Easy EZB Props

I used to hate EZB props. I had EZB prop envy. I would follow directions to the letter, using the best wood I could get, and end up with a waffly, wavy prop weighing around 150 mg. My props were the worst part of my EZBs and I did not like any of the first dozen or so I made. My models would kind of bob through the air as the prop shuffled along. There just had to be a great deal of wasted energy in all that wriggling around. After a while I got better at it, but I never actually liked any of my props. I had trouble getting wood I considered adequate, and I always managed to come out with wavy edged blades once the prop was finished. The blades would come off of the form so pretty and nice. Beautiful curves with perfect edges. Glue them to the spar and in a few days they were like all my earlier ones. No fun at all. 

It is kind of funny how things gel all at once. At one of the regular local flying sessions Larry Coslick showed up with an EZB prop dyed red and blue. The color edges were perpendicular to the prop spar, and I gave it a pretty good look to see how he did it. It turns out he dyed the wood before he made up the prop blank so that each piece was a different color. Larry had put the grain straight across the blade from edge to edge instead of the diagonal direction. He had also used very thin A grain balsa. By using a bit more substantial spar he had gotten by with using wood you would never have considered for the prop. I had some of that stuff at home! All I had to do was to sand it to thickness. I made up some blade blanks using my regular ambroid and lacquer thinner. After cutting them out I was worried. Such flimsy things! They just could not make workable blades, no way in the world. Even if they were OK off of the form, my gluing them to the spar was sure to ruin blades this thin. So glue the blades to the spar first! Who said that! Who cares, try it. I quickly slapped the spar onto the blades usinq ambroid. Normally the blades are glued to the spar with aliphatic so as to eliminate the warping from shrinkage of the glue. I figured that I was going to flatten the blades after any warping the spar gluing was going to do so I went ahead with the ambroid. Besides, I had to use waterproof glue so that the prop blades would not end up glued to the form. I cut a quick groove into the form for the spar and made my balsa sandwich. Twenty minutes in the oven at 220 and TaDa! A very nice, pretty, perfectly formed, and obviously strong and stiff enough prop blade. My best ever blade formed from wood sanded down out of 1/32" A grain balsa. Three different ideas all tried together worked out perfectly. I made four props in the next 12 hours, each better than any I had made up until then. Average weight was 125 mg using 5-pound wood and very strong spars. I like these props. Give this method a try and see if you like it too. 

Start with some four pound 1/32" balsa (100-mg props) in any cut of grain you have. If you have some really nice C grain save it for Penny Plane props. One of the secrets to sanding wood down to usable thickness is to use very coarse paper to start with and do not push hard at all. If you start with too fine a paper you will have to press down pretty firmly to get it to cut fast enough. This compresses the wood fibers and drives up the density. What you get is five and a half pound wood that makes a heavy prop. If you use a very coarse paper and very light pressure you will keep the density down and the prop light. You still finish up with very fine paper, but NO pressure. A block with 280 paper using a pair of wraps of masking tape to space the face of the paper above the board makes a nice tool for getting the wood to its final thickness. Once you start sanding the wood you need to be extra careful not to crunch the wood. Sand in one direction, away from the hand holding the sheet against the table. Let the tooth of the paper do all of the cutting do not press down! Balsa this thin is very much like a bundle of drinking straws. If you push down on the bundle you will collapse the straws and so crease the walls of each tube forming a flattened oval. Not only will the density go up, but also the collapsed tubes will have less stiffness and the wood will be very limp. To help "revive" the wood he sands, Larry Coslick has a trick where he washes the wood after sanding. This removes the imbedded balsa dust from the grain and helps expand the tubes the wood is composed of back to their original shape. He sands down to about .006" and after washing the wood returns to about .008" and is quite a bit stiffer. 

Once you have some nice wood sanded (it will seem far too limp, but do not worry) you can go ahead and use you prop template to make the prop blanks. I use very thin Ambroid to glue the section together, overlapping them about .020" or less. Cut the spars to size and glue them into place with the same thinned glue. Be careful not to use too much glue here, and to not get glue where you do not need it. You will find that gluing the blades to the spars before they are formed is much easier to do than the regular way. Note that the spar runs out to the very tip. This is necessary due to the direction of the grain of the prop blank. Let the prop halves dry before putting them onto the form. 

You will need to cut a groove for the spar in the camber form you are going to use on the prop form. Be sure it is deep enough along its entire length. Wet a prop half and place it onto the camber form, then place the camber form and the cap used to prevent damaging the blades onto the prop form and wrap with carpet thread. Bake the whole thing in a 220-degree oven for around 20 minutes. Let the form cool a bit before unwrapping the prop half. You should have a very nice looking prop blade with just a bit of curl (like the prop is under a load) and prefect pitch twist. Make the other blade and join using a wedge as shown in the illustrations. 

The resulting propellers will hold the blade twist very well and the blades made this way are very close to identical.