Odd compass direction with roll

[jk9]

 

If you watch the video you can notice the compass spins around as I roll. Is that correctly modeled? I mean a compass should point where I am going. I am not changing my direction but just rolling. So when I try banking, the compass spins and points random direction which makes me confusing where I am heading now. Others like IL-2 don't do this. It points where I am heading while I am rolling. So I just want to know this is a bug or intended to be working like this.

Edited May 13, 2012 by jk9

[JesseJames38]

It seems to be working fine to me. Keep in mind its different type of compass. the compass its self is located in the wing. the right wing i beleave and then it is connected electricaly to the guage. so its only going to read correctly when flying straight and level. On the other hand. you will also notice you have a gyro compass in the aircraft. in straight and level flight you adjust the gyro compass to the magnetic compass. the Gyro compass will give you the correct headding while in a turn. But you will need to set the gyro compass often to the magnetic compass. depending how quick the gyro compass gets out of wack

 

Jesse

[cichlidfan]

Others like IL-2 don't do this.

 

That should be the first hint that it is probably working correctly.:D

[Smokin Hole]

That's how all non-gyro compasses work. The lack of this effect is why Rise of Flight players sometimes think that flying in cloud was really possible for more than a minute or two before losing control. Compasses are only readable in a bank when headed north or south.

 

[EDIT: Wrong. It's East and West where the error is minimal or nil.]

Edited May 15, 2012 by Smokin Hole

[Fleshpiston]

That's how all non-gyro compasses work. The lack of this effect is why Rise of Flight players sometimes think that flying in cloud was really possible for more than a minute or two before losing control. Compasses are only readable in a bank when headed north or south.

 

 

They wouldn't let me in with my compass :(

[PeterP]

Everyone can try it yourself to see this effect.

get a old trusty magnetic compass and tilt it ....

 

Or simply try to image what will happen:

 

 

Well don't do it was a blow of water and a cork-needle ...:P at last not in front of your PC.

 

@Flehpiston

Good to see that there are still places of hope during this financial hard times, wondering if Steve Martin is working at the counter?

Edited May 14, 2012 by PeterP

[jk9]

I see. So it is normal. I don't understand why they had to use such a confusing compass but there must be a reason for that. Thx guys!

[sobek]

I don't understand why they had to use such a confusing compass but there must be a reason for that.

 

It was the 1940ies, not exactly high tech by todays standards, but they made do with what they had.

[PeterP]

Keep in mind that GPS is only about since 15 years in use for aerial/civil common applications.

 

Before this it was the only way to know where you are :checking known radio bacons and adjusting your instruments again according the contact.

All instruments had their known tolerance and failure at given time... - you only had to handle the absolute deviations from time to time.

Thanks - you had also a working clock with you! but in no visibility - you where almost lost - as it is hard to align yourself in level to the horizon and with no pitch, without having any visual clues, to reset the giro again.

And you will not know which instruments you can thrust 100%.

Edited May 14, 2012 by PeterP

[AlphaOneSix]

known radio bacons

 

Mmmmm bacon.

[joey45]

MMmmmmmmmmmmmmmm betwen to slices of bread and HP...

[PeterP]

guys, are you making again fun out of me?! :P

OK,OK ! its : radio beacons

[sobek]

Radio bacon? I'm sure Tesla would be proud. :D

[PeterP]

Not fair - I confessed , and still got my back beaten..., not fair at all!

:cry:

 

 

 

 

 

:D and now also good ol' Tesla got drawn in this...

[Smokin Hole]

Back to some seriousness. I've been paying some attention to this and I must say it seems a little overdone. Usually in a standard rate turn (the edge of the turn rate indicator matched to the edge of the "doghouse") the swings are 20 degrees or so in a wet compass. This compass swings 90 degrees plus. But it is also a type I have never used and maybe this type is prone to a more extreme northerly turning error.

[effte]

I noticed this effect last night. The term to google for those interested in knowing more is acceleration errors, and I think this is what we are seeing.

 

These are caused by the mechanics of the pivoting arrangement of the compass card along with the mass distribution and inerta of the card in wet compasses.

 

However, the P-51 has a remote indicating compass (with a wet/whisky compass added in some aircraft). This does not contain a compass card. Instead, it is a remote indicator where the needle is controlled by an electric field generated by coils, in turn controlled by the remote compass sensor/transmitter located out on the wing tip (caveat: the ones I'm familiar with - other designs are certain to exist).

 

Such a compass is not affected by acceleration errors!

 

This is also stated on pg. 68 of the DCS P-51D manual.

 

My first thought was that it was an attempt at modelling the effect of the inclination of the Earth's magnetic field, but slip the aircraft at a constand heading and you will find that it only reacts to acceleration and not to the bank itself.

 

Even assuming it is erroneously modelled acceleration errors, they seem way overdone.

 

By the way, remember the flux gate of "Back to the Future" fame? One name for the remote compass transmitter is a flux gate valve, so now you can bore people with this fact everytime you're rewatching that movie. ;)

[PeterP]

Now I feel even dumper as before ;) , but to the rescue there is the WWW!

 

 

A good read (with lots of pictures!!:))about the various direction instruments, the Dip error and also the Flux-valve:

http://www.americanflyers.net/aviationlibrary/instrument_flying_handbook/chapter_3.htm

 

 

 

So the question is still : What did they had in mind when they modelled this behaviour we see in the Sim ?

 

...

I have a slight guess, but this time I will shut up. The past showed me that it is not advisable to speak before my brain is still working at the answer.:)

Edited May 17, 2012 by PeterP

[flightace37]

I suspect it's modeled as a wet compass in the wing, transmitting signal to the remote compass indicator. Looking into the specifics in the PTM now.

 

EDIT: Reading done.

 

The remote indicator compass used on P-51D's replaces the conventional magnetic compass' date=' although on late series airplanes a direct-reading, standby magnetic compass is also provided. The remote compass unit is in the left wingtip and transmits its readings electrically to an indicator on the instrument panel. [b']This type of compass doesn't float around and fluctuate when the plane maneuvers, and it gives you all the advantages of a directional gyro without the precession inevitable in the directional gyro...[/b]

 

I added the bold because I like to give context around the relevant quote.

 

So this is supposed to be the first evolution of our modern remote compass systems. There's no indication of how the remote compass unit itself is supposed to work, but the text does claim that it shouldn't be affected by maneuvering fluctuations. There's a number of ways to accomplish this, but I'm not going to speculate on which one the aircraft really uses, without appropriate documentation. Maybe the repair manual will have something to say.

Edited May 17, 2012 by flightace37

[flightace37]

I found the section discussing the remote indicator compass in the maintenance manual, starting on page 248, and ending on page 253. Model AN5730-6.

 

It seems the remote indicator is used primarily to avoid the detrimental effects of armor plate.

 

The transmission of the magnetic indications of the compass to the indicator is entirely electrical' date=' the only rotating parts in the system being the compass float and the indicator rotors.[/quote']

 

So it would seem to me that the RCU is actually a standard floating compass, prone to the same set of problems. The question is, is it mounted on some sort of gimbal to keep it level and compensate for accelerations?