Maintaining Control in Stalls

[Hacker15e]

There is a theoretical argument for not using ailerons to level the wings upon recovery, but that said, I have never departed an aircraft by using this method. Worked in a cessna, and it still works in the swept wing jet I fly today.

It's not a theoretical argument at all -- it depends a lot on the aircraft you are flying. The T-38 stalls from the tips in, and depending on how much of the wing is stalled (which progresses *very* quickly in the '38) you may get absolutely nothing when you attempt to move the stick laterally. In that case, you *have* to use the rudders to level the wings.

 

[jhugz]

Worked in a cessna, and it still works in the swept wing jet I fly today.

Are you kidding me? I seem to remember 50 people dying earlier this year because of shenanigans like this.

 

[Blackhawk]

Re: Maintaing Control in Stalls

I don't get what you are getting at when you say "AOA and Chord Line".

I understand you think it is a bad idea, but why?

Normally you see a Cl graph that stops at the critical angle of attack and only shows the relationship between Cl and AOA. This graph, however, continues. Cl continues to drop as your AOA increases beyond the critical AOA; at the same time drag increases beyond the critical AOA. Alot.
So in a stall, if you deflect the stick- say to the left. The right aileron goes down. You've now increased the angle of attack on the right wing; since it is already past the critical angle of attack Cl on the right wing decreases (a decrease in lift), but drag increases. Opposite for the left wing- AOA decreases increasing the Cl and decreasing the drag.
This is normally not an issue in power off stalls. In power on stalls, however, your elevator will be effective at higher AOAs and you normally have delayed airflow seperation at the inboard portion of the wings so this can happen. I actually demonstrate this (reverse command, or some call it "wally world"), during spin training.

 

[Blackhawk]

Even the Airplane Flying Handbook (AFH) recommends leveling the wings with coordinated aileron and rudder; none of this "raise the wing with the rudder" stuff. But a wing dropping is low priority. The dropping wing is a symptom of the stall, so the first step is to break the stall, not raise the wing. The proper stall recovery technique according to the AFH is

1) Reduce AoA,
2) Apply full power, and
3) Roll level using coordinated aileron and rudder.

As for setting up the stall, I also find that using coordinated rudder and aileron works just fine, with the added advantage of having control usage consistent with other flight regimes.

I'm with T on this. The object of practicing stalls is so the pilot will recognize the onset of a stall and know how to recover. The potential for fatal stalls is low up at altitude, but increases as you get lower to the ground- say during a go around, botched landing, or departure stall. The object in practice must be getting down the skills that will save lives in these situations- lowering the AOA with a minimum loss of altitude (none of this diving to the ground &^%$). I don't want a pilot in this situation worrying about which rudder to use or possibly even using the incorrect rudder. I want them to worry about lowering the AOA, then level the wings.

 

[Douglas]

In stall right wing drops. You apply left aileron, decreases AOA on left wing, increases AOA on right wing. Right wing exceeds Critical AOA, you spin.

Normally you see a Cl graph that stops at the critical angle of attack and only shows the relationship between Cl and AOA. This graph, however, continues. Cl continues to drop as your AOA increases beyond the critical AOA; at the same time drag increases beyond the critical AOA. Alot.
So in a stall, if you deflect the stick- say to the left. The right aileron goes down. You've now increased the angle of attack on the right wing; since it is already past the critical angle of attack Cl on the right wing decreases (a decrease in lift), but drag increases. Opposite for the left wing- AOA decreases increasing the Cl and decreasing the drag.
This is normally not an issue in power off stalls. In power on stalls, however, your elevator will be effective at higher AOAs and you normally have delayed airflow seperation at the inboard portion of the wings so this can happen. I actually demonstrate this (reverse command, or some call it "wally world"), during spin training.

Juxta and blackhawk, thank for writing it all out. :beer:

I didn't mean for it to sound like Ailerons were the only control to be used, though it does look like I said that.

 

[tgrayson]

Re: Maintaing Control in Stalls

So in a stall, if you deflect the stick- say to the left. The right aileron goes down. You've now increased the angle of attack on the right wing;

The lift curve is a little misleading here. The deflected aileron doesn't change the AoA as measured by the graph; instead, the curve shifts upward and slightly to the left. I've modified your graph below to reflect this shift. This is what flaps do to the lift curve and the aileron is nothing more than a plain flap. If the wing stalls, it isn't due to the AoA increasing but due to the fact that the wing stalls at a lower AoA with a flap deflected.

Here's the key difference: even if the flapped wing stalls, it's still getting more lift than the unstalled wing without the flap. This is probably the physics that allows Darrol Stinton to argue in "Flying Qualities and Flight Testing of the Airplane":

It is argued that an increase in the apparent angle of attack through aileron deflection causes an earlier stall. I am not sure of this in practice. It can be demonstrated that AS LONG AS NO YAW IS ALLOWED TO DEVELOP one can apply full aileron, in either direction, almost at the point of the normall stall without provoking a premature asymmetric stall.
​

The key point about the yaw is that even if the flapped section of the wing doesn't experience a net loss of lift, it is still stalled with all the associated drag. If the drag causes it to yaw, the rearward motion will cause a loss of lift and a downward motion of the wing, further increasing the AoA and reducing lift, etc, etc, etc. But if the pilot avoids the yaw by using coordinated aileron and rudder, he can use the aileron with impunity.

The Airplane Flying Handbook agrees:

Even though excessive aileron pressure may have been applied, a spin will not occur if directional (yaw) control is maintained by timely application of coordinated rudder pressure. Therefore, it is important that the rudder be used properly during both the entry and the recovery from a stall. The primary use of the rudder in stall recoveries is to counteract any tendency of the airplane to yaw or slip. The correct recovery technique would be to decrease the pitch attitude by applying forward-elevator pressure to break the stall, advancing the throttle to increase airspeed, and simultaneously maintaining directional control with coordinated use of the aileron and rudder.
​

 

[///AMG]

It's not a theoretical argument at all -- it depends a lot on the aircraft you are flying. The T-38 stalls from the tips in, and depending on how much of the wing is stalled (which progresses *very* quickly in the '38) you may get absolutely nothing when you attempt to move the stick laterally. In that case, you *have* to use the rudders to level the wings.

I think I didn't word that properly. What I meant was that there is actual aerodynamics behind not using ailerons shortly following recovery, but from my experience in practice it works just fine. In the T-45 we have similar stall characteristics (well from the tips in at least) and all the way up to the stall, yes, you have to keep the wings level with rudder or you will quickly drop a wing. I meant upon recovery, after the AOA has been reduced and you are at MRT pulling recovery AOA, then smoothly rolling with ailerons is proper technique.

 

[///AMG]

Are you kidding me? I seem to remember 50 people dying earlier this year because of shenanigans like this.

Once you have broken the stall (stalled AOA), smoothly leveling the wings has never presented a problem for me. I'm not talking about being a moron at 600' in the pattern and trying to stop a wing drop with aileron in the middle of a stall. Yes, if you try to use ailerons BEFORE the AOA is reduced below stall, you will depart the aircraft or at least make things worse.

In my aircraft the ailerons are completely ineffective when w/n 2-3 units of a full stall, so it wouldn't work anyways. I've tried it in the sim and it just wallows around until it stalls fully......no idea about the jet, as I wouldn't be dumb enough to actually try that (it likes to depart and spin inverted). I seem to remember light civilian aircraft behaving a little differently, probably giving more authority to ailerons up to the stall, yes? I could see that definitely posing a problem. Either way, critical distinction between what I was suggesting, and the issue you were referring to.

 

[MikeD]

Re: Maintaing Control in Stalls

FW has it easy. You don't have to deal with things like retreating blade stall at high DAs combined with high blade loading and low rotor RPMs. Or other fun things like reverse flow and negative stall in the no-lift regions. All neat stuff when you have different velocities around different parts of a rotor system in forward flight.

 

[///AMG]

Re: Maintaing Control in Stalls

FW has it easy. You don't have to deal with things like retreating blade stall at high DAs combined with high blade loading and low rotor RPMs. Or other fun things like reverse flow and negative stall in the no-lift regions. All neat stuff when you have different velocities around different parts of a rotor system in forward flight.

Talking to my helo buddies about this stuff makes my head explode. They eat it up though....I suppose it is called "survival"

 

[bunk22]

As a prior Navy flight instructor for primary flight training, one thing we did a lot of were spins, OCF, unusual attitude recovery, Approach Turn Stalls (ATS) left or right turn, power-off stall (POS) wings level and demonstrated an acclerated stall to the right which would flip the aircraft (wing down, bottom rudder, pulling nose up). The primary thing we taught the studs during the ATS was "coordinated aileron and rudder" on recovery...breaking the stall as well of course. Students could not recover until the aircraft stalled (nose dropped). In the FITU, we would see all sorts of wild recoveries just to depart the aircraft, rolling wings level no rudder while pulling the nose excessively up, rudder reversal recovery which would flip the aircraft, etc.

 

[///AMG]

and demonstrated an acclerated stall to the right which would flip the aircraft (wing down, bottom rudder, pulling nose up)

I still remember this as being quite startling. One second you were flying, the next you were upside down falling out of the sky. Leaves a lasting impression of why you need coordinated controls in the pattern. The only other time I have seen an aircraft depart that fast was during an OCF sim in the T-45 OFT doing a 90 deg nose high cross control departure (a very prohibited maneuver outside of the sim).

 

[beasly]

As a prior Navy flight instructor for primary flight training, one thing we did a lot of were spins, OCF, unusual attitude recovery, Approach Turn Stalls (ATS) left or right turn, power-off stall (POS) wings level and demonstrated an acclerated stall to the right which would flip the aircraft (wing down, bottom rudder, pulling nose up). The primary thing we taught the studs during the ATS was "coordinated aileron and rudder" on recovery...breaking the stall as well of course. Students could not recover until the aircraft stalled (nose dropped). In the FITU, we would see all sorts of wild recoveries just to depart the aircraft, rolling wings level no rudder while pulling the nose excessively up, rudder reversal recovery which would flip the aircraft, etc.

Man, I wish I had had that training.

Great thread.

op:


b.

 

[bunk22]

I still remember this as being quite startling. One second you were flying, the next you were upside down falling out of the sky. Leaves a lasting impression of why you need coordinated controls in the pattern. The only other time I have seen an aircraft depart that fast was during an OCF sim in the T-45 OFT doing a 90 deg nose high cross control departure (a very prohibited maneuver outside of the sim).

The T-2C Buckeye OCF training was something I'll never forget. Didn't quite prepare a stud for getting out of an OCF scenario but it put it into your mind that you never wanted to get into an OCF condition.

 

[///AMG]

The T-2C Buckeye OCF training was something I'll never forget. Didn't quite prepare a stud for getting out of an OCF scenario but it put it into your mind that you never wanted to get into an OCF condition.

I wish I could have done that. We do a very abbreviated version in the -45 prior to ACM, but of course no spinning or anything other than benign ballistic profiles

 

[bunk22]

All new carrier aviators see this one even though we no longer fly the T-2C Buckeye. I flew the T-2C and this one was showed to us over and over and it's of a T-2C student who stalls the aircraft and gets into the area of reverse command. Now this wasn't all the studs fault as the AOA indexer or components there of were installed improperly, giving him false readings.

http://www.youtube.com/watch?v=tglCntrALxM

For //AMG, maybe this happens when the 45 spins?

http://www.youtube.com/watch?v=NpGwst3VQiM

 

[///AMG]

For //AMG, maybe this happens when the 45 spins?

http://www.youtube.com/watch?v=NpGwst3VQiM

That is supposedly a pretty realistic example of it's spin characteristics....we watched that video in my OCF class. Partway through you can hear the oxygen warning tone when the OBOGS stops working, presumably from a flameout.

As for the T-2 video, every landing checklist we do now incorporates an AOA crosscheck with the fuel gauge (to verify what proper on-speed should be). Not sure if you did that before, but I was told this was a result of that mishap.

 

[bunk22]

That is supposedly a pretty realistic example of it's spin characteristics....we watched that video in my OCF class. Partway through you can hear the oxygen warning tone when the OBOGS stops working, presumably from a flameout.

As for the T-2 video, every landing checklist we do now incorporates an AOA crosscheck with the fuel gauge (to verify what proper on-speed should be). Not sure if you did that before, but I was told this was a result of that mishap.

Everytime when I went to the boat in the COD, we certainly made sure what our airspeed should be, incorporating that into our scan. In the T-2, I was just holding on for dear life