Turbo Onex

[Bulldog]

Hi Guys - Is anyone planning to put the turbo on a Onex? Was that discussed at all at the open house? I'd love to know the numbers it would put out.

Nick

[MichaelFarley56]

Hi Nick,

The Sport Acro Sonex has an AeroVee Turbo on it right now. The newest AeroVee Turbo engine, currently on the engine test cell in the factory's R&D hangar, is scheduled to be installed on a Onex as soon as they're done with some last minute testing. I can't be sure but I think the plan is to put the engine on the Onex tri gear here in the next few months.

I'm sure we will all get detailed reports as soon as the airplane is flying! I can't wait to hear about it; I bet the Onex will be a rocket ship with that engine!

[thomasjones42]

Mike, Nick,
I think they actually had the test cell turbo engine mounted on a Onex tri-gear engine mount. It was crowded but apparently workable except Jeremy admitted that he still needed to figure out where to hang the battery in this instance. I sat in several of the Sonex presentations during the week to include the Aerovee Turbo session on Thursday and Jeremy was advertising improvements of 200-300 fpm in climb, +25 mph in speed, and EGTs between 1350-1367 on the Sonex; pretty much the same thing we heard at the Sunday open house. For Nick, the suprising thing was that Jeremy reported,as he has in years past, that CHTs were running about 20 degrees lower on the turbo engine. Perhaps we will see greater performance increases in the Onex, at least in climb, since it is a little lighter.

Tom Jones
Onex Kit #133

[SvingenB]

the suprising thing was that Jeremy reported,as he has in years past, that CHTs were running about 20 degrees lower on the turbo engine

I wonder why that is? The turbo engine is producing more HP, and this leads to more heat, normally. When the CHT decreases this can be caused by more/better cooling, more retarded ignition or richer mixture, and of course any combination. Still, this is a strange thing to do when the engine is producing more HP. hmmm?

[Bulldog]

Great info, thanks guys! I can't wait to hear the results! So would I be asking too much for a Turbo Onex with the SubSonex retractable gear?

Nick

[MichaelFarley56]

I wonder why that is? The turbo engine is producing more HP, and this leads to more heat, normally. When the CHT decreases this can be caused by more/better cooling, more retarded ignition or richer mixture, and of course any combination. Still, this is a strange thing to do when the engine is producing more HP. hmmm?

This is just my guess so please take it as my two cents only, but if I were to guess, I'd say it's a combination of several different factors.

First, remember that by design, the AeroInjector is already inside the cowling so by stock design, the engine is already breathing "warm" air. I absolutely agree that forced induction will raise the intake air temperature, but it may not be as huge as a temperature difference as we all think. Plus, with the "pull through" turbo setup the fuel is probably already atomizing at the turbo which may help keep things cool as the air enters the intake system.

Second, I believe turbo users will be running their engines richer than "normal". Remember, the current estimate is that we will be running close to 8 gallons per hour at full throttle with the turbo so I assume we will be swapping from the #2 needle to either a #2.5 or #3 in order to richen the mixture. Just like Jeremy said at the Oshkosh Open House, more air needs more fuel!

Third, I wonder if the RPMs will drop a little. With a higher pitch prop we may be able to get away with slightly reduced RPMs on takeoff and cruise. Right now my AeroVee is spinning around 3175 RPM at a full throttle climb and I run around 3200 in cruise. If I can spin my engine at only 3000 RPM in climb and lower RPMs in cruise, that may help temps.

Finally, with 25 miles per hour more air going into the cowling, obviously that will help cool things down as well. A good test was a test flight I did yesterday; at 5500' and 3200 RPM my hottest cylinder stabilized around 330-340 degrees. In order to perform some high airspeed tests, I left the throttle alone but pushed the nose over until I registered around 160 mph indicated. Same power but more airflow gave me much cooler CHT readings. They stabilized around 290-300 during the descent. Obviously this is a slightly skewed test, but there's some valid math behind it.

Regardless, I'm really excited that the turbo engine is staying cool. I gather that was a big concern but it's always nice to hear when it works out!

[MichaelFarley56]

Great info, thanks guys! I can't wait to hear the results! So would I be asking too much for a Turbo Onex with the SubSonex retractable gear?

Nick

Hey Nick,

It's experimental aviation, so do whatever you want!

That being said, I highly doubt it would be worth your time. You would be adding a lot of weight and complexity for minimal gains. There's been a few RV owners who have tried to add a retractable gear system into their RV only to find that speed gains were minimal. I bet you get better results by keeping your Onex straight and light!

Also, I don't think the SubSonex gear would work. I'm sure you've seen but the gear legs on the SubSonex are pretty tiny. If you want any sort of prop to ground clearance, I think you're going to need a lot longer gear legs.

Of course, a Onex with retractable gear would look pretty darn cool... :mrgreen:

[Bulldog]

I agree Mike, it would be really cool, but probably way too much involved to be worth it... probably get the same speed gains with a nice smooth set of fairings on the wheels/gear.