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Inverted stall/spin problem


pierrewind

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Roll axis to neutral , nose down , rudder opposite to spin ?

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Nope, I later tried the recovery from very high. (see track)

When in this position:

-The rudder has authority

-The pitch is "locked"

-Ailerons are ineficient

 

The only recovery that seems to work is to bring the power back to idle.

 

I have never flown a yak 52, but for an aerobatic aircraft, this behaviour is odd to say the least.

YAK 52 inverted stall bug recovery.trk

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Yep forgot to mention idle power

The engine acts like a big gyroscope

Rudder only to stop spin

Aileron certainly inefficient , can be counterproductive

Standard "Stick and Rudder" (Wolfgang Langewiesche) stuff

Not a bug

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Well, I disagree with your opinion.

 

One of the "standard" recovery is in fact PARE

-Power idle

-Ailerons neutral

-Rudder opposite

-Elevator to break the stall

 

It does work for a lot of airplanes.

 

However, an aerobatic aircraft is by definition able to play a lot more within the flight and stalled envelloppe. It can include pilot induced flat and inverted spins.

 

Now the problem to me is that on some failed maneuvers (ex: top of humpty bump), or voluntary inverted flat spins the airplane can suddently get locked into this stall. It really feels unatural.

Then , the pitch is lost wich again for an aerobatic aircraft is odd.

 

I also am able to stop the rotation with ruddders, changing the spin to a stall. A stall is normally recoverable with power. (at this point the gyroscopic precession does not apply anymore).

 

This is what makes me believe the flight model is flawed. I might be wrong, but I'd be very surprised to hear from actual yak 52 pilots that you can get locked in this upside down stall/spin only being able to recover with power to idle.

 

 

PS: I actually have this stick and rudder book at home, but it is going into the basics of flying relevant to a cub pilot. Which is not what I'm talking about. I'm talking advanced aircraft handling and playing with it way beyond that boring normal flight enveloppe. Sorry, If I confused you in any way.


Edited by pierrewind
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I'm not confused :) I just question your premise - and much else . An IRL YAK -52 pilot will doubtless be along shortly to shed light on the matter .

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I'm not confused :) I just question your premise - and much else . An IRL YAK -52 pilot will doubtless be along shortly to shed light on the matter .

 

Did you watch his track? Or get the aircraft in the same situation yourself, it’s certainly extremely unnatural. It’s like being locked into a deep stall with a T-tail jet or something. Only inverted. Elevators are completely useless even though you’re at a massive negative AoA that they certainly aren’t being blanked by anything.

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Thought I'd chime in on this one and confirm that there is an issue here. For me the Yak will actually depart from the direction of travel, only when inverted and regardless of throttle setting, after any negative flick maneuvers, be that in level flight with substantial airspeed (outside flick) or at stall (vertical flick)

It's as if the tail-plane becomes non-effective.

 

Same maneuvers but positive G and it's a right job to get rotation to continue sometimes, but never any uncontrollable pitching.

 

I'll take a look at the tracks when I get home to see if you have the same issue as me.

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I think that yak should exit flat spin or inverted as soon spin stops

engine the haviest thing in yak should deep nose down in stall

dont expect that aileron or elevator will have any significant autority in flat spin


Edited by grafspee

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Thought I'd chime in on this one and confirm that there is an issue here. For me the Yak will actually depart from the direction of travel, only when inverted and regardless of throttle setting, after any negative flick maneuvers, be that in level flight with substantial airspeed (outside flick) or at stall (vertical flick)

It's as if the tail-plane becomes non-effective.

 

Same maneuvers but positive G and it's a right job to get rotation to continue sometimes, but never any uncontrollable pitching.

 

I'll take a look at the tracks when I get home to see if you have the same issue as me.

 

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])

 

I think that yak should exit flat spin or inverted as soon spin stops

engine the haviest thing in yak should deep nose down in stall

dont expect that aileron or elevator will have any significant autority in flat spin

 

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.

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)


Edited by pierrewind
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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.

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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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.

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


Edited by grafspee

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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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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 :P 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


Edited by grafspee

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i saw bf109 with shoot off wing in dcs in flat stall :P 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. :lol:

 

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

 


Edited by Deano87
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I've done inverted stalls and spins IRL, although I wouldn't recommend doing them in a warbird. :lol:

 

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 ??


Edited by grafspee

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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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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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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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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 :P 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


Edited by grafspee

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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.

 

I agree with you. I wouldn't expect the aircraft to be stuck in this power on stall. To me it felt very unatural.

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Yeah i want check is it common bug if it is probably its not problem with yak FM more like whole DCS envirmoment

 

Its just a Yak FM issue, No other aircraft in DCS are effected by this.

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I was not aware of this issue, and haven't flown the Yak for some time. I flew it again today, took it through its paces, and entered a flat inverted spin from where I could not recover. This felt very unnatural; to some degree I could arrest the rotation with yaw input, but pitch was entirely ineffective. Power settings also had no effect other than increasing the radius of the corkscrew of the inverted flat spin.

 

I find it very hard to believe that the real Yak-52 displays similar characteristics, as inverted flat spins would be prohibited if that was the case.

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I don’t really understand why you are testing this. But you must appreciate that and aircraft will usually have a different stall speed (or angle of attack) when inverted then right way up, especially when referring to warbirds as they mostly had non symmetrical wing sections which are designed to be efficient in positive G without much concern for there performance in negative G. If you say that you cannot keep the nose on the horizon while inverted then I suggest you are probably stalling the aircraft and the nose is dropping as a result of that. The stall speed while inverted can be quite different from a normal upright stall. But, I really don’t see how this applies to the Yak-52 FM bug as we see here.

i still keep trying inverted stall in ww2 warbirds in dcs Yak-52FM behavior which you presented on short clip looks very wierd for aerobatic plane which should do inverted stall on daily basis not once in the life time

i not sure if i am staling airplane becouse speed is quite big and AOA is very low i think that problem is that i can't increase aoa below certain speed and the plane start diving keeping speed up but i cat enter any spin or wing drop in this situation full rudder dont do much beside increasing side slip

i tried extending flaps wich in normal flight drag nose down in p-51 but while flying inverted flaps did oposite thing nose of the plane imidietly dive even harder flpas did exactly oposite thing that in normal level flight

maby the plane is stalling but in very stable manner


Edited by grafspee

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  • 1 month later...

I'm wondering, have you tried just flying 'normal' instead of inverted flat spin all of the time? :lol:

 

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