Dished Spinner Bulkhead

szicree · #1 01-28-2008, 01:41 PM

I'm in the process of tidying up the cowl to spinner gap and am finding that the aft spinner bulkhead is significantly dished. I would expect this to be the natural result of the forming process, much like wing ribs. My question is what, if anything, should be done to correct it? It is nice and true so I'm thinking it might be best to leave it dished. My concern is that the prop may tend to un-dish it. Have others also had this experience and what did you do?

szicree · #2 01-29-2008, 11:33 PM

C'mon guys, I'm the only one that has seen this?

Paul Eastham · #3 01-30-2008, 05:31 AM

It may help to define "dished", but all I can tell you is that my bulkhead was perfectly flat and regular. If you are seeing anything that's asymmetrical, I think it is not airworthy. If you're talking about a symmetrical distortion, I would also ask Van's. A failure in this area can have some heavy consequences.

647jc · #4 01-30-2008, 06:47 AM

Mine was also dished by about 1/8 inch (I just remeasured it). I didn't consider this an issue since it was symetrical. I fit my spinner to the bulkhead on a flat table top and the dishing had to be considered when proping up the bulkhead for proper cowl clearance, that's where I discovered the dishing. I assume it's a remnant of the part stamping and ALL bulkheads probably have it. You probably wouldn't notice it unless you placed the part on a very flat surface and looked for the issue.

szicree · #5 01-30-2008, 10:45 AM

I've got a feeling that most people simply never checked and so never noticed. I guess my next question would be how many folks laid a straightedge across their spinner bulkhead to check for flatness? The dishing (concavity) of mine is very slight, maybe 1/8 inch, but definitely there.

szicree · #6 02-03-2008, 06:17 PM

I haven't gotten around to calling Van's yet (will tomorrow), but I have come to the conclusion that probably all spinner bulkheads are dished a bit. I actually have two rear bulkheads and one front and they are all this way. They are nice and true but when checked with a straight-edge they are about 1/16 inch concave (towards the rear). I had pretty much decided to not worry about it, but today have realized that when the prop is tightened down onto the bulkhead, its trailing edge will contact the outer edge of the bulkhead before the center and thus push the outer edge of the bulkhead aft at two points. Obviously, this will throw the bulkhead out of true. Drat! One fix would be a thin round spacer between prop hub and bulkhead. In any case, I'll be calling Van's in the morning and will probably get the "don't worry about it -- build on" , but since I've heard that the prop is a pretty important part, I'd love to hear from others on this.

L.Adamson · #7 02-03-2008, 07:09 PM

Quote:

Originally Posted by szicree

I had pretty much decided to not worry about it, but today have realized that when the prop is tightened down onto the bulkhead, its trailing edge will contact the outer edge of the bulkhead before the center and thus push the outer edge of the bulkhead aft at two points. Obviously, this will throw the bulkhead out of true. Drat!

Once you slide the spinner over the bulkhead, with an even line marked all the way around; can the bulkhead be pulled into position without much difficulty?

L.Adamson

rvbuilder2002 · #8 02-03-2008, 08:29 PM

You have never mentioned...but it might help if you said what kind of prop. you are using with this spinner.
If it will be on a fixed pitch, then sandwitching the bulkhead between the prop and prop. extention will likely take out most of it.

The main thing is that when fitting the cowl, if you do it without the prop installed...hold the spinner in position simulating the same type of installation.
I.E. use a spacer and plate that will sandwitch the bulkhead in the same way as when the spinner is installed with the propeller.

Quote:

Originally Posted by szicree

I haven't gotten around to calling Van's yet (will tomorrow), but I have come to the conclusion that probably all spinner bulkheads are dished a bit. I actually have two rear bulkheads and one front and they are all this way. They are nice and true but when checked with a straight-edge they are about 1/16 inch concave (towards the rear). I had pretty much decided to not worry about it, but today have realized that when the prop is tightened down onto the bulkhead, its trailing edge will contact the outer edge of the bulkhead before the center and thus push the outer edge of the bulkhead aft at two points. Obviously, this will throw the bulkhead out of true. Drat! One fix would be a thin round spacer between prop hub and bulkhead. In any case, I'll be calling Van's in the morning and will probably get the "don't worry about it -- build on" , but since I've heard that the prop is a pretty important part, I'd love to hear from others on this.

Fallalloveryou · #9 02-25-2009, 09:32 AM

My rear spinner bulkhead came from Vans' with a 1/8" dish in it. I'm sure everyone has the same thing since I'm sure its from the molding process. When I tighten down my wood prop on it, it forces the spinner straight where it is in contact with the prop blade. Problem is that after about 25 hours of flying, I took off the prop and I can see that bulkhead is rubbing against the prop and has even caused a 1/8" depression in the wood prop where it contacts the bulkhead.
I don't know how serious this is but I really didn't like the way the bulkhead seems to rub the prop and damage the finish.

This probably effects everyone with a wood prop so I'm interested in hearing what other wood or composite prop guys have to say about this. Has anyone else noticed this when the removed their wood prop and is there anyway to flaten out the bulkhead? Thanks, Rick Rv-9