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VNSL landings nearly impossible


Nealius

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After getting pretty good at FNSL and RVL landings, I tried doing VNSL both with AUTO flaps and STOL flaps, following the VMAT-203 training syllabus procedures:

 

Nozzles 40-50 degrees on downwind, set 85% RPM for AUTO flaps or 95-100% RPM for STOL flaps, vary nozzle angle to maintain 8-10 units of AoA.

 

Problem is, it seems impossible to achieve this. 40-50 degrees of nozzle at those RPM ranges will give you too much lift and speed. To reduce speed I increase nozzle angle to around the hover stop, then I start descending. I decrease nozzle angle back to around 50, and my descent rate increases until I gain more speed. Now I'm back to square one with too much climb. It's impossible to maintain 8-10 units of AoA and a steady glideslope with a constant RPM setting and varying nozzle angle. How do they do it in real life?

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Only encouragement I can give is to keep practicing, particularly your throttle modulation.

I fly choppers a lot in DCS, so found picking up the Harrier quite easy, as there are similarities in the use of throttle. Having said that, I’d already been flyin the Huey over a year and consider myself proficient.

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Ok, I gave this more than one try and I have exactly your same problem.

Don't know if it's a FM problem, or just I don't get how to do it. I tried many combinations and nothing works, X throttle setting with Y nozzle angle gives level flight, but as soon as I start to turn off the 180, that throttle setting is not enough to keep me airborne, speed goes down, AoA goes up, increasing nozzles angle shoudl reduce AoA but I don't have enough throttle, so I slow down. Only option is to nozzle out and add power.

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I'm gonna try a few more flights before calling it quits. It definitely is a challenging maneuver if you think about it, and I suspect there's more to it than what you can read in a manual (a case where I REALLY wish a RL Harrier pilot coudl chime in):

 

in my admittedly superficial analysis, I see the following:

 

- 10 degrees AoA in level flight can be maintained at a variety of RPM and Nozzle settings. This will also depend on the weight of the aircraft.

 

- The manual says to drop the nose 5 degrees at the 180, and start a turn. Well, if I drop the nose without reducing power, my speed will increase and my AoA will decrease, so what should I do? I have two options:

 

  1. option A: I nozzle out to increase AoA, but this will make me loose altitude and eventually increase my speed even more as I direct more thrust towards the back. I should probably pull the stick to reduce sink rate and increase AoA, but in the sim I can't do this and keep 5 degrees nose down...
  2. option B: I increase nozzle angle to slow down, momentarily the AoA will be further reduced, but my speed decreases and I start to drop, beacuse I don't have enough RPM to sustain the aircaft at such speed/weight/nozzle angle...

 

There is probably a tiny sweet spot in there somewhere...kinda hard to tell where though given that the manuals don't give any references to speeds and power settings connected to aircraft gross weight :huh:

 

 

EDIT:

I got it wrong, the manual says to increase nozzle angle to increase AoA and vice versa. So, the opposite of what I was doing.

I'm doing more testing and getting the hang of it.

It's fundamental to set the FPM where you want it with the stick, and at the same time change nozzle angle to maintain AoA. When you push the stick forward, increase nozzle angle, when you pull the stick, nozzle out.

Practice I guess!

 

Also, don't get fixated on the 40 degrees nozzle angle stated in the manual. It says to set it to 40 and then adjust as required.


Edited by bkthunder

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Just had a couple of goes. I think the problem is that the thrust levels are waaay too high in the current version of the flight model. If you set around 55% RPM rather than 85, it gives much more realistic and manageable nozzle angles. Ideally, the nozzle angle (N) wants to be around the range of 45 to 60. Much above N60 and small nozzle angle changes make a very large change to fwd thrust (geometry) and becomes very hard to fly. Because the thrust level is artificially high, you are needing very large N angles at 85%!

[edit] - It may be the aerodynamic drag modelling with the nozzles down is not high enough. Or a combination of both. Either way, the nozzle angle required is unreaslistically high.

 

 

Another good tip is to watch the trend in IAS, which will give you a clue to whether the jet is speed stable (= AOA stable - provided you have a stable glidepath) or whether IAS is reducing / increasing (= AOA about to go up / down). Small nozzle angle changes are best. 5 or 10 deg steps, then let that take effect before grabbing any more nozzle.

 

 

Try it in AUTO (since in STOL, the flaps schedule with N movement once speed is low, which makes life much more tricky!). Also, try a straight in VNSL approach first (I used a 5nm final from 1500 ft) since that doesn't give the added complication of AOA changing as you enter / roll out of turn.

 

 

Hope this helps.


Edited by viffviff
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Hard to say it's an FM issue in my opinion. From what I've seen it really depends on your weight. Try it with a full load of fuel and 85% RPM won't be nearly enough to keep you afloat with a steep N angle.

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After getting pretty good at FNSL and RVL landings, I tried doing VNSL both with AUTO flaps and STOL flaps, following the VMAT-203 training syllabus procedures:

 

Nozzles 40-50 degrees on downwind, set 85% RPM for AUTO flaps or 95-100% RPM for STOL flaps, vary nozzle angle to maintain 8-10 units of AoA.

 

Problem is, it seems impossible to achieve this. 40-50 degrees of nozzle at those RPM ranges will give you too much lift and speed. To reduce speed I increase nozzle angle to around the hover stop, then I start descending. I decrease nozzle angle back to around 50, and my descent rate increases until I gain more speed. Now I'm back to square one with too much climb. It's impossible to maintain 8-10 units of AoA and a steady glideslope with a constant RPM setting and varying nozzle angle. How do they do it in real life?

 

What fuel weight are you using for this? 203 isn't going to do this maneuver full. This is an exercise that'll be done in the pattern at the end of a flight. Like others have said, try different weights.

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Shadow_1stVFW has got it right. The maneuver would normally be done at a relatively low fuel weight. Doing it at full fuel (assuming with external tanks) would not be normal - and the pilot would probably dump fuel to get the weight down before attempting a heavy VNSL in an emergency. (As an aside, tried some low level flight today and the thrust seems high for the RPM outside of VSTOL too).... We need someone to get a thrust / RPM curve for the 107 engine!

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What fuel weight are you using for this? 203 isn't going to do this maneuver full. This is an exercise that'll be done in the pattern at the end of a flight. Like others have said, try different weights.

 

I think the heaviest I tried was 3500lbs on a clean jet. I'm not good at judging the jet's fuel burn yet so I've always made it a point to land with about 2600-2800lbs left.

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your weight looks spot on for practising VNSLs... The flight model is pretty good, but there looks to be some significant flaws in either its thrust or drag modelling. VNSLs would show this up. The AV8B is a very draggy beast (those huge intakes for a start!) and the model doesn't want to slow up even at idle in level flight - the flight model feels more like a conventional 'slippery' jet).

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What about altitude? Instead of practicing these over a field, I typically flew out to a flat area in Nevada and would mess with the nozzles in landing config to try and find that 8-10 units AoA while at around 5,000ft MSL, with a harddeck at 4000ft, to eliminate the extra cognitive load of actually putting the thing on a runway while first learning VNSLs. I'm wondering if the altitude could have exacerbated the problem?

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After getting pretty good at FNSL and RVL landings, I tried doing VNSL both with AUTO flaps and STOL flaps, following the VMAT-203 training syllabus procedures:

 

Nozzles 40-50 degrees on downwind, set 85% RPM for AUTO flaps or 95-100% RPM for STOL flaps, vary nozzle angle to maintain 8-10 units of AoA.

 

Problem is, it seems impossible to achieve this. 40-50 degrees of nozzle at those RPM ranges will give you too much lift and speed. To reduce speed I increase nozzle angle to around the hover stop, then I start descending. I decrease nozzle angle back to around 50, and my descent rate increases until I gain more speed. Now I'm back to square one with too much climb. It's impossible to maintain 8-10 units of AoA and a steady glideslope with a constant RPM setting and varying nozzle angle. How do they do it in real life?

 

Looking at the 2008 A1-AV8BB-NFM-000, paragraph 7.6.5.2 Variable Nozzle Slow Landing

page7-26 to 7-27 and Figure 7-6. I do not see anywhere that says that 40°-60° of nozzle and 85% RPM you can maintain 8° to 10° AOA. I see where it says the -408 engine should use 80% to 100%. I see it says if your using less than 90% to use autoflaps. I see where it says to maintain AOA with the nozzle.

 

What engine is the VMAT-203 training syllabus procedures base on? What version of the AV-8B N/A? What year.

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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Looking at the VMAT-203 FSG version 3.0 from 2012, FAM-2-62 to 2-64 I do not see that neither. Maybe I miss it but what versions of the AV-8B is this for? Being a training unit, is this for the TAV-8B or does it apply to other version?


Edited by mvsgas

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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Didn't see those numbers either in the manual I have. However it does say that when first selecting 40-45 deg. nozzles, the AoA should rise, while in the sim it does the opposite because at 45 degrees you are not slowing down at all.. you need much higher angles to start to slow down...

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What about altitude? Instead of practicing these over a field, I typically flew out to a flat area in Nevada and would mess with the nozzles in landing config to try and find that 8-10 units AoA while at around 5,000ft MSL, with a harddeck at 4000ft, to eliminate the extra cognitive load of actually putting the thing on a runway while first learning VNSLs. I'm wondering if the altitude could have exacerbated the problem?

 

Altitude reduces the engine performance so technically, you'd have to use less nozzle angle to maintain AOA for a given aircraft weight. So taking your experience at height, you'd need more nozzle angle lower down for the same RPM. (Stupid question (sorry), you've got the RPM switch in LOW? lower left console at the back).

 

I still believe that the thrust and/or drag FM for this early access version is not quite right yet - too much thrust for RPM, or too little drag, or a combo of both. If you set much lower RPM (in this flight model) than the manuals suggest, you get a more realistic VNSL approach.

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Didn't see those numbers either in the manual I have. However it does say that when first selecting 40-45 deg. nozzles, the AoA should rise, while in the sim it does the opposite because at 45 degrees you are not slowing down at all.. you need much higher angles to start to slow down...

 

Can you be more specific where is says that? Page number, paragraph, figure number.

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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Can you be more specific where is says that? Page number, paragraph, figure number.

 

FAM 2-62 point 2.

 

"On downwind, ensure the nozzles are no greater than 25° then select AUTO flaps and complete the landing checklist. On downwind select 40-50° nozzles. Set desired power, and as the AOA increases, anticipate the nozzle movement required to stabilize at 8-10 AOA."

 

 

As they put it, I understand that

 

1. You set the nozzles at 40-50

2. You set desired power (e.g. 85%)

3. with nozzles at 40-50, my AoA starts to increase, so then I play with nozzles to achieve 10 degrees in level flight.

 

Increasing AoA = decreasing airspeed = with nozzles at 50 I should be slowing down.

As it stands in DCS, with nozzles at 50 my speed keeps going up (and AoA goes down).

So I either have to set nozzles at something like 70-80, or reduce power (however, according to the procedure above, I shouldn't touch the throttle anymore).

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FAM 2-62 point 2.

 

"On downwind, ensure the nozzles are no greater than 25° then select AUTO flaps and complete the landing checklist. On downwind select 40-50° nozzles. Set desired power, and as the AOA increases, anticipate the nozzle movement required to stabilize at 8-10 AOA."

 

 

As they put it, I understand that

 

1. You set the nozzles at 40-50

2. You set desired power (e.g. 85%)

3. with nozzles at 40-50, my AoA starts to increase, so then I play with nozzles to achieve 10 degrees in level flight.

 

Increasing AoA = decreasing airspeed = with nozzles at 50 I should be slowing down.

As it stands in DCS, with nozzles at 50 my speed keeps going up (and AoA goes down).

So I either have to set nozzles at something like 70-80, or reduce power (however, according to the procedure above, I shouldn't touch the throttle anymore).

 

Master FSG FAM-2-62

1. NATOPS “variable nozzle slow landing (VNSL) contains the specific procedures.

2.It is important to achieve level flight at 8-10 units AOA and to reference the nozzle angle equired to maintain that condition. This nozzle angle will serve as an effective reference angle from which all other adjustments are made. Adjust the nozzles to fly 8-10 units AOA throughout the remainder of the pattern. If your AOA is low, a slightly greater nozzle angle must be used – but be patient and monitor the AOA trend. If the AOA is high, nozzle out slightly. Anticipate the nozzle movement. If you wait until reaching 10 units AOA, your AOA will over shoot and your rate-of descent will increase. The stick controls the aircraft’s glide path and the nozzles are now controlling AOA.

 

A1-AV8BB--NFM--000

[ATTACH]196269[/ATTACH]

 

1. You fly over the airfield at 350 knot, at the brake, set throttle to idle speed brakes out.

2. At 250 knots, landing gear down, flaps to Auto or STOL ( here is where you set 40°-50° nozzle angle)

3. At the 180°, Set throttle to 80 to 100, move nozzle as required to maintain 8° to 10° (Once you set the power, AOA is what is important. Set the nozzle to any angle to achieve 8° to 10° AOA.)

 

No where does it say it will pitch up or increase AOA with nozzle, this happens when you loose speed. That is why it states that if AOA is low, lower the nozzle, this will cause you to slow down. If AOA is high, raise the nozzle, this will cause you to speed up.


Edited by mvsgas

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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Master FSG FAM-2-62

1. NATOPS “variable nozzle slow landing (VNSL) contains the specific procedures.

2.It is important to achieve level flight at 8-10 units AOA and to reference the nozzle angle required to maintain that condition. This nozzle angle will serve as an effective reference angle from which all other adjustments are made. Adjust the nozzles to fly 8-10 units AOA throughout the remainder of the pattern. If your AOA is low, a slightly greater nozzle angle must be used – but be patient and monitor the AOA trend. If the AOA is high, nozzle out slightly. Anticipate the nozzle movement. If you wait until reaching 10 units AOA, your AOA will overshoot and your rate-of descent will increase. The stick controls the aircraft’s glide path and the nozzles are now controlling AOA.

 

You're missing the text I quoted in the previous post, which is before what you put here as point 2.

 

Anyway, the picture tells a slightly different procedure, and I am also not hung up on the 40-50 deg nozzle parameter. But I think this is all quite open to interpretation hence why already a few posts ago I said this is one case where input from a real harrier pilot would be invaluable.

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Not easy but definitely not impossible

Did the track with openbeta 2.5.3.22877

Took off, came around for overhead brake. At the 180° set the aircraft as per the manuals. Set RPM to ~85% for the rest of the flight. I was behind the aircraft so AOA kept overshooting like the manuals say it would. First touch and go I crape the tail, saw no damage on outside so I continued. Second go around I think was my best, still I did not maintain the proper AOA but that is my fault, not the aircraft nor the manuals. Landed on my third attempt.

[ATTACH]196272[/ATTACH]

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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But I think this is all quite open to interpretation hence why already a few posts ago I said this is one case where input from a real harrier pilot would be invaluable.

 

You are right, it is open to interpretation and I am definitely not a pilot. But my interpretation of the manuals allows me to VNSL within DCS, and it shows I need a lot more practice. Your interpretation show you can't do it, so the game must be wrong. So believe what you must.


Edited by mvsgas

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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  • 2 weeks later...
You are right, it is open to interpretation and I am definitely not a pilot. But my interpretation of the manuals allows me to VNSL within DCS, and it shows I need a lot more practice. Your interpretation show you can't do it, so the game must be wrong. So believe what you must.

 

 

Yes, they can be achieved in game, but it is more difficult since the thrust/drag models are not that accurate vs RL, and the manuals quote RL power settings.

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There is no problem in DCS with the AV8B for VNSL. You can match all the number in the manual within DCS. I posted the track proving it. If RAZBAM changes it I guess I was worng. We will see.

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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