floaty landings

[GeorgeC]

I'm a pre-solo student pilot with a dozen hours or so in the 172. For the last little while, I've been practicing right-handed patterns on a runway with no VASI. To further complicate things, it's been breezy of late, up to 14 gusting 20.

My C172 POH says that landings are okay with any flap setting. I have typically used 30° on normal approaches, but have subsequently tried 20°, 10°, and no flaps in windy conditions. The lower flap settings seem to make the plane a little more controllable and less prone to wallowing.

Things are getting easier every time I go up, but I am still prone to flaring prematurely (happens to everyone...), hesitating when it comes to chopping the throttle after I cross the runway threshold, and underestimating the power of ground effect.

That said, I'm still finding myself floating down the runway or ballooning out of ground effect. Are there other confounding factors I should be looking for, or is the wind just messing with me?

 

[Jim Logajan]

The 172N POH says 55-65 kias flaps down approach speed; I don't understand the discrepancy between this figure and 1.3 Vso. Incidentally, Vso is 33 on my checklist, but is 41 in my POH.

33 is probably KIAS and 41 probably KCAS.

I tend to remember and use KIAS since that's what I'm dealing with in the cockpit - but I'm still a student myself so my advice has no depth of experience behind it.

 

[Jim Logajan]

The 172N POH says 55-65 kias flaps down approach speed; I don't understand the discrepancy between this figure and 1.3 Vso. Incidentally, Vso is 33 on my checklist, but is 41 in my POH.

One other point - I would suggest you go with what the manufacturer's POH says for normal landing speed in KIAS - not 1.3 Vso in KIAS, KCAS, or Warp Time-Dilation calibrated speed. The latter is, I believe, a RULE OF THUMB ABSENT POH GUIDANCE.

Caveat again: I am just a student too. I expect I'll get beat up now by those who have advised 1.3 Vso!

 

[Jim Logajan]

You have that backwards. POH doesn't adjust for weight except to give you a 10 knot range. In reality, after a while, you don't need to look at airspeed because you'll be able to feel it in the elevator resistance.

"If knowledge fails you, refer to the manual"

So I shouldn't trim out that elevator resistance so I don't become a slave of the POH? :wink2:

 

[Jim Logajan]

??? Try to make sense and not confuse other students...

I thought the context made it clear my comment was about your unclear comment.

With respect to your and other poster's earlier advice about the 1.3 factor - that factor appears to derive from FAA airplane certification requirements. How they determined it is unclear to me; none of my textbooks on aerodynamics appear to have anything on it (not surprisingly.) The closest I can find is a text that refers back to FAR Part 25!

Also - to avoid confusion I would say that is essential to make clear in future advice that the values in the "1.3 time Vs or Vso" should be in KCAS. Then convert back to KIAS using the (ahem) conversion table in the POH.

 

[Jim Logajan]

Actually by the book, 1.3*Vso adjusted for your weight comes in at about 53 KCAS.

That makes the stall speed 40 KCAS. That seems low; perhaps you multiplied 1.3 by the KIAS rather than the KCAS?

The procedure should be: find stall speed in KCAS for the desired landing configuration, multiply by 1.3, then convert to KIAS using the KCAS to KIAS conversion table for the airplane in the POH to determine what is a reasonable target number, give or take.

 

[Jim Logajan]

Why?

You have plenty of reserve energy at 1.3.

Besides, you shouldn't be using the ASI much anyway -- it's a reference speed, but should be a "feel" you have (controls a bit sloppy, not a smuch lift, airplane slower, etc).

Are we talking about different things? Earlier some were advising 1.3 Vs or Vso for the target speed on final, but neglecting to clarify whether the stall number to multiply 1.3 by is in KIAS or KCAS. It makes a BIG deal at the low speeds.

Now here I think you and Henning appear to be discussing speeds in the flare and roundout - in which case of course you shouldn't be looking at the airspeed indicator.

I tried to make clear I was just a student too so my advice had no experience behind it.

Now I'm going to say that regardless of the extensive experience you and Henning have, it does no good if you do not communicate it with consistency, clarity and as unambiguously as possible. I appreciate good advice and informed opinion freely offered, but if someone like me points out that perhaps you have provided advice that contains ambiguity or may be incorrect, please don't think it is intended to insult or demean. (If I do manage that, it is due to momentary irritation on my part.)

 

[Jim Logajan]

Yep, that's a good way to get the number. Now you can also go up and fly at the verge of stall, just in the buffet, trim it up good, get a feel for what the controls feel like when you are there, now go ahead and speed up a bit until the stall horn is chirping on and off and fly around at that speed trimmed out for a while and get a feel of what the controls feel like. Now add 5 knots to that, trim it out and fly around for a while and get a feel for that. (all the while note how much you are adjusting the trim as well as the sound of the airplane) That is the feel you are setting for as you settle in from your turn base to final. Now go practice some approaches. As you settle in and trim up for for that elevator feel watch the runway and your perspective lines and adjust your power to stabilize them while maintaining that feel. As you start to come closer to the bottom, say around 50', pull out some power and start rolling that trim in and slowing down until the horn starts chirping and adjust your power for steady state to your landing spot. As you lose sight of the threshold under the nose, tap in that last nudge of trim and as the threshold passes abeam of you take out the last of the throttle and just hold your attitude as the stall horn gets louder and the plane settles in. You'll have done a perfect landing without once having looked inside the cockpit.

Thank you - that's clear procedural advice I can actually use and will try next chance I get.