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Default A321 Stabilizer Incidence Tweak


HoggyDog

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In response to what seemed to me to be an overly-nose-down attitude in all flight regimes, I modified the horizontal stabilizer incidence from 0 degrees to -4 degrees, in one-degree steps, test-flying each one to try to achieve a zero-pitch attitude in cruise.

 

When I test-flew it at -4 degrees stab incidence, I got what seems to me to be the correct attitudes. It's still almost imperceptibly nose down at 300-knot cruise in the mid twenties, maybe one degree, but dead-level at 240 KIAS and properly nose-up when descending the glideslope at Vref+5, which in this case was 122 knots.

 

Please check these screenshots and tell me if they look correct to you:

 

Level flight @8001 MSL, 243 KIAS

A321_Level_Flight-250KIAS.jpg

 

Descending Nose-up on final, ILS glidelsope, 122 KIAS

A321_Nose_Up_Descending_Dirty-122KIAS.jpg

 

Has anyone else noticed the chronic nose-down flight of the default A321, and if so, how did you fix it?

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Hi HoggyDog,

 

To me it looks more logical. That how much I can comment. In actual fact I was trying to find ways to adjust the horizontal stabilizer as I have the same problem to adjust to more sensible pitch when level flying.

 

In response to what seemed to me to be an overly-nose-down attitude in all flight regimes, I modified the horizontal stabilizer incidence from 0 degrees to -4 degrees, in one-degree steps, test-flying each one to try to achieve a zero-pitch attitude in cruise

 

So, how did you adjust your horizontal stabilizer. Thanks for your time :)

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So, how did you adjust your horizontal stabilizer. Thanks for your time :)

 

[Airplane_Geometry]

 

htail_incidence = 0.0

 

In the aircraft.cfg

 

Looks like the best guess. HoggyDog to confirm.

Still thinking about a new flightsim only computer!  ✈️

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[Airplane_Geometry]

 

htail_incidence = 0.0

 

In the aircraft.cfg

 

Looks like the best guess. HoggyDog to confirm.

 

Mrzippy,

 

Thanks for the input. Will give a try later while waiting for HoggyDog.

 

Cheers:cool:

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[Airplane_Geometry]

 

htail_incidence = 0.0

 

In the aircraft.cfg

 

Looks like the best guess. HoggyDog to confirm.

 

Yes, that's what I did- I changed htail_incidence = 0.0 to htail_incidence = -4.0.

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According to the Aircraft.cfg MDA online I use, and I quote:

 

Lift parameter

 

The cruise_lift_scalar parameter is a multiplier on the coefficient of lift at zero angle of attack Cruise lift in this context refers to the lift at relatively small angles of attack, which is typical for an airplane in a cruise condition. This scaling is decreased linearly as angle of attack moves toward the critical (stall) angle of attack, which prevents destabilizing low speed and stall characteristics at high angles of attack. Modify this value to set the angle of attack (and thus pitch) for a cruise condition. A negative value is not advised, as this will result in extremely unnatural flight characteristics. Omission of this parameter results in the default value of 1.0.

 

I hope that helps. I have it works the best. Everything I've read in the Developer's forum, including a great treatise titled Flight Dynamics in MSFS V1.0.pdf by Yves Guillaume, which is pretty much the be-all and end-all of FDE development, the Htail_incidence should always be left at Zero (0).

 

Just thought I'd throw that out there and see if anyone bat's it into the bleachers :D

Pat☺

[sIGPIC][/sIGPIC]

Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again!

Sgt, USMC, 10 years proud service, Inactive reserve now :D

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According to the Aircraft.cfg MDA online I use, and I quote:

 

I hope that helps. I have it works the best. Everything I've read in the Developer's forum, including a great treatise titled Flight Dynamics in MSFS V1.0.pdf by Yves Guillaume, which is pretty much the be-all and end-all of FDE development, the Htail_incidence should always be left at Zero (0).

 

Just thought I'd throw that out there and see if anyone bat's it into the bleachers :D

Pat☺

 

Sorry to be such a dunce, but "MDA" means "Minimum Descent Altitude" to me. :eek: What is "the Aircraft.cfg MDA?"

 

And yes, thank you for the info- I felt "queasy" about changing the stab incidence at all, unimpeded queenseconces :p and all that, which is why I started this thread.

 

On the other hand, changing the lift scalar of the wing would seem to be subject to even more unintended consequences than just warping the stab...

 

I take it, based on the lack of "here's how I fixed it" replies here, that no one but me is bothered by the bizarre attitude of this aircraft in flight, so no one is trying to fix it but me... or maybe I'm the only person around who flies the default airplanes.

 

Has anyone else even noticed that the default A321 plows along like a wheelbarrow in flight? I seem to recall a similar nose-down-in-cruise situation and discussion on the default CRJ several months ago... I think I'll go try to find that thread... maybe there's a fix shown there that I could apply here.

 

Thanks again for your info, Pat!

 

EDIT: HA! Found the CRJ Nose Down Fix thread where Chuckles the Mule from Napa Valley posits a 3-part fix. Interestingly, one part is a drastic change in the stabilizer incidence.

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I don't know what DA stands for. It's just how I saw it listed. It is here: https://msdn.microsoft.com/en-us/library/cc526949.aspx#mozTocId136011

Check the [Flight_Tuning] section. It says specifically, etc etc etc...

I use this page very extensively for ANY adjustment to the aircraft.cfg, as well as the PDF I named above. Yves specifies specifically to leave the Horizontal Stabilizer at 0, in the aircraft.cfg AND the .air files. I have used this fiix extensively on several aircraft. Apparently the term "Lift Scalar" is a trifle misleading, as is shown in the quote in my previous post. It takes very little change to the Lift Scalar to achieve a noticable alteration in the cruise AOA (and pitch angle). Trick is to check the pitch at cruise speed/altitude, make a small adjustment, like 0.1 more negative (1.0 to 0.9 for example), reload the plane and see what it's pitch or AOA may be. I've found that more negative = nose up, more positive = nose down.

Remember, when testing like this, where you have to reload the airplane often, you need to turn off AI traffic, otherwise some odd things happen, it seems. According again to the page I linked.

Nothing else is noticably altered, like the lifting ability of the aircraft. It can carry the same weight overall, and needs no more power to do what it was doing before.

But hey! I am frequently wrong about "stuff", and will be again :D

Pat☺

[sIGPIC][/sIGPIC]

Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again!

Sgt, USMC, 10 years proud service, Inactive reserve now :D

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In earlier versions of flightsim (FS98 for those of you that remember that old classic) I corrected some of the same issue although usually excessive nose high at altitude by using AirEd and editing the air file. I believe I changed the "angle of incidence of the wing. It seemed to work very well. I haven't looked in an air file for years now and maybe it has changed a bit. But I thought I would throw this out there and maybe somebody might try this???
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Sorry to be such a dunce, but "MDA" means "Minimum Descent Altitude" to me. :eek: What is "the Aircraft.cfg MDA?"

 

And yes, thank you for the info- I felt "queasy" about changing the stab incidence at all, unimpeded queenseconces :p and all that, which is why I started this thread.

 

On the other hand, changing the lift scalar of the wing would seem to be subject to even more unintended consequences than just warping the stab...

 

I take it, based on the lack of "here's how I fixed it" replies here, that no one but me is bothered by the bizarre attitude of this aircraft in flight, so no one is trying to fix it but me... or maybe I'm the only person around who flies the default airplanes.

 

I don't fly the default planes anymore, but I have noticed what you are talking

about. The CRJ or whatever it is is kind of the same way. Flies a tad too level I think.

The one you are tweaking? I'm just judging by the 737's I run, which I feel are fairly

accurate overall. But if anything, I think you might be able to add a bit more pitch up

than what it has now. Fer instance, it looks awful level for only 243 knots. With my

737's, I'd have a definite pitch up going. Heck, I do in all flight regimes with the ones

I'm running. Even at 300 knots, there is a bit of a pitch up I'm pretty sure.

And I know from flying in real 737's, you always feel like you are pitching up all the time,

no matter what speed, alt, etc. Or at least judging from a cabin seat where you are

seeing the horizon out the window.

So I think you definitely helped it vs default, and might could use just a tad more

tweaking to pitch up a bit more. And 122 knots is slow for that plane, and the AOA

would be pretty high. Unless the plane were really light, which I assume yours was,

that speed would normally get you near tail strike territory if fully loaded and all.

That's a pretty good sized plane.

 

 

One example of my 739 at cruise. I'm sure I was likely around FL370-390, and

the speed would be nearly mach .79. And it's still got a noticeable pitch up going.

When I look out my side windows, I always feel like I aiming uphill a bit..

 

edit

BTW.. I should really say I don't fly any of the default jets any more.

The systems are just too lame once you've flown a good payware jet for a

while. I used to fly the Lear 45 a lot. But haven't touched it since I got the

NGX series.. Just too lame. Now I fly the little 600 instead if I want to go to

a bit smaller airports than normal.

 

But I do still fly the default props every once in a while. To me, they aren't

quite a critical, or as grossly lacking as the FSX default jets.

And I still fly a few old planes that were converted from the FS9 days.

IE: the Beech 18, and the Spartan Executive for a couple of the oldies I like

to fly.

Both are old FS9 planes that were overhauled for FSX. And a bonus with the

Executive.. It lets me use the old FS9 glass rain effects. A few of those old

planes, and also any old FS9 planes run in FSX will let you see the rain FX as

long as you have all the old FS9 rain FX bmps.

 

 

900.jpg

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I don't know what DA stands for. It's just how I saw it listed. It is here: https://msdn.microsoft.com/en-us/library/cc526949.aspx#mozTocId136011

Check the [Flight_Tuning] section. It says specifically, etc etc etc...

I use this page very extensively for ANY adjustment to the aircraft.cfg, as well as the PDF I named above. Yves specifies specifically to leave the Horizontal Stabilizer at 0, in the aircraft.cfg AND the .air files.

 

Thanks Pat, I Googled and found the Yves pdf document you mentioned, but it isn't available for download or even browsing without paying for a monthly subscription to . Not going to do that. So I'll never know what's in there, even though I would like to have it available as I try to dig deeper into fixing some of my broken FSX stuff- especially since I learned that Dovetail is specifically prohibited from fixing/improving ANY of the FSX core errors and deficiencies under their licensing agreement with MS! :mad: Astounding, but true.

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Wow, you hit so many of my issues! Trying to do one at a time:

The CRJ or whatever it is is kind of the same way. Flies a tad too level I think.

The default CRJ flies distinctly nose-down at cruise altitudes and speeds, which is why it came to mind as I tried to finger out how to fix the default A321. The CRJ nose-down fix thread I linked to at the bottom of my OP showed a fix by Napamule using 3 tweaks: more negative stab incidence, more negative wing lift scalar and lower engine location.

 

The one you are tweaking? <...> I think you might be able to add a bit more pitch up than what it has now. Fer instance, it looks awful level for only 243 knots.

I agree, the A321 should have just a bit more nose up than where I left it in the photos I posted. I think I'll revert my stab incidence tweak and play with the wing lift scalar, based on what Pat posted.

 

With my 737's, I'd have a definite pitch up going. Heck, I do in all flight regimes with the ones I'm running. Even at 300 knots, there is a bit of a pitch up I'm pretty sure.

Right you are, sirrah, although I'm not sure that the A321 would have the same pitch attitudes. Here is an excerpt I pulled from "737 Rules of Thumb:"

++++++++++++++++++++++++++++++++++++++++++++++++++++++++

N1's & Pitch Attitudes

[table=width: 500]

[tr]

[td]Phase of flight[/td] [td]%N1[/td] [td]Attitude (deg nose up)[/td]

[/tr]

 

[tr]

[td]Level Flight:[/td]

[/tr]

 

[tr]

[td]250kts[/td] [td]65[/td] [td]4[/td]

[/tr]

 

[tr]

[td]210kts[/td] [td]60[/td] [td]6[/td]

[/tr]

 

[tr]

[td]Flap 1, 190kts[/td] [td]60[/td] [td]6[/td]

[/tr]

 

[tr]

[td]Flap 5, 180kts[/td] [td]62[/td] [td]7[/td]

[/tr]

 

[tr]

[td]Gear down, flap 15, 150kts[/td] [td]70[/td] [td]8[/td]

[/tr]

 

[tr]

[td]Gear down, on glideslope:[/td]

[/tr]

 

[tr]

[td]Flap 15, 150kts[/td] [td]52[/td] [td]4.5[/td]

[/tr]

 

[tr]

[td]Flap 25, 140kts[/td] [td]52[/td] [td]4[/td]

[/tr]

 

[tr]

[td]Flap 30, Vref + 5[/td] [td]55[/td] [td]2.5[/td]

[/tr]

 

[tr]

[td]Flap 40, Vref + 5[/td] [td]62[/td] [td]1[/td]

[/tr]

[/table]

All the above based on a gross weight of 47.5, N1 may vary by 5% and attitude by 2° at other weights.

Add 2% N1 in turns.

For single engine add 15% N1 + 5% N1 in turns.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 

And 122 knots is slow for that plane, and the AOA would be pretty high. Unless the plane were really light, which I assume yours was, that speed would normally get you near tail strike territory if fully loaded and all.

Oh lordy, here we are again discussing my "overly slow" landing speeds, which are based entirely on the published Refs for the airplane, configuration and landing weight.

 

I think I pretty thoroughly hashed that out in this post, which includes a video to prove that a Vref+5 final ILS descent was achievable without falling out of the sky, in this same airplane on the same approach and landing as the one in my photo above, so please, suffice to say here that 122 KIAS was Vref+6 for that airplane in that configuration on that day at that weight at that airport. :D

 

BTW.. I should really say I don't fly any of the default jets any more. The systems are just too lame once you've flown a good payware jet for a

while.

I have tried to find a decent payware 737 that was more accurate than the default without requiring a two-hour preflight rigamarole in the FMS when I want to make a flight. I have spent hours trying to find out what the PMDG NGX is all about. There is no question that it is a high-quality, faithful representation of the Boeing 737. However, I also learned that you either have to spend an hour or more hand-programming a route into the FMS OR use a series of addon or external programs to generate a flight plan that can be "uploaded" to the PMDG NGX FMS... but that externally-generated flight plan is not viewable in-flight "in plain English" via the kneeboard!

 

With the NGX, there is apparently no option to use the FSX Flight Planner to generate a flight plan and Nav Log viewable on the Kneeboard and then just go fly that plan. Some days, I don't even have enough Sim time available in my day to program the FMS for a short flight, which means my entire available sim time would be consumed in the FMS with zero opportunity to fly. So I rather like the "enter your destination and get an instant FSX routing, kick the tires and light the fires" simplicity of taking the default 738 on an IFR trip.

 

Also, I have read a few "horror stories" of the PMDG NGX being an absolute frame-killer on even higher-end PCs, and I'm not ready for a new computer yet, nor am I ready to turn all my scenery and/or AI traffic off or down to mimimums and my display quality down to "p*ss poor" (I'm pretty sure that's an actual setting :p ) just to fly the PMDG NGX at more than 5 fps. So all in all, while I would love to upgrade my default 738 to a more realistic and accurate payware model, especially one with HD textures so that my passenger-view wings don't look like they were done with Crayolas by a 2-year-old desperately in need of his first pair of glasses, I don't think it's going to be the NGX.

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[quote=HoggyDog;

Oh lordy, here we are again discussing my "overly slow" landing speeds, which are based entirely on the published Refs for the airplane, configuration and landing weight.

 

I think I pretty thoroughly hashed that out in this post, which includes a video to prove that a Vref+5 final ILS descent was achievable without falling out of the sky, in this same airplane on the same approach and landing as the one in my photo above, so please, suffice to say here that 122 KIAS was Vref+6 for that airplane in that configuration on that day at that weight at that airport. :D

 

Oh, I didn't say it wouldn't do it. I know it would if light. I'm just saying that I

would expect a fairly high AOA even with the light load at that low a speed.

The only reason that seems a tad slow to me is it matches my 600 much closer

than the longer planes, even with the light loads.

I thought the A321 was appx the size of a 737-800 or so.

Or at least as far as the usual pax load. But if no load..

 

I often run light as a pseudo BBJ. And my vref+5 with the 600 will often be in the

120-125 knot range. But I'd have to be really light to have speeds that low in the

longer planes. Even if real light, I would expect at least the low 130's for the 800,

being as loaded up, the speeds are a good bit higher than that. I suppose I could

test it and see what the FMC spits out for a real light load..

Just kind of surprised vref+5 would come out to 122 with that particular plane.

I would have expected a tad higher.. But it's an Airbii, which I don't fly much at all..

So not familiar with the usual speeds.

 

I have tried to find a decent payware 737 that was more accurate than the default without requiring a two-hour preflight rigamarole in the FMS when I want to make a flight. I have spent hours trying to find out what the PMDG NGX is all about. There is no question that it is a high-quality, faithful representation of the Boeing 737. However, I also learned that you either have to spend an hour or more hand-programming a route into the FMS OR use a series of addon or external programs to generate a flight plan that can be "uploaded" to the PMDG NGX FMS... but that externally-generated flight plan is not viewable in-flight "in plain English" via the kneeboard!

 

It's on the CDU. Both a route and legs page. Also progress.

 

With the NGX, there is apparently no option to use the FSX Flight Planner to generate a flight plan and Nav Log viewable on the Kneeboard and then just go fly that plan. Some days, I don't even have enough Sim time available in my day to program the FMS for a short flight, which means my entire available sim time would be consumed in the FMS with zero opportunity to fly. So I rather like the "enter your destination and get an instant FSX routing, kick the tires and light the fires" simplicity of taking the default 738 on an IFR trip.

 

You can do the same with the NGX, except that by default it's not using the

FSX GPS. So there is no "nav" hold for GPS.

But you can punch a plan into the FMC pretty much the same as with FSX ATC.

Actually, I use FSX ATC, but I make my flights on Simroutes so I can use real

world routes.

It might take a while to get cranked up at first, but with practice it becomes much quicker.

I can whip through the route and get the plane fired up pretty quick.

And you can set the panel state to have everything running and ready to go if you

wanted to.

But to each his own as far as planes.

 

Also, I have read a few "horror stories" of the PMDG NGX being an absolute frame-killer on even higher-end PCs, and I'm not ready for a new computer yet, nor am I ready to turn all my scenery and/or AI traffic off or down to mimimums and my display quality down to "p*ss poor" (I'm pretty sure that's an actual setting :p ) just to fly the PMDG NGX at more than 5 fps. So all in all, while I would love to upgrade my default 738 to a more realistic and accurate payware model, especially one with HD textures so that my passenger-view wings don't look like they were done with Crayolas by a 2-year-old desperately in need of his first pair of glasses, I don't think it's going to be the NGX.

 

It's a good bit more load than the default plane, but I ran the NGX with no problem with

the AMD Phenom IIx4 at 3.5 ghz.

The frame rate on the ground wasn't anything to get too excited about, but it was

good enough for gov work. I ran lean scenery, but that was more due to XP 32 bit and

a puny VAS, than being bogged down by the NGX. In the air, the frame rate was good

unless I was getting bombed with real thick clouds.

Heck, I thought your present puter was pretty powerful?? It should run the NGX

no sweat at all even with decent scenery settings.

 

With the present bone stock i7 4790 and only the onboard video, I'm running the NGX

with most all scenery settings at max. And the frame rate is plenty good.

And that's running FTX Global and Vector too.. Global is no big deal, but Vector does

add some load. But I'm still able to fly the NGX with most all scenery settings maxed out.

The only thing I do when flying that plane is lower the water down a bit, which gives a

good boost vs max. And I don't run a real high res.. I'd need a better video card to do that

with a good frame rate. But I can't run real high res until I get a new monitor..

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I always assumed that if I had nose down configuration for level flight the center of gravity has shifted too far from bad cargo/passenger placement.

in real life, or a real aircraft, probably. In the sim, not necessarily :)

[sIGPIC][/sIGPIC]

Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again!

Sgt, USMC, 10 years proud service, Inactive reserve now :D

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The only reason that seems a tad slow to me is it matches my 600 much closer

than the longer planes, even with the light loads.

I thought the A321 was appx the size of a 737-800 or so.

Or at least as far as the usual pax load. But if no load..

.

 

Dang.. I thought the A321 was a pretty good sized plane.. It's actually longer

than the 737-900. And the A320 is just slightly shorter than the 738 if I remember

the charts right.. I was comparing the two series a while ago..

IE: I've got charts with drawings of the Boeing 500,300,700, 800 and 900 comparing

the lengths and all, and also the same for the A318,A319,A320, and A321.

 

I knew there was something that was itching in my brain pan about the approach

speeds and the A321. Seems to me, it would almost have to be empty to use such

low approach speeds, unless it has an unusually low stall speed, and I don't think

that's really the case vs the 737's. And maybe it was as you flew it. I don't recall

what you said the fuel load was..

 

Later I'm gonna load up the 900 pseudo BBJ3, and run it across town almost empty

and see what speeds the FMC spits out.

Normally loaded vref+5 would normally be in the 140's range for the 900. Sometimes

even over 150 if really heavy I think, and ditto for V2 speeds on takeoff. IE: I recall

seeing V2 speeds of say 152 and such when running a wide load 900.

So... I was sort of expecting the A321 to use the same basic speed ranges as the

larger 737's, and not the smaller ones. IE: vref+5 in the 120's is common with the 600.

Semi rare with the 700.. Would have to be really light with it. Most 700 approaches end

up in the lower to mid 130's, with a light load maybe in the upper 120's. And faster with

the 800, and even mo faster with the 900.

 

I just checked my recent "crabby" video which is using that 900, and it was loaded light

for that flight across town. V2 was 144, and vref+5 was also 144.

And if I remember right, I had about 12,000 lb's of go juice, and I think 22 people on board,

which is what I used when I flew around the world in that plane a few months ago.

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I knew there was something that was itching in my brain pan about the approach speeds and the A321. Seems to me, it would almost have to be empty to use such low approach speeds, unless it has an unusually low stall speed, and I don't think that's really the case vs the 737's. And maybe it was as you flew it. I don't recall what you said the fuel load was..

 

Later I'm gonna load up the 900 pseudo BBJ3, and run it across town almost empty and see what speeds the FMC spits out. Normally loaded vref+5 would normally be in the 140's range for the 900. Sometimes even over 150 if really heavy I think, and ditto for V2 speeds on takeoff. IE: I recall seeing V2 speeds of say 152 and such when running a wide load 900.

So... I was sort of expecting the A321 to use the same basic speed ranges as the larger 737's, and not the smaller ones. IE: vref+5 in the 120's is common with the 600. Semi rare with the 700.. Would have to be really light with it. Most 700 approaches end up in the lower to mid 130's, with a light load maybe in the upper 120's. And faster with the 800, and even mo faster with the 900.

 

I just checked my recent "crabby" video which is using that 900, and it was loaded light for that flight across town. V2 was 144, and vref+5 was also 144.

And if I remember right, I had about 12,000 lb's of go juice, and I think 22 people on board,

which is what I used when I flew around the world in that plane a few months ago.

 

*sigh*

 

I'm sorry, but I just don't understand all the surmises, feeling this, imagining that, assuming max-weight approaches... and all of it about one or another model of the B737... when the airplane I used is the default FSX A321... also, I posted a direct link to the video page containing the ACTUAL weights used, the ACTUAL estimated fuel burn from the flight plan sheet, which drives the ACTUAL fuel load used for the flight, which in turn drives the ACTUAL landing weight and the ACTUAL Vref.

 

As far as I know, the 14,340-pound payload I used is the maximum passenger/cargo payload for this airplane- at least, it's the maximum FSX let me put into it before I loaded fuel.

 

Airlines don't tanker fuel. If a flight is estimated to burn, oh, just hypothetically ;) 8704.2 pounds of fuel for a 47-minute flight, they would not depart with full 5-hour fuel load of 52,193 pounds! They would depart with the fuel required to fly to the destination, miss the approach there and fly to the alternate, plus an additional allowance for taxi, ATC vectoring, holding, etc. depending on the actual and forecast weather. In my case, I loaded 15,471.44 pounds, which was more than 184% of the estimated fuel burn for the 47-minute flight to the destination, plus an allowance for a hypothetical alternate.

 

I honestly don't understand why so many people are imagining the use of the heaviest possible landing weights to challenge my Vref calculations (without even looking at the FSX A321 refs) when no airline on the face of the planet departs with enough fuel so as to arrive at the destination at the heaviest published landing weights.

 

You can see for yourself what the ACTUAL published Vrefs are FOR THE DEFAULT FSX A321 by looking at ...\FSX\SimObjects\Airplanes\Airbus_A321\AirbusA321_ref.htm in your own installation. Just in case you deleted that default airplane, here's a copy:

 

Airbus A321 VREF - Landing Approach Speed gear down

[table=width: 500, class: grid, align: left]

[tr]

[td]Weight (Flaps)[/td]

[td]Vref[/td]

[/tr]

[tr]

[td]113,900 lbs (flaps 3)[/td]

[td]121 KIAS[/td]

[/tr]

[tr]

[td]113,900 lbs (flaps 4)[/td]

[td]116 KIAS[/td]

[/tr]

[tr]

[td]175,300 lbs (flaps 3)[/td]

[td]151 KIAS[/td]

[/tr]

[tr]

[td]175,300 lbs (flaps 4)[/td]

[td]144 KIAS[/td]

[/tr]

[/table]

 

As info, although it is completely irrelevant to this discussion, the comparable Vrefs for the default B737-800 are 5-6 knots slower across the board- the lowest-weight Vref is 109 KIAS, so if the NGX B737s are similar to the default FSX 738, and you're flying ILS short-finals at 150 KIAS or so, I respectfully submit that you are flying them at 35 KIAS too fast OR needlessly tankering fuel such that your landing weights are much too heavy.

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I always assumed that if I had nose down configuration for level flight the center of gravity has shifted too far from bad cargo/passenger placement.

in real life, or a real aircraft, probably. In the sim, not necessarily :)

 

Full disclosure: I am not an Aerodynamicist. I'm just a pilot.

 

That said, center of gravity has NO effect at all on aircraft attitude at cruise airspeeds.

 

The first thing to consider is this: elevator effectiveness is zero until you reach a certain airspeed on the takeoff roll, and the higher the airspeed gets, the more effective all of your moveable control surfaces are, including, but not limited to, the elevators. One of the primary factors in how CG limits are set is elevator authority. If elevators had magical, unlimited authority, then it would be possible to fly with any CG position at all, from the tip of the tailcone to the radome on the nose, because your magical elevators would be strong enough at any airspeed to counteract any adverse pitch effects caused by all the weight being in the tail or nose. In the real world, however, elevators are not magical and are dependent on their physical size and the speed of the airflow acting upon them in order for them to do their job.

 

An out of envelope CG can cause loss of control at low airspeeds due to insufficient elevator authority to counteract

  • a pitch-up caused by a severely aft CG, leading to an unrecoverable stall/spin/mush; and/or
  • a pitch-down caused by a severely forward CG, leading to an unrecoverable dive

 

But the discussion at hand was about cruise attitude. If the CG was so far out of whack at takeoff that it caused any discernible difference to the pitch attitude such as detailed above, the aircraft could never have reached cruise airspeed, having already spun in, mushed in or nosedived in on the departure before ever reaching a cruise airspeed.

 

The CG moves during flight as fuel is burned off. Many aircraft require transfer-pumping of fuel to maintain CG within limits. So it is possible for a CG to be within limits at takeoff but later move out of limits at cruise airspeeds due to failure to transfer fuel appropriately. Some smaller aircraft (Beech Bonanzas are notorious examples) have CGs that can move aft out of limits as fuel is burned during flight, and there is no way to compensate for it at that point, so it must be anticipated and planned for when the aircraft is loaded.

 

Because airplane wings are generally firmly attached to the fuselage :D the pitch attitude is determined solely by the Angle of Attack (AoA) of the wing. There are only three* determinants of the AoA of the wing in level flight at any airspeed above flap-schedule speeds: aircraft weight**, indicated airspeed and pressure altitude (the density of the air). The heavier the airplane is and/or the slower the airspeed is and/or the higher the pressure altitude is, the more AoA is required and hence, the more nose-up pitch is required for the wings to support the weight of the aircraft. This is true regardless of the position of the CG.

 

Any out-of-CG condition in cruise flight is compensated for by the pitch trim and/or elevators and thus is imperceptible other than by inferring the out-of-envelope-CG from the unusual position of the pitch trim indicator. Until the pitch trim system reaches its limits, it will mask the effects of an out-of-envelope CG by keeping the airplane at whatever pitch attitude is needed for the wings to support it, and this attitude will be exactly the same attitude as it would have been with an in-envelope CG under the same weight, pressure altitude and airspeed conditions. A secondary effect will be a very slight airspeed reduction (or slightly higher N1/N2 required to maintain a given airspeed) caused by the unusually strong deflection of the pitch trim tabs on aircraft that do not have moving-stabilizer trim. Most jetliners have moving stabilizer trim.

 

So the bottom line is that CG can affect pitch attitude at the bottom end of approach airspeeds, and of course at rotation and/or flare, but not at all at speeds above those.

 

*I am deliberately disregarding the subject of "high alpha" flight as practiced by fighter jets such as the F/A-18 because this discussion is about jetliners, which are not capable of such maneuvers- or at least, not for very long. :D

 

**Turning in level flight and pulling back or pushing forward to initiate a climb or descent create additional wing loads (positive-G loads for turns and climbs, negative-G loads for noseovers) in addition to the actual static weight of the aircraft, but for this discussion those G-loads act identically to weight and so are included in "weight" as I am using that term in this post.

 

:pilot:

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And you say you're not an aerodynamicist!

 

HA!!

I need to be carefull, that HA!! is what got my father asked to resign his commission...

 

:D

 

Pat☺

[sIGPIC][/sIGPIC]

Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again!

Sgt, USMC, 10 years proud service, Inactive reserve now :D

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*sigh*

 

I'm sorry, but I just don't understand all the surmises, feeling this, imagining that, assuming max-weight approaches... and all of it about one or another model of the B737... when the airplane I used is the default FSX A321... also, I posted a direct link to the video page containing the ACTUAL weights used, the ACTUAL estimated fuel burn from the flight plan sheet, which drives the ACTUAL fuel load used for the flight.

 

As far as I know, the 14,340-pound payload I used is the maximum payload for this airplane- at least, it's the maximum FSX let me put into it before I loaded fuel.

 

Airlines don't tanker fuel. If a flight is estimated to burn, oh, just hypothetically ;) 8704.2 pounds of fuel for a 47-minute flight, they would not depart with full 5-hour fuel load of 52,193 pounds! They would depart with the fuel required to fly to the destination, miss the approach there and fly to the alternate, plus an additional allowance for taxi, ATC vectoring, holding, etc. depending on the actual and forecast weather. In my case, I loaded 15,471.44 pounds, which was more than 184% of the estimated fuel burn for the 47-minute flight to the destination, plus an allowance for a hypothetical alternate.

 

I honestly don't understand why so many people are imagining the use of the heaviest possible landing weights to challenge my Vref calculations (without even looking at the FSX A321 refs) when no airline on the face of the planet departs with enough fuel so as to arrive at the destination at the heaviest published landing weights.

.

 

I guess you are missing what I'm getting at. I know you used a light fuel load,

and have said so all along. It's not the load, I know that was light. I'm just surprised

that a plane of that size and weight would have a vref that low even with a light weight,

and was curious if it were actually realistic for that plane. It may well be.

 

About the only time I would see an appx 150 knot vref+5 with the 737 would be with

a heavy load 739. The 800 loaded, maybe mid to upper 140's..

But I run the 700 the most by far, and it's usually in the mid 130's.

And that's with normal fuel reserves, etc. Each shorter model has generally lower speeds.

I was expecting the A320 series, "including the A318 and A319", to pretty much act the

same way. IE: I could easily expect that speed with the 318 or 319, but surprised to see it

that low with the 321, which is the largest of that series.

I guess I'm not used to seeing speeds that low, cuz I never land quite that light I suppose..

IE: a 109 vref seems really low for a 737-800.. I never see anything close that that low a

speed, but I guess it's cuz I never land light enough to see that low a number.

IE: I was light on that "crabby" flight with the 900, and the FMC spit out 139 for vref..

The same exact flight and load percentage wise in the 736 would have been around 20

or so knots slower as far as the vref on average.

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[The PMDG NGX fps load is] a good bit more load than the default plane, but I ran the NGX with no problem with the AMD Phenom IIx4 at 3.5 ghz.

The frame rate on the ground wasn't anything to get too excited about, but it was

good enough for gov work. I ran lean scenery, but that was more due to XP 32 bit and

a puny VAS, than being bogged down by the NGX. In the air, the frame rate was good

unless I was getting bombed with real thick clouds. Heck, I thought your present puter was pretty powerful?? It should run the NGX no sweat at all even with decent scenery settings.

 

Well, thanks for that info- I think my Core i5 3570K is a less-capable CPU than yours, even after overclocking it from 3.4 to 4.2 GHz, while my GTX-970 is a more-capable GPU than yours, which is great for me playing games such as Skyrim, but not good for me with FSX because from everything I've read, FSX is CPU-intensive and doesn't take advantage at all of high-end GPUs. :(

 

Based on what you've said here, I may have to reconsider the NGX, especially what you said about not having to spend an hour or two programming the FMS every time I want to fly. That was always the biggest turn-off for me.

 

Thanks-

 

Doug

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I guess you are missing what I'm getting at. I know you used a light fuel load,

and have said so all along. It's not the load, I know that was light. I'm just surprised

that a plane of that size and weight would have a vref that low even with a light weight,

and was curious if it were actually realistic for that plane. It may well be.

 

About the only time I would see an appx 150 knot vref+5 with the 737 would be with

a heavy load 739. The 800 loaded, maybe mid to upper 140's..

But I run the 700 the most by far, and it's usually in the mid 130's.

And that's with normal fuel reserves, etc. Each shorter model has generally lower speeds.

I was expecting the A320 series, "including the A318 and A319", to pretty much act the

same way. IE: I could easily expect that speed with the 318 or 319, but surprised to see it

that low with the 321, which is the largest of that series.

I guess I'm not used to seeing speeds that low, cuz I never land quite that light I suppose..

IE: a 109 vref seems really low for a 737-800.. I never see anything close that that low a

speed, but I guess it's cuz I never land light enough to see that low a number.

IE: I was light on that "crabby" flight with the 900, and the FMC spit out 139 for vref..

The same exact flight and load percentage wise in the 736 would have been around 20

or so knots slower as far as the vref on average.

 

Yeah, I get that, I wasn't disputing any of that with your NGX B737 airplanes, but just pointing out that what your FMS says (in a dissimilar NGX B737) about landing at YOUR weights (which are, obviously, higher than mine, which are based on not tankering unneeded fuel) has absolutely NO relation to what my printed (not FMS) Vref references call for in a different airplane (A321) at apparently lower airline landing weights, which are the result of not tankering fuel- which is worldwide airline policy.

 

When you load your NGX, does the FMS tell you to tanker fuel, i.e. load more than the legal requirement of take off>fly to destination>missed approach>fly to alternate or 45 minutes>land plus taxi & ATC delay allowances?

 

Here's a quote I found online which perfectly details how I load fuel for a revenue flight:

The dispatcher that is working your flight plans the routing [i let FSX do this] and determines the minimum fuel required from takeoff to destination to furthest alternate with additional fuel as required by regulation you operate under. On top of this, contingency fuel is added which can account for enroute diversions, cruising at a different altitude, un-forecast winds, holding, etc. The total of this fuel is the "release fuel" and you cannot takeoff below this number. On top of this, extra fuel will be added for taxi time.

 

Are you using some "real weather" program, or setting FSX weather for the worst possible, or planning cruise speeds above Mach 0.74 or always flying east into the jet stream? Any of these might cause your FMS to call for thousands of pounds more fuel than a real airline flight would load... I'm just trying to figure out how your FMS is making you arrive at your destination weighing so much that you're getting Vrefs 40 knots higher (in any 737 up to the -800) than I'm seeing for the default 738 at "ideal" landing weights... which, in airline bean-counter world, means the lightest possible weight consistent with safety and legal requirements.

 

It doesn't help that the FSX refs don't bother showing zero-fuel weights at all... so I really have no way of knowing what the maximum PAYLOAD weight is for the 738. But as far as I know, the flight I was on when I landed at 121 KIAS was a max-payload flight, based on what FSX allowed me to load at each station.

 

I found this information online:

Boeing 737-800 (with winglets) Weights

[table=width: 500, class: grid, align: left]

[tr]

[td]Weight[/td]

[td]Kilograms[/td]

[td]Pounds[/td]

[/tr]

[tr]

[td]Empty[/td]

[td]41,413[/td]

[td]91,300[/td]

[/tr]

[tr]

[td]Max zero-fuel[/td]

[td]62,732[/td]

[td]138,300[/td]

[/tr]

[tr]

[td]Max fuel[/td]

[td]26,015[/td]

[td]57,353[/td]

[/tr]

[tr]

[td]Max payload[/td]

[td]21,319[/td]

[td]47,000[/td]

[/tr]

[tr]

[td]Max Takeoff[/td]

[td]79,016[/td]

[td]174,200[/td]

[/tr]

[tr]

[td]Max Landing[/td]

[td]66,361[/td]

[td]146,301[/td]

[/tr]

[/table]

 

Then, I found this info online:

 

Airbus A321-200 Weights

[table=width: 500, class: grid, align: left]

[tr]

[td]Weight[/td]

[td]Kilograms[/td]

[td]Pounds[/td]

[/tr]

[tr]

[td]Empty[/td]

[td]46,739[/td]

[td]103,042[/td]

[/tr]

[tr]

[td]Max zero-fuel[/td]

[td]69,500[/td]

[td]153,221[/td]

[/tr]

[tr]

[td]Max fuel[/td]

[td]18,806[/td]

[td]41,460[/td]

[/tr]

[tr]

[td]Max payload[/td]

[td]22,798[/td]

[td]50,261[/td]

[/tr]

[tr]

[td]Max Takeoff[/td]

[td]83,461[/td]

[td]184,000[/td]

[/tr]

[tr]

[td]Max Landing[/td]

[td]73,482[/td]

[td]162,000[/td]

[/tr]

[/table]

 

Interestingly, if you add the empty weight and the max payload, 103,042 + 50,261 = 153,303. That's 82 pounds OVER the max zero-fuel weight. So something is fishy in Denmark. Still, I think I'm going to update my FSX Refs with this weight info for both airplanes.

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Yeah, I get that, I wasn't disputing any of that with your NGX B737 airplanes, but just pointing out that what your FMS says (in a dissimilar NGX B737) about landing at YOUR weights (which are, obviously, higher than mine, which are based on not tankering unneeded fuel) has absolutely NO relation to what my printed (not FMS) Vref references call for in a different airplane (A321) at apparently lower airline landing weights, which are the result of not tankering fuel- which is worldwide airline policy.

 

I'm not tankering fuel either. And I plan the reserves the same way you do.

In my crabby video with the 900, I had less fuel than your A321 example.

When you load your NGX, does the FMS tell you to tanker fuel, i.e. load more than the legal requirement of take off>fly to destination>missed approach>fly to alternate or 45 minutes>land plus taxi & ATC delay allowances?

 

 

No. I calculate the reserves myself.

 

Are you using some "real weather" program, or setting FSX weather for the worst possible, or planning cruise speeds above Mach 0.74 or always flying east into the jet stream? Any of these might cause your FMS to call for thousands of pounds more fuel than a real airline flight would load... I'm just trying to figure out how your FMS is making you arrive at your destination weighing so much that you're getting Vrefs 40 knots higher (in any 737 up to the -800) than I'm seeing for the default 738 at "ideal" landing weights... which, in airline bean-counter world, means the lightest possible weight consistent with safety and legal requirements.

 

That's what aroused my curiosity about all this.. And I am landing with normal fuel

reserves. But I'm not sure how you are coming up with the vref of 40 extra knots you

say I'm getting. What vref do you consider normal for the 800 at max pax load, and

normal fuel reserves? Say less than 10,000 lb's reserve as an example?

 

It doesn't help that the FSX refs don't bother showing zero-fuel weights at all... so I really have no way of knowing what the maximum PAYLOAD weight is for the 738. But as far as I know, the flight I was on when I landed at 121 KIAS was a max-payload flight, based on what FSX allowed me to load at each station.

 

I do see the zero fuel weights in the NGX.. I can check to see what the max payloads

are for the various models. Or at least for the seating options that I have.. Also cargo.

I just fired up an 800, and with single class SWA seating, "174 pax", and a cargo

weight of 16,500 pounds which brings me to 99.9% load level, the ZFW is 138.2.

With 10,000 lbs of fuel, The gross weight shows 148.2.

The plane is set to run from KHOU to KIAH, and the FMC estimates I would have

appx 9000 lb's on arrival to KIAH.

With that load, my FMC calculated V2 speed is 149 knots. Which means the vref

should end up also being in the mid to upper 140's range. I'll actually fly it now,

and see what it spits out for vref when I arrive.. At KIAH, flaps 30 vref was 150+5,

for a total of 155 knots. Which seems perfectly normal to me for a full pax load.

I think flaps 40 vref was about 143 or so.. But I landed flaps 30 at KIAH.

So.. do you think appx 9000 lb's reserve fuel would be excessive for the typical flight?

Just for kicks, I loaded only 5000 lb's for the flight. V2 and vref only dropped a couple

of knots. Flaps 30 vref was still in the upper 140's at 148, and with the extra 5, still over

150 knots approach speed. "153" And that's with less than 4000 lb's fuel left.

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Interesting discussions! Relevance if we're talking more than one aircraft type, maybe not so much. I can't say I have experience with the planes you are discussing, but I wonder if what you're seeing is not normal for some specific configurations.

 

Take the example of the B-52. I've never been inside of one but while off the deck myself, I've observed many in flight. Some were dropping bombs during combat operations, some were in SAC Scrambles, some just in normal training, or taxi flights. But I have noticed that in each instance, they always seemed to fly nose down when traveling straight and level.

 

Luckily I know a retired bird colonel who spent most of his career flying BUFFS for SAC. I asked him why BUFFS always seem to be in a dive. He told me 2*to 5* or more nose down is considered the normal attitude for those aircraft in straight and level flight.

 

I can't comment about the normal attitudes of the various planes you are spending so much anguish over. But I have it on good authority that various fixed wing aircraft, based on original configuration, can and do fly straight and level at different attitudes.

Being an old chopper guy I usually fly low and slow.
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What vref do you consider normal for the 800 at max pax load, and normal fuel reserves? Say less than 10,000 lb's reserve as an example?

 

Well, based on the ZFW that I posted above, which is information I didn't have before this thread started (other than by calculating it from EmptyWgt+MaxPayloadWgt=ZFW), I'm beginning to believe that the default 738 is not allowing me to load a full passenger load. As you know, you can't load "170 pax" or any number of heads- you have to load passenger weights, by station. I will explore this a bit later tonight when I have more time.

 

So, with the caveat that I am now not so sure that I've been flying with a full load (shut UP Zippy :p ) I would estimate Vref between 120 and 135, depending on the actual FOB at landing.

 

The plane is set to run from KHOU to KIAH, and the FMC estimates I would have

appx 9000 lb's on arrival to KIAH.

I've never flown a leg that short- but KHOU to KIAH must be -what- 25 NM or less? :eek: Do you even bother retracting flaps or raising the gear for that grueling odyssey? ;)

 

With that load, my FMC calculated V2 speed is 149 knots. Which means the vref

should end up also being in the mid to upper 140's range.

That's interesting... for a trip leg of "normal" B738 length, say 400-1500 NM, V2 is calculated at a much heavier weight than Vref, which is calculated after burning off most of the fuel, so I would expect V2 to be considerably higher than Vref. But with your 5-minute 20-mile flight between the two Houston airports, I can see how they would be similar, as you say.

 

Do you think appx 9000 lb's reserve fuel would be excessive for the typical flight?

No, I don't- that's sounds about right to me for a typical revenue flight. Again, I don't have the benefit of an FMS, so I've just been loading the estimated fuel burn from the FSX flight plan sheet and adding 8,000 lb as a "hypothetical" reserve because FSX flight plans don't call for, or even allow, specifying an actual alternate, so I have to just SWAG it. At the beginning of the approach, I estimate my landing weight by subtracting fuel burned from departure weight then interpolating Vref from the two published Vref weights in the FSX Refs document.

 

Again, I now suspect that FSX is not allowing me to load the max payload into the airplane. I thought that it was, but after researching the ZFW and other real-world weights for this thread, I'm not so sure. If I'm (inadvertently) not departing with a full payload and you are, that could explain the 20 knot difference between my 121 and your 143- because I've been landing lighter than you have even though we're using similar fuel reserves. The only numbers I recall from my last A321 flight that started all of this was 3,500 pounds of pax in every station and when I tried to make it 5,000 FSX snapped it back to 3,500.

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