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Modern day "motorcycle of the air" aircraft class?

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blane.c

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Yes, you are right bigger diameter better ugh. But compromise is the crux of aviation. What if there is no room for big dia. props? Or the engine would spin them to fast and make the tips go supersonic and lose all efficiency? Or you have other concerns that require a reduction in dia.?

So like you pointed out practical reasons or even not so practical reasons can win out.
 

Dart

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blane.c

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FritzW

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I've been thinking about something like this for a while, in part because it's a geometry that could accommodate a huge slow prop, and have a wingspan of just under 8ft, while having more wing area than most full span planes. Upper wing would be live, or adjustable angle.
Very pretty! Is the CG going to work out?
 

cluttonfred

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Neat concept but those curves seem unnecessarily hard to build, perhaps look to the Sunny Boxwing for a simpler approach?


 

Dart

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The sunny box wing was certainly an inspiration, and yes the curves could be quite difficult to fabricate in conventional construction. It's very interesting to me as a designer that so many things are made the way (shape) they are, because it was simplest to draw up, or simplest to build.

CG does seem like a big tripping point for such a big wing, having variable angle of attack vs the rest of the plane, CL is likely to move aft, causing downward pitching, but I was hoping that control surfaces on the aft wings might be able to help with that, however if they can only do it by degrading their lift producing effectiveness, then is it worth it?

I'm not sure.

In terms of making it more simple to construct, I've been wondering about making most of it as a sort of single skinned stich and glue, like many plywood kayaks. The long overlapping joint between the upper and lower wings is so that there is room to try the upper wing in various positions. Not illustrated is a trapeze or centre frame that would join the upper wing to the fuselage at the windshield.

I'd be happy to be corrected, but after staring at the faucet plane and it's progeny for a long while, and reading about Reynolds number effects, and it seems to me that a very deep wing, meant for lower speed operation, doesn't really need to be smooth.

I'm not at all convinced that this tail assembly is the way to go. I have another configuration I'll try to dig up.
Image 2018-01-17 at 8.14 PM.jpgImage 2018-01-17 at 8.15 PM.jpgImage 2018-01-17 at 8.15 PM.jpgImage 2018-01-17 at 8.16 PM.jpg
 

cluttonfred

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Very neat! The Mignet approach would be another option...variable incidence front wing, rudder(s), no ailerons, two-axis control.
 

blane.c

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2 Blade Propeller dia. = 1.83 times the cube root of the bhp.
3 Blade Propeller dia.= 1.5 times the cube root of the bhp.
Does anyone know for a 4 Blade Propeller dia the multiplying factor of the cube root of the bhp?
So as BJC pointed out, wrong words in formula. All "cube" should be replaced with "fourth". I tried to correct this but can not figure out how.
 

erkki67

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I've been thinking about something like this for a while, in part because it's a geometry that could accommodate a huge slow prop, and have a wingspan of just under 8ft, while having more wing area than most full span planes. Upper wing would be live, or adjustable angle.


If you take the Sunny Boxwing as a base as Cluttonfred said, you could have a chance to see it fly, due to the simplified structures.

But keep in mind, that some of the qualities of the Sunny, were achieved because it is a flexwing.

Here a link for the Boxwing;

http://www.sunny-boxwing.de/
 

jedi

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This would suit me much better if the legs were extended rearward by rotating the thigh 90 degrees CCW. That does not work well on a motorcycle but would give improved ergonomics for rudder pedals and longer flights.

Then move the pivot point back to the hips and lengthen the machine by moving the tail aft an equal amount.
 

blane.c

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Further complexity and increased size would be detrimental to the design that I see sketched out here.

The cables attached to the shoes appear to be wing warping? And not un-like an Ercoupe's controls could also warp the tail.
 

Dart

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I am a big fan of joined wing designs, and this is a nice looking one. From my thinking is that from a flight dynamics point of view, isn't there a benefit from the leading wing be the upper wing? My thinking is that in steep climb the a high following wing is potentially in the airstream of the front lower wing, resulting in a potential loss of lift or change in CL?
 

Dart

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The disturbed air from the forward wing, falls down?
In the early flying flea designs the flow exiting from the forward and upper wing, in some circumstances (fast decent), would then attach to the lower (rear) wing, and cause the CL of the plane to shift strongly rearward, resulting in a further nose down attitude, and generally ending in tragedy. Later versions shifted the wings apart, resulting in a much safer airplane. The "nest of dragons" website covers this wonderfully.

So, in general, having a pair of wings horizontally separated, can result in not just negative interference, but also in big changes to CL, and airplane controllability as the airplane changes angle of attack and power level.

However, the reverse, as illustrated by Delta above, if it's moving forward at a high angle of attack, it's front wing will be directly in front of the aft wing, and it seems to me that especially as the front wing starts to experience stall, the flow over the rear wing will be disturbed as well.

The advantages of a twin wing should be reduced wingspan, and no need for the drag of a vertical stabilizer. It also opens the door however to doubled lift induced drag with four wingtip vortex's. Some experimental work does seem to show that twin wings can sometimes be arranged so the following wing smooths out some of the first wings tip vortex however this could also result in changing overall CL and loss of control.

It seems better to me to combine an upper delta wing, with a diamond, or forward swept lower wing, joining them at their tips, in the hopes of the accelerated vortical flows from the lift induced drag of the upper wing, will track down the forward swept lower wing, in a way that's stable and hopefully doesn't change the overall CL too much.
 
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