The History of the Turn & Bank and Turn Coordinator, as written by
Beechcraft Maven and Ancient Aviator.
wants us all to remember this: "If we stop the turn, we will survive."
My editorial Comment: No
matter what turn indicating electric gyro you use in your plane, have your
partial panel/instrument scan game in good shape. IMHO, Carnahan and Kennedy did not and they
and their passengers paid a terrible price for this lack of proficiency. Here
are the Kennedy
Report & Carnahan
Old Bob's history lesson:
The T&B dates from World War I days. It is a
gyroscope mounted level to the aircraft's longitudinal axis so that any time
the aircraft turns, a needle will be displaced. Some of the very early turn
needles were hinged at the top. Others were hinged at the bottom, but in
either case, the gyro was only sensitive to left or right motion. It was not
affected by pitch or by roll. Sometime between the two World Wars, the
inclinometer was added to the instrument and most manufacturers hinged the
needle at the bottom. With the addition of the inclinometer, it became
commonly known as the Turn and Bank. It didn't show the bank directly, but the
ball (inclinometer) would indicate a slip or skid as appropriate.
During and just after WWII most T&Bs were
made more sensitive and little dog houses were added on each side of the
previous single indicator to show a standard rate turn of three degrees per
second. To get a standard rate turn on an instrument that only had the single
indicator at the top, the aircraft was flown so that the side of the needle
just touched the one and only "dog house". The new style was called a double
needle width T&B. It was noted that if the instrument was not mounted square
to the longitudinal axis of the aircraft, inaccuracies were induced which
could make the needle wiggle when it should not. As an example, if the
instrument panel was angled such that the top of the panel was forward of the
bottom, the instrument would show a yaw in the wrong direction each time that
the aircraft wing was displaced up or down. If the instrument panel was angled
the other way, (I cannot imagine that ever happened) it would show a yaw in
the direction the airplane was rolling.
In either case, it was considered important
that the instrument be mounted so that it's gyroscope unit was as parallel to
the longitudinal axis of the aircraft's motion as was possible. Some very
smart engineer realized that if the gyroscope was mounted so that the front
end was higher than the rear of the instrument, it would indicate a yaw any
time the aircraft was rolled and that once it was in a stable turn it would
then indicate the actual yaw being developed by the turn.
He decided to use that effect as the basis
for an economical autopilot. Several other autopilot engineers jumped on the
idea and a standard T&B instrument mounted with the front end thirty to
forty-five degrees up in the air was used in several early light plane auto
pilots to provide sensing. There was no indication given to the pilot. It
seemed like a very good idea because if you roll, it is a good chance that the
airplane will soon be turning. After the use of a canted gyro for a low cost
autopilot had become firmly established, somebody came up with the idea that a
human pilot could benefit from that early indication of a roll just as did the
autopilot. That was when the Turn Coordinator style of indication was born.
It consists of a gyroscope mounted with the
front end higher than the rear and it will show roll as soon as it develops
and will also show yaw. What that means is that you cannot tell just by
looking at the instrument whether it is showing roll or yaw, you have to
integrate with other instrumentation to tell what is happening.
At first, it seemed like a very good idea
and most of us embraced it's use. For the reasons I have mentioned so very
often, many of us became disenchanted with the presentation. I still think it
is a good sensor for a cheap autopilot. A true attitude based autopilot will
work better, but a well damped canted gyro that is fed through a good
electronic balancing device to direct the servos will work adequately. That is
what S-Tec uses. They have been very successful in that regard. Not as good as
an attitude based unit, but more than adequate for the purpose.
More than you ever wanted to know, but that
is the history. What it means to you is that anytime the little wing on the TC
drops, you are either yawing or rolling. You cannot tell which just by looking
at the instrument. Once the aircraft is in a steady, non-rolling turn, the
instrument will be showing only yaw. If you fly a knife edge and look at the
TC it will show a wings level attitude. Obviously that is wrong, but it is
doing exactly what it should do. You are neither rolling nor yawing during a
knife edge. It is showing that you are neither rolling nor yawing. I think
that is what confuses people. The instrument cannot tell the difference
between a roll and a yaw.
For an autopilot that works just fine. It
never has to think. For we human beings, it takes more evaluation and
interpretation than some of us care to use. I think the TC should be removed
from the pilots primary scan and used only for what it does best. Drive a low
cost autopilot. If that is more confusing than informative, I apologize, but I
would be happy to answer further questions.
Here is Old Bob's discussion of the Turn &
Bank (T&B) instrument:
The T&B is undoubtedly the most reliable of the ancient
mechanical instruments, It is also the lightest and cheapest. It can be used to
recover from a spin while in cloud and it works very well when upside down. It
works in relation to acceleration forces as well as gravity.
However, the greatest benefit from the T&B will be realized if
it is retained in ones everyday scan. Those of us who learned to fly IFR in the
far distant past were taught to check for rate of turn as well as attitude.
Remember, the FAA says that all approach maneuvering is
supposed to be conducted at a rate of at least three degrees per second so as to
remain within the protected air space. If the bank angle needed to get three
degrees per second is greater than thirty degrees of bank due to higher speeds
involved, the protected area is increased or the procedure is restricted to
slower aircraft, Category A, B, C, etc. for approaches or speed limited holding
procedures as examples. The inclusion of a rate instrument in every scan gives
us a continuous check on our roll instrumentation quality.
Lets say that you have two attitude gyros placed side by side.
You could get them both included in every scan fairly easily, but there would be
no trigger for you to look at both other than as a redundancy check. However, if
as you roll into a twenty degree bank for a procedure turn, you also check the
T&B for proper rate you are automatically checking each instrument against the
Back to the dual attitude gyro. If one is failing. it rarely
gives you a flag, it generally will just get the "leans". How do you decide
which has failed? Most of us will decide based on some sort of rate indication .
Most often it will be a compass, but we need to have something stable to be able
to read a magnetic compass. Fortunately a gyro compass will allow a good
evaluation of rate.
Admittedly, I am a very old individual and I did learn to fly
IFR using only the needle ball and airspeed. Hard to teach an old dog new
tricks! I do lean heavily on an attitude gyro for normal flight these days, but
I try very hard to include rate information in every scan of the panel. I find
it much easier to check the rate by using a turn needle than any other
instrument I have used.
I am confident that some little "glass" instrument could be
made that would give us rate easily, cheaply, and reliably, but no one seems
prone to tackle that task.
Brookeridge Air Park LL22
of the Jeppesen Approach Plates
The History of the Jeppesen approach plate, as written by
Beechcraft Maven and Ancient Aviator on 11 January, 2010:
Having been using Jeppesen products
continuously since May of 1951, I find it very hard to change. Before that, I
had used the written version as published in the AIM. I do agree that the price
of using their product is very high. Unfortunately, folks who use NACO on
various computers still seem to have difficulty even when those users are
comfortable computer users. I will gladly pay fifteen hundred bucks for a device
that allows me to read approach charts as easily as I can use paper charts.
I am not anxious to learn to use the NACO
offering, but I would do that if there is a financial advantage to doing so.
However, convenience of use is more important than price so if I need to be a
computer whiz to operate the reader, it won't do what I need done. I do realize
that part of my continued use of Jeppesen is because I lived through the days
when our benevolent government did it's best to put Jeppesen out of business.
I may have a few details wrong. If so, those of you who know
better, please correct my memory.
Initially, all approach procedures were written. All
approaches were in the Airman's Information Manual which was published every 56
days and sold for a couple of bucks. There were no drawings. Captain Jeppesen
was one of us who liked looking at a picture better than reading the written
word and trying to visualize how the approach was to be conducted. He drew
sketches in a note book to aid his execution of an approach.
Other pilots saw what he was using and asked
if they could get copies of his drawings. Capt Jepp obliged by cranking out
copies on a hand operated mimeograph machine. Printed Jeppesen charts evolved
from that start.
As the years went by, almost all professional
pilots adopted the Jeppesen format. The U. S. Navy actually subscribed to
Jeppesen for their approach charts. Toward the end of WWII, the army started to
print a similar chart for the use of Army Aviators. They were on eight and a
half by eleven sheets of paper. Sure were easy to read! Not the handiest thing
in the world to have in a small cockpit.
In the late fifties, the government started to
print their own version of Jeppesen's approach charts. The cost was about the
same as Jeppesen was charging. Hardly anyone used the government charts and
almost all professionals and the U S Navy continued to use Jepp charts. The
government then decided that all approach charts had to be approved for use by
the FAA and they refused to approve the Jeppesen Charts. Jeppesen went to the
courts. After a couple of years, they managed to force the FAA to approve
Jeppesen's charts for our use. The government did force the Navy to give up
After the courts forced the FAA to approve
Jepp charts, the government cut the price of their charts about in half. The
competition that was supplied by Jeppesen is the only reason the NACO charts are
as cheap as they are. Were it not for Jeppesen, the NACO charts would likely
cost twice what Jeppesen now charges. Were the NACO charts not cheaper than
Jepps, how many of you would be using them?
When I was learning to fly, Sectional charts
sold for twenty-five cents. The local FBO paid fifteen cents a copy and was
authorized to sell them for a quarter. The dime was his profit. The last time I
looked, sectional charts were around $7.50 apiece. That is 30 times what they
sold for in 1946 and I will guarantee the FBO is NOT making three bucks off each
one he sells. Inflation has not equaled that increase in price. Were it not for
the competition given to the government by Jeppesen, how much do you think we
would be paying for NACO charts?
I think the competition given NACO by Jeppesen
is holding down the price. If another supplier beats the Jeppesen price while
delivering equivalent quality, Jeppesen will either cut their price or get out
of business. I hate paying current Jeppesen prices, but I am convinced we would
be paying NACO more for their product than we now pay for Jepps if it were not
for the competition provided by Jeppesen.
If Jeppesen is so overpriced, how come no one
else is giving them competition?
Happy to hear the opinion of others, but based
on the history I observed, I like Jeppesen!
Brookeridge Air Park LL22