Are air filters necessary on Pitot, static or TE lines?

[Pete]

Hey all,
I have noticed some gliders have what look like small fuel filters spliced into the tubing prior to avionics. I imagine this is a safeguard to dust, etc entering the avionics. Seems to make sense eventually what's outside is going to get inside....

However, is this necessary? I see a lot of old gliders without them. No mention of it in the manuals.

I'm redoing my panel with new avionics. Before I install I would like RAS's opinion if some sort of air filtering to my $2,000 variometer or shiny new ASI is good practice?
Thanks!

[Mike Oliver]

I put a water filter (fuel filter) in my pitot line after losing the ASI
whilst
cloud flying using the A/H on the Butterfly vario. The thought of water
entering the electronics was enough to convince me it was a reasonable
idea.

[Pete]

Interesting. Thanks Mike. What kind of water filter are you using? I wonder if really fine filtration (osmotic, etc) would have any negative effect on the rate of change of air pressure and thus affect instrument reading?

[Mike Oliver]

It was actually a paper motorbike fuel filter. The idea that the paper
would absorb any water. I did several cloud climbs post installation
without any issues. Sadly, I no longer own the glider.

[krasw]

The filters cost nothing and stop water droplets or dust entering your instruments. All gliders I've seen (new and old) have filters on all pitot-static tubes. Hard to imagine any reason to not install them. The water enters easily trough fuselage static ports, too.

[Pete]

What filters are you recommending that cost nothing and work well? I was thinking of going to Autozone and buying small-motor gas filters?
If there is something better I would like to use it.

[Ross]

Depending where you are based will depend on what they are called, but this is about what you are looking for:

https://shop.streckenflug.at/product_info.php?products_id=475

Cheers

[Dan Daly]

Aircraft Spruce has some. https://www.aircraftspruce.com/catalog/inpages/pitotstatic.php

[Scott Williams]

Here in Oklahoma a few years ago our club 2-33 had a malfunction of the airspeed, turned out to be a nasty smelling decaying remains of some kind of insect in the pitot tube, could have easily gotten into the instrument. on my own sailplane I have installed small engine paper element filters to minimize the possibility of contaminates getting into my spendy instruments.
Scott

[Charlie M. (UH & 002 owner/pilot)]

Some are dust/dirt/water filters. In general, the bigger the better so a dirt load is minimal to flow. Keep in mind, some use them to keep out bugs of various kinds.

Also, some are "gust filters" (online sources can define way better than I....). The basic purpose is to limit big changes in pressure in the downstream tubing......thus "gust filters".
You may have a dirt filter as well as a gust filter in the same tubing hose.

[krasw]

On Wednesday, December 12, 2018 at 6:14:54 PM UTC+2, Pete wrote:
> What filters are you recommending that cost nothing and work well? I was thinking of going to Autozone and buying small-motor gas filters?
> If there is something better I would like to use it.

Yes they are small gas filters from auto parts store. Smaller is always better, with big filter you are effectively increasing the tube volume between instrument and probe which can be problem for variometers.

[Pete]

Thanks for the input everyone.
I just redid the panel. Three new air filters for pitot, Statit and TE now installed with all new tubing. It sure does look pretty!

[Martin Gregorie]

Some of the lines in my Libelle are fitted with small paper filters: made
by Crosland and fitted to Triumph Spitfires, TR6 and MGB amongst other
cars. The body is transparent plastic, 40mm overall diameter, 45mm long
and with 30mm inlet and outlet stubs suitable for 5mm or 6mm tubing.
They've been in the glider since I got it, but their location in the
plumbing is irrational - both filters are in the TE line AFTER to Y-split
to feed both varios and nothing in either static or pitot lines.

So, I've just bought two more for connection rationalisation and
installation this winter: they were fairly inexpensive. Off eBay at just
over GBP 5.00 each including P&P.


--
Martin | martin at
Gregorie | gregorie dot org

[chip.b...@gmail.com]

Back in the 1960s, my father's 1-23B had a glass tube (IIRC, 2-3 cm diameter--may have been a test tube with one end cut off) with rubber stoppers in each end, each of which had a metal/plastic tube inserted to connect up with the standard clear plastic instrument tubing.

Each spring he filled the glass tube with silica gel crystals (not sure if he baked the old crystals to drive out moisture and reused them or just used new). The objective was to prevent moisture from entering his Cosim pellet vario. Pellet varios were notoriously sensitive to moisture, which sometimes caused the lightweight red/green pellets to stick in their tubes.

Today's varios aren't nearly as sensitive to moisture, apparently. So for all the wailing about too much technology in soaring, we've made some progress. :)

Chip Bearden

[Martin Gregorie]

On Mon, 17 Dec 2018 15:39:06 -0800, chip.bearden wrote:

> Today's varios aren't nearly as sensitive to moisture, apparently. So
> for all the wailing about too much technology in soaring, we've made
> some progress. :)
>

I rather took the remarks about small bugs crawling into my instruments
to heart and yesterday I replumbed my panel: now TE, pitot and static
lines all have a Crosland paper filter in them between the instruments
and the multi-way quick-connect that all three lines go through. It looks
a bit tidier too.

[7K]

Have used at least 10 of these over the years with very good success. Quality built and readily available at NAPA. Last glider I did (DUO) had a wad of bugs caught in one of these filters. They crawled all the way from the top of the vertical fin to just behind the wheel and made a nest in the filter.

https://www.napaonline.com/en/p/FIL3011