# Arrow-copter. This is my dream-gyro

#### Mike G

##### Junior Member
JC

Are you sure the chord is 0.25? I thought the Arrowcopter rotor used Averso blades and I think Averso are 0.2 chord.
Chris can you clarify what chord you have.

So what is the mechanism that causes high mu to increase 2/rev? I understand that link between airspeed and 2/rev?

Mike

#### ckurz7000

##### Senior Member
Higher rpm cause higher coriolis forces at higher flapping angles. And the drag difference between blades fore/aft and sideways is bigger. Both contribute to 2/rev.

-- Chris.

P.S.: I think the cord is 20 cm.

#### Jean - Claude

##### Senior Member
Mike,
Chord of Averso's blades is 0.216 m (or 21,6 cm). Arrowcopter' chord is still a mystery

#### Mike G

##### Junior Member
Chris
I knew that increasing airspeed cause an increased 2/rev due to "drag difference", JC calls it "rotating drag"I think I'd prefer "alternating drag" but I digress.

I'm not sure I understand you Coriolis argument, you'll have to explain to me (and others??) in a more simplified text how that works. I'm collecting "causes of 2/rev" and I'd like to understand this one before I add it to my list.

My interest was more in JC's use of the term mu and any direct link there could be between mu and 2/rev other than "your arrowcopter flies faster so there's more 2/rev". It's clear that by flying faster the airspeed part of the mu equation gets bigger but then so does the rpm part. OK the rpm increase might not be as great as the airspeed increase so yes mu has increases but for me that's incidental.

Is the real cause of the 2/rev increase for the Arrowcopter "drag difference" plus Coriolis (perhaps) ?

JC
When I finally get my pre rotator sorted out what data do you need to compliment your spreadsheet? I can run some tests but mass will be using my bathroom scales under each wheel, rotor rpm will be accurate (thanks to PB4) but airspeed is hopelessly inaccurate. I find most of these open tandems have very optimistic ASIs. I can measure vibration in any direction you want.

Mike G

#### Jean - Claude

##### Senior Member
Mike G;n1125020 said:
My interest was more in JC's use of the term mu and any direct link there could be between mu and 2/rev other than "your arrowcopter flies faster so there's more 2/rev". It's clear that by flying faster the airspeed part of the mu equation gets bigger but then so does the rpm part. OK the rpm increase might not be as great as the airspeed increase so yes mu has increases but for me that's incidental.
Mu characterizes a more general state of operation. It allows useful comparisons despite the change in diameter, chord, blade pitch, etc.
But if the geometrys are the same, then yes, you can consider the only increase in forward speed.

When I finally get my pre rotator sorted out what data do you need to compliment your spreadsheet?
Can you give to me your measure results of the vertical and fore/aft vibrations 2/rev at the top of the mast, during a fast flight in level? There is no need for bath room scales. Just total mass, rrpm, forward speed evalued. Thank you, Mike

#### C. Beaty

##### Gold Supporter
Coriolis effect is an imaginary force that exists only in the eye of the beholder.

An artillery shell fired in a N-S direction appears to travel a curved path when viewed from the Earth’s surface but viewed from space, follows a straight line just as Newton says it must.

Here'’s a good illustration of Coriolis effect:

ttps://media2.giphy.com/media/VvFICl2BfX5D2/200w.gif#19-grid1

When the ball is tossed across the rotating table, it appears to follow a curved path to the observer standing on and rotating with the table, but to the stationary observer, follows a straight line.

Rotor blades don’t speed up-slow down or lead-lag when viewed from their real axis of rotation, the tip plane axis. Viewed from anything except their real axis, we can imagine they do all sorts of strange things.

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#### ckurz7000

##### Senior Member
C. Beaty;n1125039 said:
Coriolis effect is an imaginary force that exists only in the eye of the beholder.

When the ball is tossed across the rotating table, it appears to follow a curved path to the observer standing on and rotating with the table, but to the stationary observer, follows a straight line.
Absolutely correct. The Coriolis force only turns "real" when the rotating observer insists on making the ball go straight in his frame of reference.

-- Chris.

#### Mike G

##### Junior Member
Chris (churz7000) PM sent to you, not sure if it worked, PM me your email.
Mike

#### C. Beaty

##### Gold Supporter
Gaspard Coriolis originated the concept of an imaginary force to explain the imaginary curvature of the ball’s path as it moves across the table. Just to keep Newton happy.