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PostPosted: Thu Jan 14, 2010 7:31 pm
by Wayne
Thankyou guys,
The standard configuration that I have seen with the Bi-props is just the washer/lock nut conbination, I don't think I have seen a crush plate added to the factory Bi-prop, but no doubt a crush plate would spead the load and reduce stress on the prop in that area.
However perhaps the original set up allows the extra moment/flex of the Bi-prop and the crush plate could cause extra stress on the prop by inhibiting the flexibility?
There is a problem with engineering and when you take the movement out of one area by stiffening/strengthening an area, the stress it is transfrered to another area so the answer is in many instances 'Flex' , thats one for the master Dale Kramer any comments ?


PostPosted: Sun Jan 17, 2010 7:07 pm
by Shannon
Bi-prop crush plate. What caused this ? No idea ? Maybe Lynn Haugo can say. I believe this failure happened to him.

PostPosted: Mon Jan 18, 2010 2:27 am
by Chappy
Most probably one of the props made from DuPont Rynite.


PostPosted: Mon Jan 18, 2010 5:05 am
by ozzie
Chappy How do you identify this type of prop?

PostPosted: Mon Jan 18, 2010 11:04 am
by gdewsbury
I see a broken exhaust manifold as well. My question is what happened first. Did the exhaust break from vibration after the prop broke or before and fly into the prop??

PostPosted: Mon Jan 18, 2010 5:38 pm
by Chappy
Hi Ozzie,

The Rynite props have a slightly different color and finish texture, are heavier and stiffer - especially compared to the normal props with a lot of time on them. The extra stiffness can be noticed sometimes as the plane will perform a bit better. The Rynite material, a glass fiber/polyester material, didn't flow as well into the molds as nicely as the original carbon fibre/nylon material. This caused voids within the props that wasn't readily apparent. Therefore they could fail anywhere along the blade or hub. Unfortunately, there is no marking on them to distinguish them as Rynite. The only reliable way to tell is to weigh them. Rynite props are more than 10 ounces, cf/nylon props under 10 ounces.

I believe the failure rate of these props was many, many, many times that of the cf/nylon ones. Part of that was because the CF/nylon props were extremely reliable. Fortunately, they constituted only a small percentage of the total number of props supplied by Ultraflight over the years. They were made in early 1983 IIRC. Technical Update Number 9.4 states that kits below A530 and above A754 had cf/nylon props. In between those kits, they may or may not have been shipped with glass/polyester props. Ultraflight didn't formally recall them as they did do with the adjustable pitch props, but rather exchanged them at cost. I have no idea what percentage were exchanged. I think it is very unwise to use them. On the other hand, if they have lots of time on them already, they "probably" are good ones - but you never really know.

If someone decides to use them even after all the warnings, make sure they are kept well balanced and in good shape (not all chipped up), use large fender style washers or crush plate under the mounting bolts, and torque only to spec. Ultraflight prohibited their use with hopped up engines.


PostPosted: Mon Jan 18, 2010 5:39 pm
by Chappy
Hi Glen,

If you look at the picture carefully, the front prop has lost both blades. One break is a clean break, but the other looks all funky. I suspect that was caused by voids in the material that let the first blade fail, then gross imbalance caused the second blade to go and also to fracture the exhaust manifold from the extreme movement of the engine. That's why I said I thought it was a Rynite prop. If the manifold caused the damage, I would suspect some damage to the rear mounted prop. The second prop might have been a nylon prop, or a polyester one that flowed well in the mold.

Of course, I could be completely wrong!


PostPosted: Mon Jan 18, 2010 5:50 pm
by lazairiii
Back in the mid 80's when I was flying A-686, I called the factory after receiving the notice about the bad batch of Rynite props, and they just had me take a hack say to the props 2" from the hub and send the hubs in for an exchane. I don't think I was charged a dime as I recall. Seeing the kit numbers from above, A-686 fell right in the middle of the recall list. My current kist A-329 is below the recall list it appears. I've still got the original Bi-props that came with the kit, and now I'm going to weigh them just for fun.

PostPosted: Mon Jan 18, 2010 10:31 pm
by Chappy
Hi George,

That wouldn't surprise me at all. Dale was always very generous to me, giving me a set of floats, a couple used Pioneer engines, a couple props, and other small stuff over the years. I know he gave a lot of stuff away to customers over the years. Later on, his wife (and company general manager) Linda pretty well put the kibosh on that. Not necessarily a bad thing when you're in business.

I know Dale's still that way.


PostPosted: Tue Jan 19, 2010 2:58 am
by Wayne
I am so glad this forum is around ! for the record my props weigh 264 grams and 265 grams or approx 9.50oz