RV-10 V Speeds

[billsplans]

We have recently completed an RV-10 with a Lycoming IO540. What results have others gotten in finding Vx and Vy?
Thanks,
Bill Barney

 

[Greg G]

A solution...

We have recently completed an RV-10 with a Lycoming IO540. What results have others gotten in finding Vx and Vy?
Thanks,
Bill Barney

Bill,

While I couldn't find anything for you on what others have come up with, your best bet is to fly the flight test technique detailed on pages 47-48 of AC90-89A (Doug has this archived at http://www.vansairforce.net/ref.htm). Basically, you pick an airspeed to start with and a floor (say 120mph and 3000ft AGL). Stabilize on-conditions at full throttle about 300 feet below your floor, and once you cross the floor hack the clock for 60 seconds. After 60 seconds, record your altitude gained (and therefore your climb rate). Drop your airspeed in steps of about 5mph until you get to your peak rate of climb and continue down to about 10mph above stall. When you draw the graph, the peak of the curve will equate to Vy and a line tangent to the curve from zero will be Vx. If you're unlucky and the first few test points result in decreasing rates of climb, you'll have to increase your airspeed in 5mph increments from your starting airspeed to find the peak of the curve. One thing to keep in mind is that Vx and Vy change with altitude, so you could either try and determine a trend by doing this test at various altitudes (recommended) or just perform it at the lowest safe altitude to get you "in the ballpark" for your numbers at ground level. Good luck!

Greg

 

[billsplans]

Thanks Greg,

Hopefully someone out there can share his numbers for comparison.

Bill

 

[Kevin Horton]

Thanks Greg,
Hopefully someone out there can share his numbers for comparison.

The numbers will vary somewhat from aircraft to aircraft, as they depend on the weight, altitude and temperature at which the test was done, the engine power, propeller model and the errors in the airspeed system. The errors in the airspeed system will depend on the ASI instrument error and the static source position error.

I've heard of ASIs with over 10 kt of instrument error, and I've also heard of RVs with 10 kt of speed error due to static source position error (these were aircraft where the builder "improved" on Van's design by installing a static port that differed from the specified pop rivet). So, the V speeds reported by one builder may be completely wrong for your aircraft.

 

[vic syracuse]

Bill, everyone is right in their advice, but I don't think you really got an answer you were looking for. Yours will vary, of course, but for mine I found that 110 kts IAS worked best at Vy, and 95-97 worked for Vx. 110-120 kts IAS worked really great for normal fllying climbs. I would hold that all the way to altitude, which in the 10 was always above 10K. The highest CHT's I would see on a prolonged heavy climb in the middle of a hot Altanta summer was around 380-390. Sometimes the oil temp would get to 220, but would start falling off around 10k feet at the OAT dropped, and then would stabilize around 190 in the summer and 180 in the winter, with CHT's around 330-350. This was with 9.5:1 pistons.

Good Luck. have fun!

Vic

 

[billsplans]

V speeds

Thanks Vic,

Your numbers are very near the ones we came up with. Sounds like you really enjoy building airplanes.

Bill