View Full Version : BMA Viscount Spool-up Behaviour

5th Feb 2008, 20:29
As a lad standing at East Midlands perimeter in the 70s, I used to be fascinated at how the engine note of a Viscount (813/4/5) on the takeoff roll would rise and then fall slightly before rising again for takeoff. This would appear to be the onset of prop speed governing (somewhere around 1100rpm?) However: as a (slightly older) student doing turnround cleaning at the same airport in the late 80s watching the same aeroplanes (not so many Viscounts by then but remnants of the same 70s fleet) the engine note appeared to rise at takeoff no dip as I recall .

Is this right? if so why .

Did I also notice a change from 4-engined taxying to 2-engined taxying over the same period. What would have driven this? fuel conservation? noise reduction? engine life stretching ? air-quality around airports? ...


6th Feb 2008, 11:49
As an ex 815-er, and to put it simplistically, on any Dart if the power is introduced slowly and gently, when the prop starts to govern, it will drag down the engine rpm, as there is not a whole lot of power applied to overcome the effects of the first coarsening. A good fist of power at this point will result in a steady rpm as the prop absorbs the applied power. (If the power stays low, more hunting of rpm will result). A steady determined application of power in the first place will result in one slight decrease as the prop "catches", and a steady note thereafter.

Think of your car. As you let in the clutch, the rpm dies away as it is engaged, then accelerates with the car. If you increase the power as the clutch is engaged, you can prevent the rpm from dying down.

Hope that helps.

6th Feb 2008, 12:13
well, i worked for BMA at LHR 1977-85 so often we would have 5 or 6 in at once, they always taxied in on 2 engines, fuel issues were quite a big thing i recall.

re the t/o engine noise hmmmm i really am sorry i cant remember,
at LHR my office was on A9 on the ramp close to the runway i/s where often our VC8's would sneak in for a short take off BUT the noise was usually drowned by a trident taxying past!
i used to go to SEN alot in the 60's and 70's to watch channel airways vc8's too..

i obviously flew in BMA ones dozens of times both in the cabin and on the jump seat but i still dont recall an engine noise dip on t/o after initial power going on....

love to go on a viscount now sigh

6th Feb 2008, 17:28
ABUKABOY - Thanks, I wondered whether rate of change of power demand had anything to do with it, though I would have expected it to be the other way around: i.e. if throttles were slammed forward, I'd expect the prop speed governor to struggle (and hence produce my 70's dip) especially if the demanded speed had changed ; for a slower throttle advance, I'd expect the governing to be much better.

Either way, do you think there might have been a change in BMA's operating procedures recommending a different throttle advance rate between the 70's and 80's ...?

Just curious. Cheers.

6th Feb 2008, 20:23
Pink Floyd - Dark Side of The moon - On The Run, about 3 minutes in, that has just got to be a Viscount running up for takeoff :ok:

6th Feb 2008, 21:07
Javelin - I think you're right - and what's more I reckon it's doing a little dip too !

6th Feb 2008, 22:22
Same thing happens with a recip if throttle is opened briskly. The prop starts out on the low-pitch stop, and takes a second or two to "grab" the overshooting engine as it goes into governing.

If the throttle is opened in a more moderate fashion, the prop can respond quickly enough that there is no overshoot.

7th Feb 2008, 03:31
If one listens very carefully, one can hear the water methanol start to flow during the takeoff, a very slight pitch (noise) change results.
Likewise with a large recip that uses ADI.

RollsRoyce Dart, a mighty fine engine.:ok:

7th Feb 2008, 07:49
I think The Beatles "Back in the USSR" had a Viscount on the soundtrack too.

7th Feb 2008, 10:10
Yes, I'd guess it's caused by the PCUs. IIRC, as has already been mentioned, it was best to apply power smoothly and firmly. If you stopped halfway then the PCUs would have a little yank up and down.

Military Argosy on approach - reached Water Meth in the checklist - FE switched all four ON with RPM above WM cut-in RPM (don't ask) - 'exercise the PCUs' wasn't in it! - very invigorating :eek:

'fine engine': radial compressor certainly ate birds - like a few pilots I've met :E

Bring back the Dak! - Didn't these guys go on! (If that refers to those I remember from the 70s)

Roy Bouchier
7th Feb 2008, 13:39
A G1 went that way. Co-pilot hit the water meth after an engine failure on t/o.
Aircraft crashed inverted.
Also, as far as taxying a Viscount on two is concerned, I seem to recall that the 700 and the 800 had the hydraulic pumps reversed, outboard and inboard.
Sometimes caused confusion!

nina wang
7th Feb 2008, 13:56
Nearly caught out a few times taxiing out at LHR on two engines when cleared for an immediate intersection departure (we could hear the controllers sniggering in the background) The last engine started would go all the way from stationary up to takeoff power as we rolled with no apparent ill effects!

8th Feb 2008, 01:07
all the way from stationary up to takeoff power as we rolled with no apparent ill effects
One is astonished! Even with little aeroplane engines.
Back in one's Merchant Navy days both steam and diesel (spits to side as required by steam engineers' convention when mentionining the 'D' word) engines were carefully warmed before starting.

ps. No relation of Vera Wang perchance? Elder daughter looking for wedding dress :)

8th Feb 2008, 09:59
I think you will find the simple answer is that the doppler effect makes it sound as if there are changes to engine / prop noise as the aircraft passes an observer.

Chris Scott
8th Feb 2008, 10:16
Sorry Paradism, as a former Dart (and Twin-Wasp) stoker I can't let your suggestion pass uncorrected. There's no Doppler effect when you are strapped in the cockpit ! The above guys know what they are talking about.


8th Feb 2008, 11:24
Thank you Chris, but if you read the first post you will note that the observer was not in the cockpit. I bow to your obviously greater knowledge in this matter. In the instance quoted, an outside observer would note a decrease in note as the aircraft passed him.her, that is straightforward physics. However, I agree it does not explain the increase in note as the aircraft lifts off.

Chris Scott
8th Feb 2008, 16:10
Paradism... ! I didn't want to be pedantic, but perhaps I needed to be.

Let me try to explain (this is the Tech Log forum, after all):

1) The rise and fall of the engine note that they are talking about is at the beginning of the take-off run, as the throttles are being advanced, not when the aeroplane is getting airborne.
2) On the Dart, the propeller is in ground-fine pitch initially (for taxying without overheating the engines, and to provide engine braking if the throttles were closed).This effectively stops the propeller coarsening its pitch enough to provide the thrust necessary for flight.
3) As the power comes on, the propeller spool and propeller therefore accelerate rapidly. At some point, the system recognises that take-off power is required, and removes the ground-fine-pitch stop. The pitch now coarsens suddenly, momentarily slowing the propeller spool (shaft) of the engine down until the rapidly-increasing power from the core spool wins the contest. [The Dart is a 2-spool engine.] From then on, the propeller continues to accelerate, even though its pitch may continue to coarsen.
4) The transition from ground-fine pitch to flight pitch - and vice-versa - is one of the key aspects that turbo-prop crews have to monitor, certainly on the Dart engine.
5) It is even more important on landing. On the Dart Herald, for example, a lever had to be pulled back when the aircraft was safely on the ground. This engaged ground-fine pitch, resulting in a momentary increase in propeller rpm and useful drag to slow you down. The Viscount may be slightly different, but the end product would be the same.
6) NB: Woe betide any Dart crew which fails to ensure that the props are in ground-fine pitch for taxying after landing. If not, opening the throttles on the taxiway may result in the TGT (turbine gas temp) going off the clock, and melted turbine blades.


The sudden coarsening of propeller pitch in (3), above, is the cause of the rise and fall of the engine note, referred to by jh5speed. Lads who inhabit the perimeter fences at airports all over the world are more than familiar with the Doppler effect. I should know - having been one of them myself. So I've heard the Dart from the perimeter fence and the cockpit.

Hope you are now convinced!

PS: The Dart sounded great, but what about the whispering Proteus...

8th Feb 2008, 16:21
Paradism - I assure you that this is not about the Doppler effect. What I (i.e. the lad at perimeter fence all those years ago) am talking about is the spool-up behaviour at the end of the runway before brakes-off. Looking at my first post - I guess I could have made this clearer. This is all about stationary aircraft.

The response so far have confirmed my suspicion that it is to do with rate of change power demand. I think the subtle change in note as the water/meth comes in is not the answer we are looking for - although I'm sure it is audible at close quarters.

The only remaining question is why things (apparently) changed in the 80's.

One thing occurs to me: were the 70's Viscount pilots those who had progressed from pistons (Argonauts in BMA's case) and tended to treat the power-levers in a different way to the 80's pilots who might have had different previous experience ? ...

8th Feb 2008, 16:36
Chris - Thanks - you just got in before me:

Just to note the Dart is a single spool animal - prop is connected to the one (and only) shaft. 2 stage of compressor (centrifugal) and 2 turbine stages though - perhaps that's what you were thinking of?

My only recollection of a Proteus (thread drift; pull up!) is the rumble I used to hear from miles away when a Redcoat Britannia used to make an occasional visit to EMA. I always wondered whether 'Whispering' referred to the experience seated within, or watching it go by.


8th Feb 2008, 17:27

True all Darts are single spool but I think the ones on the Viscount 810's were -525f's with three turbine stages. I worked on some back in the 70,s. Earlier Viscount 800,s had -515,s with two turbine stages.

When the throttle is advanced the Prop starts to govern at 11000 engine rpm and if the fuel is not being increased at a sufficient rate the speed will decay a bit.

As to Water Methanol, this only comes in at about 14500 rpm if the system is armed and operates at take off rpm (15000) until first power reduction to 14200 rpm. (or the W/M runs out).
Also the -520 series Dart, on Viscounts and F27s, W/M restores power at hight ambient temps so would not be used in the UK very often except on hot summer days, where as the -532 on the Dart Herald boosted power at all temps. so was used more often.

Hope this helps.

8th Feb 2008, 18:30
Chris Scott

Many thanks, a most comprehensive and articulate explanation.

The late XV105
8th Feb 2008, 20:56
Pink Floyd - Dark Side of The moon - On The Run, about 3 minutes in, that has just got to be a Viscount running up for takeoff :ok:

Thank you for adding second and third opinions to what I have thought ever since the album was released! Sad really! :)

pax britanica
8th Feb 2008, 21:10
I spent many happy days as a kid at the western end of 10R watching streams of BEA and other( LH KL EI ....) Viscounts whistle their cheeerful way to the Block 79?? holding point before lining up and bingo just as described here a clearly perceptible pause and drop in sound level as the whistle disappeared and was repalced by a deeper growl as the brakes came off and they disappeared towards the east. Very very distinctive and fascinating to read this thread describing possible reasons for it.
I only flew on the Viscount a couple of times-to Jersey I think but a really nice airplane from a pax view point and those windows wow!

Chris Scott
9th Feb 2008, 01:13
Quote from jh5speed:
Just to note the Dart is a single spool animal - prop is connected to the one (and only) shaft. 2 stage of compressor (centrifugal) and 2 turbine stages though - perhaps that's what you were thinking of?

Yes... Mea culpa, I've belatedly looked at a cut-away. Shouldn't have relied on memory, 37 years on. You, ABUKABOY and barit1 didn't need any help from me, you were spot on.

I think barit1 is right, a slower advance of the throttles avoids the momentary drop in rpm as the prop comes out of ground-fine into governing mode. On the Herald, the latter was announced by the pitch lever moving forward (provided the controls had been unlocked), and the green ground-fine-pitch lights going out.

For the landing, the Viscount selects its own ground-fine, apparently, by the weight switches. On the Herald, the crew had to remember it. Don't know about the F27.

411A is right that there is a change of note if/when water-meth cuts in. The note gets heavier (more thrust from coarser pitch at the same maximum rpm?) and, on the Herald, heard externally, there was often a strange, slapping sound.

Quote from dixi188:
Also the -520 series Dart, on Viscounts and F27s, W/M restores power at hight ambient temps so would not be used in the UK very often except on hot summer days, [U]where as the -532 on the Dart Herald boosted power at all temps. so was used more often.
That would explain why on the Herald (only 2 engines, if my memory hasn't failed again) ;) we often used it, together with zero flap, to satisfy the Performance-A "WAT" limit (to improve the second-segment climb angle in the engine-out case); even with fairly modest summer temperatures.

[Rather off-topic, "Whispering Giant" was a marketing slogan for the (Proteus) Britannia. Certainly quiet inside, from my (pax) experience. But, as you say, there was a deep rumble in the air, heard externally. The Bristol Proteus was 2-spool (I checked this time!), with axial-flow compressors on the N2, and 2 turbines per spool; but the air flowed forwards while being compressed, then reversing direction into the combustion chambers. This enabled the engine to be shorter (but caused the serious African icing problems early on). When taxying, at idle revs, it made an almost inaudible whisper (observed from the perimeter fence), occasionally interrupted by a "whoosh" - maybe as the props went into superfine pitch when the throttles were completely closed?
So unlike the deafening high-pitched song of the Dart... I would love to have a recording of the Proteus, but doubt finding one on a pop album.]

9th Feb 2008, 06:51
Back in 1979 as young Kiwi doing my OE I was working at LBA and got to ride in BMA Viscounts a number of times going down to London....I remember one day seeing the 10am flight from LHR arrive on a very wet and grey Leeds days....from my office window this one seemed to be going far too fast landing RWY 32....it was!!! took to the grass rather than go on to the busy Leeds-Harrogate road....as soon as it went onto the grass(it had been raining for a few days) the L/H gear collapsed and props on that side dug into the soft ground flinging grass & mud into the air...it swing about 45 degrees facing the runway and all pax and crew left the Aircraft without a scratch...and a few months later another went off the end of RWY 14 (this was before the runway was extended) I dont think Viscounts liked wet runways....One of New Zealand NAC (National Airways Corp) Viscount went off the runway at Wellington....can't remember what caused that one....but the sound of a Dart is something else.

9th Feb 2008, 09:32
Further to the 'Flight Fine' & 'Ground Fine' pitch discussion:

The -800 series VC8 had switches to motor the props to Flight Fine. Under normal circumstances there was no requirement to use these. Some misguided souls considered placing them to FF an amusing way to commence taxi. RPM would drop and TGT rise. Not a great idea.
Otherwise the system was automatic - can't remember whether it was controlled by weight-on switches.

The lever system with which the Argosy was fitted between #2 & #3 throttles clicked forward as the throttles were opened and armed the Flight Fine Pitch Stop and, on landing, had to be physically pulled back to remove the FFPS and permit the props to reduce to Ground Fine Pitch.
There was an embarassing incident caused by a take-off misunderstanding:
Power goes on and FFP lever clicks forward.
Crewmember asks if take off clearance has been received.
Throttles closed and clearance confirmed as having been received.
You can see where we're going now, can't you?
Throttles re-opened with props in FF and a couple of donks overtemped - soddit!
There but for the grace etc etc.

9th Feb 2008, 09:46

Have become all 'dewy-eyed' reading about Darts having left them behind 30+ years ago(Heralds and F27s).

Time we took tea at WW to catch up. Will PM in due course once I get a roster that will allow it.

Now back to thread!:}


9th Feb 2008, 10:14
Basil : quote : 'some misguided souls considered placing them to FF an amusing way to commence taxi. RPM would drop and TGT rise. Not a great idea.'

Is this the answer to my original question then? When would this switch have been triggered on take-off roll - just before pushing the levers forward or during the spool-up. If switched before governing mode but after start of spool-up, this would explain my 70's sound. Given it was not the best idea, perhaps operating procedures were changed to specifically prohibit it in the 80's ....

Chris Scott : as a Twin Wasp and Dart man, is there anything in my 'theory' (see previous post - more like an idle thought) that a piston driver would be in the habit (or be required by procedures) of advancing the throttles faster than a 'pure bred' turboprop driver?

Ref to my other thread - any ideas on the asymmetric Viscount tailplane?

Guest 112233
9th Feb 2008, 13:35
:hmm: Slightly off Topic (mods might roast me) - I do remember my 1st ever flight in june 66 - Brum to Dublin - Big windows and small 6 Yr old SLF - Reg G AOHH. A 702 Series ? . - Viscount and there was a momentarly drop in Prop RPM as the Throttles were opened for T/O on 33. seated RHS 4 rows from the back - Did those great Big Passenger windows mean that the VC8 Cruse Alt was restricted to conserve fatigue life in the VC8 ? .

9th Feb 2008, 14:45
FW :ok:

IIRC the switches were a backup in case the flight fine pitch stop failed so would only (except by aforementioned, dare I say, mavericks) be placed to FFP in the event of a malfunction

Yes, the windows were amazing.
Last flew G-AOHH Glasgow, Machrihanish, Islay on 11 Sep 1975. Coincidentally, the model on my bookshelf is HH.
MTOW: 29257kg Year Built: 1957
C of A Expiry: 21/08/1977
IIRC, in the 70s, the cabin alt was increased slightly above the design figure to reduce pressure diff in deference to the age of the aircraft.

It's about 30 years since I flew them and defer to those who may add to the above.

Guest 112233
9th Feb 2008, 15:43
Thanks Basil - Great to know a little of the history of "HH" -

Chris Scott
9th Feb 2008, 18:57
Quote from jh5speed:
Chris Scott :as a Twin Wasp and Dart man, is there anything in my 'theory' (see previous post - more like an idle thought) that a piston driver would be in the habit (or be required by procedures) of advancing the throttles faster than a 'pure bred' turboprop driver?

I would say probably not. Only did 450 hrs on the Dak, 40 years ago, and no other big pistons, so am no expert...

But I think anyone throwing the throttles open or shut on a radial would be asking for an unpleasant surprise. [This is particularly true if you are doing a rolling T/O, as we generally did ('cos lots of runway).] The big beasts are not that reliable, and need to be nursed.

The only advantage of the Twin Wasp vs. the Dart is that you have selected the pitch levers on each engine to full fine (but still governed, I think) before T/O. The Dart, on the other hand, does not have a propeller pitch lever as such. [The one we've been talking about on this thread - on the Herald and Argosy - is purely to enable the crew to select GROUND-fine pitch for ground manoeuvering.]

So, on the Dart, the pilot has no control over engine rpm at a particular throttle setting - some widget decides it for him. But on most piston engines with CSU-governed props, of course, you can vary the engine rpm (by moving the pitch lever) without moving the throttle.

[The asymmetric Viscount tailplane is news to me, but you are right: the Dart props were not handed, as far as I can remember.

Chris Scott
10th Feb 2008, 01:37
Quote from yours truly, above:
So, on the Dart, the pilot has no control over engine rpm at a particular throttle setting - some widget decides it for him.

Must admit to having misgivings about the above, while out for dinner.
1) "Throttle" is the wrong term; the pilot controls each engine with what is called a [U]Power Lever.
2) I got the cart before the horse. Once the engine power is increased sufficiently for T/O, and the propeller comes out of ground-fine pitch, the Power Lever is effectively an engine rpm selector. The "widget" (CASC unit?) has to decide the fuel flow appropriate for the rpm chosen. That delivered, the exact rpm is achieved by the blade-pitch adjustment of the Rotol propeller constant-speed unit. [The achieved engine torque is monitored, and if it falls below a certain low figure at take-off power, the propeller will auto-feather.]
3) The fuel-flow schedule, at a given rpm, can be modified by the crew. This is achieved by the fuel-trim switches, on a scale of 0 - 100. A fuel-trim figure for take-off is calculated and set in advance, according to the conditions. After take-off and during clean-up, the fuel trim is reduced (I think). At top of descent, it is reduced to zero, and descent rpm is set with the power lever. On the initial approach, fuel trim is increased, perhaps to 50. On finals, probably with the landing gear, it is increased to max (100), in preparation for a possible go-around.
If you get it right, the power levers (and, therefore, engine rpm) can remain untouched from TOD until the flare.

Does this sound familiar to you ex-Dart pilots? dxi188, does any of the above make sense?

10th Feb 2008, 02:12
So, on the Dart, the pilot has no control over engine rpm at a particular throttle setting - some widget decides it for him.

That 'widget' is called the throttle, or thrust lever, if that makes you feel better.
Prop and throttle (control) are combined, and together with the fuel trimmer, determine engine power output.

A completely reliable system, that operates superbly.

Brian Abraham
10th Feb 2008, 04:33
Could some one please explain the purpose of the fuel trim on the Dart. Chris Scott has touched upon its use but why the trim to modulate fuel flow? FCU of the day not up to doing the job properly or accurately enough?

10th Feb 2008, 12:16
Yes Chris it makes sense.

Throttle is directly connected to the PCU (prop control unit) and via a clever linkage to the FCU (fuel control unit). The electrical Fuel Trim Actuator is also connected via this linkage to the FCU.
This allows the RPM to be selected by the throttle and the power to be varied by the fuel trimmer. (+ or - 40 % I think)

I'd have to rummage in the loft to find a full description.

Typical power settings were as follows:-

Take off - 15000rpm max torque/ 100% trim
Climb - 14200rpm 760 degrees TGT set by trimmers (maybe 80% trim)
Cruise - 14200rpm 720 degrees TGT set by trimmers (maybe 60% trim)

These numbers are from memory and apply to the H.P. Herald.

Hope this helps.

P.S. CASC is "Combined Acceleration and Speed Control" as used on RR Spey not Dart.

10th Feb 2008, 12:26
I've forgotten if we had fuel trimmers on the Viscount but we certainly had them on the Argosy.
Low level SOP was to keep them set to datum for the prevailing OAT.
People would sometimes use them to control speed which meant that, if set to less than datum, full power was not available when the throttles were opened - as a crew discovered when trying to climb over a hill following a slight nav error in the Far East.
Just made it but rumour was they picked up a bit of foliage on the way :uhoh:

Mil Arg was 14,500/785 for T/O
WTF do I remember that? Must be creeping senility :bored:

10th Feb 2008, 13:20
IF the fuel trimmers are set improperly, at full throttle, the engines could well overtemp...the fuel trimmers are set according to the airfield pressure altitude and prevailing surface temperature, as reported by ATC, for takeoff and landing.

So, in essence, the Dart provided single lever engine power control, aided by manual fuel trim...FADEC not then being available.

10th Feb 2008, 17:40
Ah the dart!!

No ones mentioned the budgie yet!!

About 7 years and 4000 hours in the Scottish Isles - best flying I ever did!!

10th Feb 2008, 20:08
Argosies anyone?

10th Feb 2008, 20:28
The other "feature" of the Dart that has not been mentioned was to do with changes in power setting. Everything had to be done gently and if it was then everything went okay. If however you were a bit quick with the levers you could generate a strange effect that was the opposite of what you expected.

Since the power levers really acted as "rpm command" levers in flight, if you reduced power too quickly, instead of slowing down you would get a sudden slight increase in speed as the props coarsened in an effort to reduce the rpm. The opposite was a more sphincter clenching moment when advancing the levers slightly too quickly for a go-around when the props went for rpm rather than power and the aircraft slowed briefly!

10th Feb 2008, 20:54
JH, I spent my spotting days at EGNX in the early 70's listening to 'PNE, 'PND, 'SED and 'VJB make exactly the sound you describe. AND we spotted the Pink Floyd thing within a week of "Dark Side" being released!
It's thread drift I know, but some other "sounds of the '70s" also need explaining:-

1 The BAC 1-11 startup rising whine and sudden cutoff, and the spooky howling noise at about 2-4000ft and 250-170kts in the descent. Heard this around midnight near Loughborough (April 1970ish), and in the still of the night it scared the hell out of me until I realised it was new Midland 1-11 coming home!
2 The characteristic bleep at the end of a Tx from a 1-11 500srs radio.
('XLL, 'XLM, 'XLN and of course the BEA GAVM* models for example).

However, none of these audiable delights compete with the 'music' that is geneated by XV105 and her 53 beautiful sisters. :ok:

amber 1
10th Feb 2008, 21:13
Setting take-off power on the Viscount and the Budgie was much the same. Push the throttles forward a bit, wait for the props to catch up then smoothly push the throttles fully forward. If you did it properly and at the right speed, the props would spool all the way up with no "dip". Most people got the hang of it but some never did!
Also on the Budgie, when pausing to let the props catch up, it was quite common to lift the ground fine pitch lever out of its detent. This was not really necessary as advancing the throttles further would do it automatically, but it did help make the whole procedeure smoother.

11th Feb 2008, 02:38
It's been nine years since flying the Dart (attatched to a 748) in the arctic, but I seem to remember the Take off trim settings for those marks of Dart were max 85% no matter how cold it was, and the southern Manitoba summer heat could require trims as low as 65%. Obviously our TGT limits would dictate a higher / lower setting through the climb and cruise or in emergencies etc.

Stone age FADEC. Set the trims properly and you could always firewall the throttles with no ill effects. (Hawker Siddeley and BAE called them throttles.)

11th Feb 2008, 06:49
Likewise with a large recip that uses ADI.

Ah! the R2800's...Now that was an engine and a half..I recall taking off in the Convair 440 (RAAF) at Canberra and for some reason the copilot switched off the ADI before I asked him. Politely asked him to check with me first and he said sorry and switched it back on again. Now I am not sure whether there was a big bang or not because I also had the same thing happened in either a RAAF Viscount or an HS 748 whilst using water methanol and that WAS a big bang.

11th Feb 2008, 07:05
Since the power levers really acted as "rpm command" levers in flight, if you reduced power too quickly, instead of slowing down you would get a sudden slight increase in speed as the props coarsened in an effort to reduce the rpm.

I'll go along with that. Training a new Pilot Officer on the VIP HS748 at Canberra around 1968. In those days it was traditional service training to conduct instrument take offs from brakes release keeping straight on the main compass. The instructor in the RH seat offered minor corrections as he looked outside.

On rotation the QFI rapidly pulled back on throttle to simulate engine failure (bloody silly thing to do but we did bloody silly things in those days). The pilot locked on to the compass reacted immediately by applying rudder to prevent yaw etc. But as explained in the earlier post the "failed" engine momentarily coarsened its prop giving an apparent increase in power which the pilot picked up and so he applied rudder in the wrong direction. He was fast - I'll give him that and very quickly the 748 rolled under the influence of the now pulled back throttle and wrong rudder input. The lesson learned from that close shave was to in future slowly pull back the throttle to simulate engine failure and at a safe height.

11th Feb 2008, 09:29
Yes, that initial opposite effect could be a cause of embarassment in close formation :ooh:

Dick Whittingham
11th Feb 2008, 11:10
Some anorak info: During my short employment at Rolls Royce (don't ask) the Dart was under development, having flown a few year's earlier. The factory joke was that the Dart had been intended to produce 1000hp and weigh 800lb. but ended up weighing 1000lb and producing 800hp. Development when I was there (spectator only) was concentrated on improving the compression ratio by re-design of the compressors and reduction in clearances between the disk and the case. In the end compressors were milled from solid on a hugely expensive machine, leaving the front faces closed.


11th Feb 2008, 12:18

Serious thread drift.


BAC 1-11 start noise caused by Plessey CSDS (constant speed drive and starter). Some 1-11's sold to the USA had a different starter that did not make a loud noise.

Howl on descent is caused by Flap extension when air passes through the slot created when Flaps move aft, until the slot is too wide to cause noise.

Bleep at the end of VHF transmissions is from Collins 618M-1 com sets I think. Although I don't recall it on other types fitted with these com's.

Hope this helps.

11th Feb 2008, 12:22
aaaah darts and viscounts

the sounds are priceless (as is the vc10 conways)

and re the spooky flap extention noise on the bac 1-11
the 146 also does this too

funny that its the only 2 airliners that i know to do this are both uk vintage

11th Feb 2008, 19:02
Many thanks for those explanations. The bleepy radios appeared on one or two 737s in the 1980s, UK operators, but I can't remember who.
The Court Line fleet had them too of course, frequent diversions from EGGW to EGNX.
Othe great sounds include the Vanguards and the RB162 boost engine on the Trident 3.
Best Wishes to all who designed, built and flew all these amazing- sounding machines.

11th Feb 2008, 22:42

The Dart engine does not sound so wonderful when it lets go during take-off due to an uncontained failure! when a disc disintegrates and exits the cowling taking with it the fire protection system and the ancilliaries. It certainly gets your attention. Thankfully it was a rare occurance on the Dart, it only happened to me once in six years on the Budgie, but history shows that it has happened a few times throughout the world. No I am not a lover of Darts.

12th Feb 2008, 20:56
Thanks for all the interest in this folks.

Quote : Amber 1 "If you did it properly and at the right speed, the props would spool all the way up with no "dip". Most people got the hang of it but some never did!"

Sounds as if this might be the answer. I can see now (and I've tried to represent it on the plot below) that a slow throttle advance (red) might cause the dip, and how a slightly smarter PL advance (green) might avoid the kink in the speed governor line. However, a faster advance would give a lazier thrust response with the props staying in fine (?), trying to achieve the demanded speed - thus not giving much thrust increase until the end of the transient when they eventually 'bite' to catch the speed (with a bit/lot of overshoot perhaps). I presume a very fast PL slam would have a similar profile in terms of N vs time.

I guess this 'fast slam' response (blue and orange) is not particularly pleasant. The green response is presumably what we are after, where there's a nice smooth rate of change of thrust.

I'm sure I haven't got the shapes quite right - but in principle ??

It seems those 80's pilots just got better at getting the optimum response - or maybe those Viscounts just did it themselves - I remember one pilot saying they knew their own way home! Though, it is still compatible with Chris Scott's observations that someone used to pistons (e.g. those 70's pilots perhaps) might be a tad slower with the throttles than a pure-bred Darter.

Hey Zooker - I'll start a thread in Nostalgia to swap memories of EMA spotting in the 70's ...


12th Feb 2008, 21:58
Slam the power levers wide open from idle will result in a decrease in rpm to zero and a pool of molten turbine blades on the tarmac (and a P45 for the crew!)

amber 1
13th Feb 2008, 18:57

Your graph looks fine to me. The only comment would be that your "Even Faster Power-lever Advance" blue line would probably have a slight blip above the black line at the top end of the graph.
This is because if you pushed the levers up too fast, the props would give a slight over-speed before settling back down as you suggested. This did not sound very professional either.

Thankfully I never witnessed a "Slam Power-lever Advance" as you put it. The old lady did'nt like that sort of thing!