT: 1=1320F, 2=1391F, 3=1364F, 4=1330F
CHT: 1=305F, 2=376F, 3=379, 4=342F

Temp at 6000ft pressure alt. 11C
Test flown at 5,100 ft (6,000 density altitude)
MAP 24.7 (the previous test was probably in this range as well)
Oil temp = 190
Oil Pres = 80
Throttle = wide open
RPM = 2720
Mixture = rich of peak for best speed

As observed earlier this is better than the 180.0 kt test with the new forward baffle and without inlet plugs.

Perhaps I should re-fly this but I think I need to remove both the plugs and the new baffle and validate the 182.6 kt speed achieved earlier. I'll sleep on it.


Bob Axsom

Last edited by Bob Axsom : 03-26-2009 at 07:10 AM. Reason: Added photo, plug notes and added decimal to wind speed
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  #24  
Old 03-25-2009, 05:16 PM
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Kevin Horton Kevin Horton is offline
 
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Bob,

I am very impressed by all the work you are doing to improve the speed of your -6A, and congratulate you on the great results you have achieved. I offer the following advice, for you to use or discard at your discretion. No hard feelings if you ignore me

My gut feel is that you are making too many decisions on the value of a mod after just one flight's worth of data. There can be various reasons why the speed achieved on any given flight might be a knot or two different from the true performance of that configuration. Most of the mods you are making would only yield less than a knot increase per mod. If you want to fully evaluate the effect of each mod, you really should freeze the configuration, and average the performance measured on several flights. As it sits now, you may be discarding mods that are worthwhile, and keeping some clangers.

Also, the method you are using to account for non-standard conditions doesn't stand up to close scrutiny. So, even with the same configuration, if you tested on days with substantially different temperatures, selecting a test altitude using your technique, you would get different speeds. If you are interested, I can work with you on a way to correct test results to standard weight, altitude and temperature. I hadn't planned on broaching this subject until I had more data from my aircraft to validate this technique, but it'll be months before I can do any more flying.
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  #25  
Old 03-25-2009, 08:07 PM
Bob Axsom Bob Axsom is offline
 
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Default Thanks Kevin

your approach is similar to another fellow I highly respect - and I drive him nuts too (John Huft). I have to thank you both for turning me on to the NTPS spread sheet - it certainly is better that the usually underestimating average method.

I know the case may be made for exhaustive testing but I have to settle for "good enough". These little things I am playing with now are not expected to yield much if anything - if a configuration isn't clearly superior I'll probably throw it out and look elsewhere. The test I flew today yielding 181.7 kt is so close to the previous high that I think it is worth another flight test (not cheap in terms of time or money) as well as another flight in the no forward baffle and not inlet plug configuration to semi-validate the 182.6 kt top speed. I know it is hard to accept that a test program can be conducted this way but for a one man show I am satisfied that it works to determine relative merit and it keeps the program moving. I really don't care about the absolute accuracy of the numbers even though I present them as though I do. Noise level differences just aren't worth bothering with - that's just to me of course.

When I get out on the race course I want to try to get better speeds than my competitors and improve my performance. On March 15, 2009 I got beat handily by three RV-8s but I know who they are and I have my spirit fired up to pick them off. If I don't make it I don't really think it will be because I didn't test rigorously enough.

Get well Kevin and shoot me a jab anytime you see that I have blown it - again.

Bob Axsom

Last edited by Bob Axsom : 03-25-2009 at 11:45 PM. Reason: Typos
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  #26  
Old 03-26-2009, 06:56 AM
bigginsking bigginsking is offline
 
Join Date: Aug 2005
Posts: 36
Default Give your results a reality check

Bob:
Kudos to you for having the patience for this.

Your post says:
"wind was 104 kts out of 166.8 deg"
That seems like alot considering only 45 degrees away(.772 in trig)your 120 heading is telling showing 174 ish knots.

Something is wrong, Are you using magnetic heading or GPS track? Having the wrong heading makes for ugly results. I've used the same spreadsheet and the column heading asks for track not heading.

Bill Judge
N84WJ
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  #27  
Old 03-26-2009, 07:22 AM
Bob Axsom Bob Axsom is offline
 
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Default I corrected the wind speed

I have not checked the spreadsheet results but they seem very close - usually just a bit higher that the three track average. I accidently left out the decimal in the wind speed in my post - it should have been 10.4 not 104. The flight angles are GPS track angles as required by the spreadsheet. The spreadsheet says the wind speeds are in knots and the direction is calculated magnetic. The wind data is derived from the GPS track angles and GPS ground speeds speeds that I enter. I have used it for several tests but I have never checked the wind results against anything since the one number I am looking for is the calculated true airspeed. Sometime it would be interesting to look at that.

Bob Axsom
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  #28  
Old 03-26-2009, 07:33 AM
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N941WR N941WR is offline
 
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Bob,

I've enjoyed watching you make improvements on your RV and every time I wonder what I could apply to my -9.

It looks to me like you are running a CS prop. How do these changes impact your prop? Can you get to a point where the prop can no longer adjust for the increased speed?
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  #29  
Old 03-26-2009, 12:17 PM
Bob Axsom Bob Axsom is offline
 
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Default Bob Axsom

The changes I have made that work for me are all drag reduction mods but as the charts from Hartzell show me propeller efficiency does decay after peaking at some speed peculiar to the specific prop. Propellers are so expensive that I just can't experiment in that area but I know personally of several builder/pilots that have gone to the expense of buying different props and trying them. I have a half inch thick folder and a couple of books on propellers but I don't have real knowledge of propeller performance that would allow prediction - my experience is just too limited in that area. A confidential 8,000 ft propeller performance chart I received from Hartzell shows my 7666 bladed 72" prop efficiency peaks at 165 kts True Air Speed with just over 0.855 efficiency and since I am up around 182 kts now the chart shows the propellor efficiency has dropped to approximately 0.85. At 200 KTAS it is down to a little over 0.836 (where the 7496 bladed Hartzell is up around 0.878). In our speed range I believe as you gain more speed there will be some loss of prop efficiency but drag reductions will still prevail in airplane speed changes (increases).

If you get a chance to watch the video attached to the "RVs are entering the Taylor 100" thread listen to the second plane at the start and at the finish. It is Bruce Hammer's Race#91 Glasair TD I. He has a high pitch fixed pitch prop and it is really turning. He and his Brother Steve who also races a Glasair TD I (Race #73) are always in the 250 MPH group. They are both so fast that I think they enter different classes in the AirVenture Cup Race so they can both win.

Bob Axsom
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  #30  
Old 03-29-2009, 09:05 PM
Bob Axsom Bob Axsom is offline
 
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Default Two Test Flights 3-29-09

We had a nice clear day here in Northwest Arkansas so I was able to fly two test flights. The first was with no change (lower cowl front baffle and cooling air inlet restrictor plugs installed) and the second was with the cooling air inlet plugs removed. I filled the tanks before and after each flight. It was not an ideal day in so far as winds are concerned but I have to work with what I have when I can fly. West of Fayetteville, Arkansas's Drake field the Ozark hills and mountains cause some irregular flight conditions requiring some manipulation of data (out of line highs and lows were discarded and more than 1 kt differential was allowed) was necessary. Both flights were flown at 6,000ft density altitude, wide open throttle, leaned for best speed.

Parameter/Flight 1/Flight 2
Engine start/14:37/15:56
Temperature at 6,000ft/+6C/+7C
Press Alt flown/5,700ft/5,600ft
RPM/2720/2710
MAP/24.2/24.2
Oil temp & press not recorded
Track 360-1/164 kts/173 kts
Track 360-2/165 kts/172 kts
Track 360-3/168 kts/174 kts
Track 360-4/166 kts/174 kts
Track 360-5/167 kts/172 kts
Track 120-1/202 kts/199 kts
Track 120-2/204 kts/198 kts
Track 120-3/206 kts/200 kts
Track 120-4/203 kts/198 kts
Track 120-5/202 kts/200 kts
Track 240-1/170 kts/168 kts
Track 240-2/169 kts/169 kts
Track 240-3/171 kts/170 kts
Track 240-4/171 kts/172 kts
Track 240-5/169 kts/171 kts
NTPS CTAS /180.5 kts/181.7 kts
Wind speed /23.0 kts/17.3 kts
Wind Dir Mag/306.2/297.6
CHT 1/287 F/295 F
CHT 2/359 F/340 F
CHT 3/363 F/333 F
CHT 4/325 F/304 F
EGT 1/1199 F/1244 F
EGT 2/1314 F/1348 F
EGT 3/1319 F/1289 F
EGT 4/1280 F/1268 F
Eng run time/45 min/35 min
Fuel burn/6.473 g/6.096 g
Fuel cost/$23.56/$22.19

These tests duplicate the configurations flown in the two previous tests but the results are reversed. In this case the "plugs in" speed was 1.2 kts slower than the "plugs out" speed and the previous "plugs in" test speed (3-25-09). The "plugs out" speed was 1.7 kts faster than the previous "plugs out" speed (3-20-09). My conclusion once again is that the main effect of the cooling air inlet plugs is to increase the CHTs and they have not real effect on speed. This saves me having to carry the plugs and install them before races. I want to conduct one more test and that will be done after the new lower cowl front baffle is removed. One side of me hopes the 182.6 kt previous high speed water mark is reached but if that happens there will remain the question of how the addition of a baffle in the lower cowl at the front end lowers the speed of the airplane. The restriction of cooling air inlet reduced the air mass flow through the system as is indicated by the CHT rise so it can be argued that the decrease in airplane speed is not due to increased air flow efficiency and thus air mass flowing through the system cause by the fwd baffle blocking the air back flow out of the front of the cowl. Oh well, one more test without the baffle needs to be flown to validate the effect of the baffle.

Bob Axsom

Last edited by Bob Axsom : 03-30-2009 at 09:30 AM. Reason: typos, etc. added enfine run time and fuel cost
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