Low Airspeed Indication On Take Off

[johnfurey]

During the take off roll in my RV7 with a GRT Sport and a Dynon pitot tube I am airborne and climbing 30~40 feet before my airspeed indication is above stall speed. I know my real airspeed is much higher because of feel and GPS speed. As soon as speed gets above 50kts or so everything is fine. In fact the TAS/Static system calibrations show 1~3kt error. Carlos felt it was a leak in the pitot system. The pitot system is tight from the GRT to the fitting on the pitot tube but there is a leak in the tube which Dynon says is normal although Dynon says I should not have this lag and was quick to offer me another pitot tube to try. My questions are 1) do any of you experience this issue? 2) How have you solved it or did you just left it alone?

[rdoerr01]

I had something similar on a trip when I didn't cover my pitot. Bugs or other debris got in there and on takeoff I didn't have any airspeed and then it would work and then it was intermittent, so I continued flying with GPS speed knowing the wind speed and direction. After landing I disconnected the pitot line at the wing root and blew it back out through the pitot, problem solved!

Thanks

Ray
N519RV
RV-10 (800+ hours)

[BobTurner]

1. Above 50 kias everything is normal? But surely you don't lift off at less than that?
2. If you tape over the pitot's drain hole there should be no leaks.
3. Any chance you interchanged the AOA and pitot lines?

[PCHunt]

Something similar happens to me every time I take off with the pitot cover still in place.

Only difference is the airspeed never gets above about 3 kts.

I finally solved the problem by attaching a string to the pitot cover, and putting the other end of the string in the cockpit tied to a tennis ball.

I am a slow learner.

[DanH]

Originally Posted by johnfurey

During the take off roll in my RV7 with a GRT Sport and a Dynon pitot tube I am airborne and climbing 30~40 feet before my airspeed indication is above stall speed. I know my real airspeed is much higher because of feel and GPS speed. As soon as speed gets above 50kts or so everything is fine.

30~40 feet of runway length? Sounds normal. Can't say I've ever paid much attention to it, but my -8 will lift off in ground effect before the red is off the airspeed tape. I usually hold it there at about 6" altitude for a few more seconds of acceleration before a moderate pitch up, then go to normal climb pitch after further acceleration to 100.

[johnfurey]

Thanks guys. Obviously this is not a common issue. It is more of an anoyance, the biggest issue is that I can't get a valid "airspeed alive" check early in the take off roll. Dynon clearly states that even covering the drain holes that a leak is common but it should not affect performance. I will swap pitot tubes and see if there is any difference.

[bluemaule]

I have the opposite problem. AS reads OK at low end on RV7, but never goes over 130 kts at cruise even though ground speed is always around 150-170. Suspect a leak in line somewhere.

[drakerv]

Check your pitot tube lines.My dynon pitot tube lines were reversed.