Ultraflight Adjustable Propellers

[Chappy]

Lazair builders, owners and pilots,

While digging around through my old Lazair stuff recently, I came across one blade from the ill fated adjustable plastic propeller that Ultraflight attempted to design and sell. I'll post a picture below.

Each blade was about 17 1/2" long including the "knob," so that a complete prop was approximately 36 "long. The blade was about 3" wide at the root, and 1 1/2" near the tip. Each actual blade area was about 15 3/4" long. It was injection molded by Dale Kramer's brother's business (previously Dale's Dad's business) out of what I assume was carbon fiber filled nylon, as they had tried and rejected the glass reinforced plastic DuPont Rynite PET used for a short period in the small props. Each blade was relatively thick, yet weighed only about 3/4 pound. It was black in color, with a fairly smooth finish. The size and the volume of each blade pushed their smallish injection machine to the very limit of it's capability. I seem to remember that the development of the mold cost Ultraflight around 50,000 dollars in 1983, which was an investment budget buster.

Each blade required trimming around the edges, and a critical machining process of a wide groove near the root between the blade and "knob." The two blades were clamped in an aluminum hub. A pair of aluminum clamps gripped each blade at the groove, permitting the independent pitch adjustment of each blade. The parts were to be machined to very exacting tolerances so that when the blade claps were fully tightened, the blade was gripped tightly without being crushed. I don't remember the interference, but I think it was only a few thousandths of an inch.

Factory testing went without incident. There was tremendous pressure from the dealer network to get these propellers. Virtually all other Ultralights on the market by then were at least available with large engines that provided much higher climb performance than could be obtained from a Lazair with Biplane props, so the perception was that if the Lazair's performance could be improved, it would make for a larger market for it.

Soon after the first props were sold to a couple owners and they became the stock prop in newly shipping kits, a couple reports of blade failure started coming in. Within hours Dale realized that there was a serious problem, especially after pulling a sampling of prop parts from stock. Parts weren't being held to tolerance, and because of that some props had much higher interference fits than the design called for. In affect, the aluminum clamp pieces were crushing the propeller at the machined out groove in the blade, placing it under tremendous tension. Add the forces of the blade pulling on the same small area of the prop when in motion, and they were prone to fail. The failure would be without any prior symptoms, with the blade suddenly flying off. The resultant out of balance condition could, and did in one instance, rip the engine totally clear of the nacelle mount. I believe it was Max Collins that called with a wild tale of his engine and partial prop hanging by the cables and fuel line while attempting to hack off the lift strut, much less trying to get Max too. In other words, this was VERY serious.

We began calling everyone that had been shipped a prop within hours, and they were instructed to stop flying the prop, why, and to return the knob section to Ultraflight for a replacement propeller, when they became available. We thought we were probably OK. We assumed most of the new props were not in use yet since they had just been shipped in new kits. Boy, were we wrong. Most dealers, upon receipt of their first kit that contained the adjustable prop, had ripped them out and retrofitted their planes with them. And they didn't want to give them back! They had a taste of what was possible with the Rotax 185 when it was fitted with a more efficient propeller, and thought we were being too cautious. It took threats of termination of dealer contracts to get them returned. The phone bill along ran into the thousands of dollars. The loss of the prop project was a terrible financial hit for Ultraflight, and it became obvious that there would not be a redesigned replacement propellor from Ultraflight anytime soon.

My personal feeling is that this prop probably would have been safe with a minor design change. If, rather that having the machined out grove at the hub, the blade could have been cast with a ball instead. The clamping forces then would have been in compression on the blade, not tension. It would, however, have required a much thicker prop hub assembly.

Beyond the Lazair History Lesson of this letter, I want to warn anyone out their that may have come into possession of these propellers to take heed. DON'T FLY WITH THEM! Clean them up and mount them over your fireplace mantle. I wish I had one, but all I was able to hold onto was just this single blade.

Chappy

[Shannon]

P-tip in-flight adjustable prop complete with droop-tip and carbon fiber overlay. Unique as the Lazair itself !

[Shannon]

Pic 2: Droop "P" tip

[Shannon]

Pic 3 : Carbon Fiber weave over Hardrock Maple wood core

[Chappy]

I had the opportunity to see these Prince propellers recently, and they are incredibly beautiful and look to be very well made. Too bad it's not possible to compare performance to the old adjustable Ultraflight designed prop. I remember that the Ultraflight adjustable propellers provided a wonder boost to the Lazair's performance on 185 Rotaxes. They also just sounded better than any other prop I've flown with on a Lazair, but then I haven't flown behind the P props. I have, however, been hearing good stuff about the Prince props for many years.

Wouldn't it be fantastic if Prince built this prop in an adjustable pitch model? Of course, it probably wouldn't let you get much more out of the Rotax, and almost no one could afford to purchase a pair of them. Nevermind...

Chappy

[Shannon]

Aren't they nice ! I posted the pics of the carbon fiber p-tips for the benefit of the guys who have not seen what they look like. The carbon fiber weave gives them a very unique look.

[rayjb60]