Pilot_DAR wrote:
a little extra speed is a little extra stored energy, money in the bank so to speak
Yes, but gliding at minimum sink rate is the most efficient way to store energy. Pushing the nose forward will simply gently accelerate the aircraft while using more and more energy per second. You cannot “store” lost energy by increasing speed. Best L/D won’t do you any good, unless you have to cover a distance most efficiently.
The airspeed at minimum sink rate is already “fully flared” in a way, so you cannot pull the stick more and decelerate the sink more than you already are doing, which could be a problem when touching the ground. But you can push the stick fwd, accelerate and cover larger distances if needed, and this will be more efficient, energy vise, than going straight to best L/D.
LeSving wrote:
But you can push the stick fwd, accelerate and cover larger distances if needed, and this will be more efficient, energy vise, than going straight to best L/D.
So you could go a larger distance by flying faster than best glide?
That’s not what I meant. Starting at min sink rate (which is the most efficient gliding you can do), you can simply push the stick to best L/D and glide farther at any time you want, and you will have bled off less energy than the one flying constantly at best L/D.
So you’ll only be able to cover a smaller distance (at a lower speed) than if you flew all the way at best glide, but “converserve” more energy? You start with the same energy, but you are being more economical and end up having travelled a shorter distance (I am assuming no wind) (and on the ground you have no reserve energy anyway so it’s not like you end up with some more energy than “me” who flew all the way at best glide?
Don’t get me wrong, I also agree just flying best glide might not the best situation in many scenarios (where minimum sink would be), but I am having trouble assimilating this “energy” thing.
Noe wrote:
Don’t get me wrong, I also agree just flying best glide might not the best situation in many scenarios (where minimum sink would be), but I am having trouble assimilating this “energy” thing.
The energy of an aircraft is the sum of the potential energy given by its height and its kinetic energy given by its speed.
At minimum sink speed you will lose energy at the lowest rate, so in that sense it is the most efficient speed. But during the flare you are not interested in losing energy as slowly as possible — you are interested in having enough energy to arrest your descent and make a smooth landing. As the height is essentially zero, this energy must come in the form of kinetic energy, i.e. speed. What “enough” means depends on the aircraft, its configuration and descent rate and may or may not require a higher speed than minimum sink.
From here
Pilot_DAR wrote:
For my skill maintenance, nearly all of my landings at home will be power off from downwind, just for the practice. I occasionally fly a prop stopped forced approach, but usually onto a larger runway, as I self insure my planes – I’m not trying to create needless risk for myself!
Great stuff! In what plane? What pattern alt do you start at?
Snoopy wrote:
Great stuff! In what plane? What pattern alt do you start at?
Most commonly, my C 150, and Thurston Teal amphibians (which glide poorly), but also in the 182 amphibian, (which also glides poorly), the PA-18 on skis, and the 172 taildragger. All certified types can be glided to a safe landing, it’s a certification requirement. It’s just up to the pilot to master the technique best for that plane!
Snoopy wrote:
What pattern alt do you start at?
When I train power off approaches. the first rule is that they are to at least a touch and go, if not a full stop landing. No powering away from 100 AGL! SO it helps to have a runway where you don’t need to conform to a standard traffic pattern. In most power plane, what I see these days as the “pattern”, is mostly a place in the airspace from which a successful power off landing to the runway would not be possible.
If you can imagine an equilateral triangle formed from the numbers to the midpoint of the runway, with the third point off to one side of the runway, that’d be where I’d start my getting used to how the plane glides in. If you’ve got a really good glider, and are going to overshoot, overshoot, and try it a little further out. I like a slipping turn from downwind, all the way around to final approach. I will extend flaps at some point along the curing final approach, when I know I have the runway made. Once flaps are extended, do not retract them, unless you’re going around. The sideslip can be increased or decreased as desired. Yeah, I’ll even sideslip 172’s, they sideslip just fine, the placard is an “avoid”, not a “prohibited”. As long as you’re keeping the speed up, the cautioned disturbance off a flap onto the tail is not a factor.
You’ve set up really high, so you’re not trying to stretch a glide, you’re trying to get down. So fly faster – two reasons, you simply want to get down, so who cares the speed, as long as you land in your intended area. Drag increases as a square of the speed, so if you’re flying faster, you’re creating even more drag than you would have gliding at something like “best glide” speed. And, the extra speed makes judging (or misjudging) the flare and touchdown point must less a concern. Remember, if you’re going to misjudge where you’re going to touch the surface, misjudge long, rather than short. You’d rather overshoot at 20 MPH, than undershoot at 60 MPH!
Flying a curved downwind, base to final, allows you to stabilize the turn, and thus the approach. You can moderate your anticipated position over the fence by increasing or decreasing your turn radius, as well as sideslips for altitude.
These skills have come from some OMG moments during flight testing different and modified planes (knowing that mods always make them more draggy in my world. If I’m testing to establish a new power off approach speed, I’ll err to the much faster approach, and see how much too much I was too fast in the flare (how much runway I burned up holding it off). Then I’ll begin to reduce the speed, leaving everthing else the same, until I feel Happy about the opportunity to flare.
When I replaced the two blade Hartzell prop on one of my flying boats (O-360), the power off descent rate in fine pitch went from 800 FPM to 1300 FPM at an 80 MPH glide. Trying to flare, particularly onto a water landing at 80 MPH from 1300 FPM to 1 FPM is very challenging. It was some scary practicing. Then I found pulling the prop into full coarse got my right back where I wanted to be – though like turing off the mags, at full coarse, you’ve pretty well committed yourself to land – much too busy hands in the power off flare, trying to get the prop and power up for an overshoot without overspeeding it. The Caravan was great, as the PT6 can be glided in feathered prop, though again, yo’re not going around from that without wrecking the engine.
So, practice practice practice – iteratively. Once you’ve decided that you’re not trying to glide for distance, forget “best glide speed”, that’s just a certification requirement to make sure you can glide to the coast. Actually landing well from that speed may be very challenging (short time in the flare). The better you are at judging the flare, the slower you can fly the approach. The other thing to bear in mind is that where POH approach speeds (often predicated upon 1.3vs are presented in IAS, stall speeds are presented in CAS, which will be a faster speed at approach speeds. So be sure you appreciate the relationship of those speeds and scales to each other before you start really relying on the ASI during gliding. But with the nose down, a higher than normal glide speed, and an intended descent, you’re not near the stall – so one less thing to worry about! Allow it to slow to near stall speed, while you’re holding it off, over the surface!
One caution about practicing power off landings – yes, practice, but know that on cold winter days, you are at a much greater risk of shock cooling (cracking cylinder$) pulling the power to idle, and diving toward ground. So this is something I practice a lot in the summer. In the winter, I carry some power all the way down, and sideslip aggressively with flap to modulate the descent rate I want.
@Pilot_DAR Posts moved to a previous thread on this topic.
Ah, okay, I was wondering what was happening, my post was not sticking. Some deleting is probably needed now….
