the Portable Flyer's propellers (impellers ?) have a difficult job at any significant flight speed
as the inclination of their rotational axes varies the blade AoA
the inclination produces a destabilising ? net pitching moment (uncancelled by counter-rotations within the impeller system)
any propeller (even a coaxially counter-rotating one) does this (afaik eg from Morien Morgan's words)
of course a non-impelling arbitrary inclined body would also do this
The Portable Flyer is intended to be a scale-down Osprey V22:
i.e. an airplane capable for vertical take off, vertical landing and hovering.
At normal use its duty is to take off vertically and into a few seconds to cruise at high speed (say 250Km/h - 150mph) horizontally until to reach the destination wherein it turns to hovering to land vertically.
For 99%+ of the time it is to be at high speed cruising wherein the mileage maximizes and the propeller axes are at their most horizontal position (wherein the “pitching moment” per propeller is not significant).
At all speeds the pitching moment per pair of counter-rotating propellers is substantially zero.
There is no reason the Portable Flyer to loiter for long at intermediate speeds (but it is capable to do so, say at a demonstration)..
At a rescue, the mileage does not matter: it will hover for as long as it is necessary.
I agree with Tommy Cookers. Sustained horizontal flight is best achieved with the thrust axis horizontal - for many reasons. Even the Osprey only inclines its thrust axis during transition.
Back to stability. Neither of the examples you gave (bicycle and Rossy) has a stability issue comparable to the one I have pointed out. Please do not attempt horizontal flight until you (or another human) can achieve the following.
Take a table tennis bat by its handle and extend your arm straight in front of you with the bat pointing forward and the paddle parallel to the ground. Now ride in a car or motorcycle with the arm and bat pointing forward in the direction of travel and accelerate slowly. As the speed is increasing, incline the leading edge of the bat to support the weight of your arm. If you can still maintain control at 100 km/hr, you might be OK to control your flyer in horizontal flight.
“I agree with Tommy Cookers. Sustained horizontal flight is best achieved with the thrust axis horizontal - for many reasons. Even the Osprey only inclines its thrust axis during transition.”
Near its top speed the thrust axis will be not far from horizontal.
With the thrust axis at, say, 20 degrees from horizontal (cos(20deg)=0.94), and propeller tip speed well below sonic velocity…
You also write:
“Back to stability. Neither of the examples you gave (bicycle and Rossy) has a stability issue comparable to the one I have pointed out.”
Rossy’s “example” seems quite close to what the pilot of a Portable Flyer will experience at high speed flights.
A small “disturbance” of Rossy’s Delta wing inclination (say, it turns suddenly for a few degrees upwards) is not causing an “instability”; it just changes the direction Rossy flies, causing the beginning of a “loop”.
Rossy feels the acceleration and either exploits it to complete the “coming” loop, or he cancels the loop by re-directing the Delta Wing (and thrust) using the available “weight displacement” and “aerodynamic” controls.
Similar is the case for the Portable Flyer.
The previous are easy and safe because the Delta Wing and the Portable Flyer are in the open sky, away from obstacles.
In the case of the bicycler, a “destabilizing” strong side wind gust is dangerous because the bicycle cannot move outside the “available” road lane / path. Even if the bicycler achieves (by turning properly the handlebars, and by changing his body posture) to control the disturbance without falling, a side drift of the bicycle by one meter (a yard) can put the bicycler into the opposite lane.
You also write:
“Please do not attempt horizontal flight until you (or another human) can achieve the following.
Take a table tennis bat by its handle and extend your arm straight in front of you with the bat pointing forward and the paddle parallel to the ground. Now ride in a car or motorcycle with the arm and bat pointing forward in the direction of travel and accelerate slowly. As the speed is increasing, incline the leading edge of the bat to support the weight of your arm. If you can still maintain control at 100 km/hr, you might be OK to control your flyer in horizontal flight.”
OK. Thanks.
The real problem I face now is to make the engine reliable (and if possible to stabilize it on HCCI mode).
To “concentrate” is a dilemma, because you never know where the "other" path could lead you.
The stable HCCI into combustion chambers providing substantially longer piston dwell at their TDC, may prove more important than the Portable Flyer itself.
It would also make the engines of the Portable Flyer more reliable (with the spark being necessary only at “special” conditions).
It would also reduce the required quantity (and weight) of fuel, as well as the running cost and the pollution.
Mazda tried / tries with their SkyActiv-X, which was scheduled to be in mass production from early this year, but it seems it is not yet ready and – for sure – it will be too expensive (because it adds many expensive components / subsystems).
All the idea is nothing more than completing the combustion with the piston still near its TDC, a think that the mechanism of the OPRE engine / OPRE-Tilting engine does.
I remember (in the International Engine Expo 2008, Stuttgart Germany) a veteran German (maker and driver and champion of the old 2-stroke world “moto-GP”, as he said) playing for long with this cheap hand-made prototype and complaining that despite he tried for decades to invent something like this, he failed.
In the video the control shafts for the exhaust valves are fixed (so the exhaust valves operate at constant valve lift profile in this demonstration).
The central control shaft varies the duration of the intake valves from 0 to 300+ degrees (and, partially the valve lift), while the side control shaft varies the intake valves lift (from 0 to more than 12+mm).
Just think how the SkyActiv-X project of Mazda could be advanced by such a fully variable valve system:
independently variable lift from 0mm to as much as they want, and independently variable duration from 0 degrees to as much as they want.
In the International Engine Expo (2008, Stuttgart Germany), our first presentation was about the pattakon VVA’s and the second (rejected) was about the OPRE engine and the Portable Flyer.
As it turned out, it was too early even to speak about the Portable Flyer.
I had to prove I am not an elephant, until Yves Rossy came along with his Delta Wing.
Now Browning, Zapata and Mayman claim that “this is the future of transportation”.
Personal Transportation powered by jet-turbines consuming 3 liters per Kilometer doesn’t seem as the future.
The only stability / safety problem I see in the Portable Flyer is its reliability due to its new and untested engines.
The dozen OPRE-Tilting blocks of the photos are for tests.
The stable HCCI into combustion chambers providing substantially longer piston dwell at their TDC, may prove more important than the Portable Flyer itself.
Manolis Pattakos
Other than the PF, what applications are there for your engine?
I don't think people realise how close to the end of IC engines we are. Euro 6 regs will be tweaked (to include eg, Adblue emissions) then Euro 7 arrives. The major manufacturers have no intention of even trying to meet Euro 7 - electrification is where they are heading. That's automotive obviously but even hand held 2Ts have pretty onerous emission and durability testing to be permitted to be sold.
Unless you have a market where emissions testing is more lax than in the developed world, I'd check if it has a future before going much further.
To “concentrate” is a dilemma, because you never know where the "other" path could lead you.
The stable HCCI into combustion chambers providing substantially longer piston dwell at their TDC, may prove more important than the Portable Flyer itself.
Mazda: Emissions of Skyactiv-X Engine Comparable to an EV
At the forefront of Mazda’s green-vehicle strategy is its Skyactiv-X internal combustion engine. This might not seem very earth-friendly, but allow the automaker to explain.
Because two-thirds of global electricity production relies on fossil fuels, Mazda believes the “tank-to-wheel” evaluation currently used to render electric vehicles “emissions free” is disingenuous. Instead, it proposes the industry adopt a “well-to-wheel” evaluation, which takes into account fuel extraction, shipping, and manufacturing when deciding a vehicle’s CO2 emissions.
For example, a mid-sized electric car consumes around 20 kilowatt-hours of electricity per 100 kilometers. Producing this much power at a coal plant translates into 200g of C02 per km.
It would translate into 156g/km if the power were sourced from a gas plant, and to 100g/km from a natural gas plant.
It says the average well-to-wheel emissions of an EV are about 128g/km, while its current Skyactiv-G gas engine produces about 142g/km.
With the new Skyactiv-X compression ignition engine set to make huge gains in efficiency, Mazda is certain the engine will return impressive well-to-wheel emissions and will be more earth-friendly than many EVs being charged with fossil fuel-sourced energy.
“Committed to the principal of the right solution at the right time, Mazda has concluded that, until the growing quantity of power from renewables replaces the dirtiest forms of electricity generation such as brown coal, electric powertrains do not currently satisfy to society’s wish for a drastic reduction in greenhouse gas emissions,” it said.
End of Quote
Here Mazda’s engineer is explaining the SkyActiv-X and how it will affect the car driving:
After Mazda announced their SkyActiv-X tech, Toyota (the world leader n Hybrids?) increased their share in Mazda.
Back to the OPRE 2-stroke and its potential.
Even with normal “2-stroke brake thermal efficiency” (BTE about 20%) the Portable Flyer would consume a dozen times less fuel than the state-of-the-art Jet Packs (Zapata, Mayman, Browning), would pollute a dozen times less, and would have a dozen times longer range (taking off with the same quantity of fuel).
With its longer piston dwell, with the low friction losses of the 2-strokes and, potentially with HCCI combustion (and thereby lean-burn and cool combustion, i.e. lower heat losses and lower heat loads on the materials, escpecially on the lubricant film), the OPRE-Tilting seems capable for doubling-up the BTE.
These are for the Portable Flyer (based on the OPRE Tilting engines).
But the OPRE engine
and PatOP engine (which is the single crankshaft version of the OPRE),
with direct injection (either Diesels, or spark ignition or HCCI),
with their “pulling rod” architecture (which substantially increases the piston dwell at the CDC (Combustion Dead Center), increasing the time provided to the fuel for more efficient / clean combustion, increasing the “constant volume portion of the combustion” and the “actual expansion ratio”, substantially improves the BTE),
and with their “four-stroke-like lubrication (check the specific lube consumption of the Achates Power 2-strokes, whose architecture is not as good as the architecture of the OPRE-PatOP in this area, with the trust loads taken away from hot ports, at the cool side of the cylinder), can make the 2-strokes cleaner than the best existing 4-strokes.
As Mazda says:
"until the growing quantity of power from renewables replaces the dirtiest forms of electricity generation" . . .
You write: “Take a table tennis bat by its handle and extend your arm straight in front of you with the bat pointing forward and the paddle parallel to the ground. Now ride in a car or motorcycle with the arm and bat pointing forward in the direction of travel and accelerate slowly. As the speed is increasing, incline the leading edge of the bat to support the weight of your arm. If you can still maintain control at 100 km/hr, you might be OK to control your flyer in horizontal flight.”
The re-orientation of the bat relative to the flowing air seems as not representative of what the Portable Flyer pilot will experience “if the inclination of the flyer is disturbed slightly - say upwards”, because the aerodynamic lift and drag on the bat changes dramatically (say, at a hammering / impact way) when it changes direction from horizontal to leaning.
With the “cylindrical” engines of the Portable Flyer moving at high speed into the air, “if the inclination of the Flyer is disturbed slightly”, say from 45 degrees to 50 degrees, at a first approach the "aerodynamic" reaction moment on the back / torso of the pilot will change for about as much as the eccentricity of the engines (sin(50)-sin(45) ~ 6%).
Even if the engines turn totally upwards (90 degrees angle), the "aerodynamic" moment will change by ~30%.
Therefore, the “small disturbance” cannot cause an avalanche change of the moment on pilot’s back.
With pilot’s brain and body standing-by, changes / disturbances of this order are easily and instantly compensated.
DVVA
The DVVA (desmodromic VVA) videos came along only because a Swedish engineer asked, a few days ago, about its operation.
“since you are building a PatRoVa rotary valve cylinder head (https://www.pattakon.com/pattakonPatRoVa.htm),
why don’t you built in parallel a DVVA cylinder head for the same engine,
to compare their advantages and drawbacks.
You write: “Take a table tennis bat by its handle and extend your arm straight in front of you with the bat pointing forward and the paddle parallel to the ground. Now ride in a car or motorcycle with the arm and bat pointing forward in the direction of travel and accelerate slowly. As the speed is increasing, incline the leading edge of the bat to support the weight of your arm. If you can still maintain control at 100 km/hr, you might be OK to control your flyer in horizontal flight.”
The re-orientation of the bat relative to the flowing air seems as not representative of what the Portable Flyer pilot will experience “if the inclination of the flyer is disturbed slightly - say upwards”, because the aerodynamic lift and drag on the bat changes dramatically (say, at a hammering / impact way) when it changes direction from horizontal to leaning.
With the “cylindrical” engines of the Portable Flyer moving at high speed into the air, “if the inclination of the Flyer is disturbed slightly”, say from 45 degrees to 50 degrees, at a first approach the "aerodynamic" reaction moment on the back / torso of the pilot will change for about as much as the eccentricity of the engines (sin(50)-sin(45) ~ 6%).
Even if the engines turn totally upwards (90 degrees angle), the "aerodynamic" moment will change by ~30%.
Thanks
Manolis Pattakos
Hi Manolis. You need to decide.
If the aerodynamic lift of the flyer engine is negligible, its weight will create a moment at the shoulders which the pilot will have to constantly react during horizontal flight - the thrust does not help regardless of inclination.
If the aerodynamic lift of the flyer engine is sufficient to support its own weight and eliminate the moment at the shoulders, it will behave as a forward-facing control surface and the table tennis bat analogy applies.
I said I was bailing from this 'discussion' as Manolis is not accepting input and simply making verbal arguments as to stability, center of gravity, center of pressure, etc. and describing how a person, suspended flexibly at the shoulders with a harness is able, by simply moving his/her limbs, to control the attitude and direction of this 'personal flyer'. Manolis, I appreciate your engine work, but you are not understanding what is being said about stability of this 'flyer'. There is no way to apply torque to the motor to direct its thrust.
You say you are designing a mini-VTOL but you're not. The VTOL has a rigid chassis that allows for moments to be applied to the thrust vector to manage direction, Please note that the Osprey has control surfaces that remain essentially horizontal during vertical to horizontal flight and that these surfaces, as in the Pogo, as ridgidly attached to the chassis of the machine. You have a person hanging out there in space with no way to apply moments. Your machine is unstable, except possibly in vertical flight. As for your transition from forward high speed to braking, how can you possibly imagine this could be done using only input from legs while hanging from the motor? There is no mechanism for controlling the machine in horizontal flight even if there were enough power to overcome the kite lift/drag the pilot would generate.
You draw nice pictures, but they don't have a basis in reality; the flailing limbs in the drawing are a pretty good indication of what will happen to the pilot. This is a death machine. Please show how at the claimed speed of 200 mph the pilot can transition to braking mode, a reversed direction, but do it with something other than words. What is your calculated lift and drag of the pilot in horizontal flight? How do you arrive at this lift/drag? Where is the c.g. and Cp? How does the pilot's 'lift' interact with the motor unit and how does it interact with the propeller lift through the flexible coupling? How can the pilot keep his/her hands on the control arms @ 200 mph? What would be the required distance to transition from horizontal to vertical flight?
You write: “If the aerodynamic lift of the flyer engine is negligible, its weight will create a moment at the shoulders which the pilot will have to constantly react during horizontal flight - the thrust does not help regardless of inclination.
If the aerodynamic lift of the flyer engine is sufficient to support its own weight and eliminate the moment at the shoulders, it will behave as a forward-facing control surface and the table tennis bat analogy applies.”
It is not the lift of the flyer engine, it is the aerodynamic drag of the flyer engine that reduces the moment on the back / torso of the pilot.
Let me explain by “modifying” your own example:
Instead of the bat, keep a basketball ball with your hand (and your straightly extended arm) outside the window of the fast moving car.
The aerodynamic drag on the ball pushes it backwards, its weight pushes it downwards, while its aerodynamic lift is negligible (due to its shape).
No matter what the orientation of your arm is (from fully horizontal to full upwards), the backwards pushing force on the ball is the same (and it increases with the car speed square, i.e. smoothly and expectedly).
The aerodynamic moment on your shoulder (wherein your arm is connected / supported) depends only on the “vertical” offset eccentricity) of the ball from your shoulder, i.e. on the length of your arm times the sinus of your arm angle from horizontal.
This moment varies smoothly / expectantly, so it is manageable and easily compensated.
The “cylindrical” engines of the Portable Flyer (the cyan part, which is a 0.5m / 1.6ft long cylinder of some 130mm / 5inches diameter):
as the ball, has the same aerodynamic drag at all angles of the flyer, and no aerodynamic lift.
In the drawing with the forces:
the D2 is the aerodynamic drag of the flyer engine.
The vector sum of D2 (which is the aerodynamic drag on the flyer engine) and W2 (which is the weight of the flyer engine) is a force whose direction has a small offset from the support point on pilot’s back, requiring only a small reaction moment from the pilot.
At a disturbance of the flyer upwards or downwards, the change of the moment of the aerodynamic drag from flyer engines is linearly proportional to the change of the "vertical" eccentricity of the flyer engines from pilot back.
At higher speeds the pilot flies more horizontal decreasing the "vertical" eccentricity of the aerodynamic drag D2 and increasing the "horizontal' eccentricity (from pilot's back) of the weight W2 of the flyer engines.
But since the aerodynamic drag D2 increases with speed square, the change of the overall required reaction moment from pilot’s back is weak and not impact,
which means the pilot can easily and instantly compensate it by small, smooth, instinctive corrections, keeping his fight controllable and stable (unless he is asleep).
Zapata and Browning and Mayman cannot fly asleep, because their flight control is nothing more than correcting their body position and pose relative to the engines.
In all cases the flight is a little more than “feel and react to correct”
You write:
" how a person, suspended flexibly at the shoulders with a harness is able, by simply moving his/her limbs, to control the attitude and direction of this 'personal flyer'."
The pilot is NOT suspended flexibly.
He is saddled with the portable Flyer.
The Portable Flyer is secured onto his back / torso by a saddle: the brown part of the following drawing included in the application filed for the BOEING's / GoFly competition (February 28, 2020).
The Porable Flyer is like an "extension of the human body" by means of a saddle secured on pilot's shoulders/torso, as a saddle secured on a horce's back.
The pilots body is a big flexible hunk of meat. That hunk of meat is not rigid and doesn't provide the ability to generate torque for control. Do you not realize how much the human body can flex? Watch a few motocross crashes to get an idea.
