Saberwing crash in Valdosta, GA

Glad to hear the pilot's okay, but looking at that picture... How?
 
I had to google Saberwing as I had no idea what it was. Glad the pilot was OK, more or less.
 
This pic from their FB page gives some more info (no I don't fakebook, this was posted on Homebuilt Airplanes) ...


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That’s a helluva one to walk away from. Paul Bertorelli might be onto something about helmets…
 
Do I understand this correctly, Azalea is also the rebuilder of the Corvair engine that failed?
 
tobnpr said:
Do I understand this correctly, Azalea is also the rebuilder of the Corvair engine that failed?
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Yeah, but: There are more causes to a loss of engine power than mechanical failure of the engine.
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Ron Wanttaja
 
Not certain that we will ever know the reason for the loss of power but, yes, Bill designed and built the aircraft and the engine. No idea how many hours he had on it ..
 
Looking at the wreckage,happy to see the pilot survived and is going to alright
 
tobnpr said:
How do these statistics compare to certified GA aircraft?
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Don't have statistics for the overall fleet, but have looked at the Cessna 172. Its overall rate of loss-of-power accidents is about half that of homebuilts. Major factor is that non-certified engines are involved in almost half of the homebuilt accidents.

For the 172s, about 25% of the loss-of-power accidents had undetermined causes, vs. 30% of the homebuilts. 10% were related to carb ice, vice 7% of the homebuilts. Twice the percentage were related to pilot fuel management (31%). Keep in mind that the homebuilt pilots involved in accidents had about four times the flight experience as the 172 pilots; probably better at fuel management. 22% were due to engine mechanical issues, vice 31% of the homebuilts.
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Note that the above chart compares the total *number* of accidents, not comparing it to the number of power-loss cases.

Ron Wanttaja
 
Over on Homebuilt Airplanes Bill Clapp gave a reason for the engine failure in his Sabrewing:

" ... put an early (2007) 100 HP engine on it for some baseline info on carb setups/temp and timing for improvements. While performing ignition switches in flight, the sudden "jolt" on the engine (from shutting down ignition and turning on backup at high power setting) caused the cam gear key to shear and slip. At teardown we realized it was an earlier design we had tested but never flight proven (being an early test engine - 2007) Now this engine had about 20 hours on it prior to this failure and seemed fine until this particular testing."
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FWIW ...
 
TCABM said:
Sound like a keyway failed.
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I get that but he talks about, "it was an earlier design we had tested but never flight proven" and I have no idea what that refers to. To my knowledge there was no change in keyways by GM but William Wynne (FlyCorvair) does have procedure that he insist on with regards to attaching the cam gear to the cam. According to him things like this can happen if the assembly is done incorrectly. Not everyone follows his procedure. There are other differences in the approach to building these conversions between various vendors so I'd like to have more clarity as to exactly what was done that failed and why (if it can be known) it did fail.

On Homebuilt Airplanes I asked for more clarification so hopefully he'll come back and explain. Camshaft keyway failures in Corvair engines, while not unheard of, are extremely rare and generally occur in older, well worn, engines. I fly one of these things (mine was built by Dan Weseman to William Wynne specifications) so I get a bit curious when things like this are reported but the information is not real clear.
 
Daleandee said:
I get that but he talks about, "it was an earlier design we had tested but never flight proven" and I have no idea what that refers to. To my knowledge there was no change in keyways by GM but William Wynne (FlyCorvair) does have procedure that he insist on with regards to attaching the cam gear to the cam. According to him things like this can happen if the assembly is done incorrectly. Not everyone follows his procedure. There are other differences in the approach to building these conversions between various vendors so I'd like to have more clarity as to exactly what was done that failed and why (if it can be known) it did fail.

On Homebuilt Airplanes I asked for more clarification so hopefully he'll come back and explain. Camshaft keyway failures in Corvair engines, while not unheard of, are extremely rare and generally occur in older, well worn, engines. I fly one of these things (mine was built by Dan Weseman to William Wynne specifications) so I get a bit curious when things like this are reported but the information is not real clear.
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The keyway setup wasn't engineered for "performing ignition switches in flight, the sudden "jolt" on the engine (from shutting down ignition and turning on backup at high power setting) caus[ing] the cam gear key to shear and slip."

I would assume the modification done by Wynne might involve enlarging the keyway and key stock, a higher shear strength key material, heat treating of the gear, etc.
 
3393RP said:
The keyway setup wasn't engineered for "performing ignition switches in flight, the sudden "jolt" on the engine (from shutting down ignition and turning on backup at high power setting) caus[ing] the cam gear key to shear and slip."
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I would think that the engineers would have designed in enough strength that the keyway would not be compromised by a simple hiccup in the engine in regards to to the engine missing, skipping, or being restarted. There is a good load on these components when engaging the starter from a standing stop. Switching the ignitions with the engine running means the engine was still rotating and there should have been less stress than the twisiting of the starter from a full stop.

3393RP said:
I would assume the modification done by Wynne might involve enlarging the keyway and key stock, a higher shear strength key material, heat treating of the gear, etc.
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Actually it has to do with the procedure for pressing the gear into the camshaft. If not done correctly it can cause a number of issues ...
 
I asked Bill for clarification to the cause of the cam to gear failure and he was kind enough to explain. Here's his first response:

Early Testing Hubs had .002" inerference fit on the cam gear and non-hardened keys. We changed this to .004" interference fit, hardened keys and tig welded "anti-slip". We never had an early test hub shear a key or slip timing but the math indicated these changes would be prudent. Looks like the changes were warranted but this engine had many hours on it so I was not concerned until it happened.
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www.homebuiltairplanes.com

Crashes in the News - Thread

Any data on why the engine quit and lessons we need to learn to avoid engines quitting? Yes - I know reason now. Tore the engine down. As Background info....Airframe had 550 hours on it - flown to Oshkosh 5 times. 125 hours on 100 HP engine, then 50 hours on 120 HP NA engine, then 350+...
www.homebuiltairplanes.com www.homebuiltairplanes.com


I wondered about his statement that the engine had many hours on it when he stated earlier, "this engine had about 20 hours on it prior to this failure" but I didn't bring that point up. But I was still not clear on what the answer was so I queried him further and received this answer:

Ours are new and interference fit onto hub. Now the interference is tighter plus we tig weld the gear to the hub along the joint to prevent possible shear. It is a good change we made early but out of caution not out of any failure evidence.
Click to expand...
www.homebuiltairplanes.com

Crashes in the News - Thread

Any data on why the engine quit and lessons we need to learn to avoid engines quitting? Yes - I know reason now. Tore the engine down. As Background info....Airframe had 550 hours on it - flown to Oshkosh 5 times. 125 hours on 100 HP engine, then 50 hours on 120 HP NA engine, then 350+...
www.homebuiltairplanes.com www.homebuiltairplanes.com


I add this here to try and close the loop on the cause of this accident as it appears to be the improper assembly of the cam gear to the camshaft using a non-hardened key.

His process now seems to be to weld the gear to the cam. Not something I would recommend or fly but it's his business and the consumer makes their own choices ..
 
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