Bryan Wood
Well Known Member
Just thought I post this even though the answer seems so obvious. Since the first flight the airspeed on my airplane has read low and often makes me guess as to the real true airspeeds that we're doing. The problem would show itself when flying with production airplanes such as Bonanzas or Comanches where my indicated airspeed would always be lower than theirs by 7-10mph. What confused the problem was flying with other RV's whos indicated airspeeds would match mine very closely.
By using the 3 way run on known headings and recording the GPS groundspeeds I was able to prove that my indicator was indeed reading low. Since then when I set the true airspeed on the indicator so that the temp and altitude line up I always look at the resulting true indication and turn the dial for another 7 or so mph just to get it a little closer the actual speed. When doing this it always seemed like a game to make myself feel better and silly at best. There is something about a true of 180mph that isn't as good as 187mph. If the plane is doing around 190mph on a trip I don't want to see something down around 180mph, even if it doesn't mean anything in the grand scheme of things. So, what do you do if you have an indicator on an RV that reads low like this? This drove me nuts trying to come up with a way to correct it. I knew that other RV's read just like mine from flying with them. I also knew that the production planes read higher, even from different manufacturers. Simply replacing the airspeed indicator probably wouldn't change anything so for a long time I have done nothing. Until about two weeks ago.
Being due for the transponder cert. after two years per the FARS I asked the folks to hook up to the pitot and test for leaks and tell me just how far off the airspeed indicator is reading. I received a nice correction card for the airspeed indicator and the thought was to simply use it in flight to adjust the dial to a proper reading. The results however was that the pitot, and the static system were free from leaks and the airspeed indicator was within 1 knot at cruise speeds. This was truly disturbing because it implied that my airplane was much slower that believed it to be and disagreed with the 3 way speed runs done with gps. Talking with the man about this he stood back studied the bend on my pitot and said it must not be bent correctly. He stood about 15 feet off the wing tip and squatted down to that he could get a good look and had me make adjustments to the bend until it was at an angle that he believed would have the most effect from the wind hitting it head on. The difference in the bend is very subtle, but the results are dramatic. Yesterday after flying to another field to buy cheap fuel I set the power at 22sq for the trip home. At 5500' and this setting the plane now indicates what it indicated prior to fixing the bend on the pitot at full throttle and 2300rpm. This is not an exageration!!! While it isn't going any faster than it was before it sure feels good to know what it is really doing now. Also decents will be flown a little slower now that I know I was probably way into the yellow on some without even knowing it.
Best,
By using the 3 way run on known headings and recording the GPS groundspeeds I was able to prove that my indicator was indeed reading low. Since then when I set the true airspeed on the indicator so that the temp and altitude line up I always look at the resulting true indication and turn the dial for another 7 or so mph just to get it a little closer the actual speed. When doing this it always seemed like a game to make myself feel better and silly at best. There is something about a true of 180mph that isn't as good as 187mph. If the plane is doing around 190mph on a trip I don't want to see something down around 180mph, even if it doesn't mean anything in the grand scheme of things. So, what do you do if you have an indicator on an RV that reads low like this? This drove me nuts trying to come up with a way to correct it. I knew that other RV's read just like mine from flying with them. I also knew that the production planes read higher, even from different manufacturers. Simply replacing the airspeed indicator probably wouldn't change anything so for a long time I have done nothing. Until about two weeks ago.
Being due for the transponder cert. after two years per the FARS I asked the folks to hook up to the pitot and test for leaks and tell me just how far off the airspeed indicator is reading. I received a nice correction card for the airspeed indicator and the thought was to simply use it in flight to adjust the dial to a proper reading. The results however was that the pitot, and the static system were free from leaks and the airspeed indicator was within 1 knot at cruise speeds. This was truly disturbing because it implied that my airplane was much slower that believed it to be and disagreed with the 3 way speed runs done with gps. Talking with the man about this he stood back studied the bend on my pitot and said it must not be bent correctly. He stood about 15 feet off the wing tip and squatted down to that he could get a good look and had me make adjustments to the bend until it was at an angle that he believed would have the most effect from the wind hitting it head on. The difference in the bend is very subtle, but the results are dramatic. Yesterday after flying to another field to buy cheap fuel I set the power at 22sq for the trip home. At 5500' and this setting the plane now indicates what it indicated prior to fixing the bend on the pitot at full throttle and 2300rpm. This is not an exageration!!! While it isn't going any faster than it was before it sure feels good to know what it is really doing now. Also decents will be flown a little slower now that I know I was probably way into the yellow on some without even knowing it.
Best,
