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Kent Ashton

Kent's Propeller Thread

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Here's how I built a couple of props. The first one was good right out of the box--credit beginner's luck. The second one which I will discuss here took a lot of adjusting;  you might find it interesting.  At the outset, I will admit that it's easier to just buy a prop but what fun is that!   There are probably easier ways to draw prop blades with a 3D CAD program but this is was my method.

1. The first thing is to decide what length and pitch to build. I kept a list of props I read about that a people were using with a given HP and speed range and put them on a spreadsheet. (pic 1) Comparing pitch is tricky because a prop builder might be quoting the pitch of the flat side or the pitch of the prop's chord line. There can be several degrees difference.  I just assumed that every pitch was quoted at the chord line.

2. Pitch is quoted in inches at the 75% station. It is the geometric distance a prop with no slippage will advance forward in one rotation.  However, a builder must know the chord pitch angle.  My spreadsheet converted pitch-inches into a pitch angle.  I chose 26.8° chord pitch angle for my 180 hp engine and a 67“ length. From some previous experimenting, I believe length is not too critical. Pitch and tip thinness make a big difference.

3. I used six nice maple boards, 3/4” thick, so the hub thickness would be 4.5”.  I scraped them as recommended to open the pores and glued them together with Weldwood Plastic Resin glue, rolling glue on both surfaces and flipping the growth rings for each board, and clamped them tight for a couple of days. (pic 2) The Weldwood product was recommended because it has a more generous working time than Resorcinol. 

 

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

4. DRILLING THE CENTERHOLE AND BOLT HOLES: I made a 7” diameter steel template of the hub pattern (O-360 Lycoming: 6 holes, 1/2”Dia on a 2.375 radius) and an aluminum plug. First I checked the perpendicularity of my mill head and table and drilled the centerhole with a brad-point drill, then the 2.25” hole that fits on the prop flange. I put the aluminum plug in the 2.25” hole to located the steel template and the prop bolt radius.  (In the pics below, I am using my aluminum crushplate and 3/8" bolts for the first prop but later I used the steel template).  As I drilled the prop bolt holes, I inserted short 1/2” bolts to hold the template in position. Here I made a minor mistake by not drilling the prop bolts exactly in line with the blade centerline. That required a small azimuth correction later when using a Dynavibe.

 

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Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

5. DESIGNING THE BLADES: With the pitch angle and blade stations determined in step 2, I drew the 75% station pitch angle in CAD and additional lines converging on the same point on the Y-axis to determine the geometric twist (pitch) at the remaining stations. (pic 1)  No fancy adjustments here for washout or “slowdown” near the hub—just a straight geometric twist.  BTW, there is no use trying to draw any station below 30%--the inner part of the blade will have to blend into the hub.

6. PLANFORM: Then I drew out a planform of the blade shape and taper I wanted (pic 2) .  This planform is the shape you would see looking straight at the prop from the center of rotation. The planform drawing is useful later for rough-carving the wood blank. I glued the planform drawing to some scrap Formica and made a template it to rough-out the blade shape on my bandsaw.  The diagonal lines in the planform drawing are just to align the sheets of paper out of the printer.   

7. I wanted to try tapered blades such that the blade tip would be aligned with the center of the hub as in pic 3.  This turned out to be a harder prop to build than a prop where the trailing edge is straight and aligned with or in-plane with the face of the hub. Hertzler props are an example of these straight T.E. planforms. With a straight T.E., all the chord trailing edges are aligned on the builder's table and it is easier to locate the airfoils as you carve. This difference caused me a problem later because I was sloppy checking the tip alignment and built in a small tracking error between the two tips.

 

 

 

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Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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8. The planform drawn at Step 6 gave me the length of the X-axis at each station and I had the angle of the chord at each station from Step 5.  I made a little spreadsheet to trig out the chord length for each station. (Pic). Now I knew, for each station, the angle of the chord and the chord length, but what airfoil shape?

9.  CHOSING AIRFOILS: Clark-Y and R.A.F. 6 are standard flat-bottomed airfoils commonly used for props. These airfoils are easy to carve and the flat side can be quoted for the pitch but eyeballing what current designers appear to use for airfoils, I chose three Wortman airfoils that looked similar to what I saw in use.  At the tip I used an FX84W97, at station 5 (50%) I used an FX84W140, and at station 3 (30%) and FX84W218.  These are of the same airfoil family but thicker towards the root. (http://airfoiltools.com/search/list?page=f&no=5)]. There is no science here. Just a WAG. These Wortman airfoils are not exactly flat-sided and there is an angular difference between the flat-side and the chord line but they are relatively easy to carve.  There is a small reflex (curve) on the bottom surface at the trailing edge but that can be disregarded.

Now I had the chord angle and chord length for each station but I had to blend (interpolate) the three airfoils for the intermediate stations.

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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10. SIZING AND BLENDING AIRFOILS – Ah, here is some work. The three Wortman airfoils must blend together down the blade, and the chord length must change to fit the planform. With a 2D CAD program here's how I did that.

11. Each airfoil has “Selig data” in the description which defines the X, Y ordinates for a chordlength of One.    For example, here is the Selig data for FX84W140 (pic) found here  http://airfoiltools.com/airfoil/details?airfoil=fx84w140-il  The data "wraps" around the airfoil from T.E. back to T.E.   So I had the ordinates for three airfoil stations (10, 5, 3) and I needed to scale those up to the actual chord length at those stations as well as interpolate between those three for stations 9, 8, 7.5, 7, 6, and 4.    I had the chord lengths for all the stations from Step 9 above.  I plugged those into another spreadsheet.

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

12.  INTERPOLATING BETWEEN STATIONS AND SCALING UP THE ORDINATES - Here is an explaination of the spreadsheet I used (pic 1).  It has two sheets to it.  The first sheet takes the Selig data for stations 10, 5, and 3 and interpolates between them for stations 9, 8, 7.5, 7, 6 and 4.   Sheet 1 computes the various Y ordinates for each station for a chordlength of one (the X ordinate (one unit) is known from the Selig data).  Now those X and Y ordinates must be scaled up to the actual chord lengths at the stations.  The actual chord lengths are plugged in near the top of Sheet 1 but they don't get used until Sheet 2.

Sheet 2 takes the X and Y ordinates from sheet 1 and scales them up to the actual chord lengths plugged in at the top of Sheet 1 (pic 2)

Here is the actual spreadsheet.  If that format isn't readable, let me know  .PropbladeInterpolator

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Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

13.  DRAWING THE AIRFOILS - This was a bit tedious.  I copied each scaled airfoil upper and lower ordinates calculated in Sheet 2 into a plain text file for each station.  I called up a drawing of the hub and one-by-one imported the station ordinates into my hub drawing as a "spline".   Magic!  A to-scale airfoil appeared.  To this I added a chord line  from L.E. to T.E. and overlaid it on the hub with the midpoint of the chord centered on the hub.  I used the CAD's "rotate it" function to rotate the airfoil and chord (grouped together) to the correct pitch angle.  Frankly, I have forgotten the exact steps but once the spline function draws the airfoil it is pretty easy to manipulate.  Now I had a drawing like the third pic in Step 7 above.

At this point, I could have moved the airfoil to make a straight T.E. blade.  As I said earlier, that would have made it easier to carve.

Label these airfoils several place so when you start cutting out upper and lower profiles to make carving templates, you will know which one you're working with.  Here is the text file for station 7.5 (75%).  On the left are the chord stations and on the right, the upper and lower (minus) ordinates.

67x80Sta7.5.txt

Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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14.  MAKING AIRFOIL TEMPLATES - I printed out two copies of each airfoil.  You need two because your bandsaw will remove a bit of the chord line if you just cut between the upper and lower.  I glued them to some formica and cut them out on my bandsaw.  Pic 1 shows the result.  A couple of things to note:  The tops and bottoms of the templates must be accurate for using a level to check the incidence at each station while carving.  I needed to add marks for the end of the trailing edge.  Station 10 is almost too thin to work.  I was afraid to carve it that thin and it came out thicker than than drawn.  A biggie: The leading edge of station 3 is higher than the laminated prop blank.  Without some blending, you will have a sharp corner slightly behind the leading edge at Station 3.  That station has to blend into a flat hub surface so it's not a big deal to smooth it after carving.

Just to claify, the hub is 6 boards thick and there is an extra margin added above and below the hub added for Station 3, 4 and part of 5 & 6.  The magenta lines show the extent of the hub.

Pic 2 is the planform template used to rough-cut the blade profile.

CAUTION:  It is very easy (I have found) to get confused about blade orientation and wack off the wrong wood.  I mark the hub "Forward face" and draw a pic of the blade orientation on the ends of the blank.  I mark places "LE high here" and "TE low here" on the forward side and "LE low here" and "TE high here" on the aft face.   (pics 3, 4)

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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15.  USING THE PROP CARVING MACHINE - (pic 1) I glued my extra paper templates to 1/2" MDF, cut them out and floxed them to a 1/2" board to become a template in the carving machine.  Obviously you will also need a 1/2" board under your prop blank.  I was afraid I might rough out the profiles too thin so I put a thin sheet of formica under the template to raise it a tad.  This would make my rough cuts about 1/16" thicker than the basic template and the entire prop would rough-out two formica-thicknesses thicker.  Necessary?  Maybe not.

I left some extra wood on the end of the tip (pic 2) and left the tip at the full thickness of the blank for now to aid in clamping the blank.  Note that your blade centerline make must remain on the end because you'll cut away the centerline mark down the blade.  Before starting with the machine I removed some excess wood with the bandsaw, otherwise the router would not go deeply enough in the blank.  This is tricky because you could cut into the finished profile.  I marked up the blank with various lines and marks to show the general thickness of the blades at each station.  Difficult to describe how to do that.

Pic 3 - I found it was useful to use a drill bit initially and drill holes for the profile.  The drill removed wood a little easier than my burr.  The drill got hot!

Pic 4 - shows the other template for the flat side and roughed-out drill holes.  

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

16.  BURRING THE AIRFOIL PROFILES - Align the end of the burr with the template follower (pic 4).  Pic 1 shows the result with the burr.  When both sides have been profiled, return to the band saw and cut away as much excess wood as you dare.  The more you can remove, the better.  You might get down to 1/8" to 3/16" of wood left to remove by hand.  I nicked a piece out of the profile (pic 3) but it was no problem to fill later.  I used a wide-tooth wood cutting blade in the bandsaw.  Go slow.  The blade drag still stopped my bandsaw several times.

On my first prop, I took a picture of a hub and imported it into CAD, drew over the picture and scaled it as required and make a template for rough-shaping the hub (pic 5).  I didn't do that for this prop and it was a mistake.  It made the hub harder to blend into the blades and I didn't get the blend symmetric on both sides.  Sigh.

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Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

17.  CARVING THE PROP - The method that worked best for me is to use a narrow 1/4"-wide wood chisel and chisel out wood on either side of the burred station cuts about 3/8" to 1/2" on either side of the station.   That will leave the wood high between the stations which can be seen clearly and removed more quickly with a wider chisel or machine tools.    I mainly used a body when I don't want to go too fast (seen in pic 2).  I have tried a belt sander and a Harbor Freight planer but I don't think they any great advantage.  The plainer was worthless.  A 36-grit flapwheel disc on a small hand grinder will really do a fast (but dusty) job removing wood. (pic1)   A big flexible-belt sanding machine would probably be very useful.

Along the way, the face of the hub needs to be bolted level and the airfoil stations checked against level (pic 4).   You will have to keep redrawing the blade centerline and rechecking level.  Frankly, my profiles were very thin and I did not shape this prop as thin as the templates.  In particular, my tips are thicker than desired.  I worked my way out to station 9 and left the tip shaping until the end, then sort of eyeballed the shape  The templates were so small they didn't seem usable and I was leery of making the tips too fragile.  It was probably unnecessary worry.  I could have put some extras glass out there that would have reinforced them.

 A BIG MISTAKE was not checking and comparing the tip position against a flat vertical surface (i.e., my mill table).  This should have been an early check when starting the carving.  As a result I ended up with a tracking error in the finshed prop which could easily have been fixed if noticed early.  This is a problem with making a tapered prop:  the tip is sticking out above the plane of the hub face/work table and trickier to locate but with care it should be easy enough.

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Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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17.  FINISH CARVING - The hub can be shaped by eye with the flap-wheel disc on the grinder which removes wood very fast, then smoothed with rasps, body-file and sandpaper.  If you did not use a hub template as mentioned above, you might want to shape one side and make some templates from the shaped side to do the other side.  At this point my blades looked very thin--maybe (gulp) TOO thin but I think they will be fine.  It was very rewarding to see that swoopy-twist emerge from the wood.

At this point (pic 1), the blades are almost done.  I marked a high place in the root that needed some more work with the flap-wheel.  Because the blades were getting pretty thin, I wimped-out and did not absolutely sand down to make the burr pathes disappear.   In pic 2, you can see that I had more work to do thinning the blades outboard of station 8 and at the tips.  I never got the tips as thin as my profiles.  Thin tips are very important because the tip of the prop is creating about as much drag as the middle of the blade.  Big, wide, squared-off tips create huge drag.

For comparision, pics 3 and 4 are of the first prop I made.   PUT THE PROP IN THE STATIC BALANCER from time to time.  Perhaps you can remove a bit of wood to get it balanced.  Also check the that the tips track in-plane.  If you've been conscientious about checking the station profiles against level, the twist is pretty much set and should be OK,

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

18.  PREP THE OUTBOARD LEADING EDGE FOR JBWELD - I use JBWeld over the glass to protect the leading edge from erosion.  It is easy to apply and file to shape and holds up well.  There are more plastic-like materials but I have not used them.  The JBWeld only needs to be on the outboard 8-10" of the blade, IMO.    I measured that length and removed about 1/8" of the bare wood at the outboard leading edge leaving it flat.  (pic 3, but hard to see).  After glassing the prop, I build up the flat L.E. with JBWeld and file to shape.  It might be useful to use more or less JBWeld to fix a balance problem but I don't know how the weight of JBWeld compares to wood.

19.  FILL IMPERFECTIONS -  I used micro (pic 1, 2)

20.  PREP T.E. FOR A FLOX CORNER (pic 3) - Use the blade profiles to check that the T.E. is where you want it.  Then draw a cut-line along the T.E. about 5/16"-3/8" forward.  Mark the cut-line for gaps where the wood wil remain attached for glassing.  Drill 5/32" holes beside the gaps.  I ground-down a thin saber-saw blade and, starting at the drilled holes, cut along the line leaving the gaps attached.  Before glassing, apply some contact cement to the T.E. and a strip of peel-ply (pic 4)

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Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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21.  PREP CAMBERED L.E. FOR GLASS OVERLAP - See pics above.  Draw an line down the cambered side about 1" back from the L.E. and shave the wood down so the glass overlap does not creat a bump.  The flat-side glass will be two layers wrapping over onto the cambered side.  BID + UNI are ..013 + .009 thick so in theory you need to remove .022" of wood but taking that little off a curved surface is tricky so if you remove a little more wood, it won't matter.  I used a hacksaw blade to make shallow cut in the cambered wood to show depth and shaved down to the hacksaw cuts with a hand plane.  With all this stuff, the more evenly you can do it on both blades, the less it will disturb your balance.

At one point, I contemplated correcting balance with a lead puck (pic 1)--a lead bullet hammered flat--but I began to think of the centrifugal force that the lead puck would exert on the wood of the prop at 2700 RPM and decided against it.  I dug it out and filled the hole with micro.  I decided to try to correct the imbalance later with glass.  However, I have fixed imbalances before on a prop I was going to glass by drilling small shallow holes in the wood and pressing in double-ought buckshot.

Tape-off the hub (pic 2).  The hub at the crushplate and forward face need to be bare wood.  Glass-epoxy under the crushplate/flange can soften and compress and the prop bolts will lose tension.  As you know, studies have shown it is the friction between the crushplate, wood, and prop flange that keep the prop from moving on the prop flange.   Lose the friction and the prop will be destroyed.

Mark the outside of the hub for a glass overlap between the blades.  About 1" of overlap is enough, centered on the hub.  I suppose you could relieve a small area to prevent a bump.  Now you're about ready for glass.

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

22.  GLASSING THE PROP- CAMBERED SIDE: I used, one BID, one UNI, and one BID on the cambered side. BID on the 45 angle.  I made a paper pattern long enough to insure overlap on the outside of the hub between the blades and used the pattern to precut the glass and mark a couple of stations to locate it on the prop.  The arrows and "C" indicates the forward postion of the glass on the Cambered side.  Paint epoxy on the prop.  Position the layers and wet them out one by one.  As I recall, I alternated blades in order to get alternating overlaps at the hub.  Try to trim them for an even overlap centered on the center of the hub.  The cambered-side glass does not wrap the L.E. Carefully trim the glass along the LE and trim the T.E. for a small (1/4" to 3/8)" overhang.  Cut strips of peel ply 4-6" wide and peel-ply around the L.E, the blades  and the overlap area on the outside of the prop hub.   Do both blades (cambered side only).

After cure remove the peel ply. Trim the T.E. and llightly sand the edge to the final curvature. Remove the wood at the T.E. (pic 2).  Sand the L.E. glass smooth edge smooth and sand the cambered side where you relieved for the flat-side glass overlap. At this point it is probably good to to a static balance again.  You might use the 00 lead shot.   Another idea: BID weighs about .114 oz/sq. inch. You might cut a piece of dry glass and tape it to the prop tip to correct the imbalance.  Later glass it in between the layers. It is important to keep correcting the imbalance as you build.

In pic 4 I used about this much extra glass on one blade to bring the prop into balance, in lieu of the lead puck.  

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Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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23.  GLASSING THE FLAT SIDE-  Cut dry glass with a pattern and mark it up for reference.  Remember that it will overlap onto the cambered side.  BTW, when you are going to cut pieces of glass out of a roll, it is helpful to put a strip of narrow masking tape along the cut line and the cut along the center of the tape.  The tape will keep the edge of the glass in shape and keep it from unraveling.  After the glass is wet-out, cut off the tape and straighten the glass.

Fill the T.E. with wet flox and glass the flat side with one UNI and one BID (BID on a 45) both wrapping onto the cambered side.  Between the two layers, add any pieces of cloth you need for balance.  Keep in mind that the extra glass will need extra epoxy.  I don't know a good way to estimate how much extra.  Alternate glassing the blades and overlap on the hub. Where the UNI+BID overlap on the cambered side, evenly trim them to get a 7/8” to 1” overlap. Peel ply the entire prop with 4” to 5”-wide strips of peel ply

After cure, remove peel ply, trim, sand, and check static balance. If needed, add some glass on the flat side to achieve static balance. Try wetting out some glass and with the Saran still on it, tape it in place and trim to achieve balance, mark the position, remove the Saran and glass in place, peel ply.

The pic below shows the camberered side with the overlap done.  This prop is glassed!

 

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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24.  MICRO AND LEADING EDGE WORK -  Sand the glass lightly, tape off the hub face.  Mix the micro firmly enough that it does not sag too much as you turn the prop over.  Recently, I read the idea of stretching thick fishing line over an airfoil, applying micro over the fishing line to get a consistent thickness.  Try it and let me know how it works.  :-)  I just use old credit and AARP cards to apply the micro.

Sand the cured micro starting with 36 grit working down to about 320 grit.  Prep is always my weak area.  I will prime and see scratches I should have removed.  It doubles the work to get a good finish.  Don't be me.  

25. JBWeld LEADING EDGE - Again, a balance check would be prudent here.  Where you relieved the leading edge, tape off the flat and cambered sides to keep the JBWeld confined to the L.E.  Mix up some JBWeld and apply a generous bead to the L.E.  Smooth it a bit (JBWeld sets up pretty fast) and apply a very thin Saran wrap about 2" wide.  Tape the Saran on each side and work any pits and bumps out of the JBWeld.  Don't fret if it gets over your tape.

After it hardens, remove the Saran and work the JBWeld to the correct profile with files.  I have never had any JBWeld fly off my three props, but I would try to keep the buildup rather thin.  Yeah, I guess I should have said that before you relieved the leading edge.  :-(

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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26.  PRIMER -  Here she is in epoxy primer (pic 1) however, I always suggest spraying a guidecoat of thin, sandable, black, cheap, rattle-can primer and sanding it off to see imperfections (pic 2) .  Pic 3 shows the kind of imperfections (scratches) the guidecoat will reveal.

And finally, with some polyurethane (pic 4).  If the balance is close, an extra coat or two will correct an imbalance but beware doing it outdoors in any sort of breeze, which will turn a prop on a static balancer.  Story:  One time I painted a prop outside on the static balancer and walked away to let it dry.  A bit later I heard it clatter on the driveway.  The wind had rotated it all the way off the balancer.  :-(  

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-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

BALANCING THE PROP:  OK, coming to the end here.  I want to summarize the balance process here in order to finish up this thread.   I previously talked about problems with this prop here  https://www.canardzone.com/forums/topic/18661-kents-long-ez-project/page/15/#comments   but the bottom line is that because I built in a tip tracking error, I had to shave the mounting face of the hub slightly to correct the tracking.  As a result, I could not balance this prop through the centerhole any longer, either on the usual static balancer or with the hanging balancer (although I did try various bits of lead in the hub).   The first time I ran it, the vibration was so bad I was afraid to fly it.  A check with a Dynavibe showed about 1.96 IPS (inches per second) which was terrible.   After a lot of trial and error with the Dynavibe, I got the balance to the Dynavibe "Fair" range with various bolts and washers  (pic 1)

I wanted to resolve these various bolts and washers to one weight in the hub.  This is to keep the balance-weight close to the plane of imbalance (the prop!) and presumably this would also minimize coupling imbalance.  So I drew an initial CAD drawing which used the weight, radius and azimuth of each weight to convert them to vectors.  (pic 2)  A vector is just the ounces of weight X the radius (i.e. ounce-inches), at a particular azimuth.   Connecting all the vectors showed the azimuth and ounce-inches of one vector that would be equivalent to the separate weights.   Here, 13.01 oz-in. at azimuth 207.71 degrees.

Consequently, I drilled the hub for a 3 oz. bolt on a 3" radius at 208° (9 oz-in) that went most of the way through the hub and made a few more Dynavibe runs.  It only took two additional washers under the prop bolts  get a .04 ips reading at max static RPM of 2228.  Pic 4 shows the final vector drawing.

You will notice that the final vector was 11.29 oz-in at 209.37° which does not match the 13.01 oz-in at 207.71° in the first drawing but perhaps moving the weight closer to the plane of the hub meant that less weight was needed.   Azimuth agrees pretty well.  In theory, a 3.76 oz weight at 3" should be the perfect balance weight but I will probably live with the extra washers and see how it goes.

I flew this prop and it felt good.  I could get 2750 RPM at 8000 feet at peak power--an overspeed condition.  However at the lean setting I usually use, it ran about 2650 rpm and did not throw a blade so it looks like it will be a good prop and I am calling this experiment a success.  🙂  

 

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Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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One more thought:  OK so you don't own a fancy-dancy prop carving machine.  Maybe this will work as well.   The problem is how to rough-out a prop blank on a bandsaw without cutting into the as-yet-to-be-determined station profiles or leaving too much wood to be removed.

Try this: Make extra templates that will act as drill guides, showing you how much to drill down into the laminated prop blank to approximate the profile depth.  The templates can still be Formica or plywood; they just need to sit vertically on the blank.  Mark the templates with vertical lines.  Secure them on the blank at each station and drill down into the blank to match the depth shown on the drill jig.  I expect it would best be done on a drill press but could be done by hand.  It's not necessary to drill absolutely to the correct depth.   Perhaps you drill 1/8" less.

Now as you bandsaw the wood off the blank, the holes will show how close you're getting to the blade profile.   Let me know how that works.  :-)

PropDrillJig.png


-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Nice work - both on the prop and the writeup!

-Saro

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Nuggets from the late Jan Carlsson of JCPropellers.  His posts on HomebuiltAircraft.com and the Yahoo propeller group were always very interesting:

Quote

[For a] 68" diameter, half a degree (at 75% radius) is 1.4" pitch change.  Two inches [pitch] is normally the difference between a climb and standard prop and an addititonal two inches to a cruise prop.

 

Quote

[paraphrasing]  About 10-20% of the pitch selection is governed by horsepower available.  The biggest factor is speed, and pitch is almost linear with speed, but or course, the speed is affected by the power.  On the other hand, pitch is fully affected by RPM."

 

 


-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Amazing work Kent! 

I hope it pushes well.

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Saw this static prop balancing device in a Van's thread (pic 1).  What a piece of kit!  It puts my homemade balancer to shame

IMG_0160.JPG.5cb8e0c60e807f1af59bc03309348c71.JPG

IMG_0001.jpg


-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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