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Old Dec 04, 2013, 07:05 AM
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VPP for planes?

has anyone experimented with VPP for non-3d applications? i.e. for motor speed to pitch optimization? and is it worth the effort?
http://www.ramoser.de/home_e/variopr...uehrung_e.html something like this but variable in flight
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Old Dec 04, 2013, 09:46 AM
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There are props that can have the pitch adjusted in flight, used mostly by some of the 3D fliers.

But for 'optimization' of pitch and speed, I would think you either need some sort of feedback information for either the flier to know what is good or bad, or some sort of automatic feedback to the pitch servo.
Or possibly something like the full size constant speed props. Though I have no idea if that is of any use in RC models.

You may need to define what you see as system 'optimization', longer flight times ?
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Old Dec 04, 2013, 11:30 AM
aka: A.Roger Wilfong
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I remember reading a few years ago about someone who was experimenting with VPP on a stunt plane. IIRC, he was running the ESC in a heli governor mode to maintain RPM and did all of his power changes by changing pitch. Don't remember reading a followup and I don't remember his name.

- Roger
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Old Dec 04, 2013, 12:53 PM
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The problem with today's available vpp's is they are VERY inefficient. Look at a normal prop, see how its pitch changes from root to tip? That's so that every part of the prop is pushing the same amount of air, increasing efficency. The faster moving tips need less pitch than the slower moving root to move the same air. Vpp's, at least all the ones I have seen, use a symmetrical blade in order to give the same thrust in reverse as they do in forward, great for a massively overpowerd 3D plane or a 3D helicopter, in both cases the availability of reverse thrust makes the reduced efficency worthwhile, but not so good for a sport plane with no need for reverse thrust. Any efficiency by gained by keeping the motor at its most efficient speed is lost and then some by the inefficient prop blade design.
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Old Dec 04, 2013, 08:39 PM
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i mean something like this but varriable in flight
Introduction to the varioPROP (2 min 23 sec)
and by optimization exactly like constant speed props..
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Old Dec 04, 2013, 09:02 PM
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Well, I just dont think that the little bit of extra efficiency you could get from something like that is enough to outweigh the other downside to VPP's, lack of duability.... Not that "normal" props are durable, but a normal prop is cheap to replace, where a vpp is not, add the need for a hollow shaft motor, and you add more cost and less durability (the hollow shaft will bend easier)

I dont worry too much about optimizing efficency.... I can get an extra battery for my funcub for under $10, and that extra battery gives me more extra flighty time than a fragile vpp ever could.

Back in the day of brushed motors and ni-cads, a VPP might actualy have added something, allowing lots of thrust at low speed with the option for higher pitch for faster filght, while keeping the amp draw in check, but these days with inexpensive ultra powerfull brushless motors and cheap lipo's, I just dont see how it could be worth the effort and expense....
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Old Dec 05, 2013, 01:00 AM
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Originally Posted by dacaur View Post
Well, I just dont think that the little bit of extra efficiency you could get from something like that is enough to outweigh the other downside to VPP's, lack of duability.... Not that "normal" props are durable, but a normal prop is cheap to replace, where a vpp is not, add the need for a hollow shaft motor, and you add more cost and less durability (the hollow shaft will bend easier)
why not something like a heli tail?

Quote:
I dont worry too much about optimizing efficency.... I can get an extra battery for my funcub for under $10, and that extra battery gives me more extra flighty time than a fragile vpp ever could.

Back in the day of brushed motors and ni-cads, a VPP might actualy have added something, allowing lots of thrust at low speed with the option for higher pitch for faster filght, while keeping the amp draw in check, but these days with inexpensive ultra powerfull brushless motors and cheap lipo's, I just dont see how it could be worth the effort and expense....
ok i get your point but
how about big scale planes where a few grams of extra weight would not hurt and efficiency means a few more minutes?
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Old Dec 05, 2013, 04:58 AM
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Originally Posted by su33seaflanker View Post
why not something like a heli tail?


ok i get your point but
how about big scale planes where a few grams of extra weight would not hurt and efficiency means a few more minutes?
But how would you know what pitch to set for 'efficiency' ? Where does the 'feedback' come from.

If you go to fine pitch, you will have to run the motor faster to compensate. Is that noticeable more efficient than a fixed pitch prop at lower throttle ?

Plus as already pointed out, if the VPP is not very efficient compared to a fixed pitch prop you could lose out anyway.

Finding the right prop to give you exactly what you want is a very trial and error process, that's probably why I have a draw full of various props.
Depending on the model and how you fly it, will influence the type of prop, motor, battery combination. A scale warbird, and e-glider, and a long distance UAV, are all likely to use different props selected for the type of flight required.
That's why I regularly say, choose the prop for the plane first, then the motor to drive it.
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Old Dec 05, 2013, 07:40 AM
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Originally Posted by eflightray View Post
But how would you know what pitch to set for 'efficiency' ? Where does the 'feedback' come from.
well no feedback but an approximation could work

Quote:
If you go to fine pitch, you will have to run the motor faster to compensate. Is that noticeable more efficient than a fixed pitch prop at lower throttle ?
if the motor has a low pitch prop it gets more efficient in most cases
here is some data http://flybrushless.com/motor/view/48 check the apc7x4 and apc 7x5 an amp draw of ~4a less

Quote:
Plus as already pointed out, if the VPP is not very efficient compared to a fixed pitch prop you could lose out anyway.
but the VPP i'm talking about is like a normal prop just with VP
Quote:
Finding the right prop to give you exactly what you want is a very trial and error process, that's probably why I have a draw full of various props.
Depending on the model and how you fly it, will influence the type of prop, motor, battery combination. A scale warbird, and e-glider, and a long distance UAV, are all likely to use different props selected for the type of flight required.
That's why I regularly say, choose the prop for the plane first, then the motor to drive it.
well that's not always the case how about the v-22? it actually needs a VPP to work properly..
in any case i'm moving this thread to motors section.
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Old Dec 05, 2013, 08:02 AM
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In the 1970's the 'World Championship circuit' guys like Hanno Prettner and Wolfgang Matt used them quite a lot on F3A planes, with top engines such as the Webra Speed 61 and Rossis on tuned pipes. It was part of the 'constant speed though manoevres' thing and very impressive to watch. Modern F3As don't seem to have the precision they had then, but it was all too complicated and put people off giving it a try, what with tricycle retracts, 'manoevring' flaps, airbrakes, and aerodynamics that 'clamped' it to the ground on landing (landings were scored in those days) as well as VP props.They were as aerodynamically as good as regular props as reverse thrust was not required. But they were very expensive.
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Old Dec 05, 2013, 09:38 AM
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Originally Posted by Mark Powell View Post
In the 1970's the 'World Championship circuit' guys like Hanno Prettner and Wolfgang Matt used them quite a lot on F3A planes, with top engines such as the Webra Speed 61 and Rossis on tuned pipes. It was part of the 'constant speed though manoevres' thing and very impressive to watch. Modern F3As don't seem to have the precision they had then, but it was all too complicated and put people off giving it a try, what with tricycle retracts, 'manoevring' flaps, airbrakes, and aerodynamics that 'clamped' it to the ground on landing (landings were scored in those days) as well as VP props.They were as aerodynamically as good as regular props as reverse thrust was not required. But they were very expensive.
cool any pics of the F3A VPP?
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Old Dec 05, 2013, 09:40 AM
An itch?. Scratch build.
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Here's some general pictures from a Goggle Images search on, RC variable pitch propeller.

https://www.google.com/search?q=RC+v...w=1351&bih=656
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Old Dec 05, 2013, 09:53 AM
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Originally Posted by eflightray View Post
Here's some general pictures from a Goggle Images search on, RC variable pitch propeller.

https://www.google.com/search?q=RC+v...w=1351&bih=656
yes but not the types i'm looking for.. i'm looking for non reversible thrust props
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Old Dec 05, 2013, 10:25 AM
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No, but I just searched on 'kato variable pitch' and found a couple of pictures. They look much the same as regular props, but the spinner is included. Kato was also known as 'MK' and made lots of good stuff, including some nice 'F3A' kits. It wasn't called 'F3A' then of course.

There was a similar German VP prop too. Somewhere I have a picture of it in a very old UK magazine. Kavan also made one but apparently not as good as the others.

They all worked with a lever behind the spinner. With a glow motor you couldn't have a hollow shaft of course. Prettner always used one on his 'Magic' but not on his earlier and more famous 'Curare' as they had not been developed then.

F3A is going contra-rotating now. They are expensive too

PS: The planes were nice too. Not these hideous fat things that everyone uses today.
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Old Dec 05, 2013, 11:55 PM
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i found this http://www.rysium.com/videos/176-sca...ze-rc-airplane exacty what i was looking for
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