Merged DDWFTTW in a “Real” Wind

[EHocking]

No. The vane ALWAYS points to the apparent wind,

The POINT of a weathervane will, the FLETCH/RUDDER will always point downwind. For the steering wheel, we are only attaching the FLETCH. So IT will always point downwind - just as a flag or a streamer would.

if the true wind changes and comes from the rear left, it will tend to point to that.

and the BACK of a weathervane (which is all that is attached to the cart) will point to the left-front - but not for long, because the vane swivels the wheel DDW so that there is NOT an imbalance on the VANE. Just as swivelling windmill anemometer's rudder/vane will always point downwind.

If the cart should turn in that direction,

It will not, because the vane's tendency is to point parallel to the prevailing/true/apparent wind, so turning the steering wheel to point the cart DDW.

that will reduce the force from the true wind, and the vane will return to the apparent wind. It will oscillate. Wobble.

No. The vane will turn the wheel to be parallel to the wind, thus steer the cart to point DDW. That's the whole point of the jig.

Another factor is the caster. They work by slightly raising the wheel against gravity,

What??? This is a simple swivelling wheel. "they work by slightly raising the wheel against gravity"? What sort of gibberish is this?

so "self-centering",

No, No, No. This is not a self-centring caster, but a freely swivelling wheel. Again, the only way you can make your point is to totally misrepresent what is being discussed.

and the will also oppose the vane and wobble for that reason too.

Wow. 12 posts trying to understand how a rudder on a windmill or how a weathervane works. No wonder this thread is in its 2nd year.

 

[I Ratant]

Nothing too complex and no friction added to the system.

Just think of an upright attached to the front wheel's axle and at the top of the upright, a non-swivelling weathervane that is parallel to the wheel.

[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_26614d9ccdced3070.gif[/qimg]

Prevailing wind will keep the swivelling, steering wheel pointed in the direction of the wind, and hopefully the cart steering DDW.

Just the same principle that keeps a a windmill's vanes facing the wind (OK, but skewed 90^o).

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At the switch from tailwind to headwind, the wheel has to do a 180 around the pivot. Quickly. It can't stop 1/2 way round.

 

[I Ratant]

Not bad. To get past wind speed DDW without the wheel turning by 180°, one could restrict the wheel steering to < 45° and allow the vane to flip over the top, to the back.

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It had better!

 

[EHocking]

What if you are travelling 10mph south in a 15mph southwest wind?

apparently humber would get very confused.

 

[I Ratant]

All of which has nothing to do with subject of a potential system to orient I Ratant's cart's front wheel downwind.Just as I said - and so can be used to orientate the front wheel so the cart is steered DDW.And since at the moment, none of I Ratant's carts are able to travel faster than the wind, the apparent wind direction = true wind direction, so the "vane" will always point downwind, thus keeping the front wheel steering the cart DDW.

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Hope springs eternal...

 

[EHocking]

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At the switch from tailwind to headwind, the wheel has to do a 180 around the pivot. Quickly. It can't stop 1/2 way round.

Yeah, but you're yet to get your carts to go FTTW, so at the moment, not an issue!

ETA: But yes. That would be the only way it would work for >DDW. And I have no idea if it would swivel fast enough not to completely screw up the direction of the cart during the transition from <DW to >DW, considering how light they appear to be.

 

[humber]

What if you are travelling 10mph south in a 15mph southwest wind?

Tada! The idea assumes its conclusion.

 

[humber]

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It had better!

No need to bother I Ratant. The free-prop will beat the geared cart every time.

 

[humber]

The POINT of a weathervane will, the FLETCH/RUDDER will always point downwind. For the steering wheel, we are only attaching the FLETCH. So IT will always point downwind - just as a flag or a streamer would.and the BACK of a weathervane (which is all that is attached to the cart) will point to the left-front - but not for long, because the vane swivels the wheel DDW so that there is NOT an imbalance on the VANE. Just as swivelling windmill anemometer's rudder/vane will always point downwind.It will not, because the vane's tendency is to point parallel to the prevailing/true/apparent wind, so turning the steering wheel to point the cart DDW.No. The vane will turn the wheel to be parallel to the wind, thus steer the cart to point DDW. That's the whole point of the jig.What??? This is a simple swivelling wheel. "they work by slightly raising the wheel against gravity"? What sort of gibberish is this?No, No, No. This is not a self-centring caster, but a freely swivelling wheel. Again, the only way you can make your point is to totally misrepresent what is being discussed.Wow. 12 posts trying to understand how a rudder on a windmill or how a weathervane works. No wonder this thread is in its 2nd year.

Vane direction in motion depends on both the direction and speeds of the true wind and of the cart. It's what you don't know that kills you.

 

[EHocking]

What if you are travelling 10mph south in a 15mph southwest wind?

Tada! The idea assumes its conclusion.

The actual answer is of course apparent windspeed of 23.2mph, with an apparent wind direction (relative to the southerly heading) of 27.2^o.

 

[A.T.]

That was my first thought, but do you think the cart would survive the instability between 0.8X and 1.2X wind speed?

You would need a vane mechanism that locks the wheel straight, in low apparent wind. And only if it is strong enough, aligns the wheel with it.

 

[EHocking]

Vane direction in motion depends on both the direction and speeds of the true wind and of the cart.

exactly.

And if the cart is heading DDW at 10mph in a 15mph wind, the tail end of the vane(rudder/flag/streamer) will point DDW, just as per the gif I provided.

 

[EHocking]

That was my first thought, but do you think the cart would survive the instability between 0.8X and 1.2X wind speed?

You would need a vane mechanism that locks the wheel straight, in low apparent wind. And only if it is strong enough, aligns the wheel with it.

It probably would depend on the duration of the transition.

If a very light cart was accellerating sufficiently at the transition to >windspeed it might not have too averse effect on the steering.

Underline the might...

This was a purely theoretical idea to see if there was a way to "passively" steer a small, light test cart without resorting to complex systems or remote control steering, so that I Ratant's cart was always pointing DW.

About the only way to test it would be to build it and "suck it and see".

 

[humber]

exactly.

And if the cart is heading DDW at 10mph in a 15mph wind, the tail end of the vane(rudder/flag/streamer) will point DDW, just as per the gif I provided.
[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_26614d9ccdced3070.gif[/qimg]

Negative feedback from the motion of the cart will see the vane move back to the apparent wind. Vanes respond to force, not cartoons.
Funny how you assume that the tailwind will be faster than the cart. Did you know boats can tack? And what do they follow? It will wobble.
1) first error. Comparing a stationary windmill with a moving windmill
2) Second error. Comparing a self-steering boat which has both air and water flow. The latter is in a dense fluid
These are factors that engineers call "different"

But thanks for pointing out the turbines work best when directly facing the wind. That is one factor that causes the BB to accelerate faster when not ddw. The turbine force opposes the cart, and that is why the free-prop wins hands down. But, somehow, when past WS, that magically disappears. I have some of the wind data from NALSA, and it's a sail cart, for sure.

 

[humber]

It probably would depend on the duration of the transition.

Best to hope there are no headwinds. Gusty wind has those.

 

[I Ratant]

Yeah, but you're yet to get your carts to go FTTW, so at the moment, not an issue!

ETA: But yes. That would be the only way it would work for >DDW. And I have no idea if it would swivel fast enough not to completely screw up the direction of the cart during the transition from <DW to >DW, considering how light they appear to be.

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I've used front wheel and rear wheel covers on my 10-speeds, that fit over the wheel to cover the spokes.
The front wheel cover is not a good thing with a crosswind!
I don't use that any more.
Going downhill at 50 mph, I get real antsy when the front wheel gets "loose".

 

[I Ratant]

No need to bother I Ratant. The free-prop will beat the geared cart every time.

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Nope.
Not without some fancy tacking, as with a boat and probably not even then.
No fancy stuff available here.
I would like to get the driven cart to work.
Release both at the same time, and watch the freewheeler accelerate faster, but get caught and passed by the driven cart.
Theory says that'll happen.

 

[ThinAirDesigns]

.Theory says that'll happen.

Practice says it as well.

JB

 

[EHocking]

Negative feedback from the motion of the cart will see the vane move back to the apparent wind.

And the apparent wind direction, when travelling DDW at a speed <actual windspeed will always be an apparent tailwind.

Vanes respond to force, not cartoons.
Funny how you assume that the tailwind will be faster than the cart.

Since we're discussing carts going DDW at a speed <windspeed, yes. The assumption is that the tailwind will be faster than the cart.

Did you know boats can tack? And what do they follow? It will wobble.
1) first error. Comparing a stationary windmill with a moving windmill

No. We were comparing a stationary windmill with a windmill moving DDW at a speed < true windspeed. Therefore an apparent tailwind.

2) Second error. Comparing a self-steering boat which has both air and water flow. The latter is in a dense fluid

No. At not time in this discussion were we discussing a self-steering boat. The MECHANISM was alluded to as "something based on this might be used" to steer a cart.

These are factors that engineers call "different"

And so I have avoided using different scenarios and craft while discussing the steering "problem" (if there is one. You are the one that keeps derailing with irrelevant examples.

But thanks for pointing out the turbines work best when directly facing the wind. That is one factor that causes the BB to accelerate faster when not ddw.

Blackbird does not utilise a turbine. This implies that the prop drives the wheels. It is the other way around. The wheels drive the prop.

The turbine force opposes the cart, and that is why the free-prop wins hands down. But, somehow, when past WS, that magically disappears. I have some of the wind data from NALSA, and it's a sail cart, for sure.

No. and No again. The prop on the Blackbird is not a turbine driving the wheels.

 

[EHocking]

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I've used front wheel and rear wheel covers on my 10-speeds, that fit over the wheel to cover the spokes.
The front wheel cover is not a good thing with a crosswind!
I don't use that any more.
Going downhill at 50 mph, I get real antsy when the front wheel gets "loose".

And of course the whole discussion about trying to find a steering mechanism for the cart may be completely superfluous!

Does it actually need one, or do the carts "self steer" parallel to a prevailing wind anyway?