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Author Topic: Making balsa props using the laminated fan method  (Read 1482 times)
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dieterperiperi
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« on: June 06, 2017, 05:41:24 AM »

Hi all

Found this article on prop making.  This looks to me like a reasonable simple method to use. The internals corners of the laminated section could be used as a guide when sanding/finishing?

Has anyone tried this method before? And what were the results?

D

http://website.lineone.net/~raynes.pk.mac/makeprop.htm
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p40qmilj
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« Reply #1 on: June 06, 2017, 06:22:58 AM »

 Grin  i made a DA BACKASSWARDS PROP that way.  imagine Cloud Tramp as a PUSHER canard  and it flew fantastic

  JIM Grin Grin Grin Grin Grin
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dieterperiperi
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« Reply #2 on: June 06, 2017, 06:52:40 AM »

Grin  i made a DA BACKASSWARDS PROP that way.  imagine Cloud Tramp as a PUSHER canard  and it flew fantastic

Nice one Jim
Pusher is mentioned in the tutorial also. Is this prop making way only effective for pusher planes?? (sorry if this sounds like a stupid question)
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Rich Moore
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« Reply #3 on: June 06, 2017, 07:56:34 AM »

I used this a few years ago and the model flew brilliantly. Can be used to make 3-bladers as well.
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Warhawk
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« Reply #4 on: June 06, 2017, 08:31:14 AM »

The only issue I've had with these types of props is glue bumps when sanding them down.  The same thing can happen with a laminated block, but with a bit less effect.

The wood savings is significant, and you can control the pitch with the amount of overlap/slat width.

Justin
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dieterperiperi
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« Reply #5 on: June 06, 2017, 08:49:31 AM »

I used this a few years ago and the model flew brilliantly. Can be used to make 3-bladers as well.

Thanks for the feed back guys. Ive been lamenting over carving a prop.  But this method lookks way easier. Sure there are some pros and cons.

Rich a brief description of making 3bladers please. I suppose it involves joining 3 sections up? Any tips

 
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Hepcat
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« Reply #6 on: June 07, 2017, 12:08:59 PM »

Dieterperiperi

.Making a fan laminated propeller is something all aeromodellers should try at least once.  The pictures are always very seductive and the method can produce very good propellers but it is always sensible to date a few girls before you commit yourself to marriage for life because it is not quite as simple as the pictures suggest.

I think that slip-ups are often because the method is usually recommended as a good way of saving wood and with that in mind builders overdo things and make the laminae too narrow.  This can give overlaps that are too narrow for good gluing areas and perhaps not enough width for the widest part of the blade.  Another related problem often mentioned is the difficulty of applying pressure on gluing joints.

As I said earlier, give it a try but do spend a bit of time on the drawing board before you cut wood.

I did actually spend some time on my drawing board a few years ago when the question of fan laminated props came up.  I did some calculations and produced a spread sheet which asked for the following propeller details: P/D ratio, max blade width, where that occurred, the minimum wood thickness at the tip and the thickness of the wood laminations.  The spreadsheet then calculated the number of strips and their width.

I attach three pictures below. If you would like a working copy of the spreadsheet let me know an email address.
John

PS I think the easiest way to make a propeller is from a block, providing you have a long, sharp knife and the best way is by moulding something (not necessarily balsa) on a helical pitch block.

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calgoddard
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« Reply #7 on: June 07, 2017, 01:25:28 PM »

Once again Hepcat is correct. Listen to his advice, on all subjects pertinent to your building and flying.

The first built-up balsa prop I made for an outdoor model was made with the laminated method.  See the attached picture.

I built this prop for my MAXOUT X Embryo.

I doubted my carving abilities and felt like the laminated method would be easier and produce a stronger prop.  I also thought the laminated method would ensure that the finished prop has the desired P/D. I was wrong on all three.

Despite careful wood selection, the laminated prop turned out to be heavier than a balsa prop of adequate strength carved from a block. I used carpenter's glue to hold the skewed sheets together because it is easy to sand after it dries.  I thought I was careful not to use very much glue but it adds up quickly.

There is a tendency for the surface of the blades to ripple after sanding, owing to some aspect of the lamination.

Then, after considerable effort in terms of sanding and shaping, one blade turned out to have the wrong pitch.  I still don't know how this happened.  I had to saw the blade through at the root and use a toothpick segment as a dowel to re-connect and re-glue the parts together after re-pitching.  You can see the seam in the photo.

I also failed to sand the blades of my laminated prop thin enough to reduce drag.

Now I must add that despite all these errors my MAXOUT X Embryo with this laminated prop that I made is a great flier, owing to Joshua Finn's excellent design. It has won me several Kanones in heated FAC competition against others flying the Debut Embryo, and other good Embryos.

I vaguely recall making one other laminated balsa prop, but don't remember which model I used it on, if in fact I ended up using it.

Now I make my balsa props from sawed Superior Props blanks that I purchase from Volare Products.  You can certainly cut your own blanks, but I am too lazy, and I can buy the blank with the exact diameter and P/D that I want.

I covered both sides of the last balsa prop I made from a Superior Props blank with lightweight fiberglass cloth using a single coat of epoxy resin, both of which I purchased from SIG.  As I recall that prop has an eight inch diameter and its final weight, after sanding, was 4.69 grams.  See attached picture.

Some people cover their balsa props with Esaki tissue to add strength. Some just use a few coats of dope or a few layers of clear Krylon spray.    



    

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calgoddard
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« Reply #8 on: June 07, 2017, 03:01:07 PM »

OK - I found a picture (attached) of the other laminated prop I made.

It was nine inches in diameter. I made it for my Skokie.

Its weight, after carving and sanding, was pretty good.  This is without any coating, i.e., dope, fiberglass, clear Krylon spray, etc.
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rpendzick
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« Reply #9 on: June 07, 2017, 06:53:22 PM »

I used a round 1/32 ply biscuit as the hub, slotted all 3 blades to fit the biscuit. I used brown Rit dye on every other laminated balsa piece. It gives a nice grain and makes it easier to carve.
have fun - Rick
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dieterperiperi
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« Reply #10 on: June 08, 2017, 04:31:19 AM »

Thanks Hepcat and Cal for your valued info and shared experiences

I think I will try the fan liminated method and build on that to carving from block.

Cal, the light fibreglass cloth covering sound good and must certainly add lots of strenth(and a bit of weight)

John, I will PM you my email adrress for the spread sheet, thanks for sharing

Rick, you triblade looks good with the stain. I have to make some triblades for ongoing P38 Lightning build. The plywood biscuit is a good idea. I thought of leaving different layers of laminations out by the hub on each blade and slotting them back together on assembly. It can be done but might be a bit tricky.

I think when making the triblade prop fan method could work well, making two identicals and then having a spare blade if something goes wrong

Thanks everyone for you input, greatly appriciated

Dieter


 
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TimWescott
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« Reply #11 on: June 11, 2017, 06:29:31 PM »

Pusher is mentioned in the tutorial also. Is this prop making way only effective for pusher planes?? (sorry if this sounds like a stupid question)

No.  Any prop can be used as a pusher.  Even ready-made plastic props can be modified.  Basically, you just mount the prop so that the rounded face is facing forward and the under-cambered part is facing back.

For a plastic prop it's a matter of removing the freewheel notch and coming up with a freewheel method.  For any other prop, you just remember that it's the front of the prop that rides against the thrust button and build accordingly.
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dieterperiperi
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« Reply #12 on: July 22, 2017, 03:06:11 PM »

Hi all,  I've started making the fan laminated props and find it relatively easy. Made a 5" prop complete with 22g brass tube which weighed in at 0.64grams. Now I have to admit that I didnt pay much attention to pitch angle, just what looked right. Matched it up with some plastic kit prop i have and it looks pretty much identical.

Glued two more today which will be for a tri-blade prop attempt. Used 1/8 x 3/32 balsa strip. Larges props will require bigger balsa strip. Must use Hepcat's strip calculater mentioned earlier in this post also

There is room for improvement on the shape of the prop and this is where carving from block whould be easier as you can mark and cut the shape out before on balsa block. A bit harder to do on the staggered shape you have with the fan method.

Other obvious bits that are really important is that make sure the piano wire you build on is dead plumb and that holes through the strip is dead centre and when tapping up (as seen) is not too tight otherwise the the prop will be bent out of shape (one of the cons mentioned ealier in the post). I didnt carve at all on the finished prop, just sanding with 150 and 180g paper and using some of my sanding tools

Will update you all with the progress on the tri-blade

D
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dieterperiperi
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« Reply #13 on: July 24, 2017, 05:19:03 PM »

Update on the tri-blade:

I think the photos pretty much speak for them selves, but anyway. I cut the two identical (thats lie) laminated blanks in half carefully smoothed up the cut end to make the laminated sections clearly visible and saw out the notch for 2mm ply biscuit (thanks Rick for the idea)
sanded the notch bigger using glue joints as a guide and checking regularly. I think the are a tiny bit too deep but the prop has survived thus far.
Printed out the triangle with lines which i found searching images online and made the jig with some off cuts of prop material glueing them onto the printout. 
The bottom laminations slid in nicely and inwas able to sand the three jointed junction timely manupilating them in the jig till I was happy.
Made a hole in the biscuit, inserted a piece of piano wire, checked that was plumb from all sides and glued the whole lot together with aliphatic resin glue (great glue in my opinion)
Now when I first made the fan blanks the top few laminations got curved along the lenth of blank due to taping/clamping and remained that way so when jigging up the three sections made sure the original bottom ends stayed on the bottom

I was able to sand down tonight curing for 24hours and again didnt have to take a knife to it sand paper with sanding tools mostly rounded shapes. The empty silicone tube with 150g held around it worked realy well with me being able to curve it more or less as sanded the closer or futher from the hub

Now I will have to study endless amounts of tri-blade prop images to shape my prop too a decent looking thing.

There is still quite a bit of thinning out and tidying to be done but its a start.

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Hepcat
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« Reply #14 on: July 24, 2017, 05:51:14 PM »

dtpp,
That looks a very nice piece of work, particularly as a said earlier that some books suggest it is easier than it is.
John
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dieterperiperi
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« Reply #15 on: July 25, 2017, 05:06:55 PM »

Thanks John.
Here it is,  very close now.
I rigged it up with a bit 22sgw brass tubing and suitable piano wire, some rubber to see how she spins and it wasnt bad at all. What will happen when its mounted to the front of a 8gram plane is another matter.
Weight of the balsa prop only is 1.18grams plus what ever I will cover it with and the brassware. Which brings me to the next matter.

Someone suggested light fibre glass cloth and Zap Z Poxy 5minutes.  I have the zap and can get some cloth.
What about the Zap on its own or something else?

It feels quite sturdy,  but when diving into the not so long grassy ground it might well...I dont want to think about aprox 4 hours work in the bin after first powered flight... 13th flight maybe

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« Reply #16 on: July 25, 2017, 09:31:19 PM »

Good effort DTTP - it looks accurate and neat. Glass may be a bit heavy for a prop of this size. I would suggest rubbing CA along the LE and TE's of the blade and either a couple of coats of dope or a coat of urethane Spar Varnish.
The spar Varnish is rubbed on with a paper towel and then wiped off almost immediately and then left to dry for a day or so until it is no longer tacky. When fine sanded with 240 and then 400 it will give a nice smooth water proofed seal that is very light.
The sanded coats of dope will be more waterproof but also heavier.

John
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dieterperiperi
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« Reply #17 on: July 31, 2017, 03:03:04 PM »

Thanks John.
Im pleased with the look and weight of the tri-blade.  With regards to the finishing, I coated the 2 blade prop that was made earlier in the post with the Z Poxy 5min (no cloth) left it to dry which took a few days and gave it a light sanding down.
The weight increased from 0.62 to 0.96 so even though it looks like all the poxy has been sanded off some must still be soaked up in the balsa prop. I will mix the poxy with a bit less activator next time cause the thing went tacky realy quickly (I mixed 50/50) Would be better if it was runnier too. Not sure if I could add something to make it more fluid.

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« Reply #18 on: July 31, 2017, 07:46:13 PM »

The Z Poxy will probably give you a harder finish than the spar varnish. I use the spar varnish on my catapult gliders and it is pretty durable.
I haven't used 5 min Z Poxy - I use 30min in preference and find that by placing the hardener and resin bottles in hot water for a few minutes and then the mix in a small pill cup in the hot water again - it mixes better and also is thin for a short while.
This may shorten the curing time too much for the 5min epoxy.

happy building

John
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Mike Thomas
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« Reply #19 on: July 31, 2017, 08:00:29 PM »

Epoxy can be thinned with methylated spirits (denatured alcohol).
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dieterperiperi
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« Reply #20 on: August 01, 2017, 05:32:19 PM »

Thanks for that Mike will try thinned poxy on the tri-blade,which I'll mount on my 11.5" Peerless Gulfhawk

2blade 5" prop now balanced again and rigged. I used the most basic of free wheeling method (notching the front of the brass tube)
Total weight 1.4 grams 
Made to fit now on my 12.5" wingspan Peerless Rearwin Speedster (9 grams with the prop and 15" loop of 3/32 rubber)
Hope to get some video on as soon as the weather permits safe flying

Have to master the tri-blade making for two opposite rotating props for my on going Comet P38 lightning project. Reduced to a 23" wingspan which will only allow 5" props to clear the central nacelle

Not having carved a prop from block, this might be a bit out of order to say, but I think the fan laminated method is brilliant for making small props. Its relatively quick and and I find it easy to do. My props might turn out to be very ineffective for their purpose but its been a rewarding experience so far.

Surely loads of room for improvement and experimenting.

:-)
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