Simple string used as artificial horizon?

On Dec 29, 6:48*am, T8 wrote:
On Dec 29, 9:24*am, Andy wrote:





On Dec 29, 6:55*am, Bruno wrote:

I had a very interesting conversation yesterday with *a very
experienced pilot (older) who has spent a lot of time in some amazing
aircraft starting with the P51 Mustang and going up to jets including
the SR-71 blackbird and as we were looking over my glider we started
talking about the yaw string on the canopy.

He then mentioned that way back in the early days of flying they would
simply tape a string hanging from the ceiling to act as an artificial
horizon. *I've never heard this one before! *Next person who reads
this who goes up tape a string hanging from the inside of the canopy
and tell us how it works. *Now you have another reason to take off
work and go soaring.

Bruno -B4http://www.youtube.com/user/bviv

It's not April 1 already is it?

Just put a mark on your canopy and spit at it. *If spit flies left of
target, you are turning right and vice versa.

-T8- Hide quoted text -

- Show quoted text -

That'd work, except for one thing: If I'm in a situation requiring
that trick, my mouth is probably going to be too dry to spit!

On Dec 29, 9:59*pm, Darryl Ramm wrote:
On Dec 29, 4:28*pm, brian whatcott wrote:

Andy wrote:
Anything hanging in the cockpit like a pendulum (or any instruments
working on the same principle) DOES NOT tell you which way is up./snip/
9B

If you are going to take on the school master role, you had better be
right. Current solid state angular rate sensors act like a mini pendulum
or tuning fork - when *turned, the pendulum retains spatial inertia.
Foucault, an' all that. Remember?

Brian W

That has zero practical relevance. I'll leave the school master stuff
to Andy (and here I was thinking he's a management consultant with a
masters in aeronautical engineering), anyhow I managed to waste part
of my life working on precision sensors for general relativity physics
experiments. MEMS rate based devices like tuning fork designs etc.
vibrate many orders of magnitude above the signal frequency. Hanging a
weight on an about a foot long string will give a resonant period of
about one second. For movement of the aircraft that happen of order
~seconds the mass on a string is essentially a plumb-bob and the
"pendulum" will be perturbed. Again a focualt pendulum is oscillating
in it's inertial frame with a resonant frequency orders of magnitude
above above any signal frequency (the earth's rotation).

---

The pendulum in the cockpit is one of the most goofball things I've
heard in a while. On the other hand the cat idea has promise. The cat
also has the benefit of being an amusing companion in the event of a
landout, or a nutritious food source in the event of a more serious
survival situation. But unfortunately until I I can overcome my cat
allergy it's a plain old (non-edible) T&B backup for me.


I stand by my original statement. Sorry if it sounded like a school
master. Even if you had a pendulum at a high frequency - tuning fork
style - I don't believe it would be able to tell you anything about
whether you are right side up. It would only tell you about your
angular rotation about the axis along the "string" line. You could do
a roll to inverted and it wouldn't indicate anything different (ok,
the string would go limp I guess if you weren't pulling Gs).

To determine definitively an aircraft's attitude you need to be able
to measure or estimate the three Euler angles that define the
rotations about all three axes. To do this with a tuning fork/pendulum
thingy you need to measure all three angular rates and integrate (in a
calculus sense) them over time from a known, generally non-rotating,
starting point. Over time, depending on the precision of the
instrument, the integrated values will drift off of the actual angles
- this is why inertial reference platforms need to be aligned prior to
flight.

Again, the string without a weight on it will tell you zip about
aircraft attitude. The swinging pendulum might, in calm air, be able
to pick up some gradual heading changes, but so will a compass or a
GPS and I'd trust both of those a lot better than a string.

I will give the jellied cat a try. I have not tried the benign spiral
in my -27B, sounds like I should try that too. I have tried about
everything else:

http://www.youtube.com/watch?v=9aDJLDQ-5QU

9B

Andy wrote:
/snip/ Even if you had a pendulum at a high frequency - tuning fork
style - I don't believe it would be able to tell you anything about
whether you are right side up. /snip/


I need first to ask you to look for some observable change in a swinging
half second pendulum when you hold it at waist level and turn in place.
See it?

Then suppose one concedes that a swinging pendulum can act like a
rubbish single gyroscope: do you think that pilots have maintained their
composure with a turn and slip in clouds at all?
They certainly used to do something of the kind with what was called a
'limited panel'.

If you find this somewhat plausible so far, then tell me: how many gyros
are there in a turn and slip?

(It's so much fun argued against what everybody KNOWS ain't so!)

OK if you are still finding this slightly plausible, then perhaps you
can give a little more credit to a great name in aviation, as I do....

Regards

Brian W

Most have probably heard this before but an instrument rating will
significantly improve your flying even if you never use it to fly in
clouds.

I think it really benefits a soaring pilot because the instrument
student must learn a REALLY precise flying technique while learning to
form a mental picture of his surroundings without using his vision -
that really helps centering thermals. He must also learn and
understand exactly how pitch and bank relate to airspeed and rate of
turn. Beyond flying technique, you'll learn the air traffic system
which in itself can be a lifesaver.

An instrument rating isn't inexpensive or easy to get. It's not even
possible to train in a glider - it has to be earned in an airplane.
Once you have the rating, it can be used in a glider. Then, a turn
and bank will get you down through an undercast.

Even if a PP SEL Instrument rating doesn't interest you, even a few
hours with a CFII learning attitude control in a light plane will help.

On Dec 30, 9:58*am, brian whatcott wrote:
Andy wrote:
/snip/ *Even if you had a pendulum at a high frequency - tuning fork
style - I don't believe it would be able to tell you anything about
whether you are right side up. /snip/

I need first to ask you to look for some observable change in a swinging
half second pendulum when you hold it at waist level and turn in place.
See it?

Then suppose one concedes that a swinging pendulum can act like a
rubbish single gyroscope: do you think that pilots have maintained their
composure with a turn and slip in clouds at all?
They certainly used to do something of the kind with what was called a
'limited panel'.

If you find this somewhat plausible so far, then tell me: how many gyros
are there in a turn and slip?

(It's so much fun argued against what everybody KNOWS ain't so!)

OK if you are still finding this slightly plausible, then perhaps you
can give a little more credit to a great name in aviation, as I do....

Regards

Brian W

Sorry, you lost me at the first syllable - and the other syllables
didn't help.

9B