View Full Version : Aircraft compasses - going back to front

10-03-2004, 04:30 AM
Aircraft have two types of compass (that I know of anyway). The correct descriptions for these types I don€t know so I might call the compass on a Bf-109 a plan compass and that on a MiG 3 a reel compass. The former shows you your heading in a plan view facing you; the latter shows your heading looking from the side at this `reel€ on which is marked NESW. For me the plan compass is the best. It is clear and simple and it shows your heading. What I dislike about reel compasses is:

1. They are too small, sometimes obscured by other objects
2. While banking the compass `freezes€, then suddenly returns to your heading when you level off
3. The compass `spins round€ periodically for some reason
4. If you€re going NNE, it€s difficult to see markings because they are almost at 90 deg. to your line of sight.
5. Multiple compasses confuse things
6. Most `reels€ rotate anti-clockwise* and some clockwise* for a given turn direction
7. The `reel€ pitches when climbing/diving

What I like about a plan compass is when going N you bank to the right and the compass now indicates you are going NE after smoothly turning with you. It€s intuitive. The compass rotates and the needle indicating your direction stays pointing upward. You could have NESW fixed and a pointer that rotated but that seems less intuitive to me. In a reel compass you also have a stationary marker and the reel which rotates. This becomes confusing because if you bank right (from going N) in some planes the reel goes clockwise and in others anti-clockwise. In the MiG 3 if you bank right, the reel goes anti-clockwise (observed from above) i.e. a mark on the reel would be going right. Many planes compasses are like this. The P-40 has two reel compasses, so while you€re banking you have two compasses but neither informs you of the current direction in which you are flying. The lower-central compass operates in the opposite way to a MiG 3 (and a lot of other aircraft). If you bank right, the reel goes clockwise i.e. a mark on the wheel goes left. This means if you looked at this compass on plan from above the markings going clockwise would be NWSE. If I had to have a reel compass, this way of doing things to me is more intuitive. Flying the P-40 it is like the vertical marker moves to the right when banking right. Obviously the marker doesn€t move, but I find it quite logical. You are heading N, you move the stick right and E is now close to the marker. So in the P-40 I think of the marker moving in the direction of the stick, in other aircraft I think of the reel moving in the direction of the stick and in aircraft with plan compasses it€s so obvious I don€t have to think. There are many combinations:

MiG 3 Reel, 1 compass, anti-clockwise*
La 5 Reel, 1 compass, anti-clockwise*
Yak 9 Reel, 1 compass, anti-clockwise*
P-38 2 compasses, 1 plan, 1 reel, doesn€t work in game
P-39 2 compasses, 1 plan, 1 reel, anti-clockwise*
P-40 Reel, 2 compasses, 1 clockwise, 1 anti-clockwise*
P-47 Reel, 2 compasses, both anti-clockwise*
P-51 2 compasses, 1 plan, 1 reel, anti-clockwise*
Spitfire Reel, 1 compass, anti-clockwise*
Hurri Reel, 1 compass, anti-clockwise*
Fiat G50 Globe, 1 compass, anti-clockwise*
* Rotation of reel compass viewed from above when a right bank is undertaken

Russian/British are reel anti-clockwise, Germans are plan and American uses many combinations. If you must have a reel compass then I find it counter-intuitive to have them set up the way the majority of aircraft have them. Even planes like the Hurricane and Spitfire have them this way. These planes also only have a number and no NSEW markings. The optimum is one compass, plan facing you, you then have all you need. I€m not fond of those globes in the Fiat G50/Zeke either.


10-03-2004, 05:11 AM
Many aircraft have both types in the same instrument panel. One is a magnetic compass (the "reel" type) and the other is a gyro compass. The magnetic type is a wheel floating in liquid (usaully alcohol) with a magnet attached and it aligns to magnetic north. When the plane isn't level (and also when you're close to the north or south magnetic poles) the magnet isn't lined up with the earth's magnetic force lines and hence that compass performs poorly when manouvering.

The other compass uses a gyroscope as a reference. This reference is good for the location where it's calibrated, however as you travel over distance and as the earth turns on its axis it will need to be re-calibrated. The pilots in real life used the magnetic compass as a reference to re-calibrate the gyro compass during periods of flight when no manouvering was taking place.

10-03-2004, 09:07 AM
The 'reel' compasses you are talking about would be the magnetic ones. It is essentially a sphere with a magnet in it and all the degree's printed in a circle around it. This sphere is in a housing filled with some kind of liquid. This enables the compass to move freely since it completly floats in the fluid. It is the most basic of all aircraft compasses. Some low tech aircraft had them as their only compass and many of todays airliners have them as the most basic back-up compass. Since it doesn't need electrical power to operate.

The 'plan' compass you talk about is called the 'gyro compass'. It features a gyroscoop wich is powered by pneumatics (could be electric too, i don't know for sure) A gyroscope is always steady towards a certain point in space. In case of a gyro compass, it is aimed at the north pole. Altough it is a little more complicated, that's basically how it works. This compass is alot more complicated with multiple moving parts and a gyro that turns with 20.000+ RPM (modern day gyro compasses at least)The latest development is having laser gyro's installed, instead of mechanical gyro's. These make no noise, are more precise and alot more reliable then standard mechanical gyro's. That is because they don't have any moving parts at all.

You are right that there are bugs with some of the compasses in FB. I hope Oleg will have time to get rid of those bugs. Like the P-39. Look at its magnetic compass. It just keeps on turning like a marry-go-around. It never stops turning so you can tell your heading. Can be very frustrating when map icons are off on HL. But then again, the vision from the cockpit is so poor, no one will fly it in full real servers.

Anyways, I didn't notice all the bugs you have found but, the compasses in FB surely needs fixing.

10-03-2004, 12:57 PM
Platypus, I tried all 3 versions of the P-39 and the magnetic compasses (as well as the gyroscopic compasses) work. Which version are you playing - I have AEP patched to 2.04. Nothing happens when turning on either of the P-38 models, the magnetic compass just wavers around. Do you agree that the compass arrangements on UK/Russian/American planes (except the P-40), were more confusing because of the use of magnetic compasses. The Germans only seem to use gyroscopic compasses on their aircraft. Your replies explain why the P-38/P-39/P-51 have gyroscopic and magnetic compasses.