Let’s suppose you are building one of the popular go-fast 160-horsepower two-seat designs powered by a Lycoming engine. The engine choice seems straightforward-go with the one the designer had in mind. But how to choose a propeller? The designer says that two-blade wood fixed-pitch will work, as will a metal fixed-pitch or constant-speed prop. You go on the web sites and find opinions rampant, but actual facts and performance data are harder to come by. Time to shut off the computer and consider the question from first principles.
Think of your first bicycle. The one that had just one gear on the rear wheel and one chainwheel on the crank. When you went downhill, you could barely pedal fast enough to keep up with the spinning cranks, and when you pointed it uphill, you had to stand up and shove on the pedals for all you were worth to make it climb. On level ground you could pedal at a steady rhythm and make good speed for a long time. Later you graduated to a multi-speed bike with what seemed like a zillion gears, and no matter whether you were going, uphill or down, you could find a gear that let you pedal in that sweet spot where you could maintain a good pace.
Props, Not Bikes
The concept is roughly similar to flying an airplane with either a fixed-pitch or constant-speed prop. When you got that multi-gear bike, you never wanted to go back to the old one-speed again, so why would you equip your homebuilt with a fixed-pitch prop and effectively put yourself back in the one-speed world?
As usual, the choice isn’t as simple as it first appears. The fixed-pitch prop does have some advantages, and in many cases they more than offset the better performance you can get with a constant-speed prop. Chiefly, the fixed-pitch prop is cheaper, lighter, simpler. In airplanes (and bicycles) anything that costs less, weighs less and causes less trouble is generally considered a good thing. Your airplanes designer (every designer!) repeatedly emphasizes the importance of keeping the airplane light, so you rub your chin and compare propeller weights.
A wood fixed-pitch prop weighs about 12 pounds, but requires a crankshaft extension and a crushplate that brings the installed weight to 20 pounds. The metal fixed-pitch also requires an extension, but no crushplate and ends up with an installed weight of 32 pounds. An aluminum constant-speed prop weighs 50 pounds, but requires a prop governor, governor cable and an oil line, which brings the installed weight to 57 pounds. Forty-five pounds makes a real difference in a 1000-pound airplane. Further research reveals new composite-blade constant-speed propellers that weigh just a little more than the aluminum fixed-pitch. Maybe thats a solution?
Consider the Dough
At the same time the designer is pleading with you to keep the weight down, your spouse is making pointed comments about just how much this beast in the garage is extracting from the family exchequer. You didn’t marry a fool, so you take the advice to heart and investigate the comparative costs. Surveying web sites, it appears that the installed cost of the wood prop averages around $1400, though some props from popular manufacturers are considerably more expensive-up to $2000-while others are slightly less. There aren’t many choices in metal fixed-pitch props, because nothing off a production airplane is suitable for the speed range your baby can achieve. In fact, there is only one metal fixed-pitch prop available, and it was designed specifically for airplanes like yours. The designer is quite adamant that it is the only acceptable one. Bolted up, it costs $2600. You’re a bit shocked to find that an aluminum blade constant-speed retails for more than $8000, and the pain subsides only slightly when you find a deal, available through the designer, that allows you to buy it for a mere $6600. Those promising composite constant-speed units? Twelve to fifteen grand!
Of course, the prop is just the big chunk. A constant-speed prop requires those extra bits, and its a painful discovery to find that an American-made prop governor will set you back $2000. One imported from Eastern Europe is only $1200. Throw in a $30 cable bracket and a $70 cable, and your least expensive choices for an installed constant-speed prop add up to $7500-or $6100 more than that wood prop.
Then there’s the simplicity thing. A fixed-pitch prop has the technological sophistication of an ax. Other than checking the torque of the bolts attaching it to the crankshaft now and then, there really isn’t anything else to do. The constant-speed, on the other hand, requires more attention. Day-to-day maintenance is not difficult-add a little grease to the hub at annual, check for play in the blades on preflight. But Hartzell, one of the premier manufacturers of constant-speed props, says that propellers manufactured after April 1997 are to be overhauled…at 72 months. In other words, if you live by the company’s recommendations, no matter how much or how little you fly, you’ll be spending hundreds of dollars, probably over a thousand, every five years. And if you are so unfortunate as to damage the prop, you will find that you could replace your fixed-pitch two or three times for the cost of repairing the constant-speed unit.
The Score Thus Far
So the fixed-pitch prop is lighter, its cheaper, and its easier to install and maintain. Those are all reasonable arguments. But you’re not building this airplane to be reasonable. You want excitement, fun, performance, the thrill and satisfaction of breaking the surly bonds. You chose the airplane you’re building to fulfill a dream, and you do not want to hamstring it by putting on a propeller that significantly reduces performance. Just how much would you be giving up to go the reasonable route? For instance, how much slower would the airplane be with a fixed-pitch prop?
Not necessarily slower at all. Let’s go back to the bicycle analogy for a moment. Put yourself back on that one speed. You’re riding on level ground, cruising at a comfortable pace, legs turning the cranks at a steady 80 revolutions per minute. For every revolution of the crank, you make the same amount of forward progress, and the result is 18 mph. If you want to go faster, you could change the gearing to cover more ground for every revolution of the crank. You will certainly be going faster, but it will require more effort to pump the pedals at the same 80 rpm. If you keep increasing the distance traveled per crank revolution, you’ll increase the power required until no more is available and you cant maintain the rpm-whereupon you’ll find yourself going slower than you were with the lesser gear. So it is with propellers: If you optimize the fixed-pitch for maximum speed, about the best the constant-speed prop can do is equal it.
However, if you were to ride that bike-geared for top speed-away from a stop sign, it would take a lot of effort to turn the cranks over and get moving. It will take significant time and distance to achieve a speed at which you can spin the cranks efficiently. In airplane terms, a fixed-pitch prop optimized for high speed will take more distance to leave the ground and more time to climb because the high gear of the prop wont let the engine develop full power until the airplane has gained forward speed. The constant-speed allows the pilot to change gears so the engine, turning against less resistance, can make more power, which in turn means better acceleration and climb.
How much better is the question. It seems that you could expect a climb rate of about 1800 fpm with the constant-speed and about 1400 fpm with the speed-optimized fixed-pitch. Takeoff distance would shrink from 750 feet to less than 500 feet. Top and cruise speeds are much the same, though the constant-speed guys point out they can pull the rpm back while leaving throttle open and operate on 5% to 8% less fuel.
Somehow, for the mission you have in mind, those advantages don’t seem overwhelming. You don’t see yourself flying off strips less than 1300 feet long, and 1400 fpm climb is plenty, even for that short strip with the trees. After all, there are factory airplanes with half that ability operating there. Everyone would like to burn less fuel, but even if the constant-speed prop meant you could burn 10% less, it would take over a thousand hours of flying to save enough money to pay for the prop. For the mission you envision, the fixed-pitch propeller seems to fill the bill.
Sensenich
What’s Joe Say?
Just to be sure you have the true picture, you track down a pilot at a nearby airport. He’s been flying the same RV-6 for 15 years, and rumor has it he’s spent several years each with different props. Its flying with a Hartzell constant-speed unit now.
Yeah, he says. I started with a wood prop and flew it for several years. The performance was good and the prop was extremely smooth-very pleasant to fly behind. The prop weighed only about 10 pounds, so changes in rpm were almost instant when you moved the throttle. But wood props wear out. After flying in some rain, and operating off some dusty gravel runways, the wood was noticeably eroded. I also had to pay attention to the torque of the bolts holding the prop to the crank-whenever the weather or humidity changed, the prop would swell or shrink.
I moved on to a metal fixed-pitch prop. The empty weight went up about 15 pounds, all of it right on the nose, which for my CG was good. The flying characteristics didn’t change that much. Flat out the airplane was a couple mph faster, but there was a 2600 rpm restriction you had to mind. Throttle response was acceptable, but the propeller was never as smooth as the wood one was. The takeoff run increased noticeably, and it probably took an extra 150 feet to break ground.
Then I got the constant-speed bug. Because my engine was a solid-crank version that wont run a constant-speed propeller, I had to change the engine as well. Careful shopping and getting a fair price for my old engine meant that the change only cost about $5000-less than if I could have simply bought a new propeller and hung it on the same engine. The first few flights were eye-opening. The airplane jumped off the ground, and the VSI showed about 300 fpm better than it ever had before. But the biggest difference was not acceleration-it was deceleration. The blades go into finer pitch when the power is reduced and cause a lot of drag. The airplane slowed down much faster and sank like a flatiron with power off. And I could tell the difference in handling between the 1000-pound wood prop airplane and the 1045-pound constant-speed version.
Looking back after a couple years with the constant-speed prop, it occurs to me that Im still going the same places with the same loads at the same speeds I did with the fixed-pitch prop. I have better margins, and I enjoy the adrenaline rush of takeoff. I don’t enjoy landings as much-I used to fly the wing all the way to the runway; now I fly power.
So, if you had to do it all over again?
I think Id stay with the fixed-pitch. It was dirt simple, had good all-around performance, and the metal version didn’t mind rain and let me do everything my mission called for. For the difference in money, I could have fueled the airplane for two years.
Well, all of that is good information. After more thought, you may decide that the fixed-pitch will suit your airplane and the way you intend to fly it. The money you save thanks to this decision can be spent on your instrument panel or your paint job or taking that person who’s put up with that…that…obsession in your shop for so long to someplace very, very nice.
The first successful fixed-pitch propeller was developed, tested and flown by some bicycle mechanics from Ohio. Since that first flight in 1903, propeller design has progressed tremendously. While simple in theory, an efficient propeller can be complex in design and construction.
The diameter, pitch and number of blades on a given propeller is determined by the amount of power available, the rpm at which that power will be delivered and the aerodynamics of the aircraft the propeller will be bolted to. Propeller selection also has to do with aesthetics.
After all, how many people have bought a three-blade prop because they thought it looked better on the airplane than a two-blade prop? This is not to say there are not good reasons to spin a three-blade prop. After all, conventional wisdom holds that three-blade props have better ground clearance and climb better than two-blade props, even though the latter are supposed to have higher cruise numbers.
Following is a list of manufacturers who serve the Experimental/Amateur-Built market.
Arrowprop Company
www.arrowprop.com
405/279-3833
In business since 1961, Arrowprop is probably the granddaddy of the custom prop shops. The company can produce propellers with no blades (in case you need a test) up to eight blades. All propellers are made from select hardwoods, which are laminated together with a Class 1 waterproof resin. The hand-sanded props are finished with polyurethane to provide long service life.
Arrowprop propellers can be found on Experimental aircraft, ultralights, airboats, hovercraft, wind tunnels, and just about anything that requires a prop.
Engines supported: All (including small engines such as Briggs & Stratton, Robin and Kohler).
Aymar-De Muth Propellers
803/321-0569
(Web page under development)
After a relocation to Newberry, South Carolina, Michael De Muth continues to build two-blade Aymar-De Muth propellers. The company’s top-of-the-line prop is made from hard maple laminates that are wrapped in composite material with a leading edge made of steel composite. This combination is designed for use in the rain. At the other end of the line is a simple propeller made from laminates of hard maple. In between is a laminated propeller with a composite leading edge. Each can be custom crafted for a variety of Experimental and antique aircraft.
Should De Muth make a propeller that doesn’t meet the customers desired performance, a free exchange policy is offered.
Engines supported: All.
Catto Propellers
www.cattoprops.com
209/754-3553
Craig Catto manufactures composite fixed-pitch two- or three-blade propellers to order. The props start with a core of laminated hard maple that is then covered in carbon-fiber glass with an aluminum plate bonded to the back of the hub to provide a metal-to-metal contact point. The props are painted in the customers choice of colors and are often mistaken for metal by casual observers. Optional leading-edge protection is provided by PropGuard Tape to allow unrestricted operation in rain. Metal leading edges will be available this year.
Engines supported: Lycoming and Continental.
Edward Sterba Aircraft Propellers
www.greatplainsas.com/ed.html
941/778-3103
Sterba props are made from hard maple, Northern birch and cherry laminates held together with plastic resin glue and then heated until cured. The leading edge is protected by a urethane insert that wards off erosion caused by sand and rain. As with most of the propeller manufacturers listed, refinishing, re-shaping and re-pitching services are available.
Different blade planforms are available, depending on the application. A Sweptblade is for high-rpm applications such as on VW-powered aircraft, and the Race profile is for high-speed, low-rpm aircraft such as RVs, Mustangs and fast glass aircraft including pushers.
Engines supported: Lycoming, Continental and VW derivatives.
Flex Propellers, Inc.
www.bicambertechnology.com
800/776-7357 or 715/356-6856 (Wisconsin)
A subsidiary of Bicamber Technology LLC, Flex propellers are based on an improved airfoil design that makes for a smoother, quieter and more efficient propeller. An additional benefit of the bicamber blade design is that it moves the center of lift (thrust, when talking about propellers) out further on the blades, making for a more efficient prop.
The propellers are made from hard maple laminates, and are sized and carved to order with two or three blades.
Engines supported: All.
GSC Systems
www.ultralightprops.com
250/549-3772
GSC manufactures its propellers from Eastern maple hardwood for ultralights, powered parachutes and powered paragliders. Propellers can be ordered in two- and three-blade fixed-pitch configuration as well two-blade in-flight mechanically adjusted propellers for the powered paraglider market. Leading edge protection is available upon request.
Engines supported: Various. Call with your requirements.
Hertzler Propeller
480/897-8167
email: [email protected]
Hertzler is the manufacturer of the Silver Bullet two-blade propeller typically found on various canards, RVs and Lancairs. The props have a core made from five laminations of hard maple. That is covered with unidirectional carbon and bidirectional glass in addition to a urethane rubber leading edge for superior erosion protection. To produce a smooth and efficient propeller, each prop is machined to close tolerances. Propellers are available for engines up to 220 horsepower.
Engines supported: Continental and Lycoming.
Hoffman Propeller GmbH & Co.
www.hoffmann-prop.com
+49-8031-1878-0
With a full line of propellers available, Hoffmann should be able to meet the needs of any builder, regardless of the aircraft, ultralight or LSA under construction. Hoffman offers both custom fixed-pitch and ground-adjustable, lightweight composite propellers for applications ranging from aircraft to airships to hovercraft to wind tunnels.
Engines Supported: All.
Ivoprop Corporation
www.ivoprop.com
800/367-7767
The company was started when Ivo Zdarsky built and flew a tricycle delta wing aircraft to flee communist Czechoslovakia to Vienna, Austria, in 1984, pushed along by his first propeller. After moving to the U.S., he started a company to produce both fixed-pitch and ground-adjustable propellers. The company now makes composite propellers sized for ultralights up to 700 hp.
Engines supported: All.
McCauley Propeller Systems
www.mccauley.textron.com
800/621-7767
Rounding out the big three of the certified propeller manufacturers is McCauley, which builds both constant-speed and fixed-pitch propellers and has been doing so for more than 60 years. The McCauley fixed-pitched props are all aluminum, which is said to provide the owner/operator with low operating costs. McCauley does not specifically manufacture props for Experimental aircraft, but it has a selection of props for well-known designs.
Engines Supported: Lycoming, Continental and Franklin.
MT Propeller Entwicklung GmbH
www.mt-propeller.com
386/736-7762 (MT Propeller USA)
In addition to offering propeller repair services, hydraulic and electrically adjustable propellers, MT Propeller produces a full line of fixed-pitch composite propellers, made from laminations of German ash, covered with epoxy and sealed with a coating of acrylic-polyurethane paint to provide protection against chemicals such as fuel and oil. Depending on the application, some propellers may be reinforced with plywood. Erosion protection for the leading edges is provided by a stainless-steel erosion sheath that is bonded in place and may be replaced in the event of an overhaul. Protection for the intersection at the leading edge is provided by a self-adhesive PU-strip, making the prop acceptable for use in all weather conditions except known icing.
Engines supported: All 40 to 400 hp. Lengths of 50 to 100 inches (120 to 250cm).
Performance Propellers LLC
www.performancepropellersusa.com
713/417-2519
These props are made from 40 to 50 Type A Resorscinol glue impregnated hard maple laminations with a poured rainproof leading edge. Fiberglass leading edges may be added, depending on the application.
Frank Johnson recently took over the manufacturing rights to Performance Propellers from Clark Lydick after Lydicks retirement. Johnson was trained in the art of prop making by Lydick prior to his retirement.
All Performance Propellers are finished in multiple layers of two-part catalyzed polyurethane clear paint, which shows off the wood laminations.
Engines supported: All.
Prince Aircraft Company
www.princeaircraft.com
419/877-5557
Prince offers both wood and carbon-fiber propellers for large and small engines, even quarter-scale models. Their props can be manufactured with a P-tip to help control/delay the creation of tip vortices by bending the end of the propeller blade over 90. This allows a shorter blade to perform as if it were longer, similar to a tip sail on the end of a wing.
Prince touts its design as having the ability to change pitch based on the load applied, meaning that as the prop loads up for takeoff, the pitch (of its fixed-pitch prop) changes ever so slightly, providing better takeoff performance. Once the propeller is unloaded in cruise, it returns to its normal pitch, providing improved cruise performance. Custom colors and paint schemes are available.
Engines supported: All.
Props, Inc.
www.propsinc.net
541/265-3032
Props, Inc. provides wood composite propellers to both ultralight pilots and the Experimental crowd. Unlike most of the other boutique propeller manufacturers, Props, Inc. builds a ground-adjustable propeller.
The ground-adjustable prop can be ordered with two, three or four blades. Each blade is made of wood with an aluminum hub, thus retaining the best features (light weight and vibration damping) of a fixed-pitch wood/composite unit with the ability to tune the prop to the aircraft on which it is installed.
Engines supported: Lycoming, Continental and VW derivatives.
Sensenich Propellers
www.sensenich.com
717/569-0435
The grand old man of fixed-pitch props makes both wood and metal propellers for large- and small-displacement engines. Although generally thought of as providing propellers only for certified airplanes, Sensenich makes a number of propellers for the Experimental market and is more than willing to work with builders to select a propeller that best matches their projects.
In addition to the metal propellers, Sensenich also produces wood props with brass leading edges. Always one to stay at the forefront of technology, the company has recently developed a line of ground-adjustable composite propellers. These are most commonly used with Rotax 912 engines such as those used in the Vans RV-12. However, the company is also developing ground-adjustable propellers for Lycoming and Continental engines up to 180 horsepower.
Engines supported: Lycoming, Continental, Rotax and more.
Tennessee Props
931/455-4516
Tennessee Props is primarily a manufacturer of propellers for ultralights and gyroplanes, and its 24- to 48-ply props are made from laminations of hard maple, which are bonded with Class 1 waterproof resin. After they are machine milled, hand finished and balanced, the props are coated in multiple coats of unique two-component polyurethane coating containing aliphatic polyisocyanate, which is designed to protect the propellers from erosion.
Propellers can be ordered in diameters up to 72 inches and with hub thicknesses of 1.5, 1.75, 2 and 2.25 inches. For the gyroplane crowd, the company can produce propellers up to 66 inches in diameter and with a hub thickness of 3 inches.
Engines supported: All ultralight and gyroplane engines.
Warp Drive Props
www.warpdriveprops.com
251/609-0969
Often thought of as purveyors of propellers for ultralight or LSA aircraft, Warp Drive can provide a solid carbon-fiber ground-adjustable propeller with between two and 12 blades for low-horsepower engines and engines in excess of 115 hp. Nickel leading edges can be added to the propeller blades for a fee.
Engines supported: All.
WhirlWind Propellers Corporation
www.whirlwindpropellers.com
619/562-3725
Not to be mistaken with the maker of a line of Experimental constant-speed propellers (WhirlWind Aviation), WhirlWind Propellers Corporation manufactures a ground-adjustable propeller for Experimental aircraft with a Jabiru, Lycoming or Rotax engine. At 72 inches in diameter and infinitely adjustable, the 18-pound GA200L-716 two-blade prop should be a good match for any engine/airplane combination, as long as that engine is a Lycoming 150 to 180 hp with 7⁄16-inch prop bolts. A propeller hub with half-inch bolts as used on most O-360 or IO-360 engines should be available this year.
The propeller blades are manufactured from theromoset epoxy/graphite composite with an electroformed nickel leading edge to protect the prop blades from stone nicks and rain. The aerospace-grade aluminum hub is CNC machined and shot-peened for increased strength and life cycle. They are then anodized for corrosion protection.
Engines supported: Jabiru, Lycoming, Rotax.
Spinners
Many of the propeller manufacturers listed above also make matching spinners or can trim factory spinners to match their props. Contact the manufacturer for details.
Prop Extensions and Crushplates
Some kit designs require a propeller extension/spacer and most every wood propeller requires a crushplate to protect it from damage when torquing it in place. The following two manufacturers may be able to provide a solution for your prop extension needs.
Revmaster
www.revmasteraviation.com/products/prop_extension/index.htm
760/244-3074
Saber Manufacturing
www.sabermfg.com
817/326-6293
-Bill Repucci
