How about a UL Buhl Pup replica?

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Tiger Tim

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Your body is a lovely spoiler right in front of the rudder. Lengthen it a foot and take a bit off. For simplicity the MM has the fin and rudder on top. You will have to split the elevator if you hang the rudder off the back.
Splitting the horizontal tail isn’t at all bothersome, really just makes it more like so many other airplanes out there. As for the pilot hanging out the top I figure the little Pup will have a much deeper fuselage that you’ll snug down further inside… probably.

I do like the thought of stretching it out a bit though. Given the weight difference between the lightest MM’s Hirth and the bigger half-VW or Verner I’m leaning towards I suspect I’ll need a little less nose and a little more tail than a Minimax anyways.
 

Tiger Tim

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Just a quick sketch tonight to see if the rough moments, areas, and cockpit volume of a Mini Max would look about right when tweaked into a Pup.
3F68C8BC-4A91-4065-AB5E-409D6C8CFCC9.jpeg
The engine (a half VW) was more sketched than scaled and the same goes for the vertical tail but I think the fuselage/wing/gear all look passable at this point.

The fuselage was made quite a bit deeper than the MM so the pilot didn’t stick out as far and in order to get the lower attach point for the flying wires as far below the wing as practical. With the fuselage cross section being a sort of narrow upside down egg shape there should be ample room under the seat for controls, etc.
 

Tiger Tim

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Dipping my toe into some fuselage structure tonight. Would it be fair game to resolve the forces and required structure for a semi-monocoque fuselage in sections? In my mind the fuselage is three parts: forward section from engine mount to front spar/forward landing gear strut, a center section that handles spar carry-through/landing gear attach/flying wire attach/pilot‘s seat, and an aft section holding the tail and skid. Seems to me that a truss type structure can be broken down into little bits to analyze and I’m hoping a monocoque or semi-monocoque can be viewed the same.

If that’s the case, what kind of loads would be on the aft section of fuselage, or what important loads are there to consider? On a cursory pass I had this:
26965162-D9AA-49BB-A3CB-0F8AC2E083FD.jpeg
It almost seems too simple but it seems to me that there will be forces pushing up on the tail skid (or wheel), some sort of torque applied through the fin post due to rudder deflection, and an up and down force coming from the horizontal tail. The latter almost certainly being far stronger downwards (positive G) than up (negative G). Is that force really just a component of an equal but opposite moment to that of (roughly) engine weight times max load factor? My gut says too that if it can handle sufficient positive load then this almost vertically symmetrical tin can will automatically be able to handle any negative loads it would ever see.

Am I close? Any structurally versed folks want to chime in?
 

Tiger Tim

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No real progress on the little Buhl, it seems I have a hundred other things on the go.

In the meantime, this very similar little machine caught my eye: the Pander D.
1668072025932.jpeg
As you can see it’s very much like the Pup but with cantilever wings. I think the fuselage is plywood(?)
1668072152867.jpeg
Looks like the Dutch Air Force had at least one of them. I assume as an economical trainer for solo practice, or maybe it was purchased as a part of some sort of make-work subsidy for Pander.1668072283680.jpeg

Get a load of the six cylinder radial that was on one, it’s a configuration I’ve never seen before. Normally I’d say a radial engine with an even number of cylinders has to be either a multi-row or a two stroke but this one appears to be neither. It has me wondering if the firing order is 1-2-5-6-3-4, which I think would actually work. Whatever it is, it tickles my love of weird stuff.
1668072755962.jpeg
 

Lucky Dog

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This one dates back a few years. (The 1910 project) I wanted a simple to build, period piece looking UL powered by a direct drive V twin. I wanted to sit low in the fuselage to minimize the wind shadow to the rudder. The loop behind the seat is a thick wall aluminum roll bar, which turned out to be essential, because getting in and out of it would require climbing up from behind the wing and I'd need something to hold onto. In the end, after fleshing out the controls, weight and balance, I realized I was already flying a mid wing tractor (first pic), so I went off in an entirely different direction. Don't give up. The view is spectacular... but you'll probably want that lower window to peek past the wing's blind spot. Oh, and please ignore some of the pipe dream performance specs.
 

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Tiger Tim

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I like the Buhl Pup, but that forward mount landing gear leaves a lot of tail hanging back behind there. I’ve only seen Buhl Pups fly a couple of times, and one of those times ended in a ground loop.
I’ve read they can be a wild ride. I wonder why that is, they don’t look like they have the mains excessively far forward and the vertical tail looks normal size.
 

TFF

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I would not want a tail skid plane on hard surface, even dirt, and cross wind. Once the tail comes down no guarantee there is enough rudder.
 

Tiger Tim

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Did the originals have a tail skid or a tail wheel?


BJC
More than likely a skid originally, I imagine most survivors now have a wheel. I’m kind of wondering if maybe it’s a wheel alignment thing either through gear geometry or the axles flex on landing or something.
 

Lucky Dog

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I will throw this in the mix:

The Quicksilver ultralight has two types of wing. One is a single-surface that has gobs of lift, and scads of drag, and a very slow stall speed. The second is a double-surface that has gobs of lift, less drag, and a higher stall speed. The airfoil curve is the same. The difference is the double-surface is a "cleaner" wing, The difference in the stall speed is "clean" vs "dirty".

Another example of drag affecting stall speed:

The Quad City Challenger II, built dead-nuts stock with the tube n fabric nose, small windscreen, found lift struts and round main gear struts, GPL starter and 18amp battery, weighing in at 396# empty, stalls at +/- 25mph.
Fair the struts, add the big windscreen (but no doors) and she stalls at 30mph. Add the doors and the stall shoots up to 35mph. The weight gain from the additions is very small, about 12-15#. Remove the 18amp battery and you are down 10#. So, the weight difference is a wash.
So, what is the change that affects the stall speed? Drag. And all of it below the wing.

This isn't theory, it is from observed behavior.
A little late to comment on drag/lift/stall speed, but the key here may be that the wing of the draggy aircraft is not stalling completely - it just feels like it stalls because the increase in drag as the wing nears stall increases dramatically, and the mass of the aircraft isn't great enough provide lift and overcome the combined drag of the aircraft, so it settles at a lower speed - but the aircraft feels and responds as if it was a full stall landing. Remove the excess drag and the same aircraft has enough inertia to fly the aircraft nearer to the edge of the wing's actual stall angle. Light aircraft play by a slightly different set of rules than the plus 150mph club.
 

LittleBird

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No real progress on the little Buhl, it seems I have a hundred other things on the go.

In the meantime, this very similar little machine caught my eye: the Pander D.
View attachment 131557
As you can see it’s very much like the Pup but with cantilever wings. I think the fuselage is plywood(?)
View attachment 131558
Looks like the Dutch Air Force had at least one of them. I assume as an economical trainer for solo practice, or maybe it was purchased as a part of some sort of make-work subsidy for Pander.View attachment 131559

Get a load of the six cylinder radial that was on one, it’s a configuration I’ve never seen before. Normally I’d say a radial engine with an even number of cylinders has to be either a multi-row or a two stroke but this one appears to be neither. It has me wondering if the firing order is 1-2-5-6-3-4, which I think would actually work. Whatever it is, it tickles my love of weird stuff.
View attachment 131560

No real progress on the little Buhl, it seems I have a hundred other things on the go.

In the meantime, this very similar little machine caught my eye: the Pander D.
View attachment 131557
As you can see it’s very much like the Pup but with cantilever wings. I think the fuselage is plywood(?)
View attachment 131558
Looks like the Dutch Air Force had at least one of them. I assume as an economical trainer for solo practice, or maybe it was purchased as a part of some sort of make-work subsidy for Pander.View attachment 131559

Get a load of the six cylinder radial that was on one, it’s a configuration I’ve never seen before. Normally I’d say a radial engine with an even number of cylinders has to be either a multi-row or a two stroke but this one appears to be neither. It has me wondering if the firing order is 1-2-5-6-3-4, which I think would actually work. Whatever it is, it tickles my love of wei

No real progress on the little Buhl, it seems I have a hundred other things on the go.

In the meantime, this very similar little machine caught my eye: the Pander D.
View attachment 131557
As you can see it’s very much like the Pup but with cantilever wings. I think the fuselage is plywood(?)
View attachment 131558
Looks like the Dutch Air Force had at least one of them. I assume as an economical trainer for solo practice, or maybe it was purchased as a part of some sort of make-work subsidy for Pander.View attachment 131559

Get a load of the six cylinder radial that was on one, it’s a configuration I’ve never seen before. Normally I’d say a radial engine with an even number of cylinders has to be either a multi-row or a two stroke but this one appears to be neither. It has me wondering if the firing order is 1-2-5-6-3-4, which I think would actually work. Whatever it is, it tickles my love of weird stuff.
View attachment 131560

Love that radial engine! This airplane reminds me of a larger version Mummert Sport plane. I always thought it was a good lookin bird! 1668235058034.png
 
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Tiger Tim

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Dumb question of the day: what fuselage width at the shoulders makes sense? I see the Minimax is 21" across the cockpit opening and without a human-width caliper on hand that seems like my own width sitting here on the couch with a tape measure and no coat. The MM fuselage tub only comes up about waist-high so it can get away with that sort of thing but I can't with the little Pup.

What's a comfortable width for a single-seater?
 
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