'Phase advance filter'
Thread Starter
Join Date: May 2001
Location: London
Posts: 528
Likes: 0
Received 0 Likes
on
0 Posts
'Phase advance filter'
Bloke told me in a pub (so it has to be right) about a low rotor rpm warning system incorporating a phase advance filter. This warning sounded when the rate of rrpm decay reached a certain value, rather than when rrpm themselves reached a certain level. As a result it gave extra warning time after a complete engine failure.
This is good news for us low-inertia folks. Does anyone know if this system exists, and if so, where I can get one?
This is good news for us low-inertia folks. Does anyone know if this system exists, and if so, where I can get one?
Join Date: Nov 2000
Location: Vancouver, BC, Canada
Posts: 452
Likes: 0
Received 0 Likes
on
0 Posts
t'aint natural
Using the 'Lu Credo' ~ 'Look for the negatives; the positives can look after themselves'.
Might a [decay rate warning] tend to go off more frequently then a [low RRPM warning]? Could this create a 'cry wolf' syndrome where the pilot becomes desensitized to the warnings?
Dave J.
Using the 'Lu Credo' ~ 'Look for the negatives; the positives can look after themselves'.
Might a [decay rate warning] tend to go off more frequently then a [low RRPM warning]? Could this create a 'cry wolf' syndrome where the pilot becomes desensitized to the warnings?
Dave J.
Thread Starter
Join Date: May 2001
Location: London
Posts: 528
Likes: 0
Received 0 Likes
on
0 Posts
Dave: Surely a decay rate warning would be tuned to trigger only at the kind of rate of reduction you'd get in a complete engine failure, rather than the decay rates used in normal flight. It would only go off in extremis, and as such would have to be treated very seriously indeed.
If you had a partial engine failure and the decay rate was insufficient to sound the horn, then the low rrpm warning would be your first indication, as now.
If you had a partial engine failure and the decay rate was insufficient to sound the horn, then the low rrpm warning would be your first indication, as now.
Guest
Posts: n/a
We have used these filters for years on the advanced engine failure warning logic of some of our models, such as the 76B and Comanche. The intelligent look at torque, rpm and N1 values and rates tells just what the pilot would if he were staring at these indicators constantly. Rate alone is misleading, since the rate might be triggered by normal events (big power pull) but the rate downward while torque/Manifold pressure was also going down is a big indicator of engine unhealth. Conversely, if the rotor is drooping due to a big power pull, the torque/MP will be going up rapidly as the Nr is dropping, and the warning would not be generated. If the Nr is going down, and so is the torque/MP, now its time to sound the warning.
These smart indicators are much faster than conventional speed switches.
These smart indicators are much faster than conventional speed switches.
Tain't, I have had 2 of these sensors fitted for years....they are called ears and are extremely sensitive to the slightest change in Nr/engine noise/gearbox whine etc They are connected to a voice warning system that is guaranteed to say 'what the f*** was that' if anything untoward happens in the aircraft.
Join Date: Jan 2001
Location: AB, Canada
Posts: 420
Likes: 0
Received 0 Likes
on
0 Posts
crab, I was thinking along those lines as well. However, I do remember the senior pilots telling me about all these weird noises to listen to and I didn't have a clue. Now I'm one of the pilots who hear weird noises.
Thread Starter
Join Date: May 2001
Location: London
Posts: 528
Likes: 0
Received 0 Likes
on
0 Posts
Crab... I'd like to buy those ears, if you'd care to haggle...
I might add that if you had time to say "What the ***" in an R22 before you made a move, you might as well follow up with the Lord's Prayer pretty damned quick.
There's a story in the current issue of AOPA UK's magazine General Aviation written by Dick Sanford, who is Robinson's accident investigator and safety course administrator here in the UK. First time he had an engine failure in an R22 (carb icing) was when he was practising autorotations with his FIC instructor - and neither of them realised the engine had failed. It wasn't until he noticed the oil light was on... so maybe ears have their shortcomings too.
I might add that if you had time to say "What the ***" in an R22 before you made a move, you might as well follow up with the Lord's Prayer pretty damned quick.
There's a story in the current issue of AOPA UK's magazine General Aviation written by Dick Sanford, who is Robinson's accident investigator and safety course administrator here in the UK. First time he had an engine failure in an R22 (carb icing) was when he was practising autorotations with his FIC instructor - and neither of them realised the engine had failed. It wasn't until he noticed the oil light was on... so maybe ears have their shortcomings too.
No I think that's just dullness..it's a long while since I flew an R22 but I am sure it had an engine rpm needle along with the Nr needle which made it quite clear the what the engine was doing even if you were oblivious to the change in noise.
phase advance filters
How did the R-22 ever get certificated with such a crappy RRPM/ERPM gauge? RRPM IS LIFE,more important than IAS,so the instrument should be at least as prominent,not such a piddly little thing,sited in a non-prominent position- first time I saw one I thought it was the tuning whiskers for the ADF!! 
Thread Starter
Join Date: May 2001
Location: London
Posts: 528
Likes: 0
Received 0 Likes
on
0 Posts
Yeah, Crab, dullness it is. Sanford was flying with an old FIC instructor called Stan Sollett, between them they must have had 20,000 hours. God knows how they stayed alive so long, being so dumb.
I'd better make an offer on those eyes, too.
I'd better make an offer on those eyes, too.
T'aint,
I am all for improved warning systems....but....
we seem to be training to react to audio warnings as a be all end all. This is where I favour the ears and eyes concept. A good example is the number of B206s that have gone in following an N1 gauge failure. Audio goes off, pilot dumps lever, looks inside to confirm and sees big eng out light (when fitted) and generally their mind is made up. If they look further they will see temps winding down, pressures winding down, TQ decreasing rapidly and possibly an N2/NR needle split happening - all further indications of "engine failure" presented to the believing pilot due to the rapid lowering of the lever.
Another good one is the B214ST on the NW Shelf of Oz. One engine oversped just after rotation off the rig, eng out light and audio illuminated (although eng had not failed) and, in accordance with their training, they reacted to the audio straight away by lowering the lever and causing the eng to reach the overspeed limit and shutdown leaving them with a real OEI situation that they had alreay set themselves up for (and a successful ditching).
Initial training in the UH60 would always be a hard sell to trainees from Hueys that were conditioned to always dump the lever with an audio. Failing the stabilator created an audio, the trainee would dump the lever and the aircraft would execute the most violent pitch down.
Perhaps if we always taught people to look at RRPM rather than slamming the lever to the floor following an audio warning, we might circumvent some of these incidents. And we still havent mentioned the yaw!
Go the ears and eyes.
I am all for improved warning systems....but....
we seem to be training to react to audio warnings as a be all end all. This is where I favour the ears and eyes concept. A good example is the number of B206s that have gone in following an N1 gauge failure. Audio goes off, pilot dumps lever, looks inside to confirm and sees big eng out light (when fitted) and generally their mind is made up. If they look further they will see temps winding down, pressures winding down, TQ decreasing rapidly and possibly an N2/NR needle split happening - all further indications of "engine failure" presented to the believing pilot due to the rapid lowering of the lever.
Another good one is the B214ST on the NW Shelf of Oz. One engine oversped just after rotation off the rig, eng out light and audio illuminated (although eng had not failed) and, in accordance with their training, they reacted to the audio straight away by lowering the lever and causing the eng to reach the overspeed limit and shutdown leaving them with a real OEI situation that they had alreay set themselves up for (and a successful ditching).
Initial training in the UH60 would always be a hard sell to trainees from Hueys that were conditioned to always dump the lever with an audio. Failing the stabilator created an audio, the trainee would dump the lever and the aircraft would execute the most violent pitch down.
Perhaps if we always taught people to look at RRPM rather than slamming the lever to the floor following an audio warning, we might circumvent some of these incidents. And we still havent mentioned the yaw!
Go the ears and eyes.
phase advance filters
I say again -Why do manufactureres fit such stupid RRPM GAUGES?? Why do not TEST PILOTS tear the S77t out of manufacturers who do? As a test pilot it would be my No,1 priority to get RRPM gauges changed to Big,clear, and unambiguous;ie RRPM is the Dominant needle,NI/N2 MUST BE SMALLER;WHY DON`T YOU Manufacturers LISTEN!!! 
Join Date: Nov 2000
Location: Vancouver, BC, Canada
Posts: 452
Likes: 0
Received 0 Likes
on
0 Posts
Alternative
An alternative means of eliminating low rotor rpm is the use of a rotor governor The rotor governor maintains a predetermined rotor rpm, which is flight adjustable within certain limits.
The pilot still has his collective and throttle grip; but in this situation, the collective overrides the rotor governor instead of the throttle overriding the engine governor.
In other words, upon loss of power and without pilot interaction, the rotor will lose thrust but not lose rpm.
Dave J
The pilot still has his collective and throttle grip; but in this situation, the collective overrides the rotor governor instead of the throttle overriding the engine governor.
In other words, upon loss of power and without pilot interaction, the rotor will lose thrust but not lose rpm.
Dave J
Thread Starter
Join Date: May 2001
Location: London
Posts: 528
Likes: 0
Received 0 Likes
on
0 Posts
Helmet Fire:
The problem with low-inertia heads is that you simply MUST dump the lever at the very first suspicion of trouble. I don't want to restart a well-trodden thread, but at max power in the climb in an R22 you're said to have 1.1 seconds before the rrpm reaches an unrecoverable level in case of engine failure, if you do nothing.
Let's not start another puerile argument about why everyone should be flying something bigger... but let's not encourage people who hear a low rrpm warning horn to look at the gauge before they react.
The time it takes you to look in at the clocks is time wasted. If the engine goes (except in autorotation) you'll get a major left kick of the nose, and that's your cue to break your knuckles.
And a bigger Nr gauge is only going to help you make a bigger smoking hole.
The problem with low-inertia heads is that you simply MUST dump the lever at the very first suspicion of trouble. I don't want to restart a well-trodden thread, but at max power in the climb in an R22 you're said to have 1.1 seconds before the rrpm reaches an unrecoverable level in case of engine failure, if you do nothing.
Let's not start another puerile argument about why everyone should be flying something bigger... but let's not encourage people who hear a low rrpm warning horn to look at the gauge before they react.
The time it takes you to look in at the clocks is time wasted. If the engine goes (except in autorotation) you'll get a major left kick of the nose, and that's your cue to break your knuckles.
And a bigger Nr gauge is only going to help you make a bigger smoking hole.
Join Date: Jul 2002
Location: CH
Posts: 116
Likes: 0
Received 0 Likes
on
0 Posts
To proceed:
Helmetfire makes the following claim:
"Another good one is the B214ST on the NW Shelf of Oz. One engine oversped just after rotation off the rig, eng out light and audio illuminated (although eng had not failed) and, in accordance with their training, they reacted to the audio straight away by lowering the lever and causing the eng to reach the overspeed limit and shutdown leaving them with a real OEI situation that they had alreay set themselves up for (and a successful ditching)."
Point #1: eng out light and audio illuminated. Not so. Eng out warnings are predicated normally on low N1. This was never the case and no eng out warning was ever noticed by either pilot.
Point #2: Reacted to the audio. What audio? The HIGH RRPM has no audio in a Bell medium. It is probably being aware of this single fact alone that would give you the correct diagnosis.
I see by your previous posts that you are a 212 driver. From your claims above you would have been sitting in the Timor Sea as well scratching your head. I would strongly suggest you go through a high side governor failure on the 212 in the flight manual and just think through the indications you would have. When you get that sorted go back to whoever gave you a type endorsement and ask them maybe they are ignorant of the facts as well. Remember the Aussie airforce 707 incident. The indications of a high side failure will probably be an increase in RRPM possibly followed by a RPM light and NO audio - depending on the remaining power available before the N1 limit was reached. There will be no indication of an engine "failure" all you have is a governor failure. The needles N1, ITT, Q etc will indicate like a failure yet there is no "engine out" indication. The one that "looks" like it's failed will be the good one. My read of it would be to contain the high RRPM with increased collective if you can. What you would like to avoid is an overspeed of N2 and subsequent shutdown. The torque fluctuation from the overpeeding engine and then the remaining good engine trying to pick things up will certainly brighten your footwork. This is just a dopey old flyweight system that is definitely not pro-active like modern electronic systems.
After you have the Nr contained you can make an assessment of what has gone wrong and remedy because hopefully you have been through the scenario already with the indications as described.
I think London cabbies call this "The Knowledge" and in the Aussie Airforce incident the "knowledge" was not on board at the time.
Helmetfire makes the following claim:
"Another good one is the B214ST on the NW Shelf of Oz. One engine oversped just after rotation off the rig, eng out light and audio illuminated (although eng had not failed) and, in accordance with their training, they reacted to the audio straight away by lowering the lever and causing the eng to reach the overspeed limit and shutdown leaving them with a real OEI situation that they had alreay set themselves up for (and a successful ditching)."
Point #1: eng out light and audio illuminated. Not so. Eng out warnings are predicated normally on low N1. This was never the case and no eng out warning was ever noticed by either pilot.
Point #2: Reacted to the audio. What audio? The HIGH RRPM has no audio in a Bell medium. It is probably being aware of this single fact alone that would give you the correct diagnosis.
I see by your previous posts that you are a 212 driver. From your claims above you would have been sitting in the Timor Sea as well scratching your head. I would strongly suggest you go through a high side governor failure on the 212 in the flight manual and just think through the indications you would have. When you get that sorted go back to whoever gave you a type endorsement and ask them maybe they are ignorant of the facts as well. Remember the Aussie airforce 707 incident. The indications of a high side failure will probably be an increase in RRPM possibly followed by a RPM light and NO audio - depending on the remaining power available before the N1 limit was reached. There will be no indication of an engine "failure" all you have is a governor failure. The needles N1, ITT, Q etc will indicate like a failure yet there is no "engine out" indication. The one that "looks" like it's failed will be the good one. My read of it would be to contain the high RRPM with increased collective if you can. What you would like to avoid is an overspeed of N2 and subsequent shutdown. The torque fluctuation from the overpeeding engine and then the remaining good engine trying to pick things up will certainly brighten your footwork. This is just a dopey old flyweight system that is definitely not pro-active like modern electronic systems.
After you have the Nr contained you can make an assessment of what has gone wrong and remedy because hopefully you have been through the scenario already with the indications as described.
I think London cabbies call this "The Knowledge" and in the Aussie Airforce incident the "knowledge" was not on board at the time.
Join Date: Jul 2002
Location: mostly in the jungle...
Age: 59
Posts: 502
Received 0 Likes
on
0 Posts
hello again,
1) I find the R-22 rrpm/erpm gauge just fine, as you see immediately if both needles are where they are supposed to be.
Contrary for example in the EC120B with less than optimal light you might need more than a split second to check nr/nf. (regular "two needle on one dial" layout, though with analog circular bar display)
2) Dave, watch out that you donīt design all the fun out of the helicopter! I understand your desire to built the ultimately safe and easy to fly helicopter, but maybe if a helicopter is NOT so easy to fly, it might be safer, as not so many people get into the air. I believe it is good that certain people drop out of training, because they realize, it is not their thing.
The problem is, even if the machine is easy to fly, it still will able to do all the nice things you can do with a helicopter, but no matter how safe it is, performance limits will still apply to it, and there it is where people finally get in trouble (airplanes need a minimum speed to fly - you can train a monkey for that. Well you also can train a monkey to fly a helicopter straight and level...), behind the powercurve is way more critical in a helicopter than in an airplane,...my opinion...
Where is the challenge if the pilot canīt do anything wrong anymore!!
Besides even if everything is electronic (lightweight...), for a R22 size or smaller helicopter every ounce counts. On the S-92 it doesnīt matter as the weight of these sensors and actuators have a very low percentage of the gross weight.
3) And once more:
You have plenty of time in the R22 to react and check the rrpm, just do it as they show you in the safety course: DO NOT slam the collective, rather push it smoothly down, ALL while you ALSO pull slightly back on the cyclic, remember ENERGY MANAGEMENT - trade some speed for lift!! Go practise, youīll see!!
Basically it comes down to training - get a THOROUGH checkout and you should never be in a sorrow place!
3top,
1) I find the R-22 rrpm/erpm gauge just fine, as you see immediately if both needles are where they are supposed to be.
Contrary for example in the EC120B with less than optimal light you might need more than a split second to check nr/nf. (regular "two needle on one dial" layout, though with analog circular bar display)
2) Dave, watch out that you donīt design all the fun out of the helicopter! I understand your desire to built the ultimately safe and easy to fly helicopter, but maybe if a helicopter is NOT so easy to fly, it might be safer, as not so many people get into the air. I believe it is good that certain people drop out of training, because they realize, it is not their thing.
The problem is, even if the machine is easy to fly, it still will able to do all the nice things you can do with a helicopter, but no matter how safe it is, performance limits will still apply to it, and there it is where people finally get in trouble (airplanes need a minimum speed to fly - you can train a monkey for that. Well you also can train a monkey to fly a helicopter straight and level...), behind the powercurve is way more critical in a helicopter than in an airplane,...my opinion...
Where is the challenge if the pilot canīt do anything wrong anymore!!
Besides even if everything is electronic (lightweight...), for a R22 size or smaller helicopter every ounce counts. On the S-92 it doesnīt matter as the weight of these sensors and actuators have a very low percentage of the gross weight.
3) And once more:
You have plenty of time in the R22 to react and check the rrpm, just do it as they show you in the safety course: DO NOT slam the collective, rather push it smoothly down, ALL while you ALSO pull slightly back on the cyclic, remember ENERGY MANAGEMENT - trade some speed for lift!! Go practise, youīll see!!
Basically it comes down to training - get a THOROUGH checkout and you should never be in a sorrow place!
3top,
John,
I agree with your comments about the PT6 (and the 707). I thought the 214ST was fitted with a GE T700 variant as opposed to the B212 PT6 fit out - thus causing some quite distinct differences in engine warning systems that relate to the comments I made about this incident. The T700 has some intresting traps, and I was told that this incident was a good example of those traps. The pilots did exactly what they were trained to do, but remember, I wasn't there in the cockpit, and so I was talking out of turn.
What exactly happened?
t'aint,
I understand your point about low inertia heads, but even you have brought up the point that we were putting to you earlier - the yaw. This should work as a warning bell just like the RRPM horn. The total picture for a (single engine aircraft) engine failure includes yaw (you can see and feel it), RRPM decay (you can hear it), and a pitch attitude change (you can see and feel it) ON TOP OF audios and warning lights. In a low power descent, however, you may have to rely soley upon the engine out light to help.
Note that I wasn't advocating the removal of the audio horns, just that reacting to the horn with no other indications can make you come unstuck. I am not even saying that I am immune from that reaction, because I know I am not: I have done just that in the simulator. I now hope that in the real case, I will not revert to my original training that caused my red face in the sim - because it is alot uglier in the real world. In other words, I hope that I can practice what I preach!!
I agree with your comments about the PT6 (and the 707). I thought the 214ST was fitted with a GE T700 variant as opposed to the B212 PT6 fit out - thus causing some quite distinct differences in engine warning systems that relate to the comments I made about this incident. The T700 has some intresting traps, and I was told that this incident was a good example of those traps. The pilots did exactly what they were trained to do, but remember, I wasn't there in the cockpit, and so I was talking out of turn.
What exactly happened?
t'aint,
I understand your point about low inertia heads, but even you have brought up the point that we were putting to you earlier - the yaw. This should work as a warning bell just like the RRPM horn. The total picture for a (single engine aircraft) engine failure includes yaw (you can see and feel it), RRPM decay (you can hear it), and a pitch attitude change (you can see and feel it) ON TOP OF audios and warning lights. In a low power descent, however, you may have to rely soley upon the engine out light to help.
Note that I wasn't advocating the removal of the audio horns, just that reacting to the horn with no other indications can make you come unstuck. I am not even saying that I am immune from that reaction, because I know I am not: I have done just that in the simulator. I now hope that in the real case, I will not revert to my original training that caused my red face in the sim - because it is alot uglier in the real world. In other words, I hope that I can practice what I preach!!
