Vib Gauge - what is a mil?

[Iflyamouse]

Jet engines typically have a vib gauge of some kind that measures vibration in 'mils'. I know we're measuing the amount of vibration, but what exactly is a 'mil'? Millimeters out of tolerance? Is is measured on the shaft, on the fan, does it matter where it's measured?

The Vib gauge for the CF34's in the CRJ200 turn amber at 2.7 mils N1, while the N2 gets a VIB icon at 1.7 mils. What exactly is this telling me if I get one of these indications?

Thanks in advance.

 

[ackattacker]

There are many ways to measure vibration, but "mils" is simple displacement ("amplitude"). A mil is 1/1000 of an inch. It is probably measured at the shaft, but I don't know for sure.

 

[Wiggums]

I vote that they remove units from all the indicators. If it's in the yellow or red you call MX. Then I could spend my time working on stuff more useful, like figuring out if I should be watching NBC or CBS tonight.

 

[erj-145mech]

Yeah, if you can't deal with the numbers, we'll just put in an idiot light for the vibes. And while we're at it, we should take out the airspeed indicator too, and replace that with a couple of idiot lights. One red one for when you're too slow, and a green one for when you're faster than the red one is set for.

Now you can sit back and enjoy the USA Today from the hotel.

 

[mynameisjim]

And while we're at it, we should take out the airspeed indicator too, and replace that with a couple of idiot lights. One red one for when you're too slow, and a green one for when you're faster than the red one is set for.

Don't a lot of high performace military aircraft have lights for airspeed, or rather AOA?

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I've seen it in video games, so it must be true

 

[Gatorman]

There are many ways to measure vibration, but "mils" is simple displacement ("amplitude"). A mil is 1/1000 of an inch. It is probably measured at the shaft, but I don't know for sure.

You are correct, sir.
There are actually two transmitters that consist of a stack of piezo electric crystalline creamic elements which generate an electrical signal proportional to the intensity of the engine vibration. The signal is then converted by the signal conditioner in to DC voltages, suitable fot transmission into the Engine Vibration Monitoring panel.

The instrument actually says MILS DA (double amplitude)

But what really kicks arse is that pilot actually posted a mechanical question on the mechanic's board and not the gah-zillion other pilot boards and got totally flamed for it.

 

[Gorilla]

Don't a lot of high performace military aircraft have lights for airspeed, or rather AOA?

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I've seen it in video games, so it must be true

Yes, this is true. When you're at 8 or 9G and trying to stay conscious AND kill the other SOB, big lights are easier to use than a round guage.

Far more useful though are airframe rumblings. A good fighter talks to you. At optimum AOA, which is the best place to keep the jet for a sustained fight, you'll feel a nice, even rumbling vibration. Lower the AOA, it'll smooth out. Higher AOA, and the light rumblings turn into elephants dancing on the wings. This worked great for the F-4 and F-15, regardless of airspeed and G-load.

 

[propsarebest]

I vote that they remove units from all the indicators. If it's in the yellow or red you call MX. Then I could spend my time working on stuff more useful, like figuring out if I should be watching NBC or CBS tonight.

Eurocopter does that on their new helos, its a simple dial that goes from 1 to 10, and it only displays whatever paramater is closest to the "redline". Works GREAT.

 

[Coool Hand Luke]

Eurocopter does that on their new helos, its a simple dial that goes from 1 to 10, and it only displays whatever paramater is closest to the "redline". Works GREAT.

Yet another reason to fly BELL HELICOPTER(S). #1 in vertical lift. (unless of course you like being second all the time).

 

[FlyFlyFly]

I thought 1 mil was a measure of angle as in 1 mil is 1/6400 of a circle, like 1 degree is 1/360 of a circle.