What happens during a slip on final?

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nathan.maxton

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I'm aware of how to perform a slip on final, my question is what exactly are the mechanincs during an awkward movenent such as the slip? How is airflow affected? Any aeronautical engineers out there?
 
nathan.maxton said:
I'm aware of how to perform a slip on final, my question is what exactly are the mechanincs during an awkward movenent such as the slip? How is airflow affected? Any aeronautical engineers out there?
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What's to know? You drop a wing into the wind to stop drift and you add opposite rudder to keep the nose aligned with the runway.

You are now set up for a spin if you stall too soon, your stalling speed(s) increase, You need to know what you're facts ahe
 
Mason said:
You are now set up for a spin if you stall too soon, your stalling speed(s) increase, You need to know what you're facts ahe
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Well if you need the FACTS rather than myth, disregard the above.

The stalling speed does NOT change (your airspeed indicator may be affected but the airplane for practical purposes stalls in a slip the same as it does coordinated).

Second, you're extremely unlikely to spin out of a slip even if you do stall.

Third, any stall is "too soon." Despite the nomenclature of a "full stall" landing, landings typically do not involve actually stalling the plane period.
 
The thing about the slip is that you are suddenly almost broadside to the airflow...instead of a nice clean profile that you nomally present with your nose into the wind, you have a ton more parasite drag on the airframe. That means you can drastically increase your rate of decent without increasing your speed.

Put simply, it's a way to bleed off energy in the approach when you're high.
 
What kind of slip? Forward slip to bleed altitude or a side slip to correct for crosswind?
 
VanDy said:
What kind of slip? Forward slip to bleed altitude or a side slip to correct for crosswind?
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I presume from the description of the "awkward movement" he's talking about the forward slip...
 
Mason said:
What's to know? You drop a wing into the wind to stop drift and you add opposite rudder to keep the nose aligned with the runway.

You are now set up for a spin if you stall too soon, your stalling speed(s) increase, You need to know what you're facts ahe
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I won't say it's impossible to spin out of a slip that leads to a stall, but in the planes we fly it's pretty dang close. The yaw moment is in the opposite direction of what's required to induce the spin.
 
Here's a simple experiment that might help the OP...

Next time you're driving, put your hand out the window, fingertips forward, and your hand held vertically like a karate chop. This represents your air frame when you're flying normally. Not that there is little wind resistance.

Then pull the heel of your hand toward you or push away from you, keeping your hand vertical, and fingertips forward. Note the increased wind resistance. This is what happens when you conduct a slip. You are putting more of the air frame into the relative wind and increasing wind resistance.

Nathan: A good book to pick up and read that explains this and more is Stick and Rudder: An Explanation of the Art of Flying by Wolfgang Langewiesche. This is an excellent book any pilot should have explaining the aerodynamics of an aircraft..
 
I like what you said there. I always thought of a slip as something akin to doing a belly flop into the water vs a dive. You are exposing more of the aircraft's skin to the direction of motion, and using the side of the aircraft as a huge brake, creating a crap ton of drag. The hand out the window thing is much better.
 
Mason said:
What's to know? You drop a wing into the wind to stop drift and you add opposite rudder to keep the nose aligned with the runway.

You are now set up for a spin if you stall too soon, your stalling speed(s) increase, You need to know what you're facts ahe
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Lol.

No.
 
- No significant stall speed increase. Use normal approach speed

- If you happen to stall the plane in a slip, you are already holding anti-spin rudder input. You are extremely unlikely to spin. Understand the difference between a skid and a slip. Stalling in a skid has you putting in pro-spin rudder, and is the precursor to a stall/spin accident.

- Drag is increased because you are flying the plane somewhat cockeyed through the air. A slip is a great way to lose speed/altitude if you are too high or hot on final.
 
EdFred said:
I won't say it's impossible to spin out of a slip that leads to a stall, but in the planes we fly it's pretty dang close. The yaw moment is in the opposite direction of what's required to induce the spin.
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I'd say the difference is that if you stall in a slip you have a good amount of time to make a normal stall recovery. If after you stall you continue to hold the slip input and back elevator for several seconds, the plane might come around and enter a spin in the direction you are holding the rudder.

OTOH if you stall in a skid, especially an accelerated stall at your usual 1.3Vso with bank and g-loading, that wing is going to tuck under instantly when the airplane stalls. Its like a 1/4 snap roll into a spin.
 
flyingron said:
Well if you need the FACTS rather than myth, disregard the above.

The stalling speed does NOT change (your airspeed indicator may be affected but the airplane for practical purposes stalls in a slip the same as it does coordinated).

Second, you're extremely unlikely to spin out of a slip even if you do stall.

Third, any stall is "too soon." Despite the nomenclature of a "full stall" landing, landings typically do not involve actually stalling the plane period.
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My landings in a tailwheel plane generally include a full stall about 1/32" above the runway. Well, at least that's my goal. :yes:

And welcome to the OP. You'll get plenty of fact-based advice here. Some of it might even be right.
 
I always thought a nice slip was kinda graceful. No pun intended :rolleyes:
 
dell30rb said:
I'd say the difference is that if you stall in a slip you have a good amount of time to make a normal stall recovery. If after you stall you continue to hold the slip input and back elevator for several seconds, the plane might come around and enter a spin in the direction you are holding the rudder.

OTOH if you stall in a skid, especially an accelerated stall at your usual 1.3Vso with bank and g-loading, that wing is going to tuck under instantly when the airplane stalls. Its like a 1/4 snap roll into a spin.
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I've not been able to initiate a spin with full cross control during a stall. Like you said it *might* happen, but that top side wing stalls out first, and all I tend to get is a plane with Parkinson's.
 
EdFred said:
I've not been able to initiate a spin with full cross control during a stall. Like you said it *might* happen, but that top side wing stalls out first, and all I tend to get is a plane with Parkinson's.
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Ask Tony what happens when you stall the RV while cross-coordinated. :D

It's a run ride where all the 'blue' turns to 'green' and vice-versa. Not to mention a couple thousand foot of altitude loss. No spin, though. Just finish the roll and keep on going.
 
CJones said:
Ask Tony what happens when you stall the RV while cross-coordinated. :D

It's a run ride where all the 'blue' turns to 'green' and vice-versa. Not to mention a couple thousand foot of altitude loss. No spin, though. Just finish the roll and keep on going.
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Yeah, but did you ease into that, or go really fast?
 
EdFred said:
I've not been able to initiate a spin with full cross control during a stall. Like you said it *might* happen, but that top side wing stalls out first, and all I tend to get is a plane with Parkinson's.
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Same, i've tried and was unsuccessful. But that's in a cub... based on my limited aerobatics experience in one, something like a decathlon with a symmetrical wing would probably eventually end up in a spin.
 
EdFred said:
Yeah, but did you ease into that, or go really fast?
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Eased into it. Trying to simulate a student 'cheating' their overshoot turn to final with too much rudder. It took a lot of control input to get to that point, but it finally went over.

He actually explained it before we did it "In the 172, one wing will wallow down and you can recover from the stall". In the RV, there wasn't much 'wallowing' going on. ha.
 
EdFred said:
I've not been able to initiate a spin with full cross control during a stall. Like you said it *might* happen, but that top side wing stalls out first, and all I tend to get is a plane with Parkinson's.
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When NASA tried to spin the 172, experienced test pilots could only force it to actually enter the spin about 50% of the time.
 
CJones said:
Eased into it. Trying to simulate a student 'cheating' their overshoot turn to final with too much rudder. It took a lot of control input to get to that point, but it finally went over.

He actually explained it before we did it "In the 172, one wing will wallow down and you can recover from the stall". In the RV, there wasn't much 'wallowing' going on. ha.
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So a skidding stall
 
I wish Jesse still had that video up of him slip stalling a plane from like 8000ft down to about 3000. Not a spin anywhere in sight.
 
alfadog said:
When NASA tried to spin the 172, experienced test pilots could only force it to actually enter the spin about 50% of the time.
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I once badly flubbed a power on stall recovery in my 182 and added the wrong rudder. Rolled rather quickly but once I relaxed the back pressure I was flying again. So even with lots of P factor and pro spin rudder you still need to be stalled to spin.

Biggest thing I learned that day was that I want going to make that mistake twice.
 
docmirror said:
My landings in a tailwheel plane generally include a full stall about 1/32" above the runway. Well, at least that's my goal. :yes:

And welcome to the OP. You'll get plenty of fact-based advice here. Some of it might even be right.
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I don't buy it. Your aircraft is not likely stalled in a 3 point attitude. Not being able to maintain level flight does not equate to.being stalled.
 
flyingron said:
I don't buy it. Your aircraft is not likely stalled in a 3 point attitude. Not being able to maintain level flight does not equate to.being stalled.
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Full stall in a taildragger will have the tailwheel touching down first.
 
flyingron said:
I don't buy it. Your aircraft is not likely stalled in a 3 point attitude. Not being able to maintain level flight does not equate to.being stalled.
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A. The design of the three point attitude of a TW aircraft is exactly at the stall AoA at the stall speed. There are slight differences based on other factors, but basically, when you stall in ground effect, your three tires will be level with the ground.

B. The landing flare in a TW aircraft is set up so that when the wheels touch, there is no more remaining lift(you are stalled). If there were, it would bounce the plane back into the air. It's been tested a billion times by novice TW pilots everywhere. (including me)

C. Unless you have a very powerful engine, and a very light load, you will not be able to maintain 'level flight' once stalled. Also a stall can be entered at many attitudes and speeds but it is not germane to the discussion of this case.
 
I know three pointers are often referred to as a "full stall" landing but I think that's not quite true. I feel at typical three point attitudes you are maybe 3 degrees AoA shy of a full stall.

At three point you are of course way behind on the L/D curve and that's why the plane will slow quickly on its own after touchdown, and be very hesitant to bounce
 
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dell30rb said:
I know three pointers are often referred to as a "full stall" landing but I think that's not quite true. I feel at typical three point attitudes you are maybe 3 degrees AoA shy of a full stall.

At three point you are of course way behind on the L/D curve and that's why the plane will slow quickly on its own after touchdown, and be very hesitant to bounce
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maybe 3 deg? Is that lightly loaded, at fwd CG? Is it near gross at aft CG? Is that with flaps? Without?

:D
 
dell30rb said:
Same, i've tried and was unsuccessful. But that's in a cub... based on my limited aerobatics experience in one, something like a decathlon with a symmetrical wing would probably eventually end up in a spin.
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Ren, the Super D won't spin out of a slip either, up to full deflection. Same for the Pitts. But that assumes you are setting up the slip like you would for landing - power off, at a slow airspeed, and then slowly creeping the elevator back in an attempt to approach a stall. Do this, and very few airplanes (aerobatic or otherwise) will spin. But of course, if you yank the elevator hard from a higher airspeed, or with power, you can snap it from a slip, which will decay into a spin if you keep holding the controls.
 
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whifferdill said:
Ren, the Super D won't spin out of a slip either, up to full deflection. Same for the Pitts. But that assumes you are setting up the slip like you would for landing - power off, at a slow airspeed, and then slowly creeping the elevator back in an attempt to approach a stall.
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Yeah that's what I was thinking, would probably take more back pressure than just enough to initiate a stall. In that case if you held the elevator once you felt the stall, i'd guess the plane would probably bob in and out of the stall for awhile and never spin.
 
docmirror said:
maybe 3 deg? Is that lightly loaded, at fwd CG? Is it near gross at aft CG? Is that with flaps? Without?

:D
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I'm guessing this is a test as the difference between three point attitude and stall angle of attack would remain the same regardless of load.

Flaps would make a difference however
 
dell30rb said:
I'm guessing this is a test as the difference between three point attitude and stall angle of attack would remain the same regardless of load.
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Yep, thing with the CWC though (which I'm sure you notice) is that at forward CG, you can't really rotate the airplane high enough to get it to critical AOA power off, if you slowly move the stick back, as for landing. You can have the stick all the way back, and only manage to touch down perfectly 3-point, rather than tailwheel first. The stick may be all the way back, but the plane isn't stalled yet. Can't really get a true stall when playing around at altitude either, if you approach it slowly, power off at fwd CG.

I like that the Cub sits on the ground so close to the actual stall attitude. Means you can land as slow as possible without banging the mains down. Lots of tailwheel airplanes sit quite a bit flatter than the stall attitude.
 
You know, I said landing at a stall and got made fun of by a bunch of old grizzly pilots. I know, the stall warning horn going off is not the same as aerodynamic stall, but c'mon old guys....
 
docmirror said:
A. The design of the three point attitude of a TW aircraft is exactly at the stall AoA at the stall speed. There are slight differences based on other factors, but basically, when you stall in ground effect, your three tires will be level with the ground.
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Nope. Not even close. The typical taildragger is about five degrees short of stall angle when in the three-point attitude. Most airfoils will stall at around 17 degrees; go measure the ground angle of a taildragger's wing and tell us what you find. Most will be around 12 degrees. All this talk of a full-stall landing is not applicable to the typical lightplane.

It's almost impossible to achieve it even with the CH701:

short.jpg



Dan
 
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