Turns, with and without the wind

Yes, Udi. I know that energy must be conserved.

On a macro scale, the net movement is indeed zero.

On a local scale, however, the descending air flows outward before again rising.

I’l try to find the reference to descending air and Dutch windmills.
 
I am telling you guys that you are not maintaining airspeed. You can glance down at the indicator from time to time and see what you want, but somewhere in your turn your loosing airspeed and hence the need for more power.
Ron and im telling you that i was watching it to make sure it didnt drop below 45 kts ASI, and it works fine, has checked it a few times for other reasons..

Guys and gals, the problem with this debate is that the mustering guys do not operate like the sedentry flying majority, at a constant angle of bank or constant airspeed
Paul, to prove this piont i WASNT doing a sharp drop off AS turn, this time i was doing a graduall 45-50 kts ASI turn at 5' above the tree tops, to prove a point. Please dont start saying that im trying to mislead people here..

Al, for reason of keeping this simple, the sink is occuring at a point after returning to level flight from the turn. It could be 10 seconds later, not just exiting the turn. I know this is easy to say that the pilot is not maintaining airspeeed, but I have watched the ASI, and it is not bouncing around lower as should be the case in a gust or other distubrance. Just 40-45 MPh indicated, and falling like a rock at WOT. I fully understand it does not follow what should be happening and is easy to disbelieve, but it does happen every now and then.

Exactely right Scott, i can do the turn then it starts to drop, with the same ASI
 
Phil says,

Hi, when I make low level down wind turns I have to make a concious effort to exagerate the turn. If I don't, I find myself banking into the turn to shorten it.

Phil, exactly. This is what we believe is happening to the guys who observe the downwind sink. You're tightening the turn to maintain a desired ground track, because if you don't, the increased ground speed will cause you to overshoot the landmarks on the ground which define your desired pattern. That increased bank angle requires more energy be added, or you'll convert potential energy stored as speed or altitude into energy used to create rotor thrust.

What we're trying to figure out here is the claims that there's more to it than this explanation in certain situations near the ground.
 
I have experienced *sink* in turning downwind and it was at full throttle and...let's forget that weak suggestion... as to looking at the ground. If you're holding a stationary point over the ground, into a 25 mph wind, at full throttle and you turn left or right, how are you not goin' to *sink*...explain that to me. To recover you must maintain full throttle, and apply forward stick to gain additional airspeed.

Ron and others...may I offer a suggestion...if you trust your flying prowess...cover over the ASI, Rotor Tach, Eng.Tach, ALT. and go fly. I'll wager you will like flying a bit more...after a bit?!;)

I'm open for questions.


Cheers :)
Harry, with all due respects, you didnt read my post properly, here is the bit you missed;
THIS IS THE IMPORTANT BIT, ok im hovering at about 30kts ASI, so i open the tap increase it to 40kt ASI before i start to turn, by the time im in the turn it is 50 kts ASI,
You see Harry, my gyro will fly at 30 kts, at about 4800rpm,i can go to just under 20kts on full niose and still be holding straight and level, but with the wind on the nose it was only about 4500 rpm, so when i opened the tap, i had about 1000rpm extra, to increase AS, which i did BEFORE starting the turn, ok so i wasnt sitting there on full noise, then just start a turn of course you will loose hieght if you do that, that is not what i was doing....
 
Believe it or not Lillienthal gave us the answer to this problem in the century before last!
As some have pointed out the musterer's environment is somewhat different from what is experienced at higher levels. Even here inertia effects do play a part, particularly downwind gusts. I am assured that a jumbo joining a jetstream requires full power, with autopilot taking care of pitch, even then AS sinks close to minimum control speed. But that's not the real story.
I'm no aerodynamicist or physicist, but I think there is a simple explanation for what Bones, Brian and Lillienthal OBSERVED. Accusing them of failure to observe accurately is insulting and smacks of pseudointellectualism.Just a few days ago while talking to Rusty Ferguson and listening to his evidence at an Inquest he referred to the dangers of the downwind turn several times.
The best way to resolve this matter would be to repeat Lillienthal's experiment.
He set up a 10 metre tall mast (that's right in the musterer's turf). On this mast at say 1 m intervals he attached wind direction vanes with horizontal pivots, they were linked together and attached to a pointer scratching a trace on a clockwork powered smoked drum.
While the indicated direction varied a bit - up to a rise of 9 degrees the average was apparently 3 degrees. Thus the difference between an up and downwind take-off is an average of 6 degrees angle of attack.
I would suggest that critics repeat this historic experiment before accusing other observers of inaccurcy. Citing "ground referencing etc " is unhelpfull if not dishonest.
How to explain it?
I will try using the principle of conservtion of energy.
We all accept the concept that air being accellarated through a venturi results in reduced pressure, that's how a carburettor and part of the explanation of how a wing works. As I understand it part of the energy in that air mass is taken by the accellaration resulting in reduced pressure.
Now think about the converse, a mass of air moving along the earth's surface is subject to friction from various objects, so the lower bits are slowed, the energy in the air in the form of kinetic energy now becomes expressed as a rise in pressure, so the air expands, pushing following air up.
When this phenomenon was discussed a while ago on the old ASRA Forum one critic pointed out that this would leave a vacuum, however it becomes clear that conservation of energy prevents this.
Chuck, perhaps the windmill designers in Holland predated Lillienthal's experiments and so inclined the axis of their sails the wrong way. They were a bunch of Dutchmen after all! Seriously though it may have more to do with throwing the loads back into the tower for structural reasons. What do you think?

John Evans
 
Scott, Mark, A couple of questions if I may, what's the disc loading of your machines? Is the sink more pronounce with a left or right turn? Or, no difference?


My gut tells me the rotor inflow is being affected....I'm not sure exactly how.

What's rotor RPM doing?

I know that's more than a couple of questions and I appreciate your indulgence.
 
Harry, with all due respects, you didnt read my post properly, here is the bit you missed;




Mark:

I wasn't referencing nor giving that impression. I was merely stating what I did in my early years. I was totally ignorant of the physics involved in flying a gyro. I am still somewhat ignorant of the physics involved and don't try to impress anyone that I do know. I flew the gyro because of the pure joy I derived from it, which I could not achieve in a FW.

I will say this...I definitely know how to fly a gyro and have done so for almost 40 yrs.

I don't intend to go into great detail of my past flying other than to say that I flew and maneuvered in much similar fashion as you musterers do today. I seldom flew above 50 ft. and enjoyed being around trees and such...and as I said before...sans instrumentation.


Cheers :)

I don't have the desire nor the *balls* to fly in that manner anymore.
 
Mark:

I wasn't referencing nor giving that impression. I was merely stating what I did in my early years. I was totally ignorant of the physics involved in flying a gyro. I am still somewhat ignorant of the physics involved and don't try to impress anyone that I do know. I flew the gyro because of the pure joy I derived from it, which I could not achieve in a FW.

I will say this...I definitely know how to fly a gyro and have done so for almost 40 yrs.

I don't intend to go into great detail of my past flying other than to say that I flew and maneuvered in much similar fashion as you musterers do today. I seldom flew above 50 ft. and enjoyed being around trees and such...and as I said before...sans instrumentation.


Cheers :)

I don't have the desire nor the *balls* to fly in that manner anymore.

Harry i'm sorry but i meant to put it in the last post, if you were refering to my post,, so no probs :usa2: ,, thanks for replying,,,:rapture:
 
Scott, Mark, A couple of questions if I may, what's the disc loading of your machines?
Umm i think its 1.11,, well i running 27' rotors and the gyro weighs about 515Lbs
Is the sink more pronounce with a left or right turn? Or, no difference?
I seem to find myself doing mainly right hand turns, they just feel more comfortable to me


What's rotor RPM doing?

Not sure as i dont have a rotor tach on it :yo:
 
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Mark, Thank You!

I have no answer....yet.... the quicker more learned ones will probably figure it out before I......cyphering a little though..
 
John E., the difference for cowherds chasing cows as a vocation and someone flying constant radius circles for recreation is the environment.

I can fly constant radius, constant speed circles at a height of less than 50 ft. all day long, or at least until I run out of space, without gaining or losing height. But that’s in an open area where ground track is irrelevant. I wouldn’t think of doing the same thing boxed in by trees or other obstructions.

Cows don’t know much about air mass so I presume musterers must maintain contact with their animals, which restricts their maneuvering space. Their downwind turns have to be as tight as their upwind turns so they can’t fly at constant bank angle. They are forced by circumstances to fly by ground reference.

I don’t think anyone has discovered a new scientific principle.

As for windmills, I took a quick look and couldn’t find a satisfying reference for the tilt of the wheel axis.

The book, “A History of Mechanical Inventions” by Abbott Payson Usher says:

“…The desirability of setting the sail beam at an angle to the horizon is discussed at some length by Jerome Cardan in his attempt to analyze the mechanics of a windmill. We may thus infer that the increase efficiency yielded by this arrangement began to be commonly known at least by the beginning of the sixteenth century…..” But that’s nothing I would care to take to the bank.
 
Papa, mine are 25X8 SportRotors , all up weight with me and half tank of fuel is 530lbs. Again I am trying to not factor the turns in, but the worst one I ever had was about 5-10 seconds after a shallow bank right turn(not before). I never make steep angle downwind turns in stronger wind conditions. The sink happens when there is plenty of groundwind, straight and level, downwind after the turn maybe one out of 100 or 200 times. Airspeed is normal and conditions don't have to be gusty for it to happen. It has only happened at El Mirage, but it is also the only place near me(Los Angeles) where flight at 1 foot is legal, if so inclined. Normally I fly in congested city airspace with much higher minimum flight levels. I have been pushed up and down much further in mountain passes, but this is to be expected. Here is a picture of the area to give you an idea. It just does not get any flater or smoother.

Scott Heger,Laguna Niguel, Ca N86SH
 

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OK Guys

Now I am not a physicist. Altho My middle Step son is studying in his last year at University to be an engineer and has quite a few hours in physics and math.
I posed this question to him and he asked these questions. When hovering near the tree could the air have been denser (increased pressure)? When making the turn even tho the Airspeed was increased could the air have been less dense to cause this loss in altitude. Could lift have been lost during the maneuver of turning? Can the DA be variable on these set planes when low to the ground with these air mass vorticies?

I thought it was a fresh approach and could be an answer also.


Thom
 
I have a theory that I think might help explain these low level, downwinder, trouble makers' observations. I don't have it completely worked out but maybe some of you can pick up some ideas and take it to a higher level of coherence.

It has to do with the wind gradient and how the rotor disc is working within a wind gradient. When flying into strong head wind close to the ground, the forward part of the rotor disc, which is located on average oh, maybe 2-3 ft higher than the rear part of the disc, is facing a stronger relative wind than the rear part of the disc (the advancing blade is flying into increasingly strong headwind, if you will, and the retreating blade is flying into a slower headwind). As a result, the forward part of the disc is making more lift than the rear part of a disc. To overcome this imbalance the pilot has to use more fwd stick than usual for the same airspeed.

Now, when flying with a strong back wind, the opposite happens. The forward part of the disc is facing a slower relative wind than the rear part of the disc. So the rear side of the disc is making more lift than the fwd part of the disc and the pilot has to use more back stick than usual for that given airspeed.

In the transition from a strong headwind to a strong back wing the pilot has to transition from holding more fwd stick than usual entering into the turn, to holding more back stick than usual coming out of the turn.

I know this is not a perfect explanation, but it's the best I’ve got so far.

Udi
 
Tim, that’s a very interesting drawing of what appears to be a relatively modern windmill.

There were a few Dutch style mills in the US dating from colonial times but most have long ago been scrapped.

The multibladed sheet metal windmills were once everywhere for pumping water before the country was wired for electricity. You still see one from time to time pumping away and kept, I suppose, for nostalgic reasons.
 
This might well be the plan of the only one left in Australia too. It is in Western Australia outside Perth and was disassembled and transported to its current location by a Dutch immigrant couple where they have set up a resturant business. I believe it is fully operational but is only a tourist attraction. I have a photo of the finished article somewhere.
I do not believe that the head angle would be necessary for structural purposes - perhaps the wind angled down after blowing over the Dykes?
 
All very interesting Tim and Chuck, as Tim knows we have lots of windmills pumping water in Australia, I don't recall seeing the axis being inclined either way, nor do they seem to incline the axis on wind turbines. What does it matter anyway, the Dutchmen might have simply got it wrong
For some time I have been suggesting that those who doubt Lillienthal's observations, and the explanation I have offered for the musterer's observations should take the simple step of repeating Lillienthal's experiment,I would like to do it, but other projects have priority, and frankly I am prepared to believe Lillienthal!
It seems that the rising wind is known to dinghy sailors, in mild breezes they sit on the windward side of the boat in an endeavour to get the rising wind to hook under the sail and so lift the boat as well as propel it.
Come on you sceptics, this is a great opportunity to prove Lillienthal wrong, just find a flat area, erect a 10m tall pole, attach suitable vanes linked together and record where they point. If you show he was right we have a good explanation for the musterers observations, if you show he was wrong - ---well I for one will be amazed! I don't think you will!
 
All very interesting Tim and Chuck, as Tim knows we have lots of windmills pumping water in Australia, I don't recall seeing the axis being inclined either way, nor do they seem to incline the axis on wind turbines. What does it matter anyway, the Dutchmen might have simply got it wrong


I think the windmill axle is inclined because for the fact the blades have to clear the tower. As a example on my 55 foot tower you would have to have the axle shaft lenght of about 15 foot just to clear the tower legs.

As John said modern wind turbines do not have an axle that is angled.

Leon
kc0iv
 
.. As a result, the forward part of the disc is making more lift than the rear part of a disc. To overcome this imbalance the pilot has to use more fwd stick than usual for the same airspeed. -Udi

If you had greater lift at the front of the disc, then you would need to hold left stick to compensate, not forward stick. All aeronautical inputs are delayed by approx 90 degrees, whether they are a result of stick movements, or wind gradients. For example forward stick produces an angle of attack change at the 90/270 degree positions. :wave:
 
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