Heavy Jet ILS Glide Slope Problem

Whenever I fly a large jet such as a C5 Galaxy, the aircraft engages the ILS OK but the autopilot approach hold has trouble adjusting to the slope. After entering the slope, the plane is slow to react and then will have to take a rather deep dive to get down to the slope, then it overshoots and has to dive up to catch back up to which it then overshoots again. By that time, I'm over the runway & way too high to land.

Is there a way to adjust the autopilot settings in the aircraft.cfg file so the plane can adjust more quickly to the slope? I've tried the various recommended approach & landing speeds but that doesn't help.

You dont need any of that.

You need to load the aircraft correctly (fuel and pax/cargo) and be at the correct speed to intercept the Glideslope BEFORE the aircraft pitches down.

The payload is only 750 pounds and I used 50% fuel. The fuel & payload combined are well within the weight and balance envelope. I am at ATC altitude and under the glide slope when I enter it. But when the ILS slope bug starts coming down it goes down past the C5's altitude and the plane doesn't react fast enough to keep up with it. Then the ILS slope bug starts going back while the planes is descending to meet it. They pass each other which is not good. I found a workaround by pulling back on the yoke when the bug starts going back up.

Where do I find a C5 chart that tells me how much fuel to use per mile/payload?

Also... which C5 did you download? I'm using the Alpha C5 as modified by Michael Pook.

 

Also... which C5 did you download? I'm using the Alpha C5 as modified by Michael Pook.

That's the one I used! What airport are you flying into?

The payload is only 750 pounds

On a C-5? Methinks there's something odd. Do note that a lot of FS aircraft are too slow in responding with the autopilot (the AP needs adjusting, but it's not easy to do), though some are fine. That's true of default, freeware and payware.

But if Zippy did it OK with that aircraft, then you don't have the approach speed correct, are too high (thus above the GS too early), or something else isn't set up right. Note that if you're not pretty much centered on the localizer, the needed turns on some aircraft will disturb AP performance in odd ways.

Mr. Zippy,

I've had problems landing at Campbell Army Airfield & Wright-Patterson. No problem landing at Hartsfield–Jackson Atlanta. When I turn off the APP to land manually, it's like steering an elephant down main street in a parade. Very sluggish but hey, it's a big boy.

But if Zippy did it OK with that aircraft, then you don't have the approach speed correct, are too high (thus above the GS too early), or something else isn't set up right. Note that if you're not pretty much centered on the localizer, the needed turns on some aircraft will disturb AP performance in odd ways.

I'm always at ATC altitude & under the GS as I approach and I've tried different speeds including the recommended 160-165. The C5 is just slow to react when it intercepts the GS. I would think that a very small payload and half empty tanks would make it more nimble, but it doesn't.

I'm always at ATC altitude & under the GS as I approach and I've tried different speeds including the recommended 160-165. The C5 is just slow to react when it intercepts the GS. I would think that a very small payload and half empty tanks would make it more nimble, but it doesn't.

My first test flight was from Fresno to KSFO ( I wanted to be sure I got an ILS approach. I normally do not fly military aircraft into or out of civilian airports. The flight was about 150 miles and I started with 20% in each tank so was well below that when landing. I will try a longer flight into Wright-Pat.

Test flight from Langley to Wright-Patterson. ILS approach to 23Right. Very smooth turn to center-line but when the horizontal line came down and the altitude hold went off (about 6 miles out) it wanted to drop like a stone. I decided not to let it so autopilot off and I let the autothrottle hold 165 Knots until the landing threshold. All combined for an absolutely beautiful landing.

Fuel was at 15 % all tanks and a 5,000lb cargo load.

Test flight from Langley to Wright-Patterson. ILS approach to 23Right. Very smooth turn to center-line but when the horizontal line came down and the altitude hold went off (about 6 miles out) it wanted to drop like a stone. I decided not to let it so autopilot off and I let the autothrottle hold 165 Knots until the landing threshold. All combined for an absolutely beautiful landing.

 

Fuel was at 15 % all tanks and a 5,000lb cargo load.

I'm going to experiment with less fuel and a heavier payload. But it looks like you experienced what I did with the horizontal bar. Next time that happens, once the bar starts coming back up, pull back on the yoke and see if the plane gets back on slope as the horizontal bar rises. The yoke seems to respond up or down even with APP on. It doesn't respond like it does with APP off but it seems to respond enough to get back on the slope.

Do you know where I can find charts/tables about how much fuel I need for various aircraft and flight distances?

I'm going to experiment with less fuel and a heavier payload. But it looks like you experienced what I did with the horizontal bar. Next time that happens, once the bar starts coming back up, pull back on the yoke and see if the plane gets back on slope as the horizontal bar rises. The yoke seems to respond up or down even with APP on. It doesn't respond like it does with APP off but it seems to respond enough to get back on the slope.

 

Do you know where I can find charts/tables about how much fuel I need for various aircraft and flight distances?

I tend to find that most military airbases that use an ILS and Glideslope don't leave the usual 8-9 miles before touchdown as the horizontal bar reaches the midpoint and turns off altitude hold. I had about 6 miles at that point and it wanted to lose altitude too quickly. It's best to turn off A/P at that point and totally hand fly it.

My first test at KSFO 28R gave me 9 miles to bring it down in a more gentle fashion.

Sorry, no clue to where to find the charts. Maybe Google search?

Charlie - Not to question your findings, but, do you suppose it is all in the modeling of that particular aircraft? I just flew a pattern at Wright Patterson with a C17, they were using 5L ILS. I hit the glide scope from below at 2500' (also, as you indicated around 6 miles out) and the C17 just followed the glide scope all the way down, no "drop like a rock" what so ever. It was a very nice descent to landing and I was really impressed with the surroundings at Wright Patterson. Seems like something isn't right; what happens when you need that ILS when weather conditions worsen? You just can't turn off the A/P and cross your fingers? Just saying........

I have a few military fighter jets that give me some problems with ILS landings. If I try to land them at the recommended G/S altitude of 2000', they do all kinds of crazy things, one of which is like the OP says, "drops like a rock!" I tried lowering the approach altitude down to 1700' and all works well without issues. Might just be these particular aircraft, but they do seem to like the lower altitude? One airport that I use frequently is KCHS (Charleston, SC RWY 33). I'm going to keep watching this post as the OP has my curiosity going now!

Good luck Gregory, I hope you find a fix. I'll check in periodically to look for any future developments!

Thanks to you both! Rick :cool:

I just flew a pattern at Wright Patterson with a C17, they were using 5L ILS. I hit the glide scope from below at 2500' (also, as you indicated around 6 miles out) and the C17 just followed the glide scope all the way down, no "drop like a rock" what so ever.

What C17 model did you use and where can I get it?

Gentlemen, please! The 'problem' is this:

[pitot_static]

vertical_speed_time_constant= 1.9 //Increasing value= more instant reaction in the VSI //NOTE: Max=9.9

pitot_heat=1

Copy and paste to aircraft cfg. Delete the old (pitot_static) section. Go fly. Let us know if it helped. It's a simple oversight. Mr Pook I am sure would of noticed the omission if he had looked. I know - NO TIME! - and I understand completely. That is why I looked to see if I could spot something. I think this is the 'fix'. You are welcome Mr Pook. You are welcome 'expert' FSCom simmers. You too Charlie (hehe).

Chuck B

Napamule

Give me a bit, and I'll see if I can find it.

Rick

Gregory - I just sent you a PM. I am calling it a day! :rolleyes:

Rick :cool:

Gregory - Here, this might be the one I downloaded. Very close. I don't like the panel in this download, I replaced it with another that was offered as freeware. Enjoy!

FSX - FSX Modern Military

FSX Boeing C-17 Globemaster III

[ Download | View ]

Name: sc17xupdate.zip

Size: 1,145,202 Date: 03-13-2011 Downloads: 7,287

FSX Boeing C-17 Globemaster III. This is an update for FSX of the C17 by Mike Stone. The author has updated the flight dynamics, added a cargo door gauge, trim gauge, and a speed brake gauge to the panel. This is the whole aircraft. No virtual cockpit. By Bob Chicilo.

Rick :cool:

[pitot_static]

vertical_speed_time_constant= 1.9 //Increasing value= more instant reaction in the VSI //NOTE: Max=9.9

pitot_heat=1

 

 

Copy and paste to aircraft cfg. Delete the old (pitot_static) section. Go fly. Let us know if it helped. It's a simple oversight. Mr Pook I am sure would of noticed the omission if he had looked. I know - NO TIME! - and I understand completely. That is why I looked to see if I could spot something. I think this is the 'fix'. You are welcome Mr Pook. You are welcome 'expert' FSCom simmers. You too Charlie (hehe).

Chuck B

Napamule

This did not solve the problem. When entering the slope, this C5 simply doesn't react to the ILS quickly enough. At intercept, it takes about 4-6 seconds before it starts descending then it passes the horizontal localizer bar as it is going back up. It needs to react quicker. I am landing at the required 160-165 IAS and the plane has only 25% fuel and a small payload.

I am able to duplicate this several times each at Wright-Patt 5L & Vandenberg 30.

This did not solve the problem.

It might not have solved the problem, but Chuck's on the right track here - there are some missing entries in the aircraft.cfg file. I've noticed that there's a [direction_indicators] section, but there should be four other sections to go with it for a fully functional autopilot:

[altimeters]

altimeter.0=1

altimeter.1=1

[airspeed_indicators]

airspeed_indicator.0=1

airspeed_indicator.1=1

[direction_indicators]

//1 Type: 0=None, 1=Vacuum Gyro, 2=Electric Gyro, 3=Electro-Mag Slaved Compass, 4=Slaved to another

//2 Indicator number of slaving indicator if Type = 4

direction_indicator.0=1,0

[attitude_indicators]

//Type: 0=None, 1=Vacuum Gyro, 2=Electric Gyro

attitude_indicator.0 = 1

attitude_indicator.1 = 2

[turn_indicators]

//Type: 0=None, 1=Electric Gyro, 2= Vacuum Gyro

turn_indicator.0=1,1 //Turn AND Bank

Replace the existing [direction_indicators] section with all of the above sections and see if there's an improvement.

I am landing at the required 160-165 IAS and the plane has only 25% fuel and a small payload.

I think you approach airspeed is too high , I suspect that 165 is for Max landing weight .

Try doing an ILS at 140 , then next at 130 , then at 120 , then at 110 .

I suspect that at 25% fuel and small payload your approach should be at about 125 kts .

I had a similar approach airspeed problem . initially I conformed to the recommended approach speed of 160 kts for the F-111 as advised in the download .

Then I used the F-18 HUD to chart ONSPEED approach speeds for a range of Fuel % figures

that resulted in approach speeds of ,

121 kts at 16% fuel

up to

142 kts at 93% fuel

Other possible checks that you can conduct to establish approach speeds are ,

1. If you have an Angle of Attack readout , adjust throttle to maintain an AoA of 8 degrees all the way through your approach , and note your airspeed for the current weights .

or,

2. Maintain exactly the same altitude and slowly reduce power until the Stall , note the airspeed at the moment of stall , then multiply that airspeed by 1.3 to determine the approach speed for that weight .

Cheers

Karol

Replace the existing [direction_indicators] section with all of the above sections and see if there's an improvement.

I tried what you suggested and it didn't solve the problem. Alt hold goes off when the C5 intercepts the slope but the C5 doesn't descend fast enough to keep up with the slope. Then when it finally catches the slope, the slope is on it's way up; the C5 is slow to react and tries to climb to meet the slope again, overshoots it and now we are over the runway far too high to land.

I think you approach airspeed is too high , I suspect that 165 is for Max landing weight .

Try doing an ILS at 140 , then next at 130 , then at 120 , then at 110 .

[ATTACH=CONFIG]210219[/ATTACH]

I think you nailed it, Karol. With a landing speed of 142 kts, the C5 landed perfectly several times in a row. One more thing I need to fix... the GPWS keeps going off, even when I tried landing at 165 kts. I know there's a way to toggle off the GPWS but I'd rather make a change to the warning threshold via an aircraft.cfg edit. Any suggestions?