Origin of Rates of Turn on the Turn & Bank Indicator

[Centaurus]

The origin of Rate One, Two, Three, and Four turns on the Turn and Bank Indicator is explained in an old book called "Air Training Manual" - A Practical Guide to Aero-Engine Aircraft, Construction, Wireless and Electricity and Air Navigation for Members of the Air Training Corps and all interested in modern aeronautics. My guess it was published around 1937.

Now I must admit I thought it was merely a question of halving each figure eg Rate One takes two minutes to fly 360 degrees, Rate Two takes one minute, Rate Three takes 30 seconds and Rate Four takes 15 seconds.

The old Turn and Bank Indicators included an arbitrary scale up to Rate Four. Those of you that flew Tiger Moths and wartime aircraft will have used that instrument.

However on reading page 130 of the Air Training Manual under the chapter called Aircraft Instruments, it states "An arbitrary scale, numbered 1,2,3,4 to right and left, means that at Rate 1 a complete circle would be executed in 2 minutes, at Rate 2 in one minute, at Rate 3 in 32 seconds and at Rate 4 in 20 seconds."

My question is this: The rates of Turn at Rate 3 and Rate 4 are obviously not in proportion to rate 1 and 2. Why 32 seconds and 20 seconds respectively when one would have thought it would be 30 seconds and 15 seconds respectively for Rate 3 and 4?

[sycamore]

I always thought that the higher rates were simple increments of Rate 1;ie R1=3*/sec;R2=6*/sec,R3=9*/sec,R4-12*.sec,giving times for 360* of 2min,1 min ,40 secs , and 30 secs.However ,reading my copy of AP2095 Pilot`s Notes (General) (mandatory reading with a flashlight ,under the bedsheets),it says that the Instrument calibration tolerance allowed was from 157* to183* per minute for RateOne standard turns..Later on it states that `Later instruments accuracy at the higher rates has been sacrificed to achieve a `closer approximation to a 180*turn in one minute at an indicated Rate One`...
Seem to remember that the instrument is calibrated checked on a `turntable` either manually,or electrically rotated.
Of course,in flight one can only achieve the higher rates at bank angles of 35-40 *,unless one is in a helo,but helos don`t usually have T & Ss,as there`s usually to many vibes; but as the calibration was carried out on the level,there is now the element of `G` to consider,causing an over-reading of ROT(i think..!)and cannot be relied upon....

[Lordflasheart]

From AP129 6th Edition, August 1954 ... Vol 1, Part 2 Sect 1 Chapter 2

Turn and Slip Indicators

Referring to the Type B Mk. 1A it says "In British instruments this scale usually reads from 1 to 4 ....."

Referring to the Type TN300, under "Pilot's serviceability checks" it says "In the air the aircraft should turn through 180 deg in one minute with the turn indicator indicating a Rate One turn."

These models both show the turn needle at the bottom of the gauge and side slip pointer at the top.

The first real reference in this chapter to rates of turn and numbers comes in para 20 - "the Mk 1B is a later design ..." NB This page is annotated AL4 May 1955.

The Mk 1B shows the turn needle at the top and a ball-in-tube slip inclinometer below.

Seemingly referring only to the Mk 1B it continues at para 25 ....

"Use in Flight.
It should be noted that the calibration marks are Rates 1, 2, and 3, left and right, representing 180deg, 360 deg and 540 deg per minute respectively. The instrument is calibrated at the banked positions corresponding to a TAS of 260 knots. At any other airspeed there will be errors, but these do not exceed 5% at any airspeed between 85 and 350 knots."

From my experience this is a subject best left to A1 QFIs. Even then the number of different explanations will likely be equal to the number of A1s present.



Hope this helps. LFH

[GQ2]

Many people will remember the old Air Ministry T&S Mk1A, which was used from the late 1930 until it began to be gradually supplanted after the war. What many folks are not aware of, is that there was originally a Mk1 in service in the 1930's. This is almost indistinguishable to look at, but was withdrawn, as a decision was made at a high level to recalibrate them when the official 'Rates' were redefined.
Quite why this took place I can't recall, but buried away, I do have a number of the earlier type Mk1. I also recall there was mention of this recalibration with appropriate warnings to engineers and airmen in the literature of the time, which although I have it somewhere is not to hand. I seem to recall that the changeover was about 1937. March rings a bell. I presume that many of the Mk1's were rebuilt to the new Mk1A standard. (Equally, I think many escaped the net, and, since the difference was not that obvious, carried-on being used anyway..!)
If anyone knows exactly why this all took place, I'd be most fascinated to hear...! :)

[Brian Abraham]

Don't know if these may be of interest Centaurus.

http://www.flightglobal.com/pdfarchive/view/1925/1925%20-%200377.html" (http://www.flightglobal.com/pdfarchive/view/1925/1925%20-%200377.html)

http://www.flightglobal.com/pdfarchive/view/1935/1935%20-%200087.html" (http://www.flightglobal.com/pdfarchive/view/1935/1935%20-%200087.html)

[Centaurus]

Thanks for the replies to date. Fascinating history. I recall under the hood limited panel (AH and DG caged) spinning in Wirraways. The turn part of the instrument would be hard over against the stops (?) in the direction of the spin while the balance needle or ball was hard over to the opposite direction to the turn. On the hoarse command of "RECOVER" by the QFI in the back seat, the student would apply full rudder opposite to the direction of turn at the same time steadily ease the stick forward to unstall the wing. Then eyes glued to the turn needle you watched it until it suddenly moved from hard over towards the other side. As the turn needle passed central (no turn) you rapidly centred the rudder pedals and started the pull out. Same technique whether a Wirraway, Tiger Moth or Vampire.

You had to be careful though. If there was slight bank on while pulling out, the "G" would act on the now slightly offset turn needle dragging it further off centre thereby making the instrument interpretation more tricky. The thing to do then was to unload by relaxing the back pressure on the stick and the turn needle would take up the true position which could be a turn.

Good fun and marvellous training for the times when an AH would topple beyond 55 degrees angle of bank in an unusual attitude. That stuff and the old CFS instrument rating test trick flying in Dakotas of asymmetric, limited panel Aurul Null NDB approach under the hood, was considered normal training then - despite the fact the statistical chances of all that happening at the same time was probably zero - thank goodness:ok:

[teeteringhead]

Centaurus

My guess it was published around 1937.
... if it mentions the Air Training Corps, it would have to be a few years later than that.

The Air Training Corps (ATC) was formed on 1st February 1941, from the similar previous organisation known as the Air Defence Cadet Corps (ADCC).

[Centaurus]

The Air Training Corps (ATC) was formed on 1st February 1941

Good point. I could not find any date in the front of the book so decided to be a bit too conservative.