Flight safety and technical subjects for pilots to read during lockdown tea and biscuits.
Time for a nice cup of tea, a biscuit and another light read. However, you might need a very large pot of tea and a packet of biscuits for this one!!!!
The engine governor in the R22 and R44
Before I try and explain, simply, how the engine governor works, let me take you to two areas within the relevant POH.
Page 2-5 for example of the R44 POH:
‘Flight is prohibited with the governor selected off, with the exception of in-flight system malfunction or emergency procedure training’.
This paragraph is often used by flight instructors who have no manual throttle manipulation skills themselves (as they have never been taught the skill) to get out of teaching manual throttle manipulation skills to their students.
‘System malfunction’ means the pilot should be able to fly the aircraft safely and competently without the governor.
‘Emergency procedure training’ for example, means that the pilot should be able to safely and competently recover from low/high rotor RPM situations and correct power/rpm changes.
Both the above require competent throttle skills to do so.
Page 7-6 for example in the R44 POH:
‘The governor is designed to assist in controlling RPM under normal conditions’
Please note the word ‘assist’ (to support, to take action and support) which means you, the pilot, are required to be the primary throttle control and therefore need to be fully able to manually control the RPM, which means you must have the skill be able to do so. The governor is there to ‘assist you’.
In my very humble opinion, the above means that instructors should properly and comprehensively teach manual throttle manipulation skills as the throttle is a primary flight control.
Examiners should fail any pilot on any relevant test if the said pilot cannot show an acceptable level of throttle manual manipulation competence.
In my very, very humble opinion, the student should be taught to fly the aircraft with the governor selected off, then it should be switched on at the end of their training and it’s use covered as an aid, which it is.
We teach the pilot navigational skills, then cover the GPS or other forms of navigational aids as just that, an aid. They, (the aids), should not be primary!
If you fly an aircraft with an auto-pilot, you still have to be taught to fly the said aircraft manually!!!
There are far too many pilots out there who are genuinely afraid of flying the R22/R44 without the governor selected on.
There are far to many pilots out there who genuinely believe that you cannot fly the R22/R44 safely without the governor selected on.
We flew and taught pilots how to fly the R22 for years before the governor was fitted of which there were two versions.
Version one (1) sensed rotor rpm, using a second set of Hall effect senders adjacent to the normal rotor rpm senders.
Version two (2) which is the current version and, as we all know, senses engine rpm.
So, despite flying thousands of hours (instructing, test and recreational flying) without a governor, I am still around to harp on about things that I feel will help you to carry on safely enjoying the sheer privilege of flying a helicopter. For so many pilots out there, this is directly down to the vision, guts and determination of Frank Robinson and his team of design engineers headed now by the brilliant Pete Riedl.
I have had the privilege to know these people for 40 years and hope to carry on doing so for a little longer.
When I was conducting the flying on my European Robinson R22/R44 pilots flight safety courses, I would fly the whole time with the governor off to enable me to teach low RRPM recovery etc. I would also demonstrate the capability of the engine correlater by setting the rpm at 104% in the R22, get the student to confirm the set rpm and then pull the rotor and engine circuit breakers, thus removing the indicated rpm. I then cautioned the student not to make any throttle adjustments but to listen to the sound of the engine and rotor. I would then get them to just fly the aircraft to a normal approach to the hover where I would reset the circuit breakers showing that the rpm was still at the level we left it at when starting the exercise. The engine correlater had maintained the rpm during the approach. It would give the student real confidence in the ability of the correlater to look after them should the governor fail, or even if the governor and rpm indication failed.
To me this comes under ‘system malfunction’. I just add the lack of rpm information to demonstrate that the correlater does not need a visual indication of rpm to continue to maintain the rpm, plus it gives the student the experience of an rpm indication failure on top of the governor failure which for them is a really scary scenario.
Again, we need to actually safely fail these systems with the student so that they have experience to call upon if it happens during their subsequent flying. This tendency to verbally ask the student what they should do is, in my mind, a complete wast of time. You need the student to action the relevant procedure and get them to fly the aircraft to a safe landing if possible. What they tell you they would do and what they would actually do when you are not there are usually very, very different.
Again, before I talk about the governor we need to look at the engine correlater
As we are all aware, there is an engine correlater within the throttle system, which correlates the collective lever to the throttle by mechanical linkages.
Put simply; when you raise the collective lever the correlater opens the throttle and lowering the collective lever it closes the throttle.
The correlater is very good within the normal in flight power range, however, it over compensates at low pitch settings and under compensates at high pitch settings.
With the governor switched off prior to take off, the pilot would, for example, set 100% rpm and slowly raise the collective lever. As the lever is raised the correlater will open the throttle but it over compensates, so the pilot must also close the throttle slightly to prevent an over speed. The pilot learns to coordinate the collective lever and throttle during take off.
At the top end, if the pilot demands more power from the engine, which takes it outside the normal correlated range, the correlater will under compensate so the pilot must lead with the throttle to maintain rpm. Note, if the rpm is allowed to droop, then the power available from the engine is reduced.
‘Power is directionally proportional to engine rpm’.
The governor is an electro/mechanical system that is directly interfaced with the engine throttle system and you, the pilot. The governor assists the pilot to maintain rpm by physically opening or closing the throttle in order to adjust and maintain rpm during normal flight manoeuvres
Components that make up the governor system are:
Toggle switch on the end of the pilots collective lever only
An amber caution light on the instrument panel (gov off)
A set of isolated points in the engine right hand magneto
An electric motor and a small gearbox attached to the collective lever jack shaft
A control box; it’s position depends on aircraft type
The Workings of the Governor:
An arm attached to the gearbox output shaft through a slipping clutch is directly attached to the throttle system via a short control rod.
The electric motor will move the arm in response to incoming signals to the control box from a set of points in the engine right hand magneto.
The points in the magneto will open and close at a frequency that relates to the engine rpm.
This signal is analysed by the control box and relayed to the electric motor in the form of electrical power which will cause the motor to turn in the desired direction, opening or closing the throttle.
The clutch friction is set to approximately twice the inherent throttle friction, so if the electric motor causes the arm to move as stated above, the effect will be to physically change the throttle setting (open or close), which the pilot can feel happening under their hand.
The governor is only active above approximately 80% engine rpm and once the governor takes control of the throttle it will quickly accelerate the engine up to 104% R22, 102% R44.
There is a small governed range for the R22 above and below 104% but it is set to maintain 104%.
The same applies to the R44 but 102%.
Therefore, the R22/R44 have a small dead band. Within this dead band the governor is asleep but with one eye open (Inactive but alert).
The governor also includes a ‘duty response’ system. In other words, the further the rpm is away from the datum point (104% 102%) the greater the throttle movement will be to get it back there as quickly as possible.
There is of course a minimum and a maximum engine rpm limit, which if taken outside these limits the governor will default to ‘inactive’ mode. For example, if the engine rpm is taken below 80%, then the pilot would have to physically open the throttle to 80% before the governor would become active again.
The governor control box is looking for a rate of change of the engine rpm, so if it sees a change in the rpm that is such that the rate of change will not take it above or below the governed range, it will remain inactive. However, if it sees a rate of change such that it will take it above or below the governed range, the governor will become active and prevent a change by sending power to the electric motor to turn the motor in the desired direction closing or opening the throttle.
The reason for the slipping clutch in the system is so that the pilot can override the governor if required to do so. They do this by gripping the throttle, which will take the throttle friction above the clutch friction allowing the clutch to slip. The pilot would then select the governor off and fly the aircraft manually.
The amber caution light in the cockpit will illuminate when the toggle switch on the end of the pilot’s collective lever is selected to ‘off’
One of the misunderstanding of this light is that it cautions the pilot if the governor fails, ‘it does not’! It is a governor ‘off’ light and not a ‘governor fail light’ and the toggle switch only switches the power on or off to the electric motor.
I think the reason for the misunderstanding is that other amber caution lights illuminate when there is an issue.
There are two (2) cautions:
The governor masks the onset of carburettor icing, to understand this more, read my ‘no ice thank you’ document.
The governor can be prevented from assisting the pilot maintaining their rpm during stressful events, where the physical reaction to stress causes the pilot to tense up.
This tension will include the pilot unwittingly increasing their grip on the throttle, thereby increasing the throttle friction above that of the governor clutch friction causing the clutch to slip.
Knowledge is Flight Safety helping to keep your RPM in the green.