Can a B Model be slipped at a less than 40 degree?

A place to relax and discuss flying topics.

Moderators: GAHorn, Karl Towle, Bruce Fenstermacher

User avatar
juredd1
Posts: 274
Joined: Tue Dec 04, 2012 4:55 pm

Can a B Model be slipped at a less than 40 degree?

Post by juredd1 »

I get the idea of why I can't slip a B model at 40 degree of flaps but as I understand it this rule only applies to the 40 degree setting...correct? Can I not slip a B model at 0-30 degree of flaps?

You might ask why would you when you have the 40 degree setting. Just because I can (maybe) and it works well for many types of planes why not a B model.

Justin
My playground....
35°58’52.01” N 93°06’27.51” W
'54 170B White and Green with a hint of Red
User avatar
mit
Posts: 1049
Joined: Wed May 01, 2002 1:54 am

Re: Can a B Model be slipped at a less than 40 degree?

Post by mit »

plenty of info on this out there....... blanks the tail.................
Tim
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Can a B Model be slipped at a less than 40 degree?

Post by Bruce Fenstermacher »

40 degrees of flaps employed with a slip can lead to blocking out airflow over the elevator with a resulting elevator stall. The result can be a very dramatic nose down attitude, if not actually, at least feeling like the aircraft is on it's back. At an altitude of a little less than 1000ft, you'f got a problem when this happens, specially when it most often catches the pilot by surprise resulting in a natural reaction to pull full up elevator with a resulting secondary wing stall. This is likely the cause of death of at least one member and his wife and probably a few others. Many more have experienced it unexpectedly and barely survived.

Now that we have the problem out of the way, what about less than 40 degrees of flaps and a slip?

The warning from Cessna was is against a full (40 degree) flap and slip maneuver. I could see where 30 degrees flaps and a slip may bring on the same issue but it is not reported that I know of and I've not experienced it. So the answer, without hours of low wages being a test pilot in your 170 finding the definitive answer is, it's probably not an issue.

But why do it? It is not necessary in a B model. Sure slipping is fun. But it is not superior to using 40 degrees of flaps. And in slipping your B you can be setting yourself up for a negative habit that might get you without your thinking. Your high on a approach with 40 degrees of flaps, and next thing you do without thought is kick in a little rudder and wammo.

Personally I never do it. It is that simple for me.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Can a B Model be slipped at a less than 40 degree?

Post by GAHorn »

I actually have shuddered as I recall that as a much younger and stoopid flight instructor I specifically decided to demonstrate to a student that such rumors are false, and (in a 1964 172) I deployed full flaps and severely slipped the airplane at low altitude. Having satisfied that client that I was more knowledgeable and more skilled than any airplane manufacturer, we completed the days glories and survived the day. Nearly half-a-decade later I hope that poor misguided person is still alive and flying.

The reason Cessna developed this highly-effective flap system is because slips are so inefficient for the average aviator because many pilots cannot adequately control airspeed and directional control or they'd not have gotten into the fix they are already in to require an additional absurdly-steep descent to correct their already mis-handled approach-to-landing. These people are the types of decision-makers who,... rather than demonstrate the wisdom and skill-set to go-around,... prefer to perform a low-altitude, near-aerobatic maneuver they've rarely performed...added onto the lousy approach they've already screwed up.

(I don't buy the claims that slips are better than fowler flaps at getting into short strips with tall obstacles. The people who make those claims are the same ones who do not control airspeed and are deficient at slow-flight... the very ones who have no business attempting low-altitude slips. Have you ever noticed how non-proficient pilots that attempt slips usually let the airspeed get away from them?... and now they end up in a long-ground-effect float... throwing-away their attempt at short-field performance. (Plus, the increased airspeed only exacerbates the disruption of airflow over the tail.)

Section III of the Owner's Manual, under the subtitle "Landing", states "Slips with full flaps are to be avoided because if the slip is extreme enough at a relatively high airspeed, the airflow is disrupted over the tail surface resulting in a sudden and steep, downward pitch of the nose."
I agree whole-heartedly with Bruce's comments except that I'd recommend you never slip a fowler-flap Cessna with ANY flaps deployed lower than the altitudes I'd deliberately SPIN that aircraft (and while in that discussion, I'd add the necessity to be in the UTILITY category and meet any other restrictions the Spin maneuver requires in that airframe because I believe it's possible to end up in such a spin!) Spins, by the way, requires that flaps be UP...for good reason!

True, that Owner's Manual statement only mentioned full flaps. But if you have yet to deploy full flaps ...and are high/fast for this approach...then there are two things you've already mis-handled...(you've failed to make a stabilized approach,...AND you've mis-judged the amount of flaps you needed. Now, reaching the decision-point at which you now find yourself... excellent reasons to go-around and set up again.) ... And hardly the time to throw-in a near-aerobatic maneuver at which you're not proficient and which the manufacturer specifically warns against.

I was never an engineering test pilot. Those guys are in a different league than the boring production test pilot job I held. But I can tell you this: If the Cessna 170-B and early 172 series were being certified today... instead of a politely-worded caution in an unapproved document created by the Sales Department... There'd be a PROHIBITED placard required in full view of the pilot, required to be taught by check-airmen, and respected by those who wish long lives. I think testing the airplane in slips at 30-degrees with a view toward adding that maneuver to my bag-of-tricks is akin to Tickling the Tail of the Dragon, when better approach-planning skills and low-altitude full-flap go-around training is better called for.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
Watkinsnv
Posts: 187
Joined: Tue Apr 23, 2002 1:55 am

Re: Can a B Model be slipped at a less than 40 degree?

Post by Watkinsnv »

On a cross wind landing it has been said that you shouldn't use 40 degrees of flaps as its a slip approach wing low as to a crab approach. But 30 degrees is acceptable. Flaps are and can be used on any approach. I stopped using 40 degrees on cross wind landings. Can we agree that 30 degrees is an acceptable normal approach in a cross wind landing wing low.
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Can a B Model be slipped at a less than 40 degree?

Post by GAHorn »

Unless I'm at near gross wt I only use 30 degrees for landing as I find it easier to predict touchdown. I also favor wheel landings, especially with crosswinds. I use 40 on short/grass every time however, and I approach at 60 mph or less, planning my flare at 50-55, and a 3-point touchdown, kicking-in rudder in the flare just before touchdown when/where there's no chance of elevator loss-of-control.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Can a B Model be slipped at a less than 40 degree?

Post by GAHorn »

juredd1 wrote:... Just because I can (maybe) and it works well for many types of planes why not a B model.

Justin
I just realized that you may be asking a question because you've never rec'd the serious explanation of "works well for many types...why not a B model."

Here's why: The large flaps of the B-model was a fresh introduction of a new type of flap system which turns the relative wind into a huge down-wash... right in front of the tailplanes. If one remembers that the tailplanes (horiz. stabilizer) acts as an upside-down wing. It provides lift in a downward direction... using the fuselage as a lever... operating over the wing's center-of-lift as a fulcrum... to keep the nose-heavy airplane from diving toward the ground.

Now, recalling that a stall can occur when the angle-of-attack exceeds a critical point... and the horiz. stab. is an upside down wing...and the flaps increase the AOA with that huge down-washing relative wind placed just in front of that horiz. stab... It should be evident that the tail is being brought perilously close to a stall. If a slip is then introduced, the fuselage will act to blanket one-half of that horiz stab (I.E., the relative wind is blocked by the fuselage from reaching the other side of the tail).... In other words, you will have suddenly removed half the effective working surfaces of your horiz stab.... and when the sudden increase in workload is placed upon the only half doing any work... it's similar to suddenly increasing the gross weight of the aircraft for that half to keep airborne. The tail loses sufficient authority suddenly. The nose points straight down suddenly. In fact, the nose may over-rotate in the downward direction such that the airplane is at least momentarily beyond the vertical and seemingly, slightly upside down..

Worse, with all that applied rudder, ...the airplane will rapidly rotate/roll about the longitudinal axis.... you are basically in a steep, nose-down, spin from which it can take several thousand feet to recover.

I hope the mental picture is clearer.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
ghostflyer
Posts: 1390
Joined: Mon Apr 21, 2008 3:06 am

Re: Can a B Model be slipped at a less than 40 degree?

Post by ghostflyer »

Thank you for the previous advice as you answered a issue that I have with my 170A. Even with then smaller flaps on mine and extended at 100 kts slid slipping is a issue . I have had it pitch down and flick,around to the left . All the rigging is spot on . However I think I have the reason why my aircraft does this will be explained when we meet up at Cody.
User avatar
canav8
Posts: 1006
Joined: Thu Sep 25, 2008 2:34 pm

Re: Can a B Model be slipped at a less than 40 degree?

Post by canav8 »

juredd1 wrote:I get the idea of why I can't slip a B model at 40 degree of flaps but as I understand it this rule only applies to the 40 degree setting...correct? Can I not slip a B model at 0-30 degree of flaps?

You might ask why would you when you have the 40 degree setting. Just because I can (maybe) and it works well for many types of planes why not a B model.

Justin
Justin, truth is. If you have to slip with flaps 40 you are in a very unstable approach from the beginning. It is recommended that an approach with flaps 40 will yield the steepest approach should you need to do it over a tree line. The fact that the horizontal stabilizer blanking is a very real phenomenon. You should not put yourself in this situation especially since a couple others before you have gone down that path and never got to the end of the path. please heed all warnings regarding the B model slips and flaps 40. Regards, Doug
52' C-170B N2713D Ser #25255
Doug
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Can a B Model be slipped at a less than 40 degree?

Post by Bruce Fenstermacher »

I think, in many of our minds, getting the info out to all about the danger of a 40 degree flap and slip, we lose site of Justin's question. He does not want to slip with 40 degrees of flaps. His question, a good one is "Can a B model be slipped with less than 40 degrees of flaps.

There would be two reasons one might do this. A maneuver in response to a less than perfect approach to landing. And I think we've covered that. The other, a planned maneuver just for fun. No different than any other type of planned maneuver.

I can not recall ever, a story related to me in my association with the 170, about an issue with slipping with 30 degress or less flaps. And no one here so far has either.

Many of us have a distaste for any slip in a B simply because we don't want to send the wrong message to someone who does not understand the complicated issue it is. It is not that the maneuver itself it is unsafe, but a misunderstood message doing it can be. We would rather fault well into the safe zone and not do it at all.

I slip the heck out of my A model. And many times I wonder if I should cause there are to many 170 owners that don't know the difference between an A and a B.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
SteveF
Posts: 216
Joined: Fri Dec 10, 2004 4:39 pm

Re: Can a B Model be slipped at a less than 40 degree?

Post by SteveF »

Cessna went to a max of 30 degrees of flap at some time during their manufacture of the 172. I think they used the same flap as before just limited
the amount that can be applied. So did they remove the suggestion/restriction in the POH of slips with full, 30 degree, flaps at that time? Unfortunately
I don't know the answer but it would be a good indicator of how they feel about 30 degree slips. It has been said they went to 30 degrees because of the
liability with 40 degrees so if they also removed the restriction then it is a good guess it is not super dangerous to slip with 30 degrees.

With that said I survived a tail stall caused by slipping with 40 degrees of flap in a 170B and after cleaning my pants I swore never to slip with more
than 20 degrees as a safety limit. It is really scary!
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Can a B Model be slipped at a less than 40 degree?

Post by Bruce Fenstermacher »

Steve, Cessna's change to limit flaps to 30 degrees may have had more to do with departure certification and nothing to do with the 40 degree flap slip issue. They probably weren't unhappy it also relieved stabilizer stall issue. Remember, the 172 has a different shape elevator. Think it's a different shape just for aesthetic reasons? We will never likely know.

172 to 172E had 40°flap setting, placard "Avoid slips with flaps down."

172F had 40°flap setting, placard "Avoid slips with flaps extended."

172 models till the P had 40° flap settings and from the P on only 30°max. I could not find a required placard after the F model in the TCDS however at that time all placards in the POH where required and it might be there but I haven't the time to research them all.

So we can see the warning became a placard which it is not in the 170 and the placard up to the F says flaps down or extended without specifying a specific degree amount so one could interpret that as ANY flap setting other than 0.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
SteveF
Posts: 216
Joined: Fri Dec 10, 2004 4:39 pm

Re: Can a B Model be slipped at a less than 40 degree?

Post by SteveF »

Thanks Bruce!
Your stabilizer design and placard discussion certainly emphasize that slipping with flaps is not a good idea and got stressed more and more stringently by Cessna as time went on.
Just not a good idea to slip with flaps period. I have to say I enjoy slipping the Champ and would bet you have a smile when you slip the Cub though. :D
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Can a B Model be slipped at a less than 40 degree?

Post by GAHorn »

Highly opinonated comments follow:

Slips were used on flap-less airplanes to lose altitude quickly during an approach which required a steep angle that did not accommodate flap-less aircraft. Once it's advantages were discovered ..even on ordinary arrivals to adequate runways which approaches the pilot had not properly executed ...those pilots employed slips to "save" their poor approach planning.

Flaps were developed as a significant improvement to airframes/flight capabilities. Slips were added to flap-equipped airplanes by those pilots who still couldn't plan/execute an approach.

Either use flaps. Or use a slip. Don't combine the two.

Practice "go arounds" with flaps deployed.

Perform full-flap go-arounds by 1- apply takeoff power, 2-arrest descent, 3-select takeoff flap settings (20-degrees on B models), 4-maintain Vx (67 mph IAS B models), 5-retract takeoff flaps only after clearing obstacles.

(Straight 170 and 170-A models use Zero flaps for takeoff/go-around, and Vx = 76 mph IAS.) Yes, Vx is the obverse of the B model....that was not a typo.

Practice stabilized approach planning.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
n2582d
Posts: 2808
Joined: Mon Apr 29, 2002 4:58 am

Re: Can a B Model be slipped at a less than 40 degree?

Post by n2582d »

With the advent of small video cameras like the GoPro it would be interesting to see one of the professional test pilots among us tuft the tail surfaces of a 170B, go up to a safe altitude, and video the tufted tail surfaces while slipping the plane with 0º, 10º, 20º, 30º and full flaps. Not sure where one would mount the camera. Maybe replace the rotating beacon temporarily?
Gary
Post Reply