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Twisted Tooth Belt for the engagement of counter-rotating shafts


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#151 manolis

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Posted 23 November 2014 - 12:05

Hello Greg Lockock

You write:
“Without holding you to ransom, any idea when you'll be firing this up?”
Soon I hope.

It was like:

PatATi_starting.jpg

a few weeks ago.

It is a new engine.
I hope all the innovations included will collaborate as anticipated, designed and machined.

Thanks
Manolis Pattakos

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#152 manolis

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Posted 23 November 2014 - 12:28

Hello Biglegueslider.

You write:
"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)."


The propellers of the Chinook rotate at only 225rpm.
Chinook is regarded as the state-of-the-art in tandem rotor helicopters.
The “issue” with the unsteady vertical force (combined with the low frequency) would generate intolerable problems (vibrations, noise, instability etc).

In comparison, the propellers of the PatATi Portable Flyer rotate between 4,000 and 5,000 rpm.
Even if there were some translation / oscillation of the total thrust force, the frequency is such that neither the pilot, nor the Flyer can "feel" it.

Thanks
Manolis Pattakos

#153 manolis

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Posted 23 November 2014 - 12:44

Hello Roger Graham

You write:
“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?”
The props have to wash over the engine and the flyer just like the props of a helicopter wash over the turbine and the fuselage.

A pilot / rider being into the air stream can affect (interact) with it by displacing legs and hands.
Actually the pilot exploits the air-stream to control the Flyer.
The human body is very agile to take advantage of the air stream.

Thanks
Manolis Pattakos

#154 Greg Locock

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Posted 23 November 2014 - 22:14

Here's a plot of power and rpm vs mph for 100 kgf and 33 kgf thrust. The prop has too little pitch on it in all conditions, considering the power curve of the engine. I estimate a top speed of 80-90 mph. The upper line in each case refers to 100 kgf, the lower to 33 kgf.Going vertically up at 60 mph is pretty quick, but of course that assumes no drag.
Image posted in next post

Edited by Greg Locock, 23 November 2014 - 22:20.


#155 Greg Locock

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Posted 23 November 2014 - 22:16

rd0wcsat50bgp0c6g.jpg


Edited by Greg Locock, 23 November 2014 - 22:18.


#156 manolis

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Posted 24 November 2014 - 05:09

Hello Greg Locock.

So we need more pitch.


If the pitch gets too high (say 44’’) then the Portable Flyer loses its ability to take-off because the required power – in order the propellers to provide the necessary 100Kp (220lb) of thrust – exceeds the power the engine provides (with the revs remaining in the useful range of the propellers).


If the propeller pitch gets, say, 33’’ then the Portable Flyer can still take-off (in this case the engine, at take-off, will operate near to, or a little higher than, 5,000rpm and full throttle). At high speeds things improve. A maximum speed of 250Km/h (156mph) can be achieved.
Judging from Visa Parviainen first rocket-wingsuit horizontal flight (post150, 32Kp thrust force), soon after the take-off – wherein a lot of power is required – the pilot can turn to horizontal flight wherein he can reduce the engine revs and the throttle a lot, because keeping the flight horizontal requires no more than, say, 40Kp (88lb) of thrust.


While a constant pitch propeller for a Portable Flyer resembles with a single-transmission-ratio gearbox for a car, there are significant differences.
Just like an airplane, a Portable Flyer can, soon after the take-off, travel with the optimum speed / engine revs / engine load to its destination (this can cover 99% of the total time) because it is free from all the limitations existing when a car moves on the roads (start-stop, accelerations, uphill, speed limits, traffic lights, corners etc).


Let me summarize the discussion so far:

Theoretically with the PatATi Portable Flyer secured on his shoulders a man can take-off vertically and fly controllably (pure manual control) for hours at high speed.

Thanks
Manolis Pattakos

#157 Greg Locock

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Posted 24 November 2014 - 07:38

Yes, I agree these calculations suggest that the design as it exists will supply 100kgf thrust at a standstill, to take off vertically, and to fly horizontally at a reasonable speed with 33 kgf of thrust, given 70 hp, 5000 rpm, 3:1 L/D with the large prop.

 

In my opinion you will be able to improve all aspects of that performance with a better propeller design.

 

At 0 mph, ie hover, you get 100 kgf at 3800 rpm, and need only 28hp. So depending on your power curve it seems likely that more pitch would allow you to drop the rpm. The prop doesn't actually need much twist at hover.

 

At 78 mph you need 4750 rpm to generate 33 kgf of thrust, and only 25 hp. 

 

Increasing the pitch to 20 degrees from 15.37 hover drops to 3300 rpm and 24 hp, and cruise is 3600 rpm and 20 hp. So you are running a lot less revs, and 5 hp less.

 

Another advantage of dropping the rpm is that the Mach number of the rotor also drops.



#158 Greg Locock

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Posted 24 November 2014 - 08:03

On the other hand 25 degrees pitch is too much, it'll bog the engine in hover. 

 

Sorry I realise I've just run all this with 10 degrees of twist, I'll rerun it with your prop now.


Edited by Greg Locock, 24 November 2014 - 08:29.


#159 Joe Bosworth

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Posted 24 November 2014 - 09:53

As a sometimes watcher of this thread I have very deliberately stayed away.  But I think I can throw in a few bits of practicalilty which I will share.

 

I look at it with a background of both powerd fixed wing flying and non-powerd paragliding.  I have delved into the aerodynamics and performance factors for both.

 

To start with 100 kg of force at the props is substantially deficient unless you plan on a jockey sized pilot.  It is a rule of thumb for paragliding that your take off weight is naked body weight plus about 15 kg of clothes and safety gear plus wieght of the glider.  The paraglider provides a safety margin not provided by the scheme being discussed herein.  A considerable safety margin of extra thrust needs to be provided for just to maintain altitude through localised areras of downdraft.  Then of course your thrusters also need to share thrust vectors for both lift and for navigation.  Then navigation vectors also have to provide motion against the inevitable countering winds.   .

 

The power required to overcome aerodynamic forces in still air is considerable.  Using bicycle data as a marker calculate on about 500 watts of power required to move the human body at 60 kph air speed.  To that you need to add the drag factor for the power plant and prop which may be several times larger than the body drag.  The numbers might biuld up pretty fast depending on your performance desires.

 

I am considerably troubled by the fact that the project is sub - prototype for design of power plant and prop design and system configuration and understanding of flight dynamics.  All of these things feed back on one another.  Sounds to me like about a three or four year programme with less than a 50% of finding a commercial result at the end.  

 

In the meantime, enjoy the journey.  Sometimes the journey is more valuable than the result.

 

regards 



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#160 Greg Locock

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Posted 24 November 2014 - 21:29

I can think of far more useful applications for this, and I'm learning about XFOIL and BET.

 

Here's the zero twist results at hover showing the Nominal (100 kgf) and Maximum power operating points. 

 

p38fi4ur1i3afb76g.jpg

 

And here's the performance summary

 

zls01hqmopobdih6g.jpg



#161 manolis

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Posted 25 November 2014 - 05:39

Hello Joe Bosworth.

You write:
"To start with 100 kg of force at the props is substantially deficient unless you plan on a jockey sized pilot. It is a rule of thumb for paragliding that your take off weight is naked body weight plus about 15 kg of clothes and safety gear plus wieght of the glider. The paraglider provides a safety margin not provided by the scheme being discussed herein. A considerable safety margin of extra thrust needs to be provided for just to maintain altitude through localised areras of downdraft. Then of course your thrusters also need to share thrust vectors for both lift and for navigation. Then navigation vectors also have to provide motion against the inevitable countering winds."

A 75Kp (165lb) pilot is a normal sized pilot.
The complete PatATi Portable Flyer – with the fuel – weighs 25Kp (55lb).
The total weight at take-off is 100Kp (220lb).

Every Kp of thrust above the 100Kp (220lb) accelerates upwards the pilot and the Flyer.
For instance,
according Greg Locock calculations (post #160; thanks again Greg Locock for your time),
if the engine runs at 4,500 rpm at take-off, you can lift substantially more weight than 100Kp(220lb).
This is the "extra thrust".

By the way, the Portable Flyer is not a paraglider, nor it has the limitations of a paraglider.
For instance, an opposite wind of 40mph (64Km/h) towards the open sea may be a tragedy for a paraglider, while the pilot of the Portable Flyer just notices it by a relative reduction of his forward speed (or by the need for a little higher revs in order to keep the same speed).

How the "15 kg of clothes and safety gear plus wieght of the glider" relate with the weight of a Portable Flyer?



You also write:
“The power required to overcome aerodynamic forces in still air is considerable. Using bicycle data as a marker calculate on about 500 watts of power required to move the human body at 60 kph air speed. To that you need to add the drag factor for the power plant and prop which may be several times larger than the body drag. The numbers might biuld up pretty fast depending on your performance desires.”

Think of the Portable Flyer as a Powered Wingsuit.

To keep flying horizontally, Visa Parviainen used a thrust force of only 32Kp(70lb).

The 32Kp of thrust required for the horizontal fly of a wingsuiter is not calculations or theory. And it includes everything.

With the PatATi Portable Flyer providing more than 100Kp (220lb) thrust, you can fly horizontally for as long as you have fuel to burn, having at the same time a back-up of additional / spare thrust for "just in case" / safety.



You also write:
“I am considerably troubled by the fact that the project is sub - prototype for design of power plant and prop design and system configuration and understanding of flight dynamics. All of these things feed back on one another.”

There are several innovations the PatATi Portable Flyer introduces.
Think:
Is it essential / crucial for a big capacity engine secured to the shoulders of a man to be perfectly rid of vibrations of all kinds and of reaction torque?
Is it crucial the elimination of the gyroscopic rigidity of the engine-flyer? Can, otherwise, the pilot control the flight?
Is it important the small weight at landing?
Is it significant to simplify to the limit the simplest engine? (no reed valves, no rotary valves, no additional shafts; asymmetric transfer and intake, compact combustion chamber etc).
Can an 800cc two stroke provide 100bhp at 5,000 rpm? With the PatATi Opposed Piston 800cc (49 cu.in.) engine providing only 70bhp, it needs not to work hard or get stressed (reliability).



You also write:
“Sounds to me like about a three or four year programme with less than a 50% of finding a commercial result at the end.”

Wouldn't it be better some specific / justified technical objections or some useful calculations (like those of Greg Locock) than general estimations?



Regarding the safety:

The first test flights need not be more than a few centimeters (a few inches) hovering above the ground (or a couple of meters above the sea waves).
Soon I hope.

Thanks
Manolis Pattakos

#162 bigleagueslider

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Posted 25 November 2014 - 06:11

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 :

640px-Chinook_hc2_za682_arp.jpg

PatATi_Timing_Belt_arrangement_b_1.jpg

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

Indeed, the variations in lift produced by each of the CH-47s tandem rotor blades during a single rotation is greatly affected by downwash flows, wake turbulence from the preceding blade when the F/R blades intermesh, changes as each blade transitions bewteen advance and retreat, and the structural twist, flap and lead/lag deflections in each blade due to response to aerodynamic and inertia forces. All modern rotorcraft use continuous active pitch control of the main and tail blades during all regimes of flight to control the collective and cyclic roll/pitch/yaw forces produced by the rotor systems. Since your rotor blades have fixed pitch you have no way to control their combined cyclic force, and you can only control their collective force by using the throttle to change speed. Using the engine throttle to control hover flight is not an easy thing to do due to the slow response in lift provided by throttling the engine. All rotorcraft avoid this problem by operating the rotor at a constant speed and using pitch control of the blades to vary collective and cyclic lift forces. This approach provides a much higher rate control response.



#163 Greg Locock

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Posted 25 November 2014 - 22:16

Ypur point about response speeds shoots down one of my more interesting ideas, an octocopter drone. 300kg payload, noisy as all getout.



#164 manolis

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Posted 26 November 2014 - 05:24

Hello Bigleagueslider.

You write:
"Indeed, the variations in lift produced by each of the CH-47s tandem rotor blades during a single rotation is greatly affected by downwash flows, wake turbulence from the preceding blade when the F/R blades intermesh, changes as each blade transitions between advance and retreat, and the structural twist, flap and lead/lag deflections in each blade due to response to aerodynamic and inertia forces."

Worth to mention:
Several of these problems cannot be solved.
For instance, it is impossible to control the pitch of the blade that passes over the fuselage.
However, the Chinook CH-47 is one of the most successful "Flying Machines", ever.


You also write:
"All modern rotorcraft use continuous active pitch control of the main and tail blades during all regimes of flight to control the collective and cyclic roll/pitch/yaw forces produced by the rotor systems."

The PatATi Portable Flyer looks like a scale-down of the Osprey (Bell Boeing V22):
Unless I am wrong, the Osprey V22 needs not "continuous active pitch control" of its rotors. It is based on a completely different approach: it is an airplane capable to take-off and land vertically: all it takes is to turn upwards its two large counter-rotating propellers.


You also write:
"Since your rotor blades have fixed pitch you have no way to control their combined cyclic force, and you can only control their collective force by using the throttle to change speed. Using the engine throttle to control hover flight is not an easy thing to do due to the slow response in lift provided by throttling the engine. All rotorcraft avoid this problem by operating the rotor at a constant speed and using pitch control of the blades to vary collective and cyclic lift forces. This approach provides a much higher rate control response."

While the "variable pitch blades" is an option for the PatATi Portable Flyer

(not for the reasons you write, but for the sake of auto-rotation: the propellers – that can be disengaged from the engine – accumulate energy – like flywheels – and deliver it controllably according the selected pitch),

the fixed wing blades have several advantages like: simplicity, robustness, lightweight, reliability, low-cost etc.


The slower response when the throttle controls the thrust is OK.
Look at Martin’s Jet Pack:

martin-jetpack_3.png

(several millions have been invested so far; and unless I am wrong, they are looking for another 24) wherein the throttle controls the thrust.

In the Martin JetPack case, the pilot is just another mass tightly secured to the casing, with the electronics doing the control.

What happens if – for some reason – the propellers of the Martin Jet Pack (empty weight 180Kp / 396lb according wikipedia) provide a thrust of only 80% of its total weigh? Nothing. It remains on the ground.

And what happens if the propellers of the PatATi Portable Flyer provide only 80Kp (176lb) thrust? The pilot feels like weighing only 20Kp (44lb), so he can jump several meters in height and then land on his feet safely, he can run “like the wind”, he can climb on mountains etc, etc.

In the PatATi Portable Flyer the pilot / rider has the main active role.
He uses his legs, hands and body for the control of the flight.
He uses his legs / feet for the landing, he also gives with them the final push at take-off.
Just like the bird, the bats and the bugs.

The PatATi Portable Flyer is completely different than a small helicopter.
Look at it as a scaled-down Osprey V22 wherein the pilot – rider is the casing and the wings and the control and the landing system.

Thanks
Manolis Pattakos

#165 gruntguru

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Posted 26 November 2014 - 06:12

A rapid response thrust control could be provided by a mechanical "air brake" in the propeller wash. Perhaps a pair of flaps (one either side of the engine cylinder) that open "butterfly" fashion.



#166 Greg Locock

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Posted 26 November 2014 - 06:57

That's good, yes, a lift dumping flap.



#167 fykcha

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Posted 26 November 2014 - 16:05

Wikipedia mentions that the V-22 does in fact use a swashplate to provide control authority during helicopter flight. 

 

Also confirmed by an ex V-22 pilot  - http://forums.eagle....110&postcount=4

 

It also looks like the martin jet pack utilizes flaps under the ducted fans for stabilization.

 

The lack of active stabilization could limit the hovering performance of your portable flyer, especially with any crosswinds or wind shear. Perhaps some dihedral angling of the rotors could help?



#168 gruntguru

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Posted 26 November 2014 - 23:13

I was thinking about stability. Stationary hover would require the COG to lie on the thrust axis. It might be necessary for the power unit to be able to pivot on the shoulders with handlebars extending from the power unit down to a comfortable location for the hands, allowing the thrust axis to be aligned with the COG (or misaligned to translate during hover).

 

This would also increase the aerodynamic pitch control beyond that provided by bending at the hips alone - perhaps useful when transitioning from hover to forward flight?



#169 Kelpiecross

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Posted 27 November 2014 - 03:24


As ever - slightly beside the point - but there is another very simple and effective very light helicopter layout. This involves having the engine above the airframe - but mounted on a large helicopter-sized rotor. The idea being that the engine turns a normal aeroplane-sized propeller and the torque reaction turns the big rotor - very simple and it apparently works quite well.

#170 bigleagueslider

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Posted 27 November 2014 - 05:00

Wikipedia mentions that the V-22 does in fact use a swashplate to provide control authority during helicopter flight. 

 

Also confirmed by an ex V-22 pilot  - http://forums.eagle....110&postcount=4

 

It also looks like the martin jet pack utilizes flaps under the ducted fans for stabilization.

 

The lack of active stabilization could limit the hovering performance of your portable flyer, especially with any crosswinds or wind shear. Perhaps some dihedral angling of the rotors could help?

 

Indeed, the V-22 uses a swashplate to control each of its 3-blade gimballed prop-rotors. The AW-609 tilt rotor uses the same arrangement.

 

As for the Martin JetPack, it requires over twice the installed power as Manolis' design.



#171 manolis

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Posted 27 November 2014 - 06:01

Hello Gruntguru.

You write:
"A rapid response thrust control could be provided by a mechanical "air brake" in the propeller wash. Perhaps a pair of flaps (one either side of the engine cylinder) that open "butterfly" fashion."

The Martin JetPack (and the HoverBikes) are using this method.
Greg Locock call them "lift dumping flap".

It is better to control the flight without "lift dumping flaps" because this way you save weight, complexity, space, aerodynamic resistance, cost etc.

A big difference in the case of the Portable Flyer is that the pilot / rider comprises the great percentage of the total mass of the "Flying Machine".

Another big difference is that the pilot / rider, who is "hanged" from the engine, is free to displace his legs, hands and body as required. He can displace a lot – and “instantly” – his center of gravity relative to the propellers.

Another big difference is that, depending on the position of his legs / hands / body (wearing – or not wearing – a wingsuit), the pilot / rider of the Portable Flyer interacts with the fast moving air as a living / thinking flap.
Think the case you drive a car at 160Km/h (100mph); if you put your palm against the wind you feel a heavy aerodynamic force.
The pilot of the Portable Flyer is inside a fast air-stream coming from the propellers (either he flies horizontally, or he is hovering), so he can generate the forces and torques required to control the flight.
For instance, at hovering, by moving forwards his one leg and backwards his other leg, he starts rotating about his long axis at one direction, just like the following folded paper toy does if you drop it to fall:

paper_toy.gif

To make it, you start (top-left) with a rectangular piece of paper (say 10cm / 4 inches the long side).
You make three cuts as shown at top-middle.
At top-right the dashed lines show where the paper is to be folded.
At bottom-left the lower sides of the paper are folded.
At bottom-middle the “rotor wings” are folded (say for 30 degrees from the plane of the paper) oppositely from each other.
At bottom-right it is the paper-toy ready.



Hello Fykcha, hello Bigleagueslider..

Quote from the Internet:
"When the Osprey is in helicopter mode, with its nacelles vertical or nearly so – 97.5 to 60 degrees — and its rotors providing all lift, the pilot’s stick, TCL and pedals perform the way helicopter controls do. Pushing the stick forward or pulling it back makes the aircraft move forward or backward. Pushing the stick to either side makes the aircraft move laterally. Adding or removing power with the TCL makes the Osprey gain or lose altitude by collectively changing the angle at which all three blades on each rotor meet the air as they rotate. Pushing the left or right pedal makes the aircraft turn in that direction by altering the angle of the rotor blades cyclically – higher on one side, lower on the other — as they rotate through the arc they describe."

Osprey V22 uses both, collective and cyclic pitch because it has no other way to be controlled.
Its fuselage (excluding the flaps in its wings) is fixed.
The fuselage in the case of the Portable Flyer is the body of the pilot / rider, and it is anything but fixed.
The human body is agile; “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.”


The first requirement from a Portable Flyer is to be portable.

Thanks
Manolis Pattakos

#172 gruntguru

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Posted 27 November 2014 - 06:40

It is better to control the flight without "lift dumping flaps" because this way you save weight, complexity, space, aerodynamic resistance, cost etc.

It is bigleagueslider who suggests the need for faster thrust response than what is available using the engine speed alone - I only provided a solution to his concerns.

 

As to weight etc, I would estimate the flaps to add less than 0.5 kg, cost very little to implement and add no aerodynamic resistance when not deployed.



#173 Greg Locock

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Posted 27 November 2014 - 10:12

Dudes, let's get a measured thrust of 100kgf before worrying about finessing the output. 



#174 gruntguru

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Posted 27 November 2014 - 22:33

:)

+1



#175 Greg Locock

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Posted 27 November 2014 - 23:27

Incidentally if anybody is interested, I'm using XFOIL to generate CL and CD for a clark y section at all angles of attack and mach numbers. I am driving it with an excellent matlab script from the matlab file exchange - I haven't tried running the script from Octave. It takes quite a while, running on 3 processors, as the results at high alpha are very flaky. I tried to use XFOIL a long time back and failed, XFOIL has improved, the script makes it automatic, and of course PCs are much faster now.

 

The results of that are a lookup table that is used by the blade element theory model which I used to generate those plots.



#176 Kelpiecross

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Posted 28 November 2014 - 03:18

:)
+1


+2 And to be a useful/usable flying machine I would think that it needs a lot more thrust than just enough to lift it off the ground.

#177 manolis

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Posted 28 November 2014 - 06:04

Hello Grec Locock.

You write:
"Dudes, let's get a measured thrust of 100kgf before worrying about finessing the output."

Are you worrying about the propellers (and about the calculations) or about the PatATi engine?

The following info may help:

Quote from http://www.toni-clar...vm210b2info.htm :
Specification:
Displacement: 210 cc / Power: ca. 16 hp
Static thrust with 36x14" FIALA prop (2-blade): 35 kp at 4800 rpm
End of quote.

With only 16hp from the engine (it is a small displacement 4-stroke), the measured static thrust is 35Kp (77lb).
The diameter of the above propeller is only 900mm, the pitch is only 14’’.

In comparison, the PatATi prototype engine is a big displacement 2-stroke, the propellers of the Portable Flyer are 1m in diameter each.



Hello Kelpiecros.

You write:
"And to be a useful/usable flying machine I would think that it needs a lot more thrust than just enough to lift it off the ground."

If you can take-off (it requires only 100Kp static thrust; the ground effect is more assisting in case for a pair of counter-rotating propellers), then you can fly with substantially less thrust than 100Kp.
If you wear a wingsuit, in oreder to keep flying horizontally the required – measured - thrust is only 32Kp (71lb). Say 40Kp (88lb) with the PatATi engine and the propellers.



Regarding the need for flaps.

The lightweight and the simplicity are vital for a Portable Flyer.

Martin JetPack is based on flaps below the ducted fans. The electronic control displaces, by servomotors, the flaps as necessary during the flight.

The hoverbikes also use (manually controlled) flaps bellow their propellers in order to fly controllably / safely.
The hoverbike pilot needs the flaps to hover safely, just like an old man needs a cane to walk safely.

To give a cane to a young man is meaningless because he walks safely without it.

The Portable Flyer is – at the great percentage – the pilot / rider.
His legs, hands, body can be used as flaps.
An additional flap adds weight, needs to be mounted / supported somewhere, needs some cables / rods to control it.
If you can avoid it, it is better.

Thanks
Manolis Pattakos

#178 Greg Locock

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Posted 28 November 2014 - 11:02

Manolis, i have great confidence in your engine, and some confidence in my thrust calculations. But as someone who spends most of their working life making complex models, I always emphasise the importance of real world testing.



#179 Kelpiecross

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Posted 29 November 2014 - 09:25


Manny the information about the model plane engine and propeller etc. - at least demonstrates that you should be able to get a suitable prop for your Flyer fairly cheaply. I would imagine having a prop made or buying a full-size plane prop would not be cheap.

Using two model plane props should allow you to make some basic thrust tests fairly easily.

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#180 manolis

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Posted 30 November 2014 - 05:51

Hello Greg Locock.

I have more confidence in the propellers and in the calculated / measured thrust they provide, than in the engine.

Because the complicated part is the engine.

Despite it is one of the simplest two-strokes, when something is manufactured for the fist time the risks and the decisions that have to be taken are many.

For instance,
while in the OPRE and PatOP prototypes made so far, the piston rings are free to rotate inside their grooves without a problem (the exhaust and transfer ports are a series of narrow holes around the cylinder),
in the PatATi engine the port openings on the cylinder liner are wider making necessary the use a steel peg (a stop pin) to keep the ends of each piston ring away from the port openings.
A set of piston rings was sacrificed to prove – in practice - the need for steel pegs, fortunately without other complications / punishment.

It takes a lot of optimism to expect the first prototype will be functional and reliable, yet this is the only way to proceed.

Thanks
Manolis Pattakos

#181 manolis

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Posted 30 November 2014 - 06:04

Hello Kelpiecross.

The propellers is the easy part.

Besides the two pairs of aluminum propellers we have, there are pairs (I mean symmetrical, the one clockwise, the other anticlockwise) of propellers (1m diameter, at various pitch, made of carbon fibers etc) in the market at low prices.

To finish the PatATi engine is the difficult.

Thanks
Manolis Pattakos