Sonex Onex

[steingar]

How is a VW engine going to be expensive to maintain? You can do a top overhaul for a couple grand. You can buy a new one for we’ll under ten. It takes standard automotive parts which are inexpensive and plentiful.

Might need more mainentance, though I doubt it. My family had VWs as a kid, they’d run forever and soldier through just about anything. And they were in the back of the car, so I doubt they’re cooling was all that good. VW Bus’s had them in the back, and I think they’re all still running.

I recall dumb teenagers taking those things apart, putting them back together and having working engines. I know you guys are all big time experts and stuff, but what you’re saying really doesn’t jive with the treasured memories of my misspent youth.

 

[FormerHangie]

I'll shoot you a message - I have questions about the FlyBaby - it just keeps popping up in my brain...



Dude. Yes. I'm seriously thinking about trying to do the training/checkride in that thing just so I can have the experience (probably could never afford that plane though).



Yeah - I was thinking about that, but.... does anything other than the Aerovee really fit on it? I think someone here mentioned a Jabiru, that's a TON of power for a tiny plane.

I don't think it's that much. The six cylinder Jabiru produces 120 hp at something like 3300 rpm. Spin it at a more reasonable engine speed, it's not really too much power for the airframe.

If you're worried about that, use a four cylinder Jabiru, or the 80 hp Rotax. Both would be lighter than the Aerovee.

 

[kyleb]

How is a VW engine going to be expensive to maintain? You can do a top overhaul for a couple grand. You can buy a new one for we’ll under ten. It takes standard automotive parts which are inexpensive and plentiful.

Might need more mainentance, though I doubt it. My family had VWs as a kid, they’d run forever and soldier through just about anything. And they were in the back of the car, so I doubt they’re cooling was all that good. VW Bus’s had them in the back, and I think they’re all still +running.

Issue 1) Expensive to maintain. My lycoming (so far - 1100 hours) has cost consumables and a fuel pump. You'd be on your 3rd set of heads with a VW, and on at least the first rebuild. Also, I own an airplane outright. I fly it about 65 hours a year. Any maintenance time eats into flying time. Stuff like adjusting valves, replacing heads, etc. on a VW would be a bad thing and is expensive to me in terms of time...

Issue 2) Your VW's as a kid were run around town at 25 hp mostly. It isn't reasonable to expect the same reliability from one putting out 2.5 (or more) times that horsepower for long stretches.

 

[steingar]

Issue 1) Expensive to maintain. My lycoming (so far - 1100 hours) has cost consumables and a fuel pump. You'd be on your 3rd set of heads with a VW, and on at least the first rebuild.

According to it's maker you're supposed to rebuild your engine every 12 years anyway. Heads are cheap on a VW.

Also, I own an airplane outright. I fly it about 65 hours a year.

I doubt many Sonexes or other VW-powered aircraft fly that much. You rack up the hours traveling, not puttering around.

Any maintenance time eats into flying time. Stuff like adjusting valves, replacing heads, etc. on a VW would be a bad thing and is expensive to me in terms of time...

You don't build an airplane because you'e impatient to go flying. And if you can actually build an airplane you aren't allergic to a bit of tinkering.

Issue 2) Your VW's as a kid were run around town at 25 hp mostly. It isn't reasonable to expect the same reliability from one putting out 2.5 (or more) times that horsepower for long stretches.

Yours might have been. One sure as hell weren't. We were kids, remember?

 

[FormerHangie]

From the description that @kmacht has given, that sounds like either fuel system/carburetion or ignition. From what @jesse says about the carburetor, that would be the first place I'd look. It's very difficult to simulate that sort of thing in a test cell and it's seriously dangerous to fly until it's diagnosed and fixed.

We had some experience running dune buggies with nearly stock engines, and found that they had adequate cooling for normal street use, but for anything that required large throttle openings at less than highway speeds, the engines would overheat. Also, you needed to keep all the stock ducting to make the engine live. It's not a real robust design.

 

[Grum.Man]

I don't think a C85 on an experimental airplane would be any more expensive to maintain. It will last longer for sure but will cost a little bit more to overhaul particularly if the case or crank goes bad. As long as the components are in spec overhauling a C85 or similar vintage small 4 cylinder is pretty cheap especially if you go with chrome cylinders. If you consider how long it would take to fly 2000 hours in these smaller airplanes the overhaul cost work out to like 150.00 a year to put in the piggy bank.

 

[X3 Skier]

How many VW powered aircraft are flying? Is there any data on this? I’m too lazy to comb thru a registration log for the data.

Cheers

 

[wanttaja]

How many VW powered aircraft are flying? Is there any data on this? I’m too lazy to comb thru a registration log for the data.

"Flying"? No way to tell.

Registered? Perhaps.

I took a look at the 1 January 2016 FAA registry:

Aerovee: 90
Great Plains: 12
HAPI: 5
Revmaster: 145
VW: 562

However, about 15% of homebuilt registrations don't list a specific engine type, it just says "AMAT/EXP." I ran a process to determine what percentage of those engines were given types. The following are my estimates of additional aircraft with the indicated engine:

Aerovee: 44
Great Plains: 36
HAPI: 51
Revmaster: 15
VW: 357

So, adding these all up, that's about 1317 homebuilts with VW or VW-derived engines. That's 4-5% of the homebuilt fleet.

Ron Wanttaja

 

[X3 Skier]

Thanks Ron. I suppose “VW” also includes some of the specific “manufacturers” like GP, Revmaster et al.

So, the failure rate looks like one I can live with (pun intended) given the varying skill levels of the individuals assembling the kits.

Cheers

 

[mizer2167]

I like the idea of the Onex. However, you see so many Sonex's for sale with ~50 hours on the tach with auto engines it really makes me wonder what's the issue.

Not many seem to get a lot of air time but the ones with the aircraft engines do seem to have higher total times.

 

[wanttaja]

Thanks Ron. I suppose “VW” also includes some of the specific “manufacturers” like GP, Revmaster et al.

The "VW" vs. "Great Plains" vs. Revmaster" issue depends on what the aircraft was registered as. It's not unlikely that a plane with a Revmaster might be registered as having a VW.

One can be even less confident with the NTSB accident reports. The investigator is just as likely to say "VW" as "Great Plains."

Ron Wanttaja

 

[steingar]

I like the idea of the Onex. However, you see so many Sonex's for sale with ~50 hours on the tach with auto engines it really makes me wonder what's the issue.

Not many seem to get a lot of air time but the ones with the aircraft engines do seem to have higher total times.

I've seen a number of experimental aircraft for sale that way. Always figured it was folks would rather build than fly.

 

[FormerHangie]

Thanks Ron. I suppose “VW” also includes some of the specific “manufacturers” like GP, Revmaster et al.

So, the failure rate looks like one I can live with (pun intended) given the varying skill levels of the individuals assembling the kits.

Cheers

If it were me building a VW powered aircraft, I'd want one that is assembled by someone who builds engines for a living and run in on a dyno or a test cell. Also, look at where the powerband lies. A bunch of power at 3600 rpm isn't all that useful without a propeller speed reduction unit.

 

[wanttaja]

How is a VW engine going to be expensive to maintain? You can do a top overhaul for a couple grand.

Oh, a VW overhaul is cheaper than that.

Ron Wanttaja

 

[JohnAJohnson]

Friend of mine built one a few years ago and after flying off the 40 hours, he realized he really just prefered flying his 170, and having company in the plane for breakfast runs, etc. The Onex is a fairly high performance plane - not one you can lazily watch the world go by from, and I think that's why he decided to sell his.

OP, It is for still for sale, and I can vouch that it really was well built, in a tight-knit Airpark where half the occupants are builders, providing assistance and flak if someone tries to do something shoddy during the build. Give Rudy a call, he's a good guy that will answer any and all questions with 100% honesty.

I like the idea of the Onex. However, you see so many Sonex's for sale with ~50 hours on the tach with auto engines it really makes me wonder what's the issue.

Not many seem to get a lot of air time but the ones with the aircraft engines do seem to have higher total times.