2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Rodak

You write:
“But you are constantly asserting that the human body (the pilot) is actually a wing providing lift. For stability, if the body is acting as a wing, the c.g. and center of lift locations are critical for stability. If the center of lift is aft of the c.g. the object will be stable, If the center of lift is forward of the c.g. the object will tumble. This is basic aerodynamics.”


If the pilot of the Portable Flyer was frozen, you would be right.
But he is not. He continuously adjusts his body / head / limbs.

The human body is a living wing.
A living wing is not based on stability, but on instability.
And inbstability needs to be continuously corrected / adjusted.
Likewise walking.
Likewise bicycling.


Quote from page 180:

Center of gravity, support base and stability:



In the above video:

• For more than 50% of the time none of the two feet of the runner abuts on the ground (or say: for more than 50% of the time the runner flies?).
  For about 90% of the time the center of gravity of the runner is out of the support base (i.e. the runner’s footprints).

The runner actually rebounds (from foot to foot).

The equilibrium is dynamic:
the brain takes feedback from the body (eyes, otoliths, skin, etc) and locates instinctively the foot that is going to abut, and commands properly the muscles in order the body of the runner to take the “right” push from the ground.

it is not a static equilibrium. It is a step (by step) dynamic correction of an instability.

In comparison, the brain of the Portable Flyer pilot seems as having an job to perform.

For stability what is required is not a center of gravity above the support base, or under the aerodynamic lift, but a way to “feel and react to correct”.

End of quote

Thanks
Manolis Pattakos

[nzjrs]

The Portable Flyer is different than what you describe.

Quote from the page 180 of this discussion:

The following image shows at its upper-right side the “fuselage”. It is the grey-colored assembly that includes the engines, the frame (side pipes and saddle) and the pilot’s upper torso (back, chest and shoulders). This assembly / fuselage is, more or less, a fixed / rigid body.

https://www.pattakon.com/Fly_files/Fixe ... _parts.png

I don't see how this is different to what I describe. Very short questions this time.

1) When the pilot pulls down on the handlebars, do the rotor heads tilt with respect to the rigid frame or not?
2) OR does the pilot assist his twerking motion by pushing and pulling himself fore and aft using the handlebars?

[manolis]

Hello Tommy Cookers.

You write:

• "the PF could better get lift for horizontal etc flight from short chord 'ring wing' type 'cowlings' around/near the propellers
  and the twin prop configuration naturally gives a corresponding near-ideal shape for a cowling-wing
  consider - eg thick symmetrical aerofoils at these Reynolds numbers don't fully stall "

I think you mean something like this:

.

It is an electric Personal Flying Device (evtol).

Wouldn't it be a problem the take-off and landing during windy weather? Or any side gust of wind during cruising?

Thanks
Manolis Pattakos

[Rodak]

For stability what is required is not a center of gravity above the support base, or under the aerodynamic lift, but a way to “feel and react to correct”.

I agree that corrections are always being made while flying; that's what control surfaces are for, be they rudder, elevator, etc or limbs. A pilot is constantly varying controls even in level flight. You're ignoring or brushing aside basic facts of aerodynamic stability. There is always a center of lift, no matter the shape of the aircraft. There is always a center of gravity. On hang gliders the pilot moves his body to change this relationship between lift center and c.g. and is thus able to steer the machine. Your machine will also have a center of lift and a center of gravity and stability is controlled by the relationship of these two things (among others). Seems like it's time you made some models and did some wind tunnel testing. You could even hang a model out a car window to see what happens. It would be easy to incorporate an electric motor and propeller and manipulate the model's legs, etc. Right now I think you are designing a death machine.

[Tommy Cookers]

Hello Tommy Cookers.
You write:

• "the PF could better get lift for horizontal etc flight from short chord 'ring wing' type 'cowlings' around/near the propellers
  and the twin prop configuration naturally gives a corresponding near-ideal shape for a cowling-wing
  consider - eg thick symmetrical aerofoils at these Reynolds numbers don't fully stall "

I think you mean something like this - It is an electric Personal Flying Device (evtol).
Wouldn't it be a problem the take-off and landing during windy weather? Or any side gust of wind during cruising?

no I didn't mean anything long chord as in your picture
ok the ring wing is a closed wing that has various forms some ductlike

a short chord ring wing was used by Townend etc as a drag reducing ring for early radial engines
but I suggest imagine and consider a similar ring but of equal diameter to the propeller ....
designed for and acting as a high aspect ratio annular wing boosted by proximity to the propeller(s) in position and shape
and even rather stall-proof as mentioned earlier

T ring see https://en.wikipedia.org/wiki/Townend_ring
and maybe some broad descriptive value in Ring-Wing patents eg US patent 6607162 by BAe

[manolis]

Hello Nzjrs

You write:
"1) When the pilot pulls down on the handlebars, do the rotor heads tilt with respect to the rigid frame or not?"

The rotor axes are fixed to the rigid frame.


You also write:
"2) OR does the pilot assist his twerking motion by pushing and pulling himself fore and aft using the handlebars?"

Only when the pilots wants so.
He can control the Portable Flyer, from the take off to the landing, without touching the handlebars.
So consider them as optional.
They are more useful when on ground.

Thanks
Manolis Pattakos

[manolis]

Hello Rodak.

An airplane is characterized by a – more or less – constant center of gravity, by a –more or less – constant external shape, and by a small number of control surfaces providing control over the flight.

A person (or bird, or bat, or bug) is characterized by a substantially movable center of gravity, by a significantly variable overall external shape, and by a big number of independent aerodynamic surfaces (each feeding continuously the brain with information like local pressure, vibrations, speed of air) providing (in combination with the distribution of the mass and the adjustment of the overall external shape) control over the flight.


You write:
“Seems like it's time you made some models and did some wind tunnel testing. You could even hang a model out a car window to see what happens. It would be easy to incorporate an electric motor and propeller and manipulate the model's legs, etc. Right now I think you are designing a death machine.”


Try to make a robot walk like a person. It sounds simple and easy, yet is one of the most challenging projects, ever.
To remotely control some “legs” by “electric motors” is too little.

In any case, thanks for your concern.
Manolis Pattakos

[manolis]

Hello Tommy Cookers

In comparison to some "short chord ring wing", the variable pitch (PatPitch) propellers / proprotors offer more, for less.

The idea was always to keep the weight, the complexity and the cost at minimum.

Thanks
Manolis Pattakos

[Rodak]

And you have defined and investigated these exactly how? Come on manolis. All you do is post pictures and drawings and words that are generated in some virtual flight simulator devoid of testing and reality. I ask you to demonstrate how control inputs from the pilot modify the flight path and to show real numbers and methods. Verbiage is all good and well, but we are talking about a machine flying though the air at, as you claim, 200 mph. Any company certifying an aircraft for flight has to submit documentation and test data as to the flight characteristics of their aircraft. I ask you to do the same. How is this aircraft controlled? I don't think it is. Provide some data besides nice pictures; this an accident waiting to happening.

I appreciate your motor stuff, but your flight stuff.......

Try to make a robot walk like a person. It sounds simple and easy, yet is one of the most challenging projects, ever.
To remotely control some “legs” by “electric motors” is too little.

I'm not suggesting you make a walking robot, but rather that you make a model that simulates some of the control motions you claim will control the flyer and see if they actually do what you claim in real conditions. Seems pretty simple to me.....

[NathanE]

No.
It is not necessarily more difficult than bicycling.
According to Mayman (JetPack), the ordinary person after three hours of tethered training is ready for free flights over water.

Hey Manolis, first off I love that you are challenging the status quo and innovating, genuinely. Its folks like you who enable progress, well done.

Just on the biking thing, you told us a few threads back how there was no gyroscopic inertial effect in the flyer. This is one of the significant contributions to bike stability making a bike possible to ride and control. Oh, plus the fact that the riders cog is above the balance point which means control inputs are actually physically possible. An inherently unstable system with a partial stabilisation mechanism making dynamic control possible. It is a beautiful combination.

I think the comparison is really helpful because on a bike the rider steers using weight and balances using "Control surfaces" (steering). This is what i think you expect with the flyer.

Conversely an upside down bike using super sticky tyres riding on a flat "ceiling" (if such a thing were possible) would have to be ridden completely differently, like a trike, I.e. using "control surfaces" to steer and weight to balance. Watch Isle Of Man tt races and compare bikes and sidecars to see what I mean (although to avoid disappointment, don't expect to see them upside down!).

I think you have an upside down bike. I think you need to introduce control mechanisms to help the pilot. This isn't impossible in your design but it needs acceptance by the designer to make it happen.

[manolis]

Hello NathanE.

You write:

• “Just on the biking thing, you told us a few threads back how there was no gyroscopic inertial effect in the flyer. This is one of the significant contributions to bike stability making a bike possible to ride and control. “

No. This is a misconception


Quote from http://www2.eng.cam.ac.uk/~hemh1/gyrobike.htm (University of Cambridge, Department of Engineering)

Bicyles are not held up by the gyroscopic effect

How do we manage to stay up on a bike?

Gyroscopic forces are not important for the stability of a bicycle - as you can see if you read on below - but they help us to control the bike when riding with no hands.

More important than anything is "the trail".
The front wheel makes contact with the pavement at a point that lies behind the point where the steering axis intersects with the pavement - and the distance between these is called the trail.
The trail is not zero because the steering axis is tilted and the front fork is bent.
The trail works to stabilize a bike in much the same way as castors work on a tea trolley.
When you lean to the right, say, on your bicycle force at the contact point on the pavement will push the front wheel to the right.
This helps you to steer effortlessly and it allows for hands-free steering through leaning slightly left or right.
The gyroscopic effect helps but the trail is the more important factor.



Here I am pictured riding an ordinary bike, but with an extra wheel attached to the front axle.

The tyre has been removed to give a little clearance from the road and some copper cable (earthing cable with green insulation) wound around the rim in its place to replace the moment of inertia due to the tyre.

The "extra" wheel can be spun up by hand, before you start riding, at any speed you like, even several times the speed of spinning of the "actual" wheel. It can be spun either forwards or backwards and what is so clear is that it really makes no difference to the "ride" of the bike. The bike is just as easy to ride whether the extra wheel is spinning or not, forwards or backwards, fast or slow.

So this makes us wonder: "How do we stay up on a bicycle"?

The way we stay upright on a moving bike is by active control through steering. This is why we have to learn to ride a bike. If, as learners, we find ourselves falling over to the left then we learn to steer the bike to the left, which generates forces that tilt us back upright again, thereby putting the wheels back under our centre of gravity. Beginners are very wobbly, but as we become expert the corrections become smaller and we can ride in a straight line.

The faster we ride, the smaller the steering adjustment needs to be, simply because the bike moves much further in a given time. When riding very slowly the steering adjustments required are very large. When completely at rest, active steering can do nothing for us.


A good analogy is to ask, "Why is it easier to hop (or pogo-stick) along a straight path than it is to stand still on the ball of one foot?" The reason is that we use each hop to generate correcting forces and also to put our foot down in a new place that is closer to where we need it to be in order to maintain our balance.


It is worth adding here that some bikes are easier to ride than others, and this is all to do with the "trail" described above, and many other parameters such as the hight and width of the handlebars, the height of the seat and the mass of the rider.



Also note that a bike with no rider can stay up much more easily - as many of the bloggers responding to this article have said. This is because the bike is now much lighter and the centre of gravity is much lower. So the forces acting to cause the bike to fall over are smaller. This means now that both "trail" and gyro effects are much more significant in the overall dynamics of the bike and it stays up more easily.
. . .

Misconception 3:

The gyroscopic effect holds a bike up so you can ride a bike with the handlebars locked.
NO!
Try it.
You fall over immediately.
The easiest way to do this is with a rope.
Tie your handlebars to the cross bar and then tournequet the rope really tight. You will have trouble even getting started. Get someone to push you along, or ride down a hill.
Be prepared to fall!

End of quote


Thanks
Manolis Pattakos

[NathanE]

I give up, I wanted to try to help you, because i love what you are doing but there clearly is no point.

I look forward to the video of your prototype.

[gruntguru]

Not sure how accurate this image is, but the handlebars look quite redundant. IMO the handlebars need to be somewhat lower than the most flexible joint between the flyer and the pilot. Probably best achieved with flexibility at the shoulders and hand-grips at waist level.

[gruntguru]

Hello Gruntguru.

You write:
“I have to agree with Rodak on this scenario. With the mass of the flyer above his head, the pilot/flyer is "nose heavy" and will tend to point in the direction of forward velocity (like a dart). It would be very difficult (impossible?) to execute this manoeuvre from high speed forward flight.”


The distance of the legs from the chest (i.e. from the “gimbal joint”) , and the distance of the motors from the chest are more or less equal:

http://pattakon.com/Fly_files/Take_Off_ ... ntal_B.png

their weights are comparable (the legs are heavier), while the aerodynamic drag of the motors is higher due to their orientation relative to the direction of the flight.

The simpler view is "what is the location of the CG and the centre of pressure". For stability in forward flight you want CG slightly forward of CP (CL in forward flight). Too far forward and the "braking" manoeuvre you envisage will be impossible. It will also be difficult to maintain forward flight - the thrust vector will need to be constantly elevated (as shown in your images) and the flyer will be difficult to hold at that elevation with its mass well forward of the hinge joint (chest?, shoulders?)

[manolis]

Hello NathanE.

You write:
“I give up, I wanted to try to help you”


I know.
But you don’t help this way.
This is a strictly technical discussion, wherein the only that matters is what is functional / right / true / possible and what is misconception / wrong / false / impossible.

Instead of complaining, you should be pleased because you learned something: a bicycle does not need the gyroscopic rigidity in order to be controlled.
The explanation / proof / experiment is not mine; it comes from the famous Cambridge University.

Similar is the case of the “Pendulum Rocket Fallacy” article.
I know only two members in this forum who really got it.
The others either don’t talk, or snob it / laugh at it (read the comments) refusing to accept what the Newton’s laws (who, by the way, was a professor in the Cambridge University) say / predict.




The best points of the article about the usefulness, or not, of the gyroscopic rigidity in controlling / driving a bicycle, are:

• “The way we stay upright on a moving bike is by active control through steering.”

and

• "Why is it easier to hop (or pogo-stick) along a straight path than it is to stand still on the ball of one foot?" The reason is that we use each hop to generate correcting forces and also to put our foot down in a new place that is closer to where we need it to be in order to maintain our balance”.

Compare the above to what the first post in page 208 says:

• “The runner actually rebounds (from foot to foot).
  The equilibrium is dynamic:
  the brain takes feedback from the body (eyes, otoliths, skin, etc) and locates instinctively the foot that is going to abut, and commands properly the muscles in order the body of the runner to take the “right” push from the ground.
  it is not a static equilibrium. It is a step (by step) dynamic correction of an instability.
  In comparison, the brain of the Portable Flyer pilot seems as having an EASIER job to perform.”

So,
don’t give up and try harder.
The more negative your technically justified arguments, the more useful.

Thanks
Manolis Pattakos