Comments Only
If you go to
www.sportairrace.org and scroll down the page there are links to the results of all races in the years 2007, 2008 and 2009. In most cases the aircraft type is identified and the RV-4s flying in the RV Red class have 320 cu. in. engines and the RV-4s flying in the RV Blue class have 360 cu. in. engines. Race courses are often triangular and the total length is usually between 100 and 150 miles (the AirVenture Cup race is different - 400 to 500 miles). Cam Benton and Chris Murphy fly RV-4s in the RV Red class and in a quick scan I usually saw their speeds a little over 200 mph with the turns and vertical changes included.
Chris Murphy has organized two straight line time trial/speed dash events at Courtland, Alabama which used sighting devices and timers to determine speeds. These were well run and well received but there is some question of accuracy because the test method is prone to known errors. He has taken it on himself to develop a more accurate method on a private individual's resources (his). He is currently working on an IR sensor approach to start and stop the "watch" and improve the accuracy. He is giving a lot of thought, work and his own money to this effort and I'm sure he will have it debugged and ready for the race this year at Courtland on October 30 (see Calendar of Events at
www.sportairrace.org). He is also working with Eric Whyte, who runs the AirVenture Cup race, to possibly have it included as Saturday event at Mitchell, South Dakota the day before the race to Oshkosh. If you come to these events you could make a two way run and get a certified speed for your RV-4.
As far as independent testing is concerned you should always use the same method if you are trying to gain more speed with modifications or changes in propellers/engines or compare with other RV-4s. I always test in three GPS tracks (360, 120 and 240), at 6,000 feet density altitude (because the old U.S. Air Race handicap procedure that I started testing with specified 6,000 ft d alt), with wide open throttle, maximum RPM (2720-2730), leaned to 1300F EGT cylinder #4, with auto pilot holding track and altitude, recording 5 consecutive GPS ground speeds on each track that do not vary by more than 1 kt, average the five speeds for each track and plug them into the national Test Pilot School spreadsheet provided in this forum by Kevin Horton and John Huft. This mathematically eliminates the effect of wind and provides the true airspeed for the test. This is very reliable and it is essential for evaluating small mods that produce small differences in speed.
On almost every test I see a manifold pressure of 24.5" but in races at lower altitude the number increases by 3 or more inches and the indicated airspeed is higher than in my 6,000 ft tests.
Before I started modifying my airplane the speed was very close to the number provided by Van's.
Bob Axsom
