2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

P, here below is a higher boost ( 2 bar) example of a basic 2T - with add-on turbo;

https://www.youtube.com/watch?v=T44ZVTQtLUk

AFAIR, the 2T engine 'sees' the added pressure boost internally - in ratio - as it does ambient atmospheric pressure,
& accordingly, stays in 'balance'.

[Tommy Cookers]

[quote=Pinger]........numbers on is exhaust backpressure - which on a turbo 4T is apparently at least twice (often higher) than inlet manifold pressure .....[/quote]

for low boosts apparently good sources say mean exhaust pressure can be lower than inlet pressure (eg Indy and road cars)
if exhaust pressure was higher those 15000 Wright Turbo-Compounds would have been a big lie

or - CI will likely need higher mean exhaust pressure than inlet and SI likely won't (unless running super-lean)

[Pinger]

Thanks J.A.W. Pity they didn't have one more column showing backpressure along with the other data. 2bar inlet pressure so 1bar boost. Guessing you're right about the 'balance'.

for low boosts apparently good sources say mean exhaust pressure can be lower than inlet pressure (eg Indy and road cars)
if exhaust pressure was higher those 15000 Wright Turbo-Compounds would have been a big lie

or - CI will likely need higher mean exhaust pressure than inlet and SI likely won't (unless running super-lean)

That's what I've been picking up on also and is referred to as the 'holy grail' ie lower backpressure than inlet pressure. An example sited was the F1 turbo cars of the 1980's - but they were running a lot of boost.
Road cars running turbos as part of a downsizing strategy apparently suffer high backpressure at part load conditions to the detriment of cruising fuel efficiency - which is partly why the downsizing trend has stabilised.
CI turbines rely more on pressure, SI on heat so yes, lower backpressure potentially. But when discussing turbo 4T the disadvantage is the energy taken from the crank during the exhaust stroke when high backpressure prevails - backflow into the cylinder can be prevented with restricted valve overlap.
The 2T by contrast has none of the 'pumping' stroke issues but all of the backflow problem if the backpressure is too high. Get the backpressure right though - and you are genuinely supercharging.

What is also hindering me in making sense of all of this is that what I have in mind is a turbo installed on the exhaust header pipes - not at the other end of the system (which will not, cannot, be an expansion chamber) and unlike the sled turbo set-ups, I wont have the benefit of CVT to mask a laggy set-up.

And just to complicate things further, the reason for a turbo is to overcome very restrictive transfer ports so whatever pressure prevails upstream of the transfer ducts will have dissipated by the time the charge arrives at the cylinder end. Hence the requirement for low(ish) exhaust backpressure as there simply will not be the pressure in the transfer stream to fight it. (Basically, I am looking at a turbo to compensate for a sub-optimal transfer system rather than the absolute pursuit of power). A larger turbo energising later in the rev range (after the transfers have reached capacity flow) might keep back pressure in check.

Re Turbo compounds - I intend rereading the lit on the Napier Nomad - in the hope of some clues!

[Pinger]

And something totally different....
Another project I'm working on is to reduce the UBHC of the simplest 2T and finally got a little testing done today. Running a strimmer engine in standard form at a fast idle using both a standard exhaust box and then with a cat box the UBHC was 9700ppm. Modified, the same test yielded UBHC of 3300ppm with no change in mixture settings.

Too early to claim this as any real result (I need to refine my testing method and test more) but promising so far. The 'modification' is laughably simple!

[manolis]

Hello all.

Here is a Portable Flyer wherein the design is focused on the safety, without compromising in the rest areas.




ENGINE

Two OPRE Tilting engines, each having 350cc capacity (86mm bore, 30+30=60mm stroke) preferably the PatBam version for HCCI combustion (no need for high voltage circuit).

The two engine casings are secured / bolted to each other:



to form the Portable Flyer casing.

I.e. there are two independent propulsion units, each comprising an engine and two counter-rotating propellers.



Portable Flyer total mass: less than 20Kg / 44lb.


PORTABLE FLYER SIZE

With 3-blade propellers having 39’’ (991mm) diameter,
and with 21’’ (533mm) distance from propeller axis to propeller axis,
the maximum dimension of the Portable Flyer is 39’’+21’’ = 60’’ (3.5 points (35% of the maximum Final Score) in the “compact size” scoring of the GoFly competition: https://www.herox.com/GoFly/guidelines sponsored by BOEING).


QUIET TAKE OFF

Limiting the propeller tip speed at only 150m/sec (44% of the sound velocity) for “quiet” take off, the resulting propeller rpm is 2,900rpm.

With 28’’ pitch and 3 blades per propeller, the static thrust at 2,900rpm is ~35Kp / 350N (at least according http://www.godolloairport.hu/calc/strc_eng/index.htm ; if anybody has another static thrust calculator, he can check it out), while the power absorbed by each propeller is ~15bhp.

At the “quiet” take off, the total upwards thrust is 4*35=140Kp (with a total mass <110Kg, this means ~0.3g upwards acceleration) and the required power from each engine is ~30bhp.

The small tip speed keeps the noise low, and the “noiseless” scoring high (GoFly / BOEING competition: the quietness counts for some 40% of the Final Score).

With 2.4:1 “crankshaft to propeller” reduction ratio, the 2,900rpm of the propellers at the above “quiet” take-off, translates into 7,000rpm for the engines.

In order a 350cc 2-stroke engine to provide 30bhp at 7,000rpm, it needs to make 30mN of torque at 7,000rpm (~90mN/lt specific torque, which is easily attainable even with 4-stroke engines).

After the take off, the engine rpm (and the propeller rpm) increase to enable a high cruise speed (above 100mph (160Km/h)).


TOP SPEED

At top speed (> 100kts / 185Km/h) the propellers rev at 4,350rpm (propeller tip speed 2/3 of the sound velocity), and the engines are running at 10,500rpm (at 10.5m/sec mean piston speed, which is still low and improves the long term reliability).
In the scoring of the GoFly / BOEING competition (see figure “speed” at https://www.herox.com/GoFly/guidelines) this means less than 0.05 points below the maximum possible (this counts for less than 0.5% of the maximum possible Final Score).


SAFETY

In case of malfunction of the one engine, or in case one propeller falls apart, or in case a transmission tooth belt is broken, or . . ., the “healthy” propulsion unit is capable for a safe landing.

With the one only engine running at 9,000rpm (mean piston speed: 9m/sec) and driving its two 3-blade 39’’ diameter / 28’’ pitch propellers at 3750rpm (2.4:1 reduction):
the total thrust force is ~115Kp,
the tip speed is 195m/sec (57% of the sound velocity),
the power required from the running engine is ~65bhp (which means: ~50mN of torque from 350cc capacity, i.e. ~150mN/lt specific torque, which is attainable by a good 2-stroke: the Rotax 850 has more than 175mN/lt peak specific torque).

With “only” 195m/sec propeller tip speed, the Portable Flyer is quiet even during an emergency landing.


FAST TAKE OFF

With both engines running at 9,000rpm, the upwards acceleration at a “fast take off” is more than 1g (10m/sec); it is like “falling towards the sky”.

Alternatively: the Portable Flyer can carry two persons (the pilot and a passenger); in this case at a malfunction of the one propulsion unit, the emergency landing is not possible (unless the one person (the pilot or the passenger) falls, preferably with a parachute).


CRUISING / CONSUMPTION / MILEAGE

With the pilot wearing a wing suit,
at 100mph cruising (87kts / 160Km/h / 44.5m/sec) the required thrust is about 30Kp (300N, 66lb) and the calculated power is ~18bhp.

(the data are taken from http://www.dropzone.com/news/General/Fi ... t_613.html )

At cruising the propellers rev at 3,750rpm (propeller tip speed 57% of the sound velocity), and the engines rev at 9,000rpm (mean piston speed: 9m/sec)

With, say, 75% propeller efficiency, the power required from the engines is ~24bhp.
With the engines running at 35% BTE (attainable with HCCI combustion and lean mixture), the fuel consumption (gasoline) at 100mph (160Km/h) cruising is easily calculated at ~5.5lt/h (3.5l/100Km), and the mileage at 67mpg (US gallons).
For a distance of 200miles (320Km), they are required some 11lt (~8Kg) of gasoline.

Each engine has to be capable of providing, at 9,000rpm, the 65bhp required for an emergency landing (as previously described). Compared to the 24bhp required for cruising at 100mph, the engine(s) at cruising will operate at substantially light load (quite lean air fuel mixture if HCCI).

The straight line a Portable Flyer follows going to a specific destination is a big advantage as compared to a car and to a motorcycle which cover a substantially longer distance following the road.


HIGH SPEED AND SAFETY

The ability for high speed flights is mandatory for the safety; at windy weather a big size / slow moving (“hovering”) flyer is like a “feather in the wind”.
If the Portable Flyer can fly way faster than the wind, the strong wind is not a problem.


USE

In the near future the Portable Flyers (or the Personal Flyers) appear as interesting alternatives for cars / motorcycles / boats etc (which means wide use).

For special uses, the Portable Flyers appear as a passé partout.

Think of:

A “first aid” doctor arriving into a couple of minutes and landing 5m from the injured persons.

A rescue team flying to a sinking vessel.

A fireman who, at a skyscraper fire, is taking off the road and is landing in seconds on the roof of the skyscraper to help (or to take away) trapped persons (if each engine alone is capable for an emergency landing, the Portable Flyer is capable to lift, besides the pilot, a passenger (or two: the Portable Flyer mass is counted only once)).


COST

Regarding the ownership cost, a Portable Flyer like the above is way simpler than a car or motorcycle (it needs not wheels, it needs not suspension, it needs not a steering, . . .): just two simple, lightweight, vibration-free engines forming the casing, and four propellers.
Regarding the running cost, according the previous calculations a Portable Flyer appears more economical (and more green) than a car or motorcycle.


ENGINE (again)

The two OPRE Tilting engines are the heart and the backbone of the Portable Flyer.

The “OPRE” stands for Opposed piston Pulling Rod Engine while the “Tilting” refers to a valve secured on the small end of the connecting rod; the tilting valve controls the intake and the transfer (no need for reed valves or rotary valves). More at http://www.pattakon.com/pattakonTilting.htm

Each “crankcase” (actually the space underside the piston crown, inside the piston) runs not-pressurized.

The thrust loads are taken at the cold ends of the engine, away from port openings.

The synchronizing gearwheels between the two crankshafts run unloaded and serve as balance webs, too.

Each engine, alone, is perfectly vibration free, and is driving its own pair of counter-rotating propellers (zero gyroscopic rigidity).

The short piston stroke (30mm) allows high revs at low mean piston speed (reliability).

With HCCI (i.e. spontaneous) combustion into a compact bowl, the over-square design is fine; the combined stroke is 30+30=60mm; with 86mm bore, the design is by far less over-square than the famous Ducati Panigale 1299 (60.8mm stroke, 116mm bore).

The pulling rod architecture increases substantially (~40%) the piston dwell at the combustion dead center enabling more “constant volume combustion”.

The single-piece “pipe-like” casing improves the stiffness, the lightweight, the simplicity and the low cost.


THEORETICALLY SPEAKING

All the previous are just theories; yet, interesting theories.

The safety is the “big issue”.

Having two independent propulsion units (each alone capable for emergency landings),
having also a parachute (for just in case, say when it runs out of fuel),
having (optionally) three small wheels like:



for emergency airplane-like-landing on a road or on a flat field,
the safety appears better than the safety provided by the conventional airplanes and helicopters.


AMENDMENTS ARE REQUIRED

In the previous the GoFly competition (sponsored by BOEING) was mentioned only as a reference point.
Surprisingly (because the BOEING is involved) they focus on the quietness and on the maximum dimension (8.5ft maximum) of the device: 90% of the total scoring is for the noiseless take-off / landing and for the maximum dimension of the Personal Flyer.


SUMMARY

In the double-propulsion-unit OPRE Tilting Portable Flyer presented above, nothing appears near or beyond the current state of the art limits.

Lightweight carbon-fiber propellers of various designs and sizes are available in the market at low prices.

Toothed belts are common place for power transmission and revs reduction.

The structure of the Portable Flyer utilizes the engine casings as its backbone.

The perfect vibration free (including both, inertia vibrations and power pulses vibrations) is a requirement when a powerful engine is to be directly supported / secured on the body of the pilot/rider; otherwise a long (say of one or two hours) flight would be a torture.

The counter-rotating propellers eliminate the gyroscopic rigidity and allow the pilot/rider to vector the thrust immediately and effortlessly to the desired direction.

Every ounce of mass that can be omitted from a personal flyer, must be omitted. The more the mass of the flyer, the more fuel is required for a specific range and the more challenging the take-off / landing becomes.

The peroxide JetPacks consume some 30Kg of “fuel” in half a minute.
The jet powered personal flyers (Yves Rossi like, Zapata like etc) consume their fuel in ten minute, or so (BTE less than too small).
The electrical personal flyers are based on batteries; and the existing batteries have an energy density several dozens of times lower than the fossil fuels (gasoline, kerosene, Diesel etc). The energy density of the power source is more than important for a flying device.

The body and the eyes and the senses of the pilot/rider are available; why not to use them as the fuselage and the sensors and the control system?
Isn’t this what the birds are doing?
Relative to the birds, the low power to weight ratio of the human body is the only thing that restricts us from flying / hovering.
This lack of power is what the OPRE Tilting engines and the propellers are curing at a true “neutral” and efficient way.

Thanks
Manolis Pattakos

[J.A.W.]

Excellent program progression there Manolis, & I wish you all the best with realization..

I do do note, however..
..the apparent lack of a well-considered, light weight, noise-suppression/econo-power boost 2T exhaust system..

If I might suggest - perhaps Akrapovic - might well be interested in contributing a bespoke Ti design - to suit?

[Pinger]

Manolis, the next issue of Engine Technology International will have an in depth report on the current state of the art of HCCI. I'll post a link to the online version when it is published.

[Tommy Cookers]

@ Manolis

fwiw my guess is your calculations are optimistic

aren't you assuming a static 'propeller' efficiency of 100% ?
it might well be 50%
so your power requirement is optimistic

how does the lower prop work where its arc overlaps the upper propellor's ?
prop ducting would allow smaller props

regardless of power requirement
in HOGE you seem to be blasting the pilot with warm exhaust-loaded air moving at 150 mph
and HIGE won't be much better

how is this machine made (naturally or artificially) stable ?
$500 drones are - artificially

[manolis]

Hello J.A.W.

In the GoFly competition (sponsored by the BOEING), in the FINAL SCORE the 49% has to do with the noise:



Two Acrapovic exhausts are not adequate.
Five are required: one per exhaust port and one for the pilot.
I am kidding.

Yes with a good exhaust the noise from the engines can be suppressed and the engines can be tuned at the cruising revs (because for some 95% of the time the engines will operate at those revs).


Unless I am wrong, according the above GoFly / Boeing regulations / criteria:
49% of the points are for the quiet operation,
41% of the points are for the small size (the maximum dimension),
10% of the points are for the speed,
and 0% of the points are for everything else.


A few thoughts on the above “scoring”:

The safety should be the dominant “scored parameter”, with more points than the sum of the points given for the “Size”, for the “Noise” and for the “Speed”.
Safety: when something falls apart or malfunctions, what are the available means / methods for the pilot to survive?
Unfortunately the safety is absent from the scoring.

The range should be also a dominant “scored parameter”, with several points.
Now the only requirement is the “personal flying device (to be) capable of flying 20 miles while carrying a single person”.
I.e. a personal flying device having a range of 200miles (320Km) is equivalent with a personal flying device having only 20miles (32Km) range!
Daedalus and his son Icarus tried to fly, according the myth, from Crete (Minoan Palace) to Athens (~150Knots / ~280Km).
With only 20miles / 32Km range, the personal flying machine is rather a toy than a transportation means.

The score for the speed is less than poor (it counts for only ~10% of the total score, while the quietness counts for the ~49% and the size for the 41%).
I.e. a personal flying device capable for 160mph (~250Km/h) is a loser against a personal flying device capable for only 30Knots (55km/h) if the second emits just 4dBA less noise at take off.
Think of it: If you run fast enough, you can keep step with the “winner”.

The overall weight of the personal flying device is also important.

The mileage (either it is the fuel consumed per mile, or the energy consumed per mile (batteries), or the quantity of CO2 emitted to the atmosphere per mile) is also an important characteristic that should be scored.
As it is now, it doesn't matter if you consume 50lit of gasoline to cover a distance of 20 miles (32Km), or if you consume only 10lit of gasoline to cover a distance of 200 miles (320Km).


The capability of the flying device to fly in windy weather is also a quite significant characteristic.
Think a personal flying machine having 30Knots maximum speed, flying near the sea, with the wind blowing towards the sea at 35Knots.


The cost should also be a significant scored parameter. Manufacturing cost and running cost.
A US200,000$ personal flyer machine cannot be affordable for the ordinary people.
A US3,000$ personal flyer machine can change the world.


According the previous, the criteria chosen are anything but meaningful.


Suppose that “the” Bill Gates



is jealous of the fame / glory / legacy of “the” Jonas Salk (the creator of the polio vaccine):



and decides to spend a few billions of his fortune to connect, for ever, his name with the cure of a bad decease.

He sets a competition among doctors, medical researchers, pharmaceutical companies, etc, etc, for the cure of, say, the cancer decease.

The prize he sets is 10 billion US dollars.

Then he writes the regulations of the contest and the rules for the nomination of the final winner:

45% of the points are for the sweet taste and the pleasant smell of the pills,

35% of the points are for the size of the pills (only pills from 3/8’’ to 7/8’’ are allowed),

10% of the points are for the speed of the cure.

No points for the absence of side effects,
no points for the safety of the cure,
no points for the cost of the cure (it does matter a lot the cost of the pills: a 1 dollar pill is for everybody, a 1 million dollar pill is only for the rich ones),
no points for the longevity of the patient after the cure.

Bill Gates would never use such criteria.


The 10 billion dollar prize mentioned above is too much.
A billion prize can work the same well.

With a billion US dollars per decease, Bill Gates can relate his name with the cure of some 70(?) deceases.

This way, he may also avoid being the richest in the graveyard.

Thanks
Manolis Pattakos

[manolis]

Hello Pinger.

You write:
“the next issue of Engine Technology International will have an in depth report on the current state of the art of HCCI. I'll post a link to the online version when it is published.”

Thanks.
I would like to know the current state of the art.

Manolis Pattakos

[manolis]

Hello Tommy Cookers.

You write:
“aren't you assuming a static 'propeller' efficiency of 100% ?
it might well be 50%
so your power requirement is optimistic “


No.

The static thrust calculator used (http://www.godolloairport.hu/calc/strc_eng/index.htm ) ,
based on the geometrical characteristics of the propeller, on the rpm of the propeller and on the air density,
calculates the thrust and the power required by the propeller.


When I use the data from the first flight of Visa Parviainen, the maximum force from the jets is given as 16Kp (two jets: 32Kp).
The horizontal flight velocity is more than 100mph (but less than 100kts). I suppose only 100mph.
From this two numbers it results the required power: ~18bhp.

This power comes from the propellers.
Then I suppose a propeller efficiency of 75% (note: we talk for cruising, not for tak-off; at cruising is where the efficiency of the propeller is maximized).
I.e. in order to provide 18bhp to the Portable Flyer, we have to provide 18/0.75 = 24bhp to the propellers.
Then I suppose a BTE of 35% for the engines.
In order the engines to provide 24bhp mechanical power to the propellers, and supposing the engines run at 35%BTE, they consume 3.5lt/100Km.

I can’t see optimism. Please be more specific.



You also write:
“how does the lower prop work where its arc overlaps the upper propellor's ?
prop ducting would allow smaller props”


In the Portable Flyer:



the arrangement of the four propellers can be regarded:

either as two pairs of intermeshed counter-rotating propellers, the one pair below the other at ~0.3D distance (D the diameter of each propeller),

or as two pairs of contra-rotating propellers (at a 0.3D distance from each other), the one pair intermeshed with the other pair.

The counter-rotating propellers, as in the Kamov:



achieve a better thrust to power ratio (for a specific engine, it can lift a heavier load than a conventional helicopter).

The intermeshing propellers (say Flettner, Kaman etc)



also achieve a better thrust to power ratio;

Wikipedia: “ Intermeshing rotored helicopters have high stability and powerful lifting capability. The latest Kaman K-MAX model is a dedicated sky crane design used for construction work”

The Portable Flyer has contra-rotating and counter-rotating at the same time propellers, which, reasonably, reduces the calculated power required in order to create a specific amount of thrust.



You also write:
“regardless of power requirement
in HOGE you seem to be blasting the pilot with warm exhaust-loaded air moving at 150 mph
and HIGE won't be much better”


With the quantity of air -pushed by the propellers towards the pilot- being thousands of times more than the hot air exiting from the exhaust (700cc x 7,000rpm = 82lt per minute), the pilot cannot even feel any increase of the temperature of the air.



You also write:
“how is this machine made (naturally or artificially) stable ?
$500 drones are – artificially”


The body and the eyes and the senses of the pilot/rider are the fuselage and the sensors and the control system (birds like).



Quote from http://www.pattakon.com/pattakonFly.htm

Control

When a child begins riding a bicycle, it progressively learns how to react properly to the signals from the eyes and the body (i.e. on how to keep the control).

Just like driving a bicycle, the eyes / body / brain of the rider / pilot of a Portable Flyer are the sensors and the control system: the rider soon discovers the way to react properly and to keep the control. For the Portable Flyer is a true neutral propulsion unit: neither vibrations, nor reaction torque, nor gyroscopic rigidity, only a force: a force that can "instantly" and effortlessly be vectored towards the desirable direction.

In a Flyer it is better to be used the body of the rider as the main sensing and controlling equipment (birds like), than developing and paying and carrying stabilizing and flight management systems.

The birds, the bats and the bugs fly because their bodies can provide adequate power for their weight. The power provided by a man's body is not adequate to lift its weight.

What a man needs, in order to fly, is neither a vehicle, nor sensors, nor servomechanisms, nor control units, nor transmission shafts, nor differentials, nor gear-boxes, not even a seat.

What a man does need, in order to fly, is power provided in a true neutral and manageable way. The body is: the vehicle and the sensors and the control unit and the servomechanisms and the landing system, just like the bodies of the birds, bats and bugs.

With a pattakon Portable Flyer secured onto his shoulders / torso, a man can fly like a bird.

. . .

According several articles and videos published in the Internet, Yves Rossy / Jetman already "flies with the grace of an eagle, and the subtle body movements he uses to maintain flight - and perform his loops, rolls, and other maneuvers - mimics a bird of prey".

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"

End of quote


Thanks
Manolis Pattakos

[Tommy Cookers]

the exhaust isn't uniformly dispersed in the propeller slipstream so dilutions down to a few ppt are impossible
dangerous levels of CO could be ingested given there's no exhaust catalyst or breathing system for the pilot
700cc at 7000 rpm is not 82 litres/min it's 4900 litres/min
and 700cc engine's exhaust per rev is more than 700cc

your type of propeller-rotor semi overlap has rarely been tried and doesn't work well
the relative success of properly coaxial and near-coaxial rotors is irrelevant

the machine hovers if downward-accelerating a 110 kg air column of 1.25 sq m csa by 9.8 m/sec or equivalent
an air stream velocity of about 27 m/sec (ok less than I said before)
if anyone reached the 'cruise-at-speed' prop and body attitude shown - where does the lift come from ?

[manolis]

Hello Tommy Cookers

Thanks for the correction.

It is 82 lit/sec and not 82 lit/min as I wrote by mistake.

With ~40m3/sec downstream fresh air (~1.2m2 disk area and ~120Km/h air velocity) and 82 lit/sec exhaust gas, the ratio of mass of the fresh air to the exhaust gas is 40.000 lit / 82 lit = ~ 500.

The exhaust ports can be directed backwards so that the pilot cannot inhale anything but clean air.



You write:
“designers have almost always avoided your type of propellor/rotor overlap (both props cannot work well in all situations ?)”


Two modes of operation are important: the take off and the cruising.

According the calculations in a previous post, the engines are operating at partial load at the quiet take off (the required torque is calculated at less than 100mN/lit).
So, the optimization of the propellers and engines has to do mainly with the cruising speed.



You write:
“if anyone reached the 'cruise-at-speed' prop and body attitude shown - where does the lift come from ?”


It comes partly from the propellers (directed upwards) and partly from the body of the pilot / rider that acts as the fuselage and as a wing.


Let’s follow a flight:

To comply with the noise limit of GoFly / Boeing, at take-off the pilot keeps the engines revving at 7,000rpm (2,900rpm of the propellers).

The upwards thrust force is ~135Kp.

The noise measuring microphones are arranged 50ft from the take-off center.

The Portable Flyer (say 110Kg total mass, the fuel included) moves upwards with some 0.2g acceleration.



At a height of ~50ft (~15m: the time required is, according the s=0.5*g*t^2, about 3sec), wherein the distance from the microphones is 40% longer, the pilot turns the throttle wide open, the engines rev at 9,000rpm and the propellers spin at 3,750rpm.

Now the thrust is 220Kp (2,200N). This gives an upwards acceleration of 1g.

The Portable Flyer accelerates upwards strongly.

At a safety height of, say, 150m (~500ft: the time required is some 5sec), the pilot starts turning the direction of the Portable Flyer (i.e. the thrust force) towards his destination.

The upwards acceleration decreases slightly, while the horizontal acceleration (and the rhythm of horizontal speed gathering) increases.

For instance, turning the “propeller disks” from completely horizontal (0 degrees) to 20 degrees, the thrust and the upwards acceleration decrease at 206Kp and 0.88g respectively, while the horizontal thrust and acceleration increase from zero to 75Kp (750N) and 0.68g respectively.

The Portable Flyer continues gathering height and starts gathering horizontal speed (it adds 6.8m/sec horizontal speed per second).

After another 5 seconds, the height the Portable Flyer is flying at 250m, while its horizontal speed is ~28m/sec (~100Km/h, ~ 60mph).

During this horizontal acceleration, the body of the pilot gets progressively more and more horizontal because the aerodynamic resistance pushes the “center” of pilot’s body backwards, while the horizontal part of the thrust from the propellers pulls the upper end if pilot’s body forwards.



The body of the pilot starts behaving as a wing, creating aerodynamic lift.
The frontal area reduces.

When the Pilot is at his desirable height, say ~1,000m (~3,300ft) he turns the disk propellers more towards his destination (say at 60 degrees from horizontal).

Now the upwards thrust force is 110Kp (1100N) and balances the total weight of the Portable Flyer / pilot, while the horizontal thrust is 190Kp (1900N).
The Portable flyer stops gaining height: it keeps its height and flies horizontally gaining horizontal speed. As the horizontal speed increases more and more, the body of the pilot turns more and more horizontal providing a significant amount of aerodynamic lift and reducing its aerodynamic drag .

This means that the propellers need not to provide upwards thrust equal to the total weight of the Portable Flyer, but only a fraction of the weight (the rest weight is taken by the aerodynamic lift on the body of the pilot).
This in turn means that the pilot can further turn the axes of rotation of the propellers more horizontal.

As the horizontal speed increases, the propellers behave like having less and less pitch and the power absorbed reduces.

The aerodynamic lift from the body of the pilot is lower than the weight of the Portable Flyer; this means that the propellers have still to provide upwards lift to balance a part of the total weight.




With bigger pitch for the propellers things are better at cruising and tougher at emergency landing.

With 39’’ diameter propellers, 35’’ pitch and 3:1 (instead of 2.4:1) reduction ratio from crankshafts to propellers,
the thrust force at take-off is about the same (130Kp) as with the 28’’ pitch (propellers revving at the same 2,900rpm; the engine is operating at 8,700rpm).

At take off, each engine has to provide instead of 30bhp, ~40bhp (easy for a 2-stroke 350cc running at 8,700rpm: the required specific torque is only 95mN/lit).

At 3,750rpm (propeller, ~11,250 engine), the thrust per engine is 115Kp and the Portable Flyer is capable for a safe emergency landing with the one only engine. The specific engine torque required is 150mN, attainable by a good 2-stroke. The mean piston speed is still low: ~11.25m/sec.

At 11,000rpm engine, the speed is limited theoretically at 105kts (depending on the type of the propellers this limit can go to ~120kts / 220Km/h).

At 12,500rpm engine, the cruising speed is limited theoretically at 120kts (depending on the propellers it can be more than 135kts / 250Km/h).

At such speeds the pilot is almost horizontal, like the guy in the following video (from second 30) minimizing his frontal surface area.





In Formula1 and MotoGP the saying was “If engine is the best --- the rest”

Thanks
Manolis Pattakos

[gruntguru]

You don't need to accelerate vertically to transition from hover to horizontal flight. A little extra power while pitching forward slowly will transition to forward flight (helicopter mode) and lift increases as speed builds until finally achieving forward flight. This will work much better when wearing the wing suit (and cruise efficiency will be greatly improved.)

As I have said before, hover-mode will not be inherently stable and handle bars will be almost essential for adequate control.

[manolis]

Hello Grunguru.

You write:
“As I have said before, hover-mode will not be inherently stable and handle bars will be almost essential for adequate control.”


Handle bars can easily be added.
The question is whether they are really necessary.


The stability at hovering seems quite similar to the “dynamic” stability during walking, wherein the brain “feels” (mainly by the otoliths, also by the eyes etc) and responds by commanding the various muscles to expand or contract.

In the following video (you can go directly to 3:23):



the delta wing with the two jets is secured to pilot’s shoulders / torso (no handle bars).

The guy is a beginner.

Initially he is over-responding (spot on the oscillations, 3:29 to 3:33 and 3:39 to 3:42). With nothing but air around him, he has the time to learn and calm down and react properly.
Then he enjoys his fly until the moment he opens his parachute.


With the Portable Flyer secured to his shoulders / torso, the legs, hands and head of the pilot / rider are free to move relative to the Portable Flyer.

If the pilot / rider feels he starts leaning to the left, he can extend his right leg and right hand to the right, shifting the centre of gravity to the right and affecting / utilising, at the same time, the flow of the downstream air (lift and drag).

Going with 100mph on the highway and having the one hand outside the open window of the car, your palm acts as the flaps of an airplane wing: depending on its orientation the palm takes from a small to a heavy force from the air.

The stable hovering may prove in practice easier than walking.

Thanks
Manolis Pattakos