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We see sparrows with 6" wing span land on a dime, yet it seems there no GA planes you can buy or build from a kit with short bodies, short wing spans, something with a 20' landing/takeoff roll, something with folding wings you can drive out of your garage, take off from your driveway ( if you live in a non built up area) and land almost anywhere at 20mph.

It seems like GA is dying, but I think a lot more people would be interested in flying if GA planes were way more useful.

Yes, there was the BD5 which was nice and small, not STOL though, the Alaskan bush pilots are taking off/landing in 10' ( yeah!!) in their super cubs, a standard Zenith 701 STOL which can take off in 25' with a good headwind, but all have large spans

Using the Cri Cri as an example

  1. Cri Cri Monoplane: , I think it has a span of 15’ and a chord of 2’ for a wing area of 30 ft2.

  2. Cri Cri biplane: Now imagine converting it into a biplane with a span of 1/2 or 7.5’, same chord.

  3. Cri chi triplane: Now take the Cri Cri monoplane and reduce the span to 1/3, or 5', same chord.

Why can't we have planes with 5-10' wing spans.

Is it impossible to design roll stability into a plane with such a short wing span?

Is there any other reason, like 50% effectiveness, etc. at low span due to span wise flow, instead of chord wise flow, etc.

Looking at Selig's work on multi element racing car wings, their spans are only 5', with a cl of up to 4.5!! He does mention they need huge end plates to avoid span wise flow.

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  • $\begingroup$ Your first paragraph is a good description of an ultralight $\endgroup$ – TomMcW May 31 at 0:01
  • $\begingroup$ The bird can only land on a dime because it is able to temporarily settle into a semi-hover while it's touching down. $\endgroup$ – John K May 31 at 1:33
  • $\begingroup$ It's great that you were able to accept the answer to your question after three months with your own answer of a product that you have developed. $\endgroup$ – Roger Aug 14 at 15:00
  • $\begingroup$ Compare the length of the sparrow's wings to its body, then read up on the square-cube law. And think about larger birds like eagles & albatrosses. $\endgroup$ – jamesqf Aug 14 at 17:50
  • $\begingroup$ @jamesqf: What are you referring to? Length is just a moment arm, and can be adjusted shorter or longer with tail volume. Having said that, I understand most GA airplanes have almost an equal length and width. Square-cube law applies to scaling up things, but those things are just mathematical. It's all about lift, wing loading, power loading and stability, no? $\endgroup$ – Fred Aug 14 at 17:55
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Part of the reason is that bird wings can deform a lot, under detailed muscular control, while aircraft wings are usually stiff structures of metal, with at best a few controllable flaps & slots. If you made a model of a sparrow that just held its wings out in a fixed position, it would not be able to land on a dime.

Then there's the matter of thrust to weight ratio, and the general square-cube law. Sparrows don't weigh much at all, so they can take off and land with relatively little power. (And hummingbirds are even better.) Large birds like albatrosses & condors have trouble getting off the ground, and mostly fly by soaring. A human-carrying aircraft would have to weigh at least a factor of 10 more than the largest (flying) bird...

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They can, its just not a very efficient size for one that needs to cary people. The simple answer is that everything comes with a trade off, there are plenty of planes with small wing spans like this one, and this one and some planes that don't have wings at all... But smaller wing spans means a thicker wing, at some point you will run into a drag issue, a roll stability issue or both.

When it comes to aircraft people tend to be concerned with efficiency as air travel has always been about going far, fast, and for a similar cost to what you can on another means of transport. As such efficient designs win out over novel ones or ones that provide some means of limited added benefit.

On any note most of the supporting infrastructure has been designed for planes with substantial wing spans so aircraft width in the GA market is not really a huge issue. Saying a narrower wing is "way more useful" depends on your use case.

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The shorter your wingspan, the longer your landing roll is going to be.

Wide chord wings rely on lower angles of attack and higher airspeeds to work well. Stacked wings work at slow speeds, and indeed allow for shorter spans, but their lift doesn't increase linearly with the number of wings. Also, lift falls quicker than linear with reduced spans, as the fuselage and areas close to it don't contribute as much lift as the clean mid section of the wing. They are also draggy and heavy, and at some point it becomes easier to just go to a rotary wing.

5 ft wide racing car wings can produce enough lift to support a car - at 200 mph. At 200 mph, you're looking at takeoff/landing roll of about a mile. This would be of some utility to the few of us who benefit from a mile-long driveway, but since a plane with no wingspan is a pig to fly, you might as well fly a regular one with that much private land.

The 10' takeoff video was filmed with probably 40 mph of headwind. This much headwind is difficult to produce reliably, but you don't have to be the god of winds to do it - all you need is an aircraft carrier, which you turn into the wind and run at full speed. So the very few of us with a pond large enough for such a toy can similarly benefit from 10' takeoffs at any time.

And for the majority of us who don't get to play with toys like that, if you want your plane to land like a sparrow, you have to have it the size and the weight of a sparrow. A sparrow weighs just over an ounce, and scaling one up from a 6" to 6' wingspan would produce an aircraft weighing about 10 pounds gross.

Such a radical weight loss can be challenging for most pilots, but many UAV and fixed-wing drones in this weight class can indeed be launched simply with a hand toss. If they had arms of their own - that is, if their wings could flap like a bird's - they could do away with even that.

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    $\begingroup$ Re scaling up a sparrow, you're forgetting the square-cube law. 12 * 12 * 12 = 1782 ounces, or 108 pounds. $\endgroup$ – jamesqf Jun 1 at 17:21
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    $\begingroup$ @jamesqf Not quite - rather I'm exactly using the square-cube law. At fixed airspeed, the sparrow will only scale as 12*12. Same airspeed means same wing loading (roughly). A cube-scaled sparrow will also have its velocity requirements increased 12 times. $\endgroup$ – Therac Jun 1 at 19:14
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    $\begingroup$ I don't see how airspeed applies here. If you scale up a sparrow by a factor of 12, then the weight scales up by a factor of 12^3. You can find birds with a 6' wingspan and 10-15 lb weigh (e.g. the bald eagle), but their wings are much larger in comparison to the body than a sparrow's wings. $\endgroup$ – jamesqf Jun 2 at 20:16

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