Slips - How Effective?

[Z W]

I experimented yesterday with slips in my M20K 262 (231 with a 252 engine). Before doing that I researched a lot, including threads on Mooneyspace. I was mostly driven by a desire to understand another tool that would help my slick plane descend and slow down at the same time.

At 100-90 knots indicated, gear down, full flaps, adding a full right slip would increase my sink from 500 FPM to about 700 FPM. I found this to be far less effective than deploying the speed brakes, which increases it from 500 FPM to 1000 FPM. I did not attempt slipping while speed brakes were extended, mostly because I could not find any good data on what speed brakes do to stall speed in a slip.

Slips above 100 KIAS seemed to be even less effective. I did not want to slip under 90 KIAS because of this post: http://www.mooneyevents.com/flying2.html , and also just generally don't want to be anywhere near a stall in a slip or skid, for obvious reasons.

My question is, does anybody use slips more effectively than this in a mid-body K or J model? I can't think of any way to make them more effective, but with these results, I think I will always opt for speed brakes, or dump the flaps and "dive and drive". Those without speed brakes I guess would still find a slip useful.

[jetdriven]

Slips at a low IAS such as 80 KIAS don't do much for adding drag. Slips at around 100 knots work, but not nearly as much as in other airplanes. Sliping with the nose downwind helps somewhat as you are presenting more of the fuselage to the wind for drag. Still, my M20J results are about the same as yours.

It takes more skill to fly his airplane to prevent the need for slips than those others, as well.

[jlunseth]

I find that my M20K "falls" fairly well and quickly if I just throttle back and am patient. If I need more help I willuse the speedbrakes. But I have read the stuff about cross-controlled stalls and have been told my highly-Mooney-qualified instructors that issues can arise even with the K (as well as the long bodies) at slow speeds, so I have no real interest in trying that.

I come in high most of the time, and find that simply throttling back will allow the plane to fall, and that fall will accelerate the longer it happens. At some point the aircraft comes into the glideslope (as defined by the PAPI's or VASI) and at that point I will throttle up to keep the plane on a stablized approach to the runway. Throttling up allows me to push the mixture in full rich so I have it there in the event of a go around. As you may be aware, the K (at least the 231) tends to "burble" at low power during the descent unless leaned out quite a bit, so powering up allows me to put in full mixture during short final.

[aviatoreb]

I experimented yesterday with slips in my M20K 262 (231 with a 252 engine). Before doing that I researched a lot, including threads on Mooneyspace. I was mostly driven by a desire to understand another tool that would help my slick plane descend and slow down at the same time.

At 100-90 knots indicated, gear down, full flaps, adding a full right slip would increase my sink from 500 FPM to about 700 FPM. I found this to be far less effective than deploying the speed brakes, which increases it from 500 FPM to 1000 FPM. I did not attempt slipping while speed brakes were extended, mostly because I could not find any good data on what speed brakes do to stall speed in a slip.

Slips above 100 KIAS seemed to be even less effective. I did not want to slip under 90 KIAS because of this post: http://www.mooneyeve...om/flying2.html , and also just generally don't want to be anywhere near a stall in a slip or skid, for obvious reasons.

My question is, does anybody use slips more effectively than this in a mid-body K or J model? I can't think of any way to make them more effective, but with these results, I think I will always opt for speed brakes, or dump the flaps and "dive and drive". Those without speed brakes I guess would still find a slip useful.

I have read the warnings about slips in M20K and up (not a problem apparently with a J) and the warnings of possible tail stalls - they are enough to keep me from adding the operation to my list of tools. Speed brakes fill that gap for me. Do you flatten out your prop as a tool in your drag toolbox on short final?

[jetdriven]

I think those tail stall are like voter fraud. Rumored to exist but no proof. That said, dont get slow in a slip.

[kortopates]

I agree concern for slips is over exaggerated. IMO, they are a very important tool and most useful when the pilot wants to temporarily increase descent in a no flaps condition while maintaining a target airspeed, such as the (simulated) engine out landing that (I hope) we all practice. With the flaps up, there is no concern slipping at 80kts, your engine out glide speed. Speed brakes in this situation is too hard to control with any precision. But full slips with full flaps is another matter and would agree speed brakes is a better option. But such dramatic descent rates should not be necessary in the pattern and rarely ever if not on fire. I’ve used speed brakes and a full slip descending into a mountain airport in the Sierra’s due to surrounding terrain with and without the gear down (and no flaps) without any issue at approx 100 kts; but not out of necessity, just to save time.

[201er]

My M20J slips just fine and it does improve the descent angle. I don't have speed brakes so when flaps are full, throttle idle, it's the last resort to get it down. However, I have heard and found the opposite of what was previously mentioned to be true. Slowing down in a slip is more effective. At 85-90 kts you are close to best glide speed. Slowing down increases induced drag. If there is any headwind present at all, slowing down also gives the headwind more time to shorten your forward distance while losing altitude. Airspeed management is critical but I don't see a problem with slipping my 201 at 75 knots on short final. It's useful for clearing an obstacle and then landing on the earlier part of a runway (especially when it is short).

[jetdriven]

LDmax is the spot where you have minimum drag. Any slower is increased induced drag, while any faster is increased parasite drag. A slip is all parasite drag. Slowing to LDmax counteracts the effect of the slip, somewhat. Add airspeed in a slip to maximize altitude loss.

[M20F]

Some details on slipping M20K/Long body

http://www.mooneyevents.com/flying2.html

[davidsguerra]

Some details on slipping M20K/Long body

http://www.mooneyeve...om/flying2.html

this has been my limited experience. My M20k Rocket does not slip like a T-41D/Cessna 172 did.

[201er]

LDmax is the spot where you have minimum drag. Any slower is increased induced drag, while any faster is increased parasite drag. A slip is all parasite drag. Slowing to LDmax counteracts the effect of the slip, somewhat. Add airspeed in a slip to maximize altitude loss.

Not so sure that this is true. First of all, you can't go too much faster or you'll exceed flap extended speed or put unecessary stress on the gear doors. However, from my glider experience, the increase in drag on the faster side of L/D (parasitic drag) is more gradual than the increase of drag on the slower side (induced drag). In other words, if best L/D is 90 knots, slowing to 80 knots should provide a greater sink rate than putting the nose down to speed up to 100. Although the slip itself may be more effective (more parasitic drag) at 100 knots, you are on the less effective (dragwise) side of the L/D curve to begin with. On a box shaped airplane I would presume the parasitic drag gained on slip would be more effective but not so much on a slippery airplane. Furthermore you are penetrating headwind better by going faster which reduces effective sink rate (when you're in glide and not making it to target because of headwind, the only effective strategy is to speed up). Therefore based on my logic and a hunch, it seems that slipping slower than L/D is more effective than faster.

[Z W]

The plane does come down just fine with the power out, especially with the prop pulled back. It will do 1500fpm in a couple different configurations pretty easy, no slips required. The POH says 2000fpm can be done if you push it a little harder.

Mostly I just wanted to see what slips did, and I was a little surprised at how ineffective it was compared to my 172 trainer. Sounds like thats normal.

I'll have to keep them in mind for an engine out tool, that is a good point.

[BigTex]

Everything is relative... Do a slip in a cub, and the plane comes down like an elevator... My Mooney... Not so much but is still a good effective technique if you're a little high. It's not something to fear.

[aviatoreb]

I think those tail stall are like voter fraud. Rumored to exist but no proof. That said, dont get slow in a slip.

That may be true, explicit warnings from Bob Kromer about tail stall risk in M20K and up with slipping does spook me I admit.

I agree concern for slips is over exaggerated. IMO, they are a very important tool and most useful when the pilot wants to temporarily increase descent in a no flaps condition while maintaining a target airspeed, such as the (simulated) engine out landing that (I hope) we all practice. With the flaps up, there is no concern slipping at 80kts, your engine out glide speed. Speed brakes in this situation is too hard to control with any precision. But full slips with full flaps is another matter and would agree speed brakes is a better option. But such dramatic descent rates should not be necessary in the pattern and rarely ever if not on fire. I’ve used speed brakes and a full slip descending into a mountain airport in the Sierra’s due to surrounding terrain with and without the gear down (and no flaps) without any issue at approx 100 kts; but not out of necessity, just to save time.

Thank you kortopates. That is particularly interesting coming from a CFI who flies a CFI M20K. Useful information thank you.

Anyone with a M20J to M20C who says they can slip just fine, that is consistent and not contradicting the warnings that say to be careful with M20K and up.

[garytex]

201er, I am a big slipper. I like to come in to my airport, Lakeway, high. There is nowhere good to go except the runway if one looses the engine. I learned to fly in an early 170, with small flaps, and slipped it too. But 80 MPH indicated is as slow as i will let speed get in my F model, as the plane starts to feel like the bottom is close to coming out. I like to slip on a close high final, using a slipping turn off base, and indicating 90-100. I do not know exactly what the decent rate is, I'm looking out the window, and just glancing at the airspeed. But the slip is effective, allows me to get/stay in gliding range in the pattern, and helps me keep speed down.

[DaV8or]

Wow. I had no idea. I've slipped my F with full rudder well under 80 knots many times. Never had a buffet, or a nose drop. I don't have speed brakes. It's helped me on a number of occasions. I've heard all the blah, blah, blah about correct approach speeds and patterns, etc, but out where I fly, you can easily get serious up drafts on final and your only options (for me) are slip, or go around. I have always chosen the slip and it's always worked out beautifully. I would obviously like to know more about these slip issues and wonder why the FAA hasn't been notified. Don't they test something as basic as a slip during certification??!

[carusoam]

Open thoughts on Mooney slipping... These are not recommendations....

1) Body length is most important to this argument...

2) Tail structure changed in 66 also gets a mention here.

3) A,b,c,d,&e are nearly the same. 65 and younger have a smaller (shorter) rudder, less control.

4) F,G,J&K being similar (mid length).

5) L,M,r,s &TN (long bodies). Most storied

6) Modified planes with heavier engines get an extra discussion... Momentum vs control forces...

7) Shorter rudders are less effective than longer rudders, the corresponding control forces in the slip can be stronger with the larger control surface.

8) Control of the entry and exit of the slip is important. "lazily" snapping in or out of the slip is not recommended.

9) Back CG increases the risk as well. Increasing the challenge of recovering from a stall.

10) Cross controlling increases the risk. Can't slip without cross control.

11) Keep the nose controlled or pointed downward prevents the loss of speed that allows the stall. The idea of the slip is to slow down, not fall down...

12) Long bodied Moonies have been fitted with pretty effective speed brakes. Plan to use them if you have them....

13) A well known pilot of MAC was killed slipping near the ground, the best we understand. Where else would you use a slip other than near the ground?

14) Source: this is data collected from MooneySpace and is open to discussion... I am not an expert...

15) Slipping doesn't necessarily cause Mooneys to fall out of the sky. Stalling while slipping increases the risk of falling.

16) Adding up the associated risks may make you question if you want to try it the first time anywhere near the ground...

Associated risks...

Being slow, near the ground, cross controlled, snapping in or out of the slip, with large tail surface and the full fulcrum of the long body, the extra mass of a big bore engine...slide the CG back by adding some xtra weight to the baggage area, don't control speed very well or don't keep the nose down...

Did I miss anyone???

It's good to practice at safe altitudes.

Best regards,

-a-

[DaV8or]

Anyone with a M20J to M20C who says they can slip just fine, that is consistent and not contradicting the warnings that say to be careful with M20K and up.

Actually, this is from the Kromer post-

For our slip tests, we flew the M20K, the M20J and the Mooney/Porsche engineering prototypes that were at the factory at the time.

So, does include the J and by extension, you might include the F and G as well.

[jetdriven]

Note Kromer said in normal operations there is plenty of margin. With a bit of ice on the tail, you could have a tail stall, although he doesnt offer proof of one. It almost sounds like paranoia about slips due to a slight nose down pitching movement, just like in a 172. However, in the M20J at least, there is no warning about full flap slips, and no accident record I can find of an M20 accident as a result of a slip and tail stall.

I have done plenty of full flap (40 degree) slips in 172s as well. The tail shake and nose down pitch is real, but esily dealt with once experienced. A proper checkout should include one.

I would not attempt a slip with ice on a Mooney, however, I would not fly a Mooney in icing conditions, forecast, reported, or suspected. The issue, to me, sounds like ice on the airplane, not slips.

[carusoam]

Jim,

You can see what is on my mind regarding safety of flight...

I can't imagine slipping with ice on any airframe.

Best regards,

-a-

[Hank]

Slips are handy tools when your approach is messed up, whether by inattention, poor planning or by ATC. Purposely coming in high and fast does not seem like a good plan to me. I stay a little high at home to clear the trees at 80 mph, throttle to idle and make a routine descent to the 2nd or 3rd stripe. My "options" are trees on final, more trees to the left with River beyond, trees and a ridge to the right, trees at the end, then ~½ mile to Walmart with houses scattered in the trees on the way.

I had to slip going into Lunken the first time, not paying attention, avoiding Class B, looking for the field and forgetting to come down. Nothing like being 3000' agl on a 2-3 mile base leg cleared to land #2. Throttle to idle, slow to 85, full flaps, gear down and slip; people behind me can deal with it.

Other than transition and recurrent training, I slip very rarely, not because the plane won't or is dangerous, but because I try to plan my approaches so that I don't need to, just as I predict shifting and braking in the car to avoid the rattle-and-shake of the ABS system helping me stop. "Fly the numbers" isn't just airspeed, it's also power setings, altitude and descent rate.

But if you need to slip, short and medium bodies slip well; Bob K. advises caution slipping long bodies with full flaps. As for ice, try real hard to avoid it but if you have to land with ice, slip carefully. My CFI's & CFII's have always said "never extend flaps if you have any ice" so Bob's additional warnings about tail stalls when slipping long-bodies with ice should not apply to any of us.

Be careful out there!

P.S.--I avoided ice on Sunday afternoon by staying another night and coming home early Monday morning, so I would not repeat the "urgent pirep for freezing rain at 7500', 15nm west of BLF." Planning and judgement, right? The center of the airway is 17 nm west, MOCA 6300, MEA 8000. I'd rather be a couple hours late on Monday morning than never get here . . .

[N201MKTurbo]

I've been slipping my Mooneys for years, it works fine, I've never had any problems. It would be nice to have more rudder. My current Mooney is a J with speed brakes. Granted that if you fly properly you never need the speed brakes or to slip, but stuff happens.

[Piloto]

Side slip with less than 3 gallons of fuel on the low wing can cause momentary fuel starvation if running on the low wing tank. This is due to fuel unporting from the tank fuel pick up. Before proceeding with the slip make sure the fuel selector is on the high wing.

José

[fantom]

Side slip with less than 3 gallons of fuel on the low wing can cause momentary fuel starvation if running on the low wing tank.

That sir, is a FACT! Don't ask me how I know

[Cris]

In general I don't argue with what works but consider that long bodies have the potential to blanket the air flow over the rudder (misspoke, should have said elevator) with full flaps under certain air speeds. All of the Mooney's can run out of rudder when in a forward slip when you need it most like in the final landing phase correcting for drift. Thus when I teach crosswind landings I recommend only a crab. Passengers particularly seem to appreciate this more than an aggressive forward slip.