2 stroke thread (with occasional F1 relevance!)

[uniflow]

Sort of a pointless discussion now, Ive been blocked it seems, one guy is right, everyone else is wrong.
Not even about twostroke design, thats long gone.
Good luck with your personal flyer manolis, I hope it doesn't end in tears for you. Ive said what I need to.

[NathanE]

It is like the cloths / laundry hanged from a rope to dry. The wind keeps them away from vertical. The strong wind can keep them almost horizontal.

No it's not. Hang a person by their shoulders on a clothes line, have a storm with 60 mph winds come through, and see how horizontal they get.... And let's not even think about the L/D ratio.

This has got me thinking. Rotor diameter looks to be c1m (very small). Can someone with a bigger brain than mine work out the mass flow required to generate say 1.2g vertical lift for a 120kg pilot/flyer combo and translate this into airspeed for the 1.2m2 column of downward moving air that will result from the 2 intermeshing rotors?

I bet it is significantly higher than 20m/s. I can't imagine it will be much fun being in the middle of it. Given that probably 20% of this flow will immediately "hit" the pilot that will make the flow rate above an underestimate I guess.

[manolis]

Hello all.

Air hitting the pilot


The average speed of the wing-suiters is around 100mph (160Km/h, i.e. 45m/sec).

The speed of the air that "hits" the wind-dancer (video at page 238) is over 200Km/h (55m/sec), and she seems to enjoy it.

Mayman claims a top speed of 200mph (320Km/h, i.e. 90m/sec).

Yves Rossy does fly at 200mph (90m/sec):

• His body is free in the air; 90m/sec air "hits" his body.
  
  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"

See at 3:23 his hands, head and legs "steering" his Delta Wing JetPack.

Despite the high speed air that "hits" his body, Rossy feels very well and enjoys his flight.
Unfortunately, in less than 10 minutes he runs out of fuel, and the joy ends; then he has to use his parachute, again, “risking” one more landing.

Thanks
Manolis Pattakos

[NathanE]

It is like the cloths / laundry hanged from a rope to dry. The wind keeps them away from vertical. The strong wind can keep them almost horizontal.

No it's not. Hang a person by their shoulders on a clothes line, have a storm with 60 mph winds come through, and see how horizontal they get.... And let's not even think about the L/D ratio.

This has got me thinking. Rotor diameter looks to be c1m (very small). Can someone with a bigger brain than mine work out the mass flow required to generate say 1.2g vertical lift for a 120kg pilot/flyer combo and translate this into airspeed for the 1.2m2 column of downward moving air that will result from the 2 intermeshing rotors?

I bet it is significantly higher than 20m/s. I can't imagine it will be much fun being in the middle of it. Given that probably 20% of this flow will immediately "hit" the pilot that will make the flow rate above an underestimate I guess.

Ok so this will embarrassingly show how far away I am from the days when, 30 years ago I got a decent degree in aero engineering and now I can't even do high school maths! I'm going to try to remember how to work this out from first principles. I will probably be wrong in how I calculate this but it will give others something to correct.

Upthrust needs to be c1500 N, or 1500 kgm/s2.

Density of air is 1.225 kg/m3. I'm not considering compressibility.

I'm thinking that in order to get the units balanced I need to multiply kg/s of mass flow by m/s of flow velocity. This is density x area x velocity2. (Kg/m3 * m2 * m2/s2 = kgm/s2).

So here V2 = 1500/(1.225* 1.2) and V = 32 m/s or 72mph.

This intuitively feels low, but I guess thinking in "reverse" about skydive terminal velocity of 120mph maybe not. I guess the airflow is not columnar- more toroidal and if only 50% of the radius of the rotors gives true downdraft then this would be out by a factor of 4 so we could be talking up to c300mph which is going to be uncomfortable.

What have I got wrong?

[J.A.W.]

Sort of a pointless discussion now, Ive been blocked it seems, one guy is right, everyone else is wrong.
Not even about twostroke design, thats long gone.
Good luck with your personal flyer manolis, I hope it doesn't end in tears for you. Ive said what I need to.

Uniflow, do please continue to feel welcome to contribute here on 2-stroke matters,
- particularly including your own work - which is by any regard, very worthwhile.

Manolis can draw the flak, as you fly under the radar, surely?

[Tommy Cookers]

..... I guess the airflow is not columnar- more toroidal and if only 50% of the radius of the rotors gives true downdraft then this would be out by a factor of 4 so we could be talking up to c300mph which is going to be uncomfortable.
What have I got wrong?

fwiw I think that ......

you have the right concept (that the behaviour is equivalent to a column smaller than the prop disc diameter)
there's a term for the ('contraction' ?) factor driving the underlying velocity distribution of the jet
ie based on this factor an equivalent of your illustrative 50% might be ... 70 or 80% or something ?

manolis calculated a velocity - assuming a jet of uniform velocity ??

propeller maps (showing thrust over a full range of airspeeds etc ) seem as rare as unicorns
static thrust is low and thrust builds up during takeoff - this is poorly accounted
after 150 years competing propeller theories are still out there (some suggest that static thrust is infinite)

[manolis]

Hello NathanE

Here is an approach for the speed of the air that “hits” the pilot of the Portable Flyer at hovering.

Quote from NASA “Propeller Thrust” at https://www.grc.nasa.gov/WWW/K-12/airplane/propth.html :

• 
  
  Simple Momentum Theory
  Turning to the math, the thrust F generated by the propeller disk is equal to the pressure jump delta p times the propeller disk area A:
  F = delta p * A
  
  Etc, etc . . . (the link has the complete analysis)
  
  Substituting the values given by Bernoulli's equation into the thrust equation, we obtain
  F = .5 * r * A * [Ve ^2 - V0 ^2]

End of quote.


At hovering V0=0 (zero vehicle velocity), so the above formula becomes:

F = .5 * r * A * Ve ^2,
i.e. Ve=(2*F/ (r*A))^(1/2)

With your F=1,500Nt, r=1.225Kg/m3 and A=1.2m2,
the Ve (i.e. the speed of the air that "hits" the pilot of the Portable Flyer) is calculated at 45m/sec (100mph, 160Km/h).



Hello Tommy Cookers

NASA at https://www.pattakon.com/Fly_files/NASA ... Thrust.pdf gives a "formula" / relation for the Static Thrust of airplane propellers.



For instance, a propeller having 42” (3.5ft) diameter, 30” pitch (the θ about 17 degrees at 0.75R, giving a K coefficient around 60,000), revving at 3,000rpm absorbing 30 bhp, gives a static thrust of:

T = 60,000 * 30 (bhp) / (3,000 (rpm) *3.5 (ft))=170lb = 780Nt (=78Kgf).

With smaller (into some limits) pitch, the power absorbed (same rpm of the propeller) decreases, but the coefficient K increases, giving, say, a similar Static Thrust.

Another reading of the above is: Keeping the propeller rpm constant, by varying the pitch what you can do is to reduce or to increase the power required for the "same" Static Thrust, but the change of the Static Thrust due to the variation of the pitch is small.

This is the reasoning behind the PatPitch:



At hovering ("medium" engine (and propeller) revs), the PatPitch keeps the propellers at a lower pitch; at high cruise speeds ("high" engine (and propeller) revs), the PatPitch keeps (with the heavier centrifugal forces acting on the blades) the propellers at a larger pitch, allowing substantially higher top speed.



Hello J.A.W.

I can't get what you mean by "Manolis can draw the flak, as you fly under the radar, surely?"

Thanks
Manolis Pattakos

[manolis]

Hello all.


Air speed and human body leaning (from previous posts):

This photo shows Richard Hammond in a wind tunnel:



In the following photo, Browning is wearing, between his legs, of part of a "wind-suit".



The above two photos (actually slides from videos) are not fake.


If the following photo and video (from 00:37 to 00:45) are not fake, they are impressive:






Does anybody have some better photos or videos showing the relation between the speed of the hitting air and the leaning of a human body?

Thanks
Manolis Pattakos

[Rodak]

Ok so this will embarrassingly show how far away I am from the days when, 30 years ago.....

You're not alone. I started looking at this using the helicopter lift equation (here's a good site on helicopter flight): https://www.intechopen.com/books/flight ... ht-physics

L = 1/2pv²ACL (sorry, couldn't find the ASCII for rho) where p = air density, v = velocity, A = rotor area, and CL = coefficient of lift. It's unclear to me where velocity is measured; at the tip, at the middle of the rotor, rpm? CL has to be determined experimentally but can be estimated.

[nzjrs]

It's seems all of us here who are blocked here by manolis can have a nice conversation.

[Rodak]

I didn't see manolis posted the same equation....

nz, not sure what you mean about blocking, I'm seeing everything.....

[nzjrs]

I didn't see manolis posted the same equation....

nz, not sure what you mean about blocking, I'm seeing everything.....

Like uniflow said, by way of manolis never answering our questions, I assume we are blocked/ignored by manolis (so he doesn't see our posts).

Was a bit of a joke tbh

[uniflow]

[/quote]
Uniflow, do please continue to feel welcome to contribute here on 2-stroke matters,
- particularly including your own work - which is by any regard, very worthwhile.

Manolis can draw the flak, as you fly under the radar, surely?
[/quote]

Happy to, thanks for the vote of confidance. One issue I do have is I must be careful on what I disclose, manolis is watching and might run off and patent my ideas. Thats his end game after all, make money out of something he has secured via patent for himself. Thats life I guess.

I still havent organised a photo server, I must do that.
By the way JAW, how is that LC , 750 Kawasaki hybrid going?

[Rodak]

Manolis can draw the flak, as you fly under the radar, surely?

I did work on the B-2 Stealth bomber, so I just evade the radar. Funny how that flak statement paints pictures of WW2.....

[gruntguru]

One issue I do have is I must be careful on what I disclose, manolis is watching and might run off and patent my ideas.

Really? I haven't seen anything that might suggest that behaviour.

Of course disclosure on a public internet forum exposes you to the full spectrum of personality types. If you post information that could be misused for profit - it will happen.

As for patents - once you make an idea public - it can't be patented - by you or anyone else.