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  History of the T&B and Turn Coordinator (Stop the Turn & You Will Survive)

The History of the Turn & Bank and Turn Coordinator, as written by Old Bob, Beechcraft Maven and Ancient Aviator.



Old Bob 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 NTSB Report & Carnahan NTSB Report


Here is 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 other.


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.



Old Bob



Bob Siegfried

Ancient Aviator

(630) 985-8502

Stearman N3977A

Brookeridge Air Park LL22





  History of the Jeppesen Approach Plates


The History of the Jeppesen approach plate, as written by Old Bob, 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 Jeppesen charts.


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!


Happy Skies,


Old Bob



Bob Siegfried

Ancient Aviator

(630) 985-8502

Stearman N3977A

Brookeridge Air Park LL22


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