Yes...pretty much the second you relax the slip you gain speed or lift in a 172 (depending on what you do with the elevator). Slip it right to the ground and then relax it and have enough energy for the flair. I do teach slips with full flaps, not as a standard approach tool, but as a way to loose alt when you don't have a choice about it.

When I took my private check ride I had been practicing a lot of slips with full flaps just for fun. After the examiner (an old salt named Dutch Zwietzel) had me do ground reference maneuvers and stalls, we came back to the field for "5 or 6 landings". I was nervous and turned base way too early. I told the examiner that I could make the field but I would go around to be cautious (I didn't want to seem reckless). He said "Son, if you can get it on the field I want to see it". I immediately cranked into as full a slip as the controls would allow and slapped the flap leaver all the way down.We had a strong head wind, maybe 20 degrees cross and the 152 came down like an elevator, I don't think ground speed could have been over 25 knots. Right at the ground I relaxed most of the slip, keeping just enough in for the cross wind, hauled back on the yoke and it sat down right on the numbers and couldn't have rolled 150 feet. It was the best landing I had made up to that point. It must have impressed him because we didn't do any more and he passed me.

With full 40 degree flaps on Cessnas, the trim is the same as cruise. If you don't mess with the trim and use full flaps, you don't have to mess with the trim. Normal control pressure for any given pitch attitude and speed is useful in situations that require lots of attention outside the cockpit.

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I said I would defer to high-timers, and two of them just spoke, so I will not challenge their 10X more experience than mine. Sincerely.

I may have not explained myself well... the point I was trying to make is that in addition to the well known Cessna forward CG problem (causing me to "run out of elevator" trying to flare with full flap deflection)... adding one more factor by making it so the airplane is descending much faster (due to slip/drag), means that it will probably require even more elevator authority to flare than I would have required at the "normal" full flap descent rate.

So the question I would humbly pose to the more experienced Cessna drivers is... :

Two identical 172's, solo pilot flying at forward CG, both with full 40 degree flaps, power-off, into a short strip.

+ One is descending at nominally 50 MPH wings level and coordinated, and one is descending at 50 MPH in a full rudder forward slip.
+ The vertical speed (rate of descent) on the slipping aircraft is (likely) showing 1.5 times the vertical speed of the non-slipping aircraft. So, arbitrarily, the non-slipper is descending at 800 feet a minute, and the slipper is descending at 1200 feet per minute.
+ At the bottom of the descent, it is required to abruptly and decisively arrest the rate of descent to prevent damaging the aircraft.
+ The pilot of the slipping aircraft can terminate the slip any time he wants, but the rate of descent for the next few seconds is still 1.5 times the rate of descent of the non-slipping aircraft (due to vertical inertia).

Which pilot will have more elevator authority to flare the airplane safely? Which airplane will make a harder landing?

contactflying wrote:With full 40 degree flaps on Cessnas, the trim is the same as cruise.

I'm talking about flying at slow speeds, like on a short/slow final approach. With full flaps, at slow speed, at forward CG, the yoke is fairly far back in my airplane,and I don't have a lot left over for flare. It is very hard for me to land in a nose-up attitude, I'm usually lucky to land it on the mains first at all.

If I'm incorrect, and full flap does not require a lot of trim, then there was no reason for Cessna to put in a trimmable horizontal stabilizer in the next airplane they built after the 170/172.

Try more nose down trim when at 40 degrees flaps. More back pressure required to pull back in the flare, but you have more elevator authority.

All moot point anyway. Where do you really need full flaps in an old C172? Need that short to get in, you'll never get out.

Gump

GumpAir wrote:
All moot point anyway. Where do you really need full flaps in an old C172? Need that short to get in, you'll never get out.

Gump

Thats a good point.

My tailwheel conversion is a '56 with the O-300B. The vast majority of flying with this airplane over the 1000 hours I have in it now are 10-20 degrees on takeoff, and 20, sometimes 30 degrees on landings. With power and ground effect I can land as slow as I want, and wheel or three point I don't have elevator issues (except take off roll that damn tail is heavier than shit)

Gump

EZFlap wrote:.
I said I would defer to high-timers, and two of them just spoke, so I will not challenge their 10X more experience than mine. Sincerely.

I may have not explained myself well... the point I was trying to make is that in addition to the well known Cessna forward CG problem (causing me to "run out of elevator" trying to flare with full flap deflection)... adding one more factor by making it so the airplane is descending much faster (due to slip/drag), means that it will probably require even more elevator authority to flare than I would have required at the "normal" full flap descent rate.

So the question I would humbly pose to the more experienced Cessna drivers is... :

Two identical 172's, solo pilot flying at forward CG, both with full 40 degree flaps, power-off, into a short strip.
+ One is descending at nominally 50 MPH wings level and coordinated, and one is descending at 50
MPH in a full rudder forward slip.
+ The vertical speed (rate of descent) on the slipping aircraft is (likely) showing 1.5 times the vertical speed of the non-slipping aircraft. So, arbitrarily, the non-slipper is descending at 800 feet a minute, and the slipper is descending at 1200 feet per minute.
+ At the bottom of the descent, it is required to abruptly and decisively arrest the rate of descent to prevent damaging the aircraft.
+ The pilot of the slipping aircraft can terminate the slip any time he wants, but the rate of descent for the next few seconds is still 1.5 times the rate of descent of the non-slipping aircraft (due to vertical inertia).

Which pilot will have more elevator authority to flare the airplane safely? Which airplane will make a harder landing?

EZ, IN my humble opinion, the guy in the slip will have way more authority than the other one, One mistake in your supposition is the 50 MPH forward speed with the guy flying the slip, his forward speed will be way less than the guy going straight.

When you turn the slipped aircraft back to heading you immediately slow your decent with up elavator as you come out, there is no seconds of more decent.
You are taking the non wing that was falling out of the sky(less forward speed) and transitioning to the full lift and drag of the full flap wing, you are also abruptly encountering Ground Effect, where flying it in with elevator all the way back you are wallowing through it.
You have the inertia of that gravity to allow you to flare where if your just driving in with the yolk all the way back, you already have it used up! (ELAVATOR) In the slip you will have lots of elevator left to use.

I think I said that right

Next go into a short strip with engine dead and no flaps? or full flaps, You want the least forward motion you can get! Your not worrying about getting the airplane out or off the ground again, your just worried about living through it?

It's actually just the opposite of rounding out for your flare??!!

Again I think I said that right??

In answer to EZ's lack of elevator control problem: when making an approach to a very short field we will have much better speed and glide angle control with as much power as possible. On short final, we should be near to or behind the power curve. It is this extra power in a higher pitch attitude (because of the higher power) that gives us a slow and controllable rate of descent. The nose will be nearly level with the full flaps and considerable power.

The no power approach, as in the forced landing, will require more elevator accuracy, but there will be plenty of elevator. We still need to descend and slow up as much as possible before arriving at the beginning of the forced landing site. Maintaining the brisk walk apparent rate of closure with that target, rather than blindly using the airspeed indicator, to achieve this is the easiest way. If we use the airspeed indicator to maintain too much speed, we have a descend and slow down problem at the bottom. We will go long. This situation, too high and too fast, will encourage us to stay up in ground effect too long or bang it in down with flying speed. Both are worse options than gradually reducing pressure airspeed (using apparent rate of closure) to stall speed at the beginning of the landing zone.

With or without power, the brisk walk apparent rate of closure remains constant throughout the approach. While keeping our eyes outside, we automatically reduce airspeed to stall. This is because both altitude reduction and closure with the target cause us to "appear" to speed up. We correctly react by increasing pitch attitude to slow down. At the point where this becomes dangerous, the target passes out of sight below the nose. From there, very short final, we look down the runway or landing zone beyond the target.

I don't habitually use slips, because the barn doors provide more than enough drag to get me into wherever I want to go. But on occasion I practice full flap, full rudder forward slips, and honestly, lack of elevator authority is never an issue. As soon as I straighten out from the slip, there's a slight increase in airspeed, and I have all of the elevator authority I need.

Cary

RE the switch from 40 degrees to 30 degrees of flaps... I remember reading somewhere that the decrease in flap setting allowed Cessna to RAISE the max gross weight. Apparently one of the certification requirements is the ability to manage some positive rate of climb in a go around with flaps fully extended (think flap switch failure) at max landing weight. Going with flaps 30 allowed a higher weight - which is a big deal when the salesman is working his trade!

Yesterday just for the heckuvit I purposely turned base early so that I'd have to use a full flap, full slip approach if I wanted to get down anywhere near the numbers. Same as always--no phugoiding, dropped like a rock at 70 mph indicated (yeah, I could have done it slower--the AOA was on the high side of the yellow), flared and straightened out at the same time at about 5'-10' AGL, IAS jumped up a couple needle widths, lots of elevator authority.

So after landing, I took off and went around the pattern again, this time slowing to 65 mph. Angle of final approach with full flaps but no slip looked to me about the same as 70 with a full flap slip--AOA was in the middle of the yellow. Still no problem with elevator authority.

I didn't do it yesterday, but I've made several landings when practicing very short field landings at 55 mph--and that puts the AOA right at the red/yellow mark--just about as slow as I'm interested in going most of the time, but still well above stall (which is very near the bottom of the red). That makes it pretty easy to roll to a stop in 600' or less.

Other than misjudging altitude vs. touchdown point, though, I can't think of any good reason to slip with full flaps, because as Gump said, if you need both to get in, you sure won't get out again. Certainly at the elevations I fly, getting off again in 600' is close to unlikely.

Cary

Cary has demonstrated that, when planned, Cessna's 40 degree flaps are plenty adequate to get in slow enough without slipping. I have only used the full flaps and full (rudder on the stop) slip with low level forced landings after engine failures. When the engine fails while we are very low, we need to make the near field. The far fields are not even in view. Most of my ten engine failures were in Pawnee or Call Air. Neither have very good flaps. Full flap and full slip was necessary to prevent hitting something on the other end of the landing zone. Three were in Cessnas and I appreciated the better flaps, even though I used the full slip as well to be sure.

It is reasonable to consider the low level forced landing unusual. It is also reasonable to teach them, especially to those whose work is 100% low.