VNSL landings nearly impossible

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.

including the expected nozzle angles?

including the expected nozzle angles?

https://forums.eagle.ru/showpost.php?p=3661860&postcount=20

You are getting hung up on the 40° to 50° nozzle angle statement. This is there so when you lower the landing gear with flaps in auto, and the flaps automatically extend you don't hit them with hot air. The part you need to pay attention is when it says: "nozzles angle as required to maintain 8° to 10° AOA". You need to use the nozzle to control speed and thus control AOA.

I'm curious why they specify 40-50 before dropping gear. 25 is usually the standard before dropping gear, for the same reason you mentioned.

Reread the post immediately before yours for the answer to your question.

Nozzles at that angle ensure flaps can be lowered without being affected by the hot exhaust gasses.

You totally misunderstood my question.

For FNSL approaches, 25° nozzles are selected to ensure flaps can be lowered without being affected by the exhaust gasses. VNSL differs by prescribing 40-50°, and RVL by 60°.

My question, as originally asked, is why 40-50 instead of 25 when they are meant to achieve the same affect in regards to protecting the flaps? What does the 40-50° (60° for RVL) do in addition to protecting the flaps, that 25° can't?

The 40N at the end of downwind is a suggested N angle to get the speed under control. It is not to do with flap/nozzle impingement, which can occur only in STOL flap and after a dual channel flap controller failure, since both Flap 1 and 2 channels will automatically schedule the flaps as the nozzles travel beyond approx 30 deg. For example, at 40N the flap will be around 47F.

I stand by my comments regarding the thrust/drag model in DCS vs RL. It is a shame the model (which is otherwise good) is not as good as it could be in this regard, leading to some unusual RPM fiigures vs speeds or RPM vs N for VNSLs. 85% for an AUTO flap VNSL should yield N angles in the 45-60N range for a controlled approach at low aircraft weights.

Some thing that need to be reiterated, all the manual we have are from different years and should not be used together. In order to find the proper information, we would need all the manuals in a set.

As long as we are aware of that, the only manuals than mentions the 40° to 50° nozzle range is the Flight Syllabus Guide ver 3.0 from VMAT-203 2012. This manual does not specify the version of the AV8B in it but mentions the TAV8B several times. Considering that it is a training manual from a training unit, it is save to assume that the main version would be a TAV8B. An aircraft that is mention to be nose heavy in comparison to other version.

Now we ad the nozzle blast Impingement information( paragraph 11.8.6 of the A1-AV8BB--NFM--000) the aircraft has a strong nose down tendency on certain conditions.

Being a training manual, it would be save to assume this is an important aspect of the flight characteristics to watch out for.

Something else to look at is found in the A1-AV8BB--NFM--000, paragraph 11.8.15 Slow landing:

With over 80 percent rpm in a slow approach, nozzle angles are typically 60° and above.

This should be enough to make the 40° to 50° nozzle angle for VNSL moot, since the manual states this would be atypical at 85% engine RPM this is mention here

and it also mentions

Pilot workload can be reduced by decreasing nozzle angle from 60° to 50°, or by using the variable nozzle SL technique with auto flaps selected.

So, is is about lowering workload for new pilots and avoiding out of control conditions AFAIK.

I stand by my comments regarding the thrust/drag model in DCS vs RL. It is a shame the model (which is otherwise good) is not as good as it could be in this regard, leading to some unusual RPM fiigures vs speeds or RPM vs N for VNSLs. 85% for an AUTO flap VNSL should yield N angles in the 45-60N range for a controlled approach at low aircraft weights.

I guess you see the dress as gold and I see as blue.

As a previously posted

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.

I took another crack at VNSLA approaches with 3000-4500lbs fuel on a clean jet, over Lake Mead. I was able to stabilize about -3/-4° glideslope with just about 10 units AoA, 85% RPM, and nozzles in the low/mid 60s. I also tried VNSL with STOL flaps, but 95% RPM was just too much power and I couldn't find the sweet spot: I was constantly climbing, even with nozzles at the hover stop.

Now, when I tried an actual landing at Nellis with VNSLA, something strange happened. I had a good approach with 2800lbs of fuel, 85% RPM, varying nozzles between 58-63 to stay on glideslope and keeping about 10-11 units AoA, 82kts. Once I got to 60' AGL, I suddenly ballooned at 62° nozzles and 86kts. I increased nozzles to 67° to try and slow down, but my speed kept increasing up to 103kts despite having 67° selected for a good 11 seconds or so. The Witch Hat was on the horizon the entire approach.

I don't understand where this massive lift/speed increase came from when I did not change power, pitch, or nozzle range, nor do I understand how I had an increase in airspeed with 67° nozzles.

By that altitude, you should have control rate of decent with throttle.

[ATTACH]196898[/ATTACH]

Aircraft had Cap-9, empty wing tank on outer pylons, TGP on station 5, AN/ASQ-T50 pod and gun pods. The TGP kept messing with me and I was way behind the aircraft again. Been flying the Mig-29 to much lately.

Made 3 attempts on open beta version 2.5.3.23225 from Nellis. First 2 using over 90% throttle (first at around 94% and second around 96% engine RPM) and STOVL flaps. The last pass was at 86% using auto flaps. With auto flaps I almost hit the ground and some power line at the 180° position because I got to slow. At the 45° position I balloon sense I got to fast.

But I did not brake the landing gear nor the tires so good enough landing for me.

Some thing that need to be reiterated, all the manual we have are from different years and should not be used together. In order to find the proper information, we would need all the manuals in a set.

 

As long as we are aware of that, the only manuals than mentions the 40° to 50° nozzle range is the Flight Syllabus Guide ver 3.0 from VMAT-203 2012. This manual does not specify the version of the AV8B in it but mentions the TAV8B several times. Considering that it is a training manual from a training unit, it is save to assume that the main version would be a TAV8B. An aircraft that is mention to be nose heavy in comparison to other version.

 

Now we ad the nozzle blast Impingement information( paragraph 11.8.6 of the A1-AV8BB--NFM--000) the aircraft has a strong nose down tendency on certain conditions.

 

Being a training manual, it would be save to assume this is an important aspect of the flight characteristics to watch out for.

 

Something else to look at is found in the A1-AV8BB--NFM--000, paragraph 11.8.15 Slow landing:

 

This should be enough to make the 40° to 50° nozzle angle for VNSL moot, since the manual states this would be atypical at 85% engine RPM this is mention here

 

and it also mentions

 

 

So, is is about lowering workload for new pilots and avoiding out of control conditions AFAIK.

I think we need to understand which variant of engine the manuals are related to. The older engines (and possibly older manuals) would be for the lower thrust engine (-106 I believe?). For this engine, R80 would equate to around R90 in the DCS model engine (which is the later variant and for which thrust levels need about another 10% RPM at mid RPM levels; Yes, with R80 in the previous engine, it would need N60 or above. The VNSL was typically flown with R75 in the smaller engine, which needed around 50N for a stable approach.

The nose heavy tendency of the TAV8B has little to no impact on VNSL, since the fwd CofG becomes an issue in low speed VSTOL manoeuvers which rely more heavily on the front puffer for pitch authority.

This is a healthy debate, and it would be good if we could get to the bottom of the data and how we can get the model to better match RL. At the moment, it is quite a bit off (IMO) in thrust/drag modelling which is a real shame given it is such a good replication of the AV8B.

By that altitude, you should have control rate of decent with throttle.

I thought VNSL landings required a set RPM all the way down to touchdown?

Nevermind, found it in the VMAT-203 syllabus. "Cleared to use throttle below 100'"

Yes, until the last 20 feet when you can use power to control ROD at touchdown

https://forums.eagle.ru/showthread.php?t=226613

   Hi guys, did you ever figure out how to successfully fly a VNSL? I have just been practising these today and they are not easy to fly. 

One thing that made it easier is to configure early on downwind and fly level at the thrust/nozzle combo you decide on. Check air speed and make a mental note. Turning from 180 to 90 is where it gets messy for me but I found making small nozzle adjustments and 2 or 3% RPM (I know, its cheating I  guess) make it more manageable.  

Has it gotten easier with the recent engine power tweaks? I understand the engine used to be overpowered, and I'm wondering if that led to issues with maintaining proper AoA with a set RPM. 

58 minutes ago, Nealius said:

Has it gotten easier with the recent engine power tweaks? I understand the engine used to be overpowered, and I'm wondering if that led to issues with maintaining proper AoA with a set RPM. 

It's much easier now. The aircraft is more stable  (I suspect they made it heavier in the FM) hence it allows you to use the correct power settings for VNSLs. 

Can someone show how is it done properly? I cant think of a way to not gain altitude at the moment of STOL flaps scheduling activation at 165 kts without changing engine rating. So, I end up high and must lower the nose quite a bit to get to the runway, and AoA can be maintained only with getting behind hover stop during descent. I probably should elongate final and approach to 180, but slowing down in a straight line with fixed 90%+ RPM is not easy, especially if altitude needs to be maintained.

AV-8B SVNSL attempt 1.trk

I was thinking of recording a video of how to do it properly. But in short, if you are practicing VNSLs in a circuit, you turn downwind, gear down (if not already) then nozzles 25 degrees, flaps AUTO or STOL, depending on which VNSL you are practicing. 

AUTO would be used if your engine RPM is limited to around 85% (for an OIL caution) which is not enough for a STOL flap VNSL.

STOL flaps would be used if you have more power available and want to reduce our landing speed. Or, if you are doing a STOL flap FNSL and realise you haven't got enough power for a waveoff, you would then transition to VNSL. 

Anyhow, you are downwind, gear down, nzl 25* , select flaps, either leave in AUTO or select STOL.   

Once you do that, select NOZZLES to 40-50 degrees and slowly power up to the required thrust setting. 85% for AUTO flaps,  90 or >90% for a STOL flap VNSL.

Slowly let the speed trickle down and aim for 8-10 unit of AoA.  It's best to aim for 8 units or even 7.5 so that you have some margin if you get start to get too slow.  If I want it to slow down a bit quicker I use more than 50* nozzles and use something like 70* and slowly nozzle out again to around 60ish once I have the correct units of AoA. 

As you pass the abeam make sure you are at a stable speed that gives you the 7.5 or 8 units AoA.  and make a note of the speed that gives you that. Let's say it's around 115 kts for a STOL flap and 130ish for an AUTO flap.  As you turn to base and start your descent the speed may start to increase a bit, in this case use a few more degrees of nozzle to keep the speed from increasing.  Maintain that speed and units of AoA and then as you roll out on final the speed will most likely creep up again, use a few more degrees of nozzle to slow it down. 

In training you are allowed to use throttles below 100 ft.  

If your aircraft keeps climbing you are too fast and AoA is too low, SLOW DOWN by using more NZL and nail the 8 units of AoA. 

If your aircraft starts to sink and AoA is increasing beyond 8 units, you are TOO SLOW,  INCREASE SPEED by nozzling out a bit and reducing the AoA to 8 units. Be careful though as you nozzle out to less than 50* NZL with FLAPS STOL the flaps/nozzle programming will reduce the flaps deflection and you will lose lift. 

Hope all that makes sense! I'll try to make a video because it's a lot easier to show how to do it. It took me A LOT of tries to nail this but once you get it it's really not that difficult, especially with the new FM. 

Good luck! 

2 hours ago, Aernov said:

Can someone show how is it done properly? I cant think of a way to not gain altitude at the moment of STOL flaps scheduling activation at 165 kts without changing engine rating. So, I end up high and must lower the nose quite a bit to get to the runway, and AoA can be maintained only with getting behind hover stop during descent. I probably should elongate final and approach to 180, but slowing down in a straight line with fixed 90%+ RPM is not easy, especially if altitude needs to be maintained.

AV-8B SVNSL attempt 1.trk 3.67 MB · 2 downloads

I had a look at your track file. It didnt look terrible until you started climbing up and up and lost a lot of speed. When you come into the break try to maintain that altitude as best as you can and make small corrections to the speed with the nozzles. Your speed varied by something like 50 kts from 120 all the way down to 70. At 95% rpm you gonna need a slow speed in order for VNSL to work. Something like 80-ish kts will probably work. Work off the AoA. 

I tried to watch my own track, and "past me" almost crashed in a tree at break and then landed somewhere in the grass with too high descent speed ). So, tracks still don't really work still... But yeah, I need A LOT of practice with all kinds of landings since before engine update all I did is VL without approach pattern. And VNSL is definitely possible, it's just maintaining approach parameters that is difficult.

 I keep forgetting to try VNSL... So good thing you guys posted today!

After my today's AAR practice, I dumped my painstakingly newly acquired fuel and stores and went in for a VNSL at 85% with auto flaps... First time I try it... The worst part was fighting the urge of stroking the throttle but It was very interesting controlling AoA with nozzle angle and trim... 85% rpm felt like a lot for a light and clean plane, every time I tried to slow down increasing nozzle angle I tended to balloon up ...Took me some time to figure it out.   I assume you enter the pattern at 350knows , 800' ASL then break, then flaps and gear at 250 knows and then you work the nozzles? 

7 hours ago, Draken35 said:

 I keep forgetting to try VNSL... So good thing you guys posted today!

 

After my today's AAR practice, I dumped my painstakingly newly acquired fuel and stores and went in for a VNSL at 85% with auto flaps... First time I try it... The worst part was fighting the urge of stroking the throttle but It was very interesting controlling AoA with nozzle angle and trim... 85% rpm felt like a lot for a light and clean plane, every time I tried to slow down increasing nozzle angle I tended to balloon up ...Took me some time to figure it out.   I assume you enter the pattern at 350knows , 800' ASL then break, then flaps and gear at 250 knows and then you work the nozzles? 

 

 

Yes, as per my write up above, after the break when you are downwind and below 250 kts, gear down, nozzles 25, then select flaps STOL or leave in auto, then nozzles 40-50 ish or as required to slow down to get 8-ish units AoA.  If you are light you will need quite a slow speed, resist the temptation to come in too fast but also be wary that if the speed drops off too much you will quite quickly end up with high AoA and have to nozzle out, pitch down and most likely increase thrust to not stall it. 

I fly the pattern at 1000 ft as per the VMAT-203 Cherry point rules but 800 is also ok. 

3 hours ago, Bog9y said:

I fly the pattern at 1000 ft as per the VMAT-203 Cherry point rules but 800 is also ok. 

I got used to the 800ft (NAVAIR 00-80T-111)  because of carrier ops. Is 1000 standard for airfield ops or just for Cherry Point MCAS?