Narrowing down landing / approach speeds

[lowew79]

Hello!

I am looking for a way to get a better idea of what approach speed to use in the 182. The book says 60-70 flaps down or 70-80 flaps up. This range seems to be rather, uh, wide lol. Are these numbers based on max weight? If not which weight? Is there a chart or something where you can compute more exact landing speeds based on your current aircraft weight?

Its hard to know how high above the runway I am by just feel and looks. I found a fantastic video by someone your old simmers likely know well, in which he discusses a landing technique that does NOT rely on depth perception! The sticky part is that it depend on flying very very closely to stall speed x 1.3. Of course stall speeds are different based on weight and configuration as well. So is there a chart to compute stall speeds as well?

Here is the video for those who are interested https://www.youtube.com/watch?v=Rv5HEJCyTuk

[DC3]

You may have to derive your stall speed empirically by going up to about 3000 feet agl and seeing where the aircraft stalls at. Then calculate the 1.3x for approach with flaps. The 1.3x is a rule of thumb not a hard and fast rule. If you find yourself 'floating' down the runway, or 'bouncing', or 'landing long', try cutting 5 knts (mph) off your approach speed. After about 20 landings made with a controlled approach speed you will develop a 'feel' for the approach speed needed to keep the plane on the ground once the wheels are down and an approach speed that will let the flare put you in the stalled condition right as the wheels touch the runway.

As far as the visual aspect goes there are a few things that help a lot of pilots:
1. Set your approach speed with the attitude of the aircraft and trim to keep it at the desired approach speed. This will let you use the throttle to control the descent rate.
2. Pick a spot where you want to land and note if it moves up or down on the windscreen. If it moves down you will overshoot your spot, if it moves up you will undershoot your spot. Unless it is a windless day and your glide slope is perfect don't expect this spot to be static. You will need to make throttle adjustments to keep it where is should be. You may also need to make small adjustments with the yoke if the spot is moving up/down to rapidly.
3. Realize you will flare at the end of the descent and make allowances for it when you pick your spot.
4. Line up with the runway centerline as early in the approach as possible. Crab to keep the aircraft in line with the centerline. This means the nose of the aircraft will not necessarily be pointing down the centerline. Keep the wings level as much as possible and use the rudder to keep the plane headed in the correct direction (after you are on the centerline track) You can tell if you are on the centerline by noticing if the runway angles one way or the other. If the approach end of the runway is angled to the right (compared to the far end) you are left of centerline, move right. Same idea for the approach end angled left compared to the far end of the runway.
5. As you get down to short final don't worry about your landing spot, if your approach was good your spot will be fine. If your approach was not good, go around, don't force it. Forcing a landing teaches bad habits. Look at the far end of the runway and make alignment corrections with the rudders. Looking at the far end of the runway will help to judge the flare and the height above the runway. It will also help with Ron Machado's advice because you will be able to notice when the runway is getting to that point where you will be able to see both sides of it. Straighten out your aircraft to be aligned with your landing position and drop your upwind wing if necessary to keep a crosswind from blowing you off the runway.
6. Round out and hold the aircraft nose level with the far end of the runway. This should slow your descent to near 0 fpm. Now is the time when all pilots are tested. Because if you hold this position you risk falling onto the runway as the speed decays below stall speed. If you are too high above the runway you risk landing nose wheel first, or landing hard. On the other hand, if you pull the nose up from the flare too much you will gain altitude, stall, and fall rather hard back to earth. The test is if you can flare by pulling the nose up enough to let the aircraft gently settle on the runway right at or a little below stall speed. Good luck. Every landing presents all pilots with this most difficult test. When the test is successfully accomplished we all smile and get that rosy feeling that comes from greasing it on. When the test is not accomplished... well we just vow to try again next time.

-- I am sure there are other hints that others can give you. These are things I have seen through the years and that I have used in my own landings. Generally my landings are 'good' landings, in the sense that I can walk away from them, (ha ha ha). But, when I have that landing where I am not sure if I am on the runway or not, that is the landing I like the most. It is also the hardest to get and I don't get it every time. Having practices a lot of landings (IRL) and in the sim, it seems to me the most critical thing to having good consistent landings is having a good consistent approach speed. The way I get a good consistent approach speed is to pick a speed, trim for that speed, and practice landing with that speed. If I am too fast, I will lower that speed a little on the next landing, if I am too slow I will raise the speed a little on the next landing. After a while I know pretty well what approach speed I need in any particular aircraft. From there I start working backwards to what speed I need to be at when I am starting the approach sequence before I lower landing gear or lower any flaps. After a while I know where I want to start at, where I want to be, and my landings become a lot more consistent. Then I am left to deal with head winds, cross winds, turbulence and variations in weight. The winds give me more trouble than variations in weight because once a baseline is established and you know you are heavy then you can increase the speeds a little for the various parts of the approach. The increase in speed is pretty linear between your normal approach speed and weight and the approach speed at maximum weight. If you increase your weight to 50% between your normal weight and the maximum weight then increase the approach speed about 50% of the way between your normal approach speed and the approach speed at maximum weight.

Since power controls your descent it is good to know what general power settings you need at different stages of the approach. Of course adjustments will have to be made to power to account for head winds for example. A strong head wind means it will take longer to get to the runway. This means an approach with less of a descent in fpm. This means a little higher rpm on the power setting. Remember you have pitched for your approach speed so a little more power should not change anything when you get to the runway. The round out and flare should be the same. Your landing roll might be a little shorter.

I apologize for the long email, but I hope something in here will help you to figure out your answer. Remember, practice, practice, practice. And slow down your approach by getting started early setting up for the approach so you have time to adjust for attitude, descent, and alignment with the runway.

[AKar]

Just to add a general principle, stall speed typically quoted at maximum weight in the manuals, and at different weights it is proportional to the square root of the actual weight fraction. That is, if your weight is 90 % of the maximum, the stall speed would be sqrt(0.90) times the reference stall speed, though importantly, as it is with any aerodynamic figures, it is in practice in CAS, not in IAS, and you'll need to account for any airspeed indicator error variances that can be significant and non-linear near the stall speed. So, IAS -> convert to CAS -> calculate -> CAS -> back to IAS.

To give a complete example of previous, should your full flaps landing weight be, say, 2800 lbs, then:
2800 lbs / 3100 lbs ≈ 0.90.
As your quoted stall speed at 3100 lbs is approximately 50 kCAS, then the stall speed at 2800 lbs would be:
sqrt(0.90) * 50 kCAS ≈ 47 kCAS.

This is how you can calculate the stall speed for your approach speed reference. At full weight of 3100 (note: above MLW), your reference approach speed, using the 1.3-rule, would be:
50 kCAS * 1.3 = 65 kCAS ≈ 63 kIAS,
at maximum landing weight of 2950 lbs it would be:
1.3 * sqrt(2950 lbs / 3100 lbs) * 50 kCAS ≈ 63 kCAS ≈ 60 kIAS
while at 2800 lbs it would be:
47 kCAS * 1.3 ≈ 61 kCAS ≈ 57 kIAS.

So, I'd say that in most cases, the precise reference approach speed means relatively little in these planes, compared to other factors of common sense that may cause you to adjust the approach speed. Even if we take an extreme example at a light landing weight of 2300 lbs, you can calculate your approach reference speed at 56 kCAS, that is, about 50 kIAS. Note that the airspeed indicator error means more than the actual variance in weight at these speeds! Also, I've found the technique discussed in the video equally useful for wide range of speeds (btw, that is precisely why it is useful!). Obviously, if you carry some excess speed, you will float some, as mentioned above.

Calculation is similar to flaps up speeds, just use the applicable stall speed reference.

-Esa

[Great Ozzie]

I am looking for a way to get a better idea of what approach speed to use in the 182. The book says 60-70 flaps down or 70-80 flaps up. This range seems to be rather, uh, wide lol.

Commercial Practical Test Standard (U.S.) is ±5 knots for approach & landing. So if you can bracket your chosen airspeed by that amount, you are doing well. However, airspeed control is a real "challenge". This is where I have seen a real problem - the individual's (mine / others) ability to bracket their chosen speed - not so much in the manufacturers published speeds. There's a reason for those numbers (not just the margin above stall) and ordinarily (RW) should be used. Another other consideration is, you could be the cat's meow when it comes to holding a chosen airspeed, but if you are all over the place on your glidepath, your point of intended landing will suffer - which defeats the purpose of what one is trying to accomplish.

Are these numbers based on max weight?

Ordinarily, I would say, "yes". However, the one landing chart in the C182 is based on being a bit below max weight.

Is there a chart or something where you can compute more exact landing speeds based on your current aircraft weight?

Here's a link to a post I made a while back discussing this topic. There's a link there for some FAA material entitled "On Landings" (three parts / .pdfs) that is definitely worth a look.

The sticky part is that it depend on flying very very closely to stall speed x 1.3. Of course stall speeds are different based on weight and configuration as well. So is there a chart to compute stall speeds as well?

The "1.3" is 1.3 x Vso - which means means the stalling speed or the minimum steady flight speed in the landing configuration. That 1.3Vso is meant for short final only if you don't have a recommended airspeed. From the C182 POH, you can see Vso is given @ max weight - and at the most forward center of gravity. Wrt to the C182, there is just the "Short Field Landing Distance" chart in the POH using 60kias @ 2950lbs.

Now, as an example, there are Warrior II (PA-28-161) manuals, where you go to calculate landing distance, that are based on weight, where your approach speed decreases with decreasing weight. However, I have to emphasize, you cannot say to yourself, "Well... Piper allows this much reduction in airspeed for this much reduction in weight... so that's what I'll do with my Cessna." Bad idea. Again, manufacturers have a reason for those numbers - and they were part of the certification process. When I was actively flying, this was of no concern, as manufacturer provided numbers I always found to be good. Truthfully, I had absolutely *no* inclination to fly otherwise... because as I said, airspeed control was a larger factor. And, for any grass strip I was going into, I was building in a margin of 50% (or more) to the takeoff / landing distances.

If I really needed to reduce landing distance - say planning a trip where there were some short grass strips I wanted to get into *and* I was supremely confident in my ability wring-out what I currently could based on the POH (plus margins) - first thing I would do would be to find a qualified instructor and start a ground lesson.

But here in the sim, yeah... also have a look at that "On Landings" series... they're short, but very good info in them. And then have some fun applying it.

-Rob

[DC3]

Akar makes good points. I plotted the numbers presented and also a linear trend of the numbers. For practical purposes it can be seen, and Akar correctly states that other factors influence the approach speed equation to the extent that a rough estimate can be made and will be close enough to be practical for use in light aircraft. Thanks Akar for the equation, I learned something today.

[lowew79]

WOW!!

What great answers, I will have to read them several times to fully comprehend, but I can do that!

What really strikes me is that in your examples, using real world (or maybe real sim) numbers, you are calculating approach speeds that are UNDEr the 60-80 kias range thats listed in the manual and the clipboard. For the record the clipboard say 60-70 knots with flaps down, and 70-80 with flaps up. (why would you land with no flaps at all? Isn't in procedure to at least have 10 degrees flaps?)

when doing pattern work with single 200 pound pilot (um yeah sure that's right for me lol) and about half a tank, using the chart in the post up there, my approach speed should be about 55 or so, which is less than the manual says. I guess that's okay then?

it just feels weird flying slower than the clipboard or manual says, thanks for all the great info guys!

[Great Ozzie]

(why would you land with no flaps at all? Isn't in procedure to at least have 10 degrees flaps?)

Possibly for (increased) directional control in a crosswind.

Also, flaps could fail (electric motor etc.). Stuff like that.

-Rob

[Oracle427]

A no flaps landing is 100% likely when you have no power. It's good to practice then from time to time because it takes a lot more runway to land and the approach is shallower. I've witnessed a crash, thankfully with no injuries, where someone forced the airplane to land after gliding over 3/4 of the 3000 foot runway because they had no flaps. The airplane was a wreck after hitting a guardrail at the airport perimeter.

Coming in slower than the published approach speed can be done with proper training and experience. One big issue with coming in too slow is that you can end up deep behind the power curve in a high sink state. There are techniques to avoid this that are not the same as what you are taught for a normal or even short field landing when following the POH. It is much higher risk than using the published procedure. You can touchdown and come to a full stop within the length of the runway numbers in a 172 with proper technique as I've seen it done.

[DC3]

What really strikes me is that in your examples, using real world (or maybe real sim) numbers, you are calculating approach speeds that are UNDEr the 60-80 kias range thats listed in the manual and the clipboard. For the record the clipboard say 60-70 knots with flaps down, and 70-80 with flaps up....

I would say the chart is more representative of the Cherokee. I don't know if it is applicable (in terms of air speeds) to the Cessna...

[AKar]

Thanks Akar for the equation, I learned something today.

No problem. It is a quite simple result you can easily see from the (normally relatively useless) lift equation L=½ρv²ACL by noting that the lift in this case equals weight, which you determine case by case, and by definition of stall, the CL is exactly the CLmax, no matter whatever it happens to be, and therefore a constant, and by solving for v² which remains the only variable besides the lift, that is, the weight, which gets under the root.

(Or if lazy, one can just note that it is well known that the stall speed depends on the square root of load factor - the g-force - which is for this purpose exactly equivalent statement!)

Of note is that the conversions from CAS to IAS I made above were based on a correction table from 182T POH of an example using G1000 cockpit, and therefore not universal nor applicable to other types.

it just feels weird flying slower than the clipboard or manual says, thanks for all the great info guys!

Yeah, and it is good to remember that likely there has been some reasons why manufacturer recommends slightly higher approach speeds. 1.3 times the stall speed, like very many figures in aviation, is just an arbitrary number basically (though there is some reasoning behind it), and the approach speed can be determined in other ways too. Like Cessna does by just stating that it is something in between 60 and 70 knots . Likely they've found it safe and practicable enough.

-Esa

[William Hughes]

I did see cross-winds mentioned above but I thought I'd add a bit. Using more runway at a higher speed is one way to reduce the risk during a gusty crosswind landing. Don't use the flaps and go faster. If the wind suddenly switches behind you there is still some airspeed left to keep it together. And the higher speed helps reduce the amount of crab or slip required to keep the aircraft tracking down the runway.

Don't under-estimate the differences between high wing and low wing aircraft either. Gusts and crosswinds have reduced effects on a wing two feet off the ground than they do to a wing six feet off the ground. Ditto for the flaps.