[CORRECT AS IS] Viper Shudders

[BuzzU]

We think the Tomcat is the only plane that shudders and FPW planes are smooth flying.

 

Not so with the real plane. Does ED have it right?

 

[rrohde]

Does ED have it right?

 

 

DCS F-16 is in early access, so stuff is still WIP (work in progress).

[Harlikwin]

I think its something that HB does really well and most other devs dont. The harrier is a golden example. Look at any hard manouvering vids of the harrier and fly it in game, its on rails.

[tweet]

Buffet is a characteristic of high speed swept wings. It is an aerodynamic characteristic and has nothing to do with the control system. Buffet onset is much earlier at low speed or at high speed under G load than on conventional straight wing aircraft. The heavier the airplane the greater the effect generally. It's actually a really useful characteristic. You'll hear pilots talking about pulling into the tickle of light buffet as a means of identifying max performance. Heavy buffet is a warning that you're pulling past maximum performance and approaching an accelerated stall. The accelerated stall is easy to recognize because the nose stops tracking even though the airplane remains under control. I'm impressed that ED is able to model it.

[Dee-Jay]

Hi!

 

 

Maybe I missed something in OP (?) ... but at high AOA the F-16 on stable version is actually rumbling (buffeting). So it is rather ok to me.

 

I'm impressed that ED is able to model it.

 

Well. It does exist since years on other sims ... it is just a relation on AOA. No big deal.

 

Regards.

Edited December 1, 2019 by Dee-Jay

[BuzzU]

Hi!

 

 

Maybe I missed something in OP (?) ... but at high AOA the F-16 on stable version is actually rumbling (buffeting). So it is rather ok to me.

 

 

 

Well. It does exist since years on other sims ... it is just a relation on AOA. No big deal.

 

Regards.

 

 

I just tried it to make sure. I pulled a 9.3g turn and it was as smooth as a baby's butt.

[BuzzU]

DCS F-16 is in early access, so stuff is still WIP (work in progress).

 

I'm aware of that but what it has now doesn't seem hard enough. I can only observe that since I don't have the Viper yet. It does shake a little but the real plane looked more violent.

[BuzzU]

Buffet is a characteristic of high speed swept wings. It is an aerodynamic characteristic and has nothing to do with the control system. Buffet onset is much earlier at low speed or at high speed under G load than on conventional straight wing aircraft. The heavier the airplane the greater the effect generally. It's actually a really useful characteristic. You'll hear pilots talking about pulling into the tickle of light buffet as a means of identifying max performance. Heavy buffet is a warning that you're pulling past maximum performance and approaching an accelerated stall. The accelerated stall is easy to recognize because the nose stops tracking even though the airplane remains under control. I'm impressed that ED is able to model it.

 

 

Not sure how FBW has nothing to do with it. It keeps the pilot from pulling too much AOA.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

but why do straight wing planes buffet?

Edited December 1, 2019 by BuzzU

[Hummingbird]

I just tried it to make sure. I pulled a 9.3g turn and it was as smooth as a baby's butt.

 

9.3 G in the F-16 DCS? Not happening atm unless it's a pull out where gravity is assisting you. It's one of the complaints about the FM atm, the inability to consistantly hit 9.3 G's in a level turn.

[Wags]

With an AoA limiter of 25 degrees, there should be little shudder/shake. We've confirmed this with multiple Viper pilots.

 

When you attach a camera to the aircraft, any shake gets greatly exaggerated in the video playback.

 

Thanks

[BuzzU]

9.3 G in the F-16 DCS? Not happening atm unless it's a pull out where gravity is assisting you. It's one of the complaints about the FM atm, the inability to consistantly hit 9.3 G's in a level turn.

 

Look at who I quoted. Now look at his sig and you'll know what sim I was talking about. Since that's the sim he was talking about.

[BuzzU]

With an AoA limiter of 25 degrees, there should be little shudder/shake. We've confirmed this with multiple Viper pilots.

 

When you attach a camera to the aircraft, any shake gets greatly exaggerated in the video playback.

 

Thanks

 

Ok, good enough.

 

Thanks.

[tweet]

Buffeting is an aerodynamic property of airfoils. FBW filters/interprets (one way to think of it) a pilot's inputs through control laws to provide the performance requested. It does have limits as mentioned like maximum AOA allowed per the active control law. The thing is that swept wing's lift vs AOA curve is different from a fat straight wing. It is flatter and the critical angle of attack is along a flatter curve with less steep drop off at AOAcrit. The fat straight wing's curve is steeper with a sharp drop off after AOAcrit. Those wings get lower levels of buffet closer to AOAcrit and suddenly lose lift as the wing stalls. A swept wing has a longer area where boundary air begins separating from the wing and becoming turbulent. It loses lift over a greater range of AOA than the conventional wing. That separating, turbulent air is the source of buffet. Often it impacts other areas of the aircraft structure like the horizontal slab increasing the buffet a pilot feels.

 

 

So, buffet is turbulent air affecting the air frame. FBW has no means of influencing it other than limiting AOA. That might be a great idea for airliners or cargo aircraft. In a fighter where maximizing lift is one of the keys to maneuverability it's not such a good idea. There is still a lot of useful lift from the onset of buffet through AOAcrit up until the wing stalls. It makes no sense to leave it on the table.

 

 

A good example is the T-38. Load the wing and the aircraft would begin to rumble and that would increase as you continue pulling into moderate buffet. That is a result of shedding airspeed (increasing AOA) from not having enough power to maintain airspeed. When the wing finally loses enough lift the nose would stop tracking. That is the classic sign of a stall and impending full stall. The airplane talked to you rather nicely if you listened. It would begin heavier buffet and shallow wing rock all the way to full aft stick. At that point it would settle into a somewhat level attitude and gently rocking with buffet. You'd see the VVI pegged on the bottom of the scale and be descending at ~10k ft/min until you stopped pulling and recovered. Accelerated entries in a turn were slightly more lively but it had awesome handling qualities at high AOA. It had to be forced to spin but was reluctant even then. But never underestimate the power of a hamfist.

 

The one big downside to the nice handling was in the traffic pattern. Back in the day we flew aggressive tight final turns. 45 degrees of bank and light buffet with a little bottom rudder to keep the nose down in the pull. That light buffet felt normal but it was possible to develop humongous sink rates that might not be noticed before you were in serious trouble. It could also happen in less aggressive patterns or in an unintentional no flap. There were a lot of final turn accidents over the years in the Talon.

 

 

There's your very simplistic aero lesson for the morning.

 

As far as simulating buffet is concerned - yes, I've seen it before in sims. But like spins it was more a tacked on simulation of buffet through progaming gimmicks that lacked the right behavior and feel. Please don't get me started on spins in flight sims.

Edited December 1, 2019 by tweet

[Dee-Jay]

I just tried it to make sure. I pulled a 9.3g turn and it was as smooth as a baby's butt.

 

 

9Gs do not necessarily mean high AOA. ;) ... side note: pay attention also not to confuse buffeting and fluttering or LCO. :smilewink:

[BuzzU]

Buffeting is an aerodynamic property of airfoils. FBW filters/interprets (one way to think of it) a pilot's inputs through control laws to provide the performance requested. It does have limits as mentioned like maximum AOA allowed per the active control law. The thing is that swept wing's lift vs AOA curve is different from a fat straight wing. It is flatter and the critical angle of attack is along a flatter curve with less steep drop off at AOAcrit. The fat straight wing's curve is steeper with a sharp drop off after AOAcrit. Those wings get lower levels of buffet closer to AOAcrit and suddenly lose lift as the wing stalls. A swept wing has a longer area where boundary air begins separating from the wing and becoming turbulent. It loses lift over a greater range of AOA than the conventional wing. That separating, turbulent air is the source of buffet. Often it impacts other areas of the aircraft structure like the horizontal slab increasing the buffet a pilot feels.

 

 

So, buffet is turbulent air affecting the air frame. FBW has no means of influencing it other than limiting AOA. That might be a great idea for airliners or cargo aircraft. In a fighter where maximizing lift is one of the keys to maneuverability it's not such a good idea. There is still a lot of useful lift from the onset of buffet through AOAcrit up until the wing stalls. It makes no sense to leave it on the table.

 

 

A good example is the T-38. Load the wing and the aircraft would begin to rumble and that would increase as you continue pulling into moderate buffet. That is a result of shedding airspeed (increasing AOA) from not having enough power to maintain airspeed. When the wing finally loses enough lift the nose would stop tracking. That is the classic sign of a stall and impending full stall. The airplane talked to you rather nicely if you listened. It would begin heavier buffet and shallow wing rock all the way to full aft stick. At that point it would settle into a somewhat level attitude and gently rocking with buffet. You'd see the VVI pegged on the bottom of the scale and be descending at ~10k ft/min until you stopped pulling and recovered. Accelerated entries in a turn were slightly more lively but it had awesome handling qualities at high AOA. It had to be forced to spin but was reluctant even then. But never underestimate the power of a hamfist.

 

The one big downside to the nice handling was in the traffic pattern. Back in the day we flew aggressive tight final turns. 45 degrees of bank and light buffet with a little bottom rudder to keep the nose down in the pull. That light buffet felt normal but it was possible to develop humongous sink rates that might not be noticed before you were in serious trouble. It could also happen in less aggressive patterns or in an unintentional no flap. There were a lot of final turn accidents over the years in the Talon.

 

 

There's your very simplistic aero lesson for the morning.

 

As far as simulating buffet is concerned - yes, I've seen it before in sims. But like spins it was more a tacked on simulation of buffet through progaming gimmicks that lacked the right behavior and feel. Please don't get me started on spins in flight sims.

 

 

Interesting. With what you said in mind. How should the buffet feel in the Tomcat with the wings forward compared to swept all the way back?

[BuzzU]

9Gs do not necessarily mean high AOA. ;) ... side note: pay attention also not to confuse buffeting and fluttering or LCO. :smilewink:

 

 

I tried to copy what the pilot was doing in the video.

 

Anyway, we shouldn't be talking about it on this forum. Sorry mods.

[Dee-Jay]

Hi again BuzzU!

 

I tried to copy what the pilot was doing in the video.

 

I see. But ... what altitude? ... 9Gs at sea level and 9G at 25000ft => "probably" not the same effect on AOA ;) ... try it and tell us if you note a difference.

 

But, as Wags said ... camera's mounts and housing (like GoPro) can gives some clues, but shows (and sounds) something a bit different than the pilot may experience.

 

Cheers!

[BuzzU]

True. The camera is shaking and not necessarily the plane. My bad.

 

Carry on.

[Dee-Jay]

True. The camera is shaking and not necessarily the plane. My bad.

 

:thumbup:

 

 

And a last something for you ... flight manual is mentioning this:

 

Conventional cues such as aircraft buffeting forces are not

always present as AOA and g limits are approached.

 

...

 

Good flight :pilotfly: and take care!

Regards.

[tweet]

Buzz the F-14 will still have buffet. Even full forward it is a high performance swept wing. Buffet is a characteristic that can occur on all airfoils. Again, it is only turbulent air separating from the airfoil at high AOA having an effect on the air frame. Different wings and configurations will have different characteristics on the same jet or on different models.

 

 

 

Like Wags saying that their Viper pilot sources say buffet is minimal up to 25 degrees of AOA. I'm somewhat surprised but if that's their experience I can't disagree. There may well be more to the story. This may be a clean jet. What about over 25 degrees? I don't know if that is an accessible flight regime. What about with external stores? I can think of a few reasons it may be accurate in all configurations though that's probably unlikely. The Viper is interesting aerodynamically so who knows. A lot of "magic" went into the design.

[BuzzU]

It wouldn't bother me if the Viper shook my teeth out. I'd still love her. :)

[Harlikwin]

With an AoA limiter of 25 degrees, there should be little shudder/shake. We've confirmed this with multiple Viper pilots.

 

When you attach a camera to the aircraft, any shake gets greatly exaggerated in the video playback.

 

Thanks

 

I'd like to know a bit more about why that is? Vibration is just transferred better to the camera vs the sqiushy pilot? Not really for the viper but for some other aircraft that I think should have shudder/shake at the edge of the envelope based on vids (harrier is one example) but don't in DCS.

[DD_Fenrir]

Up to a point the human body acts as a spring - musculature and joints act as shock absorbers and dampen small vibrations. Add to this a seat cushion dampening a lot of high frequency vibrations and the fact that the eyeballs are to some extent self stabilising and movements that very obvious through a camera lens (usually hard mounted on a bracket arm that will amplify any vibration) will be visually imperceptible.

[Dee-Jay]

Hi!

Up to a point the human body acts as a spring - musculature and joints act as shock absorbers and dampen small vibrations. Add to this a seat cushion dampening a lot of high frequency vibrations and the fact that the eyeballs are to some extent self stabilising and movements that very obvious through a camera lens (usually hard mounted on a bracket arm that will amplify any vibration) will be visually imperceptible.

 

 

Perfect description! :thumbup:

 

However, I must admit that I like a bit of visual (and/or sound) feedbacks to compensate what we can't feel in simulation without a "But-kicker" device.

Regards.

[Harlikwin]

Up to a point the human body acts as a spring - musculature and joints act as shock absorbers and dampen small vibrations. Add to this a seat cushion dampening a lot of high frequency vibrations and the fact that the eyeballs are to some extent self stabilising and movements that very obvious through a camera lens (usually hard mounted on a bracket arm that will amplify any vibration) will be visually imperceptible.

 

Yeah, that's what I figured he was getting at. Still some of the vids I've seen its pretty extreme and I do try to compare it what would "smooth" flying.