Replacing Vacuum Instruments

The place to raise issues, ask questions, swap ideas and discuss anything related to aircraft engineering, maintenance and building.
NB Any opinions expressed in this forum are not necessarily those of LAA Engineering

Moderators: John Dean, Moderator

Replacing Vacuum Instruments

Postby concorde » Fri Sep 15, 2017 4:01 pm

Looking to remove the vacuum Horizon Gyro and Directional Indicator from a small VFR panel.
It will save 3Kg or so.
Tried the Garmin G5, but it appeared too small to readily read, and went back unopened.
We need something with a bigger screen (at least 6")
Whilst the Horizon Gyro is well covered by all of the systems at the budget end, there is very little info on the capacity to emulate a DI. (Which is the one that reassures me, and I will miss)

It was only when I stopped to have a good think about the situation that I realised that it is not so simple an issue. At the moment the pilot is the feedback system, correcting at chosen quiescent points.
That puts the pilot in charge of what is happening.

All of the budget systems seem to slavishly follow the gps, compass, or head for a location. (I suppose that you could select the north pole!) We already have a compass. The gps only tracks where you have been, not where you are, and we can use a tablet for that.
Is there any budget efis type system that holds it's gyro heading, with some form of controllable correction system.

I am looking at the iLevil, Aeolus, Avmap, Dynon, etc. Cannot stretch to a Garmin G3x.

Any thoughts?
Andrew Spurway
Posts: 5
Joined: Sun Nov 10, 2013 10:41 am

Re: Replacing Vacuum Instruments

Postby Mark A » Fri Sep 15, 2017 7:51 pm

Most of the EFIS systems have a magnetometer input that can be calibrated for the aircraft's magnetic fields.
An external one can usually be calibrated better than the internal type as it allows you to position it away from ferrous metals and high current wiring.

That gives you the option of displaying both magnetic heading and GPS track. The software corrects for bank errors and there is no acceleration error, so it behaves muck like a slaved DI, so no need to sync with compass or correct for precession as you would a mechanical gyro DI.

Have a look at the GRT mini too; very well made. Their new Horizon EX is good value if you want a larger screen.
Mark Albery
Mark A
Posts: 113
Joined: Thu Jan 03, 2008 11:48 am
Location: San Francisco

Re: Replacing Vacuum Instruments

Postby mikehallam » Fri Sep 15, 2017 10:23 pm

AvMap EFIS in my 'plane.

Has it's own solid state gyro & GPS; gives speed in the air, over the ground, wind & drift. Plus AH, slip 'ball', turn indicator, VOR, ADF and doubtless a few more things. With built in data base.
GPS aerial comes with it on a neat plug in lead to locate it within reason where you find best.

Fits standard ~3" cut-out with a neat square instrument face, only needs +12volts feed and Tee cross connections to the back of your ASI pitot & static.

mike hallam.
User avatar
Posts: 476
Joined: Sun Jan 06, 2008 4:12 pm
Location: West Sussex

Re: Replacing Vacuum Instruments

Postby concorde » Sat Sep 16, 2017 5:26 am

Many thanks for your replies. Very interesting.

I almost went for the Avmap, but it does seem a little dated now.
Even the chips in today's drones are several generations on.
I was very interested in the GRT Mini, but it is not readily available in Europe.
I think that LAS can get one through Aircraft Spruce, but would it be that well supported in the UK?

The remote 3D magnetometers, and gps with glonass receivers used are way better than the old compass and a tablet gps, and the Kalman filters, etc, are very sophisticated, but....
I cannot help feeling that the design philosophy is the wrong way round.
The DI gyro may suffer from precession, but it does provide a stable constant which simply requires minor (and known) adjustment over time. It may not be dead on, but at no point is it going to be that far off, and will certainly not get upset by a loss of gps, or dodgy magnetometer connection.
The workings of the modern efis software systems are not so clear. They seem to use the gps and compass as starting points, which then has to be processed to arrive at a stable heading.

There is a thing called a electronic gyro-compass. It is always points to true north, but seems to only be used on boats. I was half thinking about it, but boats use a different can bus. Not sure why it is not used in aircraft.
Andrew Spurway
Posts: 5
Joined: Sun Nov 10, 2013 10:41 am

Re: Replacing Vacuum Instruments

Postby AlanR » Sat Sep 16, 2017 8:43 am

If you do decide on the GRT Mini I would deal with Grand Rapids Technology directly.
Although they have no European agents I have found them an excellent company to deal with and their products are of high end quality. I had a GRT EFIS in my last aircraft and it was a brilliant piece of kit.
Alan Radford
Posts: 81
Joined: Mon Jan 07, 2008 8:50 pm
Location: Midlands

Re: Replacing Vacuum Instruments

Postby mikeblyth » Sat Sep 16, 2017 9:46 am

Mike Blyth
Posts: 101
Joined: Tue Mar 18, 2008 9:24 am
Location: Bedford UK

Re: Replacing Vacuum Instruments

Postby concorde » Sun Sep 17, 2017 10:40 pm

Thanks for more advice.

I have seen the Horis at LX avionics, and have the info.
It is bright enough, but it might still be too small for our old eyes.

I have written to GRT. Asked about the Mini and the Sport EX.
Still feel that they are very much based in the US.
Pressure appears to be only in inches Hg.
Andrew Spurway
Posts: 5
Joined: Sun Nov 10, 2013 10:41 am

Re: Replacing Vacuum Instruments

Postby PaulSS » Mon Sep 18, 2017 12:58 am

How about the MGL Discovery lite? 7" screen and seems to do all the other stuff you'd like.
Paul Simmonds-Short
Posts: 22
Joined: Wed Mar 15, 2017 7:04 am

Re: Replacing Vacuum Instruments

Postby Mark A » Mon Sep 18, 2017 7:49 pm

GRT are very much a US based firm, but they have lots of international customers and handle repairs etc avoiding incorrect tax and duty demands.
The unit systems are all configurable, so HPa or inches, knots/MPH/KPH as you desire.

I've just returned a failed GPS unit from a 10 year old installation and they've turned it round in a few days at a reasonable price.
Mark Albery
Mark A
Posts: 113
Joined: Thu Jan 03, 2008 11:48 am
Location: San Francisco

Return to Aircraft Construction & Maintenance

Who is online

Users browsing this forum: Bing [Bot] and 7 guests