R

rv4jmw

I'm New Here
My first flight of my RV4 a screw for the forward bulkhead of my Van's fiberglass spinner broke off and knicked my nice new Sensenich wooden prop. My only problem. Now after 45 hours it happened again. Something's going on. Anybody seen that or have any ideas?

Thanks,
JW

N734JW, newly flying "antique" RV
 
If you take the spark plugs out, devise some type of fixture to hold a locate device, (dial indicator is probably overkill but would certainly be ok) near the tip of the spinner, rotate the prop and check to see if the tip of the spinner has any significant wobble. If it does, as the RPM increases the wobble, rpm, vibration orders, etc are conspiring to create pulses on the screw that fatigue it and the head snaps the off.

OR

Spinner is out of balance and as RPM increases causes the same problem.

OR

Both
 
Another item...

.....is to check if the spinner is in fact resting on the forward bulkhead. I also snapped two screws and dinged my Catto. Sometimes the angle of the flange is not the same as the angle of the spinner taper and puts a side load on the screw.

Van recommends sanding the inside of the spinner and applying a thick layer of resin mixed with floss and then wax the bulkhead. Place the spinner on the airplane and the resin will "bed" the spinner to the bulkhead.

I had to order an 1/8th inch spacer from Van to move the bulkhead forward in order to contact the spinner but I used proseal on the sanded bulkhead and waxed the inside of the spinner and left the screws out.

Regards,
 
Vibration

I'd say without looking at it (a la blindfolded) that it is a vibration problem. Have somebody look at your spinner while the aircraft is running, If none seen then make sure you have positive pressure aft on the spinner when you put it on. my.02 without seeing....
best
Brian
 
A friend of mine was losing screws on the spinner of his -6 and he was baffled. I saw him fire up one day and noticed he had a significant wobble in his spinner. He had no idea it was that bad. He built a new spinner (this time making sure it spins true) and has had no problems since.
 
pierre smith said:
.....is to check if the spinner is in fact resting on the forward bulkhead. I also snapped two screws and dinged my Catto. Sometimes the angle of the flange is not the same as the angle of the spinner taper and puts a side load on the screw.

Van recommends sanding the inside of the spinner and applying a thick layer of resin mixed with floss and then wax the bulkhead. Place the spinner on the airplane and the resin will "bed" the spinner to the bulkhead.

I had to order an 1/8th inch spacer from Van to move the bulkhead forward in order to contact the spinner but I used proseal on the sanded bulkhead and waxed the inside of the spinner and left the screws out.

Regards,
Click to expand...
Thanks for your response. I'm thinking along the same lines, and will persure your suggestions. I'm thinking I do need to "snug up" the front b'head a bit. Your proseal idea is one, I'm thinking along thickening the spinner there a bit. Also rechecking the center, though I thought it was OK when I built it. Anyway thanks again, JW
 
Agreed!

I do agree the vibration is 99.9 percent the likely culprit, and will always be to some degree a fastener stressor.

What was the part number of the screws you were using, and I will see if I have some of the next better fastener of the same dimensions in my loose stock to give you that added insurance.:)
I can mail them out as samples for this case.:cool:
 
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