Author Topic: Propeller for my 5 cylinder radial  (Read 4120 times)

Offline gbritnell

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Propeller for my 5 cylinder radial
« on: May 22, 2013, 05:45:35 PM »
If you have followed my thread on the 5 cylinder radial engine you will know that I had trouble with the plastic 3 blade propeller, not enough mass. My plan was to build an aluminum prop after I got the engine running and the adjustments sorted out. I mounted a brass flywheel to the engine and got it running which was posted as a video clip.
Late last week I drew up an aluminum prop with hub and started construction. The hub was first. I made it from 2 pieces that would clamp onto the blades when finished. I drilled and reamed the center hole and drilled and tapped the the clamping screw holes for 1-72 socket head screws. The machining was fairly straightforward the only tricky part was putting the counterbored recess into the bottom of each pocket. I thought about making some kind of setup for the lathe but that would have involved using an angle plate mounted to the face plate with a lot of indicating and adjusting so instead I made up a small counterboring tool much like a miniature woodruf key cutter. The part could then be held in my dividing head as it was for most of the operations. I indicated the first hole plumb and square and then double checked the other 2. Between the 3 holes they were only out .002.
The blades were roughed from a piece of 1.00 bar stock. The diameter was brought down to .865 and the tang to fit into the hub was machined. The other end of the stock got a center drilled hole.
The blades were then put into the vise on the mill and the stock was cut to the hub boss diameter of .281
I didn't take pictures of the turning and flat milling as it was just normal machine work. In this picture you can see how the prop ends fit into the hub.
gbritnell
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Offline gbritnell

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Re: Propeller for my 5 cylinder radial
« Reply #1 on: May 22, 2013, 05:57:58 PM »
The next operation took some thinking. I needed to cut one side of the blades with an angle of  1.568 degrees. I had thought about making a piece of steel with the proper angle and clamping the pieces into the vise but that would have only got the flats done. After that I needed to machine the airfoil shape and the blades wouldn't have stuck up high enough to get that done. The solution was to use the dividing head. When the blades were initially turned I had put a center drilled hole in the outboard end. My plan was to use the tailstock for the dividing head to support the outer end.  The tailstock was set at the proper angle and a blade was mounted in the chuck. The tailstock is made so there is some room to angle it up and down from the horizontal position. The only problem is the tailstock needed to be blocked up to get to the center hole. I put some blocks under the corners to get close and then adjusted the tailstock center out until it located properly in the center hole. I verified it's position by indicating both the top and sides of the blade blank.
gbritnell
Talent unshared is talent wasted.

Offline Ramon

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Re: Propeller for my 5 cylinder radial
« Reply #2 on: May 22, 2013, 06:05:21 PM »
Nice work so far George - how long is each blade and will you be milling in varying pitch angle up the blade? That will be interesting to see if you do.

Looking forward to more - Ramon
"I ain't here for the long time but I am here for a good time"
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Offline gbritnell

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Re: Propeller for my 5 cylinder radial
« Reply #3 on: May 22, 2013, 06:05:33 PM »
The top edge of the blade was then machined to the proper thickness. I did get a little vibration on the finish cut so I pinched my fingers on the stock to dampen the vibration. The blades are going to be thicker than would be proper for a true shape but this is to add more mass. If it works as I hope I can always cut the blades down at a later date.
Next up was to put the airfoil shape onto the blades. I had made a step-off chart up to use a .375 ball mill. This time I started from the heavy side figuring it would be easier to climb cut against the stock and hopefully prevent any deflection while cutting. The outer end of the blade is only .125 thick.
gbritnell
Talent unshared is talent wasted.

Offline gbritnell

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Re: Propeller for my 5 cylinder radial
« Reply #4 on: May 22, 2013, 06:10:05 PM »
Hi Ramon,
To vary the pitch I'm going to make up a set of clamps, one to hole the blade in the vise and the other to clamp on near the outer end. Both clamps will have the airfoil shape milled into them so they fit nice and snug on the blades. The clamp on the outer end will then be twisted to reduce the angle of attack of the blade. With the blade tapered I should get a fairly uniform twist in the blade, at least that's the plan. Without CNC capabilities trying to cut a perfect airfoil is just about out of the question.
gbritnell
Talent unshared is talent wasted.

Offline gbritnell

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Re: Propeller for my 5 cylinder radial
« Reply #5 on: May 22, 2013, 06:14:24 PM »
With the machining completed I then cut some shape to the trailing edge of the blades. I made up a template so that each blade would be as close as possible to the other two. I then started filing to smooth out the airfoil and putting the radius on the leading edge. The corners around the root of the blade were also radiused and smoothed.
gbritnell
Talent unshared is talent wasted.

Offline gbritnell

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Re: Propeller for my 5 cylinder radial
« Reply #6 on: May 22, 2013, 06:20:55 PM »
When I machined the blade blanks I had left extra stock on the hub end for clamping in the dividing head. With the filing and sanding complete I sawed the extra material off and filed it to the proper width of .09. Each blade was then fit into a pocket in the hub. This is shown in the picture in the first posting.
I then set up my buffer and polished the blades. It might be a little premature if more material needs to be removed but I thought they would look better with a nice shine on them.
In the next couple of days I'll fire the engine up and see how well this works out.
gbritnell
Talent unshared is talent wasted.

Offline vcutajar

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Re: Propeller for my 5 cylinder radial
« Reply #7 on: May 22, 2013, 06:25:13 PM »
Beautiful George.

Vince

Offline Ramon

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Re: Propeller for my 5 cylinder radial
« Reply #8 on: May 22, 2013, 06:25:45 PM »
Thanks George - well jigged they should come out pretty equal.

I have often wondered if it could be done by the dividing head set in free mode with a lever attached controling rotation and bearing on a fixed angled guide - just thoughts  ;)

One things for sure it will certainly look the business on the engine  :ThumbsUp:

Regards - Ramon

Edit - Ah! just seen the pics - it does :ThumbsUp: :ThumbsUp:
"I ain't here for the long time but I am here for a good time"
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Offline b.lindsey

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Re: Propeller for my 5 cylinder radial
« Reply #9 on: May 22, 2013, 07:08:27 PM »
Lovely work as always George. Can we get another video of it running with the prop once you are all done with it?  Please  :praise2: :praise2:

Bill

Online steamer

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Re: Propeller for my 5 cylinder radial
« Reply #10 on: May 22, 2013, 07:13:10 PM »
Lovely work as always George. Can we get another video of it running with the prop once you are all done with it?  Please  :praise2: :praise2:

Bill

Video Please!....... 8).....

Dave
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Offline Bearcar1

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Re: Propeller for my 5 cylinder radial
« Reply #11 on: May 22, 2013, 07:55:36 PM »
Very nicely done George. Terrific write up and thanks for the pictures. :ThumbsUp:


BC1
Jim