2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Tommy Cookers

Here is an explanatory drawing:



from the Internet at https://base-book.com/speed-to-fly , wherefrom the following quote is:

• Your AoA is the angle at which your body’s flat plane is pointing relative to the direction of flight, relative to the air mass.

• AoA is not flight angle… AoA is the angle at which you are pointing along your direction of flight.

• In gliding flight, a lower AoA means higher airspeed. A higher AoA means a lower airspeed. AoA is not glide ratio.

• A pilot must actively manage AoA. No wingsuit will automatically settle into the perfect AoA for each aspect of flight.

End of Quote


The AOA (Angle Of Attack) is the angle of the long axis (CHORD) of the wing suiter with the FLIGHT PATH VECTOR.

If there is no wind, the wing suiter sees the air coming parallel to the FLIGHT PATH VECTOR (actually the wing suiter moves in the standstill air, but the relative motion is the only that matters).

An example: if a wingsuiter dives vertically, and keeps his long axis (CHORD) vertical too, then the angle of attack is zero, while the FLIGHT PATH ANGLE is 90 degrees.

Thanks
Manolis Pattakos

[Tommy Cookers]

you have now shown motion descending at about 20deg below the horizon - (but bizarrely call it level flight)

level flight is flight motion parallel to the horizontal (in principle for any angle of bank eg 0 deg 90 deg or 180 deg)
keeping with this definition is essential for credibility and compliance with the associated bodies of law

your diagram on P183 was (you said) showing horizontal cruise
to established legitimate aviation this means sustained flight motion parallel to the horizon aka level flight


regardless of the above ...
I can't see .....
how you get a L/D of 1.7 for the PF (it's not a wingsuit ?)
how the PF can fly moving parallel to the horizon with the proprotor axis anywhere near the 11 deg shown on P183


RETRO-EDIT
note to self - yes if the PF includes a wingsuit flight as per the P183 diagram is possible

[tok-tokkie]

Regarding the gears. If one of each pair was made of oil impregnated Tufnol there would be no lubrication issues and the pair would run silently and "for ever".
Tufnol = original phenolic linen material.

[Rodak]

So let me see if I have this correct. You have meshing as well as counter-rotating propellers? So how does the acceleration of air by the first meshed propeller affect the second overlapping propeller's activation of airflow? And, for that matter, how is the second propeller in the counter-rotating system affected by the first propellers acceleration of the airstream? These are factors that affect the efficiency of your craft. Please note that although you constantly reference the V-22 the V-22 has an actual wing to provide lift during level flight which you do not. You are relying entirely on engine power to provide lift. As discussed previously, as the angle of the propeller(s) approaches horizontal there is a huge fall off of the vertical lift component (cos Θ IIRC).

And yes, I failed to realize you were gearing the propellers. My mistake.

[manolis]

Hello Rodak.

You write:
“So how does the acceleration of air by the first meshed propeller affect the second overlapping propeller's activation of airflow? And, for that matter, how is the second propeller in the counter-rotating system affected by the first propellers acceleration of the airstream? These are factors that affect the efficiency of your craft.”


Quote from https://www.pattakon.com/GoFly/DTR_1.pdf , page 4 (it is the DEVICE TECHNICAL REPORT as filed to the GoFly / BOEING contest; more at https://www.pattakon.com/GoFly/index.html )

Counter-rotating and contra-rotating propellers

The left upper and the left lower propellers compose a pair of “contra rotating” propellers (the one driven by the right engine, the other driven by the left engine, both rotatably mounted on the same pipe).

The right propellers comprise another pair of “coaxial” contra-rotating propellers.

The two engines operate independently from each other and can run at different revs if desired (to optimize the overall thrust and mileage).
For instance, if the lower propellers are similar (same diameter, same pitch, same design etc) to the upper ones, the lower engine may run at different rpm to align its propellers with the different air stream they “see” as compared to the air stream the top propellers “see”.

The set of the four propellers can be regarded as two “contra rotating” sets of counter-rotating propellers.
A common characteristic of both, of the contra-rotating propellers and of the counter-rotating propellers, is the higher thrust to power ratio.

End of quote


You also write:
“Please note that although you constantly reference the V-22 the V-22 has an actual wing to provide lift during level flight which you do not.”

The fixed wing of the Osprey V22 gives it a stall speed of 204Km/h - 126mph (in airplane mode).
Visa Parviainen (the first powered wingsuiter who achieved a sustainable horizontal flight) had a lower stall speed.

According Wikipedia: “The V-22 loses 10% of its vertical lift over a tiltwing design when operating in helicopter mode due to the wings' airflow resistance.”

The fuselage of the Osprey V22 is also a wing.

In the Portable Flyer the wing (and the fuselage) is the body of the pilot.

A fixed wing (say, like the Delta Wing of Yves Rossy, or like the wing of the V22) can be used in the Portable Flyer too, but it would make it vulnerable to wind gusts during vertical take-off / landing.

The body of the pilot of the Portable Flyer (either wearing a wingsuit, or not) is a flexible wing and provides lift and drag. With the wingsuit the same lift is achieved at lower speeds.


You also write:
”You are relying entirely on engine power to provide lift. As discussed previously, as the angle of the propeller(s) approaches horizontal there is a huge fall off of the vertical lift component (cos Θ IIRC).”

It goes the other way:

As the speed increases, the aerodynamic lift on pilot’s body (or on the wingsuit the pilot wears) increases, allowing the propeller axes to lean more and more from vertical.



At high speeds the thrust from the propellers is used mainly to “take” (to bear) the aerodynamic drag, while at lower speeds the thrust from the propellers is used mainly to “take” (to bear) the weight.

For instance:
during hovering, 100% of the propellers’ thrust is “consumed” to keep the pilot / Portable Flyer at the same altitude / height,
while during horizontal flight at 200mph (~300Km/h), almost all the thrust from the propellers is “consumed” to cover the aerodynamic drag, which means near horizontal propeller axes.


Quote from the abovementioned DEVICE TECHNICAL REPORT :

With the pilot wearing a wing suit or a tracking suit,
at 100mph cruising speed (87kts / 160Km/h / 44.5m/sec) the required thrust is about 66lb (30Kp, 300N and the calculated power is 300N*44.5m/sec = 13.5kW = 18bhp (data taken from the “First jet powered Birdman flight” at http://www.dropzone.com/news/General/Fi ... _flight_61 3.html )

End of quote.

In order to sustain a horizontal cruise speed, the only that the wingsuiter Parviainen needed was a horizontal push of 66lb / 300Nt .
If instead of having two jet turbines secured on his legs:



Visa Parviainen was holding an OPRE Tilting engine driving two counter-rotating propellers (not necessarily as big as those of the Portable Flyer), he could sustain a horizontal cruise speed with the propeller axes being completely horizontal.

Thanks
Manolsi Pattakos

[manolis]

Hello Tommy Cookers.

You write:
“you have now shown motion descending at about 20deg below the horizon - (but bizarrely call it level flight)
level flight is flight motion parallel to the horizontal (in principle for any angle of bank eg 0 deg 90 deg or 180 deg)
keeping with this definition is essential for credibility and compliance with the associated bodies of law”

The drawing is not mine.
It is from the website https://base-book.com/speed-to-fly

The term “LEVEL” is explained at the bottom left of the image as: “LEVEL = NO BANK”
Does anybody know what this means?
For sure it doesn’t mean “Horizontal” (at least according the drawing wherein the FLIGHT PATH VECTOR is some 20 degrees from the HORIZON).


You also write:
“regardless of the above (because it's not a show-stopper at this point) ...
I can't see .....
how you get a L/D of 1.7 for the PF (it's not a wingsuit ?)
how the PF can fly moving parallel to the horizon with the proprotor axis anywhere near the 11 deg shown on P183

The page is the 182.
And here is what I write there for the wingsuiter (of the youtube video) who passes through the rock hole flying at 230Km/h:

• Judging from the trees and the horizon, his angle of descent is some 30 degrees (1.7:1 glide ratio).
  His vertical speed is 64m/sec * sin(30degrees) = 32m/sec (i.e. his weight is descending at a 32m/sec speed).

• With a total weight of 165lb (75Kp, 750Nt), the power consumed is: 32m/sec * 750Nt = 24kW = 33bhp.

• Thus,
  if the wingsuiter had a prime mover (say, some jet turbines like those of Rossy or Browning or Mayman or Zapata) providing 33bhp of push (or pull) power, then the wingsuiter could sustain a horizontal cruise speed of 230Km/h.

• With a propeller efficiency of, say, 75%, the required power output from the engines of the Portable Flyer is 44bhp for 230Km/h horizontal cruise.

• For 300Km/h speed, the required engine power is 44bhp * (300/230)^3 = 100bhp (50bhp per engine).”

The above is nothing more than an “energy conservation” equation:

From the video it is estimated the L/D ratio.
From the L/D ratio and the “estimated” weight it is calculated the energy consumed per time unit (i.e. the power consumed) during this “non horizontal” descending flight.

In order to turn the flight from descending to horizontal (D/L=0), what is required is to add energy at a rhythm equal to the rhythm energy is consumed.

The 33bhp is the “net power” required from some Jet Turbines in order to turn the wingsuiter flight from descending to horizontal. When Yves Rossy turns off his jet turbines, he starts descending; if he turns on his turbines, his flight returns to less descending or horizontal or ascending.

In order to provide the same “net power” with the propellers of the Portable Flyer, and assuming a propeller efficiency of 75%, the two OPRE Tilting engines must provide totally 44bhp of power output.

The last calculation is for the power required from the OPRE Tilting engines in order the wingsuiter to fly horizontally at 300Km/h (the power required increases with speed cube).


Is everything clear now?

Thanks
Manolis Pattakos

[Tommy Cookers]

Hello Tommy Cookers.
You also write:
I can't see .....
how you get a L/D of 1.7 for the PF (it's not a wingsuit ?)
how the PF can fly moving parallel to the horizon with the proprotor axis anywhere near the 11 deg shown on P183

The page is the 182.
And here is what I write there for the wingsuiter (of the youtube video) who passes through the rock hole flying at 230Km/h:

• Judging from the trees and the horizon, his angle of descent is some 30 degrees (1.7:1 glide ratio).
  His vertical speed is 64m/sec * sin(30degrees) = 32m/sec (i.e. his weight is descending at a 32m/sec speed).

• With a total weight of 165lb (75Kp, 750Nt), the power consumed is: 32m/sec * 750Nt = 24kW = 33bhp.[
  Is everything clear now?
  Thanks
  Manolis Pattakos

yes it's clear (I had already edited my post) that ....
if the PF pilot is wingsuited to get L/D of 1.7 the numbers support the attitude shown on P182
but only if the high speed c. 230 km/h is maintained

the wingsuit having such a low aspect ratio its L/D is even worse at higher AoA than at the 11 deg shown
11 deg is not a really high AoA for this AR - slower speeds/higher AoA require correspondingly higher thrust (or more)
the lack of formal proprotor pitch control isn't good but designing for hover below 100% rpm may help the airspeed range

[Pinger]

For an electric car (wherein the absence of vibrations, noise etc is a must), the twin in-line 2-stroke is not a good solution.

There's a fundamental difference that an engine driving a generator does not have to restrain any torque reaction via its mountings. Thus, they can be very compliant and very possibly sufficiently compliant to absorb the rocking couple of a 180 deg twin cylinder engine. A task made easier still if the engine only has to operate over a narrow rpm band. (A rubber mounted RG250 engine is beautifully smooth at high rpm and at lower rpm the mounts soak up the vibes).

[izzy]

Pat Symonds is working on making 2-strokes completely F1 relevant!

"It’s reasonably obvious that if you are going to pump that piston up and down, you might as well get work out of it every time the piston comes down rather than every other time the piston comes down," he said.

"The opposed piston engine is very much coming back and already in road car form at around 50 per cent efficiency.

"Direct injection, pressure charging, and new ignition systems have all allowed new forms of two-stroke engines to be very efficient and very emission-friendly. I think there’s a good future for them."

https://www.motorsportmagazine.com/news ... -formula-e

Sadly he's talking about making them pretty much spec by the sound of it, instead of letting HPP, Ferrari and Honda do something awesome

[J.A.W.]

Ta for that izzy, seems Pat Symonds may've been a follower of this thread, perhaps...

But as for your fears of "pretty much spec" engines, well, the current rules contraints are
quite pre/proscriptive as they are, so nothing new there, yet there are ways 'n' means,
as shown by the fact that a number of different manufacturers have taken victories, too.

Here's a link to some interesting topical stuff, (inc' a homebuilt opposed-piston 2T using magnetic
crank-timing control, & ironically enough, using Honda generators as a basis!)

http://archive.ph/zHnXJ

&, lest we forget, here's a link to how things were - nearly 1/2 a century ago, when the quickest,
yet 'biggest bang for the buck' superbike available - was a mass-produced large capacity 2T machine.

http://www.kawatriple.com/articles/MakingH2.mp4

& again ironically, here below is a currently listed, a 'road-legal' production 2T sports motorcycle,
a 250 V-twin which claims ~the same max-hp as that 750 Kawasaki linked above, but at a price
well into the - 'if you have to ask, you can't afford it' - category..

https://vinsmotors.com/en/duecinquanta-strada/

[Rodak]

I remember taking a friends Kawasaki 500 Widowmaker for a spin back in the day; scared the daylights out of me. All up cost was $999 and you could get electronic ignition or a front disc brake, but for some reason not both. I had a 350 Suzuki at the time but jumping on that 500 was amazing. Didn't handle so well, hence its name, but it sure sounded great..... Incredible bang for the buck.

[saviour stivala]

The Commer avenger opposed piston supercharged two-stroke TS3 engine used only one crankshaft.

[izzy]

Ta for that izzy, seems Pat Symonds may've been a follower of this thread, perhaps...

But as for your fears of "pretty much spec" engines, well, the current rules contraints are
quite pre/proscriptive as they are, so nothing new there, yet there are ways 'n' means,
as shown by the fact that a number of different manufacturers have taken victories, too.

Here's a link to some interesting topical stuff, (inc' a homebuilt opposed-piston 2T using magnetic
crank-timing control, & ironically enough, using Honda generators as a basis!)

http://archive.ph/zHnXJ

i love that Danish link!

There are degrees of everything and yes the existing engines are way too prescribed already and Pat is talking about making it worse, along with the 2021 aero rules. And it doesn't even work, only the redistribution will work so let's hope they do that properly

[Tommy Cookers]

https://www.odd-bike.com/2014/02/dkw-su ... e-fed.html
is very informative (eg the last prewar job having had opposed pistons)

McCulloch or DKW designs could seemingly have enabled a PF type machine in the early 1940s
McC were making target drones in 1943
afaik having free use of Kadenacy ideas (his patents unenforceable in USA due to lack of confirmatory use/proof by K)
iirc somewhere the 'net says that an opposed piston DKW was in production (WW2 and/or postwar NATO ?) as a genset unit

btw
W/Cdr Wallis had persistent magneto trouble with his McC powered gyrocopter ....
because the magneto used cheap magnets which faded when hot - no problem in the intended 5 minute life of the drone
the Commer was originally the Tilling-Stevens design used in T-S trucks etc
a few times we had a T-S school bus - fast but iirc 4 stroke-powered

[saviour stivala]

While you had a TS school-bus I was back than already servicing the TS3 engine, it was a sensation at its time.