What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Spinner bulk head crack

rwarre

Well Known Member
O320, 160 hp engine. Rv7a, the bulk head has a crack which is the same diameter as the prop hub. A friend who is an a&p said it was due to harmonic vibration and has seen it before. I have a Catto 2 blade fixd pitch but the bulk head is from Vans. Plan on ordering a new Bulk head from Vans. 2 questions: is the bulkhead a standard 13 inch(iI guess I should measure it) and has anyone seen this happen
 
O320, 160 hp engine. Rv7a, the bulk head has a crack which is the same diameter as the prop hub. A friend who is an a&p said it was due to harmonic vibration and has seen it before. I have a Catto 2 blade fixd pitch but the bulk head is from Vans. Plan on ordering a new Bulk head from Vans. 2 questions: is the bulkhead a standard 13 inch(iI guess I should measure it) and has anyone seen this happen

Ohooooo yea.... Very common. Spinner bulkhead cracks are common. I can't picture your exact crack description.

This bulkhead is just sheet aluminum that was formed soft and heat treated (I am guessing that is Van's process). I don't remember if it's 6061 or 2024 but forming causes residual stress unless heat treated will crack. It is possible Van did not HT properly or at all? Without sending the metal to the lab you don't know.

Sheet metal flex will obviously fatigue and cracks given enough cycles. You did not say how many hours.

BURR - Sharp or rough edges is a place for a crack to start. Deburr and chamfer and polish the edges and make sure there are NO scratches or gouges. Think about the washer and bolt that holds it down. Did they leave marks on the old bulkhead?

The spinner it self may not be balanced. It's just fiberglass with wet layup. If some part of spinner is resin rich or has extra ply overlap on one side, it is not balanced. How to statically balance a spinner? Don't know but it may be worth some effort to make sure it is statically balanced. At least make sure the thickness is even and selectively sand removing some material or add material (primer). The spinner thickness should be even.

I never installed a fixed prop spinner but you have two bulkheads? One front and one back?

The spinner may have been mounted slightly cockeyed. Not enough to notice but enough to cause rotational forces or vibrations.

Clearly prop balance is important.

Engine mounts get tired or were never good to start with. I am a big fanboy of LORD engine mounts with the inner deflection damper (silicon filled spacer). The price on these has gone stupid high... but they are still worth it.

Preload - The spinner should slide on and screw holes line up with out pushing on bulkhead. Pre-load is a no no.

If you get it perfect you should not crack. However perfect is not possible. Keep an eye on it. You can't see bulkheads with cowl on easily at least. However every oil changes a good inspection is important. OIL CHANGE is not oil and filter. When ever anything is opened up visually inspect everything with strong light and even magnification in some cases and look for cracks, not just spinner the whole firewall forward area. Cracks start small and grow. It does not happen in one flight.
 
Last edited:
No, it is not heat treated.
As delivered it is still relatively soft 5052 which makes it more crack resistant than the other alloys we use.
Cracks do occur but I wouldn’t call them common. When it does happen, it can usually be attributed to something specific with that airplane.

This may sound strange but does your spinner have a fwd and an aft bulkhead (I have seen the fwd one missing)?
 
I think Scott nailed it explaining the 5052 series aluminum is more ductile and forgiving when it comes to cracking and fatigue over time. Ductility is a plus when it comes to cracking. I did a lot of fatigue analysis as an engineer at a major west coast aircraft manufacturer and the fatigue life of ductile metal is much higher than heat treated or hardened metal. Just look at the 7075 series alloy. It is one of the strongest aluminum alloys but this means it is also very brittle. The Boeing 727 horizontal tail fittings were made from 7075 and it was a prize idea. Until the cracking started showing up a few years later due to the alloy being hard and brittle (hence very strong). I haven't had a Vans spinner bulkhead crack yet but I have experienced it on type certificated aircraft. I even had a Rose Parrakeet that flung a spinner in flight due to fatigue cracking. I had to land and taxi back to the hangar to look for holes in the airplane (and change my underwear).
 
Cracking

My original prop was a sensenich and Craig Catto made me one of his props. There is no forward bulkhead due to the crush platethat I am using. The rear bulkhead is 2024alum. In 2020 I had to rebuild the engine and installed a o320 160hp from the previous o320 150 hp
 
My original prop was a sensenich and Craig Catto made me one of his props. There is no forward bulkhead due to the crush platethat I am using. The rear bulkhead is 2024alum. In 2020 I had to rebuild the engine and installed a o320 160hp from the previous o320 150 hp

If you are still using the standard RV spinner but a 2024 rear bulkhead and no forward bulkhead, that is two points against having much service life. A standard 13 inch RV spinner is way too big to not have a front bulkhead. Having a rear bulkhead made from hard material makes matters even worse.
 
Ah, no forward bulkhead, better stock up on rr bulkheads & set up a frequent inspection schedule.

As for bulkhead materials, I just checked my assorted collection...
- S-605 SEN forward bulkhead appears to be 6061 or 5052, pretty soft material as the prop bolt holes deform (squash) when torqued to proper specified values. Looks like bulkhead was formed by spinning method (not hydroformed)
- S-605 same story as S-605 SEN part above.
- S-602-1 rear bulkhead has '2024' (maybe 2024-0?) inked on to the part. Brushed appearance that looks like 6061 or 5052. Hydroformed.
- S-603 has same appearance & looks same as the S602-1 bulkhead. Hydroformed.
- S-602B (C/S doubler) shiny appearance like 2024T6

Check the thickness of your Catto prop, I assume it isn't the same thickness as your original Sensenich 320 prop, but might be the same as a 360 Sensenich, which might mean that Vans might have a bulkhead that would work for you. (I have both props here but NOT easily accessible to measure)
 
Last edited:
Ah, no forward bulkhead, better stock up on rr bulkheads & set up a frequent inspection schedule.

As for bulkhead materials, I just checked my assorted collection...
- S-605 SEN forward bulkhead appears to be 6061 or 5052, pretty soft material as the prop bolt holes deform (squash) when torqued to proper specified values. Looks like bulkhead was formed by spinning method (not hydroformed)
- S-605 same story as S-605 SEN part above.
- S-602-1 rear bulkhead has '2024' (maybe 2024-0?) inked on to the part. Brushed appearance that looks like 6061 or 5052. Hydroformed.
- S-603 has same appearance & looks same as the S602-1 bulkhead. Hydroformed.
- S-602B (C/S doubler) shiny appearance like 2024T6

Check the thickness of your Catto prop, I assume it isn't the same thickness as your original Sensenich 320 prop, but might be the same as a 360 Sensenich, which might mean that Vans might have a bulkhead that would work for you. (I have both props here but NOT easily accessible to measure)

I don't know part #'s from memory..... I am guessing that the S-602-1 is the rear bulkhead doubler that is added for a constant speed prop. install, because that part is 2024.
None of the actual flanged bulkheads are 2024 because of the way they are formed. They are not hydro formed. They are turned on a lathe against a circular form block in much the same way that a metal spinner is formed.

It is fairly common for a non metal fixed pitch prop made by one of the many prop makers, to not have a thickness that matches the standard spacing between the front and rear spinner bulkheads. In this instance, a spacer(s) should be used to adjust the spacing of the front and rear bulkheads as needed so that it correctly matches the spinner. I'm not sure if we still do, but I think we used to sell 1/8" thick spacers that can be added to adjust the spacing as needed. Another alternative would be to have a machinest make a custom thickness spacer. It is a very simple project, so not very expensive.
 
Plans C-4

I don't know part #'s from memory..... I am guessing that the S-602-1 is the rear bulkhead doubler that is added for a constant speed prop. install, because that part is 2024.
None of the actual flanged bulkheads are 2024 because of the way they are formed. They are not hydro formed. They are turned on a lathe against a circular form block in much the same way that a metal spinner is formed.

It is fairly common for a non metal fixed pitch prop made by one of the many prop makers, to not have a thickness that matches the standard spacing between the front and rear spinner bulkheads. In this instance, a spacer(s) should be used to adjust the spacing of the front and rear bulkheads as needed so that it correctly matches the spinner. I'm not sure if we still do, but I think we used to sell 1/8" thick spacers that can be added to adjust the spacing as needed. Another alternative would be to have a machinest make a custom thickness spacer. It is a very simple project, so not very expensive.

Not to disagree with you Scott because you’ve provided a lot of good information as always, but my copy of drawing C-4 shows all of the bulkhead parts as 2024. Did this change or was the drawing in error?

Skylor
 

Attachments

  • FAC65148-7D24-48AF-B061-6E5233E6953D.jpg
    FAC65148-7D24-48AF-B061-6E5233E6953D.jpg
    295.2 KB · Views: 161
Not to disagree with you Scott because you’ve provided a lot of good information as always, but my copy of drawing C-4 shows all of the bulkhead parts as 2024. Did this change or was the drawing in error?

Skylor

My memory is the thing that has the error problem :eek:

I was thinking only the S-602B doubler was 2024(-T3) which I was correct about. I thought the rest were 5052. Thanks for the correction, but embarrassing because I have done a lot of work with making tooling and documenting the production process for making these parts.

The main context is still correct though... that all of the bulkheads are made from soft material, and a spinner cantilevered from the aft bulkhead with no other support, is likely to result in a cracked aft bulkhead.
 
Not to disagree with you Scott because you’ve provided a lot of good information as always, but my copy of drawing C-4 shows all of the bulkhead parts as 2024. Did this change or was the drawing in error?

Skylor

Yea but 2024 T0 as called out in the drawing is much softer than T3 and less likely to crack.
 
Back
Top