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Old Oct 11, 2007, 12:22 AM
Helis Fall With Grace & Style
RcSuperSales-Net's Avatar
Kalispell Montana BIG SKY COUNTRY!
Joined Aug 2007
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This week's installment of "How Does You Helicopter Fly?" - Sikorsky's New X2!

Week 1 - Ground Effect
Week 2 - Gyroscopic Precession
Week 3 - Sikorsky's New X2

Being a real helicopter pilot I thought I would have a significant advantage learning to fly RC Helicopters, BOY WAS I WRONG. Honestly, flying an RC Helicopter is somewhat harder to fly because you are trying to look at it and fly it. A lot different then when you are inside the thing and you can feel the heli and what not. No learning to fly nose in in a real heli

Anyways, knowing how a helicopter operates and why it does certain things certainly helps me in that respect, so I thought I would share some information once a week about Helicopters and the way they fly, and WHY they fly. I am sure a lot of you may already know some of the things I am going to be talking about, but hopefully this can help someone or maybe you can just learn something new. I love to learn, so I always jump at the chance to learn something new, which I usually do everyday on RC Groups. Oh BTW, I don't have the time nor the brain power to write all this information I am going to be posting, so I am going to be finding it on the internet and posting the material here. No sense in trying to explain info that has already been explained, and much better than I could explain it. I will have references for the writings and pictures I put here. I am in no way taking credit for any of this information. It is all on the internet, one just has to know what to look for. If anyone has any questions about anything please feel free to PM me or post on here. I check it when I can. Take care. Happy and safe flying.

Kyle

This Week's Topic 4/28/08 - Sikorsky's New X2

Sorry guys I haven't done this in a while but I will start to do it again. Also stay tuned as I am currently in development of a new Kick A$$ Helicopter site. It will be awesome, a first of its kind, and rest assured I will announe it on RcGroups when I get a little more work into it. Anyways check out this new helicopter still in the design and flight testing stages. Not really a how does your helicopter fly, but nevertheless very cool. Take care all!

Thought you guys might like to check this out. A pretty sweet new Coaxial Hybrid helicopter still in the works. Expect to see Military applications first, commercial eventually. The first one will be small and fast it sounds like. Who knows. I thought it was pretty freaking awesome, now maybe we could get someone to build an RC one! Now that would be a site to behold!

http://www.sikorsky.com/sik/innovati...technology.asp

A fiew Pics, this second one really intrigues me.







This Week's Topic 10/16/07 - Gyroscopic Precession

This came up pn the Honey Bee King 2 thread so I thought I would post this for this weeks Topic.

Note my little quote underneath my name Gyroscopic precession. Always prevalent in a helicopter. Basically as a gyro spins and you give it an input the input happen 90 degrees later. When they first were inventing helis they had the controls all wrong because this goes again all "conventional wisdom". When they first designed them they would give a forward input and the heli would move left because of Gyroscopic precession.

Here is a good explanation from http://www.copters.com/aero/gyro.html, see below.

Gyroscopic precession

Gyroscopic precession is a phenomenon occurring in rotating bodies in which an applied force is manifested 90 degrees later in the direction of rotation from where the force was applied. Although precession is not a dominant force in rotary-wing aerodynamics, it must be reckoned with because turning rotor systems exhibit some of the characteristics of a gyro. This diagram shows how precession affects the rotor disk when force is applied at a given point:



A downward force applied to the disk at point A results in a downward change in disk attitude at point B. And upward force applied at Point C results in an upward change in disk attitude at point D.

Forces applied to a spinning rotor disk by control input or by wind gusts will react as follows:

"table at bottom of page 2-44"

This behavior explains some of the fundamental effects occurring during various helicopter maneuvers. For example, the helicopter behaves differently when rolling into a right turn than when rolling into a left turn. During roll into a left turn, the pilot will have to correct for a nose down tendency in order to maintain altitude. This correction is required because precession causes a nose down tendency and because the tilted disk produces less vertical lift to counteract gravity. Conversely, during a roll into a right turn, precession will cause a nose up tendency while the tilted disk will produce less vertical lift. Pilot input required to maintain altitude is significantly different during a right turn than during a left turn, because gyroscopic precession acts in opposite directions for each."

Hope that helps some.

Week 1 - Ground Effect

This article can be found here: http://cybercom.net/~copters/aero/ground_effect.html.

Have fun!

Ground effect


The high power requirement needed to hover out of ground effect is reduced when operating in ground effect. Ground effect is a condition of improved performance encountered when operating near (within 1/2 rotor diameter) of the ground. It is due to the interference of the surface with the airflow pattern of the rotor system, and it is more pronounced the nearer the ground is approached. Increased blade efficiency while operating in ground effect is due to two separate and distinct phenomena. First and most important is the reduction of the velocity of the induced airflow. Since the ground interrupts the airflow under the helicopter, the entire flow is altered. This reduces downward velocity of the induced flow. The result is less induced drag and a more vertical lift vector. The lift needed to sustain a hover can be produced with a reduced angle of attack and less power because of the more vertical lift vector:




The second phenomena is a reduction of the rotor tip vortex:


When operating in ground effect, the downward and outward airflow pattern tends to restrict vortex generation. This makes the outboard portion of the rotor blade more efficient and reduces overall system turbulence caused by ingestion and recirculation of the vortex swirls.

Rotor efficiency is increased by ground effect up to a height of about one rotor diameter for most helicopters. This figure illustrates the percent increase in rotor thrust experienced at various rotor heights:





At a rotor height of one-half rotor diameter, the thrust is increased about 7 percent. At rotor heights above one rotor diameter, the thrust increase is small and decreases to zero at a height of about 1 1/4 rotor diameters.

Maximum ground effect is accomplished when hovering over smooth paved surfaces. While hovering over tall grass, rough terrain, revetments, or water, ground effect may be seriously reduced. This phenomena is due to the partial breakdown and cancellation of ground effect and the return of large vortex patterns with increased downwash angles.

Two identical airfoils with equal blade pitch angles are compared in the following figure:




The top airfoil is out-of-ground-effect while the bottom airfoil is in-ground-effect. The airfoil that is in-ground-effect is more efficient because it operates at a larger angle of attack and produces a more vertical lift vector. Its increased efficiency results from a smaller downward induced wind velocity which increases angle of attack. The airfoil operating out-of-ground-effect is less efficient because of increased induced wind velocity which reduces angle of attack. If a helicopter hovering out-of-ground-effect descends into a ground-effect hover, blade efficiency increases because of the more favorable induced flow. As efficiency of the rotor system increases, the pilot reduces blade pitch angle to remain in the ground-effect hover. Less power is required to maintain however in-ground-effect than for the out-of-ground-effect hover.


Kyle
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Old Oct 11, 2007, 03:33 AM
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Melbourne VIC
Joined Aug 2007
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Wow that is very helpful. I always knew a heli acts different in ground effect as opposed to while it is in the air. Now this thread has explained it all!

Great thread, this should be a sticky.
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Old Oct 11, 2007, 10:57 AM
Helis Fall With Grace & Style
RcSuperSales-Net's Avatar
Kalispell Montana BIG SKY COUNTRY!
Joined Aug 2007
864 Posts
Quote:
Originally Posted by Anthony83
Wow that is very helpful. I always knew a heli acts different in ground effect as opposed to while it is in the air. Now this thread has explained it all!

Great thread, this should be a sticky.
I'm glad it helped. I hoped it would help somebody. Just by understanding the way a helicopter flies and operates can help us become a better pilot and to understand why the helicopter has a tendency to do certain things in a given situation. Look out for next weeks article. If anyone has any questions give me a shout. Thanks for reading.

Kyle
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Old Oct 11, 2007, 11:06 AM
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Thanks for the info. I will be looking forward to your next post so I can see what else I don't know. I like you enjoy learning someting new, the problem I have is keeping the info in mind so I can use it.
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Old Oct 16, 2007, 11:21 PM
Helis Fall With Grace & Style
RcSuperSales-Net's Avatar
Kalispell Montana BIG SKY COUNTRY!
Joined Aug 2007
864 Posts
I've decided to just keep adding to this thread so all the info will be in one location and people can just see it all here rather than having separate posts. So check out Week 2 - Gyroscopic Precession. Happy and Safe Flying.

Kyle
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Old Oct 17, 2007, 04:42 AM
Afghanistanimation
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United States, TX, Killeen
Joined Sep 2006
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Wow, pictures look like exact copies of an Army manual i have. FM 1-201 Fundamental of Flight. We study that manual quite a bit in flight training.
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Old Oct 17, 2007, 01:26 PM
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Western Australia
Joined May 2007
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Precession forces opposite to description.

I have over twenty years of experience flying fixed wing planes, gliders, hang gliders and microlights but am new to rc heli flying (6 months experience).
I do most of my rc heli flying in a 5x4m room with a VenomNR2 (fixed pitch) which has now been modified with HS-55 servos, a Walkera DF4#1 head, stainless steel flybar and LiPo batteries.
Due to the limited space I noticed immediately that the heli would want to accelerate forwards when initiating a right turn and backwards when initiating a left turn. In my ignorance, I presumed it was a model specific trait and cursed Venom until I became aware of precession.
Reading this thread I believe there is a mistake in the description of precession that forms the basis of this discussion. The diagram at the root of this thread describes the exact reaction of my heli to roll inputs, but that is OPPOSITE to what is specified in the description.
My heli definitely needs a slight rearward pitch input on entering a right hand turn and a forward pitch input on entering a left hand turn.

The article on ground effect is accurate but its real benefit should be to encourage pilots to minimise the time spent within one rotor span of the ground. When you are taking off and landing, if you attempt to finesse the procedure by doing it very slowly the heli can skip sideways quickly and crash. It is much safer to power up to at least one rotor diameter on take off and power down when within one half rotor diameter of the ground on landing.
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Old Oct 17, 2007, 01:48 PM
Crazy Heli Technogeek
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USA, WA, Seattle
Joined Sep 2004
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hypoxia88 brings up a good point, your first top down diagram is for a real North American standard helis (with counter clockwise rotor rotation viewed from above)... Most european (eastern and western) run clockwise rotation rotors like our models.

Over 90% (made up figure, it's most likely much higher, hehe ) of electric model helis use clockwise rotation rotors, the only exceptions I'm aware of are tandem, coax, Lite Machines Corona series, Ballistic Tech (Corona mod based helis), and Mite E Copter helis. You will probably want to modify those images to more accurately reflect what's most common in model helis.

-Kai
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Old Oct 17, 2007, 08:18 PM
Helis Fall With Grace & Style
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Kalispell Montana BIG SKY COUNTRY!
Joined Aug 2007
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Quote:
Originally Posted by Kai_Shiden
hypoxia88 brings up a good point, your first top down diagram is for a real North American standard helis (with counter clockwise rotor rotation viewed from above)... Most european (eastern and western) run clockwise rotation rotors like our models.

Over 90% (made up figure, it's most likely much higher, hehe ) of electric model helis use clockwise rotation rotors, the only exceptions I'm aware of are tandem, coax, Lite Machines Corona series, Ballistic Tech (Corona mod based helis), and Mite E Copter helis. You will probably want to modify those images to more accurately reflect what's most common in model helis.

-Kai
Oh My Gosh guys, HA HA HA. I totally forgot and spaced it that our heli's we fly are opposite of that . Most RC's as you stated run in a clockwise rotation rather than the Counterclockwise rotation/ Man I cannot believe I overlooked that. HMM , Yes I may have to go look for some images and descriptions about Euro helis as they are the same as our RC Helis. Kind of funny that the Rc Heli's are totally opposite of North American Real Helis. I am sure it has to do with the fact that it is all coming from Asia anyways . Well DAMN. We'll see if I can get the info here in a bit. Just so busy lately but at least it will help give people a greater understanding on how their heli fly's. For the precession part, Just reverse everything LOL. I just have to keep everything separate in my mind because I fly a North American Heli.

BTW Kai, you were at the Brooks Funfly right. You made the vids on RunRyder right. Where where you at Brooks. I was with the Hotstart Heli Club from Olympia.

Quote:
Originally Posted by hypoxia88
The article on ground effect is accurate but its real benefit should be to encourage pilots to minimise the time spent within one rotor span of the ground. When you are taking off and landing, if you attempt to finesse the procedure by doing it very slowly the heli can skip sideways quickly and crash. It is much safer to power up to at least one rotor diameter on take off and power down when within one half rotor diameter of the ground on landing.
I don't know if I would say power down when within one rotor diameter but just don't try holding that position. When I come into land I just bring it in nice and slow and let the heli settle and then land. Nothing forceful and it doesn't drop just take it down nice and easy. Same with taking off. Just spin up nice and slow and as soon as you see it getting light on the skids just bring it up to about a foot or so depending on the size of your heli into a nice stable hover. Because I fly real helis and usually when we are taking off depending on the situation. You hover for a moment to check all your gauges and make sure everything is operating normally. When I fly the Rc one's I kind of do the same thing. I bring it up into a nice stable hover and then go forward, rearward, side to side and make it yaw a bit, just to check it out and make sure everything is responding correctly. That may be a little anal but I don't want to skyrocket off the ground get to 20 feet and then have my heli fall out of the sky because of a stupid mecahnical failure. I would rather be 3 feet away when that happens. Everyon just has to develop their own techniqu. But yes don't skirt around 5-6 inches off the ground because it will be very squirrely and you also could catch a skid and roll the heli over, and that is no Fun.

Thanks for reading and thanks for everyone's input. I will have to see if I can get some pics and descriptions for Euro Heli's as that will work for our RC Models.

Kyle
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Old Oct 17, 2007, 11:52 PM
Crazy Heli Technogeek
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USA, WA, Seattle
Joined Sep 2004
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Quote:
Originally Posted by RcSuperSales-Net
BTW Kai, you were at the Brooks Funfly right. You made the vids on RunRyder right. Where where you at Brooks. I was with the Hotstart Heli Club from Olympia.
Yup, Mini-Dub and I were setup just south of Kody, Anthony, and Ken's RV (even with the "crash memorial"). I was the asian guy in the black Mariners baseball cap flying the blue and silver MaxirSE around, and who managed to crash my larger heli two times, two days in a row .

-Kai
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Old Apr 28, 2008, 03:09 AM
Helis Fall With Grace & Style
RcSuperSales-Net's Avatar
Kalispell Montana BIG SKY COUNTRY!
Joined Aug 2007
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Sikorsky X2

Check out the new Sikorsky X2 at the top of the page!

Kyle
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Old Apr 29, 2008, 05:15 AM
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The Netherlands
Joined Mar 2007
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Very nice Kyle! By the way, what type of helicopter are you flying? I am currently still training on a schweizer 300. I would like to become an instrutor but this will take many years I think...I am very much interested in an article about turbine transition so if you have some spare time.... cold start, hot start...... drives me crazy!!!!
Quote:
Originally Posted by RcSuperSales-Net
Check out the new Sikorsky X2 at the top of the page!

Kyle
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Old May 25, 2008, 01:30 AM
Helis Fall With Grace & Style
RcSuperSales-Net's Avatar
Kalispell Montana BIG SKY COUNTRY!
Joined Aug 2007
864 Posts
Quote:
Originally Posted by Flying Dutchy
Very nice Kyle! By the way, what type of helicopter are you flying? I am currently still training on a schweizer 300. I would like to become an instrutor but this will take many years I think...I am very much interested in an article about turbine transition so if you have some spare time.... cold start, hot start...... drives me crazy!!!!
I am currently training in the R22 but I am moving to Montana this summer and will be flying the 300. It will be nice to finally ahve some elbow space and not have to worry about going over our MGW.

Turbine transition - Uhh that's outta my league for now. I only have 146 hours and all in a piston helicopter so I am not yet very knowledgeable about the turbine side yet. I can't wait though! I will add some new articles soon. Please feel free for anyone to contribute something to this thread and I will add it to the first post. Thanks!

Kyle
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Old May 25, 2008, 06:52 PM
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Joined Oct 2005
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I've been so tempted to mount a rearward facing rotor on the tail of my Blade CX. (There's that main rotor clash thing tho),,,,,,

Doesn't seem to be that hard of a concept to carry out tho.
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Old May 26, 2008, 12:19 PM
Bird of Pray
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The Netherlands
Joined Mar 2007
673 Posts
Wow, 146 hours! I started last November in Florida and have only 19 hours in the 300. Since the R22 only allows for 1.1 seconds to lower collective with engine failure and the 300 allows a response time of 4 seconds, therefore I promised my girlfriend to never train in the R22 (the SFAR 73 was another motivator NOT to fly the R22). On my avatar picture you can see the Dutch 300C. It is brand new and can easily lift 950 pounds!
Quote:
Originally Posted by RcSuperSales-Net
I am currently training in the R22 but I am moving to Montana this summer and will be flying the 300. It will be nice to finally ahve some elbow space and not have to worry about going over our MGW.

Turbine transition - Uhh that's outta my league for now. I only have 146 hours and all in a piston helicopter so I am not yet very knowledgeable about the turbine side yet. I can't wait though! I will add some new articles soon. Please feel free for anyone to contribute something to this thread and I will add it to the first post. Thanks!

Kyle
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