Slip approach to cross-control stall
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Slip approach to cross-control stall
Did it ever happen to anybody? How large do you consider the risk? How about during a side-slip base-to-final?
I love side and forward slips, especially on final, but the lack of airspeed reading at close ground is a bit unnerving.
How do you keep track of airspeed? Just play it by ear?
I love side and forward slips, especially on final, but the lack of airspeed reading at close ground is a bit unnerving.
How do you keep track of airspeed? Just play it by ear?
Last edited by Zonkor; 24th May 2013 at 22:16.
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I actually do it on my twin all the time, which is not normally what one does with twins, but she's a bit of a bush plane so I feel it's appropriate...
I just leave a lot of margin speed-wise and never had any troubles. Even when I've gone full deflection on rudder. But I generally keep the speed up to 80kts on final, even though she stalls at 56kts full flaps, so I have a lot of margin. Sometimes on shorter fields I'll let it get slower on final to reduce rollout and then I should remind myself not to do in such a scenario, at least not a severe one. Good you reminded me, actually.
I just leave a lot of margin speed-wise and never had any troubles. Even when I've gone full deflection on rudder. But I generally keep the speed up to 80kts on final, even though she stalls at 56kts full flaps, so I have a lot of margin. Sometimes on shorter fields I'll let it get slower on final to reduce rollout and then I should remind myself not to do in such a scenario, at least not a severe one. Good you reminded me, actually.
Never had a need to do it at low speed - that's what flaps are for.
I've utilised slips a lot for losing excess speed toward the end of a short approach without cooling the engine too fast, just until slow enough that the flaps/gear can be lowered.
I've utilised slips a lot for losing excess speed toward the end of a short approach without cooling the engine too fast, just until slow enough that the flaps/gear can be lowered.
Set the aircraft up on a stable approach, note the attitude & then maintain that attitude during the slip. You should be able to come out of the slip reliably at the same indicated airspeed as before.
Practise at height - set up the approach, slip the aircraft & then raise the nose towards the stall. The types that I've tried this in have all run out of rudder authority & started to come out of the slip before stalling.
Practise at height - set up the approach, slip the aircraft & then raise the nose towards the stall. The types that I've tried this in have all run out of rudder authority & started to come out of the slip before stalling.
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No need to look at the airspeed indicator, as long as you don't increase angle of attack. If you start a sideslip and leave the elevator alone the speed shouldn't dissipate. In this case you just add a lot of drag but your angle of attack (speed) remains the same. If you start a sideslip and pull back on the yoke you would loose airspeed - as in every other condition of flight. Am I correct with this explanation?
Heston, a forward slip is a crosswind correction on final to align the aircraft with the runway. Which is in aerodynamic terms the same as a sideslip.
Heston, a forward slip is a crosswind correction on final to align the aircraft with the runway. Which is in aerodynamic terms the same as a sideslip.
Last edited by ArcticChiller; 25th May 2013 at 09:41.
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A forward slip is one done while not turning. All slips are 'opposite rudder and aileron'. The main thing when doing turning slips is ALWAYS USE RUDDER OPPOSITE TO THE DIRECTION OF TURN. In other words, if doing a slipping turn from left base to final, use left aileron with right rudder. Never over-rudder INTO the turn - that way lies the spin!
As has been said, the ASI will probaly be innacurate in a slip so judge speed using attitude. Don't let the speed build up during the slip as that negates the purpose of doing it (Steeper rate of descent without speed building up).
Some aeroplane come down like an upside-down Harrier when you slip - Cubs, for instance, their slab-sided fuselage providing lots of drag. Others, like the Chippy with its slender and cylindrical rear fuselage, benefit less (it's the drag generated by pushing the fuselage sideways through the air that increases the rate of descent for a given speed in a slip).
As has been said, the ASI will probaly be innacurate in a slip so judge speed using attitude. Don't let the speed build up during the slip as that negates the purpose of doing it (Steeper rate of descent without speed building up).
Some aeroplane come down like an upside-down Harrier when you slip - Cubs, for instance, their slab-sided fuselage providing lots of drag. Others, like the Chippy with its slender and cylindrical rear fuselage, benefit less (it's the drag generated by pushing the fuselage sideways through the air that increases the rate of descent for a given speed in a slip).
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Aerodynamically speaking a sideslip is the same as a forward slip. You fly through the air sideways, creating drag.
The different names are just there to distinguish a different purpose.
With a sideslip you are typically on the centerline, aligned with the centerline, but want to offset a crosswind. So you bank into the crosswind first, then use rudder to keep the fuselage aligned with the centerline.
With a forward slip you are again on the centerline (and there is no crosswind), but want to create more drag without drifting off the centerline. So you lead with the rudder, and then use the ailerons to keep the aircraft on the centerline.
In both cases you are slipping: not flying in the direction the nose is pointing, but partly sideways. The difference is where your nose is pointing. With a sideslip your nose is pointing to the runway, and the sideways component of the slip is used to offset the crosswind. With a forward slip your nose is pointing maybe 30 degrees to the side of the runway, but you are using the sideways component of the slip to stay on the centerline.
Just to add that it is perfectly possible to spin if you rudder the other way too. Again, aerodynamically speaking there's no difference, but psychologically you are more likely to pull, increasing AoA and eventually stalling into the spin, if you rudder into the turn. Furthermore, if you yaw against the turn the view of the final approach typically gets better as the nose of the aircraft is no longer in the way.
The different names are just there to distinguish a different purpose.
With a sideslip you are typically on the centerline, aligned with the centerline, but want to offset a crosswind. So you bank into the crosswind first, then use rudder to keep the fuselage aligned with the centerline.
With a forward slip you are again on the centerline (and there is no crosswind), but want to create more drag without drifting off the centerline. So you lead with the rudder, and then use the ailerons to keep the aircraft on the centerline.
In both cases you are slipping: not flying in the direction the nose is pointing, but partly sideways. The difference is where your nose is pointing. With a sideslip your nose is pointing to the runway, and the sideways component of the slip is used to offset the crosswind. With a forward slip your nose is pointing maybe 30 degrees to the side of the runway, but you are using the sideways component of the slip to stay on the centerline.
Never over-rudder INTO the turn - that way lies the spin!
Last edited by BackPacker; 25th May 2013 at 11:16.
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Well, to back up Heston it's an expression I've never heard in 30 years and nearly 20,000 hrs flying...
A peculiarly American distinction. Referred to as such in various FAA publications.
The rest of us just do a slip to suit whatever the need may be at the time without giving this and that purpose different and fancy names.
A peculiarly American distinction. Referred to as such in various FAA publications.
The rest of us just do a slip to suit whatever the need may be at the time without giving this and that purpose different and fancy names.
In general, there are more pro-spin forces and moments in a skid than a slip.
Most of my students get to experience both. In the airplanes I use, a stall in a skidding turn results in an aggressive entry to a spin cf to a sideslip which is spin-resistant.
Most of my students get to experience both. In the airplanes I use, a stall in a skidding turn results in an aggressive entry to a spin cf to a sideslip which is spin-resistant.
I think the practical difference between a skid and a slip on approach is that if you stall out of a slip the aircraft will more typically roll 'over the top' (reducing bank angle) which allows the pilot time to reduce angle of attack. Conversely, stalling out of a skidding turn rapidly increases bank angle in the same direction. There is no aerodynamic difference, but gravity and the horizon aren't aerodynamic factors.
In the Cessna Aerobat flight manual there is an exercise in which the aircraft is stalled out a slip, the pilot reduces angle of attack as the aircraft rolls through level, and the plane ends up banked equally in the opposite direction. Repeating causes the plane to fly an S-turn.
In the Cessna Aerobat flight manual there is an exercise in which the aircraft is stalled out a slip, the pilot reduces angle of attack as the aircraft rolls through level, and the plane ends up banked equally in the opposite direction. Repeating causes the plane to fly an S-turn.
Last edited by Silvaire1; 25th May 2013 at 14:34.
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The definitions of (side) slip and skid have nothing whatsoever to do with centrelines, runways, or anything else of a geographical nature.
They describe only regimes of unbalanced flight.
They describe only regimes of unbalanced flight.
The definitions of (side) slip and skid have nothing whatsoever to do with centrelines, runways, or anything else of a geographical nature.They describe only regimes of unbalanced flight.
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the horizon is typically normal to the direction of gravity.
Yes, you can spin off a sideslip with out-turn rudder, but it's much less likely than during one with in-turn rudder. The latter is really asking for the nose and inside wing to suddenly drop in the direction turn and at circuit height what follows will be a brief death spiral of half a turn or less.
Last edited by Shaggy Sheep Driver; 25th May 2013 at 19:24.
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"Forward slip". Although there is tecnically no such thing & geographics don't come into it. If you apply, frinstance, right rudder & left aileron on (geographic) final with a stiff left hand crosswind, the a/c will point down the runway, track down the runway, with left wing down a bit. Geographically forward but side slipping with respect to wind.
My silly opinion.
My silly opinion.
In the Cessna Aerobat flight manual there is an exercise ...
Compare with the aggressive spin entry from a skidded turn to a stall.
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How large do you consider the risk? How about during a side-slip base-to-final?
As was pointed out in an earlier post the ASI is essentially irrelevant to safely perform a slip. As long as the correct gliding pitch attitude is maintained you can't stall.
Your average Piper/Cessna is rudder limited so you will reach maximum rudder travel at quite modest bank angles. However a slipping turn will allow you to increase the bank angle and therefore increase the sink rate. Therefore the maximum possible sink rate will be a power off full flap glide in a slipping turn, something that could be a lifesaver in the event of a forced approach.
Personally, for low time pilots, I discourage slipping on final in Cessna's. They have effective flaps so if you are so high that full flaps and idle power is not enough to make your selected touchdown point, I think the approach is so far from the ideal flight path you should just go around rather than pushing a bad approach by slipping.
Your average Piper/Cessna is rudder limited so you will reach maximum rudder travel at quite modest bank angles. However a slipping turn will allow you to increase the bank angle and therefore increase the sink rate. Therefore the maximum possible sink rate will be a power off full flap glide in a slipping turn, something that could be a lifesaver in the event of a forced approach.
Personally, for low time pilots, I discourage slipping on final in Cessna's. They have effective flaps so if you are so high that full flaps and idle power is not enough to make your selected touchdown point, I think the approach is so far from the ideal flight path you should just go around rather than pushing a bad approach by slipping.
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I agree, if for some reason you feel the need to slip always use the aileron to turn and opposite rudder to prevent a cross control stall. Once on final forward slip all you want. I have done it hundreds of times with no problem. Skidding on to final with rudder and opposite aileron will get you. Art Scholl taught me that in the 60's and he was one of our finest aerobatic pilots. He gave me the honor of teaching his aerobatics course at Flabob airport in Riverside, Ca. I was the guy that flew his clipped wing cub to all of his air shows.