Steering on final with rudder

[Powerin]

Pow. The key statement is "pick up the dropped wing" . Preventing yaw with opposite rudder is certainly what we need to do. ( if anything) . But actually bringing the wing up with rudder is only going to induce yaw in the opposite direction which could lead to an auto rotation in the opposite direction. There Is still a large school of thought that say pick it up with rudder, but I think the idea of preventing yaw is deffinately becoming the normal way. All this is of course theoretical and should not replace what your instructor taught you.Cheers

Thanks Motz. But theoretical or not, I'm not going to blindly do what any instructor says without researching the rationale or science behind it. Many instructors seem to invoke a fair bit of black magic in flying. The idea of stopping an asymmetric stall with rudder appears correct to me from what I have read and my meagre knowledge of aerodynamics, but I have little flying experience to back it up. And I'm not about to explore spins from stalls on my own.

So my questions still stand and you can answer them from your experience....but I know you hate to make definitive statements in a forum

 

What happens if you don't correct a wing drop in a stall but just recover normally (stick forward and power)?

 

Have you ever experienced auto-rotation from an uncorrected wing drop in a stall?

 

Have you ever experienced an opposite auto-rotation from trying to correct a wing drop with rudder?

 

I'm all for risk management and weighing up the odds. I guess what I'm trying to find out is if the risks of picking up the wing with rudder are greater than risks of doing nothing with the rudder in a stall.

 

 

[motzartmerv]

That's ok POW, I'll try answer without putting my foot in it. Lol

 

If you experience a wing drop and don't prevent the yaw but you DO un stall the wing, you can't be in a spin. To remain in auto rotation you have to be stalled. So you will still have a wing low condition but be flying, not stalled.

 

The result? That depends on several things, like how low the nose got? How fast you are when you recover etc, but generally ( and I do mean generally) you will just fly out of the nose low wing low with normal control inputs.

 

Yes, I hve had aircraft get upset by not preventing yaw and start to auto rotate, and yes, I have had them flick the other way when trying to pick up the wing. The later is far more violent, in my experience, then the former.

 

If you are not stalled, you can NoT be spinning:)

 

Cheers

 

 

[motzartmerv]

Ps. I used to be a pick it up man, but I had some bad experiences with students doing this, and was shown a different way years later by another instructor.

 

 

[Powerin]

That's ok POW, I'll try answer without putting my foot in it. LolIf you experience a wing drop and don't prevent the yaw but you DO un stall the wing, you can't be in a spin. To remain in auto rotation you have to be stalled. So you will still have a wing low condition but be flying, not stalled.

The result? That depends on several things, like how low the nose got? How fast you are when you recover etc, but generally ( and I do mean generally) you will just fly out of the nose low wing low with normal control inputs.

 

Yes, I hve had aircraft get upset by not preventing yaw and start to auto rotate, and yes, I have had them flick the other way when trying to pick up the wing. The later is far more violent, in my experience, then the former.

 

If you are not stalled, you can NoT be spinning:)

 

Cheers

Thanks Motz. Food for thought. And yes, I understand that a spin depends on at least one wing being stalled. I also understand there are very few absolutes in flying...except that a wing will definitely stall at a certain AoA. My take from what you have said is that the consequences, in your experience, of overdoing picking up a wing with rudder can be more violent than doing nothing. That's exactly what I was after...real world experience. Of course, this will vary from plane to plane and from situation to situation (disclaimer for you Motz ).

 

 

[grejen]

OK...would anyone else care to comment on this statement?I was certainly taught to "pick up" a dropping wing in a stall with the rudder. The rationale being that you are in an asymmetric stall and to allow the wing drop to continue could lead to a spin. You can't use ailerons because that will increase the AoA of the low wing and deepen the stall. So you use rudder to stop the yaw while simultaneously getting the stick forward and power on.

 

I have read the same procedure in books that I consider authoritative...including Noel Kruse's books mentioned above, so I have no reason to doubt what my instructor taught me. If I were to follow Dafydd's advice and not try to arrest an asymmetric stall and wing drop with rudder, but simply recover with stick forward, what would happen? A wing drop is the pre-cursor to an incipient spin is it not?

Picking up the low wing with rudder is something i learned from flying models and carried with me to full scale. Models behave a bit differently. I've since been taught 'stuff the nose down' if it's stalling, regardless of any banking happening. Stop or avoid the damn stall and you don't have to be recovering from a spin or incipient spin. Of course correcting unintended rolling in slow flight requires more and more rudder and the ailerons become less and less effective. If you're dropping a wing in slow flight on short final, your solution is a go around, not 'pickup the wing'. I think Dafydd's point is that it should never be necessary to use the rudder to pick up a dropping wing. Control yaw! Don't Stall! Well.... I'm a pretty new pilot (<50hrs) so it's great to learn from reading all this.

 

 

[Oscar]

I think a semantic difference here... in a sailplane, one can have the inner wing start to drop in a turn (thermalling, generally); and the rudder has the authority to reverse the yaw rate - normally only momentarily, don't want to lose that thermal! - which doesn't just stop the wing going down, it comes back up (all whilst holding back stick for the turn).I doubt very much Dafydd is advocating ignoring the rudder; but you yourself said, "use the rudder to stop yaw". I think Dafydd is saying, in non-sailplanes, don't fool around with the feet and ignore the stick when a wing tries to drop.

When thermalling in a glider, you're continually doing a tight(ish) turn at just above the stall for a fully-balanced turn situation (string proper straight on the canopy..) in fairly turbulent air and to get maximum lift out of the thermal and stay centred, adjusting your flight path. That requires extremely precise and gentle use of the ailerons, far more of the turn coordination is done by rudder and elevators. You will continually feel the inner wing starting to stall (usually more through the stick than anything else); a very small amount of forward stick and a bit of topside rudder and you're back balanced without chasing the aircraft all over the sky and losing the thermal. In that situation you absolutely do not try to pick the dropping wing up with aileron until you have both wings working and then only if you really need to. It's stick forward, unstall the inner wing, rudder, then aileron if needed. But ALL of those, quickly but gently (i.e. no huge control movements, just enough of each to have the necessary effect happen). In a decent high-performance glider, the stick movement is all wrist action, you don't throw your arm around the damn cockpit.

 

I personally believe that a good working knowledge of how to use secondary effects of controls is extremely desirable. I've been towed out by an inexperienced tuggie at a speed that necessitated dancing on the pedals to keep the thing level (felt like what I imagine riding a unicycle would be like), I've landed with no rudder (the adjustable pedals slipped forward beyond my leg stretch capability) and I've had to put down into several paddocks that absolutely required a speed over the fence of gasp plus 1% with a decent turn at almost zero feet required to adjust to terrain (e.g. between the irrigation ditches on one outlanding). In all of those cases, plus just generally thermalling, using secondary effects effectively was an absolute necessity to keep the aircraft under control.

 

 

[metalman]

The biggest issue with the whole using rudder for different reasons is HOW you use it, and that generally only comes with time and hours( not airline hours) in the air exploring the way your aircraft behaves, using rudder to "pick up" a stalled wing is the right way, trying to use a control surface on a wing that's not flying will give an interesting ride, but, as Motz writes over use of the rudder can get it real exciting , using direct,measured inputs comes with experiance ( that's why we have instructors beside us) to have some one slam in full rudder in a stalled condition will get the heart pumping ,unless you want to spin. The same with aileron, I've sat beside a 400 hr pilot while we lurched all over the sky on final ( it was gusty ,but not that gusty) thinking "if he lets the IAS get below 55 again I'm taking over" ,he was behind the plane and using the ailerons like he was trying to flap like a bird. Another mate has a lot to do with RV's ,he says he can tell if someone will fly it well by the way they hold the stick, " the grip of death" means a wild ride,,,,,two fingers " it be easier" , over controlling is the biggest thing a lot of us have to learn not to do.

 

Back to rudder on final, I use the rudder all the time,constantly, on final, on base, on downwind, enroute, getting to the hanger ,,,,I use it when I'm turning, climbing ,descending ,,,,,,,and it's always in company with another ( or all) control surface,,,,and hopefully in just the right amount, for all controls. Learning finesse for me was the most difficult, learning that some time the rudder might need a quick jab almost to the stops( landing here) but that the same quick jab isn't going to fix every situation, doing aerobatic endorsement , I had to learn that the stops are there so you know when to stop pushing the stick ( in some manoeuvres ) , I'm a big advocate of experimenting with the low end of flight, I've asked heaps of pilots if they've tried flying around below the posted stall speed, very rarely does anyone say "yep" , but when I mention flying a common trainer at 22 kias holding height ( with very careful use of all the controls) and I encourage them to take an instructor up and try it, not many have though.

 

I don't really know the standards or regs regarding pitot/static errors,,,,,but I do know what my plane feels like when it doesn't want to fly so well anymore, I've learnt how to land it in really sh1t winds, I've learnt ( still learning ) to land it in the shortest possible distance, which I might add is one skill that will definatly save your life one day,

 

The thing is to know the plane your in, and that can only come from experimenting on the edges,

 

Matty

 

P.s I know the ASI won't be indicating properly in a high alpha situation re all the errors in previous posts, but it's the easiest way to get an idea.

 

 

[motzartmerv]

Having a good understanding of the secondary effects is important, and part of that understanding is knowing when NOT to use them, as in this discussion.:)

 

Just curious oscar, why would you need to use rudder to stay level when being tugged too fast.?

 

 

[djpacro]

boundary layer - the boundary layer is normally a few inches thick by the tail, even with the slipstream buzzing away...

So what. Static vents are often on forward fuse or mid fuse not near the tail. Static pressure outside the boundary layer is the same, typically, as on the surface.

[Oscar]

Having a good understanding of the secondary effects is important, and part of that understanding is knowing when NOT to use them, as in this discussion.:)Just curious oscar, why would you need to use rudder to stay level when being tugged too fast.?

Too slow, not too fast... gliding camp, they'd bought in a Canadian croppie pilot who'd never tugged before but was magic in Pawnees to help out with the tug work, he thought we didn't like flying fast so was climbing out in the Pawnee hanging on the prop at just over 45 kts indicated for me. I thought he had engine trouble, when he hit a small thermal at 900 feet and waggled his wings I bunged-off instantly and managed to catch it and climb out ok. By the time I landed, the tugmaster had seen it and chatted to him, and he came over to apologise (which wasn't really necessary, but he was a great bloke so we chatted about this and that.) It turned out that glider had been trimmed for competition to the full aft c/g for a considerably heavier pilot (John Rowe, it was his personal machine) and when he checked me out for it he asked my weight but forgot I wasn't wearing a chute, so it was twitchy as hell anyway down slow.

 

 

[facthunter]

I will chuck in a few thoughts for consideration.

 

Picking up the dropped wing that has stalled, with rudder doesn't always work. If it has gone too far forget it The plane is on it's side and you won't lift the wing and the nose WILL drop due to weathercocking but you can reduce the amount it will drop with rudder so have a bit of top rudder on at that stage but the stick must NOT be held back..

 

Don't apply aileron either till you are sure the plane is not stalled.

 

I personally use power to recover from stalls unless the nose is well down already, in which case there is no point. If the plane has a fair bit of power the unstall is almost instant, but you may have to correct for torque effects. This takes practice.

 

Once you are unstalled recover from the dive carefully. The plane flies normally but don't enter a second stall

 

Your main aim is to lose the least height and get control of the plane as soon as possible. It is surprising how little (if any) height is lost.

 

I don't teach this technique at introductory stage.. Nev

 

 

[Oscar]

Nev, if it's dropped to say 70 degrees or so straight from the stall, then it's probably a Lancair 340/360 and you've forgotten the first rule of safety for them - don't ever start the bloody engine.

 

 

[Dafydd Llewellyn]

Stone the B crows! How many times does it need to be said before you buggers will grasp it? Once more:

 

The wing starts to stall when it is trying to carry more load than it can bear at the airspeed - i.e. its angle of attack is too large. To unstall the wing, the pilot must first UNLOAD it. That needs no more than a small movement of the stick, IF YOU ACT FAST ENOUGH. You do not need to generate a large excursion from the flight path to unload the wing; all you have to do is to change the curvature of the flight path to momentarily reduce the G load. This works in any attitude. IT IS IMPOSSIBLE TO STALL THE WING AT ZERO G, NO MATTER HOW SLOW THE SPEED. SO GIVE THE STICK A JAB IN THE DIRECTION THAT GETS ZERO G, AND IT WILL UNSTALL.

 

How big a jab is necessary, depends on the "stall hystereris" of the wing airfoil; some airfoils unstall almost instantly, others need their angle of attack reduced more substantially to re-establish unstalled airflow. But we're talking about maybe 7 (seven) or less degrees reduction in the angle of attack, so if you act whilst the aircraft is still mainly moving ahead, whilst it's still thinking about starting to fall, you can achieve this with very little divergance from the flight path.

 

If the pilot sits there playing with the rudder, before he unloads the wing, the loss in lift due to the initial stall will start the aircraft (or just the wing on the stalled side) falling through the air, which further increases the angle of attack and so the stall rapidly deepens. In that case, unloading the wing will take an armful of stick motion - and if autorotation sets in, a bootfull of rudder also. So yes, use the rudder to keep it straight whilst you unload the wing; but the words the instructor uses are important here; you should NOT be trying to "pick up the wing" with rudder whilst ignoring the stick; in fact doing so will only postpone the inevitable a few tenths of a second.

 

The correct way to think about stall recovery is "unload the wing whilst keeping it straight". The standard instructor patter needs to be changed - which seems to be about as easy to do as convincing people that the Earth was not flat.

 

Now, having momentarily unstalled the wing, the aircraft will usually have gained a knot or two, so it will not immediately fall back into the stall - all the pilot has to do is refrain from re-imposing the load that caused the initial stall, until the speed has increased sufficiently. The amounts to merely easing-off a trifle from whatever he was doing before.

 

As Oscar pointed out, glider pilots learn to do this as a reflex action; but the same is possible in any small aicraft that reacts quickly to control inputs. The response that matters here, is how fast you can reduce the G-load by a jab on the stick. LEARN TO USE YOUR BACKSIDE FOR SOMETHING MORE THAN SITTING ON; how hard you are pressed into the seat is the measure of how close you are to stalling, at any given speed. A quick jab on the stick can easily lift you out of your seat - and that will definitely unstall the wing. After that, it's up to you.

 

YOU STALL THE AIRCRAFT BY PULLING MORE G THAN THE WING CAN HANDLE AT THE SPEED YOU ARE FLYING (and 1G may be more than it can handle) - SO THE FASTEST WAY TO GET OUT OF A STALLED CONDITION IS TO REDUCE THE G LOAD.

 

Before the ATPL holders get their bit in, in a large aircraft the situation can get out of hand because the control responses are not fast enough. That's why those aircraft usually have devices to prevent them from getting into a stall in the first place. I'm talking about what the Americans call "small airplanes" here.

 

 

[Yenn]

I don't care what you say, it is obvious you can and should pick up a wing with rudder on final. The problem seems to be that you don't expect the pilot to release rudder when it is picked up. If using rudder to pick up a wing is so bad how can I keep a plane straight when in a stall. A few years ago I did a biannual in a Jab and was told to demonstrate a stall. I did and kept it fully stalled but straight with rudder. The instructor chipped me with "You lost 200' in that stall" he accepted my excuse of saying "Yes, I was enjoying it" Come to think, that was the most enjoyable part of the flight.

 

 

[Dafydd Llewellyn]

Trouble with the side if the fuselage is that it usually is in the prop slipstream so static pressure error increases with high power and low airspeed.

I agree that having to put an engine on an aircraft is a B nuisance; but it's difficult to avoid if you want to use the aircraft to go places. With the normal range of recreational aircraft, the slipstream effect on the static error, for flush static ports on the fuselage sides is usually small enough to ignore. They are better down the back, because there is a pressure rise just behind the propeller disc, that increases with power, but provided the ports are more than one propeller diameter downstream, that's usually negligible, too.

One can be cunning, and try to find the spot on the fuselage where the pressure rise behind the propeller balances out and reduction in static pressure from the added slipstream velocity, but that's likely to be somewhere near the wing, so the wing pressure field interferes, so not really worth the effort.

 

 

[motzartmerv]

Thanx for the advice daffyd.

 

 

[facthunter]

Oscar I don't believe the plane has to be as 'demanding ' as a Lancair to have the wing go down so far you are well over 60 degrees. I had an instructor put the wing vertical on a drifter on me when I first flew one to see if I would stuff it up.

 

I put the above up for discussion realising the difficulty of doing it here on the forum but this one has got a bit of response from a lot of thinking people., so I though it was worthwhile. I would rather be in front of you all with a whiteboard and a model plane with moving control surfaces.

 

Dafydd the larger jets really don't have any real extra aerodynamic methods of stall prevention except the ones the Flight management system has to make it fail safe when it's flying itself and warnings. At cruise levels you are close to the stall and don't usually hand fly it. It is not that easy to do and you have to have more separation from other aircraft (vertically) IF the autopilot is not available. Deep stall is a phenomenon that is peculiar to some jets and is a separate issue. Stall recovery at mid altitudes is generally nose just above the horizon and full power. Extend some flap if it will fix it.

 

Near the ground aerodynamically the controls are pretty powerful when the flaps etc are extended and all controls become fully effective. You can handle severe turbulence provided you are prepared to really drive it. Hydraulic controls are really powerful and effective in that situation with a lot of authority. Most other aircraft never approach the controllability of say a Boeing 727 100. Nev

 

 

[Oscar]

Nev, it was slightly tongue in cheek, though the Lancair 340/360 has one of the worst safety records you could ever try to chase up, for fatals from stalled turns. However, as far as I am aware, the maximum allowable wing drop from a simple stall in any certificated aircraft is way less than even 60 degrees, and I assume (but do not know) whether a somewhat similar limit applies to LSA-class (i.e. 24-reg, for us) aircraft. I most certainly do not have the experience of power flying to make any comments, but it's a given when you're in a gaggle in a thermal that all of you know how to keep on circling without suddenly dropping down through the middle of the group! (It's a bit like the time between the 5-minute gun and the start gun for a yacht race, actually). As Dafydd said above, it's an instinctive reaction and you don't have much time in the gaggle to watch the ASI, (you're watching the other buggers around you); you feel the stick pressure change first and tend to notice the bank increase slightly and it's all pretty much a rhythmic response.

 

 

[facthunter]

Oscar, rigging comes into it a lot. I flew a rather ordinary Auster that would always try to drop the right wing , what ever way you approached a stall (within reason) and it would do it rather quickly. Agree about the Lancair and have read a lot about it and have 3 friends over time who have owned them including a Turboprop Pressurised one. They are not for inexperienced pilots but I don't believe they should be deregistered. P51's killed a few too till they got wise to a few effects.

 

Stalling training needs to be revisited has been my opinion for a while. I've encouraged Emergency Manoeuver Training, (Hate that title) rather unusual attitude familiarisation and recovery techniques.

 

Typical reactions (instinctive) will be contributory to a bad result generally, so we could be doing it a lot better. Dafydd is correct in saying that to "punch the stick forward" will usually unstall the wing straight away. ( I've used the term myself for a long time). Go out there and see what is happening. It's not good enough. A couple of level stalls,power off with an aeroplane that is quite benign only instills the view that stalls are NO PROBLEM. ( I did them so tick it off). Nev

 

 

[Bob Llewellyn]

Nev, it was slightly tongue in cheek, though the Lancair 340/360 has one of the worst safety records you could ever try to chase up, for fatals from stalled turns. However, as far as I am aware, the maximum allowable wing drop from a simple stall in any certificated aircraft is way less than even 60 degrees, and I assume (but do not know) whether a somewhat similar limit applies to LSA-class (i.e. 24-reg, for us) aircraft. I most certainly do not have the experience of power flying to make any comments, but it's a given when you're in a gaggle in a thermal that all of you know how to keep on circling without suddenly dropping down through the middle of the group! (It's a bit like the time between the 5-minute gun and the start gun for a yacht race, actually). As Dafydd said above, it's an instinctive reaction and you don't have much time in the gaggle to watch the ASI, (you're watching the other buggers around you); you feel the stick pressure change first and tend to notice the bank increase slightly and it's all pretty much a rhythmic response.

yep, if an LSA to ASTM 2245 drops a wing more than 60 degrees during a straight stall (despite corrective inputs), it's a fail...

 

 

[Bob Llewellyn]

So what. Static vents are often on forward fuse or mid fuse not near the tail. Static pressure outside the boundary layer is the same, typically, as on the surface.

if the air is not moving past the surface, I agree. If it is, the continuity equations disagree. I'm with continuity of momentum, because elsewise the wing doesn't work.

 

 

[Bob Llewellyn]

I don't care what you say, it is obvious you can and should pick up a wing with rudder on final. The problem seems to be that you don't expect the pilot to release rudder when it is picked up. If using rudder to pick up a wing is so bad how can I keep a plane straight when in a stall. A few years ago I did a biannual in a Jab and was told to demonstrate a stall. I did and kept it fully stalled but straight with rudder. The instructor chipped me with "You lost 200' in that stall" he accepted my excuse of saying "Yes, I was enjoying it" Come to think, that was the most enjoyable part of the flight.

didn't lose 200ft on final didja? a decade back Bill Dinsmore asked me to stall an SB Drifter; by dancing onthe rudder pedals, i was able to keep the separation bubble centred until it was indicating about 24kts - Bill said "bloody glider pilots - MY AEROPLANE", unstalled it, and told me to do it again but keep my feet still.

There are very few aeroplanes in which one can keep the separation bubble centred to below the certification stall speed; and it's pointless as an exercise down low, as any separation bubble increases the rate of sink substantially.

 

If you look at the drag curves (NACA data) in Abbot & v. Doenhoff, or anywhere else, you will see that the airfoil L/D falls off hugely a couple of degrees before the lift curve slope becomes zero. The wing drop nibble you should be feeling - and quite reasonably picking up with rudder - is in the pre-stall, high drag part of the airfoil map. You should be fast enough on final not to get a bloody wing drop.

 

I agree that once you know your way around a particular aeroplane's flight characteristics, you can fly close to or even partially stalled - this does not make it a low-risk occupation, or even a good habit in circuit (flying too slowly, I mean!). From memory, pilot fatality rates vs experience peaks at about 100 hrs, then again at 400 or so? Is not eroding the safety margin of "minimum safe airspeed" an advanced pilotting technique?

 

 

[facthunter]

I reckon the usual stall margins applied to actual weight are about right. If it's bumpy or there are obstacles affecting the wind flow (Mechanical turbulence) a bit extra is normal. You may need to get as slow as possible because of runway length so I suggest a slower lower (has to be) powered approach but why get real slow too early. Flying really slow is not something you do without giving it your total attention. You deliberately sacrifice some safety margins in special circumstances. Nev

 

 

[djpacro]

...the continuity equations disagree..

Continuity applies along streamlines not across the boundary layer. I suggest that you revisit the definition of boundary layer displacement thickness.

[Oscar]

Oscar, rigging comes into it a lot. I flew a rather ordinary Auster that would always try to drop the right wing , what ever way you approached a stall (within reason) and it would do it rather quickly. Agree about the Lancair and have read a lot about it and have 3 friends over time who have owned them including a Turboprop Pressurised one. They are not for inexperienced pilots but I don't believe they should be deregistered. P51's killed a few too till they got wise to a few effects.Stalling training needs to be revisited has been my opinion for a while. I've encouraged Emergency Manoeuver Training, (Hate that title) rather unusual attitude familiarisation and recovery techniques.

Typical reactions (instinctive) will be contributory to a bad result generally, so we could be doing it a lot better. Dafydd is correct in saying that to "punch the stick forward" will usually unstall the wing straight away. ( I've used the term myself for a long time). Go out there and see what is happening. It's not good enough. A couple of level stalls,power off with an aeroplane that is quite benign only instills the view that stalls are NO PROBLEM. ( I did them so tick it off). Nev

Nev, as I understand it, a LOT of work was done on getting the later Lancairs tolerable after the early 340/360 kits; I believe that the (probably DoT at the time, could have been DCA) test pilot for the first Aus. assembled ones could not stop it going to about 70 degrees no matter what he did. There were, I think, two different modification schemes just in Australia alone for tail mods to the bastards.

 

Completely agree that stall and incipient spin avoidance/recovery training needs to be more comprehensive, and just 'familiarisation' is not enough. When I was training as a glider pilot, recovery from a fully-developed spin was a prerequisite for solo, and recovery (obviously!) from three fully-developed turns in a spin was required before x-country rating. I remember a check-flight in a Blanik at Polo Flat (a tight airfield) where the Instructor took control of it halfway downwind, popped the wheel up, pulled the flaps in, turned it across the strip and stood it on its tail and said: 'your aircraft' as the speed decayed off the clock. And yes, I ended up where we should have been, but it was an unusual circuit - base was but a point on the compass in the turn to final.