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		Preparing Your Prop for Flight

Now that you’ve selected the right prop, there are a few other things that you need to do to properly prepare it for use on your aircraft. Here are some good procedures to follow when drilling, balancing, installing, and safely operating any propeller.

Drilling Bolt Holes :

The most accurate way to drill a prop is to utilize a sturdy drill press as will be described here. A similar procedure may be followed with a hand drill if extra care is exercised. Always follow the manufacturer’s directions when operating these or any power tool to ensure the utmost safety.

Be sure the drill press table is level and place a flat piece of wood upon it. The prop will rest on the wood to allow the bit to cleanly pass through the hub during the drilling process. Make sure that there is no debris between any of these parts and that they rest level.

The use of an accurate drill jig is very important to get the hole pattern and alignment exact. They are available from virtually all engine manufacturers to support their products. The one shown to the right is available from Desert Aircraft and fits all 6-hole bolt patterns for DA and 3W engines. It fits into the factory-drilled 10mm center prop hole and is pushed down flush with the upper hub surface. Align the applicable hole pattern with the axis of the blade and make sure that your particular spinner will work with the chosen orientation before drilling. Here, the outer holes are shown in an appropriate position for most aluminum spinners.

Use the exact drill bit diameter required to produce the proper fit for your prop bolts. A well designed drill jig has the right hole diameters so just choose a bit that passes through them with no free play. If you use a bit that is too small, the bolts will not slide through the prop and installation will be compromised. So exercise care in bit selection here.

When drilling the holes, restrain the prop assembly with your left had with firm pressure against the table. Pre-align the bit over a jig hole prior to tuning on the drill. When satisfied with the alignment, turn on the drill and slowly advance the bit through the hole to avoid fouling. You may have to reverse the motion at times to release wood chips. Proceed in this manner all the way through the hub and slightly into the wood beneath it. This helps produce a clean exit to the hole. When satisfied, the process can be repeated for the remaining holes in the pattern.

In an effort to keep the jig from rotating when drilling successive holes, it is a good practice to place a close fitting pin into the first one or two holes. The bolts shown in the photo to the left are used in this manner. Just be certain that any exposed length does not interfere with the drill head during operation.


	After all holes are drilled remove the jig and inspect the holes on both sides of the hub. If they are all devoid of wood “burrs” and the prop bolts pass cleanly through them, you are ready to proceed to balancing. But most likely, there is some debris that needs to be cleaned from around the holes.

First, flip the prop over on the wood block and carefully drill through the holes from the back side without the jig in place. Then use a flat sanding block to ensure a level surface on each side of the hub. It is not necessary to sand into the hub to do this. Just remove any wood exposed by the drilling process.

When these procedures are correctly followed, each of the bolts should slide through the prop hub easily but with little or no excess tolerance.

Balancing the Prop :


	Vess Propellers are precisely machined and thus usually come out of the bag with little or no balancing required. But all props should be checked and balanced as need since wood density can be variable. This will minimize vibration, increase performance, and enhance safety of operation.

There are many good balancers for large props on the market but the one we have used to good effect is the innovative “High Point” type shown to the left. This particular one was last sold by Robart and Dubro makes a similar one.

Note that the balancer is aligned with the edge of a sturdy table and screwed or clamped down to avoid tipping. The supports are then adjusted to allow the balance shaft to cantilever the prop off the table edge.

Make sure that this shaft is level to the horizontal when adjusting the supports. Note that you may need to restrain the rear support as shown above to keep it from pulling out of the mounting holes due to the weight of the prop. Also, it’s important that the prop is free to rotate with minimal friction to get the most sensitivity in the balancer so make sure nothing is rubbing.

To check the prop balance, hold it in a level position and carefully release it. If either blade is heavier than the other, it will rotate downward. The speed at which it rotates is a good indication of the amount of imbalance. Use this information to guide you through the balancing procedure.

Remove the prop from the balancer and lightly sand the back of the heavy blade with 220 grit sandpaper. Here, you are simply removing some of the clear finish to achieve balance. Start at the extreme tip since it is the farthest point from the rotation axis and will produce the biggest effect. Clean off any sanding dust, recheck on the balancer, and repeat as necessary to achieve balance. Do not cut into the wood or you may alter your prop. Take your time and try to concentrate on removing only clear finish along the blade as needed.


	Perfect balance is actually indicated when the prop will remain in any position of the clock (not just horizontal) when very carefully released. Once you are satisfied with the balance and are finished sanding, simply apply some paste wax to the sanded area and buff it out to help hide the scratches and protect the altered finish.

Prop Installation:

To install your propeller, slide each of the bolts through the hub washer and prop. If you followed the drilling procedure properly, they should slip freely through the hub. If you are using a spinner, slide the backplate onto the slightly protruding bolts and push it up flush with the back of the prop. Note that you should use the same jig and methodology described above to drill the spinner, too. This will ensure that the holes align perfectly across the entire assembly.

Grab the front of the engine and rotate the crankshaft counterclockwise until it resists the motion due to compression. Next, align the prop so that one blade is at approximately “one o’clock” and match the prop bolts with the corresponding holes in the engine drive face. Gently slide the prop and spinner backplate back as you hand tighten the bolts a little. Everything should move with minimal binding.

Use the proper hex wrench to run each of the bolts down to the prop washer but don’t attempt to tighten them yet. If a bolt resists your effort do not force it. Instead, back it out and recheck alignment so that you do not damage the soft threads in the drive plate.

The tightening procedure follows a “crisscross” pattern to maintain an evenly seated prop. The photo to the left shows a good pattern to follow. Engage the short end of the hex wrench in a desired bolt and apply a modest force to the long end. Move around the pattern with similar torque input and repeat the process with slightly increased force each time. You should tighten the bolts enough to avoid loosening in use but you do not want to over tighten them and crush the wood. Use good judgment here and check the bolts periodically at the field.

Test fist your favorite spinner over the prop. It is very important to trim it as required so that there is at least 1/16 inch clearance all the way around the blades. Do not allow the spinner to touch the prop! It will cause damage that could lead to a failure.

Mount the spinner per the manufacturers instructions. Make sure that it is secure but do not over tighten it such that you cause damage to it or the prop. Here, a single bolt holds the spinner in place and is tightened with a hex wrench.

Safety Considerations :

WARNING

Do not operate any Vess Propeller until you have thoroughly
read and understood the following instructions and warnings!

A rotating propeller has the potential to be very dangerous and can cause personal injury. It is the responsibility of the user to be aware of this fact and to operate it with extreme care, common sense, and good practices. Inspect the prop before each use for any signs of damage or irregularity. Remove and replace any damaged or irregular prop. Do not attempt to repair it. Be sure that it is balanced and mounted properly. Check the prop bolts often for proper security. Do not allow a spinner to rub against the prop. Do not hand start your engine. Always remain clear of the rotating prop blades. Never reach toward a spinning prop or allow anything or anyone to come near it while in operation. Do not adjust your engine while running. Keep people behind the plane of the prop. Do not run the engine at high RPM in the proximity of personnel or property. Always operate over a firm surface. Never attempt to stop the engine by throwing any object into the propeller.

If you are unwilling to assume total responsibility
during the operation of a Vess Propeller, please
return it to your place of purchase for a full refund