Gun vibration & standby compass

If you check out this video at 7:30 in an A-10C cockpit as the gun fires the vibration causes the standby compass to swirl around. I think it would be nice to see this effect in the sim.

The gun itself doesn't cause it. Deceleration causes it.

Funny, because acceleration does affect the whiskey compass (it will tilt and swing on the takeoff roll.)

Deceleration causes it.

Do you mean recoil???

There's a certain negative thrust associated with the gun firing. Accelerations cause compass errors as you can see with every turn, pitch up/down, etc. in that video.

But the "whiskey" compass alcohol fluid is absolutely being vibrated by the gun firing. Bubbles are produced by vigorous vibration. It's almost like there's not enough fluid in the instrument. You can't fill a sealed casing 100% with an incompressible fluid or bad things happen but it didn't need to be that empty.

It'd be a cool visual effect to model in the sim.

If you check out this video at 7:30 in an A-10C cockpit as the gun fires the vibration causes the standby compass to swirl around. I think it would be nice to see this effect in the sim.

Been looking for a mod to do the same thing since I first saw that video.

Always felt the Cannon was lackluster compared to the visceral experience it appears to be irl.

Vibration causes the compass to spin. Something worth noting in the video is that you can see the miniscus at the top of the compass fluid, so the compass has been leaking and isn't all the way full like it should be. This is one sure way we have of checking to see if a compass is completely empty of fluid. We tap on the compass housing, and if the card spins, the compass needs to be overhauled. Ideally, when a compass is overhauled and refilled, the refilling is done by completely submerging the compass in a clean container of compass fluid. The compass is then rotated and rolled over and checked/rechecked for air bubbles to show up behind the glass to chase any residual air out of the fluid. Once we see no bubbles, the filler cap is installed while the compass is still submerged. There is a rubber diaphragm in the back of the Airpath compasses which compensates for changes in air pressure. So, as long as the integrity of the seals on the compass is good, there should be no air inside it to cause foaming. The fluid is there to keep the compass from being affected by vibration. The gun on the A-10 will vibrate it enough to cause it to move, but it won't spin if the case is completely filled.

Vibration causes the compass to spin. Something worth noting in the video is that you can see the miniscus at the top of the compass fluid, so the compass has been leaking .....

Thank you for the detailed explanation :thumbup:

No problem! :D

Vibration causes the compass to spin. ... but it won't spin if the case is completely filled.

Thank you for the detailed explanation

+1 awesome!

Ideally, when a compass is overhauled and refilled, the refilling is done by completely submerging the compass in a clean container of compass fluid.

Ok now the Million Dollar question...what is "Clean Compass Fluid"? We always called them Whiskey Compasses...but I doubt that's what they are filled with now.

Great explanation.

Ok now the Million Dollar question...what is "Clean Compass Fluid"? We always called them Whiskey Compasses...but I doubt that's what they are filled with now.

 

Great explanation.

Its an isoalkane, and the used compass fluid I found makes a great brush cleaner for enamel model paints. Its also great at removing every last bit of oil and moisture in the skin on your hands, so you have to wear gloves when filling the compass, or walk around with ghost white hands the rest of the day. As far as that goes, you should go with vinyl gloves instead of the usual latex. The isoalkanes break down latex pretty quickly. I generally haven't done compass overhauls in a really long time. The parts cost and time involved isn't cost effective any more for something that costs about 200 bucks brand new. We generally just replace the compass. If you move the compensator from the old one to the new one, compass swings usually go pretty quickly. If you manage to get a compass where the seals last long enough, over time, the isoalkane will start getting a brownish tint to it, so it will even start to look like whiskey. I think it might even be fermenting in there, because when it turns brown it starts to smell pretty bad.

Here's an MSDS for the stuff if anybody is interested in that kind of thing. :book:

https://www.mach-dynamics.com/sds/sds_712392632607.pdf

I saw this video the other day and noticed the compass thing. I though, naaaah no one will pick that up and ask for that to be implemented knowing how much detail some people demand in this thing we do and here I am seeing it on this forum. Ha ha ha words fail me.

It was a misunderstanding of a pretty significant visual event going on in that cockpit. The OP appears to be satisfied with the explanation of what was going on, and others who were interested gained some real world insight. The video made me curious about whether or not vibration effects on the compass are modeled, and they are. The compass card moves the appropriate amount with gun vibration, for a properly filled compass. Its not something everybody is interested in, but I'm sure those people just said to themselves "I have no interest in that" and silently moved on to other topics they do have an interest in. ;)

Its an isoalkane, [...]

Another great explanation, thank you very much! :thumbup:

Very cool!