2 stroke thread (with occasional F1 relevance!)

[Rodak]

Manolis, how the 'pilot' is attached to the motor unit is critical, as that determines what movements are possible. I ask again, is the pilot sitting in some sort of parachute harness? If not, how are the suspension and acceleration loads transferred to the 'pilot'? We can also observe that at 30° from vertical the lift force is reduced to 870 N and will continue to decrease with increasing horizontal angle. What lift component is generated, and at what angle, by the 'pilot's' body? What is the maximum angle the 'pilot' achieves in horizontal flight? Is the lift kite or Bernoulli lift? What effect will the type of lift and associated drag have on power requirements? Have you done any investigation of how the 'pilot's' legs will position themselves during steady horizontal flight?

[manolis]

Hello Tommy Cookers.

You write:
“isn't this what would have killed Mr Mayman ? (as I said a year or so ago)
(had he not chosen to fly over shallow water with rescue divers 50m behind)”


Do you, or anybody else, know about the spin of his turbines?

I.e. are the turbines of Mayman spinning at the same direction, or are they counter-rotating?



If they spin at the same direction, the gyroscopic rigidity of the turbines is a significant problem. They may have lightweight shafts, with mass at small eccentricity, however they run at high rpm.

The specifications of the JetCat P550 used in some JetPacks :



give an idea (26,000rpm idling, 83,000rpm maximum revs).
If the control has to deal with the gyroscopic rigidity, the response is slow and the restore to the right direction is difficult.



You also write:
“upwards force falls away fast and there's a great lateral acceleration swamping the attempted weightshift control
or do we rely on having enough slipstream/airspeed for aerodynamic control to succeed ? (depending on attire ?)
ok (I guess and contrary to my fears) aerodynamic reaction to rotor tilt rate will give some pitch damping ?”


If it takes 1 second to turn from vertical to horizontal, it will also take 1 second to restore to from horizontal back to vertical (hovering). I.e. the fast response is an advantage, not a drawback.

On the other hand, as the bicyclers need not to lean more than a few degrees to control their bikes, similarly the pilot of the Portable Flyer needs not to make extreme corrections, unless they want to make aerobatics.

Applying my last post approach, two seconds is the time required in order the Portable Flyer to make a complete loop (360 degrees turn of the thrust axis).
Supposing the time starts with the thrust straight upwards, the thrust will “look” downwards for only 0.5sec.



In 0.5 seconds and with 2g (20m/sec2) downwards acceleration, the height loss for a complete loop is 2.5m (8 ft).


Besides the above "weight shifting control", the Portable Flyer pilot, from take off to landing, has also full “aerodynamic control”.

If you look carefully (put the reproduction speed at 0.25) at the “wind dancer” youtube video, at 1’:33” she starts rotating about her long axis (yaw) making six complete turns in less than one second; and she cannot use any kind of “weight shifting” control”, just pure “aerodynamic control”.

Thanks
Manolis Pattakos

[gruntguru]

Hello Gruntguru.

Here is a simple approach of the Portable Flyer. . . . .

I agree with that analysis and always have.

One problem is the internal forces and moments required to support the mass of the flyer's power unit during horizontal flight when the lift is provided primarily by the pilot's body or wing suit.

Similarly if the system is hovering (or even standing on the ground) the upper mass (once displaced from a vertical axis passing through the point of articulation (the pilot's spine)) will tend to displace further under gravity ie unstable. This must be resisted by the pilot's musculoskeletal system. The simple fix is to move the point of articulation to the height of the upper mass or above.

[Rodak]

Correct me if I'm wrong, but I understand your statement to say introduce a pivot between the power unit and the 'passenger'. Is this correct?

[uniflow]

wouldnt you be better off 'flying' the rotors rather than crude weight shift controls?

[uniflow]

or better still, a deep intermeshing counter rotating rotor system. Still 'flying' the rotors via a swash plate (or two), not slow to react semi unstable weight shift.
Larger slower turning rotors are much more efficent. Isn't this the coolest rotorcraft ever invented. Just need a decient, reliable, efficent twostroke engine to power it.

[uniflow]

Even the humble autogyro 'flys' the rotor system for control, not weight shift as is often thought. It uses rotor aerodynamics and cunningness for smooth accurite rotor control.

[uniflow]

After all we seem to be talking about rotorcraft now, not twostrokes any more. .

[nzjrs]

Congratulations MP, I am proud of you for coming to your senses and engaging with us respectfully - posting some new information so we can move forward.

You mention in your last post a point I have made to you many times, I wonder if you have understood it yet.

I.e. the fast response is an advantage, not a drawback.

I've described this as you wanting to 'having it both ways'. The flyer is stable and agile.

In control engineering this is the part of the duality of controlability and stability, and that this is a dynamic system. If you believe from your static force diagrams a sub second rotation of 30 degrees is possible, then it is also possible it occurs accidentally or uncontrolled through either the pilot or external disturbances. And remember, that something is unlikely to occur is not a defense against considering it - we all only die once.

The natural consequences of this should be your realization and now you will understand what I have been getting at. That is; the rigorous analysis of the dynamic interaction of the pilot ('flight control system') with external disturbances and the static properties of the flyer are what I have been at the entire time (for hover control and hover -> flight transition, others can speak about CoP CoG in horizontal flight). What's the overshoot, what's the damping, etc etc. I hope and see that you are now starting to understand as you start to put in some numbers and start to think about the different control dynamics for different axes of flight.

[henry]

@manolis.

Returning to testing. The dual tether system you are suggesting really only works if the pilot stays vertical. As soon as the pilot inclines to transition to flight the tethers are likely to impose a torque on the flyer and so make it difficult for the pilot to learn the skills of control. In the video you showed of the jet platform the pilot and machine remain substantially vertical and so the tether forces have limited effect.

Can I suggest a modification to the trunnion system I proposed. Instead of mounting the trunnions, located at the CoG, rigidly to a ground structure, attach them from below with two flexible members. At rest the trunnions would rest on the structure but could be lifted until resisted by the flexures. When the PF is powered up these flexures would only see the excess thrust of the Flyer and any aerodynamic forces. If the pilot attempts the transition you documented above the tethers would pivot about their lower mount to take up an angle resolving the thrust and lift from the pilot.

This wouldn’t be a perfect simulation of free flight but it would allow testing of a number of characteristics including some of the aero data that @nzjrs would need to do his analysis.

I think you could use such a rig to check thrust, CoG location, aerodynamic lift, harness design, etc. and provide initial pilot training. It would be compact, safe and repeatable.

[gruntguru]

Correct me if I'm wrong, but I understand your statement to say introduce a pivot between the power unit and the 'passenger'. Is this correct?

A pivot located at the CG of the power unit. If the desired location is inaccessible, a system of linkages or flexures with instant centre at the desired location could be used.

[uniflow]

Time to stop all this foolishness, build a proper rotorhead. Use a proper engine ( a thoroughly ground tested one) and fly safely with autorotation a possibility for survival. Manolis, you know I'm right, you can not debate your way out of this, with any credibility left.

[manolis]

Hello Henry.

You write:
“Returning to testing. The dual tether system you are suggesting really only works if the pilot stays vertical. As soon as the pilot inclines to transition to flight the tethers are likely to impose a torque on the flyer and so make it difficult for the pilot to learn the skills of control. In the video you showed of the jet platform the pilot and machine remain substantially vertical and so the tether forces have limited effect.”


The tethered tests are for very slow speeds, for hovering and for yaw.
The pilot feels the device and learns to respond (as a child learns to drive a bicycle).

When the pilot gets confident, they start un-tethered tests at low height wherein they can increase their horizontal speed.

Later the pilot can increase speed and go to higher altitudes to perform all kinds of tests (high speed cruise, loops, dives, recovering, etc), with a pair of parachutes in the spinners "for just in case" something goes wrong.
Yves Rossy uses his parachute to land, i.e. once per 10 minutes of flight.

This is the way the JetPacks pilots learn to “ride” them.




You also write:
“Can I suggest a modification to the trunnion system I proposed. Instead of mounting the trunnions, located at the CoG, rigidly to a ground structure, attach them from below with two flexible members. At rest the trunnions would rest on the structure but could be lifted until resisted by the flexures. When the PF is powered up these flexures would only see the excess thrust of the Flyer and any aerodynamic forces. If the pilot attempts the transition you documented above the tethers would pivot about their lower mount to take up an angle resolving the thrust and lift from the pilot.

This wouldn’t be a perfect simulation of free flight but it would allow testing of a number of characteristics including some of the aero data that @nzjrs would need to do his analysis.

I think you could use such a rig to check thrust, CoG location, aerodynamic lift, harness design, etc. and provide initial pilot training. It would be compact, safe and repeatable.”


Thanks for your suggestion.

However the most lightweight, the simplest to built and carry, the simplest / easiest to control, etc, etc, is to secure the Portable Flyer on pilots’s body. Say, as Zapata and Yves Rossy do with their JetPacks.
Pilot’s body has its own ball joints / trunnions.
The idea is to exploit to the limit the human body.

Thanks
Manolis Pattakos

[Rodak]

Okay, for about the twentieth time please describe how the motor unit is attached to the 'pilot'. Is he tied in with ropes around his waist, in a parachute type harness, glued in, attached with some sort of 'body bolts' or what exactly? How is he attached to the power unit? Really, you must have some idea; how this is done determines how he can move and change the c.g. to control this thing and whether his arms are going to be ripped off during braking by the straps under his arm pits, not to mention the distraction as regards to piloting during the moment. So what are your thoughts?

[henry]

@manolis

I don’t think you understood my suggestion. The trunnions are part of a test rig not part of the control system. The pilot will use their limbs and joints to do the low speed hover learning you describe but within a rig that can secure them and which provides the opportunity to measure the parameters that will determine how to go to the next step of translational flight.

On another point, how will the pilot control the power of the motors? Given that their limbs are the control surfaces how do they operate a control device without impacting the aerodynamics?