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Author Topic: Propeller for "The Fly"  (Read 4528 times)
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LivingRoomFlight
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« Reply #25 on: October 10, 2015, 08:14:51 PM »

What helped me was going down with the power. So, apart from trimming mentioned, I suggest you use 1/16 rubber you have, one strand, not loop about 10" long. And go up to 12". That will not be enough power though to use propeller from ikara. You have to have balsa wood prop, which is not difficult to make. That strand of 1/16 will allow you to put ~ 2000 turns and more. That means, that the model needs to be less than one gram also. Easily you can go to 0.7g with balsa prop as I mentioned before. No expert materials are needed for that. This will increase flights to 3minutes and above.
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lincoln
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« Reply #26 on: October 11, 2015, 12:38:08 AM »

I think this is the model we're talking about, isn't it?:
https://theflyadelaide.wordpress.com/

Seems to me that most of the weight will be in the prop, the bearing, and the rear hook. They look awfully bulky. And I don't see how the model could be balanced without tail weight, unless you are using Guillow's wood* to build it. The model seems to resemble a Mini Stick. Recommend you use a homemade or Harlan bearing up front, and some kind of wire hook at the back. On a model this small, you can probably use wire around .010, or possibly even smaller. (read: use the smallest string from a guitar). If you use wire and/ or a Harlan bearing, plus a homemade prop, you should be able to get down around a gram and a half, or even less. Without going nuts. For ideas on bearings, hooks, and homemade props, you might check out the Mini Stick articles and plans at: http://indoornewsandviews.com/ and http://www.indoorduration.com/  You might find the article for the No Non Cents pennyplane handy as a reference.  It's quite well written. http://www.rcgroups.com/forums/attachment.php?attachmentid=2294852  But remember that's a MUCH larger model. Also, if you're using information about props from a Mini Stick article, you will probably want to go with a much smaller prop.


*I have measured Guillows wood at something like 23 lbs/cubic foot. That's a specific gravity around 0.37 or so. The lightest wood I've used successfully is about 3.5 lbs! The average run of balsa is around 8-12 lbs, isn't it?
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lincoln
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« Reply #27 on: October 11, 2015, 12:42:43 AM »

P.S. If you have a reasonably sized flying space, you may find limited pennyplane easier to deal with. I think the Cezar Banks design is supposed to be good, as well as the No Non Cents. I once helped a beginner get over 5 minutes under a 35 foot ceiling with a limited pennyplane. (Or is it Novice Pennyplane?) I've had my current pennyplane for many years, and I don't remember where I got the proportions, though I'm pretty sure the second prop was from the Banks model.
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Glidiator
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« Reply #28 on: October 11, 2015, 12:20:25 PM »

Hi all,

Thanks fitnezz for the inputs on rubber dimension. Will try out your suggestions. Over the last couple of months doing test flights is giving me appreciation of the effects of rubber dimension, length of motor, number of turns etc.
Made a torque meter today from instructions from http://www.gryffinaero.com/models/ffpages/tools/torque/tmeter.html
Seems to be working okay. Also made a jig to do winding off the model. So now I can get in the 2000 turns off the model without problems.
As for making a balsa prop -- a few  questions
Should it be the same Dia, pitch etc of the Ikara propeller.
Or will it just need to be a paddle propeller.
Made a propeller for my A6 a few days ago, and its test glides/ very low power flights are very encouraging. So now have better confidence in making own propellers.
Also keeping the weight in the 1gm range I will need thinner dimensions on the various components as we dont get balsa of various density here. It is just sold in 3 ft x4" sheets of various thickness. Have no idea of the density. I doubt the hobby shop even knows. As mentioned earlier I seem to be the lone Trojan dabbling in indoor rubber band free flight in India so critical issues like balsa density is yet to percolate into the scene. I should weigh a standard piece and calculate the weight per cubic foot.
Yes, I will get on to the limited penny plane as suggested.
Have just made a A6 that seems like it will give a over 1 min flight if I get the rubber motor length and thickness right. Breaking the 1 min barrier on any model will be nirvana.
Had a look at the Fly video by Aki Danjo. Will try the suggestion of reducing/removing stab tilt. And yes the motor does need to be longer.
The slew of various suggestions and analysis done of my test flight video just makes me appreciate how much there is to what seems like simple rubber band models. Enough to give any aeronautical engineer an inferiority complex.
Will  get back with the effects of implementing the various suggestions.

Pics of my A6 propeller and torque meter and winding jig attached.

Attached files Thumbnail(s):
Re: Propeller for "The Fly"
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Re: Propeller for "The Fly"
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Twinchicky
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« Reply #29 on: October 11, 2015, 03:35:57 PM »

I very much second the recommendation of building a limited pennyplane. My first LPP (an original design) did 6:34 under a 35' ceiling at high elevation with decent rubber. I'd imagine 5 minutes would be attainable with Super Sport or whatever rubber you have.

Also, nice-looking A6 prop. I notice you've sort of knife-edged the sides - if you can get your sanding technique down, it's better to have a slow, shallow taper across the whole blade than a steep one right at the edge. It saves more weight and is theoretically also more aerodynamic. You might not want to make the edge super-thin though, as that increases the chance of making little dings and chips in the edges of the blades.

When you go to wherever you go to get balsa, bring a .01 or .001-gram scale with you and weigh the sheets. You can make up a little spreadsheet for density vs. sheet size, it's not too hard. I've found a couple pieces of 4#/ft^3 wood at hobby shops this way.
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Tapio Linkosalo
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« Reply #30 on: October 12, 2015, 12:47:23 AM »

Or, for Jaakko (the original author) my recommendation would be building a "Peruslennokki", as that sort-of beginners class sees the liveliest attendance in Finland. For the time being at least, as just two weeks ago I gave a course on building F1M-limited for 10 persons, and in a week there is another one for 5 more, so maybe this autumn F1M will pass the beginners class in popularity in Finland?! Fingers crossed!
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Glidiator
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« Reply #31 on: October 12, 2015, 03:52:43 AM »

Wish there was an enthusiastic indoor free flight group in India like there are in many places around the world.

Need to take the first step and start one in my state.
Maybe involve the technical colleges first.

Anant
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lincoln
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« Reply #32 on: October 12, 2015, 04:29:54 AM »

Hi all,

snip
Should it be the same Dia, pitch etc of the Ikara propeller.
Or will it just need to be a paddle propeller.
snip
Neither. While you can get away with a paddle prop, your times will be much lower with it. The same diameter is probably a good place to start, though. You could use the same blade shape as your existing A6, I suppose. But if you wet it, then strap it to an appropriately sized cylinder while it dries, you'll get a much more efficient propellor. Be sure to use much thinner wood. EZB prop blades tare usually less than .010" (0.25mm) thick (unless you have usable 3.5 lb wood, but don't try it yet!).

If you really want to get into this, you will find most of your questions answered much faster and more completely if you get a copy of Building and Flying Indoor Model Airplanes. One of the best books I've ever read, and probably responsible for my entry into the hobby. I don't know how hard it is to get in India, but it may be worth a bit of trouble.
http://www.indoormodelairplanes.com/
The No Non Cents article I mentioned earlier is pretty good, but not as extensive. At the moment, though, it's on line.  For specifics of Mini Stick models, which are quite similar to the Fly, the other links I posted will help. However, you should scale down the prop in all dimensions. A diameter half or 2/3 of the wing span is probably easier than the same as the wing span! (Most Mini Sticks have very large props compared to the size of the model.)

Pitch on indoor duration models is usually in the range of 1.5 to 2 times the diameter. It's probably easier to start with the low end of that range.
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Hepcat
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« Reply #33 on: October 12, 2015, 05:26:07 AM »

Glidiator et al

The chart below may be useful when buying balsa (as long as you have your scale with you).

John
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Glidiator
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« Reply #34 on: October 12, 2015, 12:45:43 PM »

Hi Lincoln,

Thanks for the inputs on appropriate propeller.
Did not understand what you meant that pitch is 1.5 or 2 times Dia. How does that translate into degrees that I can set on the pitch gauge.
As for thickness of balsa -- the minimum we get here is 1 mm. Can sand it down to 0.5 mm. And avoid the knife edge as observed by twinchicky.
Yes I can wet and strap to a cylinder at 15 deg tilt to give it the required twist.
Have downloaded the No Non Cents article Will read and digest it.
The book Building and Flying Indoor Model Airplanes is available thru amazon but it costs a bomb here due to import costs.
Need to put in a lot of building time to implement all the suggestions.
Anant
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LivingRoomFlight
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« Reply #35 on: October 12, 2015, 03:23:56 PM »

Gladiator,

I hope I will not say anything wrong, but thats how I do it:

Lets say I want P/D = 2.0 for the 5" prop. (just example). Than P = 2 * D, P = 2 * 5 = 10. Also P = 2*PI*R*tanFi, for 45 deg tanFi = 1, so P = 2 * PI * R. Than you can calculate R -> 10 = 2 * PI * R,
R = 10/2*PI That is distance you need to use on your pitchgague (distance from prop hub to 45 deg slant on gauge)

Also I put the photos of bearings of my 7" amateur airplanes and prop, may be helpfull...

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Re: Propeller for "The Fly"
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Glidiator
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« Reply #36 on: October 13, 2015, 10:50:24 AM »

Hi all,

Thanks for the maths on pitch and distance of hub from the gauge.
And the balsa chart.

Built my own balsa prop for the Fly using the same profile and sizes as the Ikara 6" prop I was using earlier. Will need to build another Fly to test this prop as the first one has the Ikara nose hub glued.

My prop is lighter than the Ikara one and I can reduce the weight further by sanding the blades down some more to about 0.5 mm. It is now just a little under 1.00 mm.
Also I will be cutting the drive shaft shorter to the required length so that will remove some more metal and weight.

Pics of the two props weight is attached.
Anant


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LivingRoomFlight
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« Reply #37 on: October 13, 2015, 11:28:31 AM »

Nice progress, but keep on sanding Smiley You should sand them so long, they become almost transparent. Than wet it, form on the cylinder to add helical shape and bake it (or just let it dry). Also my suggestion would be not to use the plastic pipe as connector (if you want to have not fixed pitch, use paper tissue tube instead). Only balsa + thinnest guitarr string for the shaft 0.011" ? Smiley The prop now is at least twice as heavy as it should, so not much of the performance gain will be noticed.

I am total noob in that, but I remembered, what someone smart said, that good prop is half of the success. Apparently
good prop + average airplane >> good airplane + average prop Smiley
Still good prop + good airplane is the goal, isnt it?

Did you watch float ministick & pennyplane videos?

https://www.youtube.com/watch?v=uNJy3AR7uzE

Have a long flights + a lot of fun Smiley
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Glidiator
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« Reply #38 on: October 13, 2015, 12:12:11 PM »

Yes. Need to bring the balsa thickness down drastically. Also will use guitar string and tissue tube. All this will bring the weight down considerably.
Yes I have seen the video.

Back to the drawing board to improve on the build details.

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Glidiator
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« Reply #39 on: October 13, 2015, 12:20:24 PM »

I had posted a topic in the workshop tips on using feeler gauges to get the thickness required.

I have found this a good way to sand down to desired thickness.
Check out this thread I posted

http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=19441.0

Anant
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LivingRoomFlight
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« Reply #40 on: October 13, 2015, 06:30:43 PM »

One thing I forgot, the prop on my photo is also copy of ikara 1:1. to give you the idea of weight, we are talking about using hobby shop wood, the whole prop is 0.15g, which is still very heavy as for ministick...
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Twinchicky
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« Reply #41 on: October 16, 2015, 01:15:10 PM »

To give you an idea, here's a photo of one of my ministick props. 6.25" diameter, somewhere around 12" pitch. The high pitch means that there isn't much twist in the blades, but it's enough. http://imgur.com/X4tmMwm

The blade thickness is .014" or around .35 mm, and it's quite sturdy and could be thinner. Weight is 0.14 grams. My slightly larger 7" prop with a little bit heftier spar and the same blade thickness weighs 0.17 grams. I think that a 0.2g prop for your Fly should be no problem to make.
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Glidiator
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« Reply #42 on: October 16, 2015, 03:04:23 PM »

Have sanded another set of blades down to 0.5 mm. Weight I think was 0.15 each. Have soaked and put it on a cylinder for getting the twist. Can sand down even more to 0.35 as done by you.
Will remove from cylinder tomorrow morning and weigh again.
Just a very basic doubt. What is the direction of the wood grain with respect to the prop shape. Have seen some plans and articles that show the grain direction. Cant seem to find those references.
Will use tissue tube as hub to join spars. Would help in weight control
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LivingRoomFlight
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« Reply #43 on: October 18, 2015, 08:44:55 PM »

Hey Glidiator,

The grain direction depends on how much you want your prop to bend. I assume you are not using C-type grain balsa, so it is probably A. If the grain goes along with blade main axis (spar) the prop will bend more (esp if it is flaring type prop - take a look on the scaling down EZB topic, I learned about flaring props there). If the grain goes diagonaly against blade axis, it will bend less. I suggest you keep on sanding down as much as you can without destroying balsa sheet and let the grain go diagonally about 45deg against blade main axis - the blade will be stronger. And ikara propeller is not a flaring type anyway.

P.S. I dont know if it is truth, but I guess sanding more gives not only weight benefit. Thinner blades cut the air better and produce less drag. Please correct me anyone if I am wrong here - that is just my theory =)
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Glidiator
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« Reply #44 on: October 19, 2015, 12:37:37 PM »

Hi all,
Made a new propeller with balsa sanded down to 0.3 mm, grain 45* to length of prop. Total weight now down to 0.36 gms including bearing, nose hub, etc.
Will have to now shift the main wing posts to get the right balance on the plane as the design position was for Ikara prop which is much heavier (0.98 gms).
What is now required is to do a series of test flights.
My A6 is also awaiting test flights after correction of turning problem by giving the tail boom an offset. So also my Double Whammy.
Lot of testing to do. This time I also have a torque meter so will note readings and do some proper data recording.
Hope to break the 1 min barrier.
Pic of new propeller attached.
Anant
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Glidiator
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« Reply #45 on: October 19, 2015, 12:51:45 PM »

Fixed the 0.36 gms propeller to the Fly after removing the Ikara hub.
The balance is totally off. I guess the original dimensions of the wing and stab components was okay for the heavy Ikara propeller (0.98 gms).
Now with a propeller that is three times lighter the stab spars and ribs will have to be drastically reduced in thickness to get a proper balance.
Will  have to make a whole new model with much thinner components.
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LivingRoomFlight
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« Reply #46 on: October 19, 2015, 02:39:28 PM »

Anant,

Keeping fingers crossed, looks promissing Smiley
Probably pigtail type thrust bearing is the next thing to go.
You will definitely want to try to diferent propellers in your new model, right?
Oh, and I would not use paper for covering anymore.

Waiting for the new video.

cheers!
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Glidiator
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« Reply #47 on: October 20, 2015, 11:47:51 AM »

Hi,
Will have to build a swarm of FLYs to match the various propellers of different weights I have made.
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Twinchicky
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« Reply #48 on: October 20, 2015, 05:55:13 PM »

Anant,

I think using lighter covering will really help you out. Ray Harlan from indoorspecialties.com sells UltraFilm and SuperUltraFilm (Not sure if he ships to India, but his website doesn't specify). I use SuperUltraFilm for everything heavier than F1D and it's quite good. Using a plastic film instead of paper will save a lot of weight, and your wing structure won't have to be as heavy. There are many articles out there on covering with plastic films, including those on Ray's website.

Also, from the photo of your propeller, the edges of the blades look a little bit rough. You can hold the two blades against one another and sand the edges of both blades at the same time to both smooth out the shape and make sure the blades are identical - I realize that prop is already assembled, but just for future reference.

Best of luck!
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Glidiator
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« Reply #49 on: October 20, 2015, 10:37:55 PM »

Hi Twinchicky,

Did sand the edges with blades together. Not enough from looks of the finish. Was in a bit of a hurry. Patience is the name of the game in indoor ultra lights.
Have used mylar which I first got from freedom flight models. Have used it on my hangar rat, Biscayne baby (nice LRS), Double Whammy and my A6. Mike Woodhouse also supplies mylar of different thickness - 1,2 micron etc and is cheaper too.
Need to get fresh stock to use on models being made now with my own lighter propellers.
Pic of my A6 with mylar.
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