Downwind Faster than the Wind - Successful Run by manned cart

ThinAirDesigns said:
...this hefty plate's ability to handle the rather moderate compressive loads expected of it.B
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Thanks for the close up picture. It must be fun to drive.

Can you say something about your instrumentation? I guess you are recording with a GPS receiver to get post "flight" data. Do you have other (wind or ground speed) instruments on board?
 
RAI said:
Thanks for the close up picture. It must be fun to drive.

Can you say something about your instrumentation? I guess you are recording with a GPS receiver to get post "flight" data. Do you have other (wind or ground speed) instruments on board?
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Accepting the NALSA invitation to the "Americas Cup" event left us with a shortened construction schedule (by about a month). We built the vehicle to accept far more instrumentation than is currently operating. Some of this instrumentation has nothing to do with any sort of "proof", but is there because we hope to eventually collect some interesting data.

For the record runs, NALSA will require three independent measurements of craft speed wrt the ground, three independent measurements of wind speed and three of wind direction.

For our own purposes, we hope to collect data from our instrumented hub (torque input and thrust output) and instrumented axles (retarding force and axle rpms). From these measurements we can get wheel slip, transmission efficience and propeller efficiency numbers.

We expected to collect and use this above data to optimize the craft for 2x WS travel, but since we blew right through that window on our first run we've become less focused on that instrumentation system and more on getting the mods done in preparation for the record runs. We will work on completing those as time allows.

JB
 
RAI said:
Thanks for the close up picture. It must be fun to drive.
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It is. So far I've Bogarted the driver's seat. JB is pretty keen on keeping a close eye on various aspects of the cart from the chase vehicle. But he will undoubtely take a spin soon.

Can you say something about your instrumentation? I guess you are recording with a GPS receiver to get post "flight" data. Do you have other (wind or ground speed) instruments on board?
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We instrumented the prop hub and axle with 7 load cells and an RPM sensor primarily for our analysis purposes. This gives us prop torque, prop thrust, rolling retarding force, and prop and wheel RPM. Unfortunately, the measurements contain enough noise that we can only make limited use of them. Fortunately, these measurements became immediately much less interesting to us when we first put the cart on the dyno and found it to pull forward at all prop pitch settings, all RPM settings, and all gear ratios. The design was more efficient than we had counted on.

In the runs in Ivanpah, we could only make limted wind readings. We made readings before the start, at the end, and noted when we reached wind speed. We also had a NALSA official that noted the gust readings during our run. On our next runs we will be measuring and logging wind speed and direction along the course and on the cart itself. We also measure and log speed and position via on-board GPS. At the next event, we'll be using one of the units Sportvision designed to track race-cars (as seen on NASCAR).

ETA: I see JB already covered this while I was typing.
 
Thank you spork and ThinAirDesigns. I hadn't thought of torque measurements. I can see they would be noisy but important for future improvements. I guess you are going to need some more substantial tyres.

I gather you are working on a continuously variable pitch propeller version for the BUFC. Will you be manually controlling pitch, or do you plan an algorithm with torque/thrust sensors?
 
Spork and Thin Air: I only pray that Humber doesn't follow you onto this forum!
( for the benefit of most UK readers, he is the biggest unbeliever on the Thinkrational forum, and posts continually. I suspect he hasn't been blocked yet because of his entertainment value!)
 
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RAI said:
Thank you spork and ThinAirDesigns. I hadn't thought of torque measurements. I can see they would be noisy but important for future improvements. I guess you are going to need some more substantial tyres.

I gather you are working on a continuously variable pitch propeller version for the BUFC. Will you be manually controlling pitch, or do you plan an algorithm with torque/thrust sensors?
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The prop hub was designed to allow for adjustable pitch. We wanted to keep it "ground adjustable" for our initial runs, but are now upgrading it so the pilot can adjust on the fly. It will be adjusted manually, and indexed so the pilot can know what setting it's at.
 
Ubergeekian: Full references please to the claim. Try quoting instead of your usual straw man attempts. I remember claiming a zero AoA prop can not rotate in still air. Like you claim. But then your grasp of reality has been shown on a number of times to be a little wayward. We even have a few Videos.

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ThinAirDesigns: The whole brake design is stupid. Why not put it next to the square shaft in tension? The first thing is, that there is no strength in the disk. They "shatter" at the root of the diagonal ties to the hub. So the whole alignment is based on a piece of steel that is 1/4 inch, you say, and in compression on its longest edge. When all real bike designs have the unit hard mounted to the frame tube by very short lugs. As for the welds, yes the photos on your site do confirm that you tack mostly. Welding is a process that requires design. It is not sticking a mig torch on a sheet of steel.

The back brake design is so much worse. As there is a small square tube, a length of larger square tube, and then a bolted plate of wood to hold an axle. Then an axle length before getting to back to the brake disk. Terrible design.

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Spork: "We instrumented the prop hub and axle with 7 load cells and an RPM sensor primarily for our analysis purposes. This gives us prop torque, prop thrust, rolling retarding force, and prop and wheel RPM."

Another good point, we are talking about a linked system. Why all the sensors on essentially the same drive chain. Why not measure the axial thrust on the prop shaft bearings (fixed side) and just one point in the drive linkage. Even the chain tensioner would have been appropriate. That is the source of the noise. All that complexity on the rotor hub is just extra failure methods. The efficiency of the drive chain can be done in the workshop. The ratchet spanners (translate: wrench) should not be active during the real tests so it should be a fixed linkage with just a chain tensioner.

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ThinAirDesigns: "and not the "wrong prop". "

I can get in the little day sailor next door and sail to windward to prove a point. It has blown out sails, but it will still do it. That does not mean Oracle should have blown out sails. So I still say you have the wrong prop. If it was designed with the correct theory to support the design, then it would not look like that. Andrew Bauer's prop was better, but even his was far from the ideal.
 
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halfway said:
Andrew Bauer's prop was better, but even his was far from the ideal.
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Yes, the fact that he had a better prop allowed him to report multiples of windspeed in the 1.17x range while our machine can only do a measly 2.5x to 3x of that. Damn, I wish I had HIS prop. :rolleyes:

But keep the wrongness coming -- it's concentrated entertainment.

JB
 
Well JB, it seems humber must have been right from the start. We have gone horribly wrong at every single step. We have shamed ourselves and our sponsors. In fact, I assume our sponsors must have funded us out of pity, because we couldn't have gone about raising money very well either.

Frankly, I expect we will be extremely embarrassed when halfway brings his cart out for the big race and blows our doors off. But you gotta figure it's inevitable since he knows better ways to do virtually every aspect of this.

Incidentally, I haven't read most of his stuff. Is it even possible to go DDWFTTW? Or is this another case of us attempting the impossible AND going about it all wrong?
 
halfway said:
Ubergeekian: Full references please to the claim. Try quoting instead of your usual straw man attempts. I remember claiming a zero AoA prop can not rotate in still air. Like you claim. But then your grasp of reality has been shown on a number of times to be a little wayward. We even have a few Videos.

----

ThinAirDesigns: The whole brake design is stupid. Why not put it next to the square shaft in tension? The first thing is, that there is no strength in the disk. They "shatter" at the root of the diagonal ties to the hub. So the whole alignment is based on a piece of steel that is 1/4 inch, you say, and in compression on its longest edge. When all real bike designs have the unit hard mounted to the frame tube by very short lugs. As for the welds, yes the photos on your site do confirm that you tack mostly. Welding is a process that requires design. It is not sticking a mig torch on a sheet of steel.

The back brake design is so much worse. As there is a small square tube, a length of larger square tube, and then a bolted plate of wood to hold an axle. Then an axle length before getting to back to the brake disk. Terrible design.

----

Spork: "We instrumented the prop hub and axle with 7 load cells and an RPM sensor primarily for our analysis purposes. This gives us prop torque, prop thrust, rolling retarding force, and prop and wheel RPM."

Another good point, we are talking about a linked system. Why all the sensors on essentially the same drive chain. Why not measure the axial thrust on the prop shaft bearings (fixed side) and just one point in the drive linkage. Even the chain tensioner would have been appropriate. That is the source of the noise. All that complexity on the rotor hub is just extra failure methods. The efficiency of the drive chain can be done in the workshop. The ratchet spanners (translate: wrench) should not be active during the real tests so it should be a fixed linkage with just a chain tensioner.

----

ThinAirDesigns: "and not the "wrong prop". "

I can get in the little day sailor next door and sail to windward to prove a point. It has blown out sails, but it will still do it. That does not mean Oracle should have blown out sails. So I still say you have the wrong prop. If it was designed with the correct theory to support the design, then it would not look like that. Andrew Bauer's prop was better, but even his was far from the ideal.
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General comment:

Those that don't do, are the most unhappy with the methods of those that do.

Specific comment:

Terrible design
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And yet it manages to kick the s*** out of your DDWFTTW cart every time it's taken into the wind.

JB
 
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halfway said:
Ubergeekian: Full references please to the claim. Try quoting instead of your usual straw man attempts.
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Certainly. At 17.40 on 17-03-10 you wrote

halfway said:
On the ground the rotational speed makes the apparent wind angle close to the plane of the prop. As the air speed increases the apparent angle bends forward of the craft.
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Note that claim: the apparent angle bends forward of the craft. If that was the case, the propeller would be pushing the plane backwards

But then your grasp of reality has been shown on a number of times to be a little wayward. We even have a few Videos.
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I think you are forgetting, my dear fellow, that the videos have confirmed everything I said. I was right!

I really can't see why you feel the need to bang on so much about propellers being able to supply thrust. Of course they can. That's what they do. I would be more impressed if you were finally to answer the questions of mine which you have been dodging for some time:
  1. A propeller is turning in still air. The thrust produced is measured. With the rotational speed and pitch held steady, a tail wind (ie from the direction of thrust) starts blowing. Does the thrust produced increase, decrease or stay the same?
  2. A helicopter is hovering in still air. Thermal activity starts and the helicopter starts to rise with the air around it. Rotor pitch and speed stay the same. Does the shaft power required to turn the rotor increase, decrease or stay the same?
  3. In the above case does the work done against gravity increase, decrease or stay the same?

Once you've answered them I'll compare your answers, your theories and physical reality.
 
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Ubergeekian: "Note that claim: the apparent angle bends forward of the craft. If that was the case, the propeller would be pushing the plane backwards"

NO, not if the aerofoil is forward of the apparent wind. If the apparent wind is 4 degrees forward and the aerofoil is 10 degrees pitch the air flow is still on the correct side. How is it that you can not see such a simple issue. The diagram has been drawn for you for ages. Forward of the craft is anywhere in the forward half circle, as opposed to being in the plane of the prop. It does not just jump instantaneously to perfectly in line with the direction of travel. That would be stupid, having a discontinuity in the apparent wind.


Ubergeekian: "A propeller is turning in still air"

This is still impossible, however many times you ask it. It is also irrelevant as all these props are "sucking" and "blowing". I've never seen Oracle sucking!



Restate the problem in a way that is sensible, and shows what is happening to the air that has to move through the prop.
Some points that you might have missed:
1. The prop. Is it actually attached to the ground or on a plane in the air. You do not specify.
2. If say it is in a wind tunnel what is the ratio of tunnel diameter to prop diameter. You do not specify.
3. The events time scales are not specified in relation to momentum of the air/plane. You do not state steady state or changes.
4. You can not assume that the helicopter rises. It could be close to the land and no thermal activity is created under the disk. But around it there is activity. Height not specified.
5. Timescale not specified. Unless you also have not specified that it is a zero mass helicopter. But then that is back to la la land.
6. Is gravity constant over the different heights? You do not specify.

If you want people to play games, then do not set questions that can be interpreted different ways. The actual answer is all three. It just depends on the timescale and if it is a incremental relative or absolute change. You really should try harder.
 
ThinAirDesigns: "kick the s*** out of your DDWFTTW "

It is etiquette to act with a little decency when visiting. We have a special place for those type of comments in this community.

My vehicle lasted 30,000miles with no drive chain failures, in much higher wind speeds that yours will ever see on land. I had no accidents and never endangered any life. It has many times the power of your cart.

I can wait.
 
halfway said:
My vehicle lasted 30,000miles with no drive chain failures, in much higher wind speeds that yours will ever see on land. I had no accidents and never endangered any life. It has many times the power of your cart.
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You forgot to add this little detail -- not once did your vehicle ever manage to go DDWFTTW.


JB
 
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Ubergeekian: "that the videos have confirmed everything I said"

Not those videos!
 
ThinAirDesigns: "not once did your vehicle ever manage to go DDWFTTW"

Ah, so now you seem to have a whole new set of engineering rules for only those vehicles of your choice.

More power, higher winds, more stress. But totally irrelevant.

Why should bad safety and bad design be acceptable in a specific vehicle type. That is not sensible. This is not rocket science, you are making a go cart. Notice how there is no NASA prizes for the achievement. The bet was over 40 years ago.
 
halfway said:
Ah, so now you seem to have a whole new set of engineering rules for only those vehicles of your choice.
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No, I stated that our DDWFTTW vehicle (though designed totally wrong apparently) manages to kick the s*** out of your DDWTFFW vehicle every single time you bring it to race ours. You took issue with that fact and I'm just making sure that you don't move the goalposts.

According to you we're incompetent designers and haven't a clue how our craft works, and yet we've managed to go DDWFTTW by an overwhelmingly bigger multiple than any humans in history.

When you build a DDWFTTW vehicle from scratch that betters our achievement, I'll give you respectful nod -- until then you're just guy who has been shown to not understand even the basics of the challenge and yes loves to talks s*** through a keyboard

JB
 
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