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HelicopterMain Discussion › dissymmetry of lift question
12-01-2007 07:21 PM  9 years agoPost 1
ckd

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Saugus CA

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can that come into play with our nitro helicopters? I remeber it from flight school but wasn't sure if it would come into play say on a slow approach with a 50?

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12-01-2007 08:40 PM  9 years agoPost 2
John I

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Plymouth, Devon, UK

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Bet there's hundreds of RR regulars out there trying to come up with a good answer to that one!
Myself? I'll pass.

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12-01-2007 08:42 PM  9 years agoPost 3
SSN Pru

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Taxachusetts

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yes

our helicopters obey the laws of physics just as their bigger brothers do.

Dyssemetry of lift occurs with fast forward airspeeds. The heads usually have dampeners to counteract this and allow the blades to flap.

Stupidity can be cured. Ignorance is for life!

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12-01-2007 08:44 PM  9 years agoPost 4
John I

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Plymouth, Devon, UK

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God!! wish I'd kept my mouth shut now.

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12-01-2007 08:51 PM  9 years agoPost 5
george0079

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USA

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Because 50 size birds have such a high RPM head speed, the dissymetry is so minor that I doubt it plays any significant role.

It would be interesting to run the numbers and see what % of lift is canceled at what forward speed vs. head speed...

Hell... I can fix that.
Uh oh..
Nope.
It's ***ked!!!
RE-KIT!!!!!

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12-01-2007 08:52 PM  9 years agoPost 6
planesarenofun

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Ahwatukee, az

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dissymmetry of lift occurs with any airspeed, not just FFF.

If you're thinking about slow approaches, you might be thinking of settling with power, which certainly can occur with a model, especially a heavy scale or AP heli.

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12-01-2007 08:56 PM  9 years agoPost 7
pchristy

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Devon, England

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One thing that's always puzzled me about this subject....

People talk about dissymmetry causing a rolling action in forward flight. But, since the rotor system is a massive gyroscope, surely the reaction should occur 90 degrees later, and actually cause the heli to pitch up?

Comments, anyone?

--
Pete

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12-01-2007 09:00 PM  9 years agoPost 8
AirWolfRC

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42½ N, 83½ W

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Yes, it does cause a heli to pitch up.
The flybar takes care of that problem.

For more detail, see http://www.AirWolfRC.com/NFB.html

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12-01-2007 09:00 PM  9 years agoPost 9
John I

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Plymouth, Devon, UK

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Ever just wanted to curl up and die?

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12-01-2007 09:01 PM  9 years agoPost 10
planesarenofun

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Ahwatukee, az

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it will initially cause the nose to pitch up because of precession, but when the blade completely stalls, there will be no lift on the retreating side of the disc and it will roll.

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12-01-2007 09:03 PM  9 years agoPost 11
John I

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Plymouth, Devon, UK

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HELP!!!

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12-01-2007 09:04 PM  9 years agoPost 12
GimbalFan (RIP)

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Big Coppitt Key, FL

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you might be thinking of settling with power, which certainly can occur with a model
aka Vortex Ring Effect.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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12-01-2007 09:05 PM  9 years agoPost 13
george0079

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USA

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The flybar takes care of that problem
Now that opens a whole different question about flybarless systems and phasing.

Hell... I can fix that.
Uh oh..
Nope.
It's ***ked!!!
RE-KIT!!!!!

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12-01-2007 09:06 PM  9 years agoPost 14
wlfk

rrVeteran

uk

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Here's a terrifying video of a jack stall in a fullsize heli -

[url=http://www.griffin-helicopters.co.uk/videos/playonevideo.asp?videokey=358]

Not quite the same mechanism but I understand you both pitch and roll in a retreating blade stall.

I couldn't resist posting the video anyway, as it gives me goose-bumps!

K

A bit like a kite, but 500 times more expensive

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12-01-2007 09:10 PM  9 years agoPost 15
planesarenofun

rrApprentice

Ahwatukee, az

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jack stall is a whole other problem, that is mostly only eurocopter helis, where the loads on the rotor disc from an abrupt maneuver overpower the hydraulic servos and the controls lock up.

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12-01-2007 09:30 PM  9 years agoPost 16
John I

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Plymouth, Devon, UK

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Has anyone ever asked Curtis Youngblood what his views on the dissymmetry of lift questions are???

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12-01-2007 09:49 PM  9 years agoPost 17
da_man

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Central NC

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I had a really hard time with my rotorcraft design course because I read too many of these post.

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12-01-2007 09:56 PM  9 years agoPost 18
Divot

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Mesa, AZ

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God!! wish I'd kept my mouth shut now.
Ever just wanted to curl up and die?
HELP!!!
LMAO...easy, easy, stay with us John boy.

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12-01-2007 10:06 PM  9 years agoPost 19
John I

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Plymouth, Devon, UK

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Divot.
Thanks mate.
I felt so alone out there.
No, your not a mate, you're a buddy.

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12-01-2007 11:15 PM  9 years agoPost 20
SSN Pru

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Taxachusetts

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Because 50 size birds have such a high RPM head speed, the dissymetry is so minor that I doubt it plays any significant role.
So, I'd like to know what makes you think that dysymmetry of lift will miraculously vanish simply by increasing HS?

Surely Helicopter design companies would simply beef up the head, shorten the blades, and jack up the HS and be done with all of this blade flapping nonsense...

Stupidity can be cured. Ignorance is for life!

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