Hi there. New to the forum, considering a sonex build/or purchase but there seems to be a lack of performance numbers for the B model with the 912 or ul power. Can anyone post some real world numbers? Cruise true airspeed at say 5400rpm rotax or 3100rpm for ul power? I see a lot photos of sonex aircraft doing like 120mph and then I hear claims 180 mph too. any builders/owners in Northern california? thank you!
I have a Sonex Legacy/912ULS/Airmaster CS
I flight plan at 130 knots True (5000 rpm) for a fuel burn of 15 L/Hr 98 RON (ULP)
I no longer try for Max Speed but back in the test flying days , I went to 152 Knots True at 5550 rpm straight & level
Hi, I don’t have numbers but have a couple friends working through the conversion to Rotax power. But my son took this video at Oshkosh last year. First Sonex was Corvair powered, second was Casey Cooper’s Rotax powered Sonex. The Rotax takeoff and climb was pretty impressive!
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Thank you for the responses! Ok, so I’m not crazy for expecting 140+ knots.
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In my old Legacy Sonex with Jabiru 3300, I would flight plan at 150mph/130kts routinely. Gave a decent fuel burn, I think I was spinning the engine around 3000rpm or so in cruise if my memory serves me. My Sonex was heavy, as I put everything under the sun on it…
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I am building a legacy in Northern California. I am considering a Rotax 912 also.
Hi Ron,
Unasked for advice:
You cant go wrong with the Rotax.
You will end up with a very capable aircraft in air speed & economie of fuel & operation/hr.
Very nice & easy to Land/Take-Off. Nice 3 pointer landings can be a bit variable, due in large part to the very springy undercarriage.
My Legacy requires a bit of left boot/rudder in Take-Off/Climb but flies feet off in Cruise.
Being designed as an aerobate, it’s negatively stable, so needs constant attention to fly straight & level - within a few hours you will become intuitive & almost make corrections without thinking .
The Legacy is poor in both weight & volume carrying capacity - perfectly doable but something you will need to get used to. Make the baggage compartment as large as you can, as long as doesn’t interfere with rudder/elevator system.
Consider a centre stick - frees up cabin space, compared with duel stick (I have)
My aircraft has 2 x 30L wing tanks & a 40 L fuselage header tank = 97L usable . I would have liked to have had another 20L for touring.
For the Rotax installation you can go;
- Sonex AroVee adapter (I have this) - a bed/rail type mount and likely the most cost effective & light weight . Not the best at absorbing the Rotax engine movement at shut down - be very careful of exhaust/frame clearance.
- Sonex Ring Mount/ Rotax Mount - the best but costly.
- Build your own
Oil & coolant heat exchanger location is very important - Sonex now offer a package - I had to figure this out on my own.
I started with an API fully castering solid 4" tail wheel, but found it noisy/rough on sealed runways and not so good on grass strips after rain. Now have a API/Peter Anson 6" pneumatic - much better all round.
I strongly recomend adding additional bracing to the canopy frame. The minimalist plans frame, is so floppy you are almost guaranteed to crack the “Perspex” in only few hours. Additional or larger span corner and rear cross bracing will likly lead to a much longer lived “Perspex”.
Depending on instrument package - consider vents in glare shield for cooling air flow & ease of access for future servising/maintenace.
I have my Voltage Regulator on the back of the firewall, with a dedicated cooling blast tube. The blast tube ( T off the cabin ventilation) is a bit drafty in winter & I should have had a glare shield vent. (one day)
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Skippy, what cruise speeds/fuel burn do you plan for? What prop?
also, just like people flew over the old 1,150 gross weight, what is the consensus on flying at a 1320 pounds?
I don’t know what the consensus is, but Sonex has done some real engineering. I would not exceed the allowed 1220 lbs.
Hi Brian, I generally agree with not exceeding the designers recommended gross weight. But for years people flew over the 1150 and they re-engineered to a weight that was consistent with what people intuitively already knew was safe. With the bigger engines and people talking about extra fuel tanks, the issue of gross weight becomes a concern. I suppose it’s easy to just outgrow the airframe entirely.
I agree. When I built my Cleanex I set my gross at 1250. With the new Sonex update I’m now only 2.46% over the factory recommend number. With the proper CG I don’t find it to fly differently than an earlier VW powered Sonex that I owned. But there has to be a limit and 14 years ago my limited research (I’m not an engineer - but I know a few) led me to the 1250 lbs. limit for gross.
I know of, and flew, a 1320 lbs. rated Sonex. Again, except for the effects of having more weight the plane flew like a Sonex. There have been others to set at 1320 but let’s be real. Sonex has given 1220 and that, to me, is as far as any new builder should go. My plane is slightly above that but I’m not here to say that what I have done is safe for anyone else.
JOOMO (Just one old man’s opinion)
Dale
3.0 Corvair/Taildragger
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I don’t think a higher gross weight is necessary for those engine choices. The UL power engines are pretty light. My legacy Sonex tri-gear (+12 lbs) is sitting at 690 lbs with autopilot (+6 lbs). With the installation I think the difference between the 912is that I have and the 912ULS is around 20 lbs. I suspect the B model may be heavier but I also have electric flaps, full interior and toe brakes. I don’t think it would be hard to build something light enough to give the useable load you’re looking for. Otherwise you might be better off with a Highwing.
There are comfort limits to putting too big of people in and CG limits if you are looking for too much baggage. With the Rotax burning only around 4 GPH, before the gross weight increase I figured I could live with taking off without a full tank and still have a 2 hr range with reserve.
Here they mention wing loading and landing gear are also limitations for the gross weight:
Agreed!
I Cruise at 130 knots True
Planned fuel burn is 15 L/hr ULP .
Propeller is an Airmaster Constant Speed Whirlwind R64W 3 blade Model: AP332 SCTFH .
In Australia the aircraft builder can nominate the MTOW, however I chose to go with the Sonex recommended weight of 554 kg. For my Legacy this means a POB Max 80 kg X 2 to remain in W&B with full fuel of 97L
Skippy, thanks for the response! I need all the motivation I can get.
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Is there anyone in the greater northern California area that would be willing to show me their sonex? preferably with Ul power/rotax, but I’m open to seeing any of them. I have a plane and can fly anywhere in the area.