Peter wrote:
Yes; that’s the FAA CPL Lazy 8.
Cool, didn’t know that 
We call them lazy 8, but it’s not the same as I find when googling. It as a perfectly coordinated maneuver, and it will turn the plane in the opposite direction using little space and loosing very little energy. They can be done in series because one objective is to end up at the same spot when one 180 degree is done (more like 220-230 degree). When doing them in series alternating left and right, it describes an 8 in the horizontal plane. It starts with a pull up from cruise, approximately 30 degrees.
Yes; that’s the FAA CPL Lazy 8. A good maneuver to learn
Yes, (as long as the slowing down is converted into an increase in altitude, and not just wasted into drag), and this is what I teach, when I teach this maneuver. I don’t advocate maneuvering to extremes such that a stall or loss of control is likely, that has no benefit during an escape maneuver. You want to be in control, and aware of your position and attitude relative to the ground at all times. As “aerobatic” is commonly agreed to be roll beyond 60 degrees, I do not find it necessary to roll beyond that, 60 degrees is lots to get around quickly, and usually the comfort level of most pilots. Sustained roll angles greater than 60 degrees will impose G’s exceeding 2, which is wasteful, as you’re just surrendering valuable stored energy to drag.
That sounds like full flap is not a good idea because there is a lot more drag (usually) and Vs doesn’t benefit all that much more.
Pilot_DAR wrote:
Presuming you’ve foolishly entered the blind canyon with some speed, that’s stored energy you can use to turn and climb. I train that a rapid decision must be made as to which direction to go, and thereafter full power, pull up, roll to 45 or so, and extend takeoff flap as you climb. This will certainly cost airspeed, so stall avoidance is vital. But, as stated, the extension of flaps will reduce stall speed by 5 to 10 kts, which is useful, an increased margin of speed loss get you around safely. If you complete the maneuver pointed the other way, and with the same or greater altitude, you’ve succeeded. If you had to give up speed, that’s okay, as long as you’re not flying slower than Vx – you’ve still got full power on, you can continue to climb! I have no concern about overstressing a plane doing this, because, while carefully preventing a big drag rise (G buildup), and avoiding a stall, you’re not going to pull hard enough to damage the aircraft. Now, if you stall, dive, and recover with lots of speed, you could overstress the plane, but then you’ve done it wrong, and probably hit the ground anyway!
We train something very similar. We call them lazy 8, but it’s not the same as I find when googling. It as a perfectly coordinated maneuver, and it will turn the plane in the opposite direction using little space and loosing very little energy. They can be done in series because one objective is to end up at the same spot when one 180 degree is done (more like 220-230 degree). When doing them in series alternating left and right, it describes an 8 in the horizontal plane. It starts with a pull up from cruise, approximately 30 degrees. Then when the speed approaches stall speed, use aileron to get the inside wing down, and rudder to keep the ball centered. The aircraft will have a considerable bank, and the nose will very quickly point down again and speed increases to cruise when leveling off. Doing it correctly you end up on the same spot you started, at the same speed, and can continue doing it the other way to describe an 8. No flaps are used though.
Peter wrote:
Would it be beneficial to slow down and select full flap, for the minimum turn radius?
Yes, (as long as the slowing down is converted into an increase in altitude, and not just wasted into drag), and this is what I teach, when I teach this maneuver. I don’t advocate maneuvering to extremes such that a stall or loss of control is likely, that has no benefit during an escape maneuver. You want to be in control, and aware of your position and attitude relative to the ground at all times. As “aerobatic” is commonly agreed to be roll beyond 60 degrees, I do not find it necessary to roll beyond that, 60 degrees is lots to get around quickly, and usually the comfort level of most pilots. Sustained roll angles greater than 60 degrees will impose G’s exceeding 2, which is wasteful, as you’re just surrendering valuable stored energy to drag. For that reason, I do not advocate needlessly building up G, and certainly avoiding sustaining as much as 2G. I present the escape maneuver as a tight climbing turn, rather than a hammerhead turn or stall turn. I certainly would not want the plane pointed near vertical with rapidly decreasing airspeed if escape from rising ground is needed!
Presuming you’ve foolishly entered the blind canyon with some speed, that’s stored energy you can use to turn and climb. I train that a rapid decision must be made as to which direction to go, and thereafter full power, pull up, roll to 45 or so, and extend takeoff flap as you climb. This will certainly cost airspeed, so stall avoidance is vital. But, as stated, the extension of flaps will reduce stall speed by 5 to 10 kts, which is useful, an increased margin of speed loss get you around safely. If you complete the maneuver pointed the other way, and with the same or greater altitude, you’ve succeeded. If you had to give up speed, that’s okay, as long as you’re not flying slower than Vx – you’ve still got full power on, you can continue to climb! I have no concern about overstressing a plane doing this, because, while carefully preventing a big drag rise (G buildup), and avoiding a stall, you’re not going to pull hard enough to damage the aircraft. Now, if you stall, dive, and recover with lots of speed, you could overstress the plane, but then you’ve done it wrong, and probably hit the ground anyway!
I teach this primarily in floatplanes and amphibians, as they are somewhat more likely to be flown into these types of situations. These aircraft are more draggy anyway, so fly with lower cruise speeds, and slow more quickly when pulled up sharply, so some skill development is needed. It is critically correct that losing your horizontal reference is a real risk. I’ve known pilots who have died during entirely survivable turns in canyons, as they simply lost “up” and tumbled the plane into the ground. If you cannot maintain a very clear perception of where the visual horizon is, and will be during your turn, it’s already past time for you to leave the area with the exit plan you already have prepared – right? Remember that trees always point up, if nothing else, look for treetops to distinguish – but again, if it’s come to this, you’re way too far in!
I disagree that the extension of wing flaps degrade stall characteristics, and eliminates the affect of washout. As a refresher, washout is the slightly lower angle of incidence at the wingtips, than at the root of the wing. It is intended that the roots of the wings stall before the tips as AoA increases, so that the tips, and cautious application of aileron up to the stall, will maintain the greatest effect of keeping the wings level. As [lift] wing flaps are extended, the effective chord line changes to be an increase of the angle of incidence through the extended flaps – so the inboard part of the span is having yet more angle if incidence, and will cause the tips of the wing to have comparatively more washout, increasing the tip’s resistance to stall. Yes, as the airspeed slows, the effect of the tips, and possible application of aileron is reduced because of less airflow, and more aileron deflection may be required to maintain wings level, this is because the aircraft is flying more slowly, not simply because the flaps are extended. Any flap configuration intended to increase lift (as opposed to split flaps, which are more intended to increase drag) will make the inboard portion of the span carry more of the aircraft weight as the AoA increases, leaving the tips carrying less weight, not stalling, and able to affect roll control better.
For those who have had occasion to sit window seat around the wing in a B737 during an approach on a damp day, you will have noticed a pronounced visible vortex coming off the outboard corner of the extended flaps. This is the evidence that the flaped portion of the wing is now carrying the weight of the aircraft, and the tips are not creating much lift any more. The vortex is the evidence of the lift, and it’s not off the wingtip any more, it’s moved inboard to the outboard end of the flap – so has the lift. (The vortex off the flap is the basis of the “avoid slips with flaps extended” caution for some 172s, the vortex can impinge on the outboard end of the H stab, and result in momentary reduced pitch stability.) If the outer portion of the wing is not creating lift, it’s not going to stall, and aileron control will remain effective. We don’t use ailerons during a stall recovery, but they may be used with caution during the approach to stall, and during stall avoidance, as long as the rudder is used appropriately. On 100 series Cessnas, the rather sloppy aileron feel, and sudden roll approaching the stall can be attributed to sloppy aerodynamic design. I also notice that many pilots who experience wing drop during the approach to stall, are not using the rudder adequately. The installation of a STOL kit does a lot to correct the sloppy ailerons of a Cessna, the wing fences, and aileron gap seals make a big difference, and the wing cuff helps too. (The fancy looking droop tips not so much).
Canyon turns are easily practiced in suitable open airspace, and are entirely safe. They can be approached not so intensely, and as comfort level increases, so can the angle of bank. But the object is not an aerobatic maneuver, so don’t get carried away.
As far as S&L turn radious is concerned flaps should not matter, only speed and angle of bank, if they allow slow speed and high angle of bank I would use them (G limits, stall limits…) but they usually tend to constrain flight envelope on higher airspeed tough they may expend it a bit on the slow airspeed side?
One would have to write the formulas for his aircraft to make a call but on more than rate 1 turns I doubt extending flaps will get you out…
To Peter’s question about flaps, I suggest this is type specific. For the typical GA piston my opinion is not to use flaps:
- they lower your rate of climb
- some types have a 2 G envelope with flaps, although that should still allow a 60 degree bank
- they don’t materially lower stall speed, usually only by a few knots, say 5 to 10 knots
- they degrade stall characteristics – eliminate the benefit of washout, lower critical alpha, reduce lateral stability, increase downwash effect – just compare a clean, power on stall with a flaps 25 or 40 stall – the aircraft is likely to suffer a wing drop and recovery is more complex with greater height loss
RobertL18C wrote:
What if you entered the wrong valley?
Lots of accidents due to that in Norway – before moving map GPS software. Low ceiling, entering into the wrong fjord or valley. The problem isn’t recognized before it is too late. You try to fly as high as possible, and eventually the aircraft is forced into IMC. With terrain all around, the accident is inevitable. People have survived this as well, climbing at Vx into the cloud, hoping for the best, and then crash “landed” into terrain.
Thinking about it, I have never heard of any accidents at all where low ceiling was not a main contributor. The solution to the problem is obviously a moving map GPS and studying the map/terrain when planning. The turn technique being pretty much irrelevant for the outcome in any real accidents IMO. People aren’t very likely to willfully enter a valley of any length where a normal turn won’t do, or without energy/engine power to take it vertical. With a moving map (and adequate planning), the chance of doing it by accident is as good as zero. Narrow passes are cool though.
Would it be beneficial to slow down and select full flap, for the minimum turn radius?
The idea (as I remember) is to turn around the plane 180 degree using as little lateral space as possible (closed, narrow canyon with no chance of out-climbing the terrain)
This is a good definition of the problem. How do you safely turn 180 degrees with a minimum radius and no loss of height, and no loss of control?
One solution, and the one advocated by mountain pilot training is to change the problem so you do not need 180 degrees to get out of a fix. Hence the rule to approach ridges at a 45 degree angle and not head on. In this way if you find the terrain is outclimbing you, evidenced by you seeing less beyond the ridge as you move towards it, you only have a 90 degree turn towards lower terrain.
What if you entered the wrong valley? – quite easily done, especially where there is no human infrastructure (roads, towns) helping identify the entrance to a valley. Firstly, you need to pick a side of the valley as you need to maximise the available area to accommodate a turn – self evidently, flying down the middle of the valley halves this area. Do you fly on the shady side or the sunny side? Where there is sinking or rising air?
It requires experience to hug a valley wall, and knowledge of the terrain.
How do you then minimise your turn radius without losing height or loss of control?
There is the concept of G corner where you fly close to the accelerated stall speed at the maximum bank angle in level flight allowed by the flight envelope of your fighter, errr, aircraft. The L-4 Cub had a few enemy aircraft to its credit by luring a faster fighter, and with a higher g envelope, into a box canyon. This approach minimises your turn radius for your type of aircraft. In fighter aircraft the use of flaps during manoeuvres is built in some designs – however in GA lowering flaps usually limits the G envelope. It also reduces lateral stability and makes stall characteristics less benign. When did you last practice 60 degree banked turns with full flaps?
Probably a normal 45 degree bank turn at a 1.3 x margin of the stall speed at 45 degree bank meets the criteria set by LeSving. Recall no useful horizon in a narrow valley.
Using the turn radius formula
https://en.m.wikipedia.org/wiki/Banked_turn
and adjusting 1 g stall speed for 45 degree bank turn and 1.3x safety margin gives you a speed of approximately 1.5x clean stall speed.
A bush plane like a Super Cub would have a turning radius of 110 metres, a 172 around 130 metres – the difference being the slightly higher stall speed of the 172. Sure the Super Cub improves inverse geometrically the steeper the bank angle and at its theoretical G corner with no safety margin (recall it is a gust and load envelope) the turn radius is only 50 metres, but then the accident rate of the Super Cub is worse than the 172.
I suggest these turn radii are sufficiently small that these aircraft can be turned around early on in a valley quite safely without any semi aerobatics.
“Doing the manoeuvre in a gentler manner, say peak bank of 60 degrees (technically the limit for non aerobatics), is unlikely to result in a 180 degree turn without loss of height.”
If you’ve got height, then lose it. If you don’t have height you’re committed to putting the plane down.
