[NO BUG - FEATURE] Crazy vertical velocity changes between M0.9 and M1.2?

[Nealius]

I searched the manuals and couldn't find anything (maybe I missed it), but I've noticed that when accelerating from M0.9 to M1.2 (roughly) my VVI goes totally ape. From level flight it will suddenly go to +6000fpm so I ease the stick down. It looks like I'm just about to level out, then it shoots straight to -6000fpm. I ease the stick back, and it swings all the way back up to +6000fpm. The cycle repeats until I hit M1.2 at which point my VVI will settle and behave. When decelerating from supersonic speeds this doesn't happen; only accelerating. Is this behavior normal?

Edited March 20, 2019 by Cobra847

[some1]

That's supersonic shockwaves passing over you pitot and static air ports.

 

Though it's strange that it doesn't happen when slowing down.

[Emmy]

I was wondering about this myself...

[shagrat]

Not directly related to "fixing" the VVI, but a great tip I got from a real life pilot and think has also been said here on the forums.

Use the Altimeter (!) for vertical speed indication, when holding an altitude, not the VVI.

Just watch the needle on the altitude gauge and check CW/CCW for ascend and descent. It really helps.

The VVI is important to check the sinkRATE, but not the best gauge to monitor for holding altitude.

That tip helped me a lot.

Another important advise for me, was to do corrections by measured one at a time inputs (when cruising in formation etc.). A bit of stick aft, then neutral, wait for the effect, another bit of stick aft and then neutral, then correct with a bit forward and always go neutral immediately when the stick movement shows an effect. After a while you get a feel and muscle memory for the stick travel and corrections necessary... I am still learning this one, as old habits are hard to overcome. ;)

[Nealius]

My altimeter spins with the VVI, though. Spinning up at first, then as I try to level out it will start spinning down. VVI in the HUD (I like to cruise in TO mode because I'm pleb) checks out with the analog VVI and altimeter as well.

 

It struck me as odd since I don't experience this behavior in the MiG-21, and aside from the "Mach Tuck" in the Viggen, I don't experience it there either.

[some1]

The altimeter is also affected because it also uses static pressure ports over which the shockwave moves.

 

That's how it looked in the Concorde: https://youtu.be/KVHbvmGDqJk?t=57

Presenter points the VSI, altimeter is further back under his hand. You can see it also follows the VSI errors.

[shagrat]

The altimeter is also affected because it also uses static pressure ports over which the shockwave moves.

 

That's how it looked in the Concorde: https://youtu.be/KVHbvmGDqJk?t=57

Presenter points the VSI, altimeter is further back under his hand. You can see it also follows the VSI errors.

That's why I said "not related to fix the VVI problem"... ;)

[StandingCow]

Not directly related to "fixing" the VVI, but a great tip I got from a real life pilot and think has also been said here on the forums.

Use the Altimeter (!) for vertical speed indication, when holding an altitude, not the VVI.

Just watch the needle on the altitude gauge and check CW/CCW for ascend and descent. It really helps.

The VVI is important to check the sinkRATE, but not the best gauge to monitor for holding altitude.

That tip helped me a lot.

Another important advise for me, was to do corrections by measured one at a time inputs (when cruising in formation etc.). A bit of stick aft, then neutral, wait for the effect, another bit of stick aft and then neutral, then correct with a bit forward and always go neutral immediately when the stick movement shows an effect. After a while you get a feel and muscle memory for the stick travel and corrections necessary... I am still learning this one, as old habits are hard to overcome. ;)

 

 

Oh nice advice. I think a lot of us are "spoiled" by the F18 with it's fly by wire system. I constantly find myself climbing or diving, I will have to do as you suggest from now on.

[Nealius]

Is the Tomcat the only DCS module that has this shockwave effect modeled? I've never seen it in any other jets.

[some1]

Yes, though I've no idea if that effect is still visible on modern aircraft where air data sensors input passes through a computer.

[Nealius]

Well, the thread has been moved into the bug section so.....I guess it's not supposed to do that?

[Victory205]

Is the Tomcat the only DCS module that has this shockwave effect modeled? I've never seen it in any other jets.

 

It's because Heatblur is willing to go the extra mile, and their SME's are awesome.

[Nealius]

Now I'm confused....if it's intended behavior then this thread shouldn't have been moved to the Bugs section :huh:

[shagrat]

Now I'm confused....if it's intended behavior then this thread shouldn't have been moved to the Bugs section :huh:

Moderators may moved the thread, Heatblur devs may clarified.

The logic behind air pressure instruments, suffering from compression shockwaves of the air near supersonic speeds is compelling, by the way. :)