Can a really aggressive forward slip on final ever produce a spin?

[Andy95W]

35 minutes ago, RobertE said:

I think those stall speeds at varying level of bank angle presume level flight.  So the predicted stall speed at, say, a 20% bank angle while descending on final would be higher than shown in the POH.  How much higher??  Hmm.  No idea.

Actually, the stall speed in a descending, 20° bank base-to-final turn at 1G would be the same or less, not more, like Vance noted above.

I can only imagine that now we're going to have yet another discussion of 80 mph on final being too fast (it is) and Mike will chime in with AOA is all that really matters (it is, but that doesn't mean that all of us have AOA indicators in our airplanes).

[RobertE]

2 hours ago, N1395W said:

Actually, the stall speed in a descending, 20° bank base-to-final turn at 1G would be the same or less, not more, like Vance noted above.

I can only imagine that now we're going to have yet another discussion of 80 mph on final being too fast (it is) and Mike will chime in with AOA is all that really matters (it is, but that doesn't mean that all of us have AOA indicators in our airplanes).

I'm not trying to be argumentative here but am trying to learn (hey, I know argumentative because that's my specialty!).  Doesn't any level turn impose more than 1 G?  So there is no such thing as a 1 G, level, 20 degree turn?  I know your reference was to 1 G in a descending turn but the tables that contrast stall speed with bank angle are, by definition, more than 1 G turns, no? 

Looked at differently, a descending, 20 degree 1 G turn would have a stall speed that matched whatever the POH defined as stall speed in straight ahead flight, I think.

 

 

 

[pinerunner]

3 hours ago, N1395W said:

Actually, the stall speed in a descending, 20° bank base-to-final turn at 1G would be the same or less, not more, like Vance noted above.

I can only imagine that now we're going to have yet another discussion of 80 mph on final being too fast (it is) and Mike will chime in with AOA is all that really matters (it is, but that doesn't mean that all of us have AOA indicators in our airplanes).

80 mph on final is for the long runways I usually frequent. It gives me a nice easy flare with not too much float. For shorter strips (2150 shortest so far) I slow down to a little above 70 mph (my 64 E model isn't calibrated in nm/hr). 

I think once you're established at a constant rate of descent those tables are close to the actual G-forces. In level flight 1.06 G for 20 degrees so not much different than one. I'm aware that in an extreme angle of ascent or descent the forces can be less (i.e. in a wingover you can pull zero G in the turn so no stall even though your airspeed drops to near zero; but you pull a lot of G's when you pull up or level off) but I think the angle of descent in a standard pattern is so modest that I'd rather not take it into consideration.

 

Edited December 9, 2016 by pinerunner

[Andy95W]

4 hours ago, RobertE said:

I'm not trying to be argumentative here but am trying to learn (hey, I know argumentative because that's my specialty!).  Doesn't any level turn impose more than 1 G?  So there is no such thing as a 1 G, level, 20 degree turn?  I know your reference was to 1 G in a descending turn but the tables that contrast stall speed with bank angle are, by definition, more than 1 G turns, no? 

Looked at differently, a descending, 20 degree 1 G turn would have a stall speed that matched whatever the POH defined as stall speed in straight ahead flight, I think.

I agree- the tables are all showing a level turn, so therefore more than 1G.  And I agree, a descending 20° banked 1G turn should have the same stall speed as if it were in straight and level flight.  And if the pilot in a 20° banked turn were to allow the nose to fall as the vertical component of lift were removed, you would end up further from the critical angle of attack and therefore more MPH from a stall.  I probably said something wrong earlier.

I was hoping somebody else would step in that could explain better than me (I'm a CFI but haven't really instructed in almost two decades).

I really liked what pinerunner noted above, you can be in a wing-over at 90° bank with zero airspeed at 0G but never exceed the critical angle of attack and not stall.

 

[Yetti]

On 12/7/2016 at 9:23 PM, 201er said:

I don't really see it that way. I don't see a slip as a place I intentionally want to stay in any longer than I need to. I'm not flying a taildragger that you can only see ahead if you're flying sideways to land. I'm not going to make "fine" height adjustments through a slip. It is all or nothing. The impact of the slip is controlled with time. How long do I need to hold this full slip to join the desired glidepath. 3 seconds or 7 seconds? I'm already high when I revert to a slip so the sooner I can get on glidepath the better. By going full, I will get there sooner. And when I get there, I will let off the slip. Simple as that.

I think you have to slip to do a one main landing in a cross wind.  I have gone from a crab to a slip with the upwind wing down after having the tail get knocked around twice.  all this was done right above the runway.  and no there was not full rudder deflection. Just a little one.  also I was taught that you come off full rudder deflection to move right or left to line up the runway. But hey I am here to learn and interested in others thoughts.

[midlifeflyer]

1 hour ago, Yetti said:

I think you have to slip to do a one main landing in a cross wind.  I have gone from a crab to a slip with the upwind wing down after having the tail get knocked around twice.  all this was done right above the runway.  and no there was not full rudder deflection. Just a little one.  also I was taught that you come off full rudder deflection to move right or left to line up the runway. But hey I am here to learn and interested in others thoughts.

Yes, but the context indicates he is referring to forward slips (altitude loss) and not sideslips (crosswind correction). Yes, they are the same aerodynamically, but the purposes are different.

If the purpose is losing excessive altitude not correctable by simply adjusting pitch and power in coordinated to increase descent rate I'll do the same as @201er - put in a full correction until I my glidepath is adjusted and then return to coordinated flight.

OTOH, if the purpose is to maintain lack of drift and proper alignment for a crosswind landing, sure, that's finesse since you are using only the amount needed to correct. But even then, the closer one gets on the crosswind "slip all the way vs crab & kick" continuum,  the less time you are keeping even a sideslip in place and, at least arguably, in a pure crab & kick you are quickly going to full deflection since that what you do on the roll out.

Pretty much a choice of technique issue.

[201er]

And then there's the forward side slip...

A little high with a cross wind. You decide to do a forward slip to lose height. But to avoid drift you might have to slip additionally for the crosswind. Or do a forward slip with crab angle.

[smccray]

On 12/7/2016 at 8:42 PM, 201er said:

I do full rudder deflection forward slips lots of times to lose height. I can't slip any "more aggressively" because I am already at full rudder. Forward slips are always done at full rudder because in a slippery Mooney, even at full deflection you don't get much so there's no point in doing it unless you take it all. So, in a cross-wind side slip, there's nothing to worry about as long as you enter with normal approach angle of attack and don't pull back while executing the slip.

I even do turning slips sometimes to lose height. This is where you go full opposite rudder and aileron beyond a forward slip so that you turn with the nose lagging behind the turn. As long as the nose is down, wings unloaded, this is safe as well.

 

Interesting discussion.  I've heard the discussion about not performing forward slips in a Mooney, and I've also heard that it's primarily long bodies.  I didn't know... I ended up developing a different strategy early in my Mooney training to loose altitude if I'm high, and I've never had to do a forward slip (and not because my approaches are always perfect).  If I slow my J down below 80 kias with full flaps and I pull the power; the plane quickly compensates for an approach that is too high.  I've never been in a position where I didn't recognize that I was too high so late that this approach couldn't' compensate for the approach, but I do fly into long runways.  I prefer keeping my speed up and slowing down late to 70kias over the numbers.

[midlifeflyer]

1 hour ago, smccray said:

 

Interesting discussion.  I've heard the discussion about not performing forward slips in a Mooney, and I've also heard that it's primarily long bodies.  I didn't know... I ended up developing a different strategy early in my Mooney training to loose altitude if I'm high, and I've never had to do a forward slip (and not because my approaches are always perfect).  If I slow my J down below 80 kias with full flaps and I pull the power; the plane quickly compensates for an approach that is too high.  I've never been in a position where I didn't recognize that I was too high so late that this approach couldn't' compensate for the approach, but I do fly into long runways.  I prefer keeping my speed up and slowing down late to 70kias over the numbers.

Of course. Forward slips are primarily to correct for height that, due to proximity, can't be corrected that way. It's just another tool.

But one can be in that position even with the best of planning, with the choice being to slip or go-around, both being quite acceptable.

[201er]

44 minutes ago, midlifeflyer said:

Of course. Forward slips are primarily to correct for height that, due to proximity, can't be corrected that way. It's just another tool.

But one can be in that position even with the best of planning, with the choice being to slip or go-around, both being quite acceptable.

Some approaches (such as clearing trees or hills on short final) won't be solved with a go-around.

 

And I recognize the slow down to behind the drag curve method as another way to lose height. On a calm or steady headwind day this is very effective. However, on a gusty or turbulent day, it may be a terrible idea to be at such high angle of attack so low to the ground with so little margin. A forward slip can create additional drag/sink at a lower angle of attack (faster airspeed for the oldies) without compromising on lift reserve (stall margin).

Edited December 9, 2016 by 201er

[midlifeflyer]

1 hour ago, 201er said:

Some approaches (such as clearing trees or hills on short final) won't be solved with a go-around.

 

And I recognize the slow down to behind the drag curve method as another way to lose height. On a calm or steady headwind day this is very effective. However, on a gusty or turbulent day, it may be a terrible idea to be at such high angle of attack so low to the ground with so little margin. A forward slip can create additional drag/sink at a lower angle of attack (faster airspeed for the oldies) without compromising on lift reserve (stall margin).

There are always situational variations. We have multiple tools because we have multiple needs.

BTW, what's your thing with angle of attack vs airspeed? And I'm not sure what age has to do with it. I was taught the term "stall speed" applied to a specific configuration but that an aircraft can stall at any airspeed. Not sure if I'm an "oldie" though.

[kpaul]

25 minutes ago, midlifeflyer said:

BTW, what's your thing with angle of attack vs airspeed? And I'm not sure what age has to do with it. I was taught the term "stall speed" applied to a specific configuration but that an aircraft can stall at any airspeed. Not sure if I'm an "oldie" though.

Don't get him started!

[midlifeflyer]

10 hours ago, kpaul said:

Don't get him started!

Don't spoil the fun! 

[PTK]

On 12/7/2016 at 10:23 PM, 201er said:

I don't really see it that way. I don't see a slip as a place I intentionally want to stay in any longer than I need to. I'm not flying a taildragger that you can only see ahead if you're flying sideways to land. I'm not going to make "fine" height adjustments through a slip. It is all or nothing. The impact of the slip is controlled with time. How long do I need to hold this full slip to join the desired glidepath. 3 seconds or 7 seconds? I'm already high when I revert to a slip so the sooner I can get on glidepath the better. By going full, I will get there sooner. And when I get there, I will let off the slip. Simple as that.

I don't look at it as time. It's to whatever degree it's needed.

The trick in a forward slip is to balance aileron and rudder to lose the extra altitude while maintaining approach speed. 

How fast you lose altitude i.e. the impact of the slip or sink rate is determined by angle of bank. The steeper your bank the faster you come down. The limiting factor is your available rudder. Any excess bank angle over and above available rudder will cause a turn in the direction of bank.

So the impact of the slip is controlled by bank angle and available rudder to keep from turning away from the runway.

[Hank]

3 hours ago, PTK said:

I don't look at it as time. It's to whatever degree it's needed.

The trick in a forward slip is to balance aileron and rudder to lose the extra altitude while maintaining approach speed. 

How fast you lose altitude i.e. the impact of the slip or sink rate is determined by angle of bank. The steeper your bank the faster you come down. The limiting factor is your available rudder. Any excess bank angle over and above available rudder will cause a turn in the direction of bank.

So the impact of the slip is controlled by bank angle and available rudder to keep from turning away from the runway.

Yeah, that's how the rest of us do it. But Mike does it with one bank angle--rudder to the floor and aileron to compensate, so his only control is time. We vary bank angle and time, he can only vary time.

[Hank]

On ‎12‎/‎8‎/‎2016 at 2:10 PM, pinerunner said:

One more thing I 'd like to add to this discussion. I was reading through my operating manual not long ago and came across the table of stall speeds as a function of bank and flap setting. I found it very sobering to note the stall speeds quoted for no flaps in various banks because those speeds started to get close to my approach speeds of 90 mph and 80 mph on final. I've hadn't considered a no flap landing to be a big no-no but now I feel differently. I suppose if you keep speeds up and make very shallow turns its possible to be safe but I can't think of a reason for doing that. 2 notches of flap after reaching 90 mph and BEFORE the first turn.

I'm not flying a cub anymore.

I get the flaps up pretty quick after takeoff to avoid exceeding the max flap extension speed. Then I can drop the nose for better cooling. Shallow turns until over 100 mph are the order of the day there.

And now you know why No Flap landings are done at a higher airspeed. Still listen for the stall horn just before touchdown, but recognize that you will be at higher airspeed and groundspeed.

As for flap retraction after takeoff, I don't use flaps very often but by the time I'm higher than the trees, I pull them up. regardless of flap usage, I angle for 100 mph once I'm clear of any obstacles [almost always trees]. The quickest turnout I've ever made was well over 200' agl,and since I don't live or fly near the Redwood forests, turning below 100 mph is not something that I every do. At my old home, I did used to turn crosswind at 400-500 agl to avoid D airspace, but even then had to pull power to avoid blowing through TPA for pattern work well before the downwind turn.

[Hank]

On ‎12‎/‎8‎/‎2016 at 2:10 PM, pinerunner said:

 

dp

Edited December 10, 2016 by Hank

[Hank]

triple post . . . Haven't done this in a while!

Edited December 10, 2016 by Hank

[Hank]

Hey, look! My first ever Quadruple post!!    

And while editing these three extra posts, I've not been able to select text. But right-clicking did bring up "select all," very handy for deleting.

Edited December 10, 2016 by Hank

[jlunseth]

I think any time you may need a forward slip to make a landing you should be putting the control surfaces to use first.  Full flaps act as a pretty good air brake and if you have them, speed brakes are a big help too.  Gear should be down too, but if you are landing and don't have that done by the time you need a forward slip you have bigger problems.  I have done a few pretty exciting landings with just the control surfaces.  Most of them have been power off 180's in practice.  It teaches you to - I call it "helicopter" in for a landing.  Another useful tool in the pack is to reduce speed below best glide, because you can safely with the flaps down.  I generally accomplish that by keeping the nose up slightly, "whoa nelly."  I once did such a landing at the end of a CTL approach in IMC with an instructor on board.  When we got to the landing end of the runway there was a wall of rain and if we entered it we were going to have to go missed, so with the gear and flaps deployed I powered the plane up to about 80% to make the sharp turn from downwind without stalling, then we were about 400 feet directly over the runway so I helicoptered in.  A little power right at the end made the landing perfect.  

The K's and later, as Carusoam noted, have a reputation for not doing well with the forward slip.  Apparently the elevator is shadowed and a stall can result.  So I avoid it and use other means to get down.  I can do an aggressive forward slip in my K, but I always do it with the flaps deployed and the speed up - best glide at least which is 81 kts.  I find the helicopter technique using all the control surfaces is all I normally need and does not require cross control.

[bonal]

Good points but my C has no speed breaks and I can't deploy flaps until 100mph perhaps the long bodies aren't best suited for aggressive forward slips but for a short body it's an effective tool to control a descent. And as I pointed out many of the fields I frequent are close to mountains and I like a lot of AGL when flying above them. I think being able to control an aggressive slip is really showing an understanding of how aerodynamics work on my airplane not to mention they're fun.

[thinwing]

On 12/7/2016 at 8:24 PM, Cruiser said:

here is a copy and paste of what you are looking for.......

I also attached the link here.... http://www.donkaye.com/donkaye.com/Bob_Krommer_on_Mooney_Slips-Part_2.html

 

From the Mooney List December 3, 2005 by Bob Kromer

 

SLIPPING A MOONEY

 

Went up to the attic last night and dug through my old flight test data sheets from my Engineering Flight Test days at the factory.  I did find the observed data for the slip tests I did.  Looked over the data.  From those test results, here is some additional information that might help answer some of the questions that have been raised:

 

1.  The data shows that it's the airplanes that require lots of nose up trim for landing that are the most prone to experiencing the tail buffeting condition we talked about earlier when aggressively slipping at or below 85 KIAS.  We simply could not get the M20J prototype to buffet in a full rudder sideslip at any CG and flap condition tested, down to 1.1 Vstall.  From those test results, I think it is safe to say that the Pre-J models and the J model itself will not experience any tail buffeting/partial airflow separation over the horizontal tail in an aggressive sideslip maneuver.  So the J and Pre-J models should be okay for slipping on approach.  Not comfortable, and in my humble opinion not the way to fly a high performance airplane like a Mooney, but safe.

 

2.  It's the K models (and variations ther3of) and the "long body" models that showed the possibility of inducing a partial horizontal tail airflow separation in an aggressive sideslip condition.  I got it in both the Mooney/Porsche and the M20K model prototypes in the landing approach configuration.  These are the airplanes that require almost full (if not full) nose up trim for a hands off, trimmed condition on final approach. (Sometime, run your pitch trim to the full nose up position on the ground and look at the negative angle of attack of the horizontal tail.  Quite impressive). It's this high negative angle of attack with full nose up trim that puts the airflow over the horizontal tail at a fairly extreme condition.

 

3.  Extending the flaps adds to the downwash angle over the horizontal tail, making the negative angle of attack over the horizontal tail even greater. Mooneys spend a lot of their time at or near forward CG.  As the CG moves forward the need for more nose up trim on the approach is required for trimmed flight.  So does lower airspeed.  So the worse condition for aggressive slipping in the K and up models is slow, forward CG, full flaps - just like we are when configured for landing.  Remember, it's anything that requires the need for more nose up trim that adds to the possibility of experiencing horizontal tail buffeting when aggressively slipping on the

approach.      

 

4.  Aggressive slipping does strange things to the local airflow over the horizontal tail.  The bottom line is this - the horizontal tail will see a greater negative angle of attack in the slip maneuver.  So add an aggressive slip to the conditions noted in #3 above and you can experience the partial airflow separation over the horizontal tail and the resulting buffeting that we found in the flight tests. The Mooney is such a good design that there is no danger here - just a buffet in the control wheel from the elevator, a slight nose down pitching moment and a little loss of elevator effectiveness.  But I want to emphasize - THIS IS NO PLACE TO BE FLYING. Add a little ice to that horizontal tail leading edge or a gusty crosswind requiring heavy elevator input and look out.  That minor buffeting and airflow separation can get worse.

 

5.  Someone asked what would happen to an airplane if the horizontal tail completely stalled.  The answer - bad news.  A sharp nose down pitching moment and a loss of elevator control would result.  With increased airspeed as a result of the nose down pitch, the tail might start flying again and elevator effectiveness might be restored.  But we're talking a loss of aircraft control here - a pilot's worse nightmare.  How much altitude might be lost in this loss of control experience?  A guess - 2000 feet.

 

6.  Incidentally, ground effect helps the condition - the downwash angle over the horizontal tail is slightly reduced with the wing/flaps in ground effect.  This reduces the local negative angle of attack of the air flowing over the horizontal tail - a good thing when it comes to stalling the

horizontal tail.

 

Again - the bottom line.  Aggressive slips in your Pre-J or J should be okay from a safety of flight viewpoint.  K models and up - margins here are thinner.  Chances are you might experience some tail buffeting in the K models and up when aggressively slipping - not a place to be.  From my flight test experience, I would avoid aggressive slips on approach in the K's and up.  The Mooney is a wonderful design, but all designs have their limits.  

 

I certainly don't have all the answers and would never claim to be an "expert" or tell anyone how they need to fly their airplanes, but maybe some of my engineering flight test experiences at Mooney will help you better understand your airplanes.  I've got lots of good data in my attic.  Hope to share more of it with you in the future.

 

Best Regards;

 

Bob Kromer

This is what I remember being warned about the Bravo..and I consider Bob Kramer as an expert..k

[Tony Armour]

 If needed I'll slip the Bravo but when I do the goal is to lose altitude so the nose is pointed down and the airspeed isn't a concern (because if anything it is high) Then if airspeed is an issue at the end of the "battle" , I'll just go/slip a little lower than necessary and then out of the slip, level off to lose speed and bingo everything is in place. Oh yea, full flaps and brakes out. 

Reading thru Bobs stuff and the talk about trim, when I'm slipping it's way way before I would be at full trim for a landing. If you don't have the altitude you want by the time to put a bunch of trim in then things are just too bad to land on this approach. I've had some screwed up approaches (pilot error) and some slam dunks and haven't had to do a low approach go around. I have it figured out well before then if I can get down.

[mike_elliott]

14 hours ago, thinwing said:

This is what I remember being warned about the Bravo..and I consider Bob Kramer as an expert..k

as Mooney's test engineer for the K's and M's, Bob Kromer is THE expert. One would be well served to pay attention to what he says about how to fly a Mooney, especially about aggressive slipping a long body with full flaps at low airspeeds. The rest of us can have our opinions, he has the data. One does not need to be reminded of the tragic Max Rae/Joel Smith/ David ? fatality to know the consequences of airflow separation on the tail, and that was a J. 

[Tony Armour]

Mike, was that due to a slip ? 

What do you feel about them with plenty of airspeed ? I just have never felt the first issue. I'll admit, I've never (that I recall) heard that slips could be an issue.