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Thread: New Model by Zlin Aviation: SHOCK CUB

  1. #81
    Selvaoscura's Avatar
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    Rotax 95 hp Shock Cub at work in this new video. It seems not too bad considering the low hp available and the not much powerful braking system (at least to my eyes)...This plane deserves a superlative braking system (Beringer for example?) and at least 140/150 hp...to become a much serious contender, just my opinion.But still not bad, I like as it turns and lands... Titan 180 hp engine could make a real difference on this plane...

  2. #82

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    delete, double post
    Last edited by courierguy; 06-15-2016 at 09:43 PM.

  3. #83
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    Engine choice

    Quote Originally Posted by Selvaoscura View Post
    Rotax 95 hp Shock Cub at work in this new video. It seems not too bad considering the low hp available and the not much powerful braking system (at least to my eyes)...This plane deserves a superlative braking system (Beringer for example?) and at least 140/150 hp...to become a much serious contender, just my opinion.But still not bad, I like as it turns and lands... Titan 180 hp engine could make a real difference on this plane...
    I think a Lycoming O-233 would be a good fit for this plane. Never liked the "lawn mower" sound of the geared Rotax, nor water pump and radiators.

    Crash

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    Twice the fuel burn, less range and payload, an overall less practical plane other then a bit ( not much, hauling all that extra engine weight and fuel)more ROC. Itd be a one trick poney. I'd put a 105 HP Rotax BigBore and a big Prince prop like I currently fly behind, its 4 lbs LIGHTER then stock Rotax. Coming up on 2000 hrs this year on mine, zero problems and I fly it like I stole it. My 2 cents worth FWIW Oh yeah, also less over the nose viz, especially important at the high aoa this thing approaches at. And, it wouldn't land as short with that extra weight.

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    Quote Originally Posted by Crash View Post
    I think a Lycoming O-233 would be a good fit for this plane. Never liked the "lawn mower" sound of the geared Rotax, nor water pump and radiators.

    Crash
    Yeah, nothing like closer allowed piston ring clearances, less or NO oil burn, no fear of shock cooling, and overall greater efficiency in a smaller, lighter, and longer lived package, who'd want that? Or, the engine's torque multiplied by the reduction system, what good is that?

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    Quote Originally Posted by courierguy View Post
    Twice the fuel burn, less range and payload, an overall less practical plane other then a bit ( not much, hauling all that extra engine weight and fuel)more ROC. Itd be a one trick poney. I'd put a 105 HP Rotax BigBore and a big Prince prop like I currently fly behind, its 4 lbs LIGHTER then stock Rotax. Coming up on 2000 hrs this year on mine, zero problems and I fly it like I stole it. My 2 cents worth FWIW Oh yeah, also less over the nose viz, especially important at the high aoa this thing approaches at. And, it wouldn't land as short with that extra weight.
    Courierguy- Randy S. is in a very good position to upgrade the S-7S to match the Shock Cub, which does have some attractive features - the landing gear, slats/flaps being the major things. Not everyone is interested in really slow flight/landing capability, however, Rans would get some serious attention if it brought this type of aircraft to market based on the already well proven S-7S design not to mention a U.S.A. company with excellant customer service and support.
    I for one would order a Rans version of the shock cub if it were available. (Nothing against Zlin and Shock Cub at all- just the fact that it's so far away and the uncertainties with import, service, parts etc.)
    Is there a half a chance Rans are at the design table now? I say " get on board with ultra STOL", compete in this market and shine as they've done with they're other aircraft.
    Roddy

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    People like AOSS because theres no air or oil, been around that leakage, it will show up sooner or later. guaranteed. I hope they dont go that way if they do something different.

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    Quote Originally Posted by courierguy View Post
    Yeah, nothing like closer allowed piston ring clearances, less or NO oil burn, no fear of shock cooling, and overall greater efficiency in a smaller, lighter, and longer lived package, who'd want that? Or, the engine's torque multiplied by the reduction system, what good is that?
    LMAO!! when I read that. BUT your wasting your print. I think it's a bit like the Harley guy's. You left one thing out though. The REAL lawn mower engine is the old aircraft design engine. All that said I still don't like the gearbox but mine never gave me any grief. The sound I really like is the Beaver PW Wasp. Every other engine sounds wimpy compared to that.

    Edit: I just thought of something else and that is the ability of the geared engine to use lighter props since you don't get the "hammer" pulses of a direct drive engine. A true carbon fiber prop (no heavy wood core) is OK to use.

  9. #89
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    New Model by Zlin Aviation: SHOCK CUB

    Quote Originally Posted by Roddy View Post
    Courierguy- Randy S. is in a very good position to upgrade the S-7S to match the Shock Cub, which does have some attractive features - the landing gear, slats/flaps being the major things. Not everyone is interested in really slow flight/landing capability, however, Rans would get some serious attention if it brought this type of aircraft to market based on the already well proven S-7S design not to mention a U.S.A. company with excellant customer service and support.
    I for one would order a Rans version of the shock cub if it were available. (Nothing against Zlin and Shock Cub at all- just the fact that it's so far away and the uncertainties with import, service, parts etc.)
    Is there a half a chance Rans are at the design table now? I say " get on board with ultra STOL", compete in this market and shine as they've done with they're other aircraft.
    Roddy
    Don't know about the PC6 landing gear but I do know there is an upgrade on the flaps. I think the folks in Hayes are coming around to the STOL concept more and more, which is contrary to the founders original intention of a lazy - Sunday grass strip machine that happens to work pretty well on short stuff. Change is painful out there in the Kansas plains, but it happens anyway.

  10. #90
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    Find an A&P in Alaska who knows anything about a Rotax..... I don't know of any. Lycoming O-233 burns 4.5 to 5 gallons per hour. The Super Legend uses this engine even on amphibs. They claim it performs as good or better then a PA-18-150.

    Take care,

    Crash

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    Quote Originally Posted by Crash View Post
    Find an A&P in Alaska who knows anything about a Rotax..... I don't know of any. Lycoming O-233 burns 4.5 to 5 gallons per hour. The Super Legend uses this engine even on amphibs. They claim it performs as good or better then a PA-18-150.

    Take care,

    Crash

    That is the real downside of the Rotax. Parts availability, parts cost, mechanics with knowledge and willing to work on them, used items for emergency repairs and so on. The first time you open a double overhead cam, 8000 rpm, 4 valves per cylinder with cam chain drive engine can be a little intimidating and there is a lot to be said for simplicity.

  12. #92
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    New Model by Zlin Aviation: SHOCK CUB

    That's a little bit misleading, but maybe I read you wrong.

    The 912 series that powers the shock cub does not turn 8000 nor does it have 4 valves or overhead cam. Parts are no more difficult to find than anything else. There's a couple vendors that stock it all. Can't say the same for a vintage Cessna, by comparison. I agree that there aren't many A&P's in Alaska that know much about them. Typically this is by choice, a lot of times because Grandpa didn't do it that way. There are a couple of 3 day schools out there that can bring a mechanic up to speed with no issue. Sort of like the one the tech goes to every year to fix a new pickup truck.

    With respect to reliability, the 912 series has amassed something like 40 million flight hours. This has to do with the fact that it is powering many of today's spooky UAV's that spy on Charlie and also shoot him. The agencies that deploy these flying machines can power them with whatever they choose as the engine is but a very small percentage of the cost compared to the payload.

    I had a hard time with them at first too. But when you look in the guts of the thing you'll feel pretty good about it. Change is hard.
    Last edited by gbflyer; 06-18-2016 at 02:54 PM.

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    Quote Originally Posted by qsmx440 View Post
    That is the real downside of the Rotax. Parts availability, parts cost, mechanics with knowledge and willing to work on them, used items for emergency repairs and so on. The first time you open a double overhead cam, 8000 rpm, 4 valves per cylinder with cam chain drive engine can be a little intimidating and there is a lot to be said for simplicity.
    Clearly you've never owned or flown a 912 as they are absolutely a step forward in aircraft engine technology. Most recognize the value that these tough, light and reliable engines have brought to the light aircraft industry. Almost all of the LSAs and more at this years Sun N Fun were using 912s. And 912s are more expensive- nevertheless they are the "go to" engine.
    Roddy

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    Quote Originally Posted by gbflyer View Post
    That's a little bit misleading, but maybe I read you wrong.

    The 912 series that powers the shock cub does not turn 8000 nor does it have 4 valves or overhead cam. Parts are no more difficult to find than anything else. There's a couple vendors that stock it all. Can't say the same for a vintage Cessna, by comparison. I agree that there aren't many A&P's in Alaska that know much about them. Typically this is by choice, a lot of times because Grandpa didn't do it that way. There are a couple of 3 day schools out there that can bring a mechanic up to speed with no issue. Sort of like the one the tech goes to every year to fix a new pickup truck.

    With respect to reliability, the 912 series has amassed something like 40 million flight hours. This has to do with the fact that it is powering many of today's spooky UAV's that spy on Charlie and also shoot him. The agencies that deploy these flying machines can power them with whatever they choose as the engine is but a very small percentage of the cost compared to the payload.

    I had a hard time with them at first too. But when you look in the guts of the thing you'll feel pretty good about it. Change is hard.
    Spoken from a farmer!

    Wish they built bigger aircraft engines.
    I don't know where you've been me lad, but I see you won first Prize!

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    Hey, I grew up framing too!! I was just like GB in the regards to taking me a while to 'accept' these screamin meenies!!! As GB said, the parts are not hard to find nor are they much difference in cost to what one pays for the typical Lyc/Cont stuff. Other than for the fact that is seem like you are getting a much smaller (in size) part for the money. I was skeptical at first about tearing into one of these engines to install the Zipper kit, but once I got into it, I realized it is not really much different that any other flat type engine. The liquid cooled heads and the gearbox of course are not on most Lyc/cont engines but the core of the Rotax is very similar looking. Installing the new cylinder/pistons was pretty straight forward. Still not 100% on my Rotax 912 but overall it has been a great learning experience. I wouldn't hesitate buying another plane with one installed.

  16. #96
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    The new 915 Rotax (turbo plus injection) coming by middle next year or even before, will change the game in my opinion. The promised 135 hp (there are even some rumors about 140 hp at the end) with a full take off power available up to 15,000ft and with a service ceiling of 23,000ft are impressive numbers for a light engine as this one (probably close to 210 lbs installed with fluids).

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    [QUOTE=gbflyer;662239]That's a little bit misleading, but maybe I read you wrong.

    The 912 series that powers the shock cub does not turn 8000 nor does it have 4 valves or overhead cam. Parts are no more difficult to find than anything else. There's a couple vendors that stock it all. Can't say the same for a vintage Cessna, by comparison. I agree that there aren't many A&P's in Alaska that know much about them. Typically this is by choice, a lot of times because Grandpa didn't do it that way. There are a couple of 3 day schools out there that can bring a mechanic up to speed with no issue. Sort of like the one the tech goes to every year to fix a new pickup truck.


    I was way off on this one. I have a lot of respect for Rotax engines but I have only owned a dead reliable two stroke version myself. I just "assumed" that all the talk over the years of these being "advanced engines" meant all the modern magic that the Japanese incorporated in their motorcycle engines were in these. After reading your post I googled these and of course found they are just of a standard design push rod style, spinning faster with water cooled heads for closer tolerances. Seems like a lot of efficiency is left on the table?

    Back to the mechanic aspect of this, unless Rotax is a lot different than the motorcycle manufactures, along with closer tolerances every "new" design used to come with a lot of expense for manuals, special tools, parts and training. You would need a decent customer base to make the investment. This I have a lot of experience in.

    Anyway I'm not pro or against these, just was interested in the conversation and thought I knew what I was talking about design wise and I was wrong. I will say after googling the engine I am not as interested in it as I was, but I wouldn't have a problem buying an aircraft that had one either.

  18. #98
    gbflyer's Avatar
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    No real special expensive tools to do most things an A&P should be doing. There are a couple of things best left to a specialist, most notably the rebuild of the water pump and the gear box. But it's no big deal, sort of like sending a set of mags or a carb for a legacy engine in to a shop that specializes in that for a rebuild.

    I think the school my Dad went to is like $750. So yes, it's a chunk of change with the travel, etc. We maintain 2 of our own, and I agree with you that it would be a significant investment without a base of customers needing that service. Or, it could get a few customers, depending on location.

    It certainly has its limits. So far though, there really isn't anything out there with the power-to-weight and track record the 912 has. It will be interesting to follow the new 915 when it comes out.

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    Quote Originally Posted by Crash View Post
    Find an A&P in Alaska who knows anything about a Rotax..... I don't know of any. Lycoming O-233 burns 4.5 to 5 gallons per hour. The Super Legend uses this engine even on amphibs. They claim it performs as good or better then a PA-18-150.

    Take care,

    Crash
    You made my point, one of them anyway. That fuel burn is what I call "a lot". I average out less then 4, and it's REGULAR mo gas, sometimes with E 10 no less. I'm not trying anyone to get rid of their Lycomings, just not partially ruin a new design that is all setup for the Rotax weight and size, by putting a boat anchor (comparatively) in it. That extra weight represents a big increase percentage wise for such a light plane. Good point on the mechanic knowledge, but that's getting better, but they need one rarely in my experience, my only problem was breaking a throttle cable once. Ace Hardware parts got me home on that one.

    As much as I like my S-7S (and my S-7 before that, been flying them 20 years now) and the boys in Hayes and the products they build, they need a little marketing gung ho like the Highlander boys and others have so cleverly capitalized on. Randy S does not seem to be "into" off airport stuff, that's why his customers tweak his birds on their own. Why third party vendors offer many upgrades for off airport type use, rather then the factory offering them as an extra cost option.
    Last edited by courierguy; 06-20-2016 at 01:10 PM.

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    wow !! amazing STOL machine!!!
    one thing I did notice looking through through all the videos and pictures is that the elevator is always at full nose down trim.
    this would make me worry about how things would look when it is loaded.
    anybody got some ideas on why this would be?

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    Post #96
    "for a light engine as this one (probably close to 210 lbs installed with fluids)".

    By way of comparison, non-electric O-200 is 192.83 Lbs.

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    Quote Originally Posted by JimC View Post
    Post #96
    "for a light engine as this one (probably close to 210 lbs installed with fluids)".

    By way of comparison, non-electric O-200 is 192.83 Lbs.
    yes but the 0-200 is putting out only 95-100hp under ISO conditions, at a high DA probably only around 70-80hp,
    the Turbocharged ROTAX on the other hand will give you 130+hp all the way up to 15000ft
    that is 30-35% more power at sea level and 85% are power at high DA

  23. #103

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    Quote Originally Posted by bodumatau View Post
    yes but the 0-200 is putting out only 95-100hp under ISO conditions, at a high DA probably only around 70-80hp,
    the Turbocharged ROTAX on the other hand will give you 130+hp all the way up to 15000ft
    that is 30-35% more power at sea level and 85% are power at high DA
    That is nice, but the catch is 4000 compared to 40-50,000. Whatever kind of soup you like to eat i guess.

  24. #104

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    Experimental aircraft. Run 9.5 pistons and car gas in the O-200 for 110 hp at 2750 rpm near sea level.
    4.3 gpm cruise.

    Most I've ever developed in an O-200 during climb near sea level was about 114 hp at 2850 rpm in a J3 with a Mac 7535 prop during a 55 mph climb. I agree that the Rotax will do better up high, but it is not lighter.
    Last edited by JimC; 07-28-2016 at 01:14 PM.
    Likes gcgrant liked this post

  25. #105
    Selvaoscura's Avatar
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    The first Outback Shock (Shock Cub in Europe) should leave for USA next week and it seems that many others will arrive soon..It will have a Titan engine ..

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    Quote Originally Posted by gbflyer View Post
    No real special expensive tools to do most things an A&P should be doing. There are a couple of things best left to a specialist, most notably the rebuild of the water pump and the gear box. But it's no big deal, sort of like sending a set of mags or a carb for a legacy engine in to a shop that specializes in that for a rebuild.

    I think the school my Dad went to is like $750. So yes, it's a chunk of change with the travel, etc. We maintain 2 of our own, and I agree with you that it would be a significant investment without a base of customers needing that service. Or, it could get a few customers, depending on location.

    It certainly has its limits. So far though, there really isn't anything out there with the power-to-weight and track record the 912 has. It will be interesting to follow the new 915 when it comes out.
    I have a Kitfox SLSA with a 912 ULS, at first I couldn't find anyone to work on it. I have a friend that is an A&P, I went to Blue Ridge Community college and took a Rotax Service & Maintenace classes offered by Lockwood, at first I did the work he would watch and learn and sign it off. I finally took the 3 week Light Sport Repairman Classes, now I'm a LSR-A. I took the biannual refreshers classes on the Rotax Service & Maintenance and took the Heavy Maintenance, now I do all of my own maintenance & annuals. I really like both the SuperSTOL and I like this Shock Cub. I prefer the side by side seating, but I really like the Fowler Flaps, and I think the "Cub" design will have a better resale. I also flew a SuperSTOL and I don't like their flap mechanism design. I have flown several Kitfoxes with 914 Turbo, and I would go with it over the 912. I like the higher horsepower, and I like the performance at altitude. I'm planning on selling my Kitfox and was thinking of a SuperSTOL or maybe the Savage Shock Cub, either way it will be a Rotax W/ Turbo.
    Last edited by Paul Z; 12-24-2016 at 11:16 PM.

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    Glad you brought up resale value. I would worry about the perception of those ladder-frame wings. All these sparless airplanes can be traced back to the Avid Flyer. Spar depth less than half of any wing with a conventionally located spar. (and there's a square law relating depth to strength). I admit to starting off with a number of this type, but I still associate them with 2 stroke engines. Both of my planes have 912 power, so I'm not an extreme reactionary, I just like a minimum of 7 inches of spar depth.
    What's a go-around?

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    Both the Kitfox & the SuperSTOL have a lift & drag spar, they are about 2 1/4 to 2 1/2 in diameter aluminum tubes with an spar stiffener beam inside the lift spar. For a LSA the Spars are more than adequate.

    I have not seen a Savage Shock Cub up close to see their spar design.
    Last edited by Paul Z; 12-26-2016 at 11:30 PM.

  29. #109

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    I get the spar depth issue, and how it's "not how it's done," in other aircraft. My RANS has tubular spars, like the Avids. And for that matter, like a lot of ultralights. But now, after all this time, and fleet hours, the long term safety of the design seems to make it a non issue. It's not like there has been a rash of wings folding up! We're talking from the mid 80's now, and thousands of aircraft, I think that is long enough to provide a pretty good statistical analysis of the design. I think RANS may be using "conventional" spars in some of their newer designs, but keep in mind that may partially be due to a marketing consideration, (like offering the Titan engine) and/or a cost to manufacture. Round spars were good enough for Jim Bede anyway. I'm pretty sure the Savage is doing whatever RANS is doing, that's what they've done in the past anyway. If I was selling kitplanes, I'd make sure to offer a Lycoming of some sort, and probably conventional spars, just to keep guys like Skywalker happy. Savage is all over the marketing aspect of their planes, that's why the word CUB is in there, I'm proud of the RANS company, a design I've been flying for 20 years and 3400 hrs, hasn't stooped to that oh so obvious marketing ploy. Savage has no shame and will do whatever it takes.

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    Round spars are good enough me, too. My 9G biplane has round aluminum spars, but they're under the high point, huge and thinwall. Anything crammed into the L.E. has to be thicker wall and internally sleeved. Ladder frames served well for Quicksilver type ultralights when we just wanted bolt'em up and go flying, but you're giving up structural efficiency when you don't take advantage of the full airfoil depth.
    True, it has been a long time since I looked at a RANS. I almost bought an S-10 when I bought my bipe, but I sat in Randy's demonstrator at Sun'n'Fun and looked into the wing root. The ribs were made of 1/2" aluminum tubing, one tube curved under the top surface, one along the bottom. In between were 3 pieces of vertical tubing, held in place with twists of safety wire. Forgive me if I haven't been back.
    What's a go-around?

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    Those days, and rib retention methods, though they amazingly worked, are 25 or more years in the past. I was at Oshkosh '88, and saw something like what you mentioned, turned me off too. FWIW the S-7S was FAA certified at one point, before the LSA thing came about.

    i know a renowned airplane builder, of all types, worked for BackCountryCubs even (composites) even. Has recovered and done major work on cert older taildraggers and built a boatload of S-7 types. He says the S7 wing cant be beat for weight to strength ratio, and can provide the #'s to back this up. I get the deeper main spar, located at the thickest part of the airfoil thing, but for LSA standard category strength, what good is a wing spar many times stronger then everything else? Like the struts, fuselage attach points, etc. This is why an S7 type weighs in the 700s range, and SC doesn't. Built light but right for its gross anyway. That round spar may or may not need sleeving, if a large enough one is used. Sleeving introduces point loading, and in some cases in the past ( of ultralights and hang gliders anyway) offered up less strength as a spar that used to bow a bit, now with a doubler sleeve, didnt , stressing the unsleeved part. My point is, a round spar, if unsleeved, is not inherently wrong. My best guess is, at some higher gross weight, the round spar loses out to the taller one. At LSA weight, doesn't. If I build a third S7, I'll use whatever type spar RANS provides, they haven't let me down yet!
    .

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    Sure, ladder frame does the job, I've been flying them since 1981 and just parked my Flightstar last year. But for a given strength, deep spars are lighter. You keep saying "round spar" and I keep saying "properly located spar". I think we are talking past each other. A round spar is a bit less efficient than an I-beam, but a spar with less than half the depth has to be much heavier. Root and strut fittings are what introduce point loads, internal sleeving spreads them out. If there are load concentrations at the ends of the sleeves, they will be much less than the original. If there's no sleeving, the wall thickness goes up and the strut fittings get heavier
    When you line up my Flightstar with my friends' Firestar (properly located-round spar) he beats me off the ground, in climb, in cruise. His round spar beats my round spars with the same engine.
    Yeah, '88, the S-10 was red and had been flown in from Kansas. I have total respect for Randy. Anyone who has kept afloat all these decades in this industry, and makes cool recumbents to boot, has my respect. But I still think if he could build wings like Bob Barrows for the same money, he would. My current ride is a Bearhawk wannabee, steel tube side by side with aluminum wings. Carlson spars and struts, all the gauges you can cram into a side by side, full electric, strobes, radio, gps, elt,plywood baggage, extra fuel in the baggage, 8.00's, trim, flaps, 912 with 3 bladed prop and oil cooler. 646lbs. But someone has to build those wings and that's a sticking point for a homebuilder or a factory.
    What's a go-around?

  33. #113
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    Well, Let's see, in beam structures, cylindrical beams are not as efficient weight/strength but also in torsion, particularly as the strength comes from the hight of the web, where the I beam shines and a tube has most of its mass in the center... (as explained in section modulus.)

    Having said that, from an economics perspective, there is nothing like a cylindrical extruded spar (some call it an AL tube ) you basically cut to length and drill... easy to automate too. A Bearhawk is, well a different kind of airplane, and those spars take 300+ man hours to build, so I don't see the cost effectiveness there... if you where to compare it, then looking at the Maule design is a better solution form a cost perspective albeit a little more expensive to get started, as it cost some extra money to build the dye for an extruded spar, but its the same principle, cut to size and automate it on a CNC drill.

    Randy @ RANS has done a good job over the years, and has all my respect as far as design is concerned, and this is possible as he makes business decisions that do not jeopardise safety in his designs.

    I have been following his design for the S21, looks interesting, but I find it miss fortunate that he chose a D shape spar incorporated in the LE, this exposes the spar to any accidental contact... and in the bush this is quite common, and could leave you stranded. It does save you loads of time if your where building the wing though...

    Happy holidays!
    Last edited by SpainCub; 12-28-2016 at 04:57 PM.

  34. #114

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    My point is that the shape of the spar makes little difference compared to the depth. (square law). You mention the torque advantage of a round spar, the Kolb is a single strut fabric covered wing because of this. Yes, structurally efficient wings take much more time to build, but I think most users on this forum would put in the time for the performance gained. You seem to be making a point against LE tube spars with the dent issue. oops, you're not courierguy
    What's a go-around?

  35. #115
    Gordon Misch's Avatar
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    (square law)
    Not quite. The square relationship is for the moment of inertia about the central longitudinal axis of the cylinder. Applicable to rotation, not bending.

    The transverse area moment for a hollow cylindrical shell is given by Ix = π (do4 - di4) / 64 , which approximately equals (do4 - di4) / 21, where the subscripts o and i refer to outside and inside diameters. http://www.engineeringtoolbox.com/ar...ia-d_1328.html

    For comparison, the transverse area moment for a hollow square shell is given by (do4 - di4) / 12. Rectangular has a greater stiffness for a size of cross section. However the circular cross section is less massive for a given diameter and wall thickness, so that partly mitigates the stiffness disparity.

    Interesting discussion!
    Gordon

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  36. #116

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    I'm out.....all I'll commit to is my wings get the job done! Don't know why and don't care, as long as they work! I'll just listen and learn.

  37. #117

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    Thanks Gordon, But complete rectangular sections aren't used that much and don't serve for comparison. When the spar is moved from the LE to the high point you have the freedom to go I-beam or a C-section with extra thickness in the caps. I don't think many designers use that freedom just to go uniform rectangular.
    Your comment about the torsional stiffness of a round section explains the Kolb wing, it has one aluminum sewer pipe in the high point and a single strut. It's fabric covered so all the torsional stiffness of the wing is in that tube. I think Kolb is the only mfg that does it that way and I've never heard of one fluttering. Homer Kolb was self taught and one smart cookie. (I'm joking about the sewer pipe, it just looks that way)
    What's a go-around?

  38. #118
    Gordon Misch's Avatar
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    I agree with you re "complete" rectangular. I was just trying to point out the r-squared misapplication, but then kinda got carried away with the fact that round isn't all that great compared to rectangular, when only considering bending. Again, interesting discussion - thanks.
    Gordon

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  39. #119

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    Gordon,
    I'm trying to get a gut feel for the equation you quoted, the difference of each diameter to the fourth power. Is it possible that the strength to depth is even more sensitive than a square law relationship?
    What's a go-around?

  40. #120
    Gordon Misch's Avatar
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    Yes, that's correct. Solid round or square sections each have a moment of inertia (bending strength) that varies as size to the 4th power. The subtraction is the result of removing the center, leaving only the shell. Non-square rectangular sections have a moment of inertia proportional to the 3rd power of their height. The farther away material is from the neutral axis (the center, sorta), the more effective it is. Hence the efficiency of I-beam sections.
    Gordon

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