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

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!

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.





At 11:53 12 December 2018, Pete wrote:
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!

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?

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.




At 13:10 12 December 2018, Pete wrote:
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?

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.

On Wednesday, December 12, 2018 at 1:53:18 PM UTC+2, Pete wrote:
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!

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.

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.

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.

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!

On Wed, 12 Dec 2018 21:55:48 -0800, krasw wrote:

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.

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