Can you slip a Mooney on final?

[Jeff_S]

Hey all,

In this month's Aviation Safety magazine one of the Letters to the Editor submission was about the importance of maintaining airspeed on final to improve safety. No qualms there, of course, but the reader went on to say emphatically that "you can't slip a Mooney 201...check the POH."  I take this to mean he was implying that you can't slip a 201 on final to help bleed off speed to help salvage a landing, although this was not explicit.

Is this right? Does the POH forbid slipping an M20J?  I know that Cessnas have had some limitations on full slips when in landing configuration with full flaps, as this can disrupt airflow over the tail.  Do Mooneys have these same limitations?

 

[Cruiser]

In section II - Limitations of my 1984 M20J under Maneuver Limits it states:

 WARNING

Prolonged slideslips, steep descents, or takeoff maneuvers may cause loss of power if the selected fuel tank contains less than 48 lbs. (21.7 kg) (8 gallons - 30.3 liters - 6.6 Imp. Gal.) of fuel.

 

There are no other limitations concerning slips in the POH.

 

[skyking]

cruiser is right. Thats why you should always be on the fullest tank with the pump on when landing.

I have used slips before on final with no problems.

[piperpainter]

I don't have a 201 but I know I slip my bird all the time. I could never get into some of the places I go without using a slip. Its important to maintain your speed though. I heard a guy say he never slips his Mooney because he read something like that. Nothing in my POH restricts slips so someone is sending false info.

[LFOD]

Quote: JimR

 I slip occasionally when necessary in my 201 and it seems to slip just fine.

[Piloto]

Of course you can slip your Mooney or any FAA approved airplane. It is a required capability for crosswind landing particularly on high wing planes. Sliping into wind reduces the possibility of weather vane into the cross wind at touch down or flip over. To avoid an inadvert stall your approach speed should be slightly higher during the slip.

José

  

[PTK]

In the J its a non issue.  The long bodies however do exhibit an aggravated negative angle of attack in the horizontal tail in the trimmed (almost full nose up) landing configuration.  This is further aggravated by use of flaps and by the slip itself.  At a safe altitude the airplane will nose down going through a phase of loss of control until the horizontal tail starts flying again. AFTER LOSS OF CONSIDERABLE ALTITUDE.  Personally I don't want ANY loss of aircraft control and I cannot afford abrupt loss of altitude in the landing phase of flight! 

[Parker_Woodruff]

I think all mine says is to avoid prolonged slips with 8 or less gallons of fuel onboard the active tank.

[Immelman]

Or, I suppose, make sure you're burning fuel from the "uphill" side during your slip.

I enjoy using a slipping (not skidding) turn from downwind to final on occasion myself. I was taught that as a taildragger (citabria) pilot when practicing power off approaches but its fun to use in your bag of tricks as a Mooney pilot just as well.

[jlunseth]

I have read that article and a couple of others on the slip in Mooneys.  The advice I have read is that you can slip a 231 (other than when the tanks are low) but I just use the speedbrakes if I need to get down fast. 

[carusoam]

I used sideslips for my M20C often.  Always making sure nose is down and airspeed maintained.  Entering and exiting the slip smoothly / gently.  There is no desire to let the tail wag by over or undercontrolling.

PK, I have been reviewing the POH for the M20R (longbody)

Slips are mentioned 3 times:

cross wind landing, door closing in flight, fuel gauge accuracy only during coordinated flight.

It is a normal category airplane, so slips are acceptable (with normal precautions to avoid stall / spin).

Otherwise, speed brakes are used for additional speed control.

Directly to answer the question: The POH (Section IV - Landing) recommends crab until flare, touch down with slight wing low side slip.  (Caution: YOUR POH may vary)

The C and the R seem to be at maximum up trim during the landing phase (with two people on board).

[mooneygirl]

I too, have used the slip in my 65E when necessary.  I have found that my E is very responsive and feels very stable in a slip. 

[Ned Gravel]

I agree with Jolie. 

I slip mine all the time on crosswind finals. I find such an approach to be stable this way.  Fly 5 mph faster and use less flaps, but forward slips create fairly solid performance right down to the numbers. I do not use it as a device to reduce speed on descent or to get down faster.  Those are planning issues and I try and solve them further out - or I am going around.

I have heard from many sources that our "short body" Mooneys have a very comfortable flight envelope when it comes to slips.  My own experience (about 350 hours) in my own E model supports that view.  I hear (but I do not know) that J's are OK with slips too. I have also read that it is primarily the "long bodies" where problems can occur in attitudes and configurations that do not tend to bother our shorter birds.  

IIRC, I read about "... a former Mooney factory test pilot with more than 14,000 hours of flight test work exploring the complete flight envelope of many models of Mooney including the J ..." who ended up UWOF because of a loss of control in a cross controlled approach. An article in the May 2007 MAPA log discussed it:

On August 4, 2004, approximately 0845 Central Daylight Time, a Mooney M20J single-engine airplane was destroyed  upon impact with terrain following a loss of control while maneuvering for landing at the Olney Municipal Airport (ONY), near  Olney, Texas.

See Trey Hughes editorial in the same edition on slipping:

I don’t know how many Mooney owners or operators have had the chance to experience a cross-controlled stall in a Mooney, but those who have been unfortunate enough will agree that it is a place that no one wants to go twice. Mooneys, especially the long-body models, have a tendency to roll toward the deflected rudder when they are stalled in an uncoordinated condition. This roll can be abrupt and unannounced. Especially with flaps extended, during a slipping maneuver, it is very easy to lose elevator effectiveness and suddenly get a nose-down pitching moment. I have talked with several Mooney factory test pilots –  both present and past – who agree that a slip is not a normal maneuver in a Mooney and should not be attempted at low airspeeds and altitudes.

.....

While the short airframes (pre-J) are not as susceptible to this issue, slips in even these models should be approached  with a lot of caution. Remember a Mooney, even those with 200 hp or less, has the flight characteristics of a high  performance aircraft and should be flown as such. Slips are not part of normal operations and not how these airplanes  were designed to be flown. If a slip must be preformed, remember to keep the airspeed above about 80-85 KIAS and you  will avoid the possibility of a tail stall and the subsequent loss of control.

So, to quote Forrest Gump, "careful is as careful does."  I know my Mooney and I know how it handles a cross controlled stall (at altitude of course with an instructor on board) and Trey is correct.  It will roll toward the deflected rudder.  The difference is that my E model is not as violent in this manoeuvre as the longer bodies and can be recovered before it enters a spin.  Location of the CG can also either mitigate or compound the issue.

Now, having said all that, this is just my opinion and it is worth as much as you paid for it.

[mikefox]

Quote: edgargravel

I agree with Jolie. 

I slip mine all the time on crosswind finals. I find such an approach to be stable this way.  Fly 5 mph faster and use less flaps, but forward slips create fairly solid performance right down to the numbers. I do not use it as a device to reduce speed on descent or to get down faster.  Those are planning issues and I try and solve them further out - or I am going around.

I have heard from many sources that our "short body" Mooneys have a very comfortable flight envelope when it comes to slips.  My own experience (about 350 hours) in my own E model supports that view.  I hear (but I do not know) that J's are OK with slips too. I have also read that it is primarily the "long bodies" where problems can occur in attitudes and configurations that do not tend to bother our shorter birds.  

IIRC, I read about "... a former Mooney factory test pilot with more than 14,000 hours of flight test work exploring the complete flight envelope of many models of Mooney including the J ..." who ended up UWOF because of a loss of control in a cross controlled approach. An article in the May 2007 MAPA log discussed it:

On August 4, 2004, approximately 0845 Central Daylight Time, a Mooney M20J single-engine airplane was destroyed  upon impact with terrain following a loss of control while maneuvering for landing at the Olney Municipal Airport (ONY), near  Olney, Texas.

See Trey Hughes editorial in the same edition on slipping:

I don’t know how many Mooney owners or operators have had the chance to experience a cross-controlled stall in a Mooney, but those who have been unfortunate enough will agree that it is a place that no one wants to go twice. Mooneys, especially the long-body models, have a tendency to roll toward the deflected rudder when they are stalled in an uncoordinated condition. This roll can be abrupt and unannounced. Especially with flaps extended, during a slipping maneuver, it is very easy to lose elevator effectiveness and suddenly get a nose-down pitching moment. I have talked with several Mooney factory test pilots –  both present and past – who agree that a slip is not a normal maneuver in a Mooney and should not be attempted at low airspeeds and altitudes.

.....

While the short airframes (pre-J) are not as susceptible to this issue, slips in even these models should be approached  with a lot of caution. Remember a Mooney, even those with 200 hp or less, has the flight characteristics of a high  performance aircraft and should be flown as such. Slips are not part of normal operations and not how these airplanes  were designed to be flown. If a slip must be preformed, remember to keep the airspeed above about 80-85 KIAS and you  will avoid the possibility of a tail stall and the subsequent loss of control.

So, to quote Forrest Gump, "careful is as careful does."  I know my Mooney and I know how it handles a cross controlled stall (at altitude of course with an instructor on board) and Trey is correct.  It will roll toward the deflected rudder.  The difference is that my E model is not as violent in this manoeuvre as the longer bodies and can be recovered before it enters a spin.  Location of the CG can also either mitigate or compound the issue.

Now, having said all that, this is just my opinion and it is worth as much as you paid for it.

[hansel]

Quote: mikefox

How else do you land in a crosswind?  At some point unless you want to land with the nose not pointed down the runway and imparting sideload on your landing gear, you will be slipping

 

Crab/kick-out. Some would argue that the aerodynamics of transitioning into a "slip" from a crab on the flare (and in ground effect) are different than a full forward slip at 500-1000agl discussed above.

[Ned Gravel]

Eric: 

That is the other one I know too.  And I actually suck at the crab and kick method.  It is not a stable method for me.  Forward slip is also the method taught by our chief flying instructor - in those aircraft that can handle it.

But so as not to lead Mike astray, I do use Don Kaye's numbers for crosswinds.  Add 5 mph for every 10 kt of crosswind component and subtract 5 mph for each 300 lb under 2575 lbs.

[Jeff_S]

Well, I now have my J model and I can tell you that it slips just fine for wind correction on final. I've always preferred a forward slip to the crab/kick-out method because that way I know for sure whether or not I've got enough rudder control to keep going straight. Granted, the winds at the surface are not always the same as at 100 or 200 feet, but if anything they're usually less strong so it gives me good assurance.

As I said in my original post, what I was most interested in was the dramatic slip to slow down and lose altitude on a short final. So in my dual training we practiced some emergency power-off descents and I learned all about how to use the flaps landing gear and prop pitch to help bring her down, including a slip if necessary.  The J has a few more tools to help lose speed/altitude than my Warrior did, although it is by nature more slippery so they're needed. And mine does not have speed brakes. So I wouldn't say I'm fully proficient at the quick short approach by a long shot, but I've got the foundation to keep practicing.

[Amelia]

I just spent an hour last week in the pattern, slipping my speed-brake-less 231 to  crosswind landings... no particular problems, and what a lovely descent and short-field landing, turning off in 1000 feet. Trick seemed to be keeping nose pointed down at the numbers.

[ernie252]

If you read the article it says "aggressive slips" in the K models.  I slip my 252 on final frequently, but it is far from an aggressive slip.  it's a slip to make small adjustments in airspeed usually, and I also slip into crosswinds.  Aggressive isn't defined in the article, but I land a Citabria over trees into a 1300 ft strip regularly.  The Mooney slips don't look anything like that, and I would be very uncomfortable slipping a Mooney on final in a 60 deg bank.  So the question is, "what's an aggressive slip?"

[Buster1]

Welcome Ernie!  Did you just purchase 252ZA?  I think I had my eye on that one!

[ernie252]

Quote: Buster1

Welcome Ernie!  Did you just purchase 252ZA?  I think I had my eye on that one!

[Jerry 5TJ]

I have owned a 64E, a 99S and now have a 65C model.  The "S" model had speedbrakes whereas the 60's birds did not. 

The two short body birds have been fine with slips when they were needed, but I try to make a stabilized approach to landing that does not require a lot of late and low changes.  No, I don't always succeed.   IF needed, in normal conditions, with normal weights, and at normal G loading a full-rudder slip at 85 mph feels stable with no odd effects.  

I think a key element that is missing in this whole "can you slip" discussion is dynamic load -- if you load up the airframe to a couple of G and cross control the plane, you have just executed the classic entry procedure for a snap roll, and if performed on short final, well, you get the picture.

I sometimes demonstrate to the skeptical that the Mooney is fully controllable at 40 mph IAS -- just do a push-over to 0.5 G and there is full aileron control at that speed.   At 1.5 G, not so much.

 

 

[Targhee]

So, just though I’d share something that happened today in my 1983 M20J.  I was really high on an approach to landing and decided to side slip to reduce altitude quickly.  I stomped on the left pedal for a good 30 seconds to get down to the glide slope and then resumed a normal approach.  As soon as I pulled my foot off the rudder, the engine started running really rough and felt like it was about to quit on me (man that grabs your attention quickly!).  I was on glide slope at about 300 AGL, so even if it quit, I had the runway made.  I gave it a little more throttle, no change.  I then switched tanks and after a couple of seconds it smoothed out.  

During the pre-landing checks I noted I had about 15 gals total, 8 on the right and 7 on the left (the tank I was on).   After landing I did a run-up check.  No issues.  Several more trips in the pattern.  No issues.  I even went up to altitude and attempted to recreate the same landing approach with extended side slip.  No issues.

Driving home I remembered that small quote from the POH...  “Prolonged slideslips, steep descents, or takeoff maneuvers may cause loss of power if the selected fuel tank contains less than 48 lbs. (21.7 kg) (8 gallons - 30.3 liters - 6.6 Imp. Gal.) of fuel“...   Bingo!  

Moral of the story...  re-read your POH and don’t do extended slips in your Mooney if your on a tank with less than 8 gallons unless you want to soil your shorts.

[Ibra]

I guess electric fuel pump was ON? sure it works better with one tank dry and 15gals in the other (or never get bellow 20gals reserves in both)

Yes there is "caution" on low fuel imbalance in M20J POH against sideslip, obviously when it happens you should make the runway: one only sideslip when high & fast high near threshold (after power off and flaps can't get you down to glide path), no good reasons to sideslip with lot of power nor when low & slow and far from the thresold

On sideslip better to assume no power & no flaps & no fuel 

Edited May 13, 2020 by Ibra

[FloridaMan]

I had the engine quit in my F trying to “remain clear of the Bravo” while in a steep spiral with top rudder. I had an instructor tell me to always slip into the wind. I don’t do that. I slip with the wing I’m taking fuel from on top. I also have used slipping turns as well. And using top rudder and loading up the wing is how I managed to not bend metal when I had to put my m20f down in a field. 
 

Per the earlier quote in the thread, of course when the plane stalls in a slip it yaws towards the rudder and it’s why you use top rudder — it buys you some time to unfuck the situation as your plane rotates through the horizontal. In a slip, your fuselage shades a wing, so the forward wing has more airflow over it, both from the pressure hitting the side of the fuselage and the shading on the other wing. The forward wing has more lift. This is even more pronounced in swept wing fighters and RC aircraft that can bank with the rudder alone. Our planes bank a little with rudder alone because of this and that it is above the longitudinal axis of the airplane so it is vertically asymmetrical. 
 

When you stall uncoordinated, one wing stalls first. The forward CG pulls the nose down and accelerates the other wing, increasing that wing’s lift. If you stall the top wing first and immediately unload it, you might be able to recover before going inverted. If you stall with the bottom wing first (skid with bottom rudder), think about what happens. 
 

With all that said, I slip the F and use speed brakes with the rocket. 
 

My understanding of that Texas crash was that one of the two people was known for always wanting to make his spot on the runways. It’s presumed that the Mooney test Pilot was not the one controlling the airplane when it happened. 

Edited May 13, 2020 by FloridaMan