AoA and IAS in Forward Slip?

[iaw4]

 

Without an AoA indicator and better aerodynamic knowledge, I don't know how much lift a forward slip consumes.

What indicated airspeed is safe in a full-rudder forward slip for the CTSW?  With 15 degree flaps?  Is a constant 50 knots IAS (i.e., slow flight nose up maintaining 50) abundantly safe?

 

[FlyingMonkey]

7 hours ago, iaw4 said:

 

Without an AoA indicator and better aerodynamic knowledge, I don't know how much lift a forward slip consumes.

What indicated airspeed is safe in a full-rudder forward slip for the CTSW?  With 15 degree flaps?  Is a constant 50 knots IAS (i.e., slow flight nose up maintaining 50) abundantly safe?

 

I don't know that a slip "consumes lift"...I think it's more accurate to say a slip adds drag.

I perform a LOT of slips in my CTSW.  I use them on probably 50% of my landings, as I feel it's safer to be high and use a slip than be low on approach.  Here is what I've found:

*  The nose tends to drop in a slip.  You will probably have to add some stick back pressure to avoid picking up speed.  If you don't do this the additional speed will negate some of the sink rate you are trying to achieve with the slip, and at the bottom you'll have to deal with the extra speed, which probably means floating more than you want.  Just adjust the stick pressure as needed to maintain your target speed.

*  On my CT I have not found any IAS change in the slip, meaning the stall speeds still seem to hold.  I generally like 50-55kt at 15° flaps, and 48-52kt at 30° flaps.  Every airplane and pilot are a little different, so I'd try to hold the high number on these ranges and see how they work for you, then experiment with various speeds to see what works for you.

*  The lower the speed you use, the more you need to actively take out the slip.  That means that when you want to remove the slip, you can't just let off on the rudder pedal you are using to slip, you might have to push a little on the opposite pedal for the slip to come out quickly enough for you.  When slipping down low to the ground this has surprised me a time or two; it's never been a problem, but it is a thing.

* Remember if at any point in the approach you don't like what's happening, you can always go full power and GO AROUND.

 

Good luck and enjoy your slips!   

[iaw4]

 

great advice.  thanks.

do you do full deflection on the rudder/aileron slips?

ever get close enough to a stall to notice stall buffeting?

 

yes, the point is drag.  I just wonder what happens to the stall speed in a slip.  presumably, with a little less wing available for lift straight-on, Vs should increase.  our little winglet at the wing end probably plays a role here, too; this winglet probably means a little more loss of lift as it presents itself more forward into the flight direction.  (the Skyview flyers can probably give an estimate by looking at their AoA display.)

 

/iaw

 

[FlyingMonkey]

3 hours ago, iaw4 said:

 

great advice.  thanks.

do you do full deflection on the rudder/aileron slips?

ever get close enough to a stall to notice stall buffeting?

 

yes, the point is drag.  I just wonder what happens to the stall speed in a slip.  presumably, with a little less wing available for lift straight-on, Vs should increase.  our little winglet at the wing end probably plays a role here, too; this winglet probably means a little more loss of lift as it presents itself more forward into the flight direction.  (the Skyview flyers can probably give an estimate by looking at their AoA display.)

 

/iaw

 

Yes, I do full rudder deflection, coupled with whatever aileron it takes to hold the ground track I'm trying to maintain.  I almost always slip with right rudder and left aileron, since it puts the pilot side forward and lets me see where I'm going better.  I can't remember the last time I slipped the other direction other than just demonstrating slips to both sides.

I'm sure that slip aerodynamics are complex, and I don't claim to understand it fully.  But It seems to me that the stall speed doesn't change in a slip, since the wing is still making lift normally and the g loading is still 1.  What can definitely change is the accuracy of the airspeed indicator as the air might not be hitting the pitot tube as efficiently as if you were flying straight and level.  Though you could also argue that the component of the relative wind hitting the wing head on is what is still being measured by the pitot tube, and thus the stall number should remain accurate.  I might have this entirely twisted, and if so I'm sure somebody will correct me.

I do know that I have done many full slips with 30° flaps down to 48kt and not encountered any stall indications.  As for buffeting, my experience is that the CT does not buffet much close to the stall, whether in a slip or not.  Instead the controls soften up, the nose wants to lower, and the sink rate increases.  Simply releasing back pressure on the stick and/or adding power gets it flying again almost instantly.

[WmInce]

5 hours ago, FlyingMonkey said:

I don't know that a slip "consumes lift"...I think it's more accurate to say a slip adds drag.

I perform a LOT of slips in my CTSW.  I use them on probably 50% of my landings, as I feel it's safer to be high and use a slip than be low on approach.  Here is what I've found:

*  The nose tends to drop in a slip.  You will probably have to add some stick back pressure to avoid picking up speed.  If you don't do this the additional speed will negate some of the sink rate you are trying to achieve with the slip, and at the bottom you'll have to deal with the extra speed, which probably means floating more than you want.  Just adjust the stick pressure as needed to maintain your target speed.

*  On my CT I have not found any IAS change in the slip, meaning the stall speeds still seem to hold.  I generally like 50-55kt at 15° flaps, and 48-52kt at 30° flaps.  Every airplane and pilot are a little different, so I'd try to hold the high number on these ranges and see how they work for you, then experiment with various speeds to see what works for you.

*  The lower the speed you use, the more you need to actively take out the slip.  That means that when you want to remove the slip, you can't just let off on the rudder pedal you are using to slip, you might have to push a little on the opposite pedal for the slip to come out quickly enough for you.  When slipping down low to the ground this has surprised me a time or two; it's never been a problem, but it is a thing.

* Remember if at any point in the approach you don't like what's happening, you can always go full power and GO AROUND.

Excellent tips!

[CT2K]

Excellent tips indeed

[iaw4]

On 8/26/2019 at 7:09 AM, FlyingMonkey said:

*  On my CT I have not found any IAS change in the slip, meaning the stall speeds still seem to hold.  I generally like 50-55kt at 15° flaps, and 48-52kt at 30° flaps.  Every airplane and pilot are a little different, so I'd try to hold the high number on these ranges and see how they work for you, then experiment with various speeds to see what works for you.

1

 

At 15" flaps with a full-deflection rudder slip and nose-up, you would recommend 50 knots IAS.    One more question: Have you experimented with the stall speed in this setting?  That is, does the safety margin reach down to 45 knots IAS?

[Brian]

Instead of asking others what works for them, you should get your instructor, go up to a safe altitude in your plane, find a straight road to follow, set a "hard floor" altitude as a simulated runway and then try slips in various configurations and find out what works for YOU. Then practice slips until you're comfortable with them.

[FlyingMonkey]

2 hours ago, Brian said:

Instead of asking others what works for them, you should get your instructor, go up to a safe altitude in your plane, find a straight road to follow, set a "hard floor" altitude as a simulated runway and then try slips in various configurations and find out what works for YOU. Then practice slips until you're comfortable with them.

Agreed.

And to be clear, I recommended you start with the *high* end of the speed ranges I listed, e.g. 55kt and *not* 50kt at 15° flaps.  Don't go out and start out at the minimum speeds I listed; if your airplane is rigged differently from mine, or just has tundra wheels (my doesn't), my lower end indicated speeds might be too slow to be safe in your airplane.

[Ed Cesnalis]

I slip a lot, I always hit the numbers at home and I need to use a slip to do that because my judgement from abeam isn't that good, usually short.

Slips are useful for another reason not yet discussed. I slip at higher speeds so I keep my margin from stall and my clean configuration so I can abort and escape quickly and not near stall, not in flap range.

The mountains I frequent are really big and relatively speaking higher CT speeds are still quite slow.  Shear is a big concern so I always keep my speed up.  Often I need a steep descent so I slip it at a higher speed in a clean config.

tl;dr;  slips are useful for steep descents at higher speeds above flap speeds

[iaw4]

7 hours ago, Brian said:

Instead of asking others what works for them,

 

 

"in addition to asking others what works for them" ...