Single Bladed Rotor FAQ Response

bjt4888
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Single Bladed Rotor FAQ Response

Postby bjt4888 » Thu Mar 16, 2017 12:09 pm

Students and especially Event Supervisors should be sure to read the recently posted FAQ response that clarifies this bonus. A single blade mounted on a stick that has a free wheeling rotor on each end of the stick does not meet the definition of a rotor and does not qualify for the bonus. Read the FAQ for the official statement of this.

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Re: Single Bladed Rotor FAQ Response

Postby Bazinga+ » Thu Mar 16, 2017 1:05 pm

bjt4888 wrote:Students and especially Event Supervisors should be sure to read the recently posted FAQ response that clarifies this bonus. A single blade mounted on a stick that has a free wheeling rotor on each end of the stick does not meet the definition of a rotor and does not qualify for the bonus. Read the FAQ for the official statement of this.

Brian T


If the body has a single bladed rotor attached to it and is designed to have torque applied to it would it qualify for a bonus?
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Re: Single Bladed Rotor FAQ Response

Postby Bazinga+ » Thu Mar 16, 2017 1:06 pm

Bazinga+ wrote:
bjt4888 wrote:Students and especially Event Supervisors should be sure to read the recently posted FAQ response that clarifies this bonus. A single blade mounted on a stick that has a free wheeling rotor on each end of the stick does not meet the definition of a rotor and does not qualify for the bonus. Read the FAQ for the official statement of this.

Brian T


If the body has a single bladed rotor attached to it and is designed to have torque applied to it would it qualify for a bonus?


If not then how are 3 single bladed bonuses be possible?
Innovation =/= success

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Re: Single Bladed Rotor FAQ Response

Postby bjt4888 » Thu Mar 16, 2017 1:25 pm

Bazinga

Having judged this event several years ago when it was division B with similar rules defining bonus for single blades, this issue came up and was clarified. Read the FAQ. It is very clear. The intent, and the challenge, is that rotors be directly driven by the rubber motor. Again, read the FAQ.

One way to have three one-baded rotors is to use two or three motor sticks, each with it's own rubber motor. I believe this was done by some teams to create a chinook heli in a past season

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Re: Single Bladed Rotor FAQ Response

Postby dhdarren » Thu Mar 16, 2017 10:49 pm

bjt4888 wrote:Bazinga

Having judged this event several years ago when it was division B with similar rules defining bonus for single blades, this issue came up and was clarified. Read the FAQ. It is very clear. The intent, and the challenge, is that rotors be directly driven by the rubber motor. Again, read the FAQ.

One way to have three one-baded rotors is to use two or three motor sticks, each with it's own rubber motor. I believe this was done by some teams to create a chinook heli in a past season

Brian T

With all due respect, I disagree with your interpretation of the FAQ, and I do not it is "very clear" as you state.

If the intent and challenge of the event is that the rotors a driven DIRECTLY by the rubber motor, then I believe your interpretation is false, and contradictory to the FAQ. In the first scenario they provided ("For example, if the single bladed rotor glued/affixed directly to the stick and that end of the stick has no other rotor blade(s) and has only a hook for the end of the rubber motor"), from my interpretation of what is written, this way of spinning the bottom rotor is INDIRECT, despite qualifying for the bonus. The way this would be set up, the torque of the motor is spinning the motor stick itself (not the rotor), which is, IN EFFECT, spinning the bottom rotor.

Your statement (and the FAQ) would make more sense to me if it addressed whether the rotor actually produces lift. It seems that you are assuming that a single-bladed rotor affixed to the side of the motor stick cannot produce any lift. However, this is most definitely achievable; if the torque produced by the top rotor and bottom rotor are unequal, and differ by a significant magnitude, the motor stick WILL spin in one direction throughout the flight, and if a single-bladed rotor is affixed to this rotating motor stick, it will produce significant lift. This scenario that I just described operates in a manner no different than the first scenario brought up in the FAQ; The torque produced by the freewheeling rotors (the single rotor in the FAQ scenario, and the top+bottom rotors in the one I described) spins the motor stick, thus spinning the single-bladed rotor on the motor stick.

I believe that the FAQ scenario can only be applied if the motor stick (with the single-bladed rotor affixed) does not spin constantly in one direction. But if the rotation of the top and bottom rotor are calibrated to cause the motor stick to rotate, and the singled-bladed rotor affixed to it rotates and produces lift, then the second scenario provided in the FAQ does NOT apply. The key sentence in this FAQ regarding interpretation is as copied: "However, if the rotor does not have any counter-acting resistance, it will receive no power and as such will not provide lift." If the helicopter is calibrated as I described, then it WOULD have counter-acting resistance that spins the motor stick, and it WILL receive indirect power and WILL provide such lift. Therefore, a traditional two-rotor design with a single-bladed rotor affixed to the motor stick SHOULD qualify for the bonus. It passes everything stated in both the rules and this FAQ

I feel like I sound a bit combative in this reply, but I am interested in what your counter to the scenario I described would be. :D
Past Seasons
2015:
R | S
Bridge: 1 | 8
AirTraj: 5 | 26
WS: 12 | 9
Scrambler: 6 | 17
DP: 7 | X

2016:
Bridge: 2 | 15
AirTraj: 2 | 6
WS: 3 | 11
DP: 4 | 15
GeoMap: 4 | 25

2017:
Heli: 1 | 1
Hover: 1 | 4
Towers: 2 | 15
DP: 1 | 6
Wind: 2 | 8


2018:
R | S
Heli:
Hover:
Towers:
DP:
Eco:
MV:

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Re: Single Bladed Rotor FAQ Response

Postby Bazinga+ » Fri Mar 17, 2017 1:11 am

dhdarren wrote:
bjt4888 wrote:Bazinga

Having judged this event several years ago when it was division B with similar rules defining bonus for single blades, this issue came up and was clarified. Read the FAQ. It is very clear. The intent, and the challenge, is that rotors be directly driven by the rubber motor. Again, read the FAQ.

One way to have three one-baded rotors is to use two or three motor sticks, each with it's own rubber motor. I believe this was done by some teams to create a chinook heli in a past season

Brian T

With all due respect, I disagree with your interpretation of the FAQ, and I do not it is "very clear" as you state.

If the intent and challenge of the event is that the rotors a driven DIRECTLY by the rubber motor, then I believe your interpretation is false, and contradictory to the FAQ. In the first scenario they provided ("For example, if the single bladed rotor glued/affixed directly to the stick and that end of the stick has no other rotor blade(s) and has only a hook for the end of the rubber motor"), from my interpretation of what is written, this way of spinning the bottom rotor is INDIRECT, despite qualifying for the bonus. The way this would be set up, the torque of the motor is spinning the motor stick itself (not the rotor), which is, IN EFFECT, spinning the bottom rotor.

Your statement (and the FAQ) would make more sense to me if it addressed whether the rotor actually produces lift. It seems that you are assuming that a single-bladed rotor affixed to the side of the motor stick cannot produce any lift. However, this is most definitely achievable; if the torque produced by the top rotor and bottom rotor are unequal, and differ by a significant magnitude, the motor stick WILL spin in one direction throughout the flight, and if a single-bladed rotor is affixed to this rotating motor stick, it will produce significant lift. This scenario that I just described operates in a manner no different than the first scenario brought up in the FAQ; The torque produced by the freewheeling rotors (the single rotor in the FAQ scenario, and the top+bottom rotors in the one I described) spins the motor stick, thus spinning the single-bladed rotor on the motor stick.

I believe that the FAQ scenario can only be applied if the motor stick (with the single-bladed rotor affixed) does not spin constantly in one direction. But if the rotation of the top and bottom rotor are calibrated to cause the motor stick to rotate, and the singled-bladed rotor affixed to it rotates and produces lift, then the second scenario provided in the FAQ does NOT apply. The key sentence in this FAQ regarding interpretation is as copied: "However, if the rotor does not have any counter-acting resistance, it will receive no power and as such will not provide lift." If the helicopter is calibrated as I described, then it WOULD have counter-acting resistance that spins the motor stick, and it WILL receive indirect power and WILL provide such lift. Therefore, a traditional two-rotor design with a single-bladed rotor affixed to the motor stick SHOULD qualify for the bonus. It passes everything stated in both the rules and this FAQ

I feel like I sound a bit combative in this reply, but I am interested in what your counter to the scenario I described would be. :D


This is how I interpreted the rules and the clarifications as well.
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Re: Single Bladed Rotor FAQ Response

Postby jander14indoor » Fri Mar 17, 2017 3:32 pm

As usual, unofficial, but some of this is plain physics/mechanics, so...

I think your understanding of the physics and mechanics is incorrect in your first example.

dhdarren wrote:<SNIP> In the first scenario they provided ("For example, if the single bladed rotor glued/affixed directly to the stick and that end of the stick has no other rotor blade(s) and has only a hook for the end of the rubber motor"), from my interpretation of what is written, this way of spinning the bottom rotor is INDIRECT, despite qualifying for the bonus. The way this would be set up, the torque of the motor is spinning the motor stick itself (not the rotor), which is, IN EFFECT, spinning the bottom rotor.


Many people mistake this situation, but in reality any blades attached to the motor stick with a rigidly attached motor hook are as directly driven as the ones on the top rotor that you accept as directly driven.

Think of it this way. The top rotor is spinning freely in a bearing, driven by the rubber motor attached to the hook on the axle of that rotor. The system of the rotor from that hook up through the axle to the the spars and out to the lifting surfaces is a single rigid body.
At the bottom of the helicopter, the rubber motor attaches to a motor hook that is rigidly attached to the motor stick that is rigidly attached to the lower rotor blades through the stick and the spars. Again, this system is a single rigid body consisting of hook, motor stick, spars, lifting surfaces. Functionally NO different than the upper rotor. The blades and stick are simply one body as directly driven as the upper rotor.
To say it is indirect because the forces go through a rigidly attached motor stick would be like saying the upper rotor is driven indirectly because the rubber acts through the wire axle.

I believe this thinking arises from a commonly used, but in correct description of this style of helicopter design as one fixed and one free rotor. In reality BOTH rotors are free, they HAVE to be for the forces to work (Newton cannot be denied here, equal and opposite). What ISN'T free is the motor stick in this design.
In the primary alternate design where there is a bearing at both ends of the motor stick what you have done is NOT freed the other rotor, but simply freed the motor stick, isolating the function of the motor stick to separating the two rotors at a fixed distance. It no longer has any net torque to cause it to spin. Now this has technical advantages in that you no longer have to spin or balance the mass of the motor stick, but it does NOT change the fact that BOTH rotors are ALWAYS driven directly by the motor.

dhdarren wrote:Your statement (and the FAQ) would make more sense to me if it addressed whether the rotor actually produces lift. It seems that you are assuming that a single-bladed rotor affixed to the side of the motor stick cannot produce any lift. However, this is most definitely achievable; if the torque produced by the top rotor and bottom rotor are unequal, and differ by a significant magnitude, the motor stick WILL spin in one direction throughout the flight, and if a single-bladed rotor is affixed to this rotating motor stick, it will produce significant lift. This scenario that I just described operates in a manner no different than the first scenario brought up in the FAQ; The torque produced by the freewheeling rotors (the single rotor in the FAQ scenario, and the top+bottom rotors in the one I described) spins the motor stick, thus spinning the single-bladed rotor on the motor stick.


Hmm, this is going to be harder, because you are partly right and it may devolve into a discussion of what 'significant' lift is.
- First, this only applies to designs axial designs where there is rubber band, two rotors NOT rigidly attached to the motors stick (at least they can spin freely of each other, upper rotor, lower rotor and stick). Goal is to add a THIRD rotor by attaching a properly shaped lifting surface to the motor stick that operates to generate lift by spinning around an axis. It will be single bladed in that extends from only one side of the stick.
- In an ideal world with ideal bearings (no drag), there is no configuration of the upper and lower rotors that transfers torque to the stick to drive that third rotor. Doesn't matter if they spin at the same speeds, different speeds, whatever. Can't be done aerodynamically.
- In a practical world, there is of course some drag. But in a good design that drag will be small. More importantly, it will be in OPPOSITE directions by nature of the fact that the rotors are spinning in opposite directions. Again as a practical matter the drag will NOT match at all times, but it will be close.
- Now, you COULD change that by making one of the bearings less effective than the other. Then you'd have a net torque on the stick that could cause it to spin and provide power to that middle rotor. For sake of discussion at the moment, lets make the lower rotor have the higher drag bearing. Logic applies same, but wording is just opposite in argument below if you make it the upper bearing.
-- Here's the problem with 'judging' that design as meeting the rules requirements.
-- At one extreme the drag would be so low that no 'significant' torque is transferred so no 'significant lift. That pretty much devolves to the first FAQ which does talk in terms of generating lift.
-- At the other extreme the drag would be so high that the lower and and middle rotor would spin in the same direction at the same speed, becoming in effect a single rigid body. Hmm, haven't seen a FAQ on that this year, but in prior years, that was considered a single rotor with blades just in different planes.
HOW does an ES decide where you are on that spectrum? Well, again I think the first FAQ gives an approach. Fly with the single blade, time it.
Same winds, fly without the blade, time it. Unless there is a significant difference (there's that word again, I hate leaning on something so indefinite, but maybe 10%?) no third rotor, no bonus. And I think it has to be LESS time to show the third rotor is contributing lift.

dhdarren wrote:<SNIP>

Snipped this because we are agreeing, you could arrange it so that such a rotor blade attached to the motor stick could provide lift. But as discussed above, you better be prepared to prove it! Again, not official, in my opinion,etc.

Coaching comment on this discussion. Whenever you are pushing the edges of the rules, especially in the flying events where we specifically allow you to bring two devices, your backup helicopter/plane/glider should be clearly within the rules and well tuned for performance. If you win your point with the ES, great, you fly that one and take advantage of it. If you don't, you are prepared with a device that will still allow high performance.

Jeff Anderson
Livonia, MI

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Re: Single Bladed Rotor FAQ Response

Postby dhdarren » Sat Mar 18, 2017 4:07 am

[quote="jander14indoor"][/quote]

Thanks for your response!

Regarding the first situation, I stand corrected.

For the main situation I noted that is partly in question, you are correct that I intended to alter the bearings to make one spin faster than the other, thus causing the motor stick to turn, thus turning a single-bladed rotor.

For proving to the ES that this is effective, if I move forward with this design, I will indeed be prepared to demonstrate. However, I have another question, that might be more of a general competition question in general. For SO tournaments, is it ever allowed to contact tournament officials beforehand to clarify these issues so I do not have to spend time at the competition hashing out these issues? I would much prefer to work this out with the supervisors beforehand than spending time testing and building, to only have it shut down at competition. Or, is sending in a clarification on soinc more effective? Thanks for all of your help!
Past Seasons
2015:
R | S
Bridge: 1 | 8
AirTraj: 5 | 26
WS: 12 | 9
Scrambler: 6 | 17
DP: 7 | X

2016:
Bridge: 2 | 15
AirTraj: 2 | 6
WS: 3 | 11
DP: 4 | 15
GeoMap: 4 | 25

2017:
Heli: 1 | 1
Hover: 1 | 4
Towers: 2 | 15
DP: 1 | 6
Wind: 2 | 8


2018:
R | S
Heli:
Hover:
Towers:
DP:
Eco:
MV:

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Re: Single Bladed Rotor FAQ Response

Postby jander14indoor » Sat Mar 18, 2017 7:03 pm

In general, no there is no way, nor is it appropriate for a competitor and ES to sort this out before hand. We generally try to make all such info equally available to all and such communication couldn't be, even if a summary statement was provided to all competitors
However, there are generally mechanisms to get some feed back at all levels of competition. Usually it is through the coach submitting a question to the specific tournament director who takes it to the ES and then provides response to all teams.
Technically SOINC FAQs only apply to the national tournament, but most lower level tournaments try to abide by them if they occur early enough to be available.
Now, SOINC FAQs are certainly the most authoritative responses.

Jeff Anderson
Livonia, MI


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