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Old 04-09-2019, 05:46 AM   #11
Deano87
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Originally Posted by pierrewind View Post
I'm not sure what you are exactly referring to. However, to me the issue is mostly present on negative stalls/spins. However if a negative snapp roll (flick roll) is allowed to develop into a spin we are back to this issue. From some quick trial it will usually happens after 2 or more turns of a snapp roll. It will of course depend on your starting conditions and your technique (I start at about 200kph, full negative elevator, full rudder and full ailerons in the direction of the turn [since we are inverted, if I quick the left rudder, I will roll to the right, requiring right aileron; if i was upside I'd use left aileron])



Well your explanation is a tad simplistic. The nose should drop because airplanes are normally designed to be able to recover from a stall. It would be too hazardous otherwise. To do so, designers are required to play extensively with chord, profile, area, span, incidence, and position of the wing and elevator plus a precise position of the center of gravity.

It is simplistic to say that if I hold a hammer on any specific point, it will necessarily fall on the side of the head.
Depending on how I hold it (the air interacts with the airplane) the results could be vastly different.

To make sure an airplane flies well upside up is difficult. A lot of airplanes have some quirks and do things that are out of the expectations of anyone. This is truer when pushing the flight envelope flying aerobatics.

Also, the ailerons and the elevators do have authority. In fact the ailerons are often used to turn a normal spin into a flat spin (along with some power). And are also on some airplanes required to exit a spin.
This video shows it quite nicely. Opposite aileron makes the spin more flat, inside aileron can actually be enough to recover from a spin, and drops the nose.

The elevator is also far from useless. It can influence a lot of different things. (Such as rudder masking). It usually has some authority and is in most case necessary to exit the spin. (on the mirage III there are specific yellow hash marks on the stick and side console to give the correct stick position for a spin recovery)
Great, but none of that is related to the FM issue with the Yak. I’ve had the Yak-52 stuck in an inverted fall at -60 degrees AoA with the aicraft not rotating or spinning. With the elevator being completely useless to bring the nose down. It’s simply not how real aircraft fly lol, that is the issue being discussed here, it has nothing to do with IRL spinning or spin recovery techniques. The only reason the spin gets mentioned is that it’s the easiest way to get into this situation. I shall try to make a video to show it.
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Old 04-09-2019, 10:40 AM   #12
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Quote:
Originally Posted by pierrewind View Post
I'm not sure what you are exactly referring to. However, to me the issue is mostly present on negative stalls/spins. However if a negative snapp roll (flick roll) is allowed to develop into a spin we are back to this issue. From some quick trial it will usually happens after 2 or more turns of a snapp roll. It will of course depend on your starting conditions and your technique (I start at about 200kph, full negative elevator, full rudder and full ailerons in the direction of the turn [since we are inverted, if I quick the left rudder, I will roll to the right, requiring right aileron; if i was upside I'd use left aileron])



Well your explanation is a tad simplistic. The nose should drop because airplanes are normally designed to be able to recover from a stall. It would be too hazardous otherwise. To do so, designers are required to play extensively with chord, profile, area, span, incidence, and position of the wing and elevator plus a precise position of the center of gravity.

It is simplistic to say that if I hold a hammer on any specific point, it will necessarily fall on the side of the head.
Depending on how I hold it (the air interacts with the airplane) the results could be vastly different.

To make sure an airplane flies well upside up is difficult. A lot of airplanes have some quirks and do things that are out of the expectations of anyone. This is truer when pushing the flight envelope flying aerobatics.

Also, the ailerons and the elevators do have authority. In fact the ailerons are often used to turn a normal spin into a flat spin (along with some power). And are also on some airplanes required to exit a spin.
This video shows it quite nicely. Opposite aileron makes the spin more flat, inside aileron can actually be enough to recover from a spin, and drops the nose.

The elevator is also far from useless. It can influence a lot of different things. (Such as rudder masking). It usually has some authority and is in most case necessary to exit the spin. (on the mirage III there are specific yellow hash marks on the stick and side console to give the correct stick position for a spin recovery)
what you saying is very chaotic you throw examples from almost every airframe avilable.
i assume that yak52 is not jet fighter is not ww2 fighter is not comercial passenger yak52 is trainer/aerobatic plane so i ssume that exiting stalls should be preaty easy

Last edited by grafspee; 04-09-2019 at 12:16 PM.
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Old 04-09-2019, 02:22 PM   #13
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Originally Posted by Deano87 View Post
I’ve had the Yak-52 stuck in an inverted fall at -60 degrees AoA with the aicraft not rotating or spinning. With the elevator being completely useless to bring the nose down. It’s simply not how real aircraft fly lol
Exactly, it's an issue with negative AoA, at a certain point the tailplane is not producing any force to correct the pitch attitude toward the direction of travel (or the wing is producing too much drag forward of the CoG), the rotation continues then noticeably stops and holds the pitch at a fixed attitude. It ends up looking like the yak is descending with an invisible parachute attached to the underside of the fuselage.
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Old 04-09-2019, 02:37 PM   #14
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Exactly, it's an issue with negative AoA, at a certain point the tailplane is not producing any force to correct the pitch attitude toward the direction of travel (or the wing is producing too much drag forward of the CoG), the rotation continues then noticeably stops and holds the pitch at a fixed attitude. It ends up looking like the yak is descending with an invisible parachute attached to the underside of the fuselage.
i saw bf109 with shoot off wing in dcs in flat stall that was wierd looking
this yak situation look very similar when su-27 enters inverted stall its very hard to do anything
Btw did anyone see inverted stall/spin in RL just out of curiosity
am asking becouse for example p-47 dont even have emergency prodecures for inverted stalls

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Old 04-09-2019, 03:09 PM   #15
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i saw bf109 with shoot off wing in dcs in flat stall that was wierd looking
this yak situation look very similar when su-27 enters inverted stall its very hard to do anything
Btw did anyone see inverted stall/spin in RL just out of curiosity
am asking becouse for example p-47 dont even have emergency prodecures for inverted stalls
I've done inverted stalls and spins IRL, although I wouldn't recommend doing them in a warbird.

Anyway here is the video I mentioned. As you can see, this looks very abnormal.

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Old 04-09-2019, 04:44 PM   #16
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I've done inverted stalls and spins IRL, although I wouldn't recommend doing them in a warbird.

Anyway here is the video I mentioned. As you can see, this looks very abnormal.

agree all looks quite good until you entered inverted stall plane just calm down and you were moving controls like rudder elevator with absolutly no effect
but at the end of video you didnt explode so pilot and copilot may survive
so you are saying that in that suspended inverted stall yak should leave stall by it self ??

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Old 04-09-2019, 05:41 PM   #17
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agree all looks quite good until you entered inverted stall plane just calm down and you were moving controls like rudder elevator with absolutly no effect
but at the end of video you didnt explode so pilot and copilot may survive
so you are saying that in that suspended inverted stall yak should leave stall by it self ??
Yes. Once the rotation of the inverted spin or tumble has stopped the nose should fall by itself, It is extremely weird and unnatural for the nose to be stuck high like that.
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Old 04-09-2019, 06:48 PM   #18
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Yes. Once the rotation of the inverted spin or tumble has stopped the nose should fall by itself, It is extremely weird and unnatural for the nose to be stuck high like that.
so basicly its similar situation to normal flat spin. can you give me tips how to enter this inverted stall/sping in p-51 for example ??
im trying but i cant
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Old 04-09-2019, 06:59 PM   #19
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Fly inverted, throttle back, as the aircraft slows push full forward stick, full aileron in the direction of your choice, and full rudder in the opposite direction. So left aileron, right rudder.

After the spin has established then you can usually centralise controls and in something like a mustang I would expect it to keep going unless you put in spin recovery inputs. But I haven't tested it.

Why are you testing the P-51? To see if it has the same bug?
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Old 04-09-2019, 07:12 PM   #20
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Fly inverted, throttle back, as the aircraft slows push full forward stick, full aileron in the direction of your choice, and full rudder in the opposite direction. So left aileron, right rudder.

After the spin has established then you can usually centralise controls and in something like a mustang I would expect it to keep going unless you put in spin recovery inputs. But I haven't tested it.

Why are you testing the P-51? To see if it has the same bug?
becouse i know that p-51 is very short plane and has some prolems with weight balance when fuel in rear tank is present i think this one wil lbo most likley to enter that spin
bad thing is that p-51 is not able to fly inverted very long fuel presusre can drop and oil pressure can too
and becouse i dont have yak or cristen eagle
yeah i want check is it common bug if it is probably its not problem with yak FM more like whole DCS envirmoment
i tried hard p-51 dont want to enter inverted spin or stall
in p-51 i am not able to slow down enought to enter stall while flying inverted. Elevator is not strong to keep level flight it saddle at 140mph dont want to drop more preaty much the same with spitfire not enough elevator autority in this regard i tried with loop i was aming for the lowest speed at top of the loop but no go i cant enter any inverted spin
btw in il2 i manged to enter inverted spin in spitfire mkIX its not 100% flat but its a spin but once i stop spin nose drops down imidietly( i had to keep rudder fullu deflect to keep that spin tho)
Which of this 2 cases are realistic i have noooo idea i can belive that spit or p-51 is not able to fly invered at slow speeds becouse those are fighters not aerobatics planes no one demanded this things form those planes while designing those airframes
tried p-47 in il2 it is not able to pitch up during inverted flight at low speeds nose goes down
https://www.youtube.com/watch?v=JDEwUlA9WvY
https://www.youtube.com/watch?v=hj3tiBtQz2s

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