pkofman

Forward slips in a Bravo

Recommended Posts

11 minutes ago, alextstone said:

**Caution**:  You are about to read a comment meant to be part sarcasm and part humor, not to be taken too seriously:

Perhaps some transition training in a long body Mooney taught by @mike_elliottwould help you to understand how to handle crosswinds safely and effectively.  

I really don't have any trouble with crosswinds in the Mooney, which is surprising to me.  The way I dealt with bad crosswinds in my Cherokee was to speed up.  Can't do that too much in the Mooney, not at the airports I fly out of.  Part of how I deal with them is to put the airplane into a forward slip, to keep it aligned with runway.  Heck, I had to demonstrate a forward slip during my Private pilot check ride.  That said, while in the slip I speed up.  Stall speed goes up when you're cross controlled for a number of reasons.

That said, I honestly don't want to tell anyone who to fly their airplane.  Goodness knows they almost certainly to it better than I.  Just surprised hearing  this much grief over a fairly common maneuver.

  • Like 1

Share this post


Link to post
Share on other sites

*Members that donate $10 or more do not see advertisements*

Its as simple as this, in a forward slip which you use to descend and slow down, your "GROUND TRACK" is still Forward or straight to your destination - not off to the side  (even though nose is pointing to side). In a Side slip, your "Ground track" is moving to one side, into the wind when used for landing in a cross wind.

The Forward slip is typically much more cross controlled, perhaps all the way to the stops. Where as the Side slip is only done to the amount necessary to match the cross wind component.

But don't fret, aerodynamically they are equivalent. The difference is in the eyes of the observer, but just think of your "ground track" rather than where the nose is pointing and we'll all be on the same reference system with regard to semantics. :)  

  

  • Like 2

Share this post


Link to post
Share on other sites
27 minutes ago, jlunseth said:

The sideslip is the cross-controlled maneuver you use to keep the axis of the aircraft parallel to the center line and to keep the aircraft from moving to the right or left off the centerline during a crosswind landing.  The forward slip is the cross-controlled maneuver you use generally on final to lose altitude more rapidly without gaining airspeed.  From an aerodynamic standpoint, in the side slip you are using bank to move the aircraft relative to the crosswind component, by the same amount that the crosswind is trying to move you off the centerline, so the rudder is away from the wind and the bank is in to the wind.  In a forward slip, you just slip one way or the other on final. The main difference between the two is that during a sideslip, if you have done it right, you are in ground effect and right above the runway. If the maneuver increases the stall speed the aircraft has a very short fall to the runway surface, and the closer you are to stall speed at the moment you land the better.  In the forward slip you may have a few hundred feet to fall but you have one advantage, and that is you are descending faster than during a sideslip and hoping that the unloading of the wing will keep you from stalling.  As far as I am concerned, and I know others may dispute this, both are cross-controlled maneuvers and the potential for a stall is there in both.  If you are heavily trimmed up, the need for the elevator to fly is there in both maneuvers.  The saving grace of the side slip is that you do not have far to go to the runway surface, unless, of course, you have started the maneuver too far above the runway.  Then you will have the same problem with a stall as does the foward slip.

I don't recall anything about slips changing your stall speed as a primary effect?  The only stall risks would be from letting your airspeed decay from the increased drag, and airspeed errors from the pitot tube placement.

Share this post


Link to post
Share on other sites

As many experienced pilots have already stated, they advise against slipping in the long body Mooneys. I don’t disagree and I am certainly not recommending slips, but I have done forward slips and side slips in Bravos and Acclaims with adequate airspeed, altitude, and safety margins with no problems. I don’t use them for landing other than an occasional slight slip with a last second crab kick out to align with the runway in a stiff crosswind (see POH reference below).  I’ve got about a thousand hours tailwheel experience and former glider experience so I’m very comfortable with slips, but still maintain caution since the Mooney and other airplanes have differing flying characteristics.  I would use a slip if needed for an emergency descent and landing, but not to save a poor approach. There is a very real danger in getting slow (below 80-85 knots as was previously stated) in a slip on final. 

9F742EE4-A1C7-430B-94CD-621D099188F2.jpeg

Share this post


Link to post
Share on other sites

Steingar,

You have bumped into one of the few areas where the short body experience doesn’t directly apply to the long body experience.


Where the confusion comes in...

The OP was asking specifically about the LB and slips...

Where the LB is sensitive to shadowing the tail with the flaps...

A similar situation to what the OP is asking is a well known test pilot for Mooney was lost under similar conditions... in something shorter than the LB, iirc...

 

Since stalls during the landing phase can be un-recoverable...

A simple error in judgement can be the difference of landing safely or not.

There is little appreciation of anything other than factual discussion to this very direct question.


Can you Sense the gravity of some MS threads...?

 

Slips and going slowly, while dirty and trimmed fully up are best avoided...

The full up trim has the tail’s AOA closer to its limit...

using a lot of slip/cross control uses plenty of energy...

using a short runway demands slower air speeds...

slips to keep the plane on the Cl are usually not that strong...

When they are... use the procedure described above to transition from crab to slip at low levels....

If you want to practice with the crab to slip transition (crab/kick)... call your friendly neighborhood MS CFII... :)


See if I got that correctly...

PP summary only, not my ideas at all... stuff I learned here... not a CFII...

Best regards,

-a-

Share this post


Link to post
Share on other sites

Great info about slips, especially regarding why it is not recommended in LB Mooney's. I try to set my descents not planning on using speedbrakes, I use them where I'd normally slip and I find the increase in descent rate to be good and manageable.

I agree with crab-to-slip over the numbers. I've found my Bravo to be very stable in crosswinds using that method.

Fly Safe,
Safety Forum Mod

Share this post


Link to post
Share on other sites
20 minutes ago, jaylw314 said:

I don't recall anything about slips changing your stall speed as a primary effect?  The only stall risks would be from letting your airspeed decay from the increased drag, and airspeed errors from the pitot tube placement.

You are banking and stall speed increases with bank angle, among other issues.  You are also intentionally not in coordinated flight.

Share this post


Link to post
Share on other sites
Just now, jlunseth said:

You are banking and stall speed increases with bank angle, among other issues.  You are also intentionally not in coordinated flight.

AFAIK, banking alone doesn't increase stall speed--turning does, since there is increased wing loading from accelerated flight

Straight flight, even in a slip, should not increase your stall speed since the wing loading is still 1G

 

Share this post


Link to post
Share on other sites
39 minutes ago, HXG said:

 I would use a slip if needed for an emergency descent and landing, but not to save a poor approach. 

I agree with everything you say. I just wanted to comment that the one place the slip has in saving a poor approach is power off 180’s, esp. if you had to do a real one, which fits more into your category of an emergency descent.  When I practiced for my commercial years ago I did some forward slips, careful not to fall below 85.  What I found in my 231, is that if I need to lose alot of altitude quickly, I can do it just as easily and effectively by throwing out all the brakes, i.e. speed brakes, full flaps, gear down, and the throttle full out, and then falling straight ahead at a speed below best glide, which is around 81-85 in my aircraft depending on gross weight.  So nose up to let the speed fall to about 70.  You are not cross-controlled, not banked, and a good ten knots above stall.  I call it “helicoptering.” It works well and is safer than a slip.  You just have to remember, if you have power, to add a little at the end as in a soft field landing, to avoid a hard landing, and if you don’t, drop the nose above the runway to gain airspeed, then arrest the landing with the airspeed. My 231 tends to fall, though, compared to a J that does not want to fall so much, it wants to float forever, so I would practice it in whatever Mooney you have to see if it works for you.

That said, the usual problem in a power off 180 is not that you have too much altitude.

  • Like 1

Share this post


Link to post
Share on other sites
6 minutes ago, jaylw314 said:

AFAIK, banking alone doesn't increase stall speed--turning does, since there is increased wing loading from accelerated flight

Straight flight, even in a slip, should not increase your stall speed since the wing loading is still 1G

 

Hmm. So in a side slip, what is causing you to move into the relative wind? Remember, the relative wind is trying to move you off the centerline.  What is keeping you on the centerline? Sure, bank, but what is the bank doing?

  • Like 1

Share this post


Link to post
Share on other sites

Here, I have to leave and go to dinner in a minute but I will explain it this way.  It is a vector analysis problem. In level flight the wing is generating 1G and the vector is a line 1G long in a vertical direction. Now bank the plane 45 degrees without changing anything else, and the vector is still 1G long in a direction perpendicular to the wing, but the lift generated is split into two parts, a horizontal lift vector (moving the aircraft in the direction of the bank) and a vertical lift vector that is no longer 1G, it is less than 1G. To remain at a fixed altitude it is now necessary to change the angle of attack and increase the total lift on the wing, so that the vertical lift is 1G, otherwise you descend. So the bank causes the aircraft to turn (assuming you remain coordinated), but part of the lift generated by the wing has gone into that horizontal vector.  This happens in any bank, any time.  The bank moves the aircraft in the direction of the bank and reduces the vertical lift vector from what it would be if the plane were completely level.  If you are cross-controlled, you have two airfoils working opposite each other, but that does not change the fact that you are banking and have lost vertical lift.  It is not the turn that causes the stall, it is the loss of vertical lift. Go out and try some accelerated, cross-controlled stalls, get a good Mooney instructor to show them to you.  The stall is more abrupt (that’s why they are called “accelerated”) and happens at a higher stall speed than in level flight. The saving grace of the forward slip is that you have unloaded the wing, and it no longer needs to make 1G vertical.  This is a different issue though than the long body stall issue, which is a tail stall.  Loss of lift to the elevator because (1) you are taxing its vertical lift, converting some to horizontal, and then (2) you shadow the elevator with the preceding fuselage, wing, and flaps, it can’t keep the tail down and therefore the nose up. Colgan Air all over again, without the ice.

  • Like 2

Share this post


Link to post
Share on other sites
1 hour ago, jaylw314 said:

I don't recall anything about slips changing your stall speed as a primary effect?  The only stall risks would be from letting your airspeed decay from the increased drag, and airspeed errors from the pitot tube placement.

The air isn't flowing straight, front to back, over the wing any more, it's flowing a bit diagonally across the normal chord.   This changes the airfoil shape.   Plus, the effective wingspan is shorter, plus part of the up wing has little airflow or just turbulent airflow at the root where it is blocked from the oncoming air by the fuselage.  This increases the wing loading since the effective area of the wing is reduced.

Basically, it's no longer the wing you're usually flying.   The fact that this was extensively explored, and reported on, by the Mooney test pilots provides a ton of useful info.

I don't know how the slip directly affects the stall airspeed on a Mooney, but, as you mention, the pitot tube is also a bit goofy during a slip, so caution is warranted.

In my curious younger days I spent a lot of time exploring the extreme end of slip behavior in a Cessna 150, with flaps, without flaps, etc., etc.   I was trying to determine whether it would stall in a full slip, and on the airplanes I was flying at the time the elevator lost enough authority during a slip that you just really couldn't get enough AoA to make it do much of a stall.   If you were really determined, though, and let the nose down a bit and then gave it a good, well-timed yank to the stops and held it, one wing would stall enough to enter a spin.   One of my main take-aways from all of that was that, at least in a C-150, it didn't really behave quite the same as even usual high AoA slow flight.  It was generally pretty tame and predictable, and actually very, very difficult to make it stall or screw up, but it was different.   In the C-150 you can slip with a nose attitude that's significantly higher than the normal approach attitude, and if you're slow and don't reduce that coming out of the slip (it's pretty obvious to do that, though), it'll stall coming out of the slip.   Since this maneuver is usually employed close to the ground, when coming out of a slip I drop the nose a bit or at least make sure that the AoA when I come out of the slip will be a very happy one.   

C-150s have very manageable and predictable spin characteristics.   They're actually really fun to spin.    Since the Mooney spin characteristics are...less desirable, I've not been inclined to do any similar exploration of Mooney flight characteristics.   I do, and am not afraid at all to do, full control deflection slips in my J model, but it's with a mind toward not exploring those low-speed characteristics too much.  ;)

Probably doesn't answer your question, but I wonder about details of this stuff, too.

Share this post


Link to post
Share on other sites
53 minutes ago, EricJ said:

The air isn't flowing straight, front to back, over the wing any more, it's flowing a bit diagonally across the normal chord.   This changes the airfoil shape.   Plus, the effective wingspan is shorter, plus part of the up wing has little airflow or just turbulent airflow at the root where it is blocked from the oncoming air by the fuselage.  This increases the wing loading since the effective area of the wing is reduced.

I was talking about a primary effect of slip angle changing stall speed, e.g. something that would affect any airframe.

I know there are things like changing the airfoil profile from the wind angle, different wing loading from dihedral, fuselage obstruction, etc, but I figure those are secondary effects.  Thinking about it trigonometrically (if that's a word), the change in relative wind in a slip is at most 15 degrees (that's a guess on my part).  That means the "wingspan" of the wing decreases by only 5%.  On top of that, even though the wingspan decreases, the total wing area stays the same.  So the change in wing loading is somewhere between 0-5% more, which really doesn't account for any significant change in wing loading in theory.  The fuselage obstruction effect may be larger, but again, if the slip angle is 15 degrees, how much of the wing is it really blocking?

On the other hand, I can buy the change in turbulent airflow as being a secondary factor that is significant, but I imagine that is highly dependent on the specific airframe.  

1 hour ago, jlunseth said:

Here, I have to leave and go to dinner in a minute but I will explain it this way.  It is a vector analysis problem. In level flight the wing is generating 1G and the vector is a line 1G long in a vertical direction. Now bank the plane 45 degrees without changing anything else, and the vector is still 1G long in a direction perpendicular to the wing, but the lift generated is split into two parts, a horizontal lift vector (moving the aircraft in the direction of the bank) and a vertical lift vector that is no longer 1G, it is less than 1G. To remain at a fixed altitude it is now necessary to change the angle of attack and increase the total lift on the wing, so that the vertical lift is 1G, otherwise you descend. So the bank causes the aircraft to turn (assuming you remain coordinated), but part of the lift generated by the wing has gone into that horizontal vector.  This happens in any bank, any time.  The bank moves the aircraft in the direction of the bank and reduces the vertical lift vector from what it would be if the plane were completely level.  If you are cross-controlled, you have two airfoils working opposite each other, but that does not change the fact that you are banking and have lost vertical lift.  It is not the turn that causes the stall, it is the loss of vertical lift. Go out and try some accelerated, cross-controlled stalls, get a good Mooney instructor to show them to you.  The stall is more abrupt (that’s why they are called “accelerated”) and happens at a higher stall speed than in level flight. The saving grace of the forward slip is that you have unloaded the wing, and it no longer needs to make 1G vertical.  This is a different issue though than the long body stall issue, which is a tail stall.  Loss of lift to the elevator because (1) you are taxing its vertical lift, converting some to horizontal, and then (2) you shadow the elevator with the preceding fuselage, wing, and flaps, it can’t keep the tail down and therefore the nose up. Colgan Air all over again, without the ice.

OK, I'll buy most of that :)  My nitpicky response would be that some of the wing lift is transferred to the fuselage body, so the increase in wing loading will be less than what the angle of the lift vector would dictate :P

  • Like 1

Share this post


Link to post
Share on other sites

Maybe, and maybe the opposing airfoil, which is the rudder, generates some, but the best way to know is to get a good Mooney instructor, go up and do some.  Then report back, we would all learn something which is the point of this forum.

Share this post


Link to post
Share on other sites

Slipping any Mooney for the purpose of losing altitude is just poor form and uncomfortable for passengers.  Of course it is necessary for crosswind landings, but even then, I would practice enough that you are comfortable with the crab and transition to wing low method of landing, as the work load is significantly reduced all the way to the corrections necessary in the flare.  All  proficient Mooney pilots should be capable of recognizing the sight picture for a stabilized approach and not be high.

Having said that the long body Mooneys (M20M, M20R, M20S, M20TN) can be slipped even with full flaps. There is no prohibition in the POHs from doing them.  (In the K model there is)  If doing so, make sure it is done above the 85 knots Bob Krommer stated.  To demonstrate this, when a student is high on downwind, I'll have them full slip around the turn to base and final.  The wing is NOT loaded, the speed is greater than 85 knots (usually 90 knots), and the nose is down for the descending slipping turn.  The ball in the turn coordinator or PFD is facing the inside of the turn.  Do NOT skid around a turn as this can lead to an unrecoverable stall/spin.  I would recommend doing this first with a Mooney Specific Instructor familiar with your airplane model.  Remember, this is for demonstration purposes only and should not be the norm for flying a pattern, as I said above, the proficient pilot knows the slope at which to make all turns in the pattern.

  • Like 2

Share this post


Link to post
Share on other sites

 

On 10/9/2019 at 1:52 PM, mike_elliott said:
7 hours ago, donkaye said:

Slipping any Mooney for the purpose of losing altitude is just poor form and uncomfortable for passengers.  Of course it is necessary for crosswind landings, but even then, I would practice enough that you are comfortable with the crab and transition to wing low method of landing, as the work load is significantly reduced all the way to the corrections necessary in the flare.  All  proficient Mooney pilots should be capable of recognizing the sight picture for a stabilized approach and not be high.

Having said that the long body Mooneys (M20M, M20R, M20S, M20TN) can be slipped even with full flaps. There is no prohibition in the POHs from doing them.  (In the K model there is)  If doing so, make sure it is done above the 85 knots Bob Krommer stated.  To demonstrate this, when a student is high on downwind, I'll have them full slip around the turn to base and final.  The wing is NOT loaded, the speed is greater than 85 knots (usually 90 knots), and the nose is down for the descending slipping turn.  The ball in the turn coordinator or PFD is facing the inside of the turn.  Do NOT skid around a turn as this can lead to an unrecoverable stall/spin.  I would recommend doing this first with a Mooney Specific Instructor familiar with your airplane model.  Remember, this is for demonstration purposes only and should not be the norm for flying a pattern, as I said above, the proficient pilot knows the slope at which to make all turns in the pattern.

@donkaye  . I do use the crab method more often than  a side slip ( but I admit using a side slip - full flaps and wind ))  on final with a x wind and a slight ( at time more of a kick ) before the numbers to align with the runway centreline . But you mention that the slip is ok as per your note above. So here is a fine point sort of question and maybe it is irrelevant . In my plane I need add allot of rudder trim  in cruise. I need  what seems to me to be quite a bit to get the ball centred. You can actually feel the plane adjust its alignment to the fIight-path when I do this. I however typically do not change it once I let down to the pattern and ready  things for landing . So in my case in the landing config I already have allot of rudder trim even if not slipping or crabbing per se.,  or would you continue to change the rudder trim all the way down to  landing .  I am just in the habit of not touching it. Is it insignificant or would you modify my procedure so that im not flying in some weird config. Just curious if that changes things  ( hopefully what I just wrote above makes sense )

 

Share this post


Link to post
Share on other sites

Due to P factor I do adjust the rudder trim to minimize constant rudder pressure in climbs and descents.  It doesn't have to be done constantly, since you are climbing and descending at a constant rate.  When climbing at or below Vy some right rudder will still need to be held, as rudder trim doesn't fully cover the P factor at those speeds.

Share this post


Link to post
Share on other sites
9 hours ago, donkaye said:

Slipping any Mooney for the purpose of losing altitude is just poor form and uncomfortable for passengers.  Of course it is necessary for crosswind landings, but even then, I would practice enough that you are comfortable with the crab and transition to wing low method of landing, as the work load is significantly reduced all the way to the corrections necessary in the flare.  All  proficient Mooney pilots should be capable of recognizing the sight picture for a stabilized approach and not be high.

Having said that the long body Mooneys (M20M, M20R, M20S, M20TN) can be slipped even with full flaps. There is no prohibition in the POHs from doing them.  (In the K model there is)  If doing so, make sure it is done above the 85 knots Bob Krommer stated.  To demonstrate this, when a student is high on downwind, I'll have them full slip around the turn to base and final.  The wing is NOT loaded, the speed is greater than 85 knots (usually 90 knots), and the nose is down for the descending slipping turn.  The ball in the turn coordinator or PFD is facing the inside of the turn.  Do NOT skid around a turn as this can lead to an unrecoverable stall/spin.  I would recommend doing this first with a Mooney Specific Instructor familiar with your airplane model.  Remember, this is for demonstration purposes only and should not be the norm for flying a pattern, as I said above, the proficient pilot knows the slope at which to make all turns in the pattern.

Agree with Don. And, aerodynamically, a side slip and forward slip are the same. The difference is the flight path relative to a ground reference due to wind velocity. Keeping the wing loading down in descending base and final turns increases safety margin because the stall speed increase in a turn is due to load factor, not bank angle.  The drag in a slip is high and the nose position is low and it’s easy to let the airspeed decay if distracted, so it’s best to keep the speed up during a slip  

Skip

  • Like 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.