High Altitude / high density altitude performance

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High Altitude / high density altitude performance

Postby Wyo-flyer » Mon Apr 25, 2016 11:57 pm

I am not currently a Sonex owner, my trusty old 1959 piper Tripacer gets me around currently. I live in western Wyoming, my airport sits at 7038 feet. In the summer it's normal to have a 9000 foot density altitude or higher. My 150 hp Tripacer does fine even fully loaded to gross....it will climb out at a whopping 300-400 fpm.

I have wanted a Sonex for a couple years. I owned a sweet rans s-10 sakota a few years ago that I wish I never sold but flying behind a 2-stroke rotax always made me nervous. I've always felt like the 80 hp aerovee just won't get it done at my altitude. Is this true? With the new turbo option I've been optimistic about having enough power. I realize the jab 3300 is a good option but way more expensive. I am a fan of boost and would lean that way over the jab just as a cost benefit.

Are there any Sonex owners out there that live / fly at similar altitudes? How does your plane perform? What kind of climb out numbers do you see? How about airspeed?

In order to do aerobatics at 3000 feet agl, that puts me at a little over 10,000 feet. I need some horsepower at that altitude to compete the maneuvers. My s-10 could barely do it until I put a 670 rotax in it....but was always scared to fly behind the 2 strokes.
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Re: High Altitude / high density altitude performance

Postby fastj22 » Tue Apr 26, 2016 9:33 am

We have six Sonex flying in the Denver/Colorado Springs area. Most of us run Jabiru 3300s. One has a normally aspirated 80HP VW and another soon to fly has a turbo Aerovee.
Field elevation at KFLY is 6900ft. DAs typically over 9000. I'd say the 80HP is underpowered for these altitudes. Recently, Gary and I flew to KGUC over the rock pile. He has the 80HP and I have the 120HP Jab. He really had to work it to get over the passes. It can be done, but takes more real mountain flying skills. I just climbed direct. Coming back, I left Gary behind and just climbed to 13,500 to clear Monarch Pass which was 10 miles out. The jab had more to give me if I wanted to go higher.

I'd say the 80HP Sonex performs like a 100HP C150 here. And the Jabiru 3300 performs like a 180HP C172. Looking forward to see if the turbo Aerovee outperforms both.

John Gillis
Waiex N116YX, Jabiru 3300, Tail dragger, SkyGuard ADS-B
First flight, 3/16/2013. 350+ hours and climbing.
Home: CO15. KOSH x 4 States landed in: CO, NB, NM, TX, OK, IA, KS, WI, IL, WY
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Re: High Altitude / high density altitude performance

Postby n982sx » Tue Apr 26, 2016 11:56 am

I take off from low density altitudes here in Illinois and would not consider the 80HP Aerovee for your location. When I decided on the engine I also decided I would not plan any trips west of the Rockies.

That said, the 80HP Aerovee is a fine engine and per the previous poster you can carefully push it up high. In your case however, the turbo seems a better fit to the mission you defined.
Bob Meyers

Built and Flying Sonex N982SX http://n982sx.com
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Re: High Altitude / high density altitude performance

Postby fastj22 » Tue Apr 26, 2016 1:06 pm

Wyoflyer,
If you are looking for a flying Sonex, there's a Jab powered one at KAPA on barnstormers for a pretty darn good price. I've seen it and its a nice, well equipped plane. Especially for $32k. Motivated seller too.

John Gillis
Waiex N116YX, Jabiru 3300, Tail dragger, SkyGuard ADS-B
First flight, 3/16/2013. 350+ hours and climbing.
Home: CO15. KOSH x 4 States landed in: CO, NB, NM, TX, OK, IA, KS, WI, IL, WY
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Re: High Altitude / high density altitude performance

Postby Wyo-flyer » Wed Apr 27, 2016 12:50 am

Thanks for the quick replies! Do you guys in the Colorado area run different pitch props than the recommended sea level props that Sonex recommends?

How about fuel burn at altitude with the 3300?

I'm really curious to see how the turbos are going to work compared to the jab.

I need to wait a year and sell the tripacer before I can pull the trigger but I just want to have all my ducks in a row.

Seems like most good aerovee powered planes are in the $25k range and jab are in the $30k+ range. It would be about even if you add a turbo to a NA aerovee.

Just took my tripacer up to 14,000 last week just to mess around but it started getting pretty doggy...
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Re: High Altitude / high density altitude performance

Postby fastj22 » Wed Apr 27, 2016 8:32 am

Climb out I see 7-8 gph, fast cruise 5-6 depending on how aggressive I lean. Economy cruise burns between 4 and 5.

John Gillis
Waiex N116YX, Jabiru 3300, Tail dragger, SkyGuard ADS-B
First flight, 3/16/2013. 350+ hours and climbing.
Home: CO15. KOSH x 4 States landed in: CO, NB, NM, TX, OK, IA, KS, WI, IL, WY
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Re: High Altitude / high density altitude performance

Postby MichaelFarley56 » Wed Apr 27, 2016 3:03 pm

I've done very limited testing for high altitude ops on my turbo, but overall I have to say that, as compared to the non-turbo AeroVee, the turbo makes high altitude performance a million times better!

If you haven't seen it, I tried to make my own basic amateur video of a "high altitude" turbo flight:

https://www.youtube.com/watch?v=ytGq51tKjLk

I haven't flown a Jab 3300 powered example that high and I'm not sure if a turbo is going to offer the same performance, but it will be a lot closer than the non-turbo AeroVee. Overall it did better than even what I was expecting.

Just my two cents...
Mike Farley
Waiex #0056 - N569KM
AeroVee #0631
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Re: High Altitude / high density altitude performance

Postby Wyo-flyer » Thu Apr 28, 2016 12:09 am

Hey Michael, I have watched you're videos multiple times. You did a great job btw. I have to chuckle to myself a little when you say "I don't normally fly this high" and I'm over here like...man he's at my pattern altitude. You did an amazing job of representing the "real" performance numbers.

One thing you don't mention is you're fuel burn with the turbo. What are you averaging? Where you able to reach full rpm at altitude? I know from watching the video that you have a climb prop so you have to watch your rpm at lower altitudes to not exceed redline. Also did you change your compression ratio on your motor? Do you run auto gas or AV gas?
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Re: High Altitude / high density altitude performance

Postby MichaelFarley56 » Thu Apr 28, 2016 12:16 pm

I'm glad you like the videos! Yes, from central Ohio I rarely have a reason to go much over 5000' MSL but it's nice to know the turbo AeroVee can easily to much higher if I need it to.

Thus far I haven't spent a ton of time on fuel burn numbers, especially at your altitude. When I fly around at 3000' MSL I routinely see anywhere from 6.0-6.8 GPH, but it can vary a lot based on how hard I'm running the engine and to be honest, how hot it is outside. When I was flying to Oshkosh last summer I was running the engine pretty hard (31" MAP most of the time), it was super hot and humid, and I had my airplane loaded with camping gear. In order to keep my CHTs nice and cool I purposely ran a little rich and would see 6.5-6.8 GPH as a trip average. When it's cooler, just me, and I'm just enjoying the flight (29-30" MAP) I will lean out a little more and my fuel burns drop closer to 6.0 GPH. These aren't exact though and again, I normally run my engine pretty rich to keep things nice and cool (I aim for around 1200 degree EGTs when leaning).

My Prince Prop is a 54 X 50 size which is probably a little more of a climb prop but overall I'm very happy with it. Down at low altitudes I generally don't go much over 34-35" MAP in order to keep my RPMs at or below 3400-3500. It will easily wind up faster than that but I don't see a need to go that fast!

When I put steel cylinders on my engine, I set it up at 7.0 to 1 and I run 100LL all the time. Engine runs great!

Thanks!
Mike Farley
Waiex #0056 - N569KM
AeroVee #0631
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Re: High Altitude / high density altitude performance

Postby Wyo-flyer » Fri Apr 29, 2016 11:16 am

Great data Mike! It sounds like the turbo vee and the jab burn about the same fuel. So I assume this gives you about 2.5 hours of flight time?

One thing I like about the jabiru is the option for a constant speed electric prop. This would be a sweet option.

So as I understand the turbo vee, 40" is the maximum manifold pressure correct? So at sea level that is 10 lbs of boost. At my elevation we are sitting at 23". So in order to reach 40" that's 17 lbs of boost. So my thought is to set up the motor to not exceed 40" at my elevation and then if I go lower I can keep the boost down with the throttle. Either that or in the turbo snowmobile world we have electric boost controllers that automatically adjust the boost level based on elevation.
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