2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Rodak.

You write:
“Transition from hover to forward speed will be very tricky with a constantly changing center of pressure and gravity as the body flexes.”


It will be as easy, as simple and as controllable as in the GEN H-4, because the Portable Flyer is a symmetrical and compact GEN-H-4 (with the pilot inside the high speed downwash, offering not only "weight displacemnt control" but also"aerodynamic control").

Quote from https://www.pattakon.com/GoFly/DTR_1.pdf

“Take-off, landing, hovering and cruising
The stability and the controllability at vertical take-off, landing and hovering of the PORTABLE FLYER have no reason to be worse than in the GEN-H-4:



In the above GEN-H-4 the only control is the lever that displaces the center of gravity relative to the rotation axis of the two big (13ft / 4m diameter) contrarotating rotors. The PORTABLE FLYER looks like a symmetrical compact GEN-H-4, and can fly like the GEN-H-4.”



“The stability of the above GEN-H-4 Flyer at the fast take-off (14’’ to 18’’ of the video) is remarkable. At hovering some 30ft / 10m above the ground, the stability is excellent; this excellent stability is achieved without any noticeable effort from the pilot: From 1:02 to 1:15 of the video the pilot of the GEN-H-4 looks around calmly, as if he is seating in a chair in the veranda of his 4th floor apartment. He seems so relaxed that if he had a newspaper with him, he would read the news, too.”


You also write:
“I have no idea how you propose to transition from forward high speed to brake mode....”

See in the following video, from 1':52'' to 2':02'', Fraky Zapata accelerating and then decelerating with his FlyBoard Air.



To accelerate, Zapata leans forwards, so that the exhaust gas from his jet turbines exits downwards - backwards pushing him upwards - forwards.
To decelerate / brake, Zapata leans backwards, so that the exhaust gas from his jet turbines exits downwards - forwards pushing him upwards - backwards.

Similarly to Zapata:
In order to accelerate towards a direction, the pilot / rider of the Portable Flyer leans towards that direction: the rotors provide an upwards force that takes the weight of the pilot / Flyer, and a horizontal force that accelerates the pilot / Flyer towards the selected direction.
In order to decelerate, the pilot /rider of the Portable Flyer leans backwards: now the rotors provide an upwards force that takes the weight of the pilot / Flyer, and a backwards force that decelerates the Flyer.

The big difference from Zapata's FlyBoard-Air is that instead of having the thrust force under the feet of the pilot (and control its direction by pilot's legs / feet), in the Portable Flyer the thrust force is above the head of the pilot and its direction is controlled by his shoulders / torso / arms.
Another important difference is that Zapata at medium-low speeds has not "aerodynamic control", while the pilot of the Portable Flyter has full aerodynamic control at all stages of his flight, from take-off to landing.

Thanks
Manolis Pattakos

[manolis]

Hello Rodak.

You write:
"Instantly and effortlessly? How is the thrust force vectored? What moment arms are applying torque to change the vector? The counter torques must ultimately come from aerodynamic forces and these seem to be legs in an air stream on a flexible body."

I asked you to read the DEVICE TECHNICAL REPORT at https://www.pattakon.com/GoFly/index.html

Quote from there:

"Zero vibrations, zero gyroscopic rigidity, zero reaction torque:

• The symmetry of the engine, the zero phase difference between the
two synchronized and counter-rotating crankshafts, the common
combustion chamber (same instant pressure on the piston crowns of
the two opposed pistons, same (and opposite) instant torque on the
two crankshafts), and the symmetrical load (two counter-rotating
symmetrical propellers) rids the saddle (and the pilot) of all kinds and
orders of vibrations (zero free inertia forces, zero free inertia moments,
zero free inertia torques, and zero combustion vibrations of all kinds).
This is an absolute requirement when a powerful high revving engine is
to be tightened to the body of a person.

• The reaction torque is also permanently zero: no matter how wide the
“throttle” is opened, or how abruptly the “throttle” opens or closes, there
is no reaction torque (the only that happens is the increase or the
decrease of the thrust force provided by the propellers).

• The symmetry and the counter-rotation of the propellers and of the
crankshafts maintains the gyroscopic rigidity of the PORTABLE FLYER
zero. Even when only the one engine is running (for instance due to a
malfunction of the other engine), the gyroscopic rigidity is zero. Zero
gyroscopic rigidity means that the pilot “instantly” and “effortlessly” can
vector the engine/propellers (i.e. the thrust force) towards the desirable
direction, which is an absolute requirement for a safe, accurate and
instantaneous control of the flight.

• Without zero inertia and combustion vibrations, without zero gyroscopic
rigidity, and without zero reaction torque at the changes of the
“throttle”, the control of the flight becomes slow, inaccurate, unsafe,
uncomfortable and exhausting."

End of Quote


The following video explains the zero gyroscopic rigidity of the counter-rotating propellers / crankshafts:



Thanks
Manolis Pattakos

[Tommy Cookers]

most unusually the GEN H-4 seems to have rotors with coning built-in
the designer presumably chose this for stability

also the inertia (relative to weight) is higher

[Rodak]

Manolis, the Geh-H-4 has a rigid framework the pilot is able to push against to apply torque to direct the motor; he does this by moving his c.g. in a manner similar to flying a hang glider. You are relying on the pilot somehow moving his body while hanging from the motor harness then, when in horizontal flight, swinging his legs to provide steering and nose up/down inputs. Good luck.

[manolis]

Hello Rodak.

You write:
"Manolis, the Geh-H-4 has a rigid framework the pilot is able to push against to apply torque to direct the motor;
...
You are relying on the pilot somehow moving his body while hanging from the motor harness"


The only that matters is the displacement of the center of gravity relative to the rotation axis of the rotors (i.e. relative to the thrust force).

It does not matter whether this displacement is realized with a frame having levers, or by pilot's body.

In the second video of the first post of this page, there are neither frame, nor levers, yet Zapata controls his flight by merely changing his body posture (weight displacement) relative to his "motor" (i.e. relative to his FlyBoard Air which is secured under his feet).

Unlike Zapata, Mayman, and Browning, the pilot of the Portable Flyer:



is always (from the moment he leaves the ground, to the moment he touches the ground) inside the downwash of the propellers, which gives him full aerodynamic control, not available to the others.

Thanks
Manolis Pattakos

[Rodak]

Well, okay then.

[manolis]

Hello all.

“Aerodynamic Control” versus “Weight Displacement Control”


The GEN-H4 has only “weight displacement control”: the pilot by pulling / pushing a lever, displaces the center of gravity of the GEN-H4 relative to the rotation axis of the contra-rotating rotors (i.e. relative to the thrust force).


The Corvair POGO-XFY-1:



which weighs 5 tons (11,000lb),
has only aerodynamic control (the flaps/ailerons at its lower/back end), just like this “two-seater” Flyer:




The pilot of the Portable Flyer



has both controls:

Being always (from take off to landing) inside the downwash of the propellers, he has “full aerodynamic control” like the POGO (using his hands, feet and head as flaps / ailerons),

While by displacing his head / limbs relative to the engines he has also the “weight displacement control” of the GEN-H4 (and of Zapata / Mayman / Browing Jetpacks)



PS: Yves Rossy (BirdMan) has aerodynamic control, but ONLY after reaching a high speed. Enjoy his flight over Dubai:



Thanks
Manolis Pattakos

[Rodak]

Okay. I guess you have it all figured out.

[gruntguru]

Hello Gruntguru.

In the FDB plot the Mg should be near (or at) the center of the propeller, and the aerodynamic drag force acting on the engines of the Portable Flyer is missing (worth to mention: the frontal area of the engines is not too smaller that the frontal area of the pilot who – at supine pose - has a lower coefficient of aerodynamic friction).

For the torque:

Take the case wherein at horizontal flight (as in the FDB plot) the pilot releases the Portable Flyer which, alone, will accelerate forwards and slightly upwards (from the vertical component of the thrust force T it is subtracted the weight Mg of the Portable Flyer).

I.e. the moment from pilot's shoulders / torso (if any) is not for keeping the engines from falling downwards, but from moving upwards.

Thanks
Manolis Pattakos

Agreed, my FBD does not account for aerodynamic lift acting on the (inclined) flyer. This is the only reason I can see for inclining the flyer upward. Conventional aircraft do not do this, the thrust from the propeller is used solely to overcome drag.

If the flyer is released from the position shown in the FBD it loses a force vector "F" whose line of action passes below the CG and creates a moment tilting the flyer downwards so the "released flyer" should not be compared to the "flying system" as represented in the FBD.

Regarding the first paragraph in my post above. If the aerodynamic lift of the flyer structure is significant (eg enough to support its own weight when tilted slightly in horizontal flight) - a major problem with the flyer becomes apparent. With the centre of lift (flyer) well forward of the shoulder-hinge, the flyer becomes unstable. Think of a wing or tailplane with control surfaces (elevator, ailerons etc) forward facing and hinged to the front of the wing. Do I need to explain further?

If on the other hand the flyer assembly has negligible lift, it will become a dead-weight in horizontal flight and will require significant effort from the pilot to support it. Simplest solution is the "spine" I mentioned a couple of posts back.

[Rodak]

Being always (from take off to landing) inside the downwash of the propellers, he has “full aerodynamic control” like the POGO (using his hands, feet and head as flaps / ailerons),

My last post on this topic. Manolis, the Pogo control surfaces were huge and rigidly attached to the airframe, which was rigidly attached to the engine and propellers. When control inputs were made the aircraft acted as a single rigid unit and torques were generated to control the machine. Your hands and feet controls, flying freely in the airstream while hanging from the motor unit, will not generate controlling forces and, as they are not in any way aerodynamic, will provide random control inputs meaning the pilot will have no ability to finely (if at all) control this machine. Do some calculations re stability as I suggested earlier. If you can show some positive stability then great. I think this machine might go up and down vertically, but you have no controls capable, except in pictures, of guiding this thing, let alone rolling to sustained horizontal flight. Even the Pogo pilots found their machine very difficult to fly; the personal flyer looks like a death machine destined to spiral out of control into the ground with no way to release a parachute. Here's an idea, incorporate some sort of emergency release that will jettison the motor unit in an emergency, allowing the deployment of a parachute. Of course, the freed propeller unit may just generate the chop you are trying to avoid....

I like your motor, but I think the rest needs a lot of work and perhaps you need to learn to take input and not simply reject all suggestions with a verbal explanation. Numbers count and analysis and consideration of the actual aerodynamics would be, in my opinion, a useful exercise. I am not a novice in this area and I see serious problems and a lot of denial, which is not a river in Egypt. If you have some analyses of the aerodynamic forces it would be interesting to see them.

[manolis]

Hello Gruntguru.

In a previous post you mentioned the case with the pilot lying on a table.

When the pilot, with the Portable Flyer secured onto his shoulders / torso, is lying on a small table, abutting on it with his lower chest, with his head and engines extending outside the table from one side, and with his hips and legs extending from the opposite side of the table, pilot’s legs counterbalance the engines / propellers weight.

If the propellers “look” slightly upwards, and the engines are cranked, the upper body of the pilot tends to lift, unless the legs of the pilot bend to balance the new situation.

At horizontal flight similar things happen.

The equilibrium is anything but stationary, as when a man is driving a bicycle wherein the center of gravity most of the time is not above the “base” (support base?), but it moves outside it. The bicycler continuously “feels and counteract to correct”.
Similarly pilot’s brain and body continuously “feel and counteract to correct”.


Differently speaking:

Take the Portable Flyer together with the torso /chest of the pilot as a rigid body (the “fuselage” in the following), with the head, the waist, the hips, the shoulders, the arms and the legs hinged (directly or indirectly) from the “fuselage”.
The thrust force passes near the “overall center of gravity” of the assembly (including the pilot and the Portable Flyer).
By displacing his head and limbs relative to the “fuselage”, the pilot displaces the position of the overall center of gravity (always relative to the “fuselage”). This is how the “weight displacement control” works.
By changing the inclination of his head, hands and feet (all being inside the downwash from the propellers) the pilot deflects / restreams a part of the downwash. This is the aerodynamic control.

For instance:
Wearing a wingsuit and flying horizontally at high speed, the pilot uses his/her legs to control the lift at the back side of his body. If he feels a “nose down” coming, the pilot reduces the angle (or the surface) of the part of the wingsuit which is between his legs.

For instance:
At hovering, and in order to rotate about the vertical axis, the pilot uses his hands and or legs to deflect asymmetrically the high-speed downwards moving air stream, creating a pair of forces (moment) that spins him about his long axis (to make the same in the GEN-H4, they use an electrically controlled differential to increase slightly the revs of the one (fixed pitch) rotor and to decrease slightly the revs of the other “fixed pitch” rotor).


As regards the control of the flight,
the only difference from Mayman’s JetPack architecture wherein the center of gravity of the engines is, more or less, at the center of gravity of the pilot,
and from Zapata’s JetPack architecture wherein the weight of the engines is beneath the feet of the pilot (i.e. away from pilot's center of gravity),
is that the weight of the engines of the Portable Flyer is above the head of the pilot.
In all three cases the thrust force passes near the “overall center of gravity”, and the equilibrium is dynamic (feel counteract and correct).






Hello Rodac.

You write:
“Your hands and feet controls, flying freely in the airstream while hanging from the motor unit, will not generate controlling forces and, as they are not in any way aerodynamic, will provide random control inputs meaning the pilot will have no ability to finely (if at all) control this machine.”


Please see the video of Yves Rossy flying above Dubai (in my last post).

The control of his flight is as fine as it gets. It is a perfect control.

Please see how he flies upside down and how he rolls back (from 2:49 to 2:53 in the video).

His Delta Wing is fixed (no flaps, no ailerons) and is secured on his back (with the four jet turbines fixed onto the Delta wing).

With only an altimeter and timer, Rossy uses his skin and ears as airspeed indicators.

"You feel very well, you feel the pressure," Rossy says, "you just have to wake up these senses. Inside an airplane we delegate that to instruments. So we are not awake with our body."

As Rossy says :
"I am the fuselage, and the steering controls are my hands, head and legs".



In order Rossy to control his flight by his head / limbs, he needs a minimum velocity (say, 100mph) relative to the surrounding air.

Instead, the head and limbs of the Portable Flyer pilot are from the very begining (take off) to the end of the flight (landing) inside the high speed downwash of the rotors.
Without the aerodynamic control, the Portable Flyer pilot should be an "acrobat" like Zapata.

Thanks
Manolis Pattakos

[gruntguru]

Hi Manolis. Your reply did not address these two points which I think are critical to
1. Stability in horizontal flight. and
2. Pilot endurance in horizontal flight in terms of supporting the mass of the flyer in front of his shoulders.

1. If the aerodynamic lift of the flyer structure is significant (eg enough to support its own weight when tilted slightly in horizontal flight and thus avoiding pilot fatigue) - a major problem with the flyer becomes apparent. With the centre of lift (flyer) well forward of the shoulder-hinge, the flyer becomes unstable. Think of a wing or tailplane with control surfaces (elevator, ailerons etc) forward facing and hinged to the front of the wing. Do I need to explain further?

2. If on the other hand the flyer assembly has negligible lift, it will become a dead-weight in horizontal flight (same as pilot on table example) and will require significant effort from the pilot to support it. I am referring to the moment created by the mass of the flyer acting about the "hinge" connection at the shoulders. Simplest solution is the "spine" I mentioned a couple of posts back.

[manolis]

Hello Gruntguru.

If you have any suggestions for the correction of this drawing:



please let me know.
If not, let’s talk based on it.

The pilot by displacing his head / limbs / waist varies the position of his center of gravity (wherein his weight W1 is applied) relative to the thrust force T from the propellers.
The pilot by varying his head / limbs orientation varies the lift L (in size, position and direction - again relative to the thrust force T).

The D1 is the drag of the pilot, the D2 is the drag of the engines.

According the drawing, the loading of the pilot (moment) from the Portable Flyer is about the loading from his legs.


What is the problem with the stability at horizontal flight?
What instability the pilot cannot instantly correct by using his body parts weight and aerodynamic?

Thanks
Manolis Pattakos

[gruntguru]

The problem is D2. You are using it to balance W2 to eliminate the moment about the pilot's shoulders. If the inclination of the flyer is disturbed slightly - say upwards:

- The magnitude of D2 increases.
- The normal lever arm from D2 to the shoulders is increased
- The normal lever arm from W2 to the shoulders is decreased

All 3 of these create an upwards moment on the flyer, reacted at the shoulders. The flyer tries to pivot further upwards increasing the magnitude of the disturbance, which then further increases the magnitude of the 3 factors listed . . . . etc. This is the definition of instability. If the inclination is disturbed downwards the reverse happens - also unstable.

This is the same effect as putting the elevators on the front of a wing instead of the back - nobody does this.

This is easy to fix, the pivot needs to be not at the shoulders but at or below the CG and CL of the pilot.

[manolis]

Hello Gruntguru.

Now I see what you mean.

Let’s see an “equivalent” case:

Someone drives a bicycle.

His body is well above (say, 1m / 3ft) the support base (i.e. the area of (and between) the contact surfaces of the two tires).

Suppose a wind gust falls suddenly on the right side of the bicycler.
The air pushes the bicycler to the left creating a moment relative to the support base, the bicycler leans slightly to the left with his center of gravity passing outside the support base,
the “offset” center of gravity creates an additional moment that adds to the moment from the air and causing the further leaning of the bicycler to the left side,
the further leaning increases the moment from the offset center of gravity,
and so on, and so forth,
until the bicycler falls to the ground.

This would be the case if the bicycler was “frozen / dead” (i.e. an inflexible rigid body) without the ability to “feel and react to correct”.

But the bicycler has his “trained” brain to process the information coming from the various sensors of his body (including the eyes, the otoliths, the skin etc), the bicycler has also his muscles which, responding to the commands of the brain, change the posture / position of the body and correct the disturbance returning to stability.


If instead of a bicycle, the guy is driving a unicycle:



things are way more tricky, yet the brain / body of a man is capable of “feeling and reacting to correct”.

Because the human brain/body is “a quite awesome machine at being able to balance and control” (Browing).


Time to get back to the stability of the Portable Flyer.

You write:

“If the inclination of the flyer is disturbed slightly - say upwards:
-The magnitude of D2 increases.
-The normal lever arm from D2 to the shoulders is increased
-The normal lever arm from W2 to the shoulders is decreased”
All 3 of these create an upwards moment on the flyer, reacted at the shoulders. The flyer tries to pivot further upwards increasing the magnitude of the disturbance, which then further increases the magnitude of the 3 factors listed . . . . etc.
This is the definition of instability.
If the inclination is disturbed downwards the reverse happens - also unstable.”



This would be the case if the pilot was “dead” or frozen.
But the pilot has a running brain, working sensors (eyes, otoliths, skin etc), and spontaneously responding muscles.
Exactly as in the case of the bicycler, the brain is informed / warned by the body sensors for the disturbance and commanding properly the muscles varies the posture of the body (weight displacement control plus aerodynamic control) to cancel out the disturbance before it gets to strong.

For instance, if the pilot feels the engines going upwards, he can instantly:
lower his legs,
change the orientation of his hands,
close the throttle,
lower his head,
etc, etc.

These all are easier than walking on a street and – after a short period of training – they become instinctive.
They are built in capabilities of this “quite awesome machine at being able to balance and control”, i.e. of the human body”.


When Yves Rossy flies horizontally over Dubai with, say, 150mph (video a few posts ago) and:
“the inclination of his Delta Wing is disturbed slightly, say upwards, etc, etc”,
there is nothing for Yves Rossy to worry about, because he has everything he needs to cancel out the disturbance:
he has his brain and his body by which, as the pilot of the Portable Flyer, “feels and reacts to correct” (with both: “weight displacement control” and “aerodynamic control”).
And this without paying any attention: just intuitively.

If we substitute Rossy for a “dead weight” under the Delta Wing, then the same “slight disturbance” of the Delta Wing would end up completely different; it would do what you described (an avalanche “catastrophe”?).


By the way, see Browing taking a Guinness record yesterday:



Thanks
Manolis Pattakos