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Old Jan 18, 2013, 05:40 AM
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derk's Avatar
USA, ID, Coeur D'Alene
Joined Dec 2003
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Duration planes

so, if anyone has information on good design practices or on past models, i would love to get more knowledge on duration rc planes. i know its all about slow efficiency and carrying just enough power for the airframe.
i am not looking to set records or enter a serious competition just yet, but i would like to try and build along these lines to get the best i can build at the moment.

i have built a number of very light floaty planes before, but never all around set out for duration. the most obvious thing will be weight, as little of it as i can get away with.
as of yet the only criteria is the battery is 150mah, that weighs 3.6 grams by itself (stock parkzone cell with housing and connector)
i weighed the components i was thinking of using and it came to 5.7 grams for receiver, battery, 2 actuators and a 20.5:1 4mm gear drive.
i need to do some testing on the gear drive to see what kind of prop dimensions are going to work.
with all this i am thinking i could maybe get a larger plane in the 10-12 gram range and still have good power to weight ratio.


so any pictures or descriptions of recent duration planes would be awesome right now, anything related really
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Old Jan 18, 2013, 10:53 AM
Slope-a-Dope
Steve 0's Avatar
United States, UT, Draper
Joined Dec 2012
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Check out the video linked by balsa or carbon member.

Most of the way down page 9 of the plans of 600 + planes in the foamies scratchbuilt thread.

It sure does catch my eye. I PM'd him for any plans (doubt it) or at least the hardware used to fly it.

http://www.rcgroups.com/forums/showt...1333878&page=9

It may not be exactly what you're looking for...but at 8' WS and ultra slow flight...it could be a long distance flyer to boot.

Best of luck.

Steve
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Old Jan 18, 2013, 12:43 PM
TheyreComingToTakeMeAway!
derk's Avatar
USA, ID, Coeur D'Alene
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If you look at f1d freeflight planes, you will see the general construction people try to emulate with rc duration planes. Balsa is really the only way to get the weight to bare minimums.

Thinking that making it sectional will be the best thing for transportation as well as choosing the best sections of balsa. Removeable wings, elevator, horizontal stab and tailboom would keep it around 12 inches for any given part.
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Old Jan 18, 2013, 01:06 PM
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United States, AZ, Yuma
Joined Sep 2009
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intresting.... stock PZ battery. got to get one!
i still think the PZ gearbox is the best bet. in the AP03 vs p51 motor, the ap03 best is 50mah per gram, while the pz gets in the area of 30mah per gram.
i measured the pz shafts, 1.45mm, should be a nice fit for a 681X ball bearings. i was thinking of making an order from shapeways and getting some custome rear nuts made so as to not rub against the bearing aft end...

back on topic, what are restrictions?
aside from the stock 150, anything else?

i really want in on this!
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Old Jan 18, 2013, 02:47 PM
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Another method is to severely reduce drag, go with a faster model (compared to a floater) utilizing as much airfoil generated lift as possible.

Undercamber, I believe, is inefficient (but very effective and easy for small models).

High voltage and low current is also very efficient for small motors - but you WILL need gearing. Worm gears are also fairly inefficient, unless driven with a shaped pinion, and then still not great.
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Old Jan 18, 2013, 03:13 PM
TheyreComingToTakeMeAway!
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Nemo, this is all based on fun and trying to encourage guys to build a plane rather than fly a rtf. That might be why they picked the 150,because the night vapors dont benefit from all the extra weight the only rule was the 150mah single cell, everything else is up to us.
I'm wanting to go the bare minimums route, hence the 4mm drive. Im going to work on prop designs this weekend, and will build an adjustable hub to play with pitch changes.
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Old Jan 18, 2013, 03:30 PM
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Some rough calculations for my prop requirements;

Average motor rpm under light load: 18k / 20.5:1 = 878 rpm

I want a 2mph flying speed so 5280 feet = 63360 inches x 2mph = 126,720 in. / 60 minutes = 2112 inches per minute / 878rpm = 2.4 inches per revolution so my prop needs to be between 2.4 and 3 inch pitch to accommodate drag and prop inefficiencies.
Now i need to decide on a diameter so i can figure out the angles to get that pitch.
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Old Jan 18, 2013, 04:39 PM
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Idaho
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Props

Dereck:
Here's a couple of charts that you might take a look at when you consider prop blade angle-pitch.
You should review the rubber motor prop designs for best prop blade shapes. The Larabee blade shape formulas, I think, might be a good place to start The progressive pitch angle of the blade is extremely important for optimum power extraction under a given flight regime. For duration there are several considerations that determine best power system starting with the motor constants like how far off the no-load Kv rpm that you force the motor to perform so that you are converting as much electrical energy as possible without generating unusable heat. Its possible that a power on-off, climb-glide flight regime might have some advantage.

Just some thoughts..

Carl
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Old Jan 18, 2013, 06:26 PM
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thanks for that Carl, its almost exactly what i was thinking i needed to figure out next! your a mind reader

it also looks like my estimations were pretty dang close to your graphs as far as rpm to pitch and flight speed. encouraging to think i can build this all in my head at least, real world is another story, but thats all part of the fun.

on monday i will make a nylon prop hub, i'm thinking .25" diameter and .035 hole for a press fit on 1mm shaft. the prop blades will be on 0.8mm carbon so a .030 bit should give a press fit as well. that way i can avoid needing set screws and such.
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Old Jan 18, 2013, 09:31 PM
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Prop hubs

Dereck...
I started working on adjustable blade hubs way back. The early ones were for larger props, before even GWS stuff. The pics show some of the larger earlier ones of different types for 2mm shafts.
For the even smaller ones I found the Didel .3 mod hubs to work well. The plastic Didel hub has two cross holes which the prop bars slip into for blade retention and adjustment.
I have modified my Didel hubs with machined aly screw adapters to grip different prop bar diameters and to better lock in the blade pitch setting. The molded Didel unit is dedicated to the 12 tooth molded pinion on the output gear.
I have also machined all-aly versions of the ones pictured for direct fit to a 1mm shaft with an 0-80 setscrew on the shaft....I use this on all my indoor models where I want a propsaver for a molded prop.
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Old Jan 18, 2013, 10:30 PM
RIP Sheba :(
Robster's Avatar
Brentwood, CA
Joined Nov 2002
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[Bow to Carl] Great stuff!

If I may add one meager little helpfull hint. I've found that keeping the thrustline EXACTLY parallel with the direction of straight on-the-wing level flight will maximize efficiency. Downthrust/Upthrust will waste energy. You can adjust wing incidence for lift and speed but then adjust thrustline for parallelism. There will be a sweet spot of lowest current draw for maintaining level flight.

Rob
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Old Jan 18, 2013, 10:58 PM
RIP Sheba :(
Robster's Avatar
Brentwood, CA
Joined Nov 2002
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Quote:
Originally Posted by derk View Post
If you look at f1d freeflight planes, you will see the general construction people try to emulate with rc duration planes. Balsa is really the only way to get the weight to bare minimums.

Thinking that making it sectional will be the best thing for transportation as well as choosing the best sections of balsa. Removeable wings, elevator, horizontal stab and tailboom would keep it around 12 inches for any given part.
Actually, balsa airframes are too draggy. The Kolibri style plane has extremely low drag. The air is like pea soup for low speed duration type flying, low drag is vital! You can still keep the weight down with the Kolibri/carbon rod style plane because you need less airframe components compared to a balsa plane.
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Old Jan 18, 2013, 11:49 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
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Here's one approach by Ray Harlan. This was back in about 2003, and the duration rules at that time called for up to four 50mAh NiCd cells, so a bigger plane. Later the rules were changed for a new class that used a small LiPoly cell, about 60mAh I think, so he built a smaller plane.

I do not know the weight or dimensions of this earlier plane by Ray. It used balsa throughout. The fuselage was rolled balsa tube. The leading (and maybe trailing edge) of the wing had boron rod (thinner than a human hair, and dangerous to work with) expoxied on the top and bottom side of the balsa. This makes it sort of like an I-beam, and it doesn't flex.

The prop was a custom made CF prop with a watch gear drive and 7mm motor (green bell, cool wind). The propulsion system was optimized so the prop would pull it through the air at minimum flying speed and the motor would also be spinning at max efficiency RPM (as opposed to max power rpm that we normally go for). I helped on the motor work for this plane.

This plane flew for over an hour in the Lakehurst blimp hanger. And, that was with heavy NiCd cells.

Gordon
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Old Jan 19, 2013, 01:14 AM
RIP Sheba :(
Robster's Avatar
Brentwood, CA
Joined Nov 2002
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Awesome! Thanks for posting that Gordon. It's a shame we don't see this type of indoor style planes anymore on this forum . Times have changed...

Rob
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Last edited by Robster; Jan 19, 2013 at 01:51 AM.
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Old Feb 19, 2013, 10:41 PM
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derk's Avatar
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So doing some basic current testing on some small gear drives and motors, i am leaning toward using a kyosho Cessna gear drive. On 3.7 volts its pulling 175ma and gives about 10 grams thrust. So if this could cruise a model with a 100mah cell, at around 100ma mid throttle, i could get 45 minutes or so fairly easy. The other one i am looking at is my custom 20:1 4mm drive. I don't have a prop for it, but putting resistance on the shaft, i dont get much more than 125ma. But it would need a very light and alow airframe... As well as a optimized blade shape and pitch.
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