hotrod150 wrote:I guess I'm not sure exactly what is meant by "behind the power curve". If lift/drag max is best glide speed, I'm definitely slower than (left of?) that in the scenario I described. "In order to slow down you have to add power" sounds to me like below power-off stall speed.

How about a (better) definition of "behind the power curve"?

Think about it this way, to the right of L/D max pitch sets your A/S and power controls rate of descent (ROD)- just as you said. If you want to fly a slower approach you pitch to capture your desired speed and then adjust throttle to maintain your desired ROD. This will work, in theory, down to L/D max. Once you go to the left of L/D max (also known as "behind the curve" or the region of reverse command) the drag generated by the AOA needed to maintain your desired speed increases dramatically in proportion to the generated lift. So to capture an even slower speed you would have to ADD power to supplement the lift generated by the wing - without additional power you wouldn't be able to maintain your desired airspeed without incurring an undesirably high, or possibly even fatal if you were deep enough in the stall, ROD.

So, again in theory, if you were to determine that you needed to fly an approach at speed X in order to stop on the available landing surface, and speed X is below your L/D max, you would have to fly a behind the curve approach to attain speed X which means you would have to carry power to overcome the drag induced at the necessary AOA. Clear as mud?

This is well precedented in carrier aviation - for example the A-6 and EA-6 flew behind the curve approaches intentionally. In their case it wasn't to get sufficiently slow, it was to keep the engines throttled up sufficiently such that they could maintain the precise glide slope required and ensure they had quick throttle response if they had to wave off. Those old turbo motors had abysmal spool up time from idle.

Nice work Vick!

That is a really good analogy.

Guess I'm dense- neither Vick's explanation or Soup's link does much for me. Where is L/D max? is this best glide speed, or stall speed? Or something else entirely?

Headoutdaplane wrote:yep, I am pulling out the red card on that. I usually don't like to directly contradict someone but will do it for safety reasons. Power does indeed equal glideslope and pitch is airspeed, that is how it works.

You are correct sir, pitch does equate to airspeed - to the right of L/D max. To the left it works a bit differently. And it has nothing to do with safety, it's a discussion on theory. All we're working toward here is an understanding of that theory, application is another matter entirely.

Headoutdaplane wrote:If you are adding power to slow down, what you are actually doing is adding power to stay in the air and your pitch attitude is still controlling your airspeed.

Again, you're entirely correct about adding power to stay in the air but to decelerate further you will have to add power, not pitch for it (though in truth it would be a coordinated maneuver). What you're essentially doing is transitioning from wing borne flight to engine borne flight. Take A/S all the way to zero (assuming your VSI is zero as well) and lift would have to be entirely generated by the engine - now you're a helicopter or an airshow performer hanging on the prop.

Headoutdaplane wrote:I will say that it is really dangerous to promote theories that could get a less experienced pilot in trouble, for example: if someone read your post and is landing long, but thinks he needs to add power to slow down because of his pitch attitude.

I'm not advocating any technique, we're discussing theory and clarifying terms. And I'm not promoting some wildly wreckless or experimental theory, the L/D curve illustrates clearly what I'm discussing. If we were to take your admonition to heart we'd have to delete most of the content of this site.

It goes without saying - or maybe it doesn't - that the wisest and most responsible way to expand your operational envelope is with a qualified instructor riding shotgun. Good luck to anyone who reads some internet banter and tries for a new personal best based on what he's read.

Again I ask- what is L/D max? From the chart in Vick's post, I would say best glide speed? In my airplane, that's 65 per the POH, so any airspeed below this is to the left of L/D max -- and according to you this is the backside of the power curve. I don't know what full flaps does to that, but seems to me that best glide with flaps should be the same 65 IAS (maybe?).

Eric, go fly it.

Set up a landing configuration in your airplane, haul back until things get mushy to find your stall speed of the day, and then work at 1.1 to 1.2 Vso. Maintain your speed with elevator (trim for hands off and it's easy) and vary your VSI with throttle.

It's a lot easier in real life than it sounds with all the charts and graphs. Rate of descent too wimpy, pull back on the gas. Sinking like a brick and gonna drive the gear through the belly of the airplane when you hit, more gas. Sometimes lots. Sometimes all ya got, and even then wishing there was more.

That's the trick part. Sink too great, and you have no energy for the flare with the low airspeed. That gas pedal is your flare. Depending on your weight, inertia, and density altitude you really have to be careful on managing the sink rate and transitioning into ground effect and a flare. Practice, practice, and practice. And you need to feel exactly what the wing is doing.

It's like flying floats. Very easy to learn the basics, but then a lifetime of really learning how to work it.

Get all that squared away, then it's down on the deck in ground effect to learn how to slow things down even more. Then this shit gets fun.

Gump

GumpAir wrote:Eric, go fly it. Set up a landing configuration in your airplane, haul back until things get mushy to find your stall speed of the day, and then work at 1.1 to 1.2 Vso. Maintain your speed with elevator (trim for hands off and it's easy) and vary your VSI with throttle. It's a lot easier in real life than it sounds with all the charts and graphs......

Oh, I've got this technique down pat, been using it for quite a while. Just weak of the theory side of it-- trying to understand the point where you get "behind the power curve". Like I said, seems to me that the best L/D is also best glide speed.
as a student pilot, I never qute got all the weather stuff either.

Indicated best glide speed (L/D max) approximately equals the max rate of climb speed in most airplanes.

Note that the published best glide speed is for max gross weight and still air. Lighten the ship and L/D max speed decreases slightly.

Headwinds should be flown at best glide speed + 1/2 the headwind. This is important.

Tailwinds should theoretically be flown slightly slower than still air best glide speed but in practical terms, I would stick to still air best glide speed.

Given the natural propensity for pilots to fly too slow in dire situations, faster is usually better.

hotrod150 wrote:...trying to understand the point where you get "behind the power curve".

To boil it down then, to fly an approach at or below the power off stall speed for a given configuration you would have to carry power - that's behind the curve/region of reverse command.

Yup.....

Gump

The speeds you talk about are IAS?
Find the stall speed of the day with the plane configured for landing , then approach at 1.2 stall speed .
In my plane that would mean approching at 48mph!!!
Because usually with 2 people stalls at 40mph or even less, (it never stalls really) and I have done level effortless flight at 50mph.

Sounds exciting, will try it first at 1000 AGL though and practice this a lot at alt.

Just be realllllllllllll careful. You can get into a sink that you can't power out of without pushing the nose down to build up speed. Not a big deal at 500 feet AGL. But you'll bend that airplane doing it at 50 feet. You gotta feel the sink through the seat of your pants (and VSI) and be prepared to use a huge amount of power to flare or arrest your sink rate.

Gump

MarkGrubb wrote:Indicated best glide speed (L/D max) approximately equals the max rate of climb speed in most airplanes.

Note that the published best glide speed is for max gross weight and still air. Lighten the ship and L/D max speed decreases slightly.

Headwinds should be flown at best glide speed + 1/2 the headwind. This is important.

Tailwinds should theoretically be flown slightly slower than still air best glide speed but in practical terms, I would stick to still air best glide speed.

Given the natural propensity for pilots to fly too slow in dire situations, faster is usually better.

Might be more "important" to use best glide +1/4 headwind component, at least some of the time!

http://www.nar-associates.com/technical ... screen.pdf

GumpAir wrote: ...be prepared to use a huge amount of power....

Huge emphasis on this - flying on the backside of the curve is most safely done when you have LOTS of excess thrust/power available. Not something to fiddle with in your stock 65hp cub on a warm afternoon at Smiley Creek.

And for crissakes, if all this is new to you please go find an experienced instructor to discuss the concepts with in person and who can then keep you safe as you work on application.

Great thread. Both the discussion about full-flaps, power-off approach and flying a short-field approach on the back side of the power curve. Thanks to all the posters for good discussion.
Greg

motoadve wrote:.....Find the stall speed of the day with the plane configured for landing , then approach at 1.2 stall speed . In my plane that would mean approching at 48mph!!!............

I would sneak up on that approach speed incrementally-- try knocking 5 mph off your normal approach speed, then another couple mph, etc. Work your way down to it. You may find that you start running out of control authority when you get real slow- this can be bad news if you get into a situation that requires some corrective action due to squirrelly winds. It's nice to land slow & short but not if you end up in the ditch alongside the runway in the process.

This is my last post on this subject, since this dead horse has been beaten.

Slow airspeed at touch down = short ground roll. Go to altitude, cover up your airspeed indicator, get slow and get used to it, 30 degree banked turns left and right, get to where you are adding power in your turn to keep from stalling, and then do it in descents. Play in slow flight until you are comfortable with the stall horn on all the time (or get rid of the horn and really feel the rumble of the plane), you need to know when it will stall.

We have markings on runways that will tell you exactly how long it takes for you to land and TO, use them to figure out what you can do (yeah, yeah, I know, most off airport stuff will stop you sooner and delay your takeoff, but it is a good reference).

In training my folks have to tell me where they will land, not just length wise but laterally as well (we fly into some mine strips with alders within 5 feet on each wing). Really practice on spot landings, that will make a huge difference. Who cares if you can keep your ground roll to 300 feet if you land 50 feet after the threshold?

Do all this practice at gross weight. 'Cause really... what good is going into a short field unless you can carry something? (except for making "I love me" videos).

This stuff really isn't rocket science, it comes down to knowing your aircraft. Besides, most short fields have some wiggle room. The shortest place I go into I am not worried about the landing, but the take off (but that is a whole other can of worms).

Fly smart, Fly safe!

Still trying to get a grip on landing the 180. Today was awesome, 25 gusting 30 and crossing the fence at 40mph with power. Put it in the hangar feeling like a king today..........tomorrow she will probably try to buck me off again

G2Gorder wrote:Great thread. Both the discussion about full-flaps, power-off approach and flying a short-field approach on the back side of the power curve. Thanks to all the posters for good discussion.
Greg

I agree too!

Headoutdaplane wrote:The shortest place I go into I am not worried about the landing, but the take off (but that is a whole other can of worms).

Ya got that right. The Spam Cans most of us fly can can get into a whole lot of places we could never fly out of again. Though if you can't pinpoint a landing to within a few feet, it's a moot point anyway.

Gump