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VH-SRS 170 knot Sonerai II

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TurbAero

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I am starting a thread about a "Super Sonerai II" that has been developed in Australia by world record setter Robin Austin. His new Sonerai II is registered in Australia as VH-SRS. It is fitted with a stock Rotax 912ULS and has a cruise speed of around 170ktas with 2 on board.

I am reproducing some information from Robin that has posted on another forum:

SERA-173 (VH SRS) is the 3rd aircraft in my journey of developing evolutionary aircrafts originally based on the 1970 Monnett Sonerai II design.
The mission was to build the smallest most efficient 2 seat aircraft outside, with the biggest achievable cockpit inside.
SRS is likely the first Rotax 912 aircraft capable of carrying 2 large adults whilst achieving genuine RV series performance.
Although maintaining Sonerai heritage, SRS is considered sufficiently divergent from the original Sonerai design to warrant a new name, hence the SERA-173 (Stands for Sonerai -Evolution -Robin -Austin - 173 knots max cruise speed)

Broadly speaking the SERA 173 specs and differences from a standard Sonerai 2 are as follows (all solo)

  • Max continuous cruise speed 173 Kts
  • All day everyday cruise speed 165 Kts (24”/4800rpm)
  • Economy cruise - 160 Kt at 15.2 L/hr
  • Aerobatic +6G -5G
  • VNE 180Kts (testing included full range flutter testing up to and including 200Kts)
  • 300Kg empty - 600KG MTOW – 300Kg payload
  • RV10 cockpit dimensions - comfortable for 6’5” pilot, 6’2” PAX (Sonerai volume +67%)
  • Centreline flying from front seat
  • High strength crash resistant zone around pilot (2.5X FAR23 requirements)
  • Airframe structural strength = Sonerai +25%
  • Airframe efficiency = Sonerai +72%
  • Stall speed slightly less than Sonerai II (minimum solo 39Kts)
  • 1250 NM range at 160 Kts
  • 1700 NM range at 100 Kts
  • Also comfortable at 70 or 80 Kt “loitering” speed
  • Constant speed propeller with latest Sensenich high speed blades
  • 23” prop clearance for gravel strips
  • Full span (30 degrees deployment) electric flaperons
  • Horizontal Stabiliser - electric inflight adjustable
  • Rotax 912 reliability and operating costs

    Although now flying for 150 hrs over 3 years, SRS is still “work in progress” hence the temporary SERA 168 logo (which was based on the target design cruise speed). SRS also features 1-person-easy-folding wings to minimize hangar space requirements, or in this case negates the need for a hangar as its current home is a custom built, generous sized, air-conditioned enclosed trailer (See photos attached) which doubles as a hangar and workshop and lives right outside my garage (I can play with my toy anytime!).
The design, construct and refinement project (including trailer) has taken 8 (enjoyable) years and development continues.

And some additional information provided by Robin on the same forum:

Re prop... the blades are C65AY Sensenich. Hub and electric CSU, spinner etc. are Airmaster. All commercially available and **** good stuff too. Very well engineered. All integrated by Airmaster as turn key product.
To be honest, can’t tell you min ground roll as I operate off gravel strip and am quite conservative with power application. Not stol but still quite short. From memory it’s well under 200m solo, but don’t hold me to it.
I regularly take off and land on first half of 600m strip with minimal braking.
Wing section changes were intended for top end speed, but made biggest difference at bottom end. With flaperons, it only has to accelerate to 40 kts although I usually lift off at 50.
Initial stabilised climb is 1730 ft. per min as tested solo at ISA. Less if hotter or higher. This is less than SGS as this plane is unavoidably 30 Kg heavier as it is larger and stronger. This is the only area it has less performance than SGS.
Motor is bog standard 912 ULS. Except altitude leaning provisions.
No plans or kits proposed.



And some photos that Robin has provided:

1.jpeg2.jpeg3.jpeg4.jpeg
 

fly2kads

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I remember seeing a photo of this plane elsewhere, but it had no information about it. Sounds like quite a bit of development has gone into it!
 

Vigilant1

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Thanks for the information. Those are some amazing numbers.
Has Robin commented on his impressions of the tail/rudder authority? Maybe it's just the angle/perspective of the photos, but it looks small (even for a Sonerai). Obviously, the proof is in the flying (and spinning).
It looks great.
 

TurbAero

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I remember seeing a photo of this plane elsewhere, but it had no information about it. Sounds like quite a bit of development has gone into it!
He has an identically painted earlier one which is VH-SGS rather than SRS. SGS is the one that he achieved his world speed records in. There are plenty of online photos of that one.
 

mcrae0104

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Very cool project. I've always been tempted to build a IIL without the front seat, add a little extra turtledeck height (for taller pilots), and a sleeker canopy. I threw in some extra vertical tail too, though just for aesthetics (I don't know that it actually needs more). Here is a little before & after:

4.jpeg 4_mod.jpg
 
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TurbAero

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Is that 170 knots true air speed at altitude? Or 170 knots as stated by Robin?
Robin has been through a validated world speed record setting process with his other Sonerai. He knows how to accurately determine his true air speed. As he says, his target is 173ktas but he is only achieving 168ktas with this variant (with tweaking to go). I do not know whether his current speeds have been validated officially, but I have confidence that if he claims these speeds, they are legitimate.

While he hasn’t yet achieved his target of 173ktas, he has hit his target of an RV performance on a Rotax 912, and with the ability to carry 2 large sized people. This was never about achieving another world record, only to achieve some personal targets. He is very close to doing that and even if he doesn’t ultimately make it, he has achieved a creditable outcome for his project.
 

Robin Austin

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Hi All.

A friend correctly alerted me to something confusing in my original post which was subsequently copied to this thread. I should have been clearer.
My target design maximum continuous cruise speed (MCCS) for VH-SRS was 168 knots.
The actual MCCS has exceeded that and is currently 173.0 knots.

Also perhaps I can answer the rudder VS size question. The airflow on this aircraft (and Sonerai types in general) across the tail seems to be very clean as they have very powerful rudders despite the apparent small size.
The tail surfaces on SRS are considerably larger than a Sonerai 2 and actually work out pretty good for a sports/tourer.
It tracks really straight in turbulence, no waggle whatsoever and has positive yaw stability.
I see no reason for going larger unless someone considered it looked better. Of course, that would also create additional weight and drag.
In saying that, I always build with independent differential toe brakes and it could be possible that that masks any ground handling issues. There are certainly none in the air.

Hope that’s helpful.
Regards
Robin
 
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