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Twisted Tooth Belt for the engagement of counter-rotating shafts


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#51 imaginesix

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Posted 11 November 2014 - 07:17

Hello Imaginesix.

You write:
"Let's imagine the day comes when you complete your Flyer with the necessary performance, you need to know what you do after that."


After completing the tests and after demonstrating the Flyer to the mass media, we will calm down (say for a couple of months) trying to see the whole project / idea from a distance and to evaluate it from various viewpoints.

Depending on the demand, we will examine all options as you describe them: from putting the project aside, to putting it in mass production at an affordable price.

Judging from the millions invested so far in projects like the Pal-V and the Martin JetPack, the World seems more than thirsty for a transportation means / tool like the Portable Flyers.

Besides, think that when you are making a low-budget proof-of-project prototype, the main goal, the first priority, is to complete it and to be functional.

With a functional prototype at his hands, any engine maker can easily adjust the design for mass production.

So, first thing first.

Thanks, that answers my question very well.
 
As a proof-of-concept, the Flyer doesn't need to be optimized for weight/efficiency. Your existing synchronizing system is adequate for testing purposes. If a few pounds of extra weight make the difference between a successful proof-of-concept and a failure, then the margin for "success" would be dangerously slim.
 
Consider also that your belt system should undergo its own proof-of-concept testing before being relied upon to verify the validity of the Flyer concept. That means;
1- Make the belt.
2- Test the set up using the install method you described (tighten it on a dummy rig and then apply the dimensions between cranks to a platform with no tensioner)
3- Operate the belt at a multiple of the speed/duration you require for use on the Flyer and see if it lasts.
 
If you can do all of the above, then you can apply the belt system to the Flyer. But as I said, I don't think the belt is a necessary requirement for the Flyer proof-of-concept, just use the gears.
 
BTW, the simplest, most reliable and lightest solution is the one provided by Greg Locock:

Ah, you've provided the solution. Synchronise the sparks, then they can never get more than 10 degrees out of position. Until the engine fails, in which case you are toast anyway.



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#52 Wuzak

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Posted 11 November 2014 - 07:24

BTW, the simplest, most reliable and lightest solution is the one provided by Greg Locock:
 

Ah, you've provided the solution. Synchronise the sparks, then they can never get more than 10 degrees out of position. Until the engine fails, in which case you are toast anyway.

 


Doesn't the opposed piston engine have but one spark plug for the single combustion chamber?



#53 Wuzak

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Posted 11 November 2014 - 07:36

Do you know a better solution?

 

Yes - gears.

 

I think, at least from my perspective, reliability trumps weight and cost considerations in flying machines, I believe that belt drives are rare in aero engines, at least for driving important functions.



#54 Lee Nicolle

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Posted 11 November 2014 - 09:43

Yes - gears.

 

I think, at least from my perspective, reliability trumps weight and cost considerations in flying machines, I believe that belt drives are rare in aero engines, at least for driving important functions.

I am with you on this.



#55 MatsNorway

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Posted 11 November 2014 - 13:33

If you want crazy ideas... How about long pull rods? To avoid bending you only pull. Having flex in one direction to free it up once it goes over the center and normally starts to push.



#56 imaginesix

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Posted 11 November 2014 - 13:59

Doesn't the opposed piston engine have but one spark plug for the single combustion chamber?

Yes, and I have no idea how to synchronize a spark plug with itself but manolis is a pretty bright guy I'm sure he can figure it out.

#57 imaginesix

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Posted 11 November 2014 - 14:01

If you want crazy ideas... How about long pull rods? To avoid bending you only pull. Having flex in one direction to free it up once it goes over the center and normally starts to push.

That wouldn't allow the cranks to turn smoothly. Similar problem to an angled u-joint.

#58 Allan Lupton

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Posted 11 November 2014 - 14:36

If you want crazy ideas... How about long pull rods? To avoid bending you only pull. Having flex in one direction to free it up once it goes over the center and normally starts to push.

Using triple con-rods, like the camshaft drive on a six-cylinder Vintage Bentley, works well but does not give opposed rotation.

Bevel gears and rotating shaft give the opposed rotation.

Both are good for large centre distances.



#59 fykcha

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Posted 11 November 2014 - 15:27

Sorry to take things off topic, but I had a quick thought. Is there a mechanism to allow the pilot to rotate around the vertical axis like a conventional rotary wing aircraft? Could make for some interesting slow speed maneuvering in a hover although it wouldn't be strictly necessary as you could turn your head for the most part.



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#60 MatsNorway

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Posted 11 November 2014 - 15:55

Using triple con-rods, like the camshaft drive on a six-cylinder Vintage Bentley, works well but does not give opposed rotation.

You can do both ways with rods. And if the angles are a problem it is a easy fix with one extra gear at one end.



#61 Greg Locock

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Posted 11 November 2014 - 21:19

Yeah sorry, the spark plug idea assumed there were two motors, I had lost the will to go back and reread the entire thread.

 

A couple of points

 

70 hp is very marginal for a jetpack helicopter. The reason is that the propeller diameter is too small, so the disc loading is too high so the props don't produce much thrust at zero speed. I've got a performance predictor for them somewhere, i'll try an dig it out.

 

The second point is that the transition from up to along is a non trivial challenge, and likewise for landing. You will need to develop a speed/altitude profile for that.



#62 fykcha

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Posted 11 November 2014 - 21:36

These folks claim to have built a personal helicopter with 40hp, although with much larger rotors.

 

http://acecraftusa.c...hive/index.html

 

Even has a wiki page, although that doesn't mean much these days:

http://en.wikipedia.org/wiki/GEN_H-4

 

There's a Youtube video as well -



#63 Greg Locock

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Posted 12 November 2014 - 00:40

Yup, because they've got a much lower disk loading.



#64 manolis

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Posted 12 November 2014 - 06:20

Hello Kelpiecross.

You write:
"You demonstrated in this video the system appears to work well mechanically - maybe it is time you made a simple test rig to discover just how much thrust it can produce? Endless speculation and calculation about the system's performance is not really enough."

In the youtube video you mention, it is shown the OPRE engine (Opposed piston Pulling Rod Engine, more details at http://www.pattakon....attakonOPRE.htm )
It is a direct injection Diesel through scavenging with “four-stroke-like lubrication and built-in scavenging pumps.

img6.jpg

It is the basis for an OPRE Portable Flyer:

Flyer1.gif

that requires unconventional wide-Vee propellers (that require special materials and manufacturing).

It is a proof-of-concept low-cost prototype (for instance, its injection system comes from a low cost 400cc 4-stroke Chinese electric generator, its one-way valves are made of steel strip by hand, etc).

While nothing is optimized (for power and thrust measurements), it demonstrates several of its characteristics. For instance, it shows a perfectly vibration-free and reaction-free operation (the engine is free to move around; see the moment of the hand-cranking).
That this “propulsion unit” liberates the delicate frame of a light airplane from reaction torque and from vibrations of all kinds, is a fact and a significant advantage.

With less than 20Kg (44lb) total weight (if the unnecessary material is removed, the weight can drop a few more kilos) this 500cc direct-injection Diesel prototype (by the way: it is over-scavenged; the diameter of the scavenge side of the piston is bigger than the diameter of the combustion side of the piston) and some 30% additional time for the combustion of the “slow to get burned” diesel fuel (which means it can provide its peak power at around 6,000 rpm while all diesels have their peak power at or below 4,500 rpm) this engine can replace in many applications the conventional spark and compression ignition engines.

With the PatATi Opposed Piston Portable Flyer things get simpler.
For instance, no reed valves are required (the connecting rod in cooperation with the piston and the cylinder offer both, asymmetric intake and asymmetric transfer).
For instance, conventional propellers replace the wide-Vee unconventional propellers of the OPRE Portable Flyer.

The PatATi OP prototype is close to complete.
And there is no better dyno-test than putting a pair of propellers on the counter-rotating crankshafts and lifting a man a few centimeters above the ground.
When?
Soon I hope.




Hello Roger Graham.

I think your questions have been answered in previous posts.
The link of Greg Locock (Continental toothed belts) shows that the twisting - into limits – of a tooth belt is according the specifications of the manufacturers.
The successful use of a twisted tooth belt in the GP500 championship 50 years ago.
The use of tooth belts at the final transmission of motorcycles like the BMW 800F.

What is the difference of the PatBelt?

It synchronizes two counter-rotating shafts in a simple, lightweight and efficient way. No need for cases, or for bearings, or for lubrication.

And it can be used in other applications, too.
For instance, for driving the counter-rotating balance shaft of the cross-plane four-in-line, allowing its mounting anywhere.




Hello Imaginesix

As Wuzak explained, "the simplest, most reliable and lightest solution provided by Greg Locock", that one you like the most, is not functional.
As for the PatBelt, the solution of a long existing problem in an unconventional ans simple way is, at least, interesting.
If the PatBelt proves OK in the Portable Flyer, there are several other applications to be used.
Instead of keeping the attention towards the mass production of a prototype you are making, you can alternatively keep your attention towards the future.




Hello Wuzak and Lee Nicolle:

We know the advantages of bridging the crankshafts by gears (the OPRE prototype engines built so far use this method of synchronization), we also know their disadvantages (weight, cost, lash, bearings, casing, mounting, noise etc).
If the PatBelt operates as we expect, it is a better solution for this specific application, at least.




Hello MatsNorway

Putting a few "half a meter long" rods (actually: conecting rods), and some additional crankpins on the crankshafts, and a casing, seems more complicated and expensive than building the complete PatATi Opposed Piston engine.
Think about it.
Make a drawing of your solution and compare it to the PatBelt Twisted tooth belt.




Hello Allan Lupton

Bevel gears and rotating shaft seems as the best alternative if no toothed belts are allowed.




Hello Fykcha:

You write:
"Sorry to take things off topic, but I had a quick thought. Is there a mechanism to allow the pilot to rotate around the vertical axis like a conventional rotary wing aircraft?"

With the PatATi Portable Flyer hovering, a lot of high speed air is flowing around the pilot / rider. The legs and hands of the rider / pilot can be used to change this flow and to control, this way, the yaw (i.e. the rotation about the perpendicular axis).
If it is not clear, let me know to further explain.

Thanks
Manolis Pattakos

#65 manolis

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Posted 12 November 2014 - 06:28

Hello Greg Locock

You write:
"70 hp is very marginal for a jetpack helicopter. The reason is that the propeller diameter is too small, so the disc loading is too high so the props don't produce much thrust at zero speed. I've got a performance predictor for them somewhere, i'll try an dig it out."

Here are some interesting specifications:

MartinJetPack:

martin-jetpack_3.png

a pair or ducted fans of 520mm diameter each,
a 2,000cc, 200 bhp engine,
a maximum take-off weight of 330Kp,
a fuel capacity of 45 lt,
a range of 30Km,
a maximum speed of 74Km/h,
and a cruise speed of 56Km/h.



Ossprey (Bell Boeing V-22):

SUB-JP-OSPREY-articleLarge.jpg

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.

PatATi Portable Flyer (estimation):

Flyer_prot_1.jpg

a pair of counter-rotating propellers of 1m diameter each,
an 800cc PatATi Opposed Piston engine,
a take-off weight of 100Kp,
a range of 300Km,
a maximum speed above 200Km/h.


Disk loading (weight to propeller area at take-off):

MartinJetPack: 330Kp/0.43m2 = 776Kp/m2
Ossprey: 27,400Kp/211.4m2 = 129.6Kp/m2
PatATi Portable Flyer: 100Kp/1.57m2 = 63.7Kp/m2

The "disk loading" in the case of the PatATi is half of the "disk loading" of the Ossprey and a dozen times lower than the "disk loading" of MartinJetPack.

Think of the PatATi Portable Flyer as a small (the minimum possible) Ossprey (Bell Boeing V-22).



You also write:
"The second point is that the transition from up to along is a non trivial challenge, and likewise for landing. You will need to develop a speed/altitude profile for that."


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:

0.jpg


Quote from http://www.pattakon....pattakonFly.htm

"What a man does need, in order to fly, is power provided in a true neutral and manageable way. The body is: the vehicle and the sensors and the control unit and the servomechanisms and the landing system, just like the bodies of the birds, bats and bugs".

Thanks
Manolis Pattakos

Edited by manolis, 12 November 2014 - 07:08.


#66 RogerGraham

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Posted 12 November 2014 - 09:15

Hi Manolis,

I don't think my questions were answered in any earlier posts. But my main queries relate to the belt tensioning, which you said earlier would be achieved by changing the crankshaft spacing:

  1. as far as I can see, you haven't shown how you would do this (the design appears to be a solid unit)
  2. therefore we don't know how much weight/cost/complexity/manufacturing effort/maintenance effort this solution adds
  3. mainly, you haven't discussed the safety implications for such a system, especially what happens if tension is lost mid-flight* 

I'm no mechanical engineer, and maybe these questions aren't relevant and your solution is optimal.  However, surely the design cannot be assessed without the tensioning mechanism being described?

 

Cheers,

Roger

 

* Powered flight is obviously a far more critical usage scenario than a road bike.  In asking this question, I'm assuming that the tensioning would be carried out when the engine is stopped.



#67 imaginesix

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Posted 12 November 2014 - 12:07

Hello Imaginesix

As Wuzak explained, "the simplest, most reliable and lightest solution provided by Greg Locock", that one you like the most, is not functional.
As for the PatBelt, the solution of a long existing problem in an unconventional ans simple way is, at least, interesting.
If the PatBelt proves OK in the Portable Flyer, there are several other applications to be used.
Instead of keeping the attention towards the mass production of a prototype you are making, you can alternatively keep your attention towards the future.

My last reply to you wasn't in consideration of possible mass production. Rather, the actions I proposed were merely a suggested path towards the development a testable Flyer sooner rather than later.

Edited by imaginesix, 12 November 2014 - 13:33.


#68 imaginesix

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Posted 12 November 2014 - 13:32

Hi Manolis,
I don't think my questions were answered in any earlier posts. But my main queries relate to the belt tensioning, which you said earlier would be achieved by changing the crankshaft spacing:


  • as far as I can see, you haven't shown how you would do this (the design appears to be a solid unit)
  • therefore we don't know how much weight/cost/complexity/manufacturing effort/maintenance effort this solution adds
  • mainly, you haven't discussed the safety implications for such a system, especially what happens if tension is lost mid-flight* 
I'm no mechanical engineer, and maybe these questions aren't relevant and your solution is optimal.  However, surely the design cannot be assessed without the tensioning mechanism being described?
 
Cheers,
Roger
 
* Powered flight is obviously a far more critical usage scenario than a road bike.  In asking this question, I'm assuming that the tensioning would be carried out when the engine is stopped.

As I understand it, he's saying the crank spacing would not be adjustable. He'd build the engine to suit the needed tension of the belt. He's not considering ease manufacturing of manufacturing yet, he's simply looking to put together one piece for for the sake of testing/validation.

#69 RogerGraham

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Posted 12 November 2014 - 14:18

Ah, thanks.  Seems I misinterpreted his comment "The tightening by aligning the distance of the two crankshafts is the simplest way".  So what happens if/when the belt gets loose, or can belts be made such that that doesn't happen?



#70 Greg Locock

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Posted 13 November 2014 - 00:33

Manolis, ok, that looks good, - I really will try and find that performance program, next week. I guess Kp=kg force?



#71 manolis

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Posted 13 November 2014 - 04:31

Hello RogerGraham.

You write: "Ah, thanks. Seems I misinterpreted his comment "The tightening by aligning the distance of the two crankshafts is the simplest way". So what happens if/when the belt gets loose, or can belts be made such that that doesn't happen?"

When the belt gets loose, a new one will replace it.

Excluding the necessary tightening, during normal operation the PatBelt runs unloaded.

The only heavy load of the PatBelt (or twisted tooth belt) is during the cranking by rotating the one only crankshaft or propeller.

So the expected time between belt replacements is expected long.




Hello Imaginesix.

Suppose the PatBelt gets in mass production by a tooth belt manufacturer.

What is wrong to align the design of the PatATi Opposed Piston engine to the PatBelt and to the toothed pulleys to be used?

Without heavy loads to transfer, the necessary tightening of the PatBelt is mild. Mild tightening is good for other reasons, too.

I can’t see the problem for mass production. Please help.




Hello GregLocock.

Kp is the weight of a mass of 1 Kg.
1 Kp = 9.81 Nt
1 Kp = 2.2 lb


Thanks
Manolis Pattakos

#72 imaginesix

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Posted 14 November 2014 - 06:30

Manolis,

 

I don't know the exact reasons why tensioners are de rigueur in any belt or chain application but they are. Here are some possible explanations, followed by some ideas that might allow you to get around those issues.

 

1- There may be too much variance between belts during manufacturing to allow them to go straight on to the pulleys with the required tension. Possible solution: Measure all belts off the assembly line and discard those that are out of range.

2- It may be impossible to install a belt at the correct tension in the first place. Possible solution: develop a special installation tool/technique.

3- Installing the belt without a tensioner may stretch or damage the belt, making it too loose or unreliable to function to specification.

4- The service life of the belt would be much lower as it will stretch with use. Possible solution: Reduce service intervals (as you suggested).

 

I've seen a few applications where a belt/chain was used without a tensioner, none of which I would describe as having been properly designed or engineered. One was a FSAE car, which had a chain tensioner added as an obvious afterthought. I'm sure there's more than one such example in the FSAE universe.

 

Basically, the idea of going without a tensioner is too obvious, and it's impossible to imagine that nobody could  have figured it out successfully by now.


Edited by imaginesix, 14 November 2014 - 06:36.


#73 kikiturbo2

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Posted 14 November 2014 - 13:28

for the solution with no tensioner to work he would have to have both cranks on eccentric bearings so that he can close them togeather and really shorten the distance between pulleys... but I really do nto like that idea because the CR change is really a stupid thing to have to do..

 

Also, the super twisted toothed belt presented by the OP, is impossible to make... you cant have a 720 deg rotation in the belt.. no way... The only reason he wants to use it is so that the belt "rubs" on itself on the rear side, where there are no teeth, so that he doesnt have to use any spacers... meaning a "clean solution". Notwithstanding the fact that the belt is impossible to manufacture in any normal way, I highly doubt it could survive the twist involved. I suggest the OP to try cutting a normal belt and making the twist himself... it is aa 5 min experiment..

 

Using a normal belt, and twisting the whole thing by 180 deg is somewhat possible. it would need a separator in the middle, and that one could be also combined with a tensioner.. However, it might get into alignment issues...

 

One more thing why the tensioners are used, is vibration of the belt and various harmonics. Not one engine was lost when a unsupported toothed belt slipped of the dry sump oil pump sprocket... and those are really small belts..



#74 bigleagueslider

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Posted 15 November 2014 - 03:49

With a twisted timing belt coupling the cranks of an OP engine there are a couple things to consider with regards to belt tension. First, the belt can only transmit force from one sprocket to the other over the belt span that is in tension, and the opposing belt span that is in compression is unable to transmit any force between sprockets. Due to cyclic torque variations between the cranks, the belt span loaded in tension can alternate from one side to the other at high frequency. Second, there can be quite a change in belt tension over the engine's operating temperature range due to CTE mismatch between the belt and engine structure materials.



#75 manolis

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Posted 15 November 2014 - 04:21

Hello Imaginesix.

You write:
“I don't know the exact reasons why tensioners are de rigueur in any belt or chain application but they are. Here are some possible explanations, followed by some ideas that might allow you to get around those issues.”

Wrong.


Partial quote from bmw-motorrad (post #4 above):

"Toothed belt drive F 800 S/ F 800 ST

vis_item_beltdrive.jpg

Once the correct tension has been set during the first service, it is checked every 10,000 km, with a routine replacement being carried out at 40,000 km. The toothed belt is tightened over the bearing which guides the rear wheel in the single-sided swing arm. The mono swing arm ensures that the rear wheel is always positioned perfectly.

Since the belt is constantly under tension, possible load change reactions are minimised. This is a great advantage when compared to conventional chain drive. The load change reactions are additionally reduced by means of a jerk damper fitted with four elastomer blocks."

End of quote.


What does BMW say / do ?

They put an initial tension in the toothed belt of the final transmission of their F800S/ST motorcycle and leave the tooth belt to transfer the 85bhp of the power of the engine (and the even higher inertia loads when the fully loaded motorcycle decelerates with the engine) for 10,000Km (i.e. for about a year).

Then they realign the tension of the tooth belt and leave it work for another 10,000Km. And so on.

After 40,000Km they replace the tooth belt.

Read how proud they are for the way their tooth belt (which is constantly under tension) takes the “load change reactions”.

Things are quite easier for the PatBelt (Twisted Tooth Belt) because it runs unloaded.

Besides, in cases wherein the loads are not unidirectional, a tensioner may become the weak point of the transmission. Think about it.


You also write:
“I've seen a few applications where a belt/chain was used without a tensioner, none of which I would describe as having been properly designed or engineered. One was a FSAE car, which had a chain tensioner added as an obvious afterthought. I'm sure there's more than one such example in the FSAE universe.
Basically, the idea of going without a tensioner is too obvious, and it's impossible to imagine that nobody could have figured it out successfully by now.”


Isn’t the BMW F800S/ST properly designed / engineered?


So, have you other objections in that:

"a tensioner for a tooth belt is not mandatory",

and in that:

"without a tensioner things get simpler, cheaper, more lightweight and reliable"?

Thanks
Manolis Pattakos

#76 manolis

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Posted 15 November 2014 - 04:39

Hello Kikiturbo2.

You write:
“for the solution with no tensioner to work he would have to have both cranks on eccentric bearings so that he can close them togeather and really shorten the distance between pulleys... but I really do nto like that idea because the CR change is really a stupid thing to have to do..”

Read the post #68 wherein Imaginesix explains to RogerGraham how this can happen without “eccentric bearings” etc.


You also write:
“Notwithstanding the fact that the belt is impossible to manufacture in any normal way”

The PatBelt is an unconventional / new tooth belt and as such it requires different / unconventional manufacturing.


“I highly doubt it could survive the twist involved.”

However Continental suggests the twisting (into limits) of the tooth belt as a proper solution for angular transmission. Read at a previous post.


You also write:
“One more thing why the tensioners are used, is vibration of the belt and various harmonics. Not one engine was lost when a unsupported toothed belt slipped of the dry sump oil pump sprocket... and those are really small belts..”

For the necessity of a tensioner read my last post / reply to Imaginesix.

Thanks
Manolis Pattakos

#77 imaginesix

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Posted 15 November 2014 - 04:54

Hello Imaginesix.

You write:
“I don't know the exact reasons why tensioners are de rigueur in any belt or chain application but they are. Here are some possible explanations, followed by some ideas that might allow you to get around those issues.”

Wrong.


Partial quote from bmw-motorrad (post #4 above):

"Toothed belt drive F 800 S/ F 800 ST

vis_item_beltdrive.jpg

Once the correct tension has been set during the first service, it is checked every 10,000 km, with a routine replacement being carried out at 40,000 km. The toothed belt is tightened over the bearing which guides the rear wheel in the single-sided swing arm. The mono swing arm ensures that the rear wheel is always positioned perfectly.

Since the belt is constantly under tension, possible load change reactions are minimised. This is a great advantage when compared to conventional chain drive. The load change reactions are additionally reduced by means of a jerk damper fitted with four elastomer blocks."

End of quote.


What does BMW say / do ?

They put an initial tension in the toothed belt of the final transmission of their F800S/ST motorcycle and leave the tooth belt to transfer the 85bhp of the power of the engine (and the even higher inertia loads when the fully loaded motorcycle decelerates with the engine) for 10,000Km (i.e. for about a year).

Then they realign the tension of the tooth belt and leave it work for another 10,000Km. And so on.

After 40,000Km they replace the tooth belt.

Read how proud they are for the way their tooth belt (which is constantly under tension) takes the “load change reactions”.

Things are quite easier for the PatBelt (Twisted Tooth Belt) because it runs unloaded.

Besides, in cases wherein the loads are not unidirectional, a tensioner may become the weak point of the transmission. Think about it.


You also write:
“I've seen a few applications where a belt/chain was used without a tensioner, none of which I would describe as having been properly designed or engineered. One was a FSAE car, which had a chain tensioner added as an obvious afterthought. I'm sure there's more than one such example in the FSAE universe.
Basically, the idea of going without a tensioner is too obvious, and it's impossible to imagine that nobody could have figured it out successfully by now.”


Isn’t the BMW F800S/ST properly designed / engineered?


So, have you other objections in that:

"a tensioner for a tooth belt is not mandatory",

and in that:

"without a tensioner things get simpler, cheaper, more lightweight and reliable"?

Thanks
Manolis Pattakos

I don't know why you keep obsessing over the F800S. It has a tensioner just like every other belt- or chain-driven motorcycle. The tensioner is the rear wheel. It slides back and forth to set the tension, which is then monitored at regular intervals and readjusted as needed. None of the problems I listed apply to it, so in my estimation it is properly engineered.



#78 manolis

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Posted 15 November 2014 - 04:59

Hello Biglegueslider

You write:
"With a twisted timing belt coupling the cranks of an OP engine there are a couple things to consider with regards to belt tension. First, the belt can only transmit force from one sprocket to the other over the belt span that is in tension, and the opposing belt span that is in compression is unable to transmit any force between sprockets."

There is no belt span in compression. Both spans are in tension.
The cyclic torque variation apply to both crankshafts simultaneously, because they both share the same combustion chamber and because they have no phase difference.


You also write:
"Due to cyclic torque variations between the cranks, the belt span loaded in tension can alternate from one side to the other at high frequency."

Even if a small / tiny angle difference is created / generated, the loading of the synchronizing mechanism tends to eliminate it. A belt is superior (as compared to gear wheels, bevel gears, chain / sprockets) in damping high frequency "oscillations".


You also write:
"Second, there can be quite a change in belt tension over the engine's operating temperature range due to CTE mismatch between the belt and engine structure materials."

The synchronizing tooth belt transfers no loads (or, more correctly, no significant loads / power).
The correct tension of the belt is with the engine at operating temperature.
During the warming-up period the tooth belt runs at a little less tension.

Because of its inherent elasticity, a tooth belt appears supperior as compared to the long series of gear wheels used in the Junkers Jumo (and the similar) Opposed Piston engines wherein the total angular lash (or backlash / clearance) between the two crankshafts varies significantly as the engine warms-up; and, unless I am wrong, the biggest backlash is with the Junkers Opposed Piston engine at operating temperature.

Thanks
Manolis Pattakos

Edited by manolis, 15 November 2014 - 05:17.


#79 manolis

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Posted 15 November 2014 - 05:58

Hello Imaginesix.

You write:
“I don't know why you keep obsessing over the F800S. It has a tensioner just like every other belt- or chain-driven motorcycle. The tensioner is the rear wheel. It slides back and forth to set the tension, which is then monitored at regular intervals and readjusted as needed. None of the problems I listed apply to it, so in my estimation it is properly engineered.”

According BMW:
“Once the correct tension has been set during the first service, it is checked every 10,000 km”.

The rear wheel shaft of the F800S/ST slides back and forth to set the correct tooth belt tension.
Then it is secured tightly.
For the next 10,000Km there is no tensioner in touch with the toothed belt.
From a different viewpoint, tensioner – in this case - is the set of the two toothed pulleys which are disposed at a slightly longer distance from what the “untighten” belt defines.

In comparison, the typical tensioner of the synchronizing tooth belt between the crankshaft and the camshaft(s) of a 4-stroke engine comprises a roller and a spring. The roller touches the backside of the belt – at the unloaded span of the belt – and applies to the belt the tension of the spring.

In the PatATi Opposed Piston engine the distance of the two crankshafts is selected to provide the correct tension to the tooth belt. Then the tooth belt operates without a tensioner, just like the BMW F800S after the alignment.

A difference is that without transferring significant loads or power, the PatBelt would, reasonably, require replacement at substantially longer time intervals.

So, what makes you think that the PatBelt needs a tensioner more than the tooth belt of F800S/ST?

Thanks
Manolis Pattakos

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#80 imaginesix

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Posted 15 November 2014 - 06:33

Hello Imaginesix.

You write:
“I don't know why you keep obsessing over the F800S. It has a tensioner just like every other belt- or chain-driven motorcycle. The tensioner is the rear wheel. It slides back and forth to set the tension, which is then monitored at regular intervals and readjusted as needed. None of the problems I listed apply to it, so in my estimation it is properly engineered.”

According BMW:
“Once the correct tension has been set during the first service, it is checked every 10,000 km”.

The rear wheel shaft of the F800S/ST slides back and forth to set the correct tooth belt tension.
Then it is secured tightly.
For the next 10,000Km there is no tensioner in touch with the toothed belt.
From a different viewpoint, tensioner – in this case - is the set of the two toothed pulleys which are disposed at a slightly longer distance from what the “untighten” belt defines.

In comparison, the typical tensioner of the synchronizing tooth belt between the crankshaft and the camshaft(s) of a 4-stroke engine comprises a roller and a spring. The roller touches the backside of the belt – at the unloaded span of the belt – and applies to the belt the tension of the spring.

In the PatATi Opposed Piston engine the distance of the two crankshafts is selected to provide the correct tension to the tooth belt. Then the tooth belt operates without a tensioner, just like the BMW F800S after the alignment.

A difference is that without transferring significant loads or power, the PatBelt would, reasonably, require replacement at substantially longer time intervals.

So, what makes you think that the PatBelt needs a tensioner more than the tooth belt of F800S/ST?

Thanks
Manolis Pattakos

The disagreement seems to boil down to terminology. As I said, the BMW has a tensioner according to my definition, just like every bike. It is the adjustable spline drive on the rear wheel.

 

You can call a mechanism which allows a belt to be installed, tightened, and serviced over it's life whatever name you want, you still don't have one on the Flyer.


Edited by imaginesix, 15 November 2014 - 06:36.


#81 Wuzak

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Posted 15 November 2014 - 07:39

There is another difference betyween the BMW motorbike blet drive and the Portable Flyer - if the belt breaks on the BMW the rider rolls to a stop. If the belt brakes on the Portable Flyer the "pilot" falls out of the sky.



#82 manolis

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Posted 15 November 2014 - 15:22

Hello Imaginesix.

You write:
“You can call a mechanism which allows a belt to be installed, tightened, and serviced over it's life whatever name you want, you still don't have one on the Flyer.”

The following photo:

PatATi_Timing_Belt_arrangement_b_2.jpg

shows the PatATi prototype with the toothed pulleys (they are from Honda VTEC B16A2, they are properly modified to keep the toothed belt in place).

The toothed belt is from an Opel Antara (151 teeth, 3/8’’ step, 7/8’’ or 22mm width). You can even see its code number and the rotation direction. Manufacturer: Federal Mogul.

It uses the b arrangement (at http://www.pattakon....akonPatBelt.htm ) wherein the teethed sides of the belt face each other at the center of the “X”.


In this photo:

PatATi_Timing_Belt_arrangement_b_1.jpg

you can also see the “casing” (i.e. the structure between the rider / pilot and the engine).

You can doubt, however the toothed belt has the correct tension.



Hello Wuzak.

You write:
“There is another difference betyween the BMW motorbike blet drive and the Portable Flyer - if the belt breaks on the BMW the rider rolls to a stop. If the belt brakes on the Portable Flyer the "pilot" falls out of the sky.”

There are other differences, too.

The one belt runs unloaded. The other that runs heavily loaded, has an expected life exceeding 40,000Km / 25,000 miles.

The one belt is to move along a road, the other is to fly (yet nobody forces the rider / pilot to fly high or fast).

If he likes to fly high, he can have a parachute for an emergency landing (for instance, for the case the tooth belt breaks). A wingsuiter has a small parachute and uses it at every landing.

Thanks
Manolis Pattakos

#83 imaginesix

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Posted 15 November 2014 - 20:53

Hello Imaginesix.

You write:
“You can call a mechanism which allows a belt to be installed, tightened, and serviced over it's life whatever name you want, you still don't have one on the Flyer.”

The following photo:

PatATi_Timing_Belt_arrangement_b_2.jpg

shows the PatATi prototype with the toothed pulleys (they are from Honda VTEC B16A2, they are properly modified to keep the toothed belt in place).

The toothed belt is from an Opel Antara (151 teeth, 3/8’’ step, 7/8’’ or 22mm width). You can even see its code number and the rotation direction. Manufacturer: Federal Mogul.

It uses the b arrangement (at http://www.pattakon....akonPatBelt.htm ) wherein the teethed sides of the belt face each other at the center of the “X”.


In this photo:

PatATi_Timing_Belt_arrangement_b_1.jpg

you can also see the “casing” (i.e. the structure between the rider / pilot and the engine).

You can doubt, however the toothed belt has the correct tension.


I have already agreed that it may be possible for you to assemble a custom belt system that works as you described. The issue I am trying to explain to you now is the problem of trying to use this belt system on a production model, as you asked earlier.
 

Hello Imaginesix.

Suppose the PatBelt gets in mass production by a tooth belt manufacturer.

What is wrong to align the design of the PatATi Opposed Piston engine to the PatBelt and to the toothed pulleys to be used?

Without heavy loads to transfer, the necessary tightening of the PatBelt is mild. Mild tightening is good for other reasons, too.

I can’t see the problem for mass production. Please help.

However if you are being honest with yourself about the purpose of this project, and it really is just for testing purposes, then the line of questioning regarding production is a distraction that is removing focus from your ultimate goal of creating a proof-of-concept model of your Flyer.

It's important to be clear about your goal and to stick to it, otherwise this kind of distraction will keep happening which will only hurt the progress of your project. Stay focused.

Edited by imaginesix, 15 November 2014 - 21:43.


#84 Lee Nicolle

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Posted 15 November 2014 - 23:49

Hello Imaginesix.

You write:
“You can call a mechanism which allows a belt to be installed, tightened, and serviced over it's life whatever name you want, you still don't have one on the Flyer.”

The following photo:

PatATi_Timing_Belt_arrangement_b_2.jpg

shows the PatATi prototype with the toothed pulleys (they are from Honda VTEC B16A2, they are properly modified to keep the toothed belt in place).

The toothed belt is from an Opel Antara (151 teeth, 3/8’’ step, 7/8’’ or 22mm width). You can even see its code number and the rotation direction. Manufacturer: Federal Mogul.

It uses the b arrangement (at http://www.pattakon....akonPatBelt.htm ) wherein the teethed sides of the belt face each other at the center of the “X”.


In this photo:

PatATi_Timing_Belt_arrangement_b_1.jpg

you can also see the “casing” (i.e. the structure between the rider / pilot and the engine).

You can doubt, however the toothed belt has the correct tension.



Hello Wuzak.

You write:
“There is another difference betyween the BMW motorbike blet drive and the Portable Flyer - if the belt breaks on the BMW the rider rolls to a stop. If the belt brakes on the Portable Flyer the "pilot" falls out of the sky.”

There are other differences, too.

The one belt runs unloaded. The other that runs heavily loaded, has an expected life exceeding 40,000Km / 25,000 miles.

The one belt is to move along a road, the other is to fly (yet nobody forces the rider / pilot to fly high or fast).

If he likes to fly high, he can have a parachute for an emergency landing (for instance, for the case the tooth belt breaks). A wingsuiter has a small parachute and uses it at every landing.

Thanks
Manolis Pattakos

I feel sure that on occasion those teeth are going to clash. Any flexible drive whips around quite  a lot.  Belts or chains. Belts seem to do it less. Watch them on a beltdrive Harley riding along at a constant speed. Watch a cam belt whip around, especially when you give the engine a rev. And they have tensioners and are working in ONE direction.

Sorry that whole thing looks like an accident. 

Again too lazy too go back, it is a 2 stroke ? With one spark plug? To fire two cylinders. Not a reall problem BUT not very safe either. The reason many small 1 or 2 cyl engines have dual ignition. And in this case a bit hard to switch so both must be working all the time



#85 Wuzak

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Posted 16 November 2014 - 00:37

If he likes to fly high, he can have a parachute for an emergency landing (for instance, for the case the tooth belt breaks). A wingsuiter has a small parachute and uses it at every landing.

 

If the flyer is at 50-100m then the parachute may not deploy quickly enough to prevent the pilot from hitting teh ground very hard. Especially as he has to wait for the engine to fail and stop before the chute could be deployed.



#86 Kelpiecross

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Posted 16 November 2014 - 02:41



I am still doubtful that it would actually lift anyone - but the basic engine/propellers arrangement could be useful on an ultralight or similar type of aeroplane.

Also - very nice workmanship on the engine.

#87 manolis

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Posted 16 November 2014 - 05:15

Hello Lee Nicolle

You write:
"Again too lazy too go back, it is a 2 stroke ? With one spark plug? To fire two cylinders. Not a reall problem BUT not very safe either. The reason many small 1 or 2 cyl engines have dual ignition. And in this case a bit hard to switch so both must be working all the time"

It takes less time to look at the animation of the post #33 and at the photo of the post #82, than to write your question.

The engine is an Opposed Piston two-stroke.

There are two spark plugs oppositely located in the same combustion chamber.

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. Despite the perfectly symmetrical structure, the transfer and the intake processes (controlled by the properly formed connecting rods and pistons) are substantially asymmetrical.

If the above characteristics excite your curiosity, go to http://www.pattakon....pattakonFly.htm and to http://www.pattakon....ttakonPatAT.htm for more, and then ask anything you like.




Hello Wuzak.

You write:
"If the flyer is at 50-100m then the parachute may not deploy quickly enough to prevent the pilot from hitting teh ground very hard."

An option for the flyer is to fly near the ground or the sea level.

Another option is the use of autorotation that allows safe landings from any height – as safe as with a helicopter. For the auto-rotation you need special propellers having controllable pitch and high moment of inertia (to store the required energy), you also need one-way clutches to disengage the propellers from the engine. These are options for the future.


You also write:
"Especially as he has to wait for the engine to fail and stop before the chute could be deployed."

You suppose the engine and the propellers are, and need to stay, at top.




Hello Kelpiecross.

You write:
"Also - very nice workmanship on the engine."

The focus is only on the functionality. Thanks anyway.


You also write:
"I am still doubtful that it would actually lift anyone - but the basic engine/propellers arrangement could be useful on an ultralight or similar type of aeroplane."

Suppose the two counter-rotating propellers provide an upwards aerodynamic lift of 125Kp / 275lb (not difficult: they have 1m diameter each, they receive a lot of power from the PatATi OP engine); suppose also that the total weight of the Flyer (including the pilot and the fuel) is 100Kp / 220lb.

If the upwards aerodynamic lift was only 100Kp / 220lb, the Flyer would just hover.
With the surplus (i.e. with the remaining 25Kp / 55lb) of the aerodynamic lift, the Portable Flyer starts elevating with an acceleration of 1/4 of the gravitational acceleration (i.e. with some 2.5m/sec^2).
This means that in 2 seconds it elevates at a height of 5m, in 4 seconds it elevates at a height of 20m, and at 10 sec it elevates at a height of 125m.

If you optimize the propellers for hovering / elevating, you can have much faster elevations than the above described (for demos, for acrobatics etc).

On the other hand, you can optimize the propellers for high speed horizontal flights (provided their design allows the safe take-off / landing at full load).

You can also have the option of variable propeller pitch.

So, what makes you so "doubtful that it would actually lift anyone"?

Where specifically do you see the problem?

Thanks
Manolis Pattakos

Edited by manolis, 17 November 2014 - 04:30.


#88 Kelpiecross

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Posted 17 November 2014 - 05:12

Manny you ask - "where do I see the problem"? Basically I think it is one of simple logic - a typical 300BHP (for example) light aircraft cannot go anywhere near being able to hover vertically due to lack of thrust at zero forward speed. A 300BHP helicopter of the same weight as the light plane can hover easily and probably lift its own weight in addition. Clearly the difference in performance must be connected to the much greater diameter of the helicopter's propeller (rotor) compared to the plane's propeller. What you seem to be attempting amounts to making a helicopter with a 'plane's propeller (although you do have two propellers).

Also - you claim a lifting force of 275lb - how did you arrive at this figure? After looking at the various information on the internet about propeller efficiency (a bloody sight more complicated than I expected) it is apparently very difficult to get an accurate figure when calculating static thrust. In fact the formula for propeller efficiency is apparently related to the "advance ratio" - the graphical curve of which would indicate that a zero forward speed the efficiency is zero - no thrust. Clearly this isn't quite correct (or planes would never be able to take off from stationary) - but the prop efficiency is going to be very low. Would a helicopter fitted with a plane's propeller instead of a rotor be able to lift itself off the ground? Maybe just - but probably not at all.

As I see it two one metre diam props could maybe produce 275lb thrust at a fairly high forward speed but not at zero forward (hover) speed.

So - it all comes down to the 275lb figure - it is probably far too optimistic. The real thrust figure is likely to be less that the weight of the apparatus and pilot - so it probably won't get off the ground or only just.

But I am quite happy to be proven wrong - maybe you can do some basic propeller thrust tests (on a test rig) to see if it is possible.

#89 bigleagueslider

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Posted 17 November 2014 - 05:30

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.



#90 Wuzak

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Posted 17 November 2014 - 07:12

Manny you ask - "where do I see the problem"? Basically I think it is one of simple logic - a typical 300BHP (for example) light aircraft cannot go anywhere near being able to hover vertically due to lack of thrust at zero forward speed. A 300BHP helicopter of the same weight as the light plane can hover easily and probably lift its own weight in addition. Clearly the difference in performance must be connected to the much greater diameter of the helicopter's propeller (rotor) compared to the plane's propeller. What you seem to be attempting amounts to making a helicopter with a 'plane's propeller (although you do have two propellers).

Also - you claim a lifting force of 275lb - how did you arrive at this figure? After looking at the various information on the internet about propeller efficiency (a bloody sight more complicated than I expected) it is apparently very difficult to get an accurate figure when calculating static thrust. In fact the formula for propeller efficiency is apparently related to the "advance ratio" - the graphical curve of which would indicate that a zero forward speed the efficiency is zero - no thrust. Clearly this isn't quite correct (or planes would never be able to take off from stationary) - but the prop efficiency is going to be very low. Would a helicopter fitted with a plane's propeller instead of a rotor be able to lift itself off the ground? Maybe just - but probably not at all.

As I see it two one metre diam props could maybe produce 275lb thrust at a fairly high forward speed but not at zero forward (hover) speed.

So - it all comes down to the 275lb figure - it is probably far too optimistic. The real thrust figure is likely to be less that the weight of the apparatus and pilot - so it probably won't get off the ground or only just.

But I am quite happy to be proven wrong - maybe you can do some basic propeller thrust tests (on a test rig) to see if it is possible.

 

The "advance" I would think is the the pitch of the helix created by the prop, not the actual movement. Greatest thrust would be at zero speed.



#91 Greg Locock

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Posted 17 November 2014 - 10:22

When i find my program it would save a great deal of time  if you could identify  the rpm, diameter, chord, pitch etc of the thing.



#92 Kelpiecross

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Posted 17 November 2014 - 11:10

The "advance" I would think is the the pitch of the helix created by the prop, not the actual movement. Greatest thrust would be at zero speed.


Woozy - You would think that what you say is the obvious conclusion - that the "advance" is just the pitch - but the situation is not as simple as that unfortunately. If you look at the formula for "advance" you can see that it implies that at zero forward speed (and Wiki says that this is the "true airspeed") the thrust is zero (- it's not - but the tendency is in this direction).

GL - there several propeller thrust calculation thingos on the internet - but I think they generally don't apply very well to calculating static thrust (at zero airspeed).

It would be useful if someone with experience and knowledge on propeller aerodynamics etc. could comment on the subject so we could clear up the whole question whether Manny's idea is even vaguely feasible or not. My knowledge is only via a half-hour study on the internet.

Edited by Kelpiecross, 17 November 2014 - 11:12.


#93 gruntguru

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Posted 18 November 2014 - 00:39

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.


Edited by gruntguru, 18 November 2014 - 00:40.


#94 Greg Locock

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Posted 18 November 2014 - 01:05

That's for a moving prop, a hovering prop has a much lower CF

 

Luckily NASA have run the numbers, 

 

https://www.mediafir...ipo0cttbl6g.jpg

 

assuming conventional efficiency, rpm in particular.

 

I'll find my jet pack calculator tomorrow.


Edited by Greg Locock, 18 November 2014 - 01:16.


#95 RogerGraham

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Posted 18 November 2014 - 01:06

 

Multiply by two where appropriate for Manolis twin-rotor machine.

 

The propellers in his design overlap somewhat.  Does that result in any interference such that you'd less-than-double any of the results, e.g. thrust?



#96 gruntguru

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Posted 18 November 2014 - 02:42

Woozy - You would think that what you say is the obvious conclusion - that the "advance" is just the pitch - but the situation is not as simple as that unfortunately. If you look at the formula for "advance" you can see that it implies that at zero forward speed (and Wiki says that this is the "true airspeed") the thrust is zero (- it's not - but the tendency is in this direction).

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



#97 gruntguru

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Posted 18 November 2014 - 02:45

The propellers in his design overlap somewhat.  Does that result in any interference such that you'd less-than-double any of the results, e.g. thrust?

 No doubt. The total swept area is reduced by perhaps 25% but I don't think the thrust would be reduced by the full 25%.



#98 gruntguru

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Posted 18 November 2014 - 02:51

That's for a moving prop, a hovering prop has a much lower CF

 

Luckily NASA have run the numbers, 

 

https://www.mediafir...ipo0cttbl6g.jpg

 

assuming conventional efficiency, rpm in particular.

 

I'll find my jet pack calculator tomorrow.

 

Good chart Greg. Result seems about the same e.g. 62 kg for 24 hp = 62 x 2.2/24 = 5.7 lb/hp



#99 imaginesix

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Posted 18 November 2014 - 03:07

You guys seem to have all missed this illustration he posted. The blade length is not restricted by the centre-to-centre distance between cranks. Though this method results in a great deal more overlap.

It is the basis for an OPRE Portable Flyer:

Flyer1.gif

that requires unconventional wide-Vee propellers (that require special materials and manufacturing).



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#100 gruntguru

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Posted 18 November 2014 - 03:18

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