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0-320 cruise speed per ground speed tracking?

C

csgj

Active Member
I wanted to my 6a's real world cruise performance. I was told to do 3 legs at 90 degree headings and add up the ground speeds to calculate
So at 8500msl (DA was around 10000) at WOT and 2500rpm and 9.3GPH my average speed was 170knots ground speed
At 6500msl it was lower at about 163 knots
Seems like around 8500msl is the best altitude for RV's
Looks like I'm a little above van's speeds on his site for a 7a's
Wonder what other 0-320's are performing at? :confused:
Thanks
Craig
 
You cannot just "add up the speeds". This is a vector algebra problem, you need to eliminate the wind component.
Send me the headings or ground tracks, and the ground speeds for each one, and I'll do the algebra for you.
 
Bob Axom (smart racer and contributor here on VAF) has a very detailed method that served me well when I was testing a propeller change. I now use the same procedure for testing any affects on performance.

I wrote up my notes here.
 
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site calcs look ok...but why 3 legs?

would not flying the 4th leg, or more?....result in much better 'average' speed accuracy?
evidently 3 are adequate.
what's your extensive test experience Bob?
do you think that changing winds and turbulence over a longer test period negate the accuracy of flying additional legs?
 
You need 3 legs to eliminate the wind component. Any more legs and the problem is over determined, you would need to solve for a best fit. Any of these calculators assume the wind stays constant during the test. So you don't want the legs any longer than necessary for everything to stabilize. Of course you could repeat the whole 3 leg test, maybe using different headings, several times, and average the results.
 
Some information

Your speed sounds about right with a little difference on the good side.

I keep the records and statistics for the Sport Air Racing League in Excel so it is easy for me to single out the 320 powered RVs and average the race speeds. So far 78 such race flights have been made. The class for 320 powered RVs is RV Red. The average speed for all is 167.18 kts or 192.37 mph.

Here are the data:

AirVenture Cup 2008 7/27/08 RV Red RV-4 Murphy, Chris 186.01 214.06
Texoma 100, 2008 4/20/08 RV Red RV-4 Murphy, Chris 183.67 211.40
AirVenture Cup 2007 7/23/07 RV Red RV-4 Murphy, Chris 180.33 207.52
AirVenture Cup 2008 7/27/08 RV Red RV-3 Vasey, Bob 179.96 207.10
TVA II 2009 10/18/09 RV Red RV-4 Benton, Cam 179.23 206.25
AirVenture Cup 2007 7/23/07 RV Red RV-6A Klusmier, Larry 178.90 205.87
Thunderbird 150 10/8/11 RV Red RV-7 Baker, Seth 178.53 205.45
Grace Flight 2008 10/5/08 RV Red RV-4 Murphy, Chris 178.51 205.43
Rocket 100, 2010 11/20/10 RV Red RV-7 Baker, Seth 178.47 205.38
AirVenture Cup 2007 7/23/07 RV Red RV-3 Vasey, Bob 178.15 205.01
Taylor 100 2009 3/16/09 RV Red RV-4 Benton, Cam 178.02 204.86
Rocket 100, 2010 11/20/10 RV Red RV-8 Jones, Bryan 177.27 204.00
AirVenture Cup 2007 7/23/07 RV Red RV-6 Weisgerber, David 177.92 203.91
TVA II 2009 10/18/09 RV Red RV-4 Murphy, Chris 176.54 203.16
Rocket 100, 2011 11/19/11 RV Red RV-7 Baker, Seth 175.78 202.28
Thunderbird Air Race, 2012 10/13/12 RV Red RV-7 Baker, Seth 175.60 202.08
Rocket 100 2008 11/23/08 RV Red RV-4 Murphy, Chris 174.92 201.30
West Texas 100 6/6/10 RV Red RV-4 Benton, Cam 174.17 200.43
Rocket 100, 2007 11/18/07 RV Red RV-4 Benton, Cam 174.12 200.37
Taylor 150 4/11/10 RV Red RV-4 Benton, Cam 174.11 200.36
GNAR III, Ephrata, WA 6/16/12 RV Red RV-4 Ford, George 173.91 200.13
Grace Flight 2010 10/2/10 RV Red RV-4 Benton, Cam 173.76 199.95
Pagosa Springs 2010 9/26/10 RV Red RV-4 Benton, Cam 173.65 199.70
Taylor 150, 2013 4/13/13 RV Red RV-4 Robert Faubion, Robert 173.47 199.62
AirVenture Cup 2010 7/26/10 RV Red RV-4 Murphy, Chris 173.00 199.09
Colorado 150 2009 7/23/09 RV Red RV-4 Murphy, Chris 172.90 198.97
Memphis 100 2008 10/19/08 RV Red RV-4 Murphy, Chris 172.78 198.83
Rocket 100 2009 11/22/09 RV Red RV-7A Reiley, Darrell 172.11 198.06
Cleveland Texas Air Race 10/15/11 RV Red RV-8 Jones, Bryan 171.33 197.16
AirVenture Cup 2010 7/26/10 RV Red RV-3 Vasey, Bob 171.17 196.98
Grace Flight 2010 10/2/10 RV Red RV-7 Baker, Seth 171.00 196.77
Texoma 100, 2011 4/16/11 RV Red RV-4 Murphy, Chris 170.51 196.15
Taylor 100 2007 5/20/07 RV Red RV-4 Benton, Cam 170.43 196.13
Pagosa Springs 2010 9/26/10 RV Red RV-7 Baker, Seth 170.45 196.02
Memphis 100 2008 10/19/08 RV Red RV-4 Smith, Dwight 169.88 195.50
Pagosa Springs 100 2009 9/27/09 RV Red RV-4 Benton, Cam 169.78 195.25
Taylor 100 2007 5/20/07 RV Red RV-8 Jones, Bryan 169.45 195.00
Tennessee Valley Air Race 2010 10/30/10 RV Red RV-4 Archord, Jim 169.17 194.72
Sulphur Springs 130 7/18/10 RV Red RV-4 Benton, Cam 168.84 194.30
West Texas 100 6/6/10 RV Red RV-4 Murphy, Chris 167.83 193.14
Big Muddy, Carbondale, IL 6/4/11 RV Red RV-6 Weisgerber, David 167.82 193.12
Pagosa Springs 2010 9/26/10 RV Red RV-4 Faubion, Robert 167.80 192.97
West Texas 100 6/6/10 RV Red RV-4 Faubion, Robert 167.44 192.69
Thunderbird Air Race, 2012 10/13/12 RV Red RV-6A Ahrens, David 167.42 192.66
BSAR II, Three Forks, MT 7/7/12 RV Red RV-4 Keeler, Art 167.27 192.49
West Texas 100, 2007 10/7/07 RV Red RV-4 Benton, Cam 166.40 191.50
West Texas 100 2009 4/12/09 RV Red RV-4 Benton, Cam 166.29 191.36
AirCap 200 8/24/08 RV Red RV-6 Smith, Jim 166.21 191.27
Taylor 150 4/11/10 RV Red RV-7A Reiley, Darrell 165.94 190.96
BCAF 2013 5/3/13 RV Red RV-9 Johnson, Steve 165.76 190.76
Colorado 150, 2008 6/29/08 RV Red RV-4 Murphy, Chris 165.65 190.62
Cleveland Texas Air Race 10/15/11 RV Red RV-6 Behrends, Steve 164.72 189.55
Tennessee Valley Air Race IV 10/29/11 RV Red RV-4 Murphy, Chris 163.35 187.98
Texoma 100, 2011 4/16/11 RV Red RV-6 Smith, Jim 163.38 187.94
Taylor 100 2007 5/20/07 RV Red RV-3 Hackett, Willy 162.96 187.53
Denton 100 2008 6/15/08 RV Red RV-4 Bruggers, Ken 162.71 187.24
TVA II 2009 10/18/09 RV Red RV-6A Phillips, Mark 162.66 187.19
Taylor 150 4/11/10 RV Red RV-4 Faubion, Robert 162.24 186.71
Texoma 100, 2008 4/20/08 RV Red RV-6A Heathco, Charlie 161.75 186.17
West Texas 100 6/6/10 RV Red RV-7 Baker, Seth 161.58 185.94
Great Canadian Air Rally 2010 8/22/10 RV Red RV-9A Wilkinson, Greg 160.53 184.73
Ozark Grove AR, Grove, OK 11/3/12 RV Red RV-6A Heathco, Charlie 160.07 184.21
Northwoods 100 10/8/11 RV Red RV-9 Phillips, Tony 159.97 184.09
Cleveland Texas Air Race 10/15/11 RV Red RV-6 Bivens, Darrell 159.35 183.38
Memphis 100, 2007 10/28/07 RV Red RV-4 Smith, Dwight 158.39 182.28
Great Canadian Air Rally 2010 8/22/10 RV Red RV-9A Murray, Charlie 158.29 182.15
Texoma 100, 2013 4/6/13 RV Red RV-6 Smith, Jim 155.81 179.3
AirVenture Cup (TH) 2011 7/25/11 RV Red RV-4 Crawford, Tony 155.55 179.00
AirVenture Cup 2009 7/27/09 RV Red RV-3 Vasey, Bob 155.54 178.99
Top of the Chesapeake 7/11/10 RV Red RV-4 Winkelman, Steve 155.39 178.83
Lone Star Air Rally 5/14/11 RV Red RV-6A Bivens, Darrell 154.86 178.21
Hill Country 150, 2012 4/21/12 RV Red RV-9A Johnson, Steve 154.33 177.60
Pappy Boyington Memorial Cup 8/18/12 RV Red RV-6 Inkster, Ralph 153.42 176.56
Great NW Air Race 6/13/10 RV Red RV-6A Hungelmann, Bill 152.37 175.35
Texoma 100, 2013 4/6/13 RV Red RV-6A Heathco, Charlie 145.01 166.88
Lone Star Air Rally 5/14/11 RV Red RV-6A McGinnis, Patrick 144.92 166.77
AirVenture Cup 2009 7/27/09 RV Red RV-6 Campbell Steve & John Popel 138.33 159.19
Texoma 100 4/25/10 RV Red RV-4 Benton, Cam 132.78 152.70
Average: 167.18kts 192.37mph
 
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SARL Racing Speeds

Bob, are those 320 engine racing speeds you posted typically with prop speeds higher than 2500? I was running 2500 on a CS prop.
And what altitude are the races flown?
Seems I am about 7 knots faster at 8500 than 6500?
Craig
 
These are all out race speeds

csgj said:
Bob, are those 320 engine racing speeds you posted typically with prop speeds higher than 2500? I was running 2500 on a CS prop.
And what altitude are the races flown?
Seems I am about 7 knots faster at 8500 than 6500?
Craig
Click to expand...

RPM - Typically the throttle is wide open, the prop control is maxed out and the mixture is leaned for best power. 2700 rpm is not unusual

Altitude - Altitude is one of the critical choices that separate the winners and loosers. altitude strategy requires careful planning for each leg. For long races like the AirVenture Cup if tailwinds prevail it is not unusual for some pilots to choose 17,500 and oxygen while the next level of performance aircraft pilots choose a high no Oxygen altitude and others skim the earth at minimum FAA approved airspace limits - all in the same race. For the more typical SARL race that starts and ends at the same airport the altitude almost never goes above 3,000 except when they can't get an airspace waiver and some of the extremely fast classes have to decide between thrott ... Sorry that doesn't apply to RV Red class.

Speed with Altitude - Every test I perform is at 6,000 ft density altitude to minimize variations in the test environment and method. That seems like an unrealistic difference for 2000 ft but those are your data.

Bob Axsom
 
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