Jump to content

Landing Approaches on the Backside of the Power Curve


John Vance

Recommended Posts

If you fly a CT, you’ve noticed that sometimes the “bottom drops out” 5 feet above the runway, if you let the speed drop too low and don’t add power.  CTs seem to have a fairly sharp drop in the lift/drag ratio somewhere in the mid-40 kt range with full flaps.  About a year ago, I read about using this phenomenon for landing approaches in “Stick and Rudder”, and started playing around at altitude with lower approach speeds in the CTLS. This is standard bush pilot technique - nothing new about it, but I’d just never tried it and wasn’t about to try it for real on my own.  Last summer during my biennial review, my instructor taught me how to use it for landings, and it now gets regular use. My airplane stalls at 29 kts indicated with full flaps, power off, wings level, at gross wt (I realize that this number results partly from pitot position error). At about 43 kts indicated in my airplane, the approach angle steepens noticeably.  You can either nose down to increase stall margin when near the ground, or with enough practice (and benign weather conditions), use power and careful control of airspeed all the way down, no float. I’m using this as an alternative to slipping sometimes, because my passengers don’t like the bank/yaw angles.  I’m curious as to whether anyone else is learning/using using this technique in the CT. 

Link to comment
Share on other sites

Learning - yes, and appreciate your inputs on the topic.  Winter weather has more often had high + gusty winds, so have kept it safe not much lower than 50k approach speeds on some of the more mild days.  And I'm solo weight of plane, 1/2 fuel, + me ~ 950lb.  Slower approach speeds are the next area of my envelope exploration, but waiting for calmer conditions.  In my old C-150 with STOL package I had a good feel for low approach speeds all the way down to 40k range.  I don't plan to go beyond the bottom of the curve though, I still prefer no power landings and have no desire to try to hang this bird on the prop, backside of curve region - someone else can make video and maybe I'll change my mind!

Link to comment
Share on other sites

GrassStrip - I’m with you on the prop hanging thing, and am just cautiously exploring that last phase of the approach. You definitely will not see my video anytime soon. Another interesting thing about flying the CT in that low speed range, though, is that you can feel it when you’re there. During the last biennial, we used that to practice landings with the airspeed indicators covered up - finding that airspeed zone by feel, and maybe adding a bit of down pitch for margin.  It’s surprisingly easy. 

Link to comment
Share on other sites

I would guess that landing a CT on the back side of the power curve, where pulling the nose up increases the sink rate, and especially using power to maintain flight below the power-off stall speed, would be hard on the ventral tail fin. Maybe you can add a wheel to it.

I'd like to see the video too.

Mike Koerner

Link to comment
Share on other sites

17 hours ago, John Vance said:

If you fly a CT, you’ve noticed that sometimes the “bottom drops out” 5 feet above the runway,

I transitioned from a Piper Cub a year ago.  Stall landings @ 15 degs flaps were the norm for me which worked well in calm winds.   I believe the stall technique increases the chance of the dreaded 4-5 foot hang/float/stall/bang.

Then I went flying with a couple of amazingly skilled CT pilots and learned from their techniques.  They "Flew" the plane into the landing.  I made the transition myself to "flying" the plane into the landing and stopping the last second pull back and float/stall... my latest improvement was trimming the stabilizer to a slight "down" position (from center) forcing me to keep slight back pressure on the stick.  

Not a very scientific articulation of how my landings improved but hopefully it helps a newer CT pilot out there.

Link to comment
Share on other sites

Was out on a local hop today, and performed some approach to landing stalls @ 30 degree flap setting.  I did a few of these during check out time 6 months ago but not much since then.  I'll preface this with I was nearly full fuel and solo.  Was surprised how hard it is to get the rate of decent much pass 500 fpm even with 30 degrees, kept the plane in a constant buffer from stall to nose back down, sort of the porpoise up and down edge of stall for a long session of continuous stalls, essentially flying right on the edge of stall speed, a little break then build a few knots back to another stall.  It took fairly heavy back pressure keeping the trim at my previous cruise setting.  The nose would wander a bit as well, but did not take much for rudder inputs like a departure stall might.  I'm sure a bigger yank on the stick would have made more violent breaks, but was wanting to simulate more of a stabilized approach in a normal landing.  I was seeing indicated airspeed down to 30N or so, and never felt uncomfortable with it remaining responsive to inputs and such.

Below is a shot of the ADS-B track, started at 3500msl and flew a loooong time before ending maneuvers at 2500msl, noteworthy is how shallow the green line altitude is considering this was essentially a "stabilized stall track line", for comparison - my old Cessna would have been at least 1000 fpm in this scenario - these CT's like to fly, or is that glide!

image.png.875b5f8cb2ed655dad8e1bd2c2283340.png

Winds on my strip were perhaps 10N range, set up for 30 degree flaps and a stabilized 45-50 N approach, was dipping a tick below 45 at one point and a tiny blip of power holding approach angle the same brought back to 45N.  Landing and rotation happened slightly sooner but still felt very much the same, main difference was I hit the numbers with little runway behind me, rolled about 500' on soft turf with no brakes - that sure felt good.

Observations - I see no reason to attempt landings less than 45 N in the 30 degree flap setting, and certainly would not be doing that with a passenger extra weight in mix, or in gusty conditions, etc.  Clearly we're not flying STOL birds here.  I was confident both in conditions and me being on my game, not saying to anyone go try these lower speed approaches, but I would encourage others to do the air work at altitude, developing awareness to these edge of envelope areas.  

 

Link to comment
Share on other sites

GrassStrip - thanks for your observations.  Your story sounds very similar to my experience. The value I see In the low-speed approach is the relatively steep glide path, simultaneously with a controlled low airspeed and little float on the round-out. The descent rate (fpm) might not look impressive but since groundspeed is low, the descent angle can be similar to a slip.  For me, over the fence at 35 flaps & 45 kt is good, but sometimes hold 40 earlier on final to steepen the glide if needed.   All this assumes benign wind conditions.   I think this is a valuable thing to have in your bag of tricks, if for no other reason than familiarity with that end of the envelope.  My go-to technique has always been a slip, but I usually arrive at flare hight with a bit of extra speed.  

Link to comment
Share on other sites

49 minutes ago, John Vance said:

he descent rate (fpm) might not look impressive but since groundspeed is low, the descent angle can be similar to a slip

 

49 minutes ago, John Vance said:

or me, over the fence at 35 flaps & 45 kt is good, but sometimes hold 40 earlier on final to steepen the glide if needed.

John, would you slip at 45k's to increase the rate of descent say in a super short field approach?  And, can this speed be held at near gross weight or do you add a few knots at gross weight?  Nice write up Darrell.. thank you.

Link to comment
Share on other sites

29 minutes ago, AGLyme said:

 

John, would you slip at 45k's to increase the rate of descent say in a super short field approach?  And, can this speed be held at near gross weight or do you add a few knots at gross weight?  Nice write up Darrell.. thank you.

That’s a great question. I’ve always kept the airspeed a little higher for slips, just because it’s a cross-control situation (but better than a skid) and then there’s the transition to the flare, at a really low altitude.  It might be worth trying at altitude to see what happens.  On the other hand, on short final, the descent profile in the low 40+ kt range with 35 flaps is already a little spooky to me. 

Link to comment
Share on other sites

I won't be playing with low speed slips, and I'm comfy slipping at 55 speeds, maybe some of the higher time crew here have thoughts.  I use to enjoy spinning my first 150, am not at all afraid to mix it up.  Intentional cross controlled with low speeds is a bad situation.  I'd love to explore spinning the CT, but obviously won't be due to limitations, therefore not having any experience in spins I'll be very cautious when it comes to dancing around those edges...

Link to comment
Share on other sites

I don't intentionally fly approaches that slow, but solo I do land pretty regularly at 48kt/30° flaps and have done so a few times at 46kt/30° when trying to get in very short.  But that's not exactly what you are talking about, because power is not needed to arrest the descent.  at 43kt, I believe you are talking about the part of the envelope called the "region of reverse command", where increasing pitch doesn't slow the descent rate, but rather increases it because you are so far on the backside of the power curve.

I'm sure landings like this can be done, but you'd better be really, truly on your game when doing them.  Personally, if that's what's required to make a landing, I'm probably going somewhere else unless it's a true emergency.

Link to comment
Share on other sites

3 hours ago, AGLyme said:

 

John, would you slip at 45k's to increase the rate of descent say in a super short field approach?  And, can this speed be held at near gross weight or do you add a few knots at gross weight?  Nice write up Darrell.. thank you.

I have slipped at 46kt or so, it works fine. 

Link to comment
Share on other sites

To help clarify the topic, here's a visual.  A normal no power landing would be near the bottom of the blue line.  In my earlier post I used the slang of "hanging on the prop", which refers to pitching up more, adding power in to provide additional lift in nose up attitude, and enter the region of the slowest possible airspeed (or more precisely lower ground speed, pitot / static system questionable in these attitudes).  Adding the power in counteracts the increased induced drag extending the point of stall occurring to lowest possible airspeed, this is exactly how those STOL competitors perform the shortest of landings.

When I was taking lessons in '99, my instructor was engineer in day job (and I'm eng too).  The day we cover this topic we went out and plotted it in my 150, noted airspeed by each 100 RPM and graphed it back on the ground.  The weak 150 at gross weight just barely got into the reverse region.  The CT with better thrust to weight ratio might generate a line closer to this example, but if attempting this for landing, yeah that comment about having a wheel on tail is accurate.  Many of the STOL guys smack the tail just as they chop the power dropping it in, not a maneuver to pull off in a CT.

This curve can easily be created at altitude, and might be interesting to also chart GPS ground speed, could note both indicated and ground speeds to discern airspeed discrepancy if wind was factored in.  Maybe I'll explore this in coming weeks.

image.png.d2b9cc235e3266c44432f63e5cfc573a.png

Link to comment
Share on other sites

Thx Andy and Darrell for the clarifications. Naturally I need to make adjustments for the LS which is much heavier... I have been exploring sub 60kts on final with no issues.  Will work the slip in there at that speed and continue to experiment with ever lower until I find my comfort zone.  

Link to comment
Share on other sites

Of course weight is critical.  A CTLS is usually 50-100lb heavier than a CTSW.  When I talk about slow approaches, I'm almost always solo and with 20 gallons or so fuel, sometimes more.  I think with a similar configuration a CTLS could get with a knot or two of the same speeds, but of course only experience will tell you for sure.  When I'm flying near gross I usually use a 60kt approach speed or even higher depending on conditions.  I can use 55kt, but for non-pilot passengers a shallower approach is usually more comfortable for them.

Also, I don't go into short fields with passengers.  I have landed and taken off from 2000ft grass with trees at the end with two people, but that's about as short as I'd go unless there are very clear approaches.  And short field takeoff techniques definitely apply.

Link to comment
Share on other sites

Good advice. Andy.

Mike K, I went flying today, but I did not practice slips as I went on a quick flight and I won't get to go for a while so I did some quick 30 degs flaps takeoffs and landings.  Re your comment about students teaching themselves, I agree somewhat.  My experimenting takes place at 3,500' first... I am fully aware of the CT's stall characteristics which I did tons of when I was transition training and which I still perform from time to time.  With the Dynon, I know where the wind is coming from and how many knots at altitude which is a great feature when experimenting.  Once I am comfortable,  I take the show to the airport.  I do agree with you that many people unfortunately don't have the common sense to evaluate whether they are capable of experimenting in a conservative manner or not.  

That stupidity is in the same category of the pilots I see who fly once every six months, or, the pilots who never pre-flight, they just pull out the plane and go.  Human nature is a bitch.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...