Mounting Instruments with Lock Washers???

Now, I have mounted many instruments with their accompanying brass
screws and never used lock washers. Then a friend asked why not? I
opened my mouth to spout the obvious answer, but no sound came out. I
realized that I have never used lock washers, never seen them used,
and have never seen a loose instrument. Hmmmmm.

- Lock washers are used everywhere when vibration is an issue.
- An airplane is certainly a vibration prone environment.

So I hazarded these ideas;

- The screws, and nut, are (non-magnetic) brass and somehow brass
stays "stuck" better because brass is softer than steel.
- A brass lock washer wouldn't keep its "bite" as it would flatten
over time.
- I don't have any more good ideas.

So, why is it that we never use lock washers when mounting
instruments? And why don't the instruments vibrate loose? Please
keep the answer this side of a physics lecture.

Thanks, John

On Mar 17, 5:42*am, ContestID67 wrote:
Now, I have mounted many instruments with their accompanying brass
screws and never used lock washers. *Then a friend asked why not? *I
opened my mouth to spout the obvious answer, but no sound came out. *I
realized that I have never used lock washers, never seen them used,
and have never seen a loose instrument. *Hmmmmm.

- Lock washers are used everywhere when vibration is an issue.
- An airplane is certainly a vibration prone environment.

So I hazarded these ideas;

- The screws, and nut, are (non-magnetic) brass and somehow brass
stays "stuck" better because brass is softer than steel.
- A brass lock washer wouldn't keep its "bite" as it would flatten
over time.
- I don't have any more good ideas.

So, why is it that we never use lock washers when mounting
instruments? * And why don't the instruments vibrate loose? *Please
keep the answer this side of a physics lecture.

Thanks, John

They don't vibrate loose because there is no vibration! Without the
engine there are no serious vibrations except when rolling on a rough
surface.

In most of the power plane installations I've seen they use a brass
nut-clip that fits into the back of each instrument hole and IS a lock
nut.

In my Grob the nuts used on the instruments are plastic insert lock
nuts. That's the way it came to me.

Mike

instruments? * And why don't the instruments vibrate loose? *Please
keep the answer this side of a physics lecture.

They don't vibrate loose because there is no vibration! Without the
engine there are no serious vibrations except when rolling on a rough
surface.

I wouldn't be so sure about the "don't vibrate loose" part. On all
three gliders I've owned, two new, instrument screws have slowly
backed out. Eventually you will see empty holes in the panel and hear
funny rattling noises under the seat pan. (Don't ask how I know!)
Checking instrument screws, the screws that hold the glare shield in
place and so forth has become part of my annual.

John Cochrane

Coriolis effect: http://en.wikipedia.org/wiki/Coriolis_effect

And snapping smartly into left hand thermals keeps them tight. You
have been doing that I hope?




So, why is it that we never use lock washers when mounting
instruments? And why don't the instruments vibrate loose? Please
keep the answer this side of a physics lecture.

Thanks, John

wrote in message
...
Coriolis effect: http://en.wikipedia.org/wiki/Coriolis_effect

And snapping smartly into left hand thermals keeps them tight. You
have been doing that I hope?



Finally an answer that makes sense! Thank you, thank you, thank you! For
years I've been wondering and now I know why. Once all my instruments fell
out when I snapped smartly into a right hand thermal - - had me baffled.

bumper

You only had to ask! ;-)

Bob

And snapping smartly into left hand thermals keeps them tight. You
have been doing that I hope?

Finally an answer that makes sense! Thank you, thank you, thank you! For
years I've been wondering and now I know why. Once all my instruments fell
out when I snapped smartly into a right hand thermal - - had me baffled.

bumper

On Mar 17, 10:05*am, "bumper" wrote:


Finally an answer that makes sense! Thank you, thank you, thank
you!


This is also the reason captive nuts are common in instruments.
Without them the nuts would loosen for thermal entries one way, and
the screws would loosen if you turned the other way. Good pilots
just adapt and fly fast without turning. Less adept pilots resort to
loctite, stiffnuts, or periodic security checks.

Andy

On 17 Mar, 19:06, Andy wrote:
On Mar 17, 10:05 am, "bumper" wrote:

Finally an answer that makes sense! Thank you, thank you, thank
you!

This is also the reason captive nuts are common in instruments.
Without them the nuts would loosen for thermal entries one way, and
the screws would loosen if you turned the other way. Good pilots
just adapt and fly fast without turning. Less adept pilots resort to
loctite, stiffnuts, or periodic security checks.

Andy

Ever heard of Loctite?

bumper wrote:

Once all my instruments fell
out when I snapped smartly into a right hand thermal - - had me baffled.

Actually, this is the reason why I finally stopped to thermal
alltogether. Since I've started to just fly straight, not only my
instruments stay in place, but as a side effect I also happen to fly faster.

On Mar 17, 12:54 pm, nimbusgb wrote:
On 17 Mar, 19:06, Andy wrote:
...Less adept pilots resort to loctite, stiffnuts, or periodic
security checks...

Ever heard of Loctite?

Well, he _did_ mention it in the quoted post...

Bob K.