Prandtl multi probe receptacle used for TE only?

[Matt Herron Jr.]

I have a Prandtl type receptacle in the fin of my ASW27. The previous owner converted to to TE probe only, by tying off the static and pitot lines behind the panel. Anything wrong with this set-up? I guess there would be more potential for leaks, at a minimum. will the extra volume of air connected in the unused tubes create any adverse effects on the TE line? I get my static from the ports on the boom about 2/3 back.

Thanks for any input.

Matt

[Dave Nadler]

Hi Matt!

On Wednesday, February 14, 2018 at 6:03:47 PM UTC-5, Matt Herron Jr. wrote:
> I have a Prandtl type receptacle in the fin of my ASW27.
> The previous owner converted to to TE probe only, by tying off the static
> and pitot lines behind the panel. Anything wrong with this set-up?
> I get my static from the ports on the boom about 2/3 back.

You mean a 3-way probe, right?
The probe pitot and static are better than fuselage ports (though pitot
is easily wiped out by a bug). If your instrumentation is working OK with
fuselage ports, why mess with it?

> I guess there would be more potential for leaks, at a minimum.

Nope.

> will the extra volume of air connected in the unused tubes create
> any adverse effects on the TE line?

No, they are not connected in any way.


See ya, Dave

[JS[_5_]]

On Wednesday, February 14, 2018 at 3:44:59 PM UTC-8, Dave Nadler wrote:
> Hi Matt!
>
> On Wednesday, February 14, 2018 at 6:03:47 PM UTC-5, Matt Herron Jr. wrote:
> > I have a Prandtl type receptacle in the fin of my ASW27.
> > The previous owner converted to to TE probe only, by tying off the static
> > and pitot lines behind the panel. Anything wrong with this set-up?
> > I get my static from the ports on the boom about 2/3 back.
>
> You mean a 3-way probe, right?
> The probe pitot and static are better than fuselage ports (though pitot
> is easily wiped out by a bug). If your instrumentation is working OK with
> fuselage ports, why mess with it?
>
> > I guess there would be more potential for leaks, at a minimum.
>
> Nope.
>
> > will the extra volume of air connected in the unused tubes create
> > any adverse effects on the TE line?
>
> No, they are not connected in any way.
>
>
> See ya, Dave

The three circuits are not supposed to be connected, but if there is a bad O-ring, all bets are off.
In a perfect world, your system as plumbed will work fine. If the mod was done due to crosstalk, and there is a leak in the plugged static or pitot lines, it will be erratic.
After the lines were disconnected and plugged, there's a chance nobody has leak checked them.
They're a pain to replace. I have a spare fitting for ASW27/28/29 at home, hope to never need it. Fortunately my leak was found to be two things, a bad probe and a hidden connector in the back of the panel, which Rex found instead of replacing the fitting.
Jim

[Matt Herron Jr.]

On Wednesday, February 14, 2018 at 3:57:27 PM UTC-8, JS wrote:
> On Wednesday, February 14, 2018 at 3:44:59 PM UTC-8, Dave Nadler wrote:
> > Hi Matt!
> >
> > On Wednesday, February 14, 2018 at 6:03:47 PM UTC-5, Matt Herron Jr. wrote:
> > > I have a Prandtl type receptacle in the fin of my ASW27.
> > > The previous owner converted to to TE probe only, by tying off the static
> > > and pitot lines behind the panel. Anything wrong with this set-up?
> > > I get my static from the ports on the boom about 2/3 back.
> >
> > You mean a 3-way probe, right?
> > The probe pitot and static are better than fuselage ports (though pitot
> > is easily wiped out by a bug). If your instrumentation is working OK with
> > fuselage ports, why mess with it?
> >
> > > I guess there would be more potential for leaks, at a minimum.
> >
> > Nope.
> >
> > > will the extra volume of air connected in the unused tubes create
> > > any adverse effects on the TE line?
> >
> > No, they are not connected in any way.
> >
> >
> > See ya, Dave
>
> The three circuits are not supposed to be connected, but if there is a bad O-ring, all bets are off.
> In a perfect world, your system as plumbed will work fine. If the mod was done due to crosstalk, and there is a leak in the plugged static or pitot lines, it will be erratic.
> After the lines were disconnected and plugged, there's a chance nobody has leak checked them.
> They're a pain to replace. I have a spare fitting for ASW27/28/29 at home, hope to never need it. Fortunately my leak was found to be two things, a bad probe and a hidden connector in the back of the panel, which Rex found instead of replacing the fitting.
> Jim

I agree in normal use the three lines are not connected. However, if you just insert a TE probe into the multipart receptacle then all three ports share the same flow because the TE probe doesn't go deep enough and is not stepped like the Prandtl probe.

[Dave Nadler]

On Wednesday, February 14, 2018 at 6:57:27 PM UTC-5, JS wrote:
> They're a pain to replace.

Yup, IMHO a huge design blunder to put the O-rings in the socket
instead of on the probe. I once asked SH how to replace the O-rings,
and they said they have absolutely no idea ;-(

[[email protected]]

How to change the internal O-rings is all explained in the service section of the ESA Systems web page. That's not to say it is easy - or even possible in the case of ring 3 without removing the socket which means cutting open the fin.

[[email protected]]

The probes and sockets are produced by esa-systems in Berlin. There's an instruction on how to replace the O-rings on their website: https://www.esa-systems.com/en/support/instructions-answers/the-o-rings-in-the-mounting-adapter-are-defective-where-can-i-find-replacements-and-how-do-i-change-them/

[[email protected]]

Now tell me again...
Why aren't the O rings on the probe?

Must be an oversupply of engineers needing to design something like this O ring insertion tool.

[[email protected]]

Don't ask me.

There are two videos on YouTube explaining the process: https://www.youtube.com/watch?v=NitQF9Of4fk https://www.youtube.com/watch?v=a91LM2JIF0s

[krasw]

torstai 15. helmikuuta 2018 1.03.47 UTC+2 Matt Herron Jr. kirjoitti:
> I have a Prandtl type receptacle in the fin of my ASW27. The previous owner converted to to TE probe only, by tying off the static and pitot lines behind the panel. Anything wrong with this set-up? I guess there would be more potential for leaks, at a minimum. will the extra volume of air connected in the unused tubes create any adverse effects on the TE line? I get my static from the ports on the boom about 2/3 back.
>
> Thanks for any input.
>
> Matt

Volume of triple pneumatic tube from tail to panel might be close to half of variometer flask volume, so answer is "maybe" even in theoretical world. But there is too many variables in pitot-static system to give you systematic answer.

[krasw]

torstai 15. helmikuuta 2018 15.29.25 UTC+2 kirjoitti:
> Now tell me again...
> Why aren't the O rings on the probe?
>
> Must be an oversupply of engineers needing to design something like this O ring insertion tool.

If the grooves for O-rings were in the probe it becomes quite weak at the base. Aluminium or brass develops crack at groove area because TE probe vibrates a lot. My guess: they discovered that probe with O-rings/grooves did not last too long. BTW, one-way TE probe has usually a groove and O-ring in the probe. It cracks sometimes but it is easy to glue a new base part to an old probe. With two- or 3-way probe this is impossible.

[[email protected]]

On Thursday, February 15, 2018 at 4:26:46 PM UTC, krasw wrote:
> torstai 15. helmikuuta 2018 15.29.25 UTC+2 kirjoitti:
> > Now tell me again...
> > Why aren't the O rings on the probe?
> >
> > Must be an oversupply of engineers needing to design something like this O ring insertion tool.
>
> If the grooves for O-rings were in the probe it becomes quite weak at the base. Aluminium or brass develops crack at groove area because TE probe vibrates a lot. My guess: they discovered that probe with O-rings/grooves did not last too long. BTW, one-way TE probe has usually a groove and O-ring in the probe. It cracks sometimes but it is easy to glue a new base part to an old probe. With two- or 3-way probe this is impossible.

That makes sense. Unlike the triple probes the ESA TE/Static double probes use the ST2 socket and the probe has a short aluminium (I think) insert with O -rings on it. I had one of those break in flight at an O-ring groove inside the socket. Part way through the task I lost the ability to thermal properly and didn't understand why until I landing and found the probe drooping about 30 degrees and being held by the probe internal flexible tubing..

I contacted ESA directly and they repaired the probe very quickly for a very reasonable cost.

[[email protected]]

Sure wish ESA would redesign their UN and SUN adapter to offer a "screw-off" front end which could be exchanged when o-rings become faulty. Hey ESA, want to make more money?