The 'impossible turn' - a known killer.

[Guest Maj Millard]

Yes BLA82, that second glider looked like he may have known what he was doing. Kept the wings as flat as he could, and more ruddered it around. Pulled it off well with the height he had, but you wouldn't get away with that in most ultralights.

 

 

[Guest ozzie]

Is Tony on holidays? this would be his subject.

 

 

[BLA82]

Kept the wings as flat as he could, and more ruddered it around. Pulled it off well with the height he had, but you wouldn't get away with that in most ultralights.

:thumb_up:Tell me about it but wether you could get away with it or not, I wouldn't be keen to try it unless totally necessary:ah_oh:

 

By the way, this is a great thread, well done for starting it. It is good to hear from you guys, makes us young folk dream more:thumb_up:

 

 

[Guest keeffe]

This clip shows the perils of turing back, I ofter can't understand how experienced pilots with attempt things like this.

 

Mike

 

http://au.youtube.com/watch?v=-s62aarnTIw"]http://au.youtube.com/watch?v=-s62aarnTIw[/COLO

 

 

[Guest ozzie]

This tragic accident happened at Luskintyre in the late nineties. power loss on take off. it was debated at the time if the drag of the wingwalker being as high as it was impeded the ability of the elevator to get the nose down. unfortunatley it was witnessed by a group of young autistic children.

 

 

[Student Pilot]

Yes BLA82, that second glider looked like he may have known what he was doing. Kept the wings as flat as he could, and more ruddered it around. Pulled it off well with the height he had, but you wouldn't get away with that in most ultralights.

By "ruddering" it round all you do is increase the stall speed. The stall speed is slower in a proberly balanced turn, any slip or skid only increases stall speed.

 

 

[Guest keeffe]

I didn't want to say anything, Alot of people seem to think ruddering it around is more efficient. Even instructors I know think this.

 

They need to bring in serious Aerodynamics studies to RA

 

Mike

 

 

[Guest Brett Campany]

Personally I'd completely avoid turning back to the runway full stop. Only because it does invite the possibility of coming down hard, not making it to the airfield and ending up 6 ft under.

 

One of the first things my instructor did was tell me to get familiar with my local airfield, look at the various paddocks, beaches, open properties on both sides of the runway. I know that if I have an EFATO on runway 07 then I can lightly turn left about 10 degrees and there's a perfect paddock right in front of me that I can put her down in regardless of the conditions. Same goes for runway 25.

 

I really like that idea of a brief on the downwind leg in the event of a go-around. Might have to take that on board for sure!

 

 

[Guest High Plains Drifter]

What all the accidents in this thread have in common is lack of airspeed.

 

 

[Guest ozzie]

By "ruddering" it round all you do is increase the stall speed. The stall speed is slower in a proberly balanced turn, any slip or skid only increases stall speed.

the problem with ruddering it around is not so much the stall speed going up but due to the high aspect ratio, long wing, if i was ruddered to fast the wing on the outside would acclelerate whilst the inside slows down causing more of a imbalance of lift possibly stalling he inside wing. different than high AoB i would think

 

i think ruddering it would be much safer than a high angle of bank turn were the stall speed does go up with AoB. clearly seen when you compare both vidios

 

would i be wrong on this??

 

 

[Guest keeffe]

At the stall it is best to keep the aircraft level with rudder, however the sudden increase in AoA in a ruddered turn will still have the requirement to have a positive angle of attack in order to maintain control. Otherwise a spiral dive is a high risk or even a spin. Yaw, roll and pitch go hand in hand with each other.

 

Add rudder, prime effect is to yaw, sec affect is to roll, further effect is to drop the nose

 

Prime effect of aileron is to roll, sec effect due to increase drag of the down aileron is to yaw, and further effect is pitch again.

 

One other thing to remember is when you are at the stall the pimary reason for rudder to be used rather than aileron is it is more effective.

 

It all comes down to your co-efficient of lift, where if you increase your angle of attack your lift will increase proportionally. However for ever doubling of airspeed you gain 4 times your lift. So yes increase in lift more drag but ailerons are more draggy than the lift created by the doubling of speed.

 

Mike

 

 

[Guest pelorus32]

I think it's really important to keep this simple. Turn back accidents if they go wrong usually end in a stall (or landing short if you are lucky). If you stall in a turn back, then surprisingly often you end up in a spin.

 

So stating the obvious:

 

1. In order to stall you must pass the critical angle of attack (AOA); and
    
    
   
2. In order to spin you must asymmetrically stall - generally through crossed control input and unwise use of rudder;
    
    
   

 

 

In either event you are killed by your uncontrolled arrival in a less than optimal attitude - either steeply nose down or to some extent inverted and nose down.

 

Anecdotal evidence out of Europe supports a comment made elsewhere in this thread that you have a higher chance of living if you do something like that really low - the pitch down or roll doesn't have time to progress far enough to kill you.

 

In any event if you don't exceed the critical angle of attack you are safe. If you do exceed the critical angle of attack you are not safe. Asymmetric control input can cause one wing to reach the critical AOA earlier than the other.

 

So it follows that you should know where the stall stick position is for any a/c configuration that you fly and you should always fly balanced.

 

The reason the turnback is so dangerous at exceeding critical AOA and/or doing so in an unbalanced fashion is that it is a max performance manoeuvre and we repeatedly demonstrate that we under estimate the energy requirements - height, speed vs distance required to perform that evolution. In so doing we resort to pulling (stretch the glide) and ruddering (turning more quickly) in order to "achieve" the performance that we belatedly recognise we need. NB neither pulling nor ruddering is an appropriate response - they WILL NOT achieve what you want to achieve. Both of these responses lead directly to the early occurence of the consequences that we are seeking to avoid - they will kill you.

 

Regards

 

Mike

 

 

[Guest pelorus32]

At the stall it is best to keep the aircraft level with rudder, however the sudden increase in AoA in a ruddered turn will still have the requirement to have a positive angle of attack in order to maintain control. Otherwise a spiral dive is a high risk or even a spin. Yaw, roll and pitch go hand in hand with each other.Add rudder, prime effect is to yaw, sec affect is to roll, further effect is to drop the nose

 

Prime effect of aileron is to roll, sec effect due to increase drag of the down aileron is to yaw, and further effect is pitch again.

 

One other thing to remember is when you are at the stall the pimary reason for rudder to be used rather than aileron is it is more effective.

 

It all comes down to your co-efficient of lift, where if you increase your angle of attack your lift will increase proportionally. However for ever doubling of airspeed you gain 4 times your lift. So yes increase in lift more drag but ailerons are more draggy than the lift created by the doubling of speed.

 

Mike

I would suggest reading the FAA Airplane Flying Handbook at:

 

http://www.faa.gov/library/manuals/aircraft/airplane_handbook/media/faa-h-8083-3a-3of7.pdf

 

See page 4.6 first column. It suggests that the use of rudder is not as clear cut as we were all taught in the old days.

 

Regards

 

Mike

 

 

[Guest Maj Millard]

R461...You have the right idea, safer to go straight ahead mate.

 

BLA82.....Would be good to break the cycle of fatal turnbacks, absolutly no reason for new or young pilots to keep repeating this mistake, when many have already learnt the hard way in the past. Much safer straight ahead, with a minimum speed controlled touch down.

 

In reference to my ruddering comment. I wasn't advocating it as a 'good' thing' and I did say I didn't think it would work with ULs. It did appear to be used by that glider pilot, but the main thing is, he kept his wings as level as he could, and obviosly kept enough airspeed, as he didn't stall. It is unfortunate that people will see that low altitude, successful, turn-back footage, and think it is possible in all cases. I would reckon that the pilot was either an instructor, or very high time pilot, with lots of time in that aircraft.

 

As much as they are very educational, I don't need to view any more turnback impacts. The Tigermoth one was totally unnecessary, and very tragic. I believe we may already have got the picture. Both the glider and Tigermoth demonstrate vividly, that you are just along for the ride to the crash site, once that wing stalls, and the nose drops.

 

 

[Guest keeffe]

Pelorus32, My training and study towards my CPL is all current not old days.

 

But ask yourself this, when in the stalled condition and a wing drops the aircraft is in a state of uncoordinated flight and it yaws even if you have a very docile aircraft like I do and can pick the wing up with your ailerons the aircraft is still flying uncordinated. so opposite rudder effectively brings it into coordinated flight.

 

Second, one exercise that will show for instance the ailerons are the cause of an into turn spin is: fly straight and level pull the power and choose any angle of bank you like and hold a level turn. No ailerons are used in the turn and the outside wing will stall first violently rolling the aircraft out of the turn.

 

But in the condition of a spiral dive the inside wing will stall before the outside.

 

The drag caused by the downgoing aileron will increase the violence of stall entry, as you try and pick the wing up in say a stall occuring during a right turn with left aileron the right down going aileron will be like an air brake further increasing the yaw resulting in a spin.

 

Next time you practice spins add opposite aileron to the spin and see what happens if you hold it you can end up flat spinning.

 

Not sure who wrote that faa publication but it is dated 2004 and alot of people would write it off.

 

Mike

 

 

[Guest keeffe]

YouTube - Upright flat spin - Extra 300YouTube - Upright flat spin - Extra 300

 

This clip depicts the effect of aileron during a spin

 

Mike

 

 

[turboplanner]

Run that by me again Keefe, the faster wing with the cleaner air will stall first?

 

 

[Guest keeffe]

What are you refering to turbo

 

 

[Guest pelorus32]

Second, one exercise that will show for instance the ailerons are the cause of an into turn spin is: fly straight and level pull the power and choose any angle of bank you like and hold a level turn. No ailerons are used in the turn and the outside wing will stall first violently rolling the aircraft out of the turn.

So what we prove there had nothing to do with ailerons and everything to do with differential AOA of the two wings. In that case the "outer" wing has a higher AOA and regardless of the direction of turn the aircraft will roll wings level. You can demonstrate the same thing by leaving power on and entering a climbing turn and continuing it to the stall. The cone described by the inner wing has a lower AOA in the resulting climbing turn. Nothing to do with aileron.

 

But in the condition of a spiral dive the inside wing will stall before the outside. The drag caused by the downgoing aileron will increase the violence of stall entry, as you try and pick the wing up in say a stall occuring during a right turn with left aileron the right down going aileron will be like an air brake further increasing the yaw resulting in a spin.

The first section of this quote is accurate. In a descending turn the "inside" wing has a higher AOA and will therefore stall first causing the aircraft to roll into the turn. Again a factor of the "cone" described by the inner wing in a descending turn and the resultant AOA.

 

The second part of the quote is less accurate and confuses the picture. If you read the FAA publication it suggests _coordinated_ use of both controls. In the second part of your quote if you follow the FAA advice then you will have less resultant "into turn" yaw - it will be counteracted by the coordinated rudder.

 

In any event our first response to a stall is not to pick up the downgoing wing is it? Our first response to a stall is to reduce the AOA using elevator. I am talking here about a stall not a spin.

 

I think none of this is necessarily clear cut. I was taught to always pick up the downgoing wing with rudder at the point of stall. In so doing you are however using uncoordinated control input and you can get more than you bargain for. You are also using uncoordinated control input if you only use aileron - they are simply two sides of the same coin.

 

Kermode deals with differential angle of attack pretty well - he's worth a read. I hardly think that a 4 or 5 year old book is out of date by the way with respect to the FAA publication.

 

Regards

 

Mike

 

 

[turboplanner]

[quote=keeffe;79034

 

Second, one exercise that will show for instance the ailerons are the cause of an into turn spin is: fly straight and level pull the power and choose any angle of bank you like and hold a level turn. No ailerons are used in the turn and the outside wing will stall first violently rolling the aircraft out of the turn.

 

This led to my question.

 

 

[djpacro]

James Patton (former chief of flying ops at NASA Langley), Rich Stowell, Greg Koontz, Patty Wagstaff, Michael Goulian ...[/url]A video of a stall in a skidding turn - I regularly have instructor students swear at me when I make this sneak up on them.

[Guest keeffe]

It's due to the high angle of attack required to maintain level flight on the part of the outside wing, as it is at a greater angle of attack. If your in coordinated flight both wings are in clean airflow anyway hence the coordinated flight.

 

Is this what you were refering to turbo ?

 

Mike

 

 

[turboplanner]

The outside wing is moving faster through the relative airflow, generating more lift, how does it get a greater angle of attack?

 

 

[Guest pelorus32]

The outside wing is moving faster through the relative airflow, generating more lift, how does it get a greater angle of attack?

Hi TP,

 

It actually helps to see a picture of this. The two clear scenarios are a climbing turn (outer wing stalls first) and a descending turn (inner wing stalls first).

 

The wings are describing different flight paths and it is the AOA difference caused by the different flight paths that generates the stall behaviour. Partly because the inner wing is describing a much smaller flight path the effect of moving upward/downward in a climbing/descending turn has a much greater relative effect on the AOA than it does for the outer wing. Easier to see it drawn than explained.

 

Of course then the stalled wing will have greater drag than the unstalled wing and that creates secondary effects - indeed those effects will be there in the lead up to the stall as well, as the AOA increases so will drag, but more markedly so after the critical AOA is reached.

 

Regards

 

Mike

 

 

[Guest keeffe]

It has a greater angle of attack to the relative airflow.

 

I am surprised if you are an active flyer witha licence and never had a demonstration of this phenomenom.

 

Mike