Good Compass For Microlight

[Bernoulli]

Recently started flying a Sky Ranger around and it has two cheap wobbly compasses which differ by up to 20 degrees. Like the man with two watches who never knows the correct time I don't know the heading I'm on.

So my question to the community is can you recommend a good compass system suitable for a 3 axis microlight? Realistically I'm not going to spend a fortune but I would like something upon which I could rely.

Before anyone tells me that I should get with the 21st century and use a GPS etc etc I should state that I actually want to navigate the old fashioned way...you know...map and compass and stopwatch and brain. It feels more satisfying that way.

I'm not fussed about it being either 'old fashioned' or digital (digital would probably be better?), I simply want to know what heading I'm on. There must be something suitable out there?

Sensible suggestions gratefully received.

[Genghis the Engineer]

Having flown a fair selection of the UK microlight fleet at some point, I'm of the opinion that the best are usually big chunky boat compasses.

Something like this (I have no connection to the company, but have flow quite a few microlights with this or something extremely similar fitted).

Silva Multi-Purpose & Handheld Compass 70un (http://www.outdoorgb.com/p/multi_purpose_handheld_compass_silva_70un/?utm_source=froogle&utm_medium=directory&utm_content=GBR&currency=GBP&country=GBR&SelectedBundle=133696&gclid=COGBspXSpMgCFYMewwodb-sKXg)

G

[Small Rodent Driver]

One of these will do the trick.

PAI 700 Vertical Card Compass (http://www.transair.co.uk/sp+Aircraft-Compasses-PAI-700-Vertical-Card-Compass+4015)

More expensive than the boat type of Compasses available but designed for use in an a/c at least and has facility to adjust for compass swing.

[magpienja]

I use the panel mount version or the one in Genghis link see the one in my link...new they are around £100...mine is very good but like any compass effected by near by ferrous metal objects.

Mine is in a micro...I checked mine by standing behind it with a good hand held and compare indications...not scientific but quite good.

The one in my link may not be the best...not easy to read...but it is there racing type.

Silva 100P Bulkhead Mounted Steering Compass | eBay (http://www.ebay.co.uk/itm/Silva-100P-Bulkhead-Mounted-Steering-Compass-/111787123776?hash=item1a07082440)

Nick.

[Bernoulli]

Thanks Chaps. I like the look of SRDs proposed bit of kit. Just wondered if there was a simple digital device that can give a heading readout? Doesn't matter if the display is only three numbers, the voices in my head can help me work it all out :}

[Jan Olieslagers]

I have exactly the same as referred to by GtE. It works well, yet would work better if I could spare the time and effort to get it properly adjusted. Have you tried any adjustment on yours?

I'd be happy to receive some guidelines to this adjustment: I imagine one could do the "course" part on the ground, rotating the plane by steps of 30 or 45 degrees and adjusting until it reads ok; then confirm in flight by checking against GPS? I should think the first part can easily take two or three rounds... Is there a published procedure, somewhere?

[Genghis the Engineer]

I have exactly the same as referred to by GtE. It works well, yet would work better if I could spare the time and effort to get it properly adjusted. Have you tried any adjustment on yours?

I'd be happy to receive some guidelines to this adjustment: I imagine one could do the "course" part on the ground, rotating the plane by steps of 30 or 45 degrees and adjusting until it reads ok; then confirm in flight by checking against GPS? I should think the first part can easily take two or three rounds... Is there a published procedure, somewhere?

Set up systems and power on the ground as near as possible to flight condition. Point the aircraft to an externally referenced magnetic north.

Adjust the N-S screw, to set the compass reading correctly.

Now point the aircraft East, do the same to the E-W screw.

Now point the aircraft south, remove half the error with the N-S screw.

Now point the aircraft west, remove half the error with the E-W screw.


And normal practice is to then rotate the aeroplane in 30 degree heading changes right around, by external reference, recording the headings, and then translate that to a correction card in the cockpit.

G

[Jan Olieslagers]

Thank you very kindly, much appreciated. Will do at next visit to field and report results. Might take some time though.
I have a feeling the plane had best be away from metallic structures, such as hangars, as far as possible?

[Jan Olieslagers]

wondered if there was a simple digital device that can give a heading readout

If you want electronics OUT best go for electronics IN , i.e. gps. Any smartphone will do, these days, or so I hear. If a smartphone is simple enough, of course ;)

[abgd]

Though to be finickity a GPS will give you track, not heading. Arguably more useful but you might as well go the whole hog and have a moving map in that case.

[Genghis the Engineer]

Thank you very kindly, much appreciated. Will do at next visit to field and report results. Might take some time though.
I have a feeling the plane had best be away from metallic structures, such as hangars, as far as possible?


In an ideal world, do it well away from buildings, on level ground, where you don't believe there are any underground power lines.

Normal good practice is to mark out lines you can align the aeroplane with on the ground - this is known as a "compass rose" (better still, find a local airport with one marked out already) and have somebody help align the aeroplane and keep sightseers away from the prop whilst you operate the aircraft and write the numbers down.

Oh yes, and use a brass or plastic screwdriver on the adjustment screws, not a steel one!

G

[fireflybob]

I love part of the spec for the PAI 700 Compass:-

The compass can be flown inverted.

Thanks goodness for that - I was planning on doing an inverted cross country next week.....

[Jan Olieslagers]

@GtE: the compass is supplied with a brass screwdriver included, no issue there.

@GtE: I heard stories of the Grimbergen EBGB aerodrome at one time having a dedicated structure: a wooden base plate with circular wooden "rails", in which glass spheres rolled, supporting a wooden platform big enough to roll an aircraft onto. The plane could thus be rotated through 360° with nothing metallic near. I have a vague memory of having seen the remains, many moons ago.

@fireflybob: ROFL!

[cats_five]

I confess I have never looked at the compass in my glider when I'm flying... Of course XC gliding doesn't happen when the sun isn't visible regardless of if it's thermal or wave. At least I don't go XC without a visible sun, and I find it an invaluable navigational aid. Moving maps are wonderful, but one needs to have prepared enough to manage without should the electrics go down as can happen in a glider since they are all on batteries.

[Aerials]

The magnetic compass is the simplest of instruments! If you would like to save some money and the possibility that your new compass may disappoint, read on!

Try to investigate why there are 2 compasses fitted in the first place. Most unusual! Check to see that the compasses are in good condition and have the fluid with no bubbles. Remove both compasses and use one of them to seek very local cockpit magnetic fields that might have introduced the error in the first place.

If a local magnetic field is present, do something about it! If no local magnetic field, then look and see if there is any form of corrector fitted to either or both compasses, as described by GtE. If neither compass has correctors then re-fit the best for condition and readability. Disregard the comments below only where I write about the correctors.

Choose yourself the most readable compass with correctors then take it to a place free from magnetic anomalies. Point the lubber line at North then South. Trim the N-S correctors to minimise the error. Fit it to the aircraft in such a way that you minimise the N-S error (the 'A' error) then do a compass swing as described by GtE. Small magnetic fields within the airframe are trimmed out using the correctors and you may need to go round the 4 points of the compass twice (or more, depending................ ) because trimming the N-S can have an effect on the W-E, given earth magnetic field influenced by airframe structure.

Once you have minimised errors in N-S and W-E then a calibration swing using 8 or 12 points can be taken. This is where you make out your deviation card and don't touch the correctors.

Fitting a new compass to an airframe with residual magnetism could be a complete waste of money!

[Bernoulli]

Thanks Aerials (and all the others who have taken the time to reply)...I like the cut of your jib (sp?).

More years ago than I care to count I used to compass swing Canberras out on RAF Wyton's compass bay. It used to take hours. If it went well. I recall complex graphs with all sorts of primary and secondary errors to be quantified and compensated for.

For now I think I'll stick with what the aeroplane's kitted out with and try and identify if one of the compasses is any better than the other, if either can be adjusted and why there are two in the first place.

Thanks again.