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  #11  
Old 01-04-2010, 06:09 PM
PlaneBuilderBill's Avatar
PlaneBuilderBill PlaneBuilderBill is offline
 
Join Date: Jul 2005
Location: Euless, TX
Posts: 157
Default The Better Mousetrap....

Guys,
Here's a possible solution. My "4s" custom intake. Made by Charles Wilhite. Weight is almost nothing compared to the "Fab". There's a conical K&N filter within the larger blue cone. The front of the cone is flexible silicone that fits up to the cowl. The curved "P Trap" shape is the ideal airflow shape. I have over a year flying on this mod and I wouldn't trade it. Although I have no comparable performance data to a 4 with Van's "Fab" my "4" is at least as fast and the unit shows virtually no wear from any reason!


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Bill
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1504 Milla Ct.
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Hangar 343 T67 Hicks (D/FW Sec)
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  #12  
Old 01-04-2010, 08:43 PM
RV8R999 RV8R999 is offline
 
Join Date: Dec 2008
Location: na
Posts: 1,457
Default

Im not putting an alt source door in my -8 after all the problems. Instead I'll put a screen just fwd of the carb heat door. Did this in my other plane with no noticeable issues. This keeps little birdie and plastic bags fwd of the carb heat door which the becomes the alt air source.
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  #13  
Old 01-05-2010, 01:21 AM
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sprucemoose sprucemoose is offline
 
Join Date: Jan 2005
Location: MKE
Posts: 1,519
Default

Quote:
Originally Posted by JordanGrant View Post
That's a great idea to beef it up to .090. Unfortunately, I don't have any of that laying around, and besides I'm under the gun since I'm leaving for Iraq next week, so I just ordered another one from Van's. I like the washer idea, though, I think I might have some that will work.
I might have enough laying around to make another one. Can you give me the L X W dimensions of the part, and I'll see if I have a piece big enough. If I do, PM me your address and I'll send it to you. It might not get there in time for you to ship out, but then again, Van's part might not either! Either way you'll have it waiting when you get home.
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Jeff Point
RV-6, RLU-1 built & flying
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Milwaukee
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  #14  
Old 01-05-2010, 03:12 AM
67MK Larry 67MK Larry is offline
 
Join Date: Jul 2008
Location: Saint Charles, Illinois
Posts: 82
Red face My 6A

Had 3 long cracks in my top plate at annual 594 hrs, replaced with thicker sheet and washers to spread the load.
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  #15  
Old 01-05-2010, 06:21 AM
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dhall_polo dhall_polo is offline
 
Join Date: Nov 2006
Location: Cumming, GA
Posts: 610
Default stainless

I noticed cracking after around 50 hours. I made a doubler and added large washers. This is now on my routine oil change inspection list.

Fairings, etc made stainless replacements for the wheel pant brackets, which is another area that people have experience failures from cracking and fatigue. See http://www.fairings-etc.com/brackets.htm

If my doubler fix doesn't hold up, I'm going to pursue having a stainless steel replacement plate made. Sounds like if someone made 100 of them, they'd have no problem finding buyers.

Don
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Ticked Van's Hobbes meter at #6110, 3/7/09
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  #16  
Old 01-05-2010, 07:34 AM
Jetj01 Jetj01 is offline
 
Join Date: Mar 2005
Posts: 337
Default Form follows function!

Looks nice, must work nice!

Tailwinds!
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Eagles Nest, TX
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  #17  
Old 01-05-2010, 08:45 AM
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DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
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Quote:
Originally Posted by AlexPeterson View Post
The most likely cause is not engine movement, but the tremendous acoustic vibration going on in an induction system.
Ya'll should listen to Alex. The issue is number of stress cycles and the rate at which they accumulate per flight hour. Aluminum has no knee in its S-N curve; given enough cycles all aluminum parts fail. At low load per cycle it merely requires more cycles.

Aluminum fatigue strength is usually quoted for 10 million or 100 million cycles, an arbitrary figure on a slope which steadily (although exponentially) declines to zero strength. Ten million cycles may seem like a lot (and it is if we're talking wing spars), but it's nothing in the context of the vibe Alex describes. Assume a 2400 RPM cruise, or 4800 intake cycles per minute, or 288,000 per hour. It only takes 35 hours to reach 10 million cycles, and that doesn't count the harmonics.

Two choices...either greatly reduce material stress (to push failure way out into the far exponential reaches of aluminum's S-N curve), or change material. I'd suggest ya'll should quit fooling around and make steel mount plates. Steel does have a knee in its S-N curve, so stress below the knee doesn't fail the part no matter how many cycles you apply.
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  #18  
Old 01-05-2010, 09:58 AM
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JordanGrant JordanGrant is offline
 
Join Date: Feb 2006
Location: Virginia
Posts: 324
Question How much does beefing up the plate thickness help?

Quote:
Originally Posted by DanH View Post
Two choices...either greatly reduce material stress (to push failure way out into the far exponential reaches of aluminum's S-N curve), or change material.
Dan, does increasing the thickness of the plate effectively reduce the stress? (i.e., beefing up to a .090 plate instead of .063) If so, does that add 'cycles' nonlinearly as well?
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  #19  
Old 01-05-2010, 10:25 AM
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n5lp n5lp is offline
fugio ergo sum
 
Join Date: Apr 2006
Location: Carlsbad, NM
Posts: 1,912
Default

My latest stab at this problem was to mount two of the standard top plates epoxied together. This setup is way stiffer than the single plate and my idea is that maybe the composite construction will help dampen the vibration. Don't know how it will work yet, over time. I agree that someone needs to market a pre-cut steel plate.
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RV-6 N441LP Flying
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  #20  
Old 01-05-2010, 10:27 AM
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petehowell petehowell is offline
 
Join Date: Jan 2005
Location: MN
Posts: 2,269
Default Just Curious....

Are we seeing the same type of failures on the O-320 engines? I have ~600 hours on mine now and have not seen cracking (yet!). Alex's and my hangar mate had one crack with less than 100 and he runs his

I could not tell from the posts what engines and induction everybody had. Might be interesting to see if there are patterns. Dan and Alex can tell me if this does not make sense.

I thought maybe I was lucky until the cylinder AD hit...... so much for clean livin'
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Amateur Plane - RV-9A N789PH - 2350+ Hrs
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