Mark and Steve,

 

1. Some spinner back plates will crack because the stamping was not flat and could flex regardless of what was done to keep it whole.

 

2. A delaying fix was to rivet 1/8" doubler plates around the mounting holes.  Note: bucked rivets are better than squeezed rivets for this job as the squeezed rivets can lose their heads from work hardening.

 

3. Fiberglass spinners are flexible and should be reinforced, especially around the prop cutouts since the natural flex allows for unusual stresses on the back plate.

 

4.  The best thing  to do to eliminate any cracking is to use a forward bulkhead or support for the spinner.  Fixed pitch props allow the builder to easily install a bulkhead to the face of the prop.  Constant speed props with a cup allow for several solutions - If the cup comes close enough to the spinner, one could use Saran wrap as a release, goop a bead of sillycon on the cup or the spinner (Saran on the other part) in order to stabilize the spinner.  If it is a Hartzell prop, there are four available tapped mounting holes on the end of the cup and a bulkhead could be mounted there.

 

5. Always dynamically balance the prop after messing around with this stuff (solutions 1-4).

 

Mark - I purchased an aluminum spinner kit from Aricraft Spruce some years ago (after my backplate went Tango Uniform), placed a doubler on the back plate and constructed a forward bulkhead, lathe cut to match the angle of the spinner, from nylon (about 1/4" thick) - the final fit included a thin film of silicon around the outer edge of the bulkhead for a really tight fit to the spinner.  I do have a Hartzell CS prop.

 

This should clear up a rumor about me using a peculiar back plate.

 

Grayhawk

 

Hi,

I seem to remember someone making one out of plastic - maybe HDPE  1/2" thick or so.

I may have been Greyhawk.  If it does not come up and you can't find it in a search, you might inquire of him.

 

My 360 is up to 1444 hrs now without ever cracking the stock plates.  A clever mechanic suggested early on to make silicone rubber ridges on the frontplate so that there is supporting pressure there.  It must work.

 

Mark Ravinski

----- Original Message -----

From: Steve & Kelly Rosenzweig

To: lml@lancaironline.net

Sent: Thursday, August 14, 2008 5:53 AM

Subject: [LML] Spinner Backplate Needed

I recently accomplished my annual on my 360 MKII and found the spinner backplate was terribly cracked at all four attach points to the prop hub.  I was certainly happy to find this before it departed the airplane on it's own, but I wasn't happy when the factory told me the part is on back order with no due date in sight.

 

The mechanic at first did not want me to fly it out without the spinner, but after conferring with Hartzell and the factory, both said it would be no problem.  So I flew 30 minutes to get home with no problems in cooling or vibration.  Didn't even really notice any reduction in speed due to added drag.

 

Anyway, I'm hoping someone out there might have an extra spinner backplate that's not drilled, or a matched backplate and spinner assy.  I have a HC-F2YR-1F constant speed prop and believe the spinner mounting kit p/n is A2476-31 according to my prop log.  Just for reference, my spinner backplate is 11 3/4" dia and the dome is 12 11/16" tall.

 

I'd be happy to pay any reasonable price.  Feel free to email me off line at steven_rosenzweig2002@yahoo.com if you have parts for sale.

 

If nothing else, this is an important item to check regularly.  TTAF and engine are only 345 hrs for this plane that began flying in 2004.  I also have two entries in the prop log book showing one dynamic balance accomplished to .013 IPS and another to .03 IPS.

 

thanks

 

Steve