I love the BMS flight model
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I really love the BMS flight model and every thing that was added / changed to make it feel as real as it gets.
There is one little thing however which seems not to be 100%. It is the rollaxis. From all what i know about planes and rollaxis is that they are fixed „build“ in the plane and don‘t move.
So you would expect the rollaxis to be somewhere near the guncross and the plane will allways roll around this point. What we see however is that the plane rolls around the FPM. If you fly fast, as we mostly do, it is not so much noticable as the two points are very close to each other. The higher the AOA gets, the more you can see it and it feels like the plane uses too much rudder. It can be seen very easily when you climb with ATT Hold and HDG Hold. Then turn the HDG knob.
I did some testing with it, the rollaxis moves with the FPM. It is not influenced by wind as it seems. It does not only affect the F-16 but also all other planes regardless if you fly human or AI.
It seems that this dates back until at least original Falcon 4.0, probably even longer.
New account due to change in Callsign during recent Buchenau-LAN. Former Le_Beau in this Forum.
Thank you very much.
Gruß
Gustav -
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I’ll let Mav-JP take this one and explain about the F-16 FLCS.
But try flying the F-15 in the latest version (U3) and you will notice that it rolls around its central axis/waterline maker on the HUD rather than the FPM.
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@Gustav_Guns there’s enough RL hud videos out there, for reference… find one that exhibits what you mean?
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@airtex2019 on many videos it is not easy to see as there are often multiple inputs. On this one you can see that the plane rolls near the guncross.
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@Gustav_Guns said in I love the BMS flight model:
From all what i know about planes and rollaxis is that they are fixed „build“ in the plane and don‘t move.From?..
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@LorikEolmin flying RL planes for 35 years, building and testing them
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@Gustav_Guns said in I love the BMS flight model:
@LorikEolmin flying RL planes for 35 years, building and testing them
Fascinating point of view.
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@Gustav_Guns said in I love the BMS flight model:
@LorikEolmin flying RL planes for 35 years, building and testing them
I would strongly suggest reading articles on this page first : https://www.falcon-bms.com/articles/flight-model/
Please notice that no one is downplaying your experience but if it does not involve “electric” jets it may not be wholly relevant to the matter at hand.
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example of moderate/low speed (M ~= 0.47) roll.
the fpm and pitch ladder are offset a couple degrees, due to crosswind.
the roll axis to me looks roughly centered to the left of the fpm, which makes sense.
did a quick test in BMS and it seems quite similar, to me
TR#3 drops you into the plane in similar speed alt and even similar crosswind… put the fpm on or near a visual landmark, eg. a building at Kunsan, and give it a whirl
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The F16 rolls around its velocity axis (fpm) , not the roll axis
This is one of the fundamental of the F16 (and most of modern fighters ) and is made possible thanks to the ARI
This has be designed to reduce the alpha indicied impact from the side sleep angle during roll at high AoA
It’s explained partially in my FM / FLCS article Please read page 11 of
https://www.falcon-bms.com/wp-content/uploads/2021/08/FM_Developers_Notes_Part_4.pdf
The con is that it provokes inertial coupling
Please read the nasa TP1538 if you want to understand it fully
https://www.cs.odu.edu/~mln/ltrs-pdfs/NASA-79-tp1538.pdf
Page 14 of the document , quote :
“The control system of the F-16 incorporates an ARI and a stability-axis yaw damper which attempt to make the airplane roll about its velocity vector throughout i t s normal flight envelope.”
With BMs you are flying the closest FM to a professional f16 simulator , you can be sure I wouldn’t have made a mistake of that kind
But I have no merits , all the merits goes to the NASA engineers that have modeled this simulator , I just improved it with HFFM and real FLCS
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FYI the F15 also has ARI designed to roll around velocity vector as well
The fun thing is that in next update you will be able to desactivate roll CAs
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@Mav-jp Thank you very much, i will dig into this
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@Gustav_Guns said in I love the BMS flight model:
@Mav-jp Thank you very much, i will dig into this
You might find interesting to watch the video you referenced again, and see how it doesn’t roll on gun cross most of the time.
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@Mav-jp I dont want to sound judgy and I am grateful for the viper Fm we have and all the work that has been put behind it but in my opinion the Knife edge maneuver in both Bms And Dcs (actually a little worse over there) is a little off. The problem is that when you bank the aircraft ~85 degrees or so, it changes too much of its heading towards the side you bank. For example if you attempt a left bank knife edge when heading 100 degrees you will end up heading at 80 degrees maybe even less.
Some degrees of heading change actually happen in the real aircraft too according to hud tapes I have seen, but not so much.
The maneuver IRL only requires pedal input to keep the nose lifted, not pushing down on the stick excessively to maintain heading.
Look the video at 10:55. Its very hard to do that in bms and not change heading too much. In the videos hud tape there is no change
Is an investigation possible?
I Of course respect the awesome work you have done all this years. Dont want to sound like a …
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@frapes45 said in I love the BMS flight model:
@Mav-jp I dont want to sound judgy and I am grateful for the viper Fm we have and all the work that has been put behind it but in my opinion the Knife edge maneuver in both Bms And Dcs (actually a little worse over there) is a little off. The problem is that when you bank the aircraft ~85 degrees or so, it changes too much of its heading towards the side you bank. For example if you attempt a left bank knife edge when heading 100 degrees you will end up heading at 80 degrees maybe even less.
Some degrees of heading change actually happen in the real aircraft too according to hud tapes I have seen, but not so much.
The maneuver IRL only requires pedal input to keep the nose lifted, not pushing down on the stick excessively to maintain heading.
Look the video at 10:55. Its very hard to do that in bms and not change heading too much. In the videos hud tape there is no change
Is an investigation possible?
I Of course respect the awesome work you have done all this years. Dont want to sound like a …
Time to write en Email to the NASA about their modeling
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@Mav-jp said in I love the BMS flight model:
@frapes45 said in I love the BMS flight model:
@Mav-jp I dont want to sound judgy and I am grateful for the viper Fm we have and all the work that has been put behind it but in my opinion the Knife edge maneuver in both Bms And Dcs (actually a little worse over there) is a little off. The problem is that when you bank the aircraft ~85 degrees or so, it changes too much of its heading towards the side you bank. For example if you attempt a left bank knife edge when heading 100 degrees you will end up heading at 80 degrees maybe even less.
Some degrees of heading change actually happen in the real aircraft too according to hud tapes I have seen, but not so much.
The maneuver IRL only requires pedal input to keep the nose lifted, not pushing down on the stick excessively to maintain heading.
Look the video at 10:55. Its very hard to do that in bms and not change heading too much. In the videos hud tape there is no change
Is an investigation possible?
I Of course respect the awesome work you have done all this years. Dont want to sound like a …
the flcs will maintain 1G no matter what so if you don’t push to reach 0G you will turn naturally
So that pilot has to push the stick when doing this manoeuvering , this is as per design of the flcs
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@Mav-jp of course it maintains 1 g but in what axis is the question?
Suppose you are flying straight and you bank near 90 degrees, you are still at 1g only now the gravity is applied to the side.
The only reason in the video during knife edge the g’s drop below 1g isnt because the pilot pushes down the stick but because when banking 90 degrees the vertical stabiliser acts like a horizontal stabiliser as its now providing lift . The result is pushing the aircraft down* (that lift is not countered by anything else)… thus the 0.5 0.3G’s or so shown.
It is also the reason why this maneuver is taught by mentioning to the pilots to use the rudder pedals.
Why would the computer pull the nose like its happening in the sim?
- the vertical stabiliser is behind c.g . An aircraft banking at 90 degrees “looses” a large portion of its wing lift( doesnt actually loose but changes vector) as the main wings are becoming kind like a vertical stabiliser . The aircraft now is travelling more like a projectile or a bullet rather than an actual airplane. The vertical stabiliser is now providing lift acting behind c.g thus pushing the aircraft to a dive. Pilots are taught to cancel this resultant lift by applying opposite to the side of the bank rudder. Not, by pushing on the stick, as doing so will increase drag further reducing speed and worsen the dive.
I hope I explained it well,
I was recently on Lockheeds Martin very own sim trying exactly this . Unfortuanetely I didnt have anyone to record me for proof …
Extra fact :
The g sensors(accelerometers) are located beneath the pilots seat for flcs and near the hud to feed hud.
They give positive or negative readings always accordingly in conjuction to the seat force.(positive always pushes you towards the seat negative pushes you away from the seat -
Guys… i think you are oversimplified things A LOT! Sorry…
This is not a Cesnna 152…
@frapes45 said in I love the BMS flight model:
The only reason in the video during knife edge the g’s drop below 1g isnt because the pilot pushes down the stick
That’s precisely the reason for the Gs to drop.
@frapes45 said in I love the BMS flight model:
the vertical stabiliser acts like a horizontal stabiliser as its now providing lift. The result is pushing the aircraft down*… thus the 0.5 0.3G’s or so shown.
It’s not providing “lift” in a sense of making the aircraft to fly, it’s maintaining the nose in a pitch up attitude, and one of the ENGINE’s vector, is providing the force to maintain the aircraft “level”
@frapes45 said in I love the BMS flight model:
the vertical stabiliser is behind c.g . An aircraft banking at 90 degrees looses a large portion of its wing lift as the main wings are becoming kind like a vertical stabiliser
No, the wings are not loosing a large portion of lift, the lift vector is shifted in another direction (90 degrees), that’s why you need to push stick foward (resulting in a lower than 1G indication), to “cancel” this lift vector and maintain a straight line.
@frapes45 said in I love the BMS flight model:
The vertical stabiliser is now providing lift acting behind c.g thus pushing the aircraft to a dive
Again, the vertical stabiliser is not providing “lift” in a sense to make the aircraft fly. It’s providing the nose up attitude, and the “lift” vector of the vertical stabiliser is pointing DOWN, in the same direction of the CG. What is maintaining flying level is the engine. If you decompose the thrust vectors you will see that there is a portion of thrust pointing UP (in the direction of sky so to speak)
Perhaps the language barrier make some inputs a little hard to understand, but my point is…
There is some complexity in F-16s systems (FLCS for example) that is hard to describe.
Anyway, i was able to make the same knife pass in the video in BMS. I don’t know why we are arguing about that.
Best regards
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@VDK said in I love the BMS flight model:
It’s not providing “lift” in a sense of making the aircraft to fly, it’s maintaining the nose in a pitch up attitude, and one of the ENGINE’s vector, is providing the force to maintain the aircraft “level”
No you are wrong. Vertical stabiliser airfoil will provide some lift upwards on a left bank and since its acting behind c.g it will push the nose down
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@VDK said in I love the BMS flight model:
What is maintaining flying level is the engine. If you decompose the thrust vectors you will see that there is a portion of thrust pointing UP (in the direction of sky so to speak)
Thrust line on the f16 is zero degrees
On the f4 phantom on the other hand that would be the case indeed as it has some engine cant like 5 degrees or so.