Quote:
Originally Posted by California98Civic
The $10,000 bet with a UCLA Prof that the project doesn't work. The video is pretty remarkable. I don't want to spoil anything.
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I'll play Devil's Advocate and suggest:
1) that the math is incomplete.
2) we still lack incomplete data for the runs presented in the video.
3) the treadmill models in no way represent the dynamics of Blackbird on the dry lakebed.
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That said:
4) a 19.2-foot International Tornado catamaran, with 235-square-feet of mainsail and jib was clocked at 19.2-mph, in a 13.9-mph wind, with course angle= 90-degrees relative to true wind.
5) Windbuggy-Class ice-racers achieve velocities which are 4X the true wind velocity.
6) A.B. Bauer, mentioned in the video, achieved approximately 14-mph into an approximately 12-mph headwind, for 40-seconds, with his propeller-powered car. ( see ' Faster than the Wind,' A. B. Bauer, 1st AIAA Symposium on Sailing, California, 1969 ).
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From Hucho's 2nd-Edition, p. 215 - 216, he gets into Earth boundary layer Turbulence level, then ' wind speed gradient' ( as mentioned in the video ).
From Figure 5.3, showing a natural sidewind, the wind velocity at Blackbird's propeller could be 3.5 X the wind velocity measure at the yarn/ Mylar tattle, indicating that the while the tattle was indicating forward velocity near the ground, the propeller would still be in a tailwind.
No mast for a propeller-elevation tattle or wind speed indicator was provided to us in the video at El Mirage. Upper wind velocity was an unknown quantity.
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While propeller efficiency was mentioned, no coefficient was provided to us.
We have no mechanical efficiency values for:
1) rolling resistance of three tires on dirt
2) wheel bearing losses
3) differential gear losses
4) lower sprocket-to-chain losses
5) internal multi-link chain losses
6) upper chain-to-sprocket losses
7) propeller jackshaft bearing losses
8) propulsive efficiency of the propeller-to-atmosphere coupling ( a maximum of 93.3% as of 1935 NACA testing ).
9) we have no projected frontal area for Blackbird
10) we have no coefficient of aerodynamic drag for Blackbird, 'forwards' and 'backwards.'
11) we have no test weight with driver for Blackbird
12) sub-critical Reynolds number was never mentioned by anyone
13) we have no physical exterior dimensions for Blackbird.
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At sub-critical Reynolds number, Blackbird is a golf ball without dimples, whether going 'forwards' or 'backwards.'
Blackbird will experience terrific flow separation, casting a large wake.
If it turned out that windspeed at the propeller was indeed higher than down below at the tattle, then according to laminar boundary layer aerodynamics, the entire body of Blackbird would be in separated flow, with a low-pressure turbulent wake ( ahead of the superstructure ).
Any yarn tuft of Mylar streamer would be impelled to seek this low pressure regime, providing the 'illusion' of extra wind velocity ground speed.
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The instability of the propeller, inducing cyclic torsional displacement and deformation of the upper body, is a classic phenomena associated with 'downwind', two-bladed propeller asymmetrical wind loading of the propeller disc, from body interference. We need to pay attention to this, as it's a default wind direction indicator.
None of this was in the calculus.
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I have no skin in the game and am not convinced that Blackbird cannot do what has been purported. I would just like to see a fully-instrumented test, and all data and specifications.
It's a book keeping issue. Accounting. Complete energy balance on the spreadsheet.
