21st century Volksplane?

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Bigshu

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Thanks, Topaz, for all the feedback. I am deliberately staying lighter than LSA limits to keep things affordable and get the most out of modest power: 1320 lb on a VW is very different than 1100 lb on the same engine. Target would be 600 lb empty for 500 lb useful load knowing that keeping an enclosed two-seater that light would be a challenge.
When I learned to fly, in a Yankee, I took it to be a nice light 2 place fun trainer. Looking at its stats now, at 1500 pounds, it wasn't so light, and with 22 gallons of fuel, and 108hp, it was limited to 380 pounds useful load. That's at a little over 900 pounds empty weight. With a 24 foot span. Is it really feasible to cut a third of the weight and still have safe performance with a similar useful load and 30 or so fewer horses?
 

Topaz

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When I learned to fly, in a Yankee, I took it to be a nice light 2 place fun trainer. Looking at its stats now, at 1500 pounds, it wasn't so light, and with 22 gallons of fuel, and 108hp, it was limited to 380 pounds useful load. That's at a little over 900 pounds empty weight. With a 24 foot span. Is it really feasible to cut a third of the weight and still have safe performance with a similar useful load and 30 or so fewer horses?
It's the span that does the trick. 24 foot span isn't going to get you to 500fpm "hot and high" (5,000' density altitude) with a MTOW of 1100 and an installed power of ~65hp. 27-30 foot of span should get you close, all else being the same.

I don't know whether it was the "jet age" or what, but airplanes from the '60's tend to have short spans for their area, and bigger engines. I guess bigger engines were just cheaper then, perhaps? Look at '30's and '40's era airplanes like Cubs and Aeroncas and you'll note that they used a different formula - more span, less motor. We still seem to be obsessed with keeping span short. I don't know why. I come at flying from a different direction, where lots of span and zero power is the norm. Span doesn't bother me. I don't know why it bothers so many pilots today. "Glider" isn't an epithet, and when the noisemaker up front takes a powder and things get quiet, you'll appreciate the extra span then, too.
 

Vigilant1

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We still seem to be obsessed with keeping span short. I don't know why.
Particularly when, ironically, the availability of reasonably priced high quality CF pultrusion rods now makes more span easier/lighter than ever.
Also, maybe the "jet age" again, but many designers seem reluctant to go with a thick wing (15-18% or so). There's not much drag penalty at all at these speeds, weight penalty is minimal (unless the wing core is solid), and it structurally it allows for a lighter spar and a stiffer wing (reduced chance of flutter, etc).
 
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blane.c

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So maybe what cluttenfred is toying with in the back of his mind is the Nenadovic' biplane wings on the 21st century Volksplane?

Advertised 25% less drag 15% more lift and 51% more speed range for the same planform as a monoplane wing it could well be the answer. That would be a cool experiment with the VW and two place airplane and may well be the answer if as advertised is anywhere close.
 

Victor Bravo

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I also really wish that the original intention of this thread was made clearer at the onset.... we all spent a lot of time, had a lot of fun, and came up with a LOT of neat ideas for minimalist single seat runabouts that could do the original mission of the VP-1. I believed then and I believe now that the original VP-1 mission (inexpensive mass produced powerplant with minimum to modest aero-conversion, single seat, quick to build, no exotic materials or processes) is very very valid.

Considering Matthew's actual intention was apparently centered around a (bespoke) VW powerplant on a two-seat aircraft that was inexpensive and easy to construct, that changes the game a lot, and forces us virtually at gunpoint to go in the direction of a "floaty" powered glider, or at the very least in the direction of long span and high aspect ratio and not "too heavy" (Greg Cole Goshawk end of the spectrum).
 

Topaz

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... Considering Matthew's actual intention was apparently centered around a (bespoke) VW powerplant on a two-seat aircraft that was inexpensive and easy to construct, that changes the game a lot, and forces us virtually at gunpoint to go in the direction of a "floaty" powered glider, or at the very least in the direction of long span and high aspect ratio and not "too heavy" (Greg Cole Goshawk end of the spectrum).
You do realize that a lighter (aluminum or composite) KR-2S with even 27-foot span would meet the spec, right? Hardly "floaty". ;)
 

Tiger Tim

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  • Increase the gross weight a little (say 500 kg/1100 lb) for today's heavier people.
  • Go with a cantilever wing, perhaps a straight 16' center section with dihedral in the outer panels Thorp-style.
  • Increase the wing area and aspect ratio to improve climb performance on modest power.
  • Widen the cockpit for comfort enclose it with a cabin or canopy.
  • Keep the single center stick but the option to solo from the center may no longer be needed.
  • Keep the simple, square lines including constant-chord wing and horizontal tail surfaces.
  • I could go either way on the all-moving tails vs. stabilizer-elevator and fin-rudder.
  • Keep the big bore VW engine (Revmaster, Aeroconversions, Hummel, etc.) as standard but eventually offer Rotax 912 and maybe Suzuki-based options as well.
  • Add optional tricycle gear with a free-swiveling nosewheel and differential brakes, perhaps using dual hand levers on the stick.
  • Keep the fabric covering over everything and the wood wing, but I could see riveted aluminum tube and gusset taking over for the fuselage and/or tail surfaces.
You had me thinking ‘surely he knows about the Zenair 600-series’ right up until the wood and fabric part. I dunno, man, seems to me like the right answer nowadays for easy building is aluminum anyways. I know wood is romantic but we really don’t live in that world anymore.
 

Bigshu

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The ultimate fact of the matter is that 65hp maximum, 60hp continuous, is about what you can get out of an 1835cc "simple and inexpensive" VW conversion. If you want/need more than that, either opt for one of the larger (2100cc), more heavily-modified, and much more expensive 70-80hp conversions, or opt for a different family of engines, such as the Corvair. You're not going to find "simple", "cheap", and "80hp+" out of a VW conversion, any more than you'll find "simple," "cheap," and "300hp+" out of an O-360 "conversion."
To be fair, I didn't say it would be a simple and inexpensive conversion, just a conversion. Cassler's site list the specs for the 85 hp version being 2400 cc's, both bore and stroke being larger. Other internal parts replacement goes along with that. I saw no mention anywhere on the site about restrictions on continuous power, but I'm sure you're correct that you'd need to have them to get reliability and longevity from the conversion. My point is that we act like 65hp is a hard limit for a VP21, when plainly it isn't. Throttling back to reasonable continuous power seems like a fair exchange for the extra horses on takeoff. When we talk about the 65hp version, it's the same reality: 65hp on takeoff, throttle back to something like 60 hp at cruise? I'm not advocating flogging engines, just that more horses are available to make a VP-21, two place, 1100-1320 pound aircraft more practical to consider. As a historical consideration, both VW and Corvair engines have proud racing histories, where they were revved at well beyond 3400 rpm for extended periods of time. Still are today, burning as low as 87 octane fuel. Just saying the capabilities of these engines is as much a function of the quality of the build as it is the limitations of the components. Or the brains of the operator!
 

Bigshu

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It's the span that does the trick. 24 foot span isn't going to get you to 500fpm "hot and high" (5,000' density altitude) with a MTOW of 1100 and an installed power of ~65hp. 27-30 foot of span should get you close, all else being the same.

I don't know whether it was the "jet age" or what, but airplanes from the '60's tend to have short spans for their area, and bigger engines. I guess bigger engines were just cheaper then, perhaps? Look at '30's and '40's era airplanes like Cubs and Aeroncas and you'll note that they used a different formula - more span, less motor. We still seem to be obsessed with keeping span short. I don't know why. I come at flying from a different direction, where lots of span and zero power is the norm. Span doesn't bother me. I don't know why it bothers so many pilots today. "Glider" isn't an epithet, and when the noisemaker up front takes a powder and things get quiet, you'll appreciate the extra span then, too.
Most of the ideas I'm pursuing have spans between 27' and 30'. The exception is now I'm thinking of a tandem wing design, which would have drastically less span but similar to greater SF of wing. I lean toward folding wing designs to facilitate keeping it at home rather than an expensive hangar.
 

Topaz

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To be fair, I didn't say it would be a simple and inexpensive conversion, just a conversion. ...
True enough but, by the same token, nothing is limiting you to a VW in the first place. Why spend a bucket of money on "souping up" a VW conversion when you could spend the same amount of dollars on a used O-200? The point of doing an auto conversion is "inexpensive purchase and maintenance." If you're going to drop the dollars, might as well go for something that's more suitable from the get-go.

Most of the ideas I'm pursuing have spans between 27' and 30'. The exception is now I'm thinking of a tandem wing design, which would have drastically less span but similar to greater SF of wing. I lean toward folding wing designs to facilitate keeping it at home rather than an expensive hangar.
Rate of climb for a given power available is much more tightly bound to span (and by extension, span-loading) than it is surface area. Tandem-wing designs certainly have their strengths and uses but, for an equal MTOW and climb rate, will require a larger motor. If that's worth to you the things you gain for going tandem, then awesome and carry on. But understand the trades going in.

In both points, I'm holding to the OP's notion that a "modern Volksplane" would be very inexpensive (relatively speaking) to build. The cheapest way to get a certain MTOW to a certain climb rate (whatever that specification might be) is span, because "more span" is cheaper than "more engine," generally speaking.
 

Vigilant1

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Cassler's site list the specs for the 85 hp version being 2400 cc's, both bore and stroke being larger. Other internal parts replacement goes along with that. I saw no mention anywhere on the site about restrictions on continuous power, but I'm sure you're correct that you'd need to have them to get reliability and longevity from the conversion.
There's really no magic to getting a lot of short-term power from a big Type One VW. Just increase the compression ratio and/or run higher RPMs. Street racers, drag racers, Formula V racing aircraft, draggy planes running PSRUs and engines turning 5000 rpm--all of these have made more than 100 HP. For a very short time.

The main limitation is CHT. The heads get hot then the exhaust seats erode, or an exhaust valve breaks, or the head cracks. Regardless of the displacement, on a continuous basis, burning enough fuel to produce about 70 HP also produces more heat than can be removed with readily available forced convection. A great thing about VWs is that we've been flying them for about 6 decades now, lots and lots of things have been learned, and the limits of the engine are known. As far as this heat issue, it's not a matter of getting better valves, better rods, better balancing, etc.

Aside from the CHTs, another known limit of the Type 1 is strength of the magnesium case. The bearing saddles do wear out if pounded hard, and that leads to misalignments elsewhere that cause trouble. And the case itself eventually cracks-- maybe after thousands of hours at low CRs and rpm, maybe a lot sooner at a continuous high power. Aluminum cases are available that can help, but they are heavier and more expensive. And the head/CHT limit remains.
The VW Type 1 makes a very good airplane engine if its known limits are respected. Relatively cheap, still available brand new, light for the HP, and all the weaknesses have already been identified. For a user who wants 80hp continuous or more, it is simply not the best option. For those who can use what it can reliably offer, it is a great choice.
 
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Vigilant1

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Matthew's current requirements for a modern VP-2 are met by the Cygnet. Perhaps the structure can be simplified but the template is there.
+1. It has a lot of loyal fans, good numbers (with a VW), and a strong track record. Now, how to get the construction simplified so it can be built in about 1/3 of the claimed average of about 1700 hours. That is, how to get the VPs trademark "I could build that" factor?

Welded tube fuselage, wood lattice wings--they work great on the Cygnet, but it doesn't scream "I could build that" to the average Joe/Jane.
 

Topaz

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+1. It has a lot of loyal fans, good numbers (with a VW), and a strong track record. Now, how to get the construction simplified so it can be built in about 1/3 of the claimed average of about 1700 hours. That is, how to get the VPs trademark "I could build that" factor.
In declining order of "expensive": molded composite, matched-hole aluminum, hand-layup moldless composite.

(And yes, I'm aware that "everyone knows" that moldless composite involves "thousands of hours of sanding." That's about as valid as what "everyone knows" about VW conversions. There's a reason RAF chose it for its early kits, and Scaled for its early rapid prototyping.)
 

Vigilant1

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In declining order of "expensive": molded composite, matched-hole aluminum, hand-layup moldless composite.
I'm a moldless composite fan, too. For this slow, gotta be light, big-wing design, is the weight of a solid core beyond the mass budget? The foam core of a 13% thick wing of 48" chord weighs about 3 lbs per foot, so about 75 lbs for Matt's wing.

Waddabout: A hot wired D cell with the spar at the back (pultrusion rod caps, web laid up directly on the foam), cover the D cell with FG (open layup, vacuum bagged if desired). Ribs aft of that, and cover the whole wing in fabric. So, no need for a perfect finish on the FG (it gets covered in fabric anyway), the D cell gives good aerodynamics and damage tolerance on the LE. The wing is light, the builder saves the cost of FG and epoxy aft of the spar, etc. Things get simpler yet if flaps aren't fitted.
 
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Topaz

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I'm a moldless composite fan, too. For this slow, gotta be light, big-wing design, is the weight of a solid core beyond the mass budget? The foam core of a 13% thick wing of 48" chord weighs about 3 lbs per foot, so about 75 lbs for Matt's wing.
Dunno. I'm not willing to "eyeball" it. So much depends on how the fuselage is done, too. My motorglider uses a 12% thick airfoil, not for drag reduction but for weight reduction with a solid core wing. Costs me a little CLmax, there's still a net loss in weight, even with the small amount of extra area.

Bilski has me convinced via spreadsheet that, by the time you're done, a solid-core wing is about as light as you're going to get in composites without going to expensive molded and vacuum-bagged panels, and that any attempt to "pull weight out" actually ends up adding more weight, once you account for internal skins, etc.

I honestly don't think anyone can make a judgement about a particular construction material at this stage. Even knowing the configuration (Cygnet-like), the devil will be in the details of the final design.
 

Geraldc

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We still seem to be obsessed with keeping span short. I don't know why.
The foam core of a 13% thick wing of 48" chord weighs about 3 lbs per foot, so about 75 lbs for Matt's wing.
If you go for longer span you can go with a shorter chord and keep the same wing area with less drag. Maybe 30ft and 3ft chord.
Removable wings like rv12
 

Pops

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A Cygnet redesigned to be quick and easy to built should be a winner for a 2 place VW powered airplane. Have to save all the weight you can in the design.

Added-- I had a plans built 2 place, side by side Zenith 600. ( no not a 601). Plans shows a 1835 cc, 60 HP, VW engine. Old friend of mine built it and never finished it. I got it with no engine, cowl and canopy. Gave it to my grandson along with enough parts to built a Cont-A-75 engine and went ahead and built the engine mount . Still setting in storage.
Not a hard airplane to build.
 

Hot Wings

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Fold-a-plane composite fuselage, or an even simpler flat sided composite fuselage along the lines of a Tailwind or a Hyperbipe?
Both could either be factory built or home brewed.
Just because we are using a Cygnet as the template doesn't mean it has to look like one.
 
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