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PROP BOLT SIZE FOR PRINCE PROP

PostPosted: Mon Mar 20, 2017 8:05 am
by orenjr
Does anyone know what crush plate and bolt size is needed for the Prince prop on a 914 Rotax?
Lonnie is out till April and I need answer before then.
Also where would be the best place to buy?
Thanks! Oren

Re: PROP BOLT SIZE FOR PRINCE PROP

PostPosted: Mon Mar 20, 2017 1:33 pm
by FlyerChief
Hi Oren,
The bolts will be either 5/16" or 8 mm. depending upon the insert nuts (threaded bushings) you ordered for the back of the Rotax prop hub.
The nuts would have been one of the following part numbers:
842 634 - M8 nuts for prop shaft (set of 6)
842 639 - 5/16" x 20 nuts for prop shaft. (set of 6)

The length may be different on the new props since Lonnie is reportedly making them about 1/4" thinner than when I bought mine, but my bolts are 100mm. (4") long. I had been advised to buy Grade 8 (or Class 10.9 if you order metric) bolts to ensure the strength required. I bought cadmium plated bolts from Fastenal and carefully drilled the safety wire holes in the bolt heads using the drill press. (Although the torque on the bolts is quite low at only 140 inch pounds, for an added margin of safety I will be replacing these with rolled thread bolts before flying again!) I'm sure it's much more critical on high horsepower high performance aircraft, but better safe than sorry!

EDIT:As mentioned in BDA's post below, after further research I would recommend getting approved aircraft bolts with a rolled threads. Theoretically, weakest area of any mechanical fastener is the minor diameter of the threads. Since the thread dimensions of a cut thread and rolled thread fastener are identical, there should be no difference in strength. That said, there is some research showing that rolled threads have a 40 to 70% greater fatigue strength and 10% greater tensile strength, likely due to the heat treating process in manufacturing rolled threads and the disruption of the metal's grain when cutting threads. As well, the quality of the finish and higher thread specs of rolled bolts make for a more precise fit. I had considered using AN bolts but the size needed for the Rotax/Prince combination was unavailable and apparently the AN threads were not long enough and would have bottomed out in the inserts. Thanks for the heads up BDA...

The hub is 1/4" aluminum (not sure of the alloy as I bought it from Prince). I believe it's 4.75" to 5" in diameter, but it's inside the spinner so I will have to remove that to confirm the plate diameter.

I have the 912uls, but I am sure the 914 uses the same ones.
Dan

Re: PROP BOLT SIZE FOR PRINCE PROP

PostPosted: Mon Mar 20, 2017 1:41 pm
by BDA
Aren't Prop bolts Rolled threads??

Re: PROP BOLT SIZE FOR PRINCE PROP

PostPosted: Mon Mar 20, 2017 5:46 pm
by orenjr
THANKS! FOR YOUR HELP GREATLY APPRECIATED
Oren

Re: PROP BOLT SIZE FOR PRINCE PROP

PostPosted: Tue Mar 21, 2017 3:27 pm
by SheepdogRD
For anyone else needing information about this:

For our prop, used on a Rotax 912S with no extension and no spinner, Lonnie ordered a kit of 6 prop bolts, 12 washers, and 6 nuts, plus aluminum crush plate and 6 stainless steel lugs from Saber Manufacturing (http://www.sabermfg.com). They're at 3601 Nassau Court, Granbury, TX 76049. Phone 817-817-6652.

Here's the information on my kit:

The fasteners are plated, lot traceable & proof tested, high tensile, high ductility, long thread 5/16-24 x 4" F-911 bolts (Saber part # b95/16 40d); AN960-516 washers (Saber part # bw5); Super-9 all metal, high tensile, high ductility prevailing locking nuts that are cadmium plated and waxed (Saber part # n5).

Custom-flanged non-threaded stainless steel lugs have bored ID for slip fit (not interference fit) into the Rotax engine flange (Saber part # 10000260).

The crush plate is 5" diameter, 1/4" thick, with 5/16" noles in a 4" bolt circle (Saber part # c5000200).

The bolts may be longer if you're using an extension or a spinner.