Jimmbbo
Posts: 1179
Joined: 10/1/2003
From: Fresno, CA, USA
Status: offline
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quote:
ORIGINAL: Gravityisnotmyfriend
<<snip>>
At the risk of hijacking my own thread, I am conflicted about what type of engine to use. Namely aircraft or auto conversion. There has been an argument for both options on this thread. Aircraft engines are obviously made for aircraft and seem like the logical choice. The problem is that a/c engines have changes very little in the past several decades. Auto engines OTH, have had huge improvements made to keep up with the competitive market. Here's the way I see it:
A/C engines - Pros: proven design, make power at the proper RPM, lighter. Cons: very expensive, same basic technology since pre WWII.
Auto engine - Pros: much less expensive, vastly improved technology, readily available parts. Cons: Heavier, generally need a prop reduction drive
That's it in a nutshell..
To some extent, it depends on what you want to do with the airplane... If your only plan is Saturday daytime hops in the local area, an automobile engine makes sense. If you plan to fly the airplane over some distances over inhospitable terrain or at night or IFR, I would use a certified airworthy aircraft engine and consider the price difference as insurance... 
Granted, there are many good auto conversions, and they may have run well in the airplane, but they simply aren't designed for the 3D stresses of the aviaton enviornment. You don't know when one of the parts is gonna depart close formation, go walkabout and trash the engine, at which time I'd rather not be in the goo hoping I'll be able to see the ground when I pop out the bottom of the clouds... FWIW, the NTSB lists five RV-7/RV-7A accidents, four of which were pilot induced (three involved misjudged flare on landing... Hmm... an obvious emphasis area during flight training, I hope). This was the only one that was caused by a failure of the airplane:
NTSB Identification: CHI04LA011.
Aircraft: Domeier RV-7A, registration: N707DD
Injuries: 1 Minor.
The airplane was substantially damaged when it nosed over during a forced landing following a complete loss of engine power... The airplane was powered by a Subaru automobile engine converted for aircraft use. A postaccident examination revealed that the plastic timing-belt cover and the belts for the alternator and supercharger were broken. Pieces of the alternator belt were found within the remaining portion of the timing-belt cover. The engine intake and exhaust valves had struck the top of the cylinders.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The failure of the supercharger and alternator drive belts which resulted in foreign object damage to the valve timing system and subsequent loss of engine power...
Suggest a trip over to the EAA website http://eaa.org/ to get more information from experts in the field.
Cheers!
Jim
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RE: How safe are homebuilt planes? - 
