Question about slips

[BaronPete]

Hey guys,

Well with the ink fairly dry on my private pilot certificate, I'm still looking to polish on a few things.

I'm comfortable slipping the airplane, but I still get a bit nervous about getting in a cross controlled stall. I realize that your airspeed will read alot lower than it actually is due to the angle of relative wind, so I know there's not a specific "stall speed" of a given aircraft in a slip. That coupled with a fact that an aircraft can stall at any airspeed leads me to the nose. Is there a general rule of thumb kinda deal that would suggest your AoA is too high in a given slip?

I doubt I'd ever get one stalled, as I keep the nose fairly level when slipping, but this was just on my mind :crazy:

Thanks for your input!

 

[CDNPilotDave]

When you start to spin, the AoA was too high. It's a "feel" thing. I suggest getting the feel at altitude, not on final.

 

[MidlifeFlyer]

Two questions right back at you:

1. Do you have similar worries about crosswind landings?
2. Do you understand the difference between a slip and a skid and their relationship to entering a cross-controlled stall?

 

[CoffeeIcePapers]

Hey guys,

Well with the ink fairly dry on my private pilot certificate, I'm still looking to polish on a few things.

I'm comfortable slipping the airplane, but I still get a bit nervous about getting in a cross controlled stall. I realize that your airspeed will read alot lower than it actually is due to the angle of relative wind, so I know there's not a specific "stall speed" of a given aircraft in a slip. That coupled with a fact that an aircraft can stall at any airspeed leads me to the nose. Is there a general rule of thumb kinda deal that would suggest your AoA is too high in a given slip?

I doubt I'd ever get one stalled, as I keep the nose fairly level when slipping, but this was just on my mind :crazy:

Thanks for your input!

The aircraft can stall at any speed due to load factor. Generally, in a slip, there isn't enough load factor to make it stall at higher than published stall speeds.

 

[Cessna414JJB]

Best is really to go out with a competent CFI and play with the plane.
The "stall from a slip" is actually a good maneuver to gain a better feel for the airplane and start working available energy. If you can, do it in a glider initially. I think I learned the most about rudder use from glider flying. If you can't, read your POH on recommended max times and or flap settings. Cross control stalls can and should be demonstrated and practiced, but unfortunately it seems as if many CFI's are extremely uncomfortable with any stalls and spins. Remember that your airspeed indicator is really only a initial set up instrument and may read wrong once in the slip until shortly after coming out of it. Have fun!

 

[stesta5074]

I generally keep my speed double stall. The load factor isn't greatly increased but I question the accuracy of the pitot tube on older airplanes.

 

[BaronPete]

Two questions right back at you:

1. Do you have similar worries about crosswind landings?
2. Do you understand the difference between a slip and a skid and their relationship to entering a cross-controlled stall?

I understand the difference between the two, yes. As for their relationship, I just understand that if you stall an airplane when not in trim a spin will develop.

No real concerns when sideslipping for a cross wind landing.

 

[Cessna414JJB]

I understand the difference between the two, yes. As for their relationship, I just understand that if you stall an airplane when not in trim a spin will develop.

No real concerns when sideslipping for a cross wind landing.

A spin develops only with a developed stall and YAW. As you know yaw can be introduced by your ailerons (adverse yaw) which can, depending on plane make for a fuzzy experience.

 

[BaronPete]

When you start to spin, the AoA was too high. It's a "feel" thing. I suggest getting the feel at altitude, not on final.

Problem. The aircraft is a C150. Intentional spins prohibited per an AD. The kit may or may not have been installed, not sure.

The aircraft can stall at any speed due to load factor. Generally, in a slip, there isn't enough load factor to make it stall at higher than published stall speeds.

Ya, speeds are out the window, though.

Best is really to go out with a competent CFI and play with the plane.
The "stall from a slip" is actually a good maneuver to gain a better feel for the airplane and start working available energy. If you can, do it in a glider initially. I think I learned the most about rudder use from glider flying. If you can't, read your POH on recommended max times and or flap settings. Cross control stalls can and should be demonstrated and practiced, but unfortunately it seems as if many CFI's are extremely uncomfortable with any stalls and spins. Remember that your airspeed indicator is really only a initial set up instrument and may read wrong once in the slip until shortly after coming out of it. Have fun!

Ditto from above, I was acting as though little attention would be paid to the airspeed indicator during the maneuver until bringing the aircraft back into trim.

 

[CoffeeIcePapers]

Ya, speeds are out the window, though.

Not really. It may be slightly unreliable, but I doubt there will be a drastic change.. When doing a forward slip to land in a 150, you should probably aim to keep it about 5 knots over your approach speed. As long as you keep a relatively low angle of attack, you won't stall. Think about how high the angle of attack is when you do a power off stall.

 

[BaronPete]

Not really. It may be slightly unreliable, but I doubt there will be a drastic change.. When doing a forward slip to land in a 150, you should probably aim to keep it about 5 knots over your approach speed.

If memory serves, when I go into the slip I usually read about 40 indicated

 

[BaronPete]

Not really. It may be slightly unreliable, but I doubt there will be a drastic change.. When doing a forward slip to land in a 150, you should probably aim to keep it about 5 knots over your approach speed. As long as you keep a relatively low angle of attack, you won't stall. Think about how high the angle of attack is when you do a power off stall.

Ya! This was how I had it in my head.. Just gonna keep the horizon in view, haha.

 

[tgrayson]

I realize that your airspeed will read alot lower than it actually is due to the angle of relative wind, so I know there's not a specific "stall speed" of a given aircraft in a slip.

That really depends on the airplane. Low end Cessnas, it may be higher, may be lower depending on the direction of slip. Probably won't see a lot of difference for the aircraft that have static ports on both sides of the fuselage. And I haven't noticed much change in the Pipers with the mast under the wing.

Even at worst, the airspeed inaccuracy isn't much. Maybe 5 knots? If you have your airspeed close to your normal approach speed, you won't be stalling the airplane.

as I keep the nose fairly level when slipping

Don't use your pitch attitude as a guide; it provides limited information regarding your AoA. Your airspeed indicator is trustworthy.

As for their relationship, I just understand that if you stall an airplane when not in trim a spin will develop.

Well, you'll get a wing drop and that *may* develop into a spin if you continue to hold those inputs.

If you stall in a slip, the high wing will drop first and you've got lots of time to recover. If you stall in a skid, you'd have to be super quick to avoid hitting the ground.

Edit: And don't slip at 40 KIAS. Try 65 KIAS or so.

 

[CDNPilotDave]

My comments come from when I owned an Aeronca Chief. I enjoyed (maybe over-enjoyed is more appropriate) being cross controlled and slipping to lose altitude. Airspeed is key. Appropriate rudder and aileron control will keep things on the "non-spinning" side of the coin. Avoid over intellectualizing this. Find a CFI that will help you explore the limits.

 

[Pilot Hopeful]

When I slip an airplane, say a Cessna 152, I am looking to maximize drag and increase the rate of descent without significantly increasing airspeed. If my normal approach speed in the C152 is 55 KIAS, then, in the forward slip, I adjust indicated airspeed according to the direction of the slip. For a forward slip with the nose right (i.e., maximum right rudder deflection), I would fly about 50 KIAS; for nose left, about 58 KIAS.

How did I select these numbers? I practiced forward slips at altitude. I noticed that if I neutralize the controls and return from the forward slip to a non-slip condition, then the indicated airspeed immediately returns to 55 KIAS.

Knowing how the relative wind, pitot tube, and static source affect indicated airspeed is important to achieve maximum performance in a slip. If aircraft attitude and indicated airspeed are not adjusted appropriately, then the slip is only an exercise in control movements, not one in controlling descent rate. I often observe students and other pilots add five to ten knots when performing a slip with the sole objective of avoiding a cross-controlled stall. Unfortunately, their misunderstanding of forward slips actually defeats the purpose of performing a slip in the first place: to maximize drag and increase the rate of descent without significantly increasing airspeed.

While the discussion above is mostly mechanical, I encourage all pilots to explore the "art" of slipping an aircraft. Go practice and SEE what a properly executed slip looks like. There is more to the slip than trying to replicate certain numeric values issued on a message board.

 

[TXaviator]

When you start to spin, the AoA was too high. It's a "feel" thing. I suggest getting the feel at altitude, not on final.

agreed. go do it a bunch at altitude, with a CFI who can handle spins.

its a feel. youll feel when the plane starts getting sloppy/mushy and wanting to cut into the spin. stay above that feel.

 

[subpilot]

I understand the difference between the two, yes. As for their relationship, I just understand that if you stall an airplane when not in trim a spin will develop.

No real concerns when sideslipping for a cross wind landing.

You are dangerously incorrect. A spin develops when a stall occurs and the airplane in uncoordinated, for example...during a slip. Being out of trim has no effect on whether the plane will spin or not.

 

[shdw]

then the indicated airspeed immediately returns to 55 KIAS.... purpose of performing a slip in the first place: to maximize drag

You realize best glide is 60 clean. With the application of flaps or if you are solo (less weight) your best glide is likely 55. Best glide = minimum drag = L/D max.

Do some tests, at altitude, and you will find at 45 knots or 65-70 knots your descent angle is greater than at 55 knots. Obviously you likely won't do 45 knots, so your better selection to increase your descent angle while remaining within limits is 65-70 knots. In a 152 that is.



OP

A challenge for anyone here: Go out and do a cross controlled stall (slip) at altitude with this set up:

Flaps = 20 (30 if approved by your POH)
Power = normal approach or idle
Airspeed = normal approach speed + 5-10 knots
Slip = full rudder deflection stabilized slip (30-40 degrees opposite bank)
Elevator = once stable yank to full aft and hold it there while holding full rudder

Observe the results and you will never be scared of a slipping stall again.

Unless your in an aerobat (possibly some higher performance birds) a slip stall will be the most boring, docile, stall you will ever experience. Skids will kill you, slips are stable.

 

[shdw]

Don't use your pitch attitude as a guide; it provides limited information regarding your AoA.

I disagree, while I still think the ASI should be monitored I believe understanding and properly flying a pitch attitude is far more accurate than people give it credit for. If you set your speed to 65, never look at it again, and keep your pitch attitude exactly how it is your airspeed will remain at 65.

Using kinesthetics you can adjust for any gusts. Plane crawls up your butt, slight pitch forward, aircraft falls away, slight pitch back, all while maintaining pitch attitude. In other words, keep the kinesthetic feel the same with any pitch needed, returning to your starting point (pitch) after each gust subsides.

See that pitch enough and you can toss that ASI out of the window and start looking outside, enjoy flying.

I realize I may be taking what you said to the extreme, if you just mean the ASI is accurate +/- a few knots then never mind. But if you really mean to not use pitch attitude then...:dunno:

 

[tgrayson]

If you set your speed to 65, never look at it again, and keep your pitch attitude exactly how it is your airspeed will remain at 65.

No, it depends on your drag profile. Your pitch attitude is a combination of AoA and descent angle. If you have a steeper angle of descent and you keep the same pitch attitude, then you've just increased your AoA.

Worst case scenario is a slipping turn, where you may be varying your bank angle between 20-45 degrees to ensure proper alignment to final. You'll need to constantly adjust your pitch attitude to maintain the same airspeed.