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Flaps vs slipping

Hopefully the Cub/Super Cub thread drift on the Vx/Vy thread, can migrate here.

A student asked for a side slip demonstration today – somewhat anachronistic as our EASA PPL course may not include this in the official lesson plan.

We took the 152 and practiced side slips to left and right, flapless and flaps twenty, and flaps thirty.

Highest RofD was…drum roll…flapless, at around 1,000 fpm.

The 152 not being overly endowed on the rudder effectiveness front, only manages about 15 degrees of bank angle before running out of rudder, at 65 KIAS (ASI on the 152 being very untrustworthy in a slip). Blanking of the tailplane by flaps reduces the rudder authority further, and full flaps you might get a stable 10 degrees of bank, with only a 600 fpm RoD.

While the Super Cub has more generous rudder authority, it also exhibits lower RofD with full flaps in a side slip, than a flapless side slip – for the same reason.

A higher speed will add rudder authority, but the higher RofD will be used up the higher speed and float on round out.

This is not a side slipping turn which is taught as a an emergency descent manouever.

Most sufferers of a Super Cub fetish, guilty as charged, will seek out the lightest variant, which usually means flapless – gyros, electric systems and excessive application of dope on the fabric is also dispensed with, trying to get the empty weight down below 900 lbs.

The lesson concluded with flapless circuits in a gusty direct crosswind, using the side slip method – given the limited rudder authority in a side slip, somewhat explains the 152’s relatively modest maximum demonstrated crosswind speed of 12 knots.

Oxford (EGTK)

Piper Classique the wingspan is the same for the J3 and the PA18, 35 feet and 2.5 in.

You are correct that early Super Cubs have a slightly lighter wing, but they can still be authorised to 1750 lbs in the -150 version, same type, although they were certified to 1,500 lbs with the -95 version.

Perhaps you are thinking of the short wing tailwheel Pipers (Clipper, Pacer, etc), or the experimental aerobatic clipped wing Cub, although I am not aware of any SC’s ever getting the clipped wing treatment.

The PA11 is not a J3, different airfoil, and soloed from the front.

Ironically the Aztec/Apache share the same NACA airfoil with the SC.

Oxford (EGTK)

I think I’ve been lucky, as it was not entirely by design, to have been put in the position of flying two very different light aircraft. One (see my moniker) slips like crazy, coming down quickly when slipped in spite of low wing loading. Oh, it is so much fun even while highlighting that coming down is much easier than going up if you have only limited power.

Plane #2 doesn’t like to slip at all, having been given the heavy rudder feel that characterizes modern planes, and maybe a bit more than others. No worries – it comes down like a rock anyway when desired, for other reasons. You don’t slip it, you fly down final with power and ease it off when necessary.

I think he elimination of adverse yaw on modern planes drove designers away from light rudder feel. Why make it easy to misuse something if you don’t need to use it much anyway? That (plus flaps obviously) made slipping appear redundant. Too bad because to me slipping is a good tool, gives you such a fine degree of descent control, and is so much fun. I think birds would slip if they couldn’t retract their wings!

and is so much fun.

Yes, for us. But I once did it with a Seneca on a slightly rushed approach that I wanted to save (they had offered me a different runway at the last possible moment) and it scared the passengers to death. It was the only occasion that I heard people scream on any aircraft driven by me…

EDDS - Stuttgart

Sideslips are certainly fun, and I find myself lucky to have them an important part of our safety traditions. That is to say, standard microlight practice has us flying the final approach too high, in case the engine should quit, then once one is very sure to be within gliding distance the excess height is “slipped off”. However the more prudent instructors teach two limitations: no sideslips with flaps extended, and no slipping right till touchdown.

One less prudent instructor, at a field with lots of crosswind, enjoyed himself a good deal by teaching me to land on the “into the wind” wheel only, then let the bird roll till the other wheel dropped, still pulling the stick fully back and steering with the rudder. Great fun once I mastered it but my present field has little crosswinds, and those we have are too turbulent for this trick. I think not all passengers would enjoy it, either.

EBZH Kiewit, Belgium

I do practice slips with the C150 with my students, albeit the sink rate with 40° flaps is greater than the sliped rates. Our club has a SF25 and its slips as hell. I just have to gain some flight time on TMG before I can instruct in the bird. I think it really enriches PPL training (and is fairly cheap to operate. We charge 54 Euros per hour wet plus instructor.)

Last Edited by mh at 23 Mar 21:21
Inside the sky.
EDXE, EDXF, Germany

Probably not practical in a Seneca (!) but when seated side-by-side with a non-pilot passenger, I tell them this before slipping: ‘OK, we’re slightly high so now I’ll make the plane go a little bit sideways through the air, and that’ll fix it" I think it’s then intuitively obvious what’s going on. If the engine is making “puckity, puckity” noises like a farm tractor that probably helps with context too, i.e there’s nothing the slightest bit high tech about this!

That description really seems to work assuming you ease into it gently and slip to the left so they’re pushed into the plane, not out.

PS Jan, I’m often approaching over a built up area until very short final, so I try to take exactly the same approach (pun intended) – high until we’re got it made, then slip it off.

Last Edited by Silvaire at 23 Mar 22:13

No one has yet mentioned the use of sideslip as a variable approach control device in a forced landing or just a glide approach. Unlike flaps, if you look like being a bit short, you can come out of a sideslip without the sink usually associated with retracting flaps.

It's supposed to be fun.

PiperC good point – thanks. A form of speed brake as in a sailplane.

Oxford (EGTK)

About 75% of my training was carried out in microlights that were not fitted with flaps so sideslipping was very much part of the way things were taught. It is useful to adjust an approach when practising PFLs and for clearing obstructions on the approach on some of the smaller strips I visit . To be truthful when I’m playing, it is fun to view the runway down the wing as I slip down.

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