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-   -   Variable pitch prop (http://www.rcuniverse.com/forum/gas-engines-142/9653806-variable-pitch-prop.html)

BullardRM 04-11-2010 07:40 PM

Variable pitch prop
Anyone know of any that exist or maybe in development? It would seem logical that with CF props and the larger sizes (when compared to glow) that it would be possible.

Tired Old Man 04-11-2010 07:48 PM

RE: Variable pitch prop
There are, but not for hobby uses.

spaceworm 04-11-2010 08:01 PM

RE: Variable pitch prop
If you are building UAVs, take a look here: http://www.nwuav.com/index.html. Maybe you could scale it down.

Tired Old Man 04-11-2010 11:06 PM

RE: Variable pitch prop
Held those in my lucky little hands. $$$$$$$$$$$$$$$$$$$$$ to say the least.

w8ye 04-12-2010 12:15 AM

RE: Variable pitch prop


BullardRM 04-12-2010 06:59 AM

RE: Variable pitch prop
With electrics utilizing the teck and UAV's, it has got to be just a matter of time. If I recall correctly, Hanno used one in FAI many long years ago. (?)

Tired Old Man 04-12-2010 09:06 AM

RE: Variable pitch prop
Anything is "do-able". It's just a matter of electing to deal with the weight, cost, and complexity. F.I. for small two strokes is already in use but the price is exhorbitant. Few have the desire to spend that kind of money for little more than improved fuel usage. Same will apply to C.S. props for small gas engines. Cost versus benefit still applies across all types of technology.

pe reivers 04-12-2010 09:43 AM

RE: Variable pitch prop

spaceworm 04-12-2010 11:11 AM

RE: Variable pitch prop
Has anyone tried a constant prop speed approach using the variable diameter pulley belt drive DAF transmission? Doesn't/didn't some car use that concept. Seems simple enough, but I have no idea how the pulley diameters are controlled. My old snow blower used a driven disc that was moved across the radius line of a drive disc to vary the speed of locomotion.????????. Did/t Ford use this in the Model T?

spaceworm 04-12-2010 11:14 AM

RE: Variable pitch prop
Another random thought: Are rear rotor heli drives robust enough to use for fixed wing prop drives? The tail rotor pitch is mechanically servo controlled for YAW, but could be coupled to the throttle or airspeed or load or whatever for fixed wing application.???????????

Tired Old Man 04-12-2010 11:42 AM

RE: Variable pitch prop
Let's get real for a moment. Dreaming is nice but a reality check has to come into play eventually.

Helis use much lower rpm levels than fixed wing engines, and a whole lot less blade mass. Any truly effective constant speed device that is robust and reliable enough for larger gas engines will likely have more mass than most will want to deal with. Warbird and scale types will be the ones to make use of this stuff first. The crude design that has already been tried on 100cc gassers is not something I would want to bet my plane on.

Next comes the cost. If you knew you could have fuel injection now but had to pay a couple grand above and beyond the engine cost, would you run out and buy it? Similar price points would be applicable to a safe, robust, and effective C.S. prop hub and blades. Product liability alone will force such a product to hold high price levels for a very long time to come.

One reaches a point where cost versus benefit always butt heads and only those with unlimited funds pass that point. If we really want all those goodies, why not just fly full scale? The cost of obtaining a pilot's license would be far less than building and maintaining a model with the same capabilities as a full scale aircraft.

Everything that gets talked about in these forums has already been done and is in use, but none of the better stuff is available to modelers, and even if it was it's grossly unnaffordable. Those products will not be publically released due to the level of industrial theft that takes place with anything propulsion oriented. First hand I can state it's not just the Chinese that are doing that. You would be surprised to learn of some of the companies that "borrow" designs done by others and call them their own.

pe reivers 04-12-2010 12:05 PM

RE: Variable pitch prop
DAF uses a push belt made up of very small shacles. The vario system is quite simple, but the belt is prohibitive in small production quantities.
The system is a long shot away from variable pitch props, and is designed to provide constant engine rpm by varying exit shaft rpm for torque control.

Tired Old Man 04-12-2010 01:09 PM

RE: Variable pitch prop
Good point.

rc-cropduster 04-13-2010 04:51 AM

RE: Variable pitch prop

This looks really cool, build by RysiuM

NM2K 04-13-2010 05:22 AM

RE: Variable pitch prop


With electrics utilizing the teck and UAV's, it has got to be just a matter of time. If I recall correctly, Hanno used one in FAI many long years ago. (?)

Hanno or Wolfgang Matt?

Ed Cregger

gkamysz 04-13-2010 09:52 AM

RE: Variable pitch prop

ORIGINAL: rc-cropduster


This looks really cool, build by RysiuM
That's common in electric. It's simple when you have a hollow motor shaft and no torque impulses to deal with. It takes a bit more effort with an engine.

Rocketman_ 04-13-2010 10:55 AM

RE: Variable pitch prop
1 Attachment(s)
Way back in 1983 I bought a variable pitch prop called "Variprop". It looks like a swash plate mechanism contained in a 2-inch spinner with an 11-inch prop. Variprop was made somewhere in Switzerland but I bought it from Hobby Lobby and it cost $30. Spare blades were $3 each. It may no longer be available in the USA or anywhere for that matter. Maybe few people wanted to pay $30 for a prop.

The Variprop is infinitely variable throughout its pitch range but I only actuated it from a 2-position switch on the transmitter for froward and reverse. We weren't looking for any increased prop efficiency or constant speed or fuel savings, it was just one of those fun things that model builders liked to play with back then such as retractable landing gear, flaps, wheel brakes, etc.

Originally I used it on a Top Fflite Contender powered by a Fox Hawk .60 for provoking laughs by backing out of the pits to the runway and then taking off. Then I would make several high speed landings, flip the switch to reverse and slam the throttle to full speed to make a sudden stop. The novelty wore off and I put it away.

Twenty-two years later I resurrected the Variprop from storage in the basement and installed it on a Hangar 9 Pizazz with an OS .50sx for power. Guess what, the Variprop is stored in the basement again and I haven't seen it in over 4 years.

BullardRM 04-13-2010 12:47 PM

RE: Variable pitch prop
Wow thanks Rocketman that is great to see. Maybe someone will be motivated to pick up the challange and make one for IMAC competition. Price is not a big factor in the that competition arena. Thanks again.

Lnewqban 04-13-2010 02:03 PM

RE: Variable pitch prop
What the practical value of that capability would be?
I understand how it works in full scale, but don't for IMAC competition.[sm=72_72.gif]

pe reivers 04-13-2010 06:08 PM

RE: Variable pitch prop
In Imac, it would facilitate constant airspeed throughout the sequence. Throttle control becomes more complex, and pilots need to practice even more or they will loose points instead of winning a few. It has been tried, and abandoned as being impractical, apart from not mentioned reliability issues.

BullardRM 04-13-2010 07:05 PM

RE: Variable pitch prop
I was unaware it had been tried. It seemes to work controlling the down lines in electrics, I was wondering if the same principle could be applied to IMAC to control the down line speeds. This is a weak part of many aircraft i.e. Extras. Yaks have a definite advantage with the larger cowel to give a slower down line. Throttle has already become more complicated in an effort to control the prop sound. The whole IMAC community is in termoil over the sound issues that have been spotlighted on the sector.

Kweasel 04-14-2010 01:42 AM

RE: Variable pitch prop
I worked for a small UAV company that made a variable pitch prop for its VTOL. It was very similar to all composite rotor systems used on the latest helicopters. We used a custom multi cylinder Quadra with a belt drive.

tkg 04-14-2010 11:37 AM

RE: Variable pitch prop
Several years there was a company showing a variable pitch prop for 100 class planes. They had a booth at Toledo. I guess lack of response stopped production.

BullardRM 04-14-2010 01:41 PM

RE: Variable pitch prop
Probable the additional weight killed it. Its still refreshing to see people that are willing to step up and try, even the NA SAYERS try to kill an idea with the typical "too costly, to difficult, too small a market" approach. The same thing happened years ago when large motors were introduced, domestic suppliers said there was no market. Wonder how many wish they had taken a chance.

w8ye 04-14-2010 01:53 PM

RE: Variable pitch prop
They are times when other factors have to be in place for a new idea to take off. Maybe the world wasn't ready for the idea?

With the true turbo props coming about, the time may be correct again for a variable pitch design. The full scale turbo props are essentially a constant speed engine and the thrust is varied by the prop pitch. Here's where governors enter the picture? I notice the same company is still in business, they just do not make the props for models.

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