Wind component

Ruff T

Well-Known Member
I was having a discussion with my fellow instructor here at work about how he teaches his students on how fast to come in on approach. Please bear with me if it seems a little long winded.
I told him I teach my students how I was taught, which was that you add half the wind speed to your approach speed. For example if the wind is 320@10, you would add 5 kts to your final approach speed, so if the approach speed is usually 65, it would now be 70. If the winds were 320@10 gust 30, you would add half the peak gust speed, 15 kts, to the final approach speed, which would make the new approach speed 80, and the stronger the winds, the less flaps you use. That's how I was originally taught, and it's always worked for me, and that's how I teach my students, since the approach speeds on the POH are based on little to no winds.
He said that he's been teaching his students to only add half the gust factor to the final approach speed. For example, winds are 320@10 gust 30, he teaches to add half the wind gust component, 10 kts, to the final approach speed. So instead of coming in at 65 kts, he would come in at 75 kts.
I was wondering how you guys out there teach.
 

tgrayson

New Member
was that you add half the wind speed to your approach speed.
No real reason for that in a light propeller airplane, since a steady wind of any velocity has no aerodynamic effect on an airplane. The only reason to tack on speed is if the wind is gusty, because a fading gust can lower your airspeed below safe values. The rule of thumb offered by the FAA is what your fellow instructor said, 1/2 the gust factor. A wind of 10 gusting 20 would mean adding a 5 knot increase on your approach airspeed.

Also, no reason to reduce flaps due to wind speed, unless the wind is a crosswind and you're nearing the crosswind limitation of a full flap landing.

Although it may seem harmless to come in with excessive speed, that isn't necessarily true. A Saratoga landed at our airport with a 35 knot crosswind; he came in fast, landed nose first, lost his crosswind correction as he bounced and departed the runway into the grass, damaging a wingtip and collapsing the landing gear. Had this pilot followed the discipline of 1/2 the gust factor and not given in to fear, he likely would have landed his airplane safely.
 

MidlifeFlyer

Well-Known Member
Your fellow instructor is right.

You add 1/2 of the gust factor - 1/2 of the difference between the low and high wind values (10 kts in your example, not 1/2 of the highest wind (15 in your example). The purpose is to have a recovery buffer in the event of a sudden loss of airspeed due to gusting.

The purpose for adding 1/2 of the steady state wind is ?????

I think that either you or your instructor misunderstood when this was taught.
 

mhcasey

Well-Known Member
Also, no reason to reduce flaps due to wind speed, unless the wind is a crosswind and you're nearing the crosswind limitation of a full flap landing.
Is this number published for light aircraft?

Aside: Was bumming around in an FBO the other day when I overheard a CFI canceling his flight due to excessive winds. I think the winds were 20G25...straight down the runway. Mind boggling...
 

Douglas

Old School KSUX
We honestly teach the "come in a little faster" approach.

Be smart, fly the airplane and do hesitate to initiate a go-around if needed.

We keep it simple. Some might not like this approach.
 

Ruff T

Well-Known Member
We honestly teach the "come in a little faster" approach.

Be smart, fly the airplane and do hesitate to initiate a go-around if needed.

We keep it simple. Some might not like this approach.
I was taught the same way to come in a little faster especially when the winds get stronger.

The purpose for adding 1/2 of the steady state wind is ?????
If you were coming in on approach with a 40 knot headwind with an approach speed of 65 kts, it doesn't make sense to me why you would continue on the approach with a groundspeed of 25 knots. So by increasing your approach speed by about 1/2 the wind speed, it makes you come in a little faster, and I think it stabilizes the approach. I'm not saying that adding 1/2 the wind speed is a set rule, but I just use it as a "rule of thumb" that I use, and I try to hand it down to my students.
 

tgrayson

New Member
it doesn't make sense to me why you would continue on the approach with a groundspeed of 25 knots.
This is what I find disturbing about the whole idea. What difference does it make to the airplane what your groundspeed is? It has no relevance to the behavior of the airplane. Your aircraft cares about your airspeed, period.

That's one of the most important lessons you can teach a student, IMO.
 

USMCmech

Well-Known Member
We honestly teach the "come in a little faster" approach.
Too much airspeed is just as bad as not enough.

The last school I taught at taught student's to land 10 kts faster than Cessna recomended "for safety". Most CFIs added 5 more "just in case". They also had to replace 5 firewalls in 12 months due to students landing on the nosewheel.

Coincidence?
 

CoffeeIcePapers

Well-Hung Member
Too much airspeed is just as bad as not enough.

The last school I taught at taught student's to land 10 kts faster than Cessna recomended "for safety". Most CFIs added 5 more "just in case". They also had to replace 5 firewalls in 12 months due to students landing on the nosewheel.

Coincidence?
Maybe not, they were Indian...:)
 

mooneyguy

been around forever
The problem with carrying extra speed in a X-wind is that you increase your float, and even if you do plant it quickly you still have extra lift on the wings do to the faster rollout speed. Take the P-28-181. 10 extra knots you can float half way down the runway...the entire time you are trying to maintain center line. It's better to come in on speed and get the airplane on the ground. The same issues for a headwind, just minus the drift problem. As Tgrayson said, the airplane could care less what it's groundspeed is.
 

MidlifeFlyer

Well-Known Member
So by increasing your approach speed by about 1/2 the wind speed, it makes you come in a little faster, and I think it stabilizes the approach..
How does the speed of the =ground= make an approach more stable?

Like tgrayson, I think you may be missing something very basic here.
 

meritflyer

Well-Known Member
Also, no reason to reduce flaps due to wind speed, unless the wind is a crosswind and you're nearing the crosswind limitation of a full flap landing.
EDIT: Just read your post.

Even in the 145, we didn't have a flap crosswing limitation. Now, the great debate what the purpose of flying an approach speed with 20 degrees of flaps as opposed to 30 degrees is. Barry Schiff's seems to be somewhat poor and candidly, unsupported.

TG, your take?
 

tgrayson

New Member
Even in the 145, we didn't have a flap crosswing limitation.
Well, you do, it's just not published. ;) There is some amount of sideslip for any airplane which will overcome the rudder's ability to prevent the aircraft from turning. That's your limitation for that flap setting.

Raising the flaps a notch would decrease the tendency of the airplane to weathervane, increasing the amount of sideslip possible. Pretty much the same argument for why flaps reduce Vmc.
 

meritflyer

Well-Known Member
Raising the flaps a notch would decrease the tendency of the airplane to weathervane, increasing the amount of sideslip possible. Pretty much the same argument for why flaps reduce Vmc.
I always hear the 'gust' argument for raising the flaps.

Am I missing something? Why would raising the flaps decrease the WV tendency?
 

tgrayson

New Member
I always hear the 'gust' argument for raising the flaps.
Yeah, but that one doesn't hold water. The aircraft's sensitivity to gusts depends on a handful of factors, wing loading, velocity, and lift coefficient, lift slope. None of those are affected by flaps. (Well, for aircraft with Fowler flaps, there probably is a reduction in wing loading, making it more sensitive to gusts.)

Does any transport category aircraft recommend reducing flap settings in gusts? Never heard of one.


Am I missing something? Why would raising the flaps decrease the WV tendency?
I don't know the mechanism. There is, at the very least, NACA data showing that flaps increase directional stability, which is what you don't want if you want to maximize your crosswind landing capability. I speculate the cause is differential drag; the downwind flap is shielded by the fuselage, resulting in less drag to offset the drag of the upwind flap.

The Cessna manuals recommend the smallest flap settings for the given field length, and the book "Cessna, Wings for the World" written by their former head of development mentioned increased rudder authority with a smaller flap setting.

This topic isn't addressed in any aerodynamics book that I have, but there is enough scattered data about to suggest there is a real phenomenon here.
 

meritflyer

Well-Known Member
Does any transport category aircraft recommend reducing flap settings in gusts? Never heard of one.
At my old company, it was advised to use 22 degrees v. 45 degrees during gusty conditions to avoid several possibilities due to the apparent more responsive controls and floating. If I remember correctly, our CFM discussed floating using 45 degrees due to a higher TAS during steady, high velocity winds.
 

tgrayson

New Member
At my old company, it was advised to use 22 degrees v. 45 degrees during gusty conditions to avoid several possibilities due to the apparent more responsive controls and floating.
But this was due to the faster approach speed, I presume?

our CFM also discussed floating using 45 degrees due to a higher TAS during steady, high velocity winds.
Some transport category aircraft do recommend a higher approach speed with a steady, high velocity wind. Again, I speculate that the reasoning is that high velocity winds generally ARE gusty, regardless of what the reported weather is. Since a jet's thrust doesn't react as quickly as a prop, and there's a larger mass to accelerate, it's the lesser of two evils to carry a bit extra speed.
 

meritflyer

Well-Known Member
tgrayson said:
But this was due to the faster approach speed, I presume?
There was a higher target speed and ref with a lower flap setting.

tgrayson said:
Some transport category aircraft do recommend a higher approach speed with a steady, high velocity wind. Again, I speculate that the reasoning is that high velocity winds generally ARE gusty, regardless of what the reported weather is. Since a jet's thrust doesn't react as quickly as a prop, and there's a larger mass to accelerate, it's the lesser of two evils to carry a bit extra speed.
It was at the pilots' discretion to use such settings. The landing attitude was much less angled (i.e. flat) and apparently contributed to greater control authority.

But then again, it was the airlines. Nothing the CFM said seemed to factual or supported as opposed to someone's personal opinion.
 

tgrayson

New Member
There was a higher target speed and ref with a lower flap setting.
Right, so it wasn't the flap setting that improved control response, but the higher airspeed that went along with it. We have the luxury of flying a higher speed, but leaving the flaps at the original setting.

It was at the pilots' discretion to use such settings. The landing attitude was much less angled (i.e. flat) and apparently contributed to greater control authority.
I guess for you guys, since you don't hold it off much, a higher approach speed would tend to result in a higher touchdown speed. Still, strong winds alone don't need improved control authority; I suppose you mean when there is a strong crosswind component?

But then again, it was the airlines. Nothing the CFM said seemed to factual or supported as opposed to someone's personal opinion.
I'd be more interested in what the manufacturer said; I would expect they would have run extensive simulations in various weather conditions before setting forth their recommendations.
 
Top