Whether it’s model aviation or general aviation—a common thread between the two is how the plane goes through the air, which is often done through the use of a propeller. Recently we were invited to Hartzell Propeller Co. to learn about how propellers are made!
It is Hartzell’s 100 year anniversary, so we were honored for this opportunity to partner with them to learn and celebrate. (Did you know that their first customers were Orville and Wilber Wright? How cool!)
When we visited Hartzell, we met with JJ Frigge, Executive Vice President, and Trevor Parker, Propeller Integration Engineer. Not only did they show us how props are made, but more importantly, how they work.
You’re probably familiar with the propellers you see on a model airplane, which is typically made out of a solid piece of plastic or even the type that you would find on a 1920’s Pietenpol, but Hartzell makes their propellers a bit differently.
They do something called “constant speed.” With this type of propeller, it gives you the ability to change the pitch to give you the best climb and the best cruise. They do this by changing the oil pressure inside the prop and move the prop in mid-air to make the engine perform at maximum efficiency. It also enables you to change flight modes as you fly.
Testing the propeller
One thing we learned about the process of making the propeller is that efficiency and safety are key. Hartzell does this through something called “one and done.” This is where they make a part and test it even before it’s passed on for inspection.
“The principle is run a part, check a part,” says JJ. “You basically load in a hunk of metal, call up the program that you want to run based on the raw material that you put in, and that’s going to run through its cycle and put it on the CMM to do the laser inspection.”
A computer provides a read out of the process to ensure everything is good to go.
Types of propellers
Following that, we learned that because the props move mid-air there are different ways to mount them to give them the ability to move.
There are two different mounts that Hartzell produces:
Aluminum hubs
The clamp style hub where the blades nest in the hub and are clamped down over top of the blades.
Steel hubs
Heavier and for dirtier engine applications and the blade nests on a pilot tube against the hub and then its clamped from the outside.
Forming the propeller
After learning about the hubs, we learned how the propellers are made.
Hartzell has approximately 10-12 blade forgings that they make, which then are cut down into 500 finished part numbers for blades.
The first thing cut is the shank. The blade then gets formed from the shank outward.
“When we cut the airfoil, it will leave it with a small step over from the machine that we need to polish or grind off,” says JJ.
Blade grinding used to be done manually by 20 people and now it’s done by a machine. But that doesn’t mean the employees are no longer needed. Hartzell has these well-trained professionals to develop other parts in the process that cannot be done manually.
Did you know that every single part of the propeller—120 pieces—need to be tested? If it’s a component that’s magnetic, it is tested through magnetism to check for any faults. For parts that are aluminum, they test them through a unique process that uses black lights to see if there are any faults.
De-icing process
A propeller is nothing but a wing that spins around rapidly. But because of that, you must keep ice from forming on the leading edge in certain conditions. If ice does form, it destroys the integrity of the airfoil (air flow) that gives you lift.
Hartzell installs de-icing boots to prevent this from happening.
“Our boot room is humidity and temperature controlled where they put on the de-ice boots for any prop that is going to have de-ice capability,” says JJ. “It takes a little bit of heat plus the centripetal force of the prop spinning around and the CF flow to shed the ice.”
Assembly
Once all the components are made, they move to the assembly area. In the assembly area is where they put together all the 120 parts and test it out thoroughly. One test they do is applying sensors, put the props on a plane and fly them for several hours to check to see how the vibrations affect the materials and how they hold up.
Propeller overhaul (for when your props break down)
After we learned how the propellers were made, we were able to see how they were overhauled.
“We will check all the parts through our NDT process again,” says JJ. “And we’ll look for any sort of dimensional areas that are out of spec.”
They’ll go through a similar process they go through to create the prop in the first place. They have complete tear down and inspection and then go through several refurbishing operations. The blades and other components will also be primed and painted.
Shipping
Sometimes propellers can’t be repaired, but Hartzell wants to get pilots back in the air as soon as possible. That’s where their shipping department comes into play.
“We try to stock around 100 propellers at any given time because you never know when your prop goes in for overhaul if you’re going to get that dreaded call from the repair shop that says, ‘Hey, you got two blades and a hub that are scrap and it’s going to be a lot more than you thought it was going to be to overhaul. So do you just want to buy a new prop?’,” says JJ. “And so a customer then has choices. There’s us and then there’s competitors and so we want to have those props in stock so we can ship out in a day or two.”
Overall, it was an amazing experience getting to see how a propeller is made through raw materials, all the way up to the finished product. But what really inspired us was the people, how they were treated with respect, and how they all seemed to be passionate about aviation. Hartzell’s slogan is “Built on Honor,” which they’ve had as their motto for over 100 years and was evident during our time there. It truly was a unique experience and we are thankful for the opportunity.
Learn more about Hartzell Propeller Co.
If you’ve noticed, we have started sharing general aviation stories on the weekends! If you are passionate about general aviation and want to share your story or potentially collaborate with us, visit our general aviation page and fill out the form.
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