General > General Technical Chat
Mess with your minds: A wind powered craft going faster than a tail wind speed.
electrodacus:
--- Quote from: IanB on December 23, 2021, 07:23:45 pm ---
So, if you are moving at 60 km/h in still air, the speed is 60 km/h, and the drag force corresponds to a wind velocity of 60 km/h.
On the other hand, if you are moving at 10 km/h against a 50 km/h headwind, the speed is 10 km/h, and the drag force corresponds to an apparent wind velocity of 10 + 50 = 60 km/h (same).
The drag force is the same in both cases, but in the second case the speed is 1/6 of the first case, so the power required is also 1/6.
--- End quote ---
You are almost there. The power a vehicle needs to overcome drag is the same for 60km/h vehicle and 10km/h vehicle with 50km/h wind.
Thus you need to calculate using power then if you want to convert to force needed. You can not calculate using force directly unless you want to get super complicated.
Do you agree that a vehicle consumption (can be an electric bicycle) if we ignore the small friction and roiling resistance is mostly about drag and drag power will be the exact same for 60km/h bicycle with no wind or 10km/h bicycle with 50km/h headwind.
If you agree that power will need to be the same in both cases the force will be fairly different but not in the direction you are thinking about.
Once this is settled and understood I think it will be very important in understanding why Blackbird can not work without energy storage.
electrodacus:
--- Quote from: Domagoj T on December 23, 2021, 07:38:56 pm ---Full disclosure, I skipped quite a few pages of this discussion, for obvious reasons.
In any case, how I interpret the downwind faster than wind is just as a simple lever. The wind has arbitrarily large amount of energy (size of the propeller is not specified), it's just a matter of devising a mechanism to push against the huge energy source that is the wind.
A simple demonstration is a yo-yo (yes, the spiny toy on a string).
(Attachment Link)
Put the yo-yo on the table with the string coming from the underside of the bobbin part and pull. The yo-yo will catch up with you.
If you don't have a yo-yo at hand, substitute with a spool of solder wire.
--- End quote ---
Can you not see that direction of travel is the same as pulling direction ? This has nothing to do with either direct down wind when above wind speed or direct upwind version of Blackbird.
Also all those yo-yo games are based on energy storage.
Kleinstein:
--- Quote from: electrodacus on December 23, 2021, 08:35:38 pm ---
--- Quote from: Domagoj T on December 23, 2021, 07:38:56 pm ---Full disclosure, I skipped quite a few pages of this discussion, for obvious reasons.
In any case, how I interpret the downwind faster than wind is just as a simple lever. The wind has arbitrarily large amount of energy (size of the propeller is not specified), it's just a matter of devising a mechanism to push against the huge energy source that is the wind.
A simple demonstration is a yo-yo (yes, the spiny toy on a string).
(Attachment Link)
Put the yo-yo on the table with the string coming from the underside of the bobbin part and pull. The yo-yo will catch up with you.
If you don't have a yo-yo at hand, substitute with a spool of solder wire.
--- End quote ---
Can you not see that direction of travel is the same as pulling direction ? This has nothing to do with either direct down wind when above wind speed or direct upwind version of Blackbird.
Also all those yo-yo games are based on energy storage.
--- End quote ---
The yo-yo toy is based on stored energy, but here it is only about the same toy, used in a different way.
The yo-yo is moving in the same direction as the string is pulled, but faster than the string is pulled.
This is just like blackbird going the direchtion of the wind, and faster than the wind.
electrodacus:
--- Quote from: Kleinstein on December 23, 2021, 09:13:04 pm ---
The yo-yo toy is based on stored energy, but here it is only about the same toy, used in a different way.
The yo-yo is moving in the same direction as the string is pulled, but faster than the string is pulled.
This is just like blackbird going the direchtion of the wind, and faster than the wind.
--- End quote ---
The thing you seems to ignore is that vehicle being faster than wind in same direction can not be pushed by the wind.
There is no such problem in the yo-yo example.
IanB:
--- Quote from: electrodacus on December 23, 2021, 09:46:06 pm ---The thing you seems to ignore is that vehicle being faster than wind in same direction can not be pushed by the wind.
There is no such problem in the yo-yo example.
--- End quote ---
The yo-yo going faster than the string in the same direction as the string cannot be pulled by the string?
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version