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105 pound HAIG Minibat

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proppastie

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As a design exercise and a configuration study, what would it take to convert the Mini Bat design into an ultralight flying wing.
someone who knows aerodynamics, structures, stress analysis, and has a lot of spare time. ..... to produce a set of new plans, or a kit one would have to be really dedicated.
 

Topaz

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There appears to be reasonable interest in a small, light, simple, (as in fast build) flying wing. As a design exercise and a configuration study, what would it take to convert the Mini Bat design into an ultralight flying wing.
Well, there are some things to talk about on such a process. The Minibat design would only be a good candidate for a revival in its original role as a "sustainer" motorglider or as a pure sailplane. The design of the "slot" for the prop absolutely constrains the propeller to a very small diameter, which rules out adding a larger motor and making a "cruising" power-plane out of it. It pays to remember that the Minibat was incapable of taking off under its own power - it needed an aero-tow or auto-tow to get airborne, although it could climb (very slowly) under the power of its internal engine. There's simply no room for more propeller unless you completely redesign the entire airplane, at which point you're no longer doing a "conversion" of the Minibat design.

Within that constraint as a sustainer-motorglider/sailplane, the biggest part of the job is that you'll have to almost completely redesign the wing from scratch. The airfoil choice is bad, the wing structural design is a horror, and the extended-span "tips", while visually striking, were a kludge from their inception. Throw out the current wing and design a single-sweep planform the same as the "extended" span, with a new airfoil and twist schedule tailored to the arrangement of wing mount, sweep, and design CG range locations. This is no different than designing a flying wing from scratch, except that you're constrained by the original geometry.

After that, I'd be taking a very careful look at the fuselage structure. If the original wing structure was that bad, what is the original fuselage structure like? As with any such exercise, you'll need to develop flying and landing gear loads by analysis of the existing design, and then see how well the existing structure does against those loads. Not impossible - it's just a numbers exercise.

The "sustainer" motorglider concept had a brief heyday in the 1980's, exemplified by airplanes like the Minibat and American Eaglet designs. But they never really caught on. You get all the issues of having an on-board motor, but without the ability to self-launch. The market moved on to self-launch sailplanes, and the sustainer motorgliders faded into history. The one thing that bodes better for such a concept now is the fact that it could be done with an electric motor instead of a small ICE, which would mean a much simpler installation and operation. A "modernized" Minibat would be compact and quick to build. It would be a fun ridge-soaring glider, but the basic configuration has some fairly significant induced-drag penalties which reduce thermalling performance. It woudn't really be a great cross-country or thermalling sailplane, as a result. Or, rather, a conventional wing-tail design would thermal quite a bit better, given the same area/span wing, and aircraft weight.
 

jedi

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The configuration study does not need to retain the prop in the slot or the engine. It could be a pure glider or a multiengine motor glider.

The landing gear could be extended or converted to foot launched for powered takeoff.

My goal would be to be 103 compliant and tailless and even that is negotiable.

I appreciate your comments and suggestions. Keep them coming.
 

proppastie

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The design of the "slot" for the prop absolutely constrains the propeller to a very small diameter,
it remains to be seen if the Aluminum Dragon will self launch...The constraints I have established for diameter/stock model propellers will limit my choices if they do not work. For those not up with my design, I currently have a 3W-200 giant scale model engine. (15 lb, 200cc, 20 hp at 6800 rpm) I have a 31" diameter prop currently....I have not been able to check the static thrust numbers....that will wait until the engine is mounted on an almost finished aircraft or fuselage structure.....Also it remains to be seen if my wing survives load test without extra weight added to the structure, and if it meets design calculations weight. (mistakes happen I am never sure until I actually weigh/test).

If every thing works out a modified Carbon Dragon might be that 103 self launch glider but it will not be a quick or easy build that everyone is looking for.

One of our members has already done something similar.

https://www.homebuiltairplanes.com/forums/media/alnair-landing-after-her-maiden-flight-as-n601ce-02-17-2004.8602/
 
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Topaz

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The configuration study does not need to retain the prop in the slot or the engine. It could be a pure glider or a multiengine motor glider.

The landing gear could be extended or converted to foot launched for powered takeoff.

My goal would be to be 103 compliant and tailless and even that is negotiable....
At that point, you're essentially starting a new design from scratch and only retaining the general configuration of the Minibat. Which, even if one were to retain the original design mission, is probably where you'd end up going anyway, by the time you're done.

For powered takeoff, the easiest "conversion" would be to add a small nosewheel instead of the skid that's currently there. You'd need a wing-runner for takeoff, but that shouldn't be much of a stretch.
 

b7gwap

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The need to add wing area (I presume to be able to attain part 103 Stall and max sea level WOT speeds) would only be necessary if the engine was part of the re design. Unpowered ultralight vehicles have no speed restrictions. They do, however have a pretty restrictive max empty weight of 155 lbs.

Otherwise Topaz has hit the main points; crummy airfoil, dubious spar construction, the whole design is therefore suspect and worth a double and triple look with a slide rule.

is it just me or does the pilot in the Minibat on the magazine cover look a little scared? I’ve heard some hair raising tales about some sketchy behaviors of the Minibat. It’s a shame because the shape and mission profile are so appealing. It may be why the thing refuses to leave our collective imagination.

Austin
 

Victor Bravo

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Look into the Marske Monarch and Pioneer tailless airplanes as a starting point. They fly much better than the MiniBat. Marske used more conservative airfoils and wing areas, and because of that Marske's wings all flew well, were very soarable, etc.

So if you design a smaller 103 foot-launch glider, you will need to go cantilever (like Marske's Pioneer) and move the seat upwards to bolt directly to the front of the spar. I sketched out something almost exactly like this a couple or five years ago, let me see if I can find it and post it later when I get home.
 

b7gwap

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Not only that, Matt Kollman claims that by using some more exotic fibers, the monarch will hit the magic 155 lb empty number and therefore be part 103 legal. If you put a sustainer motor on it though, then you’d have a powered ultralight vehicle and be required to meet all the stall, max power level flight and sundry speeds, which I don’t know if the monarch would do. It’s a cute little glider. At the price Matt is offering it, I’ve considered it many times over the years.
http://kollmanwings.com/site/mobile?url=http://kollmanwings.com/Monarch_10.html#2847
 

bifft

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This is what I came up with for a small ultralight flying wing glider based on the Marske wingss. I got tired of hearing about "Air-Chair" gliders, and I wanted to reduce the drag of the pilot.... so it's the AiRecliner :)

I'm pretty sure with carbon fiber you can build this for 155 pounds, perhaps even 125.

View attachment 90612
Is the wing swept forward, or do you have a cutout for the pilot?
 

b7gwap

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If he’s using the monarch’s wing wholesale, it has both slight forward sweep and a small cutout forward of the spar that looks about head size, although most pictures show the pilot’s head below this cutout.

upload_2019-11-27_5-39-19.jpeg
 

Victor Bravo

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My drawing uses the front face of the main wing spar as the back of the seat, at shoulder height. Allows the shortest feasible load path between the weight-bearing structure and the biggest chunk of weight. Also puts the pilot weight the furthest rearward, which allows for the least amount of forward sweep.

But yes, all Marske wings are slightly swept forward at the spar or quarter-chord line, some even have slight forward sweep at the leading edge.

I was not using the Monarch wing as-is, I wanted it to be Monarch-sized but cantilever like the Pioneer series. There's not enough vertical distance between the wing attach and the wheel axle for it to be strut braced.
 
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b7gwap

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I’d be willing to bet a beer you could fit a monarch with a slick Mini-Bat-style canopy and call it good. ;)
 

b7gwap

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Agreed. Those struts are contributing to wing stiffness no doubt, but they are also stabilizing that tall skinny fuselage pod, and don’t look much longer than 6 feet on a glider with a span of 40-something. Have you analyzed the wing spar depth as is but cantilevered?

Getting rid of any drag will certainly help your L/D, and any added weight to stiffen the structure will not affect the L/D. Your sink rate and stall speed will go up though, but you know that.
 

Victor Bravo

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I am very highly qualified to run any and all detailed structural analysis on an indoor free flight rubber powered model. Anything larger or faster than that, and I have to outsource brain cells and knowledge from somewhere else :)

Fortunately I have that available to me from two or three sources.
 
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