Gusty conditions

[Robbo0885]

Hi all. Just a quickie. Last time i was flying it was starting to get a bit gusty, my instructor mentioned the practice of increasing approach speed by a factor depending on the difference between the steady wind and the gusts. Does anyone know this? He mentioned it on final with about a minute to touchdown, so it didnt lodge in my head properly. I forgot to ask him about it afterwards.

He said in gustier conditions we would incease approach, by a factor depending on the difference between steady wind and max gusts. Anyone know the specifics?

(Forecast for tomorrow as example- NE at 6kts, G26kts)

[flybymike]

I have heard a rule of thumb which says add half of the gust speed.
I do not necessarily subscribe to rules of thumb myself and would use my own best judgement dependent on the circumstances. An overly speedy approach may create more problems that in solves. :)

[PompeyPaul]

I've never been happy to do this, and in effect just don't fly. In a PA28 I fly an approach speed of 80kts. Adding 12.5, or even just 10kt, for gusty conditions means an approach of 90kts. I wonder how much longer it takes to bleed that speed off, and how much longer the float is ?

Never been keen to find out, personally.

Why only 2 notches of flap ? I've heard this bandied around a bit ? What does removing the drag flap get you ?

[SkyCamMK]

Options, IMHO. Gusts are short-lived. Keep flying, Keep in control near the ground, Keep the option to go around or to climb etc ...

[englishal]

Coming in faster gives you more rudder authority and increases the buffer in case of wind shear. With full flap on a normal approach you are wallowing around with less responsive controls, but if you were to come in faster with full flap you will float. Come in faster with less flap and you'll stop flying sooner though will have a faster touchdown speed.....

Isn't 80kts in a PA28 a bit fast for final and full flap?....I'd have thought than 65-70 kts would be better (it has been a while since I have flown a PA28 though, but it still seems quick).

[homeguard]

The recommended speeds of the Flight Manual are x1.3 the stall for any given weight. This safety factor already allows for gusty conditions. To add yet more speed creates the problem of the excess speed having to be lost at some point. Losing excess speed and fighting turbulence, during the hold off, close to the ground at 'minimum control' has never appealed to me.

Flap changes the stability of the aircraft for various reasons and therefore all three controls can become less effective, in turbulent conditions you want maximum effect. Additionally, although the stall speed is normally decreased by flap the additional drag leaves less excess thrust available over drag to go around or to resist sink as required. Mimimum flap, having considered the runway length available, will alow maximum stability and greatest power/thrust over drag.

80kts approach in a PA28 seems very high to me yet alone adding any more.

[znww5]

PompeyPaul . . . which PA28 do you fly?

I fly a PA28-161 taper wing Warrior II which stalls at 50kts clean and 45kt full flaps.

The approach speeds for that (in knots) are:

Normal: 70kt then 65kt over the fence
Glide: 75kt then 65kt over the fence
Flapless: 75kt then 70kt over the fence

Maybe it was just a typo and you meant 80mph approach?

Getting back on thread, I usually add half the mean gust difference on blowy days ie 15G25 would add 5kts to my approach speed. As most PA28 taper-wing drivers will testify, you really need to nail the approach speed accurately otherwise you'll float into the next county :).

[Robbo0885]

Thats what I fly, 65kt normal approach, and those other speeds are what I have been using. I'm glad I'm not the only one to think that 80 sounded fast!

I think the rule of thumb you use znww5 is what my instructor said...half the difference added on. I guess the reason for this is to add a buffer zone yes? Then again, I thought that the reason the approach speed was the approach speed was becuase it was the most effective+a buffer.

This is why I was wondering why you would add a factor for gusts, as I figured the approach speed already had a factor inbuilt.

[Supersport]

I fly an Archer III, normal approach speed of 70-75kts, over the numbers full flap 65kts. To be honest in gusty / windy conditions I don't really do anything differently apart from maybe leave out the drag flap because the probability of going around is a lot higher than normal. I'm more careful with the position of the aircraft, normally a tighter base leg to counter for the wind. On very short final I'm certainly not looking at my ASI, it will be all over the place anyway. All I do really is try and balance any strong gusts by shedding some power so the aircraft doesn't balloon, especially when over the numbers, and likewise adding some power if the aircraft begins sinks to much.

Sometimes though, regardless of how you do it, it is just to gusty! I remember landing at Caernarfon once 270/20 G35-40 (10 deg off), the gusts were so irregular it was almost impossible to land, bumped around all over the place! Got it down though, was a bit of a bouncy one but hey...

[tmmorris]

Positive movements of the throttle are required if you are going to cushion any sudden sink - e.g. you get a gust which makes you balloon, then the gust drops and you sink: easiest option is to go around (and that's what I was taught as a student) but you can cushion the subsequent sink with throttle if you respond quickly.

(I too hope he means 80mph in his PA28)

Tim

[modelman]

In the PA28-140 I fly with slab wing,I was instructed to approach at 80 mph,don't chop the throttle before the flare but leave it at a fast idle 900/1000 until you are down to control the sink.Have used this quite succesfully in all conditions.Will stay at flap 25 if gusty/xwind as this is what I was taught.

MM

[PompeyPaul]

Isn't 80kts in a PA28 a bit fast for final and full flap?It is a bit fast, my school changed it's advise recently from 70kt final, to 75kt (yes, 80 was a typo). But still with 10kt gust cushion taking you to 85 on top that, it is a FAST approach in gusts.

[Blinkz]

Guys I think you are missing the point of why you are increasing the speed. You increase the speed to increase the safety margin to the stall. If your flying a long at Vref and a gust makes you lose 10 knots then you could be in trouble, if however you had increased your approach speed then losing the 10 knots becomes less of a problem. On what I fly we use half the headwind component and all the gust to a max of 15 knots.

[17thhour]

the poster above me has in my opinion got it.

[flybymike]

You guys are going to be making some interesting landings at 1.3 VS plus 15 knots. :rolleyes:

[bjornhall]

This is how I think about it, FWIW...

Final approach speed in gusty conditions = final approach speed as per POH + all the gust factor. The gust factor is the largest possible amount of airspeed you could lose due to a sudden gust; e.g., headwind component of any reported gusts.

Should the gust fail to materialize we will arrive at the flare with too much airspeed , resulting in a long float. However, provided the gust factor is less than the steady headwind (if that's not the case we need to watch out!), our groundspeed is still less than the calm wind groundspeed at the normal approach speed, so landing performance should not be a problem.

BUT: This requires using the actual POH figures corrected for current conditions, including reduction for weight lower than maximum. Can't take a "standard comfort figure" such as 70 kts in a 172S and add all the gust to it...

Making sense?