How to detect the approaching stall ?
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How to detect the approaching stall ?
Hi everyone,
I am in the second semester of my final year of a Bsc(Hons)degree in industrial design. I have chosen a project for my final year concerning flight safety in general aviation.
I have been working with some great people over the last few months developing ideas that may improve safety and help build confidence and to date have produced to similar concepts that primarily deal with how the pilot is presented information in flight and a form of virtual co pilot or instructor to watch over the pilot.
What I am looking at now is how to collect the flight information traditionally presented via the 6 primary instruments.
I propose to use a combination of GPS information and a separate gyro to provide attitude information.
With these two inputs providing a three-dimensional model of the aircraft in flight.
I hope you are still with me?
Could anyone, pilots or engineers help me work out exactly what the computer would need to know in order to detect the approaching stall? The basis of the system is a computer that interprets the incoming values and compares them to type specific aircraft figures. This allows it to monitor the various factors that relate to the aircraft being flown safely. Much as your instructor watching over you would.
I am aware there are many factors that relate to the stall not just airspeed or angle of attack but don’t know exactly what they all are !
Any help at all would be hugely appreciated with regard to any of the points I have raised here.
Thank you for your time and I look forward to any information you feel may be of benefit.
Many regards,
Buster
I am in the second semester of my final year of a Bsc(Hons)degree in industrial design. I have chosen a project for my final year concerning flight safety in general aviation.
I have been working with some great people over the last few months developing ideas that may improve safety and help build confidence and to date have produced to similar concepts that primarily deal with how the pilot is presented information in flight and a form of virtual co pilot or instructor to watch over the pilot.
What I am looking at now is how to collect the flight information traditionally presented via the 6 primary instruments.
I propose to use a combination of GPS information and a separate gyro to provide attitude information.
With these two inputs providing a three-dimensional model of the aircraft in flight.
I hope you are still with me?
Could anyone, pilots or engineers help me work out exactly what the computer would need to know in order to detect the approaching stall? The basis of the system is a computer that interprets the incoming values and compares them to type specific aircraft figures. This allows it to monitor the various factors that relate to the aircraft being flown safely. Much as your instructor watching over you would.
I am aware there are many factors that relate to the stall not just airspeed or angle of attack but don’t know exactly what they all are !
Any help at all would be hugely appreciated with regard to any of the points I have raised here.
Thank you for your time and I look forward to any information you feel may be of benefit.
Many regards,
Buster
I am in the second semester of my final year of a Bsc(Hons)degree in industrial design. I have chosen a project for my final year concerning flight safety in general aviation.
Good for you, and good luck
I have been working with some great people over the last few months developing ideas that may improve safety and help build confidence and to date have produced to similar concepts that primarily deal with how the pilot is presented information in flight and a form of virtual co pilot or instructor to watch over the pilot.
The main pre-stall clues are airframe buffet, stick buffet, back-stick force, rear-stick position, audible stall warning (if fitted), pitch attitude, reduced primary control responsiveness, reduced airspeed. The stall itself is marked (in piloting terms) by the point at which full control is no longer available over the aircraft - this could be pitch break, loss of nose-up pitch authority, wing drop, wing rock, roll inverted without asking, incipient spin, or operation of some artificial advice such as a stick pusher. I've seen all of these, bur prefer the first two !
What I am looking at now is how to collect the flight information traditionally presented via the 6 primary instruments.
A domestic camcorder, mounted between the pilots heads, looking at the relevant instruments, ideally with stick position and visual horizon in the peripheral view. Record intercom using a magnetic pickup (£3.50 from Maplins last I looked, sold for recording phone calls) within one of the headsets. Oh yes, and make sure the pilots fly with the sun on one wingtip, into or down sun the picture isn't very good. A good test pilot will give running commentary that you can record, and ultimately only he can define the point of stall. Don't use anybody but a good test pilot, you'll be wasting your time and money; there are many excellent pilots out there who simply haven't had the training to do this.
I propose to use a combination of GPS information and a separate gyro to provide attitude information.
GPS is of no use to you in this context except possibly to aid the subsequent accident investigation once you screw up. If you are using a certified aircraft there should already be a PEC curve available, which is the only thing GPS has any relevance to in this exercise. If you've already got an attitude gyro, just film that and save money and possible inconsistencies between the two systems.
With these two inputs providing a three-dimensional model of the aircraft in flight.
3-dimensional position in space is irrelevant unless you have local wind data. Also, stalling tests are primarily relevant only to the pilots perception, so you need to use what he or she will perceive, not create a separate set of data that will cost you time and money to obtain, and also need calibrating. Additionally, GPS update rates are not good enough for stall testing.
I hope you are still with me?
Of course, but are you with me?
Could anyone, pilots or engineers help me work out exactly what the computer would need to know in order to detect the approaching stall? The basis of the system is a computer that interprets the incoming values and compares them to type specific aircraft figures. This allows it to monitor the various factors that relate to the aircraft being flown safely. Much as your instructor watching over you would.
See my notes above. Stall warning systems are invariably based upon AoA. The stall will always be at the same AoA for the same flap&slat setting. Also, AoA will be increasing as the stall is approached, so fit a cubic spline to the AoA .v. time curve, and you can predict the onset of stall continuously - say set it to trigger at 3 second or less
I am aware there are many factors that relate to the stall not just airspeed or angle of attack but don’t know exactly what they all are !
Depends on how you model it. For a given flap, slat & gear setting the stall may be reasonably regarded as always at the same AoA. For a given flap setting, and a rigid wing, the stall speed in CAS will be proportional to the square root of weight. The relationship between CAS and IAS will be in the POH, or failing that can be determined in an hour or three using a GPS, trailing static, calibrated chase-plane or a range course method (all in the standard textbooks). Note that pilot perceived stalling speed will be a function of CG also - reducing with aft CG, and both perceived and aerodynamic stall will occur at a lower speed / higher AoA with a greater deceleration rate.
Any help at all would be hugely appreciated with regard to any of the points I have raised here.
Hope this helped a bit. Try also the following references (all on the web somewhere): FAA AC23-8, BMAA form BMAA/AW/010a and BMAA/AW/043, various stuff on the websites of SETP, SFTE, and NASA - look at some of the links in tech log.
G
Note to moderator, if our man doesn't get any more response than mine, this post might bear moving to either tech-log or better still flight test where a lot more specialists in the field are likely to be found?
Good for you, and good luck
I have been working with some great people over the last few months developing ideas that may improve safety and help build confidence and to date have produced to similar concepts that primarily deal with how the pilot is presented information in flight and a form of virtual co pilot or instructor to watch over the pilot.
The main pre-stall clues are airframe buffet, stick buffet, back-stick force, rear-stick position, audible stall warning (if fitted), pitch attitude, reduced primary control responsiveness, reduced airspeed. The stall itself is marked (in piloting terms) by the point at which full control is no longer available over the aircraft - this could be pitch break, loss of nose-up pitch authority, wing drop, wing rock, roll inverted without asking, incipient spin, or operation of some artificial advice such as a stick pusher. I've seen all of these, bur prefer the first two !
What I am looking at now is how to collect the flight information traditionally presented via the 6 primary instruments.
A domestic camcorder, mounted between the pilots heads, looking at the relevant instruments, ideally with stick position and visual horizon in the peripheral view. Record intercom using a magnetic pickup (£3.50 from Maplins last I looked, sold for recording phone calls) within one of the headsets. Oh yes, and make sure the pilots fly with the sun on one wingtip, into or down sun the picture isn't very good. A good test pilot will give running commentary that you can record, and ultimately only he can define the point of stall. Don't use anybody but a good test pilot, you'll be wasting your time and money; there are many excellent pilots out there who simply haven't had the training to do this.
I propose to use a combination of GPS information and a separate gyro to provide attitude information.
GPS is of no use to you in this context except possibly to aid the subsequent accident investigation once you screw up. If you are using a certified aircraft there should already be a PEC curve available, which is the only thing GPS has any relevance to in this exercise. If you've already got an attitude gyro, just film that and save money and possible inconsistencies between the two systems.
With these two inputs providing a three-dimensional model of the aircraft in flight.
3-dimensional position in space is irrelevant unless you have local wind data. Also, stalling tests are primarily relevant only to the pilots perception, so you need to use what he or she will perceive, not create a separate set of data that will cost you time and money to obtain, and also need calibrating. Additionally, GPS update rates are not good enough for stall testing.
I hope you are still with me?
Of course, but are you with me?
Could anyone, pilots or engineers help me work out exactly what the computer would need to know in order to detect the approaching stall? The basis of the system is a computer that interprets the incoming values and compares them to type specific aircraft figures. This allows it to monitor the various factors that relate to the aircraft being flown safely. Much as your instructor watching over you would.
See my notes above. Stall warning systems are invariably based upon AoA. The stall will always be at the same AoA for the same flap&slat setting. Also, AoA will be increasing as the stall is approached, so fit a cubic spline to the AoA .v. time curve, and you can predict the onset of stall continuously - say set it to trigger at 3 second or less
I am aware there are many factors that relate to the stall not just airspeed or angle of attack but don’t know exactly what they all are !
Depends on how you model it. For a given flap, slat & gear setting the stall may be reasonably regarded as always at the same AoA. For a given flap setting, and a rigid wing, the stall speed in CAS will be proportional to the square root of weight. The relationship between CAS and IAS will be in the POH, or failing that can be determined in an hour or three using a GPS, trailing static, calibrated chase-plane or a range course method (all in the standard textbooks). Note that pilot perceived stalling speed will be a function of CG also - reducing with aft CG, and both perceived and aerodynamic stall will occur at a lower speed / higher AoA with a greater deceleration rate.
Any help at all would be hugely appreciated with regard to any of the points I have raised here.
Hope this helped a bit. Try also the following references (all on the web somewhere): FAA AC23-8, BMAA form BMAA/AW/010a and BMAA/AW/043, various stuff on the websites of SETP, SFTE, and NASA - look at some of the links in tech log.
G
Note to moderator, if our man doesn't get any more response than mine, this post might bear moving to either tech-log or better still flight test where a lot more specialists in the field are likely to be found?
Last edited by Genghis the Engineer; 18th Feb 2003 at 13:55.
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On the other hand, sometimes "systems" don't do their intended functions....properly.
Recall many years ago on takeoff in a Hansa Jet, at 'round about 200agl, the stick pusher tried to bury the column in the instrument panel.
Not helpful, at ALL.
Took both of us pulling hard, to keep out of the perverbial smokin' hole.
Recall many years ago on takeoff in a Hansa Jet, at 'round about 200agl, the stick pusher tried to bury the column in the instrument panel.
Not helpful, at ALL.
Took both of us pulling hard, to keep out of the perverbial smokin' hole.
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Hello Buster,
I did Aeronautical Engineering at University, so I might be able to offer a different angle to Genghis.
If you approach it from what influences the stall, then it helps to know what the stall equation is:
Vstall = Square root of [2L/(CLmax.S.rho)]
where:
L = Lift force (N) which is equal to the weight in straight and level flight,
CLmax = max coefficient of lift for the wing (can be found on the alpha graph),
S = Wing area
rho = density
I can imagine a simple program that you could use to calculate the stall speed. You could input the CLmax for a given aircraft clean and flapped, input the wing sizes clean and flapped and then you'd just need to measure the density and velocity of the aircraft in flight. You could work these out from a pitot or something similar.
Measuring the lift may proove a tad tricky - perhaps it would be easier to measure the load which could work out the lift (having inputted the mass before take-off?).
You'd then just need to tell the program what state the wing was in (clean, 10 deg flap etc etc), perhaps that could be done with a sensor by the flap or the flap lever.
It might take a bit of design iteration though!!
I did Aeronautical Engineering at University, so I might be able to offer a different angle to Genghis.
If you approach it from what influences the stall, then it helps to know what the stall equation is:
Vstall = Square root of [2L/(CLmax.S.rho)]
where:
L = Lift force (N) which is equal to the weight in straight and level flight,
CLmax = max coefficient of lift for the wing (can be found on the alpha graph),
S = Wing area
rho = density
I can imagine a simple program that you could use to calculate the stall speed. You could input the CLmax for a given aircraft clean and flapped, input the wing sizes clean and flapped and then you'd just need to measure the density and velocity of the aircraft in flight. You could work these out from a pitot or something similar.
Measuring the lift may proove a tad tricky - perhaps it would be easier to measure the load which could work out the lift (having inputted the mass before take-off?).
You'd then just need to tell the program what state the wing was in (clean, 10 deg flap etc etc), perhaps that could be done with a sensor by the flap or the flap lever.
It might take a bit of design iteration though!!
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Couldn't you use the test aircraft's exisiting stall warning devices and hardwire your data collector into that? Saves reinventing the wheel....
Do stall warning devices go off at a certain angle of attack regardless of airspeed? Surely they must.. unless their aimed at the approach config stall only? I'm confused! help!!!
(forgive the dumb question.. I'm only a wannabe test pilot ... )
Do stall warning devices go off at a certain angle of attack regardless of airspeed? Surely they must.. unless their aimed at the approach config stall only? I'm confused! help!!!
(forgive the dumb question.. I'm only a wannabe test pilot ... )
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Cypher, the stall warner I'm familiar with is a small metal tab on the wing's leading edge called a vane. It flicks up when the airflow over it passes a certain angle, completing a circuit sounding a buzzer.
I think there are also other types that use pressure switches.
I think there are also other types that use pressure switches.
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What an informed response!
Thank you all very much for your replies, it is much appreciated.
However I fear that I have not explained my idea properly. The aim of my project is to design a product, a device that could be used within a light aircraft be it a Cessna 150 or a Seneca. The idea is that the product would be used by an individual pilot for the particular type of aircraft they fly. One element of the system is that the product is to work in real time and advise the pilot immediately that the aircraft is flown in a manner that may lead to a stall/spin. It would also advise on any other event out with normal operations. This could be making them aware of approaching airspace boundaries, danger areas etc.
The pilot would be able to download or purchase a file with their aircraft limitations such as stall speed, fuel and range etc, and install that into the computer. This computer would monitor the information coming in from the GPS for speed and position and the gyro for attitude information. I was thinking that if the GPS updates once every second that it could provide at least time to issue a warning to the pilot if the speed was decaying in order for the correct action to be taken. Not all aircraft are fitted with stall warning devices.
I am aiming to create a product that is a form of HUD, which would be much the same size as a conventional GPS that could be installed on the top of the instrument panel. The projection system itself is probably going to be a form of TOLED, a Transparent Organic Light Emitting Device that projects images and text onto a clear film. I could apply this directly to the Perspex or an extending sheet much like the screens for overhead projectors. So now I am looking at intuitive ways to get this information across and capture the pilots attention in times of stress.
Of course this brings me back to the post topic. I have never used a GPS and am at this point trying to understand exactly what they can and cant do! I believed that the GPS gives you ground speed, position, limited height information depending on satellites acquired and could work out eta’s and so on. All this information if organised and screened through a computer into an easily understood display would surely enhance situational awareness for new and inexperienced pilots? This is my market at the moment, to help build confidence and offer another level of backup almost like a safety pilot. Part of the inspiration for this project as well as my own experiences is a book I read many years ago that was part of what inspired me to learn to fly. The Shepherd by Frederick Forsyth is a story about a young RAF pilot who loses all his instruments whilst out over the North Sea. The weather has also closed in and he is unable to see a way out of this situation. It’s about that terrifying feeling of isolation and how panic can build up and quickly consume your thoughts and actions. It really is a fantastic story that epitomizes the thinking behind my project. Suffice to say, if my product could in some provide a back up of instrumentation and provide a voice to both verbally and graphically watch over the pilot I will be a very happy man!
What I am asking is, are the technologies I am proposing to use able in your opinion to provide the type of speed and accuracy to warn the pilot in sufficient time, as a conventional stall warning device would.
Once again thanks you for your time, this type of feedback from professional engineers and pilots is really invaluable to my project and a great help for my own understanding.
Many thanks again, and I look forward to your replies,
Your Buster,
Thank you all very much for your replies, it is much appreciated.
However I fear that I have not explained my idea properly. The aim of my project is to design a product, a device that could be used within a light aircraft be it a Cessna 150 or a Seneca. The idea is that the product would be used by an individual pilot for the particular type of aircraft they fly. One element of the system is that the product is to work in real time and advise the pilot immediately that the aircraft is flown in a manner that may lead to a stall/spin. It would also advise on any other event out with normal operations. This could be making them aware of approaching airspace boundaries, danger areas etc.
The pilot would be able to download or purchase a file with their aircraft limitations such as stall speed, fuel and range etc, and install that into the computer. This computer would monitor the information coming in from the GPS for speed and position and the gyro for attitude information. I was thinking that if the GPS updates once every second that it could provide at least time to issue a warning to the pilot if the speed was decaying in order for the correct action to be taken. Not all aircraft are fitted with stall warning devices.
I am aiming to create a product that is a form of HUD, which would be much the same size as a conventional GPS that could be installed on the top of the instrument panel. The projection system itself is probably going to be a form of TOLED, a Transparent Organic Light Emitting Device that projects images and text onto a clear film. I could apply this directly to the Perspex or an extending sheet much like the screens for overhead projectors. So now I am looking at intuitive ways to get this information across and capture the pilots attention in times of stress.
Of course this brings me back to the post topic. I have never used a GPS and am at this point trying to understand exactly what they can and cant do! I believed that the GPS gives you ground speed, position, limited height information depending on satellites acquired and could work out eta’s and so on. All this information if organised and screened through a computer into an easily understood display would surely enhance situational awareness for new and inexperienced pilots? This is my market at the moment, to help build confidence and offer another level of backup almost like a safety pilot. Part of the inspiration for this project as well as my own experiences is a book I read many years ago that was part of what inspired me to learn to fly. The Shepherd by Frederick Forsyth is a story about a young RAF pilot who loses all his instruments whilst out over the North Sea. The weather has also closed in and he is unable to see a way out of this situation. It’s about that terrifying feeling of isolation and how panic can build up and quickly consume your thoughts and actions. It really is a fantastic story that epitomizes the thinking behind my project. Suffice to say, if my product could in some provide a back up of instrumentation and provide a voice to both verbally and graphically watch over the pilot I will be a very happy man!
What I am asking is, are the technologies I am proposing to use able in your opinion to provide the type of speed and accuracy to warn the pilot in sufficient time, as a conventional stall warning device would.
Once again thanks you for your time, this type of feedback from professional engineers and pilots is really invaluable to my project and a great help for my own understanding.
Many thanks again, and I look forward to your replies,
Your Buster,
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Hi Buster,
Sounds like you have lots of good ideas, although I'm afraid you may find that the big GPS manufacturers may have beaten you to many of them. Check out Garmin's website, particularly the small handhelds like the Pilot III and the GPSMAP 196 - these already feature an incredible array of 'situational awareness' features including warnings on approaching controlled airspace etc, calculating ETAs to each waypoint, fuel remaining, etc.
However, as Genghis says, GPS is no good for the other parts of your plan, to do with warning the pilot of an impending stall/spin situation. Predicting an impending stall is *extremely* dependent on the local wind conditions - and I don't just mean headwind/tailwind. Much more important and dangerous are small scale changes in wind conditions - updrafts, downdrafts, wind shear, turbulence, etc - and GPS can't tell you anything about those, unfortunately.
To my mind, a device that would be useful, both for stall warning and more generally, would be an angle of attack guage. As you can read in John S Denker's online book, an awful lot of key aircraft performance configurations (stall, best glide) relate to a specific AoA, but we pilots have to try to achieve those configurations based on indicated airspeed which is only indirectly related to AoA... An AoA guage, perhaps with a predictive warning based on rate of increase of AoA, would be an interesting and useful device...
cbl.
Sounds like you have lots of good ideas, although I'm afraid you may find that the big GPS manufacturers may have beaten you to many of them. Check out Garmin's website, particularly the small handhelds like the Pilot III and the GPSMAP 196 - these already feature an incredible array of 'situational awareness' features including warnings on approaching controlled airspace etc, calculating ETAs to each waypoint, fuel remaining, etc.
However, as Genghis says, GPS is no good for the other parts of your plan, to do with warning the pilot of an impending stall/spin situation. Predicting an impending stall is *extremely* dependent on the local wind conditions - and I don't just mean headwind/tailwind. Much more important and dangerous are small scale changes in wind conditions - updrafts, downdrafts, wind shear, turbulence, etc - and GPS can't tell you anything about those, unfortunately.
To my mind, a device that would be useful, both for stall warning and more generally, would be an angle of attack guage. As you can read in John S Denker's online book, an awful lot of key aircraft performance configurations (stall, best glide) relate to a specific AoA, but we pilots have to try to achieve those configurations based on indicated airspeed which is only indirectly related to AoA... An AoA guage, perhaps with a predictive warning based on rate of increase of AoA, would be an interesting and useful device...
cbl.
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Buster,
As part of my Aero Eng degree course, I designed an angle of attack indicating system for a light aircraft. The most important aspect of predicting the stall is angle of attack and as has been said above, the stall angle of attack depends on flap configuration. It looks like you are trying to cover a number of issues here and it may be worth concentrating on one or two of them, with the others as suggested extensions for the product. The reason I say this is that often in degree projects (I have done three and seen many friends with theirs), it is easy to have eyes too big for your time frame! Perhaps split it into stall prediction, navigation and airspace warnings and approaching limit warnings (such as g load and never exceed speed). The days of instruments totally failing, while not gone are diminishing and it seems like you are trying to achieve a 'catch all', which although a good idea, may be too involved and produced in other systems such as EGPWS, TCAS and Stick shake.
However:
For Navigation alerts, a GPS is great, a database can tell you where the airspace/danger ares/hills are warn you depending on rate of approach and distance etc. Some like the Skymap already do this. Added altitude information is required really, as the GPS altitude is not the altitude above sea level, but the altitude above the GPS datum, which is only an approximation to the world. GPS altitude is probably the least accurate of the paramaters GPS will give you.
For limits protection, it will depend on the limit, for example never exceed speed is an INDICATED airspeed and depends on the pitot system. For instance, in a huge wind it would be possible to be flying backward over the GROUND but approaching never exceed AIRSPEED in something like a C152 (more of a thought experipent than actuality I hasten to add!) so a GPS speed read out would be near useless. Similarly, facing the other way, our imagined aircraft could be well over the numerical never exceed in terms of groundspeed, but no where near it in terms of airspeed. Also, g limits would require a g meter, mach limits a mach meter (or at least the inputs to one and a computer). For limits protection a computer attached to a g meter and the pitot static system would be much more useful than a GPS I think.
Stall protection has already been achieved in many areas using different systems, but most are either a simple vane or reed (such as on the Cessna 152) that give a warning of a certain angle of attack. The more involved ones take account of flap position. Look at a company called Rosemount for vane and rotating slit type AOA transducers.
In the aircraft I fly (Jetstream 41) there are two AOA vanes, one each side. We have EFIS screens with a speed tape down the left hand side and the high and low speed warnings appear as a red tape next to the normal speed tape. Both vanes are active and give local angle of attack continuously. If either approaches the stall angle, the stick shaker activates, if both approach the stall angle, the stick pusher operates. The red tape changes position the whole time depending on the angle of attack the vanes sense at any given time. For instance if you were approaching the flare right on the edge of the red tape (we do not do this!) all would be well until you flared. The inertia of the aircraft would take it along the same flight path for a short time, even though the nose was raised, thereby increasing the angle of attack (for a short time, until things have settled down) so the warning tape rises a bit and the stick shaker would be set off. I have done this in the sim and it is not nice, especially if you flare suddenly and set the stick pusher off!!! The point being that with gusts, or during a manoeuvre the speed tape changes position to give you a visual warning of the stall and it takes into account the local airflow, which at that time is the most important factor affecting the stall. With flaps the red tape moves again.
Try also looking at NASA's AGATE (AGARD?) project which is something like Advanced General Aviation something or other, the project is researching glass cockpits, HUD's, and lots of other weird and wacky things to fit into light and GA aircraft and is basically mapping out the possible 'future' of GA.
Hope all this helps. Feel free to email if you want to ask anything or if you think I may be able to help.
Good luck,
J-R
[email protected]
{Edited to correct my mistake as pointed out below.}
As part of my Aero Eng degree course, I designed an angle of attack indicating system for a light aircraft. The most important aspect of predicting the stall is angle of attack and as has been said above, the stall angle of attack depends on flap configuration. It looks like you are trying to cover a number of issues here and it may be worth concentrating on one or two of them, with the others as suggested extensions for the product. The reason I say this is that often in degree projects (I have done three and seen many friends with theirs), it is easy to have eyes too big for your time frame! Perhaps split it into stall prediction, navigation and airspace warnings and approaching limit warnings (such as g load and never exceed speed). The days of instruments totally failing, while not gone are diminishing and it seems like you are trying to achieve a 'catch all', which although a good idea, may be too involved and produced in other systems such as EGPWS, TCAS and Stick shake.
However:
For Navigation alerts, a GPS is great, a database can tell you where the airspace/danger ares/hills are warn you depending on rate of approach and distance etc. Some like the Skymap already do this. Added altitude information is required really, as the GPS altitude is not the altitude above sea level, but the altitude above the GPS datum, which is only an approximation to the world. GPS altitude is probably the least accurate of the paramaters GPS will give you.
For limits protection, it will depend on the limit, for example never exceed speed is an INDICATED airspeed and depends on the pitot system. For instance, in a huge wind it would be possible to be flying backward over the GROUND but approaching never exceed AIRSPEED in something like a C152 (more of a thought experipent than actuality I hasten to add!) so a GPS speed read out would be near useless. Similarly, facing the other way, our imagined aircraft could be well over the numerical never exceed in terms of groundspeed, but no where near it in terms of airspeed. Also, g limits would require a g meter, mach limits a mach meter (or at least the inputs to one and a computer). For limits protection a computer attached to a g meter and the pitot static system would be much more useful than a GPS I think.
Stall protection has already been achieved in many areas using different systems, but most are either a simple vane or reed (such as on the Cessna 152) that give a warning of a certain angle of attack. The more involved ones take account of flap position. Look at a company called Rosemount for vane and rotating slit type AOA transducers.
In the aircraft I fly (Jetstream 41) there are two AOA vanes, one each side. We have EFIS screens with a speed tape down the left hand side and the high and low speed warnings appear as a red tape next to the normal speed tape. Both vanes are active and give local angle of attack continuously. If either approaches the stall angle, the stick shaker activates, if both approach the stall angle, the stick pusher operates. The red tape changes position the whole time depending on the angle of attack the vanes sense at any given time. For instance if you were approaching the flare right on the edge of the red tape (we do not do this!) all would be well until you flared. The inertia of the aircraft would take it along the same flight path for a short time, even though the nose was raised, thereby increasing the angle of attack (for a short time, until things have settled down) so the warning tape rises a bit and the stick shaker would be set off. I have done this in the sim and it is not nice, especially if you flare suddenly and set the stick pusher off!!! The point being that with gusts, or during a manoeuvre the speed tape changes position to give you a visual warning of the stall and it takes into account the local airflow, which at that time is the most important factor affecting the stall. With flaps the red tape moves again.
Try also looking at NASA's AGATE (AGARD?) project which is something like Advanced General Aviation something or other, the project is researching glass cockpits, HUD's, and lots of other weird and wacky things to fit into light and GA aircraft and is basically mapping out the possible 'future' of GA.
Hope all this helps. Feel free to email if you want to ask anything or if you think I may be able to help.
Good luck,
J-R
[email protected]
{Edited to correct my mistake as pointed out below.}
Last edited by Jetstream Rider; 21st Feb 2003 at 11:59.
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CBLong and Jetstream Rider, thank you very much for your replies.
I am growing increasingly concerned that the product I feel would really provide a complete system of protection and increase situational awareness for new pilots is not going to be possible in the time I have available.
CBLong I appreciate your thoughts and thanks for the link, I was hoping to avoid fitting any external components or altering the airframe in anyway as that would lead to certification issues, so the fact that the technologies I had proposed are not going to perform is a slightly worrying issue I now have to deal with!
I was aiming to create a product that could be installed much like a portable GPS.
Jetstream I think you have definitely hit the nail on the head! I am scratching my head trying to figure out how to get so much into this product so that it can cater for every eventuality. I have until the middle of April to have my final concept finalised, and start on my design report. There really is so little time.
I have some ideas concerning the visualisation of airspace and the environment we operate in and I understand the technologies to do it. Its been done on the ground already, albeit in research and I feel that its very relevant in today’s airspace. So perhaps I have to concentrate on that side and accept I cant, in the time given solve all the problems I would like to.
I suppose I’ll just have to be brutal and create a manageable project in the time given rather than trying to save the world!
Thanks everyone for your help,
Regards
Buster,
I am growing increasingly concerned that the product I feel would really provide a complete system of protection and increase situational awareness for new pilots is not going to be possible in the time I have available.
CBLong I appreciate your thoughts and thanks for the link, I was hoping to avoid fitting any external components or altering the airframe in anyway as that would lead to certification issues, so the fact that the technologies I had proposed are not going to perform is a slightly worrying issue I now have to deal with!
I was aiming to create a product that could be installed much like a portable GPS.
Jetstream I think you have definitely hit the nail on the head! I am scratching my head trying to figure out how to get so much into this product so that it can cater for every eventuality. I have until the middle of April to have my final concept finalised, and start on my design report. There really is so little time.
I have some ideas concerning the visualisation of airspace and the environment we operate in and I understand the technologies to do it. Its been done on the ground already, albeit in research and I feel that its very relevant in today’s airspace. So perhaps I have to concentrate on that side and accept I cant, in the time given solve all the problems I would like to.
I suppose I’ll just have to be brutal and create a manageable project in the time given rather than trying to save the world!
Thanks everyone for your help,
Regards
Buster,
Do a Hover - it avoids G
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the stall angle of attack depends on flap configuration, weight, gusts etc
The stall angle of attack for any given wing flying without compressibility effects is only dependant on flap angle. That is the whole beauty of the concept.
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The Safe Flight Corporation offered for many years (and still do) an angle of attack indicator that could be installed and calibrated for any specific light (and some transport) aircraft.
Highly useful and informative.
Highly useful and informative.
Ever so slight correction to JF. Pitch rate can be a player - a rapid increase in AoA can increase the stall AoA. However, it certainly won't decrease AoA so if the standard value is used for stall prediction, any errors will be conservative.
G
G
Moderator
Although probably not terribly relevant to the general discussion, at higher altitudes, Re comes into play a little ... in a manner similar to M .... and, if the pitch rate is high enough (70 odd degrees per second rings a bell in the back of the memory from a tech report I read quite some time ago) ... the dynamics can generate a significant stall angle excursion due to a vortex structure .... not very relevant to plank wings but a consideration with rotaries ...
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Pitch rate can be a player - a rapid increase in AoA can increase the stall AoA
What is affected by pitch rate is the angle which the aircraft may reach before any handling effects are apparent. Not the same thing as the angle at which the airflow changes.
Indeed such matters call for phase advance on some stall warning systems (not retardation which would be the case if the above quote was correct) so that the aircraft avoids penetrating beyond the stall angle.
There is a bit of a "new science" of unsteady aerodynamics which indicates that high pitch rates can cause flow to remain attached until rather higher AoA values than would normally be indicated by theory or conventional test techniques. I don't honestly think it's a player here, since any warning triggering at the normally determined stall AoA (plus whatever is considered the sensible safety margin) will be safe.
I spent a while last year testing a new artificial stall warner for an aircraft which had a particular stalling problem (60° wing drop, undemanded incipient spin, the usual suspects). The device (which worked well) was a spring-loaded vane parallel to the leading edge which operated when flow started to detach, releasing spring pressure. We actually looked quite deeply at deceleration / pitch rate and interestingly once it was in a setting we were happy with it was giving a more or less constant 3 seconds stall warning at any deceleration rate from 1 kn/s (i.e. about 3kn) to 5 kn/s (i.e. about 15 kn). To what extent that was unsteady aerodynamics, and to what extent it was other factors, I'm not all that sure.
I'd prefer for the usual reasons not to identify the aircraft, but the stall warner is at http://homepages.which.net/~aci.stw/ and an interesting piece of simple and effective design.
G
I spent a while last year testing a new artificial stall warner for an aircraft which had a particular stalling problem (60° wing drop, undemanded incipient spin, the usual suspects). The device (which worked well) was a spring-loaded vane parallel to the leading edge which operated when flow started to detach, releasing spring pressure. We actually looked quite deeply at deceleration / pitch rate and interestingly once it was in a setting we were happy with it was giving a more or less constant 3 seconds stall warning at any deceleration rate from 1 kn/s (i.e. about 3kn) to 5 kn/s (i.e. about 15 kn). To what extent that was unsteady aerodynamics, and to what extent it was other factors, I'm not all that sure.
I'd prefer for the usual reasons not to identify the aircraft, but the stall warner is at http://homepages.which.net/~aci.stw/ and an interesting piece of simple and effective design.
G
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weight affecting AOA...
John,
Thanks for your correction, was getting a bit mixed up late at night after a tiring day. Feel stupid to have made such a silly mistake...
I was thinking of weight affecting the angle of attack for a given speed, higher weight = higher angle of attack.
The system I designed was also to be used to set best L/D and other speeds which depend on AOA - which will of course give a differing airspeed and pitch angle if the weight is changed for a constant angle of attack. Conversely, if the speed and power are set, different angles of attack will be seen depending on the weight. Please do correct me again if need be.
J-R
Thanks for your correction, was getting a bit mixed up late at night after a tiring day. Feel stupid to have made such a silly mistake...
I was thinking of weight affecting the angle of attack for a given speed, higher weight = higher angle of attack.
The system I designed was also to be used to set best L/D and other speeds which depend on AOA - which will of course give a differing airspeed and pitch angle if the weight is changed for a constant angle of attack. Conversely, if the speed and power are set, different angles of attack will be seen depending on the weight. Please do correct me again if need be.
J-R
Last edited by Jetstream Rider; 21st Feb 2003 at 12:07.
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G
Yep unsteady aerodynamics is an interesting area. But all the guys who have talked to me about that have indicated that the effect of which you speak (flow not changing until a higher alpha than you experience with low pitch rates) is associated with wings in vortex lift. And I don’t reckon they ‘stall’ as such. But we are getting a tad away from the typical GA stall here I think.
I have only had to tune a leading edge stagnation point sensing stall warning vane on two GA types and there I set the vane so that the warning blew off before any undesirable handling effect (usually wing drop) even if you snatched it into a stall.
J
Yep unsteady aerodynamics is an interesting area. But all the guys who have talked to me about that have indicated that the effect of which you speak (flow not changing until a higher alpha than you experience with low pitch rates) is associated with wings in vortex lift. And I don’t reckon they ‘stall’ as such. But we are getting a tad away from the typical GA stall here I think.
I have only had to tune a leading edge stagnation point sensing stall warning vane on two GA types and there I set the vane so that the warning blew off before any undesirable handling effect (usually wing drop) even if you snatched it into a stall.
J
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Actually, there is an angle-of-attack rate effect on stalling angle.
It's one of the reasons gust loads can be difficult to determine. Helicopter rotor designers are also familiar with the effect.
I encountered this early in my career. Thirty years ago when I was a wind tunnel test engineer, we were testing helicopter airfoil sections in a blowdown supersonic wind tunnel.
The speeds were subsonic, but we could use variable tunnel pressure to change Reynolds No.
The airfoil sections were held in 2-D insert and oscillated at various pitch rates.
I hadn't been taught about aerodynamic hysterisis (sp?) in school so it was quite interesting to see the effects of angle of attack rate (and Rey. No.) on stall angle.
It's one of the reasons gust loads can be difficult to determine. Helicopter rotor designers are also familiar with the effect.
I encountered this early in my career. Thirty years ago when I was a wind tunnel test engineer, we were testing helicopter airfoil sections in a blowdown supersonic wind tunnel.
The speeds were subsonic, but we could use variable tunnel pressure to change Reynolds No.
The airfoil sections were held in 2-D insert and oscillated at various pitch rates.
I hadn't been taught about aerodynamic hysterisis (sp?) in school so it was quite interesting to see the effects of angle of attack rate (and Rey. No.) on stall angle.
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Thanks everyone for your replies.
As time is running out I doubt I will be able to go into quite such depth with regard to technical details however as a proving of method and technology your posts have all been invaluable.
So thank you all for your feedback,
Regards
Buster
As time is running out I doubt I will be able to go into quite such depth with regard to technical details however as a proving of method and technology your posts have all been invaluable.
So thank you all for your feedback,
Regards
Buster
