Taking off into wind

[Armchairflyer]

It was the statement that, "once in the air, an aircraft is not affected my wind (except relative to ground)" which was confusing. It made me picture the aircraft suddenly having the headwind flow of 50knots over the wings removed as it is now "in" the body of air rather than having the body of air flow over it.

Being "in" the body of air doesn't mean that the aircraft loses any speed relative to the air. Yours was apparently a kind of the "plane on a conveyor belt" confusion. The plane does not push itself into the air by spinning its wheels quickly enough (in which case it would indeed lose its airspeed as soon as it gets airborne).

[Dawdler]

Take a look at this Husky taking off into a strony wind. First TO ground run distance?

Husky Short Field Landing and Take-off - YouTube

This may illustrate the effect of windspeed over ground speed.

Edit: I think it is Bob Pooler at the controls

[mary meagher]

All you noisy pilots that require power to get airborne, may be amused by contemplating a maneuver special to certain hill sites, for example, the Long Mynd....

The wind is blowing against the ridge. The glider is moved to the edge of the ridge. A bungee rope is attached to the glider, and six able bodied people attach themselves to the rope, three on each end, (the glider is attached to the midpoint of the bungee rope). Another person is holding the tail of the glider so it won't leave too soon.

The six able bodied people begin to march down the hill, pulling the rope. When there is sufficient tension, the chap on the tail lets go, the glider trundles forward and eventually falls off the hill.

And instead of continuing downhill, is met by the wind blowing up the hill. It ascends triumphantly into the air.

If the wind is strong enough, the glider can then perform the maneuver of

THE VERTICAL CIRCUIT. Turns downwind and base leg not needed. Just fly at minimum sink speed, say 40 knots, the glider then flies backwards over the hill. Reaching the point where a final approach is desired, speed is increased to penetrate the wind, say to 60 knots, and the glider lands straight ahead. This is the rare situation where you can actually GO AROUND in a glider!

I think a bungee launch may be found on YouTube, but doubt if they ever managed to film the Vertical Circuit....

Try that one if you get the chance!

For the information of the earnest OP, the usual methods of launching gliders are by airtow, or by winch. The winch launch is cheaper. But the tow plane can tow your glider to the best thermal, and if you are any good at all, you can then stay up all day....my longest flight in the UK was 8 hours and 53 minutes, traveled a task of 511 kilometers...

That was a very good day indeed.

[foxmoth]

Try that one if you get the chance!

Been there, got the T shirt, and in a power a/c, helped by the fact that the wind at 1,000' was a tad stronger than that on the ground.

[Flyingmac]

A picture is worth a thousand words?

You Tube

[Pace]

That is a good example as looking at the video while the aircraft is stationary and enough wind speed crossing the wings to give lift causes the aircraft to lift as soon as it moves backwards with the wind the aircraft starts settling back down again with a gound speed going backwards.

Pace

[Shaggy Sheep Driver]

SSD, like many people you appear to be assuming that because you have been doing something for many years, this must mean that you understand all about it. This is a false assumption.

Nope. I knew this stuff after my first lesson in a T28 glider. Probably even before that! It's not 'ard!

So, you've powered up, overcome the drag of the 50 knots wind speed, increased your airspeed to the 60 knots needed to lift off and started flying ... But then immediately turn downwind. What happens?

Your groundspeed increases to 110 kts in a sweeping downwind turn. Absolutely nothing else happens (disregarding any wind gradient affecting the lower wing in the turn, and assuming the odd visual effects at such low level don't confuse you into reducing your airspeed and possibly stalling the aeroplane).

Now let's imagine you take off, climb through a cloud layer, then turn downwind. This time you will be unaware of the bizarre visual effects of strong winds at low level because you will be above a cloud deck which is also moving (with the air the clouds are suspended in) at 50 kts over the ground.

Let's assume you are airborne in a hot air baloon above a cloud deck in a 50 kt wind. The balloon has zero airspeed of course, as do the clouds, so as you look out over the side of the basket nothing appears to be moving - not you, not the clouds. Then the clouds disperse... and you have a view out the basket of the ground rushing past at 50 kts!

In my experience it's usually model flyers who 'don't get' this. They remain convinced that their pride and joy experiences a gain of speed on turning into wind, and a loss of speed turning downwind. Just imagine if this were true.... an airliner goes into the hold at FL70 and 190 kts. Does the wind affect the airpeed as it flies around the holding pattern? Of course not! It will affect the ground track, though.

[keith williams]

Let's assume you are airborne in a hot air baloon above a cloud deck in a 50 kt wind. The balloon has zero airspeed of course, as do the clouds, so as you look out over the side of the basket nothing appears to be moving - not you, not the clouds. Then the clouds disperse... and you have a view out the basket of the ground rushing past at 50 kts!

That's an excellent choice of scenario SSD. If we go back to the start of that balloon flight it demonstrates my point very well. I can't imagine anyone would want to launch a hot air balloon in a 50 knot wind, but as you've suggested those conditions let's go with them.

Before launch the basket is tied to the ground. Ground speed is zero but TAS is 50 knots (Produced by of the wind). The balloon would be leaning downwind quite markedly.

We release the tie-downs and the balloon starts to rise. As it rises it accelerates downwind. GS increases and TAS decreases. After a while the balloon is moving downwind at the same speed as the wind, so the TAS is zero and the ground speed is 50 knots. We have gone from a situation in which we had zero GS and 50 TAS, to one in which we have 50 GS and zero TAS.

The only thing that could have caused these changes in TAS and GS is the wind. If the wind accelerated the balloon, the balloon must have experienced the wind. In this case the wind was steady.

[shortstripper]

Your groundspeed increases to 110 kts in a sweeping downwind turn. Absolutely nothing else happens (disregarding any wind gradient affecting the lower wing in the turn, and assuming the odd visual effects at such low level don't confuse you into reducing your airspeed and possibly stalling the aeroplane).

I wondered when someone would answer ... You're right of course, but it was the wind gradient I was alluding too. If you've climbed out of it then great, but with a 50 knot windspeed the gradient will be steep and turning downwind whilst still low enough to be in it could be .... interesting?

SS

[Shaggy Sheep Driver]

There's an interesting article somewhere about the dangers of the downwind turn (pilots have died making such a manouvre). Wind gradient can be a very real danger, but perhaps the biggest is the visual disorientation of the pilot leading to inappropriate control inputs. The other killer in such a situation at low level (so just after take off, for instance) can be the much reduced climb angle relative to the ground when flying downwind in a strong wind.

Also, flying 'down in the weeds' is visually very different to doing the same at a few hundred feet. Add a strong wind, and things can become very interesting.

[Heston]

Students do get confused by this. First they get to understand the aircraft is flying in a parcel of air and that what the ground is doing is irrelevant (Shaggy's "above a layer of stratus scenario"). But then they have to partly unlearn that - when they start learning to land in a wind gradient and are told that it takes time for the aircraft to respond to the changed wind speed so that the air speed (momentarily) changes.


Oh and Shaggy - I've been waiting for you to say "its all in Stick and Rudder", but you haven't yet so I'll do it for you: its all in Stick and Rudder

[foxmoth]

Students do get confused by this. First they get to understand the aircraft is flying in a parcel of air and that what the ground is doing is irrelevant (Shaggy's "above a layer of stratus scenario"). But then they have to partly unlearn that - when they start learning to land in a wind gradient and are told that it takes time for the aircraft to respond to the changed wind speed so that the air speed (momentarily) changes.

No, the ground IS still irrelevant, you are not UNLEARNING anything, but learning a new bit, that you are still flying in a parcel of air, but that parcel is changing ( or another way to think about it is that you are moving from one parcel of air to another) and you need to allow for these changes. The ground may the the thing that is causing the change and this is good because this can be anticipated, but there are other things that can cause a change such as CBs, and other weather phenomena and these cannot always be anticipated in the same way.

[Heston]

Foxmoth - of course you're right, I am guilty of not explaining myself properly - the extra bit (that you do have to consider the inertia of the aeroplane) does nevertheless cause confusion at first. This is because the temporary change in airspeed can only be understood by referring to the speed of the aircraft in a frame of reference outside of the air - and that frame of reference is the earth, in other words ground speed. By frame of reference I mean that speed has to be expressed as movement between two things. Airspeed is the movement between the aircraft and the parcel of air it is in. When we talk about wind gradient we are using the earth as the fixed frame of reference (ie the speed between the air and the ground)and we have to use the same frame of reference for the aircraft when we want to describe what happens as the aircraft descends through the wind gradient. This does not mean that the aeroplane somehow magically knows what it is doing with respect to the ground - but we need the ground to anchor our mental description of what is going on. Hence the confusion.


This is what happens when you teach a PhD physicist to learn to fly and he unpicks your explanations...

[glum]

Should we mention that we're already moving at 67,000 miles per hour round the sun and at the equator the ground is doing about 1000mph as the earth spins?

[Heston]

Coriolis Effect anyone?