Downwind turns equal disaster??

[Gibbo]

Velocity is speed in a specified direction; Acceleration is a change in velocity. Simple?

MY OPINION - Turning downwind at low level can be a risk when the pilot's perception of a dramatic increase in GROUNDSPEED is compensated by reducing AIRSPEED, which leads to descent, which may be further complicated by raising the nose to arrest the descent; which may result in a major reduction of airspeed if aviation rule No. 1 is breached.

(n.b. Aviation Rule No. 1 - whilst in flight thou shalt not make inadvertant contact with the ground)

[overpitched]

Nick..

I have always maintained that the wind provides the force that provides the acceleration in a downwind turn. I thought it was you that said the wind had no effect.

Now if the force of the wind provides the acceleration during a downwind turn is it not possible that given the right(wrong) circumstances eg low airspeed steep turn, that the acceleration is not quick enough and you loose airspeed.

I know a lot of people here keep talking about loosing speed low due to ground references but who has ever been taught to fly ground references. Surely in visual flight we fly attitude.

And if you maintain attitude and don't increase power and we know from conservation of momentum theory that it is not just the force applied but how long it is applied, so in a quick turn the force of the wind doesn't have a lot of time to act and this may contribute to the problem ????

[Crashondeck]

CBL - thanks for the comments. I realise that Momentum is a vector quantity by virtue of its velocity component and I should have mentioned that I was comparing magnitudes rather than the whole vector quantity. I was meerly trying to demonstate that when using the ground as a reference system, things get more complicated and more difficult to visualise.

Overpitched - Ask yourself this - What is wind? It is simply the movement of air relative to the ground. No ground = no wind. The helicopter does not know whether there is ground there or not but it still flies. So how can wind affect the aerodynamics of a helicopter.

[[email protected]]

This is starting to hurt!

The wind accelerates you as you turn downwind - but only with reference to the ground.

The wind does not accelerate you as you turn downwind - with reference to the wind.


Now no-one has mentioned coriolis force/effect yet where the turning helicopter would be deflected to the right in the Northern Hemisphere, or the red or blue doppler shift as you accelerate or decelerate relative to an observer at the edge of the universe (is he coming towarsd you or going away)?

[Whirlybird]

overpitched,

Are you playing devil's advocate? I can't believe you still don't understand this. Are you just giving everyone a hard time for the sake of it?

[overpitched]

Whirly. I can't believe that you would think such a thing.

And besides I know you guys are right because I did a simple experiment.

Tonight when I was at the gym I had a run on the treadmill and while I was running a long at about 7km/h I realised it was exactly like flying into wind. As long as I didn't look at the ground my speed was 7 km/h relative to the treadmill.

And because I know you guys are right I knew it was safe midstride to turn around and run with the treadmill. Yep you guys were right, I never ended up on my arse or nothin.

You guys should try it too.

[CBLong]

Have I been had??

I used to read a motorbiking newsgroup years ago where the old hands would always wind up newbies by claiming that it's impossible to pull a wheelie on a shaft-driven bike... is the downwind turn the same thing for prooners?

[TeeS]

Well done overpitched.

I knew you would get it in the end. A word of caution, treadmills at the gym tend to be quite short so turning 'downwind' can result in you falling off the end (a bit like turning downwind into a mountain - your frame of reference changes very suddenly!)

Try it instead on an airport walkway or similar, you will see that once again it is quite easy to turn round and run in the opposite direction. Just beware that there is a tendency that as you do turn round, the apparent change in speed of the advertising hoardings gives you the impression that you are speeding up. It is not unknown that people trying this, subconsciously slow down and end up stopping on the walkway (a bit like losing translational lift when turning downwind at low level!)

Cheers

TeeS

Edited to sort my thoughts out (doh!!!)

[Bertie Thruster]

Unlike on gym treadmills, I tend to walk on airport walkways WITH the mat movement. So turning round would tend to make the hoardings slow down or even go backwards, rather than faster as TeeS has suggested.

Can you imagine it?!........."What's that tw*t doing on the walkway??"

"He's a Rotorhead Ppruner doing downwind turns"

[TeeS]

Come on Bertie, give us a break, I didn't say which direction you had to start off in, just suggested overpitched try his experiment on a larger playing field.

Anyway, I always enjoyed going up the down escalator, it's a bit like trying to make your point on this thread!!

Cheers

TeeS

[Whirlybird]

OK, overpitched. So, you made some of us who normally just fly and happily turn downwind without thinking about it give some very serious thought to airspeed, groundspeed, wind, Newton, forces, vectors, and all those good things we generally don't want to bother with. No harm done. But me, I think I'll just go back to flying. And if I ever get any students who insist on arguning about downwind turns...I'll send them in your direction. Purely becasue I know you'll enjoy it of course.

[headsethair]

How many helicopter pilots does it take to fly downwind ?

1,000,000.

1 to fly the helicopter and 999,999 to stand upwind and talk bollox.

Thereby neutralising the effects of the wind.