[Dugaru]

So there used to be pretty big gaps between my canopy side rails and fuselage, such that in flight there was a brisk flow of air from the back of my canopy then down and out the sides. (We once lost a canopy sunshade to the vacuum, it got sucked out of the plane without warning!). When flying through rain I would also get a little water feature on my canopy track, with a trickle of rain irrigating my baggage area.

So I sealed up the canopy sides using this stupendous idea. I also put some Velcro loop material at the bottom rear of the canopy skirt, another great idea I got from that same thread. These mods seem to have greatly reduced the air flow from the back of the airplane. I’m also hoping they’ll improve the cabin heat situation this winter.

And now the airplane also seems… slightly faster. By about 2 knots. I do a lot of flying in cruise, and I know the numbers pretty well, and the speed really seems just a bit higher. That’s not something I was expecting, so I don’t think it’s confirmation bias.

Could be my imagination or other factors of course. Before I start hauling out and comparing old flight data, is it even plausible the cockpit sealing could have had this effect? Or is it possible the change in cockpit pressure could affect the instrumentation somehow (and in this direction)? I remember that my TAS changed when my OAT sensor got moved out of the path of the warm exhaust…

 

[Ironflight]

If you think the airplane is slightly faster becasue of the airspeeds you’re seeing (after sealing things up), then I‘d suspect that you have a static leak somewhere…..

 

[Dugaru]

If you think the airplane is slightly faster becasue of the airspeeds you’re seeing (after sealing things up), then I‘d suspect that you have a static leak somewhere…..

That was my first thought, but it just got it tested and all was well. Also, assuming there’s a leak, wouldn’t a higher cabin pressure make the aircraft seem slower, as there would be less of a difference between pitot and “static”? Or do I have that backwards?

 

[Kyle Boatright]

Air leaks are drag. Whether you gained 2mph or .5mph, you almost certainly gained something.

 

[BoydBirchler]

I have a friend who is a Bellanca guru, One of the first things he does with a new to him Viking, is replace the door seal which he claims can make a 4 mph difference on a 4 way average speed trial.

If you have a static leak causing a change in indicated, you would observe a change in altitude/ airspeed when opening and closing the air vents while in stable flight.

 

[blaplante]

https://www.kitplanes.com/wind-tunnel-41/
any little jet of flow along the surface can disrupt the airflow.

 

[wcalvert]

Barnaby Wainfan, the author of the Kitplanes articles quoted, has forgotten more about aerodynamics than most any engineering human ever knew ... !

His articles are well written and full of information everyone should explore. Amazing

 

[Dugaru]

If you have a static leak causing a change in indicated, you would observe a change in altitude/ airspeed when opening and closing the air vents while in stable flight.

Never thought of that. I will give it a try!

 

[jrs14855]

Dave Anders discussed this in detail in a long ago Kitplanes article. Not just canopies but leakage anywhere on the airplane.

 

[RV7A Flyer]

I pick up a knot or two whenever I close both air vents (7A, NACA scoops both sides of forward fuselage).