# Why aren't more auto engines being used

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#### ekimneirbo

##### Banned
Just my opinion

Why aren't there more auto engines used in airplanes?

The basic idea to many new builders is that you purchase a used engine, mount it in an airplane and bolt a prop to it.

While this can be done, and has been done.....it really requires more thought and caution than the simplified idea

presents for consideration.

1. Well meaning builders will immediately provide a multitude of reasons why NOT to use an auto engine.

I think this is the main reason many potential builders abandon their dream. They look at the costs involved in using

an engine designed just for airplane use and decide they can't afford it, and have been sumarily cautioned against the

pitfalls of using an automotive engine.

2. Many builders have little knowledge or experience with engines and are hesitant to try to learn.They may not

have the aptitude forassembling mechanical assemblies. What they want is a proven conversion that can be

purchased for rock bottom prices. When they find that purchasing a proven conversion will rival the cost of a

certified engine, they again decide not to build.

3. There is continual misrepresentation/misinterpretation of data concerning auto engines and aero engines. One

continual comparison is that the auto engines can never compare to the reliability record built by certified engines.

While that is a somewhat true statement in airplanes, auto engines are more reliable .What you have to accept is that you are comparing the records set by professional

manufacturing companies, overseen by government regulators,and maintained by professional mechanics. They

are then installed in professionally designed, tested, and manufactured airplanes. Further, both the engines and the

airplanes are then required to be inspected and maintained to professional standards. Would you expect ALL

homebuilt airplanes to be built equally as well? I mean its a given that with every homebuilt being a prototype in its

own right, there will be some problems.

4. If an auto engineis used, you need to employ a reduction drive so you can make use of all the power available

higher rpms. Then the potential builder realizes again that costs will be high for a proven redrive,and/or the

combined weight of both the engine and redrive now makes the unit too heavy for the desired airplane.

5. Builders are continually warned that converting an engine will require the continual need to work on the

conversion and be a never-ending source of disappointing problems and poor performance.

These are what I feel are the main reasons many builders get dissuaded from using auto engines. I think the thing

potential builders should realize is that converting can be problematic, but it can also be a source of immeasurable

satisfaction. Thereare many conversions out there working well and flying well.....inexpensively. You should also

realize that automotive engine reliability is second to none. With reasonable thought and installation, you can expect

that the engine will be the least of your problems as far as reliability goes. Where the issues often develop is in

improper design or execution of the peripheral systems that support the engine. These are the things that would make

any engine stop......like the fuel supply system or the cooling system. But when one of these peripheral systems fails,

its always the engine that ultimately gets blamed in the eyes of the naysayers.

One thing I think would benefit the adaption of auto engines is if builders would get away from the idea that they

must use reduction drives with auto engines. The Corvair engine conversions have proven very successful with the

use of a 5th bearing. Its simply an adapter that bolts tothe engine and provides an extra support bearing to relieve

the crankshaft from bending loads exerted by the propeller.I think this same technology applied to an auto engine

being run at 2700/4200 rpms would be beneficial and reasonably inexpensive. This not to saythat larger homebuilt

airplanes cannot benefit from using reduction drives and higher rpms, but on smaller and slower airplanes, I think

reduction drives are unnecessary. Its a case by case decision though. The thing I recommend to builders is to

research what is out there and don't be dissuaded by wellmeaning but biased "experts" who tell you that its easier

to just install a formerly certified engine. If there were no problems with obtaining and using a certified engine there

never would have been any reason to look for alternative engines.

(Note there are some smaller engines which do use redrives successfully, but it really is a case by case decision)

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#### BJC

##### Well-Known Member
Supporting Member
eki:

You may be overthinking this issue. More auto engines are not used in airplanes for the same reason that more airplane engines are not used in cars: each was designed for it's intended use, and, even though each can, and has been, used for the other, doing so complicates the machine.

No, I am not anti auto engine conversion for use in an airplane.

BJC

#### choppergirl

##### Banned
I also assumed "weight", or more specifically, "power to weight" rules out 90% of the automobile engines right of the bat.

Consider the additional weight of a liquid cooling system added into the above equation. Most homebuilt's favor an air-cooled designed, and the number of air cooled automobile engines... is very small. You have to be an oddball or antique car to use air cooling (the VW being the most notable). Not being air cooled is striking a lot of auto engines out. In WW1 & WW2 they used some liquid cooled aircraft engines, but then the aircraft engine and cooling system were specifically designed to be as light as possible and still put out the hp needed.

Air cooled motorcycle engines would seem more promising, but most have a gearbox integral with the engine. Quite a bit of work would be involved engineering that out, or removing gears to lessen weight. Also, you get into things like a motorcycle engine not specifically designed to output the torque, and carry the same load, of an aircraft engine running at a constant speed. Somewhere on here is thread of mine where folks laid out the reasons cheap junkyard motorcycle engines aren't such a good idea for airplanes. Smaller Motorcross two stroke bikes, for example, that have high power to weight, aren't designed for constant continuous load, but rather, rapid acceleration.

However, I think if you were building an airplane engine from scratch, you could look to incorporating some major motorcycle parts to speed your build. Cylinders, cylinder barrels, cylinder heads and valves, carbs, piston rods, stuff like that. Take an extremely promising motorcycle engine, and use everything on it but the lower crankcase... and remill that from scratch to suit an aircraft engine, driving a reduction drive. Before you do, though, look at guys on Youtube building radial engines from scratch, and you'll get a taste of the amount of work involved.

If you did that though, rather than do a one off, I'd be looking to make an aircraft engine business out of it, because it probably takes a considerable bit of work and talent and measuring to cast and then lathe and drill a lower end from scratch. Plus you'd have to source a reliable supply of cheap donor motorcycle engines, or pay manufacturer prices or retail (worse) for all the parts. Not so feasible. Older motorcycle engines don't put out so much power to weight, so you'd be looking at newer motorcycle engines (as such, pricier).

Just converting a VW engine to me looks like an insane amount of work, from the videos I've watched of homebrew experts describe everything you have to do. What perseveres them is they end up with a fuel efficient, nice sounding, reliable engine made of cheap(er) parts. Long out of production, VW's however have become somewhat collectible, and VW engine parts that maybe 40 years ago were common as dirt, are now probably... not so cheap. If you can buy one already converted, in good condition, converted to aircraft use, with an airplane attached at a good price, I myself would consider it a score. People that have a converted VW seem happy with them.

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#### StarJar

##### Well-Known Member
Yeah, right on Choppergirl. And Harley (Davidson) pists, cyls and rods would be primo.
Make a cool case and crank with long nose and bearing.

#### Turd Ferguson

##### Well-Known Member
don't be dissuaded by wellmeaning but biased "experts" who tell you that its easier to just install a formerly certified engine.

I'm not biased but I am cognizant of reality. It is "easier" to install a certificated engine because the basic process is "purchase a used engine, mount it in an airplane and bolt a prop to it."

While that may be oversimplifying, the actual process is still "easier" than installing a converted auto powerplant (and a minor nit, just because one installs a certified [sic] engine into a homebuilt, does not make it 'formerly' certified [sic] engine)

To further show that I am not biased, I know of converted auto powerplants that have successfully flown ranging from 10 - 1000 hp.

Some people are just not interested in developing a powerplant from a converted auto engine. I'm cool with that. For those that are interested, show me what you got cause I'm interested too!!

#### TFF

##### Well-Known Member
You keep asking that question in every thread you start or answer. Unless you got one turning a prop to prove we are wrong, why keep hitting the same points with no satisfaction?

#### Autodidact

##### Well-Known Member
Some people are just not interested in developing a powerplant from a converted auto engine.

#### mcrae0104

##### Well-Known Member
Supporting Member
2. Many builders have little knowledge or experience with engines and are hesitant to try to learn.They may not have the aptitude for assembling mechanical assemblies. What they want is a proven conversion that can be purchased for rock bottom prices.

Would assembling an aircraft be considered to require "aptitude for assembling mechanical assemblies?" If you can follow the steps to assemble an RV (or what have you) you have the aptitude to assemble a VW or Corvair. So this reason is off the table.

What they want is a proven conversion that can be purchased for rock bottom prices. When they find that purchasing a proven conversion will rival the cost of a certified engine, they again decide not to build.

A proven conversion need not cost the same as a certified engine. You are ceding too much ground. Again, VWs and Corvairs are proven (and probably others but these are the ones I'm familiar with).

4. If an auto engineis used, you need to employ a reduction drive so you can make use of all the power available higher rpms. Then the potential builder realizes again that costs will be high for a proven redrive,and/or the combined weight of both the engine and redrive now makes the unit too heavy for the desired airplane.[/COLOR][/SIZE][/FONT]

Look, the same could be said for Lyc/Cont. Virtually anything you slap a redrive on will give you more power at RPMs useful to airplanes. There are viable direct drive auto conversions.

5. Builders are continually warned that converting an engine will require the continual need to work on the conversion and be a never-ending source of disappointing problems and poor performance.

Not if you follow a proven pattern. Make a clone of something that works and you can expect to have the same results.

#### Vigilant1

##### Well-Known Member
Supporting Member
Long out of production, VW's however have become somewhat collectible, and VW engine parts that maybe 40 years ago were common as dirt, are now probably... not so cheap.
Au contraire, mon ami! While the Beetle itself may be out of production, the factory in Brazil is still cranking out brand new Type 1 VW engine cases every week, these are useful for engines from 36HP to 80HP+, depending on the parts attached to them. And every other part needed for an air-cooled VW auto engine (valves, crankshafts, pistons, bearings--everything) and to convert it for reliable airplane use (prop hubs, carburetors, lightweight starters, accessory mounts, etc) is also still in production and reasonably priced. And, there's plenty of well-tested guidance available on how to assemble these parts into an engine, as well as folks who will take these affordable parts and build an engine for us at reasonable cost if we don't choose to do it ourselves.
A brand-new high-quality VW exhaust valve is about $15, a complete new cylinder head for each side is about$250 (drilled for two spark plugs per cyl, with new valves, seats, springs, etc).
The parts for a high-quality airworthy VW are readily available and not expensive. The engine isn't for everyone (its limits must be respected, and folks raised with self-adjusting valves, electronic ignitions, and fuel injection will find it requires a little more attention than their Honda Civic), but it's a good engine for many airplanes and remains cheap to build and to keep flying.

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#### Aerowerx

##### Well-Known Member
IIRC, both the VW bug and Corvair engines were designed by aircraft engineers, or converted from, aircraft engines. This is one thing that makes them more suitable than other auto engines. They even look something like Lycomings or Continentals (well, take your glasses off and drinking a couple pints first would help).

Now, the internal parts may have been changed for automotive use so when "converting", you would essentially be putting it back to where it started. You could take one from the scrap yard, bolt on a prop, and go flying, but it wouldn't last long without the "conversion". From what I have read, the most critical part of the conversion is to handle the axial forces from the prop thrust.

Since I am not an engine mechanic, I won't say any more---just spitting back what I have read on the topic.

#### Vigilant1

##### Well-Known Member
Supporting Member
One thing I think would benefit the adaption of auto engines is if builders would get away from the idea that they
must use reduction drives with auto engines. The Corvair engine conversions have proven very successful with the use of a 5th bearing. Its simply an adapter that bolts tothe engine and provides an extra support bearing to relieve the crankshaft from bending loads exerted by the propeller.I think this same technology applied to an auto engine being run at 2700/4200 rpms would be beneficial and reasonably inexpensive. This not to say that larger homebuilt airplanes cannot benefit from using reduction drives and higher rpms, but on smaller and slower airplanes, I think reduction drives are unnecessary. Its a case by case decision though.

The auto conversion that comes to mind that has run well and reliably without a PSRU or additional bearing support might be a small-displacement VW driving a lightweight prop from the flywheel end, using the proper crankshaft, in a plane that doesn't experience high yawing loads, at moderate RPMs. Other than that, some type of additional bearing support is usually considered necessary (i.e. a Force One prop hub for VW ($378), a "Fifth Bearing" for Corvairs ($1100-$2400), etc). And, in addition to these costs, there are often other costs for machining the case to accept them. They are good solutions for engines that can produce acceptable power at 2500-3200 RPM. But a PSRU is not necessarily the budget-killer that is being portrayed here: An SPG-3 or SPG-4 can be purchased from AirTrikes for about$2300 (bout the same price as the Fifth Bearing for the Corvair), complete with the needed bell housing to fit it to an auto engine (Suzuki, Honda) or even a motorcycle engine (BMW R1250, etc). So, it's not incredibly more expensive than some "plain" fifth bearings, but provides the needed prop support while also letting a smaller displacement engine turn at higher RPMs and produce a lot of useful HP/torque/thrust.
Bottom line: While a $2300 PSRU might be out of the budget for some projects/builders, it can be money well spent if it safely provides support for prop loads while allowing an economical, relatively small/light, widely-available, and relatively "stock" engine to provide reliable power for an airplane. If we need 100HP or so and can get it from a 1.3L-1.5L engine through use of a PSRU, this can be a very attractive option. #### plncraze ##### Well-Known Member Supporting Member Yes Turd he was the preacher. It is his example of persistence which keeps my dreams alive. #### Dan Thomas ##### Well-Known Member There is a really big reason why we don't see a lot of homebuilts powered by auto conversions, and it's the same reason we don't see a lot of guys building their own cars: the level of mechanical knowledge and experience in this society has decreased dramatically in my lifetime (I'm 63). My grandfathers and my father were all mechanical sorts, and my Dad's Dad ran his own machine shop. I can still do that stuff and many of the guys I grew up with could and can still do it. I made sure my son was able to do it, but my son is a rarity among his peers. Most of them probably couldn't change the oil in their cars, much less build the boats and other things he's made or fix their own cars and motorbikes and those of the people around him that bring him things to fix. He has machines like a lathe and milling machine that many of his friends probably couldn't identify. We have cars now that need almost no fixing in their entire lifetimes. Smaller mechanical devices are so cheap to buy that it's not worth fooling around trying to fix them when they quit, and they're too complicated anyway. So people now have lost that familiarity with engines and other doodads, and there's no way they're about to tackle building an auto conversion safe enough to fly behind. They can barely assemble a quick-build airplane kit. Most of us now live in cities where all services are available. 60 or 70 years ago most people lived in rural areas where they had to look after themselves. And they learned, or else. A generation or two ago there were plenty of homebuilder-converted VWs and Ford Model A's and Corvairs and some V-8s and so on that would show up at the airshows. That was in a day when there were far fewer homebuilts being built than there are now, too. Even for an experienced guy it's a challenge. I installed an already-converted Subaru in a Glastar, and had to come up with the engine mount, the induction and exhaust systems, the cooling system, fuel system, everything. And I have experience in machining and welding and fabricating and it still took a lot of work and thought and several tries at some of the stuff. I didn't mind it, but it sure took a lot longer and cost way more than anticipated. Bolting a Lyc to the firewall would have had it done 18 months sooner, easily. The Subaru, as installed, with the cooling system and everything, came out just a few pounds heavier than the Lycoming, so weight was easily manageable. Didn't need ballast or anything else to fix a forward CG. The engine is largely aluminum. Cast-iron engines would be way more hassle. You'd need a readily-available, proven, bolt-on conversion to get more auto engines in the air, and I don't know of many at all that are much more affordable than available certified engines. That's the problem when you have to have someone else do the design and building of something: it costs more. One can still do it, and he has access to much of the knowledge required in this day of the internet. Finding that info when I was young was really difficult. It takes studying and reading and buying tools and practicing on machinery. Work, lots of it, and it takes persistence. Not many do it. #### mcrae0104 ##### Well-Known Member Supporting Member IIRC, both the VW bug and Corvair engines were designed by aircraft engineers, or converted from, aircraft engines. I'll let others speak about the VW, but the Corvair was not designed by aircraft engineers. Rumors of this are floating around the Internet, but it was designed by Ed Cole's team (the same folks who designed the SBC) for the automobile. An interesting side note is that it was the first factory-turbocharged engine on the market in North America (maybe in the world). #### mcrae0104 ##### Well-Known Member Supporting Member the level of mechanical knowledge and experience in this society has decreased dramatically in my lifetime (I'm 63). I don't have the same length of reference but I think this is probably true regarding mechanical aptitude in the general population. On the other hand, if you can follow directions--the same skill set as building a kit plane--you can build an engine. It's not rocket science. Off-the-shelf VW and Corvair mounts are available for many airframes, too. A generation or two ago there were plenty of homebuilder-converted VWs and Ford Model A's and Corvairs and some V-8s and so on that would show up at the airshows. That was in a day when there were far fewer homebuilts being built than there are now, too. There still are plenty of VWs and Corvairs if you look anywhere other than the RV gaggle. #### gtae07 ##### Well-Known Member It's very simple (and I've mentioned it before). In the 150-300 ish hp range (i.e. typical four or six-cylinder Lyclone territory), there are no bolt-on tab-A into slot-B firewall forward packages. Nobody offers a complete FWF package with everything figured out like is offered with a Lyclone install on something like an RV. Until something like this exists, where I can stroke a check and receive a couple of crates with everything I need to hook my engine up and a good set of instructions on how, you won't see any significant penetration of auto engines into this market. As long as running an auto conversion requires any of the following, you'll never see significant market penetration: - Going to a junkyard for anything - Custom fabricating anything other than minor system brackets or baffles, wires, or hoses (so, fabricating engine mounts, cowlings, redrives, etc) - Any machining work - Performing torsional vibration studies - Significant troubleshooting/system testing/tinkering beyond what's typical for a Lyclone install (where almost any problem has been seen before and a fix documented) - Tuning the engine outside of timing and fuel/air ratio Most people don't want to design a powerplant installation. They don't want to spend hours and hours tinkering and test-flying to get a reliable engine. Most airplane builders aren't engine people (heck, most airplane builders aren't systems people, and a large fraction aren't even structural types that enjoy that work--they just want an airplane). They just want to bolt on an engine per the directions and fly. Something like this DOES exist, to varying degrees, with VW and (I think) Corvairs. I think this was the goal with the Egg conversions, but poor business practices and other issues largely sunk that idea. #### Peterson ##### Well-Known Member Quite a few Mazdas turning in the 150-300HP range. 200 is average for naturally aspirated. Being patient and checking lots of salvage yards can yield a long block for$200 or less. Another \$1200-1500 for new seals, getting the housings ported for 6000-6500RPM.

It starts to add up for ignition system, Holley 500cfm carb + cabled metering block (allows mixture adjustment from cockpit), cooling system, and stainless tubing for intake and exhaust, but still quite cost effective for a very smooth running high power to weight ratio power plant.

Then break the budget on a PSRU.

Would still have to get a very solid deal on a O-320/O-360/IO-360/6A-250/similar to hit 175+HP for less though.