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HelicopterMain Discussion › Why is autorotation easier in forward flight?
12-02-2007 03:44 PM  9 years agoPost 21
spork

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Mountain View, CA

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It's not a simplification, it's just aerodynamic's theory.
It seems they failed to cover that when I got my B.S. and M.S. in Aero. Again, can you give me the reference for the quote?

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12-02-2007 04:28 PM  9 years agoPost 22
WJackson

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Smyrna, Delaware

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The flare is used to slow forward momentum or reduce ground speed. You also have to further reduce collective while you flare to prevent ballooning. With your given of zero ground speed then all you have left is the collective to slow rate of decent. So as someone alluded to earlier little to no flair is needed.

RIP Roman
Bill Jackson
AlignUSA

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12-02-2007 05:18 PM  9 years agoPost 23
AirWolfRC

rrProfessor

42½ N, 83½ W

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I learned to do autos in zero wind . . . . straight down.
With relative wind, it's a bit like landing a plank.

In a hover a heli has much higher air velocity down through the rotor disk than in forward flight (with a relative wind) . . . . where the rotor disk is more efficient . . . . making autos easier.

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12-02-2007 05:29 PM  9 years agoPost 24
eyeinsky

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Fall River, Nova Scotia, Canada

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Regardless of wind, this the same as fwd flight; 10km wind you are flying fwd at 10km to hover, translational lift adds to your lift and the rotor becomes more efficient.

Descending vertical is not the problem. The heli will auto rotate fine theoretically. The problem is if move fwd just enough to enter the down wash that is created by the rotor displacing the air, you loose lift whether you under power or not. It will actually change the relative air flow acting on the blades. Not so much an issue the case on the RC heli because they have such a high power to weight ratio. So to be safe I would descend with fwd speed sufficient to operate out of the down wash.

When you are in auto rotation operations your blade is in a condition were they are driving and lifting. If the blade angle is to low you are creating more drive less lift and storing lots of energy with high rate of decent; vice/versa with high blade angle. Take your disc and divide it in to 2 zone center being driving outer being lifting. That said think of the disk move thru the air it constantly changes the relationship of the 2 zone. With inertia stored in your rotor it prevent your rpm's from fluctuating up down as you pass thru these various flight condition.

As you reach the ground you begin to reduce the driven zone and increase the lifting zone. The inertia stored in the rotor aids to maintaining of rpm. When you reach the point of ground effect you also have the advantage that even though you rotor rpm have been diminished your aircraft will still fly because it is now reacting with the ground on an air cushion like hover craft. Ground effect becomes ineffective after ½ rotor diameter as rule of thum.

Hope this help

Hard job competing with gravity.

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12-02-2007 07:31 PM  9 years agoPost 25
Havoc

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Ky.

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I don't know anyone else posting to this thread and to be honest some of it is crap but I can vouch for TMoore's ability to auto so just listen to him and you'll be fine.

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12-03-2007 02:50 AM  9 years agoPost 26
eyeinsky

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Fall River, Nova Scotia, Canada

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"I don't know anyone else posting to this thread and to be honest some of it is crap but I can vouch for TMoore's ability to auto so just listen to him and you'll be fine."

If a person has the need to post this statement with out being specific to what he or she disagrees with, maybe they should not say any thing at all. We can see the validity of TMoor's input.

I personal was speaking from theoretical data that I thought was interesting and was willing to share. I only interpreted this, the law of aerodynamics’ dictate the results’

I have read the post twice and do not see the crap

Hard job competing with gravity.

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12-03-2007 02:58 AM  9 years agoPost 27
Havoc

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Ky.

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I personal was speaking from theoretical data that I thought was interesting and was willing to share. I only interpreted this, the law of aerodynamics’ dictate the results’
I was speaking from real world observed data. So stick a sock in it.

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12-03-2007 03:10 AM  9 years agoPost 28
eyeinsky

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Fall River, Nova Scotia, Canada

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Real world based on you, sounds like a small place

Hard job competing with gravity.

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12-03-2007 03:26 AM  9 years agoPost 29
Havoc

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Ky.

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Well it is a small world yet few people who know what they are talking about will spend the time to 1) respond to a question on here and 2) put up with all the virtually guaranteed little annoying arguments over absolutely nothing from internet experts. So I don't think its a bad idea to help the original poster know who to listen to. Sure I could waste time and explain how to auto only to repeat what has already been said and encourage more half-twits to respond with their "theoretical" bs who claim they know because they have a background in everything other than doing autorotations. Or I can just simply say that its all been said by someone who does it well. Then I still get to put up with half-twits arguing with me just for doing that. But keep up the little mindless quips. This is entertaining.

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12-03-2007 03:51 AM  9 years agoPost 30
#55

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Red Bluff, CA

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I have done well over 50 auto's to the ground in a Bell 206.... and quite a few with my models... but I will keep my insight to myself, this is entertaining

real simple... Models, you can do an auto (from alt) with NO forward motion...in a real helicopter- you would die.

too tired to explain.

Check!

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12-03-2007 04:01 AM  9 years agoPost 31
TMoore

rrMaster

Cookeville, TN

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real simple... Models, you can do an auto (from alt) with NO forward motion...in a real helicopter- you would die.
Correctomundo and Bell 206's don't do piroflips either.

TM

Delayed Response Operator Not Engaged

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12-03-2007 04:17 AM  9 years agoPost 32
eyeinsky

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Fall River, Nova Scotia, Canada

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Sure but you did this in a way that you disrespected others that had no personal in put but to only help this chap out. If you think that ever one is not posting for this reason then be specific. Internet expert I am not just trying to help. If original poster feel that he had been mislead by any of us, should it not be his right to question this over you. I feel I am better pilot knowing the basic physic associated with this type of aircraft. I find if you let people learn and actually understanding this is a good thing. The other post covered many of the real world aspect there for it was not my place to repeat. I hope you can understand were I am coming from.

Hard job competing with gravity.

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12-03-2007 04:22 AM  9 years agoPost 33
eyeinsky

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Fall River, Nova Scotia, Canada

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quote]real simple... Models, you can do an auto (from alt) with NO forward motion...in a real helicopter- you would die.
[/quote]

Lots of stuff we would not do in a real helicoptor, life is to short

Hard job competing with gravity.

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12-03-2007 04:25 AM  9 years agoPost 34
Havoc

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Ky.

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When I said
to be honest some of it is crap
I did it because only those who felt what they said was crap would protest. And some people posted bad info so rather than get into a pissing contest with them I pointed to a good reply instead. Because if I'm known for anything, it is diplomacy . So sue me.

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12-03-2007 04:31 AM  9 years agoPost 35
jschenck

rrProfessor

La Vista, NE.

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perhaps this will help

http://wms4.streamhoster.com/jkdist...it_gyrokite.wmv

wouldn't do well in calm wind

EDIT: "The hardest part about owning a gyro-kite is waiting for the next windy day!" love it!

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12-03-2007 04:36 AM  9 years agoPost 36
eyeinsky

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Fall River, Nova Scotia, Canada

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Oh buddy you are so full of it. Long as you can live with that. It fine by me. I am just glad that there are more helpful people here, than just you.

Hard job competing with gravity.

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12-03-2007 04:59 AM  9 years agoPost 37
ZXXflyer

rrKey Veteran

stone mountain, georgia, US

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here's my help or lack of:

http://vids.myspace.com/index.cfm?f...ideoID=22027858

http://vids.myspace.com/index.cfm?f...ideoID=23246248

LOTS of negative pitch (about -6)..will be different depending on blades
Note the rpm gain in the flare...
Head wind was maybe 4 mph.

Straight down autos on a windy day require NO FLARE, ONLY correct timing on the application of pitch. You might even have to add some forward elevator...
And straight down autos on a calm day will require that you FALL LIKE A ROCK and be really good on the timing of adding pitch!!
Forward speed is your friend, and the more you are comfortable with, the better.
I'll shoot some video of a straight down auto on the next windy day... I ain't doin one on a calm day with 550mm blades if I don't have to!

Believer in Weston motors!

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12-03-2007 02:10 PM  9 years agoPost 38
w8qz

rrVeteran

Grand Rapids, MI - USA

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The book I read says that you get 'translational lift' when there is forward airspeed; a straight-down auto on a calm day you would not get that additional lift.
According to Wagtendonk's book (recommended reading, IMHO), the area of the rotor disc that is providing lift is shifted rearward, and is larger, when there is some forward airspeed (as compared to a hovering condition / zero forward airspeed auto). However, even he admits that not all the experts agree with the stated theory of 'exactly what happens in an auto'!

"The helicopter is much easier to design than the aeroplane, but is worthless when done."

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12-03-2007 02:40 PM  9 years agoPost 39
Havoc

rrElite Veteran

Ky.

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You can come in amazingly slow and vertical even without wind (especially on a cool day) although its best to push the nose over and get some relative wind by the last ten feet so you can get a boost in headspeed during the flare. A lot of negative on decent actually wastes headspeed and you'd be better off controlling your decent with cyclic and using a little negative. The high inertia and scale of these things can allow you to get by with crazy stuff but can also form bad habits as a result.

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12-03-2007 03:51 PM  9 years agoPost 40
AirWolfRC

rrProfessor

42½ N, 83½ W

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Most all model helis (50 & up) have an excess amount of energy in the rotor disk during autos.

Enough to do an inverted auto and rotate upright in the last 40 ft to land on the skids.

You're not going to do that in a full size.
- - - for one thing, full size don't have the pitch range.
- - - for another thing, they can't store that much excess energy in the disk.
- - - and they fly a lot heavier than ½lb/ft² disk loading like our models.

- - - A CH-53E is at 15lb/ft² and the V-22 is at 24lb/ft² disk loading.

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