forward slip and classic countercontrol stall/spin

12 Answers

1. 
   

   
   

   Bill Trussell on Feb 02, 2012

   The biggest differences between the two in my opinion are both realted to angle of attack.  In the cross control stall/spin case the AoA is high on both wings, but unbalanced toward the direction of the initial spin motion.  Hence, when this condition occurs the aircraft is stalled, but more so in the direction of the spin.
   In the case of the forward slip, the control inputs are balanced and the aircraft is not near the critical angle of attack when the maneuver is performed.
   Care should be exercised when performing a forward slip, keeping in mind some aircraft have limitations cited on the performance of such a maneuver in certain configurations.  Overall it is a very safe maneuver and very helpful when done properly.  If you have any doubts, take a CFI along during practice.  We love the view!

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2. 
   

   
   

   Micah on Feb 02, 2012

   A spin occurs from a skid condition; you have outward force/rotation before the stall occurs.
    
   A slip is a “cross control” condition, but your controls are crossed in opposite “directions.” Let a slip go (or go to altitude and try to stall it) and watch the forces fight to neutralize. This what Bill describes above as balanced control inputs.

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3. 
   

   
   

   Nathan Parker on Feb 02, 2012

   A slip is a safe maneuver because 1) if you stall, you will rotate towards the high wing, which provides plenty of time to correct the situation, and 2) part of the lift of the airplane is provided by the canted fuselage, so it’s a bit harder to stall the airplane.
    
   A skid is an unsafe maneuver because 1) if you stall, you will rotate towards the lowered wing, which doesn’t provide much time to correct the situation, and 2) the wing is carrying a larger load, because the fuselage is canted in such a way to provide a downforce that must be countered by an increase AoA.

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4. 
   

   
   

   Micah on Feb 02, 2012

   Also, related to this:
   this fact or my perceived belief gives me chills with fear of nose drop image whenever I attempt/practice forward slip on final
    
   There’s nothing wrong with fears/perceptions/misconceptions related to flying. These are natural and prevalent; if you want to be a competent pilot you need to be aware of the aircraft, the environment, and yourself. But remember that the universal action required to break a stall is (1) decreasing the AOA below the critical angle. If you are “low and slow” on final and fear that you might stall, your recovery steps include (1) decreasing the pitch (nose down) and, if necessary to maintain a safe altitude (2) increasing power. It is never the other way around (unless you want to practice a power-on stall at low altitude).
    
   So remember, there is nothing wrong with a native/default fear of “dropping the nose” when flying in the traffic pattern. Also remember, there is nothing wrong with “dropping the nose” to fight a stall/slow flight condition. In fact, this is the only right response.

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5. 
   

   
   

   Brian on Feb 03, 2012

   “classic conter control stall/spin that I have read about many times and that have claimed lives of pilots turning from base to final.”

   Nathan gave a wonderful recount of what is occuring aerodynamically in the two cross control conditions. So my recount is only be to reiterate that a slip is a stable cross control condition. So stable, in fact, that if you try it at altitude, power idle, in a 172 with any flap setting you will find that all you do is fall while remaining in a slipped condition. That is, no rolling or yawing occurs from a full slipped stall in a 172.

   The real reason for my reply is regarding the quote because you’re right, this is a dangerous condition. The why seems to be misunderstood, howerver. The reason it is dangerous is the pilot, let’s assume left traffic, is making a left turn from base to final. He/she looks out and sees that they’ve over shot their turn. To help it along the pilot adds left rudder (causing a skid), which results also in a dropping of the nose (see Nathans explanation). Correcting for this lower nose condition the pilot then pulls back, bringing the aircraft closer to stall. He/she doesn’t realize that though because they are fixated on saving their base to final turn. The condition repeats, more rudder, more elevator until the stall is encountered.

   By now this pilot is one step away from the classic stall spin with no realization of the condition because they are still fixated on saving the base to final turn. The stall begins, the left wing starts to drop, and the pilot makes the last reaction that seals their fate – right aileron to raise the STALLED left wing. This further stalls the left wing. On impact control inputs are – left rudder, stick back, and right aileron. That is the cross controlled condition to avoid! 🙁

   There is a very simple remidy: When turning base to final – ignore the runway! I promise it’s not going to get up and walk off. Instead, set your focus to the horizon off your nose and fly the airplane through a coordinated turn. When the runway is in site, don’t shift your view to it (this will require active thinking to avoid). If you’ve over shot simply continue a coordinated turn by reference to the horizon and make a correction. If a correction cannot be made by normal means, don’t fix it with aerobatic flight – go around!

   If we all did that I’m convinced nobody would ever perish from such a silly condition. Do keep in mind that the above becomes far more important in the event of an engine failure or other emergency that will tend to increase the probability that you fixate. Fixation kills because we fall to bad habits like trying to fly to the runway. Just fly the airplane and work on getting rid of the “fly to the runway” habit.

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6. 
   

   
   

   BC on Feb 04, 2012

   Side slip and forward slip are the same thing. Only difference is the ground track. Slips are perfectly safe. In fact, I fly most of my turns (in single engine aircraft and gliders) to short final in a slip (especially in planes without flaps). Stop flying B-52 patterns. Actually, a good B-52 pilot can easily fly a pattern inside a typical Cessna 152 pattern. Learn to fly a Pitts Special pattern and there will be no need to fear an engine failure in the pattern. OK, a Pitts pattern is a bit extreme. Make it an Extra 300 pattern.
    
   Spins require a stall and yaw. Yaw can’t easily be totally avoided, but the stall can. Don’t stall and you won’t spin. Any uncommanded yaw should instinctively be met with opposite rudder and forward stick. Practice this at higher altitudes, of course (and with an instructor).
    
   Learn to spin and recover. Learn aerobatics if you want to be a real pilot. The FAA did no one any favors by removing the spin requirements. Now most pilots are control manipulators that can’t even fly outside of 20 deg of pitch and 60 deg of bank. The problem is that the planes can. When the plane goes upside down, the pilot better be comfortable in that attitude. Learn to really fly. Learn aerobatics. You’ll be a much better pilot.
    
   Capt BC

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7. 
   

   
   

   Brian on Feb 04, 2012

   “Side slip and forward slip are the same thing. Only difference is the ground track.”

   There’s no difference. Not with ground track or, and I’m just reiterating this point, aerodynamically. A slip is a slip is a slip.

   Other than that nit pick, love and agree with the rest of your post. Aerobatics – great lessons. 🙂

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8. 
   

   
   

   BC on Feb 04, 2012

   You’re right, Brian. A slip is a slip. I don’t even know why the have the term “forward slip” except for the “ground track” (usually straight ahead and down a road or section line) that the instructor wants you to fly when asking a student to do one. Everyone needs to be proficient at slips. Do one on every approach if you can (in airplanes that are capable. Probably not a good idea in a 747, although i’ve slipped 707’s)
    
   Capt BC

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9. 
   

   
   

   Brian on Feb 04, 2012

   “Probably not a good idea in a 747”

   You chicken! 😛

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10. 
    

    
    

    BC on Feb 04, 2012

    Well, actually, normal crosswind landing procedures are to fly a wing low slip on short final. So, yes, you can and should slip a 747 during those procedures. I just wouldn’t turn downwind to final, abeam the numbers, with a ful top rudder slip in an airliner. Even though the plane can handle it, the PAX don’t like it and neither do the Feds 🙂 I got to do a lot more stuff as a USAF B-707 instructor (lazy-8’s to 90 deg bank with a B-52 tucked up under the tail and tight fingertip formation flying 🙂
     
    The 777 crosswind landings are upwind wing low slip to about 31 kts crosswind (or you’ll drag metal on the runway) and more cross than that requires adding crab up to the 38 kts crosswind limit. Often a combination of the two are best in gusty xwinds to give the wing a little more clearance. And, yes, you can land the plane in a full crab up to the full 38 kts limit (man, that landing gear sure is buit to take it. Boeing engineers must have known that I’d be flying it 🙂 ) Kicking out the crab in the flare is another ops manual technique, but your timing has to be perfect. Really, just do it like you do in a Cessna. If you can do it in a Cessna, you can do it in a 777 (actually, the 777 is easier, but don’t spread that around)
     
    I mention all this because, yes, you really do normally slip airliners (during crosswind landings). And i really like Boeings. The only fin that ever broke off a Boeing that I know of was a B-52 doing mountain wave research in extreme turbulence (topic deviation, i know). They lowered the gear and the large gear doors well aft of the CG behaved like a vertical fin and they landed safely. Sharp pilot. 
     
    Capt BC
     
     

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11. 
    

    
    

    Curtis Ide on Feb 06, 2012

    I liked Brians explanation of why the turn to final stall happens and how it can be dangerous.
    Adding to the information above one of the reasons it is safe to do a forward slip or side slip is that you have been trained to recognize a stall and to recover from a stall.  I agree with BC on learning how to recover from spins but a spin at 500ft could be very dangerous.  While doing slips you should be very attentive for the first indications of a stall and remember that your airspeed is most likely innacurate due to the disturbed airflow patterns across the static port(s) and pitot tube.  If you get any indications of a stall you should reduce the angle of attack and bring the aircraft back to coordinated flight – time for a go-around.  You will notice in a lot of the Cessna manuals it will say no slips with flaps extended.  The reason for the placard is because the controls have a tendency to buffet similar to a stall.  What they didn’t want to have happen is innacurate airspeed combined with an expectation of buffetting and then you don’t recognize the actual stall.  To wrap this up, slips aren’t dangerous unless you allow the aircraft to stall while performing one. 
    Also, wanted to say for anyone interested – A side slip is a slip performed with the longitudnal axis of the aircraft parallel with the runway and is used to reduce sideload during cross wind landings.  A forward slip is used to obtain maximum parasite drag by using full rudder deflection.  In both cases angle of bank is used to keep the aircraft aligned with the desired path.
    – A spin happens because the aircraft is stalled and there is a source of yaw (rotation).  Remember your rudder angle of attack is increased by pitch so it will still be working it’s aerodynamic magic back there.
    Hope this helped.

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12. 
    

    
    

    Curtis Ide on Feb 06, 2012

    *rudder angle of attack is not increased by pitch

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