HARTZELL AND SPORT AVIATION Wagon Wheels to Propellers

ons, not lumber mills, although the Hartzells still operate one to this day. If R. N. Hartzell turned down

Washington Street today, it would feel f a m i l i a r . His old mill is still standing there against the river. Its turn-of-the-century brick personality still intact and little changed. But

just down the block is another building that bears his name, this one of modern steel construction. The juxtaposition of the two plants being next to one another goes much deeper than simply their appearance. The technological gap between what is now taking place just a few hundred feet from where old R. N. started whittling on walnut is enormous. The

new building houses Hartzell's composite propeller manufacturing. The old building houses engineering and test while a huge production complex (150,000 plus square feet, 291 employees) sprawls across what was undoubtedly pasture land west of town during R. N.'s early days. Hartzell is one of those names that has just always "been there." Aviation has never been without it. To practically everyone currently flying, the name is synonymous with the term "constant speed/' since few remember the old walnut props they made for nearly half a century. Their brand recognition is largely the result of being the largest producer of propellers in the world and have nearly 60% of the turbine and 50% of the recip markets. We forget Hartzell was a man and is now a propeller. Atur etaixling In «n e q u a l i z i n g roam f o r t. Depending on what part of aviation days, the roughed propeller* arc you call home, Hartzell probably has a '.n the ten?* rtspn'-tment different image. To most of us, we think of two, and maybe three, blade This is an early photo taken at Hartzell Propeller. An original caption is shown on props on single engine airplanes. But the photo. that is far from the correct image. A casual walk down their enormous proRobert about making something they duction line would show that clearly. . ccording to company legend, called a propeller. Hartzell went over Few of us think of the complex fiveRobert Norris Hartzell used to have and took a look. What he said has and six-blade propellers on so many of these neighbors just down the street been lost to history, but after spending the turbine commuter liners like the who had an incredible idea. It seemed most of his youth making wagons with Dornier 328 or Shorts 360. Most of us these two brothers thought they could his father, he probably thought the don't know Hartzell is even in that fly! Robert and his father didn't tell propeller to be a simple project. No market. them they were crazy, but who knows separate parts, no careful fitting of The biggest shock of all is to find what they thought. Times were chang- spoke to felloe, no steel tire to shrink how busy they are. Two shifts, runing quickly, but the elder Hartzell was in place. An easy job. ning at max capacity and then some. still making his fortune in hardwood So, selecting some of his best wal- They can't guarantee a two-blade out (oak and walnut) lumber and wagon nut, he laminated up a blank and the door in less than 16 weeks. Four making and that part of Ohio had yet started carving the first of thousands months! to get used to that new fangled ma- and thousands of propellers to carry If there is a recession in general avichine which was just becoming his name. The year was 1917. ation, Hartzell must hope it never common place, the automobile. Wagons disappeared, Jennies ap- ends. If they are this busy now, how Still, the brothers persevered, be- peared and the Hartzell name became would they handle good times? came famous and one day talked to synonymous with airplanes, not wagDepending on which plant you're

By Budd Davisson

(Photos by the author except where noted)

A,

SPORT AVIATION 43

The hub forgings may be of aluminum or steel, depending on whether they will gu

on turbines or recips. The final blade shape, including the tip curve, is done by hand with a grinder.

drills to arrive at the shipping dock as a propeller ready to be crated. Crating, by the way, is not an easy task entering and which door you use, when the propeller in question is an you'll get a different impression based 11 foot diameter five-blade. The fifth on the material being processed. The blade is often removed to allow it to fit composite activity across town is fairly into a square crate. small, tidy and neat with the primary It is difficult to decide which of the machinery being a few big, heated production lines is more interesting, presses and a large X-Y vacuum cut- the metal or the composite. Hartzell ting table that runs the high-tech has organized its production along the equivalent of an Xacto knife through cellular concept in which like materipre-pregged carbon fiber cutting out als are worked in a particular area, i.e. the many different shaped lay-ups for steel, aluminum and composite. many different prop blades. The receiving area in the big plant The main plant, however, is far is interesting because open topped from being small. It is a manufactur- crates full of rough steel and aluing plant that receives rough forgings minum forgings for hubs and blades in one end and flows them through a stand ready for use. The hubs for combination of garage-sized CNC ma- their "compact," meaning light single chines and older, well proven gang engine, designs are clean looking two-

piece forgings that do bear a vague, but shiny, aluminum resemblance to the propeller hub they will become. The steel hubs, however, especially the five-blade ones, look like huge, crude jacks which will be played with by a giant child. They are black and rough and very heavy.

The aluminum blade blank forgings all come through receiving looking like ragged Lockheed Electra blades . . . wide and square. They look this way because many different blade types will be cut from a single style of blank. They have lots of extra meat that will be removed by CNC machines in response to the computer program which determines which blade it will be. The blanks, incidentally, are 2025 aluminum and arrive already in a T-4 condition. There is nothing done to them in-house to change their hardness. Blade processing, as with so many other parts of the propeller manufact u r i n g process, happens in many different steps. Some obvious and high tech. Others subtle and done by hand. For instance, the CNC machine dutifully whittles the blade down to a

profile that is recognizable, but still very rough, with deep, lengthwise grooves left by the cutter. Also, the tip is still wildly over length and

square, since the CNC operation de-

mands the blade be gripped at both ends and a tongue is needed at the tip for fixturing. The hand of man is never far away and it is that hand which physically grinds the blade down to its final dimension and shapes the ends of the

tips. Watching a man wipe back and Blade blanks after inspection and rough band sawing to shape. 44 JANUARY 1995

forth down the blade with what ap-

everything around it is machined away

leaving a pin. Not unlike cutting a

tenon on a wagon wheel spoke. Some things never change.

Once blades are finished they all go into a rack and receive a serial number. Then each is weighed and the serial number entered into a computerized scale. The scale runs a cross-matching

program and automatically matches up the blades by weight, giving a printout telling which blade goes with which. This greatly cuts down on the amount of weight required to balance the finished prop. All balancing is done statically, with any dynamic balancing left to the end user after they bolt it to an engine. In reality, watching the blades work The hubs progress through several stages, from rough forgings to partial external their way from one process to another, machining to internal finishing. •• there is very little that is surprising or unexpected. In fact, other than having pears to be a body grinder, it is hard to invest the capital needed to keep up to hold a fine degree of tolerance and believe they can hold the ten thou- with the newest in m a n u f a c t u r i n g balance, they are a relatively simple sandths of an inch tolerances the techniques to produce a better product piece to make. airfoil requires. in less time. As simple as the blade processing To anyone who has taken a Hartzell appears, that's how overwhelming the Chief aeronautical engineer, Rick Bowerman, says the blades work with blade out of the hub, there has always hub manufacturing appears. RegardReynolds numbers which vary from been the question as to how they ma- less of whether it is a small hub which three million (fairly normal number chined the integral actuating pin that clamps down over the blades to retain and an effective range) all the way to protrudes out of its base. Every other them, or a huge steel hub which de100,000 further down the blade, which machine operation in that part of the pends on clamps for blade retention, means the airfoil efficiency also blade is done by lathe and the pin there's a bunch of serious machining changes. This may be one of the areas seems to stick out where it would going on. where the Rn says a super smooth, ac- muck-up everything. How is it cut? Over at the composite plant blade curate surface isn't totally necessary The answer is that a sizable boss is left making takes on an entirely different all the way down the blade. during the initial machining opera- feeling. It has a textile feel to it, rather However, Jim Reedy, VP-Sales and tions. Then, after the blade is profiled Product Support, says they are work- and finished it is clamped in a fixture ing towards eliminating as much of on a lathe and the remaining boss fed the hand finishing operation as possi- lengthwise into a gigantic face cutter ble by going to newer manufacturing mounted on a lathe's headstock. methods. He is quick to point out they There's a hole in the face cutter, so

A CNC machine cuts the blade blanks down close to final dimensions before final hand finishing.

When the blanks are ready for hand

finishing they still have heavy machine marks and the tip must be shaped. SPORT AVIATION 45

Hartzell is moving towards automatic machining centers, but much of the work is still done under the experienced eye of master machinists. Most of the aluminum blades come out of basically the same forging which contains enough material to cover several different patterns. than having blacksmith overtones. Maybe that's because the basic blade is indeed made of cloth. The actual cross section of a composite blade reveals a high density foam core that is actually

Each hub is carefully inspected and then the two halves serial numbered for matching. 46 JANUARY 1995

only there for tooling purposes. It acts as a core over which the composite material can be laid. Once everything is cured, it is superfluous. The lay-ups flow down over a machined steel or titanium shank that only goes a few inches up into the blade and is largely hollow for weight. Then the shank area is wrapped in either E or S uni-glass roving (depending on whether the mother material is Kevlar or carbon fiber) which forms a solid base for machining the shank to fit in the hub. Each blade has a slightly different combination of materials and different lay-up schedules but the concept is all the same. A wet lay-up of carbon fiber is made using the many petal-shaped pieces cut from the pre-preg by the cutter. As the computer tells the high tech razor blade which shape to cut, they are numbered by hand and bundled together so the lay-up technician will know the exact schedule without looking it up. Then the bundle is popped back into the freezer until time for use. Watching one of these blades go together, it becomes a little clearer as to why a composite three-blade prop for a single engine airplane costs so much. The lay-up process alone takes nearly eight hours per blade. Then the blade is slipped into a two-piece mold which is heated by oil circulating through cavities inside the mold. The mold is an exacting piece of machine work which Hartzell says can run as high as $100,000 to have made. The mold has to be exact because it determines the final shape of the blade. The blade cures in the mold for well over four

hours, so this gigantic combination of a press and oven can only turn out two blades a day. Not a high volume production line! Once the blade pops out of the cookie oven, it is final machined and fitted with an electro-formed nickel leading edge. This flush mounted metal is glued into position and Hartzell says they seldom, if ever, have trouble with them delaminating but they do have to replace them from time to time because of erosion.

Ever wonder how all the holes were drilled in a hub flange? Gang drills such as this still do the job.

A partially machined steel hub.

The human element of Hartzell propellers is hard to miss and Jim Reedy says employees have tremendous esprit de corps and loyalty to the company. Part of that is probably because they know they are part of an elite team. Hartzell is always looking for a few good men and women and the accent is on "good." Hartzell screens their applicants thoroughly then tests them, after which they are put through a Hartzell training program. Only the best become Hartzell employees and, according to Reedy, they generally stay for the rest of their lives. Reedy says Hartzell is in a hiring mode right now and desperately needs more people. But, he wants to make sure only the best machinists and workers apply. Otherwise they won't make the cut. Although Hartzell does a lot of business with the commuter a i r l i n e r market and they see conversions (bigger engines into existing piston-engine airframes) as their fastest growing area, they still regard sport/recreational aircraft, including aerobatic birds, a primary and rapidly growing market. No one, it seems, is too busy

Notice how the blades are retained on the finished steel hub by external clamps which capture both the hub and the blade.

nuances of propeller design.

"You know the old standby for propeller clearance, the hacksaw? Bad move! It turns out propellers are designed so the prop's natural vibrating frequency is such it won't interact with the high-frequency vibrations of the engine. That's why props are certified for use on particular engines in particular airplanes, so everyone knows the vibrations aren't likely to start feeding on one another." Modify the engine or modify the prop and the installation represents a complete unknown. It is very analogous to flutter and control system balance - change anything and all bets are off. In terms of shortening a propeller... each has a published length range and

if it is clipped shorter than that, it no longer matches the engine because the vibration mode changes too much. And then there are engine modifications. The culprit is compression ratio and the way that effects high-frequency vibrations, not the increased horsepower by itself. Although it is possible to feed too much horsepower into a propeller, that is highly unlikely. However, put high compression pistons in an engine, even just going up to 9:1, and the frequencies change enough to cause possible problems. The key phrase there is " . . . possible problems." No, the prop isn't going to immediately fracture into a million pieces in the first hour, but it will definitely wear prematurely and won't make its normal TBO. Also, there IS

to have a little fun, regardless of how

successful they may be. There are actually two separate

sport aviation markets Hartzell is addressing, the hardcore aerobatic crowd

and the homebuilders. They say both need special products and have their own unique problems. After spending a little time speaking with Hartzell engineers, we began to think some of the propeller problems we have as homebuilders are brought on ourselves by underestimating the

The paint shop is in the main plant so all blades, composite and otherwise, pass through it. SPORT AVIATION 47

Hartzell makes a complete line of spinners for their propellers including complex carbon fiber units for their multi-blade commuter props.

The carbon fiber on the composite blades completely covers the aluminum hub and then is wrapped with glass roving which in turn is machined. The foam is non-structural. the possibility of failure. Hartzell engineers report hub cracking and blade loss brought about by bad mismatches of engine and propeller mods. When asked, Jim Reedy said they are willing to work with engine and a i r f r a m e people to test the engine/propeller combinations they have arrived at through modification. In fact, they traveled up to Lancair several times to develop the right prop for the Lancair IV and have developed a special short-bladed fan to go on the front of the ground-hugging Lancair 320/360s. Back in 1989 Hartzell put an experimental composite three-blade prop into the aerobatic market to test and immediately determined it needed more development. They changed the actuating system to incorporate an oil accumulator to eliminate the possibilHartzell Propeller celebrated 75 years of successful propeller manufacturing in 1992. Consistent with its reputation for innovation, in 1991, Hartzell introduced the first lightweight, dual-acting propeller pictured here on a test stand.

4H JANUAhiY

off, so more time can be spent hanging straight down.

Robert N. Hartzell passed away in 1968 so he knew what kind of a monster business he had started and what direction his product was headed. An entrepreneur to the end, his new line of products wouldn't surprise him. But, he would be proud to know that in the midst of an aviation recession, his products are still in high demand and his employees still think so much of the company they have almost zero employee turnover. Still . . . it's a long, long way from the laminated props he started hand carving in the brick building by the river. A long way. +

This 3-dimensional CNC profiling machine receives information directly from engineering. This new process makes possible greater blade-to-blade consistency and results in smoother, more vibration free propeller operations. ity of propeller over-speeding due to momentary loss of oil pressure. They also worked in everything they've learned since that time about composites and now have their props

Yes, You Can!

hanging on planes like Patty Wagstaff's Extra 300S. That has to

be one of the toughest tests a propeller can endure because of the wild gyroscopic forces current unlimited aerobatics generate. The propeller has already gone through Hartzell's certification process

on an Aviat Pitts S-2B and, as this is

being written, the paperwork is sitting

in an in-basket at the FAA awaiting final approval. That will approve the

propeller for the 260 hp AEIO-540D4A5, but then Aviat has to do their

own certification to approve it for their airplane. What does the propeller do for an airplane like the Pitts? For one thing, the lighter blade weight means the prop has much lower polar moments (17.4 in. lb./sec.2 versus 25.4 in. Ib.) and much, much lower centrifugal loads. These give the crankshaft a new lease on life. Hard akro eats crankshafts because the precession of

the prop wants to take the crank flange one way while the airplane wants to go another. The performance increases reported during testing were most notable in the low speed ranges where the additional thrust let the a i r p l a n e pull vertical and accelerate out of a low speed hole m u c h better. Also, the

three-blade has much more drag power

You Can Build and Fly Your Own Airplane. We'll Give You Everything You Need* Know-How and Confidence. Our two-day, handson, how-to workshops teach you the basic skills and inspire you to see it through to completion.

Tools and Materials* Our FREE ioo-page catalog is

filled with them. You'll find everything from calipers to knibblers, and from fabric to fasteners.

Above All - SERVICE SERVICE SERVICE. We pride ourselves on our prompt shipment, and you'll really like the way you're treated. That's a promise!

We're Involved. You Can Be, Too.

800-831-2949

LEXANDER

\ EROPLANE COMPANY, INC. Box 909, Griffin, Georgia 30224 SPORT AVIATION 49