Random facts about planes..
Discussion
V8LM said:
Aircraft still use INS, but today they are solid state (bouncing laser light) and not based on mechanical gyroscopes.
Not entirely solid state as they still need agitation to prevent laser lock in many cases. Clever bits of kit though!Edited by Krikkit on Thursday 25th May 22:26
Chuck328 said:
Yes and yes. These days the old gyroscopes have long since been replaced by laser systems and are still very much integral to the modern nav system which does use GPS as the main driver. Even though they use lasers, they still suffer the 'drift' caused by the Earths rotation. A re alignment on the ground fixes this.
An Inertial Platform is a gyro stabilised platform bearing accelerometers. Being gyro stabilised (albeit these days triple ring laser gyros are the norm) it will suffer from both Earth Rate Error (because the earth is rotating) as well as Transport Wander (the platform remains fixed in space so if you transport it across the globe it's alignment relative to the centre of the earth will change in a similar fashion to Earth Rate Error).An IN platform may be twin or triple axis. Twin axis INs do not measure pitch and will start to generate large errors once you go above about 75 degrees North (or below 75 degrees South) eg the FIN 1012 platform fitted to Nimrod MR2 - to go polar a 3 axis platform such as Carousel was temporarily fitted.
Essentially with an IN what you do is tell it where it is at start up. It then measures accelerations fore and aft and left and right (and up and down - 3 axis types). These accelerations are then double integrated WRT time so as to give distance (since acceleration = velocity / time and velocity = distance / time, ergo acceleration = distance / time / time). For N/S courses this is all you need but for E/W courses this will only be accurate if you are on the Equator. Above or below the Equator a correction factor of DSin Mean Latitude is applied (where D is the E/W distance initially derived from the IN).
Another error that INs suffer from is that of the 'Schuler Loop' - quintessentially this is owing to the Periodicity of the Earth (you can imagine an a/c flying across the globe as similar to a ball on a string being swung around your head - ie there is a Periodicity). What this means is that about every 43 minutes the IN will throw its hands up in horror and not know where it is.
WRT GPS all well and good but the accuracy of the satellite signals can be downgraded by the owner unless you have the correct decryption key - the US did this during Operation GRANBY (Gulf War 1). Additionally GPS signals would be fairly easy to shut down in Wartime with an ex-atmospheric nuclear burst.
z06tim said:
NickCQ said:
tommyjj said:
Prior to the invention of GPS, many larger airliners used complex inertial navigation systems that actually recorded every bump, climb, turn and dive, along with airspeed, to establish where the plane was. They were surprisingly accurate given how implausible the idea sounds.
Are these systems still in use anywhere? Is this the reason you often see Lat/Long written above the gate - so that the pilot can recalibrate the system?
We had a client in Feltham that used to maintain Aircraft Navigation systems manufactured for Delco Electronics.
https://en.wikipedia.org/wiki/Delco_Carousel
Speed 3 said:
Always thought is curious that the equivalent on rotary is a QHI. Some logic there states that helicopters aren't flying machines (I guess they have a point).
Helicopters don't actually fly, they vibrate at the resonant frequency of the earths crust meaning they get pushed away from its surface for a short duration. Ginetta G15 Girl said:
Chuck328 said:
Yes and yes. These days the old gyroscopes have long since been replaced by laser systems and are still very much integral to the modern nav system which does use GPS as the main driver. Even though they use lasers, they still suffer the 'drift' caused by the Earths rotation. A re alignment on the ground fixes this.
An Inertial Platform is a gyro stabilised platform bearing accelerometers. Being gyro stabilised (albeit these days triple ring laser gyros are the norm) it will suffer from both Earth Rate Error (because the earth is rotating) as well as Transport Wander (the platform remains fixed in space so if you transport it across the globe it's alignment relative to the centre of the earth will change in a similar fashion to Earth Rate Error).An IN platform may be twin or triple axis. Twin axis INs do not measure pitch and will start to generate large errors once you go above about 75 degrees North (or below 75 degrees South) eg the FIN 1012 platform fitted to Nimrod MR2 - to go polar a 3 axis platform such as Carousel was temporarily fitted.
Essentially with an IN what you do is tell it where it is at start up. It then measures accelerations fore and aft and left and right (and up and down - 3 axis types). These accelerations are then double integrated WRT time so as to give distance (since acceleration = velocity / time and velocity = distance / time, ergo acceleration = distance / time / time). For N/S courses this is all you need but for E/W courses this will only be accurate if you are on the Equator. Above or below the Equator a correction factor of DSin Mean Latitude is applied (where D is the E/W distance initially derived from the IN).
Another error that INs suffer from is that of the 'Schuler Loop' - quintessentially this is owing to the Periodicity of the Earth (you can imagine an a/c flying across the globe as similar to a ball on a string being swung around your head - ie there is a Periodicity). What this means is that about every 43 minutes the IN will throw its hands up in horror and not know where it is.
WRT GPS all well and good but the accuracy of the satellite signals can be downgraded by the owner unless you have the correct decryption key - the US did this during Operation GRANBY (Gulf War 1). Additionally GPS signals would be fairly easy to shut down in Wartime with an ex-atmospheric nuclear burst.
My old ATPL books are somewhere up in the loft tucked away in a corner. Been there for decades now. Schuler Loop, Ephemeris (GPS related?) are all words I vaguely remember. For most of us studying ATPL exams, it was (mostly) all incredibly dry/dull/boring, most of which is long forgotten. You seem to rattle this off with ease. I'd have to pull god knows what boxes out of the loft to be able to put a post up like that.
I just have a good memory. 
(I also teach Air Navigation to my local Air Cadet Sqn)
It wasn't until my Nav explained the IN to me that I finally understood what Differantiation and Integration are. I was crap at Calculus at school!.
Ah Ephemeris (Hour Angle [Right Ascension] and Declination). I had to dredge my memory on Astro Nav for that!
WRT to why the RAF uses the term QFI rather than FI I have no idea, other than it being a mark of recognition of achievement. There is also QHI (as noted) and QAI (Qualified Aircrew Instructor - Navs, NCO Aircrew, and Dominie Pilots).
I think it's something to do with recognition - you start off as C2I (Certificated to Instruct) and move up via B2, B1, A2, A1 grades. IIRC you have to become a B2 within 6 months to retain the 'Q' qualification (in the same way one has to become 'Combat Ready' or equivalent in order to retain one's 'wings'). Once you have the 'Q' you are allowed to use the post nominals 'CFS' although I don't know of anyone who does.
(I also teach Air Navigation to my local Air Cadet Sqn)
It wasn't until my Nav explained the IN to me that I finally understood what Differantiation and Integration are. I was crap at Calculus at school!.
Ah Ephemeris (Hour Angle [Right Ascension] and Declination). I had to dredge my memory on Astro Nav for that!
WRT to why the RAF uses the term QFI rather than FI I have no idea, other than it being a mark of recognition of achievement. There is also QHI (as noted) and QAI (Qualified Aircrew Instructor - Navs, NCO Aircrew, and Dominie Pilots).
I think it's something to do with recognition - you start off as C2I (Certificated to Instruct) and move up via B2, B1, A2, A1 grades. IIRC you have to become a B2 within 6 months to retain the 'Q' qualification (in the same way one has to become 'Combat Ready' or equivalent in order to retain one's 'wings'). Once you have the 'Q' you are allowed to use the post nominals 'CFS' although I don't know of anyone who does.
Edited by Ginetta G15 Girl on Friday 26th May 11:56
JoeBolt said:
Surely you either mean: -
distance = velocity x time
or (for average acceleration)
acceleration = change in velocity / time
You have to remember that the accelerations measured by the IN platform vary with time and are not just relative to the a/c's True Air Speed. Given that an acceleration is any change in velocity, then changing ones heading (for example) is an acceleration.distance = velocity x time
or (for average acceleration)
acceleration = change in velocity / time
Hence the use of the double Integration wrt time as opposed to the simple multiplication sum.
Various 'Q's in the military. A 'Q' is awarded for passing a course that is endorsed by Central Flying School.
In no particular order (Q - Qualified.......I - Instructor)
QHI Helicopter
QHCI Helicopter Crewman
QHTI Helicopter Tactics
QFI Flying
QWI Weapons
QAI Airborne
QGI Gliding
There's probably some more but can't think of them.
In no particular order (Q - Qualified.......I - Instructor)
QHI Helicopter
QHCI Helicopter Crewman
QHTI Helicopter Tactics
QFI Flying
QWI Weapons
QAI Airborne
QGI Gliding
There's probably some more but can't think of them.
Aircraft ground trades are also awarded 'Q's on passing the appropriate course.
Mine were: -
Q-AN-P Nimrod propulsion systems.
Q-AHR-5A Harrier GR5 airframe systems.
Q-AHR-5P Harrier GR5 propulsions systems. (I was a proper split-brain).
Q-AHR-5COMP(T) (Harrier GR5 composite flight servicing at technician level).
A fat lot of good that lot are these days!
I also have Q-A-VA(P) which is aircraft engine vibration analysis. I barely remember the course. Something to do with setting up and operating an ancient box of electronics.
Such 'Q' courses weren't strictly necessary and often were better avoided. 'Q' annotations could result in remaining in a hated posting for far longer than you'd like.
Mine were: -
Q-AN-P Nimrod propulsion systems.
Q-AHR-5A Harrier GR5 airframe systems.
Q-AHR-5P Harrier GR5 propulsions systems. (I was a proper split-brain).
Q-AHR-5COMP(T) (Harrier GR5 composite flight servicing at technician level).
A fat lot of good that lot are these days!
I also have Q-A-VA(P) which is aircraft engine vibration analysis. I barely remember the course. Something to do with setting up and operating an ancient box of electronics.
Such 'Q' courses weren't strictly necessary and often were better avoided. 'Q' annotations could result in remaining in a hated posting for far longer than you'd like.
How about the time I was strapped into the rear crew seat on take off from Mexico City. On climb out, Slowly, very slowly, two ovens popped open and the contents spilled out on the galley floor. It was a full ship and we had to make do and mend with help from the first class galley.
What a mess!
What a mess!
Ginetta G15 Girl said:
JoeBolt said:
Surely you either mean: -
distance = velocity x time
or (for average acceleration)
acceleration = change in velocity / time
You have to remember that the accelerations measured by the IN platform vary with time and are not just relative to the a/c's True Air Speed. Given that an acceleration is any change in velocity, then changing ones heading (for example) is an acceleration.distance = velocity x time
or (for average acceleration)
acceleration = change in velocity / time
Hence the use of the double Integration wrt time as opposed to the simple multiplication sum.
DJFish said:
JoeBolt said:
A fat lot of good that lot are these days!
I also have Q-A-VA(P) which is aircraft engine vibration analysis.
You'd be surprised how many people have issues with vibrating jet engines in this day & age....I also have Q-A-VA(P) which is aircraft engine vibration analysis.
With regards engine vibration analysis, I would hope that nowadays there is something better than a VM3C vibration meter which seemed nearly obsolete even back in 1986.
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