Pinejuice wrote:EDIT: I would also like to comment that these kinds of numbers plague the industry. The bearhawk patrol site specifications claim a landing speed of 35, lets assume that is also the stall speed... For that specific aircraft, a stall at 35mph would require a lift coefficient of 3.5!!! With nearly the same airfoil as the S21. The data on NACA airfoils (somewhat comparable to Riblett foils) is publicly available and I urge anyone interested to review the max lift coefficients achieved at reynolds numbers that these aircraft operate at. Review the stall speeds and lift coefficients reached by production aircraft (Cessna 170, 140, super cub) All reasonable values, certainly not exceeding 2.5+ CL.

Another bad offender: Cubcrafters - 3.26CL for the carbon cub FX.
Another bad offender: Kitfox - 3.55!!!! for the STi S7 Super Sport

Please note, that the lift generated by an aircraft is a function of velocity squared, knowing this, achieving just a couple extra mph is increasingly more difficult to achieve as you approach these extremely low speeds. Not to mention, measuring these speeds can be a challenge itself.

Check your assumptions and run the numbers again?
Advertised stall speeds will more commonly be tested at minimum weight, not gross weight. That's not the manufacturers lying either, that's just smart marketing.

The advertised Bearhawk speeds are accurate, and I'll stake my reputation on that. You'll note they advertise IAS, and make no secret of it. If you don't read thoroughly, it's possible to misinterpret what you are reading.
My Bearhawk 4-place will fly at 37 KTAS all day if needs be.

Battson wrote:
Check your assumptions and run the numbers again?
Advertised stall speeds will more commonly be tested at minimum weight, not gross weight. That's not the manufacturers lying either, that's just smart marketing.

Stall speed, according to the Part 23 CFRs https://www.law.cornell.edu/cfr/text/14/23.49 is generally described in a most conservative condition. While I understand that experimental aircraft manufacturers might advertise a stall speed at max power, dragging it in on fumes at the most advantageous CG on a freezing cold day below sea level, with their lightest pilot, the utility of that number is arguably useless if not dangerous to potential customers. There is a good reason why the bottom of the white band on air speed indicators is at a most conservative condition.

To your point, I do understand that aircraft performance advertising is the wild west of claims. Consider that if the numbers are derived with a bunch of extraneous unknown variables thrown in, what is the point in the number at all?

Battson wrote:The advertised Bearhawk speeds are accurate, and I'll stake my reputation on that. You'll note they advertise IAS, and make no secret of it. If you don't read thoroughly, it's possible to misinterpret what you are reading.
My Bearhawk 4-place will fly at 37 KTAS all day if needs be.

37KTAS is 43mph, 8mph faster than 35 mph. I'll assume you're flying around at 1700lbs... The Bearhawk would require a lift coefficient of 2.0, which is very much within reach, especially if you are utilizing flaps. The 4412 airfoil (if you've got the older wing) is an excellent NACA foil for that type of operation.

I did not see IAS advertised in the Patrol Specifications http://bearhawkaircraft.com/patrol-specifications/. I do see it in the 4Place specifications. With that being said, in an ideal world, we would all get to see true airspeed advertised stall speeds on a standard day at sea level (at max gross weight and most conservative CG). Indicated airspeed includes instrument error, which is not something we are particularly interested in, while the ASI is very important for in flight awareness, what we're ultimately interested in is which aircraft is truly going slower when it lands, not which one says its going slower.

Pinejuice wrote:

Battson wrote:The advertised Bearhawk speeds are accurate, and I'll stake my reputation on that. You'll note they advertise IAS, and make no secret of it. If you don't read thoroughly, it's possible to misinterpret what you are reading.
My Bearhawk 4-place will fly at 37 KTAS all day if needs be.

37KTAS is 43mph, 8mph faster than 35 mph. I'll assume you're flying around at 1700lbs... The Bearhawk would require a lift coefficient of 2.0, which is very much within reach, especially if you are utilizing flaps. The 4412 airfoil (if you've got the older wing) is an excellent NACA foil for that type of operation.
.

Actually Battson has a 4 place Bearhawk, which is 40 MPH (the patrol says 35). So his statement of 43mph is actually pretty darn close when you consider that its a homebuilt so there is always a few variances.

Not really a hot thread for a month, but I don't see much newer running on the S-21.

Good to see there was some discussion on it, a couple builders and more like me thinking about it. I think a few of you are on the ransclan forum as well, but there's a bit more objectivity here probably.

I'm considering the S-21 since my PA-18-95 is gone. My mission hasn't changed, but I'm more a tin man then a rag man, and the side by side seating will be more pleasing for my family. But still needs to be an off-asphalt slightly big tire airplane operating in and out of smaller areas. 29's, VG's, tailshock (T3/Revolver/built in) and cub-style dampened gear would be part of my build if it happens. Ideally maybe performance stol flaps, but the cost is probably over a feasible budget. Engine choice was the Titan 180, but there's something to be said for the lightweight Rotax, either a 915 (don't think Rans has tried one yet, might not have a mount?) or a 154hp 912 from Jason at Badass Power Sports. A good solid used O-320 I think would be great, although it sounds from previous comments that it's a wider deck and needs a revamped cowl. Not to say it can't be done but not ideal.

It's probably a fringe edge or outside of the mission profile that Rans designed it for, but it strikes me as being something I can work with and compromise a little, and have a good airplane. The 28 foot wingspan bothers me probably more than it should, but man is that short. I'm sure it helps attain the cruise speeds Randy is seeing, but even a foot more on each side to give me a 30 foot span would go along way towards getting stall speed under 40. A 800-1200 lb cub has a 35 wingspan. A Maule has almost a 31 footer I believe, and a lot more power. I don't think you could do the old spar-cap splice wing extensions like many planes now have. But, if Randy was willing to discuss it, maybe we could get a set of front and rear spar extrusions one foot longer. As someone else mentioned, an additional 10-12 sq feet of wing can really help on the slow end.

Always depends on the owners mission, but I'd be happy to give up 10+ mph for 4-5 mph slower stall, in a 150 mph airplane. That just fits my profile better.

Anyone else thought along these lines?

pb

Farmboy wrote:Always depends on the owners mission, but I'd be happy to give up 10+ mph for 4-5 mph slower stall, in a 150 mph airplane. That just fits my profile better.
pb

Cub style gear are going to make it a 140mph airplane, at a guess? Remember we are dealing with smaller hp compared to a Super Cub, like only 60%, then look at the speed gains on the XCub from the spring gear and a few other tweaks. Same for Skywagon 180 vs Maule, the gear configuration is a real factor even when power input is the same.

Adding bushwheels and VGs, it maybe becomes a 125mph to 130mph bushplane? If you want to extend the wingtips per the other S21 thread, expect more speed loss and also a reduced maximum g-force. You wouldn't want to fly it overloaded, noting that it's been designed for a max takeoff weight which is greater than the LSA limits (good thing!!).

Rumour is the 150mph is slightly exaggerated, that's normal for marketing numbers / early testing. Either way, they honestly say it needs 75% to 80% power to achieve that top speed. So I think 125mph - 130mph would be a realistic speed expectation for an economical cruise power for a bushplane version S21 with all the trimmings.

The gear will slow it down for sure, but the less hp only occurs if you run a std Rotax. The speed numbers they market are all based on the Titan 180, and undoubtedly with a cruise prop.
Randy has been flying the S20 with the S21 wing and a Titan and hasn’t changed his expected numbers so far.

That said, for my mission 125-130 would be fantastic, so just need to get stalls into the mid 30’s.

Regarding the other thread post, we all start with a dream list and eventually pair it down to what is feasibly achievable.

Pb

You also mentioned the weights related to the LSA limits. I’m not sure how that market is these days after the advent of basic med, but my guess is it certainly has less value.

The specs Rans puts on their S21 brochure show both LSA and non-LSA weights/performance. Randy made a statement that one of the reasons they designed the S21 to a higher gross was they believe the LSA weight limit to be increased in the future. But, even if not, if the empty weight penalty is minor, having a good usable load is paramount for sales outside LSA.

Something to consider as well is the higher wing loading of the S21 should provide a much smoother ride in turbulence as compared to an S7.

Pb

The July newsletter that Rans has up includes some data collected testing the S20/Raven with the Titan 340 and S21 wings.

*****
Performance Testing of the 0X-340 Powered Raven
We know everyone has been very anxious to see what the numbers will be for the 180 HP Outbound, and we have our final assembly team working everyday to complete another S-21. However, we have not been idle in accumulating data from the Titan powered Raven. We believe the performance numbers will be similar.
As expected, the climb rates are high, well above 1000 FPM. Climb test to 12,500 from HYS (2000') showed an average rate of 650'. This supports how viable this wing and powerplant combo will be in high elevation back country.
At 5000', DA 9830' 27.80 barometric pressure, and OAT of 79F

IAS...........................TAS....................RPM
115 MPH..................133MPH.............2350
142 MPH..................165 MPH............2700
******

So at altitude you can see some speed, although not sure why he didn't show the same rpm at different altitudes.
pb

Is it surprising or important that this airplane debuted at OSH16 with the expectation that it would be flying "second quarter next year" but it still isn't flying now, when it's almost Q3 2018? I realize basically all of the parts have flown, but there still isn't a flying S-21 with a Titan 180.

If I'd put the money down when I was tempted, I'd be nervous, impatient, or both by now.

I agree, it's hard to wait, and it seems everyone is optimistic about when something is coming out.

It sounds like (based on rumors and guesses) that orders are high so they are trying to build kits to ship at the same time build another S-21 with an O-340 in it. I'm guessing they are going to do that in a trike version.

In June they mentioned fuselage kits were shipping, and finishing kits would go out a couple months later.... which of course makes me wonder with the low build time if I would be constantly waiting for the next kit to show up.

pb

I hear that the early kits have all the usual teething issues, so holes aren't lining up, things missing, etc. But they are shipping kits I am told.

Very interesting that those speed promises were made based on a Titan 180. You don't want to run around all day at 80% power in one of those.... fuel burn and temperatures would be less than ideal.

Battson wrote: speed promises were made based on a Titan 180. You don't want to run around all day at 80% power in one of those.... fuel burn and temperatures would be less than ideal.

Whats fuel burn and temps on your IO-540?

Farmboy wrote:

Battson wrote: speed promises were made based on a Titan 180. You don't want to run around all day at 80% power in one of those.... fuel burn and temperatures would be less than ideal.

Whats fuel burn and temps on your IO-540?

Varies a lot with power settings, anything from 90 L/hr to 24 L/hr is possible in the cruise. 90 is full power. My typical setting is 42 L/hr for 125 KTAS at 6,000ft, about 63% power lean of peak. 28 L/hr gets you about 50% power and 105-110 KTAS.

Temps vary with power and mixture setting, also cowl flaps. Normally about 300*F, up to 400*F in a climb.