Crosswind take-offs. Does the side matter?

[John_Read]

This is probably another dumb question! Had a good flight today, but yesterday there was a twelve knot crosswind virtually directly across the runway, and as I am fairly inexperienced and had not flown for a while, I chickened out.

But I wondered. Is it better to have the wind from the right or the left? Or doesn't it make a difference?

What I was thinking is this: The retreating blade obviously is going "slower" than the advancing blade, which is teetering upwards. So ... does the lack of speed make the retreating blade want to flap, or is the fact that the advancing blade has teetered make IT more likely to catch that crosswind?

OK I admit I am stupid! But what do the knowledgeable guys say about this?

John

[gyromike]

John,

If I have a direct crosswind to deal with, I put it on the right side of my gyro.

My Bensen with Mac engine tends to torque-roll to the right (slightly), and the spiraling slipstream makes it yaw to the left (slightly).

So with a right crosswind it wants to climb into the wind minimizing drift, and the wind hitting the right side of the tail helps to keep the nose pointed straight ahead.

A direct left crosswind is no big deal, but why not let Mother Nature do some of the work! :)

[birdy]

but why not let Mother Nature do some of the work!

Yeh,like turn into the wind and do a VTO. :D

The control tower shouldn't mind ,solong as you slip sideways down the strip as soon as you break ground.They don't care witch way your machine is pointing,solong as you travel down the black strip. ;)

[gyromike]

True enough Bird Man, if you've got the room for it.

But sometimes if there's traffic at the 'port, it's best to sorta go with the flow.

[EI-GYRO]

My ground school lecturer reckoned you are better with the crosswind coming
from the left.
The reasoning is that the wind veers when it increases, which goes towards
a headwind, which is safer than taking an increased wind on the tail.
I have observed this one windy day, where the 10-15 kt wind was straight
up-and-down the runway, when I got to 150ft it was 30+ and the wind was on the
starboard bow.(These crow-hops are getting bigger).
Also found I had to keep a lot of throttle on when descending due to the wind
gradient.

Cheers

Fergus.

[mceagle]

Huh?????? Run that one by me again.

[StanFoster]

Tim: I think what Fergus was saying is that the winds tend to go clockwise as you leave the surface. For instance...you are on runway 36...and have a surface wind from 270. Usually as you gain altitude...that wind that was from 270 will slowly shift to 280..then 290...due to the upper air flow lagging behind the spinning earths surface. The surface air is being drug around with the earths surface while the upper air is lagging.

However.....Fergus as well as most of the readers here are on the north side of the equator. You..being from Australia will find the air to act in the opposite direction. If you are taking off on 36 with a wind from 270...it will generally start going toward a tailwind as you climb.

Just like your toilets flush the other direction.

Hey...I have to go build some curved stairways...they turn either direction no matter where you are on this great planet. :D

Stan

[EI-GYRO]

Hi Tim,

If the wind is straight across the runway, and steady in speed, we do crow-hops
in either direction. Good crosswind practice.
If the windspeed is variable or gusty, I would only fly in the direction which has
the wind coming from the left hand side.
That way, if the wind increases, it will veer (clockwise), and give me a headwind
component, which is no problem. If the windspeed drops it will back(anti-clockwise),
giving a tailwind component, but a smaller one.
Either way, no problem.
If you fly with the wind coming from the right hand side, an increase in windspeed
will give you a tailwind, not good.
A decrease in windspeed will give you a reduced headwind.
Since you are in the Southern Hemisphere, the directions will be reversed for all
of the above.
Also, the effect is greater at higher latitudes, yes, latitudes,not altitudes.
I'm at 53.5 North.
I didnt notice this until my groundschool instructor dealt with the issue, but careful
observation of the windsock confirmed it.
If you have substantial power margins, you might not notice the effect.

I noticed it more clearly on the high crow-hop due to the higher and steadier
windspeed difference.
The need to keep power on in the dive to counter the windspeed gradient with height
very nearly caught me out.

By the way, I think I saw you in Rob Fidler's 'Gyros in Australia' video.

Cheers

Fergus Kavanagh

Dublin
Ireland.

[mceagle]

No doubt someone will correct me if I am wrong, but I think that the wind movement near the ground would not vere in any direction due to the earths rotation (as there is no friction drag in space, the air mass is moving as one with the earth). Air movement is mostly related to temperature differences, creating high or low pressure gradients, but even then, will only create a didderence when crossing the centre of one which would not be likely to happen in the space of a single take off or landing.

A 90 degree cross-wind from either the left or the right hand side will slowly move towards a relative headwind as the gyroplane airspeed increases for take off. It would never become a tail wind. Similarly on landing in the same conditions, the relative head wind slowly becomes a cross wind as the airspeed decreases. It would never become a tail wind.

Differential Gyroplane responses to left or right cross winds are usually related to rudder deficiences and propeller slipstreams.

G'day Fergus. Is Fid still flying?

PS. I wonder which way water goes down a drain at the Equator?

[EI-GYRO]

Hi Tim,

This issue is not a big deal for most normal flight, but if you are self-training
and dont have much power reserve(yet) it becomes more important.

All weather systems rotate to some degree. Its a friction vs rotation issue.
I think its called geostrophic effect, but I would need to hit the books and revisit
the subject.
Suffice to say that an MD-11 ran off the side of the runway at Dublin a few
years ago, partly due to this effect in a squally shower. The wind increased and veered about thirty degrees in a few seconds, and the combination of speed and
direction change did the trick. MD-11/DC-10s are reputed to be a bit short on
tail feathers.

In our temperate climate, where thermals are not a consideration, if you have, say,
a 5kt crosswind. If that increases to 10 kts there will be a clockwise shift, maybe
10 degrees or so.
The same shift happens as you climb and the windspeed increases due to reduced
ground friction.

As you said;

"A 90 degree cross-wind from either the left or the right hand side will slowly move towards a relative headwind as the gyroplane airspeed increases for take off. It would never become a tail wind. Similarly on landing in the same conditions, the relative head wind slowly becomes a cross wind as the airspeed decreases. It would never become a tail wind. "

True, but this is a change of the resultant vector due to increasing or diminishing
airspeed combined with a constant crosswind, and isnt related to weather phenomena.

"Differential Gyroplane responses to left or right cross winds are usually related to rudder deficiences and propeller slipstreams."

True, but they are overlaid on the other effects, and may well be more noticeable,
particularly if you have a good power margin. I dont.(yet)

Last I heard, Fidler had collected a fence on his gear, so I dont know what he's
up to these days, but doubtless he'll turn up again.

Re the equator, I dont spend too much time looking down plugholes, except maybe after a good night out, but I recollect we used to get extremely heavy rainshowers
with no apparent rotation, along the Inter-tropical Convergence Zone between
Sri Lanka and the top of Sumatra, about 5 deg N.

Take care down there, and dont fall off the planet.

Cheers

Fergus.

P.S. Noticed your sig. First question they all ask is' how much distance does it
need to take off. My answer; Wrong question, right question is how much distance
does it take to land, cos takeoffs are always a matter of choice.

Makes them think.







w

[Cobra Doc]

Once you leave the ground, the aircraft doesn't even know the wind is blowing. You are over thinking the situation. The so called "down-wind stall" doesn't truly exist. It's caused by the pilot trying to make visual reference to the ground "look right" and there by stalling due to not taking the wind into consideration. As for having the cross-wind from either side, whichever gets you more wind on the nose. Unless you're flying a helicopter and point your nose into the wind or a balloon tht doesn't have a nose.
(Tim Mc: on the equator it goes straight down. No swirl at all :( )

[John_Read]

Fergus is right, though. The wind does change velocity with height. You have only to look at the low level wind charts at www.metoffice.com to see that this is so. It increases, and also changes direction, and this is because of the friction which slows the wind at ground level, and the coriolis effect.

But by the time you get up there - as has also been pointed out - you would have enough airspeed for this hardly to matter ....

Fergus, you have obviously become a man of great learning, and now know more than most of us have forgotten!

[EI-GYRO]

Hi John,

It's just that I have such a small power margin, EVERYTHING makes a difference.
On the plus side, a small power margin keeps you honest, and careful.

Cheers,

Fergus.