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HomeAircraftHelicopterHelicopter Main Discussion › Extra lift from flying into a headwind
03-14-2010 10:52 PM  8 years agoPost 1
hazchem88

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W.Mids UK

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I fly (real) planes so I know all about IAS, lift, flying into headwind etc.

But I am trying to think how this relates to heli's, if at all.

Do heli's get extra lift when flying into a headwind?
Because only the forward moving blade is getting the headwind, and the backward moving blade isn't

what am I missing?

(it isn't important for me, just curious)

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03-14-2010 11:04 PM  8 years agoPost 2
QuantumPSI

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Atlanta, GA

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Yes they do, it's called translational lift and it causes the helicopter to want to pitch up and roll to the right (CW rotating blades). If you do the math, you can show quite simply that the advancing blade produces more life than the loss of lift on the retreating blade (this is due to lift being velocity squared). This is why it takes less energy to fly around in forward flight than it does to hover.

...now where was I, dh/dt = BS-dx/dt
I will fly you forever... till earth do us part

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03-15-2010 01:40 AM  8 years agoPost 3
jkempxx

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Johnson City TN

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Yes - Just go out and try hovering while headed into the wind in very gusty conditions and you will "experience the answer" as the heli tries to act like a yo yo --

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03-15-2010 03:06 AM  8 years agoPost 4
jschenck

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La Vista, NE.

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that's also why shooting auto's into a wind is so much easier than in dead calm air.

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03-15-2010 03:37 AM  8 years agoPost 5
PC12DRVR

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USA

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I've heard of large transport helis doing rolling takeoffs for the same reason.

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03-15-2010 03:22 PM  8 years agoPost 6
BarracudaHockey

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Jacksonville FL

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Consider the rotor disk a wing in forward flight.

Andy
AMA 77227
http://www.jaxrc.com

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03-15-2010 04:00 PM  8 years agoPost 7
psych-lick

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Portland, OR

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Also, consider that in a hover your rotor is creating a down wash which doesn't provide much lift (the rotor is pushing against downward moving air).
In forward flight the down wash is almost non-existent so the rotor has better lift.

-Jeff T.

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03-15-2010 07:29 PM  8 years agoPost 8
QuantumPSI

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Atlanta, GA

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That's not exactly true psych-link. Lift is created from a change in momentum. If you draw a control volume around the helicopter, the incoming air is stagnant and the air coming from below the helicopter is the downwash. Now, if there was another helicopter above the first, then what you're saying is absolutely correct. In that case, since the air is already moving, the helicopter on the bottom has to work harder to generate the same lift (remember, lift is a change in momentum in the fluid). Since the air being moved already has momentum, it must impart MORE momentum to get the same lift.

...now where was I, dh/dt = BS-dx/dt
I will fly you forever... till earth do us part

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03-15-2010 11:33 PM  8 years agoPost 9
zaw

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Lebanon, NH - USA

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On Saturday a surprise gust of wind from tail end slammed my heli down and broke the tail fin. It was a 430mm bladed Gaui 425.

ಠ_ಠ HBK2 built with inexpensive parts! ٩๏̯͡๏)۶ Gaui425

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03-15-2010 11:55 PM  8 years agoPost 10
Falcon7X

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Los Angeles

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Lift is created from a change in momentum.
There is alot more to how lift is created than your basic attempt at explaining it, a change in momentum is only one part of the process.

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03-15-2010 11:56 PM  8 years agoPost 11
crofty

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Phoenix, AZ - USA

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Isn't this effect more on a full scale heli due to the aerofoil on the rotor? I know I have experienced it on a RC heli but would not expect it as much due to the symetrical rotor design.

I have nerves of steel but thumbs of jelly!

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03-16-2010 12:28 AM  8 years agoPost 12
QuantumPSI

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Atlanta, GA

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There is alot more to how lift is created than your basic attempt at explaining it, a change in momentum is only one part of the process.
Not really. Newton's second law: F = dp/dt or in english, change in momentum over time. Lift is a force and thus, is created by a change in a momentum. Now, if you want to get into the nitty gritty, JUST HOW that change in momentum is created, well that isn't so simple. But, lift in this case, is from a change in momentum of the fluid. No more, no less.

And just to keep it as simple as possible (cause I don't really want to get too deep into this), you can use a simple Thrust equation

T = m_dot (vel_out - vel_in)

If the velocity of the fluid exiting the CV is the same as the velocity of the fluid entering, then there is no change of momentum and thus no thrust.

This is again very basic, but that's what happening in the grand scheme of things. Like said, just HOW that change in momentum is created is not so simple, but I don't want to get into that.

...now where was I, dh/dt = BS-dx/dt
I will fly you forever... till earth do us part

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03-16-2010 12:32 AM  8 years agoPost 13
Aaron29

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USA

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translational lift also reduces the amount of power and pitch required to fly.

This can really bite you when slowing down as the heli will want to settle when it loses this lift. You have to be ready on the pitch.

It can also bite you when slow forward flight tight turns in wind.

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03-16-2010 12:35 AM  8 years agoPost 14
Falcon7X

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Los Angeles

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But, lift in this case, is from a change in momentum of the fluid. No more, no less.
You sir, a wrong again, and are hijacking this mans thread, if you want to argue aerodynamics, we can do that all day, and from reading some of your posts, it seems you are a person who likes to hear themselves talk too much.

You can sit and throw eqations all day, you stick to the paperwork, I'll stick to flying them.

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03-16-2010 12:42 AM  8 years agoPost 15
QuantumPSI

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Atlanta, GA

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You sir, a wrong again,
I really don't like being told I'm wrong, but I'm not going to get into this. You may be a pilot, and I envy you for that (I'll have my turn soon enough), but if you want to call me out on this, please, go pick up "Fundamentals of Aerodynamics" by Anderson and see for yourself. Oh and feel free to email and tell all my aerodynamics professor's they are wrong too! I'm sure you'll have no problem finding them.

...now where was I, dh/dt = BS-dx/dt
I will fly you forever... till earth do us part

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03-16-2010 12:53 AM  8 years agoPost 16
Falcon7X

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Los Angeles

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Well QPSI I'm pretty sure the USAF knows aerodynamics, you are seperating out one part of how lift is created and preaching that it is the only way, thats what I disagree with, your not wrong, its just more complex and involved than how you explained it. The mans question was answered with a simple YES, and if you are going to start posting weak information, then expect people to scrutinize it. Your posts with the equations is rediculous this is a discussion forum not physics class.

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03-16-2010 12:57 AM  8 years agoPost 17
FILE IFR

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Anytown, USA 01234

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I really don't like being told I'm wrong, but I'm not going to get into this. You may be a pilot, and I envy you for that
Did you read his Bio and Occupation?

I'll find it hard to believe Falcon 7X is not ATP rated. We do take a small aerodynamics class in our training... and know a little about how lift is created and where lift comes from.

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03-16-2010 02:55 AM  8 years agoPost 18
helibeast

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Mn

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Do heli's get extra lift when flying into a headwind?
I don't know about aerodynamic theory but I know what wind speed does. When I first started flying, I was a junky. Like all addicts I needed my fix constantly. I went flying when a flag was straight out from the pole and jumping (30 to 40 mph wind). When I went into a hover the bird jumped up 15 ft so I gave neg pitch to bring it down,the next few minutes of flying was basically having a heli yo yo.

Champion,Magic,MiniBoy,Xcell60+50,Intrepid,Intrepid Gas,Baron30,Whisper,300X,mCPXv1v2,Concept,Nexus

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03-16-2010 09:57 AM  8 years agoPost 19
hazchem88

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W.Mids UK

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Hi
thanks guys for all your comments. I can see that different people are arguing different theories!

Although everyone means well, the answers to the original question are just muddying the situation.

Persoanlly I have a pilot's license (fixed wing) and understand the principles for fixed wing. I have my own ideas about rotary. But cannot confirm it since I have not found any good books that cover this for heli ppl. I have extracted what I need from all the info, so thanks again

Anyway, I'll leave this thread open for you guys to duke it out!

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03-16-2010 10:27 AM  8 years agoPost 20
helibeast

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Mn

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This might help and even if it doesn't its a cool site.
http://www.helicopterpage.com/html/dol.html

Champion,Magic,MiniBoy,Xcell60+50,Intrepid,Intrepid Gas,Baron30,Whisper,300X,mCPXv1v2,Concept,Nexus

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