Ventus 2 ASI problems?

[John McLaughlin]

Is it normal practice to have the ASI use cockpit static and to disconnect

the external static vents, due to ASI errors when dumping water?

[Al McNamara[_4_]]

At 19:24 14 February 2020, John McLaughlin wrote:
>Is it normal practice to have the ASI use cockpit static and to disconnec
>
>the external static vents, due to ASI errors when dumping water?
>
No

[Dave Nadler]

On Friday, February 14, 2020 at 4:45:04 PM UTC-5, Al McNamara wrote:
> At 19:24 14 February 2020, John McLaughlin wrote:
> >Is it normal practice to have the ASI use cockpit static and to disconnect
> >the external static vents, due to ASI errors when dumping water?
> No

Except IIRC some are equipped with a panel switch to do so during dumping.
Normally not!

A switch is also common in some older gliders notorious for sucking water into
the statics during dump (LS-3, LS-4 come to mind).

[SoaringXCellence]

John,

The manual says to connect the ASI to the static ports under the wing, which as noted, may result in water in the static system.

Using the tailboom static ports is not "approved" for the ASI as it was not used by SH to establish the indicated airspeeds listed in the manual. Venting the ASI static to the cockpit will cause a variation in ISA depending on the pressure in the cockpit, which can vary with speed, open vents, extractor, etc. which makes it most unreliable.

I use the aft ports in my Mini Nimbus and just figure there's an error and deduct a few knots from the published figures as a safety margin.

But then I've never pushed the ship past about 95Kts and that's below most of the max indicated airspeed limitations in the manual.

MB

[[email protected]]

> Except IIRC some are equipped with a panel switch to do so during dumping..
> Normally not!
>
> A switch is also common in some older gliders notorious for sucking water into
> the statics during dump (LS-3, LS-4 come to mind).

As Dave indicated, the LS-3 standard setup included a switch that pumped pitot pressure through the aft static ports to prevent water from entering while dumping. It wasn't strong enough to blow them out if they got full of water so you had to use the switch before you dumped to pressurized them slightly--and also for a some time after because water drained down the fuselage for a while. IIRC, the ASI used the forward statics but the open pitot line reduced the pressure enough that the ASI read low while this was going on. The switch also blocked off the line leading to the older Cambridge vario that used the aft statics. Since this vario had a capacity bottle, if you gained or lost much altitude while dumping (which was most of the time, of course), you had to switch off that vario to prevent pegging it out when the pressure in the capacity bottle was vented. All in all, it was a PIA, especially when getting low and contemplating dumping to remain aloft. Not to be repeated.

When I got my ASW 24, I (like very other U.S. owner) ignored the factory dump ports on the lower wing close to the fuselage (with small diameter electric valves) and installed BIG valves that dump through a hole in the bottom of the fuselage. I've never had water get in the aft statics.

Chip Bearden
JB