2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello J.A.W.

Quote from “your” link:

“What was the pony power with the added mods? Surprise! The hopped-up YZ250 peaked at 49 horsepower at 8500 rpm, while the his full-race YZ250F peaked at 49 horsepower at 13,500 rpm. The kicker was that the YZ250 two-stroke had 9 more pound-foot of torque than the thumper. Those kinds of torque numbers are game-changers.”

End of Quote


Quote from the Internet:

2-stroke YZ250:
In 1999, the bore was further reduced to 66.4 mm and the stroke lengthened to 72 mm producing a displacement of 249 cc. The longer stroke engine resulted in a lower redline, slightly less top end power and greatly improved torque at lower RPM.The engine produces a peak 48.8 horsepower (36.4 kW) at 8,800 rpm and 30.6 foot-pounds force (41.5 N⋅m) of torque at 7,500 rpm, with a 9,000 rpm redline [2].

4-stroke YZ250F:
250cc liquid-cooled DOHC 4-stroke; 4 valves. Bore x Stroke. 77.0mm × 53.6mm.

End of Quote.


If the above quotes are correct, then:

At its peak power (49bhp at 13,500rpm) the over-square 4-stroke makes 102mN/lt specific torque at a mean piston speed of 24m/sec.

At its peak power (also 49bhp, but at only 8,500rpm) the 2-stroke makes 162mN/lt specific torque at a mean piston speed of 20.4m/sec.

At peak power the 2-stroke has 60% more torque than the 4-stroke, but the 4-stroke revs at 60% higher revs.

The 2-stroke has 0.92 bore-to-stroke ratio, while the 4-stroke has 1.44 bore-to-stroke ratio (i.e. ~60% larger bore-to-stroke ratio).


The necessary long piston stroke of the 2-stroke (to optimize its conventional ports and breathing) puts limitations to its peak power (at least as compared to a short-stroke 4-stroke of similar displacement, as above).


An answer may be the PatATE 2-stroke design:



(more at at https://www.pattakon.com/pattakonPatATE.htm )



wherein an XXL-size hybrid port serves alternatively both, the exhaust and the transfer.
Its area is so big that allows the substantial increase of the bore-to-stroke ratio in order the 2-stroke to be the unquestionable winner not only in specific torque, but in specific power as well.

Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis, thanks for your response.

Of course, dirt-bikes have different performance parameters than roadrace/air vehicles.
& the most recent Honda inline-4 'Superbike' has now adopted the 81mm bore of the MotoGP bikes.

But if you contact member here: 'Uniflow' about his 2T ECU/Fuel injection work (jumped on by KTM),
you may well get some useful data of value to your 'flyer', (especially, as he is a fellow 'airman').

[FW17]

[manolis]

Hello all.

In this video:



a wingsuiter flying at 142mph (230Km/h = 64m/sec) passes though a 10ft (3m) wide rock hole.

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).



Thanks
Manolis Pattakos

[Tommy Cookers]

ok ..... I'll take the bait .....

if the wingsuiter's glide angle is 30 deg (having a L/D ratio of 1.7) .....
how does your mannequin have the PF in level flight at an apparent AoA of only 11 deg ?

[manolis]

Hello Tommy Cookers.

You write:
“if the wingsuiter's glide angle is 30 deg (having a L/D ratio of 1.7) .....
how does your mannequin have the PF in level flight at an apparent AoA of only 11 deg ?”

The angle of attack is a different thing than the glide angle.

The 30 degrees glide angle (from horizontal) is the angle of a line L along which the wingsuiter moves / flies / falls.

Relative to this line L (and not relative to the horizon) is the angle of attack of the wingsuiter.

Thus, an 11 degrees angle of attack of the unpowered wingsuiter (who’s glide angle is 30 degrees) means that his long axis is at an angle of 30-11=19 degrees from horizontal.

If I am not clear, please let me know to make a drawing.



Hello J.A.W.

It would be good if Uniflow (with his background in injecting 2-storkes) decided to participate in this OPEN discussion.
A better injection system makes a far better engine, especially a 2-stroke one.



Hello FW17

The question is whether the combination of both cycles (spark ignition and compression ignition) in the same engine adds the advantages of both “worlds” without adding their limitations / disadvantages / issues.

For instance (quote from Wikipedia at https://en.wikipedia.org/wiki/Helical_camshaft) :

“There is no physical reason why a Helical Camshaft could not be the “driving” cam in a Valvetronic-type oscillating cam setup. (But it would be quite complex and the Valvetronic part of the arrangement would limit the Helical Camshaft's high RPM capabilities).
The result would be an almost unbelievable array of possible duration/lift combinations.”

End of quote.


The DVVA (desmodromic VVA, more at https://www.pattakon.com/pattakonDesmo.htm) :



does exactly this, providing “an almost unbelievable array of possible duration/lift combinations”:



without the limitations of either the Helical Camshaft VVA (and has a lot) or of the BMW Valvetronic VVA.

Thanks
Manolis Pattakos

[denktank]

Found this on youtube
Car compressor turned into working engine,
https://www.youtube.com/watch?v=SxqyfB83tSo
Nice to see!

[denktank]

Model engine, with rotary valve,looks a bit like PatATE design
https://www.youtube.com/watch?v=I5m7HFtHLtQ

[manolis]

Hello Denktank.

Thanks for the videos.

In the RCV-model engine (link in your last post), the cylinder spins at half crankshaft speed.

In this version of the PatATE 2-stroke engine the “rotary valve” spins at half crankshaft speed, too:



i.e. the crankshaft and the transmission of the RCV could be used for this version of the PatATE.


But the similarities end here.

• The “rotary valve” of the PatATE never “sees” the combustion pressure.

• Its sealing quality is not crucial for the operation of the engine.

• The combustion chamber is a normal combustion chamber with the spark plug located anywhere (centrally, if desired).

• The “rotary valve” of the PatATE needs not the thrust roller bearing of the RCV that takes the heavy axial loads (the axial force on the RCV rotating cylinder is equal and opposite to the gas pressure force acting on the piston)

• The working cylinder of the PatATE is immovable and takes the thrust loads (i.e. the loads due to connecting rod leaning) the conventional way (in the RCV engine, besides the heavy axial loads, somebody has to take the thrust loads from the piston skirt to the rotating cylinder).

• The piston rings in the PatATE operate the conventional way and have normal speed (in the RCV engine, the speed of the piston ring equals to the square root of the piston speed square plus the cylinder peripheral speed square).

The RCV engine can be described as an Aspin Rotary Valve engine wherein the cylinder is secured to, and spins with, the rotary valve.
It seems good for model engines, but as the size of the bore and stroke increases, the several problems worsen.


In the above GIF animation of the PatATE:

The width (along the periphery of the cylinder) of each hybrid port (there are two) is 90 degrees.

The duration of the hybrid ports is 180 crank degrees (the piston starts opening the hybrid ports at 90 degrees before the BDC and closes them at 90 degrees after the BDC).

There are two intake ports.

Thanks
Manolis Pattakos

[Rodak]

You might want to run some propeller thrust calculations. I don't know your pitch or diameter numbers but here's a nice spreadsheet for looking at thrust/power. You might also want to look at yaw, pitch, and roll control......and stability.

Edited to add: But seriously, I don't think you have any control over yaw, pitch, or roll. You have no empennage to control pitch or yaw and no ailerons to control roll. Your c.g. is on the physical axis through the 'pilot' and there is no way for him/her to exert torque to roll the machine. Once the machine starts to rotate on its axis there is no mechanism to counteract the roll. In an airplane the horizontal stabilizer is actually in negative lift, forcing the tail down; this is because for stability the c.g. must be ahead of the center of aerodynamic lift otherwise the machine will just be unstable and auger in.

The elevator provides a torque to counteract the nose down moment caused by the torque generated by the c.g. being ahead of the c.p. You make no provision for this. Further, you remove any ability of the pilot to shift c.g. (see hang gliders) to provide torque to control the machine. Run some numbers in the spread sheet I provided to see what power is needed to fly this thing vertically from the ground, then calculate for conditions of horizontal flight. It's not pretty. The human body you seem to use for lift will be hanging at an angle that is in stalled flight; kite lift will be the only upward component and the c.p. will be about in the center of the projected body area.

A good thought experiment for what you propose is to cut the wings off a Cessna 152, cut off the tail, attach some sort of hinged coupling aft of the cockpit with a tiny surface area, then try to fly the thing vertically, somehow roate to horizontal flight and continue to 200 mph; look at the propeller data. Good luck.

http://godolloairport.hu/calc/strc_eng/index.htm

[J.A.W.]

Included in this fairly recent conference on 2T technical matters is an interesting
presentation of the potential for existing Rotax 2T snowcraft engines - to meet
stringent Euro-emissions regulations - while powering a road-legal motorcycle.

https://drive.google.com/drive/folders/ ... 7R1OTJQRdm

Click on file 3_3 (its located 3rd column down, 2nd from left).

[manolis]

Hello Rodak.

It seems you did not yet read the DEVICE TECHNICAL REPORT for the Portable Flyer as filed in the GoFly / BOEING contest (https://www.pattakon.com/GoFly/DTR_1.pdf at https://www.pattakon.com/GoFly/index.html ) wherein the same thrust calculator is used:


Quote from the above DEVICE TECHNICAL REPORT:

FLYING AND CONTROL

Quiet take-off

Limiting the tip speed (of the 39’’ diameter propeller) at only 150m/sec (45% of 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 calculated (with the http://www.godolloairport.hu/calc/strc_eng/index.htm propeller thrust calculator) at ~75lb (~35Kp, 350N), while the power absorbed by each propeller is calculated at ~15bhp.
At the “quiet” take off, the total upwards thrust is 4*75lb=300lb (136Kp, 1360N); with a total weight of 250lb (114Kg, 1140N) this means ~0.3g upwards acceleration; the required power per engine is 2*15bhp=30bhp. 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.
. . .
Fast take-off (at emergency, or from distant / unpopulated areas etc)
With both engines running at 9,000rpm, the upwards acceleration at a “fast take off” is more than 1g (10m/sec^2); 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 without opening the parachutes.

End of quote.



Even if the actual thrust were only 50% of what the “thrust calculator” gives, the Portable Flyer would still be capable for a fast vertical take-off.


For the rest issues you mention (pitch, yaw and roll control, stability etc, etc), do read the above DEVICE TECHNICAL REPORT, then try to figure out how Yves Rossi,



and Zapata, Mayman, Browning:



control their JetPacks on the air, and then ask anything you can’t get.



For all:

Does anybody know what happened with the 125cc RCV (rotary cylinder valve, PGO Scooters of Taiwan)?

Thanks
Manolis Pattakos

[Rodak]

Yves Rossi is not taking off from the ground vertically. The pitch and diameter of a propeller determines its operating speed and thrust. Why do you think helicopters have such a large diameter rotor (hint: it's a wing)? I give up; you don't want input.

[manolis]

Hello Rodak.

You write:
“Yves Rossi is not taking off from the ground vertically. The pitch and diameter of a propeller determines its operating speed and thrust. Why do you think helicopters have such a large diameter rotor (hint: it's a wing)?”


Quote from https://newatlas.com/aircraft/jetman-yv ... d-takeoff/

Jetman Yves Rossy can now take off from the ground ... autonomously



…
Now, with four new, more powerful Jetcat P550 turbine engines on the wing, he's now got enough vertical lift to fly straight upwards at up to 180 km/h (112 mph) – see the video below – and has been working with a Swiss team to develop an autonomous, self-balancing vertical takeoff system…

End of quote.



Think how many times smaller “propellers” than the Portable Flyer are those used by Rossy.

Think also that the only means Rossy has to control his vertical take-off / landing (i.e. when his speed is insignificant) is some control-fins (ailerons?) at the bottom of his external turbines:



These control-fins were absent in the conventional (non able for vertical take-off /landing) Rossy’s Delta Wing JetPack because he was always moving at a high speed into the air, and was using his head / limbs as his only control means. And they were more than enough for controlling the flight.
Now, until he reaches a high enough speed (say, 60mph - 100km/h) he needs control fins for the control of yaw, pitch and roll.


Now think that the pilot of the Portable Flyer is permanently (from before the taking off until the landing) into the high speed downwash from the propellers and can use his head / limbs for the pitch / yaw / roll control and for stability.

If it is still not clear, let me know to further explain.


You also write:
“I give up; you don't want input.”

I want input.

Thanks
Manolis Pattakos

[Rodak]

The blade tips would go supersonic at about 6100 rpm and require about 130 h.p.