Choosing an engine for a Sonex A

[robysonex]

Hello all, I'm building a Leagcy Sonex, and am in doubt about the engine for it; actually I have a Sauer 2200 with camshaft for lower rpm for max. torque, but have possibilities about getting an UL Power 350 or a Jabiru 3300.
My doubts are born from comments I have heard about different problems wit UL and Jabiru, mainly about cooling problems. On the other hand I don't hear about these issues here in this forum...what kind of comments can you, forum members give me about?

Thanks and good landings,

Roberto Sonex A kit #1433

[Skippydiesel]

I have a Sonex Legacy fitted with a Rotax 912ULS (there are several here in Australia). Airmaster CS prop.

Seems to deliver extraordinary performance - 150 + knots (corrected) @ 5500 ft

Problems; So far only issue of any note is engine temperature control.
Rear mounted Rotax Radiator (in exit air hole) front mounted Rotax Large Oil Cooler. Oil temps good on ground, Coolant high. In air reversed, Coolant good Oil high. Many holes cut/recoved in cowling, ducting, etc - some improvement but not enough.
Have returned aircraft to workshop & revised cooling system & cowling air in - yet to fly. Have high hopes.

Rotax 9 cooling seems to be a common issue - many different cooling configurations are in operation. Seems most people get the temps where they want them. Would be good to have some direction from Sonex (reduce the individual trial/error/cost/time)

[daleandee]

As many know I have a 3.0 Corvair conversion on the front of a Model A taildragger (it's not endorsed, recommended, or supported by the factory). It is a great engine with lots of power, reliable, and smooth. It runs extremley cool almost to the point of being too cool. Most climbouts show less than 260ºF (reading under the two rear plugs) and cruise temps of 225ºF. Oil temps can get into the 220ºF range on a long climb but I'm using the factory cooler and others are available if more cooling is desired. In cruise OT is generally ~200ºF using Rotella 15W40 conventional oil.

Dan Weseman built the engine and told me he had similar number in his Cleanex as well as builder Chris Smith. When I asked him about these temps he wondered what problem I was trying to solve. 11 years and over 300 hours later it still uses no oil between changes (done at 30 hours), oil analysis comes back excellent, and maintenance mostly consist of oil/filter changes & plugs during the condition inspection. I did replace the alternator belt this year ...

Dale
3.0 Corvair/Tailwheel

[Bryan Cotton]

I love my Aerovee. What it lacks in performance it makes up for with economy of operation. I'm not sure the lower RPM of the Sauer is a benefit though. The airframe is optimized for a small prop and this means higher RPM. We have flown about 185 hours in 16 months and it's going up rapidly.

If I built another I'd love to have the performance of the Jabiru. The Corvair would be a worthy option too, but are they available in Europe?

Three responses, three different answers. They are all worthy of consideration. But what is important is what works for you.

[Skippydiesel]

[quote="Bryan Cotton"] ................The airframe is optimized for a small prop and this means higher RPM. We have flown about 185 hours in 16 months and it's going up rapidly. ...

Hi Bryan - Please expand on this statement ie in what way(s) is the Sonex optimised for a small prop / higher rpm?

As for Corvair in Europe - my guess - you got the money you can purchase what you want BUT as for commonly available, I would think not.

[Kai]

Another thing is what diameter is considered small? With my geared Edge EP 915 ECI of 120 HP, the Sensenich 2-blade prop still fits comfortably and allows more than enough ground clearance on my taildragger: no deviatons from the plans on the gear. The blades are indeed fatter than the spindly ones for the direct drives, but so far after 100 hours no issues what so ever.

Once you understand that conditions and the cool air in/hot air out ratio is no different on liquid cooling compared to direct air cooling, finding a workable solution is no issue. However, planning well ahead for the position of radiators, oil tanks and other assorted hardware is essential. Just hanging these things in there where there seems to be adequate room, is not going to give you peace of mind. Do not try to re invent gunpowder, you might be standing too close when it goes off!

From a distance I have watched the work of WW and DW. Especially after they came up with their fifth bearing solution, I became suitably impressed! There is also a very good YouTube series of how to build these engines and prepare them for aircraft use. Fascinating and very instructive. Alas the Chevrolet Corvair never really took off in Europe, so the availability of engine cores and replacement parts is at best very limited- better relocate to the US!

In the course of 560 hrs my Sonex wore out two Jab 22A engines. Operating these low HP engines on a long paved runway like they seem to have on every street corner in the US, is a far cry from the hair raising situations you might encounter on the rough grass airstrips very many europeans must accept. A low weight geared engine of at least around 100 HP is the way to go. IMHO to make the Sonex really sit up and talk, you should get a 120 HP motor: then the plane just becomes alive!

As far as cooling issues with direct air cooled engines, you should be aware that Jabiru previously fielded their gen 1, -2, and -3 engines. Cooling the cylinder heads was a challenge- not because the design in itself was at fault, but because the aluminium they had to select because their CNC machining production, was intolerant of excessive heat. But: Jabiru has now for some years sold their gen 4 engine: especially the hot side is so different from previous versions, both in design and material, that a direct comparison is hardly possible. A brand new Jab 33A gen 4 is a beaut! On the other hand, for the UL Power units, there are still only few engines installed in a Sonex- experience needs to be gained.

Finally, what you also need to consider, is the availability of experienced assistance should you hit the wall somewhere along the road. In Europe, Rotax is outstanding. In Italy, MW Fly is apparently rapidly becoming a factor. Sauer and Limbach have been on the market forever. UL-Power is also eager to supply. Decisions- decisions!

[Bryan Cotton]

Hi Bryan - Please expand on this statement ie in what way(s) is the Sonex optimised for a small prop / higher rpm?

Mainly a comment on limited prop clearance for a big prop.

[13brv3]

Lots of options, but in Europe, I'd imagine Rotax 9XX rules. Fortunately, the factory makes an engine mount for the A model I believe, so you won't have to make your own like I did. It was 100% worth it though. I'd go 912S and not think twice about it.

[Skippydiesel]

Sonex may have moved to supply a whole mount but I am unaware of this.

The Sonex/Rotax engine mount is/was more of an adapter than a whole mount. It has passed through a mark one & two stage and there has been some "tweaking" of the rubber mounts to reduce excessive engine movement, mainly at shut down.

I have a mark two, its okay but far from perfect - I don't like the size/gauge of the fixings from rail adapter to bed (too small), nor that the rails were supplied with the the adapter holes pre drilled out of alignment & the wrong size for the Legacy bed. The rails should have been supplied without holes, or specific to the Legacy.

[13brv3]

Looks like a whole mount, though I personally like the ring mount over the bed mount.
https://www.sonexaircraft.com/eshop/car ... t_id=17646
https://www.sonexaircraft.com/eshop/car ... t_id=17647

Looks like you also need this for either of the above:
https://www.sonexaircraft.com/eshop/car ... t_id=17645

Rusty