Accelerated Stalls

[Alfredson007]

Hello. I am here to ask a simple question that bugs me a bit.

 

The P51 is very easy to G-stall. Very easy in fact. Now, i understand this is fast plane with laminar wing that is going to stall more easier than some other models etc but still, i actually did a little test. I AM NOT here to say things are necessarily wrong. I am here to ask for an explanation, or filing a bug if there is one.

 

 

This test was done with guns, ammo, 40-45% of fuel, otherwise clean, no flaps, no rockets etc. near sea level. I stall the airplane. It buffets around 100mph, stalls a little below. Next i will get me some speed, around 300mph or so, i do a quick (but not violently yank) pull to the stick, i stall, my accelerometer show a high mark of ~5.5G, my speed at the beginning of the stall was around 270mph.

 

But MATH says, that if airplane stalls at 100mph (ours actually stalled in a bit less speed), at the stall speed for 5.5G should be around 235mph. I was WAY above 235mph all the time. Now i do understand, that airspeed doesn't stall airfoils, angle of attack does, but usually there are simple formulas to calculate G-stall speeds. IIRC, the maneuvering speed for mustang (depending on weight) is around 270-280mph, or so, so yanking stick aft beyond this speed you should be risking of having 8G+, thus endangering the airframe, rather than stall. Quickly yanking the stick at 300mph results accelerated stall and less than 7Gs, for the plane's gauge atleast.

 

Now, can somebody explain me this because this bugs me a bit. Thanks!

[Yo-Yo]

CLmax is not a constant vs Mach, that is the reason...

[Ala13_ManOWar]

I think yours probably is a controls problem. Don't know what kind of joystick you're using, but something is going on there with it. Also if you need it you can use some input curves so your pulling isn't so (apparently) violent, with a good quality Joystick they're unnecessary but. Of course if this is the first time you fly the P-51 you have to get used to it and learn to watch the clues showing you're pulling too far, but input curves can help.

 

S!

[Alfredson007]

I think yours probably is a controls problem. Don't know what kind of joystick you're using, but something is going on there with it. Also if you need it you can use some input curves so your pulling isn't so (apparently) violent, with a good quality Joystick they're unnecessary but. Of course if this is the first time you fly the P-51 you have to get used to it and learn to watch the clues showing you're pulling too far, but input curves can help.

 

S!

 

Well, it's not a controller issue i can assure you. I have very accurate hall effect stick. I admit that the mustang without curves requires very accurate joystick, i had very hard time to perform minimum speed loops on my old joystick (logitech 3d). Also, especially the corner speed test i made could be done with keyboard... it's all about quick deflection, nothing else.

 

I can fly the plane good. I have the P51, have had it for years from its early release, but eversince the TF51 came, i've preffered that, it's lighter, doesn't stall quite that easily (while stalls easily too) and the cockpit has great all round visibility, lovely plane to do aerobatics. I've never liked DCS as WW2 simulator due to georgia map etc, usually played IL2's.

 

What comes to Yo-Yo's answer. I have no idea what he is talking about. We are talking mach .3 to .4 speed here or smthng, so does so low mach really count? Dunno. Liked to hear more on that...

Edited May 1, 2016 by Alfredson007

[Yo-Yo]

Well, it's not a controller issue i can assure you. I have very accurate hall effect stick. I admit that the mustang without curves requires very accurate joystick, i had very hard time to perform minimum speed loops on my old joystick (logitech 3d). Also, especially the corner speed test i made could be done with keyboard... it's all about quick deflection, nothing else.

 

I can fly the plane good. I have the P51, have had it for years from its early release, but eversince the TF51 came, i've preffered that, it's lighter, doesn't stall quite that easily (while stalls easily too) and the cockpit has great all round visibility, lovely plane to do aerobatics. I've never liked DCS as WW2 simulator due to georgia map etc, usually played IL2's.

 

What comes to Yo-Yo's answer. I have no idea what he is talking about. We are talking mach .3 to .4 speed here or smthng, so does so low mach really count? Dunno. Liked to hear more on that...

 

This effect is very well known for unswept wings. As the wing produces lift, the local velocities at the upper surface become higher than the aircraft speed and approach to the speed of sound. This effect progressively lowers CLmax starting from 0.2...0.3M.

[Alfredson007]

Okay thank you yo-yo.

[Solty]

Well, it's not a controller issue i can assure you. I have very accurate hall effect stick. I admit that the mustang without curves requires very accurate joystick, i had very hard time to perform minimum speed loops on my old joystick (logitech 3d). Also, especially the corner speed test i made could be done with keyboard... it's all about quick deflection, nothing else.

 

I can fly the plane good. I have the P51, have had it for years from its early release, but eversince the TF51 came, i've preffered that, it's lighter, doesn't stall quite that easily (while stalls easily too) and the cockpit has great all round visibility, lovely plane to do aerobatics. I've never liked DCS as WW2 simulator due to georgia map etc, usually played IL2's.

 

What comes to Yo-Yo's answer. I have no idea what he is talking about. We are talking mach .3 to .4 speed here or smthng, so does so low mach really count? Dunno. Liked to hear more on that...

I highly recomend setting up curves for the Elevator if you do not have a stick extension. The real P-51D has a very long stick with a lot of travel, when that translates into a small and short consumer stick, it requires very delicate and stable movments. Something undesireable during a dogfight. But remember, curves will affect your max deflection on the control surface, and that means lower controlability in certain area's.

[Alfredson007]

I highly recomend setting up curves for the Elevator if you do not have a stick extension. The real P-51D has a very long stick with a lot of travel, when that translates into a small and short consumer stick, it requires very delicate and stable movments. Something undesireable during a dogfight. But remember, curves will affect your max deflection on the control surface, and that means lower controlability in certain area's.

 

I usually prefer un-curved profiles, that said dispite having rudder pedals i have added slight curve to the rudder, it's crazy sensitive as it is. And usually i am either pressing just a bit, or full travel so curving works.

 

But i might try the elevator curving at some point, though i kind of like the current feel. I just hope it would not stall so easily but that also makes it interesting to fly. This plane is very fun to fly, mostly because it is quite demanding.

[Alfredson007]

I highly recomend setting up curves for the Elevator if you do not have a stick extension.

 

Okay solty, i tried +15 curve for pitch and... i must admit.. it feels much much more natural now.. i actually blacked out for the first time ever during dogfight.. i can feel the stall coming better and .. it just feels more right. Also i feel i need to trim more now so that also feels more "right". very good. thanks!

[Ala13_ManOWar]

Welcome :music_whistling:.

 

S!

[Black Witch - Blaggards]

Welcome :music_whistling:.

 

S!

 

I've also added a curve to the pitch and think it's better, so I also added one to the rudder and the footbrakes, everything seems a bit more "precise" now imho.

 

Thanks ;)

 

Witch

[HotTom]

Get yourself a stick with force feedback. You will get ample warning of an approaching stall and you won't need to fool with curves.

[Ala13_ManOWar]

Get yourself a stick with force feedback. You will get ample warning of an approaching stall and you won't need to fool with curves.

Yeah, you all get a Warthog with stick extension like me, you don't need curves at all and the experience is not only great but as it was meant to be by devs :lol:. I don't own Thrustmasters shares :D.

 

S!

[Alfredson007]

BTW, coming back to the topic just once more and i am sorry for that but i must..

 

This should be an actual TF-51 (filename says p51 but its not) flight limits for 8000 pounds. This graph looks very much something i would expect.

 

http://zenoswarbirdvideos.com/Images/P-51/P-51OLL.gif

 

Granted, it's 1000 pounds lighter than the P-51 chart in the DCS manual (page 105), but the difference is pretty huge. I tried the DCS TF-51 with 8000 pounds and i got 6.8G from 280mph yank before accelerated stall (low altitude). DCS manual for 9000lbs calls for around 6G (so i got 0.8g more for being 1000lbs lighter), the real tf-51 page says i should have over G'd the plane.

 

I understand that the priority is probably in the P-51 rather than in the free TF-51, but according to that graph the DCS TF-51 doesn't behave as it should OR i am not again fully aware of the facts :-) also there are no signs of mach compressibility in the real page, and the graph looks pretty much i calculated in the first posts. (235mph for 5.5g etc)

Edited May 5, 2016 by Alfredson007

[Yo-Yo]

BTW, coming back to the topic just once more and i am sorry for that but i must..

 

This should be an actual TF-51 (filename says p51 but its not) flight limits for 8000 pounds. This graph looks very much something i would expect.

 

http://zenoswarbirdvideos.com/Images/P-51/P-51OLL.gif

 

Granted, it's 1000 pounds lighter than the P-51 chart in the DCS manual (page 105), but the difference is pretty huge. I tried the DCS TF-51 with 8000 pounds and i got 6.8G from 280mph yank before accelerated stall (low altitude). DCS manual for 9000lbs calls for around 6G (so i got 0.8g more for being 1000lbs lighter), the real tf-51 page says i should have over G'd the plane.

 

I understand that the priority is probably in the P-51 rather than in the free TF-51, but according to that graph the DCS TF-51 doesn't behave as it should OR i am not again fully aware of the facts :-) also there are no signs of mach compressibility in the real page, and the graph looks pretty much i calculated in the first posts. (235mph for 5.5g etc)

 

THis graph is simplified and it uses the same n~V^2 rule. We used the results of NACA tests.

By the way, it's not the first bug in manuals... :)

[Alfredson007]

I am satisfied and i will rest my case, thank you and keep up the good work.