# Would planes be better if they were more like birds?

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#### REVAN

##### Well-Known Member
The jump-flap vertical takeoff of small birds will probably not be possible for any manned ornithopter due to actuator weight (both leg and wing actuators).
Agreed. However, a zero-roll jump-flap takeoff using the wings as the launching mechanism is likely possible. The fact that birds use their legs so heavily for takeoff is probably the main thing that limits their size. The weight of the landing gear increases with the cube of the bird's size while the wing area only increases with the square. At some point, the burden of carrying the weight of the landing gear becomes too big to bear.

In contrast, pterosaurs used their wings to launch. The launch system is the same as the wing flapping system. That weight is shared, rather than having two separate systems. This is likely why pterosaurs were able to grow to be the size of an ultralight aircraft.

#### jedi

##### Well-Known Member
I believe a 1.5 meter stroke in 1/10 of a second launches an objects at 33 mph. That is a very crude calculation that does not consider acceleration, jerk or other parameters but does give and idea of the possibilities. Anybody want to do more math?

#### Toobuilder

##### Well-Known Member
Log Member
I believe a 1.5 meter stroke in 1/10 of a second launches an objects at 33 mph. That is a very crude calculation that does not consider acceleration, jerk or other parameters but does give and idea of the possibilities. Anybody want to do more math?
I'd rather do the math than ride in the fuselage of a thrashing, jerky, bird thing!

Gimme a piston engine and propeller any day!

#### REVAN

##### Well-Known Member
I believe a 1.5 meter stroke in 1/10 of a second launches an objects at 33 mph. That is a very crude calculation that does not consider acceleration, jerk or other parameters but does give and idea of the possibilities. Anybody want to do more math?
33 mph in 0.1 seconds would be 15 Gs. Although, it would do 33 mph in only 3/4 meters not 1.5, so the acceleration could be lowered if you are allowing for the extra stroke.

If we limit it to a 6 G launch, it would take 1/4 second to reach 33 mph over a 1.9 meter stroke. This assumes constant acceleration at 6 Gs. If it isn't constant due to stroke and actuator design, things would change.

For reference, a typical carrier jet catapult launch is usually in the low 3G range. Of course, this is over a longer time duration, and that matters. High Gs for very short durations are tolerable.

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#### henryk

##### Well-Known Member
High Gs for very short durations are tolerable.
=green=500 "g"/ step...

ti<0.5 ms !!!

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#### DennisK

##### Active Member
Agreed. However, a zero-roll jump-flap takeoff using the wings as the launching mechanism is likely possible. The fact that birds use their legs so heavily for takeoff is probably the main thing that limits their size. The weight of the landing gear increases with the cube of the bird's size while the wing area only increases with the square. At some point, the burden of carrying the weight of the landing gear becomes too big to bear.

In contrast, pterosaurs used their wings to launch. The launch system is the same as the wing flapping system. That weight is shared, rather than having two separate systems. This is likely why pterosaurs were able to grow to be the size of an ultralight aircraft.

Wing actuator weight does increase with cube of wingspan, since the moment arm is longer in addition to the squared area.

Using the wings to jump would indeed be awesome. I have a hard time imagining it actually working, but hopefully someone with a better imagination than me will take up the mantle of pterosaur wing development Birds are my favorite so that's what I'm doing, but I'd like to have a community working on replicating all the successful designs nature has given us, with an open source philosophy like the 3D printer community. Just look at how fast things progress when each successful idea is immediately replicated across the industry, versus the entire concept of 3D printing being functionally non-existent while the Stratasys patent was in effect. You make your money by selling good products, not by preventing others from doing the same. And having your name tied to a new design is great marketing, even if other people clone it. China clones patented things regardless.

My current wing model has 3D printed bones with copper wire feather attachment loops epoxied in, and feathers made of carbon fiber/fiberglass in 3D printed molds generated from photos of the feathers from a Canada goose wing, which are strung together with thread and elastic. It will need carbon fiber bones when scaled up to human size, but otherwise should be more or less the same. The wing itself will have a single linear actuator to extend the elbow, with the wrist and finger joints mechanically linked to it. Stick that on a 3-axis shoulder and hopefully it will have enough finesse to fly. Control will be via sensor gloves. Finger bend controls wing extension, wrist bend controls flapping motion, wrist twist controls wing humerus twist, and elbow bend controls wing sweep.

#### REVAN

##### Well-Known Member
Animation of wing launch:

#### REVAN

##### Well-Known Member
Lots of interesting information in this video, but I linked it to start at the bat wing launch. How bats take off from the ground.

#### Jerry Lytle

##### Well-Known Member
Hmmm I don't know if they would be better. Looks very uncomfortable for the passengers:

#### WonderousMountain

##### Well-Known Member
It does not seem believable; Petrosaus had large climb worthy talons. Similar to bat wing Physiometry. The outer wings are thought to have been Curled on the ground. I've considered it, but it seems less similar to people's hand manuevers.

#### jedi

##### Well-Known Member
Post # 103 and # 109 are examples of "those who can't should get out of the way of those who are" IMHO.

Edit: added. I mean no disrespect to the referenced post hosts. The goal here is to discuss some common misconceptions.

I'd rather do the math than ride in the fuselage of a thrashing, jerky, bird thing!
Gimme a piston engine and propeller any day!
Hmmm I don't know if they would be better. Looks very uncomfortable for the passengers:
These are an example of what was implied in the OrVNstabilize post # 85.

Real flapping wing propulsion is so mind-numbingly complex and difficult to emulate/replicate that even if breakthroughs and technologies in artificial muscles, tissues, joints, feathers, etc. were available, it still wouldn't be solved. IMO it has to start with the understanding of the fundamental principles and mechanisms of how birds generate lift and thrust. Many attempts at replicating the flapping motion by simplifying it into the familiar oscillating up and down motion or some type of figure 8 motion with wing articulation aren't helping to make progress and actually hurting it because people see how crude, clumsy and inefficient it is compared to propellers and just dismiss the idea of flapping propulsion altogether.
Take anything to the extreme and it can appear to be a bit strange or amusing. That is the definition of a caricature.

A caricature is a rendered image showing the features of its subject in a simplified or exaggerated way through sketching, pencil strokes, or through other artistic drawings (compare to: cartoon). Caricatures can be insulting or complimentary and can serve a political purpose or be drawn solely for entertainment. Caricatures of politicians are commonly used in editorial cartoons, while caricatures of movie stars are often found in entertainment magazines.

In literature, a caricature is a distorted representation of a person in a way that exaggerates some characteristics and oversimplifies others.[1]

The old fashioned silent movies with their un-natural frame rate made the actors motions jerky and un-natural but that was the limit of technology for the day. Today we have a refined and mature video imagery technology that can make a shark attack look like a ballet. Slow the video of post # 109 to a suitable frame rate and add the appropriate sound track and you would see a waltzing airliner.

Let me give some examples. Most people are familiar with pendulums. Old timers know them as the control mechanism of an old fashioned clock. Children do not know what a pendulum is but they do know that "Swinging" can be a lot of fun. (Please ignore the adult version of "swinging" that is also reported to be "fun".) That is because the swing frequency is driven by the laws of physics for a pendulum. Similarly, swinging in a hammock is pleasant as is sitting in a rocking chair.

The lesson here is that having the right frequency and amplitude is an important design consideration. Drive the hammock at to high of frequency and you will not get any sleep. Drive a rocking chair at the wrong frequency and amplitude and "you will be thrown off your rocker".

Although the rubber powered ornithopter of post #75 was made to work, it does not work efficiently because the rubber power has limited control over the flapping frequency. With the "three Knots" initial wind the frequency is too high. When in the end of flight one knot mode the flapping frequency is too low. Even the mid range frequency is not well regulated. Furthermore, the flapping amplitude is set by the crank geometry and can not be adjusted for the proper power required for the desired flight path be it climb, cruise or descent.

The term "rocket science" comes to mind but it does not apply here. Rocket science is not an unknown but it was out of the realm of general knowledge for those who were living in the early part of the last century. Rocket science is governed by equations such as the clear and simple F=ma but it also includes equations for thermal and fluid dynamics of subsonic and supersonic flow. In the last half of the last century that knowledge was expanded to include orbital mechanics and as pointed out in the Hollywood documentary "Numbers" IIRC. That was a significant challenge that was successfully accomplished by a politically incorrect before their time team of black women.

Rockets and their development, construction and use go well back into history originating in the 13th century Song dynasty according to Rocket - Wikipedia. Modern rocketry is muc;h more sophisticated.

Similarly flapping flight is well established in history extending well into the pre-jurassic period. Mans desire to emulate flapping flight is as old as the desire for flight itself. The accomplishment of flapping flight however is lagging well behind the accomplishment of flight itself. Is now the time to fix that?

Just as the equations of motion for the pendulum are known there are equations of motion for the unsteady motion of vortex generation and for flapping flight. One of the key equations is that of Strouhal number (https://en.wikipedia.org/wiki/Strouhal_number). The Strouhal number for flapping flight should be in the range of 0,2 to 0.4 to be within the range of good efficiency. Keep the Strouhal number within acceptable limits and use good design practices and the motion will likely be comfortable like that of sitting in a comfortable rocking chair.

It is my hope that someday someone will demonstrate that as a fact. As a pilot I would like to experience that feeling. For now all I can do is imagine it. The purpose of this post is to help you imagine what that feeling is like. Glider pilots know the feeling. Gliding is un-powered flapping flight. Next time you power pilots are flying try to imagine flight without the noise, vibration and fuel flow of the engine. Then close your eyes and imagine the soothing rhythmic motion of your favorite ship on a gentle sea. Once that is mastered the speed demons and acro pilots can up the action to gale force to suit the mood for whatever level of power you determine appropriate.

Keep in mind X-15 pilot Scott Crossfield's thoughts when you say "there has never been an aircraft built that has too much power" and remember his joy and relief when the engine finally ran out of fuel and he was once more "just a glider pilot".

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#### DennisK

##### Active Member
Watch through the KorraCam playlist to see what it's really like
With ~1m wingspan, the flap rate is a little under 5Hz, which is already soothing to listen to. Less than 2x human jogging step rate, which feels quite comfortable to us. So any human-carrying ornithopter will be uncomfortably slow, if anything (=motion sickness). Birds do have the advantage of a long auto-stabilizing neck to keep their head from getting bounced up and down along with their body, but I doubt it will be a problem since we already bounce our head up and down while jogging.

#### Toobuilder

##### Well-Known Member
Log Member
Based on the title of this thread, it's a "poll" or opinion piece. It asks the question: "would planes be better...?"

From my perspective as a pilot and engineer, the answer is a resounding "no". If you genuinely want opinions, then you have to be willing to hear those contrary to your own. OTOH, if you are asking a question and simply assume it's rhetorical, that's when forum members see opposing viewpoints as obstructive.

Personally, I'm far more interested watching birds soar or Ravens do aerobatics than seeing a pigeon flapping furiously into a headwind and getting nowhere - makes me feel exhausted! Nope, flapping flight does not appeal to me at all. What gets me all spun up and longing for flight is seeing my neighbor take off in his Rocket and rip around the airport at 200 knots on a calm evening. The sound of the big Lycoming, the Doppler shift from the prop on a low approach, the effortless vertical climbs... All of it is an intoxicating blend of visceral stimuli that says: "THIS IS FLYING!".

Flappy flappy, go nowhere.... Not so much.

#### jedi

##### Well-Known Member
And thanks toobuilder!

It is a question and I am listening to your answer. All opinions have a place. That is why boaters are divided into power and sail. I love watching a good hydroplane race also. I have been to both in Detroit and Seattle and there is as much diversity in location as there is in substance. There is no one answer for all.

Just saying power planes get a lot of designers attention and ornithopters tend to be left out. I have said in the past that I would love to get a ride in the rocket.

Is there any chance that, in your opinion, some planes could be made better even if only some of the flexible wing technology were incorporated to smooth the ride on some of those hot desert air afternoon flights?

FYI - it was the author of the article pressented in the original post that ask the question. as in happy flying! No animosity intended and peace be with you, etc.

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#### OrVNstabilize

##### Active Member
I don't think existing planes with props or jet engines would benefit much or be much better incorporating ideas such as flexible wing, blended-wing body, prandlt wing, wing grid or what have you. Sure you might get some efficiency gains here and there but it's probably not worth the hassle to change/revise a lot of the existing systems(components, infrastructure, manufacturing, safety etc) just to accommodate some edgy new design.

But if were talking about a totally different propulsion system like flapping wings then this opens up a whole new category of flying machines and new possibilities. It could never be fast or powerful but there's a place for this type of aircraft and propulsion(slow, low and silent) in which it could be better than conventional powered planes. It's about real innovation and progress, which frankly there hasn't been much of since the days of the Wright brothers.

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#### henryk

##### Well-Known Member
(slow, low and silent)
+much more energyeffective ! (big specific rhrust).

#### REVAN

##### Well-Known Member
I think flapping wings have to potential to significantly reduce the power required for flight. It will take some work to get there, implementing an appropriate stroke cycle and on an efficient airframe that can reap the advantages, but I think these mechanical issues will eventually be solved.

There will be large power demand fluctuations during the stroke cycle, and electric motors may be well suited for this task, as they have fast response, high torque and can put out massive power for short durations so long as the long timeline power demands don't overheat the motor.

If flapping wings can reduce the power requirements for a plane by half (and I think that is a realistic assumption), then flapping wings may be the missing element needed to produce a practical electric aircraft. This alone could make flapping wings a worthwhile technological pursuit.

There is already an ongoing thread on the battery and range issues.
HBA thread: Why battery-powered aircraft will never have significant range

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#### henryk

##### Well-Known Member
-Toporovs man powered ornithopter AZAZEL 12m= 12 kG/0.5 HP =24 kG/HP specific thrust !!!

#### henryk

##### Well-Known Member

=AZAZEL 12m ...acceleration ?

#### jedi

##### Well-Known Member
Post # 119 is a good example of landing gear problems of ornithopters. University of Toronto had the same problems with pitching and heaving when trying to takeoff. A single wheel at the CG would be better or at least balance the aircraft on the CG with the two lateral wheels. Raising and lowering the wheel in phase with the flapping would greatly assist with the takeoff similar to a gooney bird takeoff run.

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