Twisted Tooth Belt for the engagement of counter-rotating shafts

Hello Biglegueslider.

You write:
"Manolis- Quit acting like a lawyer.
It is impossible for a belt span that has close to zero structural buckling capability to transmit force in compression. In reality, in order for what you claim to happen to occur would require the preload tension in the belt to exceed any cyclic force variations produced during operation. In your case this would mean the preload in the belt span would need to be more than 100% of the max tension force the belt span experiences during operation. It also means that one span of the belt will be subjected to at least 200% of the max operating loads.
This is only possible if the belt operating loads are fairly modest."

You are right in that "a belt never transmits force in compression".

The capacity of the tooth belt of the PatATi Opposed Piston engine must exceed the resulting torque difference at the two crankshaft.

But note that the PatATi OP engine has a common combustion chamber giving the same instant pressure on the two piston crowns and that the zero phase difference between the two crankshafts gives the same eccentricity (normal distance of the center of the crankshaft from the line connecting the small end center with the big end center of its connecting rod) at the two sides of the engine.

The torque on each crankshaft is the product of the above "instant pressure", of the above "eccentricity", of the piston area and of the "1/cos(f)", wherein f is the leaning angle of the connecting rod from the the cylinder axis.

You need a substantial difference between the two eccentricities (i.e. a substantial phase difference between the two crankshafts) in order to have some significant torque difference to load the timing belt.

The timing belt needs to be capable to take this torque difference.

So, the PatBelt of the PatATi Opposed Piston is not dealing with the torque of, or with the power provided by, the engine, but only with the torque difference provided to the two crankshafts. As long as the belt keeps the two crankshafts in phase (or near in phase) the torque difference is several times (say a few dozens) smaller.

Compare the case with the loading of the tooth belt of the BMW F800S/ST wherein the complete amount of the torque (and power) is transmitted through the loaded span of the belt.

Thanks
Manolis Pattakos

Edited by manolis, 18 November 2014 - 07:03.

Hello Kelpiecross.

Here is the human powered helicopter



that won the US250,000$ Sikorsky Prize in 2013.

Quote from the Internet:

The rules of the American Helicopter Society Igor I. Sikorsky Human Powered Helicopter Challenge, established in 1980, specify that the craft must fly for 60 seconds, must rise to an altitude of at least 3 meters (about 10 feet), and must remain within a horizontal area no bigger than 10 meters by 10 meters (33 feet by 33 feet). The actual flight, completed at an indoor soccer stadium near Toronto, lasted 64 seconds and reached a maximum altitude of 3.3 meters.

End of quote.


Even with a small amount of power you can hover.

The power consumed depends on the size and design of the propellers.

Some friends manufacture paragliders.
They also make propellers.
The typical customer asks for the static thrust of the propeller (which is easily measured / confirmed) and forgets the rest necessary characteristics a good propeller needs to have.
A propeller providing a static thrust of 50Kp (110lb) is regarded, by the typical customer, better than another providing a static thrust of only 40Kp (88lb). But the first one may stall (actually become a brake) at 40Km/h (25mph), while the second can go on above 50Km/h (32mph). To get the difference, just imagine the case you have an opposite wind of 40Km/h (25mph) towards the open sea.

In a Portable Flyer you need propellers that are capable to provide more static thrust than the total weight of the structure (including the pilot and the fuel), but also capable to operate efficiently at the speed the Portable Flyer is to travel.

For instance, if the Portable Flyer is to be used for small distances and heavy loads (say as an air-ambulance in cities), you need, among others, small pitch propellers. With the same engine they can lift (like a crane) more weight. But you cannot go too fast with them.

For instance, if the Portable Flyer is to be used for high-speed travels (say 200mph), the pitch of the propellers needs to be big. The problem is that you need a lot of power from the engine at take-off.

Variable pitch propellers can also be used.
Or you could have a spare set of propellers with you (they are replaced easily).

I hope it is clearer now.

Thanks
Manolis Pattakos

Edited by manolis, 18 November 2014 - 05:31.

Are you saying that the rotor diameter is much greater than 1m?

The rotor size hasn't been established yet AFAIK, I'm just saying it isn't restricted by the distance between cranks.

Hello.

Regarding the overlapping of the propellers.

The OPRE Portable Flyer with the unconventional wide-Vee propellers allows a substantially smaller shaft-distance than the propellers radius.



With only 240mm crankshaft axis to crankshaft axis distance of the above OPRE engine, you can use 1m diameter wide-Vee propellers.


The PatATi Portable Flyer uses conventional propellers. The crankshaft axis to crankshaft axis distance must be a little bigger than the propellers radius.



In the PatATi Portable Flyer the crankshaft axis to crankshaft axis distance is 540 mm with the propellers having 500mm radius (1m diameter).


Contra-rotating (coaxial / oppositely rotating) propellers were used in some airplanes:

.

Contra-rotating propellers are used in several helicopters:



Counter-rotating "overlapping" propellers are used in the Chinook:



Counter-rotating at an angle (and overlapping) propellers are used in the Kaman helicopters:



In the last two cases (Chinook and Kaman) the progressive sweeping of the rotor wings is regarded as a significant advantage (quieter and more efficient operation, vibration reduction).

Thanks
Manolis Pattakos

For normal propeller designs, thrust is maximum at zero speed (static thrust). Efficiency on the other hand goes to zero at zero speed because the output power is thrust x forward speed and efficiency is P out/ P in.
 
In reality the propeller is still doing useful work at zero airspeed its just that the work-done is on the air, not the airplane. There are formulae for calculating this. This link might help.
 
http://www.jefflewis...o_prop_eff.html

You are right - I should have remembered this from the similar discussion about jet thrust a while back.

Re overlapping props, yes, you get a net advantage over a single prop, but you do get a reduction in efficiency and figure of merit. Basically the most efficient prop is a single blade (don't laugh it has been done), as you add more blades the efficincy drops (but the thrust increases) and then when you overlap counter rotating blades the same trend continues.

 

OK, I found my mythbusters jet pack (it a twin ducted fan) calcs, they are not a pot of gold. I have however found a pot of gold that gives more insight into the Figure of Merit, or CF and i'll make a worksheet on this tonight.

 

https://www.mediafir...vxadsdpme6g.jpg

 

Edited by Greg Locock, 18 November 2014 - 21:54.

http://personal.osi....esisz/strc_eng/
Have fun.
 
I used:
 
Diameter = 40"
Pitch = 15"
Type = Standard propeller
CF = 1
Number of Blades = 2
RPM = 4500
Air Temp = 86 F
 
Results.
Static Thrust = 62 kg
Engine power = 24 hp
Flying speed = 64 mph.
 
Multiply by two where appropriate for Manolis twin-rotor machine.

It is interesting to note that by putting typical small helicopter figures into this calculator (22ft rotor diam./314rpm) for about the same power as above the lift increases by about a factor of about 10 - so it is not surprising that the helicopter-type layout is preferred over the Manolis-type arrangement.

I am not sure that this calculator program is accurate when using extreme diam. figures - but it is probably not too far out I suspect.

I suspect Manny's all-up weight of 220kg is also very optimistic. I weigh that much alone - so it wouldn't lift me. I think he gives his pilot weight as 62kg (can't find it right now) - how many people weigh as little as 62kg?

Edited by Kelpiecross, 19 November 2014 - 03:31.

Single blade propellers were very popular at one time for high speed competition model planes.

Hello Kelpiecross.

The weight of the rider (or pilot) is taken 75Kp (164lb), the weight of the PatATi Portable Flyer together with the fuel is less than 25Kp (55lb).


The main advantage of a big propeller is that it needs substantially less power in order to create a specific lift.
The main disadvantage of a big propeller (and of the helicopters) is the high-speed horizontal flight.

If the Portable Flyer is to be used as a serious transportation means, besides being able to take-off vertically at full load (and to land vertically at full load, too), it also must be able to fly at high speeds and high mileage (i.e. fuel efficiently).

At take-off the engine of the Portable Flyer operates at heavy load (and the propellers at mild efficiency), i.e. it works like a helicopter having relatively small propellers. But during the rest flight (i.e. during most of the time, say during the 99% of the flight) the engine and the propellers operate like those of an airplane.

The evolution from the Chinook to the Osprey shows the differences.

The second focuses on the horizontal flight at high speeds, keeping the ability for vertical take-off and landing. Compare the fuel efficiency, the top speed and the range of the Chinook with those of the Osprey.

Chinook (Boeing CH-47):
a pair of counter-rotating propellers of 18.3m diameter each,
a pair of engines providing 4,733 bhp each,
a maximum take-off weight of 22,680Kp,
a range of 741Km,
a maximum speed of 315Km/h.

Osprey (Bell Boeing V22):
a pair of counter-rotating propellers of 11.6m diameter each,
a pair of engines providing 6,150 bhp each,
a maximum take-off weight of 27,400Kp,
a range of 1,627Km,
a maximum speed of 509Km/h.

More than double range, almost double maximum speed, much smaller propellers and heavier "propeller disk loading" for the Osprey:



By the way, look how much the flaps are rotated to aloow the downwards moving air to flow free.

The PatATi Portable Flyer:



is a scaled-down version (the minimum possible?) of the Osprey. The focus – as in the Osprey - is in the horizontal flight.

Thanks
Manolis Pattakos

Edited by manolis, 19 November 2014 - 05:00.

Hello Greg Locock

In the calculations of the efficiency take under account the need for a propeller at the backside of the helicopter to react to the rotation of the horizontal main propeller.

Kaman design (two big intermeshing propellers at a small angle) claims as main advantages the absence of the back propeller of the conventional helicopters (and of the power the back propeller consumes).
They also claim quieter / vibration-free operation as compared to contra-rotating coaxial main propellers, due to the progressive overlapping of the rotor wings of the two propellers.

In the PatATi Portable Flyer things are better because there is no overlapping of the rotor wings, at all.

Another advantage claimed by the contra-rotating / counter-rotating etc propellers is that they improve the over-all flow of the air. Zimmerman made a lot of work with his Flying Pancake:



wherein the direction of rotation of the counter-rotating propellers is significant.

Thanks
Manolis Pattakos

Less than 55lb? - surely not (Shirley Knott). I would have thought the two propellers alone would weigh about half that?

I suspect Manny's all-up weight of 220kg is also very optimistic. I weigh that much alone 

OMG!

 

KC - please see a health specialist ASAP!

So, the PatBelt of the PatATi Opposed Piston is not dealing with the torque of, or with the power provided by, the engine, but only with the torque difference provided to the two crankshafts. As long as the belt keeps the two crankshafts in phase (or near in phase) the torque difference is several times (say a few dozens) smaller.

Compare the case with the loading of the tooth belt of the BMW F800S/ST wherein the complete amount of the torque (and power) is transmitted through the loaded span of the belt.

Thanks
Manolis Pattakos

Looking at the arrangement of your design, one obvious thing is that the two rotors are 90deg out of phase, unlike the two crankshafts. Since the load on each crankshaft is produced by the rotor attached to it, the crankshaft load will vary during each rotation as the rotor lift/drag changes. In forward flight, when the advancing side of the rotor blade is normal to the airflow it will produce more lift and create more load at its crankshaft than the opposing blade that is parallel to the airflow. This will result in a large variation in the instantaneous torque reaction at each crankshaft end. If the opposing crankshafts are exactly phased, that would mean the two rotors are 90deg out of phase with the crankshafts. If you were to overlay torque curves of the rotors and crankshafts you'd probably see there is a fairly significant amount of torque reversal in the belt drive over each cycle.

Good point.

 

The "advancing" blade does have a "retreating" blade which will suffer less drag, connected to the same shaft. Nonetheless I agree there are likely to be "out of phase" aerodynamic torque loads on the two shafts. 

Edited by gruntguru, 19 November 2014 - 07:28.

Manolis - quick questions

 

weight of the flyer

weight of the pilot

 

I think you said a total of 1oo kg for them.

 

diameter of the rotor

axis to axis distance of the rotors

rpm at max power of engine

max power of engine

chord of rotor

 

I think that is all I need.

 

http://soliton.ae.ga...g2008/Part1.ppt 

 

is the pot of gold I alluded to, it includes a lot of theory, from the simple equations to blade elment theory

OMG!
 
KC - please see a health specialist ASAP!

Oh dear - slight mistake - I mean 220lb/100kg.

Hello Biglegueslider and thanks for your post.

You write:
"Looking at the arrangement of your design, one obvious thing is that the two rotors are 90deg out of phase, unlike the two crankshafts. Since the load on each crankshaft is produced by the rotor attached to it, the crankshaft load will vary during each rotation as the rotor lift/drag changes. In forward flight, when the advancing side of the rotor blade is normal to the airflow it will produce more lift and create more load at its crankshaft than the opposing blade that is parallel to the airflow. This will result in a large variation in the instantaneous torque reaction at each crankshaft end. If the opposing crankshafts are exactly phased, that would mean the two rotors are 90deg out of phase with the crankshafts. If you were to overlay torque curves of the rotors and crankshafts you'd probably see there is a fairly significant amount of torque reversal in the belt drive over each cycle."

This is a critical problem for the helicopters but not for the Portable Flyer.

Take the case of a helicopter with a main rotor having two blades.
At high speed, the lift force from the main rotor varies substantially – during a rotation of the main rotor – both, in size and in eccentricity from the long axis of the helicopter.
When the main rotor is parallel to the long axis, the lift force is at the long axis. After 90 degrees, i.e. with the main rotor normal to the long axis, the lift comes mainly from the one rotor wing (that one that moves forwards), and is at a big eccentricity from the long axis.
The low frequency a main rotor rotates (the rotation speed of a 10m diameter main rotor is substantially lower than 600rpm, that corresponds to a frequency of only 10Hz).
The higher the speed of the helicopter, the more severe the problem.

Back to the PatATi Portable Flyer.

After the take-off, the Portable Flyer turns progressively horizontal (just like the Osprey) and after some speed it flies as horizontal as an airplane.

Take a look at the wingsuiters:



With the PatATi Portable Flyer secured on their shoulders, they will continue the horizontal flight for as long as fuel is in the fuel tank.

At high speeds the axes of the two propellers of the Portable Flyer are parallel to the direction of motion (to the speed vector); this means an actually unloaded synchronizing mechanism.

Worth to mention:

At low speeds a wingsuiter having the Portable Flyer on his shoulders, needs to open his hands and legs in order to maximize the surface providing aerodynamic lift, while at higher speeds (and near the maximum speed) he must retract hands and legs to minimize the frontal area and the aerodynamic resistance (with his hands / legs open, the aerodynamic lift at high speeds is more than what is necessary to keep the flight horizontal).

What I see, is that another significant problem of the conventional helicopter is not present in the case of the Portable Flyer.

If you see the Portable Flyer as a scaled-down Osprey (i.e. as an airplane having the ability to take-of and to land vertically), or as a powered wingsuiter things get simpler.


On the other hand, what is your estimation of the loading of the synchronizing tooth belt of the PatATi OP engine in case it flies at high speed with the propeller disks horizontal, or substantially horizontal?

Thanks
Manolis Pattakos

Hello Greg Locock.

Weight of the flyer : 25Kp (55lb) with the fuel
Weight of the pilot : 75Kp (165lb)
Total mass at take off: 100Kg (220lb) .

Diameter of the rotor : 1m (39.4’’), two blades per rotor, two counter-rotating meshed (like the spur gears) rotors. Note: the rotor blades are not overlapping.

Axis to axis distance of the rotors : 544mm

Rpm at max power of engine : 5,000 rpm

Max power of engine : 70bhp at 5,000 rpm

Chord of rotor : 3’’ (7.62mm) the one set, 3.5’’ (8.9mm) the spare set.


I think you also need the pitch: use 25’’ for local flights and 34’’ for long travels at high speed.

I think you also need the power at 4,000rpm: 65 bhp.

Thanks
Manolis Pattakos

Edited by manolis, 19 November 2014 - 12:55.

Thanks, I'll do the quick stuff tonight, which just works on the power loading etc, the blade element design approach is new to me and may or may not work out. 

Edited by Greg Locock, 20 November 2014 - 09:16.

Hello Greg Locock and thanks for the calculations.

Is the 33.6HP the total power of the engine, or the power required by each propeller?

What is the pitch?

What is the aspect ratio?

At what revs (or tip velocity)?


The photos published are real and try to give the relative sizes.

I use neither octave, nor matlab

Thanks
Manolis Pattakos

No, that's based on momentum disk theory, it assumes a perfect rotor system.

 

 

When i get the next bit working I'll come up with a blade design.

Tip velocity is almost M1 at 6000 rpm

 

gulp, momentum theory ignores little details like that, the real world does not. 

 

that power is total for the two rotors, it assumes a perfect rotor design.

Edited by Greg Locock, 21 November 2014 - 01:54.

OK, using a NACA 0012 airfoil I get 101.5 kgf of thrust at 5300 rpm, 35 shp, for the 25" pitch 3" chord, with a tip speed of 0.79M, ie you will get compressibility effects, all of which are bad.

 

With the bigger prop I get 4150 rpm, 101.6 kgf thrust 33 shp, and a tip speed of 0.62M

 

Power wise you are OK, but I think the tip speed is too high, and you need to overrev the small prop. I haven't knocked anything off for transmission efficiency, or the effect of the overlapping rotors or compressibility..If we guess a 30% degradation, then you'd need 5000 rpm and 58 hp, with the big prop, and the small one only generates 91 kgf at 50 hp at 6000 rpm. 

 

This uses blade element theory, and I have not checked it. The reason it is so similar to the other result is that I guessed the CF right in the momentum theory calculation (and it was a guess). I'll see if I can check these results another way.

Maybe the Flyer could make a good alternative to a parachute?

OK, using a NACA 0012 airfoil I get 101.5 kgf of thrust at 5300 rpm, 35 shp, for the 25" pitch 3" chord, with a tip speed of 0.79M, ie you will get compressibility effects, all of which are bad.

 

With the bigger prop I get 4150 rpm, 101.6 kgf thrust 33 shp, and a tip speed of 0.62M

 

Power wise you are OK, but I think the tip speed is too high, and you need to overrev the small prop. I haven't knocked anything off for transmission efficiency, or the effect of the overlapping rotors or compressibility..If we guess a 30% degradation, then you'd need 5000 rpm and 58 hp, with the big prop, and the small one only generates 91 kgf at 50 hp at 6000 rpm. 

 

This uses blade element theory, and I have not checked it. The reason it is so similar to the other result is that I guessed the CF right in the momentum theory calculation (and it was a guess). I'll see if I can check these results another way.

 

So, marginal thrust to lift operator's weight at take-off. Or a slight deficit.

 

What is the tip speed for forward flight at around 250km/h?

Are you sure you want to fly this device yourself?  One reason conventional helicopter designs are stable in hover and forward flight is because the rotor blades are actively controlled for collective and cyclic. Plus they employ sophisticated damping devices to control lead/lag vibratiions. With your opposing rotors being 90deg out of phase plus the downwash effect as the inboard rotor span passes over the engine cylinder, you may find you have a 4P lateral oscillation of lift in hover.

The overlap may cause some lift oscillation but otherwise (without overlap) the lift vector in hover is a steady vertical force along the shaft axis.

What is the tip speed for forward flight at around 250km/h?

Vector sum of tangential speed and forward speed (mutually perpendicular) so (V1^2 + V2^2) ^ 0.5

eg (M0.6^2 + M0.2^2) ^ 0.5 = M0.63

Hello Greg Locock.

Let me help / clarify a couple of things:


Regarding the transmission efficiency:

There is no transmission at all.
Each crankshaft drives directly its propeller.
Because of the “perfect” symmetry of the structure, the synchronizing mechanism passes no loads (OK: no significant loads).


Regarding the overlapping:

The overlapping of the helicopters with the contra rotating main rotors (like the Ka-32 shown in the post #102) is complete.
Besides, at specific angles, the rotor-wings of the top main-rotor are directly above the rotor-wings of the lower main-rotor, making necessary a significant distance between the two main-rotors (noise, vibrations, efficiency).

In the Kaman helicopters things are better: the overlapping is partial, the rotor-wings of the one main-rotors pass progressively over the rotor wings of the other main-rotor.

In the Chinook helicopter the propellers are intermeshed. While the main-propeller-disks overlap each other, there is no overlapping between the rotor-wings.

The propellers of the PatATi Portable Flyer cooperate in a similar way:



While the propeller-disks are partially overlapped, the blades are away from overlapping.



According the previous, the 30% degradation for the transmission efficiency and for the overlapping of the rotors seems too much.

Even though, the required power for the 3.5’’ NACA 0012 propeller, according your calculations, becomes 33*1.3=43bhp.

To make this power at 4,150rpm, you need an engine providing a torque of 75m*Nt (53lb*ft).
An 800cc (49cu.in.) two-stroke engine makes much more.
With the additional power, the Portable Flyer takes-off and accelerates vertically (or lifts a substantially heavier load).

Thanks
Manolis Pattakos

Hello Imaginesix.

You write:
“Maybe the Flyer could make a good alternative to a parachute?”

Or a parachute that lifts you up, and enables you to travel at high speeds over long distances.




Hello Wuzak.

You write:
“So, marginal thrust to lift operator's weight at take-off. Or a slight deficit.”

With the 3.5’’ wide propellers, the calculations of Greg Locock show the opposite.

With the engine operating at only 4,150 rpm, the lift equals to the load.
At these revs, the required torque by the engine is only 75m*Nt.
But the engine can provide much more; with the surplus of torque the propellers accelerate at higher revs (say at 5,000 rpm) until the required by the propellers torque to get equal to the provided by the engine torque.
There (at 5,000rpm) the total take-off weight the Portable Flyer can lift is about 150Kp / 330lb (alternatively: with only 100Kp / 220lb total tajke-off weight, the Portable Flyer accelerates upwards with half of the gravitational acceleration).

Thanks
Manolis Pattakos

Hello Biglegueslider.

You write:
"Are you sure you want to fly this device yourself? One reason conventional helicopter designs are stable in hover and forward flight is because the rotor blades are actively controlled for collective and cyclic. Plus they employ sophisticated damping devices to control lead/lag vibratiions."

As you write, the conventional helicopters need all these controls / dampers / techniques in order to get stable in hover and forwards flight. Wouldn't it be great if you could eliminate all them?


You also write:
"With your opposing rotors being 90deg out of phase plus the downwash effect as the inboard rotor span passes over the engine cylinder, you may find you have a 4P lateral oscillation of lift in hover."

In the photo bellow it is the Chinook :





while in the above photo it is the PatATi Portable Flyer.

Compare them.

A blade of the left propeller of the PatATi Opposed Piston engine passes over the cylinder; after 90 degrees a blade of the right propeller passes over the cylinder of the PatATi; and so on,

Similarly, a blade of the rear rotor of the Chinook passes over the casing (which is like a long cylinder) of the helicopter, after 60 degrees a blade of the front rotor of the Chinook passes over the casing, and so on.

The counter-rotating rotors of the Chinook are at 60 degrees out of phase.

According your theory, their downwash effect as the inboard rotor span passes over the casing of the Chinook (combined with the only 225rpm the Chinook propellers rotate) would be a major problem.

Thanks
Manolis Pattakos

Yes I understand there are virtually no transmission losses. The discs of the rotors overlap, this causes additional losses, the rotors accelerate a cylinder of air, not just a bit close to the blade itself..

 

 

For cruising flight this design is marginal, eg at 160 kph 5000 rpm the larger prop only generates 16 kgf of thrust, whereas at 3:1 L/D it needs to generate 33. It would manage that at 145 kph.

 

So my conclusion is, yes, if the engine can generate 70 hp at 500 rpm, the larger prop will generate more than 100kgf thrust when hovering, and should give a cruising speed of 145 kph.

 

However, the tip speed is far too close to M1 and it is likely  that the flow will be locally supersonic, which degrades performance.

 

The good news is that i've checked the results a different way, and they seem to line up.

 

The NACA 0012 profile is not an especially good choice, its CL/alpha curve is only 2/3 of the theoretical 2pi/radian.

Health and Safety are going to love this

Hello Greg Locock.

A few remarks.


Tip speed:

At 5,000 rpm the 1m diameter propeller has (at hovering) a tip speed :

1m*pi*5,000/60 = 263m/sec = 942Km/h = M0.76,

which is not too close to sound velocity.

When the Portable Flyer moves horizontally at 145Km/h (with the propeller axes horizontal, too), the total tip speed is:

SquareRoot (942^2+145^2) = 953Km/h = M0.77

which is also not big.

With 34’’ pitch the speed limit at 5000rpm is some 250Km/h, which gives a tip speed:

SquareRoot (942^2+250^2) = 974Km/h = M0.79


Maximum Speed.

In order to lift at take-off, with the 3.5’’ wide / 25’’ pitch propellers, the 100Kp (220lb) of the total weight, the propellers must rotate at 4,150rpm absorbing only 43bhp.

Since the engine is capable for providing more power, a bigger pitch is better.

While the lift at 4,150rpm remains – more or less - the same, the propeller with the big pitch requires more power from the engine.
But the engine has more power to provide.
So, increasing the pitch can substantially increase the cruise speed.
The limitation is that the propellers / engine must be capable to provide 100 Kp (220lb) lift at some revs.

You are right: the NACA 0012 is not something special, yet it is something to start from (and it is thin, i.e. lightweight).

Thanks
Manolis Pattakos

You are right: the NACA 0012 is not something special, yet it is something to start from (and it is thin, i.e. lightweight).

Does this mean you are designing or building your own propellors?

I would. I only picked NACA 0012  because I found the data on it very easily. I agree the design needs more pitch.

 

Real helicopter blades can have twist along their length, and ideally, variable chord.

 

This is fun:-

 

http://www.flyingmag...istory-airfoils

 

and this is hard work:-

 

http://halfdome.arc....sman_AHSF02.pdf

 

I'll have a go at optimising the design I've got so far with the intent of lowering the rpm for 100 kgf thrust, which should give more headroom fro cruising,

 

I'm guessing I could use Bernouilli to find out whether the velocity locally is approaching m1, in practice it'll be bloody obvious even on a ground test, at some rpm you'll suddenly get an increase in white noise.

Edited by Greg Locock, 21 November 2014 - 22:51.

Hello Gruntguru.

You write: “Does this mean you are designing or building your own propellers?”

The propellers we make have an airfoil between NACA4412 and Clark-Y; i.e. nothing special.
They are made of 7050 Aluminum Alloy.
The first tests will be with them.

There is also the option to use propellers from the market; there are many manufacturers; the composite ones (carbon fibers etc) are more lightweight.


But the important in this project is neither the synchronization, nor the propellers; the PatATi engine is what counts:

How lightweight it gets,
how much vibration-free it is in practice,
how much efficient the compact combustion chamber will prove,
how good the asymmetric transfer and intake will work,
how necessary is a tuned exhaust (or any exhaust),
how much the specific lube consumption reduces, etc.

The last two seem to relate:
a tuned exhaust allows a part of the mixture to pass to the exhaust and then to return to the cylinder; imagine the oil droplets into the air-fuel mixture: their inertia traps them into the tuned exhaust (two phase flow: a liquid and a gas; the gas will rebound, the oil droplets will not); if the asymmetric intake and the asymmetric transfer do the job of the tuned exhaust, how much lubricant / pollution / smog is saved?


In order to avoid carburetors – and their weight / cost – we are going to use injection of the fuel-lubricant into the two crankcases. Through the four intake ports on the casing it will pass clean air. Controlling the opening area of the intake ports, the load is controlled.


With the PatATi Opposed Piston engine operating into a narrow rev and load range (say from 3,500 to 5,500 rpm, at medium to full load) things get simpler.

Thanks
Manolis Pattakos

Without holding you to ransom, any idea when you'll be firing this up?  All my work suggests that you need more pitch, but you also need to twist the blade so it has more angle of attack at the centre than at the tip. In an ideal world you'd also reduce the chord from the centre to the tip.

 

I've found an article on rotor overlap, 

 

http://aero.umd.edu/...2_Griffiths.pdf

 

it is not a big deal for your design

I'm not sure if I missed it earlier, but how does a device that's fixed in place (as it seems to be from your photo) allow you to transition from vertical to horizontal flight, and vice versa - just from body movement?  And how do you ensure stability?

The deafened suicide candidate is wearing a wing suit, with an L/D of about 3.

Here's my prediction for your larger prop, with no twist. This uses NACA 0012 I have not been able to find good aero data for your foils at high subsonic Mach.

 

 

and here it is with 10 degrees of twist from root to tip

 

 

It is 'only' a couple of hundred rpm different, so your current prop design should work as a proof of concept.

 

Incidentally I have not compensated the BET design for blade overlap, whereas confusingly the power used in the  'Ideal results' do have an allowance for that which judging from the paper i posted earlier is pessimistic.

The deafened suicide candidate is wearing a wing suit, with an L/D of about 3.

 

Can a wing suit actually be used for horizontal flight?

 

I thought the glide ratio was 3 - as in 3 along and 1 down. 

 

This site http://www.apf.asn.a...es/default.aspx suggests a falling speed of between 40 and 70mph and a horizontal speed of ~100mph - a glide ratio of between 2.5:1 and 1.4:1. It seems the wing suit increases drag for the descent, rather than generating lift.

That was Manolis' number, i haven't had a look at that. So far as I'm aware glideslope and L/D are directly related.

The overlap may cause some lift oscillation but otherwise (without overlap) the lift vector in hover is a steady vertical force along the shaft axis.

The lift vector is the net of the lift produced by both rotors at any given instant, and each lift vector passes thru the rotor aerodynamic center of lift rather than the rotor axis of rotation. Due to factors like downwash effects when the blade passes over the engine, advancing/retreating airflow velocity differences over the blades due to forward flight, and effects of wake turbulence as the inboard blades intermesh, the combined rotor lift vector will never be a steady vertical force parallel to the mast axes. Even in steady hover the net instantaneous lift vector of your two fixed pitch un-phased rotors will translate and oscillate in 3 dimensions. The rotor lift  forces wil also be affected by the mass CG offset of the passenger (ie. Manolis).

Hello Greg Locock.

Thanks a lot for the link regarding “the Dual Rotor Interference and Ground Effect Study”.

Quote from that link:







The test results (Fig 7), the analysis and the formula A2, all agree in a 14% increase of the required power for the arrangement of the PatATi Portable Flyer (d=0.54, D=1) as compared to the case the two propellers are not overlapping.

With the transmission losses eliminated by the direct drive of the propellers, the overall losses due to overlap and to transmission get half of the initial estimation of 30%.

It is disappointing that while the dual-rotor systems seem superior at hovering near the ground:



the analysis does not calculate the required power in case of overlapping and of non-overlapping propellers.

The direction the two propellers rotate is also important (Zimmerman work), but the study does not deal with it, too.

Thanks
Manolis Pattakos

Edited by manolis, 23 November 2014 - 09:59.

Hello Roger Graham.

Quote from the post #65:

"Please take another look at the GoFast JetPack youtube video

https://m.youtube.co...h?v=E81KQ7u3-7s

and see how easily the hovering turns into horizontal flight, and vice versa.
Note the fully manual control (neither electronics, nor servomotors, nor programming, just manual control).


In the PatATi Portable Flyer:

two counter rotating crankshafts share the same combustion chamber keeping the basis perfectly rid of inertia vibrations and of combustion vibrations,

the basis (i.e. the rider / pilot) needs not to provide any reaction torque (not even at extreme changes of revs and load),

with the symmetric counter-rotating propellers (and crankshafts), the total "gyroscopic rigidity" is zero, i.e. the rider can "instantly" (as instantly as with the propellers stopped) vector the thrust to the desirable direction.

The above make "a true neutral propulsion unit": neither vibrations, nor reaction torque, nor gyroscopic rigidity; only a force that can "instantly" and effortlessly be vectored towards the desirable direction.

As neutral as the Peroxide JetPacks"

Thanks
Manolis Pattakos

Edited by manolis, 23 November 2014 - 10:16.

By my reading, Fig 7 shows that for d/D of 0.5, you will need 10%  more  power, and from the rest of the paper, it'll generate about the same thrust. so i'm going to call that a lineball.

Hello Roger Graham.

Quote from the post #65:

"Please take another look at the GoFast JetPack youtube video

https://m.youtube.co...h?v=E81KQ7u3-7s
 

 

Thanks and apologies, I completely missed one or two earlier posts.

 

The thrust from the jetpack is in free air behind the flyer.  Does the fact that the props in your design have to wash over the engine and the flyer (who will presumably be moving about a bit) adversely affect the thrust, stability etc?

Hello Wuzak.

Quote from wikipedia:

“On 25 October 2005, in Lathi Finland, Visa Parviainen jumped from a hot air baloon in a wingsuit with two small turbojet engines attached to his feet.
The engines provided approximately 160 N (16 kgf, 35 lbf) of thrust each and ran on JET A-1 fuel.
Parviainen achieved approximately 30 seconds of horizontal flight with no noticeable loss of altitude. “

Quote from Dropzone:

“Once Visa had adorned his birdman suit and rig on the ground, it was time to test the rocket boots. Each jet engine provides around 16kgs of thrust, and is primed with a mix of butane and propane. Once ignited, the engines rely on a steady supply of kerosene (JetA1) fuel. This fuel burns at around the rate of 0.5 litres per minute, on full power, for each jet engine. The combined thrust of both power plants was calculated to be enough to sustain level human flight in a wing suit for an average weight skydiver.

Once all the gear checks were made and rigorous safety procedures executed on the ground, it was time to inflate the hot air balloon for the ascent. The Balloon Bros provided a smooth and relaxing ride up to altitude over the beautiful vista of the humble town of Lahti in middle Finland.

The Balloon ascended over the unpopulated areas around the lakes and forests of rural Lahti, visa primed and started the rockets prior to exit. After warming up the engines in the cold surrounding atmosphere, it was time to make the attempt. The high pitch whine of the jet engines sounded surreal in the calm stillness of the hot air balloon. Tensions were high that this attempt would be a successful one. It was time to go, as the fuel was rapidly running out, Visa gave the all clear sign (a quick grin) at around 2300m (7000ft) before 'edging' off the platform into the first rocket-powered-human-flight attempt.
The exit was stable and on-heading, after attaining normal bird-man flight, Visa
requested full power from the engines, which responded smoothly in horizontal acceleration. After checking the altimeter several times, it was apparent that there was no appreciable loss in altitude for this period of time. Visa next changed his angle of attack by redirected the thrust and changing his body position to attain vertical climb. This caused a loss in horizontal speed, and stalled (the body?). Recovering from the stall was made easy because of the agility of the human body to change flight profile easily.

A few more attempts at this exercise yielded the same result. Pretty soon it became apparent that fuel consumption would soon terminate the level flight portion of the jump. Visa simply rode out the rest of the jump in level flight following the highway until the fuel ran out. Visa then continued in normal bird-man flight until deployment altitude. The deployment sequence was normal, and the landing was uneventful.

The jump has proven empirically that level human flight is possible and sustainable using the combination of jet engines and a bird-man suit. The strength required to control level flight was relatively easy, and controlling the direction of flight feels surprisingly natural. The duration of flight is simply a factor of the consumption of fuel of the engine(s) powering the flight.

Visa Parviainen has proven that with a little innovation, determination and courage it has been possible to realise the dream of uninhibited human flying.”

END OF QUOTE


With only 32 Kp (64lb) thrust force, Visa Parviainen was the first to achieve to fly horizontally for 30 second.

The PatATi Portable Flyer has to be capable to provide at least 100Kp (220lb) of thrust force, otherwise it cannot take-off.

It is not clear what was the horizontal speed of Visa Parviainen, but at 62 mph (100Km/h) a 32Kp (64lb) thrust force absorbs a power of 12 bhp while at 100mph (160Km/h) a 32Kp (64lb) thrust force absorbs a power of 19bhp.


Let me repeat an important sentence from above:
"Recovering from the stall was made easy because of the agility of the human body to change flight profile easily."

Thanks
Manolis Pattakos