[Cadstat]

I observe a 2 mph drop in airspeed by GPS if I have the fresh air vents open rather than closed. Has anyone else seen this?

 

[N130PM]

I wonder if the air escaping is staying attached as a turbulent layer and creating drag? I'm chewing hard on fixing my exit air situation. Right now its canopy skirts only. That can't help my speed.

Summer flying in Fla is killing me, I just added a vent on my subpanel that blows right at my gut, so now I have a face vent and a body vent. They both blow as hard as the single used to. Its amazing how much air you can get out of one of the small eyeball vents when you take off with the canopy unlatched.

 

[Bob Axsom]

Yes!

I observe a 2 mph drop in airspeed by GPS if I have the fresh air vents open rather than closed. Has anyone else seen this?

It is a common knowledge thing in racing. If you block off the inlets entirely the speed increases even more.

Bob Axsom

 

[cguarino]

Same here

I have two RV-10 style vents on my -4 and I notice at least a 2 mph decrease with both of them open. I joke about opening the speedbrakes.

 

[Ron Lee]

Two MPH slower to be comfortable. Priceless.

 

[David Paule]

Often, cabin air exits are not designed or installed, and the air leaks out where it will. But good cabin air exits ought to reduce that loss.

Dave

 

[GAHco]

MMmm..

A pitot Static leak may affect your airspeed reading if there is a leak in the plumbing. Or it is just what previous post said about the increased drag while all that air comes in the vent. Kinda like scooping instead of skipping.