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Old 10-24-2016, 11:05 AM   #1
kumoro
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Default CW - CCW Rotation & Right - Left Tail Blade

Hi All,
Since I only have one type, CW & Right tail blade, I'm wondering What are the difference between those two (CW-CCW rotation & Left-Right Tail Rotor blade placement).
I don't know whether they're affecting the way we control when we do bank turn (since when hovering, from tail in perspective, CW rotation & right tail blade will till a liitle to the right, so I assume there's difference when we do bank turn or just flying circuit).
Thank you.
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Old 10-24-2016, 04:50 PM   #2
extrapilot
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Hi Kumoro

Just from an aerodynamic view, it doesn’t make any difference in terms of things like efficiency or top speed or handling- if you reverse the main rotor direction, but also the tail rotor side and direction of rotation. There is an exception there, where a fuselage may be designed aerodynamically to perform better with the main rotor rotation and tail rotor install side set to one or the other config).

It makes a difference from the perspective of piloting, since certain things change a bit. You mentioned one (the bank angle required to hold hover in still wind reverses). There are others that are really hard to notice at small scale- you mention one about control input for bank and pitch for a roll. Full scale, they are easy to notice, but after an hour in the machine, you adapt and don’t think about it anymore.

You probably know this, but there can be engineering differences, where a machine designed for CW or CCW rotation may not be well suited to reversing that. An example would be a machine with helical gears in the transmission, since those generate some axial force (up and down) when they are driven. And, if the machine is designed with thrust bearings or some structure to offset that in one direction but not the other, you may see mechanical failures of gears or bearings, etc.

One area where there is some difference is when you reverse the direction of the rotor, but you don’t flip the side of the tail rotor. That has some impact on aero efficiency, but the impact is very small (you wouldn’t normally notice unless you were doing endurance flying or speed record attempts…).

Enjoy you week-
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Old 10-24-2016, 07:50 PM   #3
kumoro
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HI extrapilot,
Great then, so I need no worry when I try to fly ccw & left side tail rotor. Just need a little adaptation.
Thank you for your full explanation
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Old 10-24-2016, 10:39 PM   #4
extrapilot
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Yea, the wonderful thing about flying helicopters is that we get used to adapting to changes very quickly. Mostly it will just be your getting used to a new disc orientation for hover, but at least for me- I focus on drift and not the disc in hover (since wind has so much effect)...

Maybe post back here after you have some experience with the CCW setup- would be nice to hear how you do with it!

Kind regards-
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Old 11-09-2016, 05:35 PM   #5
ticedoff8
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If you are doing this for a scale project, and you plan to use scale blades, those blades may have an actual airfoil on them.

Typical modern blades are symmetrical top & bottom.
You can flip them over and run them CC or CCW

A blade with an actual airfoil (say, an old style "Clark Y") will only "fly" in one direction.
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Old 11-10-2016, 04:07 PM   #6
extrapilot
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Quote:
Originally Posted by ticedoff8 View Post
If you are doing this for a scale project, and you plan to use scale blades, those blades may have an actual airfoil on them.

Typical modern blades are symmetrical top & bottom.
You can flip them over and run them CC or CCW

A blade with an actual airfoil (say, an old style "Clark Y") will only "fly" in one direction.
A symmetrical airfoil is still an airfoil. When the symmetrical foil is at a non-0 angle of attack, it causes the air to flow in different ways top vs bottom. The air still behaves as if the blade has camber to it. If it didn’t, the blade could not generate lift.

Same thing happens with a cambered foil. You can still fly a cambered airfoil inverted, you just need more pitch to offset the effect of the camber. In fighter aircraft- where they spend most of their time upright and need to be efficient in cruise and in high +G flight, they run cambered foils. Yet- they can still push negative G (sometimes, a lot of negative G).

Its hard to imagine a lot of applications for mounting cambered blades ‘inverted’ on a heli, but there are a couple. One is drag racing, where many competitors favor flying inverted. Another might be for someone who prefers flying inverted for most of the flight, or is trying to set an inverted hover record etc.
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Old 11-10-2016, 04:39 PM   #7
Grumpy_Old_Man
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Quote:
Originally Posted by ticedoff8 View Post
A blade with an actual airfoil (say, an old style "Clark Y") will only "fly" in one direction.
I must remember that so that I never again fly inverted with a 'Clark-Y' airfoil, like I've done countless times before with fixed wing RC planes

One of the possible problems with strongly cambered airfoils on helis is that they generate a strong negative pitching moment. This could in theory cause the blades to twist and/or become dynamically unstable and perhaps overload the servos especially at higher RPM. Full size helis i believe sometimes if not always use reflexed airfoils to reduce this negative pitching moment.
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Old 11-10-2016, 10:51 PM   #8
extrapilot
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Yes, but the reflex reduces the effect of the camber. We already have a significant problem with centrifugal restoring force- since we run huge headspeeds and untwisted blades. The camber moment is a function of the thrust generated, not the headspeed, so the tradeoff tends to happen at a very low headspeed.
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