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Feb 22, 2003, 11:14 PM
Caution:Makes sharp left turns
Troy's Avatar
Thread OP

Variable pitch prop for F5B and pattern planes


Kontroniks has been working on a variable pitch prop for F5B and possible use for pattern ships. This concept and application is not new, the Italian F5B Team tried this some time ago and a guy in the US was selling one, but still quite interesting. I didn't get the info on how the pitch is determined in flight.
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Feb 23, 2003, 02:22 AM
Speed Demon
GregG's Avatar
Kress Jets used to sell one. Helicopters use them, why wouldn't it make a good idea? You could use a larger diameter with a low pitch for great thrust in the low speed and repitch as the airframe speed increased. It would almost be like an automatic transmission.
Feb 23, 2003, 03:30 AM
I don't think that it will work very well. Propellers are pitched for a certain thrust through the whole length of the blade. if you turn the blade to angle it a little bit more then you loose that airfoil and cause more drag.

I think that what could really happen is you could put a more agressive pitched blade and launch with it turned down to let the motor unload and then put the prop to its nominal pitch as the plane accelerates with the prop and plane already up to speed.
Feb 23, 2003, 04:50 AM
f5b-uk
Mike Seale's Avatar
In 1994 F5B World Chamionships the winner was Jerry Bridgeman (direct drive Aveox), second was Rudi Freudentahler (direct drive Plettenberg brushed) and third was Urs Leodolter (geared robbe brushed motor with variable pitch - IIRC). Two years later everyone was using geared brushless motors and the best models were the lightest which meant the variable pitch had to go.

New rules mean the models have to be heavier so nowadays I can see why variable pitch is being reconsidered. The most powerful F5B model I ever launched was powered by a direct drive plettenberg 'washing machine' motor with a 14x10 prop. You didn't throw it, more like 'wait for it to rip out of your hand'. My current model uses a 16x16 prop which is stalled at launch. If that could be pitched down to 16x10 at launch it would possibly pull my arm out of its socket

I think the varaible pitch was controlled by sensors monitoring airspeed but can't be sure. It might be acceptable to programme a slow pitch change each time the motor is switched on, but this would require a different setting for launch and subsequent climbs due to different starting speeds. It would also require the pilot ot be consistent to get the most out of it. I guess with modern electronics, a speed sensor with feedback to the servo controlling the pitch won't weigh too much.

Personally, I hope this system proved to be unnecessary - F5B is expensive enough anyway

Mike
Feb 23, 2003, 02:49 PM
Registered User
dionnel's Avatar
Well, guys,
If you look more closely at the photo shown above, you will see that there is a servo (looks like a cat, smells like a cat, must be a cat) at the end of the motor....


Looks like the motor shaft is hollow and the servo is used to drive the angle of the blades. And therefore a manual operation but operated remotely and in flight.

So you may program your transmitter to adjust the angle according to the throttle setting (pattern?) or more likely to set a delay of operation. Say, for .5 sec everytime the motor is turned on the pitch will be... 10", then swith to 16" pitch.

Not entirely bad...

LD
Feb 23, 2003, 03:53 PM
f5b-uk
Mike Seale's Avatar
Quote:
Originally posted by dionnel
Well, guys,
If you look more closely at the photo shown above, you will see that there is a servo (looks like a cat, smells like a cat, must be a cat) at the end of the motor....
No...I spotted the servo. It might be that the user has to opperate the servo, but for an F5B climb that only lasts 3 to 4 seconds this will be impossible. Also, a delay will only give a good result if you fly perfectly consistently. I'd like to think that the current microprocessors could measure speed and send a signal to the servo to set the pitch for me and then change it as the model accelarates. Weight and space should not be too much these days.

Mike
Feb 25, 2003, 05:24 PM

heli constant speed sensor


Seem to me the heli constant speed sensor might work to solve the problem

In 3d heli acro it seem s to keep the speed constant even at zero degree rotors as you flip thogh the loops etc

I want to know is this pitch gadget available in the smaller size for my F5D stuff suitable to go on hacker 500L
(non f5d specs 8 *2400 with 6.5*9 home built carbon folder and hacker 500l in battle weary AeroNaut Fox about to get replaced by CZ republic rainer freddy )



Presently for deep pitch props get very good flight preformance but obliged to bungee launch due to severe torque roll no omph crash hand launch

Figure varable pich the way out of deep pitch mode induced flying styles

Stephen in europe
Feb 25, 2003, 06:29 PM
sneu's Avatar
Quote:
Originally posted by Mike Seale
No...I spotted the servo. It might be that the user has to opperate the servo, but for an F5B climb that only lasts 3 to 4 seconds this will be impossible. Also, a delay will only give a good result if you fly perfectly consistently. I'd like to think that the current microprocessors could measure speed and send a signal to the servo to set the pitch for me and then change it as the model accelarates. Weight and space should not be too much these days.

Mike
A unnamed source told me that the idea was to measure current and keep it constant. I believe that weight and size are still important. The climb rate still depends on the power to weight ratio! So we still have to be very careful!

Steve
Last edited by sneu; Feb 25, 2003 at 06:32 PM.
Feb 25, 2003, 10:55 PM
Caution:Makes sharp left turns
Troy's Avatar
Thread OP
Quote:
Originally posted by sneu
A unnamed source told me that the idea was to measure current and keep it constant.
Hmmm, I thought that was how they'd do it.
BTW: was it the Italians or the Swiss who did that years ago??
Feb 26, 2003, 12:10 PM
sneu's Avatar
Quote:
Originally posted by Troy
Hmmm, I thought that was how they'd do it.
BTW: was it the Italians or the Swiss who did that years ago??
I actually think the Germans and Swiss played around with it. Robbe made the setup--it had a airspeed sensor and little computer to control the prop pitch. Lots of parts--and problems!

Steve
Feb 26, 2003, 01:23 PM
Registered User
WimH's Avatar
Quote:
Originally posted by Troy
Hmmm, I thought that was how they'd do it.
BTW: was it the Italians or the Swiss who did that years ago??
The Swiss, and that was how they planned to do it. Apparently the program for the little electronic device was never quite up to the task and Urs Leodolter used two fixed positions in the contest, at least from what I heard. The idea was later abandoned....


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