Plumbing and Static Sources

[Six-Seven Romeo]

I looked in the RAS archives for an article that delved into my question below. No dice. So here goes.

Consider for a moment two gliders and the multiple static pressure sources found within (tee'd left/right);

Ventus CM (Motor Glider)
1) Under the wings
2) On the sides of the boom about 6 ft from the tail
3) Prandtl probe in the vertical stabilizer

DG-100/200/300
1) About at mid-calf area
2) About at hip area

Between the two ships there are more static sources that you can shake a stick at from nearly the nose to nearly the tail.

So which static source should be used? Should particular static sources be sent to specific instruments? Should some static loving instruments be kept isolated? Can some mechanical instruments that use different air pressure sources (i.e. ASI with pitot and static) cause bad mojo with other instruments that also use static? Help!

Inquiring minds want to know. If you are going to tell me to start drilling holes for an alternative "perfect" static source location, please take up knitting.

Thanks

[[email protected]]

On Tuesday, December 9, 2014 6:07:23 PM UTC-5, Six-Seven Romeo wrote:
> I looked in the RAS archives for an article that delved into my question below. No dice. So here goes.
>
> Consider for a moment two gliders and the multiple static pressure sources found within (tee'd left/right);
>
> Ventus CM (Motor Glider)
> 1) Under the wings
> 2) On the sides of the boom about 6 ft from the tail
> 3) Prandtl probe in the vertical stabilizer
>
> DG-100/200/300
> 1) About at mid-calf area
> 2) About at hip area
>
> Between the two ships there are more static sources that you can shake a stick at from nearly the nose to nearly the tail.
>
> So which static source should be used? Should particular static sources be sent to specific instruments? Should some static loving instruments be kept isolated? Can some mechanical instruments that use different air pressure sources (i.e. ASI with pitot and static) cause bad mojo with other instruments that also use static? Help!
>
> Inquiring minds want to know. If you are going to tell me to start drilling holes for an alternative "perfect" static source location, please take up knitting.
>
> Thanks

Very simple- use the ones the manufacturer specifies for the airspeed indicator because all the limits on the glider are based upon those.
Altimeters don't care about static accuracy so any factory static should do fine.
Static ref for varios, when needed are probably best on aft fuselage statics if available, from my experience.
FWIW
UH

[[email protected]]

Aft fuselage statics work well but can be more susceptible to clogging when dumping water ballast in certain gliders with lower-surface-of-wing outlets (e.g., my old LS 3, in which owners installed a switch to pump pitot pressure through the lines to keep them clear). Probes are vulnerable to ground handling damage and in-flight spearing of geese. Your call as to which is more likely.

Chip Bearden
ASW 24 "JB"
U.S.A.

[[email protected]]

As previously said - look in the manual and TC for directions from the manufacturer as to what source to use. Usually they will specify a source for the ASI system as the placard limits are in IAS using those sources. I've often found they will specify on for the altimeter too though as UH says it doesn't matter much for the altimeter. Paul Bickle and Dick Schraeder's tests usually found that the most accurate static sources are ones well aft on the fuselage sides so those should be used for varios. Static sources on the multi probe are probably very accurate too. If you have both aft fuselage statics and a multi probe you could use the fuselage ones for the mechanical vario and the multi probe for the electronic vario so that the two don't suffer from interference.

[John Galloway[_1_]]

At 00:40 16 December 2014, wrote:
>As previously said - look in the manual and TC for directions from the
>manu=
>facturer as to what source to use. Usually they will specify a source for
>t=
>he ASI system as the placard limits are in IAS using those sources. I've
>of=
>ten found they will specify on for the altimeter too though as UH says it
>d=
>oesn't matter much for the altimeter. Paul Bickle and Dick Schraeder's
>test=
>s usually found that the most accurate static sources are ones well aft
on
>=
>the fuselage sides so those should be used for varios. Static sources on
>th=
>e multi probe are probably very accurate too. If you have both aft
>fuselage=
> statics and a multi probe you could use the fuselage ones for the
>mechanic=
>al vario and the multi probe for the electronic vario so that the two
>don't=
> suffer from interference.

The last sentence is puzzling. Mechanical glider varios are connected to

the TE line and capacity and have no separate static connection. It is
connectng both an electric and mechanical vario to the same TE line by T
piece close to the instruments that has the potential for pneumatic
interference.

[John Galloway[_1_]]

At 00:40 16 December 2014, wrote:
>As previously said - look in the manual and TC for directions from the
>manu=
>facturer as to what source to use. Usually they will specify a source for
>t=
>he ASI system as the placard limits are in IAS using those sources. I've
>of=
>ten found they will specify on for the altimeter too though as UH says it
>d=
>oesn't matter much for the altimeter. Paul Bickle and Dick Schraeder's
>test=
>s usually found that the most accurate static sources are ones well aft
on
>=
>the fuselage sides so those should be used for varios. Static sources on
>th=
>e multi probe are probably very accurate too. If you have both aft
>fuselage=
> statics and a multi probe you could use the fuselage ones for the
>mechanic=
>al vario and the multi probe for the electronic vario so that the two
>don't=
> suffer from interference.

The last sentence is puzzling. Mechanical glider varios are connected to

the TE line and capacity and have no separate static connection. It is
connectng both an electric and mechanical vario to the same TE line by T
piece close to the instruments that has the potential for pneumatic
interference.

[John Galloway[_1_]]

At 00:40 16 December 2014, wrote:
>As previously said - look in the manual and TC for directions from the
>manu=
>facturer as to what source to use. Usually they will specify a source for
>t=
>he ASI system as the placard limits are in IAS using those sources. I've
>of=
>ten found they will specify on for the altimeter too though as UH says it
>d=
>oesn't matter much for the altimeter. Paul Bickle and Dick Schraeder's
>test=
>s usually found that the most accurate static sources are ones well aft
on
>=
>the fuselage sides so those should be used for varios. Static sources on
>th=
>e multi probe are probably very accurate too. If you have both aft
>fuselage=
> statics and a multi probe you could use the fuselage ones for the
>mechanic=
>al vario and the multi probe for the electronic vario so that the two
>don't=
> suffer from interference.

The last sentence is puzzling. Mechanical glider varios are connected to

the TE line and capacity and have no separate static connection. It is
connectng both an electric and mechanical vario to the same TE line by T
piece close to the instruments that has the potential for pneumatic
interference.

[[email protected]]

Sorry for the unclear writing, that was what I was trying to say - interference between mechanical and electronic vario if using the same T.E. source with a T close to the instruments.