Landing at Duncan

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Landing at Duncan

Post by CpnCrunch » Fri Mar 10, 2017 10:46 am

(moving this from the accident thread)
Cat Driver wrote: If you can not touch down on the first couple of hundred feet of runway go get some more training because you should not be instructing.
Does that not mean you'll be flaring before the threshold, i.e. in the drop-off that usually has downdrafts?
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Re: Landing at Duncan

Post by Cat Driver » Fri Mar 10, 2017 11:14 am

What would cause a downdraft at the start of a runway and would there be any indication that a downdraft may be expected?

I stated a couple of hundred feet inside the threshold not the first inch.

How far do you float after a flare on a short runway?
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Re: Landing at Duncan

Post by CpnCrunch » Fri Mar 10, 2017 11:33 am

Cat Driver wrote:What would cause a downdraft at the start of a runway
The terrain generally causes downdrafts there, for obvious reasons. And it's *before* the start of the runway we're talking about, not at the start.
How far do you float after a flare on a short runway?
I'm not sure, but probably more than 100ft in a 172 @ 2200lb.

My point is: if you start flaring in the dropoff before the runway, how do you prevent hitting the cliff if there's a downdraft? It seems that you're likely to end up like this guy:

viewtopic.php?f=118&t=104074

What possible advantage is there to landing in the first couple of hundred feet?
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Re: Landing at Duncan

Post by Cat Driver » Fri Mar 10, 2017 12:17 pm

The terrain generally causes downdrafts there, for obvious reasons. And it's *before* the start of the runway we're talking about, not at the start.
Where did I say I flare " before " the start of the runway?
I'm not sure, but probably more than 100ft in a 172 @ 2200lb.
I allowed a couple of hundred feet not one hundred feet.
My point is: if you start flaring in the dropoff before the runway, how do you prevent hitting the cliff if there's a downdraft? It seems that you're likely to end up like this guy:
And I did not say flare in the drop off before the runway.
What possible advantage is there to landing in the first couple of hundred feet.
Well I always want runway ahead of me I don't need, rather than runway ahead of of me I may need.

What disadvantage is there to landing in the first couple of hindered feet?
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Re: Landing at Duncan

Post by photofly » Fri Mar 10, 2017 12:25 pm

I'm not sure, but probably more than 100ft in a 172 @ 2200lb.
I'm not sure the weight has much to do with it, if you adjust your approach speed for your landing weight (I do recall being pilloried here a couple of years ago for the suggestion that pilots might think about doing that in a 172). If you don't adjust your approach speed in consideration of your landing weight, you'll float further the lighter you are. But then if you're keen on precision landings, you would have adjusted your approach speed appropriately.

I do like the older 172s with 40 degrees of flaps, for short landings. I think they rather spoiled the aircraft when they limited the flaps to 30.
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Re: Landing at Duncan

Post by FishermanIvan » Fri Mar 10, 2017 12:35 pm

When I flew into Duncan, I didn't do touch and goes. I backtracked, and took off.
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Re: Landing at Duncan

Post by Cat Driver » Fri Mar 10, 2017 12:39 pm

Lets look at the advantage of landing in two hundred feet or less.

I flew C117's based in Nanaimo.

My hangar was at the south end of the airport and if I was landing on runway 34 I would turn off at the taxiway about half way down the runway on the left.

If I were to touch down at the displaced threshold I would have to use a fair amount of braking to turn off at the taxiway.

Conversely if I touched down in the first hundred feet or less the need for braking was really no big deal especially in an empty airplane.
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Re: Landing at Duncan

Post by CpnCrunch » Fri Mar 10, 2017 12:53 pm

Cat Driver wrote:
Where did I say I flare " before " the start of the runway?
I did, in my initial post on the subject. I assumed you'd need to start flaring before the start of the runway.
I allowed a couple of hundred feet not one hundred feet.
So how long exactly would your float be in a 172 @ 2200lb, assuming you've had to adjust power and increase airspeed due to downdrafts on short final, and you've only 30 degrees of flap?

What disadvantage is there to landing in the first couple of hindered feet?
The risk of touching down before the runway. That seems a much higher risk than landing 300ft or 400ft down the runway, which is perfectly safe at Duncan.
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Re: Landing at Duncan

Post by Cat Driver » Fri Mar 10, 2017 1:02 pm

I can only speak for myself.

I flew airplanes for a living and thousands of hours of my flying were off airport flying, mostly in DC3's and Twin Otters.

In over five thousand hours of flying those airplanes I " NEVER EVER " landed short of a runway or ran off the end either.
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Re: Landing at Duncan

Post by CpnCrunch » Fri Mar 10, 2017 1:10 pm

Cat Driver wrote:I can only speak for myself.

I flew airplanes for a living and thousands of hours of my flying were off airport flying, mostly in DC3's and Twin Otters.

In over five thousand hours of flying those airplanes I " NEVER EVER " landed short of a runway or ran off the end either.
Neither have I. So how far do you float during a short field landing in a 172? And have you landed at Duncan since the length was reduced to 1500ft?
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Re: Landing at Duncan

Post by Cat Driver » Fri Mar 10, 2017 1:25 pm

I haven't flown a 172 for over twenty five years, and same goes for flying into Duncan.

Anyhow Crunch this conversation is going nowhere mostly because we are galaxies apart in how we fly and how we think about flying.

So I am going to let someone else give their opinions and I will just read instead of post.

I do think that I remember landing a 172 in a couple of hundred feet with a bit of wind and touching down right at the start of the runway on a few occasions....but that was a long time ago so maybe my memory is a bit blurred.

Maybe one of the guys that teach on them can comment on how short you can land a 172.
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Re: Landing at Duncan

Post by CpnCrunch » Fri Mar 10, 2017 1:52 pm

Cat Driver wrote:I do think that I remember landing a 172 in a couple of hundred feet with a bit of wind and touching down right at the start of the runway on a few occasions
Well, it's pretty easy doing that at Nanaimo, as there is a big flat bit of grass before the start of the runway (unlike Duncan which has a big cliff). A stiff headwind will also help.
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Last edited by CpnCrunch on Fri Mar 10, 2017 2:07 pm, edited 1 time in total.

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Re: Landing at Duncan

Post by CpnCrunch » Fri Mar 10, 2017 1:55 pm

photofly wrote:
I'm not sure, but probably more than 100ft in a 172 @ 2200lb.
I'm not sure the weight has much to do with it, if you adjust your approach speed for your landing weight (I do recall being pilloried here a couple of years ago for the suggestion that pilots might think about doing that in a 172). If you don't adjust your approach speed in consideration of your landing weight, you'll float further the lighter you are. But then if you're keen on precision landings, you would have adjusted your approach speed appropriately.

I do like the older 172s with 40 degrees of flaps, for short landings. I think they rather spoiled the aircraft when they limited the flaps to 30.
Well considering the stall speed varies by 15mph in a 172 depending on how it's loaded, that will make a difference to the minimum speed you can use.

I did a search for float time vs speed in a 172, but can't find anything useful. What would you estimate your flare/float time would be during a short field landing with 30 degrees of flap at mid weight?
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Re: Landing at Duncan

Post by photofly » Fri Mar 10, 2017 4:34 pm

Honestly, you can make it as long or as short as you like.
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Re: Landing at Duncan

Post by CpnCrunch » Fri Mar 10, 2017 5:21 pm

photofly wrote:Honestly, you can make it as long or as short as you like.
So, can you find a video of someone doing it in 100ft (without using power)? I can't find any. Ex:

https://www.youtube.com/watch?v=Ebwvpw4ZpEs
https://www.youtube.com/watch?v=Zx2rjCd998s

First one lands right at the start of the runway, but has a very long hold-off (dragging it in with power just above the stall). Second one is a more normal short-field landing, but still has a 3-4 second (300ft) flare.

Even this "ultra short field landing" holds it off for 4 seconds (I think it's just the wind that makes it "ultra short"):

https://www.youtube.com/watch?v=SnXPt3lkwuw
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Re: Landing at Duncan

Post by BeaverDreamer » Fri Mar 10, 2017 7:09 pm

Probably no point in arguing this but if you can't keep your flares under 200 feet in a 172 while doing short field landings you shouldn't have any business operating out of short fields... in my non-expert opinion.
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Re: Landing at Duncan

Post by photofly » Fri Mar 10, 2017 8:21 pm

So, can you find a video of someone doing it in 100ft (without using power)?
Why are you worried about the use of power?
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Re: Landing at Duncan

Post by CpnCrunch » Fri Mar 10, 2017 9:29 pm

photofly wrote:
So, can you find a video of someone doing it in 100ft (without using power)?
Why are you worried about the use of power?
I meant, not using power to drag it in horizontally.

So, can you give me numbers for approach speed and flare distance? I'm pretty sure if you use the book speed of 61kts with 30 degrees of flap you'll float about 300ft, but I could be wrong. Using much less than that doesn't seem like a great idea if you're landing somewhere with downdrafts and a cliff on short final and the windsocks pointing in different directions, but again I could be wrong.
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Re: Landing at Duncan

Post by Schooner69A » Fri Mar 10, 2017 10:13 pm

I haven't flown a -172 for some time, but it seems to me that the listed book speed of 61 knots is too fast if you're contemplating a short field landing. That may be what the book says, but you're nearly twenty knots over the stall. That's a lot of energy to dissipate.

If you're proficient on the aircraft, I'll bet you could shave 5-7 knots off the approach speed, start the flare short of the runway, and greatly minimize the resulting ground run.

In my RV, stall is around 50 knots, and a normal approach sees me initiating the flare with about 5-8 knots to play with... I could better it I'm sure, but the approach used 90% of the time has trees just short of the runway forcing a "dump" if you want to put it on near the button.

The previous comment about restricting the available flap on the 172 is right on. I'd like to have another 10 degrees on my aircraft - forty isn't nearly enough drag on those things! (;>0)
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Re: Landing at Duncan

Post by photofly » Sat Mar 11, 2017 4:51 am

For the 172S:

The calibrated Vso is 48 knots at 2550lbs. 1.3Vso is 62.4KCAS corresponding to a shade over 60 knots indicated. I guess they rounded up. That gives you a margin against the stall of 14 knots. Not 20.

Basic CPL level task: calculate an appropriate approach speed for a different weight, using the formula in the flight test guide.

Here's a sample calculation for an appropriate approach speed for a C172S landing at 2000lbs:
New approach speed is sqrt(2000/2550)*1.3*48 = 55KCAS which corresponds to 49KIAS. Call it 50 knots to make a round number.

300lbs in the front seats and half tanks puts you at 2130lbs in a 172S I fly. Approach speed works out at 51KIAS, if you want a short float.
Using much less than that doesn't seem like a great idea if you're landing somewhere with downdrafts and a cliff on short final and the windsocks pointing in different directions, but again I could be wrong.
It's up to the pilot to manoeuvre the airplane safely in all phases of flight. Different pilots with different skill levels and different levels of local experience can and should make different decisions about what they can safely achieve. Pilot A can very reasonably decide that touch and goes at a particular airport aren't safe for them, while pilot B correctly comes to the opposite decision. For this airport it sounds like it's a pilot skill issue and not an airplane capability limitation of the 172 that would determine things.
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Re: Landing at Duncan

Post by CpnCrunch » Sat Mar 11, 2017 8:44 am

photofly wrote: It's up to the pilot to manoeuvre the airplane safely in all phases of flight. Different pilots with different skill levels and different levels of local experience can and should make different decisions about what they can safely achieve. Pilot A can very reasonably decide that touch and goes at a particular airport aren't safe for them, while pilot B correctly comes to the opposite decision. For this airport it sounds like it's a pilot skill issue and not an airplane capability limitation of the 172 that would determine things.
Those approach speeds might be fine in calm air, but they put you on the backside of the power curve and you don't have much margin if there's any windshear or downdrafts, which is what we're talking about here. The 120 accident pilot applied full power but couldn't avoid stalling. A guy on this forum got too close to mountains and couldn't avoid hitting terrain when he encountered a downdraft. Steve Fossett couldn't avoid hitting the ground on a nice day with a bit of downdraft, even though he had 400fpm climb with full power (not much different from a fully loaded 150 or 172 on a hot day).

So, I think you're wrong. I think most of these accidents are more about incorrect risk tolerance calculation rather than lack of skill.
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Re: Landing at Duncan

Post by Schooner69A » Sat Mar 11, 2017 8:54 am

Photofly:

I was remiss in not noting that I was using figures from the manual for a 1978 Skyhawk "N" model with 40 flap available. However, in normal procedures, it notes a minimum approach speed of 60 KIAS at max weight for short field landings. Stall at most forward C of G is listed as 41 KIAS. So, this in this aircraft, there is a hockey sock full of energy to dissipate.

Now, I don't know what is says in the manual for the "S" model, but under "Normal Procedures" it notes: "Airspeed: 60 KIAS (until flare).

Which tells me to control my approach so as to flash across the end of the runway at "Vso plus whatever I'm comfortable with". On a nice, smooth day in a 172, the stall warning would be on or chirping, yes? (It's been years since I flew the 172...)

The RVs have little stall warning so you have to be careful when exploring that end of the envelope during landing... (;>0) There are times when I wish I still had my 1954 Cessna 170B... (It's listed as being in Terrace, now)
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Re: Landing at Duncan

Post by Schooner69A » Sat Mar 11, 2017 9:09 am

Cap'n Crunch:

Do any of the situations you list have anything to do with being on the "back side of the power curve"? I agree that you may find yourself in a situation in which you cannot arrest a descent, but it has nothing to do with being on the back side of the curve. Indeed, when trying to escape from a microburst, you may be at Vy and still going down...
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Re: Landing at Duncan

Post by photofly » Sat Mar 11, 2017 9:10 am

The speeds adjusted for weight leave you at the same angle of attack as at 61KIAS at 2550lbs. They therefore put you at exactly the same place on the power curve each time, neither more nor less "on the back side" than the recommended 61KIAS at 2550lbs. That's the reason for adjusting your speed as appropriate to your weight. Basic CPL stuff.

You are quite right. If you don't have the skill to do the manoeuvre, use your judgement not to try. If you don't have that judgment you're going to be in trouble.
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Re: Landing at Duncan

Post by CpnCrunch » Sat Mar 11, 2017 9:32 am

Schooner69A wrote:Cap'n Crunch:

Do any of the situations you list have anything to do with being on the "back side of the power curve"? I agree that you may find yourself in a situation in which you cannot arrest a descent, but it has nothing to do with being on the back side of the curve. Indeed, when trying to escape from a microburst, you may be at Vy and still going down...
I think for the 120 it might have been a factor. If you're on the back side of the power curve it will obviously be more difficult (take more time) to transition to a climb, and you might not have that time.

We're talking about downdrafts and windshear caused by 20mph winds moving over the edge of a ravine, so nothing like a microburst. Something like a 300fpm descent or 5-10mph shear. If you're on the back side of the power curve, you might not have time to recover if you're low.
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