The concept of flapping flight will eventually succeed!

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

DennisK

Active Member
Joined
Feb 5, 2019
Messages
35
Location
Missouri, USA
Since the wingtip will be traveling more than twice as fast the CoL will move outward substantially.
It's a little more complicated than that since you also have to account for the lift from forward airspeed. Let's try some math.

From this video of a macaw cruising around a park
Flap rate seems to be 5Hz or a bit less. If we guess 3.4ft wingspan, then wing length is maybe 1.6ft. Guess 60 degree total flapping range, so upstroke+downstroke = 120 degrees covered in 1/5 second = 100RPM. Due to slowdown at stroke reversal, say max speed is 1.5x higher, 150RPM. 150*1.6ft*2pi=1507fpm=17mph vertical wingtip speed due to the flapping motion. Guesstimate forward speed 25mph, then by pythagoras, sqrt(17*17+25*25)=30mph true diagonal wingtip speed, about 20% higher than forward speed. But since lift is proportional to v squared, that's close to 50% higher lift at the wingtip than the wing root.

A better mathematician than me could surely integrate that over the wingspan and figure the new CoL.

During a short takeoff when forward airspeed is very low, CoL will be way out on the hand wing. But then you don't have the lift from forward speed to deal with, so more torque can go into the flapping motion.
 
Last edited:

poormansairforce

Well-Known Member
Joined
Mar 28, 2017
Messages
1,222
Location
Just an Ohioan
During a short takeoff when forward airspeed is very low, CoL will be way out on the hand wing.
And it gets worse. Going back to Jedi's force estimates, there is the fact that the wing is creating lift for only portion of the cycle. So more flap speed is needed to create the lift missing for the other part of the cycle. And then you have to compensate for the extra load from g forces created during maneuvers as well as any negative lift created by the upstroke. It becomes easy to understand why we haven't seen any proficient man carrying ornithopters and probably never will. The structure needed to hold it all together over time as well as the mechanism to operate it will be heavy.
 

Aesquire

Well-Known Member
Joined
Jul 28, 2014
Messages
3,225
Location
Rochester, NY, USA
. The structure needed to hold it all together over time as well as the mechanism to operate it will be heavy.
While I agree with your pessimism, consider using carbon fiber tubes, plasma spray lined like a Nikasil engine cylinder, with ceramic pistons driven by combustion ( gasoline/air? ) in a double acting manner. Oh, it may be a sleeve valve monstrosity, Napier Sabre mess, but without the need to convert linear to rotary motion like conventional IC engines, sealing is simpler, and you might get very good power to weight ratios. Certainly you could expect wild noises.

Or should I patent that and sell it to DARPA? ( I doubt it's original enough ) :)
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
3,183
Location
Sahuarita Arizona, Renton Washington, USA
that's close to 50% higher lift at the wingtip than the wing root.
This is the sort of math that the blue jays do to calculate the required field length (AKA jump height) prior to departure while the cat is sneaking up from behind. "I'm good for a 4.7 hz reduced power takeoff with a 45 degree 3 kt right crosswind and 4.5 hz at 12.5 kias climb power to clear the 4 foot cain link fence." "That will be a .7 to 1.15 G 2:1 stroke."" In case of an abort, turn and attack the cat." "OK. preflight checks complete!" "Three, two, one; Go!"

Good job Dennis!
 

henryk

Well-Known Member
Joined
Mar 8, 2010
Messages
7,082
Location
krakow,poland
One of my gliders incorporated a very flexible wing which "flapped" (bent upwards and downwards like a spring) to take advantage of air gust energy. Not flapping flight specifically, but used the flapping style of movement to create thrust (reduced drag).

You can look up technical soaring papers on "the Katzmayr Effect" IIRC which is what Dr. Waibel was pursuing when he designed the layup schedule for the wings.
-more details ?
 

DennisK

Active Member
Joined
Feb 5, 2019
Messages
35
Location
Missouri, USA
And it gets worse. Going back to Jedi's force estimates, there is the fact that the wing is creating lift for only portion of the cycle. So more flap speed is needed to create the lift missing for the other part of the cycle. And then you have to compensate for the extra load from g forces created during maneuvers as well as any negative lift created by the upstroke. It becomes easy to understand why we haven't seen any proficient man carrying ornithopters and probably never will. The structure needed to hold it all together over time as well as the mechanism to operate it will be heavy.
During cruise it's only thrust that goes away for part of the flap cycle. Lift is produced continuously due to forward airspeed, and angle of attack can be manipulated to keep it relatively constant throughout the cycle.

But yes, low speed flight is much more demanding both physically and analytically because the airflow is so much more chaotic. That's why I keep harping on the idea of copying animal wings, because they've already worked out the optimal wing shape and joint configuration to handle low speed and high speed efficiently with a single machine.

In the low speed/high AoA "flying with thrust" mode, I think upstroke generates thrust as well. Watch from 2:30 in the macaw video in my post #22, and look for the slowest moving birds. This is one reason I would like to add independent control of finger extension for my robotic wings. Currently it's mechanically linked to the elbow/wrist extension, but those birds are folding their elbow/wrist pretty far during upstroke while keeping the finger extended so the primary feathers are spread.

This is the sort of math that the blue jays do to calculate the required field length (AKA jump height) prior to departure while the cat is sneaking up from behind. "I'm good for a 4.7 hz reduced power takeoff with a 45 degree 3 kt right crosswind and 4.5 hz at 12.5 kias climb power to clear the 4 foot cain link fence." "That will be a .7 to 1.15 G 2:1 stroke."" In case of an abort, turn and attack the cat." "OK. preflight checks complete!" "Three, two, one; Go!"

Good job Dennis!
Yep. And when they stop to look around every few hops on the ground, they're probably not only checking for danger, but also recalculating their available escape routes so they can make a better split-second decision if a cat does jump out.

I still haven't figured out how to do the proper integral for the wing center-of-lift calculation from my previous post, but here's some more dirty math to get the general idea:
Split the wing into 4 sections and manually calculate lift at the center of each one, so at 1/8, 3/8, 5/8, 7/8 of wing length. Resulting lift values relative to the 25mph baseline are 1.007, 1.065, 1.18, 1.354.
Averaging them gives 1.15, so peak thrust is around 15% of body weight.
I'm not 100% sure, but I think you just divide that by 2 to get the center of lift, so 0.575 versus 0.5 during glide (wing center of lift moves outward by 7.5% of wing length).
Multiplying each value by its distance from the wing hinge and averaging gives 0.612, whereas during glide (all lift values 1.0) you get 0.5, so actuator torque is 22% higher than during glide.

This is all ignoring the bell-shaped lift distribution, though. I think the real differences from glide will be larger.
 
Last edited:

Tiger Tim

Well-Known Member
Joined
Apr 26, 2013
Messages
4,447
Location
Thunder Bay
I think trying to mimic bird flight is futile, insect flight may prove fruition
I don’t understand why proponents of flapping wing flight can base their opinion on this notion that nature knows what it’s doing while simultaneously ignoring that in broad terms the larger the winged flying creature, the less it flaps to stay aloft. A fruit fly flaps like crazy, an albatross hardly ever flaps, and a quetzelcoatlus may not have flapped at all. I don’t know the reason for that trend; perhaps it’s energy management, or structural limitations, or something to do with Reynolds Numbers, or likely a bit of each.
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
3,183
Location
Sahuarita Arizona, Renton Washington, USA
I don’t know the reason for that trend; (
the larger the winged flying creature, the less it flaps to stay aloft.
) perhaps it’s energy management, or structural limitations, or ......
It has to do with sale effects. The square/cube law and stuff like that. :):)

It is the same reason why the B-747s, Airbus A380s and honey bees are in decline and do not fly much anymore.

Same for the Dornier Do X, the Vickers Vimy and many other big old planes that are never seen flying anymore.
 

J.L. Frusha

Well-Known Member
Joined
Feb 17, 2006
Messages
747
Location
Luling, Texas
I hear Macaw tastes somewhat like chicken...


Roasted Parrot with Orange Blossom Honey
~adapted from Charlie Trotter, friend of birds
Ingredients:
1 cup orange blossom honey
1/4 cup chicken stock
1 3-4 pound parrot
kosher salt and freshly ground pepper

The honey glaze creates a deliciously crispy skin. Even if you don't eat the skin, prepare it this way, and the meat underneath remains moist and flavorful.

Glaze:
Place honey and stock in small saucepan and whisk over medium heat for 5 minutes, until smooth.

Bird:
Preheat the oven to 325 degrees. Place bird in roasting rack in a roasting pan and season with salt and pepper. Generously brush the glaze all over the parrot and roast for 45 - 60 minutes, or until the juices run clear (if using smaller birds, less time will be needed). Brush on additional glaze every 15 minutes during the roasting. Remove from oven, let rest for 10 minutes, then carve.
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
3,183
Location
Sahuarita Arizona, Renton Washington, USA
I hear Macaw tastes somewhat like chicken...


Roasted Parrot with Orange Blossom Honey
~adapted from Charlie Trotter, friend of birds
Ingredients:
1 cup orange blossom honey
1/4 cup chicken stock
1 3-4 pound parrot
kosher salt and freshly ground pepper

The honey glaze creates a deliciously crispy skin. Even if you don't eat the skin, prepare it this way, and the meat underneath remains moist and flavorful.

Glaze:
Place honey and stock in small saucepan and whisk over medium heat for 5 minutes, until smooth.

Bird:
Preheat the oven to 325 degrees. Place bird in roasting rack in a roasting pan and season with salt and pepper. Generously brush the glaze all over the parrot and roast for 45 - 60 minutes, or until the juices run clear (if using smaller birds, less time will be needed). Brush on additional glaze every 15 minutes during the roasting. Remove from oven, let rest for 10 minutes, then carve.
Please clarify the instructions. Do you remove the feathers? If so then when and how? Can they be recycled into a flying machine with flapping wings? Are plans available? :)

"Birds aren't food. Birds are friends!" 😄 😾 A five year old says.
 
Last edited:

J.L. Frusha

Well-Known Member
Joined
Feb 17, 2006
Messages
747
Location
Luling, Texas
Please clarify the instructions. Do you remove the feathers? If so then when and how? Can they be recycled into a flying machine with flapping wings? Are plans available? :)

"Birds aren't food. Birds are friends!" 😄 😾 A five year old says.

Me? I remove the feathers. You? That's not my decision to make...

Well, you can do the scalding water dunk - swish - pluck, if you want that crispy skin, or you can peel them off with the skin.
Whichever method works a whole lot easier if the parrot is dead...

Tell the kid to shut up and eat the 'chicken'.
 
Top