Ask The Pilot

[jb747]

Q; Engine out at takeoff / landing. Aircraft starts roll - wing drops

Why does correcting Roll with ailerons exacerbate the roll?

If you‘ve corrected the roll with aileron, how does that exacerbate it. You’ve already corrected it….

If you’re saying that you can’t correct roll induced by an engine failure with aileron, then you‘re not correct.

On take off, except in the low vis case, yaw is immediately very noticeably, and it’s obvious to apply rudder to stop it. You will simultaneously use the aileron to fix any roll that has already happened. Why does it roll? Because of the yaw, one wing is effectively moving a little faster than the other, and it also has less wing sweep presented to the airflow, so it makes more lift. You’ll almost always end up a bit crossed up, with lots of rudder applied, and quite a bit of aileron. Just gently (slowly) apply or reduce the rudder so that the aileron input is reduced to zero. Trim it there. Don’t continually move the rudder. It’s much better to hold it steady in the wrong spot, which gives you a constant aileron requirement, than it is to chase the ‘correct’ rudder position which leads to a moving aileron target.

If you just apply aileron to fix the roll, and don’t do anything with the rudder, you’ll end up in a constant yaw. That’s not necessarily unsafe, but it won’t allow you to remain within the regulated heading requirements.

Engine failure on take off prior to lift off is easier to handle than airborne, simply because you can’t roll. Rudder to keep it straight, and you should have it sorted out by rotate. On approach it isn’t all that noticeable, as you’re operating at low power anyway, and only a small amount of rudder will be needed. Go arounds are a bit of a handful though.

Looking at this from another angle…you do not use rudder in an airliner to make roll corrections. Rudder has two uses. To correct any yaw and to act as footrests.

 

[Quickstatus]

Sorry i neglected to insert the link:

And this explanation:

Both suggest aileron correction exacerbated the roll (wing stall?)
Or am I reading it incorrectly?

Thank you for your explanation.

 

[jb747]

Sorry i neglected to insert the link:

Both suggest aileron correction exacerbated the roll (wing stall?)
Or am I reading it incorrectly?

Thank you for your explanation.

The links change the context of your question quite a bit. In your initial question, you're asking about roll control in a situation in which the aircraft is at least 23% faster than the stall (mandated tolerances for V2 and approach speeds). Roll control is quite normal at these speeds.

But, these F14 accidents happen much slower and actually involve something called Vmca1. Minimum control speed with one engine out. If you have an engine failure at very low speeds, it's possible that you won't have enough rudder authority to actually stop the yaw (and the roll it causes). Vmca1 wasn't an issue in the 380. Even Vmca2 was very slow, but not so slow that you didn't have to be wary of it. The reason the power setting that was applied is relevant, is because the more power applied, the sooner you'll run into Vmca1. Conversely, there's no such thing if you pull all of the engines to idle. The snippet of the Canadian F18 crash at the start of the video is a classic example.

Thinking about a wing, and aileron. When you move the ailerons, the aileron that goes down increases the camber of the wing, and produces more lift. So, that makes you roll away from that side. But, that wing will also produce slightly more drag, which will give you more yaw into the wing's side, thus requiring even more rudder. That's all normal. But, when you get near the stalling angle of attack, another effect comes into play. A wing with greater camber (curvature) will create more lift, but it stalls at a lower angle of attack. If you're right on the edge of the stall, application of aileron to 'pick up' the wing can stall that section of the wing over the aileron, and lead to a very rapid increase in roll in the wrong direction.

It could be induced in the Macchi, but at much higher speeds. If you really hooked into a roll, using full aileron and rudder together to get the maximum rate, and then suddenly reversed the aileron to stop the roll, the roll rate would actually increase. These were really vicious control inputs, and I'd expect that most students (and probably instructors too) never tried quite that hard. What was happening here was that the down -going wing in the roll had an appreciably greater angle of attack than the other wing. Application of full aileron would reduce the stalling angle of the outboard section of the wing, it would stall, and then rapidly flick.

Point to consider... a wing doesn't necessarily stall at the same time along it's full length.

 

[jb747]

A bit more re the F14. I can't see any reference to ailerons, which means roll control would have been handled by spoilers and differential tail. Apart from the fact that they work by killing lift, spoilers are a reasonably viceless way of controlling roll. Any yaw and drag that they produce is on the correct side. I have a friend who flew them, so I've asked him about it.

 

[Quickstatus]

Thank you!
So ailerons operation can change the angle of attack of the part of the wing it is attached to and under certain circumstances can lead to a stall over that part of the wing?

And further aileron input may worsen the stall condition just as further backstick increasing pitch will worsen stall

I’ve learnt that ailerons change the amount of lift - and it is this differential lift that rolls an aircraft…

I had thought ailerons just cause airflow pressure to roll an aircraft - ie roll to right is caused by left aileron down right aileron up, and air pressure incident on the aileron pushes the wing one way or another.

Can yaw cause a compressor stall?

An “up” aileron acts like a spoiler and kills lift??

In order to stay within the flight envelope how does a pilot ensure that a turn (involving roll and yaw) does not turn into a stall?

 

[jb747]

So ailerons operation can change the angle of attack of the part of the wing it is attached to and under certain circumstances can lead to a stall over that part of the wing?

Ailerons change the local camber (curvature) of the wing. A wing with more camber will produce more lift, but will stall at a lower angle of attack. That's what the guy in the second video you linked to was trying to demonstrate in his aircraft. Put the aircraft straight and level. Slow until just on the cusp of the stall. Put in a large amount of aileron, and you're very likely to have the aircraft roll the 'wrong' way, as that aileron causes the wing to exceed the stalling angle for its new camber.

And further aileron input may worsen the stall condition just as further backstick increasing pitch will worsen stall

In many aircraft you're now at the spin entry. Stalled, and rolling. The recovery always involves putting the ailerons and rudder to their central (neutral) position, and unstalling the aircraft with forward stick. You will almost always need opposite rudder, and you may need aileron...but if you do need aileron, it will be in the opposite direction to what you'd expect. Spinning to the left, you'd need right rudder, but left aileron.

I’ve learnt that ailerons change the amount of lift - and it is this differential lift that rolls an aircraft…

Any differential will give you some form of result....

I had thought ailerons just cause airflow pressure to roll an aircraft - ie roll to right is caused by left aileron down right aileron up, and air pressure incident on the aileron pushes the wing one way or another.
An “up” aileron acts like a spoiler and kills lift??

That's a simple explanation, but not really how they work. If you can put in enough aileron, then your wing's camber could become locally negative. So, it's still producing lift, but now in the the other direction.

Can yaw cause a compressor stall?

Yes, basically by upsetting the airflow into the engine.

In order to stay within the flight envelope how does a pilot ensure that a turn (involving roll and yaw) does not turn into a stall?

In many aircraft there is some form of angle of attack display in the HUD. You can feel the onset of the stall, and in the military got pretty good at flying right on the edge of it.

Stalling relates purely to the angle of attack. Whilst it's generally talked about as a speed, that only applies in one very specific case. It's possible to fly slower than the stall speed, and it's equally easy to make the stall speed double (and in some aircraft, triple) its nominated figure. It all relates to the amount of G. Less than one G (but not negative), and the speed reduces. More, and it increases.

 

[Saab34]

What aircraft in your careers did you wish you could have had a chance to fly but didn’t?

Or to those still flying, one you would like to fly?

JB would you like to do a few circuits in a A350-1000?

 

[jb747]

What aircraft in your careers did you wish you could have had a chance to fly but didn’t?

I was pretty lucky. Back when I was a backseater, I used to be very envious of our guys flying the A-4. So in the end, I was lucky to get to fly it. I was offered F-111s and knocked them back.

JB would you like to do a few circuits in a A350-1000?

Nope. I flew the 380. Why would I want to fly one of those dinky things? Jesting aside, I probably wouldn't have minded a look at the 747-800.

Of all the aircraft, the machine that I would most liked a go of, is the F-4.

 

[Saab34]

Nope. I flew the 380. Why would I want to fly one of those dinky things? Jesting aside, I probably wouldn't have minded a look at the 747-800.

Ha thought you might be interested to see in how Airbus has upgraded its toys with new tech. However 748 is an impressive machine. Seems to be much longer.

 

[AviatorInsight]

What aircraft in your careers did you wish you could have had a chance to fly but didn’t?

Or to those still flying, one you would like to fly?

One aircraft I wanted to fly was the 747. Just an awesome machine both inside and out.

I would love the opportunity to also fly the 767, I still have a couple of mates operating that aircraft and they love it.

My ultimate aircraft would have to be the F-14 though.

 

[jb747]

Ha thought you might be interested to see in how Airbus has upgraded its toys with new tech.

Has it? To be honest I can’t find much on the 350 that isn’t on the 380. The screens are bigger, with a nicer layout, but really, they simply emulate what was on the smaller screens. coughpit facing systems look to be more or less the same. I’m sure there’s a lot of new tech invested in the design and construction, as well as the engines, but that’s pretty much invisible from the pilots’ perspective.

I think that might be one of the reasons that the A350 has had such a seemingly easy entry to service. They built on their previous designs, and didn’t change things that weren’t broken. Personally, it’s my choice as the best airliner around. Doesn’t mean I particularly want to fly it though.

However 748 is an impressive machine. Seems to be much longer.

I was interested in seeing the progression of the aircraft, having flown all of the previous versions. Having said that, one flight would do…. I see it as another of Boeing’s wasted opportunities. It was unlikely to sell in the numbers needed to act as a competitor to the 380, and the very large amount of money that was spent on its development might have helped a lot with a replacement for the 737. Even a rebirth of the 757 would have been a better use of the money.

When you ask pilots what they’d ‘like‘ to fly, it’s a bit like visiting a supercar salon. There’s lots there that you might enjoy a ride in. Some that you’d like for the occasional weekend, and many that you’ll scratch your head over, wondering why. And of course, there are others that are simply waiting to kill the average pud-knocker.

 

[harvyk]

Today I saw a RAAF wedgetail come in to land at CBR. I'm used to seeing aircraft (inc military) coming in for a landing by flying over Royalla and approaching RWY 17 that way, but in this instance the aircraft was perhaps over the edge of Fyshwick (aka next suburb over from the airport), did a sharp left hand turn pretty much over Canberra Avenue, and lined up perhaps with no more than about 10 to 15 seconds away from landing.

Now I can't be 100% sure that it actually landed (buildings got in the way so I couldn't see it anymore). This got me wondering, since this was a very unusual approach I was wondering if the military had carte-blanche to do pretty much what they like when it came to where they overflew, or if there was something else in play?

 

[jb747]

Today I saw a RAAF wedgetail come in to land at CBR. I'm used to seeing aircraft (inc military) coming in for a landing by flying over Royalla and approaching RWY 17 that way, but in this instance the aircraft was perhaps over the edge of Fyshwick (aka next suburb over from the airport), did a sharp left hand turn pretty much over Canberra Avenue, and lined up perhaps with no more than about 10 to 15 seconds away from landing.

Now I can't be 100% sure that it actually landed (buildings got in the way so I couldn't see it anymore). This got me wondering, since this was a very unusual approach I was wondering if the military had carte-blanche to do pretty much what they like when it came to where they overflew, or if there was something else in play?

Are you sure about your runway directions. Those positions sound like 35, not 17.

Approaches over Royalla would be that standard 10 mile navex that most airliner arrivals are. The ’sharp left turn’ simply sounds like he flew a visual circuit or approach. I don’t know Canberra these days, but I don’t see anything unusual in that.

I know that the military (long after my time) coordinated a lot of the rules that they used with CASA’s, but they are in no way subject to any of CASA’s bureaucracy.

Wedgetails and Poseidon are reasonably common visitors to Albury. I’ve never seen one touch down, but they’re obviously using it for pilot training flights.

It didn't happen all that often, because it never fitted the flow, but you could occasionally get a very tight base turn (about 2 nm) in Sydney. Left hand, on to 16, and it gave a spectacular view of the harbour and bridge.

 

[harvyk]

Are you sure about your runway directions. Those positions sound like 35, not 17

Sorry, yes 35 not 17

 

[AviatorInsight]

Today I saw a RAAF wedgetail come in to land at CBR. I'm used to seeing aircraft (inc military) coming in for a landing by flying over Royalla and approaching RWY 17 that way, but in this instance the aircraft was perhaps over the edge of Fyshwick (aka next suburb over from the airport), did a sharp left hand turn pretty much over Canberra Avenue, and lined up perhaps with no more than about 10 to 15 seconds away from landing.

Now I can't be 100% sure that it actually landed (buildings got in the way so I couldn't see it anymore). This got me wondering, since this was a very unusual approach I was wondering if the military had carte-blanche to do pretty much what they like when it came to where they overflew, or if there was something else in play?

I was in Adelaide the other day and witnessed an A330 MRTT land onto runway 23 and straight away taxi out and depart in front of us for Canberra for air work to be joined by another A330 who had departed from elsewhere. Could be the RAAF burning up some cash before the financial year is out?

The sharp left turn isn’t part of any instrument approach there so this sounds like a visual approach to me.

 

[jb747]

I was in Adelaide the other day and witnessed an A330 MRTT land onto runway 23 and straight away taxi out and depart in front of us for Canberra for air work to be joined by another A330 who had departed from elsewhere. Could be the RAAF burning up some cash before the financial year is out?

An actual landing, instead of a touch and go. We did them occasionally on 767/747 base training. In the real world that's what you'll hopefully be doing, not a crash and dash.

I'd have hoped that sort of financial silliness had disappeared many years ago, but I guess you never know. The issue was that if you didn't burn all of your hours in a given year, then the number you actually flew ended up as you baseline going into the future.

The sharp left turn isn’t part of any instrument approach there so this sounds like a visual approach to me.

Looking out the window. Not a dead art yet....

 

[Saab34]

AV with NSW out of action for what appears might be a few weeks how much does this hit your overall operation. I’d assume NSW is 1/3 of your operation?

 

[harvyk]

So in the sim (my 747 sim project there are photos if you ask ), I try and fly actual routes. I use SkyVector: Flight Planning / Aeronautical Charts to help selecting airways, and then use the aerodrome and procedure charts from Airservices Australia (which I grab from here Airservices Australia AIS - DAP 167 - Aerodrome & Procedure Charts). I notice that say from Sydney, there are a variety of SID's which get you onto airways heading inland, but unless I'm missing something I don't see any SID's for heading out towards the Tasman.

So using sky vector I'm assuming if I was to fly to AKL, I'd fly on airway L521, but I see no published SID's that would connect me from SY to EVONN (I could of course be blind and just missing it).

Is it a case that you'd expect vectors from ATC which would take you to EVONN to join L521, is there some other procedure which us mere mortals don't have access to, or am I simply in my own world and that's not how airways work at all?

 

[AviatorInsight]

Looking out the window. Not a dead art yet....

I agree, it's the best part! Unfortunately there's a few pilots out there that believe it should be maximum automatics...so I shut up and just let the flying do the talking once they disconnect.

 

[AviatorInsight]

AV with NSW out of action for what appears might be a few weeks how much does this hit your overall operation. I’d assume NSW is 1/3 of your operation?

At the moment nothing has changed to my roster. VIC and QLD have just mentioned that they are still open to other LGAs other than the ones mentioned as hot spots. I'm on a couple of days off at the moment (just got my first dose of the vaccine today) but I'm closely monitoring my flights (BNE/OOL/MEL) over the weekend.

Edit: now cancelled and I’m put on standby.