2 stroke thread (with occasional F1 relevance!)

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.
manolis
manolis
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Re: 2 stroke thread (with occasional F1 relevance!)

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Hello Gruntguru.

You write:
  • In the diagrams below, the flyer is hovering and thrust is sufficient to maintain altitude. Because the thrust is not vertical, the system is accelerating to the left. The CG shown is combined CG of pilot + flyer. Vector components are shown in some cases but it only necessary to look at the two "resultant" vectors to visualise the overturning couple.

So, you take “one moment in time” (one instant) for which you show the thrust force T which is offset to the overall center of gravity.

Then you replace the thrust force by an equal / parallel force passing from the overall center of gravity (the direction of this force in the FBD should be opposite, I think) and a moment (the “circular” arrow at top) equal to the thrust force T times its eccentricity from the overall center of gravity (how many forum members do really understand and can apply this “equivalency”?).

Then we should add the overall weight (a vertical – downwards looking – force from the overall center of gravity).

Then we should take the sum of all forces (which is a force acting on the overall center of gravity, is normal to the T, and is looking to the left / left-bottom) and the free moment and calculate their effect.
The result would be an acceleration of both parts (the thruster and the pilot) towards the left / left-bottom ( I called this acceleration an “oblique free fall”), and an accelerating clock-wise rotation of the assembly about its center of gravity.

Now comes the “living” pilot to control the situation:

The pilot displaces – either by his hands or by his feet (or lower legs) – the pole / stick until the thrust T to point to the right creating a reverse moment and a (more or less) “opposite” overall force (it will point to the right / right-bottom).
Now the Flyer/Pilot assembly accelerates at the ”reverse direction” (to the right / right-bottom) and turns “counter-clock-wise”.
  • For those who still doubt

    The angular displacement of the thruster about the pivot at the feet of the pilot causes an “opposite” displacement of the pilot.

    Just think what happens during a skydive:

    Can the skydiver open widely and then close completely his legs?
    Can the skydiver retract his limbs / head to form a “ball” and then extent his body parts to straight his body and continue his fall like an arrow head-down?

    The same happens when the pilot holds the Broom-Flyer thruster: the thruster is (becomes) a part of pilots body; the pilot can displace it at all directions, provided his legs, head and arms are displaced properly to “balance” the displacement (linear and angular) of the thruster.
According the previous, instead of true hovering we have a combined linear and angular oscillation.

If the thruster was a rocket, and the assembly was in the space (no air), the oscillation would continue.
But being in the air, the oscillation will progressively fade-out due to the aerodynamic friction of the parts with the surrounding air.

And if the pilot uses his head / limbs (being in the downstream of the propellers), he can almost instantly cancel out the above linear and angular oscillations and turn to “stable” hover (correcting continuously the instability by smooth , almost unnoticeable, movements of his body parts (which hold and displace the pole)).



You also write:
  • The shoulder-mounted flyer (without handlebars) is less stable. The system is experiencing a moment which is tending to rotate the thrust further away from vertical. Also the mass of the flyer creates a moment which tends to increase the difference between the thrust axis and the pilot axis (the axis passing through the hinge and the pilot's CG). To recover from this position to a stable hover requires the pilot to reverse the angle of the hinge to move the CG to the right of the thrust axis. To operate this system without handlebars requires a rigid connection at the shoulders with zero backlash. If this action requires "arching" his back, it will be impossible to recover from extreme angles.


I can’t follow.

So, when the pole is pivotally mounted to (near) the feet of the pilot, the system can recover to hovering, but when the pivot is closer to the overall center of gravity the recovery is problematic?

The thrust of the Portable Flyer (say, the plane defined by the axes of the propellers) cannot lean this way:

Image

What is shown at right is a thrust at an eccentricity of about 0.5m from the overall center of gravity, and a pivot at the top of pilot’s head. No matter how hard the pilot tries, it is impossible to achieve such eccentricity of the thrust.

The actual arrangement of the Portable Flyer:

Image

keeps this eccentricity much smaller (the pivot / gimbal joint is the spinal cord of the pilot in his upper torso).

Drawing the thrust at the allowable eccentricity, the pilot in order to recover just bends a little his waist and more his legs to the right displacing the overall center of gravity to the right of the thruster axis.
This creates an opposite moment that turns the Portable Flyer clockwise. Etc, etc. . .

It is similar to the way Mayman controls his JetPack.


As for the:
  • Also the mass of the flyer creates a moment which tends to increase the difference between the thrust axis and the pilot axis (the axis passing through the hinge and the pilot's CG).
as explained, when both parts of the Pendulum (the thruster (i.e. the Portable Flyer) and the pilot) are at a “free fall” (oblique or straight), the weight of each of them cannot apply forces or moments to the other: they both free fall).


PS.
If you agree with the above, please explain them to the rest forum members: you are a third party and you are English speaking.

Thanks
Manolis Pattakos

nzjrs
nzjrs
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Location: Austria

Re: 2 stroke thread (with occasional F1 relevance!)

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manolis wrote:
Tue Jun 30, 2020 5:12 am
If you agree with the above, please explain them to the rest forum members: you are a third party and you are English speaking.
The problem isn't that we don't understand what you say, we understand perfectly, the problem is that you believe we don't.
Last edited by nzjrs on Tue Jun 30, 2020 3:11 pm, edited 1 time in total.

Rodak
Rodak
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Re: 2 stroke thread (with occasional F1 relevance!)

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manolis, build a model with an electric motor and test it.

gruntguru
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Re: 2 stroke thread (with occasional F1 relevance!)

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manolis wrote:
Tue Jun 30, 2020 5:10 am
Hello Gruntguru.

You write:
  • A FBD is always useful to snapshot a moment in time. The system does not need to be in static equilibrium.

The question is how many “moments in time” are required to correctly describe the “running of the runner” or the “walking of a person” or . . .
Thousands?
I would say Millions.
Those who persistently ask for “force diagrams” do really understand what they ask?

Thanks
Manolis Pattakos
That is not the point. One moment in time is sufficient to determine what the flyer will do with no pilot inputs. From there it is easy to determine what the next pilot input needs to be to regain - for example - a stationary hover.
je suis charlie

manolis
manolis
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Re: 2 stroke thread (with occasional F1 relevance!)

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Hello Gruntguru.

You write:
  • “One moment in time is sufficient to determine what the flyer will do with no pilot inputs. From there it is easy to determine what the next pilot input needs to be to regain - for example - a stationary hover.”

Let me show my point with an example:

Image

In the above slide (instance) from a youtube video, none of the feet of the runner is abutting on the ground.

Differently speaking, at the specific instance the runner is – literally – flying.

What the FBD can say or show?
The only force (suppose no aerodynamic resistance) is the weight of the runner acting at his center of gravity.

Is the above "moment in time” and FBD sufficient to determine what the runner will do the next instances?


What is required in order to predict / to calculate the next "instances" is the velocity of each individual piece of mass of the runner (initial conditions), also what his brain is commanding (or has commanded) every one of the muscles of the runner and the delay of the muscles to respond. These cannot be shown in a FBD or in a "Force diagram".


As for the “with no pilot input”, think what happens when a person is walking and his brain is “switched off” (blackout) for half a second. He/she collapses.


So my question:
“Those who persistently ask for “force diagrams” do really understand what they ask?”
Is well justified.


The brain is a great control system: it receives continuously a huge quantity of information from the “sensors” it is connected to, it evaluates the situation and it commands the muscles of the body to properly respond in order to achieve what the brain is planning (or planned a few instances ago).


The brain is so good in sensing and controlling, that it makes (intuitively) an instability seem as a “rock stable” stability.

Thanks
Manolis Pattakos

Rodak
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Re: 2 stroke thread (with occasional F1 relevance!)

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Yep. Sure.

gruntguru
gruntguru
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Re: 2 stroke thread (with occasional F1 relevance!)

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Hi Manolis. The arrow above each FBD is just to indicate the direction the body will tend to rotate.

The analysis assumes the flyer thrust is sufficient to maintain altitude ie vertical component of thrust = Mg.

The two FBDs are intended to illustrate a thrust pivot point either above the CG or below the CG. If the pivot is at the same height as the CG, the pilot cannot control rotation through re-alignment of the thrust axis - he can only use the aerodynamic effect of realigning body parts in the prop-wash. (Zapata can apply strong roll and pitch moments to the system (in hover) without access to a prop-wash).

Comparing the "above CG" pivot to "below CG" (imagine the "hinge" is locked), the latter has a stability advantage because it tends to rotate the thrust vector towards vertical, opposing the lateral acceleration.

Furthermore,imagine a situation where the flyer in a stable hover with thrust axis vertical and CG directly below, begins to tilt. If the broomstick pilot pushes against the stick to push his body towards the vertical (an intuitive action), he is also tilting the thrust axis away from the vertical which will tend to rotate the system back towards vertical as in the FBD.

In the same situation with the shoulder mounted flyer, the pilot must try to incline his body further from the vertical (non-intuitive) in order to apply a restoring torque to the system. However, if the pilot has hand grips positioned below the pivot the action will be much more intuitive - (falling forward - push, falling back - pull).
je suis charlie

manolis
manolis
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Joined: Tue Mar 18, 2014 9:00 am

Re: 2 stroke thread (with occasional F1 relevance!)

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Hello Gruntguru.

You write:
  • If the pivot is at the same height as the CG, the pilot cannot control rotation through re-alignment of the thrust axis - he can only use the aerodynamic effect of realigning body parts in the prop-wash. (Zapata can apply strong roll and pitch moments to the system (in hover) without access to a prop-wash).

The center of gravity is not fixed, i.e. it cannot permanently coincide with the center of the pivot (unless the pilot is frozen or dead).

By lifting / bending his legs, the pilot of the Portable Flyer (at right in your FBD) elevates the overall center of gravity relative to the “pivot” / thruster (i.e. relative to the Portable Flyer).

By straightening his legs, the pilot lowers the overall center of gravity (relative to the thruster or pivot, again).

By bending his waist backwards or forwards or to the sides, the pilot shifts the overall center of gravity around (always relative to the engines / propellers of the Portable Flyer or relative to the pivot).

Similarly for the arms / head.

  • Worth to mention here:

    In the case of the Portable Flyer, the eccentricity of the overall center of gravity from the pivot is some ten times smaller than what your FBD shows at right.

    Image

    In the “weight displacement control”, the center of gravity “plays” around the thrust axis (actually the thrust axis “plays” around the center of gravity). Excluding the yaw, the control is full.

    Then it comes the “aerodynamic control” to reinforce and complet e (yaw) the “weight displacement control”.


You also write:
  • “Comparing the "above CG" pivot to "below CG" (imagine the "hinge" is locked), the latter has a stability advantage because it tends to rotate the thrust vector towards vertical, opposing the lateral acceleration.”

At the middle of the page 192 it is presented the “Pendulum Rocket Fallacy”.

If the hinge is locked, none of the two cases of your FBD is “stable” (this is what the Pendulum Rocket Fallacy claims). More correctly: none of the two can maintain its direction: they will soon turn and fall hitting the ground.

Image

If the hinge is unlocked, again none of the two is “stable” (this is what the Pendulum Rocket Fallacy says). As before, none of the two can maintain its direction; they will turn and fall to the ground.

In order to be “stable” (“stable” in their instability), they need something (or someone) to properly – and continuously - vector the thrust.
And this is exactly what the living pilot does: he vectors the thrust so that the thrust axis to be to the left, to the right, forwards, backwards etc of the overall center of gravity, correcting his "instability".



From a different viewpoint:

For the case with the pivot “below CG” (your FBD, at left), let’s agree that initially the thrust vector does rotate towards vertical, and that after a while it becomes completely vertical; what stops it from further rotating?


According the “Pendulum Rocket Fallacy”, the lower of higher center of gravity is, for the “stability”, the same.

You were saying the same in your following post at page 187:
manolis wrote:
Fri Jan 24, 2020 8:41 am
Mayman:
But the pilot has to be on top. So the thing is literally dynamically unstable. Inherently unstable. And it has to be flown by computer. So that's what we're building. And the prototype is exactly that. The engines are clustered together, we purposely put the weight above that, and then we try to fly it.”
gruntguru wrote:
Sat Jan 25, 2020 7:46 am
This is nonsense. In a hover situation with an axial thruster, the stability is the same no matter how low or high the CG might be relative to the thruster. An axial thruster always exerts its force along the same axis as that axis tilts. Although somewhat non-intuitive the situation is not the same as a parachute where the thrust remains upwards as the system tilts. (A parachute needs to be above the CG)
Thanks
Manolis Pattakos

gruntguru
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Re: 2 stroke thread (with occasional F1 relevance!)

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“Comparing the "above CG" pivot to "below CG" (imagine the "hinge" is locked), the latter has a stability advantage because it tends to rotate the thrust vector towards vertical, opposing the lateral acceleration.”
As you say - it is not stable - but it does have a "stability advantage". This makes it more controllable - as do the handlebars located below the hinge.

Your aim should be to build a bicycle. Once mastered - it is easy to build a unicycle version for the experts. Most sales will be bicycles.
je suis charlie

joshuagore
joshuagore
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Re: 2 stroke thread (with occasional F1 relevance!)

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I know this video isn't directly relevant, but the visual of him holding the wings had me thinking of the Manolis project.


I agree with the bicycle/unicycle analogy. I built some linkage forks for bikes, tried some very weird rake/trail, after months or years I could optimize, but never really gained the confidence I built from my youth riding telescopic suspension. I eventually optimized the linkage setup around typical telescopic movement and it was the best setup I had, it was even marketable, someone else made it and it sells. I remember hearing a quote from a rider after riding a top level 2 wheel motorcycle equipped with an alternate front suspension saying 'if you trained someone as a child to use this they would be faster'. If that is how it is at the bleeding edge of the bell curve you have to develop product around a much broader window to be successful in mass. People can learn to kickflip a skateboard, it can take a day for many, years for some, but if you really want to learn you can, and likely only one trip to the hospital at worst. Even more people can learn to take off and land a powered parachute, yet 1/1000000th people ever try. Why? Well if you fail on one task you may die, the other you may scuff your elbow or sprain and ankle. These sort of thoughts have to come into play when entering any market.

Many have gotten muddled into the complicated physical and kinematic arguments about control of flight, I'm not smart enough to say, but stand by the above, great products which catch on to the greatest degree, which involve human input, have some basic limits to human control which attempts to reduce risk or accomplish some goal, be it transportation or joy of operation, or labor reduction, and even others a combination of all of the above... Very few have succeeded where death is the result of the humans immediate inability to have an intricate grasp of humans orientation in space. If somehow the Manolis Personal flyer could be operated in such a way where ones dead operation resulted in a perfect hover in many wind conditions assuming a fixed pre determined power input that would be a start. Many planes fly a wind influenced heading with a dead stick assuming some human or autopilot got it to that point.

TLDR: I think it makes sense to refine control inputs besides that of the humans ability to move their mass in relation to a thrust vector. Maybe someones will marry poppins their way, but too few to be debatable. Far fewer than those who ordered their gyro-copter plans, and even further fewer than those who built and flew their own.

manolis
manolis
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Joined: Tue Mar 18, 2014 9:00 am

Re: 2 stroke thread (with occasional F1 relevance!)

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Hello Gruntguru.

You write:
  • As you say - it is not stable - but it does have a "stability advantage". This makes it more controllable - as do the handlebars located below the hinge.

But, does the “pivot below CG” really have a “stability advantage”?


Case of high speed cruise.

Zapata has the thrust under his feet, just like this Broom version:

Image

The pivot is at pilot’s ankles (pivot below CG).

At high speed cruising, Zapata has to lean substantially forwards; the aerodynamic resistance (drag) on his body is substantially ahead / above the pivot.
At a disturbance (say a gust of wind, an opening or closing of the “throttle” etc) the equilibrium changes; the drag and thrust “pair” tends to rotate Zapata so that the drag to go behind the thrust.

A kite flies with its tail always behind:

Image

Like the kite, the Portable Flyer at high speed cruising “corrects automatically” the disturbances because the drag is behind the pivot. The drag and thrust pair tends to keep / restore the device at its previous position.

In a fast wind, a guy who is hanged by his hands from a fixed point leans as much as the wind commands, and remains stable:



but the guy who walks against the wind, is unstable (his support point is behind the drag): if the wind stops, he falls face down, if the wind increases he turns upwards and then he falls back:



By the way, the first video is for more than two times stronger wind.


Case of hovering

Zapata uses his feet to displace the thrust faster and more widely. The question is whether this is good.

The Fly-Board-Air of Zapata weighs 20Kgf (44lb) and its center of gravity is at a distance of more than 1m from the center of gravity of the pilot.

The Portable Flyer weighs the same and its center of gravity is at a distance well less than 1m from the center of gravity of the pilot.

What is necessary at hovering, is the pilot to feel to where he leans and in response to turn the thruster properly to cancel out the leaning at its beginning.
In both cases the pilot keeps the thrust quite close to the overall center of gravity, displacing / turning it smoothly (see the videos of Zapata how close to his center of gravity is permanently the thrust).

If, for some reason, the eccentricity of the thrust from the overall center of gravity becomes too large (too large means: no more than 0.1m for the Portable Flyer and more than 1m for the Zapata JetPack), the pilot has to react immediately, otherwise he may tumble.
With some 10 times smaller maximum eccentricity, the Portable Flyer appears substantially more stable.

Do I miss something?

Where the improved stability of the Zapata JetPack comes from?

Is the FBD sufficient to show all these details?

Thanks
Manolis Pattakos

nzjrs
nzjrs
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Re: 2 stroke thread (with occasional F1 relevance!)

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manolis wrote:
Thu Jul 02, 2020 12:33 pm
Is the FBD sufficient to show all these details?
Oh manolis, you are embarrassing yourself.

There are many tools in the quantitative analysis and modelling toolbox, FBD, rigid body modelling, simulation software etc etc. One tool you wont find however is pictures of kites, animals and babies downloaded from the internet.

manolis
manolis
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Re: 2 stroke thread (with occasional F1 relevance!)

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Hello all.

Wind Tunnel - Richard Hammond:

Image

Thanks
Manolis Pattakos

Rodak
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Re: 2 stroke thread (with occasional F1 relevance!)

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And therefore what?

nzjrs
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Re: 2 stroke thread (with occasional F1 relevance!)

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Rodak wrote:
Fri Jul 03, 2020 6:02 pm
And therefore what?
In manolis defense, this is quite quantitative by his standards - quite an improvement from the baby photo. Notice how he has inscribed 45 degrees on the picture and shown a speed measurement.

As the old saying goes, the exploration of the parameter space of flight dynamics begins with a single data point!

#-o