Understanding VX and VY to Fly safe.

Ground effect is so easy to demonstrate and quantify in a gyroplane; I thought its existence was indisputable.
It certainly should be indisputable, Vance, but people will dispute all sorts of things here.

When folks insist on comparing falling parachutes to level-flying rotor systems, you're bound to see some confusion.
 
I realized what I wrote sounded as though I was being critical of those that did not share my opinions on gyroplane aerodynamics.

My intent was to express my surprise rather than to suggest others were foolish for not sharing my opinions.

I find all of this confusing and endeavor to be confused on a higher level.

This is good practice for me to prepare to teach gyroplane aerodynamics.

Thank you all for articulating your theories about the aerodynamics of the gyroplane.

I am sorry I can’t find the words to articulate my point of view in a way that resonates.
 
It's all about those big circular air currents forming off the end of the wingtip, where the faster air over the top of the wing is free to mix with the slower air passing under it.
Just a slight clarification,
Air under the tip is drawn round the tip to the LOW pressure top side.
But i know you knew that Al. ;)


BTW Vance, nun of this is anyones oppinion, its long understood basic phisics.
And your one of the least confused ere, you got a pretty good grip onit. :)
But your rite, just coz theres no clouds of dust getn kicked up, dont mean those little vortexs aint effected.
Air pressure diffusion is almost instant in such a small distance, so dont expect to be able to see it with your eye.
Shut you eye and its clear as crystal.
 
If you look beginning at 1:19 on this http://youtu.be/Mh-tRy2bE14
When he hovers close to the ground.

Is this the beginning of ring state?
You can see rings to the ground.


That is one of the best examples of air movement around a helicopter rotor.

It is a hydrogen Peroxide tip-jet that produces a steam cloud visible in cool air.

If we could pump a Scott Essex smoke kit through a hollow spar of a gyro rotor it would allow us to "see" what the air is doing , in flight , during the flare , crosswinds , or whatever. Would sure answer a lot of questions.
 
Interesting thread.

My take, understand the basic theory and what the numbers mean. Through practice educate the ‘seat’ (seat-of-the pants), then, through the judicious use of both learn how to fly safely.

Gyro flight is unique and very different in some core ways to FW flight. Knowing the differences is imperative to a FW pilot transitioning to gyros.

Basic rotor control learned in a gyro without a pre-rotator is invaluable, even if it is just sitting in a little stationary single seat learning how to speed up and slow down the blades, experiencing the onset of blade flap and what to do when that happens. That ‘experiencing’ is worth hours of explanation and reading the thread.
 
Guys,

As a newbie here, it was not my intention to start any arguments. I just wanted an answer to a genuine question. Yes, of course there are differences and similarities between FW, RW and Gyro flight. As an experienced RW and FW pilot who has just started flying Gyroplanes, I wanted to get my head around this issue. Sorry to have caused so much angst! I also accept that many of you have had experience of ground effect but I just wanted to know why. My gut tells me Waspair is closest so far but some quantitative evidence would be great.

A few points though:
Originally Posted by SandL
in the video .. after the water landing you can see the rotorblade "down wash" spreading around and infront of the gyro.
SandL, this is a good observation which actually reinforces my point about what was happening to any 'downwash' in straight flight. The only time you see the effect on the surface is when there is a) no forward speed and b) the power to the propeller has been cut. Therefore the 'downwash' in straight flight is masked by inflow through the disc and probably prevented from interacting with the surface by the existence of the propwash.

PW_Plack

Arfur, perhaps we should turn the tables here. What is your aerodynamic basis for imagining that a gyroplane is different in this regard from an airplane?

Sure, although a straight answer would have been preferable. My aerodynamic point is that any 'downwash' from the trailing edge of the blade in forward flight is masked by the inflow through the disc, resulting in a cylindrical area of turbulent air - behind and above (relative to the blade upper surface) the rotor disc tip plane - which is essentially parallel to the ground until well behind the aircraft. There will be a downward component behind the masked area.

PW_Plack: The biggest obstacle to envisioning this properly is misunderstanding the cause of ground effect. It has little to do with whether the downwash reaches the ground.
Do you want to rethink that? :)

Vance: Ground effect is so easy to demonstrate and quantify in a gyroplane; I thought its existence was indisputable.
Without wishing to be flippant, Vance, because I respect your opinion, but in times gone by the evidence that the Sun revolved around the Earth was indisputable...

Resasi: Gyro flight is unique and very different in some core ways to FW flight. Knowing the differences is imperative to a FW pilot transitioning to gyros.

I couldn't agree more!

Kind regards to you all.
 
Jeff- When I mentioned serpentine path....that is exactly what the incoming air does when it goes up and over the airfoil....then it is MANDATORY that enough air has to the be accelerated downward to satisfy the law of physics. There is indeed ground effect in a gyro both felt and measurable....its just not a whole lot, but still allows you to fly slower one foot off the runway than 10 feet off.
Thanks Stan,
Yes I am not questioning ground effect due to tip vortices etc, I was just clarifying my own understanding of direction of overall airflow through a gyro rotor vs a heli. I think there have been two slightly different threads running through this, one as it relates to ground effect and the other direction of airflow through the rotor, I have probably been conflating the two. I would simplistically understand the mechanism of ground effect in a gyro to function similar to a FW, as I always think of a rotor blade as a rotating wing.
 
Guys,

As a newbie here, it was not my intention to start any arguments. I just wanted an answer to a genuine question. Yes, of course there are differences and similarities between FW, RW and Gyro flight. As an experienced RW and FW pilot who has just started flying Gyroplanes, I wanted to get my head around this issue. Sorry to have caused so much angst!

You didn't actually start this. It has come up before in other threads, and was first raised here by Cammie, as I recall. The subject/question causes angst, not the one who asks, so no worries. This is one of our more civil debates, believe it or not.
 
Arfur- What gets panties in a wad is the downwind turn argument ...which is about time to rear its head. Have you come across that hot topic in your past flying experience?
 
No angst on my part Arfur. I like the polite way you ask your questions and handle the sometimes impolite responses.

It is great to have someone question the accepted way of thinking about things and helps me understand what people may misconstrue.

It appears we approach things from different directions. I experience something flying, find a way to repeat it and measure it against the things I was taught or have read. You read about something or see something and want to read more about it. You question what appear to be inconsistencies in the explanations. You want to compare it against your own fundamentals.

In training and with simple explanations often things are simplified to make them easier for someone without a lot of background to understand. My objection to that is that eventually people bump into the misdirection.

Sometimes people with a helicopter background want to know why they don’t have to manage rotor rpm so closely in a gyroplane and the easy answer is as long as the air is going up through the rotor the rotor will maintain a rotor rpm that will fly the aircraft. It is easy to imagine that up through the rotor is the only way the air flows.

Anyone who has been around helicopters has noticed the mess they stir up with their rotor down wash so it is again easy to imagine that the air only goes up through the rotor of a gyroplane because the down wash is less evident.

A fixed wing is pushing just as much air down and yet it doesn’t disturb things on the ground in the same way a helicopter does. That is why I posted the videos of the float planes landing because they didn’t disturb the water much either. Anyone who has flown a fixed wing has experienced ground effect during landing.

Most of my rotorcraft hours are in a heavy two place tandem and I had my initial training in heavy two place side by sides (modified RAF and Sparrow Hawk).

I didn’t feel ground effect during the landing and had enough power to climb out even if I lifted off a below my target indicated air speed.

Some people I respect wrote that gyroplanes didn’t have ground effect and my experience fit what they were postulating.

Some other people here I respect insisted that gyroplanes did have ground effect so I set out to disprove them.

To my surprise I found ways to repeat evidence of ground effect and reconsidered what I had been taught and what I had read in the rotorcraft flying handbook. I became confused on a higher level.

Not believing that a gyroplane rotor was driven by the driving region and still accelerates air down through the rotor disk didn’t get me into trouble and what I feel is my confusion on a higher level wasn’t particularly helpful.

When I flew a lighter, less draggy gyroplane for several hundred hours; this information become more important. The Cavalon has a lower polar moment and linked nose wheel steering so as I learned to fly her in gusting winds she would often lift off early and slow as I worked to keep the nose wheel off the ground during the takeoff roll. With a big passenger and full fuel (near gross weight) and at high density altitude she needed that ground effect to build up the airspeed and begin the climb out. I had trouble keeping her aligned with the runway and had more than one touchdown misaligned with my direction of travel. Understanding and using ground effect to manage this situation became valuable.

For my commercial gyroplane certificate I needed to land minus nothing and plus 50 feet. The Cavalon was both lower and more aerodynamic so she has a tendency to float. I took my practical test in her with very little experience and it was just good luck that I was able to meet the standard.

For my CFI rating I needed to be able to teach someone while flying to commercial standards. I flew our tandem for the practical test and still needed to use my understand of ground effect to fly to commercial standards while dealing with a recalcitrant student.

Please keep asking questions and I wish you all the best on your gyroplane adventure.
 

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I'm a very quick learner..
Yet I too am confused at at higher lever.

Normally one of my Gurus on here end up writing a short explanation in the simplest terms... I've not seen that yet but have seen parts of it in different post.

The photo explains part of the trouble and my thoughts are following.

Keep an open mind and look at it from all angles, put yourself in the other person shoes and then realize you may have missed something and agree to disagree as it's only an opinion worth what you paid for it.
 

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I learn every day, and this site is a mine of golden information.

With some flying in various types, I was lucky enough to stumble on both gyros, and the Rotary Forum. Both have been enormously rewarding in both person, and on line.

Various Bensen days have been immensely rewarding. Jungly, if you get a chance go, put names to faces, and get a finger on the pulse of the original heartbeat of Gyro world USA, if you can’t no worries, enough of them here from around the globe to steer you right and see you through most problems you may have.


Immensely privileged to have met a few, taking a short break to sort a problem or two before, I hope returning to the fold.

With an open mind and you asking the right questions, I think you will be able to get a very good idea of what it’s all about. Enjoy enjoy enjoy.:)
 
It is well proven that ground effect exists!

I’m going to try and put 4 or 5 of our gurus posts and summarize as I understand what’s been written here about rotorcraft as well as what I learned about and experienced it in all FW aircraft from the past It has two components.

1St all wings have downwash off the trailing edge! If you think about it this make perfect since. All wings are cambered (the root at the leading edge is higher than the trailing edge of the wing)

A sheet of plywood held out a car window while driving will create the same downwash as long as the front is higher than the back and you should be able to visualize the downwash as it’s simply directs the flow of air DOWN towards the ground at the same angle you are holding the leading edge above the horizontal as you come close to the ground it hits the ground compressing the downwash flow creating more lift from the pressure hitting the ground.

2nd all wings have sections at least that create drag and can be seen in wind tunnels with vortices trailing form these areas. You can also see in wind tunnel tests that as you get closer to the surface these vortices start to diminish and many go away completely!

This occurs because the vortices are squeezed out as the air is squeezed between the wing and the ground it compresses (more pressure like holding your finger over a hose you are compressing the fluid). This pressure decreased aerodynamic drag with fewer vortices so the aircraft's wings are generating more lift when they are close to a fixed surface.

The lower the wing and closer to the surface the more ground effect is created and observed. Our spinning wings are very high compared to FW so it's effect is going to be less but it's starts with the length of the wing and increases much more at 1/2 the wing distance to the ground and then it really starts to increase after that.

Also with wings that are spun by air there has to be a driven section or they would not spin so that’s adds another difference/complexity for all of us to understand and never thought about while flying only FW’s. It would make sense to me however that if the driven section is cambered it too has downwash.

OK Gurus please correct my homework!
 
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I learn every day, and this site is a mine of golden information.

With some flying in various types, I was lucky enough to stumble on both gyros, and the Rotary Forum. Both have been enormously rewarding in both person, and on line.

Various Bensen days have been immensely rewarding. Jungly, if you get a chance go, put names to faces, and get a finger on the pulse of the original heartbeat of Gyro world USA, if you can’t no worries, enough of them here from around the globe to steer you right and see you through most problems you may have.


Immensely privileged to have met a few, taking a short break to sort a problem or two before, I hope returning to the fold.

With an open mind and you asking the right questions, I think you will be able to get a very good idea of what it’s all about. Enjoy enjoy enjoy.:)
I've too have learned so much from this site more than any other about any other subject.
 
After reading it I also realized, if correct, that is should explain why even in autorotation there IS DOWNWASH as all cambered wings have downwash.
It seems to me and I do not know.
Do wings being spun/driven by the air to 300 RRPMs or more the down wash would be greater than a FW that is only landing at the same air speed we are.
It seem to me that the airspeed of my gyroplane wings are flying at 300 miles an hour or more?

Is this true and if so then it would mean that there is a great deal more downwash being created with wings flying at 300 than in fix wings landing at the same passengers air speed of 60.
 
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Chaps,

Many thanks for all your advice and kind words. I hope to contribute more frequently in future!

Kind regards and may you walk away from all your landings. :)
 
I'm trying to learn more about this effect in gyroplanes, being from a helicopter background. I know the ground effect is there in the gyroplane that I fly, as I experience it regularly. Some good points have been brought out regarding the cause and effect of this phenomenon, but seems to me that there are still some gray areas. So here are some of my thoughts....

We all know that lift is produced both by the reaction of the air striking the airfoil ((Newton's third law), as well as by Bernoulli's principle where the airflow is speeded up due to the lower pressure when there is a constriction in the flow.

I feel that there is an increase in the amount of air being forced through the rotor disc as a result of the increased pressure as it gets closer to the ground. This air increases in velocity as it passes upwards and rearwards through the disc.

So my question is that in the absence of a clearly noticeable downwash in the videos, is it possible that the increased velocity of the passing air through the disc closer to the ground causes an increase in lift, but also a decrease in induced drag?

This decrease in drag then requires less power.
 
...
I feel that there is an increase in the amount of air being forced through the rotor disc as a result of the increased pressure as it gets closer to the ground. This air increases in velocity as it passes upwards and rearwards through the disc.
...
.
I've been asking myself the same question. The math of the Physics says yes; it should as if you dropped a sheet of plywood flat to the ground it goes swish not bang?
Some of you with more experience in landing should have heard, seen and increase in RRPM, right before you flare if this is true?

I hope one of our Gurus chimes in soon.
 
John- A rotors airfoil is moving few hundred of mph faster than a fixed wing, but one of the multipliers in the lift formulae is width of the airfoil. A 7-8 inch airfoil isn't going to have the same downwash as a 4 foot wide airfoil on an airplane wing holding up the same weight...unless it is moving very fast.
 
John- A rotors airfoil is moving few hundred of mph faster than a fixed wing, but one of the multipliers in the lift formulae is width of the airfoil. A 7-8 inch airfoil isn't going to have the same downwash as a 4 foot wide airfoil on an airplane wing holding up the same weight...unless it is moving very fast.
Thank you Brother. I knew about the larger blade.
To ask this so I make sure I'm understanding the point.
Because it so much thinner than my FW it has to move faster to make up for the difference width between FW and rotor wing but it still equals a 4 foot wing.

This would negate my theory as too the increased downwash for the higher airspeed rotating at 300+ RRPM!!!
 
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