EndlessLift is about Simplicity and Sharing
In this tutorial I will show you how to carve a propeller from a block of balsa or other wood. The sizing of the block is discussed elsewhere. Here I will assume you have obtained the block dimensions from a plan or decided the dimensions on your own. You will also need a blade pattern. That might come from a plan, a book, you can trace the outline from a prop you have or you may draw your own. Once the dimensions and shapes have been decided, the carving can begin.
Carving a propeller may look very complicated. It is, but like building an airplane, it is done one simple step at a time. You can do each step and so you can carve your own prop. There are many reasons to carve your props yourself. Some early model airplane designs originally included a balsa prop. Copies and kits that use a heavy plastic prop instead will be nose heavy. The Flying Aces Moth and the Sig Tiger will be easier to balance and lighter with a balsa prop. Duration planes will fly better with a higher pitch prop than what is available in plastic and they will stay up longer with the lighter prop. You will be able to carve props that better meet the requirements of your airplanes. There is a great deal of satisfaction in flying your plane with a prop that you carved yourself. A prop is a thing of beauty.
There are about two dozen ways to lay out and carve a prop from a block of wood. I will show you one of the earliest and simplest methods of laying out and carving a prop, known as the X-block method. This produces a helical prop.
Before we start carving the prop we must collect a few tools. There are several ways to carve a prop. You may do it without all of these tools or you may use others. Some carve entirely with the knife, others may use a spoke shave. These pictures show how I do it.
You will need a sharp pencil for marking the lines and blade outline on the wood. The pencil can be sharpened to a chisel point by rubbing it on fine sandpaper at a shallow angle. A scale and straightedge will be needed for locating marks and drawing lines. I use a block of wood to properly align the scale with the faces of the propeller block. To start the hole for the prop shaft, I use a small nail or a round file with a sharp point. The drill is best held in a pin vise. This shows a 1/32″ drill and a 1/16″ drill in the vise. You would use one at a time, to avoid poking your hand. If you don’t have a pin vise, you can wrap the end of the drill tightly with masking tape to give you a better grip. The 1/32″ drill would be used if a 1/32″ steel wire prop shaft was going to be put through the prop, bent back and glued in place. The 1/16″ drill would be used if a 1/16″ brass or aluminum tube was going to be inserted through the prop as a hub. The pyramidal drill guide holds the drill at a right angle to the face of the prop block. The brass tube insert is used in the guide if the 1/32″ drill is going to be used. Learn how to make a Drill Guide on EndlessLift. It is good to have a finished prop on hand as a reference. A cardboard pattern is used to trace the blade shape onto the carved back of the prop. It has slits cut into it on alternating edges to permit it to twist. You can remove the excess wood entirely by carving with a sharp knife, but it is faster to cut off large chunks with a coping saw. The finer saw is better for cutting close around the perimeter of the blade. Final shaping and finishing is done with several grades of sandpaper. 100 grit is used for quick removal and rough shaping. 150 grit is used for final shaping and balancing. 220 grit is used for smoothing and 320 grit is used for final polishing. A short piece of sturdy cardboard tube is used as the sanding block. This one is from a badminton shuttlecock container. Sturdy mailing tubes are another source. Round bottles and jars also can be used. Bits of dowel can be used for small props. A dust mask will prevent you from inhaling the irritating sanding dust, or you can work outdoors in a wind. Some people dope or varnish their props, others cover them with tissue or fiberglass. I won’t be doing that here.
We are going to carve a standard right hand prop. A right hand prop turns clockwise when seen from behind. Reversing things will produce a left hand prop. It is important that both blades be carved with the same orientation. If you carve one blade right handed and the other left handed, the propeller will not work. This is where the example prop is a useful guide.
A right handed prop moves in the direction of the right thumb when it is rotated in the direction the fingers curl on the right hand. It sort of screws itself through the air.
The two blades are identical, each will rotate exactly into the place of the other. There is no right blade and left blade, as there are right and left wings.
A note on nomenclature: the surfaces of the blade may be referred to as front and back or top and bottom. When thinking of the prop blade as a lifting wing, it is usual to refer to top and bottom. When thinking of the prop mounted on the prop shaft, pointing forward, it is usual to refer to the front and back. The top becomes the front and the bottom becomes the back. Sometimes the leading edge of the blade may be referred to as the front and the trailing edge might be referred to as the back, adding to the confusion.
Carving a propeller is like sculpture. You remove anything from the block that is not propeller and what is left is the propeller. You can see that wood must be removed from the right places on the block to properly shape the prop. It helps to have a clear idea of what must be removed and what must be left.
The darkened area must be removed to reveal the top surface of the blade.
The darkened area must be removed to form the edge of the blade and hub of the prop.
The darkened area shows an end view of what must be removed to expose the under surface of the blade.
Some directions tell you to draw diagonals between the corners of the block and drill the shaft hole where the diagonals cross. I find that this is not a reliable way to locate the center of the face. The point on the front will not correspond to the point on the back, the shaft will be at an angle and the prop will not balance. Small discrepancies in the locations of lines intersecting at a shallow angle make a big difference to the point of intersection. Put two rulers down crossing at a small angle and move one slightly to see. It is necessary to measure to the exact center from each end and each edge of the block.
Sharpen the pencil to a chisel point on some fine sandpaper.
Press the end of the prop block and the end of the scale against a flat block of wood to align them exactly and make a mark at half the prop diameter about half way across the width. Do the same from the other end as a check. If the marks don’t match, make your final mark midway between them, or cut another block of wood.
Make a mark half way across the width of the block on the first mark. Do the same from the opposite edge as a check. You will have a small + at the center of the face.
Draw diagonals through the center and opposite corners. Remember that the pencil mark will be slightly off the face of the straightedge, so use the pencil point against the straightedge to locate the point over the center and corners.
The finished markings. You can see why this is called the X-block method of laying out a prop for carving.
We must drill the hole through the center while we still have flat faces. A twist drill does not have a pointed end. If you start drilling on a flat surface the drill will wander before it digs in. Therefore we make a starter hole. I use the point of a tapered circular file. The point of a small nail will work quite well, too. Make the hole exactly centered and just a little smaller than the drill diameter.
Check that the starter hole is big enough to keep the drill centered.
Put the drill through the drill guide and place its point into the starter hole. Make a drill guide here. Most instructions tell you to use a drill press. That is fine if you have one, but most modelers don’t. This drill guide is small enough that you can put it in your prop making box and carry it with you. It does not require an electric outlet.
Press the base of the drill guide flat to the surface of the prop block while keeping the point of the drill centered in the starter hole. Hold the drill guide firmly in place as you twist the drill, pressing it lightly downward.
The pin vise bottoms out against the drill guide before the drill goes all the way through the prop block.
The hole is deep enough now that it can guide the drill the rest of the way. The picture doesn’t show it, but I put the prop block up on those other two blocks on either side of the drill so the drill will not go into the table top when it goes through. Don’t drill against your hand!
This shows the drill coming through. This also tells you why it is not a good idea to place the block against your hand while you are drilling.
Check that the hole came through on the center of the opposite face.
Check that it is centered on the diameter. If it is off, try to figure out what went wrong. (If your drill is loose in the drill guide, try wrapping it with tissue paper until it is a snug fit.) You can sand a dowel from some balsa of the same density as the prop block and glue it in the hole. Wait for the glue to dry completely, trim it close with a razor blade and sand it with fine sandpaper. Then try again, after you have corrected whatever was wrong the first time. You can also put a piece of brass tube or steel wire through the hole and spin the block. If it isn’t too wobbly and out of balance, you might decide to go ahead with the carving. With a carefully made and used drill guide, that shouldn’t happen.
If you are happy with the position of the back hole, draw diagonals on the back of the block.
Also draw diagonals on the end of the block corresponding to the tip of the prop blade. This is a good time to consult that sample prop. This diagonal connects one of the diagonals on the front face, the one corresponding to the leading edge of the prop blade, with one of the diagonals on the back face, the one corresponding to the trailing edge of the prop blade.
Here is the end diagonal. It is oriented so when the prop turns clockwise, the prop will move forward. The diagonals on both ends have the same orientation. This diagonal determines the slant of the blade. Rotate end for end to double check that both blades will slant the same way.
I am going to leave the center of the prop 1/4″ wide for the hub. Mark 1/8″ on either side of the center. (Use the dimension shown on the plan if you are working from a plan.)
Draw lines through those points parallel to the sides of the block.
These lines delineate the hub area of the prop. In the previous pictures showing the wood to be removed darkened, you saw another way to lay out the hub, with a 1/4″ circle and curved conforming lines. That works if you are going to carve the blades entirely with a knife, a little at a time. We are going to cut large chunks of excess wood off straight through with a coping saw and must cut evenly on each opposite face before shaping the fairing of the blades into the hub.
Use the coping saw to cut off the excess wood just outside the lines.
Cut all the way to the other end, then cut the other side in the same way. This could be carved away with a knife at the same time the faces are carved, but the saw is quicker, safer and easier.
This shows both edges cut away. It’s already beginning to look like a prop. You could start carving down to the faces with a knife right now, but I prefer to saw off big chunks of waste all at once. Several ways of sequencing the cuts will work. You can saw off and sand the back faces first, then saw and sand the front faces, then saw around the blade outline. On this one, I am going to saw both the front and back faces, sand the back face, mark and saw out the blade pattern, sand the undercamber and then sand the front face to shape.
Now we will mark out the excess above and below the blades that can be sawed off. Draw a line on the end parallel with the diagonal and about 1/8″ away from it.
Extend that line onto the edge of the blank.
Extend that line onto the face of the blank.
Draw a line through that mark, parallel with the near edge of the blade.
Extend that line around the corner onto the edge of the blank.
Draw a line between that mark and the one made earlier from the line on the end.
The triangular pyramid is excess wood that may be cut off with a saw. You will note that one of the X lines will be cut off. (If you rotate the saw as you cut, you could cut off even more in the hub region, but I am keeping these cuts straight for simplicity.)
Cut along the lines to remove that excess wood. Similarly mark out the other three pyramids of excess wood and cut them off. You will find it convenient to raise the prop off the table with a small block of wood, to allow clearance for the saw above the table top as it cuts through the end.
This shows the six chunks of excess wood cut off with the saw. I drew a 1/4″ circle for the hub on this prop. This is similar to the prop blanks that were included in kits, except this is thicker at the inside end of the blade, since the saw wasn’t rotated as it cut .
You can get prop blanks finished to about this stage from Volare Products.
Check the sharpness of the knife by slicing a piece of paper along the entire length of the blade. If it cuts smoothly without hangups, it is sharp. If it catches on the paper at all, it needs to be sharpened.
We use a very sharp knife to shave the back surface flat. A sharp knife cuts more easily and is easier to control. It does not get hung up and does not require excessive force. A dull knife is actually less safe than a sharp knife. It gets hung up, can require excessive force and can get out of control when it breaks loose. Keep your fingers behind the cutting edge and away from the point. These large initial cuts can be made with a long sweeping action, drawing the knife a little like a saw.
The goal is to cut down almost to a flat chord line running from the leading edge X line on the front face to the trailing edge X line on the back face. You will find that cutting from the hub to the tip in the outer portion of the blade is easy. The blade is cutting across the grain and not being pulled into it. Do not cut into the wood that will be in the finished prop. Later we may sand some undercamber into the back of the blade, but for now we will keep it flat. We need a flat surface for drawing the blade outline.
When coming in toward the hub, we find that the grain of the wood makes it easier to cut the other direction. Be especially careful here to protect the thumb and fingers of the other hand behind the wood. Bracing both hands against the table top will limit their motion.
As we get closer to the finished surface, we make smaller cuts with the curved part of the blade.
Here I am using my left thumb to block the cutting hand in case the blade slips. At this point I am taking off small slices of wood.
For the more precise cuts, the left thumb can apply direct pressure to the back of the blade. Wood is taken off in small chips with the most curved part of the blade.
For final smoothing, the blade can be drawn over the surface at a shallow angle like a plane or spoke shave.
Once you have the back of the blank as flat as you can get it with the knife, you will smooth it with sandpaper. Because we are working on a twisted surface, a flat sanding block will not do. We must use a round sanding form. This one was cut from the container for badminton birdies. Mailing tubes or anything similar will work if it is sturdy enough to hold its shape. You may be able to use cans, jars or short lengths of wood dowel. Smaller sizes can be used to shape the smaller radius curves where the blade conforms with the hub, or you can wrap the sandpaper around a thumb. There will be a lot of sanding dust, so a dust mask is recommended to protect your lungs, or work outside where a wind can blow the dust away from you.
Note that the pyramid of excess wood was not sawed off the front faces of this prop blank. I made photos of the carving of six different props and each was carved a little differently. I left the pyramid on the front of this blank for stiffness during the carving. I found that it was not necessary. You can cut the pyramids of excess wood off all four faces before you start carving, or you can do them two at a time. The front pyramid of this one will be cut off later.
Start with the coarse sandpaper. Sand back and forth across the blade to tear the wood fibers and remove material quickly. Hold the tube perpendicular to the prop. We want to sand straight across along the chord from leading edge to trailing edge.
Now sand along the length of the blade, rotating the tube with a sweeping motion, at the same time rotating the prop around its diameter.
Use a smaller radius form for sanding the transition to the hub. Small dowels can be used for small radii.
The back of the blade should be flat going across.
Mark the position of the tip of the blade on the end diagonal. In this case, the tip of the blade is at the midpoint of the diagonal.
Align the mark at the tip of the blade pattern with the mark you just made on the diagonal and align the leading edge of the pattern with the leading edge X line. Note that the pattern has slits cut in from the edge to the axis to allow it to twist and conform with the twisted back surface of the blade.
Trace the leading edge of the pattern onto the block.
Trace the outer part of the trailing edge.
Trace the inner part of the trailing edge.
The completed blade pattern traced onto the flat back of the blank. Do the same on the opposite blade.
With the fine coping saw, cut slightly outside the line along the leading edge to the tip. Keep the blade perpendicular to the face of the blade.
Cut around the trailing edge at the tip.
Continue cutting toward the hub, rotating the saw to keep it perpendicular to the back of the blade.
Cut straight through the hub with the blade perpendicular to the axis. Turn the prop over and do the same from the opposite end.
Cut into the center until the waste separates from the blank at the back of the hub.
If you didn’t cut the pyramids of excess wood off the fronts of the blades already, now is the time to do it.
Sand the perimeter down to the line. Keep the block perpendicular to the surface at the point of contact. You can use a flat sanding block on the convex parts.
Use the round sanding form to sand the back of the hub. Get it square with the axis in the center.
Now use the round sander to form the undercamber of the blade airfoil. Sand with a combined sliding and rotating action. Sand a little deeper near the leading edge. The deepest undercamber will be at about 40% of the blade chord. If you want an exact airfoil, make templates for several stations along the radius. Otherwise, study a sample and copy it as best you can by eye and feel.
As you come in closer to the hub, increase the angle between the sander and the blade.
Exactly at the hub, the sander would be perpendicular to the prop. You may want to switch to a smaller diameter sanding form for final shaping of the hub. Finish rough shaping the backs of both blades with coarse sandpaper, then bring them to final form with medium sandpaper.
Now begin the rough carving of the front faces of the blades.
Carve into the wood along the grain, but not into the grain.
In some places you may need to reverse the direction of the cuts. Be very careful here.
Finish the final rough shaping with the knife on both blades.
Frequently feel the prop with your fingers to check for symmetry and bumps.
Shave down any high places.
Use the coarse sandpaper to rough sand the upper surface of the blade airfoil across the grain.
Finish the roughing out with your fingers pressing the paper to the curved upper surface of the blade airfoil, this time sanding with the grain.
Do the final shaping of the hub conform with the paper curved around the ball of your thumb.
The prop in its nearly final form, ready for final balancing and smoothing.
Push a piece of 1/16″ tube or wire through the hole and check the balance. It is likely that one blade will be heavier than the other and will hang down. Run the blades through your fingers and see if you can find any thick spots.
Sand away from the heavy blade with medium grit paper and recheck until the prop balances.
Sand lightly overall with fine paper to get a smooth surface. Recheck the balance. Dampen the prop to raise the fuzz and let it dry.
Finally sand with the finest paper and you are done. Admire your work. You can put it on the balancing rod for a final balance check, then spin it and feel the breeze on your face.
That completes the carving part of making a wood prop. There are many ways to make a hub, shaft and freewheeler, and attach the prop to your plane.
There are many ways to arrange a freewheeler for your prop. This site has 18 articles on freewheelers:
Take your pick!
"It is a source of national shame
that a single citizen should have to go
to bed unable to carve a propeller."
The Idiot's Guide to Prop Carving v2.02
By David Dodge
IntroCarving props is one of the very nice things about flying rubber models. It is a truly mellow occupation. God, the department of mental health and the blood pressure police will give you points. You can do it while visiting with your friends - like knitting. If you stick with the program it is a lot easier than it seems and they all will be impressed.
With a little practice, and the confidence that comes from it, the actual carving part from the block to fine finish sanding can be done in twenty to thirty minutes. Trust me you can do it. The very worst that can happen is that the rain forests will have given up an ounce of balsa in vain.
Props are a complex science and one can spend much time and thought studying them. Fortunately you don't have to know all this arcana to make a decent prop. I will do the very basics at the end of the note.
Advantages of Balsa Props
The BlankThe big trick is to lay out a prop blank first. This is a piece of balsa that has the geometry made physical so you don't have to think and cut at the same time. You carve to the edges of the block and the prop appears.
You can order ready made blanks from Aerodyne, or make them yourself. What follows is one way to make a blank. This makes a "Bilgri" prop. The other kind of blank, (hourglass) defies my ability to describe without pictures. Frequently the plans will show a prop blank.
Lets Get Started!
Step #1: Get yourself a piece of nice even balsa with the following dimensions.
This block will result in a prop with a fairly high pitch to diameter ratio (P/D) of 1.8. While fine for some things, folks might wish to start with a lower P/D if they are having trouble getting a plane to fly well. Starting with the width being 2.6 times the height will give you a P/D of about 1.2. This lower pitch should be easier to trim, at the expense of some duration. (sample spreadsheet for other P/D's below)
|The width need only be about right and can be altered to suit the available wood sizes, but the height should then be carefully measured to maintain the desired P/D. Lay this piece down flat and draw a diagonal on the top. Cut the piece in half along the line. |
Step #3: Now if you take the two triangular pieces and lay them tip to tip, you will see the beginnings of your prop. Overlap the triangles at the tips and glue them together. That's what the 1/2" was about. Drill a nice straight hole thru the center. This is for the prop shaft. The tricky way to do this is to lightly pre-notch the blanks as shown above. On EACH tip, draw a diagonal line going up and to the right. There it is - A prop blank.
Carving the Blank
Step #4: Here is where the fun really begins as you carve the bottom or back of your prop. We will be working upside down, to match the drawing, and prevent cutting off a thumb. Take the carving blade and cut away everything above the edges marked by the "up and to the right" line you just drew. The carved surface should be straight between the leading and trailing edges. Lay the straight edge of the carving blade across the face and check from time to time.
Step #5: Sand in a little curve, or undercamber, after you have it flat. If you wrap a piece of sandpaper around a drinking glass this is pretty easy. Do the same thing on the other blade. Don't forget to start from the "up and to the right" diagonal for the second blade.
|Step 6: Now flip the prop over to do the tops in an airfoil shape. Rough it out with the knife and finish with sandpaper. From time to time hold the blade up to a light to check that the thickness is even. Careful here or you will break it. But if you do, no matter, glue it back with Ambroid and take a walk while it dries. You can use Cya but if you use too much you will get a lump where you sand the glue joint. When this happened to me, the prop worked fine but looked grotty. The other thing that can go wrong here is that you get a spot that is too thin. Just cut the thin spot out, glue in a piece of sheet and sand. Cya is the way to go here.|
Finishing upStep #7: You are really getting close now. Sand in a little radius at the corners on the tip of each blade. There you have it!! A prop! This planform is called a Langley prop, and I kind of like the old timey look. You can mount and fly it as it is. But if you want, you can cut away any planform that tickles your endorphin flow. I draw the shape I want on one blade and cut away the extra. Then I use the scrap to mark the other blade.
The Very Basic Brainy StuffHere's the basic brainy stuff. A prop has 2 numbers; the diameter and the pitch. The diameter is what you think it is. The pitch is a measure of the "twist". It is the distance it would screw itself forward if it was working in butter and had no slip. If you look at a prop from the end you will see that it is an airfoil at an angle. Imagine that as it turns it advances along this angle. The tip will travel around the circumference of a circle
Circumference = pi x the diameter.
Pitch = pi x diameter x slope
For beginners the pitch should be constant and if you use the block I suggested it will be close enough. Pitches of a little more than 1 are about right. You can work out the pitch of the block I gave you "As an exercise for the student" I just stole it off a Burnham twin pusher plan.
The HoleHere is a sneaky way to make the hole, in case you didn't read the directions carefully or look at the pictures. Before you glue the two pieces together, take a little right angle and draw a line in each tip where the hole is going to go. Cut a little groove here. Now glue the pieces together.
AddendumThe Aerodyne blocks I have seen will produce a very low pitch prop. You might want to order one with an oversize diameter and cut the tips off.
Jim Anderson has provided an prop blank drawing and spreadsheet for working with the different, and perhaps more traditional, hourglass shaped prop block.
return to Tips Index or view a Thayer's first balsa prop
Copyright 1998-2015, Thayer Syme. All rights reserved
Introduction: Wood Propeller Fabrication
This tutorial will show the steps needed for anyone to carve a propeller out of wood.
Step 1: Obtain Propeller Cross Sections
First you must have full size cross sections (about 10, from root to tip) of your propeller. There are tools online for designing propellers, but you will need some CAD software to create the drawings and 2-D cross sections. I used CATIA, but any 3-D modeling software will do. (I also have a detailed instructions on design of propellers here (www.aerodyndesign.com) Of course you will have to print out the cross sections of the propeller on to paper, at full scale size. Because you will need to cut them out and glue them to thin peice of aluminum or tin.
Step 2: Choose Your Wood and Prep It
You will need to choose your wood. This propeller is made of Hard Maple. If you are creating a propeller for acual load bearing use, you will need a hard wood like Maple. You then cut your wood into thin boards and glue them together like in the picture. You must glue them together with no gaps. You will need lots of clamps.
Step 3: Cut Out Paper Templates and Glue to Thin Sheets of Metal
You will now glue your templates onto thin sheets of metal, and then you tin snips to cut out the cross section.
You will need to file down the rough edges because the template needs to be dead on.
Typically you will want about 10 stations, or 10 cross sections from blade root to tip
Step 4: Cut the Propeller Profile
By marking the profile of the propeller (looking down on the wood) you can use a hand saw to cut out the profile of the propeller, this will save you time when you go to 'hog out material'
Step 5: Begin Hogging Out Material
Now this is the most time consuming part, you will use a chisle or draw knife, or any cutting tool to start widdling away wood material until you can start fitting on you templates to see where material needs to be taken out.
Step 6: The Fun Part Is When You Get Down to the Templates
Once you have hogged out most of the unwanted wood, you can now use the templets and hold them up to the correct stations along the blade to see where material needs to be removed. Be careful not to remove too much, you can't put it back once its gone. The hardest part will be the root area, were the templates are hard to align. Marking the front and back of the propeller with a small notch will help align the templates.
Step 7: Final Step Is to Sand and Add Stain
You can use sand paper to sand down and smooth out the contour. Be sure to start will rought paper 40 grit to 100 grit, and work you want down to a nice 600 grit or finer. Then you will apply some water proof finish. If it is an outdoor propeller you will need to use a thick water proof varnish. This propeller is for an airboat (http://www.aerodyndesign.com/FAN_BOAT/FAN_BOAT.htm)
Step 8: Propeller Duplicator
If your really ambitious, you can make a propeller duplicator, which can more or less duplicate anything, but right now its duplicting a propeller, so we call it a propeller duplicator.
I might make an instructables on how we made it, but for now some pics and a video here: http://www.aerodyndesign.com/PROP_DUP/PROP_DUP.htm
1 Person Made This Project!
Did you make this project? Share it with us!
Rocks, Gems, and Stones Speed Challenge
3D Printed Student Design Challenge
Tinkercad Student Design Contest
Rubber model propellers from 1/2" balsa sheet
Text by Mike Woodhouse, drawings and layouts by Terry Rose.
This is a transcription of an original article in BMFA News, October 2002. It is reproduced here in slightly edited form with the permission of the authors.
It would appear that the activity that stops many from making a rubber model is the carving of a propeller from a square chunk of balsa. The purpose of this web page is to allay that fear. Basically if you can build the rest of the model then you can carve a propeller.
The answer is quite simple, the "secret" lies in the careful planning of said construction. What I will explain is how to lay out the propeller blank through to final finishing. I will not deviate into propeller theory, as I for one will soon get lost! The propeller is constructed using 12mm (1/2") thick sheet rather than a large block of balsa. The use of sheet is cheaper and allows for a more careful selection of material.
I will base this description on the construction of a 560mm x 660mm (22" x 26") propeller with helical pitch washed out 2 degrees at the tip. I said no theory, however I do need to explain what this translates to in English.
- 560mm refers to the diameter of the propeller arc
- 660mm refers to the pitch; this is the distance that the propeller travels forward in the space of one revolution
- helical pitch refers to the twist in the blade being such that the angles give the same 660mm pitch along the total diameter of the propeller. The angles being set higher towards the root as the distance travelled is less than that of the tip
- 2 degrees washout refers to a reduction in the pitch towards the tip of the blade. Washout is added to prevent the propeller tip from stalling.
Laying out the propeller
The pitch diagram is drawn for the propeller. This process can be adapted for any diameter/pitch combination. Note the 2 degree washout adjustment has been applied.
"R" = radius of the blade from the centre of the shaft: 560 / 2 = 280 mm (11")
"P" = pitch, the distance travelled forward in one revolution: 660mm (26")
"C" = circumference of the propeller disk (2 pi R) = 2 * 3.142 * R = 1760 mm (69") The next stage is to apply the propeller blade outline and fit this to the pitch angles that have been drawn.
This stage is the most critical and is probably the hardest bit of laying out the blank. As the process uses 12mm thick sheet, the sheet has to be set at an angle to match the twist of the blade. The best way is to take the angle near the centre and widest points of the blade. This may take a little bit of fiddling to get the best position. A bit of practise will soon resolve any dilemmas.
Once you have decided the angle the sheet must be set at apply this angle to each pitch station that you have drawn. Place the "sheet" in such a way that it allows the blade to twist evenly through the 12mm blank. A good way is to allow the tip template leading edge to be at the bottom of the blank and that nearest the hub to be close to the top after allowing for the thickness of the blade. Ideally the sections should rotate about the centre line of the blade.
Fit the 12mm blank to all other sections along the blade. Once you have done this you are ready to transfer the details to the propeller material and to start working in three dimensions.
Select a piece of 12 mm sheet of about 0.25 kg/m^3 (6 lbs/cu.ft.) density and of even texture. If you are able, try to have a block that will allow quarter grain to show in the majority of the blade – this will stiffen the blade. Cut the blanks out to the general shape of the blade. Cut them from the sheet as shown below. Cut them facing the same way to ensure that the grain is the same in both blades; this will ensure that they will flex in the same manner.
Mark out the leading and trailing edges of the blades using the distances from the lower surface of the blank that were measured from the pitch template. Connect the pitch positions. This should present a smooth line round the blank. If the line is not smooth check your drawing. You will soon see what needs to be adjusted.
Temporarily attach the blades to your building board at the angle that you have decided for the blank. Fix them in position with templates made from a piece of scrap wood.
Using a set square mark a rectangle on the hub end of the blade. This will be the hub of the blade.
Carefully pare the block away for about 25mm (1") or so. Note the slight outwards taper. Check and double check that you have cut the area away correctly. Remember to measure twice and cut once. When you are happy face the hub with 0.8mm (1/32") plywood. Again keep checking, making sure that both blades match each other and the template.
You are now ready to carve. Work on each blade alternatively and do the bottom first. A few saw cuts positioned at 25mm (1") intervals will help in the removal of the surplus wood. Carve and carefully sand in the appropriate undercamber. Now trim the blade to its final outline and again match both blades. Carefully carve and sand the top surface to section. Check with the blade template that you have both the section and the thickness correct.
Fit a brass bush and stop into holes drilled through the hub. Make sure using a template that the bush is set square and that the pitch is correct. Make sure both blades are the same. Many plans show an angled hinge to improve the way the propeller folds against the fuselage sides. However, if this is your first propeller I suggest that you concentrate on getting everything dead square. I'll do a note at the end about angled hinges. The stop and bush are fixed into the blade using a small quantity of 24 hour epoxy.
Check that the propeller balances (for this you will need a wire hub – see below). If you have selected a homogenous piece of timber and worked consistently then there should not be too much difference in blade weights. Correct the balance by comparing the blades, spotting where there is extra bulk on the heavier blade and removing it. The blades can now be finished by covering with light tissue and applying a couple of coats or so of thin dope. Lightly sand between coats of dope and recheck the balance.
Traditional nose block and wire hub
Having made the blades you need to make the nose block and wire hub. The shaft is bent and soldered as shown.
The nose block is cross- laminated pieces of scrap sheet that is then carved and sanded to a conical shape. The plug for the nose block that fits into the fuselage is a piece of hard balsa faced with ply. A brass bush is inserted for the shaft: this bush must be fitted square in all directions.
All the joints must be well made because a solder joint failure will be catastrophic for the model. A small compression spring is slid onto the shaft followed by a ball race; a biro spring cut to size is ideal. The shaft is inserted into the bush and bent over on the other side, taking care not to bend the shaft itself. Keep the clearance to about 3mm (1/8"), sufficient for the compression spring to pull the bent shaft against the stop pin. The end of the shaft is then finished to accommodate whatever rubber fixing you prefer. I've shown the fixing to be used with a wire loop, this is my preferred method.
To make a neater propeller fold an angled hinge can be added. The idea is that as the propeller folds it twists so it fits flatter to the fuselage sides. The hinge has to be a compound angle that is mirrored in the hub and propeller blade. 15 degrees is a typical angle. Care has to be taken when making angled hinges in order that the wire hub and blade are compatible.
To wood propeller how a make balsa
.Making a Wooden Aircraft Propeller - Shaped with Basic Tools
You will also like:
- Pencil tip cover
- Minecraft dog names
- Acupuncture lancaster ohio
- Muskegon mi 49445
- Withings watch app
- Destiny 2 how many heroic adventures
- Fun finder
- Watamote online free
- Outback toy hauler
- Kia ardmore ok