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BMA Viscount Spool-up Behaviour

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BMA Viscount Spool-up Behaviour

Old 11th Feb 2008, 07:05
  #41 (permalink)  
Join Date: Jun 2000
Location: Australia
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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.
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Old 11th Feb 2008, 11:10
  #42 (permalink)  
Join Date: Oct 2000
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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.

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Old 11th Feb 2008, 12:18
  #43 (permalink)  
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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.
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Old 11th Feb 2008, 12:22
  #44 (permalink)  
Join Date: Feb 2008
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spooky flap noise

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
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Old 11th Feb 2008, 19:02
  #45 (permalink)  
Join Date: Jan 2008
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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.
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Old 11th Feb 2008, 22:42
  #46 (permalink)  
Join Date: Dec 2001
Location: South of France
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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.
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Old 12th Feb 2008, 20:56
  #47 (permalink)  
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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 ...

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Old 12th Feb 2008, 21:58
  #48 (permalink)  
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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!)
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Old 13th Feb 2008, 18:57
  #49 (permalink)  
Join Date: Oct 2007
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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!

Last edited by amber 1; 13th Feb 2008 at 20:00.
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