Single-seat ultralight puddlejumper: the "Carbonmax"

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cluttonfred

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BoKu, I wonder if a little less "swoopiness" (I am sure that's the technical term!) might make things easier. The rear fuselage could be made from two identical sections (left/right or top/bottom) complete with the joggles (male on one side, female on the other) so only one form is needed. Ditto the cockpit area if it were done as top and bottom sections to form a rectangular cross-section with rounded corners, you'd just have to cut out the cockpit area (or leave it out when doing the layup). With that approach you could make the whole fuselage aft of the firewall with two of your chipboard-and-aluminum-sheet molds.
 

plncraze

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Wow! You have really thought this through! So are imagining some fuselage pieces and plans as the "kit" or is are you still too early in the process to get that specific? Once again thank you for sharing your ideas.
 

BoKu

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BoKu, I wonder if a little less "swoopiness" (I am sure that's the technical term!) might make things easier...
Easier, sure. But there are already mass quantities of small airplanes that are essentially collections of conic sections concatenated at cusps that fairly shout "um, yeah, but no." I want to make an airplane that is affordable yet offers smooth, unbroken curves from nose to tail. That's one of my competitive differentiators.

...The rear fuselage could be made from two identical sections (left/right or top/bottom) complete with the joggles (male on one side, female on the other) so only one form is needed...
That's a good idea, and bears some thinking on. Thanks!

...Ditto the cockpit area if it were done as top and bottom sections to form a rectangular cross-section with rounded corners, you'd just have to cut out the cockpit area (or leave it out when doing the layup). With that approach you could make the whole fuselage aft of the firewall with two of your chipboard-and-aluminum-sheet molds...
Thanks, but hard pass on that one. That results in a hard contour break where the ruled surfaces of the forward fuselage meet the ruled surfaces of the aft fuselage, just like zillions of little tin birds.
 

BoKu

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Wow! You have really thought this through! So are imagining some fuselage pieces and plans as the "kit" or is are you still too early in the process to get that specific? Once again thank you for sharing your ideas.
Thanks! This may only be my second rodeo, but it ain't my first. I'm imagining a semi-kit for which the plans and molded forward fuselage panels are the only required purchases. You can buy the molded aft fuselage skins from me as well, as well as a bunch of the composite materials, but you can pretty much either make those yourself or get them from a composites supplier.
 

sming

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It looks to me like the three forward fuselage skins (right side, left side, top/glareshield) would nest into a cardboard carton 1600mm x 700mm x 300mm. Is that an unreasonable size for international shipment?
Just quickly tried the ups quote system, from LA to France, it says 1300$! Dimensional weight applies apparently... they say it's 147lbs.
Need more investigating (usps?)
 

daveklingler

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What BoKu seems to be proposing is the two main spars over lap each other through the fuselage like a sailplane, and are then pinned in two places to each other and the fuselage. When you do the skinny fuselage, the pin joints may have to be pretty close to each other, meaning bigger loads in the pins and joint than with a wider space, but it is all amenable to good design work. Look at a sailplane with a less than two foot wide fuselage and a 50 foot span - the joint spacing looks pretty small there too...
A few years ago I saw how sailplanes did it and concluded that was a fantastic way to do a cantilevered high-wing puddle jumper with fabric-covered wings and carbon spars. I've been putzing around with a 3/4-scale Cub design ever since that bears remarkable philosophical similarities to what BoKu is proposing here.
 
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wanttobuild

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MiniMax will be disappointed to see this aircraft in production.

Have you had a chance to check out Henkle fast cure resin? Developed for fast cycle times for the corvette leaf springs, very viscous, made to be injected and vacuum clamped, fast cure, I forgot what the brand name is

Nice design, I hope you make a ton of money.
 

BoKu

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Yesterday I added the pool-noodle stiffeners to the test part. The stiffener cores are actually a material called "backing rod," it round-profile you cram into cracks to seal them. I bought 1/2", 5/8", and 3/4" diameters, and settled on the 5/8" diameter after seeing that 12oz 4HS carbon, cut on the bias, stretched conformed to it okay. Here's the part this morning after the epoxy cured:
20200301_093301.jpg
Here's the outside of the part after demolding:
20200301_093307.jpg
The finish shape conforms exactly to the mold, of course. It came out pretty smooth and shiny, though next time I'll probably not use rattle can primer, and I'll probably use a tie coat prior to the first ply of carbon. The primer was actually a bit uncured and tacky after demolding, and that's a week after I sprayed it. Also, there was some pinhole print through that we don't see with ours standard vinylester primer.

I didn't weigh it, but it felt about right for a part of that size. According to my calculations, if I use the same layup schedule, the field-molded aft fuselage will have a total weight of about 15 lbs with stiffeners and finish.

Going forward, I'll probably go with Cluttonfred's idea of making the aft fuselage in two identical halves, right and left. However, that makes the joining kind of awkward, especially at the very aft end where the curvature is tight. And at the forward end, it's awkward because the 48" sheet width doesn't leave much room for the edges of the part, and not really enough to include a joggle. I'll probably jigger the dimensions to see if I can make room for the joggle.
 

plncraze

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So you started this thread on Valentine's Day. You are doing preproduction parts 15 days later. Is this idea becoming a thing?
 

TiPi

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Yesterday I added the pool-noodle stiffeners to the test part. The stiffener cores are actually a material called "backing rod," it round-profile you cram into cracks to seal them. I bought 1/2", 5/8", and 3/4" diameters, and settled on the 5/8" diameter after seeing that 12oz 4HS carbon, cut on the bias, stretched conformed to it okay. Here's the part this morning after the epoxy cured:
I did a smiliar thing on my thin ply sheets on the fuselage (1mm), but used XPS foam strips of 10x25mm covered with 1 layer of G40 glass (40g/m2). The glass strip was about 15mm on the ply either side (cut 75mm wide). This provided sufficient stiffness for the ply to get that more solid feel and no wavyness. Using foam strips might be easier as there is a 90deg angle between the foam and the ply where the glass easily conforms once pushed into the corner when brushing the expoxy on. The difficulty with a full-round foam is the angle at the contact points and the reduced contact area (I glued most of them with SIKA polyurethane glue, the glue bond is much stronger than the foam).
upload_2020-3-2_12-11-44.jpeg
upload_2020-3-2_12-12-17.jpeg
 

lr27

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snip
I want to make an airplane that is affordable yet offers smooth, unbroken curves from nose to tail.
Snip
Belly tank! Surely you can find a mold. It wouldn't look like anything else in the air.
;-)
 

Tiger Tim

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Belly tank! Surely you can find a mold. It wouldn't look like anything else in the air.
;-)
Well, except for the Piper Skycycle which was a belly tank, and the American Electric Piranha which was a napalm(!) tank.
 

lr27

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Don't forget the Prue 160. Note that I wrote "in the air" as opposed to "used to be in the air".
 

Burgher

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You know, I like it! But food for thought. For two whole days at Copperstate, I watched guys crawl on and off my buddies airbike—the same airbike he flew 900 miles one way...in some pretty fierce winds. Old crippled guys like me, big tall guys (6’4”), fat guys, little guys, and people just loved it. It is a whole lot easier to get ON than IN. I recently made a post about finding video on getting in and out of a Legal Eagle, and a kind member provided a link. The Airbike is a lot easier. Step over, sit down, and put your feet up. Skinny airplanes are cute. Erikk has something there. But...what are the issues with carrying a cantilever wing with a skinny fuse?

I concur..............rather biased.
 

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Hot Wings

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Yesterday I added the pool-noodle stiffeners to the test part
Rather than use the whole of the backer rod have you considered making up a quick hot wire at the end of a piece of PVC tube so yo could quickly slice the rod in half - making 2 semicircles? Seems to me that they would be easier to laminate into place than the full found? Maybe even tack glue the resulting 1/2 round in place?

The hot wire tool could be made from a cheap resistance style soldering iron by just about any builder.
 

BoKu

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...slice the rod in half - making 2 semicircles? Seems to me that they would be easier to laminate into place than the full found? Maybe even tack glue the resulting 1/2 round in place?...
Thanks, but I don't see any compelling advantages in doing that. It adds time, doesn't save much mass, and reduces the stiffening effect a lot.
 

lr27

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If you were going to hot wire the rod, might as well zip off some Styrofoam strips on the table saw instead.
 

Hot Wings

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and reduces the stiffening effect a lot.
IF - you used the same diameter. I was thinking double the diameter and - then - cut it in half.
You still have the same "I" for the top fibers, but less for the ones on the side. A second narrow strip of UNI on the top eliminates the disparity with little added work and probably less weight than using the round form for the same stiffness.

If you were going to hot wire the rod, might as well zip off some Styrofoam strips on the table saw instead.
A whole lot more mess and cost than the hot-wired backer rod. The backer rod is cheap and the hot wire would be very quick. No dust, but a few easily vented fumes. A hot wired foam shape might be almost as quick and easy as the backer rod - but backer rod is still cheaper, faster, and more easily bent into shape.

I understand the reluctance to use 'squishy foam' for this but it is there just for the shape and to use as a form.
 
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