I just finished a complete restoration of 1946 J3 with an C-90 and a new wood Sensenich prop and have come across a bit of a puzzle. The aircraft flew completely straight right out of restoration, not quite sure how I managed that but I ran into this minor issue which I don’t understand.
The airspeed indications are erratic at certain RPM. Between aprx 1800 and 2100 rpm the airspeed bounces all over from 40-60. At higher rpm and lower rpm completely stable or as stable as it gets.
Of course this happens on landing.
I have a slip indicator so I am coordinated, I put a static line in the wing thinking it was cabin pressure from the slipstream door open or closed but that did not change things.
There is no vibration causing things to jump around.
That kinda leaves me with pitot air. It’s mounted normally at what I think is the right angle.
Leads me to believe the prop slipstream is affecting the pitot tube somehow.
I know airspeed indicators in these aircraft just kinda fill a hole in the panel but I this to be an odd problem where I am probably over looking something
The airspeed indications are erratic at certain RPM. Between aprx 1800 and 2100 rpm the airspeed bounces all over from 40-60. At higher rpm and lower rpm completely stable or as stable as it gets.
Of course this happens on landing.
I have a slip indicator so I am coordinated, I put a static line in the wing thinking it was cabin pressure from the slipstream door open or closed but that did not change things.
There is no vibration causing things to jump around.
That kinda leaves me with pitot air. It’s mounted normally at what I think is the right angle.
Leads me to believe the prop slipstream is affecting the pitot tube somehow.
I know airspeed indicators in these aircraft just kinda fill a hole in the panel but I this to be an odd problem where I am probably over looking something
