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RE: How safe are homebuilt planes? - 8/17/2006 9:29:38 PM   
LuvaraAir



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quote:

ORIGINAL: Gravityisnotmyfriend
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

If people want to discuss the pros and cons of auto vs A/C engines go ahead. I think I've got my answer as far as safety is concerned.

-edited beacuse " turn to !QUOT! after spell check.


I wouldn't call it "vastly improved" technology for auto engines. If it was so improved, that technology would be in airplane engines. Airplane engines are basic technology for one reason - it's simple, less stuff to break and that is what mitigates the safety risk.

Chris


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RE: How safe are homebuilt planes? - 8/17/2006 10:56:44 PM   
Gravityisnotmyfriend



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Status: offline 		Yes, something like overhead cams would be more complicated but anything that is failing should be easily detected at an annual inspection. And there is no reason that any parts wouldn't last between major overhauls. I guess I can see your point about the simplicity, but can you explain the price?

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RE: How safe are homebuilt planes? - 8/18/2006 2:41:15 AM   
iflyj3



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quote:

ORIGINAL: Gravityisnotmyfriend

I guess I can see your point about the simplicity, but can you explain the price?


Supply, demand, FAA certification and liability insurance.



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RE: How safe are homebuilt planes? - 8/18/2006 6:14:18 AM   
Jimmbbo



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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? - 8/18/2006 6:24:58 AM   
Jimmbbo



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quote:

ORIGINAL: LuvaraAir

I wouldn't call it "vastly improved" technology for auto engines. If it was so improved, that technology would be in airplane engines. Airplane engines are basic technology for one reason - it's simple, less stuff to break and that is what mitigates the safety risk.

Chris

Chris,

I suspect most designers would give up their pocket protectors for the electronic engine controls and the fuel injection found on a standard Honda Accord instead of the magnetoes and float carbs or continuous flow injection on most GA airplanes... the electronic answer would be so much cheaper to produce, lighter, and more efficient... However.... Certifying a new engine is a very lengthy, expensive process, so the cost of certification of a new engine for a relatively small market keeps most manufacturers with the "tried and true" -

Since the price of "old tech" engines is already pretty steep due to product liability and the ever decreasing market (also due to run-amok lawsuits), the costs of certifying such an engine (which must be passed on, making the engine more expensive yet) just can't be justified...

Cheers!

Jim



< Message edited by Jimmbbo -- 8/18/2006 6:27:50 AM >

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RE: How safe are homebuilt planes? - 8/18/2006 6:31:14 AM   
Jimmbbo



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quote:

ORIGINAL: MajorTomski

Noticed yesterday that there's a RV-7 kit for sale on Ebay motors.


Divorce sale??

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RE: How safe are homebuilt planes? - 8/18/2006 6:33:54 AM   
Jimmbbo



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quote:

ORIGINAL: beenie

... I took mine for a ride in a Super Cub one nice afternoon to a friend's grass strip. When we got there, she turned to me and said that we needed to get one of these for pleasure flying and a V35 for travel...

Ben


Ben,

You got a keeper!!

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RE: How safe are homebuilt planes? - 8/18/2006 2:57:20 PM   
Sport_Pilot



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quote:

ORIGINAL: LuvaraAir

quote:

ORIGINAL: Gravityisnotmyfriend
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

If people want to discuss the pros and cons of auto vs A/C engines go ahead. I think I've got my answer as far as safety is concerned.

-edited beacuse " turn to !QUOT! after spell check.


I wouldn't call it "vastly improved" technology for auto engines. If it was so improved, that technology would be in airplane engines. Airplane engines are basic technology for one reason - it's simple, less stuff to break and that is what mitigates the safety risk.

Chris



Ahh comon! You have never owned an airplane. Aircraft engines are vastly inferior to automobile engines. Their valves get stuck, the magnetos must be repaired every annual and replaced or overhauled every 300 to 500 hours. The magnetos on one plane I had were exactly like the one on my grandfathers tractor! No electronic ignition here. Cylinders have to be replaced, carb float's sink, the injection systems regularly flood the engine on startup. Made well but only if you compare it to 1940's quality! The bottom end is stronger than a car, but then they are built for lower RPM and higher torque, plus the precession of the prop. Most auto engines need a speed reducer of some sort and that should take the prop precession load as well. Properly inspected belts should not be a problem. I haven't had so much as a water pump or airconditioner belt go out on my car's in 20 years or more. Never had a timing belt go out. It's not like airplanes are without belts either. Plastic covers are not a problem either, in fact it would appear the Subaru cover that someone posted about was broke due to the broken belt inside. If you inspect every annual and replace accordingly there shouldn't be a problem.

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RE: How safe are homebuilt planes? - 8/18/2006 3:00:54 PM   
Sport_Pilot



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quote:

also due to run-amok lawsuits


Although they exist, most of the lawsuits are fair and reasonable when you consider the junk GA produces. Airplanes that burst in flames when the wing tip hits a hanger during taxi, Bonanza tails that fall off in the sky, wings that fold up, etc.

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RE: How safe are homebuilt planes? - 8/18/2006 3:29:41 PM   
Flyfalcons



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quote:

ORIGINAL: Sport_Pilot
I haven't had so much as a water pump or airconditioner belt go out on my car's in 20 years or more. Never had a timing belt go out. It's not like airplanes are without belts either. Plastic covers are not a problem either, in fact it would appear the Subaru cover that someone posted about was broke due to the broken belt inside. If you inspect every annual and replace accordingly there shouldn't be a problem.


Yeah but you don't run your car at 65% power for hours on end either. Car engines simply aren't designed to be run as hard as aircraft engines. If/when I build a plane that stalls faster than 30mph, it's getting an aircraft engine.

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RE: How safe are homebuilt planes? - 8/18/2006 4:25:59 PM   
flycfii


 

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RE: How safe are homebuilt planes? - 8/18/2006 6:22:55 PM   
Sport_Pilot



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quote:

Yeah but you don't run your car at 65% power for hours on end either. Car engines simply aren't designed to be run as hard as aircraft engines. If/when I build a plane that stalls faster than 30mph, it's getting an aircraft engine.


Another myth. Car engines run faster and hotter than an airplane engine. Their only real drawback is that the higer revs result in lower TBO, and weight. Cars normally run about the same revs around town and run harder than aircraft engines on the freeway. They can often do that till TBO without as much as changing the spark plug. I have had several cars which had no more maintenance than replacement of filters and cleaning of the original plugs. Aircraft plugs are lucky to last one annual because of all the crappy lead in them. Even the wires seem to go out soon, though partly because they are shielded.

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RE: How safe are homebuilt planes? - 8/18/2006 8:41:15 PM   
Flyfalcons



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Status: offline 		How is what I said a myth? Car engines in cars may run at a higher RPM range but it doesn't mean they are running harder at all. Anyone who has flown a CS prop understands that. How often do you floor your car engine, let alone leave the pedal mashed for 5-10 minutes (average climb time on a short-medium length flight)? Based on fuel consumption, if your car is burning roughly 3gph on the highway (60 mph at 20 mi/gallon), then you are producing somewhere in the range of 30 hp. Not much of a load on a car engine that is rated for 160 horsepower. A 172 in cruise, burning 10gph, is producing around 100 of its rated 160 hp, and it will happily do it for hours on end. An engineer friend of mine taught me the 1gph = 10hp trick, and it is fairly accurate on all of the piston aircraft engines I have run when looking at power % and fuel burn charts.

As for the leaded fuel, more aircaft engines are being certified to run on auto fuel. I've flown a 182 with the STC, and it ran well, though a little cold-blooded on startup if the temperatures are low. I don't own the plane so I don't know how long the plugs are lasting.

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RE: How safe are homebuilt planes? - 8/19/2006 12:06:10 AM   
Jimmbbo



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quote:

ORIGINAL: Sport_Pilot

quote:

Yeah but you don't run your car at 65% power for hours on end either. Car engines simply aren't designed to be run as hard as aircraft engines. If/when I build a plane that stalls faster than 30mph, it's getting an aircraft engine.


Another myth. Car engines run faster and hotter than an airplane engine. Their only real drawback is that the higer revs result in lower TBO, and weight. Cars normally run about the same revs around town and run harder than aircraft engines on the freeway. They can often do that till TBO without as much as changing the spark plug. I have had several cars which had no more maintenance than replacement of filters and cleaning of the original plugs. Aircraft plugs are lucky to last one annual because of all the crappy lead in them. Even the wires seem to go out soon, though partly because they are shielded.


Hmm.. I disagree that car engines run hotter and faster.... Let's compare a 160 HP airplane with a similar car on a cross-country trip....

Normal cruise power in light airplanes is 65-75% of rated HP - Take Flyfalcon's sample 160 HP Cessna 172 - that equates to 120 HP at 75%. The airplane will probably cruise at around 130 mph true airspeed. The block hour fuel consumption will be around 10 gph...

In my 160 HP Honda, I get around 25 mpg, using probably 40 hp and cruising at 65 mph for a block hour fuel consumption of 2.6 GPH

So, double the speed, four times the fuel consumption... Why the discrepancy? The airplane has to overcome more drag, requiring more HP and more fuel (Since drag increases as the square of the speed - double the speed, quadruple the drag, quadruple the HP required and quadruple the fuel flow (not entirely accurate, but close enough for our purposes)) Don't understand how a car is running hotter and faster when it is running at a fraction (25%) or the same rated power while the airplane engine is chugging away at 75%

While I agree that the technology of modern automobile engines is decades (literally) ahead of purpose-designed airplane engines, a