Inverted ILS

[A Very Civil Pilot]

This has been bugging me for a few days. Ignoring the reasons of how and why you got there in the first place, if you were in inverted flight on an ILS would any of the LOC G/S commands be in the correct sense?

[hetfield]

Sure, CAT IIIC approved.

[kijangnim]

Greeting,
Aerobatic manoeuvers are not permitted on a passenger transport aircraft :}

[roljoe]

Not really interested to experience this kind of approach..:} anyway..I'm pretty sure that the corrections will be made toward the correct way..this according to the electronically concept..Now..Hope for you that the GS antenna is not located around the main gear...in that specific case..only your shoes will appreciate the threshold !! the rest..:E

[inbalance]

LOC will be ok,
GS will still show in the right direction, but you have to use the elevator the other way around.

Inbalance

[Cornish Jack]

Standard sim demonstration for new VC10 tanker crews by our USAF exchange 'Major Fred'. Everything exactly where it should have been :D ... until the flare!!:eek:

[barit1]

A more complete explanation:

You are on approach, high and to the right of C/L, and you perform a 360 aileron roll while maintaining this track. The needles will not move during the roll; the LOC & GS antennae do not care about the airplane's attitude. :)

Well, almost. :confused:

Both antennas, being dipoles, will be at cross-polarization at the 90 and 270 points during the roll, and so signal strength will fall off for a second, and the needle displacements may decrease at these points. It may not even be noticeable, though. :D

[mona lot]

But how would you know when to flare or close the thrust levers because the Rad alt will be U/S?:confused::confused::confused:

[ChristiaanJ]

An explanation referrring back to ancient history, a bit simplified...

The ancient Lorenz approach system worked by transmitting two beams, one slightly to one side of the runway, modulated with dots, and one to the other side, modulated with dashes. If you were on the centre line, dots and dashes merged into a continuous tone.
The moment you can visualise this, you'll see that the attitude of the plane (even inverted) had nothing to do with it. If you were on the 'dots' side, you'd hear dots even with your head down.

The LOC and G/S system works somewhat differently... but the principle remains the same, it shows your position relative to the runway centre line and glidepath.

Now the kicker.... if you fly upside down, and hence you've turned the instrument upside down (think of the old Zero Reader), of course the indication is the wrong way round as welll

Think about it...
In normal flight, if the LOC needle is to the left, you turn to the left (towards the needle) to get back on the centreline.
In inverted flight, if the LOC needle is to the left, you now have to turn to the right to get back on the centreline.

Have fun.

CJ

[mona lot]

Is this a serious question or a **** take?

[Jofm5]

Is this a serious question or a **** take?


Does that really matter ?

It will only have been a waste of time if nobody has learnt anything - if it adds value what is the problem with a theoretical situation ?

The true professional will be able to tell you what they dont know - the others have not realised that yet. Lets not discourage questions !

[Flash2001]

Beware the position of the G/S ant on the aircraft though!

You might not be able to use the airplane again!

[V1... Ooops]

The true professional will be able to tell you what they don't know...

That's why I love this forum... :}

[NSEU]

So, in summary...

The pointers would not move if you did a roll on the ILS, but you would have to turn in the opposite sense to centre the needle if you were off the centreline.

I knew there was a good reason for that Backcourse selection on my Standby Attitude Indicator! :}

[FCS Explorer]

the LOC has two "coils" each side of the centerline, one called "yellow" at 90Hz and the other "blue" at 150Hz.
lets assume we're on ILS27, pointers centered and NOT inverted. now we're drifting off to the north. the LOC-pointer/needle moves to the left.
draw it on a piece of paper incl view to rwy and ils instrument.
then turn it up side down.
WHOA!

[barit1]

draw it on a piece of paper incl view to rwy and ils instrument.
then turn it up side down.
WHOA!

Push to make trees & cars look bigger.
Pull to make trees & cars look smaller.
Pull some more, trees & cars look bigger still.

Or is it the other way 'round? :eek:

[ChristiaanJ]

Push to make trees & cars look bigger.
Pull to make trees & cars look smaller.
Pull some more, trees & cars look bigger still.
Or is it the other way 'round?
You forgot to specify if you're 'right side up' or inverted...... :=
Which is precisely the subject of this topic!

CJ

[FE Hoppy]

Push to make trees & cars look bigger.
Pull to make trees & cars look smaller.
Pull some more, trees & cars look bigger still.


I thought it was cows? and in this case wouldn't it be clouds?

[BizJetJock]

A long, long time ago - in a galaxy far, far away :eek:- I was involved in this very exercise. Not, I hasten to add, in a transport category aircraft but a suitable steed. One chap did it as a sponsored fund raising exercise on a nice day with a safety pilot. I was involved with the planning of how it would work.
Bizarrely, the localiser works "normally". Needle left, you need to roll left - and push! The G/S works in reverse, high you need to "raise" the nose as you are looking at it and vice versa.
Those were the days when such things weren't frowned upon, but seen as useful training. Oh, well:{

[Bullethead]

A long, long time ago - in a galaxy far, far away

At similar place in time, I flew B707s in the RAAF for many years and for part of that time did a lot of simulator training and so spent a fair bit of time in the box developing training exercises. In my spare time in the box I used to explore different aspects of operation and the inverted ILS idea came up one day.

The way I did it was to takeoff and fly up the ILS at the upwind end of the runway and level off at 3,000' and accelerate and then at about 15dme perform half a loop, remaining on the LLZ, and re-intercept the G/S and then fly back down the ILS inverted.

As BizJetJock says the localiser appeared normal but the push/pull to stay on the G/S was reversed. The first couple of approaches were a bit of a challenge but after that were not too difficult. I never required any of my students to try flying one though. The B707 sim didn't know it didn't have inverted fuel and oil systems so it would fly around all day 'inverted'.

An interesting but rather pointless excercise which doubtless would have been more of a handfull if you were inverted and hanging in the straps.

Regards,
BH.

[eharding]

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.

[mona lot]

It will only have been a waste of time if nobody has learnt anything

Well I have learnt the square root of FA.

Quote;

"The very best in practical technical discussion on the web":ugh::ugh::ugh:

[NSEU]

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)

[DFC]

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

[james ozzie]

"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.

[NSEU]

The important thing to remember here is that we are talking about a pilot interpreted aid to navigation.

True.

http://www.ozemail.com.au/~b744er/UpsideDown.GIF

[ChristiaanJ]

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

[AerocatS2A]

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.

[roljoe]

Fully correct Christiaan..:ok:

[DFC]

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.



No. I think that you have it wrong.

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

[NSEU]

NSEU, I would say IMHO your fig. B) confuses the issue, because a) you've drawn it upside down,

As DFC has said, no I haven't drawn it upside down. It's the pilot's view. Only the horizon changes in this situation. ILS instruments don't know that you have changed orientation, so the pointer remains in the same position on the instrument.

(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).

[Big Pistons Forever]

And then there ws the famous request to tower for a "gear up" low and over
:}

[Short_Circuit]

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.