R Austin

A few clarifications re VH-SRS resulting from recent questions off this thread.... - The target maximum continuous cruise speed (MCCS) for VH-SRS was 168 knots. The actual MCCS has exceeded this and is currently 172.3 knots using Rotax’s latest maximum continuous cruise power for 95 RON fuel (91 US), or 174 knots using 98 RON (93 US) or avgas, if you like an average of 173.1 knots (199 MPH). - All stated performance numbers are at favourable weights and CG. Variations to these parameters eg adding a passenger will reduce performance. - The aerobatic weight is 430Kg (or 450Kg using part filled wing tanks), not 600 Kg gross. Cheers Robin

Your interpretation of my explanation of 2 blade vs 3 blade Is correct. And thanks for the invite. I may even do that! Cheers.

It’s hard to predict what effect a CS will have on your plane. if your existing prop is really fine, then it will be all in cruise and top end. If it’s really coarse, then the improvements will be in TO and climb. it also depends on target cruise density altitude among other things. I’m pretty sure you understand that. It can be calculated if you have accurate MP, RPM and density altitude for a particular max speed scenario now. If you are running out of revs badly now, 10+ kts is quite plausible. Just don’t have enough info and don’t want you to have unrealistic expectations if you hand over your dough. From memory, the Airmaster 2 blade uses a more expensive hub, perhaps milled from an exotic alloy or not as large a production run or something, and that offsets the blade saving. I suspect most 10+ knots Cessna gained over the “all round” fixed pitched was in the U/C drag reduction. I’m estimating Maybe 70%.??.

I only went 3 blade cause this is my last major project and I didn’t want any compromises this time around. Spare no expense! Ha ha! Also, as I get older, comfort and smoothness is getting more important to me. Prior to this I have always gone with 2 blade. For ultimate performance, 2 blade is ahead based on all my testing., no question. As they say, 2 for go, 3 for show! But (I might be biased) that 3 blade does look good! Last thought. On some planes, the 3 blade makes the bottom cowl really hard to get off, particularly Sonerai non stretched versions.

Hi SkippyD. In reply to your prop query. You are in the speed range where you might just justify a CS prop. But you will have the same expense as a faster plane, with less benefit, this makes it a hard decision. I imagine that’s why Cessna couldn’t quite justify one on the 172, but made it standard on faster models. On yours, depending on where you are pitched now, I t will give a bit more go, or at least liveability at both ends, but another benefit is that you can always find a smooth spot for cruise at any speed. Something that fixed props don’t always do. re 3 vs 2 blade. From my experience, the biggest benefit with a 3 blade is even more smoothness. Buy expect to pay more and on your plane, lose just over 1 knot. Hope that’s helpful. Regards Robin

Hi skippydiesel and anyone else interested. That sounds bad, can I ask your first name please? i will respond to your prop question soon. Also. Thought you may be interested, I’m having a parallel conversation on the Sonerai.net site under “world record plane 12 years on” covering similar subject matter if you wish to tune in. cheers Robin

I spoke to Mr Monnett senior and junior at Oshkosh in 2011. Not specifically on that specific idea, but I did offer to get involved with the onex in a drag reduction role. They seemed little interested so I left it at that. It’s not unusual for designers over the years to seem perhaps quietly offended by others messing with their design. I detected that may have been the case here, but couldn’t be sure.

Hi Skippydiesel. Sorry, embarrassingly your name escapes me even though you’re my number 1 fan! Thank you sincerely for that and the kind words you write. I’ll let you know if I discover a number 2 ha ha. Re prop... the blades are C65AY Sensenich. Hub and electric CSU, spinner etc are Airmaster. All commercially available and damn 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. Too hard, too old, too lazy ha ha. Plus, the Chinese (or Nigerian scammers) would just steal all the IP. I’m not smart enough to protect myself! hope that’s helpful. cheers.

Hi Lyle. Good to hear from you! Yes, the wing fold is essentially as per original Sonerai plans, but I just refined it all the way through construction so that it is a genuine easy and fast 1 man job. I trailer it and set it up for each days flying. About 140 times so far. Keeps getting a bit quicker as I think of little refinements. 5 min to unload and 5 min to assemble and preflight. Quicker if I need to be. Typically 10 minutes from arriving at the airfield till turning the key. Might be a bit of a job retrofitting it to a finished aircraft though! Cheers Robin

Ok, too much resolution. Won’t open now. Sorry about the false starts, but it seems I can’t delete once posting. 1 last try.

The pics are a bit grainy. I compressed them too much. I’ll try again.

Hi. Here is the description of SRS that I promised. Apologies for the formatting. 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. Robin