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Old Jan 03, 2005, 01:51 AM
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billystiltner's Avatar
United States, VA, Clintwood
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Calculators and more calculators

Hey
I made a new website over the weekend.
I'm worn out and just have a skeleton of a site up but have the calculators mostly done.

The website is here http://www.geocities.ws/billy_stiltner

You will have to keep closing the annoying geocities ad on the upper right corner .

The site style is kind of a retro style from when the internet was all about sharing information and software before it was littered with spam, spyware and vermin.

The calculators you will find there are basla density calculator , flight speed, wing loading , wing area which all take and spit out information in Metric and Imperial as well as a gear center calculator. My brain is about fried from doing all the conversions and keeping up with all the variables.

I have some questions. I havent finished a prop calculator just yet but started one based on Dannysoars prop carving page. But was thinking there may be someway to go about designing a prop around a models minimum flightspeed and your propshaft rpm at some point between your motors max power and max efficiency. I have made the flight speed calculator spit out flight speed in inches per minute so that if it is possible this value could be used in the prop design calculator. Does anyone know how to go about calculationg prop pitch if you know how fast or slow you want your plane to go and how fast the rpm of the propshaft will be? I know pitch is theoretically how far your prop will travel through the air if it were butter but air is not butter. Please help!
Is there a fudge factor or egyptian constant you can throw in to a calculation to choose prop pitch from flightspeed and rpm?

Billy
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Old Jan 03, 2005, 03:15 AM
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willin's Avatar
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Hooray for Billy! Thank you sir for caring enough about us to take the time and troble for what you have done.

As for your question a prop going thru the air is not the same as dragging a plane behind it. Please don't think I am talking down to you as I am sure you already knew that. I contribute the wording of your question to your weariness.
That same prop/motor/battery set up would perform differently of course on different models. Weight of differing planes would be a factor. Wingloading another.A scale biplane with lots of rigging would be much more draggy than a plane with a low aspect delta wing.
Your question still has merit and I hope someone brughter than I can address it for you.

Thanks again Billy for your site, my hat is off to you Sir. humbley, Robert
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Old Jan 03, 2005, 03:21 AM
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After a few minutes of consideration, one might be able to, using a specific model or models with known recomended target weights come up with a usable database the way Motocalc does using several variables.

Robert
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Old Jan 03, 2005, 10:17 AM
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Mike Taylor's Avatar
Camarillo, California
Joined Apr 2002
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Billy,

I was just browsing through the 1953 Frank Zaic yearbook last month and the figure he gave for working pitch was (I believe) something like 80% of the geometric pitch. I'll have to dig the book out and see what it actually says. I would imagine that prop airfoil and thickness has a lot of influence on the figure as well. I'm sure my old copy of propellor and helicopter aerodynamics has fomulas for such things as well if you want to do the calculus...
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Old Jan 03, 2005, 02:01 PM
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Robert
Thanks.

Mike
I'm not really good with calculus but can usually convert the equations to computer programs. I think I'll go see if the source is available for Martin Heppeler's JavaProp and see what I can find in there.

Billy
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Old Jan 03, 2005, 05:31 PM
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Leicester England
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Billy
Do you have a design for a machine that can balance micro props?
I have been balancing them on a fine wire but this seems unreliable for sub 2" dia props.
I have tried dropping the balde into water to see if one end drops vertically but this is not too good either
I tried the navigators method of deliberate error by makign one blade longer and trying to reduce that blade until balance is found - nope !
Micro props and motors are very sensitive to balance and can add 30 per cent to the current load of the motor

Thanks in advance

Mark
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Old Jan 03, 2005, 07:58 PM
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guadalajara, jalisco, mexico
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Billy, congratulations, your web page is very nice ( I love the Komet plan ) thanks for share your efforts.

Feliz año nuevo, desde México.

Alfredo Rubio
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Old Jan 03, 2005, 09:04 PM
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Mark
I have been balancing them by spinning them on a wire like you.
I spin them several times to see which blade is heavier.
I sanded away a glob of glue from the front of one of my props the other day
and then when I flew the plane it vibrated pretty bad. I then remembered the glob of glue was a quick fix for balancing the prop so I sanded the other blade a bit and it ran smoother. I'll have to do some thinking about making a prop balancing machine.
Do you know of a site that has any photos and decription of a prop balancer for larger props?

Alfredo
Thanks The CLG plans are a bit rough around the edges and were drawn pretty quick.
There was a postal contest running for the simple delta sheet gliders as well as 6" span HLG and CLG so I drew up some plans. I got the best times with a scaled down 6" span Phantom22. It was weird the plane was light but would launch higher than the rest.

Billy
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Old Jan 04, 2005, 11:43 AM
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Rochester Monroe Cty, New York, United States
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Thanks

Billy,

Thanks for the calculators. Great work.

I haven't done this, but would a flimsy mount with a test motor work? A flexible mount would accentuate the vibrations. Randomly picking one blade and noting improvement or degredation would get things started. This would be a clunky dynamic balancing method. It is just a variation on your method after the glue removal.

John
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Old Jan 04, 2005, 11:55 AM
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John,

That sounds good. A small piece of tape on one blade and it will either get better or worse. As long as you have a variable power supply to keep things from getting out of hand. Once the bad blade is determined it should be pretty straight forward to work on it slowly. Will also probably have to try twisting the blades a bit as difference in pitch can be a problem with these cheap little props. Good to hear from you again.

Dave
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Old Jan 04, 2005, 12:23 PM
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I have checked most of the calculators against others but may have missed something.
So if you spot any errors please let me know. I guess some things to add would be g/sqm and such for comparing covering material. Plus lb per sq ft on the wing loading calculator to compare wing loading of real planes as well as several other flightspeed units. I havent seen any gear center calculators so only checked that by measuring some gears and making a gearbox. It seems to work out with watch gears so I reckon ought to work with larger gears. A weird thing about the module formula was I had to multiply the result by 10 to get the module in mm. I guess that the original formula was assuming the units would be in cm. Also I think that 0.005mm is a good mesh allow distance for 0.125mod watch gears.

John
Thanks.
That is a good idea.
Dave
That is also another good idea.


All my less than 2 inch props have been made with either maple or obeche and were easy to balance on a wire. It may help on lighter props to put the prop on a shaft and put the shaft in a tube then hold the tube with a clamp.

It is wild that an out of balance prop can be 30% less efficient than an in balance prop.

Billy
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Old Jan 04, 2005, 12:54 PM
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United States, OH, Galena
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Quote:
Originally Posted by billystiltner
It is wild that an out of balance prop can be 30% less efficient than an in balance prop.
Billy
Is it not that the prop is less efficient, but that it makes the motor be less efficient by increasing the friction in its bearings?
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Old Jan 04, 2005, 01:02 PM
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Mike Taylor's Avatar
Camarillo, California
Joined Apr 2002
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My prop balancer is just a piece of CF rod the prop slips on without filling the hole. I mount the cf rod off the end of a table. The heavy blade has enough weight to swing it down. When it is balanced, it will stay in any position you set it. This works good enough to determine whether to take material off the front or the back of a blade or off one side of the hub...
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Old Jan 04, 2005, 01:16 PM
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rance's Avatar
Northern VA
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Mark,

Have you tried a magnetic balancer? Sounds like it may be the best for tiny stuff. See http://www.rcgroups.com/forums/showthread.php?t=1323 (open the manual for the Tower model)

If you want to make your own mag. balancer, you could start with one of the hard steel rods (rails) found in a CD rom drive that move the head fwd/back. Chuck it up in a drill to sand a point on one or both ends. However, these rods are prob. too big for your small props. Maybe do the same with a piece of music wire.

Rance
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Old Jan 04, 2005, 02:10 PM
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United States, VA, Clintwood
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JMP

I think you are correct.


Billy
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