Entering autos: discussion split from Glasgow crash thread
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Bordeaux Bob - Its not difficult at all to overspeed the head on many aircraft, especially if you have a high DA, high AUM and then you load the disc by turning or flaring. In simulator training, I regularly see students going "off the clock" where the Nr indication is above 120%, and the readout shows "--- " instead of an actual figure, because it is so high it won't read it.
Sims are fine but is your Sim actually duplicating the reaction of a properly Rigged aircraft?
Also...what are the Transient Limits on the Aircraft you fly?
Most are very tolerant of transient over speeds....as there is a time limit associated with the Over Speed Limit.
Dig into your Aircraft Maintenance Manual for computing the Power Off Main Rotor RPM's for a given Aircraft Gross Weight, Pressure Altitude and OAT....and see what procedures are involved. Ensuring the Aircraft is tested in as close to the conditions as possible to how it will be flown operationally is important as well.
I will bet you that in reality it is very hard to harm an Aircraft if it is properly rigged per the Approved Maintenance Manual. My experience is that particular maintenance effort is not given the attention it should and close enough is good enough for far too many Operators.
The operative words here are "Properly Rigged".
My experience on over a dozen different Types tells me I am right. I have done all sorts of CofA Air Tests, Maintenance Test Flights, Production Test Flights and have never had a problem so long as the aircraft was properly rigged and flown.
All it takes to avoid any over speed is proper application of Collective....if the Main Rotor RPM starts to go high....simply input a bit of UP Lever....and that problem is solved.
The Danger is getting the rigging wrong and not having enough Autorotative RPM as there is not much One can do to remedy that situation besides turning or flaring but those gains are only temporary and result in either an increased ROD or loss of Airspeed....both of which are not desirable in an EOL situation.
I always tried to set the Autorotative RPM at the High side limit for that reason.
Also...what are the Transient Limits on the Aircraft you fly?
Most are very tolerant of transient over speeds....as there is a time limit associated with the Over Speed Limit.
Dig into your Aircraft Maintenance Manual for computing the Power Off Main Rotor RPM's for a given Aircraft Gross Weight, Pressure Altitude and OAT....and see what procedures are involved. Ensuring the Aircraft is tested in as close to the conditions as possible to how it will be flown operationally is important as well.
I will bet you that in reality it is very hard to harm an Aircraft if it is properly rigged per the Approved Maintenance Manual. My experience is that particular maintenance effort is not given the attention it should and close enough is good enough for far too many Operators.
The operative words here are "Properly Rigged".
My experience on over a dozen different Types tells me I am right. I have done all sorts of CofA Air Tests, Maintenance Test Flights, Production Test Flights and have never had a problem so long as the aircraft was properly rigged and flown.
All it takes to avoid any over speed is proper application of Collective....if the Main Rotor RPM starts to go high....simply input a bit of UP Lever....and that problem is solved.
The Danger is getting the rigging wrong and not having enough Autorotative RPM as there is not much One can do to remedy that situation besides turning or flaring but those gains are only temporary and result in either an increased ROD or loss of Airspeed....both of which are not desirable in an EOL situation.
I always tried to set the Autorotative RPM at the High side limit for that reason.
Purveyor of Egg Liqueur to Lucifer
Sims are fine but is your Sim actually duplicating the reaction of a properly Rigged aircraft?
Don't forget that many factors affect how the aircraft will handle and the pilot react in any given situation, especially in autorotation. Factors such as density altitude, weight, rotor rotational speed, forward airspeed, visibility, sudden loss of ANR, disorientation, arousal, distraction, reaction, landing area available, etc.
All of these conditions can easily be factored in with a simulator yet highly problematic with the real aircraft. Real sights and sounds, varying environmental conditions, a police observer beside you, day/night and you'll find the sim will come into its own. You can even induce fatigue prior to the sim trip to simulate those those 4am round and round and round and round round and round and round and round …. tasks.
Powered autorotations in a real aircraft shortly after the sim trip would then compliment the training.
We all do auto training on the 6 monthly OPC, both day and night, to a clear area; but we also all know full well that when it happens its not going to be at 1500' over an airfield.
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Can I ask if any consideration has been given to the possibility that the reason for the agricultural evidence of a auto was that the inputs were not from the pilot? Any TFO with a bit of experience would know the basics of aircraft inputs, and let's face it the only control input they could have accessed is the collective. Just a thought....and clearly I'm just sorry that the families feel they haven't had the closure they wanted over this tragedy.
Sid,
Answer the question please.
How do you know your Sim is programmed to react as a properly Rigged Aircraft?
As you alter the Environmental and Operational Criteria on your Sim....does it also alter the Rigging Data?
My experience on Sims...having taught at two Factories is that the Sim only somewhat replicates those characteristics.
The Sim Operator can do workarounds on most parameters but the basic aircraft data can be hard to change.
Example....Israeli Defense Forces came to us wanting to do some Sim work and try to replicate a crash they had when a crew way overloaded an external hoist.
The only way we could do that was by adding seat weights on that side of the aircraft until we achieved both the Aircraft Weight and CG's both Lateral and Longitudinal. The question one would have to decide is if the Sim Aeronautical Model would then hold true for Instrument Indications and reactions to control inputs. The one thing we did learn is recovery from that situation was counter intuitive.....if our Sim was showing us accurate performance.
Sims are great for training but they are not exact duplicates of the actual aircraft.
They at best are just pretty good guesses by Aircraft Test/Design Engineers and Software Engineers as to how the actual aircraft reacts.
Anyone that thinks their aircraft shall react just like the Sim simply do not understand the complexity of computer modeling.
They are great for teaching procedures and CRM and other imitations of real life aviating but they very much have their limitations.
Answer the question please.
How do you know your Sim is programmed to react as a properly Rigged Aircraft?
As you alter the Environmental and Operational Criteria on your Sim....does it also alter the Rigging Data?
My experience on Sims...having taught at two Factories is that the Sim only somewhat replicates those characteristics.
The Sim Operator can do workarounds on most parameters but the basic aircraft data can be hard to change.
Example....Israeli Defense Forces came to us wanting to do some Sim work and try to replicate a crash they had when a crew way overloaded an external hoist.
The only way we could do that was by adding seat weights on that side of the aircraft until we achieved both the Aircraft Weight and CG's both Lateral and Longitudinal. The question one would have to decide is if the Sim Aeronautical Model would then hold true for Instrument Indications and reactions to control inputs. The one thing we did learn is recovery from that situation was counter intuitive.....if our Sim was showing us accurate performance.
Sims are great for training but they are not exact duplicates of the actual aircraft.
They at best are just pretty good guesses by Aircraft Test/Design Engineers and Software Engineers as to how the actual aircraft reacts.
Anyone that thinks their aircraft shall react just like the Sim simply do not understand the complexity of computer modeling.
They are great for teaching procedures and CRM and other imitations of real life aviating but they very much have their limitations.
Purveyor of Egg Liqueur to Lucifer
Of course you're right Sasless, every six months we will have every pilot in the company go up both day and night with the varying weights, air densities, etc etc etc in all weathers, in a real aircraft launching thenselves to the ground with no engines and fatigue setting in, all in the name of training .... oh yes, they'd have to be solo, with a TFO in the front seat, a TFO in the back and for good measure we can throw in a dog handler with their smelly dog. (Not all police dogs are smelly)
I'm not a sim expert, there may be some here, so how properly rigged do you need the sim to be to fulfil the above?
I'm not a sim expert, there may be some here, so how properly rigged do you need the sim to be to fulfil the above?
Sims etc
Just a note that may or may not be applicable. FAA and I'd assume the CAA follows a similar criteria in this regard, does not require simultaneous dual engine cuts throughout the flight envelope. So, there would likely be zero flight test data with which the sim design staff could rely on for this failure case. Behavior of the rotor and aircraft in stall conditions following a dual cut can be highly non-linear, thus very possibly* beyond the ability of the existent stability and control math to predict with any accuracy.
*If one said " probably". I for one wouldn't disagree.
*If one said " probably". I for one wouldn't disagree.
The Aerodynamic Model for a Sim comes from the Manufacturers Flight Test and Engineering Data as Brother Dixson confirmed. The Sim Geeks can only use the Data they have to create their Model. There lies one of the problems with making a Sim exactly mimic the actual aircraft.
Perhaps DB or someone with connections with some Sim Experts can confirm this.
Perhaps DB or someone with connections with some Sim Experts can confirm this.
Avoid imitations
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I wouldn't call myself an expert on simulators, however I was in the team who first introduced helicopter sim training to the RAF, using an existing commercially owned sim. I later ran the project for the RAF.
We were duty bound to find out how accurate the response of the simulator was. At first, it wasn't at all realistic, not surprising because it was designed around a later mark of aircraft, with a different cockpit layout, different engines, different aerodynamics.
The simulator programmer guru simply plugged in a keyboard, got out his computer language manuals (which he had written from scratch) and rewrote the programme it until it flew like the RAF version. We then had to select our version of aircraft when booting up the sim.
We later found that the sim would go into "crash mode" if certain parameters were exceeded, such as slight yaw or roll rate at touchdown. We were doing double engine failures to EOLs (in the dark, btw) and this was inconvenient because the sim needed to be reset each time, rather than just repositioned. This wasted valuable training time, let alone put the $hits up the average student because it could be quite violent, being a full motion sim. Again, the programmer simply rewrote the software in a couple of minutes, so it wasn't so sensitive. I spent a lot of time talking to this guy, over the years I was in that job. He told me that certain responses could never be assumed to have been programmed correctly. For example, tail rotor drive failures. No-one can be persuaded to deliberately fly an aircraft in this condition to obtain data, so an estimated response of the aircraft is all you can hope for.
As I understand it, these "best guesses" are known as "off model responses".
So, take simulators to be the "complete authority" of actual aircraft response at your own risk!
We were duty bound to find out how accurate the response of the simulator was. At first, it wasn't at all realistic, not surprising because it was designed around a later mark of aircraft, with a different cockpit layout, different engines, different aerodynamics.
The simulator programmer guru simply plugged in a keyboard, got out his computer language manuals (which he had written from scratch) and rewrote the programme it until it flew like the RAF version. We then had to select our version of aircraft when booting up the sim.
We later found that the sim would go into "crash mode" if certain parameters were exceeded, such as slight yaw or roll rate at touchdown. We were doing double engine failures to EOLs (in the dark, btw) and this was inconvenient because the sim needed to be reset each time, rather than just repositioned. This wasted valuable training time, let alone put the $hits up the average student because it could be quite violent, being a full motion sim. Again, the programmer simply rewrote the software in a couple of minutes, so it wasn't so sensitive. I spent a lot of time talking to this guy, over the years I was in that job. He told me that certain responses could never be assumed to have been programmed correctly. For example, tail rotor drive failures. No-one can be persuaded to deliberately fly an aircraft in this condition to obtain data, so an estimated response of the aircraft is all you can hope for.
As I understand it, these "best guesses" are known as "off model responses".
So, take simulators to be the "complete authority" of actual aircraft response at your own risk!
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Any good heli sim will have an underlying physics model that gets the device a majority of the way to the correct behavior. The flight test data is then used to confirm correct simulator behavior, and if necessary tweak the simulator physics model to achieve a data match.
The black magic and art of creating a good heli model resides in the ability of the engineer to tweak the physics model using the flight test data without introducing incorrect behavior in the flight regime where no flight test data is provided.
These days, our ability to simulate helicopter behavior is pretty respectable. So while the sim might not be perfect, it should be accurate enough to give you some sense of how to survive an emergency situation in the actual aircraft, regardless of whether that situation has been validated by flight test data or not.
The black magic and art of creating a good heli model resides in the ability of the engineer to tweak the physics model using the flight test data without introducing incorrect behavior in the flight regime where no flight test data is provided.
These days, our ability to simulate helicopter behavior is pretty respectable. So while the sim might not be perfect, it should be accurate enough to give you some sense of how to survive an emergency situation in the actual aircraft, regardless of whether that situation has been validated by flight test data or not.
Dreaded Virus
Uh-oh. I can see that in spite of efforts from manufacturers test pilots all over the globe aimed at stamping it out, that dreaded virus " Simulitis " is still around. Beware!
Avoid imitations
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I went to counselling and managed to get over it.
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Apart from being a "Victim" of simulators for a good few years I had very little understanding of how these machines are built and work. I am slowly getting more knowledgeable in my current job.
This is what I Know (or think I know).
1. The best possible simulator is achieved by using the manufacturers flight data pack.
2. However, as someone already mentioned, there is little appetite amongst the Flight Test community to test dangerous failures such as TR drive and in some large MEH, full EOLs. Therefore some of the flight test data is absent to support all the failures in the RFM.
3. Contrary to many beliefs, an FFS is built to reflect the design and therefor the failure modes prescribed in the RFM. Going off piste by trying to simulate conditions not prescribed in the RFM is very problematic but far worse than that is someone trying to draw conclusions about the heli, in a sim that was never designed to meet the conditions applied.
4. The simulation of actual aircraft software behaviours such as AFCS, FADEC etc is very important in modern sophisticated helicopters so for the most part real black boxes/software should ideally be used. However, if the flying characteristics (flight loop) has not been accurately captured even this strategy becomes unrealistic.
In the end it then comes down to subjective opinion. Does it behave, feel, smell, sound right? The more experienced the source of that opinion, the better the result after subsequent tuning. IMHO the best source of that opinion is obviously the Type Certificate Test Pilot(s).
But to be honest, again IMHO, entering autorotation is often poorly trained both in FFS and the aircraft. So many times I see poor pilot performance matched only by the poor quality of the debrief points. Very very often Instructors fail to point out the relationship between collective and cyclic in respect of NR stability!
The collective sets the datum and the cyclic creates instability in that datum (when waggled around). In aircraft with good ATT AFCS mode, often a quick stab on the trim release and leaving the cyclic still for a moment, regenerates pilot capacity to process the subsequent actions. In this respect simulators are invaluable PROVIDED sufficient time on the OPC cycle is allocated to this exercise. Sadly, all too often, its squeezed in at the end of a session generally with little or almost no real training given.
I have to say that since this accident I genrally start the OPC cycle with a good hour of EOLs, TRDS, and TR malfunctions with the emphasis on Training the candidate rather than testing. Most pilots need this after 6 or so months blasting along in the cruise. I am very lucky, I have an FFS with the full OEM Datapack. Even so I am sometimes painfully aware hat I am training pilots to "Fly the sim" in respect to these exercises, where the aircraft may behave differently to some degree.
This is what I Know (or think I know).
1. The best possible simulator is achieved by using the manufacturers flight data pack.
2. However, as someone already mentioned, there is little appetite amongst the Flight Test community to test dangerous failures such as TR drive and in some large MEH, full EOLs. Therefore some of the flight test data is absent to support all the failures in the RFM.
3. Contrary to many beliefs, an FFS is built to reflect the design and therefor the failure modes prescribed in the RFM. Going off piste by trying to simulate conditions not prescribed in the RFM is very problematic but far worse than that is someone trying to draw conclusions about the heli, in a sim that was never designed to meet the conditions applied.
4. The simulation of actual aircraft software behaviours such as AFCS, FADEC etc is very important in modern sophisticated helicopters so for the most part real black boxes/software should ideally be used. However, if the flying characteristics (flight loop) has not been accurately captured even this strategy becomes unrealistic.
In the end it then comes down to subjective opinion. Does it behave, feel, smell, sound right? The more experienced the source of that opinion, the better the result after subsequent tuning. IMHO the best source of that opinion is obviously the Type Certificate Test Pilot(s).
But to be honest, again IMHO, entering autorotation is often poorly trained both in FFS and the aircraft. So many times I see poor pilot performance matched only by the poor quality of the debrief points. Very very often Instructors fail to point out the relationship between collective and cyclic in respect of NR stability!
The collective sets the datum and the cyclic creates instability in that datum (when waggled around). In aircraft with good ATT AFCS mode, often a quick stab on the trim release and leaving the cyclic still for a moment, regenerates pilot capacity to process the subsequent actions. In this respect simulators are invaluable PROVIDED sufficient time on the OPC cycle is allocated to this exercise. Sadly, all too often, its squeezed in at the end of a session generally with little or almost no real training given.
I have to say that since this accident I genrally start the OPC cycle with a good hour of EOLs, TRDS, and TR malfunctions with the emphasis on Training the candidate rather than testing. Most pilots need this after 6 or so months blasting along in the cruise. I am very lucky, I have an FFS with the full OEM Datapack. Even so I am sometimes painfully aware hat I am training pilots to "Fly the sim" in respect to these exercises, where the aircraft may behave differently to some degree.
I agree with much of your post but:
Do you have any justification for this point? My understanding regarding flight testing for the sim flight model is that the manufacture's flight testing is primarily about certification. The sim data is taken from that as a secondary consideration and thus the test flights are not optimised to sim flight model data gathering.
By contrast a third party manufacturer (Frasca in our case) does a lot of fully instrumented test flying dedicated solely to sim flight model data gathering. As a result, the flight model data is more comprehensive.
Well that's what Frasca told me anyway! And it does seem reasonable.
It may be a bit problematic, but when the flight manual, is wrong, or has significant omissions in mentioned failure modes, there isn't much choice.
By contrast a third party manufacturer (Frasca in our case) does a lot of fully instrumented test flying dedicated solely to sim flight model data gathering. As a result, the flight model data is more comprehensive.
Well that's what Frasca told me anyway! And it does seem reasonable.
It may be a bit problematic, but when the flight manual, is wrong, or has significant omissions in mentioned failure modes, there isn't much choice.
Not defensive, I have no vested interest anymore. I was just interested in what the truth of the matter was. I got one side of the story, you got the other, I wonder where the truth lies?
Sim Data
HC, you are correct in surmising that OEM's now typically add specific flight test data flights at the direction of the sim manufacturers design/software group.
Kidding about " Simulitis " aside, it is fair to say that the fidelity ( if that is the word ) of helicopter flight siimulation today is far superior to what it used to be, and is presently being pushed particularly by the OEM's effforts in bringing fly by wire technology into the industry. Still, as efforts in the RAH-66, S-92 Canadian MHP, X2 have shown to date, and now ( I'd expect ) with the 53K, the sim work allows flight test to proceed safely, but one should expect a good deal of flight control software mods based on flight test results.
Getting back to this accident, there are the questions re the reaction to the dual engine stoppage, and then the behavior of the rotor at perhaps very low Nr. Can we place any confidence in a present day flight simulation of this sort of event? I have a mental list of problems that showed up in flight test at SA which did not show up in preparatory Gen Hel simulations: empennage issues, rotor stability issues, that type of thing, and I think that some degree of skepticism remains a healthy attitude to take toward simulation applied to the edges of the flight envelope. Guess I'm saying that readers ought to pay attention to both HC and DB.
Kidding about " Simulitis " aside, it is fair to say that the fidelity ( if that is the word ) of helicopter flight siimulation today is far superior to what it used to be, and is presently being pushed particularly by the OEM's effforts in bringing fly by wire technology into the industry. Still, as efforts in the RAH-66, S-92 Canadian MHP, X2 have shown to date, and now ( I'd expect ) with the 53K, the sim work allows flight test to proceed safely, but one should expect a good deal of flight control software mods based on flight test results.
Getting back to this accident, there are the questions re the reaction to the dual engine stoppage, and then the behavior of the rotor at perhaps very low Nr. Can we place any confidence in a present day flight simulation of this sort of event? I have a mental list of problems that showed up in flight test at SA which did not show up in preparatory Gen Hel simulations: empennage issues, rotor stability issues, that type of thing, and I think that some degree of skepticism remains a healthy attitude to take toward simulation applied to the edges of the flight envelope. Guess I'm saying that readers ought to pay attention to both HC and DB.
Flying on the outside of the Envelope is inherently dangerous and it is certain to me that thinking a Simulator is going to be dead nuts accurate in that same realm is very dangerous.
