Inverted ILS
A little less conversation,
a little more aviation...
Join Date: Jun 2003
Location: Bracknell, UK
Posts: 696
Likes: 0
Received 0 Likes
on
0 Posts
A Slingsby Firefly did indeed fly an inverted ILS approach into Benson donkey's years ago, with the GodFather (or, if you will, GodUncle) of British Aerobatics in command. Well before my time, but, as has been outlined above, the localiser does work in the correct sense.
Join Date: Sep 2008
Location: The Middle East
Posts: 118
Likes: 0
Received 0 Likes
on
0 Posts
It will only have been a waste of time if nobody has learnt anything
Quote;
"The very best in practical technical discussion on the web"
Join Date: Feb 2004
Location: Australia
Posts: 1,307
Likes: 0
Received 0 Likes
on
0 Posts
Seems to me that this issue has still not been resolved. Some are saying opposite sense, others are saying same sense. Some say the LOC will vary from the GS.
The ILS system is based on "depth of modulation" and instruments are designed to show deviation from the ILS centreline using this depth of modulation. If you're flying on the left of the Loc, your loc pointer will command you to fly to your relative right irrespective of which way up you are (assuming the ILS pointers are not biased out of view at large roll angles)
Inverted, if you roll to your relative right, which way does your aircraft go? Unfortunately, drawing your instrumentation on a piece of paper and inverting it would seem to suggest that if you flew towards the needle, you would fly further away from the centreline. In this respect, it's opposite sense. However, it's probably more a question of aerodynamics. If you're upside down and turn the wheel right, will you fly away from or to the Loc centreline?
Rgds.
NSEU (not a pilot)
The ILS system is based on "depth of modulation" and instruments are designed to show deviation from the ILS centreline using this depth of modulation. If you're flying on the left of the Loc, your loc pointer will command you to fly to your relative right irrespective of which way up you are (assuming the ILS pointers are not biased out of view at large roll angles)
Inverted, if you roll to your relative right, which way does your aircraft go? Unfortunately, drawing your instrumentation on a piece of paper and inverting it would seem to suggest that if you flew towards the needle, you would fly further away from the centreline. In this respect, it's opposite sense. However, it's probably more a question of aerodynamics. If you're upside down and turn the wheel right, will you fly away from or to the Loc centreline?
Rgds.
NSEU (not a pilot)
Join Date: Mar 2002
Location: Euroland
Posts: 2,814
Likes: 0
Received 0 Likes
on
0 Posts
The localiser system provides the pilot with position information relative to the extended centerline. It tells the pilot if they are on, left or right of the extended centerline.
If the aircraft is left of the centerline and performs a loop over a point on the ground the indication of position relative to the extended centerline will not vary - nor will the indication.
Similarly the Glideslope provides the pilot with position information relative to an imaginary surface starting at the touchdown point and set as thre approach angle.
If the aircraft is above the glideslope and performs a slow roll then the glideslope indication will not move - nor will the indication.
The important thing to remember here is that we are talking about a pilot interpreted aid to navigation.
The indications always say the same thing - upright or inverted since the position of the aircraft relative to the centerline and approach slope have not changed and therefore the way that the aircraft (as an object) has to travel to regain the centerline (which is a vertical plane) and/or glideslope (which is a plane set at a specific angle) has not changed.
As in other aspects of inverted flight, if one imagines onself sitting upright on the underside of the aircraft and moves the controls appropriately, then imagine what that would happen with the end of the stick and rudder pedals you are holding while hanging upside down.
Regards,
DFC
If the aircraft is left of the centerline and performs a loop over a point on the ground the indication of position relative to the extended centerline will not vary - nor will the indication.
Similarly the Glideslope provides the pilot with position information relative to an imaginary surface starting at the touchdown point and set as thre approach angle.
If the aircraft is above the glideslope and performs a slow roll then the glideslope indication will not move - nor will the indication.
The important thing to remember here is that we are talking about a pilot interpreted aid to navigation.
The indications always say the same thing - upright or inverted since the position of the aircraft relative to the centerline and approach slope have not changed and therefore the way that the aircraft (as an object) has to travel to regain the centerline (which is a vertical plane) and/or glideslope (which is a plane set at a specific angle) has not changed.
As in other aspects of inverted flight, if one imagines onself sitting upright on the underside of the aircraft and moves the controls appropriately, then imagine what that would happen with the end of the stick and rudder pedals you are holding while hanging upside down.
Regards,
DFC
"in a galaxy far, far away - I was involved in this very exercise. Not, I hasten to add, in a transport category aircraft but a suitable steed"
I think you are incorrect - a Galaxy must fall into the category of transport aircraft.
I think you are incorrect - a Galaxy must fall into the category of transport aircraft.
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes
on
0 Posts
NSEU,
I think you're confusing the issue...
The centreline is on your 'right'.
In normal flight, A) is what you see, and your starboard wing is pointing towards the centreline.
You now bank by dropping your starboard wing to fly towards the centreline.
In inverted flight, A) is still what you see, since both your head and the instrument are upside down.
But with your port wing now pointing towards the centreline, you drop your port wing to bank and fly towards the centreline.
Never having tried it myself, I now take BizJetJock's and Bullethead's words for it, that you do this automatically, i.e., the instrument tells you to bank to the right, and even if you're upside down, your brain tells you that "right" is relative to the ground, so you now drop your port wing to bank to the right and hence curve your flightpath to the right relative to the ground.
NSEU, I would say IMHO your fig. B) confuses the issue, because a) you've drawn it upside down, whereas the pilot still sees it "right side up", and because b) the instrument indicates you're on the righthand side of the centreline, contrary to your "runway and plane" view.
CJ
I think you're confusing the issue...
The centreline is on your 'right'.
In normal flight, A) is what you see, and your starboard wing is pointing towards the centreline.
You now bank by dropping your starboard wing to fly towards the centreline.
In inverted flight, A) is still what you see, since both your head and the instrument are upside down.
But with your port wing now pointing towards the centreline, you drop your port wing to bank and fly towards the centreline.
Never having tried it myself, I now take BizJetJock's and Bullethead's words for it, that you do this automatically, i.e., the instrument tells you to bank to the right, and even if you're upside down, your brain tells you that "right" is relative to the ground, so you now drop your port wing to bank to the right and hence curve your flightpath to the right relative to the ground.
NSEU, I would say IMHO your fig. B) confuses the issue, because a) you've drawn it upside down, whereas the pilot still sees it "right side up", and because b) the instrument indicates you're on the righthand side of the centreline, contrary to your "runway and plane" view.
CJ
When you're inverted your ailerons appear to work in the reverse sense, e.g, if you want to turn left you must push the stick right. The localiser also works in the reverse sense when inverted, the two reversals cancel each other so from the pilots perspective it works in the correct sense. The G/S will be reversed though.
Join Date: Mar 2002
Location: Euroland
Posts: 2,814
Likes: 0
Received 0 Likes
on
0 Posts
NSEU, I would say IMHO your fig. B) confuses the issue, because a) you've drawn it upside down, whereas the pilot still sees it "right side up", and because b) the instrument indicates you're on the righthand side of the centreline, contrary to your "runway and plane" view.
Forget the horizon for a moment. In both A and B the localiser indicates correctly that the aircraft is to the left of the centerline. The position of the aircraft has not changed from A to B and the indication has not changed either.
No look at the horizon in isolation.
Right way up - sky is near your head and ground is near your feet.
Roll the aircraft upside down and now the ground is near your head and sky near your feet.
A correctly represents the sky / ground position as you would see them during erect flight.
B correctly represents the sky / ground position as you would see them during inverted flight.
Perhaps it is easier for you to forget the ILS display on a horizon and think of the following -
If the final approach course is 270 degrees and the aircraft at A and B is on a heading of 270. With the course bar on the HSI set to 270, what will the picture be and how would that change if the aircraft rolled inverted?
The answer is that the heading will not change and that the HSI indication will not change either because the aircraft position relative to the centerline has not changed.
I said earlier that it is a pilot interpreted aid. It tells you where the aircraft is in relation to the centerline. Based on that you have to interpret how to get the aircraft back to the centerline and how to keep it there.
Banking the aircraft left or right does not get you back to the centerline - in the extreme all it does is fly you round in a circle.
What gets you back on the centerline is selecting an appropriate heading that will acheive that.
So assuming the final approach course is 270. Both the A and the B indications tell me that a track greather than 270 is required to regain the centerline.
If I am heading 270 and there is no wind, I may choose a new heading of 280.
Having decided to change my heading from 270 to 280, now for the first time I have to pay attention to the horizon position because the control inputs to acheive that are different in A and B.
Regards,
DFC
Join Date: Feb 2004
Location: Australia
Posts: 1,307
Likes: 0
Received 0 Likes
on
0 Posts
NSEU, I would say IMHO your fig. B) confuses the issue, because a) you've drawn it upside down,
(Edit) Think of ILS displays as colour and volume. Colour (traditionally blue&yellow) is aircraft position, right or left of the centreline. Volume is distance from the centreline. Neither has changed by inverting the aircraft, so the displays remain the same (as presented to the pilot).
Last edited by NSEU; 31st May 2009 at 01:27.
And then there ws the famous request to tower for a "gear up" low and over
Join Date: Sep 2007
Location: Up left - Down right
Posts: 946
Likes: 0
Received 0 Likes
on
0 Posts
The display in NSEU’s post 26 is correct. The bars indicate the position of the C/L relative to the A/C. Fly to the bar.
In the diagram, the A/C is to the left of C/L in both cases and the indicator displays this. The problem is it was to the pilots right side, it is now to the pilots left side as the pilot interprets it (pilot being inverted) but still to the right of the A/C.
The same will happen to G/S, it will display relative to the A/C, so if the G/S C/L is below the A/C initially, when inverted it is still below the A/C but displayed in the indicator into the blue. Bars are not dependent of the ball orientation.
To give some credence to this, when ground testing it does not matter where the test set antenna is located, above, below, left or right of the A/C it is the signal strength of the individual LOC & GS frequencies emitted by the test set that determines where the bars indicate.
In the diagram, the A/C is to the left of C/L in both cases and the indicator displays this. The problem is it was to the pilots right side, it is now to the pilots left side as the pilot interprets it (pilot being inverted) but still to the right of the A/C.
The same will happen to G/S, it will display relative to the A/C, so if the G/S C/L is below the A/C initially, when inverted it is still below the A/C but displayed in the indicator into the blue. Bars are not dependent of the ball orientation.
To give some credence to this, when ground testing it does not matter where the test set antenna is located, above, below, left or right of the A/C it is the signal strength of the individual LOC & GS frequencies emitted by the test set that determines where the bars indicate.
