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Old Feb 15, 2003, 10:53 PM
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Does anyone know how to make a prop from yogurt cartons?

??????????/

I heard rumors of this. But cannot find any method?
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Old Feb 15, 2003, 11:51 PM
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Establish a (reference) line from the top to the bottom of the container, now create a second line (off set) at 30% from the first. Draw your prop using the second line as the leading edge or center.

This procedure will be explained in detail where ever you find peanut scale FF modeling.
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Old Feb 16, 2003, 05:52 AM
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Here is a picture of a styrofoam coffee cup showing the same technique. When you have your blades glue a spar(toothpick or other hardwood stick) down the middle. Then make a hub from a peice of tubing. Drill a hole in the hub for your prop shaft. Stick the spars into the hub. Now you have a yogurt pot prop.
If you need more info let me know there are numerous websites
describing this technique using balsa sheet formed on a cylinder instead of plastic. The plastic is more durable but heavier than balsa. You can increase the strength of a balsa blade by adding material to the front like tissue(i have used leftover christmas ribbon).

A good alternative to plastic and balsa is styrofoam. Fits in between them weightwise and strengthwise methinks.

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Old Feb 17, 2003, 11:57 PM
del
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There are "bottle props" and "bucket props"...
The difference is that one comes from a cylinder and the
other comes from a cone. Generally, a prop that
comes from a conical piece of material stands a better
chance of having a good pitch distribution than something
made out of a cylinder.

Years ago a friend of mine, Fred Rash, worked out the math
for making a helical pitch prop on a conic form. Ya might
try a web search for "Bucket Prop"... I seem to remember an
article in an old issue of the NFFS Symposium.

Making props ain't easy, but it is...

If you have a prop of the same pitch you're trying to make lighter,
put it in the yogert can and do a "best fit". That'll be
the angle that ya need to make yer cuts along.

For a helicical pitch, the blade angle is:
a = arctan ( pitch / 2 * pi * r)
where a is the angle from the prop shaft and r is the radius from the hub.

If you need to know more, let me know,

I don't know everything. Who does?.
All I can say is, the more props I make, the better they work.

Maybe I should go back to work on my old prop-calc javascript
web page?

--del
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Old Feb 18, 2003, 01:16 AM
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@del
I was trying to look on your webpage for information a while back. I cant remember what info or where I found out about it.
Anyways the link I followed didnt go anywhere.
It was probably an old link that referenced something you put on there temporarily.
I am very interested in your information on props. seems like the more I make the better they get also. I have done quite a study on props. I havent been into this hobby long but have learned quite a bit in a short time. I was going to write a javascript prop thing but havent got a round tuit or a wooden nickel either. I have seen them(round tuit and wooden nickel) though.
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Old Feb 18, 2003, 09:21 PM
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There is a good description in Wayne's World.
http://www.ezonemag.com/articles/199...yne0799htm.htm
You can make quite a variety depending on the shape and material of the "bottle".

Rick.
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Old Feb 19, 2003, 12:01 AM
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I tried that 2 liter bottle prop thing and the prop ended up ridiculously heavy for small models. The plastic on those bottles is a bit flimsy also. A better plastic is the plastic on plastic cups if you can find smooth ones. I guess if you can find the right yougurt container this would work as well.

@Del I think I was looking for something about A-6 plans or props.
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Old Feb 19, 2003, 02:55 AM
del
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Prop-calc araises from its ashes

Friends,
My old propeller web page, with a blade angle javascript calculator has
risen from its ashes. With some new info.

Y'all can find it at:

http://n-lemma.com/indoorrc/propcalc.htm

If ya wanna have some fun, try to get an article about making
props published in R/C Microflight. I got told that no matter
how slow the prop turned, or how little it weighed, no prop construction
article would be published by Air Age! It might put somebody's eye out!
Yet, they have no problem advertising the crap out of speed 300 ARF's...

Is anyone out there old enough to remember when Model Airplane News
had articles about _building_ model airplanes?

--del

p.s. wish me luck. got a new indoor model on the bench. trying to get
a 120 sq in rffs-100 model to come in at a gross weight of around 10 grams...
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Old Feb 19, 2003, 11:37 AM
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@del

I think that is what I was looking for.
Thanks.
You could put 2 buttons beside the degree box 1 for calc pitch and 1 for calc radius so that you could just enter a pitch and angle or a radius and angle. That way if you have a fixed degree pitch guage you can tell where to put the angle for a desired pitch. It works ok though the way it is by plugging numbers till you get it close. Things get messy with javascript when there are too many options and input box combinations.
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Old Feb 19, 2003, 03:12 PM
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Re: Prop-calc araises from its ashes

Quote:
Originally posted by del
I got told that no matter
how slow the prop turned, or how little it weighed, no prop construction article would be published by Air Age! It might put somebody's eye out! Yet, they have no problem advertising the crap out of speed 300 ARF's...
But the 300 ARF's are Hobby Lobby's liability concern. RCMF has lots of airplane construction articles and did have one on Chris Martin's ARC props and jigs.
You really can't blame Air Age. A single lawsuit could end publication of all their magazines forever.

I've also seen carbon fibre prop blades molded on and cut from a bottle, if you think the blades from PETE are too heavy. Might have even been described on this board.

Rick.
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Old Feb 20, 2003, 12:16 AM
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rpage53

I should have said too heavy for my application. The prop ended up weighing more than the airframe.
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Old Feb 20, 2003, 12:19 AM
del
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babysitter,

Glad the prop-calc page comes close to what you were lookng for.

Yes, I could modify the javascript to solve for radius and pitch,
but why? When I'm carving prop forms, I know what pitch I'm going
for and what diameter. All I need to know is what angle to mark
on the end of the block. I'll leave it alone for now..

But, hey, man, if ya know javascript, why not crank out "pitch-calc"???
Input radius and angle, and out comes pitch.

What _is_ the pitch of a U-80, or whatever, prop?
Most folks talk about the maker's model number, but that doesn't tell
me what I wanna know...

Have a big time.
--del
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Old Feb 20, 2003, 01:04 AM
del
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Re: Re: Prop-calc araises from its ashes

Quote:
Originally posted by rpage53
But the 300 ARF's are Hobby Lobby's liability concern. RCMF has lots of airplane construction articles and did have one on Chris Martin's ARC props and jigs.
You really can't blame Air Age. A single lawsuit could end publication of all their magazines forever.

I've also seen carbon fibre prop blades molded on and cut from a bottle, if you think the blades from PETE are too heavy. Might have even been described on this board.

Rick.
True enough, Rick, I have no problems with RCMF. I'm a happy
subscriber. And I thank John and Tom for the good work they've done.

But Air Age Publications in general seems to me to have contributed
to a dumbing-down, of model mags. In essense, Model Airplane News, and
Backyard Flyer have become little more than illustrated catalogs for
their advertisers.

Even the AMA rag, Model Aviation, seems to have gone over to the
dark side of the force.. Fewer construction articles, fewer column
inches for sub-groups like indoor and outdoor Free Flight.

OK, ok, maybe I'm just an old fool who wants to make consumers
suffer through learning to cover with tissue paper.. But I also think it's
way-cool to watch something that ya hatched from between yer ears
fly. I learned to make models by reading design and constuction articles.
And I see them less frequently...

Enough! I'm off the soap box...

Anyhoo, back on props..

On the kitchen counter sits a Kentucky Fried Chicken foam cole slaw container.
My wife asked, "Why are you keeping this?" I responded, "Wouldn't a
propeller with Col, Sanders' picture on it look cool?" She just shook
her head and walked away with a look that said, 'I should have known better
than to ask...'...

--del
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Old Feb 20, 2003, 01:22 AM
del
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Quote:
Originally posted by rpage53
There is a good description in Wayne's World.
http://www.ezonemag.com/articles/199...yne0799htm.htm
You can make quite a variety depending on the shape and material of the "bottle".

Rick.
Yea, fine, but...
That's a bunch of work for a prop that _might_ work.

I'd rather belive that I think I know what I'm dealing with in terms of pitch distibution, and strive toward an optimum prop/gear/motor combo.

Assuming that's possible...
--del
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Old Feb 20, 2003, 07:34 AM
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Del,

Best I can tell, using your pitch program, the U80 is 3.125"D x 1.5"P. First time I ever tried to "read" a prop, so if someone else would double check me that would be great.
To clarify this, I measured a 25 degree angle, 1/2" out from the prop center.

Dave Wulff

Del, PS per your email, ..Herr walnut (17" s&t) Cessna 180, very slowly.
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