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Author Topic: Making balsa props using the laminated fan method  (Read 808 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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« Last Edit: June 07, 2017, 01:55:53 PM by calgoddard » Logged
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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