Lownverted

My Feedback: (4)

That would be correct for groundspeed, but for airspeed it would be identical. C'mon people! Haven't you learned ANYTHING? Sheesh....

highhorse

My Feedback: (2)

Dumb question! (Lol) Haven't you learned anything from the Mythers?

1) It's obvious that because the backwards spin of the ball creates lift (it actually does, no joke) the 5kt tailwind means that the ball will lose lift and not go as far.

2) Probably will go backwards if kicked eastward, because there's no way a kicker's leg is powerful enough to overcome the speed of the earth's rotation.

3) If kicked to the west...better get a new ball, cus that ones over in the next county somewhere

Like, Duhhhhh.
;-)

flyinfool1

My Feedback: (2)

That's easy
If the kickers foot is capable of launching the ball at 90kts, then the airspeed at the moment the ball leaves the kickers foot will be 95kts kicking into the wind and 85kt kicking down wind, but in either case the balls ground speed will be 90kts.

Since the spin of the ball does in fact create lift, but drag also goes up exponentially with airspeed, kicking into the wind will get more hang time but less distance, and down wind will get more distance and less hang time. And just to mess this theory up, a good kicker will alter the trajectory of the kick to compensate as much as possible for these effects.
If you watch during the game the downwind kicks will go farther due to the reduced airspeed and less drag.

cfircav8r

My Feedback: (1)

It all stems from misunderstanding the relationship of different aspects of physics. Ground speed is very important to certain aspects of flying, but not in every aspect of flying. airspeed and ground speed are tied together when dealing with navigation, but groundspeed is irrelevant to actual control of the aircraft.

Lownverted

My Feedback: (4)

Any new news on this? Have we figured it out yet? I saw a plane at my local club die the other day. The pilot swears it was the downwind turn that got him.

JackD

My Feedback: (4)

No news. Physics haven't changed since last post. Remains a myth...

PacificNWSkyPilot

My Feedback: (19)

I'm sure that's just when he lost it. As pointed out by others, there are a variety of factors involved. For instance, how many engines were on the model, and how many were running at the time? Turning into a dead engine has been the mythical downwind turn for many a model, and I've seen several of them stall-and-fall. One of them was mine. Take the dead engine out of the equation, and on a single-engine craft, a brisk headwind combined with low model speed in a downwind turn is essentially the equivalent of turning into a dead engine. That headwind-turned-tailwind shift can reduce your model's airspeed to the point of stall-and-fall.
Did the model just kind of fall into one wing and sort of spin and head straight for the ground? If so, odds are pretty good it was a stall-and-fall.
When we take off into the wind, the extra wind under the wings becomes a substitute for airspeed, and the plane takes off at what appears to be a much slower speed than usual. The wing doesn't think so, though!
Take that same speed we're seeing, and turn the plane around, and that wind is no longer moving front-to-back under the wing. The airspeed is drastically reduced. Simply put, the wing can't fly at that speed, and stalls.

I guess it's important to also point out that once your airspeed is high enough to remain flying downwind, the windspeed can contribute to and increase your flying speed. Passenger jets take advantage of tailwinds in the jetstream to arrive ahead of schedule whenever they can manage it.

I hope this is of some help.

Jim

JackD

My Feedback: (4)

5....4....3....2....1.... showtime!

radfordc

My Feedback: (14)

I'm sure it was aliens! Makes about as much sense as a "downwind turn".

radfordc

My Feedback: (14)

The definitive test for the "downwind turn" is as follows:
1. Take your plane and go for a hot air balloon ride on a day with a strong wind (lets make it 50 mph just for the sake of argument). Make sure the hot air balloon is flying above a cloud layer so you can't see the ground. You will notice that in the balloon you don't feel any wind blowing at all....the balloon is drifting along at exactly the same speed as the wind. You also can't judge what is happening with the earth because the clouds are drifting also at the speed of the wind.
2. Launch the plane and fly in circles around the balloon. Look to see if the plane climbs on one half of the circle and dives on the other half. For the downwind myth to be true it would have to.
3. Fly straight and them make a quick 180 degree turn. See if the model stalls more when turning on one particular heading. If the downwind myth is true, then when the model is turning in the same direction the wind is blowing (ie, downwind) then it should lose airspeed due to the 50 mph "downwind" factor.

Of course, none of these things will happen because as far as the balloon, you, and the plane are concerned there is no wind at all. You are moving with the wind at exactly the same speed.

rgburrill

There's that irrefutable "evidence". From the "experts" that have commented on this in the past it seems that since a frame of reverence can be moving then any point can be chosen as a frame of reference. These "experts" like to chose the leading edge of the wing as that frame of reference. And if that were indeed so then I would agree with them. However, an INERTIAL reference frame can have NO forces acting on it. Therefore, AS THE PLANE IS TURNING, is has several forces acting on it and that point on the wing is no long an inertial frame of reference. The center of the earth is.

BaldEagel

Can't believe this thread is still alive. but it does need a bit of artificial respiration, or is that reverence, or even reference.

Mike

PacificNWSkyPilot

My Feedback: (19)

Hmmm. . . .It COULD be aliens. My book might explain it. Might not.



In the meantime, unless you remove the propeller and engine and gravity from the mix, the wind speed can't be the only factor to be considered. The plane is going to be going faster (relative to the ground) when going upwind past the balloon, and faster (relative to the ground) when going downwind past the balloon, and I would venture the probability that the people in the balloon basket could see the difference in speed.

Planes typically won't drop out of the sky from a downwind turn. Most of the time. Because they're going fast enough that they won't stall.

Here's a typical scenario.

Most of us push that throttle stick forward until the engine/motor is at full power, and we leave it that way right through the first turn. THAT plane isn't going to fall out of the sky from that downwind turn, it's got lots of wind from the throttle, and from the airspeed. Zero problems, fly all day and forget it.

Here's another. A conscientious, intermediate pilot takes off. His model has plenty of wing area. It's a cub, and he's barely got the throttle at 1/3rd today, because there's a nice, brisk wind coming right down the runway, and the model lifted off effortlessly today. It's not going fast, but it's steady, and it looks quite solid. The model flies well, droning along at a lazy pace, and then he banks it gently for the downwind run. It's looking fine, and is halfway through that bank when the plans starts to falter. The sticks aren't responsive, and without warning, that cub just falls into the turn and spirals straight into the ground.

Why did the cub fall out of the sky? Because on the takeoff run, the pilot substituted windspeed for airspeed, and failed to compensate with more airspeed before he banked and lost that extra help he and the cub had grown dependent upon, tooling along at that slow, steady speed.

THAT'S the downwind turn, and THAT'S when it's dangerous.



Jim

Lownverted

My Feedback: (4)

Jim,

The tailwind adds ground speed, airspeed stays the same. This is the point people seem to have the most trouble with, separating airspeed from groundspeed.

Lownverted

My Feedback: (4)

I'm bored, couldn't help it. lol

cfircav8r

My Feedback: (1)

So where are you getting your knowledge? I have been flying models since 82 teaching people to fly models since 86, started flying full scale since 93 and teaching full scale since 96 and my degree is in aeronautics. Where does your knowledge about flying come from?

You talk of inertia as if the plane must overcome the inertia added by the wind, but you miss the part that it is always there, influencing the plane in the same direction through a change in ground speed and track. The plane doesn't need to overcome it, you just need to understand how it affects your perception while navigating through your maneuvers.

JackD

My Feedback: (4)

If the cub needs power to go from up to down wind (relative to the ground), then gliders are doomed to crash!!!!!

This is not frona balloon, but kinda helps too... Enjoy
https://m.youtube.com/watch?v=AnmDjt...ature=youtu.be

roger.alli

Thanks Jack.. That's the coolest thing I've seen on RCU for a long time.. Must have been great fun..

CraigG

My Feedback: (40)

Interesting that you would choose this example. That's exactly what we did with my hot air balloon and an F-104. There were no clouds so we did it at night so we couldn't see the ground. We had a heck of a time in the balloon keeping up with the F-104 but since the balloon was much larger, the wind acted on it with greater force (particularly when we turned downwind), and we were able to manage the inertia to keep up with the F-104.

The results were inconclusive because it was dark and we were blinded every time I fired the burner. We decided to land and discuss the issue over a few beers. But alas, we still couldn't agree what had actually happened. We never did see the F-104 again.

Hope this helps,

Craig

Top_Gunn

My Feedback: (6)

Some (but certainly not all) of the misunderstandings about the downwind turn may come from the fact that RC fliers sometimes use the expression "downwind turn" to refer to the turn you make from the downwind leg of your landing pattern to the base leg, and to the turn from base to final. Those aren't "downwind turns" in the sense of turning toward the downwind direction (just the opposite, in fact), but as they take place after the downwind leg, some people call them "downwind turns." And they do present dangers, for two reasons. First, because your ground speed on the downwind leg is high in a strong wind, and you don't have an airspeed indicator in a model, you can be flying just above stall speed and not know it. Make a turn when you're doing that and you'll stall. Second, because your ground speed is high when flying downwind, making a turn that looks good from the ground requires a steeper bank, and therefore more up elevator, than normal, and that too creates a danger of stalling.

If you were to keep a record of where and how often people's rc planes stall and crash at your field, I'd bet you'd find that almost all of them are when turning from downwind, or from a crosswind: exactly the opposite of what the people who fall for the downwind turn myth think. The ones you do get when turning toward downwind are going to be turns after losing power right after takeoff. That turn is dangerous no matter what direction the wind is coming from, simply because your airspeed is low.

None of this has anything to do with the mistaken idea that a plane will gain airspeed when turning into the wind or lose it when turning downwind.

j41captn

My Feedback: (5)

How about this? You're flying straight and level heading due north 360', 100 kts. indicated airspeed with a ground speed of 50 kts. (50 kts headwind). You do a 45' bank turn to the south 180'. What will your ground speed be at the moment you level your wings? Will it be 150 kts instantly or will it take a moment to get your momentum up?

Top_Gunn

My Feedback: (6)

If your airspeed is 100 knots at all times, your ground speed will be 150 knots when you are headed south. This is arithmetic, not physics. But unless you are concerned with something like navigation, what does it matter what your ground speed is?

Here's a simple proof, suggested by a discussion in another one of these threads:

1. Suppose you are flying a 2000-pound plane due east on a calm day at 100 mph. Calculate your momentum.

2. Now turn the plane 180 degrees until you are flying due west at 100 mph. Calculate your momentum.

3. Calculate the difference between these two momentums.

4. Now do the same calculations, with the same 100 mph airspeed, but with a wind blowing straight from the east at 50 mph.

5. Unless you made a mistake in your arithmetic, the change in momentum in still air and with the 50 mph wind will be the same. So the change in momentum turning from east to west is not affected by the presence of wind.

I've forgotten who first pointed this out, or I'd give him credit.

radfordc

My Feedback: (14)

What the groundspeed is and how it changes is totally irrelevant to the plane. If the airplane has 100 kts IAS upwind, it will also have 100 kts IAS downwind. As far as the airplane is concerned the wind doesn't exist.

The myth exists because people fly the plane in reference to themselves and don't let the plane fly naturally in the air. If you fly the plane so that it has the same "groundspeed" while flying in both directions you may crash. A normal 45 degree banked turned "looks" different when the wind is blowing hard.

PacificNWSkyPilot

My Feedback: (19)

A cub moving slowly into the wind is flying on the wind, not on actual airspeed. Change the direction of flight away from the wind and that's when you find out if there's enough wind moving under the wings to provide lift. If there's not, it falls. I have to laugh at how very simple this is, and apparently how difficult it is for so many here to understand. If you're all smarter than you appear to be here and you actually DO understand how it works, then you're all just arguing phrasing and semantics. That's futile, and it involves egos, not knowledge.

Here's a suggestion. Reduce your wing loading. Use a bigger motor/engine, or push the throttle stick forward more. Problem solved.

Jim

BobbyMcGee

55 pages and1373 posts and we still haven't passed square 1. Now we add a football and soccerball to the mix!? This won't be solved in our lifetime.

I tell ya, it all has to do with the rotation and y axis offset of the earth that is causing this problem. Just don't make right turns in the Northern Hemisphere or left turns in the Southern Hemisphere until Superman corrects the axial tilt.